Abstract ID 16983

Poster Board 569

Background: Recent evidence has shown that changes in the gut microbiome occur with chronic opioid use in both rodent and human models (1-2). Opioid induced dysbiosis has been implicated in some of the pharmacological effects of opioids. However, it is unclear how chronic opioid use alters the gut microbiome. Interestingly, studies have also shown that the gut epithelial barrier is disrupted by chronic morphine (2). An important constituent of the commensal microbiome are bacterial species that ferment fibers into short chain fatty acids (SCFA). The SCFA butyrate is known to improve the integrity of the epithelium and enhance antimicrobial peptide release. Based on this, we hypothesized that sodium butyrate can relieve peripheral hypersensitivity as well as reduce primary nociceptor hyperexcitability in experimental models of opioid induced peripheral hypersensitivity.

Methods: Animals were administered a ramping dose of morphine (Mor), and organized into the following treatment groups: Mor (20mg/kg i.p b.i.d on day 1 to 80mg/kg i.p b.i.d on day 4) ± sodium butyrate (NaBut) (250mM p.o b.i.d), and Saline ± NaBut (250mM p.o b.i.d) . Animals were assayed using a 50°C hot-plate for opioid-induced hyperalgesia, and primary nociceptors from L4-S1 dorsal root ganglia were collected for whole-cell patch clamp electrophysiological recordings.

Results: Chronic opioid exposure induced thermal hypersensitivity (14.8s ± 0.568 Mor vs 28.16s ± 0.848 saline), which was reversed by NaBut (250mM p.o b.i.d) (24.84s ± 0.675) (N=14 per treatment group). Electrophysiological recordings demonstrated Mor treated animals elicited a greater number of action potentials (APs) compared to controls (Mor: 4.44 ± 0.532 vs 2.1 ± 0.182 APs Saline), indicating enhanced excitability. NaBut treatment attenuated this enhanced excitability (Mor + NaBut 2.29 ± 0.354 APs) (N=6 n=17 per treatment). Phase plane analysis of hyperexcitable cells indicated significant changes in sodium channel kinetics which was prevented by in-vivo butyrate administration but not by direct application of butyrate to DRG neurons. In order to investigate the specific contribution of the gastrointestinal tract on Mor-induced neuronal hyperexcitability, conditioned media was collected from colonic tissues (colonic conditioned media (CCM)) and applied to naïve DRG neurons. CCM from Mor-treated colons enhanced excitability (Mor 5.6 vs Saline 2.47 APs) that was absent in CCM from the Na-butyrate treatment group (3.15 APs).

Discussion/Conclusion: In both the in-vivo behavioral assays of peripheral hypersensitivity and in ex-vivo electrophysiological experiments, butyrate reversed the enhanced excitability and hypersensitivity of Mor-treated animals. These findings demonstrate that the SCFA butyrate, a major metabolite of the gut microbiome plays an important role in preventing the development of opioid-induced peripheral hypersensitivity.

References

1.) Kang M, Mischel RA, Bhave S, Komla E, Cho A, Huang C, Dewey WL, Akbarali HI. The effect of gut microbiome on tolerance to morphine mediated antinociception in mice. Sci Rep. 2017 Feb 17;7:42658.

2.) Cruz-Lebrón A, Johnson R, Mazahery C, Troyer Z, Joussef-Piña S, Quiñones-Mateu ME, Strauch CM, Hazen SL, Levine AD. Chronic opioid use modulates human enteric microbiota and intestinal barrier integrity. Gut Microbes. 2021 Jan-Dec;13(1):1946368.

Funding for this research genereously provided by the following NIH grants:

P30DA033934, T32DA007027