Overexpression of cationic amino acid transporter-1 increases nitric oxide production in hypoxic human pulmonary microvascular endothelial cells

1. The endogenous production of and/or the bioavailability of nitric oxide (NO) is decreased in pulmonary hypertensive diseases. L-arginine (L-arg) is the substrate for NO synthase (NOS). L-arg is transported into cells via the cationic amino acid transporters (CAT), of which there are two isoforms in endothelial cells, CAT-1 and CAT-2. 2. To test the hypothesis that hypoxia will decrease CAT expression and L-arg uptake resulting in decreased NO production in human pulmonary microvascular endothelial cells (hPMVEC), cells were incubated in either normoxia (21% O(2), 5% CO(2), balance N(2)) or hypoxia (1% O(2), 5% CO(2), balance N(2)). 3. The hPMVEC incubated in hypoxia had 80% less NO production than cells incubated in normoxia (P < 0.01). The hPMVEC incubated in hypoxia had significantly lower CAT-2 mRNA levels than normoxic hPMVEC (P < 0.005), and the transport of L-arg was 40% lower in hypoxic than in normoxic hPMVEC (P < 0.01). In hypoxic cells, overexpression of CAT-1 resulted in significantly greater L-arg transport and NO production (P < 0.05). 4. These results demonstrate that in hPMVEC, hypoxia decreased CAT-2 expression, L-arg uptake and NO production. Furthermore, the hypoxia-induced decrease in NO production in hPMVEC can be attenuated by overexpressing CAT in these cells. We speculate that the CAT may represent a novel therapeutic target for treating pulmonary hypertensive disorders.

Hypoxia-induced pulmonary endothelin-1 expression is unaltered by nitric oxide

Nitric oxide (NO) attenuates hypoxia-induced endothelin (ET)-1 expression in cultured umbilical vein endothelial cells. We hypothesized that NO similarly attenuates hypoxia-induced increases in ET-1 expression in the lungs of intact animals and reasoned that potentially reduced ET-1 levels may contribute to the protective effects of NO against the development of pulmonary hypertension during chronic hypoxia. As expected, hypoxic exposure (24 h, 10% O(2)) increased rat lung ET-1 peptide and prepro-ET-1 mRNA levels. Contrary to our hypothesis, inhaled NO (iNO) did not attenuate hypoxia-induced increases in pulmonary ET-1 peptide or prepro-ET-1 mRNA levels. Because of this surprising finding, we also examined the effects of NO on hypoxia-induced increases in ET peptide levels in cultured cell experiments. Consistent with the results of iNO experiments, administration of the NO donor S-nitroso-N-acetyl-penicillamine to cultured bovine pulmonary endothelial cells did not attenuate increases in ET peptide levels resulting from hypoxic (24 h, 3% O(2)) exposure. In additional experiments, we examined the effects of NO on the activity of a cloned ET-1 promoter fragment containing a functional hypoxia inducible factor-1 binding site in reporter gene experiments. Whereas moderate hypoxia (24 h, 3% O(2)) had no effect on ET-1 promoter activity, activity was increased by severe hypoxic (24 h, 0.5% O(2)) exposure. ET-1 promoter activity after S-nitroso-N-acetyl-penicillamine administration during severe hypoxia was greater than that in normoxic controls, although activity was reduced compared with that in hypoxic controls. These findings suggest that hypoxia-induced pulmonary ET-1 expression is unaffected by NO.

Safety and Efficacy of AAV Retrograde Pancreatic Ductal Gene Delivery in Normal and Pancreatic Cancer Mice

Recombinant adeno-associated virus (rAAV)-mediated gene delivery shows promise to transduce the pancreas, but safety/efficacy in a neoplastic context is not well established. To identify an ideal AAV serotype, route, and vector dose and assess safety, we have investigated the use of three AAV serotypes (6, 8, and 9) expressing GFP in a self-complementary (sc) AAV vector under an EF1α promoter (scAAV.GFP) following systemic or retrograde pancreatic intraductal delivery. Systemic delivery of scAAV9.GFP transduced the pancreas with high efficiency, but gene expression did not exceed >45% with the highest dose, 5 × 10¹² viral genomes (vg). Intraductal delivery of 1 × 10¹¹ vg scAAV6.GFP transduced acini, ductal cells, and islet cells with >50%, ∼48%, and >80% efficiency, respectively, and >80% pancreatic transduction was achieved with 5 × 10¹¹ vg. In a Kras^G12D-driven pancreatic cancer mouse model, intraductal delivery of scAAV6.GFP targeted acini, epithelial, and stromal cells and exhibited persistent gene expression 5 months post-delivery. In normal mice, intraductal delivery induced a transient increase in serum amylase/lipase that resolved within a day of infusion with no sustained pancreatic inflammation or fibrosis. Similarly, in PDAC mice, intraductal delivery did not increase pancreatic intraepithelial neoplasia progression/fibrosis. Our study demonstrates that scAAV6 targets the pancreas/neoplasm efficiently and safely via retrograde pancreatic intraductal delivery.

