Carlos Devia

Long-term reparative effects of mesenchymal stem cell therapy following neonatal hyperoxia-induced lung injury.

Background:Mesenchymal stem cell (MSC) therapy may prevent neonatal hyperoxia-induced lung injury (HILI). There are, however, no clear data on the therapeutic efficacy of MSC therapy in established HILI, the duration of the reparative effects, and the exact mechanisms of repair. The main objective of this study was to evaluate whether the long-term reparative effects of a single intratracheal (IT) dose of MSCs or MSC-conditioned medium (CM) are comparable in established HILI.Methods:Newborn rats exposed to normoxia or hyperoxia from postnatal day (P)2)–P16 were randomized to receive IT MSCs, IT CM, or IT placebo (PL) on P9. Alveolarization and angiogenesis were evaluated at P16, P30, and P100.Results:At all time periods, there were marked improvements in alveolar and vascular development in hyperoxic pups treated with MSCs or CM as compared with PL. This was associated with decreased expression of inflammatory mediators and an upregulation of angiogenic factors. Of note, at P100, the improvements were more substantial with MSCs as compared with CM.Conclusion:These data suggest that acute effects of MSC therapy in HILI are mainly paracrine mediated; however, optimum long-term improvement following HILI requires treatment with the MSCs themselves or potentially repetitive administration of CM.

Brainstem Amino Acid Neurotransmitters and Ventilatory Response to Hypoxia in Piglets

The ventilatory response to hypoxia is influenced by the balance between inhibitory (GABA, glycine, and taurine) and excitatory (glutamate and aspartate) brainstem amino acid (AA) neurotransmitters. To assess the effects of AA in the nucleus tractus solitarius (NTS) on the ventilatory response to hypoxia at 1 and 2 wk of age, inhibitory and excitatory AA were sampled by microdialysis in unanesthetized and chronically instrumented piglets. Microdialysis samples from the NTS area were collected at 5-min intervals and minute ventilation (VE), arterial blood pressure (ABP), and arterial blood gases (ABG) were measured while the animals were in quiet sleep. A biphasic ventilatory response to hypoxia was observed in wk 1 and 2, but the decrease in VE at 10 and 15 min was more marked in wk 1. This was associated with an increase in inhibitory AA during hypoxia in wk 1. Excitatory AA levels were elevated during hypoxia in wk 1 and 2. Changes in ABP, pH, and ABG during hypoxia were not different between weeks. These data suggest that the larger depression in the ventilatory response to hypoxia observed in younger piglets is mediated by predominance of the inhibitory AA neurotransmitters, GABA, glycine, and taurine, in the NTS.

Toll-like receptor 4–deficient mice are resistant to chronic hypoxia-induced pulmonary hypertension

ABSTRACT Current data suggest that Toll-like receptor 4 (TLR4), a key molecule in the innate immune response, may also be activated following tissue injury. Activation of this receptor is known to induce the production of several proinflammatory cytokines. Given that pulmonary inflammation has been shown to be a key contributor to chronic hypoxia-induced pulmonary vascular remodeling, the authors hypothesized that TLR4-deficient mice would be less susceptible to pulmonary hypertension (PH) as compared to mice with intact TLR4. TLR4-deficient and TLR4-intact strains of inbred mice were exposed to 4, 8, and 16 weeks of hypoxia (0.10 FiO2) or normoxia (0.21 FiO2) in a normobaric chamber. After chronic hypoxic exposure, TLR4-intact mice developed significant PH evidenced by increased right ventricular systolic pressure, right ventricular hypertrophy, and pulmonary artery medial thickening. In contrast, TLR4-deficient mice had no significant change in any of these parameters and this was associated with decreased pulmonary vascular inflammatory response as compared to the TLR4-intact mice. These results suggest that TLR4 deficiency may decrease the susceptibility to developing PH by attenuating the pulmonary vascular inflammatory response to chronic hypoxia.

