IL-22 and Its Interaction with Amino Acid and Glycolipid Metabolite in Polycystic Ovary Syndrome (PCOS) Patients
Polycystic ovary syndrome (PCOS) is a complex endocrine and metabolic disorder that affects women of reproductive age, with a prevalence of approximately 5.61%. Despite its widespread occurrence, the pathogenesis of PCOS remains poorly understood. This condition is characterized by a range of symptoms, including hyperandrogenism, ovulatory dysfunction, and metabolic abnormalities such as insulin resistance and dyslipidemia. Recent research has highlighted the role of abnormal amino acid metabolism in the development of PCOS, suggesting that these metabolic disturbances may contribute to the condition’s hallmark features.
Interleukin-22 (IL-22) is a cytokine produced by both innate and adaptive immune cells, with a specific focus on epithelial cells. IL-22 plays a crucial role in maintaining mucosal homeostasis and has been shown to have diverse metabolic benefits. These include improving insulin sensitivity, preserving gut mucosal barrier function, reducing endotoxemia and chronic inflammation, and regulating lipid metabolism in the liver and adipose tissues. Previous studies have demonstrated that IL-22 levels are decreased in the serum and follicular fluid of PCOS patients. Furthermore, administration of IL-22 has been shown to reverse abnormal estrous cycles, improve ovarian function, and reduce insulin resistance in PCOS models. However, the relationship between IL-22 and amino acid metabolism in PCOS patients has not been thoroughly explored.
This study aimed to investigate the correlation between IL-22, glycolipid markers, and amino acid metabolism in PCOS patients. The research involved 23 PCOS patients and 23 body mass index (BMI)-matched healthy controls. The findings revealed that IL-22 levels in the serum of PCOS patients were significantly reduced compared to those in healthy controls. Partial least squares discriminant analysis (PLS-DA) of serum amino acids demonstrated a distinct clustering pattern between PCOS patients and healthy controls, indicating significant differences in amino acid metabolism between the two groups.
The study focused on the correlation between IL-22 and three amino acids—sarcosine, L-alanine, and b-alanine—which exhibited the strongest associations with IL-22. Sarcosine was found to have a positive correlation with fasting glucose levels, fasting insulin levels, homeostasis model assessment of insulin resistance (HOMA-IR), and low-density lipoprotein cholesterol (LDL). Conversely, sarcosine showed a negative correlation with high-density lipoprotein cholesterol (HDL). Similarly, L-alanine and b-alanine were positively correlated with fasting glucose levels, fasting insulin levels, and HOMA-IR, while negatively correlated with HDL.
PCOS is a multifaceted disorder that not only affects reproductive health but also has significant metabolic implications. The treatment of PCOS often focuses on addressing hyperandrogenism and infertility, but there is an increasing recognition of the need to manage its metabolic abnormalities. Metabolomics has emerged as a promising tool in PCOS research, offering insights into the metabolic markers of the disorder and potentially improving diagnostic and treatment strategies. Previous studies have shown that carbohydrate, lipid, and amino acid metabolisms are altered in PCOS patients. For instance, ovulatory dysfunction in PCOS has been associated with elevated levels of serine, threonine, phenylalanine, tyrosine, and ornithine. Additionally, increased levels of valine and leucine, along with decreased glycine concentrations, have been linked to insulin sensitivity in PCOS patients.
IL-22, a member of the IL-10 family, plays a critical role in modulating tissue responses during inflammation. In some disease models, IL-22 has protective effects, while in others, it contributes to inflammation. In the context of PCOS, IL-22 has been shown to improve metabolic abnormalities, including insulin resistance and lipid metabolism disorders. This study found that IL-22 levels were negatively correlated with fasting glucose levels, fasting insulin levels, HOMA-IR, and LDL in PCOS patients. These findings align with previous research suggesting that IL-22 has beneficial effects on metabolic health. However, the precise mechanisms by which IL-22 regulates metabolic disorders in PCOS patients remain to be elucidated.
