Close Association Between Abnormal Expressed Enzymes of Energy Metabolism and Diarrhea-Predominant Irritable Bowel Syndrome
Irritable bowel syndrome (IBS) is a prevalent functional bowel disorder characterized by abdominal pain or discomfort associated with changes in bowel habits. Among its subtypes, diarrhea-predominant IBS (IBS-D) is particularly debilitating, significantly impacting patients’ quality of life. Despite its high prevalence, the pathogenesis of IBS remains poorly understood. This study aimed to explore the potential role of abnormal energy metabolism in the colonic mucosa of IBS-D patients by identifying differentially expressed proteins and assessing their implications in the disease process.
The study enrolled 42 IBS-D patients and 40 control subjects, all recruited from the Chinese PLA General Hospital between July 2007 and June 2009. The IBS-D patients met the Rome III diagnostic criteria, while the control subjects were selected based on stringent exclusion criteria to ensure they had no underlying gastrointestinal or metabolic disorders. The study was approved by the Ethics Committee of the Chinese PLA General Hospital, and informed consent was obtained from all participants.
The research employed a multi-step approach to identify and validate differentially expressed proteins in the colonic mucosa of IBS-D patients. Initially, protein expression profiles were examined using two-dimensional gel electrophoresis (2-DE) and mass spectrometry (MS) in a subset of five IBS-D patients and five controls. This was followed by Western blot and immunohistochemical analysis to validate the findings in a larger cohort of 27 IBS-D patients and 27 controls. Finally, high-performance liquid chromatography (HPLC) was used to measure ATP concentrations in the colonic mucosa of 10 IBS-D patients and 8 controls.
The 2-DE analysis revealed more than 1000 protein spots, with 41 spots showing significant differences (greater than 2-fold change) between IBS-D patients and controls. Among these, 11 spots were upregulated, and 30 were downregulated in IBS-D patients. Twelve spots were selected for further identification based on reproducibility, consistency, and successful identification via Q-TOF analysis. The identified proteins included enzymes involved in energy metabolism, such as alpha-enolase (ENOA), isobutyryl-CoA dehydrogenase (ACAD8), acetyl-CoA acetyltransferase (CT), and ATP synthase subunit d (ATP5H).
ENOA, a key enzyme in the glycolytic pathway, was found to be significantly downregulated in the sigmoid colon and caecum of IBS-D patients compared to controls. Immunohistochemical analysis confirmed this finding, showing reduced expression of ENOA in the colonic mucosa of IBS-D patients. Western blot analysis further validated the decreased expression of ENOA in both the sigmoid colon and caecum of IBS-D patients. The reduction in ENOA expression suggests a potential disruption in glycolysis, which could impair energy production and contribute to the functional disturbances observed in IBS-D.
ACAD8, an enzyme involved in the metabolism of branched-chain amino acids and short-chain fatty acids, was also significantly downregulated in the sigmoid colon of IBS-D patients. This reduction in ACAD8 expression may disrupt the metabolism of essential nutrients, further contributing to the energy deficits observed in IBS-D patients.
In contrast, the expression of CT, an enzyme involved in cholesterol and ketone body synthesis, was significantly upregulated in the caecum of IBS-D patients. This increase in CT expression may represent a compensatory mechanism in response to the energy deficits caused by impaired glycolysis and fatty acid metabolism.
ATP5H, a subunit of the mitochondrial ATP synthase complex, was found to be upregulated in the sigmoid colon of IBS-D patients. While the exact role of ATP5H in IBS-D remains unclear, its increased expression may reflect an attempt to enhance ATP production in response to energy deficits. However, despite this upregulation, the ATP concentration in the sigmoid colon of IBS-D patients was significantly lower than in controls, suggesting that the compensatory mechanisms are insufficient to meet the energy demands of the colonic mucosa.
The HPLC analysis confirmed that the ATP concentration in the sigmoid colon of IBS-D patients was significantly lower than in controls. This finding underscores the presence of energy metabolism abnormalities in the colonic mucosa of IBS-D patients and suggests that these abnormalities may play a critical role in the pathogenesis of the disease.
The study’s findings highlight the potential role of abnormal energy metabolism in the pathogenesis of IBS-D. The downregulation of key enzymes such as ENOA and ACAD8, coupled with the upregulation of CT and ATP5H, suggests a complex interplay of metabolic disturbances in the colonic mucosa of IBS-D patients. These disturbances may lead to energy deficits, impairing the physiological functions of the colon and contributing to the symptoms of IBS-D.
The study also emphasizes the importance of considering regional differences in the colon when investigating the pathogenesis of IBS-D. The significant differences in protein expression and ATP concentrations between the sigmoid colon and caecum suggest that the molecular mechanisms underlying IBS-D may vary depending on the location within the colon.
In conclusion, this study provides compelling evidence for the involvement of abnormal energy metabolism in the pathogenesis of IBS-D. The identification of differentially expressed proteins and the measurement of ATP concentrations in the colonic mucosa of IBS-D patients offer new insights into the molecular mechanisms underlying this condition. These findings may pave the way for the development of novel diagnostic markers and therapeutic targets for IBS-D, ultimately improving the quality of life for patients suffering from this debilitating disorder.
doi.org/10.1097/CM9.0000000000000003
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