A treadmill exercise reduced cardiac fibrosis, inflammation and vulnerability to ischemia-reperfusion in rat pristane-induced arthritis

AIMS

To explore cardiac structural and functional parameters and myocardial sensitivity to ischemia in a rat model of chronic arthritis, pristane-induced arthritis (PIA), and to investigate the effects of a running exercise protocol on cardiac disorders related to rheumatoid arthritis (RA).

MAIN METHODS

3 groups of male Dark Agouti rats were formed: Controls, PIA and PIA-Exercise. The PIA-Exercise group was subjected to an individualized treadmill running protocol during the remission phase. At acute and chronic phases of PIA, cardiac structure was analyzed by histology. Cardiac function was explored in isolated hearts to measure left ventricular developed pressure (LVDP), cardiac compliance and infarct size before and after ischemia/reperfusion. Cardiac inflammation was evaluated through VCAM-1 mRNA expression by RT-qPCR. Plasma irisin levels were measured by ELISA.

KEY FINDINGS

PIA rats exhibited myocardial hypertrophy fibrosis and inflammation at the 2 inflammatory phases of the model. At chronic phase only, LVDP and cardiac compliance were lower in PIA compared to controls. As compared to sedentary PIA, exercise did not change cardiac function but reduced fibrosis, inflammation, infarct size, and arthritis severity and increased irisin levels. Cardiac inflammation positively correlated with fibrosis, while irisin levels negatively correlated with cardiac inflammation and fibrosis.

SIGNIFICANCE

In the PIA model that recapitulated most cardiac disorders of RA, a daily program of treadmill running alleviated cardiac fibrosis and inflammation and improved resistance to ischemia. These data provide arguments to promote the practice of exercise in RA patients for cardiac diseases prevention.

Cadmium exposure induces a sex-dependent decline in left ventricular cardiac function

AIMS

Cadmium exposure is a worldwide problem that has been linked to the development of cardiovascular disease. This study aimed to elucidate mechanistic details of chronic cadmium exposure on the structure and function of the heart.

MAIN METHODS

Male and female mice were exposed to cadmium chloride (CdCl2) via drinking water for eight weeks. Serial echocardiography and blood pressure measurements were performed. Markers of hypertrophy and fibrosis were assessed, along with molecular targets of Ca2+-handling.

KEY FINDINGS

Males exhibited a significant reduction in left ventricular ejection fraction and fractional shortening with CdCl2 exposure, along with increased ventricular volume at end-systole, and decreased interventricular septal thickness at end-systole. Interestingly, no changes were detected in females. Experiments in isolated cardiomyocytes revealed that CdCl2-induced contractile dysfunction was also present at the cellular level, showing decreased Ca2+ transient and sarcomere shortening amplitude with CdCl2 exposure. Further mechanistic investigation uncovered a decrease in sarco/endoplasmic reticulum Ca2+-ATPase 2a (SERCA2a) protein expression and phosphorylated phospholamban levels in male hearts with CdCl2 exposure.

SIGNIFICANCE

The findings of our novel study provide important insight into how cadmium exposure may act as a sex-specific driver of cardiovascular disease, and further underscore the importance of reducing human exposure to cadmium.

Overview of the cardiovascular effects of environmental metals: New preclinical and clinical insights

Environmental causes of cardiovascular diseases (CVDs) are global health issues. In particular, an association between metal exposure and CVDs has become evident but causal evidence still lacks. Therefore, this symposium at the Society of Toxicology 2022 annual meeting addressed epidemiological, clinical, pre-clinical animal model-derived and mechanism-based evidence by five presentations: 1) An epidemiologic study on potential CVD risks of individuals exposed occupationally and environmentally to heavy metals; 2) Both presentations of the second and third were clinical studies focusing on the potential link between heavy metals and pulmonary arterial hypertension (PAH), by presenting altered blood metal concentrations of both non-essential and essential metals in the patients with PAH and potential therapeutic approaches; 3) Arsenic-induced atherosclerosis via inflammatory cells in mouse model; 4) Pathogenic effects on the heart by adult chronic exposure to very low-dose cadmium via epigenetic mechanisms and whole life exposure to low dose cadmium via exacerbating high-fat-diet-lipotoxicity. This symposium has brought epidemiologists, therapeutic industry, physicians, and translational scientists together to discuss the health risks of occupational and environmental exposure to heavy metals through direct cardiotoxicity and indirect disruption of homeostatic mechanisms regulating essential metals, as well as lipid levels. The data summarized by the presenters infers a potential causal link between multiple metals and CVDs and defines differences and commonalities. Therefore, summary of these presentations may accelerate the development of efficient preventive and therapeutic strategies by facilitating collaborations among multidisciplinary investigators.

Role of metallothionein in cadmium traffic and toxicity in kidneys and other mammalian organs

Metallothioneins are cysteine-rich, small metal-binding proteins present in various mammalian tissues. Of the four common metallothioneins, MT-1 and MT-2 (MTs) are expressed in most tissues, MT-3 is predominantly present in brain, whereas MT-4 is restricted to the squamous epithelia. The expression of MT-1 and MT-2 in some organs exhibits sex, age, and strain differences, and inducibility with a variety of stimuli. In adult mammals, MTs have been localized largely in the cell cytoplasm, but also in lysosomes, mitochondria and nuclei. The major physiological functions of MTs include homeostasis of essential metals Zn and Cu, protection against cytotoxicity of Cd and other toxic metals, and scavenging free radicals generated in oxidative stress. The role of MTs in Cd-induced acute and chronic toxicity, particularly in liver and kidneys, is reviewed in more details. In acute toxicity, liver is the primary target, whereas in chronic toxicity, kidneys are major targets of Cd. The intracellular MTs bind Cd ions and form CdMT. In chronic intoxication, Cd stimulates de novo synthesis of MTs; it is assumed that toxicity in the cells starts when loading with Cd ions exceeds the buffering capacity of intracellular MTs. CdMT, released from the Cd-injured organs, or when applied parenterally for experimental purposes, reaches the kidneys via circulation, where it is filtered, endocytosed in the proximal tubule cells, and degraded in lysosomes. Liberated Cd can immediately affect the cell structures and functions. The resulting proteinuria and CdMT in the urine can be used as biomarkers of tubular injury.