Lessons from the Akita mouse

Diabetic nephropathy (DN) is a major cause of ESRD worldwide. While many attempts have been made to develop reliable animal models that mimic human disease—ob/ob, db/db obese diabetes type 2 diabetes models, NOD1 mice, streptozotocin (STZ)-induced diabetes model etc., current mouse models still do not display full spectrum of functional and pathological process of human DN (JASN 2009). In addition, it was revealed recently that genetic background has an important effect on the development and severity of diabetic nephropathy. Indeed, C57BL/6 strain, most commonly used for many experimental studies, is highly resistant to diabetic injury. Recently, Akita mouse gained great interest in research of DN. Let’s start with some history of Akita mouse.

Akita mouse was initially reported as a mouse model mimicking MODY (maturity onset diabetes of the young) in late 1990s (Diabetes 1997). Later, they were found to exhibit type 1 diabetes mellitus via a spontaneous point mutation (C96Y) in the Ins2 gene (Wang JCI 1999), which disrupts a disulphide bond between the insulin A and B chains in a dominant negative way, resulting in misfolding and accumulation of insulin molecules (a.k.a ER stress). Akita C57BL/6 develops spontaneous hyperglycemia at 400-500 mg/dl range, mild hypertension, and albuminuria approximately 50-100 microgram/ day, at around 3-4 weeks of age. Difference in disease susceptibility, especially in severity of albuminuria, depending on genetic backgrounds was reported. (Gurley, Am J physiol Renal Physiol 2010, Methods Mol Biol 2012)

Here are recent research updates on Akita mice:

 KKS (Kallikrein-kinin system)—bradikinin 1/2 receptor deficiency in Akita mouse
ACE inhibitors exhibit renoprotective effects via decrease in intra-glomerular pressure by dilating efferent arterioles. Another explanation of renoprotective effects of ACE inhibitors is via kallikrein-kinin system (KKS). B1R and B2R are the two bradikinin receptors; B2R expresses constitutively and, on the other hand, B1R is inducible by inflammatory stress and DN. Studies by Kakoki et al. (Kakoki PNAS 2004 and PNAS 2010) showed B1R and B2R KO mice developed more severe kidney albuminuria (1.7 x (B2R KO-Akita) and 3.0 x (BR double KO-Akita) compared to Akita WT) and glomerular pathology at 6 or 12 months of age, suggesting potential renoprotective effects of KKS. Hypothesis is that the lack of B2R/B1R enhances oxidative stress via reduction of eNOS and prostaglandins as well as mitochondorial dysfunctions. More details to follow.
 eNOS (endothelial Nitric Oxide) deficiency in Akita mice 
In humans, three variants in the endothelial NOS (eNOS) gene NOS3—G894T in exon 7, tandem repeats in intron 4, and C786T in the promoter—are associated with DN. Actually, the frequency of G894T is relatively common and 5-9% individuals are homozygous for TT and thus with less activity of eNOS. Wang et al. (Wang et al. PNAS 2011) developed eNOS-/-Akita mouse in B6-129 hybrid background (eNOS-/-Akita in C57BL/6 is lethal around 5 months before developing DN), and showed eNOS KO resulted in increase in glomerular filtration (increase at 3 mo, then decrease at 7 mo), basement membrane thickening, glomerulosclerosis and albuminuria, independent of blood glucose and blood pressure. 
 Other models in Akita mouse
ACE2 (anigiotensin-conversion enzyme 2) deficiency (Wong et al. Am J physiol 2007) and ketogenic diet (Poplawski et al. PlosONE 2011) in Akita mice have been explored and details to follow.

In summary, Akita mouse is an excellent model of human DN, mimicking both pathophysiology (hyperfiltration and albuminuria) and pathology (GBM thickening and glomerular sclerosis) of kidneys exposed to high serum glucose.

Naoka Murakami

Combo

Azilsartan medoxomil is a relatively new angiotensin receptor blocker and a study was recently published in Hypertension which compared the combination of two different doses of this drug with chlorthalidone against olmesartan in combination with hydrochlorothiazide for the treatment of stage II hypertension. Both combinations were effective at treating hypertension although the reduction in systolic blood pressures was significantly higher in both azilsartan medoxomil/chlorthalidone arms. There was very little difference between the higher and lower doses of azilsartan medoxomil in terms of effectiveness but there was a higher incidence of adverse effects (mostly dizziness/hypotension or an elevated creatinine) in the high dose group.

