Linoleic Acid Augments Oxidative Damage and Initiates Fibrosis in Cardiomyocytes and Fibroblasts

Abstract

Cardiac fibrosis following the demise of cardiomyocytes is pivotal to cardiac remodeling and heart failure. Considering the rising rates of cardiovascular disease (CVD) and the preponderance of linoleic acid (LA) in the Canadian diet, we hypothesized that excess LA could initiate cell death and fibrosis in the heart. Four-month-old female C57/Bl6 mice were fed a high LA diet (HLA; corn oil rich) for 5 weeks, and a separate low LA diet group (LLA, canola oil rich) was kept as the isocaloric, isonitrogenous control. HLA feeding increased cardiac TUNEL positivity as amarker of cell death, protein expression of matrix metalloproteases (MMP-2 and -9) and downregulated tissue inhibitor of metalloproteases (TIMP-1 and -2). Sirius red and Masson's Trichrome staining of heart sections demonstrated augmented collagen deposition. Oxidative stress biomarkers such as nitrotyrosine and 4-hydroxynonenal also increased, whereas antioxidants including glutathione and superoxide dismutase were downregulated. To confirm that LA specifically plays a causative role, NIH-3T3 fibroblasts and differentiated H9c2 cardiomyoblasts were incubated with oleic, palmitic, or linoleic acid at concentrations from 0.1 to 1.0 mM over 24 hours. Mitochondrial redox potential in H9c2 cardiomyocytes was decreased with both palmitic acid and LA, but not oleic acid. Only incubation with LA demonstrated a dose-dependent reduction in cell viability in H9c2 cardiomyocytes. These results suggest that excess LA, a common dietary omega-6 PUFA, can augment cell death, oxidative damage, and loss of mitochondrial membrane potential in the heart and can contribute to current CVD rates in Canada.