Blood-cell bioenergetics are associated with physical function and inflammation in overweight/obese older adults

Abstract

Background: Physical function and strength decline with age and lead to limited mobility and independence in older adults. Alterations in mitochondrial function are thought to underlie numerous age-related changes, including declining physical ability. Recent studies suggest that systemic changes in bioenergetic capacity may be reported by analyzing mitochondrial function in circulating cells. The objective of this study was to determine whether the bioenergetic capacity of peripheral blood mononuclear cells (PBMCs) is related to differences in physical function among older, overweight/obese, adults. To address this, we tested the hypothesis that greater PBMC respirometric capacity would be associated with better physical function, muscular strength, leg lean mass, and muscle quality. Furthermore, we tested whether the respirometric capacity of PBMCs is related to cellular composition and inflammatory status reported by interleukin-6 (IL-6).

Methods: Fasted PBMC respiration (pmol/min/500,000 cells), expanded short physical performance battery (Ex-SPPB), peak knee extensor (KE) strength (Nm), grip strength (kg), leg lean mass (kg, via dual energy X-ray absorptiometry [DXA]), muscle quality (Nm/kg), and plasma IL-6 (pg/mL) were analyzed in 15 well-functioning, community-dwelling, sedentary overweight/obese older men (n=9) and women (n=6) aged 65 to 78 (mean 68.3 ± 3.5 years). Pearson and partial correlations were calculated to determine associations between PBMC respiration and these variables.

Results: Higher maximal respiration of PBMCs was associated with better Ex-SPPB (r=0.58, p=0.02), greater KE strength (r=0.60, p=0.02), greater grip strength (r=0.52, p=0.05) and lower IL-6 (r=-0.58, p=0.04). Higher spare respiratory capacity was associated with better Ex-SPPB (r=0.59, p=0.02), greater KE strength (r=0.60, p=0.02), greater grip strength (r=0.54, p=0.04), greater leg muscle quality (r=0.56, p=0.04), and lower IL-6 (r=-0.55, p=0.05). Monocyte and lymphocyte counts were not related to PBMC respiratory capacity.

Conclusions: Our results indicate that respirometric profiles of readily obtainable blood cells are associated with physical function and strength. Future studies should be undertaken in order to determine whether blood-based bioenergetic profiling can provide an objective index of systemic mitochondrial health.

Keywords: Bioenergetics; Blood; Inflammation; Mitochondria; Physical function.

Copyright © 2015 Elsevier Inc. All rights reserved.

Figures

Figure 1:

Expanded SPPB plotted against (A) SRC (Maximal Respiration minus Basal Respiration; pmol/min/500,000 cells), (B) Maximal Respiration (pmol/min/500,000 cells), and (C) Basal Respiration (pmol/min/500,000 cells) in peripheral blood mononuclear cells. Peak knee extensor strength (Nm) plotted against (D) SRC, (E) Maximal Respiration, and (F) Basal Respiration in peripheral blood mononuclear cells. Grip strength (kg) plotted against (G) SRC, (H) Maximal Respiration, and (I) Basal Respiration in peripheral blood mononuclear cells. SPPB, short physical performance battery; SRC, spare respiratory capacity. N=15.

Figure 2:

Leg Lean Mass (Kg) plotted against: (A) SRC (Maximal Respiration minus Basal Respiration; pmol/min/500,000 cells), (B) Maximal Respiration (pmol/min/500,000 cells), and (C) Basal Respiration (pmol/min/500,000 cells) in peripheral mononuclear cells. SRC, spare respiratory capacity. N=14.

Figure 3:

Muscle Quality (peak knee extensor strength divided by leg lean mass; Nm/kg) plotted against: (A) SRC (pmol/min/500,000 cells), (B) Maximal Respiration (pmol/min/500,000 cells), and (C) Basal Respiration (pmol/min/500,000 cells) in peripheral mononuclear cells. SRC, spare respiratory capacity. N=14.

Figure 4:

Interleukin-6 level (pg/mL) plotted against: (A) SRC (Maximal Respiration minus Basal Respiration; pmol/min/500,000 cells), (B) Maximal Respiration (pmol/min/500,000 cells), and (C) Basal Respiration (pmol/min/500,000 cells) in peripheral mononuclear cells. SRC, spare respiratory capacity. N=13.

Figure 5:

Monocyte cell count (cells/mL blood; square root transformed) plotted against: (A) SRC (Maximal Respiration minus Basal Respiration; pmol/min/500,000 cells), (B) Maximal Respiration (pmol/min/500,000 cells), and (C) Basal Respiration (pmol/min/500,000 cells). Lymphocyte cell count (cells/mL blood) plotted against: (D) SRC (pmol/min/500,000 cells), (E) Maximal Respiration (pmol/min/500,000 cells), and (F) Basal Respiration (pmol/min/500,000 cells) in peripheral blood mononuclear cells. SRC, spare respiratory capacity. N=15.