Glutathione-S-transferase protects against oxidative injury of endothelial cell tight junctions.

Oxidative damage of endothelial tight junction permeability is involved in the pathophysiology of a variety of vascular diseases. The authors studied the role of the antioxidant enzyme, human glutathione-S-transferase A4-4 (hGSTA4-4), in regulating expression of major molecules of tight junction in vascular endothelial cells under oxidative stress induced by H(2)O(2). A vascular endothelial cell line, mouse pancreatic endothelial cells (MS1), was transduced with recombinant adenoviral vector containing hGSTA4-4 gene. hGSTA4-4 induced expression of tight junction proteins occludin and zonula occludens (ZO)-1 under oxidative stress. Increased hGSTA4-4 expression correlated with increased transepithelial electrical resistance and decreased tyrosine phosphorylation of occludin and ZO-1 following exposure to H(2)O(2). In addition, morphologic dissociation of occludin, ZO-1, and F-actin during oxidative stress was reduced in hGSTA4-4-expressing cells. To explore a genetic approach for vascular diseases associated with disruption of tight junction proteins, we introduced the same viral vector to blood vessels of mice, rats, and rabbits ex vivo and found strong expression of hGSTA4-4 in endothelial cells. These results demonstrate that oxidative stress mediated disruption of tight junctions in endothelial cells may be attenuated by hGSTA4-4 expression.

Acrolein generation stimulates hypercontraction in isolated human blood vessels.

Increased risk of vasospasm, a spontaneous hyperconstriction, is associated with atherosclerosis, cigarette smoking, and hypertension-all conditions involving oxidative stress, lipid peroxidation, and inflammation. To test the role of the lipid peroxidation- and inflammation-derived aldehyde, acrolein, in human vasospasm, we developed an ex vivo model using human coronary artery bypass graft (CABG) blood vessels and a demonstrated acrolein precursor, allylamine. Allylamine induces hypercontraction in isolated rat coronary artery in a semicarbazide-sensitive amine oxidase activity (SSAO) dependent manner. Isolated human CABG blood vessels (internal mammary artery, radial artery, saphenous vein) were used to determine: (1) vessel responses and sensitivity to acrolein, allylamine, and H(2)O(2) exposure (1 microM-1 mM), (2) SSAO dependence of allylamine-induced effects using SSAO inhibitors (semicarbazide, 1 mM; MDL 72274-E, active isomer; MDL 72274-Z, inactive isomer; 100 microM), (3) the vasoactive effects of two other SSAO amine substrates, benzylamine and methylamine, and (4) the contribution of extracellular Ca(2+) to hypercontraction. Acrolein or allylamine but not H(2)O(2), benzylamine, or methylamine stimulated spontaneous and pharmacologically intractable hypercontraction in CABG blood vessels that was similar to clinical vasospasm. Allylamine-induced hypercontraction and blood vessel SSAO activity were abolished by pretreatment with semicarbazide or MDL 72274-E but not by MDL 72274-Z. Allylamine-induced hypercontraction also was significantly attenuated in Ca(2+)-free buffer. In isolated aorta of spontaneously hypertensive rat, allylamine-induced an SSAO-dependent contraction and enhanced norepinephrine sensitivity but not in Sprague-Dawley rat aorta. We conclude that acrolein generation in the blood vessel wall increases human susceptibility to vasospasm, an event that is enhanced in hypertension.

Vasoactive effects of methylamine in isolated human blood vessels: role of semicarbazide-sensitive amine oxidase, formaldehyde, and hydrogen peroxide.

