Background: There is a strong relationship between pain and immune function. The development of neuropathic pain after peripheral nerve damage occurs with inflammation at the injury site. T lymphocyte function, a part of cell-mediated immunity, has been implicated in the pathogenesis and nociceptive processing of peripheral neuropathic pain. Pregabalin [(S)-3-(aminomethyl)-5-methylhexanoic acid], which was developed as an antiepileptic drug, has shown clinical and laboratory efficacy for neuropathic pain. To assess the possible influence of pregabalin therapy on immunomodulation, we assessed natural killer (NK) tumoricidal activity against YAC-1 murine lymphoma cells and phytohemagglutinin-stimulated T lymphocyte proliferation in a neuropathic mouse model.
Methods: The neuropathic model was induced by chronic constriction injury (CCI) to the right sciatic nerve in male BALB/c mice. Mechanical hyperalgesia was measured with a dynamic plantar aesthesiometer. After confirming hyperalgesia, pregabalin or saline (for control mice) in a volume of 10 mL/kg was administered orally at a dosage of 30 mg/kg, twice daily from day 2 after surgery. On day 7 postsurgery, NK cell cytotoxic activity and splenocyte proliferation were measured. NK cell activity was assessed by lactate dehydrogenase assay. Various numbers of effector cells were added to the wells of a microtiter plate containing 1 × 10(4) target YAC-1 cells in 100 μL, to achieve final effector-to-target cell ratios of 80:1, 40:1, and 20:1. The proliferative response of splenocytes to phytohemagglutinin was measured by bromodeoxyuridine detection. Stimulation index was calculated to quantify cell proliferation based on the measurement of bromodeoxyuridine incorporation in cellular DNA. For in vitro study, NK cell activity and splenocyte proliferation from isolated spleen cells were determined at different concentrations of pregabalin (3, 10, and 30 μg/mL).
Results: CCI caused marked mechanical allodynia on day 7 and orally administered pregabalin reversed mechanical hyperalgesia. NK cell activity and splenocyte proliferation were significantly increased in CCI mice compared with control mice. Pregabalin treatment in CCI mice significantly suppressed NK cell activity and proliferation of splenocytes. NK cell activity was 8.4% ± 4.7% in control and 29.2% ± 20.2% in CCI mice; pregabalin treatment reduced cytotoxicity to 6.8% ± 2.4% in CCI mice. Stimulation index was 169% ± 71% in CCI mice but pregabalin treatment reduced it to 67% ± 52% compared with control. In vitro, NK cell activity was suppressed at a pregabalin concentration of ≥10 μg/mL (P < 0.05).
Conclusions: Neuropathic pain increased immunological reactivity and pregabalin treatment modulated this reactivity. Increased NK cell activity and splenocyte proliferation were inhibited by pregabalin treatment.