[Pulmonary Vascular Remodeling Characteristics of Pulmonary Arterial Hypertension Mouse Model Induced by Left Pneumonectomy and Jugular Vein Injection of Monocrotaline Pyrrole]

Objective

To compare and investigate the differences and characteristics of pulmonary vascular remodeling in three mouse models of pulmonary arterial hypertension (PAH) constructed by left pneumonectomy, jugular vein injection of monocrotaline pyrrole, and left pneumonectomy combined with jugular vein injection of monocrotaline pyrrole, to explore for a PAH animal model that approximates the clinical pathogenesis of PAH, and to create a model that will provide sound basis for thorough investigation into the pathogenesis of severe PAH.

Methods

59 male C57/BL mice (10-12 weeks, 24-30 g) were randomized into four groups, a control group ( n=9), a group that had left pneumonectomy (PE, n=15), a group that had jugular vein injection of monocrotaline pyrrole (MCTP, n=15), and the last group that had left pneumonectomy combined with jugular injection of monocrotaline pyrrole (P+M, n=20). To evaluate the effect of modeling and the characteristics of pulmonary vascular remodeling, hemodynamic and morphological parameters, including right ventricular systolic pressure (RVSP), right ventricle/(left ventricle plus septum) (RV/LV+S), percent of wall thickness in the pulmonary artery (WT%), muscularization of non-muscular arteries, neointima formation, and vascular obstruction score (VOS), were measured in each group.

Results

1) Compared with those of the control group, the RVSP, RV/LV+S, WT%, and the degree of small pulmonary arteries muscularization in the P+M group were significantly increased ( P<0.01). The MCTP group had just slightly higher findings for these indicators ( P<0.05), while no significant change in these indicators was observed in the PE group ( P>0.05). 2) Neointima formation in the acinus pulmonary arteries, which caused obvious stenosis of the lumen, was observed in the P+M group, the VOS being 1.25±0.80 points ( P<0.001). In contrast, neointima formation was not observed in the MCTP group or the PE groups, the VOS being 0 point ( P>0.05).

Conclusion

Left pneumonectomy combined with jugular intravenous injection of MCTP could induce severe PAH formation in mouse. The model provides a good simulation of neointima formation, the characteristic pathological change of clinical severe PAH.

[Monocrotaline pyrrole induces A549 cells and activates TGF-β1/SMAD2/SMAD3 pathway to promote proliferation and migration of human pulmonary artery smooth muscle cells]

Objective To explore the effects of A549 cells on the proliferation and migration of human pulmonary arterial smooth muscle cells (HPASMCs) and its mechanism. Methods A549 cells and HPASMCs were cultured in vitro. The A549 cells were randomly divided into four groups: control group, dimethylformamide (DMF) solvent group, monocrotaline pyrrole (MCTP) group, MCTP combined with SB431542 group. The cells were assigned into four groups: HPASMC group, A549 and HPASMC co-culture group, MCTP-stimulated A549 and HPASMC co-culture group, MCTP and SB431542-stimulated A549 and HPASMC co-culture group, and IL-6-stimulated HPASMC group. A549 cell viability was detected by CCK-8 assay. The level of IL-6 in the A549 cell culture supernatant was tested by ELISA. The mRNA levels of SMAD2 and SMAD3 in the A549 cells were detected by real-time PCR. The protein levels of TGF-β1, SMAD2, SMAD3 and p-SMAD2, p-SMAD3 in the A549 cells were detected by Western blot analysis. The protein levels of TGF-β1, SMAD2, SMAD3 and p-SMAD2, p-SMAD3 in the A549 cells were examined by Western blot analysis. The protein levels of osteopontin (OPN) and proliferating nuclear antigen (PCNA) in the HPASMCs were determined by Western blot analysis. The migration ability of HPASMCs was measured by wound healing and Transwell^TM assay. Results In the A549 cells, compared with the control group, the cell proliferation ability decreased, the production of IL-6 increased, the mRNA levels of SMAD2 and SMAD3, and the expression of TGF-β1, SMAD2, SMAD3, p-SMAD2, p-SMAD3 proteins significantly increased in the MCTP group. Compared with the MCTP group, the cell proliferation ability increased, the production of IL-6 decreased, the mRNA levels of SMAD 2 and SMAD3, and the expression of TGF-β1, SMAD2, SMAD3, p-SMAD2, p-SMAD3 proteins significantly decreased in the MCTP and SB431542-stimulated group. In the co-culture system, compared with the HPASMC group, the expression of PCNA and OPN proteins and migration ability did not change significantly in the A549 and HPASMC co-cultured group. The expression of PCNA and OPN proteins significantly increased in the MCTP-stimulated A549 and HPASMC co-culture group, and the cell migration ability increased. Compared with the MCTP-stimulated A549 and HPASMC co-culture group, the expression of PCNA and OPN proteins significantly decreased in MCTP and SB431542-stimulated A549 and HPASMC co-culture group, and the cell migration ability decreased. Compared with the HPASMC group, the migration ability of HPASMCs increased and the expression of PCNA and OPN proteins increased in the IL-6 control group. Conclusion Activation of the TGF-β1/SMAD2/SMAD3 signaling pathway in A549 cells induced by MCTP increases IL-6 secretion, thus promoting the proliferation and migration of HPASMCs.

Adipose-derived mesenchymal stromal cells improve hemodynamic function in pulmonary arterial hypertension: identification of microRNAs implicated in modulating endothelial function

Pulmonary arterial hypertension (PAH) is characterized by pulmonary arterial endothelial hyperproliferation and dysfunction. Restoration of endothelial function is a common goal of available treatments. In the present study, human adipose-derived mesenchymal stromal cells (ASCs) were co-cultured with monocrotaline pyrrole-treated human pulmonary arterial endothelial cells (HPAECs); increased proliferation of HPAECs and expression of vascular endothelial growth factor (VEGF) were observed. High throughput sequencing results showed that six microRNAs (miMNAs) of ASCs were significantly dysregulated. In monocrotaline-induced PAH rat models, ASC transplantation improved the right ventricle systolic pressure, right ventricle hypertrophy and pulmonary endothelium hyperproliferation, and four of the six miRNAs were validated in the lung tissue samples. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis showed that these dysregulated miRNAs were involved in the regulation of transcription, signal transduction, negative regulation of cell proliferation through mitogen-activated protein kinase (MAPK) signaling pathway, Wnt signaling pathway, VEGF signaling pathway, cytokine-cytokine receptor interaction, regulation of actin cytoskeleton, transforming growth factor (TGF)-beta signaling pathway and P53 signaling pathway. Our data indicates that the unique six miRNA expression signature could be involved in the PAH endothelial repair by ASCs.

7-cysteine-pyrrole conjugate: A new potential DNA reactive metabolite of pyrrolizidine alkaloids

Pyrrolizidine alkaloids (PAs) require metabolic activation to exert cytotoxicity, genotoxicity, and tumorigenicity. We previously reported that (±)-6,7-dihydro-7-hydroxy-1-hydroxymethyl-5H-pyrrolizine (DHP)-derived DNA adducts are responsible for PA-induced liver tumor formation in rats. In this study, we determined that metabolism of riddelliine and monocrotaline by human or rat liver microsomes produced 7-cysteine-DHP and DHP. The metabolism of 7-glutathionyl-DHP by human and rat liver microsomes also generated 7-cysteine-DHP. Further, reaction of 7-cysteine-DHP with calf thymus DNA in aqueous solution yielded the described DHP-derived DNA adducts. This study represents the first report that 7-cysteine-DHP is a new PA metabolite that can lead to DNA adduct formation.

[Beneficial effects of renal denervation on pulmonary vascular remodeling in experimental pulmonary artery hypertension]

OBJECTIVE

To explore the effects of renal sympathetic denervation (RSD) on pulmonary vascular remodeling in a model of pulmonary arterial hypertension (PAH).

METHODS

According to the random number table, 24 beagles were randomized into control, PAH and PAH+RSD groups (n=8 each). The levels of neurohormone, echocardiogram and dynamics parameters were measured. Then 0.1 ml/kg dimethylformamide (control group) or 2 mg/kg dehydromonocrotaline (PAH and PAH+RSD groups) were injected. The PAH+RSD group underwent RSD after injection. At week 8 post-injection, the neurohormone levels, echocardiogram, dynamics parameters and pulmonary tissue morphology were observed.

RESULTS

The values of right ventricular systolic pressure (RVSP) and pulmonary arterial systolic pressure (PASP) in PAH and PAH+RSD groups were both significantly higher than those in control group ((42.8±8.7), (30.8±6.8) vs (23.2±5.7) mmHg (1 mmHg=0.133 kPa) and (45.1±11.2), (32.6±7.9) vs (24.7±7.1) mmHg). Meanwhile, the values of RVSP and PASP in PAH group were higher than those in PAH+RSD group (all P<0.01). The levels of serum angiotensin II (Ang II) and endothelin-1 significantly increased after 8 weeks in PAH dogs ((228±41) vs (113±34) pg/ml and (135±15) vs (77±7) pg/ml, all P<0.01). And Ang II and endothelin-1 were higher in lung tissues of PAH group ((65±10) and (96±10) pg/ml) than in those of control group ((38±7) and (54±6) pg/ml) and PAH+RSD group ((46±8) and (67±9) pg/ml) (all P<0.01). Pulmonary tissues had marked collagen hyperplasia and lamellar corpuscles of type 2 alveolar cells were damaged more severely in PAH dogs than in PAH+RSD dogs.

CONCLUSIONS

RSD suppresses pulmonary vascular remodeling and decreases pulmonary arterial pressure in experimental PAH. And the effect of RSD on PAH may contribute to decreased neurohormone levels.