It is hypothesized that methylamine (MA) and semicarbazide-sensitive amine oxidase (SSAO) activity are involved in the cardiovascular complications in human diabetics. To test this, we 1) determined the acute vasoactive effects of MA (1-1,000 micromol/l) in uncontracted and norepinephrine (NE; 1 micromol/l)-precontracted human blood vessels used for coronary artery bypass grafts [left internal mammary artery (LIMA), radial artery (RA), and right saphenous vein (RSV)]; 2) tested whether MA effects in LIMA and RSV were dependent on SSAO activity using the SSAO inhibitor semicarbazide (1 mmol/l, 15 min); 3) determined the effects of MA metabolites formaldehyde and hydrogen peroxide in LIMA and RSV; 4) tested whether the MA response was nitric oxide, prostaglandin, or hyperpolarization dependent; 5) measured the LIMA and RSV cGMP levels after MA exposure; and 6) quantified SSAO activity in LIMA, RA, and RSV. In NE-precontracted vessels, MA stimulated a biphasic response in RA and RSV (rapid contraction followed by prolonged relaxation) and dominant relaxation in LIMA (mean +/- SE, %relaxation: 55.4 +/- 3.9, n = 30). The MA-induced relaxation in LIMA was repeatable, nontoxic, and age independent. Semicarbazide significantly blocked MA-induced relaxation (%inhibition: 82.5 +/- 4.8, n = 7) and SSAO activity (%inhibition: 98.1 +/- 1.3, n = 26) in LIMA. Formaldehyde (%relaxation: 37.3 +/- 18.6, n = 3) and H(2)O(2) (%relaxation: 55.6 +/- 9.0, n = 9) at 1 mmol/l relaxed NE-precontracted LIMA comparable with MA. MA-induced relaxation in LIMA was nitric oxide, prostaglandin, and possibly cGMP independent and blocked by hyperpolarization. We conclude that vascular SSAO activity may convert endogenous amines, like MA, to vasoactive metabolites.

Culture medium enhances semicarbazide-sensitive amine oxidase activity.

Components of fetal calf serum (FCS) are known to contribute to growth and maintenance of cultured cells. Fetal calf serum supplementation of media also may contribute to the cytotoxicity of other substances to cells grown in vitro. Semicarbazide-sensitive amine oxidase (SSAO) enzyme, present in FCS, metabolizes primary amines and contributes to amine cytotoxicity in vascular smooth muscle cells (VSMC). In cell culture experiments, the media used may greatly affect enzymic activities such as SSAO. In these studies, the SSAO activity in FCS, cultured rat aortic VSMC, and rat plasma was determined in the presence and absence of various culture media. Semicarbazide-sensitive amine oxidase activity in FCS (5-20 microl) was significantly enhanced (approximately 1.5- to 2-fold) in the presence of various culture media, with Dulbecco modified Eagle medium (DMEM), causing the greatest enhancement. Dulbecco modified Eagle medium enhanced the SSAO activity of cultured VSMC in two of the four passages but reduced activity in two passages. Activity in rat plasma was reduced by approximately 25% in the presence of DMEM. The concentrations of various media components, such as glucose, sodium pyruvate, pyridoxine.HCl, and L-glutamine, were not correlated with enhancement. This study identifies an important enhancement effect of culture media on the FCS enzyme, SSAO, although the media components responsible for the enhancement are yet to be identified.

Identification of biochemical pathways for the metabolism of oxidized low-density lipoprotein derived aldehyde-4-hydroxy trans-2-nonenal in vascular smooth muscle cells.

Oxidation of low-density lipoproteins (LDL) generates high concentrations of unsaturated aldehydes, such as 4-hydroxy trans-2-nonenal (HNE). These aldehydes are mitogenic to vascular smooth muscle cells and sustain a vascular inflammation. Nevertheless, the processes that mediate and regulate the vascular metabolism of these aldehydes have not been examined. In this communication, we report the identification of the major metabolic pathways and products of [(3)H]-HNE in rat aortic smooth muscle cells in culture. High-performance liquid chromatography separation of the radioactivity recovered from these cells revealed that a large (60-65%) proportion of the metabolism was linked to glutathione (GSH). Electrospray mass spectrometry showed that glutathionyl-1,4 dihydroxynonene (GS-DHN) was the major metabolite of HNE in these cells. The formation of GS-DHN appears to be due aldose reductase (AR)-catalyzed reduction of glutathionyl 4-hydroxynonanal (GS-HNE), since inhibitors of AR (tolrestat or sorbinil) prevented GS-DHN formation, and increased the fraction of the glutathione conjugate remaining as GS-HNE. Gas chromatography-chemical ionization mass spectroscopy of the metabolites identified a subsidiary route of HNE metabolism leading to the formation of 4-hydroxynonanoic acid (HNA). Oxidation to HNA accounted for 25-30% of HNE metabolism. The formation of HNA was inhibited by cyanamide, indicating that the acid is derived from an aldehyde dehydrogenase (ALDH)-catalyzed pathway. The overall rate of HNE metabolism was insensitive to inhibition of AR or ALDH, although inhibition of HNA formation by cyanamide led to a corresponding increase in the fraction of HNE metabolized by the GSH-linked pathway, indicating that ALDH-catalyzed oxidation competes with glutathione conjugation. These metabolic pathways may be the key regulators of the vascular effects of HNE and oxidized LDL.

