Nongenomic, endothelium-independent effects of estrogen on human coronary smooth muscle are mediated by type I (neuronal) NOS and PI3-kinase-Akt signaling

Sex steroids exert profound and controversial effects on cardiovascular function. For example, estrogens have been reported to either ameliorate or exacerbate coronary heart disease. Although estrogen dilates coronary arteries from a variety of species, the molecular basis for this acute, nongenomic effect is unclear. Moreover, we know very little of how estrogen affects human coronary artery smooth muscle cells (HCASMC). The purpose of this study was to elucidate nongenomic estrogen signal transduction in HCASMC. We have used tissue (arterial tension studies), cellular (single-channel patch clamp, fluorescence), and molecular (protein expression) techniques to now identify novel targets of estrogen action in HCASMC: type I (neuronal) nitric oxide synthase (nNOS) and phosphatidylinositol 3-kinase (PI3-kinase)Akt. 17beta-Estradiol (E(2)) increased NO-stimulated fluorescence in HCASMC, and cell-attached patch-clamp experiments revealed that stimulation of nNOS leads to increased activity of calcium-activated potassium (BK(Ca)) channels in these cells. Furthermore, overexpression of nNOS protein in HCASMC greatly enhanced BK(Ca) channel activity. Immunoblot studies demonstrated that E(2) enhances Akt phosphorylation in HCASMC and that wortmannin, an inhibitor of PI3-kinase, attenuated E(2)-stimulated channel activity, NO production, Akt phosphorylation, and estrogen-stimulated coronary relaxation. These studies implicate the PI3-kinase/Akt signaling axis as an estrogen transduction component in vascular smooth muscle cells. We conclude, therefore, that estrogen opens BK(Ca) channels in HCASMC by stimulating nNOS via a transduction sequence involving PI3-kinase and Akt. These findings now provide a molecular mechanism that can explain the clinical observation that estrogen enhances coronary blood flow in patients with diseased or damaged coronary arteries.

A second-generation cementless total hip arthroplasty mean 9-year results

Two hundred fifty-eight primary total hip arthroplasties in 231 patients were implanted using a circumferentially, proximally porous-coated, collared femoral component and a cementless, hemispherical, porous-coated acetabular component and followed up for a mean of 9 years (5-14 years). Four femoral components were revised (2 stems for infection and 2 stems for aseptic loosening). One additional femoral component was radiographically loose at last follow-up. Nine hips underwent acetabular revision (4 for instability, 2 for infection, 2 for loosening, and 1 for osteolysis). Ten-year survivorship with revision or loosening of any component as the end point was 92%; with femoral component aseptic loosening as end point, survivorship was 98%; with acetabular aseptic loosening as the end point, survivorship was 99%. Osteolysis was identified in 26 hips (13%).

Protein phosphatase 2A and Ca2+-activated K+ channels contribute to 11,12-epoxyeicosatrienoic acid analog mediated mesenteric arterial relaxation