L-Arginine uptake and metabolism following in vivo silica exposure in rat lungs

Pulmonary inflammation increases nitric oxide (NO) production via inducible nitric oxide synthase (iNOS). This study was performed to determine some of the factors that affect the availability of the NOS substrate, L-arginine (L-arg), in the intact lung subjected to silica-induced inflammation. Nitrate production, as an index of NO production, was significantly greater in silica-exposed lungs (53.5 +/- 12.1 nmol/90 min) compared with controls (22.5 +/- 5.1 nmol/90 min, P < 0.05). This was accompanied by greater (P < 0.0001) 90-min [(3)H]L-arg uptake (62 +/- 3% control, 82 +/- 1% silica), a significantly (P < 0.005) increased permeability-surface area product for L-arg (0.28 +/- 0.05 ml/min control, 0.63 +/- 0.07 ml/min silica), and a significantly (P < 0.001) increased urea production (1.16 +/- 0.08 micromol/90 min control, 1.77 +/- 0.06 micromol/90 min silica). There was no difference in eNOS protein between groups and eNOS mRNA was not detectable in either group, whereas silica exposure resulted in the appearance of both iNOS protein and mRNA. Silica exposure increased CAT-1 and CAT-2 mRNA approximately 8-fold compared with controls. We conclude that the increase in NO production in silica-exposed lungs was associated with increased L-arg uptake from the vasculature, presumably resulting from increased CAT-1 and CAT-2, and by increased L-arg metabolism via arginase.

Cytokine-induced arginase activity in pulmonary endothelial cells is dependent on Src family tyrosine kinase activity

We hypothesized that the Src family tyrosine kinases (STKs) are involved in the upregulation of arginase and inducible nitric oxide synthase (iNOS) expression in response to inflammatory stimuli in pulmonary endothelial cells. Treatment of bovine pulmonary arterial endothelial cells (bPAEC) with lipopolysaccharide and tumor necrosis factor-alpha (L/T) resulted in increased urea and nitric oxide (NO) production, and this increase in urea and NO production was inhibited by the STK inhibitor PP1 (10 microM). The STK inhibitors PP2 (10 microM) and herbimycin A (10 microM) also prevented the L/T-induced expression of both arginase II and iNOS mRNA in bPAEC. Together, the data demonstrate a central role of STK in the upregulation of both arginase II and iNOS in bPAEC in response to L/T treatment. To identify the specific kinase(s) required for the induction of urea and NO production, we studied human pulmonary microvascular endothelial cells (hPMVEC) so that short interfering RNA (siRNA) techniques could be employed. We found that hPMVEC express Fyn, Yes, c-Src, Lyn, and Blk and that the protein expression of Fyn, Yes, c-Src, and Lyn could be inhibited with specific siRNA. The siRNA targeting Fyn prevented the cytokine-induced increase in urea and NO production, whereas siRNAs specifically targeting Yes, c-Src, and Lyn had no appreciable effect on cytokine-induced urea and NO production. These findings support our hypothesis that inflammatory stimuli lead to increased urea and NO production through a STK-mediated pathway. Furthermore, these results indicate that the STK Fyn plays a critical role in this process.

L-lysine decreases nitric oxide production and increases vascular resistance in lungs isolated from lipopolysaccharide-treated neonatal pigs

