Nitric Oxide and Sickle Cell Pain

Sickle cell disease is a systemic disorder whose proximate cause is a mutation in the beta-globin chain of hemoglobin. Although it is characterized by differing degrees and patterns of clinical manifestations, its major features include severe episodes of pain. The sickle cell pain crisis is one of the most typical characteristics of this disease and pain associated with crisis is reported to be more intense than other types of clinical pain by those with sickle cell disease and displays both nociceptive and neuropathic qualities. Pain in sickle cell disease is more widely experienced and poorly managed than previously considered. In one community sample, more than 50 percent of the patients reported experiencing pain on more than half the days of the study period. Painful crisis consist of pain experienced in different areas of the body, typically in the extremities, back, abdomen and chest and some studies suggest that patients experience prodromal or pre-crisis phases of their pain, some of which last up to 24 hours before developing the typical features of a pain crisis. The nature of pain experience in patients with sickle cell disease is not well documented nor are the mechanisms of sickle cell pain well understood. Objectives: The first objective of the study is to characterize genetic expression data of sickle cell disease and matched controls at weekly time points over a 4 week period. The second objective is to measure levels of exhaled Nitric Oxide (eNO) and other biomarkers in sickle cell patients and in matched controls over the same time points. The third objective is to evaluate experimental pain perception in both groups. Population: By stratifying patients by pain level, this study will recruit sickle cell patients with a range of symptom severity (N=45) and sex-, race-, ethnicity and age-matched controls (N=45) without sickle cell trait from the NIH Patient Recruitment and Referral Service. Design: This is a prospective, exploratory study of steady state and acute pain phase in sickle cell patients. Participants will undergo evaluations (eNO and blood collection) during weekly clinic visits and keep a pain diary for 4 weeks after the first visit. All participants will also undergo one session of quantitative sensory testing. Importance: The purpose of this study is to improve the understanding of the biochemical and molecular genetic mechanisms associated with sickle cell pain by characterizing the transcriptome of sickle cell disease during steady state and pain phases. It is hypothesized that analysis of the transcriptome will result in a panel of biomarkers that correlate with the severity level of pain and perhaps signal the onset of a painful episode. The successful elucidation of these relationships may identify novel targets for intervention leading to attenuation of sickle cell pain, improved treatment and less impact on quality of life and functional status.