Epoxyeicosatrienoic acids (EETs) are considered to be endothelium-derived hyperpolarizing factors, and are potent activators of the large-conductance, Ca(2+)-activated K(+) (BK(Ca)) channel in vascular smooth muscle. Here, we investigate the signal transduction pathway involved in the activation of BK(Ca) channels by 11,12-EET and 11,12-EET stable analogs in rat mesenteric vascular smooth muscle cells. 11,12-EET and the 11,12-EET analogs, 11-nonyloxy-undec-8(Z)-enoic acid (11,12-ether-EET-8-ZE), 11-(9-hydroxy-nonyloxy)-undec-8(Z)-enoic acid (11,12-ether-EET-8-ZE-OH) and 11,12-trans-oxidoeicosa-8(Z)-enoic acid (11,12-tetra-EET-8-ZE), caused vasorelaxation of mesenteric resistance arteries. Mesenteric myocyte whole-cell (perforated-patch) currents were substantially (approximately 150%) increased by 11,12-EET and 11,12-EET analogs. Single-channel recordings were conducted to identify the target for 11,12-EET. 11,12-EET and 11,12-EET analogs also increased mesenteric myocyte BK(Ca) channel activity in cell-attached patches. Similar results were obtained in cell-free patches. Baseline mesenteric myocyte BK(Ca) channel activity (NPo) in cell-free patches averaged less than 0.001 at +50 mV and 11,12-EET (1 micromol/L) increased NPo to 0.03+/-0.02 and 11,12-EET analogs (1 micromol/L) increased NPo to 0.09+/-0.006. Inhibition of protein phosphatase 2A (PP2A) activity with okadaic acid (10 nmol/L) completely reversed 11,12-EET stimulated BK(Ca) channel activity and greatly attenuated 11,12-ether-EET-8-ZE mesenteric resistance artery vasorelaxation. 11,12-EET and 11,12-EET analogs increased mesenteric myocyte PP2A activity by 3.5-fold. Okadaic acid and the EET inhibitor, 14,15-epoxyeicosa-5(Z)-enoic acid (14,15-EEZE) inhibited the 11,12-EET mediated increase in PP2A activity. These findings provide initial evidence that PP2A activity contributes to 11,12-EET and 11,12-EET analog activation of mesenteric resistant artery BK(Ca) channels and vasorelaxation.

Effect of PKC isozyme inhibition on forskolin-induced activation of BKCa channels in rat pulmonary arterial smooth muscle

Signaling mechanisms that elevate cyclic AMP (cAMP) activate large-conductance, calcium- and voltage-activated potassium (BKCa) channels in vascular smooth muscle and cause vasodilatation. In pulmonary vascular smooth muscle (PVSM), BKCa channel modulation is important in the regulation of pulmonary arterial pressure, and inhibition (closing) of the BKCa channel causes pulmonary vasoconstriction. Protein kinase C (PKC) modulates BKCa channels in systemic vascular smooth muscle, but little is known about the effect of PKC on BKCa channel activity in PVSM. A novel finding from our laboratory showed that PKC activates BKCa channels in rat pulmonary arterial smooth muscle and, having observed that cAMP-elevating agents also open BKCa channels, we hypothesized that PKC may open BKCa channels via a cAMP-dependent mechanism. Forskolin (10 microM), an activator of adenylyl cyclase, which increases cAMP concentration, opened BKCa channels in single pulmonary arterial smooth muscle cells (PASMC) of the Sprague-Dawley rat. The effect of forskolin was completely blocked by the PKC inhibitor Go 6983, which selectively blocks the alpha, beta, delta, gamma, and zeta PKC isozymes, and, by rottlerin, which selectively inhibits PKCdelta, and partially blocked by Go 6976, which selectively inhibits PKCalpha PKCbeta, and PKCmu. These results indicate that specific PKC isozymes mediate forskolin-induced activation of BKCa channels in PASMC, which suggests that a signaling pathway involving PKC activation and cAMP exists in pulmonary arterial smooth muscle to open BKCa channels.

PGI2 opens potassium channels in retinal pericytes by cyclic AMP-stimulated, cross-activation of PKG

