Intraluminal casein model of necrotizing enterocolitis for assessment of mucosal destruction, bacterial translocation, and the effects of allopurinol and N-acetylcysteine.

Abstract

An intraluminal casein model (ICM) of necrotizing enterocolitis (NEC) is able to produce small-bowel changes reminiscent of human NEC in neonatal animals. We studied bacterial translocation (BT) in NEC induced by using the ICM in neonatal piglets. We also studied whether allopurinol (AL) and N-acetylcysteine (NAC) have an effect on BT and mucosal changes in the ICM of NEC. Twenty-eight neonatal piglets were randomized into four groups. NEC was induced in 21 by injecting casein-d-gluconate into a loop of terminal ileum: group Cas (n = 7) had no premedication, in group Cas/AL (n = 7) intravenous (i.v.) Al (100 mg/kg), and in group Cas/NAC (n = 7) i.v. NAC (200 mg/kg) was given. Group Sham (n = 7) had the ileum injected with 0.9% saline with no premedication. Immediately after the injection a mesenteric lymph node (MLN) adjacent to the loop was harvested for quantitative aerobic bacterial culture; 4 h after the injection another MLN and samples of spleen, liver, kidney, and lung were harvested and cultured. Comparison of the incidence of samples with positive bacterial cultures and the number of colony-forming units (CFU) in samples was made between groups. The severity of NEC in the ileum was graded from 0 to 3 according to macroscopic and histologic findings. NEC changes in the bowel were most severe in Cas piglets, less severe in Cas/NAC piglets ( P < 0.5), and sham piglets had the least severe changes ( P < 0.05). piglets with NEC changes in the ileum had a higher incidence of BT into the MLN than piglets without NEC changes ( P < 0.05), but the difference in CFU was not significant ( P > 0.05). In Cas and Cas/NAC piglets a high incidence of BT into the MLN was noted as early at -5 min after casein injection. The incidence of BT into the MLN was significantly higher in Cas and Cas/NAC piglets than in Sham piglets ( P < 0.05), the difference in CFU being not significant ( P > 0.05). BT in Cas/Al piglets was not significantly different from that of Cas piglets ( P > 0.05), but less than in Cas/NAC piglets ( P < 0.05). Four hours after casein injection into the ileum there was significant BT into the MLN. Premedication with NAC was associated with less severe NEC changes, but neither NAC nor AL significantly affected BT.