Abstract
Introduction Effective pain management is essential for improving the quality of life. Currently, we have medications to address both mild and severe pain, but there remains a therapeutic gap for pain that is not adequately managed by over-the-counter (OTC) or prescription non-steroidal anti-inflammatory drugs (NSAIDs). Prescription opioids can lead to addiction, respiratory suppression, and even death. OTC pain relief options often lack the potency required to alleviate more intense pain, while stronger treatments, though effective, carry risks of addiction and other adverse effects, limiting their long-term use. This situation underscores the urgent need for safer, nonopiate alternatives. Both musculoskeletal pain and pain from animal toxin envenomation share common mechanisms, including structural changes to the plasma membrane that trigger signaling cascades from membrane-associated phospholipases. Diethyl azelate (DEA), a medium-chain fatty acid ester, represents a new class of NSAIDs that reversibly alter plasma membrane structure and function. DEA mitigates insulin resistance, dyslipidemia, and musculoskeletal pain, and inhibits both exogenous and endogenous phospholipases PLD and PLA2, which are involved in pain signaling. This study aimed to evaluate the analgesic properties of DEA in combination with topical penetration enhancers. Methodology Analgesic activities of DEA, dimethyl sulfoxide (DMSO), turpentine, 32 miscellaneous terpenes (including D-limonene, menthol, a and b-pinene), cannabinoid oil, pelargonic acid vanillylamide, and non-prescription analgesics drug controls were examined as single entities and in mixtures in cutaneous mechanical sensitivity (CMS) assays that utilized standardized Von Frey monofilaments (fibers) of variable forces. In addition, DEA, DMSO, and D-limonene were tested as single reagents and mixtures in hemolysis assay in vitro. Inhibition of hemolysis was used as a surrogate endpoint for PLA2 enzymatic activity in bee venom. Results Mixtures of DEA and DMSO showed synergy that was most pronounced at equimolar ratios of the components. The maximum duration of sensitivity suppression in CMS assay of 72 h was achieved at 78% DEA and 22% DMSO. Multi-component mixtures of DEA, DMSO, limonene, a-pinene (but not b-pinene), and menthol demonstrated additional enhancement of synergy with DEA at a relatively narrow range of concentrations. Both DMSO and limonene showed bell-shaped dose responses, suggesting that the enhancement of the effects of DEA is not merely due to enhancement of tissue penetration. The activities of multi-component mixtures suggested competition between individual components in certain concentration ranges. The synergy of DEA in mixtures with DMSO and limonene in CMS assays was not observed with related diesters of azelaic acid, diethyl suberate, and diethyl sebacate. In hemolytic assays, DEA, DMSO, and limonene were ineffective as single agents at the examined concentrations, but a specific mixture thereof significantly suppressed hemolysis caused by PLA2. Conclusion The findings warrant further development of the mixtures of DEA, DMSO, and select terpenes as novel modalities.