Probiotic and high-fat diet: effects on pain assessment, body composition, and cytokines in male and female adolescent and adult rats.

Obesity in adolescence is increasing in frequency and is associated with elevated proinflammatory cytokines and chronic pain in a sex-dependent manner. Dietary probiotics may mitigate these detrimental effects of obesity. Using a Long-Evans adolescent and adult rat model of overweight (high-fat diet (HFD) - 45% kcal from fat from weaning), we determined the effect of a single-strain dietary probiotic [ 299v (Lp299v) from weaning] on the theoretically increased neuropathic injury-induced pain phenotype and inflammatory cytokines. We found that although HFD increased fat mass, it did not markedly affect pain phenotype, particularly in adolescence, but there were subtle differences in pain in adult male versus female rats. The combination of HFD and Lp299v augmented the increase in leptin in adolescent females. There were many noninteracting main effects of age, diet, and probiotic on an array of cytokines and adipokines with adults being higher than adolescents, HFD higher than the control diet, and a decrease with probiotic compared with placebo. Of particular interest were the probiotic-induced increases in IL12p70 in female adolescents on an HFD. We conclude that a more striking pain phenotype could require a higher and longer duration caloric diet or a different etiology of pain. A major strength of our study was that a single-strain probiotic had a wide range of inhibiting effects on most proinflammatory cytokines. The positive effect of the probiotic on leptin in female adolescent rats is intriguing and worthy of exploration. A single-strain probiotic (Lp299v) had a wide range of inhibiting effects on most proinflammatory cytokines (especially IL12p70) measured in this high-fat diet rat model of mild obesity. The positive effect of probiotic on leptin in female adolescent rats is intriguing and worthy of exploration.