Quantitative Morphology in Kidney Research
February 13-14, 2012 Conference Videos

Panel Discussion: Challenges and Unresolved Issues in Determining Glomerular Number in Autopsy and Biopsy Studies
John Bertram (Chair), Monash University, Australia
Bryan Myers, Stanford University
Julie Ingelfinger, Harvard University
Michael Mauer, University of Minnesota
Kathryn White, Newcastle University, United Kingdom

Video Transcript

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JEFFREY KOPP: And now we’ll have a panel discussion sort of rolling into these same topics. We’ll have John Bertram, Bryan Myers

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unfortunately couldn’t be here, Julie Ingelfinger, Mike Mauer, Kathryn White, and I think some of those individuals may have brought short slide

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presentations, which they’re welcome to show now maybe to launch things.

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JOHN BERTRAM: I’ll introduce our panel, Julie Ingelfinger from Harvard, of course; Mike Mauer from the University of Minnesota; Kathryn White

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from Newcastle University in the U.K.; and Kevin Lemley will also say a few words. Bryan Myers was not able to be with us. So I think you’ve

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heard a fair bit from me and so I think what I will do is ask perhaps the panel to give their thoughts on what they’ve heard this afternoon and their

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views and other concerns or additions or questions or comments and then we’ll open up to the floor. So perhaps, Mike, you don’t have slides

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but you might have some…I’m sure you’ve got some ideas and thoughts you’d like to share with the audience, if you want to do that we’ll just then

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go through the panel and get those ideas out there and then we’ll throw it open to general discussion if that’s all right. So, Mike do you want

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to lead us off?
MIKE MAUER: I think it’s been an excellent set of

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discussions so far and hit some really important points. I might just mention some pitfalls that we need to worry about. John Basgen and I some

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years ago studied dogs to see if we could estimate glomerular number from biopsies and learned some things from doing that. So we did

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MRIs of the dogs and then removed their kidneys, and removing the kidney from the circulation decreased the volume of the kidney by about

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30%, so I think that’s physiologically an important variable. Needles compress tissue and affect the volumes and their relationships with one another,

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and we learned that recently in a study in which one center used the biopsy gun, another center used a Vim-Silverman, and the effect, for

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example, on interstitial fractional volume was about a 15% difference based on the needle alone. So I think it’s very important that, in terms

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of how we sample, that we’re careful that the sampling is very consistent. We looked at glomerular volumes in autopsy material of

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accident victims, compared that to glomerular volumes in biopsy material, and the difference was 100% increase in autopsy compared to

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biopsy of normal individuals that were matched in other ways. So, it’s very important in setting up these studies that they’re very systematic, that

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these variables that contribute to variants are considered in the study design, and it’s very nice to see the work that’s been talked about this

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afternoon because of the consistency and the way the material is handled and the way the studies are done.

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JOHN BERTRAM: All right, thanks very much. You’re completely right and I’m very familiar with the work that you and John did with the combined

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biopsy MR approach. In fact, there’s a recent paper out of Jens Nyengaard’s lab in Denmark doing a similar kind of a strategy and they’re might

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be opportunities there as these imaging—noninvasive imaging—techniques are developed, which I’m sure they will be, to more of that type

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of combination, but the point of how you obtain the tissue in the striking effects on dimensions and ratios and something is probably something I

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wasn’t totally across but it certainly has to be considered very carefully. Kathryn, do you want to get your slides up and perhaps make your

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points please?
KATHRYN WHITE: I actually sort of want to take

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a slight step back as the challenges we’re talking about, I know, are measuring glomerular number. I want to sort of take a step back from the

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methodological challenge and just generally a challenge that I come across is actually convincing people that we need to do it in the first

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place, and so I really want to address a couple of issues—it might be a U.K. thing, maybe we’re lazy, I don’t know—but why aren’t we all

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recounting number and it doesn’t necessarily just apply to glomerular number, it can be cell number and why should it be counted? So I do a lot of

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work with people, with other groups, that have got animal models maybe looking at diseases, and if I suggest that maybe we should count

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glomerular number, podocyte number, or just do stereology. I get the answer it’s too time consuming, it’s too expensive, and yes, it is time

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consuming and time is money so it’s expensive. But if you get meaningful results from your data is, is it too expensive? Is it too time consuming? I

