Effects of LY117018 and the estrogen analogue, 17alpha-ethinylestradiol, on vascular reactivity, platelet aggregation, and lipid metabolism in the insulin-resistant JCR:LA-cp male rat: role of nitric oxide

Rat models of cardiometabolic diseases: baseline clinical chemistries, and rationale for their use in examining air pollution health effects

Individuals with cardiovascular and metabolic diseases (CVD) are shown to be more susceptible to adverse health effects of pollutants. Rodent models of CVD are used for examining susceptibility variations. CVD models developed by selective inbreeding are shown to represent the etiology of human disease and metabolic dysfunction. The goal of this article was to review the origin and the pathobiological features of rat models of varying CVD with or without metabolic syndrome and healthy laboratory rat strains to allow better interpretation of the data regarding their susceptibility to air pollutant exposures. Age-matched healthy Sprague-Dawley (SD), Wistar (WIS) and Wistar Kyoto (WKY), and CVD-prone spontaneously hypertensive (SH), Fawn-Hooded hypertensive (FHH), SH stroke-prone (SHSP), SHHF/Mcc heart failure obese (SHHF) and insulin-resistant JCR:LA-cp obese (JCR) rat models were considered for this study. The genetics and the underlying pathologies differ between these models. Normalized heart weights correlated with underlying cardiac disease while wide differences exist in the number of white blood cells and platelets within healthy strains and those with CVD. High plasma fibrinogen and low angiotensin converting enzyme activity in FHH might relate to kidney disease and associated hypertension. However, other obese strains with known kidney lesions do not exhibit decreases in ACE activity. The increased activated partial thromboplastin time only in SHSP correlates with their hemorrhagic stroke susceptibility. Increases plasma lipid peroxidation in JCR might reflect their susceptibility to acquire atherosclerosis. These underlying pathologies involving CVD and metabolic dysfunction are critical in interpretation of findings related to susceptibility variations of air pollution health effects.

Rimonabant-mediated changes in intestinal lipid metabolism and improved renal vascular dysfunction in the JCR:LA-cp rat model of prediabetic metabolic syndrome

Rimonabant (SR141716) is a specific antagonist of the cannabinoid-1 receptor. Activation of the receptor initiates multiple effects on central nervous system function, metabolism, and body weight. The hypothesis that rimonabant has protective effects against vascular disease associated with the metabolic syndrome was tested using JCR:LA-cp rats. JCR:LA-cp rats are obese if they are cp/cp, insulin resistant, and exhibit associated micro- and macrovascular disease with end-stage myocardial and renal disease. Treatment of obese rats with rimonabant (10 mg.kg(-1).day(-1), 12-24 wk of age) caused transient reduction in food intake for 2 wk, without reduction in body weight. However, by 4 wk, there was a modest, sustained reduction in weight gain. Glycemic control improved marginally compared with controls, but at the expense of increased insulin concentration. In contrast, rimonabant normalized fasting plasma triglyceride and reduced plasma plasminogen activator inhibitor-1 and acute phase protein haptoglobin in cp/cp rats. Furthermore, these changes were accompanied by reduced postprandial intestinal lymphatic secretion of apolipoprotein B48, cholesterol, and haptoglobin. While macrovascular dysfunction and ischemic myocardial lesion frequency were unaffected by rimonabant treatment, both microalbuminuria and glomerular sclerosis were substantially reduced. In summary, rimonabant has a modest effect on body weight in freely eating obese rats and markedly reduces plasma triglyceride levels and microvascular disease, in part due to changes in intestinal metabolism, including lymphatic secretion of apolipoprotein B48 and haptoglobin. We conclude that rimonabant improves renal disease and intestinal lipid oversecretion associated with an animal model of the metabolic syndrome that appears to be independent of hyperinsulinemia or macrovascular dysfunction.

Irbesartan-mediated reduction of renal and cardiac damage in insulin resistant JCR : LA-cp rats

BACKGROUND AND PURPOSE

Angiotensin II receptor antagonists (ARBs), originally developed for antihypertensive properties, have pleiotropic effects including direct vascular actions. We tested the hypothesis that the ARB irbesartan would be effective against micro- and macrovascular complications of the prediabetic metabolic syndrome using the obese, insulin-resistant JCR : LA-cp rat that exhibits micro- and macrovascular disease with ischaemic myocardial lesions and renal disease.

EXPERIMENTAL APPROACH

Obese male rats were treated with irbesartan (30 mg.kg(-1).day(-1), incorporated into chow) from 12 to 25 weeks of age.

