Maria Glibetic

Deregulation of cyclooxygenase and nitric oxide synthase gene expression in the inflammatory cascade triggered by experimental group B streptococcal meningitis in the newborn brain and cerebral microvessels

Group B Streptococcus (GBS) is the most common cause of neonatal sepsis and meningitis. Despite antibiotics, GBS in the newborn initiates a cascade of molecular and biological events leading to altered cerebral perfusion, blood-brain barrier disruption, cerebral edema, intracranial hypertension, neurological damage, and even death. Having previously shown that GBS infection impairs cerebral blood flow autoregulation and increases prostaglandin (PG) levels, we examined the regulation of some crucial inflammatory mediators (PGs, nitric oxide (NO), tumor necrosis factor-a) in the brain and cerebral microvessels (MVs) from newborn piglets. Cyclooxygenase (COX), the key enzyme in PG biosynthesis, exists in two isoforms, COX-1 and COX-2. Both may be directly induced by NO in a model of renal inflammation. Besides its neurotransmitter role, NO is a potent vasorelaxant whose production is catalyzed by at least three distinct nitric oxide synthases (NOS) (bNOS, ecNOS, iNOS). Western blot analyses showed that the newborn (4 day old) brain expressed lower levels of COX-1 (8-fold), COX-2 (20-fold), bNOS (12-fold), and ecNOS (5-fold) than in the 1 day old. MV showed approximately equal levels of COX-2, lower levels of COX-1 (4-fold), bNOS (5-fold), and higher levels of ecNOS (20-fold) in comparison to 4-day-old cerebral MV. A 4-day-old brain expressed lower levels of bNOS (5-fold), ecNOS (10-fold), and COX-1 (2-fold) than the 6-week-old pig. COX-2 protein was undetected in a 4-day-old pig brain, but present in great excess in MV. Purified MV showed lower ecNOS (14-fold), COX-1 (2-fold), and about equal levels of bNOS and COX-2 in comparison with MV from 6-week-old pigs. Reverse transcription polymerase chain reaction analyses confirmed these results. Treatment with noo-nitro-L-arginine (LNA), a NOS inhibitor, downregulated COX-1 expression in the newborn brain and both COX-1 and COX-2 cerebral MV expression. GBS infection (10(9) colony-forming units, 0.5 mL intracerebroventricular) of sedated newborn piglets induced the expression of tumor necrosis factor-alpha in the cerebrospinal fluid after 2 hours, upregulated bNOS expression in both brain and MVs, upregulated ecNOS in MVs, and downregulated COX-1, COX-2, and ecNOS in the brain. GBS did not trigger the expression of iNOS. Our data suggest that there is a net deficiency of NOS isoforms in the immature brain and microvasculature of the 4-day-old piglet and that the differences in expression lead to the immature control of NO and PG production, rendering newborns particularly susceptible to neurological damage because of the undeveloped nature of their response mechanisms. Moreover, the GBS-induced cascade deregulates the gene expression of interacting inflammatory mediators and may cause a net vasoconstrictor/vasodilator imbalance, leading to cerebral hypertension and edema in the early stages of infection. Pharmacological manipulations of the inflammatory cascade could lead to novel therapeutic approaches for the treatment of GBS meningitis.

PGE2/TXB2 imbalance in neonatal hypoxemic respiratory failure

Background: An imbalance of vaso‐constrictor and ‐dilator mediators has been implicated in the pathogenesis of the pulmonary hypertension accompanying neonatal hypoxemic respiratory failure (NHRF).

Systemic levels following PGE1 inhalation in neonatal hypoxemic respiratory failure

Aim: To measure plasma prostaglandin E1 (PGE1) levels in newborns with hypoxemic respiratory failure (NHRF) following inhaled PGE1 (IPGE1), normal term newborns, and newborns with congenital heart disease (CHD) following intravenous PGE1. Methods: Twenty newborns with NHRF received IPGE1 by jet nebulizer in doses of 25, 50, 150, and 300 ng/kg/min followed by weaning. Blood for PGE1 assay using enzyme immunoassay was available in eight neonates with NHRF, 10 normal newborns, and three neonates with CHD. Results: There were no differences in PGE1 levels between cord arterial blood in normal newborns and baseline samples from newborns with NHRF. Oxygenation improved significantly following IPGE1 (p=0.024) in newborns with NHRF. No adverse events were identified. Although a reversible increase in PGE1 levels was detected following a dose of 50 ng/kg/min (p <0.05), there was no association between PGE1 levels and IPGE1 duration, Pa O2, temperature, heart rate, and blood pressure.

Heat stress protects against lung injury in the neutropenic, endotoxemic rat.

