Lipopolysaccharide Regulates Pro- and Anti-Inflammatory Cytokines, Corticosterone, and Melatonin in Toads

Abstract

Glucocorticoids and melatonin (MEL) show integrated and complex immunomodulatory effects, mostly described for endotherms, yet underexplored in amphibians. In this context, the RT-qPCR of molecules mediating inflammatory processes in amphibians is a valuable tool to explore the relationships among molecular biology, endocrine mediators, and immune response in these animals. In this study, toads (Rhinella diptycha) received an intraperitoneal saline injection or lipopolysaccharide (LPS; 2 mg/kg). Six hours post-injection, we analyzed plasma corticosterone (CORT) and MEL levels and pro and anti-inflammatory molecules (IL-1β, IL-6, IL-10, IFN-γ, and C1s). We found increased CORT and decreased MEL levels in response to LPS. Also, IL-1β, IL-6, and IL-10 were upregulated in LPS-injected toads compared with saline-injected. Overall, our results demonstrate an LPS-induced inflammatory response with endocrine and immune modulation in R. diptycha toads, exhibiting expected patterns for an inflammatory stimulus within this timeframe (6 h post-injection). Toads were responsive to LPS by secreting different cytokines, such as proinflammatory cytokines IL-1β and IL-6, related to immune cell attraction to inflammatory sites and the anti-inflammatory cytokine IL-10, which limits the rate of leukocyte infiltration, inflammation, and downregulates the expression of proinflammatory cytokines. Increased circulating CORT levels are probably associated with the activation of the hypothalamus-pituitary-interrenal axis by the LPS and the endocrine actions of IL-6. Furthermore, decreased circulating MEL levels are likely due to inhibited MEL secretion by the pineal gland by inflammatory stimuli, indicating the activation/existence of the immune-pineal axis in amphibians.

Diet- and salinity-induced modifications of the gut microbiota are associated with differential physiological responses to ranavirus infection in Rana sylvatica

“…High-salinity conditions could also lead to increased inflammation by supporting the proliferation of Gram-negative bacteria. Gram-negative bacteria have cell walls that contain lipopolysaccharides, which are antigens in vertebrate hosts that elicit local and systemic inflammatory responses in diverse taxa [79], including amphibians [80]. At the genus level, Dysgonomonas and Shewanella increased in abundance in high-salinity-basic diet conditions, but not in algae-supplemented larvae.…”

The Effect of Polyethylene Terephthalate Microplastics on the Growth of Mice

“…MPs have been found to have an impact on appetite in mice. Exposure to PET MPs resulted in insulin resistance (IR) in mice feed with normal chow diet (NCD) or high-fat diet (HFD), accompanied by increased plasma lipopolysaccharide and proinflammatory cytokines [36]. Additionally, exposure to MPs caused a decrease in the richness and diversity of gut microbiota, particularly an increase in the relative abundance of Gramnegative bacteria [10].…”