Glutathione Homeostasis & Oxidant Damage in Kwashiorkor

描述（由申请人提供）：氧化应激有助于儿童PEM水肿综合征的临床和病理生理表现的证据是基于组织氧化损伤生物标志物的较高血浆浓度和普遍存在的抗氧化剂/解毒剂GSH的较低血液浓度。我们已经证明，缺乏半胱氨酸（csy），谷胱甘肽的前体，负责较慢的谷胱甘肽合成。半胱氨酸供应不足的原因，在水肿，而不是在非水肿PEM，尚不清楚。为了确定水肿性PEM中半胱氨酸缺乏的原因，将测试以下假设：1)在水肿性PEM中，而不是在非水肿性PEM中，蛋白质分解率的显著抑制导致半胱氨酸合成的蛋氨酸可用性降低。这一假设的一个推论是，补充蛋氨酸允许充分的半胱氨酸合成，因此，更快的谷胱甘肽合成非规范化，从而减少氧化损伤。2)另外，由于谷胱甘肽是SAMe合成酶的调节剂，降低谷胱甘肽的有效性会损害蛋氨酸向SAMe的转化，从而通过转甲基化-转硫途径向半胱氨酸的转化。这一假设的一个推论是，补充半胱氨酸或富含半胱氨酸的乳清配方的营养康复将允许谷胱甘肽合成和可用性更快正常化，从而恢复蛋氨酸对SAMe的代谢，从而恢复对半胱氨酸的代谢。使用生化、免疫学和稳定同位素示踪方法，这些假设将在6-18岁的PEM婴儿中进行测试。实验方案1将确定患有水肿性PEM与非水肿性PEM的儿童在以下方面的差异：1)蛋氨酸通量及其从蛋白质水解中释放、向同型半胱氨酸的转化（转甲基化速率）、同型半胱氨酸向蛋氨酸的转化（再甲基化速率）和向半胱氨酸的转化（转硫化速率）：总、蛋白质源性和蛋氨酸源性半胱氨酸通量、同型半胱氨酸和SAMe浓度。实验方案2和3将比较在1和2中概述的相同动力学参数下，喂养a)蛋氨酸与丙氨酸补充饮食，b)半胱氨酸与丙氨酸补充饮食，以及富含半胱氨酸的乳清饮食对患有水肿的PEM儿童的影响，再加上红细胞GSH的合成、氧化损伤指标的血浆浓度、免疫功能、蛋白质合成、身体成分以及减轻水肿、肝脏脂肪和恢复食欲所需的时间。所获得的数据将深入了解蛋氨酸有效性及其代谢在半胱氨酸缺乏中的作用，从而了解水肿性PEM中谷胱甘肽的缺乏，以及旨在补充蛋氨酸和半胱氨酸供应的治疗方法是否会加速水肿性PEM综合征儿童的临床和代谢恢复。

DESCRIPTION (provided by applicant): Evidence that oxidative stress contributes to the clinical and pathophysiologic manifestations of the edematous syndromes of childhood PEM is based on higher plasma concentrations of biomarkers of tissue oxidant damage and lower blood concentrations of the ubiquitous antioxidant/detoxicant GSH. We have demonstrated that deficiency of cysteine (csy), a GSH precursor, is responsible for slower GSH synthesis. The cause of inadequate cysteine supply in edematous, but not in non-edematous PEM, is not known. To determine the cause of this cysteine deficiency in edematous PEM the following hypotheses will be tested: 1) In edematous but not in nonedematous PEM, a marked suppression of protein breakdown rate results in reduced methionine availability for cysteine synthesis. A corollary to this hypothesis is that methionine supplementation permits adequate cysteine synthesis and hence, faster nonnalization of GSH synthesis thereby reducing oxidant damage. 2) Alternatively, because GSH is a regulator of SAMe synthetase, decreased GSH availability impairs conversion of methionine to SAMe, and hence to cysteine via the transmethylation-transsulfuration pathway. A corollary to this hypothesis is that nutritional rehabilitation with cysteine supplementation or a cysteine-rich whey based formula will permit faster normalization of GSH synthesis and availability thereby restoring methionine metabolism to SAMe and hence to cysteine. Using biochemical, immunological and stable isotope tracer methods, these hypotheses will be tested in 6-18 mo. old infants with PEM. Experimental protocol 1 will determine differences in children with edematous versus non-edematous PEM in 1) methionine flux and its release from proteolysis, its conversion to homocysteine (rate of transmethylation) and conversion of homoeysteine to methionine (rate of remethylation) and to cysteine (rate of transsulfuration) :!) total, protein-derived and methionine-derived cysteine fluxes, homocysteine and SAMe concentrations. Experimental protocols 2 and 3 will compare in children with edematous PEM the effect of feeding a) a methionine versus alanine supplemented diet and b) a cysteine versus alanine supplemented diet versus a cysteine-rich whey based diet on the same kinetic parameters outlined in I & 2 plus the synthesis of erythrocyte GSH, plasma concentrations of indicators of oxidant damage, immune function, protein synthesis, body composition and time taken to lose edema, liver fat, and to restore appetite. The data obtained will provide insight into the role of methionine availability and its metabolism in the cysteine deficiency, hence the GSH deficiency of edematous PEM and whether therapeutic approaches aimed to replenish methioninc and cysteine supply will accelerate clinical and metabolic recovery in children with the edematous PEM syndromes.