Chronic Treatment With the ACE Inhibitor Enalapril Attenuates the Development of Frailty and Differentially Modifies Pro- and Anti-inflammatory Cytokines in Aging Male and Female C57BL/6 Mice

Abstract

Studies on interventions that can delay or treat frailty in humans are limited. There is evidence of beneficial effects of angiotensin converting enzyme (ACE) inhibitors on aspects related to frailty, such as physical function, even in those without cardiovascular disease. This study aimed to longitudinally investigate the effect of an ACE inhibitor on frailty in aging male and female mice. Frailty was assessed with a clinical frailty index (FI) which quantifies health-related deficits in middle-aged (9-13 months) and older (16-25 months) mice. Chronic treatment with enalapril (30 mg/kg/day in feed) attenuated frailty in middle-aged and older female mice, and older male mice, without a long-term effect on blood pressure. Enalapril treatment resulted in a reduction in the proinflammatory cytokines interleukin (IL)-1α, monocyte chemoattractant protein-1 and macrophage inflammatory protein-1a in older female mice, and an increase in the anti-inflammatory cytokine IL-10 in older male mice compared with control animals. These sex-specific effects on inflammation may contribute to the protective effects of enalapril against frailty. This is the first study to examine the longitudinal effect of an intervention on the FI in mice, and provides preclinical evidence that enalapril may delay the onset of frailty, even when started later in life.

Keywords: Frailty index; IL-10; IL-1α; MCP-1; MIP-1α.

Figure 1.

Enalapril treatment delayed frailty in mice. (A, B) Mean ± SEM frailty index (FI) scores for enalapril-treated and control mice. Middle-aged female mice (A, n = 13–17) and middle-aged male mice (B, n = 14–15) were treated for 4 months. (C, D) Older female mice (C, n = 4–16) were treated for 5 months, and older male mice (D, n = 10–25) were treated for 9 months. Linear mixed model analysis was used to assess the effect of age and drug on FI score and enalapril dose. For FI scores, age and drug were both significant factors for middle-aged females, older females and older males. For middle-aged males only, age was significant. For enalapril dose, age was significant for middle-aged mice, and both age and sex were significant for older mice. *p < .05 compared with enalapril-treated group at the same time point.

Figure 2.

Control and enalapril-treated mice display a range of individual FI deficits. The proportion of mice scored for a specific deficit in enalapril-treated and control mouse groups. (A) Older females at 21 months of age, (B) older males at 21 months of age, and (C) older males at 25 months of age. (A) 6 drug, 4 control; (B) 23 drug, 12 control; (C) 11 drug, 10 control. *p < .05 with chi-squared analysis, compared with enalapril-treated group.

Figure 3.

Blood pressure in middle-aged and older mice treated with enalapril. Systolic and diastolic blood pressure (BP) measured in middle-aged (A–D) and older (E–H) mice either 6 weeks after treatment started (A, B, E, F) or at the end of treatment (4 months for middle-aged, C, D; 5/7 months for older mice, G, H). Two-way ANOVA, with post hoc analysis, was used to analyze the effects of treatment and sex on systolic and diastolic blood pressure at each time point. Middle-aged 6 weeks male 6 drug, 6 control and female 3 drug, 5 control; middle-aged end of treatment male 5 drug, 5 control and female 6 drug, 6 control; older 6 weeks male 13 control, 11 drug and female 9 control, 8 drug; older end of treatment male 13 control, 19 drug and female 4 control, 5 drug. *p < .05 compared with corresponding control group.

Figure 4.

Proinflammatory cytokine levels are increased with age and attenuated by enalapril treatment in females. Levels of cytokines interleukin (IL)-6, IL-10, IL-12p40, eotaxin, granulocyte-colony stimulating factor (G-CSF), macrophage inflammatory protein (MIP)-1α, monocyte chemoattractant protein (MCP)-1, IL-1β, IL-1α, and IL-4 were assessed in serum from female mice (A–J). Levels for female mice were assessed at 13 months of age after 4 months of treatment (middle-aged) and at 21 months of age after 5 months of treatment (older). Two-way ANOVA, with post hoc analysis, was used to examine the effect of age and treatment on serum levels of each cytokine. Middle-aged female 6 drug, 5 control; older female 9 drug, 5 control. *p < .05 compared with corresponding control group. ^#p < .05 compared with corresponding middle-aged group.

Figure 5.

Proinflammatory cytokine levels are increased with age in males but enalapril treatment increases anti-inflammatory cytokine levels. Levels of cytokines interleukin (IL)-6, IL-10, IL-12p40, eotaxin, granulocyte-colony stimulating factor (G-CSF), macrophage inflammatory protein (MIP)-1α, monocyte chemoattractant protein (MCP)-1, IL-1β, IL-1α, and IL-4 were assessed in serum from male mice (A–J). Cytokine levels for male mice were assessed in serum at 13 months of age after 4 months of treatment (middle-aged) and at 25 months of age after 7 months of treatment (older). Two-way ANOVA, with post hoc analysis, was used to examine the effect of age and treatment on serum levels of each cytokine. Middle-aged male 8 drug, 9 control; older male 12 drug, 9 control. *p < .05 versus corresponding control group. ^#p < .05 versus corresponding middle-aged group.