P4-181: Homocysteine, S-adenosylmethionine/s-adenosylhomocysteine ratio, glutathione and nitric oxide levels in TgCRDND8 mice fed with B vitamin–deficient diet

Abstract

Increasing evidence indicates that oxidative and nitrosative stress, impaired glutathione (GSH) and homocysteine (Hcy) metabolism can interact in a vicious cycle, which is central to AD pathogenesis. Synthesis of GSH is regulated by cysteine, which is synthesized from Hcy via the transsulfuration pathway. Deficiencies of folate, vitamins B12 and B6 are important for S-adenosylmethionine (SAM)/Hcy metabolism alterations, leading to hyperhomocysteinemia and decrease of SAM/SAH ratio, known as “methylation potential” (MP). Nitric oxide (NO) is involved in physiological functions and in pathological processes leading to tissue damage due to its free radical nature. The production of NO is strongly related to Hcy metabolism, through the regulation of ADMA (asymmetric dymethyl arginine) levels. We already showed, in vitro, that SAM administration can regulate PS1 and BACE expression and β-amyloid production, and in vivo that inhibition of methylation reaction by diet induced hyperhomocysteinemia is able to up-regulate PS1 and BACE. Thus, it was intriguing to study the relationships between Hcy, SAM/SAH ratio, GSH/GSSG and NO levels to understand the link between aberration in redox homeostasis and methylation potential in AD models. We used transgenic mice that have an accelerated amyloid accumulation since they are a good model to study the metabolic alterations caused by B vitamins deprivations in AD. TgCRND8 mice together with wild type mice were fed with a deprived diet (without folate, vitamin B12 and B6) or with a control diet. Then, they were sacrificed to analyze Hcy, SAM, SAH, GSH and NO in plasma and tissues by Imx, HPLC and colorimetric assay kits. The deficient diet lead to a marked hyperhomocysteinemia, to a decrease in SAM/SAH ratio in plasma and brain, to an increase of GSH/GSSG ratio in TgCRND8 brain probably due to the attempt to compensate for the increased oxidative damage resulting from amyloid β. There is also a brain NO decrease in diet B in TgCRND8 mice, while there are no significant differences in plasma. Additional experiments with SAM administration in condition of hyperhomocysteinemia are actually in progress, to test the effect of SAM in GSH and NO production, and amyloid production.