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also get that, “Oh, it’s too mathematical, I don’t understand.” Well I’m not a mathematician. I’ve been doing this now for more years than I care to

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remember. I’m still not a mathematician. There’s a lot of people out there who are mathematicians that are in this room; they’re quite scary, they’re

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very mathematical. You don’t have to be a mathematician to do stereology; you have to be able to count. I can count. You have to

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understand the basic concepts of stereology but you don’t have to design these. There are people out there that are sitting amongst the audience

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here that design these techniques. They’re tools; stereology is a tool. So then I get, “So why bother?” Well, we’ve heard various reasons why

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you should count glomerular number here; there’s a lot of links between low glomerular number in the development of kidney disease and

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hypertension. As I said, I tend to these days look more at animal models of disease, and this can give you an idea of maybe the pathogenesis of

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disease if you look at glomerular number. And I’d just like to show an example here of some work we’ve done on a mouse model of

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glomerulosclerosis which, by six months, has quite severe glomerulosclerosis. Now I get sort of…they say they don’t really want to do

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counting. They’ll sort of send me this up and say, “Can you just have a look at it? Don’t bother with this counting stuff. Just have a look. What do you

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see?” Well, I can see it’s sclerosed and that was at six months. We looked at both in these mice and it’s a WT1 mutation and the wild-type at birth

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have immature glomeruli because nephrogenesis continues for two weeks after birth. So, they have podocytes but they haven’t got foot

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processes. They have endothelial cells but they don’t have fenestration. This is in a lot of the glomeruli. Some are mature but in general you get

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quite a lot of immature glomeruli. In the mutant the majority of the glomeruli were actually more mature; the podocytes had well-formed foot

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processes and the endothelial cells had fenestrations. It was an interesting observation. We also counted glomerular number at one

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month, so this is before there was any evidence of glomerulosclerosis and there was reduction in the number of glomeruli in the mutant compared to

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the wild-type. So, my argument was that yes, the observation was interesting, but if you combine it with robust stereological data you start to be able

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to find out what might be going on; it gives you a lot more information. So now when people sort of say to me, “Do you have to bother with all that,

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can you not just have a look?” Well, I’m a great believer in that what you put in, you get out. So if you do put a bit more of sort of time and effort

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into this, you get more information and hopefully more answers. Sometimes you just get more questions, but hopefully more answers. So yes,

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its time consuming and I agree with John that the developments with MRI are really going to help and we may not have to do such a time

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consuming thing, but I really wanted to say that it is an important thing to be doing.

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JOHN BERTRAM: Ok thanks Kathryn. Julie if you want to follow on please.

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JULIE INGELFINGER: I think my comments will follow on from Kathryn’s and what I need to say is really based on being a clinician who went

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from that to the lab, and so in a number of studies looking a perinatal programming, colleagues of mine and I, at some extent, have looked at

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glomerular number in low protein models in the rat and in high salt models and by counting glomeruli and having people who can do stereology have

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found very important data, and Shao-Ling Zhang who’s a colleague who’s here has been doing this in models of diabetic pregnancy and finding

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more apoptosis and finding differences in numbers of glomeruli. I still look at things as a clinician and so I want to come at these

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comments from the point of view of somebody who is thinking about needs for the future since that’s one of the objects of this conference. What

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I have here is something we all know. If you are unlucky enough to be born early you have a lot of weeks of nephrogenesis remaining and just

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shown here is, by very first grade arithmetic, how many weeks more of nephrogenesis there will be. So we have a very important cohort of

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people whom we could follow longitudinally and about whom we do want to know what happens to glomerular number as well as total nephron

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number because these people get, at least from our survey of our nursery, up to 14 nephrotoxins in the course of their NICU stay; and I’m picking

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this as one example of a cohort of people. So, what we don’t know and what we need is just

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as what I wanted to simply enumerate and that is: we need to find a way to do longitudinal studies with counts or surrogate counts and think that

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would be very important. It may be at first very time-consuming and it will need the kind of study that’s been published that John Bertram

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mentioned today and that will be discussed in detail tomorrow and such better imaging will ultimately bring to the clinic methods to count

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glomeruli in vivo, and what we also need, I think, is a better assessment of kidney function with imaging. What I don’t think we know in the human

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over time is what happens to tubular volume. We know that can certainly increase and decrease in