[Research on effects of bone marrow mononuclear cells implantation on model of experimental pulmonary artery hypertension]

In the present study, we carried out intratracheal administration of bone marrow-derived mononuclear cells (BM-MNCs) to dehydromonocrotaline (DMCT)-induced canine pulmonary artery hypertension (PH) of rat model to examine the security and feasibility, and the aim was to discuss the mechanism. All animals (n=30) were randomly divided into 3 groups (n=10 in each group), i. e. control group, PH group and BM-MNCs group. Six weeks after the transplantation, the hemodynamic data and right ventricle weight ratio were significantly improved for those in BM-MNCs group compared with those in PH group. The lung mRNA levels of vascular endothelial growth factor (VEGF) were higher, while preproendothelin-1 (ppET-1), interleukin-6 (IL-6) and tumor necrosis factor-alpha (TNF-alpha) were lower compared with those in the PH group (P<0. 05). Immunofluorescence and histochemical results confirmed that 6 weeks after the administration, transplanted BM-MNCs were still alive and could differentiate into pulmonary vascular endothelial cells. These results showed that intratracheal administration of BM-MNCs could obviously reduce or even reverse the DMCT induction of PAH process. The mechanism could be explained as that the function was mainly through the paracrine effect to promote renewable and reduce inflammation.

Dehydropyrrolizidine alkaloids, including monoesters with an unusual esterifying acid, from cultivated Crotalaria juncea (Sunn Hemp cv.'Tropic Sun')

Cultivation of Crotalaria juncea L. (Sunn Hemp cv. 'Tropic Sun') is recommended as a green manure crop in a rotation cycle to improve soil condition, help control erosion, suppress weeds, and reduce soil nematodes. Because C. juncea belongs to a genus that is known for the production of toxic dehydropyrrolizidine alkaloids, extracts of the roots, stems, leaves, and seeds of 'Tropic Sun' were analyzed for their presence using HPLC-ESI/MS. Qualitative analysis identified previously unknown alkaloids as major components along with the expected macrocyclic dehydropyrrolizidine alkaloid diesters, junceine and trichodesmine. The dehydropyrrolizidine alkaloids occurred mainly as the N-oxides in the roots, stems, and, to a lesser extent, leaves, but mainly as the free bases in the seeds. Comprehensive spectrometric and spectroscopic analysis enabled elucidation of the unknown alkaloids as diastereoisomers of isohemijunceine, a monoester of retronecine with an unusual necic acid. The dehydropyrrolizidine alkaloid contents of the roots, stems, and leaves of immature plants were estimated to be 0.05, 0.12, and 0.01% w/w, respectively, whereas seeds were estimated to contain 0.15% w/w.

Senescent endothelial progenitor cells from dogs with pulmonary arterial hypertension: a before-after self-controlled study

Previous studies have underlined the importance of endothelial dysfunction and microvascular occlusion in the pathogenesis of pulmonary artery hypertension (PAH). Since the endothelial progenitor cells (EPCs) are involved in maintaining endothelial homeostasis, we observed the change of peripheral EPCs in canines before and after PAH onset. PAH was induced by intra-pulmonary artery injection of dehydromonocrotaline (DHMC) in nine beagles. Before and 48 h and 6 weeks after DHMC injection, 40 ml peripheral blood was obtained from the femoral vein. Circulating EPCs were identified as CD133 + KDR + cells and numerated by fluorescence-activated cell sorter; the EPCs functional capacity was determined by in vitro tubule-forming assay. The senescence of EPCs was determined by beta-galactosidase staining. At each time point, 2 ml blood from femoral artery was obtained for arterial oxygen pressure (PaO(2)). Forty-eight hours after DHMC injection, treated beagles suffered from hypoxemia; however, both the number and the tubule-forming capacity of EPCs were transiently raised. Six weeks later, PAH was confirmed by obviously high mean pulmonary arterial pressure (20.2 +/- 1.64 vs. 11.3 +/- 2.0 mmHg, p < 0.05) and low PaO(2) (69.30 +/- 9.15 vs. 95.94 +/- 1.43 mmHg, p < 0.01) in beagles after DHMC treatment, and their EPCs exhibited a predominant decrease in either the number (206.1 +/- 26.8 vs. 632.8 +/- 42.8 cells/ml blood, p < 0.01) or the tubule-forming capacity (21.1 +/- 2.8 vs. 11.2 +/- 2.8 tubules/x200 field, p < 0.01). Additionally, senescence-associated beta-galactosidase-positive EPCs were significantly increased. Our data suggested that, after the acute stage of DHMC injury to pulmonary vessels, the EPCs from PAH beagles suffered from exhaustion and senescence.

[Quantitative and functional changes of circulating endothelial progenitor cells in dogs with dehydromonocrotaline-induced pulmonary artery hypertension]

OBJECTIVE

To determine the quantitive and functional changes of circulating endothelial progenitor cells (EPCs) in dogs with dehydromonocrotaline-induced pulmonary artery hypertension (PAH).

METHODS

Dehydromonocrotaline was injected into the canine right ventricle to induce pulmonary hypertension. Circulating EPCs were enumerated as AC+(113), KDR+ cells by fluorescence-activated cell sorter using counting beads, and the number and activity of EPCs after in vitro expansion were determined by acLDL uptake/lectin staining assay and in vitro tubule forming assay.

RESULTS

Nine of the 10 beagles survived after dehydromonocrotaline injection. Six weeks later, mean pulmonary artery pressure increased from (11.3 +/- 2.0) mm Hg (1 mm Hg = 0.133 kPa) to (20.2 +/- 1.6) mm Hg (t =10.307, P < 0.01), and the AC+(133) and KDR+ cells decreased from (632.8 +/- 42.8) cells/ml to (206.1 +/- 26.8) cells/ml (t = 25.361, P < 0.01). UEA- I and DiLDL positive cells deceased from (41 +/- 6) EPCs/ x 200 field to (22 +/- 6) EPCs/ x 200 field (t = 6.510, P < 0.01). In addition, in vasculogenesis assay, PAH EPCs formed less quantitative (11.2 +/- 2.8 vs 21.1 +/- 2.8 tubules/ x 200 field, respectively, t = 7. 583, P <0. 01) and less qualitive tubules than baseline EPCs.

CONCLUSION

The number and vessel forming ability of EPCs are impaired in this canine model of dehydromonocrotaline-induced pulmonary hypertension.

Dehydromonocrotaline inhibits mitochondrial complex I. A potential mechanism accounting for hepatotoxicity of monocrotaline

Monocrotaline is a pyrrolizidine alkaloid present in plants of the Crotalaria species, which causes cytotoxicity and genotoxicity, including hepatotoxicity in animals and humans. It is metabolized by cytochrome P-450 in the liver to the alkylating agent dehydromonocrotaline. We evaluated the effects of monocrotaline and its metabolite on respiration, membrane potential and ATP levels in isolated rat liver mitochondria, and on respiratory chain complex I NADH oxidase activity in submitochondrial particles. Dehydromonocrotaline, but not the parent compound, showed a concentration-dependent inhibition of glutamate/malate-supported state 3 respiration (respiratory chain complex I), but did not affect succinate-supported respiration (complex II). Only dehydromonocrotaline dissipated mitochondrial membrane potential, depleted ATP, and inhibited complex I NADH oxidase activity (IC50=62.06 microM) through a non-competitive type of inhibition (K(I)=8.1 microM). Therefore, dehydromonocrotaline is an inhibitor of the activity of respiratory chain complex I NADH oxidase, an action potentially accounting for the well-documented monocrotaline's hepatotoxicity to animals and humans. The mechanism probably involves change of the complex I conformation resulting from modification of cysteine thiol groups by the metabolite.

Monocrotaline pyrrole induces Smad nuclear accumulation and altered signaling expression in human pulmonary arterial endothelial cells

The mechanistic relationship between the widely used monocrotaline model of primary pulmonary hypertension and altered TGFbeta family signaling due to genetic defects in the Bone Morphogenetic Protein type II receptor in affected humans has not been investigated. In this study we use fluorescent microscopy to demonstrate nuclear translocation of Smad 4 in human pulmonary arterial endothelial cell (HPAEC) cultures treated with monocrotaline pyrrole (MCTP), Bone Morphogenetic Protein (BMP) and TGFbeta. While MCTP induced transient nuclear accumulation of phosphorylated Smad 1 (P-Smad 1) and phosphorylated Smad 2 (P-Smad 2), only expression of P-Smad 1 was significantly altered in western blots. P-Smad 1 expression significantly increased 30 min following treatment with MCTP correlating with P-Smad 1 and Smad 4 nuclear translocation. Although a modest, but significant decrease in P-Smad 1 expression occurred 1 h after treatment, expression was significantly increased at 72 h. Evaluation of components of the signal and response pathway at 72 h showed decreased expression of the BMP type II receptor (BMPrII), no change in TGFbeta Activin Receptor-like Kinase 1 (Alk 1), no change in Smad 4 but increase in the inhibitory Smad 6, decrease in the alternate BMP signaling pathway p38(MAPK) but no change in the psmad1 response element ID 1. Our results suggest transient activation of Smad signaling pathways in initial MCTP endothelial cell toxicity, and a persistent dysregulation of BMP signaling. Electron microscopy of cell membrane caveoli revealed a dramatic decrease in these structures after 72 h. Loss of these structural elements, noted for their sequestration and inhibition of receptor activity, may contribute to prolonged alterations in BMP signaling.

Effects of bone marrow-derived cells on monocrotaline- and hypoxia-induced pulmonary hypertension in mice

BACKGROUND

Bone marrow -derived cells (BMDCs) can either limit or contribute to the process of pulmonary vascular remodeling. Whether the difference in their effects depends on the mechanism of pulmonary hypertension (PH) remains unknown.

OBJECTIVES

We investigated the effect of BMDCs on PH induced in mice by either monocrotaline or exposure to chronic hypoxia.

METHODS

Intravenous administration of the active monocrotaline metabolite (monocrotaline pyrrole, MCTp) to C57BL/6 mice induced PH within 15 days, due to remodeling of small distal vessels. Three days after the MCTp injection, the mice were injected with BMDCs harvested from femurs and tibias of donor mice treated with 5-fluorouracil (3.5 mg IP/animal) to deplete mature cells and to allow proliferation of progenitor cells.

