Gut Permeability and Microbiome in Preterm Infants

Plain-language summary

: NEC, a life-threatening, GI emergency characterized by increased IP, affects approximately 7 to 10% of preterm neonates, and typically occurs within 7 to 14 days of birth (37, 38) with mortality as high as 30-50% (39). NEC symptoms mainly involve GI dysfunction, such as abdominal distension and feeding intolerance, but the presentation can be non-specific with few warning signs. Current therapies may be invasive, including surgical interventions that are often ineffective due to the rapid progression of the disease. Prematurity is the greatest risk factor for development of NEC (40, 41), due to physiological immaturity of the GI tract and altered levels of the normal GI microbiota. Several studies suggest that the initiation of an intense systemic and local inflammatory cascade leads to intestinal necrosis (42-47). Antenatal exposure to infection/inflammation may predispose the developing intestinal mucosa to subsequent injury or dysregulated inflammatory responses. Previous studies have linked presence of amniotic fluid infection/elevated cytokines, (48) cord blood cytokines, (49, 50) and umbilical cord inflammation (51) with risk for NEC in preterm neonates. In a rat model of NEC, maternal prenatal exposure to microbial LPS led to increased frequency and severity of intestinal injury (52). Taken together, these observations suggest that intestinal injury may be initiated in utero and contributes to increased IP at birth in the preterm neonate. Many of the defense mechanisms present in the mature intestine, such as peristalsis and tight junctions between intestinal epithelial cells (37) are decreased in an immature intestine, and thus bacteria normally confined to the intestinal lumen are able to reach systemic organs and tissues. Bacterial translocation triggers the activation of an exaggerated inflammatory response, which leads to further epithelial damage. Our analysis of the initial cohort of 43 preterm infants, and others' previous studies have shown that IP is high at birth in preterms (\<33wk gestation) with a rapid maturation of the intestinal barrier over the first 2 weeks. However, in some infants, high IP persisted and/or recurred in association with altered levels of the normal microbiota (bacteria community composition). Specifically, we observed that (1) rapid maturation of intestinal barrier function, characterized by decreased IP, correlates with increased microbial community diversity (Figure 1), and most outstandingly, the increased abundance of beneficial bacteria Clostridiales (Figure 2); (2) Clostridiales is highly transcriptionally active and co-active with the probiotic bacterium Bifidobacterium; (3) neonatal factors, including early introduction of breast milk, shorter period of antibiotic exposure, and later gestational age, favor the early colonization of the gut microbiota by members of Clostridiales and Bifidobacterium, which altogether are associated with improved intestinal barrier in preterm infants; (4) low Clostridiales spp. abundance (\<5%) and early gestational age (\<31.7wk) were identified to be the most discriminatory features for elevated IP by supervised learning scheme, reaching an accuracy of 86.1%. (5) Clostridiales and Bifidobacteriales are the most abundant bacteria groups in later stages (phase II/III at 6-18 months of age) as shown in Figure 2, suggesting a process of gaining prosperity of these two bacterial groups during intestine development after birth. Altogether our preliminary results suggest the early colonization of the natural occurring probiotics strains Clostridiales and Bifidobacterium strongly associate with rapid maturation of intestinal barrier function, and their measurement are highly promising for early detection and as potential nutritional supplement to prevent NEC in the high-risk preterm population. We propose in this study to recruit additional 150 mother-infant dyads (justified in study size analysis in research design), to address our hypothesis that the two naturally occurring beneficial bacteria Clostridiales and Bifidobacterium are rapidly gaining prosperity during normal intestine development in association with improved barrier function measured by La/Rh ratio. This continuation of the initial study builds on the previous findings that identified commensal bacteria Clostridiales and Bifidobacterium species as a strong indicator to the lowered IP and rapid maturation of intestinal barrier, to substantiate measurement of these probiotic strains combined with associated neonatal factors to form an accurate, rapid detection of intestinal permeability abnormality. We propose in this study to recruit additional 150 mother-infant dyads (justified in study size analysis in research design), to address our hypothesis that the two naturally occurring beneficial bacteria Clostridiales and Bifidobacterium are rapidly gaining prosperity during normal intestine development in association with improved barrier function measured by La/Rh ratio.

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