Thromboxane-associated pulmonary hypertension during three types of gram-positive bacteremia in piglets

Causal effects between gut microbiota and pulmonary arterial hypertension: A bidirectional Mendelian randomization study

BACKGROUND

Multiple studies have highlighted a potential link between gut microbes and the onset of Pulmonary Arterial Hypertension (PAH). Nonetheless, the precise cause-and-effect relationship remains uncertain.

OBJECTIVES

In this investigation, we utilized a two-sample Mendelian randomization (TSMR) approach to probe the presence of a causal connection between gut microbiota and PAH.

METHODS

Genome-wide association (GWAS) data for gut microbiota and PAH were sourced from MiBioGen and FinnGen research, respectively. Inverse variance weighting (IVW) was used as the primary method to explore the causal effect between gut flora and PAH, supplemented by MR-Egger, weighted median (WM). Sensitivity analyses examined the robustness of the MR results. Reverse MR analysis was used to rule out the effect of reverse causality on the results.

RESULTS

The results indicate that Genus Ruminococcaceae UCG004 (OR = 0.407, P = 0.031) and Family Alcaligenaceae (OR = 0.244, P = 0.014) were protective factors for PAH. Meanwhile Genus Lactobacillus (OR = 2.446, P = 0.013), Class Melainabacteria (OR = 2.061, P = 0.034), Phylum Actinobacteria (OR = 3.406, P = 0.010), Genus Victivallis (OR = 1.980, P = 0.010), Genus Dorea (OR = 3.834, P = 0.024) and Genus Slackia (OR = 2.622, P = 0.039) were associated with an increased Prevalence of PAH. Heterogeneity and pleiotropy were not detected by sensitivity analyses, while there was no reverse causality for these nine specific gut microorganisms.

CONCLUSIONS

This study explores the causal effects of eight gut microbial taxa on PAH and provides new ideas for early prevention of PAH.

Cross-tolerance between bacterial endotoxin and group B Streptococcus in neonatal rats

Although endotoxin tolerance can be induced in newborns, potential cross-tolerance to group B Streptococcus (GBS), a common Gram-positive neonatal pathogen has not been investigated. In the present study we tested the hypothesis that endotoxin or recombinant tumor necrosis factor (rTNFα) can induce tolerance to lethal injection of heat-killed GBS in rat newborn pups and vice versa. The effect of such cross-tolerance on endogenous generation of plasma TNFα was subsequently evaluated. Rat pups (18-24 h old) were pretreated intracardially (i.c.) with either phosphate buffered saline (PBS), Salmonella enteritidis endotoxin (30 μg/kg) or rTNFα (35, 70 or 140 μg/kg). The pups were pretreated for either 4, 24, 48, 96 or 240 h prior to a lethal heat-killed GBS challenge. The susceptibility of the neonates to GBS-induced mortality was dependent on the duration of the pretreatment period. At 4 h of pretreatment with endotoxin or TNF, GBS-induced mortality was augmented relative to the PBS group. However, by 24-48 h the endotoxin and TNF pretreated neonates became more resistant to GBS-induced mortality. In a converse of the above experiment, neonates were pretreated with heat killed GBS (0.7 mg/kg) or rTNFα (70 μg/kg) and sensitivity to endotoxin was determined at 4-240 h after pretreatment. The data were qualitatively similar to endotoxin pretreatment. The 4 h GBS or TNF pretreatment rendered the neonates more susceptible to endotoxin-induced mortality. However, by 24-48 h the pretreatment groups were more resistant (P < 0.05) to endotoxin than the PBS controls. Plasma TNFα levels were increased (P < 0.05) 2 h after challenge i.c. with lethal heat-killed GBS or S. enteritidis endotoxin. In the 4 h pretreatment groups that received either GBS or endotoxin and then challenged with endotoxin or GBS, respectively, the plasma TNFα response was markedly augmented (P < 0.05). By 48 h of pretreatment, however, the plasma TNFα response in these groups to the stimuli was significantly reduced (P < 0.05) compared to the PBS pretreated groups. Therefore, plasma TNFα parallels lethality induced by GBS or endotoxin pretreatment. The ability of GBS and endotoxin to induce cross tolerance suggests that common pathophysiological pathways are involved in these syndromes.

Group B Streptococcus exposure and self-limited respiratory distress in late preterm and term neonates

BACKGROUND

Self-limited respiratory distress is a common neonatal respiratory morbidity for which effective treatments are lacking. Supportive care with non-invasive respiratory support is the norm. Animal models suggest that intrapartum exposure to group B Streptococcus (GBS) may cause mild pulmonary hypertension in the neonate, resulting in self-resolving respiratory distress. Treatments for pulmonary hypertension are currently not provided to neonates with self-limited respiratory distress empirically.

