Neonatal group B streptococcal sepsis: effects of late treatment with dazmegrel

Group B streptococci (GBS) injure lung endothelium in vitro: GBS invasion and GBS-induced eicosanoid production is greater with microvascular than with pulmonary artery cells

Neonatal group B streptococcal (GBS) sepsis and pneumonia cause lung endothelial cell injury. GBS invasion of the lung endothelium may be a mechanism for injury and the release of vasoactive eicosanoids. Pulmonary artery endothelial cells (PAEC) and lung microvascular endothelial cells (LMvEC) were isolated from neonatal piglets and were characterized as endothelial on the basis of morphology, uptake of acyl low-density lipoprotein, factor VIII staining, and formation of tube-like structures on Matrigel. PAEC and LMvEC monolayers were infected with COH-1 (parent GBS strain), isogenic mutants of COH-1 devoid of capsular sialic acid or all capsular polysaccharide, or a noninvasive Escherichia coli strain, DH5 alpha. Intracellular GBS were assayed by plate counting of colony-forming units resistant to incubation with extracellular antibiotics. All GBS strains invaded LMvEC significantly more than PAEC, showing that the site of lung endothelial cell origin influences invasion. DH5 alpha was not invasive in either cell type. Both isogenic mutants invaded PAEC and LMvEC more than COH-1 did, showing that GBS capsular polysaccharide attenuates invasion. Live GBS caused both LMvEC and PAEC injury as assessed by lactate dehydrogenase release; heat-killed GBS and DH5 alpha caused no significant injury. Supernatants from PAEC and LMvEC were assayed by radioimmunoassay for prostaglandin E2 (PGE2), the stable metabolite of prostacyclin (6-keto-PGF1 alpha), and the thromboxane metabolite thromoxane B2. At 4 h, live COH-1 caused no significant increases in eicosanoids from both PAEC and LMvEC. At 16 h, live COH-1, but not heat-killed COH-1, caused a significant increase in 6-keto-PGF1 alpha greater than PGE2 from LMvEC, but not PAEC. We conclude that live GBS injure and invade the lung microvascular endothelium and induce release of prostacyclin and PGE2. We postulate that GBS invasion and injury of the lung microvasculature contribute to the pathogenesis of GBS disease.

Effect of amrinone during group B Streptococcus-induced pulmonary hypertension in piglets

Intravenous infusion of group B Streptococcus (GBS) into neonatal animals produces pulmonary hypertension, ventilation/perfusion (VA/Q) mismatch, and an increase in serum levels of thromboxane B2 (TxB2) and tumor necrosis factor (TNF) alpha. The vasodilator amrinone (amr) is a cGMP-inhibited phosphodiesterase inhibitor and is reported to inhibit thromboxane A2 and TNF production. We hypothesized that infusion of amr would cause pulmonary vasodilation and reduce serum TxB2 and TNF levels in piglets with late phase GBS-induced pulmonary hypertension. The effect of amr on gas exchange was also determined. A continuous infusion of GBS was administered for 5 hr to 4 groups of anesthetized, mechanically ventilated neonatal piglets. An amr bolus of 8 mg/kg was given at 4 hr followed by a 1 hr continuous infusion of either 10 or 20 micrograms/kg/min of amr (amr 10 and amr 20, respectively). Control piglets received a bolus and 1 hr infusion of amr carrier. The infusion of amr, but not of carrier reversed late phase GBS-induced pulmonary hypertension. Piglets infused with amr 20 showed transient selective pulmonary vasodilation, based on a reduced ratio of pulmonary to systemic vascular resistance (PVR/SVR ratio) value at 30 min but not at 1 hr, compared to pre-amr treatment values. The PVR/SVR ratio values for amr 10 and control group did not change after treatment with either amr or carrier. Treatment with amr 10 or 20 did not decrease serum TxB2 or TNF levels or increase VA/Q mismatch.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of inhaled nitric oxide during group B streptococcal sepsis in piglets

