Associations Among Nitric Oxide and Enkephalinases With Fibromyalgia Symptoms

Abstract

Background: Fibromyalgia (FM) is a complex syndrome of uncertain aetiology, characterized by the presence of widespread pain. Both nitric oxide (NO) and enkephalinases modulate pain perception. Objectives: The aim of this study was to evaluate the relationships among serum NO levels, oxytocinase activity and enkephalin-degrading aminopeptidase (EDA) activity with pain-related clinical manifestations in women with FM. Methods: We performed an observational case study in a population of fifty-eight women diagnosed with FM. Serum NO levels were analyzed by an ozone chemiluminescence-based assay. Both serum oxytocinase and EDA activities were fluorometrically determined. Pain threshold and pain magnitude were evaluated using the Pain Matcher. The pressure pain thresholds (PPTs) were measured using a digital pressure algometer. We used a Visual Analog Scale (VAS), the Central Sensitization Inventory (CSI), the Revised Fibromyalgia Impact Questionnaire (FIQ-R), and the Beck Anxiety Inventory (BAI) to assess the global level of pain, the symptoms associated with the Central Sensitization Syndrome, the severity of FM, and the anxiety level, respectively. Results: Multiple linear regression analysis adjusted by age, body mass index, and menopause status revealed significant associations between NO levels and dominant occiput PPT, non-dominant occiput PPT, and FIQ-R.1. Significant associations of oxytocinase activity with VAS and dominant knee PPT were also found. Moreover, results showed a significant association between EDA activity in patients with high EDA activity levels and dominant second rib PPT. Discussion: Our data have shown significant relationships of serum NO levels and oxytocinase and EDA activities with some body PPTs, the daily activity level, and the global intensity of pain in women with FM. These results suggest that pain, which is the main symptom of this syndrome, may be related to alterations in NO levels and in oxytocinase and EDA activities in patients with FM.