Endothelial Protein Changes Indicative of Endometriosis in Unexplained Infertility, an Exploratory Study

Previous research has linked both endothelial protein changes and vitamin D with infertility. This study was undertaken to investigate the association of proteins associated with endothelial function and vitamin D status in the luteal phase at day 21 in a group of non-obese women prior to in vitro fertilization (IVF) with either unexplained infertility (UI) or male factor infertility (MFI). Twenty-five non-obese Caucasian women from a UK academic center with MFI (n = 14) and UI (n = 11) were recruited. Blood was withdrawn at day 21 of the menstrual cycle at the time of mock embryo transfer. Vitamin D parameters were measured by tandem mass spectroscopy. Off-rate Modified Aptamer (SOMA)-scan plasma protein measurement was undertaken for 20 protein markers of endothelial dysfunction. Baseline demographics did not differ between groups and parameters of response following IVF did not differ. Vitamins D₂ and D₃, and 1,25 Vitamin D₃ did not differ between groups. In UI, markers of endothelial activation/dysfunction were investigated; vascular cell adhesion molecule 1 (VCAM-1) decreased and this is associated with endothelial stress; vascular endothelial growth factor (VEGF) decreased and this may suggest impaired endometrial angiogenesis; while intercellular adhesion molecule 1 (ICAM-3) increased (p < 0.05) and is associated with increased immunological activity. A marker of vascular integrity, angiopoietin-1, increased while soluble angiopoietin-1 receptor (sTie-2) decreased (p < 0.05), suggesting increased vascular development. Endothelial markers of inflammation, coagulation, and endothelial progenitor cells were unchanged. Vitamin D and its metabolites show no relationship to UI, but endothelial activation/dysfunction and vascular integrity changes in VCAM-1, VEGF, sICAM-3, angiopoietin-1, and sTie-2 may contribute to UI, though the mechanisms through which they work require further evaluation; however, these protein changes have been associated with endometriosis, raising the suggestion that subclinical/undiagnosed endometriosis may have contributed to UI in these subjects.