The present review aims at providing a complete and comprehensive summary of current literature relevant to oxysterols and related diseases. Oxidation of cholesterol leads to the formation of a large number of oxidation products, generally known as oxysterols. They are intermediates in the biosynthesis of bile acids, steroid hormones, and 1,25-dihydroxyvitamin D3. Although oxysterols are considered as metabolic intermediates, there is a growing body of evidence that many oxysterols are bioactive, and their absence or excess may be part of the cause of a disease phenotype. These compounds derive from either enzymatic or non-enzymatic oxidation of cholesterol. This study provides comprehensive information about the structures, formation, and types of the oxysterols even when involved in certain disease states, focusing on their effects on metabolism and linkages with these diseases. The role of specific oxysterols as mediators in various disorders, such as degenerative (age-related) and cancer-related disorders, have now become clearer. Oxysterol levels may be employed as suitable markers for the diagnosis of specific diseases or in predicting the incidence rate of diseases, such as diabetes mellitus, Alzheimer’s disease, multiple sclerosis, osteoporosis, lung cancer, breast cancer, and infertility. However, further investigations may be required to confirm these mentioned debates.

Background Limited available animal and human data suggest an association between dysbiosis of gut microbiota and PCOS. We aimed to determine whether gut microbiota in lean women with PCOS shows any alterations compared to healthy women. Materials and methods Twenty‐four lean patients with PCOS phenotype A according to the Rotterdam 2003 diagnostic criteria and 22 BMI‐matched healthy women were included in this study. Anthropometric, hormonal and biochemical measurements were carried out in all participants. 16S rRNA gene V3‐V4 region amplicon sequencing was performed on stool samples. Preprocessing of the raw data was performed using QIIME, and both QIIME and R packages were used for microbiome analysis. Results Bacterial richness and diversity did not show a significant difference between patients and controls. Beta diversity was similar between the groups. However, Erysipelotrichaceae, Proteobacteria, Gammaproteobacteria, Enterobacteriaceae, Planococcaceae, Gemmules and Bacillales were significantly abundant in PCOS group according to LEfSe analysis. Clostridium cluster XVII showed increased abundance in patient group, while Clostridium sensustricto and Roseburia were decreased compared to controls. Random forest prediction analysis revealed Clostridium cluster XIVb as the most discriminative feature of patient group and Roseburia for healthy controls. Testosterone and androstenedione were negatively correlated with alpha and phylogenetic diversity. Conclusions Our results suggest that gut microbiome of lean PCOS patients with full phenotype shows compositional alterations with similar bacterial richness and diversity compared to controls and that hyperandrogenism is associated with dysbiosis.

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