Serotonin potentiates angiotensin II--induced vascular smooth muscle cell proliferation

Vascular smooth muscle cell (VSMC) proliferation is a key feature in the development of atherosclerosis and restenosis after angioplasty, which can occur in response to many different humoral and mechanical stimuli. We investigated the growth promoting activities of two potent vasoactive substances, angiotensin II (Ang II) and serotonin (5-HT), on cultured rabbit VSMCs. Growth-arrested VSMCs were incubated with serum-free medium containing different concentrations of Ang II in the presence or absence of 5-HT. [3H]thymidine incorporation into VSMC DNA was measured as an index of cell proliferation. Ang II and 5-HT stimulated DNA synthesis in a dose-dependent manner with a maximal effect at 1.75 microM for Ang II (202%) and 50 microM for 5-HT (205%). When added together, low concentrations of Ang II (1 microM) and 5-HT (5 microM) synergistically induced DNA synthesis (363%). Candesartan (1 microM), an AT(1) receptor antagonist, but not PD 123319 (1 microM), an AT(2) receptor antagonist, inhibited the mitogenic effect on Ang II and its interaction with 5-HT. Sarpogrelate (10 microM), a 5-HT(2A) receptor antagonist, and pertussis toxin (10 ng/ml) inhibited the mitogenic effect of 5-HT and its interaction with Ang II. The protein kinase C inhibitor Ro 31-8220 (0.1 microM), the Raf-1 inhibitor radicicol (10 microM), and the MAPK kinase inhibitor PD 098059 (10 microM) abolished mitogenic effects of Ang II and 5-HT, and also their synergistic interaction. The JAK2 inhibitor AG 490 (10 microM) had only a minimal inhibitory effect of Ang II-induced DNA synthesis but significantly inhibited the interaction of Ang II with 5-HT. The synergistic effect on Ang II (1 microM) with 5-HT (5 microM) on DNA synthesis was completely reversed by the combined use of both candesartan (1 microM) and sarpogrelate (10 microM). Our results suggest that Ang II and 5-HT exert a synergistic interaction on VSMC proliferation via AT(1) and 5-HT(2A) receptors. The activation of MAPK and JAK/STAT pathways may explain the synergistic interaction between Ang II and 5-HT.

Synergistic effect of urotensin II with serotonin on vascular smooth muscle cell proliferation

BACKGROUND

Urotensin II (U-II), the most potent vasoconstrictor, and serotonin (5-HT) are known to play an important role in pulmonary hypertension. However, little is known about the effect of U-II and its interaction with 5-HT on vascular smooth muscle cell (VSMC) proliferation.

OBJECTIVE

We assessed the interaction between U-II and 5-HT in inducing VSMC proliferation.

METHODS

Growth-arrested rabbit VSMCs were incubated in serum-free medium with different concentrations of U-II and 5-HT. VSMC proliferation was examined by the increase in [3H]thymidine incorporation into DNA and cell number.

RESULTS

U-II or 5-HT induced [3H]thymidine incorporation in a dose-dependent manner with a maximal effect at a concentration of 50 nmol/l (161%) or 50 micromol/l (205%), respectively. When added together, low concentrations of U-II (50 nmol/l) and 5-HT (1 micromol/l) interacted synergistically in inducing [3H]thymidine incorporation (382%). These effects on [3H]thymidine incorporation were paralleled by an increase in cell number. The G-protein inactivator GDP-beta-S (100 micromol/l), protein kinase C (PKC) inhibitor Ro31-8220 (0.1 micromol/l), Src family tyrosine kinase inhibitor PP2 (1 micromol/l), and mitogen-activated protein kinase (MAPK) kinase inhibitor PD098059 (10 micromol/l) inhibited the mitogenic effects of U-II and 5-HT and also their interaction in inducing [3H]thymidine incorporation.

CONCLUSION

Our results suggest that U-II and 5-HT may induce the synergistic interaction in inducing VSMC proliferation via a G-protein-coupled receptor/PKC/Src tyrosine kinase/MAPK pathway, thus contributing to the relatively rapid development of atherosclerosis in hypertensive vascular disease.

Synergistic effect of urotensin II with mildly oxidized LDL on DNA synthesis in vascular smooth muscle cells

BACKGROUND

The urotensin II (UII) found in coronary atheroma is the most potent vasoconstrictor known to date. Mildly oxidized LDL (moxLDL) contributes to atherogenesis and plaque formation. We assessed the effect of UII and its interaction with moxLDL and the oxidative components of moxLDL on vascular smooth muscle cell (VSMC) proliferation. Methods and Results-Growth-arrested VSMCs were incubated in serum-free medium with different concentrations of LDL, moxLDL, oxLDL, hydrogen peroxide, lysophosphatidylcholine, or 4-hydroxy-2-nonenal, with or without UII. [(3)H]Thymidine incorporation into DNA was measured as an index of VSMC proliferation. UII stimulated [(3)H]thymidine incorporation in a dose-dependent manner, with a maximal effect at a concentration of 50 nmol/L (161%). Low concentrations of UII potentiated the mitogenic effect of LDL (108% to 242%), oxLDL (129% to 302%), moxLDL (120% to 337%), hydrogen peroxide (177% to 226%), lysophosphatidylcholine (115% to 332%), and 4-hydroxy-2-nonenal (142% to 299%). The synergistic interaction between UII and moxLDL was partially inhibited by anti-Gq/11alpha antibody, the epidermal growth factor receptor tyrosine kinase inhibitor erbstatin A (10 micromol/L), and the intracellular free radical scavenger N-acetylcysteine (400 micromol/L) and was completely inhibited by the c-Src tyrosine kinase inhibitor radicicol (10 micromol/L), the protein kinase C (PKC) inhibitor Ro31-8220 (0.1 micromol/L), and the mitogen-activated protein kinase (MAPK) kinase inhibitor PD098059 (10 micromol/L).

CONCLUSIONS

Our results suggest that UII acts synergistically with moxLDL in inducing VSMC proliferation via the c-Src/PKC/MAPK pathway, which may explain the relatively rapid progression of atherosclerosis in patients with hypertension and hypercholesterolemia.

Monocyte chemotactic protein 1 amplifies serotonin-induced vascular smooth muscle cell proliferation

Monocyte chemotactic protein 1 (MCP-1), which is synthesized by vascular cells, is a chemoattractant for monocytes and has been implicated in a wide range of acute and chronic inflammatory processes characterized by monocyte infiltration, including atherosclerosis. However, it is unclear whether MCP-1 is able to modulate vascular smooth muscle cell (VSMC) proliferation. We assessed the effect of MCP-1 on VSMC proliferation and its interaction with serotonin (5-HT), a mitogen for VSMCs. Growth-arrested VSMCs were stimulated with different concentrations of MCP-1 (25-200 ng/ml) and 5-HT (5 and 50 microM) in serum-free medium. DNA synthesis in VSMCs was measured by [3H]thymidine incorporation. 5-HT at concentrations of 5 and 50 microM significantly stimulated DNA synthesis by 1.8- and 2.1-fold over the control value, respectively (p < 0.0001). However, MCP-1 at the concentrations tested did not have any significant effect on DNA synthesis. Even though MCP-1 (50 ng/ml) by itself is not mitogenic, when added to 5-HT, it significantly amplified the mitogenic effect of 5-HT compared with that of 5-HT alone (p < 0.0001). The 5-HT2A receptor antagonist sarpogrelate (10 microM) and its major metabolite M-1 (0.1 microM), pertussis toxin (10 ng/ml), Src family protein tyrosine kinase (PTK) inhibitor PP2 (1 microM), protein kinase C (PKC) inhibitor Ro31-8220 (0.1 microM) and mitogen-activated protein kinase (MAPK) kinase inhibitor PD098059 (10 microM) significantly inhibited the mitogenic effect of 5-HT and its interaction with MCP-1. Anti-MCP-1 antibody (2 microg/ml) and the Janus kinase 2 (JAK2) inhibitor AG490 (10 microM) significantly inhibited the interaction of MCP-1 with 5-HT. Further, the amplified mitogenic effect of 5-HT with MCP-1 was completely reversed by the combined use of sarpogrelate with anti-MCP-1 antibody. Our results suggest that MCP-1 amplifies the mitogenic effect of 5-HT on VSMCs. The mitogenic effect of 5-HT may be mediated by the G protein-Src family PTK-PKC-MAPK pathway. The activation of the JAK2/signal transducer and activator of transcription 3 pathway by MCP-1 in addition to the MAPK pathway by 5-HT may explain the potentiating effect of MCP-1 on 5-HT-induced mitogenesis.

Mildly oxidized low-density lipoprotein acts synergistically with angiotensin II in inducing vascular smooth muscle cell proliferation

OBJECTIVES

Considerable attention has been focused on both mildly oxidized low-density lipoprotein (mox-LDL) and highly oxidized LDL (ox-LDL) as important risk factors for cardiovascular disease. Further, angiotensin II (Ang II) appears to play a crucial role in the development of hypertension and atherosclerosis. We assessed the effect of oxidatively modified LDL and its major oxidative components, i.e., hydrogen peroxide (H2O2), lysophosphatidylcholine (LPC), and 4-hydroxy-2-nonenal (HNE) and their interaction with Ang II on vascular smooth muscle cell (VSMC) DNA synthesis.

METHODS

Growth-arrested rabbit VSMCs were incubated in serum-free medium with different concentrations of native LDL, mox-LDL, ox-LDL, H2O2, LPC, or HNE with or without Ang II. DNA synthesis in VSMCs was measured by [3H]thymidine incorporation.

RESULTS

Ang II stimulated DNA synthesis in a dose-dependent manner with a maximal effect at a concentration of 1 micromol/l (173%). Ang II (0.5 micromol/l) amplified the effect of native LDL at 500 ng/ml, ox-LDL at 100 ng/ml, and mox-LDL at 50 ng/ml on DNA synthesis (108 to 234%, 124 to 399%, 129 to 433%, respectively). H2O2 had a maximal effect at a concentration of 5 micromol/l (177%), LPC at 15 micromol/l (156%), and HNE at 0.5 micromol/l (137%). Low concentrations of H2O2 (1 micromol/l), LPC (5 micromol/l), or HNE (0.1 micromol/l) also acted synergisitically with Ang II (0.5 micromol/l) in inducing DNA synthesis to 308, 304, or 238%, respectively. Synergistic interactions of Ang II (0.5 micromol/l) with mox-LDL, ox-LDL (both 50 ng/ml), H2O2 (1 micromol/l), LPC (5 micromol/l), or HNE (0.1 micromol/l) on DNA synthesis were completely reversed by the combined use of probucol (10 micromol/l), a potent antioxidant and candesartan (0.1 micromol/l), an AT1 receptor antagonist.

