In vivo myocardial protection from ischemia/reperfusion injury by the peroxisome proliferator-activated receptor-gamma agonist rosiglitazone

BACKGROUND

Diabetes is associated with increased risk of mortality as a consequence of acute myocardial infarction. This study determined whether rosiglitazone (ROSI) could reduce myocardial infarction after ischemia/reperfusion injury.

METHODS AND RESULTS

Male Lewis rats were anesthetized, and the left anterior descending coronary artery was ligated for 30 minutes. After reperfusion for 24 hours, the ischemic and infarct sizes were determined. ROSI at 1 and 3 mg/kg IV reduced infarct size by 30% and 37%, respectively (P<0.01 versus vehicle). Pretreatment with ROSI (3 mg. kg(-1). d(-1) PO) for 7 days also reduced infarct size by 24% (P<0.01). ROSI also improved ischemia/reperfusion-induced myocardial contractile dysfunction. Left ventricular systolic pressure and positive and negative maximal values of the first derivative of left ventricular pressure (dP/dt) were significantly improved in ROSI-treated rats. ROSI reduced the accumulation of neutrophils and macrophages in the ischemic heart by 40% and 43%, respectively (P<0.01). Ischemia/reperfusion induced upregulation of CD11b/CD18 and downregulation of L-selectin on neutrophils and monocytes; these effects were significantly attenuated in ROSI-treated animals. Likewise, intercellular adhesion molecule-1 expression in ischemic hearts was markedly diminished by ROSI, as was the ischemia/reperfusion-stimulated upregulation of monocyte chemoattractant protein-1.

CONCLUSIONS

ROSI reduced myocardial infarction and improved contractile dysfunction caused by ischemia/reperfusion injury. The cardioprotective effect of ROSI was most likely due to inhibition of the inflammatory response.

A comparison of carvedilol and metoprolol antioxidant activities in vitro

Carvedilol is a vasodilating beta-blocker and antioxidant approved for treatment of mild to moderate hypertension. angina, and congestive heart failure. Metoprolol is a beta1-selective adrenoceptor antagonist. When carvedilol and metoprolol were recently compared in clinical trials for heart failure, each showed beneficial beta-blocker effects such as improved symptoms, quality of life, exercise tolerance, and ejection fraction, with no between-group differences. When thiobarbituric acid reactive substance (TBARS) levels were measured in serum as an indirect marker of free radical activity, there were also no between-group differences. However, we had noted superior cardioprotection by carvedilol in comparison to metoprolol in ischemia and reperfusion models. We therefore examined antioxidant activity directly in cells and tissues. Here we show that in cultured rat cerebellar neurons, and in brain and heart membranes, carvedilol has far greater antioxidant activity than metoprolol, which is essentially inactive as an antioxidant in these model systems. The antioxidant activity of carvedilol could be explained by a greater degree of lipophilicity, as measured by its ClogP value of 3.841 as contrasted to a ClogP value of 1.346 for metoprolol. Alternatively, the molecular structure of carvedilol favors redox recycling, which the structure of metoprolol does not. Therefore, carvedilol could have additional pharmacologic effects that are favorable for long-term therapy.

Molecular characterization of a human scavenger receptor, human MARCO

Murine MARCO has been identified recently in subsets of macrophages located in the peritoneum, marginal zone of the spleen, and the medullary cord of lymph nodes, where it has been proposed that it serves as a bacteria-binding receptor. A scavenger receptor family member with an extended collagenous domain, murine MARCO has also been demonstrated in atherosclerotic lesions of susceptible mice. We report here the identification, tissue and chromosomal localization, and pharmacological characterization of human (h)MARCO. hMARCO was identified from a macrophage cDNA library by electronic screening with the murine MARCO sequence. Nucleotide sequence analysis confirmed that the full-length hMARCO clone encoded a 519-amino acid protein sharing 68.5% identity with murine MARCO. RNA blot analysis indicated that the hMARCO transcript is 2.0 kb in length and is predominantly expressed in human lung, liver, and lymph nodes. Radiation hybrid mapping localized hMARCO to chromosome 2q14. Ligand-binding studies of COS cells expressing hMARCO demonstrated significant specific binding of both Escherichia coli and Staphylococcus aureus. In contrast, the hMARCO receptor expressed in COS cells did not specifically bind the scavenger receptor ligand acetylated low-density lipoprotein (LDL), despite its similarity to the elongated collagen-like binding domain of the macrophage scavenger receptor. In addition, acetylated (Ac)LDL and oxidized (Ox)LDL did not inhibit E. coli binding to hMARCO. These data suggest that hMARCO may play an important role in host defense, but it has no obvious role in the accumulation of modified lipoproteins during atherogenesis.

Induced expression of adipophilin mRNA in human macrophages stimulated with oxidized low-density lipoprotein and in atherosclerotic lesions

Oxidized low-density lipoprotein (OxLDL) plays a critical role in foam cell formation and atherosclerogenesis. A cDNA encoding adipophilin was identified in cultured human macrophages stimulated with OxLDL using mRNA differential display. Adipophilin is a 50 kDa protein known to be a specific marker for adipocyte cell differentiation and lipid accumulation in a variety of cells. The time-dependent induction of adipophilin mRNA in macrophages was specific to OxLDL but not native LDL, and not to various cytokines and serum. In human atherosclerotic lesions, adipophilin mRNA expression was localized in a subset of lipid-rich macrophages. These data suggest that adipophilin-expressing macrophages may represent foam cells and this gene expression is likely to be associated with the lipid accumulation in foam cells of the atherosclerotic lesions.

Calcitonin gene-related peptide receptor independently stimulates 3',5'-cyclic adenosine monophosphate and Ca2+ signaling pathways

Calcitonin gene-related peptide (CGRP) is a neuropeptide with diverse biological properties including potent vasodilating activity. Recently, we reported the cloning of complementary DNAs (cDNAs) encoding the human and porcine CGRP receptors which share significant amino acid sequence homology with the human calcitonin receptor, a member of the recently described novel subfamily of G-protein-coupled 7TM receptors. Activation of this family of receptors has been shown to result in an increase in intracellular cAMP accumulation and calcium release. In this study, we demonstrate that HEK-293 cells expressing recombinant CGRP receptors (HEK-293HR or PR) respond to CGRP with increased intracellular calcium release (EC50 = 1.6 nM) in addition to the activation of adenylyl cyclase (EC50 = 1.4 nM). The effect of CGRP on adenylyl cyclase activation and calcium release was inhibited by CGRP (8-37), a CGRP receptor antagonist. Both effects were mediated by cholera toxin-sensitive G-proteins, but these two signal transduction pathways were independent of each other. While cholera toxin pretreatment of HEK-293PR cells resulted in permanent activation of adenylyl cyclase, the same pretreatment resulted in an inhibition of CGRP-mediated [Ca2+]i release. Pertussis toxin was without effect on CGRP-mediated responses. In addition, CGRP-mediated calcium release appears to be due to release from a thapsigargin-sensitive intracellular calcium pool. These results show that the recombinant human as well as porcine CGRP receptor can independently increase both cAMP production and intracellular calcium release when stably expressed in the HEK-293 cell line.

Modulation of CXCR4 expression and SDF-1alpha functional activity during differentiation of human monocytes and macrophages

Chemoattraction of monocytes by the CXC chemokine stromal cell-derived factor-1alpha (SDF-1alpha) and its receptor CXCR4 may be involved in vascular diseases like atherosclerosis. We studied the regulation of CXCR4 transcription and SDF-1-induced functional responses in human monocytes during their differentiation in the presence of granulocyte-macrophage colony-stimulating factor (GM-CSF), oxidized low-density lipoprotein (Ox-LDL), and unmodified LDL. Our results reveal that the rapid decline of SDF-1-mediated [Ca2+]i influx after monocyte isolation is followed by a gradual functional restoration and a concomitant reexpression of CXCR4 mRNA over time. A further three- to fourfold induction of CXCR4 mRNA occurred in macrophage-derived foam cells on treatment with Ox-LDL. HL-60 cells induced with phorbol myristate acetate (PMA) showed a rapid fourfold stimulation of CXCR4 mRNA within 1 h, declining to barely detectable levels at 3 h, with eventual restoration over time, mirroring the expression pattern in monocytes. Surface expression of CXCR4 is maintained in HL-60 cells during PMA-induced differentiation, as demonstrated by flow cytometry. GM-CSF had no effect on CXCR4 mRNA in HL-60 cells and does not cause its down-regulation in human macrophages.

Identification of a small-molecule, nonpeptide macrophage scavenger receptor antagonist

Class A scavenger receptor (SR-A) antagonists may prevent the initiation of atherosclerosis, because a recent report found that SR-A/apolipoprotein E (apoE) double-knockout mice had 60% smaller lesions than apoE single-knockout littermates. We transfected human embryonic kidney (HEK) 293 cells with SR-A type I or II receptors to find small-molecule antagonists. Uptake of 1,1'-dioctadecyl-3,3,3', 3'-tetramethylindocarbocyanine perchlorate-labeled acetylated low-density lipoprotein (DiI-AcLDL) showed that among common polyanionic ligands, polyinosine was the most potent, with an IC50 of 0.74 microgram/ml, whereas the novel compound (E)-methyl 4-chloro-alpha-[4-(4-chlorophenyl)-1, 5-dihydro-3-hydroxy-5-oxo-1-(2-thiazolyl)-2H-pyrrol-2-ylidene]benzene acetate gave an IC50 of 6.1 microgram/ml (13 microM). The novel antagonist also inhibited DiI-AcLDL uptake in cultured human peripheral and rat peritoneal macrophages with IC50 values of 21 microM and 17 microM, respectively. With [125I]AcLDL as ligand for transfected HEK 293 cells, binding/uptake and degradation at 37 degrees C for 5 h was saturable and selective. In a comparison of both types of receptor, we found no difference between the capacity of SR-AI or SR-AII for either binding or degradation. Polyinosine competed both [125I]AcLDL binding and degradation with a Ki of 1 microgram/ml, whereas the novel antagonist competed with a Ki of 19 microgram/ml (40 microM) and 8.6 microgram/ml (18 microM), respectively, for binding and degradation. Saturation binding in the presence of the ionophore monensin indicated that the novel compound behaved as a noncompetitive antagonist and perhaps as an allosteric effector. This is the first report to describe a small-molecule macrophage scavenger receptor antagonist. Utilization of this permanently transfected HEK 293 cell line will allow the identification of more potent macrophage scavenger receptor antagonists, so that their utility as therapeutics for atherosclerosis can be determined.

