Neonatal necrotizing enterocolitis (NEC) is a common disease of newborn infants. Among premature infants of low birth weight, the incidence of NEC is particularly high, the morbidity rate is 1.6–7.3% and mortality can be as high as 50–80% (1). Although animal experiments and clinical studies have been conducted to investigate NEC, its exact pathogenesis remains to be determined, and a more sensitive diagnostic method and effective treatment approach have yet to be identified. Previous results repeatedly stress that an inflammatory cascade reaction is, not only a starting factor of NEC, but also plays an important role in the evolution and prognosis of NEC (2). The roles of platelet-activating factor (PAF), interleukins (IL-1, IL-10) and tumor necrosis factor-α (TNF-α) have been confirmed in NEC animal models and their corresponding antagonists can be useful to reduce the disease damage and improve clinical effects (3). Furthermore, associated signal transduction pathways, such as signal peptide RhoA and Toll-like receptors, are involved in the occurrence of NEC (4).

However, since scientific and comprehensive data at present remain scarce, these inflammatory factors are rarely used in clinical diagnosis, treatment and prognosis evaluation. Most clinical studies focus on the detection of inflammation indexes in infants that have been diagnosed with NEC, and there are few detection time points (5). In the present study, through rigorous experimental design and careful observation of the evolution of the inflammatory process prior to and at the onset of NEC, PAF, IL-1, TNF-α and IL-10 were found to be important in the pathogenesis of NEC, albeit their levels were not useful as prognostic markers.

At present, the pathogenesis and specific mechanisms of NEC remain to be elucidated. However, it is considered to be a result of various factors acting at the same time. Newborns with asphyxia, hypoxia, hypotension, acidosis, and shock upon birth, are prone to defensive reflex blood redistribution, decreased mesenteric blood flow and intestinal mucosal ischemia and necrosis (6). Furthermore, the weakened intestinal mucosal barrier functions result in the propagation and translocation of a large number of intestinal pathogenic bacteria, and the release of a large number of toxic substances, such as endotoxin, IL-6, TNF-, and IL-4 (7). These inflammatory factors also promote the cascade reaction of intestinal mucosal inflammation, cause more extensive mucosal necrosis, enable more toxic substances to enter into the circulation of the blood, and lead to bacteremia, sepsis and shock (8).

It is possible that the first inflammatory factors secreted in NEC patients are TNF-α and PAF (9). When the homeostatic environment of the patient is disrupted, macrophages become activated and produce and release large amounts of TNF-α, which, combined with specific receptors, produces various biological effects, leading to mitochondrial dysfunction, and ultimately mitochondrial apoptosis (10). After bacterial lipopolysaccharide and TNF-α injections into animal models, the animals develop intestinal necrosis. However, the degree of intestinal necrosis can be greatly alleviated by using pentoxifylline to inhibit TNF-α (11). PAF is an inflammatory cytokine that can lead to epithelial cell injury and apoptosis, and promote leukocyte and platelet aggregation, blood vessel contraction, and increased permeability (12). The addition of PAF-AH in infant formula can reduce the incidence of NEC. It is also known that premature infants lack endogenous PAF-AH. Thus, PAF is important in the pathogenesis of NEC (13). The results of the present study have shown that the levels of PAF and TNF-α in NEC infants began to increase on days 1–3 after birth, increasing by 50 and 45% of the initial value, respectively; the values reached a peak on days 7–10, increasing by 280 and 80%; and then declining on days 14–21 to almost normal levels. PAF and TNF levels in the NEC group were significantly higher than those in the normal preterm group, and those in the full-term normal group were the lowest of all the levels. There were no high values in the premature or full-term normal groups.

TNF-α and PAF probably induced the release of IL-1, and the high concentrations of IL-1 and TNF-α jointly stimulated the body to release IL-6. These inflammatory factors interact with each other and form a feedback mechanism that can lead to the release of more inflammatory factors and the formation of a reaction cascade (14). Some scholars even believe that IL-1 can be used as a marker for reflecting cell factor cascade activation, revealing the association between disease severity and inflammatory response, and as a marker for sepsis and SIRS prognosis (15). At the same time, the expression levels of IL-11, and IL-10, as well as related receptors gradually increase, which may be useful to alleviate the excessive inflammatory response and NEC damages (16).

The results of the present study have shown the levels of IL-1 began to increase on days 1–3 after birth in premature infants, increasing by approximately 18%; reached a peak on days 7–10, increasing by approximately 230%; and then declined on days 14–21 to close to normal levels. Interleukin-1 levels in the NEC group were significantly higher than those in the normal preterm group, and the full-term normal group had the lowest levels. Interleukin-10 began to increase on days 7–10 after birth, increasing by approximately 30%; and reached a peak on days 14–21, increasing by approximately 90%. Interleukin-10 levels in the NEC group were significantly higher than those in the normal preterm group, and the lowest values were found in the normal group.

In the present study, we monitored the fluctuations in the values of serum inflammatory factors within the first three weeks of life of infants and observed a clear difference between the values of full-term and premature infants. Of note, we found a statistically significant difference between the immature infants who went on to develop NEC and those who did not develop NEC. Thus, the present findings set a firm base showing that given an appropriate sample size, it is possible to obtain a reference range for the development of NEC in infants with high sensitivity and specificity. Such a reference index may provide a simple and powerful clinical tool for the early prediction of NEC.

Nevertheless, the present results also found that the prognosis of NEC cannot depend on the monitoring of any of the inflammatory factors tested, as it was found that none of the four indicators compared in the NEC survival and death group, showed statistical differences. The present study did not include a regression analysis of the prognostic factors. Thus, it was hypothesized that the prognosis may not only be associated with the level of inflammation, but also with the severity of the disease, the infants' basic state and the related treatment methods (17,18). Therefore, the value of other inflammatory factors in the prediction of prognosis cannot yet be excluded.

In conclusion, the pro-inflammatory factors PAF, IL-1, TNF-α and the anti-inflammatory factor IL-10 may be involved in the pathogenesis of NEC, and monitoring their presence in the patient's blood can be used as a key to predict the occurrence of NEC. However, these factors may not prove useful in the prognosis of the disease.