Role of Mast Cells in HIV-associated Chronic Widespread Pain

Chronic widespread pain (CWP) in people with HIV-1 (PWH) is associated with a high rate of disability and low quality of life, with prevalence estimates ranging from 25%-85%. However, the specific mechanisms that contribute to CWP in HIV are not understood. Previously we demonstrated that PWH with CWP have increased hemolysis, elevated plasma levels of cell-free heme, and attenuated levels of the heme degrading enzyme, heme oxygenase 1 (HO-1). We also found that high cell-free heme and low HO-1 were associated with hypersensitivity in animals. In this study, we hypothesized that high heme and low HO-1 activates mast cells leading to degranulation and release of pain mediators like, histamine and bradykinin in HIV. PWH who self-report CWP were recruited from the University of Alabama at Birmingham HIV clinic. Animal models used in the study included, C57BL/6 mice subjected to hemolysis by intraperitoneal injection of phenylhydrazine hydrochloride (PHZ), HO-1 knockout mice, and HIV-1 transgenic rats overexpressing HIV-1 proteins. Cellular studies were performed in MC/9 mast cells. Human findings show that PWH with CWP have elevated plasma levels of histamine and bradykinin. HIV-1 transgenic rats also have elevated plasma levels of histamine and bradykinin and are hypersensitive as estimated by a decrease in withdrawal threshold to von Frey stimulation. In addition, data in mice with elevated plasma levels of free-heme, or decreased expression of HO-1, show significantly elevated levels of the pain mediators, histamine and bradykinin. Cellular data shows that high heme or low HO-1 induces mast cell degranulation and the release of histamine and bradykinin. Together, these data suggest that heme-dependent mast cell degranulation and the release of pain mediators may be contributing CWP in HIV. Future studies will focus on determining strategies to stabilize mast cell membrane in HIV and reduce hypersensitivity. Grant Number: RO1DA049657 Grant Name: Chronic Widespread Pain in HIV: Novel Mechanisms and Therapeutics.