Pericytes exert an important influence on the control of retinal blood flow; however, little is known regarding the molecular basis of retinal pericyte excitability. The purpose of this study was to elucidate the signaling pathway of how prostacyclin (PGI2), an important endogenous regulator of retinal blood flow, stimulates potassium channel activity in retinal pericytes. Retinal pericytes were isolated from porcine eyeballs and plated on glass coverslips. Immunocytochemistry was performed to verify expression of the pericyte-specific ganglioside marker, 3G5 and smooth muscle alpha-actin. Activity of the large-conductance, voltage- and calcium-activated potassium (BKCa) channel was measured in retinal pericytes via single-channel patch-clamp, and channel identification was confirmed via biophysical and pharmacological characterization. PGI2 (10 microM) or beraprost (30 microM; more stable prostacyclin analog) dramatically stimulated the activity of BKCa channels isolated in cell-attached patches. These experiments strongly suggested that PGI2 stimulated BKCa channel activity via a diffusible second messenger. Similarly, chlorophenylthio (CPT)-cAMP (100 microM; membrane permeable cAMP derivative) induced a significant increase in BKCa channel activity; however, inhibition of the cAMP-dependent protein kinase (PKA) with 300 nM KT5720 could not reverse the stimulatory effect of either PGI2 or CPT-cAMP. In contrast, activation of BK(Ca) channels with either CPT-cAMP or PGI2 was abolished by 300 nM KT5823 (n=5, p<0.01), an inhibitor of the cGMP-dependent protein kinase (PKG). In addition, PGI2-stimulated channel activity was also attenuated by Rp-8-CPT-cGMPS, which inhibits PKG activity via a different mechanism. These findings demonstrate that prostacyclin, the most abundant prostanoid in the retinal circulation, is a potent stimulator of BKCa channel activity in retinal pericytes. Interestingly, this response appears to involve cAMP-stimulated cross-activation of PKG, and not PKA. Taken together, these findings could explain, at least in part, the cellular/molecular basis for PGI2-induced pericyte relaxation and augmentation of blood flow in the retina. Further, we propose PKG-dependent stimulation of BKCa channel activity as a new potential therapeutic target to combat decreased retinal blood flow seen in some disease states (e.g., diabetic retinopathy).

Cementless total hip arthroplasty in patients 50 years or younger

This report examines the mean 9-year results of 100 second-generation cementless total hip arthroplasty in 91 patients 50 years or younger. The mean age at arthroplasty was 39 years (range, 14-50 years), and follow up averaged 9 years (range, 5-13 years). There were 13 revisions (7 related to polyethylene wear and/or osteolysis, 5 for instability, and 1 for infection). No femoral components were revised for loosening and none were radiographically loose. Two acetabular shells were revised for loosening secondary to extensive osteolysis. Ten-year survivorship using revision for any reason as the end point was 87.5%, using femoral component aseptic loosening as the end point was 100%, and using acetabular component aseptic loosening as the end point was 97.1%.

Hypoxia modulates cyclic AMP activation of BkCa channels in rat pulmonary arterial smooth muscle

The signal transduction mechanisms defining the role of cyclic nucleotides in the regulation of potassium channel activity in pulmonary vascular smooth muscle are currently an area of great interest. Normally, signaling mechanisms that elevate cyclic AMP (cAMP) open potassium channels. Modulation of the large-conductance, calcium- and voltage-activated potassium (BKCa) channel is important in the regulation of pulmonary arterial pressure, and inhibition (closing) of the BKCa channel has been implicated in the development of pulmonary vasoconstriction. Accordingly, studies were done to determine the effect of cAMP-elevating agents on BKCa channel activity under normoxic and hypoxic conditions using patch-clamp studies in pulmonary arterial smooth muscle cells (PASMC) of the fawn-hooded rat (FHR). Forskolin (10 microM; n = 4), a stimulator of adenylate cyclase and an activator of cAMP-dependent protein kinase (PKA), and CPT-cAMP (100 microM; n = 3), a membrane-permeable derivative of cAMP, opened BKCa channels in single FHR PASMC under normoxic conditions. Exposure of FHRs to 4 weeks of 10% O2 (hypoxia) significantly attenuated the effect of both forskolin (n = 7) and CPT-cAMP (n = 14) on BKCa channel activity in PASMC. These results suggest that this phenomenon may serve as a physiological mechanism to cause hypoxic vasoconstriction in the pulmonary circulation via modulation of BKCa channels.

Estrogen receptor alpha mediates acute potassium channel stimulation in human coronary artery smooth muscle cells