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a number of things over time and very quickly. We don’t know how much glomeruli change in their volume just in the course of a day. I do know from

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studies I did 30 years ago sieving glomeruli and dumping different vasoactive substances on them, that the volume of glomeruli that we sieved

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would increase four-fold or decrease four-fold very easily, so that would be very important. We need dynamic measures of glomerular filtration

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rate and estimated renal plasma flow with something that allows us to do it serially in the short run to measure something that looks like

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renal functional reserve. The present methods for that are very cumbersome but I think correlating that with glomerular number will be very helpful

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and we need more to look at biomarkers, as Wendy presented today, and we need to find out what that means. So, there’s a lot that we don’t

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know that we need to combine with stereology and being able to count and I’ll stop there.

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JOHN BERTRAM: Thanks very much Julie. Bryan Myers wasn’t able to be with us but Kevin Lemley has volunteered to say and make a few

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comments and then I’ll open it up to the floor for general discussion.

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KEVIN LEMLEY: So, since Bryan couldn’t make it I’m just going to give you, say in Monty Python, now for something completely different: a

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combined functional structural way of estimating glomerular number, because as you saw from John, sometimes we get somewhat disparate

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values. The motivation was we had been engaged for quite a number of years in a study of normal aging and the glomerulus, getting

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intraoperative preimplantation transplant biopsies from living and deceased donors, and we wanted to estimate glomerular number. So our

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surgeon was very nice to us and he would take a wedge biopsy, he didn’t do a needle biopsy, at the preimplantation time and these patients had

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been measured or these donors if they were living had been measured in advance for MRI, so we had a cortical volume, and when we just

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looked at the estimated glomerular density per volume times the cortical volume we got what seemed like very high numbers because we still

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were firm believers in the [---] Benson approach which was 617,000. And so, we tried an alternative method which was to estimate the

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number of functioning glomeruli by measuring with true measures for GFR, single kidney GFR—actually in this case dual kidney GFR divided by

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2—and then divide by an estimate of the single nephron GFR. Now, single nephron GFR can be estimated in humans from the ultrafiltration

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capacity, which we’ll call SNKf, of the glomerulus and the mean transcapillary driving pressure, and in work over quite a few years in the rat we

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found that you can actually get quite good estimates of SNKf from what you can do from an electron micrograph from the surface area for

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filtration and the hydraulic permeability of that area. The driving pressures are from the measured plasma oncotic pressure and an

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estimation of what the intracapillary pressure is; which in rats you can actually measure but not in humans. What we see here are the values we

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got in older and younger donors, because again, we’re looking at an aging effect here, and the biopsies provided an estimation that changed

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quite a bit. Again, if you look at the younger donors they were pretty much in the range that other people were getting and this is, of course,

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the number of functioning glomeruli. When you do it this way it isn’t just what glomeruli are there, it’s the ones that are actually contributing GFR, and

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what was interesting was the measured sclerosis rate could not account for the fairly big decrease with age that you saw in the number of

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functioning, implying that you have a loss of glomeruli over time with “normal aging” that do not leave remnants there. Whoops, that’s for another

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day, I’m not going to show that.
FEMALE: How did you measure the global

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sclerosis rate?
KEVIN LEMLEY: Global sclerosis was measured

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in the biopsy sections with a correction because we estimate the cross sectional diameter because that affects your chance of hitting

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sclerotic, so there’s a small correction because they’re smaller so that you adjust for that.

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JOHN BERTRAM: Okay. So, I’d like to open this discussion up now to the floor if you come to the microscope…the microscope [laughs]…what’s

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that thing called? Yeah. It’s a new kind of microscope. Please say your name.

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JULIE INGELFINGER: I feel right at home at the microscope. That’s a very ingenuous approach to try to look at functioning glomeruli but the

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additional confounder, of course, is the wedge biopsy which I deal with all the time looking at donor biopsies. It’s superficial and not only does it

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overestimate the total number of globally sclerotic glomeruli in the screened donor who doesn’t have overt kidney disease, it also is not

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representative of the single nephron GFR of all nephrons when you make your assessments and your inferences and your assumptions from that,

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so there are several levels of assumptions. We know very well in many other mammalian species that superficial and deep glomeruli don’t have the

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same uniform single nephron GFR.
FEMALE: My name is Marjan Afrouzian from the

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University of Texas. I’m probably one of the few people who have just come to this field to see what beautiful things you are doing and maybe

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it’s a little bit too much to ask but I would like to know if I want to start to come to your field what shall I do regarding my preimplantation biopsies?

