Biomedical subjects

B R Pitt

Publications and source records attributed to B R Pitt.

At least 55 records · Page 3Linked to original sources

PubMed1996

The heat-shock response attenuates lipopolysaccharide-mediated apoptosis in cultured sheep pulmonary artery endothelial cells.

We recently reported that lipopolysaccharide (LPS) induces apoptosis in cultured sheep pulmonary artery endothelial cells (SPAEC). Information about survival signals against this and other stimuli for endothelial cell apoptosis is limited to factors in the extracellular space. In other cell types, apoptosis is also affected by intracellular gene products. The heat-shock response is a highly conserved cellular stress response affording cytoprotection against a variety of cytotoxic conditions. Accordingly, we tested the hypothesis that prior induction of the heat-shock response would affect apoptosis in cultured SPAEC. Exposure of SPAEC to either heat (43 degrees C, 90 min) or sodium arsenite (100 microM, 90 min) induced expression of heat-shock protein-70 (HSP-70). LPS (0.1 microg/ml) treatment of SPAEC induced apoptotic morphology, cell detachment, high molecular weight (> 30 kb) DNA fragmentation, and internucleosomal DNA fragmentation. Prior induction of the heat-shock response attenuated LPS-mediated apoptosis, a protective event associated with a concomitant attenuation of rapid (within minutes) LPS-stimulated superoxide anion (O2.-) generation. Subsequent experiments involving transient overexpression of HSP-70, by direct gene transfer, suggest a direct role for HSP-70 in the attenuation of LPS-mediated apoptosis. We conclude that the heat-shock response is an intracellular survival signal against LPS-mediated apoptosis, and that the protective mechanism may involve HSP-70 directly, as well as inhibition of LPS-mediated O2.- generation.

Animals↗

PubMed1996

Vascular gene transfer of the human inducible nitric oxide synthase: characterization of activity and effects on myointimal hyperplasia.

BACKGROUND: Nitric oxide (NO) has been shown to decrease myointimal hyperplasia in injured blood vessels. We hypothesize inducible No synthase (iNOS) gene transfer even at low efficiency will provide adequate local no production to achieve this goal. MATERIALS AND METHODS: A retroviral vector containing the human iNOS cDNA (DFGiNOS) was used to transfer the iNOS gene into vascular cells and isolated blood vessels to answer the following questions: can vascular endothelial and smooth muscle cells support iNOS activity and will low efficiency iNOS gene transfer suppress myointimal hyperplasia in injured porcine arteries? RESULTS: DFGiNOS-infected sheep pulmonary artery endothelial cells (SPAEC) expressed significant iNOS mRNA and protein, releasing nitrite levels of 155.0 +/- 10.7 nmol/mg protein/24 h vs. 5.5 +/- 1.1 by control cells. Transduced rat smooth muscle cells (RSMC) also expressed abundant iNOS mRNA and protein, but, in contrast to SPAEC, NO synthesis was dependent on exogenous tetrahydrobiopterin (BH4) (291.8 +/- 10.4 nmol nitrite/mg protein/24 hr with BH4, 37.7 +/- 2.6 without BH4). Only porcine arteries infected with DFGiNOS following balloon injury exhibited a 3-fold increase in total NO synthesis and a 15-fold increase in cGMP levels over control vessels in a BH4 dependent fashion, despite only a 1% gene transfer efficiency. Transfer of iNOS completely prevented the 53% increase in myointimal thickness induced by balloon catheter injury; the administration of a NOS inhibitor reversed this effect. CONCLUSIONS: These in vitro findings suggest that vascular iNOS gene transfer may be feasible. Furthermore, a low gene transfer efficiency may be sufficient to inhibit myointimal hyperplasia following arterial balloon injury, although a source of BH4 may be required.

Animals↗

PubMed1995

Loss and degradation of enzyme-bound heme induced by cellular nitric oxide synthesis.

We report here that, like nonheme iron, protein-bound intracellular heme iron is also a target for destruction by endogenously produced nitric oxide (NO). In isolated rat hepatocytes NO synthesis results in substantial (approximately 60%) and comparable loss of catalase and cytochrome P450 as well as total microsomal heme, and decreased heme synthetic (delta-aminolevulinate synthetase and ferrochelatase) and increased degradative (heme oxygenase) enzymatic activities. The effect is reversible, and intact cytochrome P450 apoproteins are still present, as judged by heme reconstitution of isolated microsomes. The effects on delta-aminolevulinate synthetase and heme oxygenase are likely to be secondary to heme liberation, while the effects on ferrochelatase appear to be a direct effect of NO, perhaps destruction of its nonheme iron-sulfur center.