KEY RESULTS

Irbesartan treatment caused no change in food intake or body weight. Fasting glycaemic control of the JCR : LA-cp rats was marginally improved, at the expense of increased plasma insulin levels ( approximately 50%). Fasting plasma triglycerides were marginally reduced ( approximately 25%), while cholesterol concentrations were unchanged. Elevated concentrations of adiponectin, monocyte chemotactic protein-1 and plasminogen activator inhibitor-1 were reduced along with severity of glomerular sclerosis. Macrovascular dysfunction (aortic hypercontractile response to noradrenergic stimulus and reduced endothelium-dependent relaxation) was improved and frequency of ischaemic myocardial lesions reduced (62%).

CONCLUSIONS AND IMPLICATIONS

Irbesartan reduces markers of inflammation and prothombotic status, improves macrovascular function and reduces glomerular sclerosis and myocardial lesions in a model of the metabolic syndrome. Unlike pharmaceutical agents targeted on metabolic dysfunction, irbesartan reduced end-stage disease without major reduction of plasma lipids or insulin. The protective effects appear to be secondary to unknown intracellular mechanisms, probably involving signal transduction pathways. Understanding these would offer novel pharmaceutical approaches to protection against cardiovascular disease.

Pair feeding-mediated changes in metabolism: stress response and pathophysiology in insulin-resistant, atherosclerosis-prone JCR:LA-cp rats

Rats of the JCR:LA-cp strain, which are homozygous for the cp gene (cp/cp), are obese, insulin-resistant, and hyperinsulinemic. They exhibit associated micro- and macrovascular disease and end-stage ischemic myocardial lesions and are highly stress sensitive. We subjected male cp/cp rats to pair feeding (providing the rats each day with the amount of food eaten by matched freely fed animals), a procedure that alters the diurnal feeding pattern, leading to a state of intermittent caloric restriction. Effects on insulin, glucose, and lipid metabolism, response to restraint stress, aortic contractile/relaxant response, and myocardial lesion frequency were investigated. Pair-fed young (12-wk-old) cp/cp rats had lower insulin and glucose levels (basal and following restraint), consistent with increased insulin sensitivity, but a greater increase in plasma nonesterified fatty acids in response to restraint. These effects were unrelated to lipolytic rates in adipose tissue but may be related to reduced fatty acid oxidation in skeletal muscle. Older (24-wk-old) pair-fed cp/cp rats had significantly reduced plasma triglyceride levels, improved micro- and macrovascular function, and reduced severity of ischemic myocardial lesions. These changes indicate a significant amelioration of end-stage disease processes in this animal model and the complexity of metabolic/physiological responses in studies involving alterations in food intake. The effects illustrate the sensitivity of the JCR:LA-cp rat, an animal model for the metabolic syndrome and associated cardiovascular disease, to the environmental and experimental milieu. Similar stress-related mechanisms may play a role in metabolically induced cardiovascular disease in susceptible human beings.

Metabolic effects of a novel silicate inositol complex of the nitric oxide precursor arginine in the obese insulin-resistant JCR:LA-cp rat

Insulin resistance is a major contributor to macro- and microvascular complications, particularly in the presence of the metabolic syndrome, and is also associated with polycystic ovary syndrome. Impaired nitric oxide metabolism and endothelial function are important components of the vascular disease. Increasing the bioavailability of arginine, the precursor of nitric oxide, thus potentially offers protection against end-stage disease. We have recently demonstrated that dietary supplementation with a novel silicate inositol arginine complex reduces vasculopathy and glomerular sclerosis in the insulin-resistant JCR:LA-cp rat. The objective of this study was to address the absorption of, and the underlying metabolic alterations caused by, the arginine silicate inositol complex and arginine HCl (as a reference agent) in obese insulin-resistant male and female JCR:LA-cp rats. Male and female rats were treated with the preparations at 1.0 mg/(kg d) (expressed as arginine HCl) from 8 to 12 and 12 to 18 weeks of age, respectively. Obese female, but not male, rats treated with the arginine silicate inositol complex showed a reduced rate of weight gain without concomitant reduction in food intake. Plasma silicon levels were raised very significantly in arginine silicate-treated rats, consistent with significant absorption of the complex. In male rats, arginine levels were elevated by treatment with arginine silicate only; and female rats responded to both preparations. Plasma concentrations of oxides of nitrogen in rats treated with the silicate complex showed a dimorphism, decreasing in male and increasing in female rats. Fasting insulin levels were elevated in male rats treated with the arginine silicate complex, whereas fasting and postprandial insulin levels were decreased in female rats. Furthermore, female, but not male, rats treated with either of the arginine preparations showed significant reductions in cholesterol, triglyceride, and phospholipid concentrations. We conclude that the arginine silicate inositol complex is absorbed efficiently, raising plasma arginine levels, and is more biologically effective than the free amino acid hydrochloride. This has different beneficial metabolic effects in both sexes of an animal model of insulin resistance and cardiovascular disease, consistent with reduction in end-stage disease.