Astrocytic demise precedes delayed neuronal death in focal ischemic rat brain

Active neuronal-glial interaction is important in the maintenance of brain homeostasis and is vital for neuronal survival following brain injury. The time course of post-ischemic astroglial dysfunction and neuronal death was studied in the spontaneously hypertensive rat (SHR) brain following permanent middle cerebral artery occlusion (MCAO). In situ hybridization with 35S-labeled riboprobes for GFAP and GLUT3 was used to monitor mRNA expression in glia and neurons. Astrocytic proteins GFAP, vimentin, S100, Glutathione-S-Transferase Yb (GST Yb) and neuronal protein TG2 were detected by immunofluorescence. Cells were co-stained with in situ end labeling (ISEL) to detect DNA fragmentation, a hallmark of cell death. GFAP mRNA expression declined rapidly in the ischemic region of the cortex and was almost absent by 12 h. Immunohistochemical studies revealed a parallel decline in the corresponding protein: a reduction in GFAP staining was apparent in the infarct after 3 h and by 24 h, there was essentially no remaining GFAP. Three other glial proteins (vimentin, S100 and GST Yb) disappeared from infarct over a similar time course. A few ISEL positive cells were observed in the infarct at 6 h, but maximal detection was not seen until 24-48 h. Most of the ISEL-positive cells were neurons, identified by co-staining with the neuronal marker TG2. Few cells expressing GFAP or other glial markers were positive at any time point. Neuronal GLUT3 mRNA declined more slowly than GFAP mRNA in the ischemic core and disappeared during the period of neuronal death. Concurrent with the loss of GFAP mRNA and protein expression in the infarct, there was a rapid rise in GFAP mRNA in the peri-infarct region of ipsilateral hemisphere and proximal region of the contralateral hemisphere. This was followed by the enhanced GFAP protein expression characteristic of reactive astrocytes, but over a significantly slower time course. These studies show that MCAO leads to a rapid decline of GFAP mRNA and glial proteins, which appears to precede the decline in neuronal mRNA and neuronal death within the infarct. Early astroglial dysfunction may play a critical role in determining the outcome of acute hypoxic-ischemic injury by compromising neuronal-glial interactions.

BMP-2 gene expression and effects on human vascular smooth muscle cells

Bone morphogenetic proteins (BMPs) and their serine/threonine kinase receptors have been identified in atherosclerotic arteries and vascular smooth muscle cells, respectively. Thus, BMPs (the largest subfamily of the TGF-beta superfamily) have been implicated in the pathogenesis of atherosclerosis. However, the origins of BMP biosynthesis and the functional roles of BMP in blood vessels are unclear. The present study explored BMP-2 gene expression in various human blood vessels and vascular cell types. Functional in vitro studies were also performed to determine the effects of recombinant human BMP-2 on migration (transwell assay) and proliferation ([3H]-thymidine incorporation) of human aortic vascular smooth muscle cells (HASMC). RT-PCR experiments revealed BMP-2 gene expression in normal and atherosclerotic human arteries as well as cultured human aortic and coronary vascular smooth muscle cells, human umbilical vein endothelial cells (HUVECs) and human macrophages. In cellular migration studies, incubation with BMP-2 produced efficacious (</=610-fold), concentration- and time-dependent chemotaxis of HASMCs (EC50 = 0.8 microM) with little or no effect on HUVEC chemotaxis. The increased HASMC motility induced by BMP-2 was inhibited by coincubation with an anti-BMP-2 mAb. In addition, subthreshold concentrations of BMP-2 produced a dramatic synergistic effect upon platelet-derived growth factor (PDGF)-induced chemotaxis. In contrast to PDGF, BMP-2 had no significant effet on [3H]-thymidine incorporation in HASMC at chemotaxic concentrations (</=6.0 microM) nor did it synergize with the mitogenic effects of PDGF. In conclusion, the expression of BMP-2 by numerous cell types in the blood vessel wall may play a chemotactic or cochemotactic role in the smooth muscle cell response to vascular injury.

Neuroprotective activities of carvedilol and a hydroxylated derivative: role of membrane biophysical interactions

Carvedilol is a vasodilating beta-blocker and antioxidant approved for treatment of mild to moderate hypertension, angina, and congestive heart failure. SB 211475 (4-[2-hydroxyl-3-[[2-(2-methoxyphenoxy)ethyl]amino]propoxyl]-9H-++ +carbazol-3-ol), a hydroxylated carvedilol analogue, is an even more potent antioxidant in several assay systems. Carvedilol also has neuroprotective capacity with modulatory actions at N-methyl-D-aspartate (NMDA) receptors and Na+ channels. In the present study, we demonstrated that in cultured rat cerebellar neurons, SB 211475 has 28-fold greater antioxidant activity than carvedilol, but is 2- to 6-fold less potent, respectively, at inhibiting neurotoxic activities at Na+ channels and at NMDA receptor channels. To determine a biophysical rationale for these differential activities, small angle x-ray scattering data were obtained from model lipid and brain membrane bilayers containing either carvedilol, SB 211475, or dihydropyridine calcium channel blockers. Electron density profiles revealed that the location of SB 211475 was restricted to the glycerol backbone/hydrocarbon interface and significantly reduced membrane width by 5%, whereas the time-averaged location for carvedilol and flunarizine also extended to the hydrated surface of the bilayer. Comparison of carvedilol with several dihydropyridines showed a correlation between high ClogP values (lipophilicity), Na+ channel inhibitory potency, and bilayer localization. The antioxidant activity of SB 211475 could be explained by restricted intercalation into the glycerol phosphate/hydrocarbon interface, creating an increase in volume associated with the phospholipid acyl chains, which would then become resistant to lipid peroxidation. Differential channel modulation may also be explained by these membrane structural results, which indicate that carvedilol and the less spatially restricted dihydropyridine molecules are more likely to inhibit transmembrane receptor channels.

Prolonged expression of interferon-inducible protein-10 in ischemic cortex after permanent occlusion of the middle cerebral artery in rat

Focal cerebral ischemia elicits local inflammatory reaction as demonstrated by the accumulation of inflammatory cells and mediators in the ischemic brain. Interferon-inducible protein-10 (IP-10) is a member of the C-X-C chemokine family that possesses potent chemoattractant actions for monocytes, T cells, and smooth muscle cells. To investigate a potential role of IP-10 in focal stroke, we studied the temporal expression of IP-10 mRNA after occlusion of the middle cerebral artery in rat by means of northern analysis. IP-10 mRNA expression after focal stroke demonstrated a unique biphasic profile, with a marked increase early at 3 h (4.9-fold over control; p < 0.01), a peak level at 6 h (14.5-fold; p < 0.001) after occlusion of the middle cerebral artery, and a second wave induction 10-15 days after ischemic injury (7.2- and 9.3-fold increase for 10 and 15 days, respectively; p < 0.001). In situ hybridization confirmed the induced expression of IP-10 mRNA and revealed its spatial distribution after focal stroke. Immunohistochemical studies demonstrated the expression of IP-10 peptide in neurons (3-12 h) and astroglial cells (6 h to 15 days) of the ischemic zone. To explore further the potential role of IP-10 in focal stroke, we demonstrated a dose-dependent chemotactic action of IP-10 on C6 glial cells and enhanced attachment of rat cerebellar granule neurons. Taken together, the data suggest that ischemia induces IP-10, which may play a pleiotropic role in prolonged leukocyte recruitment, astrocyte migration/activation, and neuron attachment/sprouting after focal stroke.

Chemokine receptors in human endothelial cells. Functional expression of CXCR4 and its transcriptional regulation by inflammatory cytokines

Chemokines play an important role in the regulation of endothelial cell (EC) function, including proliferation, migration and differentiation during angiogenesis, and re-endothelialization after injury. In this study, reverse transcriptase-polymerase chain reaction was used to reveal expression of various CXC and CC chemokine receptors in human umbilical vein EC. Northern analysis showed that CXCR4 was selectively expressed in vascular EC, but not in smooth muscle cells. Compared with other chemokines, stromal cell-derived factor-1alpha (SDF-1alpha), the known CXCR4 ligand, was an efficacious chemoattractant for EC, causing the migration of approximately 40% input cells with an EC50 of 10-20 nM. Of the chemokines tested, only SDF-1alpha induced a rapid, though variable mobilization of intracellular Ca2+ in EC. Experiments with actinomycin D demonstrated that CXCR4 transcripts were short-lived, indicating a rapid mRNA turnover. Interferon-gamma (IFN-gamma) caused a pronounced down-regulation of CXCR4 mRNA in a concentration- and time-dependent manner. In a striking functional correlation, IFN-gamma treatment also attenuated the chemotactic response of EC to SDF-1alpha. IL-1beta, tumor necrosis factor-alpha, and lipopolysaccharide produced a time course-dependent biphasic effect on CXCR4 transcription. Expression of CXCR4 in EC is significant, more so as it and several CC chemokine receptors have been shown to serve as fusion co-receptors along with CD4 during human immunodeficiency virus infection. Taken together, these findings provide evidence of chemokine receptor expression in EC and offer an explanation for the action of chemokines like SDF-1alpha on the vascular endothelium.

