Animal models to study pathogenesis and treatments of cardiac disorders in rheumatoid arthritis: Advances and challenges for clinical translation.

Although cardiac diseases such as acute myocardial infarction, heart failure and arrhythmias are the leading cause of cardiovascular complications in rheumatoid arthritis (RA), their pathogenesis is far from being understood and optimal therapeutic options to treat specifically these disorders in RA are lacking. Preclinical studies on animal models of arthritis can help to decipher the complex link between arthritis and the heart, and to identify critical pathways and novel therapeutic targets. This review presented the available data on cardiac disorders in animal models of RA, as well as the current knowledge on pathophysiology and pharmacology of these disorders. Future directions for translational studies in a cardiorheumatic perspective are proposed.

Adjuvant-induced arthritis is a relevant model to mimic coronary and myocardial impairments in rheumatoid arthritis.

OBJECTIVES: To determine if the adjuvant-induced arthritis model reproduced coronary and cardiac impairments observed in rheumatoid arthritis patients. The link between disease activity and circulating levels of angiotensin II and endothelin-1 have been studied, as well as the myocardial susceptibility to ischemia. METHODS: At the acute inflammatory phase, coronary reactivity was assessed in isolated arteries, and cardiac function was studied in isolated perfused hearts, before and after global ischemia/reperfusion. Ischemic insult was evaluated by the infarct size, lactate dehydrogenase and creatine phosphokinase levels in coronary effluents. Cardiac myeloperoxidase activity was measured, as well as angiotensin II and endothelin-1 levels. RESULTS: Compared to controls, adjuvant-induced arthritis had reduced coronary Acetylcholine-induced relaxation associated with cardiac hypertrophy, both being correlated with plasma levels of endothelin-1 and angiotensin II, and arthritis score. Although cardiac function at baseline was similar from controls, adjuvant-induced arthritis rats exhibited lower cardiac functional recovery, increased myeloperoxidase activity, higher infarct size and creatine phosphokinase levels after ischemia/reperfusion. CONCLUSIONS: The adjuvant-induced arthritis model displays coronary endothelial dysfunction associated with myocardial hypertrophy and a reduced tolerance to ischemia. This model might be useful for deciphering the pathophysiology of cardiac dysfunction in rheumatoid arthritis and paves the way for studying the role of endothelin-1 and angiotensin II.

Bacopa monnieri extract increases rat coronary flow and protects against myocardial ischemia/reperfusion injury.

BACKGROUND: This study explored Bacopa monnieri, a medicinal Ayurvedic herb, as a cardioprotectant against ischemia/reperfusion injury using cardiac function and coronary flow as end-points. METHODS: In normal isolated rat hearts, coronary flow, left ventricular developed pressure, heart rate, and functional recovery were measured using the Langendorff preparation. Hearts were perfused with either (i) Krebs-Henseleit (normal) solution, (control), or with 30, 100 µg/ml B. monnieri ethanolic extract (30 min), or (ii) with normal solution or extract for 10 min preceding no-perfusion ischemia (30 min) followed by reperfusion (30 min) with normal solution. Infarct volumes were measured by triphenyltetrazolium staining. L-type Ca2+-currents (ICa, L) were measured by whole-cell patching in HL-1 cells, a mouse atrial cardiomyocyte cell line. Cytotoxicity of B. monnieri was assessed in rat isolated ventricular myocytes by trypan blue exclusion. RESULTS: In normally perfused hearts, B. monnieri increased coronary flow by 63 ± 13% (30 µg/ml) and 216 ± 21% (100 µg/ml), compared to control (5 ± 3%) (n = 8-10, p < 0.001). B. monnieri treatment preceding ischemia/reperfusion improved left ventricular developed pressure by 84 ± 10% (30 µg/ml), 82 ± 10% (100 µg/ml) and 52 ± 6% (control) compared to pre- ischemia/reperfusion. Similarly, functional recovery showed a sustained increase. Moreover, B. monnieri (100 µg/ml) reduced the percentage of infarct size from 51 ± 2% (control) to 25 ± 2% (n = 6-8, p < 0.0001). B. monnieri (100 µg/ml) reduced ICa, L by 63 ± 4% in HL-1 cells. Ventricular myocyte survival decreased at higher concentrations (50-1000 µg/ml) B. monnieri. CONCLUSIONS: B. monnieri improves myocardial function following ischemia/reperfusion injury through recovery of coronary blood flow, contractile force and decrease in infarct size. Thus this may lead to a novel cardioprotectant strategy.

Dietary magnesium intake alters age-related changes in rat adipose tissue cellularity.

