Ketogenic Substrate Supplementation Attenuates Acute Inflammatory Responses in a Mouse Model of DNFB-Induced Allergic Contact Dermatitis

Background/Objectives: Fasting-induced elevation of blood ketone body levels suppresses allergic reactions; however, the underlying mechanism remains unclear. This study investigated whether elevated ketone body levels affect allergic contact dermatitis (ACD) and explored nutritional interventions that effectively increase β-hydroxybutyrate (BHB) levels. Additionally, we examined the role of GPR109A in ketone body–induced allergy suppression through ingestion of a ketogenic substrate. Methods: To evaluate the effects of ketone body precursors, medium-chain triglyceride (MCT) oil or 1,3-butanediol (BD) was administered as a single oral dose (2 g/kg body weight) under fed conditions. Blood BHB concentrations were measured at the time of euthanasia. ACD was induced using 2,4-dinitrofluorobenzene (DNFB), and its severity was assessed by measuring ear swelling and mast cell (MC) degranulation. To determine whether GPR109A mediates ketone body–induced allergy suppression, mepenzolate bromide (MPN), a GPR109A antagonist, was subcutaneously administered before BD treatment. Results: Both MCT oil and BD significantly increased the blood BHB levels. Elevated BHB concentrations were accompanied by reduced ear swelling and MC degranulation in DNFB-treated mice. The anti-allergic effects of BD were abolished by MPN administration, indicating that these effects were mediated by GPR109A activation. Conclusions: Nutritional supplementation with ketogenic substrates, such as MCT oil and BD, may serve as a dietary intervention for ACD by elevating blood BHB levels. GPR109A activation appears to be involved in ketone body–induced allergy suppression, suggesting a mechanistic link between ketone metabolism and immunomodulation.