Increased insulin sensitivity and reduced micro and macro vascular disease induced by 2-deoxy-D-glucose during metabolic syndrome in obese JCR: LA-cp rats

BACKGROUND AND PURPOSE

The metabolic syndrome, characterized by obesity, insulin resistance and dyslipidemia, is a major cause of cardiovascular disease. The origins of the syndrome have been hypothesized to lie in continuous availability of energy dense foods in modern societies. In contrast, human physiology has evolved in an environment of sporadic food supply and frequent food deprivation. Intermittent food restriction in rats has previously been shown to lead to reduction of cardiovascular risk and a greater life span. The non-metabolizable glucose analogue, 2-deoxy-D-glucose (2-DG) is taken up by cells and induces pharmacological inhibition of metabolism of glucose. We hypothesized that intermittent inhibition of glucose metabolism, a metabolic deprivation, may mimic intermittent food deprivation and ameliorate metabolic and pathophysiological aspects of the metabolic syndrome.

EXPERIMENTAL APPROACH

Insulin resistant, atherosclerosis-prone JCR:LA-cp rats were treated with 2-DG (0.3% w/w in chow) on an intermittent schedule (2 days treated, one day non-treated, two days treated and two days non-treated) or continuously at a dose to give an equivalent averaged intake.

KEY RESULTS

Intermittent 2-DG-treatment improved insulin sensitivity, which correlated with increased adiponectin concentrations. Further, intermittent treatment (but not continuous treatment) reduced plasma levels of leptin and the inflammatory cytokine IL-1 beta. Both 2-DG treatments reduced micro-vascular glomerular sclerosis, but only the intermittent schedule improved macro-vascular dysfunction.

CONCLUSIONS AND IMPLICATIONS

Our findings are consistent with reduction in severity of the metabolic syndrome and protection against end stage micro- and macro-vascular disease through intermittent metabolic deprivation at a cellular level by inhibition of glucose oxidation with 2-DG.

Insulin-Sensitizing and Cardiovascular Effects of the Sodium-Hydrogen Exchange Inhibitor, Cariporide, in the JCR

The effects of the sodium-hydrogen (Na/H) exchange inhibitor cariporide (HOE642), on insulin sensitivity and vascular function were studied in the JCR:LA-cp rat and the db/db mouse. In the insulin-resistant rat, cariporide reduced fasting insulin levels (42%, P < 0.02) and insulin response in a meal tolerance test (50%, P < 0.01), indicating increased insulin sensitivity. The ACE inhibitor, ramipril, used as a reference agent, reduced the insulin response to the meal, but not fasting levels. The EC50 for acetylcholine-mediated relaxation of phenylephrine-precontracted aortic rings was significantly lower in cariporide-treated rats (P < 0.002), but not in ramipril-treated rats. Flow response of the coronary circulation to bradykinin was significantly greater in both cariporide- and ramipril-treated rats, (3-fold decrease in the EC50, P < 0.05). Cariporide-treated hearts were smaller, slower beating, with greater developed LVP. In the obese db/db mouse, chronic treatment with cariporide obviated vascular hypercontractility and improved endothelial function. Thus, cariporide had beneficial effects on the abnormal insulin metabolism and associated vascular dysfunction in the JCR:LA-cp insulin-resistant rat, which develops advanced cardiovascular disease and ischemic myocardial lesions. It also improved vascular function in a similar mouse model of insulin resistance. These effects were markedly greater than those of ramipril.

A novel complex of arginine-silicate improves micro- and macrovascular function and inhibits glomerular sclerosis in insulin-resistant JCR:LA-cp rats

AIMS/HYPOTHESIS

The metabolic syndrome, with associated vasculopathy, is a major cause of cardiovascular disease and nephropathy. Impaired nitric oxide (NO) metabolism and endothelial function is an important component of the disease process. Increasing the availability of arginine, the precursor of NO, might enhance vascular function and protect against end-stage disease.

MATERIALS AND METHODS

Insulin-resistant JCR:LA-cp rats were treated with arginine-silicate-inositol complex or arginine-HCl at 1.0 g kg(-1) day(-1) (expressed as arginine-HCl) from 8 to 13 weeks of age. The contractile/relaxant function of thoracic aortae and coronary arteries was assessed in vitro. Kidneys were assessed for severity of glomerular sclerosis.

RESULTS

Arginine-silicate complex, but not arginine-HCl, normalised the hypercontractile response of the aorta to phenylephrine via an NO-dependent pathway. Coronary artery function, as indicated by reactive hyperaemia to warm ischaemia, was enhanced by both arginine compounds. In addition, the arginine-silicate complex increased coronary vasodilatation in response to bradykinin. Glomerular sclerosis was significantly reduced in rats treated with the arginine-silicate complex.

