S. M. Koehler1, K. Fredrich1, M. Christensen1, T. Nghiem-Rao2, D. Gourlay1 2Children’s Hospital Of Wisconsin,Neonatology,Milwaukee, WI, USA 1Children’s Hospital Of Wisconsin,Pediatric Surgery,Milwaukee, WI, USA
Introduction: Intestinal alkaline phosphatase (IAP) is an enzyme secreted from the mucosa of the gut which exerts a number of beneficial effects on the gut, including the enhancement of barrier function, reducing excessive inflammation, maintaining commensal bacteria and detoxifies lipopolysaccharide. The premature gut has a permeable intestinal barrier and an immature microbiome which predispose the premature neonate to necrotizing enterocolitis (NEC). Minimal research has focused on the activity of IAP in the premature gut, thus we sought to determine normal IAP activity levels for premature infants.
Methods: This is an observational prospective trial involving 10 neonates, ranging in age from 26 to 37 weeks estimated gestational age, in the neonatal intensive care unit at Children’s Hospital of Wisconsin (CHW). Inclusion criteria included: capable of per rectum stooling, parents/guardians consent to the study, and born at or transferred to CHW within 72 hours of life. Patients were excluded if they had life threatening congenital anomalies, congenital intestinal obstruction, or colostomy/ileostomy due to causes other than NEC. If possible, the first stool was collected and then weekly thereafter. The stool was homogenized and the amount of protein per volume determined. An AP activity assay was performed using a p-Nitrophenyl phosphate (pNPP) colorimetric assay. Absorbance of all samples was measured in triplicate at 405nM. The AP activity was measured in the presence of IAP and tissue nonspecific alkaline phosphatase inhibitors. A standard curve of pNPP dilutions was used to quantify the amount of AP activity.
Results: AP activity in all stool samples of premature infants is almost completely inhibited by phenylalanine, an IAP specific inhibitor, but minimally inhibited by a tissue non-specific alkaline phosphatase inhibitor. This cohort of premature infants has a heterogeneous amount of AP activity. For the majority of patients, there is a substantial drop in the AP activity beginning at approximately day of life 4. This decline was followed by an increase in AP activity over the following 2-3 weeks which generally reached and just exceeded the AP activity in the first stool. Only one patient, who had stool samples at the appropriate time points, did not follow this trend of increasing AP activity after an initial drop and this patient was being treated with meropenem for bacteremia.
Conclusions: AP activity in the stool of premature infants is almost exclusively due to IAP as it is inhibited by phenylalanine. The activity of IAP, while initially higher, declines rapidly within days of birth and then rises slowly over the following 3 weeks. The relatively high initial level of AP activity could explain the decreased incidence of NEC in the early postnatal period. Larger studies will be necessary to determine if the heterogeneity of the baseline IAP levels has a physiologic significance.