The Effect of Escherichia coli Endotoxin Infusion on the Ventilatory Response to Hypoxia in Unanesthetized Newborn Piglets

To determine the effects of endotoxemia on the neonatal ventilatory response to hypoxia, 17 chronically instrumented and unanesthetized newborn piglets (≤7 d) were studied before and 30 min after the administration of Escherichia coli O55:B5 endotoxin (n = 8) or normal saline (n = 9). Minute ventilation, oxygen consumption, heart rate, arterial blood pressure, and blood gases were measured during normoxia and 10 min of hypoxia (fraction of inspired oxygen, 0.10). Basal ventilation was not modified by E. coli endotoxin infusion (mean ± SE, 516 ± 49 versus 539 ± 56 mL/min/kg), but the ventilatory response to hypoxia was markedly attenuated at 1 min (955 ± 57 versus 718 ± 97 mL/min/kg, p < 0.002, saline versus endotoxin) and at 10 min (788 ± 51 versus 624 ± 66 mL/min/kg, p < 0.002). A larger decrease in oxygen consumption was observed during hypoxia and endotoxemia (6.3 ± 2.8 versus 18.3 ± 2.7%, p < 0.03, pre-versus post-endotoxin). A significant correlation was demonstrated between the changes in minute ventilation and oxygen consumption with hypoxia during endotoxemia (r = 0.9, p < 0.002). The ventilatory response to hypoxia was not modified by the saline infusion. These data show a significant attenuation in the ventilatory response to hypoxia during E. coli endotoxemia. This decrease in ventilation was associated with a significant decrease in the metabolic rate during hypoxia and endotoxemia.

Effects of GABA Receptor Blockade on the Ventilatory Response to Hypoxia in Hypothermic Newborn Piglets

Hypothermic newborn piglets have a depressed ventilatory response to hypoxia, and this may be due to an increase in CNS γ-aminobutyric acid (GABA) levels. To evaluate the effects of GABAA receptor blockade on the ventilatory response to hypoxia in hypothermic piglets, 31 anesthetized paralyzed mechanically ventilated newborn piglets (2–7 d) were studied at a brain temperature of 38.5 ± 0.5°C [normothermia (NT), n = 15] or 34 ± 0.5°C [hypothermia (HT), n = 16]. The central respiratory output was evaluated by measuring burst frequency and moving time average area of phrenic nerve activity. Measurements of minute phrenic output (MPO), arterial blood pressure, heart rate, oxygen consumption, and arterial blood gases were obtained at room air and during 20 min of isocapnic hypoxia [fraction of expired oxygen (Fio2) = 0.10]. After 10 min of hypoxia, a bolus injection of 20 μL of bicuculline methiodide (BM; 10 μg) or Ringers solution was administered into the cisterna magna over a 1-min period, and the piglets remained in hypoxia for an additional 10 min. There was an initial increase of 50 ± 6% in MPO during the first minute of hypoxia followed by a decrease to values 24 ± 8% above baseline at 10 min in the NT group. In contrast, in the HT group, the initial increase in MPO with hypoxia was eliminated, and, at 10 min, there was a decrease to a mean value 35 ± 4% below baseline level (NT versus HT, p < 0.03). After administration of BM, a significant increase in MPO with hypoxia was observed in both groups compared with their placebo groups (p < 0.002 in NT-BM group, p < 0.0001 in HT-BM group). However, the magnitude of the increase in MPO during hypoxia was significantly greater in the HT group after administration of BM (NT versus HT, p < 0.0001). Changes in oxygen consumption, arterial blood pressure, heart rate, pH, partial pressure of oxygen (Pao2), and base excess with hypoxia were not different between NT and HT groups before and after the administration of BM. The cardiorespiratory response to hypoxia was not modified after administration of Ringers solution to NT and HT placebo groups. These data suggest that the depression in hypoxic ventilatory response produced by HT is in part modulated by an increased CNS GABA concentration.