Obesity and related metabolic diseases are associated with increased risk of cardiovascular disease. We have previously shown the beneficial effects of dietary magnesium (Mg) supplementation on cardiovascular disease in rats. Therefore, we aimed to examine the effect of an Mg-deficient or supplemented diet on adipose tissue cellularity changes during aging, and on blood pressure (BP), in rats. Male rats received for one (young adult) or 22 months (old), an Mg-deficient (Def) (150 mg/kg), standard (Std) (800 mg/kg) or Mg-supplemented (Sup) (3200 mg/kg) diet. Adipose tissue development and cellularity, BP and leptinemia were evaluated. In rats fed a standard diet, the large increase in adipose tissue weight observed during aging was related to an increase in both size and number of adipocytes. In young adult rats, although adiposity was unchanged, Mg supplementation resulted in a shift of the frequency distribution of adipocytes toward greater sizes, adipose cell weight increasing by 62%. Mg deficiency did not modify adipocyte size, but increased their number (30% more than for the standard or Sup-diet). In old rats, the Def-diet led to relative adipocyte hypotrophy, which was counterbalanced by an increase in the number of adipocyte. Conversely, adipocyte size and number were similar in the Sup-diet and standard diet-fed rats. BP was modified in old rats according to dietary Mg, whereas it remained unchanged young adult rats regardless of the diet received. This study suggests that Mg intake may affect age-related changes in rat adipose tissue lipid storage capacity.

Physical training and hypertension have opposite effects on endothelial brain-derived neurotrophic factor expression.

AIMS: Changes in circulating brain-derived neurotrophic factor (BDNF) levels were reported in patients with or at risk for cardiovascular diseases associated with endothelial dysfunction, suggesting a link between BDNF and endothelial functionality. However, little is known on cardiovascular BDNF. Our aim was to investigate levels/localization, function, and relevance of cardiovascular BDNF. METHODS AND RESULTS: BDNF levels (western blotting) and localization (immunostaining) were assessed in the heart and aorta from rats with impaired (spontaneously hypertensive rats [SHR]), normal (Wistar Kyoto rats [WKY]), and improved (SHR and WKY subjected to physical training) endothelial function. BDNF levels were also measured in cultured endothelial cells (CECs) subjected to low and high shear stress. The cardiovascular effects of BDNF were investigated in isolated aortic rings and hearts. The results showed high BDNF levels in the heart and aorta, the expression being prominent in endothelial cells as compared with other cell types. Exogenous BDNF vasodilated aortic rings but changed neither coronary flow nor cardiac contractility. Hypertension was associated with decreased expression of BDNF in the endothelium, whereas physical training led to endothelial BDNF up-regulation not only in WKY but also in SHR. Exposure of CECs to high shear stress stimulated BDNF production and secretion. CONCLUSION: Cardiovascular BDNF is mainly localized within endothelial cells in which its expression is dependent on endothelial function. These results open new perspectives on the role of endothelial BDNF in cardiovascular health.

Dietary Mg2+ regulates the epithelial Mg2+ channel TRPM6 in rat mammary tissue.

The epithelial Mg(2+) channel TRPM6 is considered a pivotal component in active Mg(2+)absorption and re-absorption in the intestine and kidney, but its expression and function in other tissues are largely unknown. We have previously demonstrated that extracellular Mg(2+) availability modulates TRPM6, but not the ubiquitous TRPM7, in cultured mammary epithelial cells; in addition, TRPM6 protein expression correlated to Mg(2+) influx capacities. Our results closely remind the modulation of TRPM6 described by others in murine kidney and colon following Mg(2+) dietary restriction. We sought to validate our observations by investigating whether TRPM6 modulation by extracellular Mg(2+)also occurs in vivo. To this aim, we exploited a model consisting of rats fed either with a Mg(2+)-deficient or a Mg(2+)-enriched diet, and studied TRPM6 expression in breast and kidney tissues. Immunohistochemical and western blot analyses confirmed that rat mammary tissues express TRPM6 protein levels similar to those found in the kidney, and that protein expression is modulated by dietary Mg(2+). In particular, Mg(2+) restriction upregulated TRPM6 expression, while Mg(2+) supplementation resulted in a significant decrease in protein levels. This work confirms and extends our previous results on TRPM6 modulation by Mg(2+) availability in mammary tissues. Further studies are required to clarify the functional significance of these findings, and the role of TRPM6 in tissue-specific magnesium homeostasis.

Exercise reverses metabolic syndrome in high-fat diet-induced obese rats.