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Shall I put them in formaldehyde? What resin method should I do? We need really some guidelines from you for our next patients, not just

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normal kidneys. But this field, whatever you are doing, is going to change what we are doing in pathology for our patients. The way we are

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processing our kidney biopsies or wedge biopsies, for myself I would like to know if you are giving guidelines to us to start coming parallel

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to you with our pathology specimens.
JOHN BERTRAM: Well, I guess I, in my

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introductory talk, kind of put that out there as an idea to try to develop some guidelines and we certainly talked about it briefly as the organizing

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team for the meeting as something that might develop from this. I don’t think any of us underestimate nor any of us believe that would

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be a straightforward and simple or necessarily a quick process, but again, they’ve managed to do it in the lungs. So, if the lung guys can do it then

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maybe those of us south of the diaphragm can have some success as well. I don’t work that much with clinical biopsies so I can’t tell you

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exactly what to do, how to do it now—some people may want to contribute—but that could very well be an outcome from this kind of this

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meeting as a catalyst for it down the track. Jeffrey might have his own thoughts on that particular comment.

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JEFFREY KOPP: No, I have no thoughts, but I’d love to hear Mike or Agnes or other people tackle that one because that is a big question: how to

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apply these stereology principles to clinical tissue.

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MIKE MAUER: I think this a very important question. One approach that one might consider with clinical biopsies would be to initially limit the

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number of sections that are taken and stained for a routine study and let the pathologist decide whether the initial sections are adequate and

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whether they need more and save some of the tissue for studies that you might be able to do more quantitation on. Now this is very much a

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sort of a clinical judgment call of the pathologist who needs to make those decisions but that’s one way in which we might be able, for example,

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that saves tissue for serial sections and for more quantitation, and that will vary in the condition being looked at. So, Agnes obviously is going to

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look at this from the pathologist point of view but let me just give you an example. When we look at FSGS on renal biopsies we sometimes wonder

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why there was such rapid progression when only 25% of the glomeruli showed FSGS lesions. In fact, on serial sections, 25% is about 85% so

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really we are way underestimating it. So, I think it’s at least worth considering our approaches to handling biopsy tissue, clinical biopsy material.

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AGNES FOGO: Thank you for opening the door for discussing renal pathology and diagnosis; that’s a very favorite subject of mine. I think that it

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is very true that we do not have to exhaust the tissue block that is submitted to us for analysis to make a diagnosis but when you the word “limit”

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that could make somebody think that you only have to do maybe one or two or three sections. So, I want to share with you an experience I had

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when I visited China about a dozen years ago and I explained that we routinely did several step levels with several stains at these levels—so in

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our lab we cut 13 slides with a few levels on each slide, so that’s about 40 levels, 50 levels on each biopsy—and I was speaking slowly and this

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was being translated every three or four sentences and I was asked to repeat what I had said, and after I had repeated it three times my

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host in Beijing decided the translator should be fired and they brought in a big board like we have up there and asked me to please draw the slides

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that I stained and sectioned. So, I drew 13 slides, we stained 9 of them, we keep the intervening ones for other studies and drew the tissue and

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the question then came, “But Professor Fogo, you only do this when the diagnosis is FSGS, correct?” I think renal pathologists—my

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colleagues—are really awesome but I don’t think that any of them or I can tell that it’s FSGS before we have done the sections. So the follow up to

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that when I visited China some seven to eight years later, the incidence in Beijing of nephrotic patients with minimal change verses FSGS, the

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ratio had flipped completely from minimal change disease being much more common in biopsied nephrotic steroid-resistant patients to FSGS being

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much more common. So, how many sections can we get? We did the study—maybe you also did—of serially sectioning focal segmental sclerosis

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patients to see how many glomeruli are involved if it indeed is focal; it still is focal when you exhaustedly section. We can section about 80 to

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100 sections—2 micron sections—from a typical core. We don’t do that on the front end. We have been very fortunate to have an ARRA grant

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funded to look at the FSGS clinical trial biopsies. We are getting the unstained tissue sections, the frozen tissue, and what remains in the paraffin

