Jana Ortmann

Role of Podocytes for Reversal of Glomerulosclerosis and Proteinuria in the Aging Kidney After Endothelin Inhibition

The cause of focal-segmental glomerulosclerosis as a consequence of physiological aging, which is believed to be inexorable, is unknown. This study investigated whether inhibition of endothelin-1, a growth-promoting peptide contributing to renal injury in hypertension and diabetes, affects established glomerulosclerosis and proteinuria in the aged kidney. We also determined the role of endothelin receptors for podocyte injury in vivo and in vitro. Aged Wistar rats, a model of spontaneous age-dependent glomerulosclerosis, were treated with the orally active endothelin subtype A (ETA) receptor antagonist darusentan, and evaluation of renal histology, renal function studies, and expression analyses were performed. In vitro experiments using puromycin aminonucleoside to induce podocyte injury investigated the role of ETA receptor signaling for apoptosis, cytoskeletal injury, and DNA synthesis. In aged Wistar rats, established glomerulosclerosis and proteinuria were reduced by >50% after 4 weeks of darusentan treatment, whereas blood pressure, glomerular filtration rate, or tubulo-interstitial renal injury remained unaffected. Improvement of structural injury in glomeruli and podocytes was accompanied by a reduction of the expression of matrix metalloproteinase-9 and p21Cip1/WAF1. In vitro experiments blocking ETA receptors using specific antagonists or RNA interference prevented apoptosis and structural damage to podocytes induced by puromycin aminonucleoside. In conclusion, these results support the hypothesis that endogenous endothelin contributes to glomerulosclerosis and proteinuria in the aging kidney. The results further suggest that age-dependent glomerulosclerosis is not merely a “degenerative” but a reversible process locally confined to the glomerulus involving recovery of podocytes from previous injury.

Obesity-associated activation of angiotensin and endothelin in the cardiovascular system

The renin-angiotensin system (RAS) and the endothelin system have been implicated in the pathogenesis of human cardiovascular and renal diseases, and inhibition of the RAS markedly improves morbidity and survival. Obesity in humans is associated with an increased risk for the development of hypertension, atherosclerosis and focal-segmental glomerulosclerosis, however the exact mechanisms underlying these pathologies in obese individuals are not known. This article discusses the clinical importance of obesity and the current evidence for local activation of the renin-angiotensin system and its interactions with the endothelin system in obesity and the cardiovascular pathologies associated with it.

Lovastatin stimulates human vascular smooth muscle cell expression of bone morphogenetic protein-2, a potent inhibitor of low-density lipoprotein-stimulated cell growth

Bone morphogenetic proteins (BMPs) stimulate ectopic bone formation in skeletal muscle. Here we show that human vascular smooth muscle cells (VSMC) abundantly express mRNA encoding for BMP receptor type II, BMP-2, and BMP-7 proteins. Treatment with the 3-hydroxy-3-methylglutaryl coenzyme A inhibitor lovastatin (34 microM) increased BMP-2 gene transcription >14-fold as measured by real-time PCR analysis (P<0.05 vs. solvent control). Moreover, VSMC proliferation stimulated with native low-density lipoprotein (100 microg of protein/mL) was prevented by either human recombinant BMP-2 or BMP-7 at concentrations of 100 ng/mL (P<0.05). Both BMPs also inhibited basal cell proliferation (P<0.05). Induction of BMPs and subsequent inhibition of VSMC growth and/or induction of vascular bone formation could contribute to the mechanisms by which statins increase plaque stability in patients with coronary atherosclerosis.

Activation of Pro-Inflammatory and Anti-Inflammatory Cytokines in Host Organs During Chronic Allograft Rejection: Role of Endothelin Receptor Signaling

This study investigated whether allograft rejection is associated with local inflammatory activation in host organs and whether endothelin ETA receptor signaling is involved. Expression of IL‐1β, IL‐1ra, IL‐6, IL‐10 and TNF‐α was investigated in host liver, lung and native heart in a rat model of chronic rejection 8 weeks after heterotopic cardiac transplantation in the absence of immunosuppression. In the presence of rejection, circulating levels of cytokines increased, while tissue level activation was dependent on the organ involved. Similarly, tissue‐specific regulatory patterns were observed regarding transcriptional activation. Although chronic ETA receptor blockade did not reduce transplant vasculopathy or tissue protein expression, treatment had pronounced effects on plasma levels and transcriptional regulation of chemokines. These data provide evidence for distinct pro‐inflammatory local activation in host organs during chronic rejection and suggest a role for ETA receptors contributing to regulation of cytokine plasma levels and transcriptional activity.

