Effects of Exercise Frequency on Aortic Calcification in Hyperlipidemic Mice
Cardiovascular disease risk is associated with coronary artery calcification and is mitigated by regular exercise. However, the optimal regimen (activity level and frequency) for benefitting cardiovascular health is not clear. The surface area of calcium deposits, in addition to the quantity of calcium mineral, is a key factor in the risk of plaque rupture in humans due to compliance mismatch of edges with surrounding distensible tissue resulting in debonding. We previously found that aortic PET tracer uptake, a marker of mineral surface area, was reduced in hyperlipidemic (Apoe-/-) mice that underwent treadmill exercise, especially those in the low-speed (12.5 meters/min) regimen. To test the optimal exercise frequency on cardiovascular health, hyperlipidemic mice with baseline aortic calcification were subjected to none, 3- or 5-day/week treadmill regimen (12.5 meters/min for 30 min/day) for 5 weeks. MicroPET/microCT imaging and echocardiography were performed before and after the 5-week study. Results show that aortic calcification significantly progressed in all 3 groups, and 18F-NaF uptake increased in the control and 3-day groups, but not in the 5-day group. As for cardiac function, left ventricular (LV) systolic function was not affected but LV mass and wall thickness decreased in the 5-day group, suggesting cardiac remodeling. Skeletal bone density assessed at lumbar vertebrae shows that bone density decreased in all 3 groups. These findings suggest that, in mice with underlying calcific atherosclerosis, low-speed exercise and a frequency of 5 days/week is optimal for benefitting cardiovascular health.