Introduction: The diabetic heart is metabolically inflexible, displaying maintained fatty acid oxidation (FAO) but impaired glucose uptake. Amylin is co-released with insulin by pancreatic β-cells, forming deposits locally and in hearts of patients with Type II diabetes mellitus (T2DM). This contrasts with rodent amylin which has a reduced propensity to aggregate. In HIP rats expressing human amylin, deposits occur in the pancreas, and heart, and T2DM ensues. This is not observed in hyperglycaemic (UCD) rats expressing rodent amylin.
Objective: To investigate if cardiac amylin aggregates exacerbate mitochondrial and metabolic changes in diabetic cardiomyopathy.
Methods: All animal experiments conform to the NIH guide for the care and use of laboratory animals and were approved by the Institutional Animal Care and Use Committee at University of Kentucky. Cardiac mitochondrial respiration was studied in male, wild-type (WT), HIP, and UCD rats (14-16 months) using a protocol optimised for frozen samples. Enzyme activities were measured by spectrophotometric assays, and gene expression by qPCR. Respiratory oxygen fluxes (JO2) were normalised to cardiac tissue wet weight and analysed by One-way ANOVA (n=10).
Results: In HIP rats, cardiac respiratory capacity was lower than in WTs and UCDs. Complex I (CI), Complex I and II (CI&II), and Complex IV-supported (CIV) respiration rates were 57.3% (P<0.01), 49.0% (P<0.01), and 34.7% (P<0.05) lower, respectively, than in WTs. CI&II and CII-supported rates were 39.7% and 56.5% lower than UCDs (P<0.05). In comparison with WTs, β-hydroxyacyl CoA dehydrogenase (HOAD) activity was unchanged in UCDs, with a trend towards decreased activity in HIP rats, alongside a trend towards lower expression of other components important for fatty acid oxidation: Ppara, Cpt1b, Ucp3.
Conclusion: Cardiac amylin aggregation in HIP rats suppresses mitochondrial respiratory capacity, and potentially fatty acid oxidation, compared with UCDs and WTs.