Arginine↗

PubMed1995

Enhanced sensitivity to oxidative stress in cultured embryonic cells from transgenic mice deficient in metallothionein I and II genes.

Embryonic cells from transgenic mice with targeted disruption of metallothionein I and II genes expressed no detectable metallothionein either constitutively or after treatment with cadmium, in contrast to cultured cells that were wild type or heterozygous for the loss of the metallothionein genes. Metallothionein null cells were most sensitive to the cytotoxic effects of cadmium, the membrane permeant oxidant tert-butylhydroperoxide, and the redox cycling toxin paraquat. No marked differences were seen among the wild type, heterozygous, or metallothionein null cells in glutathione levels or in the activity of CuZn-superoxide dismutase, glutathione peroxidase, or catalase. Nevertheless, metallothionein null cells were more sensitive to tert-butylhydroperoxide-induced oxidation as ascertained by confocal microscopic imaging of dichlorofluoroscein fluorescence. These results indicate basal metallothionein levels can function to regulate intracellular redox status in mammalian cells.

Animals↗

PubMed1995

The effect of nitric oxide on fetal pulmonary artery smooth muscle growth.

Endothelium-derived nitric oxide (NO) relaxes fetal pulmonary arterial vessels through activation of guanylate cyclase and increasing smooth muscle cyclic guanosine 3', 5'-monophosphate (cGMP). Exogenous NO administered as a gas at low concentrations shares this effect, decreasing pulmonary artery resistance and increasing in pulmonary blood flow. NO, endogenously synthesized or inhaled as a gas, may affect cellular growth in the underlying pulmonary vascular smooth muscle media. We report the effects of NO and cGMP upon DNA synthesis and proliferation of passaged pulmonary vascular smooth muscle cells from fetal rats. Smooth muscle cells from rat fetal pulmonary artery (RFPASM; 18-19 day gestation; term 21 days) were treated in culture with sodium nitroprusside (SNP), isosorbide dinitrite (ISDN)--both NO-generating vasodilators--or 8-bromo-cGMP, a cell-permeant cGMP analog. All agents inhibited thymidine uptake at concentrations of 10(-3)-10(-2) M. Lower concentrations (10(-5)-10(-4) M) of SNP and ISDN increased [3H]-thymidine ([3H]TdR) uptake, an effect not seen with cGMP at similar concentrations. Exposing RFPASM to authentic NO gas in a deoxygenated medium inhibited [3H]TdR uptake only. NO appears to have a biphasic effect on DNA synthesis in passaged RFPASM, with stimulation at micromolar concentrations and inhibition at higher levels. NO may thus alter vascular smooth muscle growth and pulmonary vascular remodeling in conditions complicated by pulmonary hypertension and treated with inhaled NO.

Animals↗

PubMed1995

Phenoxyl radicals of etoposide (VP-16) can directly oxidize intracellular thiols: protective versus damaging effects of phenolic antioxidants.

