Intermittent treatment with elamipretide preserves exercise tolerance in aged female mice

Abstract

The pathology of aging impacts multiple organ systems, including the kidney and skeletal and cardiac muscles. Long-term treatment with the mitochondrial-targeted peptide elamipretide has previously been shown to improve in vivo mitochondrial function in aged mice, which is associated with increased fatigue resistance and treadmill performance, improved cardiovascular diastolic function, and glomerular architecture of the kidney. However, elamipretide is a short tetrameric peptide that is not orally bioavailable, limiting its routes of administration. This study tested whether twice weekly intermittent injections of elamipretide could recapitulate the same functional improvements as continuous long-term infusion. We found that intermittent treatment with elamipretide for 8 months preserved exercise tolerance and left ventricular mass in mice with modest protection of diastolic function and skeletal muscle force production but did not affect kidney function as previously reported using continuous treatment.

Keywords: Aging; Fatigue; Mitochondria; Sarcopenia.

Fig. 1

Mass and survival. A Weekly masses over the course of treatment normalized to initial body masses N = 20 at baseline and N = 8–10 at endpoint. B Survival curves of animals that did not reach endpoint. C Tibialis anterior mass normalized to tibia length N = 11–12. D Gastrocnemius mass normalized to tibia length N = 11–12. E Heart mass normalized to tibia length N = 9–10. All data expressed as means ± SE

Fig. 2

Treadmill running times. Elamipretide significantly preserves treadmill endurance. Data expressed as means ± SE. Mixed effects ANOVA, with Sidak’s correction for multiple comparisons, p < 0.05. N = 20 at baseline; N = 10–12 at endpoint

Fig. 3

In vivo skeletal muscle function. A Force time integral (FTI) of fatigue normalized to resting force at baseline before entering study, N = 19–20 (B) at 8 weeks, N = 16–18 (C) at 16 weeks, N = 15–17 (D) and at endpoint of study, N = 13 (E) Maximum force time integral over the course of the study. Data expressed as means ± SE. Mixed effects ANOVA, with Sidak’s correction for multiple comparisons, p < 0.05

Fig. 4

Cardiac effects. A Ea/Aa ratio over the course of the study, N = 7–12. B Left ventricular mass index over the course of the study, N = 7–12. Data expressed as means ± SE. Mixed effects ANOVA, with Sidak’s correction for multiple comparisons, p < 0.05

Fig. 5

Mitochondrial respiration and amplex red signal. A Respiration in permeabilized gastrocnemius fibers in forward flow, N = 8–10. B Respiration in heart homogenate in forward flow, N = 6–8. C Peroxide production in permeabilized gastrocnemius fibers in forward flow, N = 8–10. D Peroxide production in heart homogenate in forward flow, N = 6–8. Data expressed as means ± SE. Mixed effects ANOVA, with Sidak’s correction for multiple comparisons, p < 0.05

Fig. 6

Kidney pathology. A Kidney glomeruli were scored for aging glomerulosclerosis. Because glomerular size differs by kidney region, glomeruli were separated for scoring by cortical location as either occupying the outer cortex or near the medulla (juxtamedullary/JM). B Example images of immunohistochemistry of p57 to identify podocyte nuclei (dark brown, DAB) and counter stained with periodic acid Schiff (PAS) and hematoxylin (blue nuclei). Relative scores, for example, images shown. C Average number of podocytes per individual glomerular tuft. D Average diameter of podocyte nuclei within all glomeruli analyzed within each mouse. E Average volume of glomerular tuft. F Average density of podocytes within all glomeruli scored for each compartment was calculated as the number of podocytes normalized to tuft volume. All control and ELAM-treated groups were analyzed by individual Student’s t-test, and no significant differences were detected. N = 4–6