Amine metabolism: a novel path to coronary artery vasospasm.

We hypothesized that allylamine (AA) induces subendocardial necrosis in mammals via coronary artery (CA) vasospasm. Additionally, AA toxicity is likely dependent on the enzyme semicarbazide-sensitive amine oxidase (SSAO), which is highly expressed in the aorta of rats and humans. We tested whether AA or acrolein (1, 10, 100, and 1000 microM), a highly reactive product of AA metabolism by SSAO, could contract CA or thoracic aorta (TA) in vitro and if the AA effects involved SSAO. AA or acrolein produced a similar pattern of responses in both CA and TA rings at 100 and 1000 microM, including (1) increased basal tension, (2) enhanced agonist-induced contraction (hypercontractility or vasospasm), (3) remarkable, agonist-induced slow wave vasomotion (vasospasm), and (4) irreversible reduction in vessel contractility after 1 mM exposure. Endothelium-dependent acetylcholine-induced relaxation was not altered during vasospasm in either vessel. Pretreatment with the SSAO inhibitor semicarbazide (1 mM; 10 min) prevented or significantly reduced the majority of AA's effects in both CA and TA rings and inhibited 100% of the SSAO activity present in rat TA and human CA and TA. We propose a two-step model for AA induction of CA vasospasm and resultant myocardial necrosis: (1) metabolism of AA to acrolein by coronary arterial SSAO activity and (2) acrolein induction of CA vasospasm independent of endothelial injury-a novel path.

Initiation of alcoholic fatty liver and hepatic inflammation with a specific recall immune response in alcohol-consuming C57Bl/6 mice.

Whether immunological responses are involved in initiation and progression of alcoholic liver disease is unclear. We describe a mouse model of alcoholic liver injury characterized by steatosis and hepatic inflammation initiated by a recall immune response. Mice immune to Listeria monocytogenes fed a liquid diet containing ethanol and challenged with viable bacteria developed steatosis within 24 h and, at a later time, elevated serum alanine aminotransferase levels, indicating more liver damage in this group. Listeria antigen also induced steatosis and increased serum alanine aminotransferase levels in immune ethanol-consuming mice. The production of tumour necrosis factor by a recall immune response in this model is a major, but not the only, component in initiation of alcoholic liver disease.

Cultured rat vascular smooth muscle cells are resistant to methylamine toxicity: no correlation to semicarbazide-sensitive amine oxidase.

Methylamine (MA), a component of serum and a metabolite of nicotine and certain insecticides and herbicides, is metabolized by semicarbazide-sensitive amine oxidase (SSAO). MA is toxic to cultured human umbilical vein and calf pulmonary artery endothelial cells. Endothelial cells, which do not exhibit endogenous SSAO activity, are exposed to SSAO circulating in serum. In contrast, vascular smooth muscle cells (VSMC) do exhibit innate SSAO activity both in vivo and in vitro. This property, together with the critical localization of VSMC within the arterial wall, led us to investigate the potential toxicity of MA to VSMC. Cultured rat VSMC were treated with MA (10-5 to 1 M). In some cultures, SSAO was selectively inhibited with semicarbazide or MDL-72145 [(E)-2-(3,4-dimethoxyphenyl)-3-fluoroallylamine]. Cytotoxicity was measured via MTT, vital dye exclusion, and clonogenic assays. MA proved to be toxic to VSMC only at relatively high concentrations (LC(50) of 0.1 M). The inhibition of SSAO with semicarbazide or MDL-72145 did not increase MA toxicity, suggesting that the production of formaldehyde via tissue-bound, SSAO-mediated MA metabolism does not play a role in the minimal toxicity observed in isolated rat VSMC. The omission of fetal calf serum (FCS), which contains high SSAO activity, from media similarly showed little effect on cytotoxicity. We conclude that VSMC--in contrast to previous results in endothelial cells--are relatively resistant to MA toxicity, and SSAO does not play a role in VSMC injury by MA.

