Humanin increased mitochondrial respiration rate in RPE cells. Real-time continuous measurement of mitochondrial respiration in RPE cells. Oxygen consumption rate was determined in nonpolarized RPE cells treated with 150 μM tBH or 150 μM tBH plus 10 or 20 μg/mL HN or 10 μg/mL HN only for 24 hours. Basal respiration (A), maximal OCR (B), ATP turnover (C), reserve capacity (D), and proton leak (E) were significantly reduced in tBH-treated cells versus control, whereas HN cotreatment increased all mitochondrial metabolic parameters studied when compared to tBH-treated group. *P < 0.01, **P < 0.01.