This begs the question whether the increased effectiveness of the new combination was due to the effect of the azilsartan medoxomil or the chlorthalidone. Chlorthalidone and hydrochlorothiazide have never been directly compared in a randomized trial and this study is unlikely to ever be done because it simply is not cost effective. However, there is a growing consensus that chlorthalidone is the more effective drug for the treatment of hypertension and prevention of secondary events. Add this to the fact that the majority of patients are on suboptimal doses of hydrochlorothiazide and there is an argument that we should be starting patients primarily on chlorthalidone (if not switching existing patients). To give the authors of this paper their due, they did not gloss over this fact and included a paragraph in both the introduction and discussion about the relative effectiveness of chlorthalidone vs. hydrochlorothiazide and suggested that this could have contributed to the increased effectiveness of their combination drug.

I believe that we should always try to give patients as few tablets as possible and as a result, there is a certain logic to combinations of ARB/ACEi + thiazide diuretics. This is the first ACE/ARB that has been combined with chlorthalidone in a single pill and it may be an attractive option for that reason. See this review about the relative benefits of chlorthalidone vs. hydrochlorothiazide (although these authors did not think that the evidence was sufficient to argue convincingly for one over the other), and this previous post by Lisa about the relative efffectiveness of the two drugs.

It's a pity that this study was not done as a direct comparison of two ARBs in combination with chlorthalidone as it would have been easier to judge the relative merits of the drugs without this significant confounding factor.

Pregnancy and ACE inhibitors

Treating hypertension on pregnancy sometimes feels a little like going back in time. As Nate posted previously, the list of anti-hypertensives that are considered safe in pregnancy is relatively short – first line agents include labetalol, hydralazine, methyldopa and some calcium channel blockers, while beta-blockers and diuretics are relatively contraindicated and ACEi and ARBs are definitely contraindicated. ACEi have been associated with a constellation of fetal injuries when used in later pregnancy while a study published in 2006 suggested that they were associated with fetal malformations when used in the first trimester. Given the prevalence of hypertension in the general population and the ubiquity of ACEi, this lead to some understandable anxiety about whether these classes of drugs should be prescribed at all to women of child-bearing potential.

However, two recent studies published in the BMJ and the Journal of Obstetrics and Gynecology have challenged this orthodoxy. The first is a large registry study while the second is a meta-analysis of all studies of ACEi in early pregnancy. These two large studies found that although the risk for fetal malformations was higher than controls with first trimester use of ACEi, there was a similar increased risk associated with the use of any other class of anti-hypertensive and in women with untreated hypertension. There was no excess risk of ACEi over these other groups. This suggests that it is the hypertension itself that is causing the increased risk of malformations rather than any effect of an individual medication. It is important to note that the previously documented association between fetal malformations and the use of ACEi in the second and third trimesters was confirmed in the BMJ study. This indicates that the drugs are not safe for use throughout pregnancy and should be stopped when a woman becomes pregnant. That said, it should bring some relief to mothers who have conceived while taking an ACEi that they have not done any inadvertent harm to their children.

I recommend this excellent editorial on the topic

ACE-inhibitor induced hyponatremia

I’ve always been skeptical about ACE inhibitors as a cause of hyponatremia, despite there being almost 20 case reports of this complication in the literature. Given the fact that so many patients I see are taking an ACE inhibitor, I’ve always felt I’d have encountered this problem more often if it were real. Anyway, I’ve now seen 3 convincing cases and have had to reconsider my position. The following is one such case, and is interesting as it suggests a possible mechanism:

Case: An elderly man with dementia and type 2 DM was admitted following a protracted diarrheal illness associated with poor oral intake. Clinically, he appeared volume depleted, although his blood pressure was normal. He was hyponatremic, with a high urinary sodium and high Uosm (numbers below). The primary team had given him a lot of saline (~6L over 48 hours), which aggravated his hyponatremia, but he continued to appear volume depleted. Urine sodium remained high (65-80), as did his urine output. Despite this Addisonian-type picture, the cort-stim test was normal; renin and aldo were pending.