Phenolic compounds can act as radical scavengers due to their ability to donate a mobile hydrogen to peroxyl radicals producing a phenoxyl radical if the phenoxyl radical formed in the radical scavenging reaction efficiently interacts with vitally important biomolecules, then this interaction may result in cytotoxic effects rather than in antioxidant protection. In the present work we have chosen two model compounds--a phenolic antitumor drug, VP-16, known to be highly cytotoxic, and a homolog of vitamin E, 2,2,5,7,8-pentamethyl-6-hydroxychromane (PMC)--as typical representatives of phenoxyl radicals to study interactions of their phenoxyl radicals with intracellular thiols. Using a water-soluble source of peroxyl radicals, the azo-initiator 2,2'-azobis(2-aminodinopropane) (AAPH), we found that both PMC and VP-16 are very efficient scavengers of peroxyl radicals as evidenced by their ability to inhibit AAPH-induced chemiluminescence of luminol and oxidation of PnA incorporated into DOPC liposomes. Both PMC and VP-16 were also able to protect against AAPH-induced oxidative degradation of DNA in nuclei from human leukemic K562 cells. In contrast, there was a dramatic difference in the ability of VP-16 and PMC to protect GSH against AAPH-induced oxidation: while PMC inhibited AAPH-induced oxidation of GSH in a concentration-dependent manner, VP-16 did not protect GSH against oxidation. We hypothesized that this was due to different reactivities of the phenoxyl radicals formed by AAPH-derived peroxyl radicals from VP-16 and PMC toward GSH. To substantiate this hypothesis, we compared interactions of the phenoxyl radicals generated from VP-16 and PMC with intracellular thiols in K562 cell homogenates. While the PMC phenoxyl radicals were only slightly affected by thiols, the VP-16 phenoxyl radicals were reduced by thiols. This is evidenced by (i) a significant inhibition of the tyrosinase-induced VP-16 consumption upon addition of K562 cell homogenates, (ii) a depletion of endogenous thiols in K562 cell homogenates induced by VP-16+tyrosinase, (iii) a transient disappearance of the VP-16 phenoxyl radical signal from the ESR spectra and its reappearance after depletion of endogenous thiols, and (iv) elimination of the lag period for the appearance of the VP-16 phenoxyl radical ESR signal subsequent to depletion of thiols by mersalyl acid. To evaluate the contribution of GSH and protein thiols to reduction of the VP-GSH-peroxidase + cumeme hydroperoxide to specifically deplete endogenous GSH.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1995

Nitric oxide and intracellular heme.

Figure 2 depicts a working hypothesis for these results. Activation of .NO synthesis results in nitrogen oxide-induced loss of protein-bound heme from CYP proteins, which remain relatively intact. This heme liberation results in a decrease in heme synthesis (decreased ALAS) and an increase in heme degradation (increased HO). In addition, .NO synthesis results in direct inhibition of ferrochelatase, which further contributes to inhibition of heme synthesis. There also appears to be a mechanism to repair or resynthesize CYP after .NO synthesis is inhibited. Finally, a result of this effect may be protection against cellular injury, since increased HO is an important response against cellular injury from a variety of insults.

Animals↗

PubMed1995

Metallothioneins and cell death by anticancer drugs.

Both pharmacologic and genetic methods are now available to manipulate intracellular levels of the protein thiol metallothionein. These approaches have begun to reveal the protective roles metallothioneins (MTs) have against oxygen, nitrogen, and carbon-centered free radicals, as well as the contributory role of MT to resistance to a broad range of electrophilic therapeutic agents, including antineoplastic drugs. We suggest MTs are enlisted to act as primative antioxidant defense mechanisms in mammalian cells and, thus, may have widespread importance in the biology of cell death.

Animals↗

PubMed1995

Pulmonary alveolar epithelial inducible NO synthase gene expression: regulation by inflammatory mediators.

Nitric oxide (.NO) is a short-lived mediator that can be induced by different cytokines and lipopolysaccharide (LPS) in a variety of cell types and produces many physiological and metabolic changes in target cells. In the current study, we show that a combination of cytokines, LPS, and zymosan-activated serum (ZAS; called for convenience cytomix Z) induces production of high concentrations of the NO oxidation products nitrite (NO2-) and nitrate (NO3-) by cultured rat fetal lung epithelial type II cells in a time-dependent fashion. Interferon-gamma and tumor necrosis factor-alpha alone did not significantly affect .NO synthesis, whereas ZAS, LPS, and interleukin-1 beta caused only a modest increase in formation of .NO oxidation products. Production of NO2- and NO3- was inhibited by NG-monomethyl-L-arginine and cyclohexmide. After exposure of these cells to a combination of the above cytokines, Escherichia coli LPS, and ZAS (cytomix Z), enhanced inducible nitric oxide synthase (iNOS) expression was indicated by an elevation in steady-state mRNA specific for iNOS (via Northern blot analysis) and increased immunofluorescence for iNOS after cell permeabilization, incubation with anti-iNOS antibody, and treatment with Cy3.18-conjugated rabbit-specific antibody. The extent of inflammatory mediator-induced.NO production by alveolar epithelium, which exceeds that of other lung cell types, reveals new insight into mechanisms of pulmonary host defense and pathways of free radical-mediated lung injury.

