Hedayat, Ahmad F.

Introduction: The metabolic syndrome (MetS) leads to cardiac vascular injury, which may reflect in increased retention of endothelial progenitor cells (EPC). Coronary endothelial cell (EC) mitochondria partly regulate vascular function and structure. We hypothesized that chronic mitoprotection would preserve EC mitochondria and attenuate coronary vascular injury and dysfunction in swine MetS. Methods: Pigs were studied after 16 weeks of diet-induced MetS, MetS treated for the last 4 weeks with the mitochondria-targeted peptide elamipretide (ELAM, 0.1mg/kg SC q.d), and lean controls (n=6 each). Coronary artery and sinus blood samples were collected. EC mitochondrial density (electron microscopy), endothelial nitric oxide (eNOS) immunoreactivity (staining), myocardial microvascular density (3D micro-CT), and coronary endothelial function (organ bath) were assessed ex-vivo. The number and arteriovenous gradient of CD34+/KDR+ EPC was calculated by FACS (a negative gradient indicating EPC retention). Results: MetS and MetS+ELAM pigs developed similar MetS (obesity, hyperlipidemia, insulin resistance, and hypertension). EC mitochondrial density decreased in MetS compared to lean, but normalized in MetS+ELAM. ELAM also improved eNOS immunoreactivity, subendocardial microvascular density, and coronary endothelial function. ELAM-induced vasculoprotection was reflected in decreased coronary retention of EPCs. Conclusions: These observations underscore the role of mitochondria in regulating the cardiac circulation in experimental MetS, and the benefits of mitoprotection to preserve EC myocardial microvascular integrity.

Abstract BACKGROUND The collateral circulation is important in maintenance of blood supply to the ischemic kidney distal to renal artery stenosis (RAS). Obesity metabolic syndrome (MetS) preserves renal blood flow (RBF) in the stenotic kidney, but whether this is related to an increase of collateral vessel growth is unknown. We hypothesized that MetS increased collateral circulation around the renal artery. METHODS Twenty-one domestic pigs were randomly divided into unilateral RAS fed an atherogenic (high-fat/high-fructose, MetS-RAS) or standard diet, or controls (n = 7 each). RBF, glomerular filtration rate (GFR), and the peristenotic collateral circulation were assessed after 10 weeks using multidetector computed tomography (CT) and the intrarenal microcirculation by micro-CT. Vascular endothelial growth factor (VEGF) expression was studied in the renal artery wall, kidney, and perirenal fat. Renal fibrosis and stiffness were examined by trichrome and magnetic resonance elastography. RESULTS Compared with controls, RBF and GFR were decreased in RAS, but not in MetS-RAS. MetS-RAS formed peristenotic collaterals to the same extent as RAS pigs but induced greater intrarenal microvascular loss, fibrosis, stiffness, and inflammation. MetS-RAS also attenuated VEGF expression in the renal tissue compared with RAS, despite increased expression in the perirenal fat. CONCLUSIONS MetS does not interfere with collateral vessel formation in the stenotic kidney, possibly because decreased renal arterial VEGF expression offsets its upregulation in perirenal fat, arguing against a major contribution of the collateral circulation to preserve renal function in MetS-RAS. Furthermore, preserved renal function does not protect the poststenotic kidney from parenchymal injury.

New Findings What is the central question of this study ? We hypothesized that chronic mitoprotection would decrease renal vascular remodelling and dysfunction in swine metabolic syndrome. What is the main finding and its importance ? This study shows that experimental metabolic syndrome exerts renal microvascular and endothelial cell mitochondrial injury, which were attenuated by mitoprotection, underscoring the contribution of mitochondrial injury to the pathogenesis of metabolic syndrome‐induced vascular damage. Abstract The metabolic syndrome (MetS) induces intrarenal microvascular disease, which may involve mitochondrial injury. The mitochondrial cardiolipin‐targeting peptide elamipretide (ELAM) improves the microcirculation in post‐stenotic kidneys, but its ability to attenuate MetS‐induced renal vascular damage is unknown. We hypothesized that chronic treatment with ELAM would decrease renal vascular remodelling and function in swine MetS. Pigs were studied after 16 weeks of diet‐induced MetS, MetS treated for the last 4 weeks with daily injections of ELAM (0.1 mg kg −1 ), and lean control (Lean) animals ( n = 6 each). Single‐kidney regional perfusion, blood flow and glomerular filtration rate were measured with multi‐detector computed tomography (CT). Peritubular capillary (PTC) endothelial cell (EC) mitochondrial density and cardiolipin content were assessed in situ , as were PTC‐EC apoptosis and oxidative stress. The spatial density of PTCs (Haematoxylin and Eosin staining) and renal microvessels (micro‐CT), and renal artery endothelial function (organ bath) were characterized. Regional perfusion and serum creatinine were preserved in MetS pigs, but renal blood flow and glomerular filtration rate were higher compared with Lean. Mitochondrial density and cardiolipin content were diminished in MetS PTC‐ECs, but improved in ELAM‐treated pigs, as did PTC density. Elamipretide also attenuated PTC‐EC oxidative stress and apoptosis. Furthermore, ELAM improved renal microvascular density, decreased microvascular remodelling and restored endothelial nitric oxide expression and endothelium‐dependent relaxation of renal artery segments. In conclusion, MetS‐induced mitochondrial alterations might contribute to renal PTC and microvascular loss and might impair renal artery endothelial function in pigs. Mitoprotection with ELAM preserved a hierarchy of renal vessels, underscoring its potential to ameliorate renal vascular injury in MetS.

Microvascular rarefaction distal to renal artery stenosis is linked to renal dysfunction and poor outcomes. Low–energy shockwave therapy stimulates angiogenesis, but the effect on the kidney microvasculature is unknown. We hypothesized that low–energy shockwave therapy would restore the microcirculation and alleviate renal dysfunction in renovascular disease. Normal pigs and pigs subjected to 3 weeks of renal artery stenosis were treated with six sessions of low–energy shockwave (biweekly for 3 consecutive weeks) or left untreated. We assessed BP, urinary protein, stenotic renal blood flow, GFR, microvascular structure, and oxygenation in vivo 4 weeks after completion of treatment, and then, we assessed expression of angiogenic factors and mechanotransducers (focal adhesion kinase and β 1-integrin) ex vivo . A 3-week low–energy shockwave regimen attenuated renovascular hypertension, normalized stenotic kidney microvascular density and oxygenation, stabilized function, and alleviated fibrosis in pigs subjected to renal artery stenosis. These effects associated with elevated renal expression of angiogenic factors and mechanotransducers, particularly in proximal tubular cells. In additional pigs with prolonged (6 weeks) renal artery stenosis, shockwave therapy also decreased BP and improved GFR, microvascular density, and oxygenation in the stenotic kidney. This shockwave regimen did not cause detectable kidney injury in normal pigs. In conclusion, low–energy shockwave therapy improves stenotic kidney function, likely in part by mechanotransduction-mediated expression of angiogenic factors in proximal tubular cells, and it may ameliorate renovascular hypertension. Low–energy shockwave therapy may serve as a novel noninvasive intervention in the management of renovascular disease.