CONCLUSIONS

Our results suggest that mox-LDL, ox-LDL, and their major components H2O2, LPC, and HNE act synergistically with Ang II in inducing VSMC DNA synthesis. A combination of antioxidants with AT1 receptor blockade may be effective in the treatment of VSMC proliferative disorders associated with hypertension and atherosclerosis.

A peptide analogue of thrombin receptor-activating peptide inhibits thrombin and thrombin-receptor-activating peptide-induced vascular smooth muscle cell proliferation

The serine protease thrombin, in addition to its pivotal role in the coagulation cascade, plays an important role in the development of atherosclerosis and restenosis by inducing smooth cell proliferation. Thrombin exerts its cellular effects mainly by cleaving its own receptor, leaving a new NH2-terminus that can act as a tethered ligand to activate the thrombin receptor. Peptides derived from the new NH2-terminus are able to fully activate thrombin receptor and mimic cellular effects of thrombin. Peptides with structural similarities to the tethered ligand have been tested for their ability to prevent thrombin- and tethered ligand-induced platelet aggregation and thrombus formation. We synthesized a peptide with multiple alanine substitutions in both critical and noncritical residues of tethered ligand that specifically inhibited platelet aggregation induced by thrombin and thrombin receptor-activating peptide and prevented thrombus formation in a rabbit thrombosis model. In the present study we demonstrate that this peptide inhibited only thrombin- and tethered ligand-induced human vascular smooth muscle cell proliferation as determined by (3H)-thymidine incorporation and has no effect on platelet-derived growth factor and serum-induced smooth muscle cell proliferation. The inhibitory effect of this peptide is dependent on the concentration of the antagonist used and length of preincubation time. The possible mechanism by which this peptide exerts its inhibitory effect may by desensitizing the thrombin receptor. The results of the present study suggest that apart from being antithrombotic, tethered ligand antagonist peptides can also act as antiatherosclerotic or antirestenotic agents.

The cyclization of farnesyl diphosphate and nerolidyl diphosphate by a purified recombinant delta-cadinene synthase

The first step in the conversion of the isoprenoid intermediate, farnesyl diphosphate (FDP), to sesquiterpene phytoalexins in cotton (Gossypium barbadense) plants is catalyzed by delta-cadinene (CDN) synthase. CDN is the precursor of desoxyhemigossypol and hemigossypol defense sesquiterpenes. In this paper we have studied the mechanism for the cyclization of FDP and the putative intermediate, nerolidyl diphosphate, to CDN. A purified recombinant CDN synthase (CDN1-C1) expressed in Escherichia coli from CDN1-C1 cDNA isolated from Gossypium arboreum cyclizes (1RS)-[1-2H](E, E)-FDP to >98% [5-2H]and [11-2H]CDN. Enzyme reaction mixtures cyclize (3RS)-[4,4,13,13,13-2H5]-nerolidyl diphosphate to 62.1% [8,8,15,15,15-2H5]-CDN, 15.8% [6,6,15,15,15-2H5]-alpha-bisabolol, 8.1% [6,6,15,15,15-2H5]-(beta)-bisabolene, 9.8% [4,4,13,13-2H4]-(E)-beta-farnesene, and 4.2% unknowns. Competitive studies show that (3R)-nerolidyl diphosphate is the active enantiomer of (3RS)-nerolidyl diphosphate that cyclized to CDN. The kcat/Km values demonstrate that the synthase uses (E,E)-FDP as effectively as (3R)-nerolidyl diphosphate in the formation of CDN. Cyclization studies with (3R)-nerolidyl diphosphate show that the formation of CDN, (E)-beta-farnesene, and beta-bisabolene are enzyme dependent, but the formation of alpha-bisabolol in the reaction mixtures was a Mg2+-dependent solvolysis of nerolidyl diphosphate. Enzyme mechanisms are proposed for the formation of CDN from (E,E)-FDP and for the formation of CDN, (E)-beta-farnesene, and beta-bisabolene from (3RS)-nerolidyl diphosphate. The primary structures of cotton CDN synthase and tobacco epi-aristolochene synthase show 48% identity, suggesting similar three-dimensional structures. We used the SWISS-MODEL to test this. The two enzymes have the same overall structure consisting of two alpha-helical domains and epi-aristolochene synthase is a good model for the structure of CDN synthase. Several amino acids in the primary structures of both synthases superimpose. The amino acids having catalytic roles in epi-aristochene synthase are substituted in the CDN synthase and may be related to differences in catalytic properties.

Angiotensin II and serotonin potentiate endothelin-1-induced vascular smooth muscle cell proliferation

BACKGROUND

Vascular smooth muscle cell (VSMC) proliferation induced by various growth factors has been implicated in a wide variety of pathological processes, including hypertension, atherosclerosis and restenosis after angioplasty.

OBJECTIVES

To investigate the interactions among well-known potent vasoconstrictor substances, endothelin-1 (ET-1), angiotensin II (Ang II), and serotonin (5-HT), on VSMC proliferation.

METHODS

Growth-arrested rabbit VSMCs were incubated with different concentrations of ET-1 in the absence or presence of Ang II, 5-HT, or both. VSMC proliferation was examined by increases in incorporation of [3H]thymidine into DNA and in cell number.

RESULTS

ET-1, Ang II and 5-HT stimulated DNA synthesis in a dose-dependent manner. ET-1 had a maximal effect at a concentration of 0.5 micromol/l (259% of control), Ang II at 1 micromol/l (173%), and 5-HT at 50 micromol/l (205%). When added together, ET-1 (0.1 micromol/l) and Ang II (1 micromol/l) synergistically induced DNA synthesis (341%). When the vasoconstrictors were tested in combination, even non-mitogenic concentrations of ET-1 (0.01 nmol/l) potentiated 5-HT (5 micromol/l)-induced DNA synthesis (404%). Co-incubation of ET-1 (0.01 micromol/l) with Ang II (1 micromol/l) and 5-HT (5 micromol/l) synergistically induced DNA synthesis (566%). These effects on DNA synthesis were paralleled by an increase in cell number. The ETA/B non-selective receptor antagonist, TAK044 (1 micromol/l) and the ETA receptor antagonist, BQ123 (1 micromol/l), but not the ETB receptor antagonist, BQ788 (1 micromol/l), inhibited the mitogenic effect of ET-1 and its interaction with Ang II or 5-HT. In addition, TAK044 (1 micromol/l) or BQ123 (1 micromol/l) along with the angiotensin II type 1 (AT1) receptor antagonist, candesartan (1 micromol/l), the 5-HT2A receptor antagonist, sarpogrelate (10 micromol/l), or both, inhibited the interactions of ET-1 with Ang II or 5-HT.

CONCLUSIONS

Our results suggest that Ang II and 5-HT could potentiate ET-1-induced VSMC proliferation. Inhibition of ETA, AT1, and 5-HT2A may be effective in the treatment of VSMC proliferative disorders associated with hypertension, atherosclerosis and restenosis after angioplasty.

Lysophosphatidylcholine and reactive oxygen species mediate the synergistic effect of mildly oxidized LDL with serotonin on vascular smooth muscle cell proliferation

BACKGROUND

Mild oxidation of LDL enhances its atherogenic potential and induces a synergistic interaction with serotonin (5HT) on vascular smooth muscle cell (VSMC) proliferation. Because of its complex chemical nature, the mitogenic components of mildly oxidized LDL (moxLDL) remain unclear.

METHODS AND RESULTS

We examined both the effects of lysophosphatidylcholine (LPC) and hydrogen peroxide (H(2)O(2)), a donor of reactive oxygen species, as major components of moxLDL and their interactions with 5HT on VSMC proliferation. Growth-arrested VSMCs were incubated with different concentrations of moxLDL, LPC, H(2)O(2), or LPC with H(2)O(2) in the absence or presence of 5HT. DNA synthesis in VSMCs was examined by [(3)H]thymidine incorporation. MoxLDL, LPC, H(2)O(2), and 5HT stimulated DNA synthesis in a dose-dependent manner. MoxLDL had a maximal stimulatory effect at a concentration of 5 microg/mL (211%), LPC at 15 micromol/L (156%), H(2)O(2) at 5 micromol/L (179%), and 5HT at 50 micromol/L (205%). Added together, moxLDL (50 ng/mL) and 5HT (50 micromol/L) synergistically increased DNA synthesis (443%). Coincubation of LPC (1 micromol/L) with H(2)O(2) (0.5 micromol/L) and 5HT (5 micromol/L) resulted in a synergistic increase in DNA synthesis (439%), which was nearly equal to that of moxLDL with 5HT (443%). The combined effects of LPC, H(2)O(2), and 5HT on DNA synthesis were completely reversed by the combined use of an antioxidant, N:-acetylcysteine (400 micromol/L) or butylated hydroxytoluene (20 micromol/L), with a 5HT(2) receptor antagonist, LY281067 (10 microg/mL).

CONCLUSIONS

Our results suggest that both LPC and reactive oxygen species may contribute to the mitogenic effect of moxLDL on VSMCs and its synergistic effect with 5HT.