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blocks to do additional immunostaining that we hope will elucidate something about the disease. We can get 10, 20, sometimes 30 sections from

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remaining tissue in the paraffin block. In addition, there are wonderful studies being done by Neptune, Matthias Kretzler, by others, where you

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may on the front end decide that you, with informed consent, are going to do an additional core in the patient and if the diagnosis is clear

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from the initial materials submitted then you will not process and submit that additional core, but all of this comes together. So, I just want to be

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really careful when we talk about limit the use of tissue that you do have to do more than one section and one stain to be able to adequately

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diagnose all of the processes but that doesn’t mean that we have to exhaust the block, and there’s a lot of tissue left in the block. If you have

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excellent histotechs who don’t apply general surgical pathology technique, which is we have to face the block and get well into the tissue so

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we have a good slice right through the middle before we start picking it up, if your histotechs…any of you deal with nephrologists or renal

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pathologists are doing that then you’re throwing away half the tissue which could be used for research or diagnostic purposes.

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MIKE MAUER: I think I’m in total agreement the clinical diagnosis comes first, but I think if we husband the tissue very carefully there may be

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residual tissue in the block that could be looked at in a more careful way in terms of clinical research. One other comment I’d like to make and

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go back to Julie’s point about atubular glomeruli: I think that is an area in which we haven’t looked at sufficiently carefully. What we do know is that

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atubular glomeruli can look like normal but on average they are smaller than glomeruli with proper, normal glomerular tubular junctions, so

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some of the variability that we’re seeing in glomerular volume, that we’re seeing in these high risk populations, may in fact represent

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heterogeneity in regard to the glomerular tubular junction. That could easily be driving the hypertrophy of the residual functioning nephrons

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that are not separated from their tubules and could be an explanation of some of the findings. What is common about atubular glomeruli is that

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very proximal to them are atrial [---] tubules, so if there’s a substantial amount of tubular atrophy in the tissues, that should be something which

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should be suspected.
JEFFREY KOPP: So, I’d like to return to the issue

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of acquiring tissue and make the statement that as nephrologists we used to all use 14-gauge needles and some of us still do, but there has

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been a migration to have a radiologist do it who tend to favor the 16- or the 18-gauge needles that often go into medulla and so don’t yield as

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many glomeruli. So I would say for somebody who’s setting out to try to do some of these stereology techniques, the more tissue the better

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and there are multiple ways to acquire it by a larger needle and several passes and making sure you stay in cortex. But I wanted to come

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back, John, to a couple of more questions about how the autopsy studies were done. You settled on 30 glomeruli, one question is maybe you could

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talk a little bit about that. Presumably you did some prior studies that looked at larger numbers and felt that the parameters tend to destabilize after

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stopping at 30 and then how did you select the 30?

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JOHN BERTRAM: 30 from memory and Wendy can correct me if I’m wrong. We figured we wanted to count the same size, the same number,

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of glomeruli per layer of cortex as Wendy’s already mentioned. So, from memory I think it was a bit of an empirical decision to choose 10 from

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the outer third of the cortex, 10 from the middle third and 10 from the inner third of the cortex. We have looked at some work in the last year or so

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and published a paper in NDT I think about 6

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months or so ago asking the question, “Do we really need to do all those 30?” because it is dissector Cavallieri so it is very time consuming,

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and we found that we could get reasonably robust estimates if we did around 9 or 10 in most glomeruli in most situations. But again, I

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emphasize these are not samples of kidneys from patients with overt renal disease, this is our autopsy series, so in a sitting of pathology that

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number may well be not accurate. I think Kathryn may have done a study some years ago looking at the numbers of glomeruli in biopsies to estimate

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volume with Cavallieri and to get kind of a robust estimate. Do you want to speak to that?

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KATHRYN WHITE: Yeah. We did a study and we looked to see how many glomeruli we had to measure volume in and we did it in 10 per biopsy

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and also compared it—we’d just done 5—and the variation was minimal, so we decided to just count 5 glomeruli per biopsy and it gave us a

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good estimate of glomerular volume. But of course that was in a biopsy core, so you weren’t going to see variations going from one lope to

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another different area of the kidney, so within a biopsy we could get away with just 5.

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JOHN BERTRAM: That was an Epon-imbedded tissue from memory and you were using it in 1-micron sections?

