Parenteral Nutrition Suppresses the Bactericidal Response of the Small Intestine

Background Parenteral nutrition (PN) increases infectious risk in critically ill patients compared with enteral feeding. Previously, we demonstrated that PN feeding suppresses the concentration of the Paneth cell antimicrobial protein secretory phospholipase A2 (sPLA 2 ) in the gut lumen. sPLA 2 and other Paneth cell proteins are released in response to bacterial components, such as lipopolysaccharide (LPS), and they modulate the intestinal microbiome. Because the Paneth cell protein sPLA 2 was suppressed with PN feeding, we hypothesized PN would diminish the responsiveness of the small bowel to LPS through reduced secretions and as a result exhibit less bactericidal activity. Methods The distal ileum was harvested from Institute of Cancer Research mice, washed, and randomized for incubation with LPS (0, 1, or 10 μg/mL). Culture supernatant was collected and sPLA 2 activity was measured. Bactericidal activity of the ileum segment secretions was assessed against Pseudomonas aeruginosa with and without an sPLA 2 inhibitor at 2 concentrations, 100 nmol/L and 1 μmol/L. Institute of Cancer Research mice were randomized to chow or PN for 5 days. Tissue was collected for immunohistochemistry (IHC) and ileal segments were incubated with LPS (0 or 10 μg/mL). sPLA 2 activity and bactericidal activity were measured in secretions from ileal segments. Results Ileal segments responded to 10 μg/mL LPS with significantly greater sPLA 2 activity and bactericidal activity. The bactericidal activity of secretions from LPS stimulated tissue was suppressed 50% and 70%, respectively, with the addition of the sPLA 2 -inhibitor. Chow displayed greater sPLA 2 in the Paneth cell granules and secreted higher levels of sPLA 2 than PN before and after LPS. Accordingly, media collected from chow was more bactericidal than PN. IHC confirmed a reduction in Paneth cell granules after PN. Conclusion This work demonstrates that ileal segments secrete bactericidal secretions after LPS exposure and the inhibition of the Paneth cell antimicrobial protein sPLA 2 significantly diminishes this. PN feeding resulted in suppressed secretion of the sPLA 2 and resulted in increased bacterial survival. This demonstrates that PN significantly impairs the innate immune response by suppressing Paneth cell function.