Biomedical subjects

G Filippov

Publications and source records attributed to G Filippov.

10 recordsLinked to original sources

PubMed2001

Cytokines decrease sGC in pulmonary artery smooth muscle cells via NO-dependent and NO-independent mechanisms.

Exposure of rat pulmonary artery smooth muscle cells (rPASMC) to cytokines leads to nitric oxide (NO) production by NO synthase 2 (NOS2). NO stimulates cGMP synthesis by soluble guanylate cyclase (sGC), a heterodimer composed of alpha(1)- and beta(1)-subunits. Prolonged exposure of rPASMC to NO decreases sGC subunit mRNA and protein levels. The objective of this study was to determine whether levels of NO produced endogenously by NOS2 are sufficient to decrease sGC expression in rPASMC. Interleukin-1beta (IL-1beta) and tumor necrosis factor-alpha (TNF-alpha) increased NOS2 mRNA levels and decreased sGC subunit mRNA levels. Exposure of rPASMC to IL-1beta and TNF-alpha for 24 h decreased sGC subunit protein levels and NO-stimulated sGC enzyme activity. L-N(6)-(1-iminoethyl)lysine (NOS2 inhibitor) or 1H-[1,2,4]oxadiazolo-[4,3-a]quinoxalin-1-one (sGC inhibitor) partially prevented the cytokine-mediated decrease in sGC subunit mRNA levels. However, cytokines also decreased sGC subunit mRNA levels in PASMC derived from NOS2-deficient mice. These results demonstrate that levels of NO and cGMP produced in cytokine-exposed PASMC are sufficient to decrease sGC subunit mRNA levels. In addition, cytokines can decrease sGC subunit mRNA levels via NO-independent mechanisms.

Animals↗

PubMed1999

Maturational changes in ovine pulmonary vascular responses to inhaled nitric oxide.

Developmental changes in modulation of pulmonary vasomotor tone by endothelium-derived nitric oxide (EDNO) may reflect maturational differences in endothelial synthesis of and/or vascular smooth muscle response to nitric oxide. This study sought to determine whether pulmonary vascular sensitivity and responsiveness to nitric oxide change during newborn development, and whether this is related to changes in guanylate cyclase activity. Pulmonary artery dose-responses to inhaled nitric oxide (iNO, 0.25-100 parts per million) were measured in hypoxic, indomethacin-treated, isolated lungs from 1-day (1-d)- and 1-month (1-m)-old lambs. The lungs of 1-m-old lambs were ventilated with 4% (oxygen) O2, and lungs of 1-d-old lambs were ventilated with either 4% or 7% O2 in order to achieve similar stimuli or vasomotor tone. Cyclic guanosine monophosphate (cGMP) concentrations in the perfusate were measured at iNO concentrations of 0, 5, and 100 parts per million (ppm). Basal and stimulated pulmonary guanylate cyclase activity was also measured in lung extracts in vitro. The effects of iNO were similar in both 1-d groups, even though baseline hypoxic tone was significantly higher in 1-d lungs ventilated with 4% O2 than with 7% O2. Furthermore, both the 1-d 7% O2 and 1-d 4% O2 lungs exhibited greater responsiveness and sensitivity to iNO than 1-m lungs. Perfusate cGMP concentrations and soluble guanylate cyclase activity were higher under stimulated than basal conditions, but neither differed statistically between 1 d and 1 m. These data suggest that pulmonary vascular responsiveness and sensitivity to nitric oxide decrease with age, but the mechanisms underlying these maturational changes require further investigation.

Administration, Inhalation↗

PubMed1998

Adenovirus-mediated gene transfer of cGMP-dependent protein kinase increases the sensitivity of cultured vascular smooth muscle cells to the antiproliferative and pro-apoptotic effects of nitric oxide/cGMP.

