Dysregulation in Sphingolipid Signaling Pathways is Associated With Symptoms and Functional Connectivity of Pain Processing Brain Regions in Provoked Vestibulodynia

Abstract

Provoked vestibulodynia (PVD) is a chronic pain disorder characterized by local hypersensitivity and severe pain with pressure localized to the vulvar vestibule. Despite decades of study, the lack of identified biomarkers has slowed the development of effective therapies. The primary aim of this study was to use metabolomics to identify novel biochemical mechanisms in vagina and blood underlying brain biomarkers and symptoms in PVD, thereby closing this knowledge gap. Using a cross-sectional case-control observational study design, untargeted and unbiased metabolomic profiling of vaginal fluid and plasma was performed in women with PVD compared to healthy controls. In women with PVD, we also obtained assessments of vulvar pain, vestibular and vaginal muscle tenderness, and 24-hour symptom intensity alongside resting-state brain functional connectivity of brain regions involved in pain processing and modulation. Compared to healthy controls, women with PVD demonstrated differences primarily in vaginal (but not plasma) concentrations of metabolites of the sphingolipid signaling pathways, suggesting localized effects in vagina and vulvar vestibule rather than systemic effects. Our findings reveal that dysregulation of sphingolipid metabolism in PVD is associated with increased vulvar pain and muscle tenderness, sexual dysfunction, and decreased functional connectivity strength in pain processing/modulatory brain regions. This data collectively suggests that alterations in sphingolipid signaling pathways are likely an important molecular biomarker in PVD that could lead to new targets for therapeutic intervention. PERSPECTIVE: This manuscript presents the results of a robust, unbiased molecular assessment of plasma and vaginal fluid samples in women with provoked vestibulodynia compared to healthy controls. The findings suggest that alterations in sphingolipid signaling pathways are associated with symptoms and brain biomarkers and may be an important molecular marker that could provide new targets for therapeutic intervention.

Keywords: Ceramides; functional connectivity strength; graph theory; metabolomics; pain; provoked vestibulodynia; resting-state brain connectivity; sphingolipid metabolism; vulvodynia.

Figure 1.

Mean functional connectivity strength for cortical regions of interest. Bar plots representing the mean functional connectivity strength with 95% confidence intervals. Abbreviations: L = Left, R = right.

Figure 2.

Mean functional connectivity strength for subcortical regions of interest. Bar plots representing the mean functional connectivity strength with 95% confidence intervals. Abbreviations: L = Left, R = right.

Figure 3.

Box plots of concentrations (untransformed) of sphingolipid signaling pathway metabolites in vaginal fluid showing alterations in women with PVD compared healthy controls. The box was drawn from the first quartile to the third quartile. The horizonal line through the box represents the median untransformed concentration. Individual subject data points are represented as circles. Abbreviations: HC = Healthy Controls, PVD = provoked vestibulodynia.

Figure 3.

Box plots of concentrations (untransformed) of sphingolipid signaling pathway metabolites in vaginal fluid showing alterations in women with PVD compared healthy controls. The box was drawn from the first quartile to the third quartile. The horizonal line through the box represents the median untransformed concentration. Individual subject data points are represented as circles. Abbreviations: HC = Healthy Controls, PVD = provoked vestibulodynia.

Figure 3.

Box plots of concentrations (untransformed) of sphingolipid signaling pathway metabolites in vaginal fluid showing alterations in women with PVD compared healthy controls. The box was drawn from the first quartile to the third quartile. The horizonal line through the box represents the median untransformed concentration. Individual subject data points are represented as circles. Abbreviations: HC = Healthy Controls, PVD = provoked vestibulodynia.

Figure 4.

Metabolite-brain-symptom association network in provoked vestibulodynia. This figure depicts the significant correlations (P < .05) between altered metabolites, PVD symptoms, and brain functional connectivity as a tri-partite association network. The nodes of the network (i.e., circles) are color coded and include sphingolipid signaling pathway metabolites (green) altered in PVD, symptom measures (yellow) and function connectivity strength of pain processing and pain modulatory brain regions (blue). The edges (i.e., lines) reflect correlations. Positive correlations are depicted by red lines and negative correlations by blue lines. A compound spring embedding algorithm was used to organize the nodes of the network based on similar patterns of correlations. Abbreviations: Symptoms: FSFI, female Sexual Functioning Index Full Scale Score; Vmuscle, Vaginal muscle tenderness total score, vPain = Vulvar vestibular pain total score, 24hSxINt, 24-hour symptom intensity score. Brain: L, left; R, Right. Amyg, Amygdala; CaN, Caudate Nucleus; Hip, Hippocampus; InfCirIns, inferior segment of the circular sulcus of the insula; LoInG_CInS, long insular gyrus and central sulcus of the insula; Nacc, Nucleus Accumbens; PaCL, paracentral lobule, SupPrCS, superior part of the precentral sulcus; Tha, Thalamus (color version of figure is available online.).