Dietary Cysteine Intake is Associated with Blood Glutathione Levels and Isometric Strength

Abstract

Glutathione is the most abundant cellular antioxidant and regulates redox homeostasis. Healthy individuals with certain antioxidant inadequacies/deficiencies exhibit impairments in physiological functions. The aim was to investigate whether low levels of dietary cysteine intake are associated with a) lower erythrocyte glutathione, b) increased plasma F 2 -isoprostanes, and c) impaired muscle function. Towards this aim, we recorded the dietary intake of the three amino acids that synthesize glutathione (i. e., glutamic acid, cysteine, and glycine) in forty-one healthy individuals, and subsequently measured erythrocyte glutathione levels. Maximal isometric strength and fatigue index were also assessed using an electronic handgrip dynamometer. Our findings indicate that dietary cysteine intake was positively correlated with glutathione levels (r=0.765, p<0.001). In addition, glutathione levels were negatively correlated with F2-isoprostanes (r=− 0.311, p=0.048). An interesting finding was that glutathione levels and cysteine intake were positively correlated with maximal handgrip strength (r=0.416, p=0.007 and r=0.343, p=0.028, respectively). In conclusion, glutathione concentration is associated with cysteine intake, while adequate cysteine levels were important for optimal redox status and muscle function. This highlights the importance of proper nutritional intake and biochemical screening with the goal of personalized nutrition.

Urinary Sulfate, Kidney Failure, and Death in CKD: The African American Study of Kidney Disease and Hypertension

“…Methionine is an essential amino acid, whereas cysteine can be synthesized as long as sulfur is available. Sulfur is principally stored as glutatione (31), and sulfur deficiency may favor cysteine and protein synthesis at the expense of other molecules such as glutathione. Glutathione is a powerful antioxidant whose activity decreases with protein restriction.…”

The redox signal: A physiological perspective

“…Regarding antioxidant deficiencies, we have repeatedly shown that such deficiencies lead to increased resting oxidative stress levels and impaired exercise capacity (e.g., maximal oxygen uptake, muscle function, time trial performance). [65][66][67][68] Moreover, this impaired exercise capacity was reversed only when the antioxidant in deficiency was administered and not a random one. 13 Beyond exercise, a series of studies have shown that vitamin E deficiency (and predominantly the α-tocopherol isomer) adversely affects neural development and cognitive function, embryonic development, thiol homeostasis, while it also leads to genetic and transcriptional dysregulation resulting in metabolic dysfunction.…”

“…Regarding antioxidant deficiencies, we have repeatedly shown that such deficiencies lead to increased resting oxidative stress levels and impaired exercise capacity (e.g., maximal oxygen uptake, muscle function, time trial performance) 65–68 . Moreover, this impaired exercise capacity was reversed only when the antioxidant in deficiency was administered and not a random one 13 .…”

Algae Supplementation for Exercise Performance: Current Perspectives and Future Directions for Spirulina and Chlorella

“…Specifically, the flawed assays of TBARS and TAC are inadequate today in redox biology ( 30 ). Considering spirulina contains approximately 0.45 g of cysteine/100 g and that adequate cysteine levels are essential for optimal glutathione concentration levels, redox status, and muscle function ( 31 ), equivocal results might also be attributed to the inter-individual baseline differences of glutathione before starting supplementation. For example, a recent study demonstrated that individuals with moderate-high baseline levels of glutathione did not benefit from N-acetylcysteine supplementation, yet those with low baseline levels improved V̇O 2max , time trial and Wingate tests by 13.6, 15.4, and 11.4%, respectively ( 32 ).…”