Sandeep Vetteth

Central role for the cardiotonic steroid marinobufagenin in the pathogenesis of experimental uremic cardiomyopathy.

Patients with chronic renal failure develop a “uremic” cardiomyopathy characterized by diastolic dysfunction, cardiac hypertrophy, and systemic oxidant stress. Patients with chronic renal failure are also known to have increases in the circulating concentrations of the cardiotonic steroid marinobufagenin (MBG). On this background, we hypothesized that elevations in circulating MBG may be involved in the cardiomyopathy. First, we observed that administration of MBG (10 &mgr;g/kg per day) for 4 weeks caused comparable increases in plasma MBG as partial nephrectomy at 4 weeks. MBG infusion caused increases in conscious blood pressure, cardiac weight, and the time constant for left ventricular relaxation similar to partial nephrectomy. Decreases in the expression of the cardiac sarcoplasmic reticulum ATPase, cardiac fibrosis, and systemic oxidant stress were observed with both MBG infusion and partial nephrectomy. Next, rats were actively immunized against a MBG-BSA conjugate or BSA control, and partial nephrectomy was subsequently performed. Immunization against MBG attenuated the cardiac hypertrophy, impairment of diastolic function, cardiac fibrosis, and systemic oxidant stress seen with partial nephrectomy without a significant effect on conscious blood pressure. These data suggest that the increased concentrations of MBG are important in the cardiac disease and oxidant stress state seen with renal failure.

Marinobufagenin Stimulates Fibroblast Collagen Production and Causes Fibrosis in Experimental Uremic Cardiomyopathy

We have observed recently that experimental renal failure in the rat is accompanied by increases in circulating concentrations of the cardiotonic steroid, marinobufagenin (MBG), and substantial cardiac fibrosis. We performed the following studies to examine whether MBG might directly stimulate cardiac fibroblast collagen production. In vivo studies were performed using the 5/6th nephrectomy model of experimental renal failure (PNx), MBG infusion (MBG), PNx after immunization against MBG, and concomitant PNx and adrenalectomy. Physiological measurements with a Millar catheter and immunohistochemistry were performed. In vitro studies were then pursued with cultured isolated cardiac fibroblasts. We observed that PNx and MBG increased MBG levels, blood pressure, heart size, impaired diastolic function, and caused cardiac fibrosis. PNx after immunization against MBG and concomitant PNx and adrenalectomy had similar blood pressure as PNx but less cardiac hypertrophy, diastolic dysfunction, and cardiac fibrosis. MBG induced increases in procollagen-1 expression by cultured cardiac fibroblasts at 1 nM concentration. These increases in procollagen expression were accompanied by increases in collagen translation and increases in procollagen-1 mRNA without any demonstrable increase in procollagen-1 protein stability. The stimulation of fibroblasts with MBG could be prevented by administration of inhibitors of tyrosine phosphorylation, Src activation, epidermal growth factor receptor transactivation, and N-acetyl cysteine. Based on these findings, we propose that MBG directly induces increases in collagen expression by fibroblasts, and we suggest that this may be important in the cardiac fibrosis seen with experimental renal failure.

Marinobufagenin induces increases in procollagen expression in a process involving protein kinase C and Fli-1: implications for uremic cardiomyopathy