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KATHRYN WHITE: It was, which goes back a bit to this sampling that we’ve been talking about. It sounds like there needs to be a bit of

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communication between pathologists, nephrologists, and researchers but from a technical point-of-view I know that generally

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pathologists seem to still use paraffin-embedded tissue and I don’t know whether—there’s a lot of advances in resin-imbedded tissue that can be

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used for lots of different histological stains and immuno work—whether there’s any sort of room to go to a different embedding medium that may

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be good because you can cut thinner sections, possibly. You get more out of it and I don’t know whether that would be of use between the

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pathologists and researchers. Agnes is shaking her head so she doesn’t….

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AGNES FOGO: You can’t set up a clinical high-quality lab for more time-consuming difficult-to-handle research studies unless it’s funded, so if

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you were going to do that for all clinical biopsies, it would require changes across [---].

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MICHAEL MAUER: Also, it might limit the use of, let’s say, formalin-fixed paraffin-embedded tissue for certain immunohistochemical gene expression

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studies and so on.
AGNES FOGO: [inaudible comment]

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KATHRYN WHITE: There’s lots of different resins than Epon, though. There’s a lot that take histological stains.

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JEFFREY KOPP: So Kathryn, could you enunciate what the advantage of the Epon is? Is it less shrinkage? You talked about the thinner section;

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is that important for a measure of glomerular volume?

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KATHRYN WHITE: It was a study that we were doing, mainly electron microscopy, so it was a resin that we use for electron microscopy and it’s

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not good for histological stains, it will only take one, but there are other resins that you can use but the reason we used that was because we

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predominately do an electron microscopy study.
PAUL KIMMEL: Thank you. I was very struck by

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Kathryn’s and Julie’s comments because I think we also have to step back and take a clinical viewpoint and I am a clinician and I’m sitting here

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and thinking about what can we do with these wonderful data because I know we’re not going to change anybody’s glomerular number; we

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don’t have a good drug for that. So, I would encourage all of us over the next 18 hours that we have, to think about the clinical utility, the

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clinical utility of our measurements. We’re not going to longitudinally biopsy a huge number of patients, although I know that Mike has done that,

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but that’s not going to be a clinical tool. So, I think we have to categorize our studies and the utility of what we have in terms of pathogenetic

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factors, biomarkers I like very much and I can see biomarkers as a potential use, and the clinical applicability, and I think providing a framework for

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what our measurements should be and where our research could go could be very useful for the institute in planning. So, I’d like to encourage

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that kind of structure for where we’re going, what’s research, what’s going to be clinically applicable.

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MICHAEL MAUER: If I could comment...I think that the data that have been presented this afternoon suggest there are some important relationships

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between glomerular number and certain kinds of outcomes or risk. It’s also been suggested that we should spend the money to develop a way of

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estimating glomerular number in living patients. So, the possibility may be that loss of glomerular number is a sensitive indicator of early renal

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disease progression before loss of GFR or proteinuria or other variables come into play, and so it may be important as a risk predictor, it may

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be important as an outcome for clinical trials of early disease. So, it’s taking these laborious methodologies that tell us that glomerular number

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is important, let’s see if there’s a way that we can accurately estimate it in people and then see how it…maybe that is a biomarker.

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PAUL KIMMEL: Well, that’s exactly what I’m talking about, Mike. I think we have to have clinically useful, testable hypotheses.

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So, that’s what I’d like to encourage in the discussions tomorrow,

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which are broken down regarding technical groups. I’m thinking about grants that are going to come in

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and proposals that are going to come in and things that review groups will look at and say, “Well, you know, we’re never going to be able to

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do that,” versus clinically applicable tests that can be done. There’s something nice to do with cohorts. You have to follow these premature

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children for a long period of time if you were going to start at the time they were born. Can you do those studies starting out with 20-year-olds?

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Can you do them cross-sectionally? I’d just like to keep the clinical focus in everybody’s mind because I think that’s going to help us use the

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data better.
FEMALE: One thing I would like to add to what

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you just said is that if there were a way that one could estimate glomerular number at the end of, say, discharge from a NICU—neonatal intensive

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care unit—it would, if there were cohorts, provide a group who could be followed for quite some time. Whether the technology through either

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MR or PET scans with markers will come to pass in the next 5-10 years, I think that will be a very…[inaudible section]…until they’re 20, you can look

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at them much earlier.
PAUL KIMMEL: Right, but then it’s a question of

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when do you assess them? I think that’s what the promise is of non-invasive methods and I think we have to consider them very seriously.