Lipid peroxidation product 4-hydroxy-2-nonenal acts synergistically with serotonin in inducing vascular smooth muscle cell proliferation

Formation of an atherosclerotic lesion is in part mediated by inflammatory and oxidative mechanisms including lipid peroxidation. To characterize the potential role of lipid peroxidation products in atherogenesis, we assessed the effect of 4-hydroxy-2-nonenal (HNE), a component of oxidatively modified lipids on vascular smooth muscle cells (VSMCs) proliferation, and its interaction with serotonin (5-hydroxytryptamine, 5-HT), a known mitogen for VSMCs. Growth-arrested rabbit VSMCs were incubated with different concentrations of HNE in the absence or presence of 5-HT. VSMCs proliferation was examined by increases in [3H]thymidine incorporation into DNA and cell number. HNE and 5-HT stimulated DNA synthesis in a dose-dependent manner. HNE had a maximal proliferative effect at a concentration of 1 microM (143% of the control) and 5-HT at 50 microM (211%). When added together, low concentrations of HNE (0.1 microM) and 5-HT (5 microM) synergistically induced DNA synthesis (273%). These effects on DNA synthesis were paralleled by an increase in cell number. A 5-HT2 receptor antagonist LY 281067 (10 microg/ml) and pertussis toxin (10 ng/ml) inhibited the mitogenic effect of 5-HT only. Protein tyrosine kinase inhibitor erbstatin A (10 microM) completely inhibited the mitogenic effect of HNE and partially that of 5-HT and the combined effect of HNE+5-HT. Protein kinase C inhibitor Ro 31-8220 (0.1 microM) completely inhibited mitogenic effects of both HNE and 5-HT, and also the combined effect of HNE+5-HT. The synergistic effect of HNE+5-HT on DNA synthesis was completely reversed by the combined use of LY 281067 (10 microg/ml) and antioxidants N-acetylcysteine (400 microM), vitamin C (200 microM), or vitamin E (20 microM). Our results suggest that HNE acts synergistically with 5-HT in inducing VSMCs proliferation. Combined use of both antiplatelet and antioxidant therapies may be useful for the prevention of VSMCs proliferative disorders associated with atherosclerosis and restenosis after angioplasty.

Synergistic interaction between thromboxane A2 and mildly oxidized low density lipoproteins on vascular smooth muscle cell proliferation

Low density lipoprotein (LDL) and mildly oxidized low density lipoprotein (mox-LDL) are known mitogens for vascular smooth muscle cell (VSMC). Since aggregating platelets at sites of atherosclerotic injury release thromboxane A2(TXA2), a known mitogen for VSMC, we examined whether TXA2 can act synergistically with mox-LDL or its oxidative components in inducing VSMC proliferation. Growth arrested primary aortic rabbit VSMCs in 1st or 2nd passage were incubated with different concentrations of LDL or mox-LDL or lysophosphatidylcholine (LPC) or H2O2 or 4-hydroxy-2-nonenel (HNE) for 24 h followed by incubation with TXA2 mimetic U46619 for another 24 h. The amount of 3[H]-thymidine incorporated into the DNA was measured. Both LDL and mox-LDL at a concentration of 120 microg/ml induced proliferation of VSMC (168% or 184% respectively) when compared to the control. U46619 induced VSMC proliferation was observed at a concentration of 5 microm/L. As compared to native LDL, the mitogenic effect of mox-LDL on VSMC proliferation was markedly potentiated by U46619 to 301% or 316% at 0.5 or 5 microm/L U46619 respectively. LPC, H2O2 and HNE induced DNA synthesis was also marked by enhanced by U46619. These results suggest that even low concentration of TXA2 released from aggregating platelets may potentiate the mitogenic effect of mox-LDL at sites of vascular damage. The mitogenic effect of mox-LDL may be mediated via its oxidation products LPC, H2O2 (reactive oxygen species donor), and HNE.

Vascular smooth muscle cells preloaded with eicosapentaenoic acid and docosahexaenoic acid fail to respond to serotonin stimulation

Epidemiological, animal and clinical studies indicate that n-3 fatty acids may benefit individuals with known history of cardiovascular disease or at risk of developing it. Though there is indirect evidence to suggest that the beneficial effects of n-3 fatty acids may be because of their ability to inhibit smooth muscle cell (SMC) proliferation, there are no studies that have examined this hypothesis. In this study, the mitogenic effect of serotonin (5HT) and platelet derived growth factor (PDGF), known mitogens for vascular SMC, on aortic SMCs preloaded with eicosapentaenoic acid (EPA) and/or docosahexaenoic acid (DHA) is examined. 5HT and PDGF could only partially stimulate proliferation of SMC that were preloaded with EPA or DHA as compared to the control cells. gamma-Linolenic acid (LA) and oleic acid (OA) did not block the 5HT or PDGF induced 3[H]thymidine incorporation suggesting that the anti-proliferative effect was specific to n-3 fatty acids only. Further, when EPA and DHA were combined in the ratio they are present in fishoils, there was a synergistic interaction in inhibiting the proliferation of SMC. Further, SMC grown in the presence of EPA or DHA, when stimulated with 5HT, failed to show an increase in 5HT(2) receptor mRNA. One of the potential mechanism by which fish oils may prevent the development of atherosclerosis or restenosis could be inhibition of the mitogen induced SMC proliferation. Combination of EPA with DHA is likely to be more beneficial.

Interactions of the 5-hydroxytryptamine 3 antagonist class of antiemetic drugs with human cardiac ion channels

Administration of the 5-hydroxytryptamine 3 receptor class of antiemetic agents has been associated with prolongation in the QRS, JT, and QT intervals of the ECG. To explore the mechanisms underlying these findings, we examined the effects of granisetron, ondansetron, dolasetron, and the active metabolite of dolasetron MDL 74,156 on the cloned human cardiac Na(+) channel hH1 and the human cardiac K(+) channel HERG and the slow delayed rectifier K(+) channel KvLQT1/minK. Using patch-clamp electrophysiology we found that all of the drugs blocked Na(+) channels in a frequency-dependent manner. At a frequency of 3 Hz, the IC(50) values for block of Na(+) current measured 2.6, 88.5, 38.0, and 8.5 microM for granisetron, ondansetron, dolasetron, and MDL 74,156, respectively. Block was relieved by strong hyperpolarizing potentials, suggesting a possible interaction with an inactivated channel state. Recovery from inactivation was impaired at -80 mV compared with -100 mV, and the fractional recovery was impaired by drug in a concentration-dependent manner. IC(50) values for block of the HERG cardiac K(+) channel measured 3.73, 0.81, 5.95, and 12.1 microM for granisetron, ondansetron, dolasetron, and MDL 74,156, respectively. Ondansetron (3 microM) also slowed decay of HERG tail currents. In contrast, none of these drugs (10 microM) produced greater than 30% block of the slow delayed rectifier K(+) channel KvLQT1/minK. We concluded that the antiemetic agents tested in this study block human cardiac Na(+) channels probably by interacting with the inactivated state. This may lead to clinically relevant Na(+) channel blockade, especially when high heart rates or depolarized/ischemic tissue is present. The submicromolar affinity of ondansetron for the HERG K(+) channel likely underlies the prolongation of cardiac repolarization reported for this drug.

Effects of dopamine beta-hydroxylase inhibition with nepicastat on the progression of left ventricular dysfunction and remodeling in dogs with chronic heart failure

BACKGROUND

Inhibition of dopamine beta-hydroxylase (DBH) results in a decrease in norepinephrine synthesis. The present study was a randomized, blinded, placebo-controlled investigation of the long-term effects of therapy with the DBH inhibitor nepicastat (NCT) on the progression of left ventricular (LV) dysfunction and remodeling in dogs with chronic heart failure (HF).

METHODS AND RESULTS

Moderate HF (LV ejection fraction [LVEF] 30% to 40%) was produced in 30 dogs by intracoronary microembolization. Dogs were randomized to low-dose NCT (0.5 mg/kg twice daily, n=7) (L-NCT), high-dose NCT (2 mg/kg twice daily, n=7) (H-NCT), L-NCT plus enalapril (10 mg twice daily, n=8) (L-NCT+ENA), or placebo (PL, n=8). Transmyocardial (coronary sinus-arterial) plasma norepinephrine (tNEPI), LVEF, end-systolic volume, and end-diastolic volume were measured before and 3 months after initiating therapy. tNEPI levels were higher in PL compared with NL (86+/-20 versus 13+/-14 pg/mL, P:<0.01). L-NCT alone and L-NCT+ENA reduced tNEPI toward normal (28+/-4 and 39+/-17 pg/mL respectively), whereas HD-NCT reduced tNEPI to below normal levels (3+/-10 pg/mL). In PL dogs, LVEF decreased but was unchanged with L-NCT and increased with L-NCT+ENA. L-NCT and L-NCT+ENA prevented progressive LV remodeling, as evidenced by lack of ongoing increase in end-diastolic volume and end-systolic volume, whereas H-NCT did not

CONCLUSIONS

In dogs with HF, therapy with L-NCT prevented progressive LV dysfunction and remodeling. The addition of ENA to L-NCT afforded a greater increase in LV systolic function. NCT at doses that normalize tNEPI may be useful in the treatment of chronic HF.

Inhibition of arterial thrombosis by a peptide ligand of the thrombin receptor

Thrombin plays an important role in promoting arterial thrombosis by platelet activation and by catalyzing fibrin formation. Use of thrombin inhibitors that block both the platelet-activating and fibrin formation properties of thrombin are associated with hemostasis. This problem might be overcome by developing agents that block only the platelet-activating property of thrombin. Because the platelet-activating property of thrombin is mediated by the thrombin receptor, antagonists of the thrombin receptor might be efficacious and potentially safer with regard to bleeding complications. We investigated whether a peptide ligand (AFLARAA) of the thrombin receptor that blocked alpha-thrombin and thrombin receptor activating peptide-induced platelet aggregation could inhibit thrombosis. A partially occlusive thrombus was generated by application of electric current in rabbit carotid artery. In control animals, the artery was completely occluded within 42+/-12 min after the current was discontinued. When the thrombin receptor activating peptide antagonist was given (100 micromol/kg as an IV bolus followed by 900 micromol/kg infusion for a period of 180 min) starting at the time the current was stopped, blood flow remained patent throughout the infusion period and for an additional 60 min after the infusion was stopped. The antithrombotic effect of the antagonist peptide was not associated with increased bleeding tendency, as judged by the amount of blood adsorbed by a gauze pad placed in a surgical incision extending to the muscle tissue and by a standard template bleeding time. These results indicate that thrombin receptor antagonist peptides can be used as antithrombotic agents.

Hyperlipemic-very low density lipoprotein, intermediate density lipoprotein and low density lipoprotein act synergistically with serotonin on vascular smooth muscle cell proliferation

BACKGROUND

Previous studies have shown that very low density lipoprotein (VLDL), intermediate density lipoprotein (IDL) and low density lipoprotein (LDL) from hyperlipidemic plasma are more atherogenic than those from normal plasma. Since platelet aggregation at sites of atherosclerotic injury exposes the cells to high concentrations of serotonin (5HT), a known mitogen for vascular smooth muscle cells (VSMCs), it was examined whether VLDL, IDL or LDL from plasma of 1% cholesterol-fed rabbits can potentiate the mitogenic effect of 5HT on VSMC.

