Abstract
This study was designed to investigate mechanisms of lipid metabolic inflexibility
in human obesity and the ability of fenofibrate (FENO) to increase skeletal muscle
fatty acid oxidation (FAO) in primary human skeletal muscle cell cultures (HSkMC)
exhibiting metabolic inflexibility. HSkMC from 10 lean and 10 obese, insulin resistant
subjects were treated with excess fatty acid for 24 h (24hFA) to gauge lipid-related
metabolic flexibility. Metabolically inflexible HSkMC from obese individuals were
then treated with 24hFA in combination with FENO to determine effectiveness for increasing
FAO. Mitochondrial enzyme activity and FAO were measured in skeletal muscle from subjects
with prediabetes (n=11) before and after 10 weeks of fenofibrate in vivo. 24hFA increased
FAO to a greater extent in HSkMC from lean versus obese subjects (+49% vs. +9%, for
lean vs. obese, respectively; p<0.05) indicating metabolic inflexibility with obesity.
Metabolic inflexibility was not observed for measures of cellular respiration in permeabilized
cells using carbohydrate substrate. Fenofibrate co-incubation with 24hFA, increased
FAO in a subset of HSkMC from metabolically inflexible, obese subjects (p<0.05), which
was eliminated by PPARα antagonist. In vivo, fenofibrate treatment increased skeletal
muscle FAO in a subset of subjects with prediabetes but did not affect gene transcription
or mitochondrial enzyme activity. Lipid metabolic inflexibility observed in HSkMC
from obese subjects is not due to differences in electron transport flux, but rather
upstream decrements in lipid metabolism. Fenofibrate increases the capacity for FAO
in human skeletal muscle cells, though its role in skeletal muscle metabolism in vivo
remains unclear.
Key words
mitochondria - fat oxidation - insulin resistance