We were called 3 days into the admission, and decided to stop his lisinopril and continue with normal saline. The results were pretty dramatic, as you can see from the graph below. He immediately became sodium avid (Una fell to less than10 meq/L) and had a water diuresis, correcting his plasma sodium to 132 meq/L over the next few days.

It seems to me that lisinopril was preventing a normal physiological recovery from volume depletion i.e. mineralocorticoid production. Once the ACE was stopped, he became salt-avid under the influence of aldosterone, allowing him to correct the volume depletion and switch off the physiological stimulus to ADH production (hence the water diuresis). This was not SIADH - his ADH axis was functioning normally, as evidenced by his ability to produce dilute urine and correct his plasma Na once the ACE was stopped.

The other 2 cases of ACE-associated hyponatremia I have seen have been remarkably similar to this, where severe volume depletion developed in a patient on chronic ACEi therapy. As such, in my limited experience, the presentation differs from other types of drug-induced hyponatremia, where the sodium falls shortly after the introduction of a new agent, say an SSRI or a thiazide. This insidious mode of presentation may explain why ACE-induced hyponatremia may not be on most people’s radar. Another reason for this may be that ACE-inhibitors can also paradoxically help correct hyponatremia in CHF patients, by improving cardiac output. I’m very interested to hear if anyone else has seen a similar case, as this is a controversial topic (as I’m sure the comment bar will attest!).

ARBs and cancer risk?

In the summer of 2010, I came across a health report on the national news that was titled “Angiotensin Receptor Blockers Linked to Cancer”.  The headline was based on a publication that demonstrated an increased cancer signal associated with the use of ARB therapy.  The results appeared in the July 2010 edition of Lancet Oncology.  Riding on the tail of ONTARGET hysteria (see Nate’s article), the results of this study abruptly prompted an FDA safety review on the potential link between ARBs and cancer.  Given the provocative conclusions of this study, I felt it deserved critical review and acknowledgement within RFN.

BACKGROUND

Sipahi et al published “Angiotensin-receptor blockade and risk of cancer: meta-analysis of randomized controlled trials” in July 2010.  The hypothesis for this study was based on experimental studies showing that the renin-angiotensin system, particularly angiotensin II receptors, play an integral role in the regulation of cell proliferation, angiogenesis, and tumor progression.  However, there was a recent study in JCI showing increased longevity in angiotensin II receptor type 1A (AT1A) KO mice and another study in mice showing less tumor growth in AT1A KO mice.

In human studies, the Candesartan in Heart failure Assessment of Reduction in Mortality and Morbidity (CHARM) trial, which assessed ARBs in heart failure, reported an unexpected finding of significantly higher fatal cancers in the candesartan group than with placebo. 

OBJECTIVE

The primary aim of the study was to examine the effect of ARBs on the incidence of new cancer diagnoses.  Secondarily, the study aimed to determine the affect of ARBs on the occurrence of specific solid-organ cancers and mortality related to cancer.  

METHOD

Data was collected using medical search engines.New cancer data were available for 61,590 patients from five trials. Data on common types of solid organ cancers were available for 68,402 patients from five trials, and data on cancer deaths were available for 93, 515 patients from eight trials.

RESULTS

·      Patients randomly assigned to receive ARBs had a significantly increased risk of new cancer occurrence compared with patients in control groups (7.2% vs6.0%, risk ratio [RR] 1.08, 95% CI 1.01–1.15; p=0.016)

·      When analysis was limited to trials where cancer was a pre-specified endpoint, the RR was 1.11 (95% CI 1.04–1.18, p=0.001)

·      Only new lung-cancer occurrence was significantly higher in patients randomly assigned to receive ARBs than in those assigned to receive control (0.9% vs0.7%, RR 1.25, 1.05–1.49; p=0.01)

·      No statistically significant difference in cancer deaths was observed (1.8% vs1.6%, RR 1.07, 0.97–1.18; p=0.183)

LIMITATIONS

·      META-ANALYSIS, not a prospective trial

·      Studies analyzed were not designed or powered to examine cancer incidence or outcomes

·      Cancer data was not available in all trials, suggesting possible publication bias

·      Individual cancer data and timing of cancers was not available

·      The study design precluded adjustment for age, sex, smoking history, etc

·      Most trials used were less than 5 years in duration (too short to adequately assess cancer signal)

In an accompanying editorial, Nissen called for an urgent regulatory review of ARBs and described the study findings as “disturbing”.  Moreover, Nissen stated that ARBs should be used with greater circumspect by the medical community.

