Biochemistry & Analytical Biochemistry

Abstract

Opiorphin Secretion Pattern in Healthy Volunteers: Gender Difference and Organ Specificity

Dufour E, Villard-Saussine S, Mellon V, Leandri R, Jouannet P, Ungeheuer MN and Rougeot C

Background: Opiorphin is an endogenous human peptide regulator of enkephalin bioavailability. It inhibits enkephalin-inactivating ectopeptidases to produce analgesia and antidepressant-like effects in standard rodent models via activation of μ and/or δ opioid pathways. Our aim was to establish the quantitative profile of secretion and distribution of this regulator in young adult volunteers. Methods: We developed a specific ELISA-based method, in tandem with RP-HPLC chromatography, to determine opiorphin levels in blood, urine, semen and milk of healthy male and female volunteers. We also investigated the presence of the mature opiorphin in tears and saliva because it was previously reported that PROL1 gene, encoding opiorphin precursor, is primarily expressed in human lachrymal and salivary glands. Results: Opiorphin circulates as an endocrine messenger in the human bloodstream at 0.3-1.1 ng/ml median ranges. Its physiological concentration under basal conditions is higher in males than in females while it is significantly lower in sixth month pregnant compared to non-pregnant volunteers. It is eliminated in the urine with a significant higher rate in men compared to women. Opiorphin is distributed, at rates 10 times higher than in plasma, in the semen of normozoospermic donors and in the milk of lactating women as both free molecular and cation mineral-binding forms. Opiorphin is secreted in tears and saliva at the highest physiological concentrations, demonstrating that salivary and lachrymal glands are the tissues of major expression and secretion of PROL1 gene mature products. Discussion: Our data, associated with database searches from human transcriptome and our previous functional findings, provide evidence that opiorphin exerts organ-specific and gender-specific functions in human physiological systems through neuroendocrine, paracrine/autocrine and/or exocrine mechanisms.