RESULTS

BMDCs significantly attenuated PH as assessed by reductions in right ventricular systolic pressure (20 +/- 1 mmHg vs. 27 +/- 1 mmHg, P < or = 0.01), right ventricle weight/left ventricle+septum weight ratio (0.29 +/- 0.02 vs. 0.36 +/- 0.01, P < or = 0.03), and percentage of muscularized vessels (26.4% vs. 33.5%, P < or = 0.05), compared to control animals treated with irradiated BMDCs. Tracking cells from constitutive GFP-expressing male donor mice with anti-GFP antibodies or chromosome Y level measurement by quantitative real-time PCR showed BMDCs in the lung. In contrast, chronically hypoxic mice subjected to the same procedure failed to show improvement in PH.

CONCLUSION

These results show that BMDCs limit pulmonary vascular remodeling induced by vascular injury but not by hypoxia.

Transgenic mice overexpressing the 5-hydroxytryptamine transporter gene in smooth muscle develop pulmonary hypertension

One intrinsic abnormality of pulmonary artery smooth muscle cells (PA-SMCs) in human idiopathic pulmonary hypertension (iPH) is an exaggerated proliferative response to internalized serotonin (5-HT) caused by increased expression of the 5-HT transporter (5-HTT). To investigate whether 5-HTT overexpression in PA-SMCs is sufficient to produce PH, we generated transgenic mice overexpressing 5-HTT under the control of the SM22 promoter. Studies in SM22-LacZ(+) mice showed that the transgene was expressed predominantly in SMCs of pulmonary and systemic vessels. Compared with wild-type mice, SM22-5-HTT(+) mice exhibited a 3- to 4-fold increase in lung 5-HTT mRNA and protein, together with increased lung 5-HT uptake activity, but no changes in platelet 5-HTT activity or blood 5-HT levels. At 8 weeks of age, SM22-5-HTT(+) mice exhibited PH, with marked increases in right ventricular systolic pressure (RVSP), right ventricle/left ventricle+septum ratio, and muscularization of distal pulmonary vessels, but no changes in systemic arterial pressure. PH worsened with age. Except a marked decrease in Kv channels, no changes in the lung expression of mediators of pulmonary vascular remodeling were observed in SM22-5-HTT(+) mice. Compared with wild-type mice, SM22-5-HTT(+) mice showed depressed hypoxic pulmonary vasoconstriction contrasting with greater severity of hypoxia- or monocrotaline-induced PH. These results show that increased 5-HTT expression in PA-SMCs, to a level close to that found in human iPH, lead to PH in mice. They further support a central role for 5-HTT in the pathogenesis of PH, making 5-HTT a potential therapeutic target.

Monocrotaline pyrrole targets proteins with and without cysteine residues in the cytosol and membranes of human pulmonary artery endothelial cells

A single injection of monocrotaline produces a pulmonary insult in rats with a phenotype similar to human primary pulmonary hypertension. Although extensively used as a model, the mechanism(s) by which this chemical insult mimics a condition with genetic and environmental links remains an enigma, although formation of protein adducts has been implicated. Monocrotaline (MCT) is non-toxic and must undergo hepatic dehydrogenation to the soft electrophile monocrotaline pyrrole as prerequisite to damaging endothelial cells lining arterioles at remote pulmonary sites. In this report we extend our earlier investigation (J. Biol. Chem. 2000, 275, 29091-29099) by examining protein adducts to lower abundance adducts, a pI range not covered before, and subcellular localization of adduct-forming proteins associated with plasma membranes. Human pulmonary artery endothelial cells were exposed to [(14)C]MCT pyrrole (MCTP) and protein targets were identified using 2-DE with IPG 4-11. Adducted proteins were identified by pI, apparent molecular weight, and PMF using MALDI-TOF MS. Results of this study show that the majority of adducts form on proteins that contain reactive thiols in a CXXC motif, such as protein disulfide isomerase A(3) (ERp57), protein disulfide isomerase (PDI), and endothelial PDI. These same proteins were the major adduct-forming proteins associated with the plasma membrane. Other proteins found to be targets were thioredoxin, galectin-1, reticulocalbin 1 and 3, cytoskeletal tropomyosin, mitochondrial ATP synthase beta-chain, annexin A2 and cofilin-1. For the first time, MCTP adducts were observed on proteins not known to contain cysteine residues. However, known reactive proteins including nucleophosmin did not form detectable adducts, potentially indicating that MCTP did not reach the interior of nucleus to the same extent as other cellular sites. These findings suggest that molecular events underlying MCTP toxicity are initiated at the plasma membrane or readily accessible subcellular regions including the cytosol and membranes of the endoplasmic reticulum and mitochondria.

Monocrotaline pyrrole-induced megalocytosis of lung and breast epithelial cells: Disruption of plasma membrane and Golgi dynamics and an enhanced unfolded protein response

The pyrrolizidine alkaloid monocrotaline (MCT) initiates pulmonary hypertension by inducing a "megalocytosis" phenotype in target pulmonary arterial endothelial, smooth muscle and Type II alveolar epithelial cells. In cultured endothelial cells, a single exposure to the pyrrolic derivative of monocrotaline (MCTP) results in large cells with enlarged endoplasmic reticulum (ER) and Golgi and increased vacuoles. However, these cells fail to enter mitosis. Largely based upon data from endothelial cells, we proposed earlier that a disruption of the trafficking and mitosis-sensor functions of the Golgi (the "Golgi blockade" hypothesis) may represent the subcellular mechanism leading to MCTP-induced megalocytosis. In the present study, we investigated the applicability of the Golgi blockade hypothesis to epithelial cells. MCTP induced marked megalocytosis in cultures of lung A549 and breast MCF-7 cells. This was associated with a change in the distribution of the cis-Golgi scaffolding protein GM130 from a discrete juxtanuclear localization to a circumnuclear distribution consistent with an anterograde block of GM130 trafficking to/through the Golgi. There was also a loss of plasma membrane caveolin-1 and E-cadherin, cortical actin together with a circumnuclear accumulation of clathrin heavy chain (CHC) and alpha-tubulin. Flotation analyses revealed losses/alterations in the association of caveolin-1, E-cadherin and CHC with raft microdomains. Moreover, megalocytosis was accompanied by an enhanced unfolded protein response (UPR) as evidenced by nuclear translocation of Ire1alpha and glucose regulated protein 58 (GRP58/ER-60/ERp57) and a circumnuclear accumulation of PERK kinase and protein disulfide isomerase (PDI). These data further support the hypothesis that an MCTP-induced Golgi blockade and enhanced UPR may represent the subcellular mechanism leading to enlargement of ER and Golgi and subsequent megalocytosis.

Formation of DHP-derived DNA adducts from metabolic activation of the prototype heliotridine-type pyrrolizidine alkaloid, lasiocarpine

Pyrrolizidine alkaloids (PAs) are probably the most common poisonous plants affecting livestock, wildlife, and humans. The PAs that have been found to be tumorigenic in experimental animals belong to the retronecine-, heliotridine-, and otonecine-type PAs. Our recent mechanistic studies indicated that riddelliine, a tumorigenic retronecine-type PA, induced tumors via a genotoxic mechanism mediated by the formation of 6,7-dihydro-7-hydroxy-1-hydroxymethyl-5H-pyrrolizine (DHP)-derived DNA adducts. The same adducts were formed from clivorine, a tumorigenic otonecine-type PA from metabolism of clivorine by rat liver microsomes in the presence of calf thymus DNA. In this study, we report that metabolism of lasiocarpine, the prototype heliotridine PA, by F344 rat liver microsomes resulted in the formation of DHP. When incubated in the presence of calf thymus DNA, the same DHP-derived DNA adducts were formed. These results suggest that these DHP-derived DNA adducts are potential biomarkers of exposure and tumorigenicity for all types of PAs.

Excess l-arginine restores endothelium-dependent relaxation impaired by monocrotaline pyrrole

The pyrrolizidine alkaloid plant toxin monocrotaline pyrrole (MCTP) causes pulmonary hypertension in experimental animals. The present study aimed to examine the effects of MCTP on the endothelium-dependent relaxation. We constructed an in vitro disease model of pulmonary hypertension by overlaying MCTP-treated bovine pulmonary artery endothelial cells (CPAEs) onto pulmonary artery smooth muscle cell-embedded collagen gel lattice. Acetylcholine (Ach) induced a relaxation of the control CPAEs-overlaid gels that were pre-contracted with noradrenaline, and the relaxation was inhibited by L-NAME, an inhibitor of NO synthase (NOS). In contrast, when MCTP-treated CPAEs were overlaid, the pre-contracted gels did not show a relaxation in response to Ach in the presence of 0.5 mM l-arginine. Expression of endothelial NOS protein, Ach-induced Ca2+ transients and cellular uptake of l-[3H]arginine were significantly smaller in MCTP-treated CPAEs than in control cells, indicating that these changes were responsible for the impaired NO production in MCTP-treated CPAEs. Since cellular uptake of l-[3H]arginine linearly increased according to its extracellular concentration, we hypothesized that the excess concentration of extracellular l-arginine might restore NO production in MCTP-treated CPAEs. As expected, in the presence of 10 mM l-arginine, Ach showed a relaxation of the MCTP-treated CPAEs-overlaid gels. These results indicate that the impaired NO production in damaged endothelial cells can be reversed by supplying excess l-arginine.

