A Ketogenic Diet Prevents Methylglyoxal-Evoked Nociception by Scavenging Methylglyoxal

Abstract

Methylglyoxal is a reactive dicarbonyl byproduct of glycolysis that has been implicated in a growing number of chronic pain conditions, including diabetic peripheral neuropathy (DPN). We previously demonstrated the efficacy of a ketogenic diet in reversing sensory symptoms in a rodent model of DPN. The purpose of this study was to determine whether a ketogenic diet modified methylglyoxal-evoked nociception as a potential mechanism of improving sensory symptoms of DPN. We delivered methylglyoxal to C57Bl/6 mice by intraperitoneal or intraplantar injections. Sensory behaviors were quantified for mechanical thresholds as assessed by von Frey filament testing and spontaneous nonreflexive nociceptive behaviors (shaking, biting, lifting, etc. of the injected paw). Intraperitoneal methylglyoxal injection induced lasting mechanical allodynia in standard chow-fed mice, while ketogenic diet-fed mice were protected. Importantly, ketogenic diet-fed mice exhibited significantly decreased methylglyoxylated-protein concentrations following injection relative to standard, chow-fed mice, and methylglyoxylated-protein concentration correlated negatively with blood ketones. A reaction between the ketone body acetoacetate and methylglyoxal was recently demonstrated in vivo as a potential mechanism of methylglyoxal detoxification, consistent with this observation. To assess whether ketone bodies modified methylglyoxal-evoked nociception by direct methylglyoxal detoxification, we incubated methylglyoxal with either β-hydroxybutyrate or acetoacetate overnight prior to intraplantar injection. Mice receiving an injection of methylglyoxal alone exhibited an increase in spontaneous nociceptive behaviors, whereas coincubation of either acetoacetate or β-hydroxybutyrate reduced these behaviors. In summary, a ketogenic diet prevented the onset of methylglyoxal-evoked mechanical allodynia and increased scavenging of circulating methylglyoxal. Ketone bodies were individually capable of detoxifying methylglyoxal to prevent nociception. These findings provide insight to a potential mechanism by which a ketogenic diet improves DPN in mice and provide a rationale for exploring a ketogenic diet as a therapeutic intervention in other chronic pain conditions associated with elevated methylglyoxal. This work was supported by NIH grants RO1 NS043314 (DEW), the Kansas Institutional Development Award (IDeA) P20 GM103418, Kansas University Training Program in Neurological and Rehabilitation Sciences (NIH T32 award) supported by NIH Award Number T32HD057850, and core support from the Kansas IDDRC P30 HD00228. Methylglyoxal is a reactive dicarbonyl byproduct of glycolysis that has been implicated in a growing number of chronic pain conditions, including diabetic peripheral neuropathy (DPN). We previously demonstrated the efficacy of a ketogenic diet in reversing sensory symptoms in a rodent model of DPN. The purpose of this study was to determine whether a ketogenic diet modified methylglyoxal-evoked nociception as a potential mechanism of improving sensory symptoms of DPN. We delivered methylglyoxal to C57Bl/6 mice by intraperitoneal or intraplantar injections. Sensory behaviors were quantified for mechanical thresholds as assessed by von Frey filament testing and spontaneous nonreflexive nociceptive behaviors (shaking, biting, lifting, etc. of the injected paw). Intraperitoneal methylglyoxal injection induced lasting mechanical allodynia in standard chow-fed mice, while ketogenic diet-fed mice were protected. Importantly, ketogenic diet-fed mice exhibited significantly decreased methylglyoxylated-protein concentrations following injection relative to standard, chow-fed mice, and methylglyoxylated-protein concentration correlated negatively with blood ketones. A reaction between the ketone body acetoacetate and methylglyoxal was recently demonstrated in vivo as a potential mechanism of methylglyoxal detoxification, consistent with this observation. To assess whether ketone bodies modified methylglyoxal-evoked nociception by direct methylglyoxal detoxification, we incubated methylglyoxal with either β-hydroxybutyrate or acetoacetate overnight prior to intraplantar injection. Mice receiving an injection of methylglyoxal alone exhibited an increase in spontaneous nociceptive behaviors, whereas coincubation of either acetoacetate or β-hydroxybutyrate reduced these behaviors. In summary, a ketogenic diet prevented the onset of methylglyoxal-evoked mechanical allodynia and increased scavenging of circulating methylglyoxal. Ketone bodies were individually capable of detoxifying methylglyoxal to prevent nociception. These findings provide insight to a potential mechanism by which a ketogenic diet improves DPN in mice and provide a rationale for exploring a ketogenic diet as a therapeutic intervention in other chronic pain conditions associated with elevated methylglyoxal. This work was supported by NIH grants RO1 NS043314 (DEW), the Kansas Institutional Development Award (IDeA) P20 GM103418, Kansas University Training Program in Neurological and Rehabilitation Sciences (NIH T32 award) supported by NIH Award Number T32HD057850, and core support from the Kansas IDDRC P30 HD00228.