Tobias Traupe

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 increases prostanoid-mediated vasoconstriction and vascular thromboxane receptor gene expression.

Objectives Vasoconstrictor prostanoids have been implicated in abnormal vasomotion in atherosclerosis and hypertension. Method Using lean and diet-induced obese mice, we investigated whether obesity affects vascular function or expression of genes involved in prostanoid action. Results In lean C57BL/6J mice, at high concentrations acetylcholine caused endothelium-dependent contractions in the carotid artery but not in the aorta. Endothelium-dependent contractions to acetylcholine were blocked by the non-selective cyclooxygenase (COX) inhibitors indomethacin and meclofenamate, or a prostaglandin H2/thromboxane A2 receptor antagonist, but not by inhibitors of COX-2, thromboxane synthase or cytochrome P450 monooxygenase. Obesity increased endothelium-dependent contractions to acetylcholine in the carotid artery, and prostanoid-mediated vasoconstriction was now present in the aorta. Similarly, contractions to endothelin-1 were largely blocked by meclofenamate and were increased in the aorta of obese mice. Real-time quantitative polymerase chain reaction analysis of the thromboxane receptor gene in the carotid artery revealed a robust upregulation in obese animals (18-fold, P < 0.05); in comparison, obesity had a less pronounced effect on thromboxane synthase (2.1-fold increase, P < 0.05), or preproendothelin-1 gene expression (4.2-fold increase, P < 0.05). Conclusions These data demonstrate that obesity augments prostanoid-dependent vasoconstriction and markedly increases vascular thromboxane receptor gene expression. These changes are likely to promote the development of vascular disease, hypertension and thrombosis associated with obesity.

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.

Distinct Roles of Estrogen Receptors α and β Mediating Acute Vasodilation of Epicardial Coronary Arteries

This study investigated the contribution of estrogen receptors (ERs) &agr; and &bgr; for epicardial coronary artery function, vascular NO bioactivity, and superoxide (O2−) formation. Porcine coronary rings were suspended in organ chambers and precontracted with prostaglandin F2&agr; to determine direct effects of the selective ER agonists 4,4′,4″-(4-propyl-[1H]pyrazole-1,3,5-triyl)tris-phenol (PPT) or 2,3-bis(4-hydroxyphenyl)-propionitrile (DPN) or the nonselective ER agonist 17&bgr;-estradiol. Indirect effects on contractility to U46619 and relaxation to bradykinin were assessed and effects on NO, nitrite, and O2− formation were measured in cultured cells. Within 5 minutes, selective ER&agr; activation by PPT, but not 17&bgr;-estradiol or the ER&bgr; agonist DPN, caused rapid, NO-dependent, and endothelium-dependent relaxation (49±5%; P<0.001 versus ethanol). PPT also caused sustained endothelium- and NO-independent vasodilation similar to 17&bgr;-estradiol after 60 minutes (72±3%; P<0.001 versus ethanol). DPN induced endothelium-dependent NO-independent relaxation via endothelium-dependent hyperpolarization (40±4%; P<0.01 versus ethanol). 17&bgr;-Estradiol and PPT, but not DPN, attenuated the responses to U46619 and bradykinin. All of the ER agonists increased NO and nitrite formation in vascular endothelial but not smooth muscle cells and attenuated vascular smooth muscle cell O2− formation (P<0.001). ER&agr; activation had the most potent effects on both nitrite formation and inhibiting O2− (P<0.05). These data demonstrate novel and differential mechanisms by which ER&agr; and ER&bgr; activation control coronary artery vasoreactivity in males and females and regulate vascular NO and O2− formation. The findings indicate that coronary vascular effects of sex hormones differ with regard to affinity to ER&agr; and ER&bgr;, which will contribute to beneficial and adverse effects of hormone replacement therapy.