The pleiotropic effects of estrogen are mediated via stimulation of two estrogen receptor (ER) subtypes, ERalpha and ERbeta. Although a number of studies have identified expression of one or both subtypes in estrogen target tissues, fewer studies have correlated ER expression with a functional role of these proteins in regulating cellular excitability. In the present study, we have combined cellular fluorescence, immunocytochemistry, and molecular expression techniques with single-channel patch-clamp studies to determine which ER mediates estrogen-stimulated potassium channel activity in human coronary artery smooth muscle cells (HCASMC). We had demonstrated previously that estrogen stimulates activity of the large-conductance, calcium- and voltage-activated potassium (BK(Ca)) channel in HCASMC via a nongenomic mechanism. We now demonstrate expression of both ERalpha and ERbeta subtypes in HCASMC. Functionally, however, expression of ERalpha antisense plasmid abolished the acute effect of estrogen on these channels, whereas estrogen retained its ability to stimulate BK(Ca) channels in cells transfected with only green fluorescence protein. In contrast, overexpression of ERalpha enhanced the stimulatory action of estrogen in HCASMC. Transfection with ERalpha antisense/sense plasmid did not alter ERbeta expression. These findings indicate that the ERalpha isoform mediates estrogen-induced stimulation of BK(Ca) channels in HCASMC and thereby provide evidence for a receptor-dependent signaling mechanism that can mediate estrogen-induced inhibition of cellular excitability.

Estrogen-induced contraction of coronary arteries is mediated by superoxide generated in vascular smooth muscle

Although previous studies demonstrated beneficial effects of estrogen on cardiovascular function, the Women's Health Initiative has reported an increased incidence of coronary heart disease and stroke in postmenopausal women taking hormone replacement therapy. The objective of the present study was to identify a molecular mechanism whereby estrogen, a vasodilatory hormone, could possibly increase the risk of cardiovascular disease. Isometric contractile force recordings were performed on endothelium-denuded porcine coronary arteries, whereas molecular and fluorescence studies identified estrogen signaling molecules in coronary smooth muscle. Estrogen (1-1,000 nM) relaxed arteries in an endothelium-independent fashion; however, when arteries were pretreated with agents to uncouple nitric oxide (NO) production from NO synthase (NOS), estrogen contracted coronary arteries with an EC(50) of 7.3 +/- 4 nM. Estrogen-induced contraction was attenuated by reducing superoxide (O(2)(-)). Estrogen-stimulated O(2)(-) production was detected in NOS-uncoupled coronary myocytes. Interestingly, only the type 1 neuronal NOS isoform (nNOS) was detected in myocytes, making this protein a likely target mediating both estrogen-induced relaxation and contraction of endothelium-denuded coronary arteries. Estrogen-induced contraction was completely inhibited by 1 muM nifedipine or 10 muM indomethacin, indicating involvement of dihydropyridine-sensitive calcium channels and contractile prostaglandins. We propose that a single molecular mechanism can mediate the dual and opposite effect of estrogen on coronary arteries: by stimulating type 1 nNOS in coronary arteries, estrogen produces either vasodilation via NO or vasoconstriction via O(2)(-).

Absence of human papillomavirus in esophageal carcinomas from southwestern Kenya

Esophageal squamous cell cancer is highly prevalent in south-western Kenya. The role of human papillomavirus (HPV) in esophageal cancers from this region was evaluated. Biopsies of 29 esophageal squamous cell cancers were assayed for HPV DNA sequences by reverse line blot polymerase chain reaction, using 27 HPV type-specific probes. Viral sequences were found in none of the specimens. These results suggest the HPV is unlikely to be an etiologic factor for esophageal squamous cell cancers in this region.

Estrogen reduces carbachol-induced constriction of asthmatic airways by stimulating large-conductance voltage and calcium-dependent potassium channels

Both the incidence and severity of asthma in women are influenced by fluctuations in estrogen (E(2)) levels, raising the possibility that E(2)s may reduce the hyperresponsiveness that is characteristic of asthma. We examined the effect of E(2) and its downstream signaling pathways in isolated mouse bronchial and tracheal rings passively sensitized either with serum from patients with atopic asthma (ATR) or with serum from control subjects (CTR). ATR exhibited significantly higher sensitivity to carbachol than CTR. Pretreatment of ATR with E(2) shifted the carbachol concentration-response curve (CCRC) toward that of CTR. The E(2) effect was abolished by the nitric oxide synthase inhibitor, L-nitroarginine methyl ester, the soluble guanyl cyclase inhibitor, quinoxalin-1, or the protein kinase G inhibitor, KT5823. Inhibition of the large-conductance, calcium-activated potassium (BK(Ca)) channel activity with iberiotoxin also attenuated the E(2) effect on ATR. In patch-clamp studies, E(2) increased by 50-fold the BK(Ca) channel activity in freshly isolated airway smooth muscle cells. This increase was completely blocked by KT5823. These studies suggest that, at physiologic concentrations, E(2) can prevent cholinergic-induced constriction of asthmatic tracheal rings by activating the nitric oxide-cGMP-protein kinase G pathway to increase BK(Ca) channel activity.