Metabolic activation of the tumorigenic pyrrolizidine alkaloid, retrorsine, leading to DNA adduct formation in vivo

Pyrrolizidine alkaloids are naturally occurring genotoxic chemicals produced by a large number of plants. The high toxicity of many pyrrolizidine alkaloids has caused considerable loss of free-ranging livestock due to liver and pulmonary lesions. Chronic exposure of toxic pyrrolizidine alkaloids to laboratory animals induces cancer. This investigation studies the metabolic activation of retrorsine, a representative naturally occurring tumorigenic pyrrolizidine alkaloid, and shows that a genotoxic mechanism is correlated to the tumorigenicity of retrorsine. Metabolism of retrorsine by liver microsomes of F344 female rats produced two metabolites, 6, 7-dihydro-7-hydroxy-1-hydroxymethyl-5H-pyrrolizine (DHP), at a rate of 4.8 +/- 0.1 nmol/mg/min, and retrorsine-N-oxide, at a rate of 17.6 +/- 0.5 nmol/mg/min. Metabolism was enhanced 1.7-fold by using liver microsomes prepared from dexamethasone-treated rats. DHP formation was inhibited 77% and retrorsine N-oxide formation was inhibited 29% by troleandomycin, a P450 3A enzyme inhibitor. Metabolism of retrorsine with lung, kidney, and spleen microsomes from dexamethasone-treated rats also generated DHP and the N-oxide derivative. When rat liver microsomal metabolism of retrorsine occurred in the presence of calf thymus DNA, a set of DHP-derived DNA adducts was formed; these adducts were detected and quantified by using a previously developed 32P-postlabeling/HPLC method. These same DNA adducts were also found in liver DNA of rats gavaged with retrorsine. Since DHP-derived DNA adducts are suggested to be potential biomarkers of riddelliine-induced tumorigenicity, our results indicate that (i) similar to the metabolic activation of riddelliine, the mechanism of retrorsine-induced carcinogenicity in rats is also through a genotoxic mechanism involving DHP; and (ii) the set of DHP-derived DNA adducts found in liver DNA of rats gavaged with retrorsine or riddelliine can serve as biomarkers for the tumorigenicity induced by retronecine-type pyrrolizidine alkaloids.

Human liver microsomal reduction of pyrrolizidine alkaloid N-oxides to form the corresponding carcinogenic parent alkaloid

Retronecine-based pyrrolizidine alkaloids, such as riddelliine, retrorsine, and monocrotaline, are toxic to domestic livestock and carcinogenic to laboratory rodents. Previous in vitro metabolism studies showed that (+/-)6,7-dihydro-7-hydroxy-1-(hydroxymethyl)-5H-pyrrolizine (DHP) and pyrrolizidine alkaloid N-oxides were the major metabolites of these compounds. DHP is the reactive metabolite of pyrrolizidine alkaloids and pyrrolizidine alkaloid N-oxides are generally regarded as detoxification products. However, a previous study of rat liver microsomal metabolism of riddelliine N-oxide demonstrated that DHP and its parent compound, riddelliine, were generated as the major metabolites of riddelliine N-oxide. In this study the metabolic activation of the three retronecine-based pyrrolizidine alkaloid N-oxides by human liver microsomes is investigated under oxidative and hypoxic conditions. Results shows that both the DHP and the corresponding parent pyrrolizidine alkaloids are the major metabolites of the human liver microsomal metabolism of pyrrolizidine alkaloid N-oxides. Under oxidative conditions, reduction of the N-oxide to pyrrolizidine alkaloid is inhibited and while under hypoxic conditions, DHP formation is dramatically decreased. The oxidative and reductive products generated from the metabolism of pyrrolizidine alkaloid N-oxides are substrate-, enzyme- and time-dependent. In the presence of troleandomycin, a microsomal CYP3A inhibitor, DHP formation is inhibited by more than 70%, while the N-oxide reduction was not affected. The level of microsomal enzyme activity in human liver is comparable with rats. The rate of in vitro metabolism by either human and rat liver microsomes follows the order of riddelliine > or = retrorsine > monocrotaline, and DHP-derived DNA adducts are detected and quantified by 32P-postlabeling/HPLC analysis. Similar DHP-derived DNA adducts are found in liver DNA of F344 rats gavaged with the pyrrolizidine alkaloid N-oxides (1.0 mg/kg). The levels of in vivo DHP-DNA adduct formation is correlated with the level of in vitro DHP formation. Our results indicate that pyrrolizidine alkaloid N-oxides may be hepatocarcinogenic to rats through a genotoxic mechanism via the conversion of the N-oxides to their corresponding parent pyrrolizidine alkaloids, and these results may be relevant to humans.

Monocrotaline pyrrole-induced endothelial cell megalocytosis involves a Golgi blockade mechanism

Pyrrolizidine alkaloids initiate disease in the lung (pulmonary hypertension), liver (veno-occlusive disease and cirrhosis), and kidneys (afferent arteriolar block and mesangiolysis) by inducing a megalocytotic phenotype in target endothelial and parenchymal cells. A "hit-and-run" type of exposure to the bioactive pyrrolizidine results, within 2-3 days, in enlarged cells with large nuclei and enlarged Golgi and endoplasmic reticulum, while the cells remain in G2/M block. In the present study, we recapitulated monocrotaline pyrrole (MCTP)-induced megalocytosis in cultures of bovine pulmonary arterial endothelial cells (PAEC), human Hep3B hepatocytes, human type II-like alveolar epithelial cells (A549), and human pulmonary arterial smooth muscle cells (PASMC) and investigated the subcellular mechanism involved. There was an inverse relationship between reduction in caveolin (Cav)-1 levels and stimulation of promitogenic STAT3 and ERK1/2 cell signaling. In megalocytotic PAEC, the Golgi scaffolding protein GM130 was shifted from membranes with heavy density to those with a lighter density. This lighter Golgi fraction was enriched for hypo-oligomeric Cav-1, indicating dysfunctional trafficking of cargo. Immunofluorescence imaging studies confirmed the trapping of Cav-1 in a GM130-positive Golgi compartment. There was an increase in Ser25 phosphorylation of GM130 (typically a prelude to Golgi fragmentation and mitosis) and increased association between pGM130, cdc2 kinase, and Cav-1. Nevertheless, megalocytotic MCTP-treated cells showed reduced entry into mitosis upon stimulation with 2-methoxyestradiol (2-ME), reduced 2-ME-induced Golgi fragmentation, and a slowing of Golgi reassembly after nocodazole-induced fragmentation. These data suggest that a disruption of the trafficking and mitosis sensor functions of the Golgi may represent the subcellular mechanism leading to MCTP-induced megalocytosis ("the Golgi blockade hypothesis").

Comparison of hepatic in vitro metabolism of the pyrrolizidine alkaloid senecionine in sheep and cattle

OBJECTIVE

To compare hepatic metabolism of pyrrolizidine alkaloids (PAs) between sheep and cattle and elucidate the protective mechanism of sheep.

SAMPLE POPULATION

Liver microsomes and cytosol from 8 sheep and 8 cattle.

PROCEDURE

The PA senecionine, senecionine N-oxide (nontoxic metabolite) and 6,7-dihydro-7-hydroxy-1-hydroxymethyl-5H-pyrrolizine (DHP; toxic metabolite) were measured in microsomal incubations. The kcat (turnover number) was determined for DHP and N-oxide formation. Chemical and immunochemical inhibitors were used to assess the role of cytochrome P450s, flavin-containing monooxygenases (FMOs), and carboxylesterases in senecionine metabolism. The CYP3A, CYP2B, and FMO concentrations and activities were determined, in addition to the role of glutathione (GSH) in senecionine metabolism.

RESULTS

DHP concentration did not differ between species. Sheep formed more N-oxide, had higher N-oxide kcat, and metabolized senecionine faster than cattle. The P450 concentrations and isoforms had a large influence on DHP formation, whereas FMOs had a large influence on N-oxide formation. In cattle, CYP3A played a larger role in DHP formation than in sheep. FMO activity was greater in sheep than in cattle. Addition of GSH to in vitro microsomal incubations decreased DHP formation; addition of cytosol decreased N-oxide formation.

CONCLUSIONS AND CLINICAL RELEVANCE

Hepatic metabolism differences alone do not account for the variation in susceptibility seen between these species. Rather, increased ruminal metabolism in sheep appears to be an important protective mechanism, with hepatic enzymes providing a secondary means to degrade any PAs that are absorbed from the rumen.

Disruption of endothelial-cell caveolin-1alpha/raft scaffolding during development of monocrotaline-induced pulmonary hypertension

BACKGROUND

In the monocrotaline (MCT)-treated rat, there is marked stimulation of DNA synthesis and megalocytosis of pulmonary arterial endothelial cells (PAECs) within 3 to 4 days, followed by pulmonary hypertension (PH) 10 to 14 days later. Growing evidence implicates caveolin-1 (cav-1) in plasma membrane rafts as a negative regulator of promitogenic signaling. We have investigated the integrity and function of endothelial cell-selective cav-1alpha/raft signaling in MCT-induced PH.

METHODS AND RESULTS

Although PH and right ventricular hypertrophy developed by 2 weeks after MCT, a reduction in cav-1alpha levels in the lung was apparent within 48 hours, declining to approximately 30% by 2 weeks, accompanied by an increase in activation of the promitogenic transcription factor STAT3 (PY-STAT3). Immunofluorescence studies showed a selective loss of cav-1alpha and platelet endothelial cell adhesion molecule-1 in the PAEC layer within 48 hours after MCT but an increase in PY-STAT3. PAECs with cav-1alpha loss displayed high PY-STAT3 and nuclear immunostaining for proliferating cell nuclear antigen (PCNA). Biochemical studies showed a loss of cav-1alpha from the detergent-resistant lipid raft fraction concomitant with hyperactivation of STAT3. Moreover, cultured PAECs treated with MCT-pyrrole for 48 hours developed megalocytosis associated with hypo-oligomerization and reduction of cav-1alpha, hyperactivation of STAT3 and ERK1/2 signaling, and stimulation of DNA synthesis.

CONCLUSIONS

MCT-induced disruption of cav-1alpha chaperone and scaffolding function in PAECs likely accounts for diverse alterations in endothelial cell signaling in this model of PH.

DNA cross-linking by dehydromonocrotaline lacks apparent base sequence preference

Pyrrolizidine alkaloids (PAs) are ubiquitous plant toxins, many of which, upon oxidation by hepatic mixed-function oxidases, become reactive bifunctional pyrrolic electrophiles that form DNA-DNA and DNA-protein cross-links. The anti-mitotic, toxic, and carcinogenic action of PAs is thought to be caused, at least in part, by these cross-links. We wished to determine whether the activated PA pyrrole dehydromonocrotaline (DHMO) exhibits base sequence preferences when cross-linked to a set of model duplex poly A-T 14-mer oligonucleotides with varying internal and/or end 5'-d(CG), 5'-d(GC), 5'-d(TA), 5'-d(CGCG), or 5'-d(GCGC) sequences. DHMO-DNA cross-links were assessed by electrophoretic mobility shift assay (EMSA) of 32P endlabeled oligonucleotides and by HPLC analysis of cross-linked DNAs enzymatically digested to their constituent deoxynucleosides. The degree of DNA cross-links depended upon the concentration of the pyrrole, but not on the base sequence of the oligonucleotide target. Likewise, HPLC chromatograms of cross-linked and digested DNAs showed no discernible sequence preference for any nucleotide. Added glutathione, tyrosine, cysteine, and aspartic acid, but not phenylalanine, threonine, serine, lysine, or methionine competed with DNA as alternate nucleophiles for cross-linking by DHMO. From these data it appears that DHMO exhibits no strong base preference when forming cross-links with DNA, and that some cellular nucleophiles can inhibit DNA cross-link formation.