METHODS

Growth arrested primary aortic VSMC in 1st or 2nd passage were incubated with different concentrations of VLDL, IDL or LDL in the presence or absence of pertusis toxin (PTX) for 24 h followed by incubation with 5HT for 24 h. The amount of [3H]thymidine incorporated into the DNA as well as the increase in cell number was measured.

RESULTS

Either VLDL, IDL or LDL at a concentration of 60 microg/ml induced proliferation of VSMC by themselves (196, 137 or 122% increase in [3H]thymidine incorporation, or 122, 119 or 122% increase in cell number, respectively when compared to the control, P<0.05). This effect on DNA synthesis was markedly potentiated by 50 microM 5HT to 465, 714 and 1369%, respectively. PTX reversed the mitogenic effect of 5HT, but not that of VLDL, IDL or LDL.

CONCLUSION

These results suggest that even low concentration of VLDL, IDL or LDL from hypercholesterolemic plasma may significantly potentiate the mitogenic effect of 5HT, that is released by aggregating platelets at sites of vascular damage.

RAR gamma agonists inhibit proliferation of vascular smooth muscle cells

The multifactorial and unpredictable nature of human restenosis will probably necessitate interventional strategies that target multiple processes involved in neointimal proliferation. Retinoids represent a growing class of pleiotropic biologic response modifiers with demonstrable efficacy in managing several pathologic conditions pertaining to neointimal proliferation. However, retinoid treatment is associated with a high incidence of adverse effects. The action of all-trans-retinoic acid is mediated by two families of nuclear receptors, RARs and RXRs, each containing three isoforms alpha, beta, and gamma. Because synthetic retinoids that are receptor and function specific have been shown to differ from each other by several orders of magnitude in their potencies and are associated with limited adverse effects, we examined the effect of synthetic retinoids on serum- and serotonin-induced vascular smooth muscle cell (VSMC) proliferation. Naturally occurring retinoids were used as controls. All-trans-retinoic acid at nanomolar concentrations inhibited smooth muscle cell proliferation. In this study, we report that RAR gamma subgroup-specific agonists are the most potent inhibitors of serum and serotonin VSMC proliferation, as compared with other RAR pan-agonists and naturally occurring retinoids tested. Our results indicate that RAR gamma subgroup-specific agonists should be assessed further in in vivo models of neointimal proliferation.

Safe and effective management of hypertension with fixed-dose combination therapy: focus on losartan plus hydrochlorothiazide

Treatment of hypertensive patients with fixed-dose combination therapy consisting of losartan and hydrochlorothiazide (HCTZ) has several potential benefits over monotherapy with each of the individual components: more effective blood pressure control, a reduction in the likelihood of adverse effects, and facilitation of patients staying on therapy due to a simple once-daily regimen. Losartan plus HCTZ fixed-dose combination therapy lowers blood pressure in mild to moderate or severe hypertensive patients to a level comparable with other classes of antihypertensive drugs in combination with HCTZ. Fixed-dose combination therapy with losartan plus HCTZ is therefore an excellent choice for hypertensive patients in whom combination therapy is necessary to achieve additional blood pressure reductions.

Modulation of endothelial cell proliferation by retinoid x receptor agonists

One feature that contraindicates the wide therapeutic use of natural retinoids is their adverse effects during systemic use and the lack of receptor selectivity. In contrast, synthetic retinoids are distinguishable from each other on the basis of their partial or exclusive preference in binding and activation of selective retinoid receptors. We examined the inhibitory activities of natural and synthetic retinoids for their ability to reverse basic fibroblast growth factor-induced endothelial cell proliferation. Both the naturally occurring retinoids at nanomolar concentrations reversed basic fibroblast growth factor-induced endothelial cell proliferation. Among the synthetic retinoids tested, retinoic acid receptor/retinoid x receptor pan-agonist AGN 191659 [(E)-5-[2-(5,6,7, 8-tetrahydro-3, 5,5,8,8-pentamethyl-2-naphtyl) propen-1-yl]-2-thiophenecarboxylic acid] and retinoid x receptor pan-agonist AGN 191701 [(E)-2-[2-(5,6,7,8-tetrahydro-3, 5,5,8, 8-pentamethyl-2-naphthyl) propen-1-yl]-4-thiophenecarboxylic acid] at nanomolar concentrations reversed the basic fibroblast growth factor-induced endothelial cell proliferation. Since none of the retinoic acid receptor agonists tested had any effect, the inhibitory effect of AGN 191659 could be attributed to its retinoid x receptor receptor activity. These results suggest that retinoid x receptor agonists may be more selective anti-angiogenic agents due to their ability to inhibit endothelial cell proliferation.

Endothelial cells regulate the proliferation of monocytes in vitro

Monocytes (MPhis) are among the first cells to accumulate in early atherosclerotic lesions and generally are believed to be incapable of proliferation. However, recent studies indicate that the number of MPhis in atherosclerotic lesion may increase due to induction of local proliferation. Since proliferation of hematopoietic lineage cells is strongly influenced by interaction with neighboring cell types, we examined the ability of vascular endothelial cells (EC), smooth muscle cells or fibroblasts to stimulate MPhi proliferation. In this study, we show that only when seeded at high densities MPhis could proliferate in culture. However, when contact co-cultured with EC, MPhis proliferated at a higher rate (260% on day 6) than those cultured alone or co-cultured with smooth muscle cells or fibroblasts. Endothelial cells could stimulate the proliferation of MPhis even at non-proliferating densities. Only EC that were growth arrested or in lag phase could induce MPhi proliferation, whereas those in the exponential proliferating phase were non-stimulatory. Conditioned medium prepared from EC in growth arrested or lag phase failed to stimulate MPhi proliferation. Similarly physical separation of MPhis from EC also resulted in no proliferation. These results suggest that EC induced MPhi proliferation is contact dependent and no soluble factors are involved in this induction. This EC induced MPhi proliferation may have a profound effect on the rate of progression of atherosclerosis.

Vascular smooth muscle proliferation: synergistic interaction between serotonin and low density lipoproteins

OBJECTIVES

The purpose of this study was to examine whether low density lipoproteins (LDLs) or mildly oxidized LDL (mox-LDL) are mitogens for vascular smooth muscle cells (VSMCs) and whether they can act synergistically with serotonin (5HT), a known mitogen for VSMC, in potentiating the proliferative effect of 5HT on VSMC.

BACKGROUND

Whether LDL or mox-LDL has a mitogenic effect on VSMC has been controversial. It is possible that LDL may not be mitogenic to VSMC but modification of LDL may confer mitogenic properties on LDL. A known mitogen for VSMC is 5HT that is released by aggregating platelets at sites of atherosclerotic changes or endothelial dysfunction. It is possible that LDL may interact with 5HT to enhance VSMC proliferation induced by 5HT.

METHODS

Growth arrested primary VSMCs were incubated with different concentrations of LDL or mox-LDL for 24 h followed by incubation with 5HT for another 24 h (mild oxidation of LDL was achieved by incubating LDL with Cu++ which increased the thiobarbituric acid product formation without a change in electrophoretic mobility). The increase in cell number or the amount of 3H-thymidine incorporated into the DNA was then measured.

RESULTS

Low density lipoprotein and mox-LDL induced significant VSMC proliferation by themselves and this effect was potentiated by 5HT. The 5HT2 receptor antagonist (LY281067) and pertussis toxin reversed only the proliferative effect of 5HT. Polyinosinic acid (poly-I), an inhibitor of scavenger receptors, did not inhibit the proliferative effect of LDL or mox-LDL or their synergistic interaction with 5HT.

CONCLUSIONS

These results suggest that LDL and mox-LDL act synergistically with 5HT in inducing VSMC proliferation. The synergistic interaction could be blocked by LY281067 and pertussis toxin but not by poly-I acid.

Beta(2)-glycoprotein I promotes the binding of anionic phospholipid vesicles by macrophages

Beta(2)-Glycoprotein I is a single-chain 50-kDa protein that circulates in plasma at a concentration of approximately 200 microg/mL. Its physiological role remains uncertain, but an important clue is the frequent presence of antibodies to this protein in patients with recurrent thrombosis. We have isolated beta(2)-glycoprotein I and examined its effect on the binding of phosphatidylserine (PS) vesicles by human monocyte-derived macrophages and by phorbol ester-stimulated THP-1 cells. beta(2)-Glycoprotein I stimulated the binding of PS vesicles by these cells in a concentration-dependent manner. Vesicles containing other anionic phospholipids, such as cardiolipin, phosphatidic acid, or cardiolipin, inhibited the binding, whereas PC vesicles had no effect. Platelet-derived microvesicles, which contain anionic phospholipid on the outer leaflet of their phospholipid bilayer, also inhibited beta(2)-glycoprotein I-dependent binding of anionic phospholipid vesicles. The binding is associated with incorporation of phospholipid in the cell membrane and internalization of beta(2)-glycoprotein I. These findings suggest a physiological function for beta(2)-glycoprotein I in the clearance of procoagulant anionic phospholipid-containing cell surfaces from the circulation.

Eicosapentaenoic acid and docosahexaenoic acid block serotonin-induced smooth muscle cell proliferation

Eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) present in fish oils have been ascribed as having significant antithrombotic and antiatherosclerotic effects. Vascular smooth muscle cell (SMC) proliferation plays an important role in the pathogenesis of atherosclerosis and restenosis. Recent studies have indicated that serotonin at concentrations present at sites of vascular injury stimulates SMC proliferation and may contribute to the restenotic process. In the present study we demonstrate that among the fatty acids tested, only EPA and DHA could block the mitogenic effect of serotonin on vascular SMC. Further, when added together these fatty acids act synergistically in blocking the mitogenic effect of serotonin. EPA and DHA blocked the 5HT-induced increase in the 5-HT(2) receptor mRNA. This antimitogenic effect of EPA and DHA may partially explain some of the beneficial effects of fish oils.