Attenuation of isoproterenol-mediated myocardial injury in rat by an inhibitor of polyamine synthesis.

OBJECTIVE: Ornithine decarboxylase (ODC) is an initial rate-limiting enzyme in the synthesis of polyamines (putrescine, spermidine, and spermine) that play a role in cell growth and differentiation. Recent studies have shown that spermidine and spermine cause injury to a variety of cells including myocytes in vitro. In this investigation, we used alpha-difluoromethylornithine (DFMO), a specific and irreversible inhibitor of ODC activity and polyamine synthesis to test the hypothesis that polyamines contribute to myocardial injury in rat. METHODS: Male Sprague Dawley rats were treated with (i) saline (0.2 ml/day, s.c.), (ii) isoproterenol (ISO) (5 mg/kg/day for 8 days, s.c.) to produce necrotizing myocardial injury, or with (iii) DFMO + ISO. DFMO was started 2 days before the initiation of ISO and both ISO and DFMO were continued until the end of the experimental period. Myocardial injury was assessed by determining the increased release of creatine phosphokinase (CPK) and lactate dehydrogenase (LDH) into the plasma, and by morphometric analysis of the lesion area in heart sections stained with Gomori trichrome. RESULTS: ISO induced the release of CPK and LDH by 6 hr and 24 hr, respectively, and produced subendocardial necrosis, which was both acute and resolving following 8 days of ISO. DFMO treatment inhibited ISO-induced increases in (i) ODC activity and putrescine and spermidine levels in heart, (ii) CPK and LDH activity in plasma, and (iii) the area of subendocardial lesions. CONCLUSIONS: These observations suggest that polyamines are one of the intracellular factors that contribute to ISO-mediated cardiac injury in the rat.

Oncogenic ras results in increased cell kill due to defective thermoprotection in lung cancer cells.

BACKGROUND: The survival response of normal cells to heat stress is an upregulation of heat shock proteins and ras protein activation. We hypothesized that in lung cancer cells the presence of oncogenic ras interferes with thermoprotective mechanisms resulting in cell death. METHODS: An equal number of lung tissue culture cells (normal and cancerous) were subjected to either heat stress and then recovery (43 degrees C for 180 minutes, 37 degrees C for 180 minutes) or recovery alone (37 degrees C for 360 minutes). End points were surviving number of cells, cell-death time course, heat shock protein (HSP70, HSC70, HSP27) expression before and after heat stress, and time course for HSP70 expression during heat stress and recovery. Heated cells were compared with unheated control cells, then this difference was compared between cell types. RESULTS: Heat stress in normal cells caused an 8% decrease in cell number versus a 78% +/- 5% decrease in cancer cells (p < 0.05). In normal cells, heat stress caused a 4.4-fold increase in HSP70, no change in HSC70, and a 1.7-fold increase in HSP27. In contrast, cancer cells initially contained significantly less HSP70 (p < 0.05), and there was a 27-fold increase in HSP70 and a 2-fold increase in HSC70 with no HSP27 detected (comparison significant, p < 0.05). HSP70 time course in normal cells showed that HSP70 increased 100-fold, reaching a vertex at 2 hours and remaining elevated for 24 hours; in cancer cells, HSP70 maximum expression (100-fold) peaked at 5 hours,,then decreased to slightly elevated at 24 hours. CONCLUSIONS: Cancer cells with oncogenic ras have defective thermoprotective mechanism(s) causing increased in vitro cell death, which provides an opportunity for thermal treatment of lung cancer.

Development of a human to murine orthotopic xenotransplanted lung cancer model.

