On my way to the hospital today, I heard the Top 40 Hits of this week in 1973. For you youngsters, the Top 40 involved the sales of small vinyl records with 1 song you wanted on one side and something completely random on the other. These small discs turned at 45 revolutions per minute and were often called 45's or singles. Based on sales, they ranked the top songs in the US.
Somewhere in the middle of the pack was the song, Dead Skunk in the Middle of the Road :
While at Experimental Biology, I wrote here about a number of presentations of interest. These studies revolved around cool animal models and very basic mechanisms of disease. None of them will result in a change in patient care in the next year (nor perhaps in the next 5 years). All of them are essential to advancing human health, because each is a drop of water in the river of science.
A river flows along, with new streams pouring into it all the time. All these bits of water run together, sometimes slowing to mix in eddies, other times tumbling over rapids and falls, producing a whole new arrangement of the molecules that make up the river. As new flows come together, the pattern of the river may change, its rate increasing. Sometimes a rockslide or a beaver provides an obstacle that stops flow, although ultimately the river will overcome a blockage.
In science, new facts and ideas constantly flow into the world, sometimes bumping into each other and mixing in unexpected ways. Sometimes a technical issue will prevent progress on an idea; at other times, a new tool will speed the flow and move the information flow forward faster.
The important part of the metaphor is that we have no idea what information will be the critical piece that solves a puzzle, just as we cannot call out a particular raindrop or snowflake as the one that overcomes the dam. If we want to make progress, we have to continue to study it all. Eventually, the critical pieces will fall into place.
That's why it's so important to study lots of different science, even if it appears to have no implications that we can use. Down the road, it may provide that critical information that revolutionizes our world. And we simply cannot know until it happens.
Dahl salt-sensitive rats provide a useful model of salt-sensitive hypertension. What if we used something besides NaCl to give them sodium? What happens with sodium bicarbonate, for example?
Bicarbonate Therapy Alleviates Hypertension-Induced Renal Injury in Dahl Salt-Sensitive Rats Independent of System Blood Pressure. D Irsik et al.
Telemetry-monitored rats were treated with NaCl of equimolar NaHCO3 in their drinking water. Blood pressure rose identically in the two groups of rats, so sodium really seems to be the drive of that response. A variety of indices of kidney damage, including glomerulosclerosis tubular casts, and interstitial fibrosis, were significantly reduced in the rats receiving bicarbonate.
Na excretion was similar in both groups, although net acid excretion rose dramatically in the NaCl rats. This consisted of both NH4+ as well as a significant component of titratable acids.
Some of the numbers are rather preliminary, but serum pH and bicarbonate levels were similar in the two groups (7.49 for pH and ~27 for bicarbonate). Potassium was reduced in both groups, although lower with NaCl (3.59 vs 3.33). Numbers in each group are too small for statistical comparisons, but that should be corrected in the near future.
For a clinician, this work from Paul O'Connor's lab raises many interesting points. First, the groups had essentially identical pH and bicarbonate. If these results hold up as they expand their numbers, it has human implications. I would not have targeted either group for bicarbonate therapy based on serum levels.
I would like to see them do a clinically relevant experiment. When we give base (usually as NaBicarbonate) to patients, we are not generally substituting it for NaCl. Rather, we are adding another 30-50% of daily Na intake to their usual NaCl intake. How would doing that in this model change the outcomes? Would the additional sodium have any untoward effects?
As those of us at the Gottschalk lecture know, there are complex interactions between Na, H+, and K+ at the epithelial Na Channel in salt-sensitive states. Reducing the presence of acid (H+) in the filtrate may be beneficial, both in preserving potassium levels and, perhaps, other yet unidentified effects.
A number of disorders plague us as we age. Blood pressure rises with age, and increasingly so do blood glucose levels. Some argue that hypertension is a component of type 2 diabetes, but other times it precedes the hyperglycemia. Clinically, it is often difficult to sort out consequences of hyperglycemia and hypertension in the kidney. This abstract shows us how it can be done.