Centrally acting antihypertensive drugs: re-emergence of sympathetic inhibition in the treatment of hypertension

Central regulation of the sympathetic nervous system plays an important role in the maintenance of blood pressure. In a subset of patients with essential hypertension, sympathetic activation may contribute to the development and maintenance of hypertension. Unlike the first generation of centrally active antihypertensive drugs, the second generation may be superior because of its selectivity to I1-imidazoline receptor and selective binding to the vasomotor center. Lack of a2 effects differentiates moxonidine from clonidine with respect to monoxidine"s superior side-effect profile (little or no sedation or dry mouth). Clinical trials show that moxonidine is as effective as angiotensin-converting enzyme inhibitors (eg, enalapril and captopril), b-blockers (e.g., atenolol), calcium-channel blockers (e.g., long-acting nifedipine), and diuretics (eg, hydrochlorothiazide) in lowering blood pressure and that it has superior tolerability. Thus, central modulation of the sympathetic nervous system has re-emerged as an exciting target for blood pressure reduction. Given the multiple adverse effects of sympathetic stimulation in various disease processes, including congestive heart failure, moxonidine may be the next therapeutic option for the management of hypertension and the prevention of target organ dysfunction.

Serotonin fails to induce proliferation of endothelial cells preloaded with eicosapentaenoic acid and docosahexaenoic acid

Diets rich in fish oils are associated with a reduced risk of cardiovascular disease including reduction of atherosclerosis and restenosis. We examined the effect of omega-3 fatty acids eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), major components of fish oils, on serotonin (5HT) stimulated vascular endothelial cells proliferation as a possible mechanism for this vascular protective effect. In this study we demonstrate that 5HT, a known mitogen for vascular endothelial cells, failed to stimulate proliferation of endothelial cells pre-incubated with EPA and DHA. This inhibitory effect was specific for omega-3 fatty acids only and not shared by other fatty acids like oleic acid (monounsaturated) or arachidonic acid (polyunsaturated) or palmitic acid (saturated). When endothelial cells were exposed to EPA and DHA in the ratio present in fish oils, EPA and DHA were shown to act synergistically in inhibiting the proliferative effect of 5HT. These results suggests that one of the mechanisms by which fish oils may confer vascular protective effect is by making the endothelial cells less responsive to mitogenic stimuli of growth factors such as 5HT that are released by aggregating platelets at sites of vascular injury. This inhibition of endothelial cell proliferation may account for the clinically observed effects of fish oil in attenuating the progression of atherosclerotic changes or neointimal proliferation following vascular injury.

Platelet microparticles promote platelet interaction with subendothelial matrix in a glycoprotein IIb/IIIa-dependent mechanism

BACKGROUND

Platelets, on activation, release vesicular particles called platelet microparticles. Despite their procoagulant activity, their functional role in platelet-vessel wall interactions is not known.

METHODS AND RESULTS

We examined the binding of microparticles to vessel wall components in vitro and in vivo. Microparticles bound to fibrinogen-, fibronectin-, and collagen-coated surfaces. Compared with activated platelets, we observed minimal binding of microparticles to vitronectin and von Willebrand factor. The glycoprotein IIb/IIIa (GP IIb/IIIa) inhibitors abciximab and eptifibatide (Integrilin) inhibited the binding to fibrinogen and fibronectin but had minimal effect on binding to collagen. Furthermore, monoclonal antibodies to GP Ib or anionic phospholipid-binding proteins (beta2-glycoprotein I or annexin V) had no effect in these interactions. Microparticles did not bind to monolayers of resting or stimulated human umbilical vein endothelial cells (HUVECs), even in the presence of fibrinogen or von Willebrand factor. However, under similar conditions, microparticles bound to extracellular matrix produced by cultured HUVECs. Abciximab inhibited this interaction by approximately 50%. In a rabbit model of arterial endothelial injury, the infusion of 51Cr-labeled microparticles resulted in a 3- to 5-fold increase of microparticle adhesion to the injured site compared with the uninjured site (P<0.05%). Furthermore, activated platelets bound to surface-immobilized microparticles in a GP IIb/IIIa-dependent mechanism. This binding increased in the presence of fibrinogen by approximately 30%.

CONCLUSIONS

Platelet microparticles bind to subendothelial matrix in vitro and in vivo and can act as a substrate for further platelet binding. This interaction may play a significant role in platelet adhesion to the site of endothelial injury.

Thromboxane A2 fails to induce proliferation of smooth muscle cells enriched with eicosapentaenoic acid and docosahexaenoic acid

Thromboxane A2 (TXA2) released from aggregating platelets and injured vessel wall stimulates smooth muscle cell proliferation, which may contribute to the development of vascular lesion formation after percutaneous transluminal coronary angioplasty. Polyunsaturated fatty acids (n-3) present in the fish oils have been shown to have anti-atherosclerotic effects. In view of this, we examined the effect of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), the active ingredients of fish oils on TXA2 induced smooth muscle cell proliferation. To find out the specificity of these fatty acids we used gamma-linolenic acid (n-6) and oleic acid (n-9) as controls. It was found that TXA2 failed to stimulate proliferation of smooth muscle cells preloaded with EPA or DHA but not with gamma-linolenic acid or oleic acid. Further, when smooth muscle cells were preloaded with both EPA and DHA, they acted together in preventing the TXA2 induced smooth muscle cell proliferation. These results demonstrate that one of the mechanisms by which fish oils may prevent neointima formation is by making smooth muscle cells less responsive to TXA2 induced proliferation of smooth muscle cells.

Serotonin-induced endothelial cell proliferation is blocked by omega-3 fatty acids

Serotonin (5HT) released from aggregating platelets at sites of vascular injury is a known mitogen for vascular endothelial cells. Recent studies have indicated that regenerating endothelial cells at sites of vessel wall injury may play a role in the development of restenosis by synthesizing and releasing growth factors for vascular smooth muscle cells, proliferation of which may result in the development of neointima. Diets rich in fish oils (omega-3 fatty acids) are associated with reduced risk of cardiovascular disease including atherosclerosis and restenosis. This study examined the effect of the omega-3 and other fatty acids, eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), on 5HT induced endothelial cell proliferation. Among the fatty acids examined only EPA and DHA could reverse the mitogenic effect of 5HT on vascular endothelial cells, whereas oleic acid or palmitic acid did not have any effect. When added together, EPA and DHA potentiate each other in reversing the mitogenic effect of 5HT. EPA and DHA also inhibited the 5HT-induced increase in the 5HT2 receptor mRNA, without a change in the receptor density or affinity. This data suggests that one of the mechanisms by which omega-3 fatty acids may attenuate the development of atherosclerosis or restenosis is to inhibit the mitogen induced growth of vascular endothelial cells, which attenuates the release of growth factors for vascular smooth muscle cells.

Effect of serotonin and thromboxane A2 on endothelial cell proliferation: effect of specific receptor antagonists

Platelet aggregation at sites of vascular injury releases both peptide growth factors and vasoactive compounds. Although significant attention has been focused on peptide growth factors, very little is known about the mitogenic effect of vasoactive compounds. We evaluated the effect of serotonin (5-HT) and thromboxane A2 (TXA2) mimetic U46619 alone and in combination on aortic endothelial cells. Stimulation of endothelial cells by 5-HT resulted in an increase in tritiated thymidine uptake and an increase in cell number, whereas U46619 did not have any significant effect. However, when endothelial cells were exposed to both compounds, U46619 potentiated the mitogenic effect of 5-HT on endothelial cells. When endothelial cells were preincubated with LY281067 (a 5-HT2 receptor antagonist) or ridogrel (a combined TXA2 synthase inhibitor and receptor antagonist), LY281067 blocked the mitogenic effect of 5-HT and ridogrel blocked the potentiating effect of U46619 on 5-HT2-induced tritiated thymidine incorporation. When endothelial cells were preincubated with both antagonists, the effects of both 5-HT and U46619 were blocked. Recent studies have indicated that regenerating endothelial cells at sites of vascular injury may release growth factors for vascular smooth muscle cells, leading to smooth muscle cell proliferation and development of neointima. This study suggests that the combined use of 5-HT and TXA2 receptor antagonists may inhibit the growth of endothelial cells at sites of vascular injury and attenuate the formation of neointima.

Cardiolipin binding a light chain from lupus-prone mice

Autoantibodies in systemic lupus erythematosus react with multiple epitopes on highly conserved molecules such as nucleic acids, cytoskeletal proteins, phospholipids, and phospholipid-binding proteins. Analysis of the heavy- and light-chain variable sequences (VH and VL) has shown that a restricted set of V genes gives rise to these autoantibodies. Several monoclonal antibodies were developed from a strain of mouse prone to lupus (F1 male NZW x BXSB). Two of these antibodies, A1.72 and A1.84, reacted directly with cardiolipin and their VH and VL sequences were analyzed. Surprisingly, these two antibodies had identical light-chain variable sequences despite having substantially different heavy-chain variable sequences. This VL sequence, VL 72/84 was 97% identical with the germ-line sequences with only four single nucleotide substitutions. When this VL sequence was shuffled with the VH sequence of other monoclonal antibodies and expressed as single chain variable fragment (scFv) in Escherichia coli, it imparted cardiolipin-binding activity to the hybrids. Furthermore, the VL 72/84 sequence, when expressed alone without any VH sequence, also bound to cardiolipin. The antibodies and their recombinant fragments were immunoaffinity-purified on cardiolipin liposomes. The dissociation constant of the light chain for cardiolipin was similar to the intact molecule (21 +/- 0.01 vs 20 +/- 0.03 nM). These studies demonstrate that the VL sequence alone, in the absence of any other immunoglobulin domains, can mediate cardiolipin binding, raising the possibility that antigen specificity of certain antibodies may exclusively reside in their light-chain sequences.

Effect of serotonin, thromboxane A2, and specific receptor antagonists on vascular smooth muscle cell proliferation

BACKGROUND

Restenosis is a major complication that limits the long-term efficacy of coronary angioplasty. Migration and proliferation of activated medial smooth muscle cells (SMCs) is considered an important mechanism in this process. Because at sites of vascular injury, aggregating platelets release both serotonin (5-HT) and thromboxane A2 (TXA2), we examined whether 5-HT and TXA2 can induce SMC proliferation and whether there is synergistic interaction between these two mediators.