Assessment of the Human Coronary Collateral Circulation

Cardiovascular disease is the leading cause of death in industrialized countries and may become the most important reason for mortality worldwide.1 In patients suffering from coronary artery disease (CAD), the size of myocardial infarction mainly determines outcome.2 Accordingly, the primary strategy to reduce cardiovascular mortality is by shrinking infarct size (IS) (Figure 1A).3 In the clinical setting of acute myocardial infarction, Antoniucci et al4,5 documented in 1164 patients undergoing primary percutaneous coronary intervention (PCI) that the presence of angiographic collaterals before PCI purported a survival benefit compared with the situation without them (Figure 2). As a surrogate for IS, studies on the effect of myocardial salvage procedures have employed the magnitude of ECG ST-segment elevation during coronary balloon occlusion (Figure 3).6,7 IS, measured as the degree of ECG ST-segment elevation during a 1-minute coronary occlusion, is influenced by the following factors: duration of occlusion, ischemic area at risk for myocardial infarction (AR), collateral blood supply to the ischemic zone, ischemic preconditioning, and myocardial oxygen consumption.8 In the context of a single brief artificial coronary occlusion of uniform duration without preceding bouts of ischemia (Figure 3),6 ECG signs of ischemia are influenced predominantly by the AR and by collateral supply to this region. Furthermore, Figure 1B3 illustrates that AR and collateral supply are inversely related to each other (ie, AR tends to shrink toward zero in the presence of well-functioning collaterals). They are termed sufficient if they prevent an ECG ST-segment elevation of ≥0.1 mV during a 1-minute coronary balloon occlusion; otherwise, they are termed insufficient collaterals. Figure 1. Schematic drawing of the coronary artery circulation without (A) and with interarterial anastomoses (B) between the right coronary artery and the occluded left anterior descending artery (occluded downstream …

Coronary collateral growth by external counterpulsation: a randomised controlled trial

Background The efficacy of external counterpulsation (ECP) on coronary collateral growth has not been investigated in a randomised controlled study. Objective To test the hypothesis that ECP augments collateral function during a 1 min coronary balloon occlusion. Patients and methods Twenty patients with chronic stable coronary artery disease were studied. Before and after 30 h of randomly allocated ECP (20 90 min sessions over 4 weeks at 300 mm Hg inflation pressure) or sham ECP (same setting at 80 mm Hg inflation pressure), the invasive collateral flow index (CFI, no unit) was obtained in 34 vessels without coronary intervention. CFI was determined by the ratio of mean distal coronary occlusive pressure to mean aortic pressure with central venous pressure subtracted from both. Additionally, coronary collateral conductance (occlusive myocardial blood flow per aorto-coronary pressure drop) was determined by myocardial contrast echocardiography, and brachial artery flow-mediated dilatation was obtained. Results CFI changed from 0.125 (0.073; interquartile range) at baseline to 0.174 (0.104) at follow-up in the ECP group (p=0.006), and from 0.129 (0.122) to 0.111 (0.125) in the sham ECP group (p=0.14). Baseline to follow-up change of coronary collateral conductance was from 0.365 (0.268) to 0.568 (0.585) ml/min/100 mm Hg in the ECP group (p=0.072), and from 0.229 (0.212) to 0.305 (0.422) ml/min/100 mm Hg in the sham ECP group (p=0.45). There was a correlation between the flow-mediated dilatation change from baseline to follow-up and the corresponding CFI change (r=0.584, p=0.027). Conclusions ECP appears to be effective in promoting coronary collateral growth. The extent of collateral function improvement is related to the amount of improvement in the systemic endothelial function.