Amino Acid Oxidoreductases↗

PubMed1995

TGF-beta regulates production of NO in pulmonary artery smooth muscle cells by inhibiting expression of NOS.

We have previously reported that a mixture of lipopolysaccharide and cytokines stimulates cultured rat pulmonary artery smooth muscle cells (RPASM) to express elevated levels of mRNA for inducible nitric oxide synthase (iNOS), and to produce large amounts of nitric oxide (NO). The current study tests the hypothesis that transforming growth factor-beta (TGF-beta) modulates this process. Accordingly, RPASM were treated with a mixture of LPS (10 micrograms/ml) and the cytokines interleukin-1 beta (5 U/ml), tumor necrosis factor-alpha (500 U/ml), and interferon-gamma (100 U/ml). In the absence of TGF-beta 1, NO production (indicated by colorimetric assay of cumulative nitrite levels at 24 h) was greatly increased, as previously observed. Under identical conditions, TGF-beta 1 caused a concentration-dependent decrease in NO production. The addition of neither excess L-arginine nor sepiapterin reversed the inhibition, indicating that the effect of TGF-beta 1 was not due to limitation of enzyme substrate or cofactor tetrahydrobiopterin, respectively. Northern and Western analyses showed that TGF-beta 1 reduced levels of iNOS mRNA and protein to baseline at all time points examined up to 24 h. Complete suppression of iNOS protein expression was evident even when TGF-beta 1 was added at postinduction time points. One mechanism of action of TGF-beta 1 was demonstrated in experiments in which degradation of iNOS protein was greatly increased by the addition of TGF-beta 1. These results demonstrate that TGF-beta 1 regulates production of NO in RPASM by inhibiting iNOS expression in part by increasing degradation of existing iNOS protein.

Amino Acid Oxidoreductases↗

PubMed1995

Collagen is a survival factor against LPS-induced apoptosis in cultured sheep pulmonary artery endothelial cells.

Lipopolysaccharide (LPS) causes direct pulmonary endothelial injury that can precipitate cell death. We investigated the ability of LPS to produce apoptosis in sheep pulmonary artery endothelial cells (SPAEC) grown in monolayer on plastic or collagen. When SPAEC were grown on plastic, LPS (100 ng/ml) caused internucleosomal DNA fragmentation (IDF) to 180- to 200-base pair ladders after 4 h. Higher-order chromatin damage, producing 50-kilobase DNA fragments, occurred within 2 h. Significant DNA strand breaks were seen in attached cells within 1 h incubation with > or = 1 ng LPS/ml, using in situ labeling by break extension (ISBE). DNA strand breakage in attached cells peaked after 2 h and remained elevated after 4 h. Detachment of SPAEC from the monolayer did not begin until 4 h. SPAEC cultured on collagen were protected from LPS-induced apoptosis; DNA damage measured by IDF, high-molecular-weight DNA fragmentation, and ISBE were suppressed. The protective effect of collagen was not due to inactivation of LPS. Thus LPS-induced apoptosis occurs in SPAEC after genotoxic damage and this process is suppressed by the extracellular matrix.

Animals↗

PubMed1995

Expression of iNOS in cultured rat pulmonary artery smooth muscle cells is inhibited by the heat shock response.

The heat shock response is a highly conserved stress response known to alter patterns of gene expression in many cell types. We hypothesized that interleukin-1 beta (IL-1 beta)-mediated inducible nitric oxide synthase (iNOS) gene expression would be inhibited after induction of the heat shock response in cultured rat pulmonary artery smooth muscle cells (RPASMC). Exposure of RPASMC to sodium arsenite or heat led to expression of heat shock protein-70 (HSP-70) in a time- and concentration-dependent manner. Prior induction of the heat shock response inhibited IL-1 beta-mediated iNOS gene expression in a time- and dose-dependent manner. The inhibitory effects were not due to cytotoxicity, since cell viability was not affected by either sodium arsenite, heat, IL-1 beta, or their combination. Transcriptional analysis via transient transfection of the murine macrophage iNOS promoter [-1592 and -367 base pairs (bp)], upstream from the reporter gene luciferase, revealed that the heat shock response did not affect IL-1 beta-mediated promoter activation, as measured by luciferase activity. We conclude that induction of the heat shock response inhibits IL-1 beta-mediated iNOS gene expression in cultured RPASMC.