METHODS AND RESULTS

The mitogenic effects of 5-HT and TXA2 either alone or in combination was examined in serum-free medium on canine aortic SMCs by [3H]thymidine incorporation into DNA and by cell counting. 5-HT induced SMC proliferation at a concentration of 100 nmol/L, whereas the effect of TXA2 (U46619, a stable TXA2 mimetic) on inducing proliferation of SMCs was observed at a concentration of 100 nmol/L. When these two mediators were added together, there was a synergistic interaction on inducing SMC proliferation even at subthreshold concentrations. The mitogenic effect of 5-HT and its synergistic interaction with TXA2 on SMC proliferation was abolished by a 5-HT2 receptor antagonist, LY281067, without affecting the contribution of TXA2. Similarly, the TXA2 synthase inhibitor/receptor antagonist ridogrel abolished the mitogenic effect of TXA2 and the interaction between 5-HT and TXA2 without affecting the response to 5-HT. When LY281067 and ridogrel were used together, they abolished the mitogenic effects of 5-HT and TXA2.

CONCLUSIONS

At sites of vascular injury, platelet-induced SMC proliferation may also be modulated by nonpeptide growth mediators. A combination of a 5-HT2 receptor antagonist and TXA2 synthase inhibitor/receptor may be useful for attenuation of restenosis after angioplasty.

Inhibition of arterial thrombosis by recombinant annexin V in a rabbit carotid artery injury model

BACKGROUND

The procoagulant effect of anionic phospholipid may play a major role in the development of arterial thrombosis.

METHODS AND RESULTS

Annexin V, a calcium-dependent anionic-phospholipid-binding protein, was expressed and isolated from Escherichia coli and its antithrombotic effect examined in a rabbit carotid artery thrombosis model. A partially occlusive thrombus was formed in the left carotid artery by application of electric current to produce an approximately 50% occlusion of the lumen. After the current was discontinued, flow ceased completely within 42+/-12 minutes (n=6) because of continuing platelet/fibrin thrombus formation. When annexin V was given at doses of 2.8 to 16.6 microg x kg(-1) x min(-1) for a period of 180 minutes, starting at the time the current was stopped, there was a dose-dependent inhibition of thrombus formation. At a dose of 5.6 microg x kg(-1) x min(-1), blood flow remained patent throughout the infusion and for an additional 60 minutes after the infusion was stopped. In addition, there was a decrease in thrombus weight (16+/-7.4 versus 2.0+/-1.0 g), (125)I-fibrin deposition (approximately 45% reduction, P<.001), and (111)In-labeled platelet accumulation (approximately 43% reduction, P<.001). Prior mixing of annexin V with phosphatidylserine micelles abolished the antithrombotic effect of annexin V, whereas mixing with phosphatidylcholine micelles had no effect. The antithrombotic effect of annexin V was not associated with bleeding tendency, as judged by the amount of blood absorbed in a gauze pad placed in a surgical incision extending to the muscle tissue and by the standard template bleeding time.

CONCLUSIONS

These observations support a potentially important role for anionic phospholipid exposure in platelets in arterial thrombosis, and inhibition of this activity could be a novel target for therapy in coronary thrombosis and stroke and after angioplasty.

Acute and long-term effects of the angiotensin-converting enzyme inhibitor, enalapril, on adrenergic activity and sensitivity during exercise in patients with left ventricular systolic dysfunction

Patients with heart failure and left ventricular systolic dysfunction exhibit increased adrenergic activity but blunted adrenergic responsiveness. We studied patients enrolled in the Studies of Left Ventricular Dysfunction, examining exercise responses of heart rate (HR) and plasma norepinephrine (PNE). Eighty-seven patients were studied before randomization; 65 of these were examined 1 year after randomization to placebo or enalapril. Compared with prevention trial (asymptomatic) patients, patients in the treatment trial (symptomatic) had higher resting HR and PNE levels and less increase in HR with a greater increase in PNE with exercise. Acute administration of enalapril increased the resting HR in patients in the prevention trial only but had no significant effect on PNE. After 1 year of therapy, patients in the prevention trial exhibited no change. Within the treatment trial, the placebo group displayed both a higher peak PNE and increase in PNE with exercise than did the enalapril group, whose HR response was maintained in spite of a reduction of exercise PNE. We conclude that (1) compared with asymptomatic patients, symptomatic patients with reduced left ventricular ejection fraction manifest greater resting and exercise adrenergic activity, with blunted HR response; and (2) in symptomatic patients, 1 year of enalapril treatment effected an augmented HR response to adrenergic stimulation, supporting an interaction between the renin/angiotensin and adrenergic nervous systems. Normalization of adrenergic tone and response likely contributes to the benefits of long-term angiotensin-converting enzyme inhibitor therapy.

Angiotensin AT1 receptor inhibition. Effects on hypertrophic remodeling and ACE expression in rats with pressure-overload hypertrophy due to ascending aortic stenosis

BACKGROUND

We tested the hypothesis that long-term administration of the specific angiotensin II subtype 1 (AT1)-receptor blocker BMS-186295 will regress hypertrophy and modify left ventricular angiotensin converting enzyme (ACE) expression in rats with ascending aortic stenosis.

METHODS AND RESULTS

Six weeks after surgery, rats with ascending aortic stenosis were randomized to receive either the AT1-receptor blocker BMS-186295 50 mg.kg-1.d-1 (n = 49), amlodipine 2.5 mg.kg-1.d-1 (n = 48) as a positive control for systemic vasodilation, or no drug (n = 48) and compared with sham-operated rats (n = 39). Drug treatment was continued for 15 weeks. Left ventricular ACE mRNA levels were measured by ribonuclease protection assay. The left ventricular/body weight ratio was increased 43% in hearts from rats with untreated left ventricular hypertrophy (LVH) versus control hearts (P < .05). However, there was no difference in either the left ventricular/body weight ratio (2.78 +/- 0.08 versus 2.81 +/- 0.20 mg/g; P = NS) or myocyte cross-sectional area in the AT1-blocker-treated versus untreated LVH hearts. Amlodipine also showed no effect on regression of hypertrophy. In vivo left ventricular systolic pressure was significantly higher in untreated LVH versus sham-operated rats (193 +/- 8 versus 118 +/- 4 mm Hg; P < .05), and there was a similar severe elevation of left ventricular systolic pressure in the AT1-blocker- and amlodipine-treated LVH groups (189 +/- 9 and 188 +/- 16 mm Hg; P = NS versus untreated LVH). In vivo left ventricular end-diastolic pressure was higher in the untreated LVH than in the sham-operated rats (14.8 +/- 2.3 versus 7.0 +/- 0.5 mm Hg; P < .05). Left ventricular end-diastolic pressure was lower in the AT1-blocker-treated (11.0 +/- 1.7 mm Hg) and amlodipine-treated rats (11.5 +/- 1.8 mm Hg) and was similar to left ventricular end-diastolic pressure in the sham-operated rats (P = NS). Left ventricular ACE mRNA levels were elevated in untreated LVH rats but were normalized in both the AT1-blocker-treated rats and amlodipine-treated rats.

CONCLUSIONS

Long-term AT1-receptor blockade did not regress LVH in rats with persistent systolic pressure overload due to ascending aortic stenosis. However, both AT1-receptor blockade and amlodipine improved in vivo left ventricular end-diastolic pressure in association with the normalization of left ventricular ACE mRNA levels.

Randomized, double blind, dose-response trial across four oral doses of dolasetron for the prevention of acute emesis after moderately emetogenic chemotherapy. Oral Dolasetron Dose-Response Study Group

BACKGROUND

This double blind parallel group study assessed the acute antiemetic efficacy of four oral doses of dolasetron mesylate in cancer patients receiving their first course of intravenous chemotherapy with doxorubicin and/or cyclophosphamide.

METHODS

Patients were randomized to receive 25, 50, 100, or 200 mg of dolasetron mesylate 30 minutes prior to chemotherapy and were monitored for nausea and emetic episodes for the next 24 hours.

RESULTS

Three hundred and nineteen cancer patients at 32 sites completed the study. Most patients were female (81%); of this group, 69% had breast carcinoma. A highly statistically significant linear trend demonstrating improved response with higher doses was detected for complete response (no emetic episodes and no rescue medication) (P < 0.001), for complete plus major response (0-2 emetic episodes and no rescue medication) (P < 0.001), and for patient visual analog scale assessments of nausea (P = 0.001) and general satisfaction with antiemetic therapy (P = 0.001). No serious adverse events were noted. The most frequent adverse event was mild, self-limiting headache, which has been reported with other drugs in this class.

CONCLUSIONS

Single oral doses of dolasetron mesylate were found to be effective in preventing acute emesis in cancer patients receiving moderately emetogenic chemotherapy.

Oral dolasetron mesylate in patients receiving moderately emetogenic platinum-containing chemotherapy. Oral Dolasetron Dose Response Study Group

PURPOSE

This double-blind, dose-response study was conducted to assess the safety and efficacy of four oral doses of dolasetron mesylate for preventing acute emesis in cancer patients receiving their first course of moderately emetogenic platinum-containing chemotherapy.

PATIENTS AND METHODS

Patients were randomized to receive a single oral dose of 25, 50, 100, or 200 mg dolasetron 30 minutes before receiving IV carboplatin (275-400 mg/m2)- or cisplatin (20-50 mg/m2)-containing chemotherapy, then monitored for nausea and vomiting for 24 hours.

RESULTS

Three hundred seven cancer patients from 32 sites completed the study. There was a statistically significant dose response across the four doses for complete response (no emetic episodes or rescue medication): 44.7%, 71.3%, 73.2%, and 82.5% for the 25, 50, 100, or 200 mg doses of dolasetron, respectively. Patients' nausea severity and patient satisfaction visual analogue scale scores also showed a statistically significant trend with dose. All doses of dolasetron were well tolerated. The most common adverse events were headache (17.6%) and dizziness (2.0%).

DISCUSSION

This study demonstrates the safety and antiemetic efficacy of oral dolasetron mesylate in patients receiving moderately emetogenic platinum-containing chemotherapy with the highest antiemetic activity observed at 200 mg.

Hemodynamic and cardiac effects of the selective T-type and L-type calcium channel blocking agent mibefradil in patients with varying degrees of left ventricular systolic dysfunction

OBJECTIVES

This study sought to assess the hemodynamic and cardiac effects of two dose levels of mibefradil in patients with varying degrees of ischemic left ventricular dysfunction.