Nitric oxide (NO) production may depend on the uptake of L-arginine (L-arg), the substrate for NO synthase in inflammatory lung diseases. The cellular transport of L-arg occurs via the cationic amino acid transporters (CAT), and L-lysine (L-lys) competitively inhibits CAT. Neonatal pigs were treated with lipopolysaccharide (LPS) or vehicle for 4 h. LPS increased exhaled NO (exNO; 0.026 +/- 0.003 to 0.046 +/- 0.003 nmol. kg(-1). min(-1); p < 0.005) and decreased mean systemic arterial blood pressure (89 +/- 4 to 67 +/- 4 mm Hg; p < 0.05), whereas vehicle did not affect exNO or mean systemic arterial blood pressure. The lungs were then isolated and perfused; exNO was greater in lungs from LPS-treated animals (0.08 +/- 0.01 nmol/kg/min) than in lungs from vehicle-treated animals (0.05 +/- 0.01 nmol. kg(-1). min(-1); p < 0.05). The addition of L-arg (0.3 mM) significantly (p < 0.05) increased exNO production in both groups of lungs (mean increase 0.04 +/- 0.01 nmol. kg(-1). min(-1) LPS-treated lungs, p < 0.05; mean increase 0.02 +/- 0.01 nmol. kg(-1). min(-1) vehicle-treated lungs); however, L-arg decreased pulmonary vascular resistance (PVR) only in LPS-treated lungs (mean decrease 0.03 +/- 0.01 mm Hg. ml(-1). kg(-1). min(-1), p < 0.05). L-lys caused a dose-dependent decrease in exNO production and a dose-dependent increase in PVR in LPS-treated lungs. L-lys decreased exNO only at 30 mM and had no effect on PVR in vehicle-treated lungs. In four lungs each from vehicle- and LPS-treated animals, reverse transcriptase-PCR demonstrated CAT-2 mRNA only in LPS-treated animals. These results suggest that the increased NO production in the lungs from LPS-treated animals depends on the uptake of vascular L-arg.

A single nucleotide polymorphism in the dimethylarginine dimethylaminohydrolase gene is associated with lower risk of pulmonary hypertension in bronchopulmonary dysplasia

AIM

Pulmonary hypertension (PH) develops in 25-40% of bronchopulmonary dysplasia (BPD) patients, substantially increasing mortality. We have previously found that asymmetric dimethylarginine (ADMA), an endogenous inhibitor of nitric oxide (NO) production, is elevated in patients with BPD-associated PH. ADMA is metabolised by N(ᴳ) ,N(ᴳ) -dimethylarginine dimethylaminohydrolase (DDAH). Presently, we test the hypothesis that there are single nucleotide polymorphisms (SNPs) in DDAH1 and/or DDAH2 associated with the development of PH in BPD patients.

METHODS

BPD patients were enrolled (n = 98) at Nationwide Children's Hospital. Clinical characteristics and 36 SNPs in DDAH1 and DDAH2 were compared between BPD-associated PH patients (cases) and BPD-alone patients (controls).

RESULTS

In BPD patients, 25 (26%) had echocardiographic evidence of PH (cases). In this cohort, DDAH1 wild-type rs480414 was 92% sensitive and 53% specific for PH in BPD, and the DDAH1 SNP rs480414 decreased the risk of PH in an additive model of inheritance (OR = 0.39; 95% CI [0.18-0.88], p = 0.01).

CONCLUSION

The rs480414 SNP in DDAH1 may be protective against the development of PH in patients with BPD. Furthermore, the DDAH1 rs480414 may be a useful biomarker in developing predictive models for PH in patients with BPD.

Gene transfer with inducible nitric oxide synthase decreases production of urea by arginase in pulmonary arterial endothelial cells

Nitric oxide (NO) is a vasodilator produced from L-arginine (L-Arg) by NO synthase (NOS). Gene therapy for hypertensive disorders has been proposed using the inducible isoform of NOS (iNOS). L-Arg also can be metabolized to urea and L-ornithine (L-Orn) by arginase, and L-Orn can be metabolized to proline and/or polyamines, which are vital for cellular proliferation. To determine the effect of iNOS gene transfer on arginase, we transfected bovine pulmonary arterial endothelial cells (bPAEC) with an adenoviral vector containing the gene for iNOS (AdiNOS). As expected, NO production in AdiNOS bPAEC was substantially greater than in control bPAEC. Although urea production was significantly less in the AdiNOS bPAEC than in the control bPAEC, despite similar levels of arginase I protein, AdiNOS transfection of bPAEC had no effect on the uptake of L-Arg. Inhibiting NO production with Nomega-nitro-L-arginine methyl ester increased urea production, and inhibiting urea production with L-valine increased nitrite production, in AdiNOS bPAEC. The addition of L-Arg to the medium increased urea production by AdiNOS bPAEC in a concentration-dependent manner. Thus, in these iNOS-transfected bPAEC, the transfected iNOS and native arginase compete for a common intracellular pool of L-Arg. This competition for substrate resulted in impaired proliferation in the AdiNOS-transfected bPAEC. These findings suggest that the use of iNOS gene therapy for pulmonary hypertensive disorders may not only be beneficial through NO-mediated pulmonary vasodilation but also may decrease vascular remodeling by limiting L-Orn production by native arginase.

