The effect of endotoxin on the neonatal erythrocyte

Intestinal ischemia is considered a major factor in the development of necrotizing enterocolitis (NEC). Despite this, the majority of affected infants lack documentation of clinical events associated with obvious gut hypoperfusion. Recent evidence in adults suggests that endotoxin may impair flow in the microcirculation through alterations in erythrocyte deformability. As the gut serves as a semipermeable reservoir of endotoxin in the stressed neonate, such localized activity may result in intestinal ischemia at the microcirculatory level through alterations in the red cell membrane. This study evaluates the role of endotoxin on neonatal erythrocyte membrane viscosity. Paired anticoagulated whole blood specimens were obtained from the umbilical cord of 10 neonates at delivery. Samples were incubated with either 2 μg/mL of E coli endotoxin (LPS) or an equal volume of saline (control). Following incubation, erythrocytes were isolated, washed, and incorporated with the fluorescent membrane probe TMA-DPH. Membrane viscosity was assessed by spectroscopic analysis of the fluorescent emissions induced by excitation of the probe at 365 nm. Results were calculated as anisotropy and analyzed for differences by ANOVA. Endotoxin resulted in a significant increase in red cell membrane viscosity as compared to control (LPS 291.2 ± 5.1 sv Control 271.7 ± 3.3, P < .01). As the effects of endotoxin are known to be primarily the result of white blood cell (WBC) activation, this study was repeated in an additional 10 neonates in whom WBCs were removed prior to endotoxin/saline incubation. In the absence of WBCs, endotoxin failed to induce any significant alteration in membrane viscosity (LPS 288.8 ± 4.4 v Control 292.2 ± 4.7, P = NS). Endotoxin results in increased membrane viscosity in the neonatal erythrocyte. These changes are modulated by the WBC. Such membrane alterations may impair flow in the intestinal microcirculation and serve as a potential inciting event in the development of NEC.