Interaction of Hypertension and Diabetes in Progressive Nephropathy: Role of ER Stress.Z Wang et al.
This study, from John Hall's group at Mississippi, starts with Goto-Kakizaki (GK) rats that spontaneously develop type 2 diabetes about 6 months of age. At time zero, they placed a telemtry device to measure blood pressure in the aorta of these animals. After a couple of weeks fro recovery and baseline measurements, they then used an abdominal coarctation model to produce systemic hypertension that one kidney gets exposed to, but the other sees low flow and pressure.
Used with permission of authors
A coarctation of the aorta may occur spontaneously during fetal development, resulting in hypertension because the kidneys both see low blood flow. Their efforts to correct that, through increased production of renin and all of its effects, causes hypertension. By creating the narrowing of the aorta between the left and right kidneys (see diagram), the upper right kidney gets exposed to the elevated pressure, while the left kidney senses a reduced pressure. For those of you who have not seen this anatomy in the rat, this surgery is a pretty neat trick.
After two more weeks for recovery and measurements, they then added treatment with tauroursodioxycholic acid (TUDCA), an inhibitor of endoplasmic reticulum (ER in the title) stress. ER stress disorders protein folding and transport within cells, contributing to disease and scarring.
Functional and structural markers of kidney damage were increased in the hypertensive kidney compared to the one that had normal or low pressure, as were markers of ER stress. TUDCA treatment lowered these markers, as well as reducing kidney dysfunction in the hypertension-exposed organ.
This elegant study shows that hypertension may accelerate kidney injury from hyperglycemia, at least in part through ER stress. Now, if you have high blood pressure and diabetes, don't head online to try and buy TUDCA yet. As with all animal models, this one is not quite ready for translation to the bedside. First, the GK rat is not obese, so not a typical type 2 diabetes model. Of course, obesity adds a whole lot more issues to this equation, but also makes surgery in this area more difficult. Second, the "unexposed" kidney is the source of the trouble. It's cranking out renin, and we know that the renin-angiotensin system is active within the kidney as well as systemically. Many of these components can affect the kidney; however, I would expect that to blunt the difference between the kidneys rather than increase it. However, it will be interesting to see if TUDCA proves as effective in models that do not depend on renin activation.
This lovely study does convince us that hypertension interacts with hyperglycemia in the kidney to accelerate kidney damage. It also confirms the role of pressure in ER stress.
Every day many people in the world volunteer to lose a kidney. It may be to cure a condition, but more often they give a healthy organ for transplantation to someone with permanent kidney failure. In general, kidney donors who have been carefully screened seem to have little kidney morbidity over the long-term.
What are the consequences of uninephrectomy that may not relate directly to kidney function?
Metabolic Consequences of Experimental Uninephrectomy.D Arsenijevic et al
This group (sponsored by Jean-Pierre Montani) performed uninephrectomy or sham procedure in 6-week-old male rats (so an early teenager in human time, an age where removing a functioning kidney is almost unheard of). They then studied body composition and a number of metabolic markers at 1, 2, and 4 weeks following the procedure.
Body weight remained similar between the groups, but fat mass was reduced in the animals that lost a kidney. In addition, there were alterations in circulating lipolytic cytokines, a sign of systemic inflammation.
Systemic inflammation can be bad for your cardiovascular system.
These findings are intriguing, but there are a lot of unanswered questions. First, a 4-week endpoint in a 10-week-old rat is hardly a long-term study. I want to know how these boys do over at least 6 months. Is this an early change that then resolves with time, or one that becomes more pronounced?
What about female rats? I spent too many years considering sex differences to leave that out. Also, it would be interesting to see if uninephrectomy in adult animals (at least 14 weeks of age) has similar effects. That age would be more analogous to the situation in kidney donors.
Since we do so many kidney donor surgeries, there is excellent opportunity to also measure these parameters in people. Measuring fat mass can be expensive and annoying, but drawing blood for lipolytic cytokines would certainly be feasible. Come on - let's get translational!