OBJECTIVES

This study examines the hypothesis that the incidence and severity of self-limited respiratory distress are altered by intrapartum exposure to GBS and antibiotic prophylaxis (IAP) in a human population.

METHODS

This is a 10-year single-center cohort study of retrospective data of late preterm and term neonates diagnosed with self-limited respiratory distress. Multiple logistic models were fitted to examine associations between exposure to GBS and IAP, and markers of self-limited respiratory distress severity. Additional linear regression models were fitted to examine the association between exposure to GBS and IAP, and duration of respiratory support for self-limited respiratory distress. Finally, crude and gestational age-adjusted incidence of self-limited respiratory distress among GBS-exposed and -unexposed infants, as well as the odds of self-limited respiratory distress based on GBS exposure were calculated.

RESULTS

584 neonates met study criteria. Neither GBS exposure nor IAP exposure was associated with severity of self-limited respiratory distress in multiple models. Crude and adjusted incidence of self-limited respiratory distress among neonates did not differ by GBS exposure history.

CONCLUSIONS

Although animal studies indicate that GBS-mediated pulmonary hypertension may contribute to self-limited respiratory distress, neither exposure to GBS nor IAP was associated with an increased severity or incidence of self-limited respiratory distress in our human study population. Treatments for pulmonary hypertension are unlikely to speed symptom resolution for patients with self-limited respiratory distress.

Hypothesis: Neonatal respiratory distress may be related to asymptomatic colonization with group B streptococci

BACKGROUND

Phospholipids from the group B streptococcal (GBS) cell wall cause pulmonary hypertension in experimental animals. When exposed to penicillin, Streptococcus mutans releases phospholipids immediately. We hypothesize that newborns colonized with GBS receive bacterial phospholipids leading to pulmonary hypertension and respiratory distress, especially in the situation of newborns of penicillin-treated mothers. We examined clinical and epidemiologic data on these relations.

METHODS

We used data from a prospective multicenter GBS study conducted from 1995 to 1999 in which 1674 of 17,690 newborns cultured at 4 sites were colonized with GBS. Our analyses included 1610 colonized newborns > or =32 weeks gestation without early-onset disease. Clinical features were compared between 1003 lightly colonized (GBS positive at < or =2 sites) and 607 heavily colonized (positive at 3 or 4 sites) newborns. The rates of respiratory distress were compared between colonized newborns of penicillin-treated mothers and those of untreated mothers.

RESULTS

Of the 1610 colonized newborns, 8.8% had signs of respiratory distress within 48 hours after birth (cases). Oxygen supplementation was used in 60% of the cases, mechanical ventilation was required in 5% and persistent pulmonary hypertension was diagnosed in 2%. Compared with light colonization, heavy colonization increased the rate of respiratory distress 1.73-fold (95% CI, 1.26-2.38), a discharge diagnosis of respiratory disorder 2.02-fold (95% CI, 1.16-3.52), a blood/cerebrospinal fluid obtained for culture 1.54-fold (95% CI, 1.24-1.93) and antibiotic administration after birth 1.87-fold (95% CI, 1.34-2.61). Penicillin use during labor was associated with a 2.62-fold (95% CI, 1.79-3.83) increase in respiratory distress in the colonized newborn.

CONCLUSIONS

Our findings support the association of neonatal respiratory distress with asymptomatic GBS colonization and with penicillin use during labor. These data require confirmation.

Perinatal infections and cerebral palsy

Infections of the mother, the intrauterine environment, the fetus, and the neonate can cause cerebral palsy through a variety of mechanisms. Each of these processes is reviewed. The recently proposed theory of cytokine-induced white matter brain injury and the systemic inflammatory response syndrome with multiple organ dysfunction syndrome is critically evaluated.