Induction and expression of human cartilage glycoprotein 39 in rheumatoid inflammatory and peripheral blood monocyte-derived macrophages

Human cartilage glycoprotein 39 (HC gp-39) has been described as a major secreted product of cultured articular chondrocytes, synovial fibroblasts, and the osteosarcoma line MG63. However, its expression in these cells types has not been directly linked to corresponding cell types in vivo. In this report, expression of HC gp-39 is demonstrated from peripheral blood-derived macrophages in association with their differentiation from monocytes to macrophages. Consistent with macrophage specificity, HC gp-39 expression is also induced upon selective stimulation of the pluripotent promyelocytic leukemia cell line HL-60 toward the monocyte/macrophage lineage with vitamin D3 or phorbol 12-myristate 13-acetate (PMA), while treatments stimulating granulocyte and eosinophilic pathways do not induce expression. Furthermore, HC gp-39 expression levels correlate with the degree of morphological differentiation induced by PMA and vitamin D3 treatments. PMA-induced mRNA expression occurs by 36 h and is a secondary transcriptional response since its synthesis is inhibited by cycloheximide. Apparently, HC gp-39 expression is tied to later events in the differentiation of monocytes into macrophages. The in vivo significance of these results is validated by the in situ detection of HC gp-39 mRNA in inflammatory macrophages associated with rheumatoid synovium. Thus, macrophages appear to be an important source of HC gp-39, which has been shown to be present at elevated levels in the blood and synovium of rheumatoid arthritis patients. The implications of this extend well beyond the previously restricted observations in cell types associated with the joint and suggest a potential involvement of macrophage-derived HC gp-39 in other aspects of inflammation, tissue remodeling, and host defense.

Tumor necrosis factor-alpha. A mediator of focal ischemic brain injury

BACKGROUND AND PURPOSE

Tumor necrosis factor-alpha (TNF-alpha) is a pleiotropic cytokine that rapidly upregulates in the brain after injury. The present study was designed to explore the pathophysiological significance of brain TNF-alpha in the ischemic brain by systematically evaluating the effects of lateral cerebroventricular administration of exogenous TNF-alpha and agents that block the effects of TNF-alpha on focal stroke and by examining the potential direct toxic effects of TNF-alpha on cultured neurons to better understand how TNF-alpha might mediate stroke injury.

METHODS

TNF-alpha (2.5 or 25 pmol) was administered intracerebroventricularly to spontaneously hypertensive rats 24 hours before permanent or transient (80 minutes and 160 minutes) middle cerebral artery occlusion (MCAO). Animals were examined 24 hours later for neurological deficits and ischemic hemisphere necrosis and swelling. In some of these studies, neutralizing anti-TNF-alpha monoclonal antibody (mAb) (60 pmol) was injected intracerebroventricularly 30 minutes before exogenous TNF-alpha (25 pmol). In addition, the effects of blocking endogenous TNF-alpha on permanent focal ischemic injury were determined with the use of either mAb (60 pmol) or soluble TNF receptor I (sTNF-RI) (0.3 or 0.7 nmol) administered intracerebroventricularly 30 minutes before and 3 and 6 hours after MCAO. Finally, the direct neurotoxic effects of TNF-alpha were studied in cultured rat cerebellar granule cells exposed to TNF-alpha (10 to 2000 U/mL for 6 to 24 hours), and neurotransmitter release, glutamate toxicity, and oxygen radical toxicity were studied.

RESULTS

TNF-alpha increased the percent hemispheric infarct induced by permanent MCAO in a dose-related manner from 13.1 +/- 1.3% (vehicle) to 18.9 +/- 1.7% at 2.5 pmol (P < .05) and 27.1 +/- 1.3% at 25 pmol (P < .0001). The high dose of TNF-alpha increased ischemia-induced forelimb deficits from 1.6 +/- 0.2 to 2.3 +/- 0.2 (P < 0.1). TNF-alpha (2.5 pmol) also increased the infarction induced by 80 or 160 minutes of transient MCAO from 1.9 +/- 0.9% to 4.3 +/- 0.4% (P < .01) and from 14.2 +/- 1.3% to 21.6 +/- 2.2% (P < .05), respectively. The exacerbation of infarct size, swelling, and neurological deficit after exogenous TNF-alpha was reversed by preinjection of 60 pmol mAb. Blocking endogenous TNF-alpha also significantly reduced focal ischemic brain injury. Treatment with 60 pmol mAb before and after permanent MCAO significantly reduced infarct size compared with control (nonimmune) antibody treatment by 20.2% (P < .05). Reduced brain infarction also was produced by brain administration of 0.3 nmol (decreased 18.2%) or 0.7 nmol (decreased 26.1%, P < .05) sTNF-RI before and after focal stroke. The intracerebroventricular administration of TNF-alpha or sTNF-RI did not alter brain or body temperature, blood gases or pH, blood pressure, blood glucose, or general blood chemistry. In cultured cerebellar granule cells, the application of TNF-alpha did not directly affect neurotransmitter release or glutamate or oxygen free radical toxicity.

CONCLUSIONS

These studies demonstrate that exogenous TNF-alpha exacerbates focal ischemic injury and that blocking endogenous TNF-alpha is neuroprotective. The specificity of the action(s) of TNF-alpha was demonstrated by antagonism of its effects with specific anti-TNF-alpha tools (ie, mAb and sTNF-RI). TNF-alpha toxicity does not appear to be due to a direct effect on neurons or modulation of neuronal sensitivity to glutamate or oxygen radicals and apparently is mediated through nonneuronal cells. These data suggest that inhibiting TNF-alpha may represent a novel pharmacological strategy to treat ischemic stroke.

2-Methoxyestradiol, an endogenous estrogen metabolite, induces apoptosis in endothelial cells and inhibits angiogenesis: possible role for stress-activated protein kinase signaling pathway and Fas expression

2-Methoxyestradiol (2-ME) is an endogenous metabolite of estradiol-17beta and the oral contraceptive agent 17-ethylestradiol. 2-ME was recently reported to inhibit endothelial cell proliferation. The current study was undertaken to explore the mechanism of 2-ME effects on endothelial cells, especially whether 2-ME induces apoptosis, a prime mechanism in tissue remodeling and angiogenesis. Cultured bovine pulmonary artery endothelial cells (BPAEC) exposed to 2-ME showed morphological (including ultrastructural) features characteristic of apoptosis: cell shrinkage, cytoplasmic and nuclear condensation, and cell blebbing. 2-ME-induced apoptosis in BPAEC was a time- and concentration-dependent process (EC50 = 0.45 +/- 0.09 microM, n = 8). Nucleosomal DNA fragmentation in BPAEC treated with 2-ME was identified by agarose gel electrophoresis (DNA ladder) as well as in situ nick end labeling. Under the same experimental conditions, estradiol-17beta and two of its other metabolites, estriol and 2-methoxyestriol (< or =10 microM), did not have an apoptotic effect on BPAEC. 2-ME activated stress-activated protein kinase (SAPK)/c-Jun amino-terminal protein kinase in BPAEC in a concentration-dependent manner. The activity of SAPK was increased by 170 +/- 27% and 314 +/- 22% over the basal level in the presence of 0.4 and 2 microM 2-ME (n = 3-6), respectively. The activation of SAPK was detected at 10 min, peaked at 20 min, and returned to basal levels at 60 min after exposure to 2-ME. Inhibition of SAPK/c-Jun amino-terminal protein kinase activation by basic fibroblast growth factor, insulin-like growth factor, or forskolin reduced 2-ME-induced apoptosis. Immunohistochemical analysis of BPAEC indicated that 2-ME up-regulated expression of both Fas and Bcl-2. In addition, 2-ME inhibited BPAEC migration (IC50 = 0.71 +/- 0.11 microM, n = 4) and basic fibroblast growth factor-induced angiogenesis in the chick chorioallantoic membrane model. Taken together, these results suggest that promotion of endothelial cell apoptosis, thereby inhibiting endothelial cell proliferation and migration, may be a major mechanism by which 2-ME inhibits angiogenesis.

Extracellular human immunodeficiency virus type 1 Tat protein promotes aggregation and adhesion of cerebellar neurons

Recombinant human immunodeficiency virus (HIV-1) Tat protein added to the culture medium of rat cerebellar neurons promoted aggregation and formation of spoke-like neurites in a dose-dependent manner. Tat proteins containing mutations in the Arg-Gly-Asp (RGD) cell adhesion motif or a deletion of the cysteine-rich domain had no effect on neuronal morphology. In contrast, a Tat protein that contained a deletion of the proline-rich domain promoted neuronal aggregation. Aggregation of neurons was inhibited by the addition of monoclonal antibodies directed against the RGD and basic domains of Tat, but not against the proline-rich domain. The same domains of Tat required to induce aggregation also mediated adhesion of neurons to Tat-coated substrates. The HIV-2 Tat protein, which lacks an RGD sequence but contains cysteine-rich and basic domains similar to HIV-1 Tat, induced aggregation and acted as a substrate for adhesion when added at higher concentrations than HIV-1 Tat. Vitronectin, fibronectin, and RGD-containing peptides did not induce morphological changes in neurons or act as substrates for adhesion. The ability of Tat to induce morphological changes and promote adhesion was independent of the ability of Tat to transactivate HIV gene expression. Our results suggest that extracellular Tat protein most likely alters neuronal morphology and mediates adhesion by acting in a manner similar to an extracellular matrix protein.

