Toll-like receptor-4 antagonist (+)-naloxone confers sexually dimorphic protection from inflammation-induced fetal programming in mice

Abstract

Inflammation elicited by infection or non-infectious insults during gestation induces pro-inflammatory cytokines that can shift the trajectory of development to alter offspring phenotype, promote adiposity and increase susceptibility to metabolic disease in later life. Here we utilize mice to investigate the utility of a small molecule TLR4 antagonist (+)-naloxone, the non-opioid isomer of the opioid receptor antagonist (-)-naloxone, for mitigating altered fetal metabolic programming induced by a modest systemic inflammatory challenge in late gestation. In adult progeny exposed to LPS challenge in utero, male but not female offspring exhibited elevated adipose tissue, reduced muscle mass and elevated plasma leptin at 20 weeks of age. Effects were largely reversed by co-administration of (+)-naloxone following LPS. When given alone without LPS, (+)-naloxone elicited accelerated post-weaning growth and elevated muscle and fat mass in adult male but not female offspring. LPS induced expression of inflammatory cytokines Il1a, Il1b, Il6, Tnf and Il10 in fetal brain, placental and uterine tissues, and (+)-naloxone suppressed LPS-induced cytokine expression. Fetal sex-specific regulation of cytokine expression was evident, with higher Il1a, Il1b, Il6 and Il10 induced by LPS in tissues associated with male fetuses, and greater suppression by (+)-naloxone of Il6 in females. These data demonstrate that modulating TLR4 signaling with (+)-naloxone provides protection from inflammatory diversion of fetal developmental programming in utero, associated with attenuation of gestational tissue cytokine expression in a fetal sex-specific manner. The results suggest that pharmacologic interventions targeting TLR4 warrant evaluation for attenuating developmental programming effects of fetal exposure to maternal inflammatory mediators.