Rat Jejunum Controls Luminal Thiol-Disulfide Redox

Abstract

The control of luminal thiol-disulfide redox state may be important for several intestinal functions, including absorption of iron or selenium and maintenance of mucus fluidity. Disulfides are present in the diet, and although luminal thiols are supplied in bile, little is known about the ability of the small intestine to reduce disulfides to maintain the luminal thiol-disulfide redox state. The objective of the current study was to determine whether the isolated, vascularly perfused jejunum, free from biliary thiols, could reduce intraluminal glutathione disulfide (GSSG) to glutathione (GSH). GSSG was introduced in a deoxygenated solution to inhibit the reoxidation of any GSH formed, and preparations were pretreated with acivicin to inhibit the degradation of GSH by gamma-glutamyltransferase. GSSG (250 micromol/L) was reduced to GSH, with the luminal redox potential (E(h)) for GSSG/2GSH changing from >0 to -111, -132 and -143 mV at 10, 20 and 30 min, respectively. The E(h) for luminal cystine/2cysteine was approximately 20 mV more reducing than that for GSSG/2GSH at each time point, suggesting that cysteine could function in the reduction of GSSG in the lumen. Measurements in specific regions showed that GSSG reduction was more rapid in the duodenum and proximal jejunum than in the distal jejunum. Preparations without acivicin treatment showed that E(h) values were unaffected by inhibition of gamma-glutamyltransferase despite differences in GSH and cysteine pool sizes. Rat intestine has a mechanism to adjust the luminal thiol-disulfide redox. In principle, dysfunction of this mechanism could contribute to malabsorption or other nutritional disorders.

Control of extracellular cysteine/cystine redox state by HT-29 cells is independent of cellular glutathione

“…The range of steady-state E hCySS values maintained in cultured cells is identical to the E hCySS in human plasma (Ϫ80 Ϯ 9 mV) (7,16,18). Of potential importance, plasma E hCySS becomes oxidized in association with age (18) and oxidative stress (24), raising the possibility that plasma E hCySS could be important in determining the balance of cell populations in vivo.…”

“…Concentrations of thiols and disulfides were determined by integration relative to the internal standard. Extracellular redox states (i.e., half-cell reduction potentials, E h) of the GSH/GSSG and Cys/CySS pools were calculated from concentrations of GSH, GSSG and Cys, CySS in molar units with the following forms of the Nernst equation for pH 7.4 (7,15)…”

“…Although the E hGSSG is about Ϫ230 mV in tissues (23) and the E h for reduction of O 2 to H 2 O is Ͼ600 mV, the E hCySS in plasma of young healthy individuals is Ϫ80 Ϯ 9 mV (16). The relatively small variation for E hCySS despite the large difference between the GSH/GSSG and H 2 O/O 2 couples indicates that mechanisms exist to control extracellular E hCySS (7).…”

Cystic Fibrosis-Related Oxidative Stress and Intestinal Lipid Disorders

“…GSH from the intestinal lumen comes from the diet, de novo synthesis, and biliary secretion, which corresponds to 50% of hepatic GSH (10). Luminal GSH is involved in trapping divalent metals, maintaining mucus fluidity, capturing peroxidized lipids, and reducing their lymphatic transport (9,36,75). Any abnormality in biliary secretion could therefore influence intestinal luminal redox equilibrium by disturbing GSH metabolism.…”

“…Their redox status in the compartment is highly more oxidized than in cellular cytoplasm. It is so well oxidized that CySS is considered the major determinant of redox potential in this compartment (36). The redox status of extracellular GSH/GSSG is considered to be the best reflection of tissular antioxidant defense, whereas that of extracellular Cys/CySS appears to regulate cell functions (80,110).…”