In a rotenone-induced mouse model of Parkinson’s disease, metformin administration (300 mg/kg/day) attenuated the loss of tyrosine hydroxylase (TH+) neurons in the substantia nigra (SN), decreased cleaved caspase-3 and α-synuclein accumulation in the SN, and reduced the levels of malondialdehyde (MDA) and 4-hydroxynonenal (4-HNE), indicating decreased lipid peroxidation, compared to the rotenone-only group [268]. The gene discussed is TH; the disease is Parkinson disease.