Transplantation of Endothelial Progenitor Cells into the Lung to Alleviate Pulmonary Hypertension in Dogs

Primary pulmonary hypertension (PPH) is still a refractory disease, and patients deteriorate despite any treatment. We hypothesized that neovascularization in the lung could increase the volume of the vascular bed in the pulmonary circulation and thus reduce the development of pulmonary hypertension (PH). Endothelial progenitor cells (EPCs) might be a potential cell source for neovascularization. We examined the effects of EPC transplantation into the lungs of dogs with dehydromonocrotaline-induced PH. The lung parenchyma of PH model dogs was injected with ex vivo-expanded, autologous EPCs originated from peripheral blood (experiments, n=4) or culture medium (control, n=3), using a bronchoscope. EPC transplantation gave significant improvements in mean pulmonary artery pressure, cardiac output, and pulmonary vascular resistance. Histological evaluation revealed both improvement in the medial thickness of the small pulmonary artery and neovascularization of the lung tissue. These results indicate that EPC transplantation into the lung is effective at preventing the progression of dehydromonocrotaline-induced PH in dogs, and suggest a new therapeutic option for PPH.

Right ventricle–sparing heart transplantation effective against iatrogenic pulmonary hypertension

BACKGROUND

Right heart failure is the predominant cause of death following heart transplantation, occurring with disturbingly high frequency in patients with severe antecedent pulmonary hypertension. We have recently reported a novel technique of heart transplantation that spares the recipient right ventricle, excising only the recipient left ventricle. The resulting model has 2 right hearts and 1 left heart. The aim is to preserve the recipient's right ventricle, which is already conditioned to pulmonary hypertension. The hope is that, in this way, death due to right heart failure can be prevented in humans. Our prior report was a feasibility study in normal dogs. This study challenges this new technique by creating iatrogenic pulmonary hypertension in the recipient animals.

METHODS

Iatrogenic pulmonary hypertension was created in 4 recipient canines by intravenous injection of the pulmonary toxin monocrotaline pyrrole (single bolus of 3.5 to 4.5 mg/kg intravenously [i.v.]).

RESULTS

Within 6 weeks of monocrotaline administration, relative pulmonary hypertension occurred (mean pulmonary artery [PA] pressure 20 mm Hg vs 10 mm Hg for controls [p < 0.01]) (pulmonary vascular resistance [PVR] 4.2 vs 1.5 Wood units [P < 0.01]), and right ventricular (RV) hypertrophy developed (RV thickness 11 mm vs 2 mm [P < 0.04]). Histologic examination confirmed severe muscle infiltration and thickening of the media of the pulmonary arterioles. RV-sparing heart transplantation was performed successfully in all 4 animals with pulmonary hypertension. In all cases, the animals were weaned without difficulty from cardiopulmonary bypass, despite the ambient pulmonary hypertension, on low-dose epinephrine, maintaining systolic blood pressure of 104 mm Hg at right atrial pressure of 7 mm Hg. Both right hearts contracted well without dilation or strain. A single "control" traditional orthotopic transplant experiment in an animal with monocrotaline-induced pulmonary hypertension resulted in immediate death from right heart failure.

CONCLUSIONS

Right ventricle-sparing heart transplantation ("one-and-one-half heart model") can handle pulmonary hypertension without difficulty. This evidence adds impetus for further pursuing of right ventricle-sparing heart transplantation to decrease the incidence of death from right heart failure in recipients with severe antecedent pulmonary hypertension.

Riddelliine N-oxide is a phytochemical and mammalian metabolite with genotoxic activity that is comparable to the parent pyrrolizidine alkaloid riddelliine

Pyrrolizidine alkaloids (PAs) and their N-oxide derivatives are naturally-formed genotoxic phytochemicals that are widely distributed throughout the world. Although, the quantities of PAs and PA N-oxides in plants are nearly equal, the biological and genotoxic activities of PA N-oxides have not been studied extensively. PA N-oxides are major metabolites of PAs and are generally regarded as detoxification products. However, in this study, we report that rat liver microsomes converted riddelliine N-oxide to the genotoxic 6,7-dihydro-7-hydroxy-1-hydroxymethyl-5H-pyrrolizine (DHP) metabolite. Metabolism of riddelliine N-oxide by rat liver microsomes under hypoxic conditions (argon) generated predominantly the parent PA, riddelliine. The reduction of riddelliine N-oxide to riddelliine was diminished, when the metabolism of riddelliine N-oxide with rat liver microsomes was conducted aerobically. Rat liver microsomal incubations of riddelliine N-oxide in the presence of calf thymus DNA produced a set of DHP-derived DNA adducts as detected and quantified by 32P-postlabeling/HPLC. The same DHP-derived DNA adducts were also found in liver DNA of F344 rats fed riddelliine N-oxide or riddelliine. When rats received doses of 1.0 mg/kg riddelliine N-oxide for three consecutive days, the level of DNA adducts was 39.9 +/- 0.6 adducts/10(7) nucleotides, which was 2.6-fold less than that measured in rats treated with riddelliine at the same dose. We have previously shown that these DHP-derived DNA adducts are produced by chronic feeding of riddelliine and that the adduct levels correlated with liver tumor formation. Results presented in this paper indicate that riddelliine N-oxide, through its conversion to riddelliine, is also a potential genotoxic hepatocarcinogen.

Identification of DNA adducts derived from riddelliine, a carcinogenic pyrrolizidine alkaloid

Riddelliine is a naturally occurring carcinogenic pyrrolizidine alkaloid that produces liver tumors in experimental animals. Riddelliine requires metabolic activation to dehydroriddelliine and 6,7-dihydro-7-hydroxy-1-hydroxymethyl-5H-pyrrolizine (DHP) to exert its toxicity. Previously, (32)P-postlabeling HPLC was used to detect a set of eight DHP-derived adduct peaks from DNA modified both in vitro and in vivo. Among these DHP-derived DNA adducts, two were identified as epimers of DHP-2'-deoxyguanosine 3'-monophosphate. In this study, the remaining adducts have been characterized as DHP-modified dinucleotides. A series of dinucleotides, TpGp, ApGp, TpCp, ApCp, TpAp, ApAp, TpTp, and ApTp, were obtained by enzymatic digestion of calf thymus DNA with micrococcal nuclease (MN) and spleen phosphodiesterase (SPD) followed by HPLC separation and structural identification by negative ion electrospray tandem mass spectrometry (ES/MS/MS). Incubation of individual dinucleotides with DHP produced DHP-modified dinucleotide adducts that were also characterized using LC-ES/MS/MS. A parallel analysis of the isolated DHP-modified dinucleotides using (32)P-postlabeling recapitulated the series of unidentified adduct peaks that we previously reported from DHP-modified calf thymus DNA in vitro and rat liver DNA in vivo. Intact calf thymus DNA was also reacted with DHP and then digested by MN/SPD under the same conditions. The adduct profile obtained from LC-ES/MS/MS analysis was similar to that observed from the isolated dinucleotides. Structural analysis using LC-ES/MS/MS showed that DHP bound covalently to both 3'- and 5'-guanine, -adenine, and -thymine bases (but not cytosine) of dinucleotides to produce two or more isomers of each DHP-dinucleotide adduct. By comparing adduct formation at dissimilar bases within individual dinucleotides, the relative reactivity of DHP with individual bases was determined to be guanine > adenine approximately thymine. Identification of the entire set of DHP-derived DNA adducts further validates the conclusion that riddelliine is a genotoxic carcinogen and enhances the applicability of these biomarkers for assessing carcinogenic risks from exposure to pyrrolizidine alkaloids.

Effects of monocrotaline pyrrole and thrombin on pulmonary endothelial cell junction and matrix adhesion proteins

Previous work in our laboratory has shown that monocrotaline pyrrole (MCTP) interacts with actin and potentiates thrombin-mediated endothelial barrier permeability through increasing the overall surface area of intercellular gaps. To better characterize endothelial barrier leak in this model, we examined the effects of MCTP and thrombin on the localization and structure of three adhesion associated proteins that directly or indirectly interact with actin in regulating barrier function: cell-cell occludens junction molecule (ZO-1), the cell-cell adherens junction linker, ss-catenin, and the cell-matrix intermediary signaling protein, focal adhesion kinase (FAK). Immunohistochemistry demonstrated that thrombin treatment resulted in radial reorganization of focal adhesions and broader distribution of adherens and occludins junctions at the cell border suggestive of membrane stretching in contracture. MCTP pretreatment resulted in fewer and more disorganized focal adhesions and marked thinning of occludins and adherens junctions. MCTP pretreatment also interfered with thrombin stimulated junctional reorganization. Western blot analysis showed thrombin stimulated catalysis of ZO-1 and FAK while MCTP pretreatment resulted in FAK fragmentation similar to previous reports for apoptosis. We conclude that both MCTP and thrombin alter critical endothelial cell adhesion molecules and this may be an underlying mechanism for the potentiating effect MCTP has on thrombin induced vascular permeability in vitro.

[Monocrotaline induce pulmonary hypertension in animal models]

The pulmonary hypertension is a serious disease, difficult to treat, and its mechanisms remain however to be elucidated. It is known that administration of small doses of MCT or its active metabolite, monocrotaline pyrrole (MCTP); to rats causes delayed and progressive lung injury characterized by pulmonary vascular remodeling which induces pulmonary hypertension. The purpose of this article is to get used to vascular, cellular and molecular changes in pulmonary hypertension, in order to create a personal experimental animal model. This experimental model will try to find new ways of therapeutical strategies in human pulmonary hypertension.