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FEMALE: Could I just support that theme further? I’m sort of an adult nephrologist. I think we need to consider the circumstances under which a

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non-invasive technique for glomerular number and volume and volume heterogeneity—I must get that in—would be useful, and from my point-

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of-view it’s less about the terminal end stages of renal disease than deciding if somebody really has a problem and if they’re progressing from

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early stages to medium sorts of stages, and I think just sort of working out in one’s mind when that might be useful and when it might make a

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difference is important. Then I’d like a discussion or for me to understand: what are the obstacles to developing this technology? I’m of the

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understanding that we have the tools available to us now; that the resolution to pick up a glomerulus is now with us and that there are

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various characteristics of a glomerulus. For example, be it flow or be it water transport or be it a marker or whatever, that it could be identified,

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could be labeled, could be sized. Is it that I don’t understand something about the state of the obstacles to the technique or we have not been

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forceful enough going to our radiological colleagues and imaging colleagues and saying, “Can you work this one through with us? What

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are the approaches?” Now, maybe many of you know what stages have been reached in getting this towards such a technology—non-invasive,

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non-toxic—in humans, non-damaging, that I don’t, but I’d like a discussion about what those obstacles are and what the approaches might be.

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JOHN BERTRAM: We are going to discuss this at some length tomorrow but there’s been a lot of talk today about non-invasive imaging, so maybe I

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could ask Kevin and Norbert Gretz maybe for just one or two minutes each just to give us some things to think about overnight before we discuss

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this at greater length tomorrow because there’s clearly a lot of interest. Norbert, do you want to kick that off, perhaps?

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NORBERT GRETZ: I think the idea is great but what we are currently doing is we are working ex vivo, so we are far off and it’s probably not

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suitable for all disease types so you definitely need an adequate, stable basal membrane. If that is not the case, forget it.

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JOHN BERTRAM: Kevin?
KEVIN LEMLEY: I want to add to that. We’ve done

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some work in vivo in animals. The problem is, the contrast agent has to be cleared for regulation so we’re working on that at the moment and actually

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moving an agent like that to clinical trials, so we’re using a specific contrast agent that labels the glomeruli; so if you want to do counting, that kind

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of thing. The real place where there needs to be improvement is in sort of moving through the regulatory process for things like that. The

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second part is, the resolution at sort of the in vivo level in humans is not as high as it is in animals specifically because the gradient strength isn’t

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strong enough and I’ll talk about that tomorrow in the meeting, but it’s really just sort of a technological challenge. We have all the tools to

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make it happen, it’s just most people just don’t buy that kind of equipment, and that’s for this specific type of measurement. There are people…Vivian

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Lee who was at NYU and now she’s at Utah, has done a lot of work on contrast agent uptake in the kidneys measuring flow and stuff and I

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think that those things at sort of a lower resolution give you estimates of gs like GFR and that kind of thing. thinJOHN BERTRAM: Bob?

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ROBERT CHEVALIER: Bob Chevalier, University of Virginia. I want to get back to the question of atubular glomeruli that’s been surfacing for the

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last couple of hours. I think the reason that this has been under-appreciated in human tissue is it’s been so difficult to document. Jean Oliver first

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described this with microdissections over 50 years ago and then Marcussen had a series of papers in the 90s showing a large variety of

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diseases using serial sectioning, whether it be renal artery stenosis, transplant rejection, a whole host of disorders characterized by this,

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and it now looks like the rate at which atubular glomeruli develop depends on the disorder. Jess Thoene published a couple of years ago that in

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cystinosis it’s extremely rapid and by the time kids are 10 years old most of their glomeruli are disconnected and it’s not surprising because this

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disease attacks the proximal tubule; and Michael Mauer was Type I diabetes…there’s a paper in Type II that seems to happen later. So, young

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adults get it with Type I, later in Type II. So there’s a spectrum and I do think it’s important to know, when you’re looking at glomeruli, whether they’re

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connected or not and it would seem that the imaging techniques may give us a window in this. The glomeruli are smaller but with the overlap it

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probably is difficult to know what the story is with the connected tubule. We published a paper in the rat ureteral obstruction model in AJP last

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year showing there’s a trick in the mouse that, since there are columnar parietal epithelial cells that are around the urinary pole in a normally

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connected glomerulus, that the Lotus staining goes away if that glomerular tubular junction is damaged. In a survey section it’s possible to get

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the proportion of glomeruli that are staining versus those that are not as a rough measure of the health of the glomerular tubular junction in the

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mouse model.
JOHN BERTRAM: Thanks.