The role of endothelin converting enzyme inhibition during group B Streptococcus-induced pulmonary hypertension in newborn piglets

An endothelin-converting enzyme mediates the conversion from low-potency pro-endothelin to potent endothelin-1 (ET-1). Increased ET-1 levels have been observed in pulmonary hypertension of various etiologies in infants. We hypothesized that increased ET-1 levels induce pulmonary hypertension during group B Streptococcus (GBS) infusion, and this can be attenuated by the administration of an endothelin-converting enzyme inhibitor (ECEI). Twenty-two unanesthetized, chronically instrumented newborn piglets received a continuous infusion of GBS (3.5 × 108 colony-forming units/kg/min) while exposed to 100% O2. They were randomly assigned to receive a placebo (PL) or an ECEI (phosphoramidon, 30 mg/kg i.v.) 15 min after sustained pulmonary hypertension. Comparison of hemodynamic measurements and arterial blood gases at baseline and over the first 210 min from the onset of pulmonary hypertension was performed between groups. GBS infusion caused significant increases in mean pulmonary artery pressure, pulmonary vascular resistance (PVR), systemic vascular resistance (SVR), and PVR/SVR, and significant decreases in cardiac output, pH, and base excess. After the administration of ECEI, a significant reduction in pulmonary artery pressure (p < 0.0001), PVR (p < 0.001), and PVR/SVR (p < 0.01) and an improvement in cardiac output (p < 0.01) were observed during GBS infusion. The decrease in pH (p < 0.001) and base excess (p < 0.001) during GBS infusion was less marked after the administration of ECEI compared with the PL. Plasma ET-1 levels were obtained in 20 additional piglets; levels were significantly lower in the ECEI compared with PL after 3 h of GBS infusion (p < 0.02). All animals in the ECEI group survived the study period as opposed to 25% survival in the PL group (p < 0.001). These data suggest that the increased circulating ET-1 levels mediate, in part, the GBS-induced pulmonary hypertension.

The Role of Angiotensin II Receptor-1 Blockade in the Hypoxic Pulmonary Vasoconstriction Response in Newborn Piglets

Background: Angiotensin-converting enzyme activity is increased in newborn infants with respiratory distress syndrome and in animals with alveolar hypoxia. Objective: To test whether angiotensin II (Ang II) mediates the pulmonary vasoconstriction induced by acute hypoxia in newborn piglets. Methods: Eight unanesthetized chronically instrumented newborn piglets (mean ± SEM; age 6.6 ± 0.6 days; weight 2,181 ± 174 g) were randomly assigned to receive a saline solution or the Ang II type 1 receptor (AT1) antagonist, losartan, in a crossover study design, with an interval of at least 48 h between the first and second study. Pulmonary artery (Ppa), wedge, systemic arterial (Psa) and right atrial pressures, cardiac output (CO), pulmonary (PVR) and systemic (SVR) vascular resistances, and arterial blood gases were obtained in room air, before and during the saline or losartan infusion (6 mg/kg followed by 3 mg/kg/h), and during 6 h of hypoxia (FiO2 = 0.11) and saline or losartan infusion. Data were analyzed by repeated measures analysis of variance. Results: The pulmonary vasoconstriction induced by acute hypoxia was significantly attenuated during losartan infusion, while Psa, SVR, CO, pH, PaCO2, PaO2 and base excess did not differ between groups. During room air, Ppa, PVR, Psa, SVR and CO values were not modified by saline or losartan infusion. Conclusion: These data suggest that the pulmonary vasoconstriction induced by acute hypoxia in newborn piglets is partially mediated by Ang II, acting via AT1.

Decreased ventilatory response to hypoxia in sedated newborn piglets prenatally exposed to cocaine

