Correcting glutathione deficiency to restore mitochondrial fat oxidation in aging

描述（由申请人提供）：老年人超重和肥胖的患病率最高，表明能量平衡存在缺陷。在生理条件下，在禁食状态下选择的主要燃料是非酯化脂肪酸（NEFA）。然而，随着年龄的增长，禁食状态下的NEFA氧化受损，葡萄糖利用增加，这表明线粒体b-氧化存在缺陷。线粒体依靠抗氧化剂来防止氧化损伤，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，我们观察到老年人缺乏谷胱甘肽，与年轻人相比，这与脂肪氧化降低50%和血浆NEFA水平升高65%有关。我们发现，由于谷胱甘肽前体氨基酸半胱氨酸和甘氨酸的可用性降低，老年人的谷胱甘肽缺乏是由于合成减少而发生的。在这些老年受试者的饮食中补充半胱氨酸和甘氨酸2周，完全恢复了谷胱甘肽的合成和浓度，并显著降低了氧化应激引起的细胞损伤标志物，达到年轻对照组的水平。GSH恢复后，空腹NEFA氧化增加30%，空腹血浆FFA下降36%，表明衰老过程中NEFA氧化受损是一种可逆缺陷。为了研究衰老过程中GSH缺乏是否与NEFA氧化受损以及身体和组织脂肪的过度积累有关，我们研究发现，与20周龄的年轻小鼠相比，80周龄的小鼠骨骼肌和肝脏中的GSH显著降低，全身NEFA氧化受损，全身和肝内脂肪总量较高。在老年小鼠的饮食中添加半胱氨酸和甘氨酸6周，可以纠正肌肉和肝脏的谷胱甘肽缺乏，恢复全身NEFA氧化，降低体脂、肝脂和体重。这些数据表明，在衰老过程中，谷胱甘肽缺乏易导致NEFA氧化受损以及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谷胱甘肽缺乏症，可以恢复NEFA氧化并逆转这些缺陷。该提案将确定GSH缺乏与老年人线粒体NEFA氧化受损之间的联系机制，并测试一种简单、安全、廉价的治疗方法，该方法基于通过补充GSH前体氨基酸半胱氨酸和甘氨酸来改变饮食成分，以纠正GSH缺乏并恢复线粒体NEFA氧化。该提案还将测试恢复GSH和NEFA氧化是否会导致老年人体脂、肝内脂肪和细胞内脂肪的损失。

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.