Induction of T-Cell Infiltration and Programmed Death Ligand 2 Expression by Adeno-Associated Virus in Rhesus Macaque Skeletal Muscle and Modulation by Prednisone

Use of adeno-associated virus (AAV) to transduce genes into skeletal muscles can be associated with T-cell responses to viral capsid and/or to transgenic protein. Intramuscular mononuclear cell infiltrates primarily consisting of CD8+ T cells and also containing FOXP3+ regulatory T cells were present in rhesus macaque skeletal muscle treated with rAAVrh74.MCK.GALGT2 by vascular delivery. Administration of oral prednisone prior to AAV gene delivery and throughout the study reduced such infiltrates by 60% at 24 weeks post AAV delivery compared with AAV-treated animals not receiving prednisone, regardless of the presence of pre-existing AAV serum antibodies at the time of treatment. The majority of CD8+ T cells in AAV-treated muscles expressed activated caspase 3 and programmed cell death protein 1 (PD1), suggesting ongoing programmed cell death. AAV-transduced skeletal muscles also had elevated expression of programmed death ligand 2 (PDL2) on skeletal myofibers, and this increase in expression extended to muscles where transgene was not overexpressed. These data demonstrate that prednisone can reduce the extent of intramuscular T-cell infiltrates in AAV-treated muscles, which may aid in achieving long-term transgene expression, as may the induction of PDL2 expression on skeletal myofibers to promote PD1-mediated programmed T-cell death.

Maturational changes in the regulation of pulmonary vascular tone by nitric oxide in neonatal rats

Nitric oxide (NO) is an important regulator of vasomotor tone in the pulmonary circulation. We tested the hypothesis that the role NO plays in regulating vascular tone changes during early postnatal development. Isolated, perfused lungs from 7- and 14-day-old Sprague-Dawley rats were studied. Baseline total pulmonary vascular resistance (PVR) was not different between age groups. The addition of KCl to the perfusate caused a concentration-dependent increase in PVR that did not differ between age groups. However, the nitric oxide synthase (NOS) inhibitor N(omega)-nitro-L-arginine augmented the K(+)-induced increase in PVR in both groups, and the effect was greater in lungs from 14-day-old rats vs. 7-day-old rats. Lung levels of total endothelial, inducible, and neuronal NOS proteins were not different between groups; however, the production rate of exhaled NO was greater in lungs from 14-day-old rats compared with those of 7-day-old rats. Vasodilation to 0.1 microM of the NO donor spermine NONOate was greater in 14-day lungs than in 7-day lungs, and lung levels of both soluble guanylyl cyclase and cGMP were greater at 14 days than at 7 days. Vasodilation to 100 microM of the cGMP analog 8-(4-chlorophenylthio)guanosine-3',5'-cyclic monophosphate was greater in 7-day lungs than in 14-day lungs. Our results demonstrate that the pulmonary vascular bed depends more on NO production to modulate vascular tone at 14 days than at 7 days of age. The observed differences in NO sensitivity may be due to maturational increases in soluble guanylyl cyclase protein levels.

Lung development alterations in newborn mice after recovery from exposure to sublethal hyperoxia

Exposure of newborn mice to hyperoxia arrests lung development, with resultant pathological characteristics similar to bronchopulmonary dysplasia in infants born prematurely. We tested the hypothesis that aberrations in lung development caused by 14 days of sublethal hyperoxia would be reversed during 14 days of recovery to room air (RA) when the concentration of oxygen exposure was weaned gradually. Newborn FVB mice were exposed to 85% oxygen or RA for 14 days. Weaning from hyperoxia was by either transfer directly into RA or a decrease in the concentration of oxygen by 10% per days. At 28 days, pups were euthanized, and the lungs were inflation fixed and assessed. At postnatal day 28, lungs of mice weaned abruptly from hyperoxia had fewer (6 ± 0.6 versus 10 ± 0.7; P < 0.001) alveoli per high-powered field and larger alveoli (4050 ± 207 versus 2305 ± 182 μm(2)) than animals weaned gradually; both hyperoxia-exposed groups were different from lungs obtained from air-breathing controls (20 ± 0.5 alveoli per high-powered field; P < 0.001). The results are consistent with the absence of catch-up alveolarization in this model and indicate that the long-term consequences of early exposures to hyperoxia merit closer examination. The effects of abrupt weaning to RA observed further suggest that weaning should be considered in experimental models of newborn exposure to hyperoxia.