Animals↗

PubMed1995

Induction of lipopolysaccharide-binding protein gene expression in cultured rat pulmonary artery smooth muscle cells by interleukin 1 beta.

Lipopolysaccharide (LPS)-binding protein (LBP) binds with high affinity to LPS, and the LBP-LPS complex enhances cellular inflammatory responses to LPS. Although it is present in normal serum, LBP is also induced as part of the acute phase response. Synthesis of LBP is though to be limited to the liver, but we have recently reported significant extrahepatic (including pulmonary) LBP mRNA expression in in vivo rat models of sepsis and inflammation. In the present study, we tested the hypothesis that a cellular source of pulmonary LBP in the rat may be vascular smooth muscle, by exposing cultured rat pulmonary artery smooth muscle cells (RPASMC) to cytokines and LPS. Treatment of RPASMC for 4 and 24 h with a combination of tumor necrosis factor alpha, interleukin 1 beta (IL-1 beta), interferon gamma, and LPS resulted in significant LBP mRNA expression. Of this mixture, IL-1 beta alone was sufficient to induce LBP mRNA expression in both a time- and dose-dependent manner. The effects of IL-beta on LBP mRNA expression were significantly antagonized by IL-1 receptor antagonist protein. Furthermore, supernatants from RPASMC treated with IL-1 beta enhanced the binding of [125I]ASD-LPS by the macrophage cell line RAW 264.7, indicative of LBP bioactivity. We conclude that pulmonary artery smooth muscle cells stimulated with IL-1 beta produce a transcript for LBP or a homologous product in vitro. Local production of LBP could play an important role in the pulmonary response to inflammation and sepsis.

Acute-Phase Proteins↗

PubMed1995

Retrovirus-mediated gene transfer in lungs of living fetal sheep.

In utero somatic gene transfer may be a useful therapeutic strategy for a variety of inherited disorders. In the present study, we demonstrate transgene expression in the airways of fetal lamb lungs, 2-3 weeks after injection of Moloney murine leukemia retrovirus based vectors containing cDNA for beta-galactosidase (lacZ) or human interleukin receptor antagonist protein (IRAP), into the fluid filled future airspace of fully catheterized twin fetal lambs (104-117 days gestational age; term 147 days). Expression of lacZ or IRAP was limited to the twin that received the respective vector and was apparent, at light microscopic level, in the epithelium and submucosal space of proximal airways, and to a lesser extent, in the respiratory epithelium of the distal airways. These data demonstrate for the first time that transfer of foreign DNA to fetal lung can be accomplished. These findings support the use of retroviral vectors for somatic lung DNA transfer and suggest that inherited disorders such as cystic fibrosis may be approached therapeutically via gene transfer, in utero.

Animals↗

PubMed1994

Gene therapy and endothelial cell targeting for cancer.

The endothelium represents a potentially critical target for gene therapy because of its anatomical location and its importance in the viability in both normal and malignant tissues. Protecting the endothelium of normal tissues, such as the lungs, from the toxic effects of current antineoplastic agents and the destruction of the tumor vasculature are reasonable goals. As a target, however, the endothelium continues to represent a significant challenge. While gene delivery to cultured endothelial cells is possible, improved delivery systems are required, as well as cell-specific promoters, before in vivo gene therapy to important endothelial populations can be accomplished.

Amino Acid Sequence↗

PubMed1994

Cytoplasmic metallothionein overexpression protects NIH 3T3 cells from tert-butyl hydroperoxide toxicity.

Metallothioneins (MT) are ubiquitous low molecular weight metal-binding proteins that may act as antioxidants. We examined the sensitivity of NIH 3T3 cells transfected with a plasmid containing mouse metallothionein-I gene (NIH3T3/MT) to the membrane permeant oxidant, tert-butyl hydroperoxide (tBH). NIH3T3/MT cells had a 4-fold increase in intracellular metallothionein as compared to cells transfected with a plasmid containing an inverted gene (NIH3T3/TM). Newly expressed metallothionein appeared to be localized to the cytoplasm as determined by immunofluorescence and confocal microscopy. NIH3T3/MT cells were 6 times more resistant than NIH3T3/TM cells to the cytotoxic effects of tBH. The antioxidant activity of NIH3T3/MT cells was greater than NIH3T3/TM cells, since exposure to tBH resulted in significantly less: (a) thiobarbituric acid-reactive substances and (b) fluorescence after loading cells with the oxidant-sensitive dye, 2'7'-dichlorodihydrofluorescein diacetate. Furthermore, homogenates of NIH3T3/MT cells were more capable of scavenging in vitro generated phenoxyl radicals as quantified by electron spin resonance detection. In contrast, overexpression of cytoplasmic MT did not protect against tBH-induced DNA damage, suggesting that subcellular location of MT is important for its function and that DNA damage is not a key determinant of cytotoxicity. These data provide direct support for an antioxidant role for MT, since physiologically relevant elevations in cytoplasmic MT interfere with tBH-induced cytotoxic peroxidation.