Development of a (32)P-postlabeling/HPLC method for detection of dehydroretronecine-derived DNA adducts in vivo and in vitro

Pyrrolizidine alkaloids are naturally occurring genotoxic chemicals produced by a large number of plants. Metabolism of pyrrolizidine alkaloids in vivo and in vitro generates dehydroretronecine (DHR) as a common reactive metabolite. In this study, we report the development of a (32)P-postlabeling/HPLC method for detection of (i) two DHR-3'-dGMP and four DHR-3'-dAMP adducts and (ii) a set of eight DHR-derived DNA adducts in vitro and in vivo. The approach involves (1) synthesis of DHR-3'-dGMP, DHR-3'-dAMP, and DHR-3',5'-dG-bisphosphate standards and characterization of their structures by mass and (1)H NMR spectral analyses, (2) development of optimal conditions for enzymatic DNA digestion, adduct enrichment, and (32)P-postlabeling, and (3) development of optimal HPLC conditions. Using this methodology, we have detected eight DHR-derived DNA adducts, including the two epimeric DHR-3',5'-dG-bisphosphate adducts both in vitro and in vivo.

Metabolic activation of the tumorigenic pyrrolizidine alkaloid, riddelliine, leading to DNA adduct formation in vivo

Riddelliine is a representative naturally occurring genotoxic pyrrolizidine alkaloid. We have studied the mechanism by which riddelliine induces hepatocellular tumors in vivo. Metabolism of riddelliine by liver microsomes of F344 female rats generated riddelliine N-oxide and dehydroretronecine (DHR) as major metabolites. Metabolism was enhanced when liver microsomes from phenobarbital-treated rats were used. Metabolism in the presence of calf thymus DNA resulted in eight DNA adducts that were identical to those obtained from the reaction of DHR with calf thymus DNA. Two of these adducts were identified as DHR-modified 7-deoxyguanosin-N(2)-yl epimers (DHR-3'-dGMP); the other six were DHR-derived DNA adducts, but their structures were not characterized. A similar DNA adduct profile was detected in the livers of female F344 rats fed riddelliine, and a dose-response relationship was obtained for the level of the total (eight) DHR-derived DNA adducts and the level of the DHR-3'-dGMP adducts. These results suggest that riddelliine induces liver tumors in rats through a genotoxic mechanism and the eight DHR-derived DNA adducts are likely to contribute to liver tumor development.

Vascular remodeling in experimentally induced subacute canine pulmonary hypertension

We quantified in vivo pulmonary vascular remodeling in a large animal model of pulmonary hypertension (PH). In group PH (n = 6), 3 mg/kg dehydromonocrotaline (DHMC) was administered to 12-week-old beagles via a right atrial injection. Eight weeks after DHMC in group PH, pulmonary artery pressure increased significantly (P < .05) from 18 +/- 2 mm Hg at baseline to 30 +/- 4 mm Hg. Medial wall thickness and medial wall area as a percentage of total vessel diameter or area was significantly higher (P < .05) in group PH (29 +/- 9% and 48 +/- 12%) than in a control group (n = 5) (7 +/- 1% and 14 +/- 1%). Neointimal proliferation was observed in 42% of pulmonary arterioles in the PH group but never in the control group. We conclude that a single injection of DHMC in young beagles, in addition to the development of moderate degrees of PH after 8 weeks, causes significant pulmonary vascular remodeling, with features similar to those observed in patients with primary PH.

Protein targets of monocrotaline pyrrole in pulmonary artery endothelial cells

A single administration of monocrotaline to rats results in pathologic alterations in the lung and heart similar to human pulmonary hypertension. In order to produce these lesions, monocrotaline is oxidized to monocrotaline pyrrole in the liver followed by hematogenous transport to the lung where it injures pulmonary endothelium. In this study, we determined specific endothelial targets for (14)C-monocrotaline pyrrole using two-dimensional gel electrophoresis and autoradiographic detection of protein metabolite adducts. Selective labeling of specific proteins was observed. Labeled proteins were digested with trypsin, and the resulting peptides were analyzed using matrix-assisted laser desorption ionization mass spectrometry. The results were searched against sequence data bases to identify the adducted proteins. Five abundant adducted proteins were identified as galectin-1, protein-disulfide isomerase, probable protein-disulfide isomerase (ER60), beta- or gamma-cytoplasmic actin, and cytoskeletal tropomyosin (TM30-NM). With the exception of actin, the proteins identified in this study have never been identified as potential targets for pyrroles, and the majority of these proteins have either received no or minimal attention as targets for other electrophilic compounds. The known functions of these proteins are discussed in terms of their potential for explaining the pulmonary toxicity of monocrotaline.

DNA damage cell checkpoint activities are altered in monocrotaline pyrrole-induced cell cycle arrest in human pulmonary artery endothelial cells

Monocrotaline pyrrole (MCTP) causes cyto- and karyomegaly and persistent cell cycle arrest in the G2 stage of the cell cycle in cultured bovine pulmonary artery endothelial cells. To better characterize the cell cycle regulatory mechanisms of this process as well as determine whether this process would occur in cells of human origin, we treated human pulmonary artery endothelial cell (HPAEC) cultures with MCTP and determined, by flow cytometry, the expression of cyclin B1 and p53 in conjunction with DNA content. We also validated by Western blots that the persistence of cdc2 in its inactivated phosphorylated state, previously described in bovine cell cultures, occurred in HPAEC. Alterations in p53, cyclin A, cyclin B1, and cdc25c expression were also examined in Western blots of treated HPAEC extracts. The response of HPAEC to MCTP was compared with that of adriamycin and nocodazole, agents known to cause cell cycle alterations. Results of these experiments demonstrate that HPAEC treated with MCTP develop a population of cells in G2 that has increased cyclin B1 expression. These cells express increased amounts of cdc2 but not cdc25c. The ratio of inactive triphosphorylated cdc2 to the active monophosphorylated form increased moderately from control cultures in contrast to predominance of the active form in nocodazole-treated cultures. In addition, a second population of cells expressing cyclin B1 had continued incorporation of BrdU and DNA content consistent with 8 N chromosomes. A similar 8 N cell population was evident in nocodazole-treated cells but these cells had both cyclin B1 positive and negative components. Compared with adriamycin, a known inducer of p53, MCTP-treated HPAEC expressed p53 only at high concentrations and p53 expression was not coordinated with G2 arrest or polyploidy. We conclude that HPAEC treated with low concentrations of MCTP develop G2 arrest in association with persistent cyclin B1 expression, failure to completely activate cdc2, and continued DNA synthesis through a pathway that is unrelated to altered expression of p53.

Molecular and functional mechanisms of right ventricular adaptation in chronic pulmonary hypertension

BACKGROUND

Chronic pulmonary hypertension can lead to compensatory changes in the right ventricle. In this study, the adaptive mechanisms of the right ventricle in the setting of pulmonary hypertension were assessed at the molecular and functional level using a canine model of monocrotaline pyrrole-induced pulmonary hypertension.

METHODS

Animals underwent pulmonary artery catheterization to measure pulmonary hemodynamics before and 8 weeks after an injection of monocrotaline pyrrole, 3 mg/kg (n = 8) or placebo (n = 8) (controls). Systolic function was assessed with load-insensitive means (preload-recruitable stroke work). Myocardial biopsy specimens were collected to analyze membrane alpha1- and beta-adrenergic receptor density and adenylate cyclase activity.

RESULTS

Eight weeks after injection, significant increases in pulmonary hemodynamic indices were noted in monocrotaline-injected dogs. Significant increases in right ventricular preload-recruitable stroke work were also observed in these animals compared with controls and occurred in association with significant increases in right ventricular alpha1- and beta-adrenergic receptor density and isoproterenol hydrochloride-stimulated adenylate cyclase activity. No significant differences in basal adenylate cyclase activity in the right ventricle were noted between the two groups.

CONCLUSIONS

These data suggest that alterations in right ventricular function in the setting of chronic pulmonary hypertension may partially be due to changes in myocardial adrenergic receptor signaling.

Dehydromonocrotaline generates sequence-selective N-7 guanine alkylation and heat and alkali stable multiple fragment DNA crosslinks

Monocrotaline is a pyrrolizidine alkaloid known to cause toxicity in humans and animals. Its mechanism of biological action is still unclear although DNA crosslinking has been suggested to a play a role in its activity. In this study we found that an active metabolite of monocrotaline, dehydromonocrotaline (DHM), alkylates guanines at the N7 position of DNA with a preference for 5'-GG and 5'-GA sequences. In addition, it generates piperidine- and heat-resistant multiple DNA crosslinks, as confirmed by electrophoresis and electron microscopy. On the basis of these findings, we propose that DHM undergoes rapid polymerization to a structure which is able to crosslink several fragments of DNA.

Species differences in the hepatic microsomal enzyme metabolism of the pyrrolizidine alkaloids

Species differences in pyrrolic metabolites and senecionine (SN) N-oxide formation among eight animal species (sheep, cattle, gerbils, rabbits, hamsters, Japanese quail, chickens, rats) varying in susceptibility to pyrrolizidine alkaloid (PA) intoxication were measured in vitro by hepatic microsomal incubations. The results suggested that there is not a strong correlation between the production of pyrrolic metabolites and susceptibility of animals to PA toxicity. The rate of PA activation in hamsters, a resistant species, measured by formation of (+/-)6,7-dihydro-7-hydroxy-1-hydroxymethyl-5H-pyrrolizine (DHP) far exceeded the rate of SN N-oxide formation (detoxification) (DHP/N-oxide = 2.29). In contrast, SN N-oxide was the major metabolite in sheep, another resistant species, with much lower production of DHP (DHP/N-oxide = 0.26). The roles of cytochrome P450s and flavin-containing monooxygenases (FMO) in bioactivation and detoxification of pyrrolizidine alkaloids (PA) were studied in vitro using sheep and hamster hepatic microsomes. Chemical and immunochemical inhibition data suggested that the conversion of SN to DHP is catalyzed mainly by cytochrome P450s (68-82%), whereas the formation of SN N-oxide is carried out largely by FMO (55-71%). There also appeared to be a high rate of glutathione-DHP conjugation in hamster (63%) and sheep (79%) liver microsomal incubation mixtures. Therefore, low rates of pyrrole metabolite production coupled with glutathione conjugation in sheep may explain the resistance of sheep to SN, whereas the high rate of GSH-DHP conjugation may be one of the factors contributing to the resistance of hamsters to intoxication by this PA.