The goal was to develop a clinically relevant animal model that could be used to assess the efficacy of therapeutic interventions in lung cancer. Two cell lines, noncancerous control (BEAS2-B, immortalized human bronchial-epithelial cell line) and cancerous (BZR-T33, H-ras transformed BEAS2-B) were implanted into nude (athymic) mice. Two groups (n = 10 each) received dorsoscapular subcutaneous injection of 10(6) cells from either cell line. BEAS2-B cells were nontumorigenic, whereas mice with BZR-T33 cells had tumors (9,510 +/- 4,307 mm3) confirmed by histology, and a significantly smaller body weight (BZR-T33, 28.5 +/- 0.49 vs. BEAS2-B, 30.7 +/- 0.75 g, p < .05). The next phase evaluated invasion/metastasis. Two groups (n = 10 each) received 10(6) cells from either cell line injected into tail veins. Animals receiving BZR-T33 cells had a smaller body weight, palpable lung masses (67%), obvious tail masses (44%), and average tumor burden (1,120 +/- 115 mm3), and histology revealed invasion of lung tissue and interstitial hemorrhage. In development of the orthotopic xenotransplanted model, mice (2 groups, n = 10 each) received 10(6) cells from either cell line implanted into the lungs through a tracheotomy. Animals with BZR-T33 cells did not survive past 59 days and had a smaller body weight, increased lung weight, lung masses (100%), and metastatic loci (30%). Magnetic resonance imaging (MRI) confirmed the presence of masses in intubated live mice, later confirmed by histology. In summary, the H-ras transfected cell line developed lung masses following tail-vein injection and endotracheal seeding. Evaluation by MRI allows for a comprehensive model with significant potential in the study of lung cancer.

The role of plasma semicarbazide-sensitive amine oxidase in allylamine and beta-aminopropionitrile cardiovascular toxicity: mechanisms of myocardial protection and aortic medial injury in rats.

Allylamine (AA; 3-aminopropene) and beta-aminopropionitrile (betaAPN) combined treatment (AA + betaAPN) results in myocardial protection from AA-induced subendocardial necrosis and a rapid and extensive aortic medial smooth muscle injury in rats. To determine the mechanisms of AA + betaAPN-induced vascular toxicity, cardiovascular parameters were monitored during a 10-day exposure by gavage in male Sprague-Dawley rats (180-200 g). Water intake and urine output were measured in rats treated with water, AA (100 mg kg(-1) body weight), betaAPN (1 g kg(-1) body weight), and AA + betaAPN for 10 days in metabolic cages. Plasma and urine samples were analyzed for blood urea nitrogen, CO2, creatinine, hematocrit, electrolytes (Na+, K+, Cl-), and osmolality. Heart and plasma semicarbazide-sensitive amine oxidase metabolic capacity (SSAO)was also measured following 1, 3 and 10 days of treatment. Following 10 day exposure to control or AA + betaAPN treatment, thoracic aortic rings (approximately 3 mm) were removed, and aortic reactivity to contractile and relaxant agonists was tested in vitro. In addition, cultured rat aorta vascular smooth muscle cells or rat heart beating myocytes were exposed to various concentrations of AA and betaAPN or AA metabolites and betaAPN to test for synergism in vitro. Several of the changes in in vivo cardiovascular parameters were shared, both in direction and magnitude, between the AA + betaAPN and the AA alone or the betaAPN alone treatments. This suggests that these effects (e.g. increased water intake and urine flow, decreased hematocrit, decreased heart and plasma SSAO metabolic capacity) were dependent on an AA alone or a betaAPN alone effect and were not AA + betaAPN specific effects. Significant inhibition of plasma and heart SSAO metabolic capacity occurred in the betaAPN alone and the AA + betaAPN treatments, but not in the AA alone treatment. Aortic rings from AA + betaAPN treated rats were contracted significantly less than anatomically-matched control rat aortic rings by 100 mM potassium chloride or by 10 microM norepinephrine. BetaAPN offered substantial protection against AA cytotoxicity in cultured vascular smooth muscle cells and beating myocytes, but did not alter the cytotoxicity of AA metabolites (i.e. acrolein, H2O2, or ammonia) in vascular smooth muscle cells as determined by the MTT viability assay. Overall, these data suggest that myocardial protection from AA injury that occurs in the combined AA + betaAPN treatment is likely due to inhibition of plasma SSAO. This may result in an increase in the AA dose accumulation and metabolism in the aorta leading to the severe aortic medial injury.

