Glutathione is found at high concentrations in the lens (3.5–5.5 mmol/g wet weight), especially in the epithelial layer. Glutathione has many important roles in the lens, including:
Protein mercaptan is kept in a reduced state, which helps to maintain lens transparency by preventing the formation of high molecular weight crystalline protein aggregates.
Protect mercaptan groups involved in cation transport and permeability; For example, oxidation of the -SH group of the Na+,K+ -ATPASE pump leads to increased permeability to these ions.
Prevent oxidative damage (see later in this chapter).
Removal of isobiomass; Glutathione - S-transferase catalyzes the binding of glutathione to hydrophobic compounds with electrophilic centers.
Amino acid transport
Glutathione has a half-life of 1-2 days and is continuously recycled through the gamma-glutamyl cycle. Its synthesis and degradation occur at roughly the same rate. Glutathione is synthesized from L-glutamate, L-cysteine, and glycine by a two-step process using 11% -- 12% lens ATP. Reduced glutathione can also be introduced into the lens from aqueous solution. Reduced glutathione transporters that allow glutathione uptake by lens epithelium have been characterized. The breakdown of glutathione releases its amino acids, which are recycled.
Little is known about whether dietary components can modulate the efficacy of fluorouracil in colon cancer patients. Glutathione is an important antioxidant and anticancer agent and is present in varying amounts in many foods.
The effect of cellular glutathione concentration on the growth of human colorectal adenocarcinoma cell HT-29 and the cytotoxic activity of fluorouracil in these cells has been investigated [133]. Glutathione and sulfoxine sulfoximide were used to increase or decrease glutathione concentration in these cells, respectively. A 34% increase in cell glutathione concentration had no effect on the growth of HT-29 cells, nor on the cytotoxic activity of fluorouracil. A 50% reduction in cellular glutathione concentration increases the cytotoxicity of fluorouracil by 20-31%, depending on the fluorouracil concentration.
Glutathione is the main antioxidant in the lens and is found in foods such as Onions, garlic, avocados, cruciferous vegetables, asparagus and watermelon. Glutathione and its boosters are mercaptan compounds that scavenge free radicals. These glutathione enhancers include L-cysteine, lipoic acid and methyl sulfonyl methane. Glutathione also retains proteolytic enzymes in cortical lens fibers. In studies in the late 1960s, mature cataracts extracted were shown to contain very low levels of glutathione and ascorbic acid; This finding is thought to represent a second aspect of cataract formation. In retrospect, this defect appears to be a primal event that can be managed through nutrition.