Endothelial therapy of atherosclerosis and its risk factors.

Atherosclerosis is a chronic systemic disease of the vasculature with an inflammatory component. It accounts for the majority of cardiovascular morbidity and mortality in industrialized countries and its incidence is increasing in developing countries. The impairment of vascular endothelial cell function in atherosclerosis and in conditions associated with increased cardiovascular risk is an important determinant of disease progression. The reduction of endothelium-dependent relaxation in the coronary and systemic circulation in atherosclerosis is in part due to decreased bioavailability of nitric oxide and increased release of oxygen-derived free radicals. Atherosclerosis also increases the formation of vasoconstrictors and growth factors, adhesion of leukocytes, thrombosis, inflammation, cell proliferation, as well as increases in vascular tone. Here we review mechanisms and therapeutic approaches to improve endothelial pathways in atherosclerosis. Restoration of NO bioactivity through pharmacological inhibition of the renin-angiotensin system, statin therapy, or endothelin receptor blockade, ameliorates vascular function in experimental hypercholesterolemia, hypertension and heart failure. These treatments also have therapeutic benefit for patients at risk or with overt atherosclerosis, to reduce vascular and myocardial complications of this disease.

Downregulation of Renal Endothelin-Converting Enzyme 2 Expression in Early Autoimmune Diabetes

To determine whether renal expression of endothelin-converting enzymes (ECEs) and endothelin (ET) is affected in the early stages of autoimmune diabetes mellitus and whether ETA receptors are involved, prediabetic nonobese diabetic (NOD) and control mice were treated with the ETA receptor antagonist BSF461314 (a follow-up compound of darusentan) or with placebo. Blood samples were analyzed for glucose levels, and renal gene expression of ECE-1, ECE-2, and prepro-ET-1 was determined using real-time polymerase chain reaction. Renal morphology was assessed using standard histologic techniques. ECE-1, ECE-2, and prepro-ET-1 mRNA was detected in the kidneys of NOD and control mice. Despite normal renal histology, expression of ECE-1 and prepro-ET-1 was reduced in NOD mice by approximately 50% compared with controls (P < 0.01); ECE-2 was markedly decreased by almost 90% compared with controls (P < 0.001). Treatment with BSF461314 for 6 weeks delayed the onset of diabetes (P < 0.05) and increased expression of all three genes (P < 0.05) in NOD mice only. Hyperglycemia at an early stage of autoimmune diabetes is associated with transcriptional downregulation of ECE-1, ECE-2, and prepro-ET-1 in the kidney. Blockade of ETA receptors inhibits diabetes-associated gene regulation and delays the onset of diabetes, suggesting its therapeutic potential for the treatment of autoimmune forms of diabetes.

Amiodarone Acutely Inhibits Vascular Activity of Endothelin-converting Enzymes

Endothelin has been implicated in arrhythmogenesis. Amiodarone, initially developed for the treatment of angina pectoris, is a potent inhibitor of ventricular arrhythmias. We investigated whether amiodarone (34 μg/mL) affects the vascular endothelin system of healthy Wistar-Kyoto rats. Contractility to big endothelin-1 and endothelin-1 was determined in aortic and carotid artery rings suspended in organ chambers. Functional activity of endothelin-converting enzymes was calculated for each concentration, and endothelin-converting enzyme-1 gene expression was analyzed using real-time polymerase chain reaction. Activity of functional endothelin-converting enzymes was sevenfold higher in the carotid artery than in the aorta (P < 0.001). Contractions to big endothelin-1 (0.1 μmol/L) were attenuated by amiodarone in the carotid artery (50 ± 9% vs 90 ± 8%, P < 0.01) but not in the aorta. Accordingly, contractility to endothelin-1 (0.1 μmol/L) was decreased by amiodarone in carotid rings only (105 ± 7% vs 132 ± 6%, P < 0.01). After acute exposure to amiodarone, functional activity of endothelin-converting enzymes at 0.1 μmol/L was slightly increased in the aorta (17 ± 2% vs 11 ± 2%, P < 0.05), but decreased in the carotid artery (40 ± 9% vs 76 ± 5%, P < 0.05). Endothelin-converting enzyme-1 mRNA expression in the aorta was not affected by amiodarone treatment. Thus, amiodarone acutely affects the activity of vascular endothelin-converting enzymes depending on the anatomical localization of the artery. Acute effects of amiodarone on endothelin-converting enzymes may contribute to its antiarrhythmic properties.