Role of glutathione S-transferase 8-8 in allylamine resistance of vascular smooth muscle cells in vitro.

Allylamine (AA) is a cardiovascular toxin that causes lesions resembling atherosclerosis in several mammalian species. AA's toxic effects are thought to be exerted through its conversion to acrolein (AC), a potent electrophilic alkylating agent and atherogen. Semicarbazide sensitive amine oxidase (SSAO) catalyzes the oxidation of AA to AC. Glutathione S-transferases (GST) can catalyze the first step of detoxification of AC to mercapturic acid. Our previous studies suggest that the isozyme rGST8-8 is a principal defense against electrophilic stress exerted by alpha,beta-unsaturated carbonyls such as AC. In the present studies, we use cultured rat vascular smooth muscle cells (VSMC) to examine the relative roles of SSAO and rGST8-8 in the cytotoxic effects of the atherogens, AA and AC. Exposure derived AA-resistant cells (VSMC-AA) were 3.5-fold more resistant to AA when compared to VSMC and 1.8-fold more resistant to acrolein. SSAO activity was 2-fold higher in VSMC-AA than in VSMC. Consistent with the role of SSAO in biotransformation of AA, the SSAO inhibitor semicarbazide (SC; 100 microM) provided nearly complete protection from AA to both VSMC-AA and VSMC. As expected, SC did not affect the cytotoxicity of AC. Pretreatment with 100 microM sulfasalazine (SS), a GST inhibitor, potentiated AA and AC toxicity in both VSMC-AA and VSMC, indicating a protective role of GST. Catalytic efficiency (K(cat)/K(m)) of GSTs was higher toward 4-hydroxynonenal (4-HNE) (0.65 mM(-1) s(-1)) than toward 1-chloro-2, 4-dinitrobenzene (CDNB) (0.14 mM(-1) s(-1)) for VSMC. In VSMC-AA, K(cat)/K(m) was increased 4.1-fold toward CDNB (0.58 mM(-1) s(-1)) and 6-fold toward 4HNE (3.9 mM(-1) s(-1)) when compared to VSMC, indicating a preferential increase in VSMC-AA of GST isozymes which utilize alpha,beta-unsaturated carbonyls. Western blots confirmed induction of rGST8-8 in VSMC-AA. Expression of recombinant mGSTA4 (the mouse homolog of rGST8-8) in VSMC caused a 1.6-fold increase in resistance to AA and AC. This resistance was fully reversed by 50 microM SS. Our results demonstrate that GSTs are an important defense against electrophilic atherogens and that isozymes with high activity toward alpha,beta-unsaturated carbonyls are particularly important in the vascular wall.

Iron exacerbates aniline-associated splenic toxicity.

Our earlier studies have shown that aniline exposure in rats causes time- and dose-dependent accumulation of iron in the spleen, which may exacerbate aniline splenotoxicity by catalyzing free-radical reactions. The present studies were conducted to test whether aniline-induced splenic toxicity could be potentiated by iron overload. For 30 d male Sprague-Dawley rats received the following treatments: 0.5 mmol/kg/d aniline hydrochloride (AH) by gavage (AH group); 3% carbonyl iron-supplemented diet (IR group); 0.5 mmol/kg/d AH by gavage and iron-supplemented diet (AH + IR group); or no treatments (controls). Treatment-related significant increases in total iron, low molecular weight chelatable iron, lipid peroxidation, and protein oxidation were observed in the spleens of all the groups compared to control. However, these changes were much greater in the combined AH + IR group. The aniline-induced morphological changes in the spleen were consistent with our earlier observations, but were more pronounced in the AH + IR group. The increased toxicity, as evident from greater oxidative stress and morphological changes in the AH + IR group, suggests that iron potentiates the splenic toxicity of aniline.

Oxidative modification of lipids and proteins in aniline-induced splenic toxicity.

