In aged male mice, baseline cardiac mitochondrial carnitine acetyltransferase (CrAT) enzyme activity is lower than in aged female mice, and GlyNAC supplementation restores CrAT activity in aged male mice to the level observed in aged female mice without changing CrAT protein expression.

In older male mice, the heart accumulates too much oxidative damage, which blocks the enzyme CrAT from working properly. Giving GlyNAC provides the building blocks to make more glutathione, which cleans up the damage. This lets CrAT function normally again, improving how the heart uses fuel, without changing how much enzyme is present. Female mice already have less damage and more natural protection, so adding GlyNAC does not help and may even disrupt their balance.