Abstract:
Background: The development of diabetes and cardiovascular disease is linked with excess fructose consumption, where heart failure is one of the leading causes of mortality in diabetes. Dietary studies indicate that elevated fructose may contribute to the development of diabetic cardiomyopathy, but whether these effects are due to direct actions of fructose on the heart, or are secondary to systemic effects is unclear. Serum and cardiac fructose levels are elevated in diabetes and investigation into the primary effects of elevated fructose exposure on cardiomyocyte function could provide valuable insight into the development of diabetic cardiomyopathy. Objectives: This body of work set out to investigate the primary effects of elevated fructose exposure on cardiomyocytes energetics, glycogen and lipid storage, growth and viability, using a tightly-controlled in vitro cultured cardiomyocyte setting. Methods: Neonatal rat ventricular myocytes (NRVMs) were isolated from 1-2 day old Sprague Dawley rats and maintained in growth media for 2 days, before being exposed to fructose (0.1 to 10 mM range) for 24 hours. Cardiomyocyte basal and stressed glycolytic and mitochondrial activity were measured via the Seahorse XFp bioanalyzer energy phenotype assay. Cardiomyocyte glycogen and lipid content were measured via amyloglucosidase enzymatic assay and Oil Red O staining. Cell viability was assessed via a blinded, cell counting method using phase microscopy images of NRVMs, and cell size was measured via a backgroundexclusion method using brightfield images of haematoxylin-stained fixed NRVMs. Results: The overall findings of this investigation are that: 1. Fructose exposure upregulated cardiomyocyte glycolytic capacity (1.27-fold, p<0.05) during maximum stressed states, without changing mitochondrial respiration. No change in baseline glycolytic flux and mitochondrial respiration was observed. 2. Elevated fructose exposure increased cardiomyocyte lipid count and lipid droplet size by 26 and 13% respectively, but did not change cardiomyocyte glycogen levels. 3. Fructose exposure significantly increased cardiomyocyte size by 14%, without affecting cell viability. Conclusions: This study provides the first evidence that pathological fructose exposure directly influences cardiomyocyte glycolytic metabolism, lipid storage and cellular growth. These findings suggest that fructose exposure may contribute to the development of lipotoxicity and hypertrophy observed in settings of high cardiac fructose, such as diabetic cardiomyopathy.