SB 201823-A antagonizes calcium currents in central neurons and reduces the effects of focal ischemia in rats and mice

BACKGROUND AND PURPOSE

Excessive calcium entry into depolarized neurons contributes significantly to cerebral tissue damage after ischemia. We evaluated the ability of a novel neuronal calcium channel blocker, SB 201823-A, to block central neuronal calcium influx in vitro and to reduce ischemic injury in two rodent models of focal stroke.

METHODS

Patch-clamp electrophysiology and intracellular Ca2+ imaging in rat hippocampal and cerebellar neurons were used to determine effects on neuronal calcium channel activity. Middle cerebral artery occlusion was performed in Fisher 344 rats and CD-1 mice to determine the effects on rodent focal ischemic injury and neurological deficits. Cardiovascular monitoring in conscious rats was conducted to determine cardiovascular liabilities of the compound.

RESULTS

In cultured rat hippocampal cells, calcium current measured at plateau was reduced by 36 +/- 8% and 89 +/- 4% after 5 and 20 mumol/L SB 201823-A, respectively. In cerebellar granule cells in culture, pretreatment with 2.5 mumol/L SB 201823-A totally prevented initial calcium influx and reduced later calcium influx by 50 +/- 2.5% after N-methyl-D-aspartate/glycine stimulation (P < .01). KCl depolarization-induced calcium influx also was reduced by more than 95%. In rats, a single treatment with 10 mg/kg IV SB 201823-A beginning 30 minutes after focal ischemia decreased (P < .05) hemispheric infarct by 30.4% and infarct volume by 29.3% and reduced (P < .05) forelimb deficits by 47.8% and hindlimb deficits by 36.3%. In mice, treatments with 10 mg/kg IP SB 201823-A beginning 30 minutes after focal ischemia significantly reduced infarct volume by 41.5% (P < .01). No blood pressure effects were observed with the therapeutic dose of the compound.

CONCLUSIONS

These results indicate that the new neuronal calcium channel blocker SB 201823-A can block stimulated calcium influx into central neurons and can provide neuroprotection in two models of focal cerebral ischemia without affecting blood pressure. Data from several different studies now indicate that the neuronal calcium channel antagonists are a promising therapy for the postischemic treatment of stroke.

Developmental expression of endothelin receptors in cerebellar neurons differentiating in culture

We describe the identification and expression of endothelin (ET) receptor subtypes in differentiating cultured cerebellar neurons. Using [125I]ET-1 and the subtype-selective ligands BQ-123 and sarafotoxin 6c as selective ligands for the ETA and ETB receptors, respectively, we found that cerebellum from 8-day-old rats displayed only the ETB receptor subtype. We next cultivated cerebellar granule cell neurons to study ET receptor differentiation between 2 and 22 days in vitro. Using the above reagents, we found that while unlabeled ET-1 displayed monophasic competition curves, BQ-123 and sarafotoxin 6c displayed partial displacement curves, indicating the presence of both ETA and ETB receptors on these neurons. The proportion of ETB receptors gradually decreased from day 2 onwards the proportion of ETA receptors gradually increased. On days 2, 3, 4, and 5 of culture, the ETB:ETA receptor ratios were 90:10, 70:30, 60:40, and 40:60, respectively. There was no further change in receptor subtype ratio beyond day 5 and up to day 22. Northern blot analysis showed that ETB receptor message expression was 6.9-fold higher than that of ETA receptor expression on day 2, but steadily decreased with time, whereas ETA receptor message expression was minimal on day 2 and maximal by day 3 and 4. By day 7, receptor message was of equal abundance, which was in good agreement with the binding studies. This novel, developmentally regulated process predicts the existence of endogenous mediators of neuronal ET receptor expression.

Interleukin-1 beta induces expression of adhesion molecules in human vascular smooth muscle cells and enhances adhesion of leukocytes to smooth muscle cells

Increased expression of cell adhesion molecules is an important pathological event during the development of atherosclerosis. The smooth muscle cell (SMC) is one of the cell types present in the atherosclerotic lesion. To evaluate the regulation of adhesion molecules in human vascular SMCs and its possible role, we studied the expression of adhesion molecules in SMCs stimulated with interleukin 1-beta (IL-1 beta), a pleiotropic cytokine that is involved in the pathological development of vascular diseases including atherosclerosis and restenosis. Our data demonstrated that IL-1 beta markedly induced the adhesiveness of human vascular SMCs for monocytes and neutrophils in a concentration (10 pM - 10 nM)- and time (0.5-24 h)-dependent manner. The maximal induced adhesion by IL-1 beta (1 nM) was reached at 4 h, with 4.6-fold and 3.3-fold for monocytes and neutrophils, respectively. This induction was dose-dependently inhibited by the IL-1 receptor antagonist (IL-1 ra). The IL-1 beta-induced expression of intercellular adhesion molecule 1 (ICAM-1), vascular cell adhesion molecule 1 (VCAM-1) and E-selectin 1 (ELAM-1) on SMCs was examined by reverse transcription/polymerase chain reaction (RT/PCR). Unstimulated, serum-deprived SMCs expressed a low or undetectable level of mRNA for these adhesion molecules. The expression of ICAM-1 and VCAM-1 but not ELAM-1 mRNA was significantly induced with IL-1 beta in a concentration (1 fM - 1 nM)- and time (0.5 - 24 h)-dependent manner. The maximal increase in ICAM-1 and VCAM-1 mRNAs was reached at 4 h after IL-1 beta stimulation. The IL-1 beta-induced adhesion of SMCs for monocytes was partially inhibited by monoclonal anti-human ICAM-1 and anti-human VCAM-1 antibody, but not by anti-human ELAM-1 antibody. Pretreatment of monocytes with anti-human integrin beta 2 antibody significantly reduced the adhesion of monocytes to IL-1 beta-stimulated SMCs. These results suggest that IL-1 beta is a potent inducer for ICAM-1 and VCAM-1 expression in human vascular SMC, and could play a role in the pathogenesis of atherosclerosis by recruitment and retention of inflammatory cells such as monocytes and neutrophils in the lesions.

Binding of the nonpeptide antagonist, SB 209670, to endothelin receptors on cultured neurons

We studied the binding characteristics of a novel, nonpeptide endothelin antagonist, SB 209670, to two subtypes of endothelin (ET) receptor in cultured rat cerebellar granule cell neurons. Displacement binding studies of [125I]ET-1 performed in the presence of the ETB receptor-selective agonist, sarafotoxin 6c (S6c), allowed us to measure a Ki of 4.0 +/- 1.5 nM for (+/-)SB 209670 at the ETA receptor (n = 4). Similarly, binding studies in the presence of the ETA receptor-selective antagonist, BQ123, allowed us to measure a Ki of 46 +/- 14 nM for (+/-)SB 209670 at the ETB receptor (n = 4). These studies indicate that the novel endothelin antagonist, SB 209670, has high affinity for both types of neuronal endothelin receptor.

Neuroprotective effects of tetrodotoxin as a Na+ channel modulator and glutamate release inhibitor in cultured rat cerebellar neurons and in gerbil global brain ischemia

BACKGROUND AND PURPOSE

Studies examining the role of tetrodotoxin-sensitive ion channels in hypoxic-ischemic neuronal damage have concluded that sodium influx is an important initiating event. We examined the neuroprotectant effect of tetrodotoxin on both cultured cerebellar neurons and on CA1 hippocampal neurons of gerbils exposed to brain ischemia.

METHODS

We studied neuroprotective mechanisms using cultured rat cerebellar granule cells exposed to veratridine, which induced cytotoxicity, neurotransmitter release, and calcium influx. Survival of gerbil CA1 neurons was examined by direct neuron counts 7 days after 6 minutes of global ischemia with reperfusion.

RESULTS

Tetrodotoxin protected cultured neurons in a dose-dependent manner from veratridine-induced toxicity (protective concentration [PC50] = 22 nmol/L). Veratridine induced [3H]aspartate efflux that was sodium dependent, only 25% calcium dependent, and was inhibited by tetrodotoxin (inhibitory concentration [IC50] = 60 nmol/L). Veratridine initiated increases in intracellular calcium that were also reversed by tetrodotoxin (IC50 = 63 nmol/L); reversal was dependent on the sodium-calcium exchanger and the sodium-potassium pump. Neuroprotection of 90% (n = 10; P = .001 versus vehicle) of gerbil CA1 hippocampal neurons was achieved by pretreatment with 2 ng of tetrodotoxin delivered three times intracerebroventricularly, without causing hypothermia.

CONCLUSIONS

Sodium channel blockers like tetrodotoxin may have utility in treatment of ischemic neuronal injury by preventing excessive neuronal depolarizations, limiting excitotoxic glutamate release through reversal of the sodium-dependent glutamate transporter, preventing intracellular calcium overload, preserving cellular energy stores, and allowing recovery of ionic homeostasis through operation of the sodium-calcium exchanger.

Carvedilol, a new antihypertensive drug with unique antioxidant activity: potential role in cerebroprotection

The antioxidant activities of carvedilol have been demonstrated in a wide variety of test systems, including (i) physicochemical (EPR studies), (ii) biochemical (measurement of lipid peroxidation and endogenous antioxidant depletion), (iii) cellular, and (iv) in vivo. The antioxidant activity of carvedilol clearly emanates from the carbazole moiety which is unique to carvedilol. The antioxidant activity resides equally in both of the enantiomers of carvedilol, as well as in some of its metabolites which are devoid of either the alpha 1-adrenoceptor blocking activity or beta-adrenoceptor blocking activity. This novel antioxidant property of carvedilol may account, at least in part, for its cerebroprotection. The data discussed in this article suggest that carvedilol may not only provide effective and safe antihypertensive therapy and therefore reduce a major risk factor for stroke, but will also be better able to provide additional benefits to patients by protecting against oxygen free radicals generated during cerebral ischemia and stroke.

