[Predictive value of neutrophil free fatty acid receptor 3 for secondary infection in patients with severe acute pancreatitis].

Objective: To evaluate the predictive value of neutrophil free fatty acid receptor 3 (FFAR3) for secondary infection in patients with severe acute pancreatitis (SAP).

Methods: (1) Biological information analysis: peripheral blood microarray data sets related to acute pancreatitis (GSE194331) were obtained from the Gene Expression Omnibus (GEO), including data from 32 healthy adults, 52 patients with mild acute pancreatitis, 20 patients with moderate-to-severe acute pancreatitis, and 10 patients with SAP. The original data of GSE194331 dataset were downloaded for quality control, pruning, quantification, annotation and difference analysis, and the different genes were obtained. (2) Clinical study: a prospective observational study was conducted. Forty-five SAP patients admitted to the critical care medicine department of the Eastern Theater Command General Hospital of the Chinese People's Liberation Army from January to November 2022 were enrolled, and they were divided into infected group and non-infected group according to whether secondary infection occurred during intensive care unit (ICU) stay. At the same time, 10 healthy adult volunteers were enrolled as control. Peripheral blood of subjects in each group was collected, neutrophils were isolated, and FFAR3 mRNA expression was detected by real-time fluorescence quantitative reverse transcription-polymerase chain reaction (RT-PCR). Spearman correlation method was used to analyze the correlation between neutrophil FFAR3 mRNA expression and secondary infection in SAP patients. Multivariate Logistic regression analysis was used to evaluate whether neutrophil FFAR3 mRNA expression was a risk factor for secondary infection in SAP patients. Receiver operator characteristic curve (ROC curve) was plotted to evaluate the predictive value of neutrophil FFAR3 mRNA expression on secondary infection in SAP patients.

Results: (1) Results of biological information analysis: the analysis of GSE194331 dataset showed that 301 genes were differentially expressed in peripheral blood cells between healthy controls and patients with pancreatitis. By biological function analysis, 8 biological functions involved in immune response were obtained, and 44 differential expressed genes were enriched in these 8 biological functions. The results of cell distribution analysis showed that there were 21 differential expressed genes expressions on neutrophils significantly higher than other immune cells, and the gene related to lipid metabolism was FFAR3. These results indicated that FFAR3 expression was closely related to the occurrence and development of SAP. (2) Clinical study results: out of the 45 SAP patients, 24 developed into secondary infection during ICU stay, 21 did not develop into secondary infection. The expression of neutrophil FFAR3 mRNA in SAP patients with secondary infection was significantly higher than that in SAP patients without secondary infection and healthy controls [2^-ΔΔCt: 3.8 (3.0, 4.2) vs. 1.4 (1.1, 2.7), 1.0 (0.8, 1.1), both P < 0.05]. Spearman correlation analysis showed that neutrophil FFAR3 mRNA expression was positively correlated with secondary infection in SAP patients (r = 0.799, P < 0.001). Multivariate Logistic regression analysis showed that increased FFAR3 mRNA expression was an independent risk factor for secondary infection in SAP patients [odds ratio (OR) = 17.212, 95% confidence interval (95%CI) was 3.004-98.613, P = 0.001]. ROC curve analysis showed that the area under the ROC curve (AUC) of neutrophil FFAR3 mRNA expression for predicting secondary infection in SAP patients was 0.856 (95%CI was 0.750-0.981, P < 0.001). When the optimal cut-off value was 2.37, the sensitivity was 95.83% and the specificity was 76.19%. According to the optimal cut-off value of neutrophil FFAR3 mRNA expression (2.37) for predicting secondary infection in SAP patients obtained by ROC curve analysis, 45 SAP patients were divided into two groups for subgroup analysis. It suggested that the incidence of secondary infection in SAP patients with FFAR3 mRNA expression level ≥2.37 was significantly higher than that in SAP patients with FFAR3 mRNA expression level < 2.37 [82.14% (23/28) vs. 5.88% (1/17)], and the difference was statistically significant (P < 0.01).

Conclusions: The expression of FFAR3 mRNA in neutrophils is closely related to the secondary infection in SAP patients, and monitoring its level can effectively predict the secondary infection in SAP patients.