Learning curve for the two-incision total hip replacement

Recently there has been increased interest in doing total hip replacement through small incisions. One such technique is the two-incision approach. After initial investigations into its feasibility, Zimmer developed a training program for surgeons interested in doing the so called MIS 2-Incision Hip Procedure. An "index case" study was initiated to track the early experiences of trained surgeons, which includes 159 surgeons who have completed such training and recorded data on their initial cases. The purpose of this report is to present the data available from this index case study regarding the process of developing proficiency with the two-incision total hip replacement. We found a significant decrease in the mean operative time and fluoroscopy time from the first to tenth case. Key complications did not show a systematic decrease as a function of case number for the first ten cases. Clarification of the entire learning curve for this technique requires further investigation but may last beyond case ten for many surgeons. In addition, data from this study suggests that patient characteristics and surgeon experience have a significant effect on the prevalence of complications with the two-incision technique. The evolution of minimally invasive joint replacement is clearly in its infancy. Complication rates and the demonstrated learning curve may be altered by changes in training and surgical techniques.

PKC activates BKCa channels in rat pulmonary arterial smooth muscle via cGMP-dependent protein kinase

Normally, signaling mechanisms that activate large-conductance, calcium- and voltage-activated potassium (BK(Ca)) channels in pulmonary vascular smooth muscle cause pulmonary vasodilatation. BK(Ca)-channel modulation is important in the regulation of pulmonary arterial pressure, and inhibition (decrease in the opening probability) of the BK(Ca) channel has been implicated in the development of pulmonary vasoconstriction. Protein kinase C (PKC) causes pulmonary vasoconstriction, but little is known about the effect of PKC on BK(Ca)-channel activity in pulmonary vascular smooth muscle. Accordingly, studies were done to determine the effect of PKC on BK(Ca)-channel activity using patch-clamp studies in pulmonary arterial smooth muscle cells (PASMCs) of the Sprague-Dawley rat. The PKC activators phorbol myristate acetate (PMA) and thymeleatoxin opened BK(Ca) channels in single Sprague-Dawley rat PASMC. The activator response to both PMA and thymeleatoxin on BK(Ca)-channel activity was blocked by Gö-6983, which selectively blocks PKC-alpha, -delta, -gamma, and -zeta, and by rottlerin, which selectively inhibits PKC-delta. In addition, the specific cyclic GMP-dependent protein kinase antagonist KT-5823 blocked the responses to PMA and thymelatoxin, whereas the specific cyclic AMP-dependent protein kinase blocker KT-5720 had no effect. In isolated pulmonary arterial vessels, both PMA and forskolin caused vasodilatation, which was inhibited by KT-5823, Gö-6983, or the BK(Ca)-channel blocker tetraethylammonium. The results of this study indicate that activation of specific PKC isozymes increases BK(Ca)-channel activity in Sprague-Dawley rat PASMC via cyclic GMP-dependent protein kinase, which suggests a unique signaling mechanism for vasodilatation.

A comparison of cementless acetabular components of the same design: spiked versus supplemental screws

The purpose of this report was to compare the results of a series of otherwise-identical, cementless acetabular components with screws to a group with spikes in primary total hip arthroplasty. Between April 1993 and August 1997, 339 primary total hip arthroplasties were performed using a cementless acetabular component in 312 patients. There were 227 acetabular components with screws and 112 with spikes only. Radiographic evaluation was performed at a mean of 4.8 years' postarthroplasty (range, 2-8.6 years). No significant difference was identified between the 2 groups in regard to radiographic or clinical parameters.

