Rat jejunum controls luminal thiol-disulfide redox

Area of Science:

• Gastroenterology
• Physiology
• Biochemistry

Background:

• Luminal thiol-disulfide redox state is critical for intestinal functions like nutrient absorption and mucus properties.
• The small intestine's capacity to reduce dietary disulfides to maintain this redox state is largely unknown.
• Bile supplies luminal thiols, but their role in disulfide reduction needs further investigation.

Purpose of the Study:

• To determine if the isolated, vascularly perfused jejunum can reduce intraluminal glutathione disulfide (GSSG) to glutathione (GSH) in the absence of biliary thiols.
• To investigate the potential role of cysteine in the reduction of GSSG within the intestinal lumen.
• To assess regional differences in GSSG reduction capacity along the small intestine.

Main Methods:

• Isolated, vascularly perfused rat jejunum model.
• Introduction of GSSG (250 micromol/L) in deoxygenated solution to prevent GSH reoxidation.
• Pretreatment with acivicin to inhibit gamma-glutamyltransferase and prevent GSH degradation.
• Measurement of luminal redox potential (E(h)) for GSSG/2GSH and cystine/2cysteine couples.
• Regional analysis of GSSG reduction in duodenum, proximal jejunum, and distal jejunum.

Main Results:

• The jejunum effectively reduced intraluminal GSSG to GSH, evidenced by a significant shift in the GSSG/2GSH redox potential from >0 mV to -111, -132, and -143 mV over 30 minutes.
• Luminal cystine/2cysteine redox potential was consistently ~20 mV more reducing than GSSG/2GSH, suggesting cysteine's involvement in GSSG reduction.
• GSSG reduction was faster in the duodenum and proximal jejunum compared to the distal jejunum.
• Inhibition of gamma-glutamyltransferase did not affect E(h) values, despite altering GSH and cysteine pool sizes.

Conclusions:

• The rat small intestine possesses an intrinsic mechanism to reduce luminal GSSG to GSH, thereby regulating the thiol-disulfide redox state.
• Cysteine likely plays a role in facilitating intraluminal GSSG reduction.
• Dysfunction of this intestinal redox control mechanism may contribute to malabsorption and nutritional disorders.