(190) Hyperosmolar salt concentrations slow digestion of milk and meconium by pancreatic enzymes.

Background: Meconium ileus (MI) is a life threatening presentation of cystic fibrosis (CF) that occurs in approximately 20% of newborns [1]. Current treatments with hyperosmolar or N-acetylcysteine (NAC) enemas often fail to relieve MI. Approximately 75% of newborns with MI ultimately require surgery [2]. Most newborns with MI have pancreatic insufficiency, indicating a possible role for pancreatic enzymes in the pathogenesis and treatment of MI. We find that meconium from CF pigs is digestible with pancreatic enzymes, but it does not break down in NAC or hypertonic solutions. Because hypertonic solutions are often used in treating MI, our goal was to determine how salt concentration affects pancreatic enzyme function using milk and meconium as substrates.

Methods: To compare digestion kinetics at different salt concentrations, we used powdered milk in water at 31.9 g/L. We added [NaCl] over a range of doses with max range of 333 millimolar. Because pH influences pancreatic enzyme function, we buffered the solutions at pH = 7.0 with 3.3 mM PIPES. We added 4.2 units of lipase/mL of mixed pancreatic enzymes (Epizyme), then assessed the digestion of milk at 37 °C kinetically by measuring absorbance at 600 nm every 5 minutes with a plate reader. In ongoing studies, we are digesting 0.7 gram pieces of CF pig meconium with 10 mg/mL of mixed pancreatic enzymes in different [NaCl] for at 37 °C with constant agitation. We measure meconium digestion at 16 hours by comparing release of pigments (A₄₀₅) and by residual weight of meconium solids.

Results: In the absence of added salt, pancreatic enzymes rapidly clarified powdered milk, decreasing the A_600. Increasing [NaCl] at doses above 0.0833 decreased the rate enzymatic digestion in a dose-dependent manner. At 0.166 M NaCl, enzymatic digestion of milk was approximately two times slower than the samples without added salt (Figure 1). We compared digestion of CF meconium pieces by pancreatic enzymes in normal saline (0.15 M) and 7 % NaCl (1.1 M). We found that residual meconium was lower in normal saline.

Conclusions: We found that digestion of powdered milk and CF meconium by pancreatic enzymes was faster with lower salt conditions. Endogenous pancreatic enzymes are insufficient in patients with MI and hyperosmolar solutions could also slow meconium digestion. Future studies are needed to establish ideal conditions for dissolving obstructive meconium in animal models, with the ultimate goal of relieving intestinal obstruction in newborns with MI.

Acknowledgements: Anthony Fischer, Christian Zirbes

References: [1] Sathe M, Houwen R. Meconium ileus in Cystic Fibrosis. J Cyst Fibros. 2017;16 Suppl 2:S32-s9.

[2] Escobar MA, Grosfeld JL, Burdick JJ, Powell RL, Jay CL, Wait AD, et al. Surgical considerations in cystic fibrosis: a 32-year evaluation of outcomes. Surgery. 2005;138(4):560-71; discussion 71-2.