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MICHAEL MAUER: I think these are important comments and I would throw pyelonephritis into Marcussen’s work showing how important it is in

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that disease. One clue, I think, is to pay attention to Bowman’s capsule. I think that when you start to see towards the tubular pole serious

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abnormalities—re-duplication, thickening of Bowman’s capsule—start to worry about this process. I think looking at the surrounding of the

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glomerulus, if the nearby tubules are atrophic, if the Bowman’s capsule is abnormal, I think your index of suspicion should go up and then you

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want to start looking through the sections and I think we will find many more of these abnormalities than we initially thought. One other

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comment I’d like to make and I think it’s a conceptual one that’s important to keep in mind along with Paul telling us to pay attention to the

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clinical, and that is that we may think differently about the role of some of the variables that we’re thinking about at different stages of disease, and I’ll

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give you an example to illustrate this. If we look at people who are diabetic, who get a brand new kidney in a transplant, and we do research

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biopsies an average of 12 years later and we take people with two kidneys who had diabetes for the same duration as the transplant as being in

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the diabetic environment with similar levels of A1C, etc., then the rate of development of lesions in the one kidney versus the two kidney

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populations is absolutely superimposable. So for genesis, nephron number may not be so critical, at least for diabetic nephropathy. For

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progression, from established advanced injury that turned into uremia is probably a totally different story. So depending on the stage of the

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illness that you’re looking at, the importance of these variables may be very, very different.

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JOHN BERTRAM: I’m cognizant of the time, but perhaps one final question? Thanks.

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TAKAMUNE TAKAHASHI: I am Takamune Takahashi at Vanderbilt University and I have a brief question about the clinical application of the

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glomerular number data. There are many of the obesity people and I think that obesity increased their glomerular volume and

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my question is: does this depend on the glomerular number or is glomerular number independent? So my question is: does obesity

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increase in the glomerular volume depend on the glomerular number or independent?

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JOHN BERTRAM: Certainly, the relationship between BMI and mean glomerular volume is quite clear. I don’t know, Wendy, whether we’ve…I’m

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sure you have looked at the relationship between Nglom and BMI as it applies to the glomerular size. Do you want to comment on that if that was the

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question you were asking?
TAKAMUNE TAKAHASHI: Yes. Do you think that

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obesity affects the glomerular volume? Obesity affects the glomerular volume, do you think?

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JOHN BERTRAM: Yes, I do. In fact, we’ve shown it in terms of average glomerular size and also in the expansion of the variation in the glomerular

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size, absolutely, with a greater spread in those with the larger BMI, for sure.

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TAKAMUNE TAKAHASHI: So my question: is this glomerular number independent or dependent?

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JOHN BERTRAM: I’m not sure on that. Wendy, have we looked at that in terms of the setting of obesity and whether this expansion of Vglom

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relates to the nephron number? I don’t know that we’ve done that.

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WENDY HOY: I’m sorry. I can’t really answer it precisely accurately but they’re both independently significant in multivariate equations

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of influencing Vglom via BMI and lower Nglom and you get a lot of explanation of variants by equations that have them both in, and you get a

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lot of explanation of variants looking at Nglom in the context of current body size. The question is, if people with very marginal low Nglom became

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very fat, would they have more glomeruli hypertrophy than those with robust Nglom? I think the answer is probably conceptually “yes.” I’d

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have to go back and dig around and figure out a way to demonstrate that, but indeed, that’s what the multivariate data suggest.

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JOHN BERTRAM: So conceptually, yes. We may not have exactly done that analysis that you’ve asked for. Okay. Thanks very much and I’ll hand

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over to Jeffrey to wrap things up.
JEFFREY KOPP: Well, thank you to our speakers,

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the discussants, the audience. I think this has been really a remarkable afternoon and early evening discussion, and we’ll continue with more

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tomorrow at 8:00, so I’ll see you then.




Date Last Updated: 10/3/2012

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