Our earlier studies with aniline suggested the involvement of oxidative stress as an early toxic event in the spleen. In order to understand the status and consequences of the damaging oxidative reactions, especially during the progression of characteristic splenic lesions, time-dependent subchronic studies were conducted in rats. Male Sprague-Dawley rats were treated with 65 mg/kg/day aniline in the drinking water, while control rats received drinking water only. The animals were euthanized after 1, 2, or 3 months of aniline exposure. Total iron content was remarkably greater in the aniline-treated rats than in age-matched controls. There were time-dependent increases in splenic lipid peroxidation of aniline-treated rats. Malondialdehyde-protein adducts were quantitated by a competitive ELISA and showed greater concentrations in the spleens of aniline-treated rats, further substantiating our lipid peroxidation results. Protein oxidation in the spleens of aniline-treated rats was also greater, with a maximum increase of approximately 76% at 3 months. Western blot analysis for oxidized proteins showed two distinct protein bands at approximately 114 kD and approximately 69 kD in both post-nuclear and mitochondrial fractions of the spleens. Furthermore, densitometric analysis of the blot showed increased band intensities of the oxidized proteins in both these spleen fractions from aniline-treated rats, suggesting the susceptibility of these proteins to aniline-induced oxidative stress. The most prominent morphological changes in the spleens of aniline-treated rats included thickening of the capsule, and capsular cells with nuclear prominence and hyperchromia indicative of capsular hyperplasia. These capsular changes and fibrosis of capsule, splenic trabeculae, and red pulp were noted at all three time points after aniline exposure. Our studies thus suggest that aniline-induced oxidative stress in the spleen is an ongoing event that leads to oxidative modifications of biomolecules. Such oxidative modifications, directly or indirectly, could contribute to the splenic toxicity leading to deleterious consequences, including capsular hyperplasia and fibrosis, as observed in this study, and possibly tumorigenesis in chronic aniline exposure conditions.

Developmental vasculotoxicity associated with inhibition of semicarbazide-sensitive amine oxidase.

The endogenous substrate(s) and physiological function(s) of semicarbazide-sensitive amine oxidase (SSAO), a group of enzymes exhibiting highest activity in vascular smooth muscle cells of the mammalian aortic wall, remain undetermined. This study examines the pathophysiological effects in the thoracic aortic wall resulting from specific in vivo SSAO inhibition. Weanling Sprague-Dawley rats were treated acutely or chronically with either semicarbazide hydrochloride or the allylamine derivatives MDL-72274 or MDL-72145 (Marion Merrell Dow Research Institute, Cincinnati, OH). Treatment with these compounds produced acute (6 and 24 h) and chronic (21 day) lowering of SSAO activity in aorta and lung with little effect on the activity of the vital matrix-forming enzyme, lysyl oxidase, in aortas of chronically treated animals. Chronic SSAO inhibition produced lesions consisting of striking disorganization of elastin architecture within the aortic media accompanied by degenerative medial changes and metaplastic changes in vascular smooth muscle cells. No significant difference in the total weight of dry, lipid-extracted aortic elastin and collagen components were observed between chronically SSAO inhibited and control animals. However, the amount of mature elastin was lowered and mature collagen was raised in the aortas of animals treated chronically with semicarbazide. Descending thoracic aortic rings isolated from chronically SSAO-inhibited animals had larger cross-sectional diameters (i.e., exhibited dilation) when compared to corresponding rings from control animals. This study demonstrates that developmental toxicity, characterized by striking vascular lesions and dilated thoracic aortas, can result from specific in vivo SSAO inhibition, suggesting a role for SSAO in connective tissue matrix development and maintenance, and specifically in the development of normal elastin.

Heart donation after lightning strike.

We present the first reported case of heart donation after lightning strike. Approximately 150 to 300 generally young and healthy people die from lightning strike in the United States each year. These unfortunate victims may make good heart donors. Pertinent pathophysiology of lightning strike is briefly reviewed.

The role of glutathione S-transferases as a defense against reactive electrophiles in the blood vessel wall.