Protein kinase C inhibits BKCa channel activity in pulmonary arterial smooth muscle

Signaling mechanisms that elevate cyclic AMP (cAMP) activate large-conductance, calcium- and voltage-activated potassium (BKCa) channels in pulmonary vascular smooth muscle and cause pulmonary vasodilatation. BKCa channel modulation is important in the regulation of pulmonary arterial pressure, and inhibition (closing) of the BKCa channel has been implicated in the development of pulmonary vasoconstriction. Protein kinase C (PKC) causes pulmonary vasoconstriction, but little is known about the effect of PKC on BKCa channel activity. Accordingly, studies were done to determine the effect of PKC activation on cAMP-induced BKCa channel activity using patch-clamp studies in pulmonary arterial smooth muscle cells (PASMC) of the fawn-hooded rat (FHR), a recognized animal model of pulmonary hypertension. Forskolin (10 microM), a stimulator of adenylate cyclase and an activator of cAMP, opened BKCa channels in single FHR PASMC, which were blocked by the PKC activators phorbol 12-myristate 13-acetate (100 nM) and thymeleatoxin (100 nM). The inhibitory response by thymeleatoxin on forskolin-induced BKCa channel activity was blocked by Gö-6983, which selectively blocks the alpha, beta, delta, gamma, and zeta PKC isozymes, and Gö-6976, which selectively inhibits PKC-alpha, PKC-beta, and PKC-mu, but not by rottlerin, which selectively inhibits PKC-delta. Collectively, these results indicate that activation of specific PKC isozymes inhibits cAMP-induced activation of the BKCa channel in pulmonary arterial smooth muscle, which suggests a unique signaling pathway to modulate BKCa channels and subsequently cAMP-induced pulmonary vasodilatation.

Indications for lateral retinacular release in total knee replacement

The rule of no thumb test was compared with the towel clip test in determining the need for lateral retinacular release in 200 consecutive primary total knee replacements. The towel clip test was positive in 13 knees (6.5%) and the rule of no thumb test was positive in 78 knees (39%). Using a positive towel clip test as the indication for lateral retinacular release, there was no radiographic evidence of patellar tilt, subluxation, or dislocation in any knee at 6 months postoperatively. Therefore, the rule of no thumb test falsely predicted the need for lateral release in 65 knees (32.5%). The authors advocate the towel clip test to determine the need for lateral retinacular release.

Estradiol relaxes rat aorta via endothelium-dependent and -independent mechanisms

The effects of estrogen on arterial function are heterogeneous with respect to vessel and/or species. We have investigated 17beta-estradiol-induced relaxation in isolated rat aorta with regard to the role of the vascular endothelium and ionic mechanisms. Estrogen induced a concentration-dependent relaxation of 46.5 +/- 7.9% and 70.1 +/- 12.2% (10(-8) and 10(-7)M), which was reduced by endothelial denudation. Furthermore, L-nitroarginine methyl ester completely abrogated this effect; however, estradiol did not relax KCl-contracted rings. Tetraethyl ammonium (1 mmol/l) completely blocked estradiol-induced relaxation. Estradiol increased [cGMP] in isolated aortic rings via NO, but did not significantly affect NOS activity in endothelial cells. Thus, estrogen can relax rat aorta in vitro via both endothelium-dependent and -independent mechanisms involving the NO/cGMP and potassium channel signaling system.

cAMP activates BKCa channels in pulmonary arterial smooth muscle via cGMP-dependent protein kinase