Deficiency of mitogen-activated protein kinase phosphatase-1 results in iNOS-mediated hypotension in response to low-dose endotoxin

Mitogen-activated protein kinase phosphatase-1 (MKP-1) is essential in limiting the proinflammatory response to lipopolysaccharide (LPS). We hypothesized that Mkp-1(-/-) mice would respond to low-dose LPS with a fall in blood pressure due to augmented expression of inducible nitric oxide (NO) synthase (iNOS). To test this hypothesis, Mkp-1(-/-) mice and their wild-type littermates were treated with 10 microg/kg iv LPS, and mean arterial blood pressure (MAP) and exhaled NO production (exNO) were measured. Tissues were harvested for an assessment of iNOS protein levels. Wild-type mice had no change in MAP or exNO during the experimental period, whereas Mkp-1(-/-) mice had a fall (P < 0.005) in MAP [79 +/- 5% of baseline (BL)] and an increase (P < 0.01) in exNO (266 +/- 50% of BL) after 150 min. The tissue levels of iNOS were greater in Mkp-1(-/-) than in wild-type mice. In additional experiments, 60 min after LPS treatment, Mkp-1(-/-) and wild-type mice were given N(omega)-nitro-l-arginine methyl ester (l-NAME) or aminoguanidine, and MAP and exNO were monitored for 90 min. Treatment with l-NAME prevented the LPS-induced increase in exNO and decrease in MAP but resulted in decreased exNO and elevated MAP in wild-type mice. Aminoguanidine prevented the increase in exNO and the fall in MAP caused by LPS in Mkp-1(-/-) mice, without significantly affecting MAP or exNO in wild-type mice. These results demonstrate that a deficiency of MKP-1 results in an exaggerated hypotensive response to LPS mediated by augmented iNOS expression. We speculate that defects in the Mkp-1 gene may increase susceptibility for the development of septic shock.

Enzyme activity dot blots: a rapid and convenient assay for acetyltransferase or protein kinase activity immobilized on nitrocellulose

Methods are described for assaying (Tetrahymena) histone acetyltransferase activity and (Drosophila) casein kinase II activity by spotting extracts on nitrocellulose filters. The methods are quantitative over a wide range of enzyme concentrations and are almost as sensitive as liquid assays. Examples are presented for illustrating the use of these methods for enzyme purification, concentration, and desalting, as well as for electrophoretic blotting from agarose gels. A simple method for autoradiographic enhancement of nitrocellulose filters is also described.

An arginase-1 SNP that protects against the development of pulmonary hypertension in bronchopulmonary dysplasia enhances NO-mediated apoptosis in lymphocytes

Arginase and nitric oxide synthase (NOS) share a common substrate, l‐arginine, and have opposing effects on vascular remodeling. Arginase is the first step in polyamine and proline synthesis necessary for cellular proliferation, while NO produced from NOS promotes apoptosis. Previously, we identified a single nucleotide polymorphism (SNP) in the arginase‐1 (ARG1) gene, rs2781666 (T‐allele) that was associated with a decreased risk for developing pulmonary hypertension (PH) in a cohort of infants with bronchopulmonary dysplasia (BPD). In this study, we utilized lymphocytes from neonates (the only readily available cells from these patients expressing the two genotypes of interest) with either the rs2781666 SNP (TT) or wild type (GG) to test the hypothesis that the protection of the ARG1 SNP against the development of PH in BPD would involve augmented NO production leading to more apoptosis. Lymphocytes were stimulated with IL‐4, IL‐13, and phorbol myristate acetate (PMA). We found that TT lymphocytes had similar levels of arginase I and arginase II expression, but there was a tendency for lower urea production (a surrogate marker of arginase activity), than in the GG lymphocytes. The TT lymphocytes also had significantly greater NO production than did GG lymphocytes despite no differences in iNOS expression between genotypes. Furthermore, the TT lymphocytes had lower numbers of viable cells, and higher levels of cleaved caspase‐3 than did GG lymphocytes. Inhibiting NOS activity using N_ω‐Nitro‐l‐arginine methyl ester hydrochloride (l‐NAME) significantly decreased cleaved caspase‐3 levels in the TT lymphocytes. These data demonstrate that the TT genotype results in greater levels of NO production leading to more apoptosis, which is consistent with the concept that BPD patients with the TT genotype are protected against the development of PH by producing greater basal levels of endogenous NO.

