Background Chronic pain, usually considered to be continuous or episodic pain of at least six months duration, is a common cause of major disability. Chronic pain involves affective, behavioural and social dimensions. The opioid system plays a major role in the pain controlling systems.
Objectives Therefore, our main focus was to investigate the patients health status and differences in the expression of opioid receptors in skin and muscle tissues of chronic pain patients with fibromyalgia (FM), osteoarthritis (OA), psychosis (PS), rheumatoid arthritis (RA) and healthy controls (C).
Methods The Visual Analogue Scale (VAS) and the Short Form 36-item (SF-36) Health Survey questionnaire were given to the patients. Snap frozen sections from skin and muscle tissues (taken from the left deltoid region) were obtained from 8 FM (all female, 30–65 years of age), 4 OA (2 females and 2 males aged 48–72 years), 5 female PS patients (aged 40–79 years), 3 RA (1 female and 2 males aged 48–72 years), and 9 age-matched healthy females (C). Total RNA was extracted, reverse transcribed, amplified and quantified by real time PCR (TaqMan, Perkin Elmer) using fluorogenic probes and specific primers for Delta (DOR), Kappa (KOR) and Mu opioid receptors (MOR). Intensity of expression in each tissue was determined. The expression of 18S mRNA was used as an internal control.
Results We observed a significantly reduced score in all patient groups compared to the control group regarding physical function in the SF-36 as well as in the VAS. An increase of DOR mRNA expression was found in PS and RA muscle, a decrease of KOR mRNA expression could be detected in OA skin compared to C. An increased expression of DOR (81.0 fold p = 0.001) and of KOR (13.6 fold p = 0.009) mRNA was detected in FM skin compared to skin of healthy controls. This expression was more increased in FM than any other investigated chronic pain condition. MOR was detected only in one skin and one muscle sample of two different PS patients.
Conclusion Patients expressing high levels of DOR and KOR including patients with FM, PS, and RA might be treated with novel therapeutic approaches modulating opioid receptors expression by selective opioids.
Dr. Salemi was supported by the Zurzach foundation and Dr. Sprott by the AFSA and the Olga Mayenfisch foundation.
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