N-Acetylcysteine, a Potent Anti-Oxidant, Rescues the Malignant Hyperthermia and Environmental Heat Stroke Phenotype of Calsequestrin-1 Knockout Mice

Abstract

Calsequestrin type 1 (CASQ1) is both the major Ca2+ binding protein in the sarcoplasmic reticulum (SR) in skeletal muscle and a direct modulator of type 1 ryanodine receptor (RYR1) Ca2+-release channel activity. Mice lacking CASQ1 (CASQ1-null) exhibit increased susceptibility for Malignant Hyperthermia (MH) and Environmental Heat Stroke (EHS), life-threatening disorders triggered by volatile anaesthetics and high temperature, respectively. Excessive oxidative stress during MH/EHS crises are proposed to result in increased RYR1 nitrosylation, and subsequently, enhanced SR Ca2+ leak that leads to hypercontractures and rhabdomyolysis. Here, we treated CASQ1-null mice for 2 months (from 2-to-4 months of age) with N-acetylcysteine (NAC, a potent anti-oxidant) provided ad libitum in their drinking water (1% w/v). NAC treatment significantly protected CASQ1-null mice from lethal episodes induced by both halothane (2%, 1h at 32°C) and heat challenge (41°C, 1h) with the rate of mortality being 79 vs 25% and 86 vs 30% in control vs NAC-treated mice, respectively. This protection resulted from several factors including: a) reduced oxidative stress measured as both GSH/GSSG ratio and the frequency of mitochondrial superoxide flash activity (P<0.05); b) decreased maximum core temperature during heat challenge (from 42.1 to 40.8°C); and c) reduced number of fibers undergoingrhabdomyolysis (from 37.6 to 11.6 %). Furthermore, in-vitro contracture test (IVCT) showed that the threshold for caffeine-induced contracture is back to normal values. These results support the hypothesis that excessive production of reactive oxygen species plays a critical role in the onset of MH/EHS crises. Therefore, anti-oxidants may be useful for the treatment and prevention of oxidative stress related skeletal muscle disorders.