Role of angiotensin II in diabetic cardiovascular and renal disease:

Treating hypertension while protecting the vulnerable islet in the cardiometabolic syndrome

Hypertension, a multifactorial-polygenic disease, interacts with multiple environmental stressors and results in functional and structural changes in numerous end organs, including the cardiovascular system. This can result in coronary heart disease, stroke, peripheral vascular disease, congestive heart failure, end-stage renal disease, insulin resistance, and damage to the pancreatic islet. Hypertension is the most important modifiable risk factor for major health problems encountered in clinical practice. Whereas hypertension was once thought to be a medical condition based on discrete blood pressure readings, a new concept has emerged defining hypertension as part of a complex and progressive metabolic and cardiovascular disease, an important part of a cardiometabolic syndrome. The central role of insulin resistance, oxidative stress, endothelial dysfunction, metabolic signaling defects within tissues, and the role of enhanced tissue renin-angiotensin-aldosterone system activity as it relates to hypertension and type 2 diabetes mellitus are emphasized. Additionally, this review focuses on the effect of hypertension on functional and structural changes associated with the vulnerable pancreatic islet. Various classes of antihypertensive drugs are reviewed, especially their roles in delaying or preventing damage to the vulnerable pancreatic islet, and thus delaying the development of type 2 diabetes mellitus.

Attenuation of NADPH oxidase activation and glomerular filtration barrier remodeling with statin treatment

Activation of reduced nicotinamide-adenine dinucleotide phosphate (NADPH) oxidase by angiotensin II is integral to the formation of oxidative stress in the vasculature and the kidney. 3-Hydroxy-3-methylglutaryl-coenzyme A reductase inhibition is associated with reductions of oxidative stress in the vasculature and kidney and associated decreases in albuminuria. Effects of 3-hydroxy-3-methylglutaryl-coenzyme A reductase inhibition on oxidative stress in the kidney and filtration barrier integrity are poorly understood. To investigate, we used transgenic TG(mRen2)27 (Ren2) rats, which harbor the mouse renin transgene and renin-angiotensin system activation, and an immortalized murine podocyte cell line. We treated young, male Ren2 and Sprague-Dawley rats with rosuvastatin (20 mg/kg IP) or placebo for 21 days. Compared with controls, we observed increases in systolic blood pressure, albuminuria, renal NADPH oxidase activity, and 3-nitrotryosine staining, with reductions in the rosuvastatin-treated Ren2. Structural changes on light and transmission electron microscopy, consistent with periarteriolar fibrosis and podocyte foot-process effacement, were attenuated with statin treatment. Nephrin expression was diminished in the Ren2 kidney and trended to normalize with statin treatment. Angiotensin II-dependent increases in podocyte NADPH oxidase activity and subunit expression (NOX2, NOX4, Rac, and p22(phox)) and reactive oxygen species generation were decreased after in vitro statin treatment. These data support a role for increased NADPH oxidase activity and subunit expression with resultant reactive oxygen species formation in the kidney and podocyte. Furthermore, statin attenuation of NADPH oxidase activation and reactive oxygen species formation in the kidney/podocyte seems to play roles in the abrogation of oxidative stress-induced filtration barrier injury and consequent albuminuria.

Attenuation of endocrine-exocrine pancreatic communication in type 2 diabetes: pancreatic extracellular matrix ultrastructural abnormalities

Ultrastructural observations reveal a continuous interstitial matrix connection between the endocrine and exocrine pancreas, which is lost due to fibrosis in rodent models and humans with type 2 diabetes mellitus (T2DM). Widening of the islet-exocrine interface appears to result in loss of desmosomes and adherens junctions between islet and acinar cells and is associated with hypercellularity consisting of pericytes and inflammatory cells in T2DM pancreatic tissue. Organized fibrillar collagen was closely associated with pericytes, which are known to differentiate into myofibroblasts-pancreatic stellate cells. Of importance, some pericyte cellular processes traverse both the connecting islet-exocrine interface and the endoacinar interstitium of the exocrine pancreas. Loss of cellular paracrine communication and extracellular matrix remodeling fibrosis in young animal models and humans may result in a dysfunctional insulino-acinar-ductal-incretin gut hormone axis, resulting in pancreatic insufficiency and glucagon-like peptide deficiency, which are known to exist in prediabetes and overt T2DM in humans.

Myocardial myocyte remodeling and fibrosis in the cardiometabolic syndrome

Myocardial cellular and extracellular matrix remodeling are important in the development of left ventricular hypertrophy and are essential for the adaptive and maladaptive changes associated with the cardiometabolic syndrome. This brief review of myocyte remodeling also presents preliminary observational findings regarding myocardial adaptive hypertrophy remodeling, including an increase in mitochondria and capillaries, convolutions and lengthening of intercalated discs, the addition of sarcomeres, thickened Z lines, and the novel presence of pericapillary fibrosis (in addition to perivascular arteriolar fibrosis). The 11-week-old TG(mREN-2)27 transgene rat model of tissue angiotensin II overexpression, which develops hypertension and insulin resistance, was chosen to examine both myocyte hypertrophy and extracellular matrix fibrosis. This review and the preliminary observational findings may provide the clinician and researcher a better understanding of remodeling changes in the myocardium and ultimately foster earlier recognition and therapeutic interventions.

Isletopathy in Type 2 diabetes mellitus: implications of islet RAS, islet fibrosis, islet amyloid, remodeling, and oxidative stress

This review focuses primarily on islet structural and functional changes related to an activated islet renin- angiotensin system (RAS), islet oxidative-redox imbalance, the concurrence of islet fibrosis (pericapillary, intra- and peri-islet), and islet amyloid deposition (pericapillary, intra- and peri-islet). The islet-acinar-portal vascular pathway and the emerging important anatomical and functional region, the islet-exocrine interface, are also discussed. Because there is an associated histopathological islet disease in type 2 diabetes mellitus (T2DM), the term isletopathy is discussed in detail. The isletopathy in T2DM is equally important as the other complications of diabetes. Special stains and special lighting (bright field and crossed polarized light) are utilized, along with light and transmission electron microscopy, in order to better understand islet structural remodeling in T2DM. The importance of an isletopathy in T2DM is supported by numerous remodeling changes within the islet and the islet-exocrine interface. While some of the structural findings are only preliminary observations, additional investigation in this area should lead to the development of new pathophysiological concepts and new therapies regarding the prevention and treatment of T2DM.