Type-2 diabetic aldehyde dehydrogenase 2 mutant mice (ALDH 2*2) exhibiting heart failure with preserved ejection fraction phenotype can be determined by exercise stress echocardiography

Abstract

E487K point mutation of aldehyde dehydrogenase (ALDH) 2 (ALDH2*2) in East Asians intrinsically lowers ALDH2 activity. ALDH2*2 is associated with diabetic cardiomyopathy. Diabetic patients exhibit heart failure of preserved ejection fraction (HFpEF) i.e. while the systolic heart function is preserved in them, they may exhibit diastolic dysfunction, implying a jeopardized myocardial health. Currently, it is challenging to detect cardiac functional deterioration in diabetic mice. Stress echocardiography (echo) in the clinical set-up is a procedure used to measure cardiac reserve and impaired cardiac function in coronary artery diseases. Therefore, we hypothesized that high-fat diet fed type-2 diabetic ALDH2*2 mutant mice exhibit HFpEF which can be measured by cardiac echo stress test methodology. We induced type-2 diabetes in 12-week-old male C57BL/6 and ALDH2*2 mice through a high-fat diet. At the end of 4 months of DM induction, we measured the cardiac function in diabetic and control mice of C57BL/6 and ALDH2*2 genotypes by conscious echo. Subsequently, we imposed exercise stress by allowing the mice to run on the treadmill until exhaustion. Post-stress, we measured their cardiac function again. Only after treadmill running, but not at rest, we found a significant decrease in % fractional shortening and % ejection fraction in ALDH2*2 mice with diabetes compared to C57BL/6 diabetic mice as well as non-diabetic (control) ALDH2*2 mice. The diabetic ALDH2*2 mice also exhibited poor maximal running speed and distance. Our data suggest that high-fat fed diabetic ALDH2*2 mice exhibit HFpEF and treadmill exercise stress echo test is able to determine this HFpEF in the diabetic ALDH2*2 mice.

Fig 1. High-fat diet induces obesity in C57BL and ALDH2*2 mutant mice.

Body weight increase in high-fat fed C57BL and ALDH2*2 mutant diabetic mice (DM) compared to their respective non-diabetic controls (Ctrl.). Data are presented as mean ± standard error of the mean (SEM). ^*p<0.05, ^**p<0.01 and ^***p<0.001 vs Respective Ctrl.

Fig 2. High-fat diet induces hyperglycemia and glucose intolerance in C57BL and ALDH2*2 mutant mice.

Increase in blood glucose levels (refer values at the zero minutes) and glucose intolerance with IPGTT up to 120 minutes was observed in high-fat fed C57BL and ALDH2*2 mutant diabetic mice (DM) compared to their respective non-diabetic controls (Ctrl.).Data are presented as mean ± standard error of the mean (SEM). ^*p<0.05, ^**p<0.01 and ^***p<0.003 vs Respective Ctrl.

Fig 3. High-fat diet induces hyperinsulinemia in C57BL and ALDH2*2 mutant mice.

Serum insulin levels were measured using insulin ELISA kit. ^*p<0.05 and ^**p<0.01 vs. Respective Ctrl.

Fig 4. Increase in heart rate with exercise stress.

Increase in heart rate is lower in diabetic mice compared to control mice. Data are presented as mean ± standard error of the mean (SEM). ^$p<0.05 and ^$ $ $p<0.001 vs C57 Ctrl. ^**p<0.01 vs. Respective Ctrl. ^##p<0.01 and ^###p<0.001 vs before exercise stress of same group; ^Ωp<0.05 vs. C57DM.

Fig 5. Changes in systolic contractile functional parameters with exercise stress.

Larger decrease in %FS (B) and %EF (C) in diabetic mice compared to control mice. Decrease in diastolic functional parameter, cardiac relaxation rate (CRR) (D) is observed in diabetic mice compared to control mice. Data are presented as mean ± standard error of the mean (SEM). ^*p<0.05, ^**p<0.01 and ^***p<0.001 vs. Respective Ctrl.; ^#p<0.05 and ^###p<0.001 vs before exercise stress of same group; ^Ωp<0.05 and ^ΩΩΩp<0.001 vs. C57DM.

Fig 6. Running distance and duration of control and diabetic mice.

Lower running duration (A) and distance (B) in diabetic mice compared to control mice. Data are presented as mean ± standard error of the mean (SEM). ***p<0.001 vs. C57 Ctrl.; Ωp<0.05 and ΩΩΩp<0.001 vs C57 DM.

Fig 7. Correlation graphs.

A positive correlations between % change in cardiac output (CO) and running distance (A) as well as % FS after run and running distance (B).

Fig 8. Cardiomyocyte hypertrophy in diabetic mice.

Serum BNP levels (A). Cardiomyocyte hypertrophy (B) and its quantification data (C) Data are presented as mean ± standard error of the mean (SEM). ^**p<0.01 and ***p<0.001 vs. Respective Ctrl.; Ωp<0.05 vs C57 DM.