This abstract is really a teaser, I hope, designed to make us want more answers. In that case, it worked like a charm!
The kidneys provide half of our acid-base balance in the body, with the rest being performed by our lungs. Our pulmonary system regulates the intake and output of carbon dioxide, while the kidneys excrete acid and retain or generate bicarbonate, the primary buffer in the fluids outside of our cells.
It’s amazing how much of this process has been figured out over time. It takes a very complex system to regulate the balance of a critical component so tightly, yet we still find new systems to take into account.
Elucidating the Physiological Role of Gprc5c, a Novel Orphan GPCR in the Kidney. P Rajkumar and JL Pluznick
G protein coupled receptors (GPCRs) are a class of membrane bound molecules that sense signals outside a cell and then trigger other effects. This group found an orphan GPCR, one whose ligand (fancy science talk for the signal it senses). It was interesting, in part, because it is found abundantly within the kidney, at a comparable level to angiotensin receptors. Other investigators had developed an antibody to it, as well as a mouse with this gene knocked-out, making it an excellent target for further study.
The antibody showed lots of this protein, mostly in the apical or inside-membrane of proximal tubule cells. The proximal tubule of the kidney is a workhorse. These tubes have to reabsorb most of what gets filtered from the blood, since the kidney cleans blood by removing most stuff and then returning the good stuff. It’s similar to some organization shows on TV; instead of trying to take out unnecessary clutter, they start by clearing the room (filtration) and then putting only the useful, wanted things back in (proximal tubule reabsorption).
For their next step, they wanted to screen ligands, starting with known functions of the proximal tubule. Gprc5c becomes active when exposed to alkaline pH. No other GPCR studied does the same thing!
Metabolic studies on the knock-out mice that lack Gprc5c reveal mild acid build-up in the blood and loss of alkali in the urine. These observations are consistent with a role for this “orphan” in sensing alkali in the urine and promoting its reabsorbtion.
It’s fascinating to see systems we thought we had figured out get a new player. Of course, eventually this means altering my medical student lectures. I guess that’s the price of science!
I have written many times about my arch nemesis, hemolytic uremic syndrome (HUS). This disorder is what we medical docs call a thrombotic microangiopathy. Something damages the lining of small (micro) blood vessels (angio), causing platelets to clump (thrombotic) and form webs across the tiny capillaries. For some reason, organs hit by this damage include the kidney, brain, pancreas, and then pretty much anything else at random.
We see two forms of HUS in childhood. Atypical forms result from mutations in the complement system, a series of immune system proteins that respond rapidly to threats. This system is pretty complex, as shown in the diagram below from a great article; click the picture for the full reference. This system is always "on" and is regulated by proteins that dampen it. In atypical HUS, these regulatory proteins are deficient, allowing complement to rampage at will. The critical component is the Membrane Attack Complex (MAC) which destroys cells, be they foreign or host.
Click for source and review article.
Currently we can treat atypical HUS with eculizumab, an antibody to complement component C5, a protein just before the MAC. Antibody at c5 prevents formation of the MAC and provides miraculous results for patients with atypical HUS.
The most common form of HUS follows an episode of bloody diarrhea due to a bacteria that produces shiga toxin, most commonly E. coli. We will call this eHUS today. This toxin provides the damage to the blood vessels that triggers the thrombotic microangiopathy. Once the toxin clears, the patient usually recovers but with a high risk of kidney failure many years down the road.
In really bad cases of eHUS we have used eculizumab to help patients (desperate times and desperate measures, you know). It seems to turn off the thrombotic microangiopathy rapidly, suggesting that complement may be involved in these patients as well.
Human Mannose-Binding Lectin (MBL2) Inhibitor Prevents Renal Injury in a Novel Animal Model of Enteropathic Hemolytic Uremic SyndromeM Ozaki et al
This group, led by Gregory Stahl, took mice that lacked the mouse form of mannose-binding lectin (MBL2) and gave them the gene for the human form of this molecule. In the complement diagram above, MBL2 is a component of the Lectin activation pathway for the complement system. They then treated these mice with shiga toxin with or without an antibody to MBL2.