BACKGROUND

Mibefradil is a new, selective T-type and L-type calcium channel blocking agent. Because L-type channel blockade may depress myocardial performance, an invasive hemodynamic study was performed to assess the safety of this agent.

METHODS

We performed an open label study, examining the effects of two intravenous doses of mibefradil, selected to produce plasma levels comparable to those measured after oral administration of 50 mg (dose 1: 400 ng/ml) or 100 mg (dose 2: 800 ng/ml) of the drug. Variables studied included the indexes of left ventricular function and neurohormone levels. Patients were stratified according to ejection fraction (EF) (> or = 40%, n = 26; < 40%, n = 24) and the presence (n = 15) or absence (n = 35) of heart failure.

RESULTS

In patients with preserved systolic function, dose 1 had no clinically significant hemodynamic effects, but dose 2 decreased mean aortic pressure and systemic vascular resistance (-8.5 mm Hg, -12%, both p < 0.01) and also reduced end-systolic stress and volume, thus improving EF (52% to 58%, p < 0.01). Heart rate tended to decrease. In patients with depressed EF, heart rate decreased significantly with both doses. The effects of dose 1 mimicked those observed after dose 2 in patients with preserved EF. Dose 2 (plasma levels 1,052 +/- 284 ng/ml) still decreased left ventricular systolic wall stress and improved EF (24.0% to 28.5%, p < 0.05) but also significantly depressed the maximal first derivative of left ventricular pressure. Examination of individual pressure-volume loops in two patients with heart failure showed a clear rightward shift of the loop despite a decrease in systolic pressure, suggesting negative inotropy. Neurohormone levels were unchanged at both dose levels and in all subgroups.

CONCLUSIONS

Intravenous mibefradil was well tolerated and produced an overall favorable cardiovascular response. However, high plasma concentrations might produce myocardial depression in patients with heart failure, and caution should be exerted in this setting.

Improved left ventricular function after chronic left ventricular unloading

BACKGROUND

This study assessed the effect of prolonged left ventricular unloading on native ventricular function.

METHODS

We reviewed data from 31 patients (30 men, 1 woman) supported more than 30 days (mean, 137 days; range, 31 to 505 days) with the HeartMate left ventricular assist system. The patients' mean age was 46 years (range, 22 to 64 years); 17 had idiopathic and 14 had ischemic cardiomyopathy. Data (anatomic, physiologic, hemodynamic, histologic, and biochemical) were collected at the time of HeartMate implantation, during support with the device temporarily off, and at the time of device explantation.

RESULTS

Routine chest roentgenogram showed improvement in cardiothoracic ratio (0.62 +/- 0.04 to 0.55 +/- 0.03; p < 0.0001). Echocardiography performed with the pump off showed a significant decrease in left ventricular end-diastolic dimension (6.81 +/- 0.87 cm to 5.39 +/- 1.08 cm; p < 0.0005) and a significant improvement in ejection fraction (0.11 +/- 0.05 to 0.22 +/- 0.17; p < 0.02). Cardiac index increased (1.96 +/- 0.52 L.min-1.m-2 to 2.93 +/- 0.73 L.min-1.m-2; p < 0.0001), mean aortic pressure increased (71.40 +/- 10.63 mm Hg to 76.33 +/- 16.84 mm Hg; p = 0.48), pulmonary capillary wedge pressure decreased (24.18 +/- 6.27 mm Hg to 14.48 +/- 3.01 mm Hg; p < 0.0001), and pulmonary vascular resistance decreased (3.34 +/- 2.00 Wood units to 2.51 +/- 0.88 Wood units; p < 0.05). Comparisons of tissue samples taken at the time of implantation and at the time of transplantation showed a marked reduction in myocytolysis. Calcium uptake, calcium-binding rates, and lipid levels normalized in patients studied. Plasma norepinephrine levels decreased to near normal levels.

CONCLUSION

Prospective studies are now indicated to determine whether device removal without transplantation may be beneficial in selected patients.

Prognostic significance of plasma norepinephrine in patients with asymptomatic left ventricular dysfunction. SOLVD Investigators

BACKGROUND

Elevated plasma neurohormonal levels are associated with increased mortality rates in patients with symptomatic heart failure. A previous Studies of Left Ventricular Dysfunction (SOLVD) trial suggested that neurohumoral activation precedes the development of symptoms as demonstrated by increased neurohormonal levels in patients with asymptomatic left ventricular dysfunction. However, the significance of this early neurohumoral activation is unclear. The goals of this study were to determine the prognostic significance of the plasma concentrations of plasma norepinephrine (PNE) and atrial natriuretic peptide (ANP) and the renin activity (PRA) in patients with asymptomatic left ventricular dysfunction.

METHODS AND RESULTS

PNE and PRA were measured before randomization in 514 patients with left ventricular ejection fractions < or = 35% who did not require treatment for congestive heart failure and were enrolled in the SOLVD Prevention Trial. Plasma ANP levels were measured in a subset of 241 patients owing to study design. Using the Cox proportional hazards model that included left ventricular ejection fraction, New York Heart Association functional class, age, sex, treatment assignment to placebo or enalapril, and cause of heart failure, we examined whether these neurohormones predicted all-cause mortality, cardiovascular mortality, hospitalization for heart failure, development of heart failure, or development of ischemic events (myocardial infarction or unstable angina). PNE was the strongest predictor of clinical events in this patient population. PNE levels above the median of 393 pg/mL were associated with a relative risk of 2.59 (P = .002) for all-cause mortality, 2.55 (P = .003) for cardiovascular mortality, 2.55 (P = .005) for hospitalization for heart failure, 1.88 (P = .002) for development of heart failure, 1.92 (P = .001) for ischemic events, and 2.59 (P = .005) for myocardial infarction. PNE remained the most powerful predictor for all-cause mortality and ischemic events when the analysis included only the patients with histories of ischemic left ventricular dysfunction. The increases in other neurohormonal levels were not useful in predicting the subsequent development of clinical events.

CONCLUSIONS

Increased PNE levels in patients with asymptomatic left ventricular dysfunction appear to predict all-cause and cardiovascular mortalities and development of clinical events related to the onset of heart failure or acute ischemic syndromes. Thus, measurement of PNE may be a possible early marker for assessment of disease progression in patients with left ventricular dysfunction, and modulating the release or effect of PNE may lead to improved prognosis and/or a reduction in morbidity.

Single-blind study of the effects of intravenous dolasetron mesylate versus ondansetron on electrocardiographic parameters in normal volunteers

A single-blind, randomized, five-way cross-over, safety and tolerability trial was conducted to determine whether intravenous (i.v.) dolasetron mesylate at varying single doses induces changes in ECG intervals in healthy volunteers and to compare these changes with a single intravenous dose of ondansetron or placebo. Thirty healthy male volunteers received 1.2, 1.8, and 2.4 mg/kg i.v. dolasetron mesylate, 32 mg i.v. ondansetron, and placebo on 5 separate days. ECGs were recorded at intervals during the 24 h after study drug administration. The changes in ECG intervals observed after dolasetron mesylate or ondansetron were acute, transient, and asymptomatic. Dolasetron mesylate resulted in slight but statistically significant dose-related increases in heart rate (HR) and PR and QRS intervals (between h 0 and 4). A statistically significant increase in QTc interval was detected with both dolasetron mesylate (2.4 mg/kg) and ondansetron. Ondansetron also produced a slight but statistically significant increase in JT interval and a decrease in HR. These changes in ECG intervals were usually observed between h 0 and 4; all parameters returned to baseline within 8 h of treatment. The results demonstrate that both dolasetron mesylate and ondansetron prolong the QTc interval. However, dolasetron mesylate predominantly altered ECG parameters indicative of ventricular depolarization (QRS duration), whereas ondansetron predominantly affected ventricular repolarization as measured by a prolongation in the JT interval. Both dolasetron and ondansetron were well tolerated. The adverse event (AE) rate was 13.3% (4 of 30); all AE were of mild or moderate severity and were distributed across all dose arms.

Relation of ventricular size and function to heart failure status and ventricular dysrhythmia in patients with severe left ventricular dysfunction

Patients with severe left ventricular (LV) dysfunction may or may not have overt heart failure and ventricular dysrhythmia. To study factors behind this variability, we examined a subset of 311 patients from the Studies of Left Ventricular Dysfunction-95 with a history of moderate heart failure (treatment trial) and 216 with no failure (prevention trial), all with ejection fractions <0.35. Echocardiographic variables were compared between trials and also correlated with dysrhythmia in 258 patients, and with neurohormones in 199 patients. Compared with prevention patients, treatment patients had larger LV end-diastolic diameter, end-systolic volume, sphericity index, and ratio of early to late diastolic filling velocity by Doppler (E/A ratio), lower LV ejection fraction and atrial contribution to ventricular filling, and similar LV mass, end-diastolic volume, and estimates of systolic wall stress. With prevention and treatment patients combined, the prevalence of abnormally elevated atrial natriuretic peptide was 92% in the highest tertile of E/A ratio compared with 55% in the lower tertiles (p=0.006). Across tertiles of LV end-diastolic volume, there was an increase in the prevalence of nonsustained ventricular tachycardia (24%, 45%, and 45%; p=0.007) and premature ventricular complexes >10/hour (48%, 62%, and 80%; p<0.001). Thus, in severe LV dysfunction, ventricular filling indexes suggestive of high filling pressures, along with larger and more spherical ventricles, are particularly common in patients with overt heart failure, thus suggesting that diastolic properties and the degree of ventricular remodeling affect clinical status. Once ejection fraction is significantly reduced, the prevalence of ventricular dysrhythmia correlates with LV size rather than systolic function. This observation lends support to previous experimental findings on the role of myocardial stretch and scar in the genesis of dysrhythmia.

Single-dose, placebo-controlled, phase I study of oral dolasetron

STUDY OBJECTIVES

To evaluate the safety, tolerability, and pharmacokinetics of single, escalating doses of oral dolasetron mesylate, a new 5-HT3 receptor antagonist.

DESIGN

Double-blind, placebo-controlled, dose-escalating phase I study.

SETTING

A clinical research center.

PATIENTS

One hundred twenty healthy male volunteers.

INTERVENTIONS

Subjects received either placebo or oral dolasetron mesylate 50, 100, 150, 200, 250, 300, or 400 mg.