Needless to say, the conclusions of this meta-analysis and the accompanying editorial ignited a myriad of assertive retorts criticizing the study design and conclusions.  Experts lashed out against the authors and journal, calling the results “very skewed” and “a bad example of science”.  Interestingly, 10 years ago similar cancer risks were postulated to be associated with amlodipine.  In a subsequent meta-analysis published in the very same journal, Bangalore et al. identified NO excess risk of cancer or cancer death associated with any single anti-hypertensive agent. 

In my opinion, to change practice patterns based on one meta-analysis (that generated data from studies that were never intended to examine cancer occurrences and outcomes) appears immoderate.  The nature of the study design, at best, only suggests a possible link between cancer and ARB therapy.  I have not changed my prescribing pattern based on this study.  What are your thoughts?  

Michael Lattanzio DO

Should you stop ACE inhibitors prior to major surgery for renoprotection?

I must admit that I have always routinely advised holding ACE/ARB prior to major surgery, given the possibility of hemodynamic instability and assumed risk of AKI due to impaired renal autoregulation when perfusion pressure is low. I’m prepared to accept that I might be biased, as so much of the AKI I see relates to ACEi use, especially in the elderly. But, as it turns out, the question of continuing ACEi pre-operatively is surprisingly controversial. It seems cardiac surgeons are completely split down the middle on the question. Of 167 practicing UK cardiac surgeons who were asked “Do you think it’s beneficial to stop ACEi pre-surgery?” 40% said yes, 40% said no and 20% just grunted. Some even advocate their use for the prevention of AKI. So, you may yet have a friendly tete a tete with your local cardiac surgeon over this issue, and a brief recap of the evidence may stand to you in such an event.

What is immediately striking when you begin read around this issue is the existence of 2 pitched positions, similar to the ongoing debate on renal artery stenting. On the one hand Nephrology journals mostly carry studies supporting ACE avoidance, whereas Anesthetic/Cardiothoracic Surgical journals only seem to have trials that support of ACE continuation. This observation is of itself unsettling, as it suggests to me the existence of publication bias.

Evidence for continuing ACEi:

1. Although small (N=14 CABG patients), this prospective study of 48 hours of iv enalaprilat vs placebo showed that cardiac index, SVR, renal plasma flow (measured by hippurate) and creatinine clearance (measured by timed urine collection) were all significantly improved in the treatment arm and the effects lasted up to post-operative day 7.

2. This small placebo-controlled double blind trial (enalapril vs. placebo) of 40 patients with LVEF < 35% undergoing CABG also showed improved GFR in the treatment arm (GFR increased from 66 to 80; p=0.009 vs no change in placebo).

3. Finally, a prospective multivariate analysis of 536 patients undergoing on-pump CABG, where AKI was defined as a 50% decrease in GFR. The authors observed a reduced rate of AKI associated with pre-op ACEi use (ACE OR 0.48 0.23‐0.77 p = 0.04). The authors tried to reduce selection bias through the use of propensity scores – adjusting for likely group membership (i.e. ACE vs. no ACE) – which are controversial.

Evidence against continuing ACEi:

1. A larger study by Arora et al. (1358, mostly CABG patients), but retrospective and, again, employing propensity scoring to try and mitigate selection bias. Nonetheless, they did observe a 40% increased risk of AKI in multivariate regression analyses.

So where does this leave us? Two small, randomized, prospective studies show a benefit in hemodynamic parameters and GFR. These are consistent with the known vasodilatory effects of ACEi on the systemic and renal circulation, and I have no trouble believing them. However, they do not address the issue of response to a hypotensive insult while on an ACE, which is the crux of the problem in my opinion. Then, we have conflicting evidence from 2 larger observational studies, both of which are concerning for selection bias, with one suggesting the possibility of harm. Based on the above, I would agree with Thomas Berl’s assessment at this years ASN, and invoke Pohl’s rule: “Never trade an unknown benefit for a potential complication.” Given there is no convincing renal benefit to continuing ACE/ARB prior to surgery, and the real possibility of harm, I would hold these drugs for surgeries where post-op hemodynamic instability is likely.