PURPOSE: Chronic consumption of a high-fat diet induces obesity. We investigated whether exercise would reverse the cardiometabolic disorders associated with obesity without it being necessary to change from a high- to normal-fat diet. METHODS: Sprague-Dawley rats were placed on a high-fat (HFD) or control diet (CD) for 12 wk. HFD rats were then divided into four groups: sedentary HFD (HFD-S), exercise trained (motor treadmill for 12 wk) HFD (HFD-Ex), modified diet (HFD to CD; HF/CD-S), and exercise trained with modified diet (HF/CD-Ex). Cardiovascular risk parameters associated with metabolic syndrome were measured, and contents of aortic Akt, phospho-Akt at Ser (473), total endothelial nitric oxide synthase (eNOS), and phospho-eNOS at Ser (1177) were determined by Western blotting. RESULTS: Chronic consumption of HFD induced a metabolic syndrome. Exercise and dietary modifications reduced adiposity, improved glucose and insulin levels and plasma lipid profile, and exerted an antihypertensive effect. Exercise was more effective than dietary modification in improving plasma levels of thiobarbituric acid-reacting substance and in correcting the endothelium-dependent relaxation to acetylcholine and insulin. Furthermore, independent of the diet used, exercise increased Akt and eNOS phosphorylation. CONCLUSIONS: Metabolic syndrome induced by HFD is reversed by exercise and diet modification. It is demonstrated that exercise training induces these beneficial effects without the requirement for dietary modification, and these beneficial effects may be mediated by shear stress-induced Akt/eNOS pathway activation. Thus, exercise may be an effective strategy to reverse almost all the atherosclerotic risk factors linked to obesity, particularly in the vasculature.

Effects of cadmium on cardiac metallothionein induction and ischemia-reperfusion injury in rats.

Myocardial ischemia-reperfusion injury is associated with an imbalance between the formation and the scavenging of reactive oxygen species. In this context, the protective role of the antioxidant metallothionein, a thiol-rich protein that is induced in different organs in response to heavy metals and oxidative conditions, has mainly been investigated in metallothionein-knockout mice or metallothionein-overexpressing mice. The aim of this study was to evaluate whether the administration of cadmium has a protective effect against cardiac ischemia-reperfusion injury and whether this is associated with induction of in vivo cardiac metallothionein. Forty-eight hours after an injection of 0, 1, or 2 mg/kg cadmium, isolated perfused rat hearts were submitted to 30 min of total global ischemia and 30 min of reperfusion. The ischemia-reperfusion sequence was associated with a significant decrease in cardiac metallothionein levels. Pretreatment with cadmium at a dose of 2 mg/kg (i) prevented this decrease and (ii) improved the postischemic recuperation of the coronary flow, the ventricular developed pressure, and therefore, the global postischemic functional recovery. These results showed that pretreatment of rats with 2 mg/kg cadmium induced cardioprotection against ischemia-reperfusion injuries, perhaps through an in vivo metallothionein induction that may be related to a metal activation of antioxidant systems.

Effects of long-term dietary intake of magnesium on oxidative stress, apoptosis and ageing in rat liver.

In the present study, we investigated the effect of long-term dietary Mg intake on the rate of oxidative stress, apoptosis and ageing in rat livers. To address this issue, rats were fed diets containing either a moderately deficient (0.15 g Mg/kg diet), a standard (0.8 g Mg/kg diet) or a high (3.2 g Mg/kg diet) Mg dose for two years. It is noteworthy that a higher percentage of animal mortality was observed in the lowest Mg diet, as compared to the other groups. Oxidative stress and antioxidant status were evaluated by measuring different enzyme activities, among which glutathione peroxidase activity was significantly reduced when Mg content was decreased in the diet. Moreover, we obtained an activation of caspase-3 and a higher lipid peroxidation in the Mg-deficient group, as compared to the Mg standard group, while no changes in Mg-supplemented group were observed, in accordance with our previously published data in primary cultures of rat hepatocytes (Martin et al., J Nutr 2003). Telomere shortening was measured in rat livers, as a marker of ageing. We found that telomere length was decreased in old animals, as compared to young animals confirming that telomere shortening correlated well with ageing events. Moreover, in old animals, we obtained a decrease of telomere length in the Mg-deficient group, as compared to the other groups. Taken together, our results show that a long-term chronic Mg deficiency led to oxidative stress, apoptosis and an acceleration of ageing in rat livers.

Long-term moderate magnesium-deficient diet shows relationships between blood pressure, inflammation and oxidant stress defense in aging rats.

Epidemiological and experimental studies have indicated a relationship among aging, dietary Mg, inflammatory stress, and cardiovascular disease. Our aim in the present study was to investigate possible links between dietary Mg, oxidant stress parameters, and inflammatory status with aging in rats. We designed a long-term study in which rats were fed for 22 months with moderately deficient (150 mg/kg), standard (800 mg/kg), or supplemented (3200 mg/kg) Mg diets. Comparisons were made with young rats fed with the same diets for 1 month. Compared to the standard and supplemented diets, the Mg-deficient diet significantly increased blood pressure, plasma interleukin-6, fibrinogen, and erythrocyte lysophosphatidylcholine, particularly in aging rats, it decreased plasma albumin. The impairment of redox status was indicated by increases in plasma thiobarbituric acid reactive substances and oxysterols and an increased blood susceptibility to in vitro free-radical-induced hemolysis. We concluded that Mg deficiency induced a chronic impairment of redox status associated with inflammation which could significantly contribute to increased oxidized lipids and promote hypertension and vascular disorders with aging. Extrapolating to the human situation and given that Mg deficiency has been reported to be surprisingly common, particularly in the elderly, Mg supplementation might be useful as an adjuvant therapy in preventing cardiovascular disease.