Studies in vitro have underestimated the importance of cGMP-dependent protein kinase (PKG) in the modulation of vascular smooth muscle cell (SMC) proliferation and apoptosis in vivo. This is attributable, in part, to a rapid decline in PKG levels as vascular SMC are passaged in culture. We used a recombinant adenovirus encoding PKG (Ad.PKG) to augment kinase activity in cultured rat pulmonary artery SMC (RPaSMC). Incubation of Ad. PKG-infected RPaSMC (multiplicity of infection = 200) with 8-Br-cGMP decreased serum-stimulated DNA synthesis by 85% and cell proliferation at day 5 by 74%. The effect of 8-Br-cGMP on DNA synthesis in Ad.PKG-infected RPaSMC was blocked by KT5823 (PKG inhibitor), but not by KT5720 (cAMP-dependent protein kinase inhibitor). A nitric oxide (NO) donor compound, S-nitrosoglutathione, at concentrations as low as 100 nM, inhibited DNA synthesis in Ad. PKG-infected RPaSMC, but not in uninfected cells or in cells infected with a control adenovirus. In addition, 8-Br-cGMP and S-nitrosoglutathione induced apoptosis in serum-deprived RPaSMC infected with Ad.PKG, but not in uninfected cells or in cells infected with a control adenovirus. These results demonstrate that modulation of PKG levels in vascular SMC can alter the sensitivity of these cells to NO and cGMP. Moreover, these observations suggest an important role for PKG in the regulation of vascular SMC proliferation and apoptosis by NO and cGMP.

Adenoviridae↗

PubMed1998

Cyclic-GMP-binding, cyclic-GMP-specific phosphodiesterase (PDE5) gene expression is regulated during rat pulmonary development.

Increased nitric oxide (NO) production plays a critical role in the mammalian pulmonary vascular adaptation to extrauterine life. NO activates soluble guanylate cyclase, increasing intracellular cGMP concentrations, thereby inducing relaxation of vascular smooth muscle. cGMP is inactivated by cyclic nucleotide phosphodiesterases (PDEs). One PDE isozyme, PDE5, specifically hydrolyzes cGMP, is abundant in lung tissues, and modifies the pulmonary vasodilatory response to exogenous NO. To investigate the regulation of PDE5 gene expression during pulmonary development, PDE5 mRNA levels, as well as cGMP-metabolizing PDE enzyme activity, were measured in the lungs of perinatal and adult rats. RNA blot hybridization revealed that PDE5 mRNA was detectable in fetal lung tissue as early as 18.5 d of the 22-d term gestation and reached maximal levels in neonatal lungs. mRNA levels in adult rat lungs were 3-4-fold less than the levels measured in lungs of 1- and 8-d-old rats. Pulmonary cGMP hydrolytic activity in 1-d-old animals was 30-fold greater than the cGMP hydrolytic activity of adult rat lungs. Zaprinast, a specific PDE5 antagonist, inhibited 52 and 56% of cGMP hydrolytic activity in lungs of 1- and 8-d-old rats, respectively, but only 18% of the activity in adult lungs. In situ hybridization revealed that PDE5 mRNA transcripts were present in the vascular smooth muscle cells of neonatal and adult lungs. PDE5 mRNA was also detected in the alveolar walls of neonatal rat lungs. These results demonstrate that the gene encoding PDE5 is abundantly expressed in the lungs of perinatal rats, and is available to participate in the mammalian pulmonary vascular transition to extrauterine life. Extravascular PDE5 gene expression in neonatal lungs suggests a potentially important nonvascular role for this enzyme during pulmonary development.

3',5'-Cyclic-GMP Phosphodiesterases↗

PubMed1997

Nitric oxide decreases stability of mRNAs encoding soluble guanylate cyclase subunits in rat pulmonary artery smooth muscle cells.

Nitric oxide stimulates soluble guanylate cyclase (sGC) to convert GTP to the intracellular second messenger cGMP. In rat pulmonary artery smooth muscle cells, sGC is an obligate heterodimer composed of alpha1 and beta1 subunits. We investigated the effect of NO donor compounds on sGC subunit gene expression in rat pulmonary artery smooth muscle cells. Sodium nitroprusside and S-nitroso-glutathione decreased sGC subunit mRNA and protein levels, as well as sGC enzyme activity. 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one, an sGC inhibitor, blocked the effect of sodium nitroprusside on sGC subunit gene expression, whereas 8-bromo cGMP decreased subunit mRNA levels, demonstrating that NO-mediated decrease in sGC subunit mRNA levels is cGMP-dependent. sGC subunit mRNA levels decreased more rapidly in rat pulmonary artery smooth muscle cells exposed to NO than in cells exposed to actinomycin D, suggesting that NO decreases sGC subunit mRNA stability. Actinomycin D and cycloheximide blocked the ability of NO to decrease sGC subunit mRNA levels. These results demonstrate that NO decreases sGC subunit mRNA stability via a transcription- and translation-dependent mechanism.