Shiga toxin damaged the cells lining blood vessels, releasing MBL2. This then turned on the complement system,and these mice got thrombotic microangiopathy with kidney damage. Those that received the antibody to MBL2 with the shiga toxin had far less damage from the toxin. Giving the antibody up to a day later also provided some protection from HUS.
This study is so exciting! First, it provides a mouse model of eHUS that we can use to examine the complement pathways in more detail and to develop new drug targets. Second, their anti-MBL2 antibody may be used as a treatment someday. #Winning!
Atypical HUS without treatment almost always results in kidney failure, and the disease more often than not destroys transplanted kidneys as well. Patients with eHUS recover and come off of dialysis in 90% of cases; however, they generally have 2-4 weeks of hospitalization with multiple surgeries. A treatment that could rapidly reverse kidney failure would provide substantial reductions in costs and make patients much happier. They also face an increased lifetime risk of kidney failure, depending on the level of damage at the time of the illness. New treatments beyond supportive care with dialysis may reduce this issue as well.
As a pediatric kidney doc, this study makes me very, very happy!
As a pediatric nephrologist (children's kidney doctor), hydronephrosis or water on the kidney is one of the most common problems I see. The kidney can be thought of as two general parts: (1) A bunch of blood vessels that filter “dirty” blood and return it to the body after cleansing and (2) Tubes made of cells that carry filtered material from the blood vessels, taking good stuff back into the body and taking out more bad stuff to make urine.
As these tubules travel through the kidney, they eventually come together to form bigger and bigger tubes until they form the pelvis (see diagram), the main part of the urine collecting system within the kidney. When these central collecting systems look enlarged on ultrasound or other study, we call it hydronephrosis.
The pelvis of the kidney becomes a fine muscular tube, the ureter, once it leaves the kidney. This transitional area, the ureteropelvic junction (UPJ, lower image) is a fairly common place for obstruction to develop before children are born. In most cases, the actual obstruction resolves early on, leaving an enlarged but fully functional collecting system. Think of a balloon that you have blown up and then the air let out. It is never as tight as it was before (and so seems a little floppy), but nothing is blocking it up.
In some cases, the UPJ obstruction persists after birth but gets better over months to years. In other cases, the obstruction tightens and may require surgical repair or result in the loss of kidney function.
We know all of this from following lots and lots of kids with UPJ obstruction for years. What we do not know is why this portion of the collecting system is so prone to obstruction.
A Novel Transgenic Mouse Model for Congenital Obstructive Nephropathy; AJ Lee et al
One reason we know so little about the how and why of UPJ obstruction is that there have been no non-surgical models where it develops spontaneously. That no longer seems to be a problem as this group, led by Ben Fogelgren at the University of Hawaii (I'm available to collaborate and I will come to you) now has a mouse that develops severe UPJ obstruction. Unfortunately, these mice have complete anuria, resulting in death at birth.
How did they do this? The model involves a conditional knock-out of Sec10 in the ureteric buds of embryonic mice. These cells are destined to become the ureter and pelvis within the kidney. Sec10 is a protein in exocysts, structures in the cells that help other proteins get to their correct location.
Cells run on proteins. Some have to be in the apical (top) membrane, some have to be in the basal (bottom) membrane, while others have to attach to stuff within the cell. The cells in the developing ureter have a number of proteins that must be on the apical membrane that lines the tube. One of these proteins, Uroplakin 3, fails to end up there in these mice. The cells look abnormal, and other cells (muscle or scar cells) grow more until the ureter tube closes.
This model obviously has some differences from what we see in people. Most children have mild UPJ obstruction only on one side, so it seems likely that environmental factors may disrupt these processes transiently in clinical situations. However, this model should increase our understanding of what controls this process and why it happens in this particular location.
This model provides an important opportunity to study a major cause of pediatric kidney problems. I look forward to seeing a lot more data from this lab!