Novel frog cathelicidin HR-CATH2 demonstrates potent antimicrobial, anti-inflammatory, and anti-sepsis activities

Cathelicidins are crucial components of innate immunity, offering broad-spectrum antimicrobial activity and immunomodulatory functions. Despite their promise as next-generation anti-infective agents, a comprehensive understanding of their dual roles remains incomplete. The global rise of antimicrobial resistance and the high mortality associated with sepsis, a dysregulated host response to infection, underscore the urgent need for novel therapeutic strategies. Current antibiotics often lack immunomodulatory effects, and existing anti-inflammatory drugs can compromise host defense, leaving a critical gap for agents that can simultaneously combat pathogens and modulate excessive inflammation.

Researchers identified a novel 30-amino acid cathelicidin peptide, HR-CATH2, from the skin of the Chinese tiger frog (Hoplobatrachus rugulosus). They characterized its structure, finding it adopted a highly amphipathic α-helical conformation. Functional analyses in vitro assessed its antimicrobial activity against various microorganisms, investigating mechanisms via intracellular reactive oxygen species (ROS) accumulation and direct bacterial membrane disruption. Immunomodulatory effects were evaluated in RAW264.7 macrophage cells stimulated with lipopolysaccharide (LPS), measuring proinflammatory cytokine (interleukin-6, interleukin-1β, tumor necrosis factor-α) and nitric oxide (NO) production, and investigating MAPK signaling pathways. In vivo efficacy was tested in a mouse model of cecal ligation and puncture (CLP)-induced sepsis, assessing acute inflammatory response and mortality.

HR-CATH2, a 30-amino acid peptide, exhibited potent antimicrobial activity by inducing intracellular ROS accumulation and directly disrupting bacterial membrane integrity. Beyond its direct antibacterial effects, HR-CATH2 demonstrated significant immunomodulatory properties. It inhibited the overproduction of proinflammatory cytokines, specifically interleukin-6, interleukin-1β, and tumor necrosis factor-α, as well as nitric oxide (NO), in LPS-stimulated RAW264.7 cells. This anti-inflammatory effect was mediated through LPS binding, which subsequently led to the inactivation of MAPK signaling pathways. The most critical finding was its in vivo efficacy:

HR-CATH2 markedly attenuated the acute inflammatory response and significantly reduced mortality in mice subjected to CLP-induced sepsis. These results collectively identify HR-CATH2 as a multifunctional cathelicidin with a unique combination of antibacterial, LPS-neutralizing, and anti-inflammatory actions.