Group B streptococcus (GBS), a common gram-positive pathogen, causes similar pathophysiologic changes in newborn humans and animals. Infusion of GBS into neonatal animals produces pulmonary hypertension and ventilation/perfusion (Va/Q) mismatch in both early-phase (< 1 h) and late-phase (2 to 6 h) responses. Contrary to early phase, late phase causes pulmonary vascular injury. Nitric oxide (NO) is an inhaled vasodilator whose effect on pulmonary hypertension and Va/Q matching during early and late phases of GBS sepsis is unclear. We hypothesized that inhaled NO (150 ppm) would: (1) reverse early-phase GBS-induced pulmonary hypertension; (2) demonstrate less effectiveness in reversing late-phase GBS-induced pulmonary hypertension because of vascular injury; (3) improve late-phase GBS-induced Va/Q mismatching. Anesthetized, mechanically ventilated piglets (n = 10; 14 +/- 4 days of age) received a 240-min infusion of GBS (1.5 x 10(9) CFU/kg/h). Piglets received 30 min of NO (Study) or N2 (Control) at 30 and 210 min of GBS infusion. We found that inhaled NO selectively reversed early- and late-phase GBS-induced pulmonary hypertension and that NO was equally as effective in each phase. Inhaled NO did not reverse Va/Q mismatching during late-phase GBS. We conclude that 4 h of GBS sepsis does not injure neonatal pulmonary vascular smooth muscle sufficiently to impair its response to inhaled NO.

Acute changes in vasoactive lipid mediators in experimental hyaline membrane disease

Endothelial release of the arachidonate derivative PGI2 may be increased in response to cyclic lung stretching. We therefore sought to determine if the stable metabolite of PGI2, 6-keto-PGF1 alpha, would be found in increased quantities in primates ventilated with conventional mechanical ventilation (CMV) compared to treatment with high frequency oscillatory ventilation (HFOV). We also sought to determine if other membrane-derived vasoactive substances such as LTC4, PAF and TXB2 would be elevated in plasma and lung tissue of animals developing hyaline membrane disease (HMD) and if the levels would correlate with the severity of the respiratory distress. Twenty prematurely delivered monkeys were treated with either CMV or HFOV from the first breath after Cesarean delivery until sacrifice at 6 h of age. We found a significant increase from birth to 5 min and from 5 min to 5 h in 6-keto-PGF1 alpha, and a significant increase from 5 min to 5 h in TXB2. We found a significant decline from cord blood to 5 min of LTC4, without further change by 5 h. PAF was present in all plasma samples but showed no upward or downward trend. There was no difference in the 5-h plasma level or in the lung homogenate level of any of the lipid mediators between the two types of assisted ventilation. There was no correlation between any lipid mediator level and severity of the HMD, as measured by gas exchange, radiographic or histologic criteria, when assessed by each ventilator group alone or with both groups combined. We conclude that the immediate postnatal increases in TXB2 and PGI2 and decrease in LTC4 are not altered substantially by use of HFOV.

Group B streptococcus induces tumor necrosis factor in neonatal piglets. Effect of the tumor necrosis factor inhibitor pentoxifylline on hemodynamics and gas exchange

Group B streptococcus (GBS), a common neonatal gram-positive pathogen, causes similar pathophysiologic features in human newborns and neonatal animal models of sepsis. Previous reports suggest that mediators in addition to TxA2 and PGI2 contribute to the late effects of GBS infusion (2 to 4 h), which include persistent increases in Ppa, hypoxemia, systemic hypotension, and a progressive fall in CO. Tumor necrosis factor (TNF) infusion in animals produces several of the late GBS effects. We hypothesized that GBS causes increased serum TNF levels 2 to 4 h into infusion in neonatal piglets. We also postulated that the TNF inhibitor, pentoxifylline (PTF), would attenuate both GBS-induced TNF production and late GBS effects. In piglets infused with 1.25 x 10(9) cfu/kg/h of GBS, serum TNF levels (pg/ml, ELISA assay) significantly increased at 2 h (231 +/- 41) and at 4 h (1,047 +/- 290, n = 9). In piglets infused with concomitant GBS + PTF, serum TNF levels at 4 h (208 +/- 39, n = 8) were reduced compared to GBS alone piglets (p less than 0.02). Control piglets infused with 0.9% saline or PTF alone for 4 h had no detectable serum TNF (less than 35). GBS alone and GBS + PTF infusion caused similar increases in serum TxB2 levels at 1, 2, and 4 h. Serum 6-keto-PGF1 alpha levels (pg/0.1 ml) significantly increased at 4 h (85 +/- 18) with GBS alone, and were more elevated at 4 h (306 +/- 75) with GBS + PTF infusion.(ABSTRACT TRUNCATED AT 250 WORDS)