IL-22 is primarily produced by innate lymphoid type 3 (ILC3) cells in the intestine, which are an important source of this cytokine. Previous studies have shown that both IL-22 levels and ILC3 cells are reduced in PCOS patients and animal models. This study further revealed that IL-22 has a negative correlation with 11 different types of amino acids, including 5-aminovaleric acid hydrochloride, L-2-aminobutyric acid, L-methionine, r-aminobutyric acid, L-isoleucine, L-tyrosine, sarcosine, L-tryptophan, L-leucine, L-alanine, and b-alanine. These findings suggest that PCOS patients exhibit abnormal amino acid metabolism, which may be linked to intestinal immune imbalance and reduced IL-22 secretion by ILC3 cells.
PCOS is associated with a wide range of metabolic abnormalities, affecting pathways related to steroid hormones, amino acids, carbohydrates, lipids, bile acids, purines, and the citric acid cycle. This study focused on amino acid metabolism, revealing that L-serine levels were significantly increased in PCOS patients. Elevated serine levels have been previously associated with anovulatory PCOS and are closely linked to insulin resistance and obesity. Additionally, L-alanine and b-alanine levels were found to be increased in the PCOS group, with both amino acids showing positive correlations with fasting glucose levels, fasting insulin levels, and HOMA-IR, and negative correlations with HDL. These findings suggest that abnormal alanine levels may play a role in the metabolic disturbances observed in PCOS.
Alanine is produced through two main pathways: direct protein degradation and the transamination of pyruvate by alanine aminotransferase (ALT). Women with PCOS have been shown to have elevated ALT levels in the serum, which could accelerate the conversion of pyruvate to alanine. ALT is also an independent predictor of nonalcoholic fatty liver disease (NAFLD), a condition that is often associated with metabolic comorbidities such as type 2 diabetes. While some studies have reported decreased alanine levels in PCOS patients, the findings of this study suggest that alanine levels may be elevated in certain PCOS populations. Further research is needed to clarify the role of alanine and other amino acids in PCOS.
Sarcosine, an intermediate in glycine biosynthesis and degradation, was found to be increased in the PCOS group and positively correlated with fasting glucose levels, fasting insulin levels, HOMA-IR, and LDL. Conversely, sarcosine showed a negative correlation with IL-22 and HDL. Elevated sarcosine levels have been linked to impaired glucose homeostasis and iron excess in metabolic syndrome subjects, suggesting that increased sarcosine in PCOS patients may contribute to abnormal glucose metabolism. Previous studies have also identified sarcosine as one of several metabolites that are elevated in PCOS serum, indicating that women with PCOS may have a diminished ability to switch from glucose/amino acid to lipid oxidation during fasting.
This study is the first to demonstrate that decreased IL-22 levels in PCOS patients are negatively correlated with fasting glucose levels, fasting insulin levels, HOMA-IR, and LDL. Additionally, IL-22 showed a negative relationship with 11 different types of amino acids, including sarcosine, L-alanine, and b-alanine, which are known to have adverse effects on metabolism. These findings suggest that IL-22, glycolipid metabolites, and amino acids interact in the pathogenesis of PCOS. Abnormal amino acid metabolism is a key feature of PCOS and may contribute to insulin resistance, ovarian dysfunction, and long-term complications in affected patients. The interplay between IL-22 and amino acids may have profound implications for the development and progression of PCOS, and these molecules could serve as characteristic biomarkers for diagnosing and predicting the severity of metabolic abnormalities in PCOS patients.
In conclusion, this study provides new insights into the relationship between IL-22, amino acid metabolism, and glycolipid metabolites in PCOS patients. The findings highlight the potential role of IL-22 and amino acids as biomarkers for diagnosing and managing PCOS. The decreased levels of IL-22 in PCOS patients, along with the negative correlations between IL-22 and key amino acids, suggest that intestinal immune imbalance and metabolic disturbances are closely linked in this condition. Future research should focus on developing a PCOS assessment model based on IL-22, glycolipid metabolites, and amino acids, which could improve the accuracy of PCOS diagnosis and treatment.
doi.org/10.1097/CM9.0000000000001915
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