The glutathione transferases (GSTs) are a family of ubiquitous enzymes that catalyze the conjugation of reduced glutathione (GSH) with reactive electrophiles. Rat vascular tissue contains GST isoforms that represent a major cellular defense mechanism against atherogenic alpha,beta-unsaturated aldehydes (Misra et al., Toxicol. Appl. Pharmacol. 133, 27-33, 1995). In this study we examined the role of GSTs in providing protection to cultured neonatal vascular smooth muscle cells (VSMCs) from the alpha,beta-unsaturated carbonyl cardiovascular toxins, allylamine and its metabolite, acrolein. Confluent cultured cells were exposed to 2 to 10 microM allylamine (a cardiovascular toxin that is metabolized in vivo and in vitro by VSMCs to the reactive aldehyde, acrolein) or to acrolein (2-10 microM) for 48 h; dose-cytotoxicity curves were generated utilizing a tetrazolium-dependent cytotoxicity assay. Concommittant treatment with sulfasalazine, an established inhibitor of GST, was found to markedly increase allylamine- or acrolein-induced cytotoxicity, decreasing the LC50 by two- to threefold at 50 to 100 microM sulfasalazine. A clonogenic survival assay in VSMCs exposed to these compounds for 4 h confirmed lethal toxicity and enhanced toxicity following cotreatment with sulfasalazine. Isobologram analysis (which statistically defines the limits of additivity of two independent treatments) showed that the sulfasalazine effect on both allylamine and acrolein cytotoxicity was supraadditive, or synergistic. Sulfasalazine was not cytotoxic to VSMCs in the range of concentrations that augmented acrolein or allylamine cytoxicity; total GST activity was inhibited, however, in a dose-dependent manner in that range. GST purified by GSH-affinity chromatography from pelleted untreated cells gave specific activities and kinetic constants consistent with those previously reported for rat aorta total GSTs. The catalytic efficiency (Kcat/Vm) was found to be much greater for 4-hydroxy-2-nonenal than for 1-chloro-2,4-dinitrobenzene (0.058 vs 0.4 s-1 mM-1). Western blot of purified total GSTs using antibodies against rec-mGSTA4-4 revealed a single band at 25 kDa, confirming the presence of a GST isozyme immunologically similar to rat GST8-8, which is known to utilize alpha,beta-unsaturated carbonyls as preferred substrates. Our data indicate that GSTs are an important defense in the vascular media, protecting blood vessels against alpha,beta-unsaturated carbonyl cardiovascular toxins that are involved in initiating atherosclerotic lesions.

Phenylhydroxylamine: role in aniline-associated splenic oxidative stress and induction of subendocardial necrosis.

To elucidate the role of N-phenylhydroxylamine (PHA, N-hydroxylated metabolite of aniline) in the selective toxicity of aniline to the spleen, dose-dependent studies were conducted with PHA in rats. Male Sprague-Dawley rats were given four doses each (1 dose/day) of 0.025, 0.05, 0.1, or 0.2 mmol/kg PHA in 0.5 ml of aqueous agar (0.25%) by gavage. The control animals received an equal volume of vehicle only. The animals were euthanized 24 h following the last dose. PHA toxicity in the blood was evident from a dose-dependent increase of methemoglobin. The most affected organ was spleen, which appeared dark and enlarged (splenomegaly) and showed increased spleen-to-body weight ratios, which were 28, 40, 66, and 87% at PHA doses of 0.025, 0.05, 0.1, and 0.2 mmol/kg, respectively. Splenic lipid peroxidation (malondialdehyde content) was higher in all PHA-treated groups, whereas splenic protein oxidation (carbonyl content) increased in only the 0.05, 0.1, and 0.2 mmol/kg groups. The total iron content in the spleen also showed increases of 88, 135, 168, and 209% at PHA doses of 0.025, 0.05, 0.1, and 0.2 mmol/kg, respectively. These biochemical changes were accompanied by a dose-dependent vascular congestion in the spleen, a characteristic feature of aniline toxicity. Although the ratio of organ to body weight increased for both testes and heart at the highest dose, striking morphological changes were observed only in heart. The cardiac lesions consisted of a both acute and resolving multifocal subendocardial necrosis involving predominently the left ventricle. Our results suggest that PHA is a splenotoxin and thus contributes to the toxicity of aniline, while at a high dose, it is also cardiotoxic, perhaps due to anoxia associated with the marked methemoglobinemia. These results further support the involvement of oxidative stress in the splenotoxicity of aniline which may be caused by its reactive metabolite(s) such as PHA.