Correcting glutathione deficiency to restore mitochondrial fat oxidation in aging

描述(申请人提供)：老年人超重和肥胖的发生率最高，这表明能量平衡存在缺陷。在生理条件下，禁食状态下的主要选择燃料是非酯化脂肪酸(NEFA)。然而，在衰老过程中，空腹状态下的NEFA氧化受损，葡萄糖利用率增加，这表明线粒体b-氧化存在缺陷。线粒体对氧化损伤的保护依赖于抗氧化剂，而谷胱甘肽(GSH)是最丰富的内源性抗氧化剂。在过去和正在进行的研究中，我们观察到老年人GSH缺乏，与年轻人相比，这与脂肪氧化降低50%，血浆NEFA水平高65%有关。我们发现，老年人GSH缺乏是由于合成减少，因为GSH前体氨基酸半胱氨酸和甘氨酸的可获得性降低。在这些老年受试者的饮食中补充半胱氨酸和甘氨酸两周，完全恢复了GSH的合成和浓度，并显著降低了由于氧化应激而造成的细胞损伤标记物，使其降至年轻对照组的水平。GSH恢复后，空腹NEFA氧化增加30%，空腹血浆FFA下降36%，提示衰老过程中NEFA氧化受损是一种可逆性缺陷。为了研究衰老过程中GSH缺乏是否与NEFA氧化受损有关，并易于体内和组织脂肪过度积累，我们研究发现，与20周龄年轻小鼠相比，80周龄小鼠骨骼肌和肝脏GSH显著降低，全身NEFA氧化受损，全身和肝内脂肪增加。给老年小鼠补充半胱氨酸和甘氨酸6周，可纠正肌肉和肝脏GSH缺乏，恢复全身NEFA氧化，并降低总体脂、肝脏脂肪和体重。这些数据表明，在衰老过程中，GSH缺乏易导致NEFA氧化受损和身体和组织脂肪过剩；通过在饮食中补充半胱氨酸和甘氨酸来纠正GSH缺乏，可以恢复NEFA氧化，并逆转这些缺陷。这项建议将确定老年人GSH缺乏与线粒体NEFA氧化受损之间的联系，并测试一种简单、安全、廉价的治疗方法，其基础是通过补充GSH前体氨基酸半胱氨酸和甘氨酸来改变饮食组成，以纠正GSH缺乏并恢复线粒体NEFA氧化。该提案还将测试GSH和NEFA氧化的恢复是否会导致老年人体内脂肪、肝脏内脂肪和心肌细胞内脂肪的损失。

DESCRIPTION (provided by applicant): Elderly humans have the highest prevalence of being overweight and obese, suggesting a defect in energy balance. Under physiological conditions, the predominant fuel of choice in the fasted state is non-esterified fatty acids (NEFA). However in aging, NEFA oxidation in the fasted state is impaired and there is increased glucose utilization, suggesting a defect in mitochondrial b-oxidation. Mitochondria rely on antioxidants fo protection against oxidative damage, and glutathione (GSH) is the most abundant endogenous antioxidant. In past and ongoing studies, we observed that elderly humans were deficient in GSH and this was associated with a 50% lower fat oxidation and 65% higher plasma NEFA levels compared to younger humans. We found that GSH deficiency in elderly humans occurred due to decreased synthesis, because of decreased availability of the GSH precursor amino acids cysteine and glycine. Supplementing the diet of these elderly subjects with cysteine and glycine for 2-weeks fully restored GSH synthesis and concentrations, and significantly lowered markers of cellular damage due to oxidative stress to levels found in young controls. After GSH restoration, fasted NEFA oxidation increased by 30%, and fasted plasma FFA fell by 36%, suggesting that impaired NEFA oxidation in aging is a reversible defect. To investigate whether GSH deficiency in aging is linked to impaired NEFA oxidation and predisposes to excess accumulation of body and tissue fat, we studied and found that 80-week old mice had significantly lower GSH in skeletal muscle and liver, impaired whole-body NEFA oxidation, and higher total body- and intrahepatic- fat, compared to young 20-week old mice. Supplementing diets of older mice with cysteine and glycine for 6-weeks corrected GSH deficiency in muscle and liver, restored whole-body NEFA oxidation, and lowered total body fat, hepatic fat and body weight. These data suggest that in aging, GSH deficiency predisposes to impaired NEFA oxidation and excess body and tissue fat; correcting GSH deficiency by supplementing cysteine and glycine in the diet restores NEFA oxidation and reverses these defects. This proposal will identify mechanisms linking GSH deficiency to impaired mitochondrial NEFA oxidation in elderly humans, and test a simple, safe, inexpensive therapy based on altering dietary composition by supplementing GSH precursor amino-acids cysteine and glycine to correct GSH deficiency and restore mitochondrial NEFA oxidation. The proposal will also test whether restoration of GSH and NEFA oxidation will result in loss of body fat, intrahepatic fat and intramyocellular fat in elderly humans.