The signal transduction mechanisms defining the role of cyclic nucleotides in the regulation of pulmonary vascular tone is currently an area of great interest. Normally, signaling mechanisms that elevate cAMP and guanosine-3',5'-cyclic monophosphate (cGMP) maintain the pulmonary vasculature in a relaxed state. Modulation of the large-conductance, calcium- and voltage-activated potassium (BK(Ca)) channel is important in the regulation of pulmonary arterial pressure, and inhibition (closing) of the BK(Ca) channel has been implicated in the development of pulmonary hypertension. Accordingly, studies were done to determine the effect of cAMP-elevating agents on BK(Ca) channel activity using patch-clamp studies in pulmonary arterial smooth muscle cells (PASMC) of the fawn-hooded rat (FHR), a recognized animal model of pulmonary hypertension. Forskolin (10 micro M), a stimulator of adenylate cyclase and an activator of cAMP-dependent protein kinase (PKA), and 8-4-chlorophenylthio (CPT)-cAMP (100 micro M), a membrane-permeable derivative of cAMP, opened BK(Ca) channels in single FHR PASMC. Treatment of FHR PASMC with 300 nM KT5823, a selective inhibitor of cGMP-dependent protein kinase (PKG) activity inhibited the effect of both forskolin and CPT-cAMP. In contrast, blocking PKA activation with 300 nM KT5720 had no effect on forskolin or CPT-cAMP-stimulated BK(Ca) channel activity. These results indicate that cAMP-dependent vasodilators activate BK(Ca) channels in PASMC of FHR via PKG-dependent and PKA-independent signaling pathways, which suggests cross-activation between cyclic nucleotide-dependent protein kinases in pulmonary arterial smooth muscle and therefore, a unique signaling pathway for cAMP-induced pulmonary vasodilation.

Oxidative activation of acylguanidine prodrugs: intestinal presystemic activation in rats limits absorption and can be inhibited by co-administration of ketoconazole

1. The disposition of acyl prodrugs was studied to improve the delivery of a guanidine-containing parent compound with poor membrane permeability and poor absorption. 2. The prodrugs were evaluated in vitro and in vivo for conversion to drug. Prodrugs were evaluated for hydrolytic or oxidative bioactivation in intestinal homogenate and rat liver S9 or microsomes. The disposition of the prodrugs in vivo was monitored in bile duct-cannulated rats. 3. Compounds with n-alkylacyl groups were efficiently bioactivated, but were hydrolysed before absorption. 4. Hydrolytic bioactivation could be blocked in vitro by branching in the alkyl chain. These compounds showed modest improvements in absorption, despite favourable permeability. Experiments with liver microsomes demonstrated efficient NADPH-dependent oxidative bioactivation, which was proposed to occur through a CYP-mediated side chain oxidation followed by cyclization and release of parent compound. Ketoconazole co-administration yielded approximately a twofold increase in absorption. 5. The hydrolytically stable prodrugs were successful in increasing absorption of parent drug and were efficiently bioactivated, but they did not yield increased systemic levels of drug.

PGE2 action in human coronary artery smooth muscle: role of potassium channels and signaling cross-talk

Cyclic AMP-stimulating agents are powerful vasodilators, but our knowledge of the signal transduction mechanisms of these agents, particularly in human arteries, is limited. We now report direct molecular effects of prostaglandin E(2) (PGE(2)) on cultured human coronary artery smooth muscle cells (HCASMC). Patch-clamp studies revealed that 10 microM PGE(2) opens a high-conductance (approximately 200 pS), calcium-stimulated potassium (BK(Ca)) channel in intact HCASMC. In contrast, PGE(2) had no direct effect on channels in cell-free patches, indicating involvement of a soluble second messenger. Enzyme immunoassay demonstrated that PGE(2) enhances production of cAMP in HCASMC, but does not increase [cGMP]. Furthermore, forskolin, CPT-cAMP, or CPT-cGMP mimicked the stimulatory effect of PGE(2) on BK(Ca) channel activity. Interestingly, the response to PGE(2) was unaffected by inhibiting the cAMP-dependent protein kinase, but was antagonized by inhibitors of the cGMP-dependent protein kinase (PKG). Furthermore, cAMP-stimulated PKG activity mimicked the effect of PGE(2). These studies suggest a novel PGE(2) action in human arteries: opening of BK(Ca) channels via cAMP cross-activation of PKG in HCASMC. It is proposed that this signaling mechanism may mediate the vasodilatory response to cAMP-dependent agents in the human coronary and other vascular beds.

