An analog of Clarias gariepinus Pituitary Adenylate Cyclase-Activating Polypeptide (PACAP-38) contributes to immune homeostasis and defences against Vibrio parahaemolyticus in Litopenaeus vannamei

Disease outbreaks in aquaculture are a major challenge, often leading to the widespread use of antibiotics for prevention and treatment. However, excessive and improper antibiotic use leads to antimicrobial resistance, posing risks to both aquatic species and human health. Therefore, researchers are looking into new alternatives such as antimicrobial peptides. Pituitary adenylate cyclase-activating polypeptide (PACAP), a neuropeptide with antimicrobial and immunomodulatory properties, has shown potential applications in fish and shellfish aquaculture. Nevertheless, few studies have been conducted to date in shellfish species. Given the importance of crustacean aquaculture, the current study aimed to assess the effect of synthetic Clarias gariepinus PACAP-38 and a PACAP modified sequence in shrimp L. vannamei during a Vibrio parahaemolyticus infection. Shrimp were treated for one week with four injections of each peptide administrated every 48 h. After the last treatment, animals were inoculated with a sublethal dose of V. parahaemolyticus, and samples were collected at 0-, 20-, and 68-h post-inoculation. The immunological status of the shrimp was assessed by measuring hemolymph immunological indicators and RT-qPCR. The results suggest that the modified form of PACAP exhibited an immunomodulatory effect, mostly maintaining stable levels of immune parameters throughout the challenge, unlike the native PACAP-38 and control groups, which exhibited more fluctuating responses. This modified variant of PACAP also demonstrated a strong antibacterial effect against V. parahaemolyticus. Overall, our findings provide more insights regarding the role of PACAP in crustacean immunology and its potential use as an alternative to antibiotics in aquaculture.