Inhaled nitric oxide, oxygen, and alkalosis: dose-response interactions in a lamb model of pulmonary hypertension

Inhaled nitric oxide (NO) is currently used as an adjuvant therapy for a variety of pulmonary hypertensive disorders. In both animal and human studies, inhaled NO induces selective, dose-dependent pulmonary vasodilation. However, its potential interactions with other simultaneously used pulmonary vasodilator therapies have not been studied. Therefore, the objective of this study was to determine the potential dose-response interactions of inhaled NO, oxygen, and alkalosis therapies. Fourteen newborn lambs (age 1-6 days) were instrumented to measure vascular pressures and left pulmonary artery blood flow. After recovery, the lambs were sedated and mechanically ventilated. During steady-state pulmonary hypertension induced by U46619 (a thromboxane A2 mimic), the lambs were exposed to the following conditions: Protocol A, inhaled NO (0, 5, 40, and 80 ppm) and inspired oxygen concentrations (FiO2) of 0.21, 0.50, and 1.00; and Protocol B, inhaled NO (0, 5, 40, and 80 ppm) and arterial pH levels of 7.30, 7.40, 7.50, and 7.60. Each condition (in randomly chosen order) was maintained for 10 min, and all variables were allowed to return to baseline between conditions. Inhaled NO, oxygen, and alkalosis produced dose-dependent decreases in mean pulmonary arterial pressures (P < 0.05). Systemic arterial pressure remained unchanged. At 5 ppm of inhaled NO, alkalosis and oxygen induced further dose-dependent decreases in mean pulmonary arterial pressures (P < 0.05). At inhaled NO doses > 5 ppm, alkalosis induced further dose-independent decreases in mean pulmonary arterial pressure, while oxygen did not. We conclude that in this animal model, oxygen, alkalosis, and inhaled NO induced selective, dose-dependent pulmonary vasodilation. However, when combined, a systemic arterial pH > 7.40 augmented inhaled NO-induced pulmonary vasodilation, while an FiO2 > 0.5 did not. Therefore, weaning high FiO2 during inhaled NO therapy should be considered, since it may not diminish the pulmonary vasodilating effects. Further studies are warranted to guide the clinical weaning strategies of these pulmonary vasodilator therapies.

Thromboxane inhibition and monocrotaline-induced pulmonary hypertension in rats

Monocrotaline (MCT)-induced pulmonary hypertension (PH) is a useful model for the investigation of this disorder in humans. The role of thrombocytes in the genesis of PH has already been addressed; however, the exact mechanism by which they induce PH remains to be elucidated. We investigated the effects of a thromboxane A2 (TXA2) synthase inhibitor (OKY-046) and a TXA2/prostaglandin H2 (PGH2) receptor antagonist (ONO-8809) on the development of MCT-induced PH. A single dose of MCT (60 mg/kg bodyweight; BW) was injected subcutaneously in Wistar rats 24 h after the administration of OKY-046 or ONO-8809. The TXA2 inhibitors were administered by gavage daily for 3 weeks. Urinary excretion of eicosanoids was determined by radioimmunoassay. At the end of the treatment period, the lungs, heart and kidneys were morphologically examined. The per cent medial thickness of the muscular pulmonary arteries (%MT) and the ratio of the right to the left ventricular mass including the septum (RV/LV + S) increased significantly in MCT-treated rats compared with the control rats. The %MT was attenuated by the administration of ONO-8809. Either OKY-046 or ONO-8809 attenuated the increase in RV/LV + S. In addition, both TXA2 inhibitors reduced urinary excretion of 11-dehydro-TXB2, particularly during the early phase of PH, suggesting that platelet aggregation was reduced. These findings suggest that the inhibition of TXA2 by synthase inhibition or receptor antagonism reduces or delays the development of MCT-induced PH in rats, probably by inhibiting platelet aggregation.

Involvement of protein kinase C in reduced relaxant responses to the NO/cyclic GMP pathway in piglet pulmonary arteries contracted by the thromboxane A2-mimetic U46619

