Background & Aims

An inefficient balance between the excitatory neurotransmitter glutamate and inhibitory neurotransmitter GABA is implicated in central sensitization and pathological pain. Elevating endogenous levels of GABA may temper abnormal hyperexcitability to restore homeostasis as an analgesic approach ?(1)?. Current drugs with this therapeutic potential might promote GABA reuptake inhibition, on the other hand, are limited by side effects. We aim to investigate whether suppressing GABA metabolism through inhibition of its degradation enzyme, GABA aminotransferase (GABA-AT), would increase endogenous GABA levels as an analgesic strategy avoiding adverse effects ?(2)?. The next-generation GABA-AT inhibitor OV329 is more efficient than vigabatrin in inactivating GABA-AT and shows preclinical efficacy as an anticonvulsant ?(3)?. Here, we evaluated whether OV329 would behave as a broad-spectrum analgesic in preclinical models of inflammatory and neuropathic pain and its potential for side effects.

Methods

C57BL/6J mice of both sexes were used in this study. Paclitaxel was injected intraperitoneally to generate neuropathic nociception. Complete Freund’s adjuvant (CFA) was injected unilaterally into the hind paw to generate inflammatory nociception ?(2,4)?. Mechanical paw withdrawal thresholds were measured using an electronic von Frey anesthesiometer. Brain punches from the anterior cingulate cortex (ACC) and lumbar spinal cords (SC) were used to measure levels of GABA and glutamate by liquid chromatography/mass spectrometry (LC/MS). Locomotor activity was measured using an activity meter and rota-rod test ?(5)? A conditioned place preference assay was used to evaluate whether OV329 produced reward or aversion. Finally, an intravenous drug self-administration paradigm was used to determine whether OV329 would be reinforcing and be self-administered in comparison to morphine ?(6).?

Results

OV329 attenuated the development and maintenance of mechanical hypersensitivity induced by the chemotherapeutic agent paclitaxel. OV329 synergized with paclitaxel to enhance tumor cell line cytotoxicity in vitro without altering viability of normal cells. Intrathecal OV329 suppressed paclitaxel-induced allodynia without development of tolerance. Prophylactic OV329 normalized paclitaxel-induced increases in glutamate levels in the lumbar spinal cord, consistent with restoration of homeostasis in excitatory/inhibitory balance in neurotransmission. OV329 attenuated CFA-induced inflammatory nociception with efficacy comparable to morphine. However, unlike morphine, OV329 did not produce reward in a conditioned place preference assay in mice and was not self-administered intravenously by rats.? OV329, administered acutely, did not impair motor function, or produce motor ataxia, unlike the first-generation GABA-AT inhibitor vigabatrin.

Conclusions

OV329 produces antinociceptive efficacy in preclinical models of chemotherapy-induced peripheral neuropathy (CIPN) and inflammatory pain. OV329 normalized glutamate levels in the lumbar spinal cord, providing a mechanistic basis for these effects. OV329 also lacked unwanted side effects at therapeutic doses (e.g., reward, motor impairment). Our studies raise the possibility that inhibition of GABA-AT with OV329 represents a first-in-class analgesic mechanism to achieve a more beneficial spectrum of therapeutic effects through enzyme regulation.

References

??1.Xu D, Zhao H, Gao H, Zhao H, Liu D, Li J. Participation of pro-inflammatory cytokines in neuropathic pain evoked by chemotherapeutic oxaliplatin via central GABAergic pathway. [cited 2024 Jan 22].

?2.Bráz JM, Wang X, Guan Z, Rubenstein JL, Basbaum AI. Transplant-mediated enhancement of spinal cord GABAergic inhibition reverses paclitaxel-induced mechanical and heat hypersensitivity. Pain [Internet]. 2015 [cited 2024 Jan 22];156(6):1084.

?3.Feja M, Meller S, Deking LS, Kaczmarek E, During MJ, Silverman RB, et al. OV329, a novel highly potent GABA aminotransferase inactivator, induces pronounced anticonvulsant effects in the pentylenetetrazole seizure threshold test and in amygdala-kindled rats. Epilepsia [Internet]. 2021 Dec 1 [cited 2024 Jan 22];62(12):3091.

?4.Tan BCD S, Liu HB, Wang ACEG Y, Zhu Corresponding Author S, Zhu S. The Molecular Mechanisms Associated with the Effects of Propofol in a Rat Model of Pain Due to Inflammation Following Injection with Complete Freund’s Adjuvant. 2019 [cited 2024 Jan 22]; 25:10190–7.

?5.Shiotsuki H, Yoshimi K, Shimo Y, Funayama M, Takamatsu Y, Ikeda K, et al. A rotarod test for evaluation of motor skill learning. J Neurosci Methods. 2010.

?6.Gutierrez T, Crystal JD, Zvonok AM, Makriyannis A, Hohmann AG. Self-medication of a cannabinoid CB2 agonist in an animal model of neuropathic pain. Pain [Internet]. 2011 Sep [cited 2024 Jan 22];152(9):1976.

?7.Mercadante S, Arcuri E, Santoni A. Opioid-Induced Tolerance and Hyperalgesia. CNS Drugs [Internet]. 2019;33(10):943–55. ?

Presenting Author

Luana Assis Ferreira

Poster Authors

Luana Ferreira

PhD.

Indiana University

Lead Author

E-mail

Carlos Alves Jesus

PhD

Indiana University, Dept. of Psychological and Brain Sciences

Lead Author

E-mail

Jonah Wirt

Indiana University Bloomington

Lead Author

E-mail

Idaira Oliva

Indiana University

Lead Author

E-mail

Jonathon D. Crystal

Indiana University

Lead Author

E-mail

Taylor Woodward

Indiana University

Lead Author

E-mail

Robert H. Pepin

Indiana University

Lead Author

E-mail

Richard B. Silverman

Northwestern University

Lead Author

E-mail

Zilli Xu

Indiana University

Lead Author

E-mail

Topics

  • Models: Chronic Pain - Neuropathic