Intratracheal adenoviral-mediated delivery of iNOS decreases pulmonary vasoconstrictor responses in rats

We hypothesized that adenovirus-mediated inducible nitric oxide synthase (iNOS) gene transduction of the lung would result in time-dependent iNOS overexpression and attenuate the vascular constrictor responses to a thromboxane mimetic, U-46619. Rats were treated via the trachea with surfactant alone (sham), surfactant containing an adenoviral construct with a cytomegalovirus promoter-regulated human iNOS gene (Adeno-iNOS), or an adenoviral construct without a gene insert (Adeno-Control). Adeno-iNOS-transduced rats demonstrated human iNOS mRNA and increased iNOS protein levels only in the lungs. Immunohistochemistry of lungs from Adeno-iNOS-treated animals demonstrated transgene expression in alveolar wall cells. In the lungs from Adeno-iNOS-transduced rats, the expression of iNOS protein and exhaled nitric oxide concentrations were increased on days 1-4 and 7 but returned to baseline values by day 14. The administration of the selective iNOS inhibitor L-N6-(1-iminoethyl)lysine dihydrochloride (L-NIL) decreased exhaled nitric oxide concentrations to levels found in Adeno-Control-transduced lungs. In a second group of rats, the segmental vasoconstrictor responses to U-46619 were determined in isolated, perfused lungs 3 days after transduction. Lungs from rats transduced with Adeno-iNOS had reduced total, arterial, and venous vasoconstrictor responses to U-46619 compared with sham, Adeno-Control, and control groups. In a third set of experiments, the response to 400 nM U-46619 in the presence of 10 microM L-NIL was not different in the isolated lungs from Adeno-Control- and Adeno-iNOS-transduced rats. We conclude that adenovirus-mediated iNOS gene transduction of the lung results in time-dependent iNOS overexpression, which attenuates the vascular constrictor responses to the thromboxane mimetic U-46619.

An Isolated Limb Infusion Method Allows for Broad Distribution of rAAVrh74.MCK.GALGT2 to Leg Skeletal Muscles in the Rhesus Macaque

Recombinant adeno-associated virus (rAAV)rh74.MCK.GALGT2 is a muscle-specific gene therapy that is being developed to treat forms of muscular dystrophy. Here we report on an isolated limb infusion technique in a non-human primate model, where hindlimb blood flow is transiently isolated using balloon catheters to concentrate vector in targeted leg muscles. A bilateral dose of 2.5 × 1013 vector genomes (vg)/kg/limb was sufficient to induce GALGT2-induced glycosylation in 10%-60% of skeletal myofibers in all leg muscles examined. There was a 19-fold ± 6-fold average limb-wide increase in vector genomes per microgram genomic DNA at a bilateral dose of 2.5 × 1013 vg/kg/limb compared with a bilateral dose of 6 × 1012 vg/kg/limb. A unilateral dose of 6 × 1013 vg/kg/limb showed a 12- ± 3-fold increase in treated limb muscles compared to contralateral untreated limb muscles, which received vector only after release into the systemic circulation from the treated limb. Variability in AAV biodistribution between different segments of the same muscle was 125% ± 18% for any given dose, while variability between the same muscle for any given treatment dose was 45% ± 7%. These experiments demonstrate that treatment of muscles throughout the leg with rAAVrh74.MCK.GALGT2 can be accomplished safely using an isolated limb infusion technique, where balloon catheters transiently isolate the limb vasculature, but that intra- and inter-muscle transduction variability is a significant issue.

Bridging from Intramuscular to Limb Perfusion Delivery of rAAV: Optimization in a Non-human Primate Study

Phase 1 and phase 2 gene therapy trials using intramuscular (IM) administration of a recombinant adeno-associated virus serotype 1 (rAAV1) for replacement of serum alpha-1 antitrypsin (AAT) deficiency have shown long-term (5-year) stable transgene expression at approximately 2% to 3% of therapeutic levels, arguing for the long-term viability of this approach to gene replacement of secreted serum protein deficiencies. However, achieving these levels required 100 IM injections to deliver 135 mL of vector, and further dose escalation is limited by the scalability of direct IM injection. To further advance the dose escalation, we sought to bridge the rAAV-AAT clinical development program to regional limb perfusion, comparing two methods previously established for gene therapy, peripheral venous limb perfusion (VLP) and an intra-arterial push and dwell (IAPD) using rAAV1 and rAAV8 in a non-human primate (rhesus macaque) study. The rhesus AAT transgene was used with a c-myc tag to enable quantification of transgene expression. 5 cohorts of animals were treated with rAAV1-IM, rAAV1-VLP, rAAV1-IAPD, rAAV8-VLP, and rAAV8-IAPD (n = 2-3), with a dose of 6 × 1012 vg/kg. All methods were well tolerated clinically. Potency, as determined by serum levels of AAT, of rAAV1 by the VLP method was twice that observed with direct IM injection; 90 μg/mL with VLP versus 38 μg/mL with direct IM injection. There was an approximately 25-fold advantage in estimated vector genomes retained within the muscle tissue with VLP and a 5-fold improvement in the ratio of total vector genomes retained within muscle as compared with liver. The other methods were intermediate in the potency and retention of vector genomes. Examination of muscle enzyme (CK) levels indicated rAAV1-VLP to be equally safe as compared with IM injection, while the IAPD method showed significant CK elevation. Overall, rAAV1-VLP demonstrates higher potency per vector genome injected and a greater total vector retention within the muscle, as compared to IM injection, while enabling a much greater total dose to be delivered, with equivalent safety. These data provide the basis for continuation of the dose escalation of the rAAV1-AAT program in patients and bode well for rAAV-VLP as a platform for replacement of secreted proteins.