1. Impairment of nitric oxide (NO)/cyclic GMP production and/or increased activities of thromboxane A2 (TXA2) and endothelin-1 (ET-1) have been associated with pulmonary hypertension. We have analysed the interactions of noradrenaline (NA), the TXA2-mimetic U46619 and ET-1 with the relaxation induced via cyclic GMP in isolated piglet intrapulmonary arteries. 2. The contractions induced by NA were augmented by endothelium removal or by methylene blue and pre-contracted rings were fully relaxed by acetylcholine, sodium nitroprusside (SNP), atrial natriuretic peptide and 8-bromo-cyclic GMP. In contrast, U46619- and ET-1 induced contractions were endothelium-independent and only partially relaxed by the latter vasodilators. Whereas the reduced responses to SNP in arteries contracted by U46619 were independent of the U46619-induced tone, a higher concentration of ET-1 (tone higher than that induced by NA) was required to reduce the vasodilator responses to SNP. NA, U46619 and ET-1 had no effect on the SNP-induced increases in cyclic GMP. 3. The reduced relaxant responses to SNP in arteries pre-contracted by U46619 were specific for piglet pulmonary arteries since they were not observed in piglet mesenteric or coronary arteries or in rat pulmonary arteries. Furthermore, there were no differences in the relaxant response to the adenylate cyclase activator forskolin in piglet pulmonary arteries pre-contracted by either NA, U46619 or ET-1. 4. SNP-induced relaxation was inhibited by thapsigargin (but not by inhibition of the membrane Na+/ K+ ATPase nor K+ channels) indicating a role for Ca2+ sequestration by the Ca2+ ATPase in the effects of SNP. 5. The phorbol ester 12-myristate, 13-acetate inhibited the relaxant response to SNP. The inhibitory effect of U46619 on SNP-induced relaxation was abolished by the protein kinase C inhibitor (PKC) staurosporine suggesting that PKC may be a part of the signal transduction mechanism. 6. In summary, piglet pulmonary arteries when activated by a TXA2-mimetic show abnormally reduced relaxant responses to the NO/cyclicGMP pathway. This effect appears to be mediated by activation of PKC.

Effects of group B Streptococcus on the responses to U46619, endothelin-1, and noradrenaline in isolated pulmonary and mesenteric arteries of piglets

The release of endogenous vasoconstrictors together with changes in the vascular responses are central to the pathophysiology of sepsis. The effects of in vitro incubation for 20 h with heat-killed group B Streptococcus (GBS, 3 x 10(7) colony-forming units mL-1) on the vasoconstrictor responses to noradrenaline (NA, 10(-8) to 10(-4) M), the thromboxane A2 analog 9,11-dideoxy-11 alpha, 9 alpha-epoxymethanoprostaglandin F2 alpha (U46619; 10(-10) M to 10(-6) M) and endothelin-1 (ET-1, 10(-11) to 3 x 10(-9) M) were evaluated on isolated intrapulmonary and mesenteric arteries from 10-17-d-old piglets. The incubation with GBS reduced the maximal contractile response to NA and ET-1 (p < 0.01) in both arteries. The nitric oxide (NO) synthase (NOS) inhibitor N omega-nitro-L-arginine methyl ester (L-NAME; 10(-4) M) completely reversed this hyporesponsiveness. GBS-treated mesenteric arteries also showed a significant reduction of the maximal contractions induced by U46619 (p < 0.05) and this effect was inhibited by 10(-4) M L-NAME. In contrast, the maximal contractile responses to U46619 were similar in control and in GBS-treated pulmonary arteries. Addition of L-NAME did not modify the contractile responses to U46619 in GBS-treated pulmonary arteries. In conclusion, GBS-treated systemic arteries from neonatal piglets showed decreased responses to NA, U46619, and ET-1 due to enhanced NO release. GBS-treated pulmonary arteries also exhibited decreased responses to NA and ET-1 but not to U46619. Induction of NOS in vascular smooth muscle may play a key role in the hypotension and loss of systemic vascular responsiveness that occurs in GBS sepsis. The absence of pulmonary hyporesponsiveness to U46619 may partially explain the coexistence during sepsis of pulmonary hypertension and lung NOS induction.

Group B streptococcal sepsis impairs cerebral vascular reactivity to acute hypercarbia in piglets