A comparison of (+)SK&F 10047 and MK-801 on cortical spreading depression

MK-801 and (+)SK&F 10047 produced a dose-related inhibition of the EEG suppression and cortical hyperemia associated with cortical spreading depression (CSD) and reduced the CSD propagation rate; ED50 = 1 mg/kg, i.v. and 15 mg/kg, i.v., respectively. MK-801 had a delayed onset of action (inversely related to dose) and a prolonged duration of action at all doses (> 2 h). In contrast, (+)SK&F 10047 had a rapid onset of action (< 30 min) and a predictable dose-related duration of action. These results suggests that an efficacious compound acting with moderate affinity as a non-competitive antagonist at the NMDA-receptor channel may possess a preferable time-course and toxicity profile when compared to agents acting similarly, but with high affinity.

Neuroprotective effects of carvedilol, a new antihypertensive, as a Na+ channel modulator and glutamate transport inhibitor

The potent antioxidant activity of carvedilol could explain part of its protective action in brain ischemia, and interaction as a low-affinity non-competitive (uncompetitive) antagonist of the N-methyl-D-aspartate (NMDA) receptor would provide rapid channel blockade at this subtype of glutamate receptor. We have now found carvedilol to be neuroprotective (PC50 = 306 nM) against 40 microM veratridine which kills cerebellar granule cell neurons in 60 min regardless of energy state. Carvedilol was also a potent inhibitor (IC50 = 1.7 microM) of veratridine-stimulated 3[H]aspartate release from preloaded neurons, caused by reversal of the Na(+)-dependent glutamate transporter. Veratridine caused a sustained 4.3-fold increase in intracellular Ca2+ ([Ca2+]i) up to 368 nM (n = 22). Carvedilol reversed the [Ca2+]i levels by a maximum of 73% with an IC50 of 0.9 microM. Such reversal of [Ca2+]i was facilitated by Na+/Ca2+ exchange since the stoichiometry of exchange could be disrupted by prior treatment with 1 microM ouabain to inhibit the Na+/K+ pump. These data suggest that, in addition to its antihypertensive effects, antioxidant activity and ability to act as a non-competitive inhibitor at the NMDA receptor, carvedilol has additional neuroprotective activity as a Na+ channel modulator and glutamate release inhibitor.

SB 211475, a metabolite of carvedilol, a novel antihypertensive agent, is a potent antioxidant

The antioxidant effects of SB 211475, a metabolite of carvedilol, a novel antihypertensive agent, were studied and compared with carvedilol and other antioxidants such as U78517F, U74500A and probucol. SB 211475 inhibited Fe(2+)-vitamin C-initiated lipid peroxidation, assessed as thiobarbituric acid reactive substance, in brain-homogenate with an IC50 of 0.28 microM. Under the same conditions, the IC50s of probucol, carvedilol, U74500A and U78517F were 50, 8.1, 0.71 and 0.16 microM, respectively. SB 211475 inhibited oxidation of human low density lipoprotein by mouse macrophages with an IC50 of 0.043 microM. In the same model, the IC50s of carvedilol, U78517F and probucol were 3.8, 0.15, and 0.80 microM, respectively. SB 211475 protected cultured bovine pulmonary artery endothelial cells against hydroxyl radical-initiated lipid peroxidation (IC50 = 0.15 microM) and cell damage (lactate dehydrogenase release, IC50 = 0.16 microM), and promoted cell survival with an EC50 of 0.13 microM. SB 211475 also protected endothelial cells against xanthine/xanthine oxidase-initiated cytotoxicity and protected rat cerebellar neurons from hydroxyl radical-mediated cell death (EC50 = 0.19 microM). Moreover, SB 211475 inhibited superoxide (O2-) release from human neutrophils stimulated by phorbol myristate acetate. These observations indicate that SB 211475 is a potent antioxidant and may potentially contribute to the therapeutic effects of carvedilol in vivo.

Neuroprotective effects of carvedilol, a new antihypertensive, at the N-methyl-D-aspartate receptor

Carvedilol's potent antioxidant activity could explain its protective action in brain ischemia, but may not apply to glutamate-induced excitotoxicity in cultured cerebellar granule cells, since glutamate neurotoxicity was not associated with the formation of lipid peroxidative products. Rather, carvedilol diminished the N-methyl-D-aspartate (NMDA)/glycine-induced increase in intracellular calcium ([Ca2+]i), lowering [Ca2+]i by a maximum of 66 +/- 5% (n = 8) with a 50% inhibitory concentration of 0.8 microM. Prior addition of 5 microM dihydropyridines did not shift the dose-response of carvedilol, but did significantly lower the NMDA/glycine-stimulated response to 64% of untreated (n = 8, P = 0.014). Inclusion of 5 microM carvedilol before the additions of NMDA/glycine prevented 85% of the increase in [Ca2+]i. Furthermore, carvedilol displaced 3[H]MK-801 binding to rat brain cortical membranes with a Kd of 29.4 +/- 2.2 microM (n = 6) and no selectively for the glutamate or glycine binding sites. These data therefore suggest that, in addition to its antihypertensive and anti-lipid peroxidative functions, carvedilol has neuroprotective activity as a calcium channel blocker and as a non-competitive inhibitor at the NMDA receptor.

Carvedilol, a new antihypertensive, prevents oxidation of human low density lipoprotein by macrophages and copper

Growing evidence indicates that oxidized low-density lipoprotein (LDL) may promote atherogenesis. Therefore, inhibition of LDL oxidation may impede this process. Carvedilol is a vasodilating, beta-adrenoceptor blocking agent. As a new antihypertensive drug, carvedilol is unique by virtue of its potent antioxidant activity. Therefore, we tested the ability of carvedilol to inhibit the oxidation of LDL by either macrophages or Cu2+. Carvedilol inhibited LDL oxidation by macrophages in a dose-dependent manner, with an IC50 value of 3.8 microM, as assessed by a thiobarbituric acid reactive substance (TBARS) assay. Under the same conditions, propranolol showed only a mild inhibitory effect (IC50 > 100 microM), while pindolol, atenolol and labetalol had almost no effect. Carvedilol, at 10 microM, almost completely inhibited the macrophage-induced increase in electrophoretic mobility of LDL, while other beta-blockers at 50-300 microM had no significant effect. Carvedilol inhibited superoxide release from mouse macrophages, which correlated well with its inhibition of LDL oxidation. Carvedilol also inhibited Cu(2+)-induced LDL oxidation with an IC50 value of 17 microM, while all other beta-blockers were inactive up to 300 microM. These observations suggest that carvedilol might not only be an effective antihypertensive drug, but might also be effective in prevention of atherosclerosis.

Neuroprotective effects of carvedilol, a new antihypertensive agent, in cultured rat cerebellar neurons and in gerbil global brain ischemia

BACKGROUND AND PURPOSE

Free radical generation mediates part of the ischemic neuronal damage caused by the excitatory amino acid glutamate. Carvedilol, a novel multiple-action antihypertensive agent, has been shown to scavenge free radicals and inhibit lipid peroxidation in swine heart and rat brain homogenates. Therefore, we studied the neuroprotective effect of carvedilol on cultured cerebellar neurons and on CA1 hippocampal neurons of gerbils exposed to brain ischemia.

METHODS

Neuroprotective mechanisms were studied using an in vitro ischemia model of cultured rat cerebellar granule cell neurons exposed to either glutamate or oxygen free radical-generating systems. Prevention of lipid peroxidation by carvedilol was studied by measuring the formation of thiobarbituric acid-reactive substance. Gerbil CA1 neuron survival was examined by direct neuronal count 7 days after 6 minutes of global ischemia with reperfusion.

RESULTS

Carvedilol protected cultured neurons in a dose-dependent manner against glutamate-mediated excitotoxicity (inhibitory concentration [IC50] = 1.1 microM) as well as against a 20-minute oxidative challenge (IC50 = 5 microM). The IC50 against the oxidative challenge was lowered to 1.3 microM by growing neurons for 24 hours in the presence of carvedilol. At 10 microM carvedilol inhibited lipid peroxidation 50% and 73% (n = 4, p < 0.001) in neurons exposed to two different free radical-generating systems. Neuroprotection of 52% (n = 22, p = 0.009 versus vehicle) of gerbil CA1 hippocampal neurons was achieved by pretreatment and posttreatment with subcutaneous injection of 3 mg/kg carvedilol twice a day for 4 and 3 days, respectively.

CONCLUSIONS

Carvedilol provided neuroprotection in both in vitro and in vivo models of neuroinjury, where oxygen radicals are likely to play an important role. Therefore, carvedilol may reduce the risk of cerebral ischemia and stroke by virtue of both its antihypertensive action and its antioxidative properties.

Release of proinflammatory and prothrombotic mediators in the brain and peripheral circulation in spontaneously hypertensive and normotensive Wistar-Kyoto rats

BACKGROUND AND PURPOSE

We reported previously that stroke risk factors prepared the brain stem for the development of ischemia and hemorrhage and induced the production of tumor necrosis factor following an intrathecal injection of lipopolysaccharide, a prototypic monocyte-activating stimulus. This study evaluates whether blood or brain cells of hypertensive rats produce more proinflammatory and prothrombotic mediators than do blood or brain cells of normotensive rats.

METHODS

Levels of tumor necrosis factor, platelet-activating factor, 6-ketoprostaglandin F1 alpha, and thromboxane B2 in the cerebrospinal fluid and blood of spontaneously hypertensive and normotensive Wistar-Kyoto rats were monitored before and after a challenge with lipopolysaccharide.