Chronic pulmonary hypertension--the monocrotaline model and involvement of the hemostatic system

Monocrotaline (MCT) is a toxic pyrrolizidine alkaloid of plant origin. Administration of small doses of MCT or its active metabolite, monocrotaline pyrrole (MCTP), to rats causes delayed and progressive lung injury characterized by pulmonary vascular remodeling, pulmonary hypertension, and compensatory right heart hypertrophy. The lesions induced by MCT(P) administration in rats are similar to those observed in certain chronic pulmonary vascular diseases of people. This review begins with a synopsis of the hemostatic system, emphasizing the role of endothelium since endothelial cell dysfunction likely underlies the pathogenesis of MCT(P)-induced pneumotoxicity. MCT toxicology is discussed, focusing on morphologic, pulmonary mechanical, hemodynamic, and biochemical and molecular alterations that occur after toxicant exposure. Fibrin and platelet thrombosis of the pulmonary microvasculature occurs after administration of MCT(P) to rats, and several investigators have hypothesized that thrombi contribute to the lung injury and pulmonary hypertension. The evidence for involvement of the various components of the hemostatic system in MCT(P)-induced vascular injury and remodeling is reviewed. Current evidence is consistent with involvement of platelets and an altered fibrinolytic system, yet much remains to be learned about specific events and signals in the vascular pathogenesis.

Monocrotaline pyrrole interacts with actin and increases thrombin-mediated permeability in pulmonary artery endothelial cells

One of the earliest morphologic changes evident in the monocrotaline (MCT) model of pulmonary hypertension in rats is microvascular leak. Whether this represents a direct effect of MCT metabolites or is secondary to inflammatory and thrombotic changes remains uncertain. To determine whether MCT directly affects endothelial cell permeability barrier function, we characterized the interaction of the reactive pyrrole intermediate of MCT (MCTP) with endothelial cell actin and characterized its effects on thrombin-mediated signal transduction and monolayer permeability. Bovine pulmonary endothelial cells (BPAEC) treated with MCTP had altered distribution of filamentous actin evident by fluorescence microscopy. Correlative Western blots and autoradiography of actin isolated from BPAEC treated with 14C-MCTP showed comigration of actin and MCTP-derived 14C. MCTP treatment did not alter cellular free Ca2+ concentrations nor did it interfere with thrombin-mediated intracellular Ca2+ signal. Pretreatment with MCTP significantly augmented the thrombin-mediated transudation of Evan's blue albumin in BPAEC monolayers apparently by increasing the size of intercellular gaps. We conclude that MCTP directly interacts with actin to alter its polymerization state but does not significantly affect endothelial cell response to contractile stimulus. Our results suggest that MCTP may affect endothelial cell barrier function through alterations in intracellular junctions.

Monocrotaline pyrrole induces apoptosis in pulmonary artery endothelial cells

In the monocrotaline (MCT) model of pulmonary hypertension, the pulmonary vascular endothelium is the likely early target of the reactive metabolite monocrotaline pyrrole (MCTP). Incubation of cultured bovine pulmonary arterial endothelial cells (BPAEC) with MCTP results in covalent binding to DNA, cell cycle arrest, and delayed but progressive cell death. The mode of cell death in MCTP-induced endothelial damage has not been addressed previously. Since DNA damage is frequently associated with apoptosis, the presence or absence of apoptosis in adherent BPAEC was determined by several techniques, including morphologic and terminal deoxynucleotidyl transferase (TdT)-mediated dUTP nick end labeling. Two concentrations of MCTP (5 and 34.5 microgram/ml) along with a vehicle control were examined with each assay. Both concentrations of MCTP induced increasing numbers of cells to undergo apoptosis over time beginning as early as 6 h after exposure to MCTP in the high concentration group. Control and vehicle control cells exhibited small amounts of apoptosis (1-2%), which did not change over the duration of the experiment. Additionally, cell membrane integrity was assessed over time by either exposure to membrane-impermeant dyes or measuring LDH release. By either method, BPAEC had increased membrane permeability after about 48 h of either low or high concentration MCTP exposure. We conclude that both a low or high concentration of MCTP causes cell death in BPAEC by inducing apoptosis.

Hemodynamic and inotropic effects of milrinone after heart transplantation in the setting of recipient pulmonary hypertension

BACKGROUND

Right ventricular failure remains an important cause of early morbidity and death after heart transplantation and is commonly related to preexistent recipient chronic pulmonary hypertension, which occurs as a result of long-standing congestive heart failure. In this study, the hemodynamic and inotropic effects of milrinone were assessed after bicaval heart transplantation in the setting of monocrotaline pyrrole-induced recipient chronic pulmonary hypertension.

METHODS

Twenty dogs were used for 10 successfully completed transplantation experiments. Recipient animals underwent right atrial injection of 3 mg/kg monocrotaline pyrrole 4 months before transplantation. Hemodynamic and functional data were taken 1 hour after termination of cardiopulmonary bypass and after milrinone infusion. Myocardial function was assessed with load-insensitive means (preload-recruitable stroke work) and pulmonary vascular impedance was calculated with Fourier analysis.

RESULTS

At the time of transplantation, before cardiopulmonary bypass, pulmonary hemodynamic indexes in recipient animals were significantly increased when compared with donors and were further significantly increased after cardiopulmonary bypass. Two animals died after transplantation as a result of acute right ventricular failure. In surviving animals milrinone infusion led to significant increases in right ventricular function, which occurred in association with significant improvements in pulmonary vascular impedance and transpulmonary efficiency.

CONCLUSIONS

In the setting of monocrotaline pyrrole-induced recipient pulmonary hypertension, milrinone was associated with significant improvements in pulmonary vascular impedance, right ventricular function, and transpulmonary efficiency. These data suggest that milrinone is an effective means to improve right ventricular dysfunction and pulmonary vascular efficiency after bicaval heart transplantation in the setting of recipient chronic pulmonary hypertension.

Prolonged cell-cycle arrest associated with altered cdc2 kinase in monocrotaline pyrrole-treated pulmonary artery endothelial cells

Monocrotaline pyrrole (MCTP), a metabolite of the pyrrolizidine alkaloid monocrotaline, is thought to initiate damage to pulmonary endothelial cells resulting in delayed but progressive pulmonary interstitial edema, vascular wall remodeling, and increasing pulmonary hypertension. MCTP was previously shown to inhibit pulmonary endothelial cell proliferation and cause cell-cycle arrest in vitro. To determine the persistence of arrest and better characterize the cell-cycle stage at which it occurs, bovine pulmonary artery endothelial cells (BPAEC) under differing growth conditions were exposed to low (5 microg/ml) or high (34.5 microg/ml) concentrations of MCTP for varying times. Flow cytometric cell-cycle analysis was coupled with Western blot and biochemical analysis of cdc2 kinase and measurements of cell size. MCTP treatment induced a G2 + M phase arrest in 48-h exposed confluent BPAEC that persisted for at least 28 d and was associated with continued cellular enlargement. A short-duration MCTP exposure of confluent (low and high concentration) and log phase (high concentration) BPAEC caused persistent cell-cycle arrest for 1 wk, whereas a low-concentration exposure in log phase cells resulted in cell-cycle arrest with reversal 96 h after exposure. Western blot examination revealed that by 24 h of MCTP exposure, the phosphorylation state of cdc2 was consistent with the inactive form of the kinase (confirmed by biochemical assay); this alteration persisted through at least 96 h of exposure. We conclude that MCTP induces a progressive irreversible endothelial cell dysfunction leading to inactivation of cdc2 kinase and irreversible cell-cycle arrest at the G2 checkpoint.

The response of pulmonary vascular endothelial cells to monocrotaline pyrrole: cell proliferation and DNA synthesis in vitro and in vivo

Monocrotaline pyrrole (MCTP) causes pulmonary vascular endothelial cell (EC) injury followed by progressive pulmonary vascular leak in vivo and the inhibition of EC proliferation in vitro. It was hypothesized that MCTP inhibits cell proliferation in vitro by interfering with cell cycle progression in a cycle phase-specific manner. Furthermore, it was proposed that early alterations in MCTP-induced lung injury leading to hypertension were associated with a similar inhibition of EC proliferation. Subconfluent cultures of bovine pulmonary artery endothelial cells (BECs) were synchronized with aphidicolin (APH), a reversible G1-S phase inhibitor. Upon removal of APH, BECs were exposed to MCTP (5 micrograms/ml) or its vehicle for a 4-h interval corresponding to either the G1-S, S-G2, or G2 through mitosis (M) phases of the cell cycle. Fluorescence-activated cell sorting (FACS) was used to identify MCTP-induced changes in cell cycle progression in BECs, and the transit of S phase cells through the cycle was characterized through the incorporation of bromodeoxyuridine (BrdU). Synchronized BECs exposed to MCTP between mid-S-G2 or G2 through M were briefly delayed in G2-M at 12 h but underwent cell division by 24 h. By contrast, BECs treated with MCTP immediately after release from APH block became arrested in G2-M at 24 h and showed evidence of continued DNA synthesis and hypertetraploidy, but they did not divide. In vivo, MCTP (3.5 mg/kg i.v.) administration caused an increase in arterial EC BrdU incorporation between Days 3 and 7, but no increase in EC density. During this same interval, pulmonary vascular permeability increased and persisted. In summary, MCTP inhibits cell proliferation in a cell cycle phase-dependent manner in vitro. The results suggest that a similar mechanism could occur in vivo and may be associated with delayed EC repair, a process that could contribute to persistent pulmonary vascular leak.