CONCLUSIONS/INTERPRETATION

Treatment with exogenous arginine, in an efficiently absorbed form, improves vascular function and reduces nephropathy in an animal model of insulin resistance and cardiovascular disease, via mechanism(s) independent of insulin concentration. Enhancement of NO metabolism through increased availability of the precursor arginine appears to offer protection against micro- and macrovascular disease associated with the metabolic syndrome and insulin resistance.

Vasopeptidase inhibition improves insulin sensitivity and endothelial function in the JCR:LA-cp rat

The insulin-resistant, hyperinsulinemic, normoglycemic, and obese JCR:LA-cp rat was used to study the effects of ramipril (an ACE inhibitor) and AVE7688 (a dual inhibitor of ACE and neutral endopeptidases) on insulin sensitivity and vascular function. Both compounds reduced the surge of plasma insulin in a meal tolerance test by approximately 50%. Ramipril had no effect on acetylcholine-induced relaxation but increased the sensitivity to sodium nitroprus-side at low concentrations. AVE7688 significantly reduced the EC50 for acetylcholine to relax phenylephrine-contracted aortic rings. None of the compounds affected the baseline coronary flow and reactive hyperemia. Coronary flow response to bradykinin in AVE7688- and ramipril-treated rat hearts showed a significantly lower EC50 than in control rats. Maximum flow rate was not different between groups. In summary, both ramipril and AVE7688 had significant hypoinsulinemic and insulin-sensitizing effects. Whereas ramipril had limited vascular effects, AVE7688 had more marked beneficial vascular effects, probably of endothelial origin and possibly related to lowered insulin levels.

Effects of the selective estrogen receptor modulator LY117018 on growth hormone secretion: In vitro studies

Sex steroids play an important role in modulating pulsatile growth hormone (GH) release, acting at both hypothalamic and pituitary level in both humans and experimental animals. Selective estrogen receptor modulators (SERMs) act as either estrogen receptor agonists or antagonists in a tissue-selective manner. In postmenopausal women, serum GH levels correlate positively with endogenous estradiol levels and insulin-like grwoth factor-I (IGF-I) is positively related to bone mineral density (BMD) at the spine and hip. The aim of the present study was to evaluate, for the first time, the direct effect of LY117018, an analog of raloxifene, on GH secretion from both human and rodent pituitary cells in vitro. Our results demonstrated that pharmacological concentrations of the raloxifene analog LY117018 can stimulate GH secretion through a direct action on the pituitary. LY117018 also showed an estrogen-like activity, inducing the proliferation of rat pituitary GH-secreting adenomatous cells (GH1).

Ovariectomy leads to increased insulin resistance in human apolipoprotein B transgenic mice lacking brown adipose tissue

We studied the role of estrogen in the gender differences in insulin resistance observed in the apoB/BATless mouse, a model of obesity, insulin resistance, and hyperlipidemia. Ovariectomized apoB/BATless mice were more obese and more insulin-resistant than sham ovariectomized apoB/BATless mice. Estrogen replacement by subcutaneous pellet reversed the obesity, lowered plasma insulin levels, and normalized both glucose tolerance and insulin sensitivity associated with ovariectomy. The apoB/BATless mouse should be a good model to delineate the molecular mechanisms whereby estrogen protects against insulin resistance.

Improvement of vascular dysfunction and blood lipids of insulin-resistant rats by a marine oil-based phytosterol compound

The syndrome that is characterized by obesity, insulin resistance, and hyperlipidemia is increasingly prevalent in all prosperous societies. It is now recognized as a major contributor to cardiovascular disease. Vascular dysfunction in the form of hypercontractility and impaired nitric oxide-mediated relaxation is a significant component of cardiovascular disease, predisposing to ischemic events. The JCR:LA-cp strain of rats exhibits all major aspects of the obesity/insulin resistance syndrome, including vascular dysfunction and ischemic lesions of the heart. Dietary lipid intake may have a marked effect on plasma lipid levels and, potentially, on vascular disease. We have investigated the effects of a novel preparation, ONC101 (a phytosterol esterified with fish oil), on plasma lipids and vascular function in the insulin-resistant JCR:LA-cp rat. Treatment of obese male rats with ONC101 from 8 to 12 wk of age resulted in no change in plasma lipid concentrations at 0.5 g/kg body weight. At the higher dose of 2.6 g/kg, plasma TG fell 50% (1.26 vs. 2.59 mmol/L, P < 0.002) and cholesterol esters were significantly reduced (1.34 vs. 1.61 mmol/L, P < 0.002). Food intake and body weights were unaffected by ONC101 treatment. At the low dose of 86 mg/kg, the hypercontractility of aortic rings in response to phenylephrine was normalized and the relaxant response to acetylcholine was significantly improved. The results indicate that ONC101 at high doses has significant hypolipidemic effects and, at very low doses, has beneficial effects on endothelial and vascular smooth muscle cell function.