Buprenorphine extended-release (Ethiqa XR) impacts the immunological response in mice exposed to aerosolized Burkholderia pseudomallei or Yersinia pestis

Introduction Ethiqa XR is an extended-release formulation of the potent partial opioid buprenorphine and has been FDA-indexed for mice and other laboratory animal species to relieve pain. Unfortunately, the use of analgesia may produce confounding effects that distort physiological and pathophysiological responses during laboratory animal studies. Since various reports have indicated that Ethiqa XR can affect the inflammatory response in several in vivo models, we sought to evaluate the effects of Ethiqa XR treatment on the immune response to and disease pathogenesis associated with bacterial biothreat agents. Methods BALB/c and C57BL/6 mouse strains were treated or not with Ethiqa XR before and 48 h after challenge with aerosolized Burkholderia pseudomallei K96243 or Yersinia pestis CO92. Control mice were similarly treated with Ethiqa XR but were not challenged. Mice were euthanized 60-72 hours post-treatment/challenge to harvest blood, serum, lung, brain and spleen for bacterial burden and immunological profiling. Results Both C57BL/6 and BALB/c mouse strains showed higher bacterial dissemination to the spleen 60-72 h after B. pseudomallei challenge when treated with Ethiqa XR. Consistently, we found increased concentration of pro-inflammatory cytokines in the spleen (e.g., IFN-γ and IL-6) in Ethiqa XR-treated mice. Compared to BALB/c, C57BL/6 mice had trends of higher cytokine dysregulation not only in the spleens, but also in the lungs and brains. In contrast, we found less profound differences in either mouse strain treated with Ethiqa XR and challenged with Y. pestis . In the absence of bacterial challenge, both BALB/c and C57BL/6 mouse strains treated with Ethiqa XR had an overall higher concentration of pro-inflammatory cytokines in the lungs and spleens. However, C57BL/6 mice showed a higher dysregulation of the cytokine profile in both lungs and spleens. We also found decreased macrophage activity (iNOS concentration) in the spleens of BALB/c mice and decreased neutrophil activity (MPO concentration) in the lung of C57BL/6 mice treated with Ethiqa XR. Discussion These results suggest that the effect of Ethiqa XR on the immune response and disease pathogenesis increases the complexity of data interpretation. Thus, prior to providing analgesia to laboratory animals, bridging studies and cost benefit analyses must be considered to avoid misinterpretation of immunological data collected during the development, testing, and evaluation of medical countermeasures.