Effect of monocrotaline metabolites on glutathione levels in human and bovine pulmonary artery endothelial cells

After being dehydrogenated by cytochrome P450 enzymes in the liver, monocrotaline's highly-reactive pyrrole metabolite, dehydromonocrotaline, is believed to interact with pulmonary artery endothelial cells to initiate a pulmonary vascular toxicity resembling pulmonary hypertension. Glutathione, an abundant antioxidant in pulmonary artery endothelial cells, has been shown to react with and detoxify the pyrrolic metabolites derived from monocrotaline in the liver. Using high-performance liquid chromatography with electrochemical detection, glutathione levels were measured in a time- and dose-dependent manner in human pulmonary artery endothelial cells following treatment with dehydromonocrotaline, dehydroretronecine and N-ethylmaleimide and bovine pulmonary artery endothelial cells after treatment with dehydromonocrotaline. The bovine cells had 40% less glutathione than the human in the control groups. Bovine pulmonary artery endothelial glutathione levels were depleted 20% more than the human at 15 minutes when treated with 100 microM dehydromonocrotaline. 15 microM N-ethylmaleimide caused an 80% depletion of glutathione compared to a 30% depletion with 15 microM dehydromonocrotaline in human pulmonary artery endothelial cells.

Pulmonary vascular impedance and recipient chronic pulmonary hypertension following cardiac transplantation

STUDY OBJECTIVES

Recipient chronic pulmonary hypertension (CPH), secondary to long-standing congestive heart failure, represents a significant risk factor for right ventricular (RV) dysfunction following orthotopic cardiac transplantation (TX). This study was designed to characterize the changes occurring in pulmonary hemodynamics, pre-TX and post-TX, using Fourier analysis, a canine model of bicaval TX, and monocrotaline pyrrole (MCTP)-induced recipient CPH.

DESIGN

Prospective, controlled study.

SETTING

Experimental laboratory.

PARTICIPANTS

Twenty adult male mongrel dogs (23 to 26 kg).

INTERVENTIONS

Recipients underwent pulmonary artery injection of 3 mg/kg MCTP 4 months pre-TX. On the day of TX, donor hearts were instrumented with an ultrasonic flow probe and micromanometers. Harmonic derivation of functional data was achieved with Fourier analysis.

MEASUREMENTS AND RESULTS

At the time of TX, significant increases were observed in the mean pulmonary artery pressure and pulmonary vascular resistance of recipient animals in comparison to donors, which were further significantly increased following the termination of cardiopulmonary bypass. Significant increases were also observed in the input resistance, characteristic impedance, and RV hydraulic power post-TX compared to pre-TX, and occurred in association with a significant decrease in the transpulmonary efficiency.

CONCLUSIONS

In the setting of MCTP-induced recipient CPH donor hearts were exposed to significant alterations in cardiopulmonary hemodynamics following bicaval TX. Pulmonary blood flow is maintained by a significantly higher energy expenditure by the RV, but at a lower level of efficiency. This experimental model may provide a useful means by which to evaluate therapeutic options to better manage cardiopulmonary hemodynamics in order to prevent RV failure following TX in the setting of recipient CPH.

Bioactivation of monocrotaline by P-450 3A in rat liver

Monocrotaline (MCT) is bioactivated in liver cytochrome P-450s to MCT pyrrole (MCTP), which primarily injures the lung endothelium to result in the development of pulmonary hypertension (PH) in rats. However, whether there is a relation between the degree of PH and the activity of liver cytochrome P-450 to convert MCT to MCTP remains unclear. To examine the relation between these physiological and biochemical changes, we first measured the severity of MCT-induced (20 mg/kg) PH in male, female, castrated male, and phenobarbital (PB, liver P-450s inducer)-pretreated male rats. The degree of right ventricular hypertrophy was more severe in PB-pretreated male than in control male rats. It was also more severe in male than in either female or castrated male rats, suggesting that sex-specific P-450s could be involved in the metabolic pathways of MCT in the liver. Further to explore which of the isozymes (2A2, 2C11, and 3A) of P-450s in the liver is responsible for the bioactivation of MCT, we measured the rate of MCTP production in hepatic microsomes by a modified Mattock's method. Treatment of male rats with PB and pregnenolone 16alpha-carbonitrile (PCN), which is the specific inducer of P-450 3A, increased the rate of MCTP production, suggesting that P-450 3A may contribute to the conversion to pyrrole. Therefore we measured the amount of P-450 3A protein by immunoblotting and attempted to inhibit MCT metabolism by using antibodies to P-450 3A. P-450 3A was significantly induced by PCN (6.5-fold) and PB (4.6-fold) treatment and reduced by castration (0.38-fold). The amount of P-450 3A was closely correlated with the production of MCTP, and the conversion of MCT to MCTP was strongly inhibited by antibodies against P-450 3A. These results indicated that P-450 3A was predominantly responsible for the metabolism of MCT to MCTP in rat liver and suggested a tight linkage between the degree of PH and the activity of liver P-450 3A.

Hypertrophy and prolonged DNA synthesis in smooth muscle cells characterize pulmonary arterial wall thickening after monocrotaline pyrrole administration to rats

Monocrotaline pyrrole (MCTP) is a highly reactive pneumotoxic metabolite of the pyrrolizidine alkaloid plant toxin monocrotaline. When administered to rats, it causes a delayed and progressive lung injury, vascular remodeling, and pulmonary hypertension. Structural remodeling consists of endothelial cell swelling followed by increased thickness of the vascular media in small pulmonary arteries and muscularization of normally nonmuscular arteries. Experiments were performed to characterize DNA synthesis and cell proliferation in vascular smooth muscle cells (VSMCs) after MCTP and to determine their relationship to changes in the thickness of the arterial medial layer of pulmonary resistance vessels. Male Sprague-Dawley rats were treated with MCTP (3.5 mg/kg, intravenously) or its vehicle (dimethylformamide). To label cells actively synthesizing DNA, rats were given the thymidine analog, bromodeoxyuridine (BrdU), 3 times by intraperitoneal injection during the 24 hr preceding euthanasia. Using immunohistochemistry, BrdU incorporation was quantified as a ratio of labeled nuclei to total nuclei. Within 5 days after MCTP administration, the thickness of the medial smooth muscle layer in arteries 60-250 microm in diameter was increased, prior to evidence of right heart hypertrophy. BrdU incorporation by VSMCs in pulmonary arteries was not different in vehicle- and MCTP-treated rats for the first 48 hr after treatment. However, MCTP caused a significant increase in DNA synthesis in VSMC on days 3-8 in arteries up to 250 microm in diameter. Although increased DNA synthesis precedes cell proliferation, the relative number of medial VSMCs did not increase over 8 days, suggesting that hypertrophy alone was responsible for the increased thickness of the arterial media. These results demonstrate that MCTP causes thickening of the media of pulmonary vessels through VSMC hypertrophy and that the prolonged DNA synthesis that accompanies VSMC hypertrophy is not followed by proliferation.

Association of dehydromonocrotaline with rat red blood cells

The association of radiolabeled monocrotaline pyrrole (DHM) with red blood cell (RBCs) ghosts, globins, and heme was examined to determine their role in the transport and stabilization of this hepatic produced putative toxic metabolite of the pyrrolizidine alkaloid monocrotaline (MCT). Rats were administered 5 mg of DHM/kg, i.v., and RBCs and plasma were harvested at 4 and 24 h. Extensive washing of the RBCs with isotonic phosphate buffer did not decrease the amount of radioactivity associated with the cells. The level of DHM equivalents recovered in the RBCs did not decrease between 4 and 24 h, while the plasma levels, which were 29- and 75-fold lower, respectively, decreased from 5.0 to 2.2 nmol of DHM equiv/g of plasma. Globin chains were found to contain 383 and 453 pmol of DHM equiv/mg of protein, respectively. Rats receiving 10 mg of DHM/kg, i.v., with RBCs collected at 2 h, had approximately double the level of radioactivity associated with their RBCs in addition to 2 times the amount of adducts on the globin chains. Globins and ghosts plus heme (2 h) contained 69% and 2% of the radioactivity, respectively. Globin chains treated with an acidic ethanol solution containing AgNO3 resulted in the removal of 31% of the associated radioactivity. GC/ MS and TLC separation of AgNO3-displaced material revealed the presence of the ethyl ether derivatives of 7-hydroxy-1-(hydroxymethyl)-6,7-dihydro-5H-pyrrolizine. The HPLC separation of globin chains revealed that the majority of radioactivity coeluted with the beta-chains. In conclusion, this study found that the administration of radiolabeled DHM resulted in extensive radioactive labeling of RBCs; similar findings have been reported for [14C]MCT.

Hemodynamic and inotropic effects of nitric oxide in pulmonary hypertension

Right ventricular failure following cardiac transplantation is most commonly related to pre-existent recipient pulmonary hypertension secondary to chronic congestive heart failure. Although nitric oxide has had some role clinically in improving pulmonary hemodynamics and right ventricular function in this setting, an appropriate large-animal model of stable pulmonary hypertension has not been available for basic investigation of this problem. This study was designed to examine the hemodynamic and inotropic effects of inhaled nitric oxide using a canine model of monocrotaline pyrrole-induced chronic pulmonary hypertension. Eight mongrel dogs (22-25 kg) were used. All animals underwent percutaneous pulmonary artery catheterization to measure right heart hemodynamics prior to and 8 weeks after a right atrial injection of monocrotaline pyrrole. Eight weeks post-injection, all hearts were instrumented with a pulmonary artery flow probe, sonomicrometric dimension transducers, and micromanometers. Data were collected at baseline and following nitric oxide administration. Eight weeks post-monocrotaline pyrrole injection, significant increases were observed in the pulmonary hemodynamics compared to pre-injection. Nitric oxide led to significant decreases in pulmonary vascular impedance. Significant improvements in pulmonary blood flow, transpulmonary efficiency, and right ventricular contractility were also observed. This investigation demonstrates the well-known clinical effects of nitric oxide in improving pulmonary hemodynamics which were also associated with an increase in pulmonary blood flow, transpulmonary efficiency, and right ventricular contractility in the setting of monocrotaline pyrrole-induced pulmonary hypertension.