Hypoxic proliferation requires EGFR-mediated ERK activation in human pulmonary microvascular endothelial cells

We have previously shown that hypoxic proliferation of human pulmonary microvascular endothelial cells (hPMVECs) depends on epidermal growth factor receptor (EGFR) activation. To determine downstream signaling leading to proliferation, we tested the hypothesis that hypoxia-induced proliferation in hPMVECs would require EGFR-mediated activation of extracellular signal-regulated kinase (ERK) leading to arginase II induction. To test this hypothesis, hPMVECs were incubated in either normoxia (21% O₂, 5% CO₂) or hypoxia (1% O₂, 5% CO₂) and Western blotting was performed for EGFR, arginase II, phosphorylated-ERK (pERK), and total ERK (ERK). Hypoxia led to greater EGFR, pERK, and arginase II protein levels than did normoxia in hPMVECs. To examine the role of EGFR in these hypoxia-induced changes, hPMVECs were transfected with siRNA against EGFR or a scrambled siRNA and placed in hypoxia. Inhibition of EGFR using siRNA attenuated hypoxia-induced pERK and arginase II expression as well as the hypoxia-induced increase in viable cell numbers. hPMVECs were then treated with vehicle, an EGFR inhibitor (AG1478), or an ERK pathway inhibitor (U0126) and placed in hypoxia. Pharmacologic inhibition of EGFR significantly attenuated the hypoxia-induced increase in pERK level. Both AG1478 and U0126 also significantly attenuated the hypoxia-induced increase in viable hPMVECs numbers. hPMVECs were transfected with an adenoviral vector containing arginase II (AdArg2) and overexpression of arginase II rescued the U0126-mediated decrease in viable cell numbers in hypoxic hPMVECs. Our findings suggest that hypoxic activation of EGFR results in phosphorylation of ERK, which is required for hypoxic induction of arginase II and cellular proliferation.

Nitric oxide suppression of cellular proliferation depends on cationic amino acid transporter activity in cytokine-stimulated pulmonary endothelial cells

Inducible nitric oxide (NO) synthase (iNOS) is a stress response protein upregulated in inflammatory conditions, and NO may suppress cellular proliferation. We hypothesized that preventing L-arginine (L-arg) uptake in endothelial cells would prevent lipopolysaccharide/tumor necrosis factor-α (LPS/TNF)-induced, NO-mediated suppression of cellular proliferation. Bovine pulmonary arterial endothelial cells (bPAEC) were treated with LPS/TNF or vehicle (control), and either 10 mM L-leucine [L-leu; a competitive inhibitor of L-arg uptake by the cationic amino acid transporter (CAT)] or its vehicle. In parallel experiments, iNOS or arginase II were overexpressed in bPAEC using an adenoviral vector (AdiNOS or AdArgII, respectively). LPS/TNF treatment increased the expression of iNOS, arginase II, CAT-1, and CAT-2 mRNA in bPAEC, resulting in greater NO and urea production than in control bPAEC, which was prevented by L-leu. LPS/TNF treatment resulted in fewer viable cells than in controls, and LPS/TNF-stimulated bPAEC treated with L-leu had more viable cells than LPS/TNF treatment alone. LPS/TNF treatment resulted in cleaved caspase-3 and cleaved poly(ADP-ribose) polymerase expression, which was attenuated by L-leu. AdiNOS reduced viable cell number, and treatment of AdiNOS transfected bPAEC with L-leu preserved cell number. AdArgII increased viable cell number, and treatment of AdArgII transfected bPAEC with L-leu prevented the increase in cell number. These data demonstrate that iNOS expression in pulmonary endothelial cells leads to decreased cellular proliferation, which can be attenuated by preventing cellular L-arg uptake. We speculate that CAT activity may represent a novel therapeutic target in inflammatory lung diseases characterized by NO overproduction.

