Assessment of the anti-oxidant reduced glutathione in oral squamous cell carcinoma - Systematic review and meta-analysis

Background: The excess reactive oxygen species or free radicals reaction leads to oxidative injury to the biological components such as cells and tissues, which would result in the initiation and progression of carcinogenesis. The magnitude of oxidative damage depends primarily on the balance between free radicals (pro-oxidants) and antioxidant system activity. Aim: To assess antioxidant status by evaluating the reduced glutathione (GSH) levels in various biological samples of patients with oral squamous cell carcinoma (OSCC) using available literature. Materials and Methods: An electronic literature search was carried out in PubMed (MeSH), Science Direct, Scopus and Cross Reference by using specific keywords. Results: The systematic electronic search identified 704 articles. After studying the articles' titles and abstracts, 657 articles were excluded for the following reasons; duplicated articles, animal studies, studies of low quality and not relevant to the research question. The remaining 47 articles were selected for full-text assessment. After eliminating the articles that did not match the objectives, the present qualitative synthesis finally included 27 articles for evaluation. The ten studies, which showed coherent data, were included in quantitative analysis. The GSH levels in OSCC groups are significantly decreased (P < 0.001) in plasma and erythrocyte samples compared to healthy controls. Conclusion: The selected studies showed significantly lower levels of GSH in various biological samples of OSCC. Hence, future studies are required to validate the expression of GSH as a prognostic biomarker in oral cancer.