The cardiotonic steroid marinobufagenin (MBG) has been implicated in the pathogenesis of experimental uremic cardiomyopathy, which is characterized by progressive cardiac fibrosis. We examined whether the transcription factor Friend leukemia integration-1 (Fli-1) might be involved in this process. Fli-1-knockdown mice demonstrated greater cardiac collagen-1 expression and fibrosis compared with wild-type mice; both developed increased cardiac collagen expression and fibrosis after 5/6 nephrectomy. There was a strong inverse relationship between the expressions of Fli-1 and procollagen in primary culture of rat cardiac and human dermal fibroblasts as well as a cell line derived from renal fibroblasts and MBG-induced decreases in nuclear Fli-1 as well as increases in procollagen-1 expression in these cells. Transfection of a Fli-1 expression vector prevented increased procollagen-1 expression from MBG. MBG exposure induced a rapid translocation of the delta-isoform of protein kinase C (PKCdelta) to the nucleus. This translocation was prevented by pharmacological inhibition of phospholipase C, and MBG-induced increases in procollagen-1 expression were prevented with a PKCdelta- but not a PKCalpha-specific inhibitor. Finally, immunoprecipitation studies strongly suggest that MBG induced phosphorylation of Fli-1. We feel these data support a causal relationship with MBG-induced translocation of PKCdelta, which results in phosphorylation of as well as decreases in nuclear Fli-1 expression, which, in turn, leads to increases in collagen production. Should these findings be confirmed, we speculate that this pathway may represent a therapeutic target for uremic cardiomyopathy as well as other conditions associated with excessive fibrosis.

The cardiotonic steroid hormone marinobufagenin induces renal fibrosis: implication of epithelial-to-mesenchymal transition

We recently demonstrated that the cardiotonic steroid marinobufagenin (MBG) induced fibrosis in rat hearts through direct stimulation of collagen I secretion by cardiac fibroblasts. This stimulation was also responsible for the cardiac fibrosis seen in experimental renal failure. In this study, the effect of MBG on the development of renal fibrosis in rats was investigated. Four weeks of MBG infusion triggered mild periglomerular and peritubular fibrosis in the cortex and the appearance of fibrotic scars in the corticomedullary junction of the kidney. MBG also significantly increased the protein levels and nuclear localization of the transcription factor Snail in the tubular epithelia. It is known that activation of Snail is associated with epithelial-to-mesenchymal transition (EMT) during renal fibrosis. To examine whether MBG alone can trigger EMT, we used the porcine proximal tubular cell line LLC-PK1. MBG (100 nM) caused LLC-PK1 cells grown to confluence to acquire a fibroblast-like shape and have an invasive motility. The expressions of the mesenchymal proteins collagen I, fibronectin, and vimentin were increased twofold. However, the total level of E-cadherin remained unchanged. These alterations in LLC-PK1 cells in the presence of MBG were accompanied by elevated expression and nuclear translocation of Snail. During the time course of EMT, MBG did not have measurable inhibitory effects on the ion pumping activity of its natural ligand, Na(+)-K(+)-ATPase. Our data suggest that the MBG may be an important factor in inducing EMT and, through this mechanism, elevated levels of MBG in chronic renal failure may play a role in the progressive fibrosis.

Fanconi Syndrome and Antiretrovirals: It Is Never Too Late.

Antiretroviral medications such as tenofovir have been associated with Fanconi syndrome (FS) usually identified within the first 1–29 months after exposure to the medication. We present a case of life-threatening FS which developed in a 37-year-old woman with HIV after 8 years of asymptomatic tenofovir use. The patient was diagnosed with HIV in 1996 at 20 years of age, hepatitis C 10 years later, and Staphylococcus aureus sepsis with secondary osteomyelitis of the spine 3 years before admission for FS. She developed nausea, vomiting, diarrhea, and generalized weakness over a 2-week time period and presented to the hospital. In the emergency department, her serum potassium was 1.5 mEq/L, bicarbonate was 12 mEq/L, chloride was 111 mEq/L, phosphorus was 1.8 mg/dL, and creatinine was 1.95 mg/dL (baseline, 1.4). Arterial blood gas revealed a non–anion gap (hyperchloremic) metabolic acidosis. Type 2 renal tubular acidosis induced by antiretroviral therapy (ART) was suspected and the ART was discontinued with resolution of the renal abnormalities within 7 days. A non–tenofovir-containing ART regimen consisting of lamivudine/abacavir and efavirenz was begun, and over the next 8 months, the patient was without recurrence of the FS. This case report demonstrates the acute development of FS after prolonged exposure to tenofovir without exposure to additional nephrotoxins such as nonsteroidal medications or aminoglycosides. Tenofovir can cause FS at any time and should be considered in any patient presenting with renal tubular acidosis type 2 while on tenofovir regardless of the duration of drug exposure.