ACE inhibitors and PD

Back to the subject of ACE inhibitors again. There are a number of reasons why ACEi might be particularly beneficial for patients on PD and two recent editorials in KI and CJASN laid these out very well.

1. Preservation of the peritoneal membrane
2. Preservation of residual renal function

Peritoneal mesothelial cells produce angiotensin II in response to glucose and dialysis solutions. This stimulates the release of pro-inflammatory TNF-alpha and IL-6 and also leads to upregulation of profibrotic factors (TGF-beta) and angiogenic factors such as VEGF.

This causes increased submesothelial zone thickness and neoangiogenesis which leads to increased vascular permeability and small solute transport. This in turn leads to faster absorption of glucose with subsequent loss of the osmotic gradient and UF failure. This ‘high transport’ state is associated with a worse long-term prognosis.

As Lisa mentioned in a previous post ACE inhibitors appear to have a beneficial effect on this process. They have been shown to decrease the expression of TGF-beta and VEGF in the peritoneum in response to glucose.

When rats were exposed to high glucose concentrations and were treated with enalapril or placebo, ACE inhibitor-treated rats had reduced TGF-B levels, reduced peritoneal thickness and improved UF. There have been a small number of mostly retrospective studies in humans comparing patients on and off ACE inhibitors and although no survival benefit has been noted, ACE inhibitors have been shown to increase Kt/V and prevent the increase in small solute transport possibly preserving UF in the long term.

The CANUSA and ADEMEX studies both found that the most important factor in predicting survival on PD was residual renal function. In the CANUSA study, for every 5L/week increase in residual function, there was a 12% increase in survival. Peritoneal clearance and peritoneal UF were not associated with survival. Increased residual function has been associated with better BP control, less LVH and a decreased risk of peritonitis.

In small trials, both ramipril and valsartan have been shown to decrease the rate of loss of residual function in patients on PD and at the end of one year, patients treated with ACE inhibitors were less likely to be anuric. This effect was independent of BP control and was seen in normotensive as well as hypertensive patients.

So the question arises, should we be using ACE inhibitors routinely in PD patients even if they are normotensive? The jury is still out on that one and larger studies are needed to determine the answer.

Of snakes and men

As mentioned in a previous post, there is not much salt available in the Amazon and as a result, the inhabitants (human and otherwise) have developed very active renin/angiotensin systems in order to retain whatever salt they can find. Nature being what it is, some predators have evolved to take advantage of this.

Bothrops Jaracara, or the Brazilian Pit Viper, is a poisonous snake that lives in this region. Along with anticoagulants, in the 1960s it was discovered that its venom contains "bradykinin potentiating peptides" that inhibit the angiotensin converting enzyme. In this salt-deprived environment, a bite from this snake would rapidly lead to hypotension and syncope. Captopril, the first commercially available ACE inhibitor, was derived from these peptides in the 1970s. Thus, something which provided a competitive advantage to a viper in the Amazon has become a mainstay in the treatment of hypertension and renal disease today. Similar peptides have been found in the venom of another snake, Agkistrodon Halys Blomhoffii, which is native to Japan and China.

Thank you to commenter Trevedy who pointed me in the direction of an article on the origin of ACE inhibitors.

The bad habit of ACEI!!!!

Coming to the transplant clinic from 2 years of CKD clinic, prescribing ACEI/ARBs was a habit, a good one I guess. Does this hold truth in the transplant world, well... I am not sure anymore after I read this meta analysis in Transplantation last year. The reason simply is that kidney recipients are biologically different from CKD patients. Most of our kidney transplant patients are on calcineurin inhibitors (CNI) which induce afferent arteriolar vasoconstriction. Thus, the advantage of calcium channel blockers (CCB) over ACEI in this population is that it may promote vasodilation of afferent arterioles which may counteract CNI’s effect.

In this meta analysis of 60 trials, enrolling 3802 recipients:

· 29 trials (2262 patients) compared calcium channel blockers (CCB) with placebo or no treatment

· 10 trials (445 patients) compared angiotensin-converting enzyme inhibitors (ACEi) with placebo or no treatment

· 7 studies (405 patients) compared CCB with ACEi

CCB compared with placebo or no treatment (plus additional agents in either arm as required) reduced graft loss (risk ratio [RR] 0.75, 95% confidence intervals [CI] 0.57–0.99) and improved glomerular filtration rate (GFR; mean difference [MD] 4.5 mL/min, 95% CI 2.2–6.7).

