Left ventricular structure and function and the link with oxidative stress in young adults : The African-PREDICT study

Abstract

In developed counties, the contribution of cardiovascular diseases (CVDs) to morbidity and mortality rates is well documented. In a study conducted in South Africa (N=4506), it was found that 92% of the study population (mean age 53 years) were suffering from CVDs, 53.5% of which were hypertensive and 47.1% of which suffered from heart failure. Oxidative stress is a well-known contributor to cardiovascular diseases. However, previous studies that linked oxidative stress to cardiac structure and function were done in older individuals or experimental animal studies. Less is known about the link between cardiac structure and function and oxidative stress-related markers in young populations before the development of CVDs. This study, therefore, focused on young and healthy adults to uncover early associations of cardiac structure and function with oxidative stress-related markers. Objectives The objectives of this study were (i) to compare cardiac structure and oxidative stress-related markers and (ii) to explore independent associations of cardiac structure and function with oxidative stress-related markers. This study formed part of the African Prospective Study on the Early Detection and Identification of Cardiovascular Disease and Hypertension (African-PREDICT). We included 361 individuals with complete oxidative stress data. The participants were from Potchefstroom and surrounding areas. They were aged between 20 and 30 years, had to have an office blood pressure of less than 140 mmHg systolic and 90 mmHg diastolic, were of self-reported black or white ethnicity and were apparently healthy. Standardised methods were used to determine anthropometric measurements. Biochemical measurements, including oxidative stress-related markers (gamma-glutamyl transferase (GGT), glutathione peroxidase (GPx), total glutathione (tGSH); and total antioxidant status (TAS) and traditional CVD risk markers (such as total cholesterol, high-density lipoprotein cholesterol, C-reactive protein and cotinine levels). Echocardiographic measurements, including let ventricular mass index (LVMi), relative wall thickness (RWT), ejection fraction (EF) and fractional shortening (FS), were determined by standard transthoracic echocardiography. Several interactions were identified for ethnicity and gender on the association between measures of LV structure and function markers and oxidative stress-related markers. The participants were therefore stratified according to gender and ethnicity. Independent t-Tests and Chi-square tests were performed to compare means and proportions among groups. Partial and multiple regression analyses were used to investigate the relationship between LV structure and function and oxidative stress-related markers while considering possible confounding factors. We found that the LVMi was comparable among the men and women and the RWT was higher in both the black women (p<0.001) and the black men (p=0.014). Ejection fraction and FS were comparable among the women, but lower in the white men than in the black men (p=0.013). Oxidative stress-related markers revealed higher GGT in the black women than in the white women (p<0.001), whereas in the men, GGT was comparable. Glutathione peroxidase (p<0.001) and TAS (p<0.001) were lower, but tGSH (p<0.001) was higher among both the black groups. In multiple regression analyses, after adjusting for confounding factors, LVMi was independently associated with GPx in black women (β=–0.286; p=0.010) and white men (β=0.329; p=0.004). In the white men only, both EF (β=–0.345; p=0.018) and FS (β=–0.335; p=0.019) were inversely associated with GGT. These results indicate the importance of adequate antioxidant capacity to prevent the onset of early cardiac dysfunction. Further investigations are warranted to clarify the opposing associations between iLVM and GPx in the black women and white men