Myocardial Salvage Through Coronary Collateral Growth by Granulocyte Colony-Stimulating Factor in Chronic Coronary Artery Disease A Controlled Randomized Trial

Background— The efficacy of granulocyte colony-stimulating factor (G-CSF) for coronary collateral growth promotion and thus impending myocardial salvage has not been studied so far, to our best knowledge. Methods and Results— In 52 patients with chronic stable coronary artery disease, age 62±11 years, the effect on a marker of myocardial infarct size (ECG ST segment elevation) and on quantitative collateral function during a 1-minute coronary balloon occlusion was tested in a randomized, placebo-controlled, double-blind fashion. The study protocol before coronary intervention consisted of occlusive surface and intracoronary lead ECG recording as well as collateral flow index (CFI, no unit) measurement in a stenotic and a ≥1 normal coronary artery before and after a 2-week period with subcutaneous G-CSF (10 &mgr;g/kg; n=26) or placebo (n=26). The CFI was determined by simultaneous measurement of mean aortic, distal coronary occlusive, and central venous pressure. The ECG ST segment elevation >0.1 mV disappeared significantly more often in response to G-CSF (11/53 vessels; 21%) than to placebo (0/55 vessels; P=0.0005), and simultaneously, CFI changed from 0.121±0.087 at baseline to 0.166±0.086 at follow-up in the G-CSF group, and from 0.152±0.082 to 0.131±0.071 in the placebo group (P<0.0001 for interaction of treatment and time). The absolute change in CFI from baseline to follow-up amounted to +0.049±0.062 in the G-CSF group and to −0.010±0.060 in the placebo group (P<0.0001). Conclusions— Subcutaneous G-CSF is efficacious during a short-term protocol in improving signs of myocardial salvage by coronary collateral growth promotion.

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.

Effects of obesity on endothelium-dependent reactivity during acute nitric oxide synthase inhibition: modulatory role of endothelin

This study investigated vascular reactivity in response to acetylcholine, in the presence of acute inhibition of nitric oxide synthase, in the carotid artery and aorta of obese C57Bl6/J mice fed on a high-fat diet for 30 weeks, and of control mice. A subgroup of obese animals was also treated with the ET(A) receptor antagonist darusentan (50 mg x kg(-1) x day(-1)). In vascular rings from control animals, acetylcholine caused endothelium-dependent contractions in the carotid artery, but not in the aorta. In vascular rings from obese mice, contractility to acetylcholine was also evident in the aorta, and that in the carotid artery was increased compared with control mice. ET(A) receptor blockade by darusentan treatment of the obese mice prevented enhanced vasoconstriction to acetylcholine, resulting in mild vasodilatation. Thus obesity increases endothelium-dependent vasoconstriction in the absence of endothelial nitric oxide. This effect can be completely prevented by chronic ET(A) receptor blockade, suggesting that endothelin modulates increased endothelium-dependent vasoconstriction in obesity.

The effect of heart rate reduction by ivabradine on collateral function in patients with chronic stable coronary artery disease

Objective To evaluate the effect of heart rate reduction by ivabradine on coronary collateral function in patients with chronic stable coronary artery disease (CAD). Methods This was a prospective randomised placebo-controlled monocentre trial in a university hospital setting. 46 patients with chronic stable CAD received placebo (n=23) or ivabradine (n=23) for the duration of 6 months. The main outcome measure was collateral flow index (CFI) as obtained during a 1 min coronary artery balloon occlusion at study inclusion (baseline) and at the 6-month follow-up examination. CFI is the ratio between simultaneously recorded mean coronary occlusive pressure divided by mean aortic pressure both subtracted by mean central venous pressure. Results During follow-up, heart rate changed by +0.2±7.8 beats/min in the placebo group, and by –8.1±11.6 beats/min in the ivabradine group (p=0.0089). In the placebo group, CFI decreased from 0.140±0.097 at baseline to 0.109±0.067 at follow-up (p=0.12); it increased from 0.107±0.077 at baseline to 0.152±0.090 at follow-up in the ivabradine group (p=0.0461). The difference in CFI between the 6-month follow-up and baseline examination amounted to −0.031±0.090 in the placebo group and to +0.040±0.094 in the ivabradine group (p=0.0113). Conclusions Heart rate reduction by ivabradine appears to have a positive effect on coronary collateral function in patients with chronic stable CAD. ClinicalTrials.gov Identifier: NCT01039389.