Elevated circulatory proline to glutamine ratio (PQR) in Patients with endometriosis revealed by targeted NMR based serum metabolomics

Endometriosis (EM) is a chronic pain condition affecting women in reproductive age and involves the growth of uterine lining (endometrium) outside of the uterus. EM is often associated with altered inflammatory and immune processes and shares some cancer-like characteristics such as activated glutaminolysis. However, preclinical studies suggest mitochondrial dysfunction and decreased energy production in uterine endometriosis tissue. As proline catabolism in mitochondria serve as an important source of energy production and previous transcriptomics studies have demonstrated that there is reduced activity of proline oxidase (POX, a mitochondrial inner-membrane flavoenzyme involved in the catabolic degradation of the proline) due to overexpression of microRNA (known as MiR-23b). Based on this, we hypothesized and demonstrated that circulatory proline to glutamine ratio (PQR) are elevated in the EM patients and may serve as an indicative biomarker to improve the clinical diagnosis of EM.