OBJECTIVE Infants exposed to cocaine in utero have been reported to have a higher incidence of apnea and altered ventilatory response to carbon dioxide and hypoxia. We investigated whether in utero cocaine exposure results in greater ventilatory depression during hypoxia in piglets. METHODS Cocaine hydrochloride, 1.0 or 2.0 mg/kg given intramuscularly, or saline solution was administered daily to pair-fed pregnant sows during the last month of gestation. Thirteen cocaine-exposed piglets (mean +/- SD: age, 4.4 +/- 1.3 days; weight, 2.10 +/- 0.10 kg) and 15 saline solution-exposed piglets (age, 4.6 +/- 1.1 days; weight, 2.32 +/- 0.42 kg) were studied under chloral hydrate sedation. Minute ventilation (VE), arterial blood pressure (BP), heart rate (HR), oxygen consumption (VO2), and arterial blood gases were measured in room air. During hypoxia (fraction of inspired oxygen = 0.10), the values for VE, BP, and HR were obtained at 1, 5, and 10 minutes, VO2 was calculated during the last 5 minutes, and arterial blood gas samples taken after 10 minutes. RESULTS Basal VE did not differ between saline solution- and cocaine-exposed animals. The increase in VE at 1 minute of hypoxia was also similar. However, at 5 and 10 minutes of hypoxia, VE was significantly lower in the cocaine group than in the saline group (6% +/- 9% and 4% +/- 10% vs 15% +/- 13% and 21% +/- 14%; p < 0.02). Mean baseline BP and the initial increase in BP during hypoxia were not different between groups. However, BP remained increased throughout hypoxia only in the saline solution-exposed animals (p < 0.05). Changes in HR, VO2, arterial oxygen tension, and base excess during hypoxia were similar between groups. CONCLUSIONS These results show a decrease in the ventilatory response to hypoxia in newborn piglets prenatally exposed to cocaine. This change is most likely to be centrally mediated because the initial hypoxic hyperventilation was not modified by the intrauterine cocaine exposure. This decrease in ventilation cannot be explained by changes in metabolic rate or in cardiovascular or acid-base status.

Role Of Glutamate On The Ventilatory Response To Hypoxia During Lactic Acid Infusion In Newborn Piglets. |[diams]| 1638

The hyperventilatory response to hypoxia is mediated by an increase in the CNS glutamate (GLU) levels. Metabolic acidosis decreases CNS GLU levels and thus may affect the ventilatory response to hypoxia. To evaluate the role of GLU on the ventilatory response to hypoxia during metabolic acidosis, 14 awake, unanesthetized and chronically instrumented newborn piglets(mean±SD; age, 6.6±3.2; wt, 1.9±0.5 kg) were studied before and after an infusion of either placebo (PL; n=7) or lactic acid (LA; n=7) at a mean dose of 19±4 mM/kg/h. The dose of LA was titrated to induce a progressive metabolic acidosis to achieve a base excess of -8 to -12 mEq/L in 120 min and to maintain an additional 60 min of steady state acidosis. Minute ventilation (VE), arterial blood pressure (ABP), arterial blood gases (ABG) and CNS glutamate levels were measured during normoxia (RA) and 15 min of hypoxia (FiO2=0.10). Extracellular GLU levels were measured in the nucleus tractus solitarius (NTS) by microdialysis. Samples were collected at 5 min intervals and analyzed using HPLC with electrochemical detection. (See table).

EFFECTS OF L-GLUTAMATE ON THE VENTILATORY RESPONSE TO HYPOXIA IN HYPOTHERMIC NEWBORN PIGLETS. |[dagger]| 2022

We have previously demonstrated that hypothermic newborn piglets have a depressed ventilatory response to hypoxia. This is accompanied by a decrease in the extracellular glutamate (GLU) concentration in the nucleus tractus solitarius (NTS)(Pediatr Res 37: 342A, 1995). To assess whether microinjection of L-GLU into the NTS of newborn piglets can reverse the hypoxic ventilatory depression observed during hypothermia, 7 anesthetized, paralyzed, mechanically ventilated piglets < 7 days old were studied at a brain temperature of 35± 0.5°C. L-GLU (50 nmol bolus over 10 sec, followed by 200 nmol/min for 10 min) or the vehicle solution were administered in random order into the area of the NTS upon initiation of hypoxia. Central respiratory output was assessed by measuring burst frequency and moving time average area of phrenic nerve activity. Minute phrenic output (MPO), arterial blood pressure (ABP), heart rate (HR), and arterial blood gases were obtained in room air (RA) and during isocapnic hypoxia (FiO2= 0.10). Mean± SD values for MPO (au/min) were: Table