Animals↗

PubMed1997

Pulmonary soluble guanylate cyclase, a nitric oxide receptor, is increased during the perinatal period.

Nitric oxide (NO) has an important role in the pulmonary vasodilatation associated with the transition from fetal to neonatal life. NO activates pulmonary soluble guanylate cyclase (sGC), an obligate heterodimer composed of alpha1- and beta1-subunits, increasing synthesis of guanosine 3',5'-cyclic monophosphate (cGMP) and leading to vasodilation. In this study, regulation of sGC subunit expression during pulmonary development was examined. RNA blot hybridization revealed abundant alpha1- and beta1-subunit mRNA in lungs of late-gestation fetal and neonatal Sprague-Dawley rats, with markedly reduced levels detected in adult lungs. Pulmonary sGC enzyme activity in the presence of 1 mM sodium nitroprusside, a NO-donor compound, was approximately sevenfold greater in 1- and 8-day-old rats than in adult rats (P < 0.03). With the use of immunoblot techniques, pulmonary alpha1-subunit concentrations closely correlated with mRNA levels. With in situ hybridization, alpha1- and beta1-subunit mRNAs were readily detected in pulmonary vascular and bronchial smooth muscle cells as well as alveolar and serosal epithelial cells in lungs of 1-day-old rats. In adult lungs, sGC subunit mRNAs were present at low levels and were found nearly exclusively in bronchial and vascular smooth muscle cells. These results demonstrate that abundant pulmonary sGC is available to respond to the increased NO produced during the perinatal period. High-level expression of sGC subunit genes outside the vasculature of lungs of 1-day-old rats suggests an important role for NO-cGMP signal transduction in the perinatal regulation of pulmonary epithelial function and bronchial tone.

Animals↗

PubMed1996

Hyporesponsiveness to inhaled nitric oxide in isolated, perfused lungs from endotoxin-challenged rats.

Inhaled nitric oxide (iNO) causes selective pulmonary vasodilation and improves oxygenation in patients with the adult respiratory distress syndrome (ARDS). Approximately 30% of ARDS patients fail to respond to iNO. Because sepsis syndrome often accompanies a decreased response to iNO, we investigated NO responsiveness in isolated, perfused lungs from rats exposed to lipopolysaccharide (LPS). Eighteen hours after intraperitoneal injection of 0.5 mg/kg LPS, rat lungs were isolated, perfused, and preconstricted with U-46619. Ventilation with 0.4, 4, and 40 parts per million by volume NO vasodilated LPS-pretreated lungs 75, 47, and 42% less than control lungs (P < 0.01 value differs at each concentration). The diminished vasodilatory response to iNO was associated with decreased NO-stimulated guanosine 3',5'-cyclic monophosphate (cGMP) release into the perfusate. Soluble guanylate cyclase activity did not differ in lung extracts from LPS-pretreated and control rats. LPS increased pulmonary cGMP-phosphodiesterase (PDE) activity by 40%. The PDE-sensitive cGMP analogue 8-bromoguanosine 3',5'-cyclic monophosphate vasodilated lungs from LPS-pretreated rats less than lungs from control rats. In contrast, the PDE-insensitive 8-para-chlorophenylthioguanosine 3',5'-cyclic monophosphate vasodilated lungs equally from both groups. After LPS challenge, the rat pulmonary vasculature becomes hyporesponsive to iNO. Hyporesponsiveness to iNO appears partly attributable to increased pulmonary cGMP-PDE activity.

Administration, Inhalation↗

PubMed1995

Three members of the nitric oxide synthase II gene family (NOS2A, NOS2B, and NOS2C) colocalize to human chromosome 17.