Post-reperfusion syndrome during renal transplantation: a retrospective study.

Post-reperfusion syndrome (PRS) is a serious, widely reported complication following the reperfusion of an ischemic tissue or organ. We sought to determine the prevalence, risk factors and short-term outcomes of PRS related renal transplantation. We conducted a retrospective, case-control study of patients undergoing renal transplantation between July 2006 and March 2008. Identification of PRS was based on a drop in mean arterial pressure by at least 15% within 5 minutes of donor kidney reperfusion. Of the 150 consecutive renal transplantations reviewed, 6 patients (4%) met criteria for post-reperfusion syndrome. Univariate analysis showed that an age over 60, diabetes mellitus, Asian race, and extended criteria donors increased the odds of developing PRS by 4.8 times (95% CI [1.2, 20]; P=.0338), 4.5 times (95% CI [1.11, 18.8]; P=.0378), 35.5 times (95% CI [3.94, 319.8]; P=0.0078) and 9.6 times (95% CI [1.19, 76.28] P=0.0115) respectively. Short term follow-up revealed increased graft failure rate within 6 months (6% vs. 16% P=0.0125) and almost twice the number of hospital days post-transplant in PRS cohorts (5.43 ± 2.29 vs. 10.8 ± 7.29 P=<0.0001). Despite limited reporting, PRS appears to be a relatively common complication of renal transplantation and is associated with increase morbidity.

Haemoperitoneum post colonoscopy in a continuous ambulatory peritoneal dialysis patient.

We present the case of a patient on peritoneal dialysis (PD) who had an uneventful oesophagogastroduodenoscopy and colonoscopy. His peritoneal dialysis after colonoscopy had bright red peritoneal dialysate. The patient was completely asymptomatic and a CT scan was performed which did not reveal any retroperitoneal haematoma and showed no signs of perforation or splenic tear. His PD dialysate cleared up with time. We do not find any such case in the literature in which a patient has had haemoperitoneum after a colonoscopy without any obvious cause to account for it. Our patient was unique due to his CAPD in combination with his immunosuppression for his kidney transplant which may have predisposed him to the intraperitoneal bleed after colonoscopy or it may just have been a normal phenomenon after colonoscopy. More studies need to be done as the realisation of its pathology can prevent unnecessary testing and avoid patient and healthcare workers anxiety.

Cardiotonic Steroids and Cardiac Fibrosis

It is well known and has been shown that patients who have chronic renal failure tend to develop and die of cardiac causes. These patients are known to develop a cardiomyopathy that is characterized by left ventricular hypertrophy and significant diastolic dysfunction. It has also been shown that the chronic renal failure condition is characterized by significant sodium pump inhibition due to increases in the circulating levels of cardiotonic steroids (CTS) such as marinobufagenin (MBG). In this review we will try to elucidate the mechanisms involved in the pathogenesis of uremic cardiomyopathy and the role of CTS in the pathogenesis as well as the possible areas of therapeutic interventions.

Cardiotonic Steroids, Hypertension and Cardiovascular Disease

It has been known for some time that dietary salt intake correlates with the prevalence of cardiovascular disease. However, the molecular link between dietary salt and cardiovascular disease is poorly understood. On this background, it has been observed that there are a class of hormones called cardiotonic steroids whose concentrations increase in response to increases in dietary salt. We have shown that some of these hormones may be natriuretic, but we have also shown that they may also be responsible for progressive renal and cardiac injury. Based on data summarized in this review, we propose cardiotonic steroids may serve as the molecular link between dietary salt and cardiovascular disease.