The objective of this study is to determine if heat stress prior to endotoxemia diminishes cardiopulmonary dysfunction by attenuating the cytokine inflammatory response. Rats were assigned to either: 1) neutropenia; 2) heat; 3) neutropenia, LPS; or 4) heat, neutropenia, LPS. Heart rate, blood gases, and blood, lung lavage, and lung mRNA for tumor necrosis factor (TNF)-α, interleukin (IL)-1β, and macrophage inflammatory protein (MIP)-2 were measured. Heat given before LPS resulted in a similar A-a O2 gradient as the heat-alone and neutropenic groups (8 ± 8 versus 8 ± 7 versus 4 ± 3 mm Hg) and a lower A-a O2 gradient when compared to the neutropenic, LPS rats (8 ± 8 versus 22 ± 8 mm Hg, p < 0.003). Blood, lung lavage, and lung mRNA for TNF-α, IL-1β, and MIP-2 were similar in the LPS rats regardless of heat. Heart rate was similar in both LPS groups but higher than non-LPS groups. Heat pretreatment attenuates lung injury in the neutropenic, endotoxemic rat but not by decreasing TNF-α, IL-1β, or MIP-2 in the lung. Heat prior to LPS did not prevent cardiac dysfunction in neutropenic rats.

Chorioamnionitis and ontogeny of circulating prostaglandin and thromboxane in preterm infants

Our objective was to determine the effect of chorioamnionitis on plasma prostaglandin E2 (PGE2) and thromboxane B2 (TxB2) during the first week in preterm infants. Plasma PGE2 and TxB2 were measured at 1, 3, and 7 days of age in preterm infants (birth weights 501 to 1500 g), with ( N = 26) and without ( N = 22) chorioamnionitis. Infants with maternal chorioamnionitis had significantly lower mean gestational age ( P = 0.0001) and birth weight ( P = 0.03) and a marginally higher rate of bronchopulmonary dysplasia (37% versus 12.5, P = 0.05), a result that may be related to the lower mean gestational age. Plasma PGE2 and TxB2 varied widely, more so on the first day but did not significantly differ between the two groups. TxB2 was lower among infants who died or developed morbidities. Circulating PGE2 and TxB2 concentrations in preterm infants in the first week vary considerably, are relatively unaltered by chorioamnionitis, and are lower in association with mortality and clinical morbidities. Further research on their role in the causation of adverse neonatal outcomes is necessary.

Comparison of the systemic and pulmonary inflammatory response to endotoxin of neutropenic and non-neutropenic rats

BackgroundNeutrophil infiltration commonly occurs in acute lung injury and may be partly responsible for the inflammatory response. However, acute lung injury still occurs in the neutropenic host. The objectives of this study are to determine if inflammation and acute lung injury are worse in neutropenic versus the normal host after endotoxemia.MethodsRats were divided into four groups: 1) control, 2) neutropenic, 3) endotoxemic and 4) endotoxemic and neutropenic. Tumor necrosis factor (TNF)-α and macrophage inflammatory protein (MIP-2) were measured in the blood, lung lavage and for mRNA in the lung. Arterial blood gases were measured to determine the alveolar-arterial oxygen gradient which reflects on lung injury.ResultsIn endotoxemia, the neutropenic rats had lower plasma TNF-α (116 ± 73 vs. 202 ± 31 pg/ml) and higher plasma MIP-2 (26.8 + 11.9 vs. 15.6 + 6.9 ng/ml) when compared to non-neutropenic rats. The endotoxemic, neutropenic rats had worse lung injury than the endotoxemic, non-neutropenic rats as shown by increase in the alveolar-arterial oxygen gradient (24 ± 5 vs. 12 ± 9 torr). However, lavage concentrations of TNF-α and MIP-2 were similar in both groups.ConclusionNeutrophils may regulate TNF-α and MIP-2 production in endotoxemia. The elevation in plasma MIP-2 in the endotoxemic, neutropenic rat may be secondary to the lack of a neutrophil response to inhibit production or release of MIP-2. In endotoxemia, the severe lung injury observed in neutropenic rats does not depend on TNF-α or MIP-2 produced in the lung.

Heat stress response results in increased macrophage inflammatory protein-2 concentration in a lipopolysaccharide-exposed macrophage cell line.

Pretreatment with heat confers cardiopulmonary protection in endotoxemic animals. This mechanism may be through suppression of pro-inflammatory mediator production. The objectives of this study were to determine the effect of heat stress on tumor necrosis factor-α (TNF-α) and macrophage inflammatory protein-2 (MIP-2) in a lipopolysaccharide-exposed macrophage cell line and to study the relationship between TNF-α and MIP-2 production. Heat pretreatment resulted in decreased TNF-α transcription and translation by lipopolysaccharide-exposed macrophages; and increased MIP-2 concentration without additional effect in transcription. Administration of TNF-α antibody prior to exposure to lipopolysaccharide resulted in increased MIP-2 concentration suggesting that TNF-α acts to down-regulate MIP-2 production. The mechanism by which heat stress causes an increase in MIP-2 concentration may be secondary to its suppressing effect on TNF-α production.