Salivary miRNAs are potential biomarkers for the accurate and precise identification of inflammatory response after tail docking and castration in piglets

The present study aimed to investigate whether acute pain associated with castration and tail docking of male piglets may modulate the expression of salivary microRNAs (miRNAs) and to explore their potential use as biomarkers. Thirty-six healthy 4-d-old piglets (Hermitage × Duroc) were randomly assigned to three groups: the first group (12 piglets) has been pretreated with anesthetic and anti-inflammatory drugs (ANA) and then castrated and tail docked; the second one (12 piglets) has been castrated and tail docked without any drugs (CONV); the third one (12 piglets) has been only handled (SHAM). Saliva was collected 10 min before (control group) and 30 to 45 min after the procedures. Salivary cortisol has been quantified. The expression concentrations of seven miRNAs, namely miR-19b, miR-27b-3p, miR-215, miR-22-3p, miR-155-5p, hsa-miR-365-5p, and hsa-miR-204, were measured and assessed as potential biomarkers of pain by quantitative Polimerase Chain Reaction using TaqMan probes. The area under the receiver operating curve (AUC) was used to evaluate the diagnostic performance of miRNAs. The concentration of salivary cortisol increased after treatment in CONV and ANA, while no significant variation was observed in the SHAM group. The comparative analysis demonstrated that the concentrations of salivary miR-19b (P = 0.001), miR-27b (P = 0.042), and miR-365 (P < 0.0001) were significantly greater in CONV as compared with pretreatment. The AUC of pretreatment vs. CONV and CONV vs. ANA were excellent for miR-19b and miR-365 and fair for miR-27b. Combining two miRNAs, namely miR-19b and miR-365, in a panel increased the efficiency of distinguishing between pre- and post-treatment groups. No differences have been identified between SHAM and ANA groups. mRNA potential targets of differentially expressed-miRNA were investigated, and genes related to pain and inflammation were identified: miR-19b potentially modulates TGF-beta and focal adhesion pathways, miR-365 regulates cytokines expression (i.e., IL-1, Tumor Necross Factor-alpha, and IL-8 cytokine), and miR-27b regulates macrophage inflammatory protein pathways (i.e., MIP1-beta). In conclusion, we demonstrated that the abundance of miR-19b, miR-27b, and miR-365 increases in the saliva of piglets castrated and tail docked without the administration of pain-relieving drugs. Further studies are needed to assess their potential during routine husbandry procedures and to extend their assessment in other stressful events, such as weaning or chronic pain.