The Metabolic Mechanism Underlying the Enhancing Effects of Glycine and Tryptophan on Kidney Function: How to Reduce EGFR Inhibitory Effect on AAs

Background: Chronic kidney disease (CKD) leads to a progressive decline in kidney function that eventually progresses to end-stage renal disease. It is critical to identify people at risk for renal disease and to intervene early to avoid kidney damage. Tryptophan hydroxylase (TPH-1) is an accurate biomarker for CKD early stage. The loss of tryptophan hydroxylase contributes to kidney injury. N-acetylcysteine, glycine, and tryptophan can arrest renal fibrosis development and progression through the anti-fibrotic effect of tryptophan hydroxylase and the protective effect of N-acetylcysteine. Objectives: This study aims to assess the metabolic effect of N-acetyl-l-cysteine on kidney function as an EGFR inhibitor and its effect on AAs depletion. In addition, to evaluate the effect of glycine and tryptophan on kidney injury and renal fibrosis progression. Results: Eight weeks of administration of pemetrexed led to a significant increase in serum, urea, creatinine, and uric acid. Administration of N-acetylcysteine (NAC with pemetrexed) resulted in a significant decrease in biochemical kidney function. Also, glycine and tryptophan directly affect renal function; increased expression of tryptophan hydroxylase with decrease expression of EGFR and transforming growth β (TGF-β), compared to N-acetylcysteine group. Conclusion: N-acetylcysteine, glycine, and tryptophan can halt the depletion of AAs in the presence of urea and EGFR. Glycine and tryptophan both have a direct effect on renal function due to their uric acid-lowering properties.