RESULTS

Little or no activity from these mediators was found in the cerebrospinal fluid or blood of saline-injected control animals. Intravenous administration of lipopolysaccharide (0.001, 0.1, and 1.8 mg/kg) produced dose-dependent increases in blood levels of all mediators in hypertensive rats. In normotensive rats the levels were less than in hypertensive rats and were not clearly dose-related. When lipopolysaccharide was injected intracerebroventricularly, more tumor necrosis factor was measured in the cerebrospinal fluid than in the blood, suggesting local synthesis of this cytokine. Levels of tumor necrosis factor and platelet-activating factor in the cerebrospinal fluid were higher in hypertensive than in normotensive rats. The thromboxane A2/prostacyclin ratio was not altered significantly between the two rat strains.

CONCLUSIONS

It is suggested that the higher incidence of brain stem ischemia and hemorrhage after the intrathecal injection of lipopolysaccharide in hypertensive rats than in normotensive rats might be related to the higher levels of the two cytotoxic factors tumor necrosis factor and platelet-activating factor produced in response to such challenge.

Carvedilol, a new vasodilator and beta adrenoceptor antagonist, is an antioxidant and free radical scavenger

The antioxidant effect of carvedilol, a new vasodilating, beta adrenoceptor blocker was studied and compared with five other beta blockers. Carvedilol rapidly inhibited Fe(++)-initiated lipid peroxidation, measured as thiobarbituric acid reactive substance (TBARS), in rat brain homogenate with an IC50 of 8.1 microM. Under the same conditions, the IC50 values of atenolol, pindolol propranolol, celiprolol and labetalol were over 1.0 mM. Carvedilol protected against Fe(++)-induced alpha-tocopherol depletion in rat brain homogenate with an IC50 of 17.6 microM; propranolol, celiprolol and labetalol, up to 200 microM, did not show any effect. Using dihydroxyfumarate/Fe(++)-ADP as a OH.radical generating system and 5,5-dimethyl pyrroline-N-oxide (DMPO) as a trapping agent, the characteristic DMPO-OH signals were monitored by electron paramagnetic resonance. Carvedilol dose-dependently decreased the intensity of the DMPO-OH signal, with an IC50 of 25 microM, whereas propranolol, at 500 microM, and U74500A, a 21-aminosteroid, at 100 microM, had no effect. The antioxidant effect of carvedilol mainly resides in the carbazole moiety, and the substitution of a hydroxyl group at certain positions on the phenyl ring of either carbazole or the ortho-substituted phenoxylethylamine part of carvedilol resulted in an increase in antioxidant activity. Furthermore, the protective effect of carvedilol analogs against OH.-mediated neuronal death positively correlated to their antioxidant effect. We conclude that carvedilol is a far more potent antioxidant than other commonly used beta blockers. The apparent mechanism of carvedilol's inhibition of lipid peroxidation is mainly via scavenging free radicals. This novel property of carvedilol may contribute to the known cardioprotective activity of this compound.

Neuroprotective mechanism of (+)SKF 10,047 in vitro and in gerbil global brain ischemia

BACKGROUND AND PURPOSE

The N-methyl-D-aspartate receptor is believed to mediate part of the ischemic neuronal damage caused by the excitatory amino acid glutamate. (+)SKF 10,047, the prototypic sigma-agonist, interacts with the N-methyl-D-aspartate receptor. Therefore, we studied the neuroprotective effect of (+)SKF 10,047 on cultured rat cerebellar neurons and on CA1 hippocampal neurons of gerbils exposed to brain ischemia.

METHODS

Mechanisms of neuroprotection were studied in vitro by measuring calcium influx into cultured rat cerebellar granule cells loaded with fura 2-AM. In vivo neuroprotection of gerbil CA1 hippocampal neurons was studied in a posttreatment regimen following 5 minutes of bilateral carotid artery occlusion and 7 days of reperfusion.

RESULTS

In primary cultured rat cerebellar granule cell neurons, (+)SKF 10,047 in a dose-dependent manner diminished intracellular calcium levels of N-methyl-D-aspartate-stimulated neurons by a maximum of 87% (n = 8), with a 50% inhibitory concentration of 0.8 microM. (+)SKF 10,047 did not prevent subsequent calcium influx stimulated by kainic acid or KCl, nor did it interfere with modulation of the kainate response by quisqualic acid. Neuroprotection of 64% (p = 0.006, n = 15) of gerbil CA1 hippocampal neurons was achieved by posttreatment injection followed by minipump infusion.

CONCLUSIONS

Neuroprotection by (+)SKF 10,047 most likely involves interaction at the N-methyl-D-aspartate receptor. These results suggest that the benzomorphan class of sigma-agonists may provide neuroprotection in cerebral ischemia and stroke.

Effects of coronary angioplasty on plasma platelet-activating factor in man

Platelet activating factor (PAF) is a mediator of ischemia and reperfusion-induced tissue damage which was found to be synthesized in culture by endothelial cells. We hypothesized that PAF levels may be increased in the coronary system following coronary angioplasty. PAF levels were measured in the great cardiac vein of 16 patients before, during and following angioplasty of the left anterior coronary artery. PAF concentration was significantly higher in the cardiac vein than in the peripheral circulation at all time points. Interestingly, while PAF levels tended to decrease in the periphery they tended to increase in the coronary system over time. We conclude that PAF levels are higher in the coronary system than in the peripheral circulation in patients undergoing coronary angioplasty and that PAF may be released into the coronary artery following the procedure.

CGRP stimulates the adhesion of leukocytes to vascular endothelial cells

Calcitonin gene-related peptide (CGRP) stimulates the adhesiveness of human umbilical vein endothelial cells for U937 cells and human neutrophils in a dose- and time-dependent manner. The onset of CGRP-induced adhesives of HUVEC was rapid (30 min), independent of protein synthesis, and lasted over 24 h in the continuous presence of the peptide. The stimulatory effect of CGRP was completely blocked by the CGRP antagonist, CGRP(8-37). The present study provides evidence in support of the potential role of sensory nerve-derived neuropeptides in the modulation of leukocyte adhesion to vascular endothelial cells.

Neuroprotective effects of SKF 10,047 in cultured rat cerebellar neurons and in gerbil global brain ischemia

BACKGROUND AND PURPOSE

Excitatory amino acids and their receptors are involved in mediating ischemic neuronal damage. The sigma-agonists are believed to interact with the N-methyl-D-aspartate receptor. Therefore, we studied the neuroprotective, hypothermic, and motor deficit effects of the sigma-agonist SKF 10,047 and the N-methyl-D-aspartate antagonist MK-801.

METHODS

Neuroprotective effects were compared using an in vitro ischemia model of cultured rat cerebellar granule cells and the gerbil model of global brain ischemia induced by 5 minutes of bilateral carotid artery occlusion followed by 7 days of reperfusion.

RESULTS

In vitro, (+)MK-801 protected against 100 microM glutamate with a 50% protective concentration of 30 nM, followed by (-)MK-801 (150 nM), cyclazocine (0.5 microM), (+)SKF 10,047 (3.3 microM), pentazocine (5 microM), and (-)SKF 10,047 (10 microM). In vivo, (+)SKF 10,047 pretreatment (60 mg/kg) or multiple postischemic treatments provided neuroprotection comparable with MK-801 pretreatment (10 mg/kg). When ischemic animals were administered the multiple dosing regimen of (+)SKF 10,047, no hypothermic effect was noted in the temporalis muscle over 4 hours' postischemia. Motor deficits monitored by a swing grid test showed that 50% recovery from (+)SKF 10,047 was 5.5 times faster than recovery from MK-801.

CONCLUSIONS

These results are the first to report a hypothermia-free, in vivo neuroprotective effect of (+)SKF 10,047, a prototypical drug of the sigma-agonist class.

Neuroprotective effects of phenyl-t-butyl-nitrone in gerbil global brain ischemia and in cultured rat cerebellar neurons

We examined the ability of phenyl-t-butyl-nitrone (PBN), an electron spin trapper, to attenuate ischemia-induced forebrain edema and hippocampal CA1 neuronal loss in gerbils, and to protect rat cerebellar neurons in primary culture from glutamate-induced toxicity. PBN, given i.p. at 75 or 150 mg/kg 30 min before ischemia (5 min occlusion), increased survival (at 7 days) of CA1 neurons from 60 +/- 14 (vehicle-treated, n = 17) to 95 +/- 15 (P less than 0.05, n = 15) and 145 +/- 3 (P less than 0.01, n = 15), respectively. When gerbils were treated with PBN (50 mg/kg, i.p.) immediately and 6 h after reperfusion, followed by b.i.d. for an additional 2 days, CA1 neurons survival improved from 35 +/- 9 (vehicle, n = 20, 6 min occlusion) to 106 +/- 17 (P less than 0.01, n = 13). In gerbils exposed to a more severe ischemia (10 min), pretreatment with 150 mg/kg PBN increased the survival of CA1 neurons from 6 +/- 6 (vehicle) to 27 +/- 10 (P less than 0.05, n = 11). Pretreatment with PBN, at 150 mg/kg, reduced forebrain edema (following 15 min ischemia) by 24.7% (P less than 0.01, n = 16). PBN at 50 mg/kg, i.p. had no hypothermic effect and at 75 or 150 mg/kg caused a transient hypothermia. The presence of PBN in the brain was confirmed in microdialysis samples and brain tissue extract using HPLC. In vitro, PBN protected rat cerebellar neurons against 100 microM glutamate-induced toxicity with an EC50 value of 2.7 mM. Our results further support the concept that free radicals contribute to brain injury following ischemia and suggest the potential therapeutic application of electron spin trappers in stroke.

