Sulfur amino acid restriction and caloric restriction induce divergent redox metabolism-related adaptations in male F344 rats.

INTRODUCTION: To discover novel mechanisms, we compared changes in redox metabolism markers induced by caloric restriction (CR) and sulfur amino acid restriction (SAAR).
METHODS: We fed 16-week-old male F344 rats either a control diet (CD, 0.86% methionine), a sulfur amino acid-restricted diet (SAAR, 0.17% methionine), or a control diet pair-fed to 60% of the CD's ad libitum intake (CR, caloric restriction). We quantified small redox molecule concentrations, mRNA levels, and protein levels of relevant markers.
RESULTS: Compared with CR, SAAR decreased the hepatic total free glutathione (tGSH), increased GSSG:tGSH, protein-bound GSH:tGSH, and lowered glucose-6-phosphate dehydrogenase levels, indicating a pro-oxidant milieu. SAAR and CR differentially affected the NADPH-generating enzymes. SAAR increased the cytosolic malic enzyme (ME1) without affecting mitochondrial ME3, while CR increased ME3, but not ME1. CR elevated cytosolic methylenetetrahydrofolate dehydrogenase 1 (MTHFD1) without affecting mitochondrial MTHFD2, whereas SAAR increased MTHFD2 without affecting MTHFD1. Folate cycle changes include increases in Aldh1l1 and Aldh1l2 by SAAR and MTHFD1L by CR. SAAR, but not CR, upregulated the gene expression of compartment-specific (de)glutathionylation enzymes; both diets had distinct effects on glutathionylation of the hepatic proteome.
CONCLUSIONS: SAAR and CR engage different pathways to generate compartment-specific NADPH. Protein glutathionylation may contribute to SAAR-induced benefits.