Impact and Aggravating Factors of Chronic Pain in Sickle Cell Disease: Results of the Analysis of Promis® Questionnaires and the Metabolomic Profile of Brazilian Adult Patients

Introduction and aims: Chronic pain is a frequent and debilitating complication of Sickle Cell Disease (SCD). The aim of this study was to evaluate the impact of chronic pain on the mental health and quality of life of patients, in addition to seeking to identify molecules associated with its occurrence, in prospecting for new therapeutic targets. Methods: Adult patients with SCD followed at the UNICAMP Blood Center completed PROMIS (Patient-Reported Outcomes Measurement Information System) questionnaires validated for the Portuguese language, in the domains of depression, anxiety and pain interference in daily life. The results were reported as T scores in relation to a reference population, and used to search for correlations with clinical and laboratory data. In parallel, plasma samples from the same patients and healthy controls were subjected to metabolomic profiling analysis by untargeted Ultra Performance Liquid Chromatography-High Resolution Mass Spectrometry (UHPLC-HRMS) in the search for possible molecular markers differentiating patients with or without chronic pain. Results: Forty-three patients were included, with a median age of 43 years (15-78), of whom 27 (63%) were female, 25 had HbSS, 08 had HbSC, 7 had Sbeta-thalassemia and 3 had HbSD. Comparing individuals according to the presence or absence of chronic pain: individuals with chronic pain had a higher median age (39.3 vs. 48.7, p = 0.026), higher Hgb levels (9.9 vs. 8.7 g/dL, p=0.038), lower total leukocyte counts (6.35 vs. 7.68 x 103/mm3, p=0.04), though no significant differences in the PROMIS test results. However, the occurrence of at least one vasoocclusive crisis (VOC) in the previous 6 months or the diagnosis of avascular bone necrosis had statistically significant relationships with worse results in the 3 PROMIS domains tested. Furthermore, the lower the patients' income, the worse the impact of pain on daily life (r=-0.46, p<0.001). Regarding the UHPLC-MS analyses, 107 molecules with significant differences in expression were identified between healthy controls, patients with chronic pain or without chronic pain. Among them, a higher expression of molecules of the endocannabinoid system (2-Arachidonoylglycerol and 2-Eicosapentaenoyl-glycerol) was observed in patients without chronic pain, and a higher expression of lysoplasmenylcholine and adrenic acid in the group affected by chronic pain. Conclusions: In this cohort of Brazilian patients, the occurrence of VOCs, the diagnosis of bone necrosis and low income were demonstrated to be related to worse rates of anxiety, depression and pain interference in daily life. The increased expression of molecules of the endocannabinoid system may indicate a protective factor in patients who are not affected by chronic pain. In patients with chronic pain, the increase in adrenic acid may be associated with a higher occurrence of ferroptosis, a mechanism previously described as being involved in the development of neuropathic pain; and lysoplasmenylcholine is released in response to hypoxia and thrombin generation, and increases cellular adhesion to the endothelium, revealing possible microvascular mechanisms associated with a higher occurrence of pain. This is the first study using untargeted UHPLC-HRMS for exploratory analysis of metabolites involved in chronic pain in Sickle Cell Disease, identifying potential therapeutic targets to be explored in future clinical trials.