Nitric oxide synthases (NOSs) are a family of enzymes responsible for the synthesis of nitric oxide from L-arginine and molecular oxygen. Three human NOS enzymes (I, II, and III) with differing cellular distribution and regulatory mechanisms have been identified. To determine whether additional NOSs are encoded in the human genome, a bovine NOS II-related cDNA was used to screen two human genomic libraries. Clones containing three independent genes were isolated. One clone encoded the previously identified NOS II gene (NOS2A). The two other genes specified amino acids homologous, but not identical, to human NOS II (NOS2B and NOS2C). Southern blot hybridization demonstrated that all three genes are present in the human genome. DNA from human-mouse somatic cell hybrids were used to determine the chromosomal location of the NOS II-related genes. All three NOS II-related genes colocalized to human chromosome 17 between bands p13.1 and q25. These observations suggest that there is more than one NOS II-related gene in the human genome. This finding may have important implications for the design of NOS isoform-specific inhibitors.

Amino Acid Sequence↗

PubMed1995

Constitutive endothelial nitric oxide synthase gene expression is regulated during lung development.

Nitric oxide (NO), a potent vasodilator, is a free-radical gas synthesized from L-arginine by nitric oxide synthases (NOS). NO appears to have an important role in perinatal changes in pulmonary vascular resistance. We previously identified mRNA encoding the constitutive endothelial NOS (ceNOS) isoform in human pulmonary tissue. To begin investigating functions of this enzyme in perinatal pulmonary development, we measured ceNOS mRNA and immunoreactivity in the developing rat lung. With the use of RNA blot hybridization, abundant pulmonary ceNOS mRNA was detected during the late fetal and postnatal period. The highest levels were detected within 24 h after birth, and elevated mRNA levels persisted for 16 days. In contrast, much lower levels of ceNOS mRNA were found in adult rat lung. With the use of immunoblot techniques, ceNOS protein levels were found to be correlated with mRNA levels. To identify the pulmonary cell types expressing the ceNOS gene, in situ hybridization with a digoxigenin-labeled cRNA probe was performed on sections from lungs of 1-day-old and adult rats. In lungs from 1-day-old rats, ceNOS mRNA was detected in alveolar and serosal epithelial cells as well as in endothelial cells lining small and medium-sized blood vessels. In contrast, in adult lungs, ceNOS gene transcripts were detected in rare endothelial cells. These observations suggest that ceNOS gene expression is regulated during lung development and that ceNOS is available to participate in the postnatal reduction of pulmonary vascular resistance. ceNOS gene expression in nonendothelial cells in the neonatal rat lung suggests that NO may also contribute to nonvascular functions in the developing lung.

Amino Acid Oxidoreductases↗

PubMed1995

In vivo lipopolysaccharide pretreatment inhibits cGMP release from the isolated-perfused rat lung.

Administration of bacterial lipopolysaccharide (LPS) to rats stimulates synthesis of nitric oxide (NO), a free radical molecule that activates soluble guanylate cyclase, thereby increasing intracellular guanosine 3',5'-cyclic monophosphate (cGMP) concentration and inducing systemic vasodilatation. To investigate the effect of endotoxemia on the pulmonary NO/cGMP signal transduction system, we measured the release of cGMP by isolated-perfused lungs of rats that received an intraperitoneal injection of LPS (1 mg/kg) or saline 2 days earlier. Over 90 min, 1.4 +/- 0.78 and 0.079 +/- 0.016 nmol cGMP accumulated in pulmonary perfusates of saline- and LPS-treated rats, respectively (P < 0.05). Despite addition to the perfusate of Zaprinast, superoxide dismutase, or A23187, markedly less cGMP was released from the lungs of rats exposed to LPS than from the lungs of control rats. In contrast, after ventilation with 100 parts per million NO gas, cGMP accumulating in the perfusate of the lungs of both groups of rats was markedly increased, and the quantity of cGMP released from the lungs of LPS-treated rats was similar to that released by control rat lungs (2.8 +/- 0.57 vs. 3.3 +/- 0.88 nmol, P = NS). With the use of immunoblot techniques, equal concentrations of constitutive endothelial NO synthase were detected in the lungs of rats treated with saline or LPS. These results demonstrate that the NO/cGMP signal transduction system is abnormal in the lungs of rats exposed to LPS, at least in part, at the level of endothelial NO synthase activation.

Animals↗