Exercise frequency affects morphology of aortic calcium deposits in female hyperlipidemic mice as determined by 18F-NaF PET

Abstract

While exercise is known to benefit cardiovascular health, the optimum regimen, in terms of both speed and frequency, remains unclear, especially for those with existing calcific atherosclerosis. We previously found that, in atherosclerotic female mice, lower speed, but not higher speed, treadmill running had a beneficial effect on the morphology of aortic calcium mineral deposits, as determined by ¹⁸F-NaF PET imaging, where ¹⁸F-NaF tracer uptake reflects mineral surface area, which, in turn, reflects risk. To determine optimal exercise frequency at the lower speed, ¹⁸F-NaF tracer uptake and histochemical analysis of alkaline phosphatase, calcium mineral, and CD68 in the aortas of aged Apoe^-/- mice exercising 0, 3, or 5 days/week were performed. Images were acquired at baseline and at the end of the study. Although by histochemistry, all 3 groups had similar levels of osteoblastic differentiation and similar numbers of aortic calcium deposits, ¹⁸F-NaF tracer uptake increased significantly over the study duration in the 0- and 3-days/week. groups but not in the 5-days/week. group. Calcification also had a significant negative correlation with macrophage infiltration in the 5-days/week. group. In summary, the findings suggest that greater frequency running regimens alter aortic calcification in ways that may provide better cardiovascular benefits.

Keywords: PET/CT; calcification; exercise; hyperlipidemia.

FIGURE 1

MicroPET imaging of aortic calcification. (Top) Schematic diagram of experimental design. (Bottom) Aortic ¹⁸F‐NaF tracer uptake, assessed by microPET imaging. N = 11–13/group.

FIGURE 2

Histological assessment of aortic roots. (a, b) Calcification was assessed by Alizarin red staining N = 11–13/group. Gray arrows denote dense, possibly coalesced, calcium deposits. Magnification: 2×. The rectangular dotted outlines indicate the locations for the close‐ups in (b). Control and 3‐days/week groups also have regions of speckled calcium deposits (blue). (c) Osteoblastic differentiation was assessed by alkaline phosphatase histochemical staining (red arrows). N = 11–13/group. (d) Atheromatous lesion area was assessed by oil red O histochemical staining (red arrows). Oil red O positivity in the adventitial layer was not included in the calculation. N = 11–13/group, magnification: 2×. (e) Correlation of histochemical calcification and infiltration of CD‐68 positive cells, such as macrophages, in mice exercised 5‐days/week. N = 12.

FIGURE 3

Effects of exercise frequency on skeletal BMD. Skeletal BMD at lumbar vertebrae 3, assessed by microCT imaging. N = 11–13/group.