We investigated whether group B streptococcal (STREP) infusion impairs the cerebral blood flow (CBF) response to acute hypercarbia in piglets, and whether STREP-induced prostanoids or hemodynamic alterations could account for this impairment. Piglets, 2-3 wk old, were anesthetized, paralyzed, and mechanically ventilated (50% O2; partial pressure of arterial CO2 (PaCO2) approximately 40 torr). CBF was assessed by internal carotid artery blood flow (ICBF). Group 1 (n = 5) received a continuous infusion of STREP for 4 h (2.0-8.0 x 10(7) org/kg-min). Group 2 (n = 5) was pretreated with indomethacin (5 mg/kg), then received the identical STREP infusion. Group 3 (n = 6) did not receive STREP, but cardiac output (CO) and systemic blood pressure (BP) were reduced to levels equal to that of group 1 by incremental inflation of a left atrial balloon (LAB) catheter. Cerebral vascular reactivity to acute hypercarbia (PaCO2 approximately 70 torr for 7.5 min) was assessed at baseline and after each hour of STREP infusion or LAB inflation. We found that 4 h of STREP infusion caused CO to fall significantly (634 +/- 121 to 324 +/- 172 mL/min, group 1; 600 +/- 68 to 291 +/- 80 mL/min, group 2) and BP to fall significantly (104 +/- 20 to 57 +/- 4 mm Hg, group 1; 91 +/- 11 to 53 +/- 16 mm Hg, group 2) By design, in group 3 LAB inflation caused CO (573 +/- 181 to 375 +/- 159 mL/min) and BP (104 +/- 14 to 60 +/- 9 mm Hg) to fall to values not significantly different from septic groups 1 and 2. At 4 h, unilateral ICBF decreased significantly during STREP infusion in group 1 (32.0 +/- 10.8 to 21.0 +/- 7.3 mL/min) and group 2 (22.9 +/- 9.9 to 13.1 +/- 4.3 mL/min), but not in nonseptic group 3 (23.1 +/- 7.4 to 19.6 +/- 6.3 mL/min). At baseline, hypercarbia induced an increase in ICBF (% delta ICBF = 68.7 +/- 13.0% in group 1, 62.2 +/- 15.6% in group 2, and 87.7 +/- 34.0% in group 3). After 4 h of STREP, this response was completely ablated as ICBF fell during hypercarbia by -7.8 +/- 23.2% (group 1). Indomethacin did not protect cerebral vascular reactivity after 4 h of STREP infusion, as % delta ICBF fell during hypercarbia by -10.9 +/- 17.7% (group 2). In contrast, despite equivalent reductions in CO and BP after 4 h of LAB inflation in nonseptic group 3, ICBF rose during hypercarbia by 61.8 +/- 23.2%, not significantly different from baseline, but significantly different from the decrease in % delta ICBF in groups 1 and 2. We conclude that STREP infusion reduces ICBF and cerebral vascular reactivity to acute hypercarbia in piglets. This phenomenon is not accounted for by STREP-induced reduction in CO or BP, and is not mediated by prostanoids.

Group B streptococcus has no effect on piglet diaphragmatic force generation

Recent studies indicate that diaphragmatic contractility is adversely affected by bacterial infection. Using transdiaphragmatic pressure (Pdi) with phrenic nerve stimulation, the effect of continuous Group B Streptococcus (GBS) infusion on diaphragmatic force output was studied in seven anesthetized, spontaneously breathing 1-month old piglets. Pdi was measured under baseline condition (50% O2/50% N2) and at 1, 2, and 4 h of GBS infusion. The GBS was infused at a level that caused a doubling of the pulmonary artery pressure and a 32% decrease in cardiac output but which avoided hypotension or acidosis--both of which can decrease diaphragmatic contractility. In addition, the piglets were kept hyperoxic (PaO2 greater than 100) and no piglet with hypercapnia (PaCO2 greater than 65) was studied, as hypoxia and hypercapnia also can cause respiratory muscle dysfunction. Pdi in response to phrenic nerve stimulation did not change during GBS infusion. We conclude that GBS infusion, in the absence of hypotension, hypercapnia, hypoxia, or acidosis, has no effect on diaphragmatic force generation in the piglet.

Prostanoid inhibition and group B hemolytic streptococci (GBS) induced neutropenia in newborn piglets

GBS (Group B Hemolytic Streptococci) cause pulmonary hypertension with associated neutropenia. We investigated whether there is a correlation between the neutropenia of sepsis and GBS-induced pulmonary vasoconstriction, through study of the effects of inhibiting pulmonary vasoconstriction on the neutropenia of GBS in newborn piglets. Fifteen piglets were infused with GBS. After one hour, animals were given either a thromboxane inhibitor (DAZ), a combined cyclooxygenase/lipoxygenase inhibitor, BW755C, or placebo. With GBS infusion, WBC and PMN counts dropped steadily, from similar baselines, to 2250 +/- 570, 3300 +/- 500 and 5400 +/- 1100 cells/mm3 respectively (p less than 0.05; DAZ and BW vs. placebo). PMN's dropped similarly to 710 +/- 320, 2390 + 1240 and 3130 +/- 1050 cells/mm3 respectively (p less than 0.05; DAZ vs. BW and placebo). The drop in WBC's predominantly resulted from proportional decreases in PMN's (DAZ: r = 0.98; BW: r = 0.88; placebo r = 0.93). Compared to GBS alone, DAZ reduced pulmonary vasoconstriction, but exacerbated the granulocytopenia. BW755C similarly reduced pulmonary hypertension: however, it ameliorated the exacerbation of GBS induced neutropenia described above. These data imply that there is no direct correlation between GBS induced granulocytopenia and pulmonary hypertension.