3T3 Cells↗

PubMed1994

Serotonin increases DNA synthesis in rat proximal and distal pulmonary vascular smooth muscle cells in culture.

Cultured smooth muscle cells obtained from rat lung periphery (RPC) and proximal pulmonary artery (RSMC) expressed mRNA for serotonin (5-HT) type 2 receptor (5-HT2) and 5-HT transporter (by Northern blot analysis). Functional expression of these genes was evident since both cell types 1) bound 125I-labeled lysergic acid diethylamide (LSD; 5-HT2 receptor antagonist) that was equally effectively displaced by either ketanserin or mianserin; and 2) transported 5-[3H]HT in an imipramine-sensitive manner. Serotonin (10(-9)-10(-5) M) stimulated DNA synthesis (as measured by [3H]thymidine uptake) in RPC and RSMC. The 5-HT-induced increase in DNA synthesis was significantly inhibited in both cell types by the 5-HT2 receptor antagonist, ketanserin (10(-7)-10(-6) M), and by fluoxetine (10(-6) M), a putative 5-HT transport inhibitor. Acute exposure to 5-HT (1-100 microM) caused an abrupt rise in intracellular calcium ([Ca2+]i) in single pulmonary vascular smooth muscle cells as microspectrofluorometrically determined using the calcium-sensitive dye, fura 2. The 5-HT-induced change in [Ca2+]i was completely abolished in the presence of 10(-6) M ketanserin as well as imipramine or fluoxetine (10(-6) M). The calcium transients due to 5-HT persisted in a Na(+)-free condition (in which the transporter activity was completely abolished) and imipramine and fluoxetine (and ketanserin) were effective inhibitors of 5-HT under these conditions. Therefore, the 5-HT2 receptor, but not the transporter, is responsible for initiating the acute effects (e.g., calcium transients) of 5-HT in cultured rat pulmonary vascular smooth muscle cells and fluoxetine (1 microM) may have 5-HT2-receptor antagonist properties.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1994

Tetrahydrobiopterin synthesis and inducible nitric oxide production in pulmonary artery smooth muscle.

We recently reported (Am. J. Respir. Cell Mol. Biol. 7: 471-476, 1992) that a mixture of lipopolysaccharide (LPS) and cytokines produced a time-dependent increase in mRNA and protein expression of inducible nitric oxide synthase (iNOS) in cultured rat pulmonary artery smooth muscle cells (RPASM). In the current study we extend observations on regulation of iNOS in RPASM by showing that de novo synthesis of tetrahydrobiopterin (BH4) is critical for LPS and cytokine-induced NO production. A mixture of LPS and the cytokines gamma-interferon, interleukin-1 beta, and tumor necrosis factor-alpha increased steady-state levels of mRNA of GTP-cyclohydrolase-I (GTP-CH), the rate-limiting enzyme in BH4 biosynthesis. Levels of mRNA to GTP-CH became detectable by 4 h, with further increases at 24 h by Northern blot analysis and reverse-transcriptase polymerase chain reaction. Total intracellular biopterin levels, undetectable under basal conditions, increased after 24 h exposure to LPS and cytokines (to 32.3 +/- 0.8 pmol/mg protein). LPS and cytokine-induced NO production, determined by nitrite concentrations in the medium, was decreased in a concentration-dependent manner by the GTP-CH inhibitor, 2,4-diamino-6-hydroxypyrimidine (DAHP) at 24 h. DAHP also inhibited completely the LPS- and cytokine-induced accumulation of intracellular biopterins. Sepiapterin, which supplies BH4 through a salvage pathway independent of GTP-CH, reversed the effect of DAHP on LPS and cytokine-induced NO production.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