MEASUREMENTS AND MAIN RESULTS

Compared with placebo, subjects receiving dolasetron mesylate reported a greater frequency of headache, light-headedness, dizziness, increased appetite, and nausea. There were no clinically significant changes in mean laboratory values from before to after treatment. Adverse events were transient, mild or moderate, and similar to those after single intravenous doses of the drug. No clinically significant electrocardiographic changes occurred, but lengthening of the QRS complex duration and dose-dependent lengthening of PR and QTc intervals were observed 1-2 hours after dosing. These effects were asymptomatic and were mainly associated with higher doses (< or = 300 mg).

CONCLUSION

Dolasetron mesylate is well tolerated when administered in single oral doses up to 400 mg to healthy volunteers. Clinical trials are under way to evaluate the agent's efficacy in preventing chemotherapy-induced and postoperative nausea and vomiting with doses up to 200 mg.

Multiple-dose, placebo-controlled, phase I study of oral dolasetron

STUDY OBJECTIVES

To evaluate the safety, tolerability, and pharmacokinetics of increasing dose levels of oral dolasetron mesylate, a new 5-HT3 antagonist.

DESIGN

Double-blind, placebo-controlled, dose-ranging phase I study.

SETTING

A clinical research center.

PATIENTS

Forty healthy male volunteers.

INTERVENTIONS

Eight subjects at each dose level were randomized in a ratio of 3:1 to receive either dolasetron mesylate 25, 50, 100, 150, or 200 mg in a single oral dose on days 1 and 9, and twice/day on days 2-8, or placebo for 9 days.

MEASUREMENTS AND MAIN RESULTS

Dolasetron was well tolerated at all dose levels. The adverse event rates for dolasetron- and placebo-treated subjects who experienced at least one adverse event were 80% and 50%, respectively. Most frequently reported by subjects receiving dolasetron were headache, constipation, flatulence, and lightheadedness. They generally were mild, and none was severe. No dose-response relationship was apparent for any adverse event. There were no clinically significant changes in mean laboratory values or vital signs. Asymptomatic treatment-related electrocardiographic changes were consistent with the drug's electrophysiologic properties. These changes have been well characterized and have thus far been clinically unimportant. Pharmacokinetics of the reduced metabolite were dose independent, and multiple-dose exposure of this metabolite can be predicted from its single-dose values.

CONCLUSION

Oral dolasetron mesylate was well tolerated when administered in doses up to 200 mg/day for 9 days in healthy volunteers.

New variant of human tissue plasminogen activator (TPA) with enhanced efficacy and lower incidence of bleeding compared with recombinant human TPA

BACKGROUND

The thrombolytic properties of a new variant of tissue plasminogen activator (TPA) (T103N, N117Q, KHRR 296-299 AAAA, or TNK-TPA) with longer plasma half-life, greater fibrin specificity, and increased resistance to inhibition by plasminogen activator inhibitor (PAI-1) were investigated in a rabbit thrombosed carotid artery model.

METHODS AND RESULTS

After 60 minutes of arterial occlusion, TPA (1.5, 3.0, 6.0, or 9.0 mg/kg as a front-loaded IV infusion for 90 minutes; n = 22) or TNK-TPA (0.38, 0.75, or 1.5 mg/kg as IV bolus; n = 16) was administered. Blood flow through the artery was monitored for an additional 120 minutes. Bleeding was assessed by weighing the amount of blood absorbed in a gauze pad placed in a subcutaneous muscular incision. Recanalization rates and duration of recanalization were dose dependent. The doses that produced > 80% recanalization rates with the longest duration of recanalization were 9.0 mg/kg for TPA and 1.5 mg/kg for TNK-TPA. At these doses, time to reperfusion (mean +/- SEM) was significantly faster (11 +/- 2 versus 23 +/- 7 minutes) and duration of recanalization longer (77 +/- 9 versus 51 +/- 18 minutes) for TNK-TPA compared with TPA (P < .025). Weights of the residual thrombi of the TPA group were greater than those of the TNK-TPA group (P = .004). Concentrations of fibrinogen, plasminogen, and alpha 2-antiplasmin at 120 minutes were significantly higher for TNK-TPA-treated animals compared with TPA-treated animals (P < .001). ANOVA of the blood loss data determined that there were significant differences between thrombolytic agents but not between doses. After correction for saline controls, total blood loss for pooled doses of TPA and TNK-TPA was 82 +/- 6 mg and 40 +/- 4 mg, respectively (P < .01).

CONCLUSIONS

From these data, we conclude that TNK-TPA, given as a bolus, produces faster and more complete recanalization of occluded arteries in a rabbit experimental model compared with TPA, without increasing systemic plasmin generation or peripheral bleeding. In addition, we observed that TNK-TPA, unlike TPA, did not potentiate collagen-induced aggregation of platelets obtained from human plasma. This lack of effect on platelet aggregation by TNK-TPA potentially could be associated with a decreased risk of reocclusion after successful thrombolysis.

Differential induction of 3-hydroxy-3-methylglutaryl CoA reductase in two cotton species following inoculation with Verticillium

Gossypium barbadense cottons are typically more resistant to wilt pathogens than are Gossypium hirsutum cultivars. Both species make terpenoid phytoalexins in response to infection, implicating isoprenoid biosynthesis as a factor in resistance. Conserved regions in plant 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMGR), the first enzyme in the terpene biosynthesis pathway, were used to design polymerase chain reaction primers for cloning a fragment of a cotton HMGR gene. The clone was used as a probe on Northern blots to show that induction of HMGR mRNA following introduction of Verticillium dahliae spores into the vascular system is much more rapid in Seabrook Sea Island, a restant G. barbadense cotton, than it is in Rowden, a susceptible G. hirsutum. The amount of HMGR mRNA returned to near control levels in 4 days in the former variety but continued to accumulate in the latter. Specific enzyme activity of HMGR also increased more rapidly in stele extracts of Seabrook Sea Island than in Rowden.

A double-blind, placebo-controlled, dose-ranging safety evaluation of single-dose intravenous dolasetron in healthy male volunteers

The safety and tolerability of dolasetron mesylate, a potent and selective 5-HT3 receptor antagonist, were evaluated after single intravenous doses in healthy male volunteers. In this double-blind, placebo-controlled, randomized, phase I study, 80 subjects received either placebo or dolasetron in escalating doses (0.6 to 5.0 mg/k). Subjects were monitored for adverse events, vital sign and laboratory alterations, and changes in electrocardiographic (ECG) intervals and electroencephalographic (EEG) patterns. Overall, the percentage of subjects reporting adverse events was similar in those receiving dolasetron (44/64; 68.8%) or placebo (10/16; 62.5%); most adverse events were mild in severity. Subjects receiving dolasetron reported a higher incidence of central nervous system (headache and dizziness/lightheadedness), gastrointestinal (increased appetite and nausea), and visual adverse events and taste alterations. No clinically significant changes in laboratory variables were observed. Transient and asymptomatic ECG changes (small mean increases in PR interval and QRS complex duration versus baseline) were noted in several subjects at 1 to 2 hours after infusion at doses > or = 3.0 mg/kg. Transient, mild blood pressure decreases were observed in five subjects, including one on placebo. Dolastron mesylate was well tolerated in single intravenous doses up to 5.0 mg/kg in healthy male volunteers. Clinical studies of the drug are ongoing for antiemetic indications.

Novel 21-aminosteroidlike compounds prevent iron-induced free radical-mediated injury to vascular endothelial cells

Free radicals appear to play a major role in the reperfusion injury of the myocardium. Iron chelators and antioxidants can prevent the reperfusion injury. The cellular source of free radicals during reperfusion is not clearly established. However, an important source may be the endothelial cells (EC). The protective effect of iron chelators and antioxidants on reperfusion injury of the myocardium may be partially mediated by their effect on vascular EC, which may attenuate the formation of hydroxyl radicals. We examined the protective effect of deferoxamine and antioxidants on iron-dependent free radical-mediated damage to EC and membrane lipid peroxidation and compared it with those of a new class of compounds (21-aminosteroids: U-74389F, U-74500A, U-78517F) which have both antioxidant and iron chelating properties. We examined viability of the EC and membrane lipid peroxidation using primary aortic EC. First, the effect of increasing iron concentration (0-3.8 microM) (added as ferric ammonium citrate) was characterized. We then examined the effect of deferoxamine (1-10 microM), butylated hydroxytoluene (BHT 1-10 mM), probucol (0.5-5.0 mM), allopurinol (1-1,000 microM), U-74389F (2-20 microM), U-74500A (1-5 microM), and U-78517F (0.1-1.0 microM) on reversing the effect of iron. With increasing iron concentration, there was a significant decrease in the viability of dog aortic or bovine pulmonary arterial EC as compared with NIH 3T3 or human fibroblasts. Equally, there was also a significant increase in lipid peroxidation of the cellular membranes. There were significant differences between the compounds with respect to their ability to maintain the viability of EC and prevent membrane lipid peroxidation.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of long-term enalapril therapy on neurohormones in patients with left ventricular dysfunction. SOLVD Investigators

The aim of this study was to compare the long-term effects of treatment with enalapril or placebo on plasma neurohormones in patients with left ventricular (LV) dysfunction. Elevated neurohormonal levels are associated with increased mortality in patients with congestive heart failure. Multiple studies have shown that angiotensin-converting enzyme inhibitors decrease mortality and morbidity in these patients. In Studies of Left Ventricular Dysfunction (SOLVD), enalapril significantly reduced mortality in patients with symptomatic LV dysfunction (treatment trial). In contrast, in patients with asymptomatic LV dysfunction (prevention trial), there was no significant reduction in mortality with enalapril therapy. The effect of enalapril was examined in 333 prevention trial and 129 treatment trial patients. Plasma norepinephrine (NE) and plasma renin activity were measured in these patients at baseline, and at 4 and 12 months of follow-up. In a subset of these patients, atrial natriuretic peptide (ANP) and arginine vasopressin were also measured. Analysis of covariance models were used to determine the effect of enalapril on each neurohormone. Participants in the treatment trial had significantly higher neurohormonal levels when compared with those in the prevention trial or normal control subjects. In the treatment trial, patients taking enalapril had a greater decrease in plasma NE levels than patients taking placebo (p < 0.08).(ABSTRACT TRUNCATED AT 250 WORDS)