Aging is associated with impaired fasted oxidation of
nonesterified fatty acids (
NEFA) suggesting a
mitochondrial defect. Aging is also associated with deficiency of
glutathione (GSH), an important mitochondrial
antioxidant, and with
insulin resistance. This study tested whether GSH deficiency in aging contributes to impaired mitochondrial
NEFA oxidation and
insulin resistance, and whether GSH restoration reverses these defects. Three studies were conducted: (i) in 82-week-old C57BL/6 mice, the effect of naturally occurring GSH deficiency and its restoration on mitochondrial (13) C1 -
palmitate oxidation and
glucose metabolism was compared with 22-week-old C57BL/6 mice; (ii) in 20-week C57BL/6 mice, the effect of GSH depletion on mitochondrial oxidation of (13) C1 -
palmitate and
glucose metabolism was studied; (iii) the effect of GSH deficiency and its restoration on fasted
NEFA oxidation and
insulin resistance was studied in GSH-deficient elderly humans, and compared with GSH-replete young humans. Chronic GSH deficiency in old mice and elderly humans was associated with decreased fasted mitochondrial
NEFA oxidation and
insulin resistance, and these defects were reversed with GSH restoration. Acute depletion of GSH in young mice resulted in lower mitochondrial
NEFA oxidation, but did not alter
glucose metabolism. These data suggest that GSH is a novel regulator of mitochondrial
NEFA oxidation and
insulin resistance in aging. Chronic GSH deficiency promotes impaired
NEFA oxidation and
insulin resistance, and GSH restoration reverses these defects. Supplementing diets of elderly humans with
cysteine and
glycine to correct GSH deficiency could provide significant metabolic benefits.