Priming by platelet-activating factor of endotoxin-induced lung injury and cardiovascular shock

Platelet-activating factor (PAF) is a glycerophospholipid known for its unusual potent vasoactive and proinflammatory activities. The present study examined whether PAF might serve as a priming factor in endotoxin-induced tumor necrosis factor-alpha (TNF alpha) synthesis, cardiovascular shock, and lung injury in anesthetized rats. Intravenous infusion of PAF (1 pmol/kg/min for 60 minutes, n = 5) alone or endotoxin (0.1 micrograms/kg i.v. bolus, n = 5) failed to alter blood pressure, serum TNF alpha and thromboxane B2, platelet and leukocyte count, and hematocrit, nor was lung histology, myeloperoxidase activity, and water content changed. In contrast, the combined administration of PAF and endotoxin markedly elevated serum TNF alpha (1,359 +/- 362 pg/ml, n = 5, p less than 0.01) and thromboxane B2 (43 +/- 5 pg/100 microliters, n = 8, p less than 0.01) along with hypotension, hemoconcentration, leukopenia, and thrombocytopenia. Most notably, the combined regimen caused neutrophil aggregation, adhesion, and accumulation into the lung parenchyma along with platelet-fibrin deposits in postcapillary venules, pulmonary edema, and increased lung myeloperoxidase activity. The role of PAF in this process was confirmed by 1) the prevention of the priming effect by pretreatment with the PAF antagonist BN 50739 (n = 5), and 2) the failure of lyso-PAF, the cardinal nonactive PAF-metabolite, to prime for endotoxin-induced production of TNF alpha (n = 4). These data suggest that PAF could serve as a key mediator in priming for endotoxin-induced tissue injury, especially the typical pulmonary pathophysiology of adult respiratory distress syndrome, a severe pathological outcome of septic shock, burns, and multiple organ injury.

Platelet-activating factor (PAF) receptor-mediated calcium mobilization and phosphoinositide turnover in neurohybrid NG108-15 cells: studies with BN50739, a new PAF antagonist

Platelet-activating factor (PAF) is an unusually potent lipid autacoid with a variety of biological activities. The growing body of evidence suggests that PAF might play an important role in modulation of central nervous system function, particularly during ischemia- and trauma-induced neuronal damage. However, the mechanisms involved in PAF actions on neuronal or other brain cells is virtually unknown. Therefore, this study was designed to characterize PAF receptor-mediated cellular signal transduction in neurohybrid NG108-15 cells with the aid of a new potent PAF antagonist, BN 50739. PAF induced an immediate and concentration-dependent increase in [Ca++]i with an EC50 of 6.8 nM. PAF-induced [Ca++]i mobilization was inhibited by several structurally unrelated PAF antagonists such as BN 50739, WEB 2086, SRI 63-441 and BN 52021, in a dose-dependent manner with IC50 values of 4.8, 6.9, 809 and 98500 nM, respectively. The calcium channel blockers nifedipine (5 microM) and diltiazem (10 microM) had no effect on the PAF-induced increase in [Ca++]i, but omission of CA++ from the incubation buffer caused an 82% reduction of PAF-induced [Ca++]i elevation; the remainder contributed from intracellular sources was completely inhibited by 10 microM TMB-8, an intracellular Ca++ blocker. NG108-15 cells exhibited homologous desensitization to sequential addition of PAF, but no heterologous desensitization between PAF and other agonists such as bradykinin, endothelin, angiotensin II and ATP was observed. PAF stimulated phosphoinositide metabolism in a dose-dependent manner with an EC50 of 5.1 nM for IP3 formation, which was also inhibited by the PAF antagonist BN 50739 in a dose-dependent manner (IC50 = 3.6 nM).(ABSTRACT TRUNCATED AT 250 WORDS)

Identification of endothelin receptors in cultured cerebellar neurons

We have described the binding of [125I]endothelin-1 (ET-1) to cultured rat cerebellar granule cells. Binding of [125I]ET-1 was specific, saturable, and time-dependent. Scatchard analysis of saturation binding data indicated a single class of high affinity binding site with a KD of 95 pM, and a Bmax of 8110 receptors/cell. Functionally, the binding of ET-1 stimulated phosphatidylinositide (PI) hydrolysis in a dose- and time-dependent fashion. PI turnover was found to be inhibitable by 1 microM phorbol dibutyrate but not by 1 microgram/ml pertussis toxin, suggesting that the ET-1-mediated response is regulated by protein kinase C and a pertussis toxin-insensitive guanine nucleotide (GTP) binding protein.

Excitatory amino acid neurotoxicity at the N-methyl-D-aspartate receptor in cultured neurons: protection by SKF 10,047

SKF 10,047 (N-allylnormetazocine) was found to be neuroprotective against glutamate-induced excitotoxicity in our model system of energy-stressed neurons which rapidly succumb to glutamate via N-methyl-D-aspartate (NMDA) receptor-mediated events. The 50% protective concentration (PC50) of the (+) and (-) enantiomers was 3.3 microM and 9 microM, respectively, against the toxic action of 100 microM glutamate. Protection by SKF 10,047 seemed to be mediated by the lower-affinity phencyclidine (PCP) binding site rather than the higher-affinity sigma-site since the potent sigma-ligand (+)-3-(3-hydroxyphenyl-N-1-propyl)piperidine [+)-3-PPP) did not protect at concentrations up to 2 mM. A reversed stereoselectivity was apparent for neuroprotection since (-)-3-PPP was weakly protective with a PC50 of 1.5 mM. These data suggest that energy-stressed rat cerebellar granule cells are a useful model for identifying neuroprotective agents, as shown by SKF 10,047.

Platelet-activating factor. A putative mediator in central nervous system injury?

Platelet-activating factor (1-O-hexadecyl-2-acetyl-sn-glycero-3-phosphorylcholine) is a potent lipid autacoid produced by many cell types. Platelet-activating factor is produced by cerebellar granule cells in culture and has been extracted from brain tissue. Multiple platelet-activating factor receptors have been demonstrated in brain tissue. Activation of platelet-activating factor receptors in transformed neuronal cell lines involved increases in intracellular calcium. Platelet-activating factor has potent actions on cerebral vessels and cerebral metabolism when administered in vivo, but may not have direct effects on brain microvessels. Excessive platelet-activating factor production in pathological states of the nervous system such as neurotrauma and stroke has been shown in only a few models (e.g., spinal cord ischemia and reperfusion or focal repercussion brain injury). In multiple studies using highly specific and potent platelet-activating factor antagonists, reversal or prevention of key consequences of brain injury such as hypoperfusion following ischemia, reperfusion and edema, inflammatory cell accumulation, neurologic/motor deficits, and neuronal salvage were demonstrated. This review provides and analyzes evidence in support of the role that platelet-activating factor might have in modulation of brain function and pathophysiological processes in brain ischemia and trauma.

Effect of endothelins on cytosolic free calcium concentration in neuroblastoma NG108-15 and NCB-20 cells

The effects of endothelin(ET)-1, ET-2, ET-3 and Big ET on intracellular level of Ca2+ ([Ca2+]i) were studied in neuroblastoma NG108-15 and NCB-20 cells. All ETs, except Big ET, induced an increase in [CA2+]i in NG108-15 cells in a dose-dependent manner, with EC50: 6.7, 11.2 and 71 nM, respectively. However, none of the ET increased [Ca2+]i in NCB-20 cells. Calcium channel blockers diltiazem or nicardipine had no effect on ET-induced increase in [CA2+]i, but extracellular Ca2(+)-depletion significantly reduced the response of NG108-15 cells to ETs. NG108-15 cells exhibited a homologous desensitization to sequential addition of ETs, but no heterologous desensitization among ET, bradykinin and PAF was observed. These data suggest that ET-induced receptor activation results in increased intracellular Ca2+ via a non voltage calcium channel mechanism and intracellular Ca2+ release.

Production of platelet-activating factor from rat cerebellar granule cells in culture

Platelet-activating factor (PAF) is a potent lipid mediator implicated in various pathological conditions, including CNS neuronal injury. However, the production of PAF by mammalian CNS neurons has not as yet been demonstrated. In the present study, we demonstrate that PAF is produced by cultured rat cerebellar granule cells. PAF was identified on the basis of chemical and enzymatic characteristics, biological activities with washed rabbit platelets, and behavior on TLC and HPLC. PAF was detected both in the cells and in the incubation medium, a result indicating the release of PAF from cultured neurons. The amount of PAF produced during a 30-min incubation was as follows: 1.02 +/- 0.10 and 0.93 +/- 0.09 pmol/4 X 10(7) cells in incubation buffer and cells, respectively (n = 10). The calcium ionophore A23187 (2.5 microM) had only a mild stimulatory effect on PAF production, a finding indicating that the neuron-generated PAF might be synthesized mainly by the de novo pathway of PAF production.

Neurotoxicity at the N-methyl-D-aspartate receptor in energy-compromised neurons. An hypothesis for cell death in aging and disease

Our results demonstrated that the neurotoxicity of glutamate and closely related agonists was mediated by the NMDA receptor in rat cerebellar granule cells. Evidence was presented to support our hypothesis that the pivotal event in the transition of these EAAs from neurotransmitters to neurotoxins is relief of the voltage-dependent Mg++ block of the NMDA channel due to changes in membrane potential which can be caused by depletion of highly phosphorylated nucleotides or by other depolarizing stimuli. Persistent stimulation of NMDA receptors whose channels are unblocked by Mg++ can permit excessive influx of Na+ and Ca++ and neuronal death can follow by a mechanism not yet understood. Glutamate is not toxic at kainate receptors although they are present on these cells. These findings underline the potential importance of perturbations in energy metabolism in a variety of neurodegenerative disorders and in the normal process of aging which share the common feature of the loss of neurons.