Asymmetric dimethylarginine does not inhibit arginase activity and is pro-proliferative in pulmonary endothelial cells

Asymmetric dimethylarginine (ADMA) is an endogenously produced nitric oxide synthase (NOS) inhibitor. L-Arginine can be metabolised by NOS and arginase, and arginase is the first step in polyamine production necessary for cellular proliferation. We tested the hypothesis that ADMA would inhibit NOS but not arginase activity and that this pattern of inhibition would result in greater L-arginine bioavailability to arginase, thereby increasing viable cell number. Bovine arginase was used in in vitro activity assays with various concentrations of substrate (L-arginine, ADMA, N(G) -monomethyl-L-arginine (L-NMMA) and N(G) -nitro-L-arginine methyl ester (L-NAME)). Only L-arginine resulted in measurable urea production (Km = 6.9 ± 0.8 mmol/L; Vmax = 6.6 ± 0.3 μmol/mg protein per min). We then incubated bovine arginase with increasing concentrations of ADMA, L-NMMA and L-NAME in the presence of 1 mmol/L l-arginine and found no effect of any of the tested compounds on arginase activity. Using bovine pulmonary arterial endothelial cells (bPAEC) we determined the effects of ADMA on nitric oxide (NO) and urea production and found significantly lower NO production and greater urea production (P < 0.003) with ADMA, without changes in arginase protein levels. In addition, ADMA treatment resulted in an approximately 30% greater number of viable cells after 48 h than in control bPAEC. These results demonstrate that ADMA is neither a substrate nor an inhibitor of arginase activity and that in bPAEC ADMA inhibits NO production and enhances urea production, leading to more viable cells. These results may have pathophysiological implications in disorders associated with higher ADMA levels, such as pulmonary hypertension.

Chronic hypoxia decreases arterial and venous compliance in isolated perfused rat lungs: an effect that is reversed by exogenous L-arginine

Chronic hypoxia (CH)-induced pulmonary hypertension is characterized by vasoconstriction and vascular remodeling, leading to right ventricular dysfunction. Given the role of arterial compliance (C(a)) in right ventricular work, a decrease in C(a) would add to right ventricular work. Nitric oxide (NO) is a potent vasodilator made by NO synthases from L-arginine (L-Arg). However, little is known of the effect of L-Arg on vascular compliance (C(v)) in the lung. We hypothesized that exposure to CH would decrease C(a) and that this effect would be reversed by exogenous L-Arg. Sprague-Dawley rats were exposed to either normoxia or CH for 14 days; the lungs were then isolated and perfused. Vascular occlusions were performed and modeled using a three-compliance, two-resistor model. Pressure-flow curves were generated, and a distensible vessel model was used to estimate distensibility and a vascular resistance parameter (R(0)). Hypoxia resulted in the expected increase in arterial resistance (R(a)) as well as a decrease in both C(a) and C(v). L-Arg had little effect on R(a), C(a), or C(v) in isolated lungs from normoxic animals. L-Arg decreased R(a) in lungs from CH rats and redistributed compliance to approximately that found in normoxic lungs. CH increased R(0), and L-Arg reversed this increase in R(0). L-Arg increased exhaled NO, and inhibition of L-Arg uptake attenuated the L-Arg-induced increase in exhaled NO. These data demonstrate that the CH-induced decrease in C(a) was reversed by L-Arg, suggesting that L-Arg may improve CH-induced right ventricular dysfunction.

A first-in-human phase I/IIa gene transfer clinical trial for Duchenne muscular dystrophy using rAAVrh74.MCK.GALGT2

In a phase 1/2, open-label dose escalation trial, we delivered rAAVrh74.MCK.GALGT2 (also B4GALNT2) bilaterally to the legs of two boys with Duchenne muscular dystrophy using intravascular limb infusion. Subject 1 (age 8.9 years at dosing) received 2.5 × 1013 vector genome (vg)/kg per leg (5 × 1013 vg/kg total) and subject 2 (age 6.9 years at dosing) received 5 × 1013 vg/kg per leg (1 × 1014 vg/kg total). No serious adverse events were observed. Muscle biopsy evaluated 3 or 4 months post treatment versus baseline showed evidence of GALGT2 gene expression and GALGT2-induced muscle cell glycosylation. Functionally, subject 1 showed a decline in 6-min walk test (6MWT) distance; an increase in time to run 100 m, and a decline in North Star Ambulatory Assessment (NSAA) score until ambulation was lost at 24 months. Subject 2, treated at a younger age and at a higher dose, demonstrated an improvement over 24 months in NSAA score (from 20 to 23 points), an increase in 6MWT distance (from 405 to 478 m), and only a minimal increase in 100 m time (45.6-48.4 s). These data suggest preliminary safety at a dose of 1 × 1014 vg/kg and functional stabilization in one patient.