Data on ACEi versus placebo or no treatment were inconclusive for GFR (MD -8.1 mL/min, 95% CI -18.6–2.4) and inconsistent for graft loss, precluding meta-analysis.

In direct comparison with CCB, ACEi decreased GFR (MD 11.5 mL/min, 95% CI 7.2–15.8), proteinuria (MD 0.28 g/day, 95% CI 0.10–0.47), hemoglobin (MD 11.5 g/L, 95% CI 7.2–15.8), and increased hyperkalemia (RR 3.7, 95% CI 1.9–7.7). Graft loss data were inconclusive (RR 7.4, 95% CI 0.4–140).

So according to this study there is no advantage of ACEI/ARBs over CCB, with more side effects from angiotensin inhibitors. Obviously, a good randomized trial is needed to resolve this issue.

These data suggest that CCB may be preferred as first-line agents for hypertensive kidney transplant recipients and the KDIGO guidelines consider ACEI/ARB as first line therapy for HTN in renal transplant patients only if their proteinuria is > 1gm/day. A good practice would be to hold them in acute illness as those patients are very sensitive to dehydration due to afferent arterioles vasoconstriction by CNI.

A great combination

Since the retraction of the COOPERATE trial by the Lancet late last year (following Regina Kunz's famous 'letter of concern'), combination RAAS blockade has suffered something of a fall from grace. This was dealt a second blow by the results of the ONTARGET trial, where combination treatment in diabetics with vascular disease was associated with an increased rate of AKI and adverse events, without additional benefit. However, it must be remembered that patients in that trial did not have proteinuria, and the study endpoint was a composite outcome of death from cardiovascular causes, not progression of renal disease. As nephrologists, we are commonly faced with the problem of patients with CKD and heavy proteinuria not controlled by an ACE or ARB alone, and whom we know are at high risk for progressive renal disease. Is there evidence for combination therapy in this context?


In the latest AJKD, this trial by Bianchi et al. makes for provocative reading, although I feel the results must be interpreted with caution. They randomized 128 patients with a clinical diagnosis of idiopathic chronic GN to either intensive therapy (ACE + ARB + spironolactone + high dose statin) or conventional therapy (ACE + low dose statin). The endpoints were change in GFR, proteinuria and adverse events at 3 years. The intensive arm experienced a far greater reduction in proteinuria and stable GFR over time compared to the conventional arm (who lost ~ 7ml/min over the study period) at the expense of more hyperkalemia and discontinued therapy.


I was surprised at how little hyperkalemia developed in the intensive arm (9 vs 3 events). I would have to admit to being pretty nervous of triple RAAS blockade for fear of this complication. That said, if patients can tolerate the combination, the outcomes based on this small study look promising.

Thanks to Dr. Rafael Santamaria for bringing this trial to my attention.

Cyclosporine in Membranous Nephropathy: A non-immune modulatory effect to maintain remission?

This is the story of a 64 year old male mason with past medical history notable for hypertension and hyperlipidemia who was referred to me for evaluation of proteinuria.

The patient noted onset of lower extremity edema nine months prior to the clinic visit. At the time, he was admitted to the hospital due to increasing complaints of lower extremity edema and shortness of breath, and received the presumptive diagnosis of congestive heart failure. He had an echocardiogram showing preserved ejection fraction and no valvular abnormalities. A chest CTA was negative for pulmonary embolism and imaging of the lower extremities was negative for deep venous thromboses. His serum albumin at the time was 2.5 g/dl down from his baseline of 4.0 g/dl a few months prior. No urinalysis data was available from that admission. He was treated with furosemide to which he responded with resolution of his shortness of breath, but with no effect on his notable 3+ pitting edema. He was discharged from the hospital with cardiology follow up as an outpatient.

Teaching point: not all edema is heart failure! A simple urinalysis would have been revealing.

Now back to the case...