Excitatory amino acid neurotoxicity at the N-methyl-D-aspartate receptor in cultured neurons: pharmacological characterization

L-Glutamate neurotoxicity at the N-methyl-D-aspartate (NMDA) receptor was characterized in cultured cerebellar granule cells. When deprived of glucose for 40 min, these cells were killed by 20-60 microM L-glutamate. However, the neurons were resistant to glutamate at concentrations as high as 5 mM when glucose and Mg2+ were present throughout. Both competitive and non-competitive NMDA receptor antagonists completely blocked neurotoxicity due to glutamate and other NMDA receptor agonists. CPP [+/-)-3-(2-carboxypiperazin-4-yl)-prophyl-1-phosphonic acid) was the most effective competitive antagonist with full protection at 100 microM while MK-801 [+/-)-10,11-dihydro-5-methyl-5H-dibenzo[a,d]-cyclohepten-5,10-imin e) was the most effective non-competitive antagonist with full protection at 20 nM. Other antagonists with higher selectivity for other subtypes of glutamate receptors were ineffective. We conclude that glutamate toxicity in energy-deprived cerebellar granule cells is mediated by NMDA receptors. Results are discussed in terms of an hypothesis offering an explanation for the transition of glutamate from neurotransmitter to neurotoxin which emphasizes the responsiveness of the receptor to agonists rather than focusing on the presence of high concentrations of agonist.

Excitatory amino acid neurotoxicity at the N-methyl-D-aspartate receptor in cultured neurons: role of the voltage-dependent magnesium block

Results of the present report show that cerebellar neurons in primary culture are resistant to glutamate concentrations as high as 5 mM in the presence of glucose and Mg2+, but sensitive to glutamate concentrations lower than 35 microM when the neurons are deprived of glucose. Glutamate toxicity is also potentiated when Mg2+ is removed but glucose and EDTA are present; in this case, higher concentrations of glutamate (1 mM) are required for full toxicity. Glucose concentrations as low as 50 microM are fully protective against the toxicity of 100 microM glutamate; pyruvate and, to a lesser extent, lactate are also protective. Significantly, increasing concentrations of extracellular Mg2+ are fully protective against the toxicity of 100 microM glutamate in the absence of glucose and against the toxicity of 1 mM glutamate in the presence of glucose and EDTA. We interpret these results as support for our hypothesis that the pivotal event in glutamate's transition to neurotoxin is relief of the Mg2+ block of the N-methyl-D-aspartate (NMDA) receptor channel, which is known to be voltage-dependent. Partial depolarization in response to depletion of high-energy phosphates relieves the voltage-dependent block enabling glutamate to stimulate an excessive ion influx which results in the death of the neuron by a mechanism which is not yet understood. We propose that this mechanism may be operative in the neuronal damage associated with a variety of neurodegenerative disorders.

Glutamate becomes neurotoxic via the N-methyl-D-aspartate receptor when intracellular energy levels are reduced

The N-methyl-D-aspartate (NMDA) subtype of glutamate receptor appears to play a pivotal role in enabling glutamate to express its neurotoxic potential in a variety of neurological disorders. Our results show that the transition of glutamate from neurotransmitter to neurotoxin is facilitated when cellular energy is limited in cultured cerebellar neurons. Omission of glucose, exclusion of oxygen, or inclusion of inhibitors of oxidative phosphorylation or of the sodium/potassium pump, enables the excitatory amino acids glutamate or NMDA to express their neurotoxic potential. We interpret these results as demonstrating that glucose metabolism, ATP production, and functioning Na+,K+-ATPases are necessary to generate a resting potential sufficient to maintain the voltage-dependent Mg2+ block of the NMDA receptor channel; relief of the Mg2+ block enables the excitatory amino acids to act persistently at the NMDA receptor, resulting in the opening of ion channels and subsequent neuronal damage. These findings are discussed in the context of perturbations or abnormalities which lead to decreased availability or utilization of glucose and oxygen in the brain which may trigger endogenous excitatory amino acids to become neurotoxic by this mechanism.

Uptake of imipramine in neurons cultured from rat cerebellum

Imipramine was taken up by rat cerebellar neurons in primary culture. The process was dependent on time, temperature and pH and was reduced in the presence of the adenosine triphosphatase (ATPase) inhibitor dicyclohexylcarbodiimide or in the absence of glucose. Uptake approached saturation at 100 microM imipramine where approximately 42 nmol of the drug accumulated intracellularly per mg cell protein. Propranolol, but not serotonin, competed for imipramine uptake and uptake was inhibited by the 'lysosomotropic' amine chloroquine and by the Na+/H+ ionophore monensin, both of which dissipate proton gradients. Neurons were fractionated on Percoll gradients and the fractions exposed to [3H]imipramine. MgATP-dependent accumulation of [3H]imipramine was found mainly in fractions enriched for dense lysosomes. We conclude that imipramine was taken up by cerebellar neurons in primary culture and accumulated at high concentrations in intracellular compartments.

Transport of beta-adrenergic antagonists in the absence of beta-adrenergic receptors in rat pituitary tumor cells

We have demonstrated that the rat pituitary tumor cell line GH3 has a carrier-mediated active transport system for the beta-adrenergic antagonist dihydroalprenolol (DHA). Transport of DHA in GH3 was saturable, with an apparent Km of 1.4 microM, was temperature and pH dependent, and was inhibited by the ionophore monensin and the amine transport inhibitor reserpine. Propranolol competed for DHA transport, but not in a stereoselective fashion. The tricyclic antidepressant imipramine also competed for DHA transport, but catecholamines or serotonin did not. This amine transport system in GH3 cells appeared to be identical to the one we recently described in several other cell types; however, analysis in those cells was complicated by the fact that they contain beta-adrenergic receptors which bind beta-adrenergic ligands. In this report we show that GH3 cells do not possess detectable beta-adrenergic receptors, based on their inability to bind the partial agonist CGP-12177, their inability to bind nanomolar concentrations of DHA in a saturable, stereospecific manner, and their failure to produce cAMP in response to stimulation by beta-adrenergic agonists. Characterization of the amine transport system in GH3 cells clearly distinguishes it from receptor-mediated phenomena and should facilitate our efforts to fully understand its mechanism and significance.

Differentiation between amine transport and beta-adrenergic receptor-mediated binding in cultured mammalian cells

We have found that several types of cultured mammalian cells, including both normal and transformed human, rat, and mouse cell lines, have an active transport system for a diverse group of structurally related compounds possessing an amine group and various types of aromatic ring structures. Ligands such as the beta-adrenergic antagonists (-)-[3H] dihydroalprenolol (DHA), (-)-[3H]propranolol, and (-)-[125I] iodocyanopindolol, and the tricyclic antidepressant [3H]imipramine, which are used to assess cell surface receptors for catecholamines and serotonin, appear to be actively transported into cells rather than simply bound to cell surface sites or accumulated by passive diffusion. DHA transport was competed by many structurally related amines including imipramine and certain alpha-and beta-adrenergic ligands, but not by catecholamines or serotonin. Ligand transport in HeLa cells was saturable at micromolar levels, selective, nonstereospecific, temperature- and pH-dependent, and sensitive to the ionophore monensin and the amine transport inhibitor reserpine, thus indicating dependence on a carrier system driven by a transmembrane proton gradient. In C6 glioma cells, amine transport was clearly distinguishable from beta-adrenergic receptor binding which could be measured with the recently developed hydrophilic beta-blocker (+/-)-[3H] 4-(3-tertiarybutylamino-2-hydroxy-propoxy)-benzimidazole-2-on hydrochloride (CGP-12177); binding of this ligand met rigorous pharmacological criteria, was not influenced by monensin or reserpine, and, therefore, did not appear to be transported. Membrane vesicles from HeLa and C6 cells transported DHA but not CGP-12177 via a MgATP-dependent mechanism which was inhibited by N,N'-dicyclohexylcarbodiimide, monensin, and reserpine, indicating a carrier system driven by a proton gradient maintained by a proton-pumping ATPase.

Gonococcal strains from homosexual men have outer membranes with reduced permeability to hydrophobic molecules

Loci designated penA, penB, and mtr contribute additively to penicillin G resistance in Neisseria gonorrhoeae; the mtr locus also confers resistance to hydrophobic dyes, detergents, and antibiotics, env mutations suppress the phenotypic expression of mtr and penB and are responsible for increased sensitivity to various hydrophobic molecules. We postulated that the host environment is important in the selection of gonococcal strains with these particular outer membrane phenotypes. Thus, mtr strains should predominate in environments that are high in hydrophobic molecules. To test this hypothesis we determined the outer membrane phenotype of 152 strains of N. gonorrhoeae. Rectal and urethral isolates from 58 homosexual men, urethral isolates from 55 heterosexual men, and cervical and rectal isolates from 39 heterosexual women were used in this study. Strains from 43 of the homosexual men were matched with those from heterosexual men with respect to auxotype and year and season of isolation. Cell envelope phenotype was determined for each strain on the basis of its resistance to various hydrophobic compounds. The identity of mtr strains was confirmed by genetic transformation. Among the matched pairs, mtr strains were significantly more prevalent among isolates from homosexual men than among those from heterosexual men (P = 0.03). Serogrouping by coagglutination demonstrated that 17 of 19 mtr strains versus 76 of 131 non-mtr strains belonged to coagglutination group WII (P = 0.01). Coagglutination group WII strains were also associated with homosexuality (P = 0.02). Gonococci were also tested for resistance to fecal lipids, mtr strains were more resistant to growth inhibition by fecal lipids than were non-mtr strains.