During this time period, the patient’s lower extremity edema and exertional dyspnea had not improved in spite of escalating doses of furosemide. He was admitted to the hospital again two months prior to the renal clinic visit, this time for hypertensive emergency treated with intravenous labetalol followed by escalation in his anti-hypertensive regimen which included beta blocker, calcium channel blocker and a small amount of ACE inhibitor. A urinalysis sent at this time showed 3+ protein. He was also subsequently noted to have a serum albumin of 1.3 g/dl. Of note, his renal function was normal at his baseline of 1.0 mg/dl on presentation to renal clinic. Quantification of his proteinuria revealed 13 gms/day.

The patient denied a family history of kidney disease or any known past episodes of kidney problems. He denied fever, headache, chest pain, visual problems, rashes, joint pain, muscle pain, abdominal pain, nausea, vomiting, dysuria, hematuria, or hemoptysis. He had noticed foamy urine over the past few months. He also complained of occasional dyspnea on exertion, which was markedly different from his baseline a year prior. Renal ultrasound was notable for kidneys measuring 14 cm bilaterally with no hydronephrosis and no masses. Ultrasound evaluation of the renal arteries revealed no renal artery stenosis.

He underwent a renal biopsy which revealed membranous glomerulonephritis.

The patient was initially managed with angiotensin converting enzyme inhibitor, angiotensin receptor blocker and diuretics. After a six month period -- fifteen months since the onset of symptoms -- during which there was no sign of spontaneous remission, we initiated treatment with Cyclophosphamide and high dose Prednisone.

The patient developed severe leukopenia, so Cyclophosphamide was discontinued. While we have some experience with Rituximab at our institution, this patient had normal renal function and therefore appeared to be a good candidate for a trial of Cyclosporine. We therefore initiated treatment with Cyclosporine at a dose of 3 mg/kg/day.

He responded well with reduction of his proteinuria to less than 2 gms/day. However, due to an episode of VZV/shingles, the Cyclosporine dose had to be decreased to 1 mg/kg/day, which resulted in trough levels less than 40 ng/ml. In spite of Cyclosporine levels well below these known to have a significant immunomodulatory effect, the patient achieved a surprising partial remission. It is of course conceivable that his remission was spontaneous, but this is not supported by the fact that he had been persistently nephrotic for 1.5 years prior to initiation of Cyclosporine treatment. Furthermore, the fact that the patient continues to be in remission 3 years later suggests that Cyclosporine may continue to exert a beneficial effect.

It is not surprising that Cyclosporine can be successfully used to achieve remission in patients with IMN. However, past experience has shown that many patients with IMN have recurrence of proteinuria once Cyclosporine is removed. On the other hand, the chronic use of Cyclosporine is known to result in a decline of renal function, and nephrologists have been reluctant to use it for a prolonged period of time in the nontransplant setting. It would therefore seem advantageous to devise therapeutic strategies for the use of low dose Cyclosporine to prevent recurrence of nephrosis.

Intriguingly, a 2008 study by the Mundel group suggests that Cyclosporine may have a new target: the glomerular podocyte. The authors present data in mouse models of acquired proteinuria, and specifically in mice that have been genetically modified to express calcineurin in a constitutive fashion. Interestingly, these mice develop severe albuminuria. Through a series of experiments, the authors subsequently determine that Cyclosporine confers an anti-proteinuric benefit through its protective effect on a critical, podocyte-specific molecule called synaptopodin. The preservation of synaptopodin ensures that the podocyte cytoskeleton remains intact, preventing the disruption of the glomerular filtration barrier.

These findings challenge our understanding of Cyclosporine as an immune modulatory agent for proteinuric kidney disease, and our long held belief that Cyclosporine puts patients in remission through its effects on T-cell activity. These data necessitate a closer look at the effects of traditional “immune modulatory” agents on the podocyte cytoskeleton.

Extrapolating from these data, is it possible to maintain podocyte health – and keep nephrotic patients in remission – by using Cyclosporine, or preferably targeted agents with similar podocyte-specific effects?

My patient enjoys a partial remission (currently proteinuria is less than 0.8 gm/day) on what would be considered "subtherapeutic" levels of Cyclosporine. However, if we begin to think of Cyclosporine as a podocyte-modulating agent, perhaps we also need to redefine what levels are “therapeutic.” This case suggests that lower doses may allow us to use Cyclosporine to maintain patients in remission with less concern for its nephrotoxicity. We have now employed this approach in a few other patients with IMN, with encouraging results thus far. Moreover, the use of low dose Prograf in some of our patients with FSGS has also proven to be effective in maintaining remission. Future clinical studies on these questions will be revealing. In the meantime, we are hard at work in the lab to identify new podocyte-specific anti-proteinuric agents.

Are ACE inhibitors good for the peritoneal membrane?

While it has long been postulated that ACE inhibition may help PD patients preserve their residual renal function, there may be another benefit to angiotensin blockade: preservation of peritoneal membrane transport . Last year, a group from the Netherlands analyzed a cohort of incident PD patients in the Netherlands Cooperative Study on Adequacy of Dialysis, and found that the D/P creatinine ratio in patients on ACE inhibitors increased at a significantly slower rate than those not on ACEIs. An increase in small solute transport is thought to represent an increase in membrane neoangiogenesis, likely mediated by TGF-beta and VEGF, which have also been shown to promote peritoneal fibrosis. The study’s authors postulate that ACE inhibitor-mediated downregulation of TGF beta and VEGF explains the slower rate of membrane transport alteration. While no difference in mortality or residual renal function was noted, there did appear to be a beneficial effect on technique survival, one which might have reached statistical significance if the study had continued beyond its 2-4 year duration. Ultrafiltration efficacy was not analyzed, but one might expect increased UF difficulty with increased membrane transport. 



Patients on PD have a number of reasons to be on ACE inhibitors, including their high rates of cardiovascular disease and hypertension, as well as desire to preserve residual renal function. Membrane preservation may be yet another reason to add to the list.

A trap for angiotensin type 1 receptors

The renin-angiotensin system is powerful regulator of blood pressure homeostasis. An article published in the March 24 issue of JASN highlights an emerging area of research into the modulation of AT1 receptors on different tissues.

The majority of well-known angiotensin II actions are mediated via AT1 receptor stimulation, and angiotensin converting enzyme inhibitors (ACEi) and AT1 receptor blockers (ARBs) have been widely used as antihypertensive agents with cardiovascular protective effects. Elucidating factors that regulate AT1 receptor expression levels in different tissue compartments will hopefully lead to novel agents to treat hypertension and its associated end-organ damage (ESRD, CHF and Stroke). Recent studies have demonstrated the existence of several proteins interacting with AT1 receptors that may modulate AT1 receptor expression level, sensitivity and internalization. A recent review article highlights this emerging field. Atrap (AT1 receptor-associated protein) is the best characterized protein and the focus of the March 24 article by Oppermann et al.

It was previously reported that Atrap (a 19kD protein) interacts specifically with the carboxyl-terminal domain of the A1a receptor and catalyzes its internalization in cultured cells. Prior in vivo studies over-expressing the Atrap protein in the heart, aortae and femoral artery in mice demonstrated a protective effect in these tissues in response to angiotensin II infusion. Overall, the prevailing literature suggested an inhibitory or protective effect of Atrap on AT1 receptor function. This group knocked out the Atrap gene in mice to test this hypothesis in vivo.

They reported that Atrap KO mice have a higher resting blood pressure (by 10 mmHg) as measured by radiotelemety. Suggesting that Atrap is important in regulating basal blood pressure and that its absence leads to systemic hypertension. Interestingly, they found that Atrap is highly expressed in the kidney (then testis=adrenal>heart>lung=liver=aorta=brain). Specifically, they showed that Atrap is highly expressed in the proximal tubule of the kidney. Previous investigations have focused on the distal tubule as potential sites that affect blood pressure as most of the known genetic mutations in sodium transport causing hyper/hypotension are linked to the distal nephron (Bartter, Little, Gitelman syndromes, etc). This group reports that Atrap KO mice have more AT1 receptors in the proximal tubule which allows for increased angII-dependent NHE-3 activity causing volume expansion and hypertension.

This highlights the importance of investigating novel pathways regulating the renin-angiotensin system. Modulation of this system with the use of ACEi, ARBs and now direct renin inhibitors have continued to be the mainstay of therapy for patients with heart failure, diabetes, hypertension and kidney disease. Activation of Atrap may be more specific and more physiological for inhibition of At1 receptor signaling. New drug discovery modulating Atrap protein expression could lead to novel therapy. For now, much more research is needed.