Sorption and degradation characteristics of phosmet in two contrasting Australian soils

The organophosphate insecticide phosmet [phosphorodithioic acid, s-((1,3-dihydro-1,3-dioxo-2H-isoindol-2yl)methyl), o,o-dimethyl ester] is used to control red-legged earth mites (Halotydeus destructor), lucerne flea (Sminthurus viridis), and Oriental fruit moth (Cydia molesta) in horticulture and vegetable growing. This study was undertaken with two soils of contrasting properties to determine the extent to which sorption and degradation of the insecticide might influence its potential to leach from soil into receiving waters. Two soils were used: a highly organic, oxidic clay soil (Ferrosol) and a sandy soil low in organic matter (Podosol), sampled to 0.3 m depth. The extent of sorption and decomposition rate of a phosmet commercial formulation were measured in laboratory experiments. Sorption followed a Freundlich isotherm at all depths. The Freundlich coefficient K was significantly correlated (p = 0.005) with organic C content in the Podosol, and significantly correlated (p = 0.005) with organic C and clay content in the Ferrosol. K was highest (48.8 L kg-1) in the 0- to 0.05-m depth of the Ferrosol, but lowest (1.0 L kg-1) at this depth in the Podosol. Degradation followed first-order kinetics, with the phosmet half-life ranging from 14 h (0-0.05 m depth) to 187 h (0.2-0.3 m depth) in the Ferrosol. The half-life was much longer in the sandy Podosol, ranging from 462 to 866 h, and did not change significantly with depth. Soil organic C and to a lesser degree clay content influenced phosmet sorption and degradation, but the interaction was complex and possibly affected by co-solvents present in the commercial formulation.

Potassium (BK(Ca)) currents are reduced in microvascular smooth muscle cells from insulin-resistant rats

Insulin resistance (IR) syndrome is associated with impaired vascular relaxation; however, the underlying pathophysiology is unknown. Potassium channel activation causes vascular smooth muscle hyperpolarization and relaxation. The present study determined whether a reduction in large conductance calcium- and voltage-activated potassium (BK(Ca)) channel activity contributes to impaired vascular relaxation in IR rats. BK(Ca) channels were characterized in mesenteric microvessels from IR and control rats. Macroscopic current density was reduced in myocytes from IR animals compared with controls. In addition, inhibition of BK(Ca) channels with tetraethylammonium (1 mM) or iberiotoxin (100 nM) was greater in myocytes from control (70%) compared with IR animals (approximately 20%). Furthermore, activation of BK(Ca) channels with NS-1619 was three times more effective at increasing outward current in cells from control versus IR animals. Single channel and Western blot analysis of BK(Ca) channels revealed similar conductance, amplitude, voltage sensitivity, Ca2+ sensitivity, and expression density between the two groups. These data provide the first direct evidence that microvascular potassium currents are reduced in IR and suggest a molecular mechanism that could account for impaired vascular relaxation in IR.

Endothelium-independent effect of estrogen on Ca(2+)-activated K(+) channels in human coronary artery smooth muscle cells

OBJECTIVE

Postmenopausal estrogen replacement therapy lowers the incidence of cardiovascular disease, suggesting that estrogens support cardiovascular function. Estrogens dilate coronary arteries; however, little is known about the molecular basis of how estrogen affects the human coronary circulation. The cellular/molecular effects of estrogen action on human coronary smooth muscle were investigated in the present study.

METHODS

Patch-clamp and fluorescent microscopy studies were performed on human coronary myocytes in the absence of endothelium.

RESULTS

Estrogen increased whole-cell currents over a range of membrane potentials, and further studies indicated that the large-conductance (186.5 +/- 3 pS), calcium- and voltage-activated potassium (BK(Ca)) channel was the target of estrogen action. Channel activity was stimulated approximately 15-fold by nanomolar concentrations of 17 beta-estradiol, and this stimulation was reversed >90% by inhibiting cGMP-dependent protein kinase activity with 300 nM KT5823. 17 beta-Estradiol increased the level of cGMP and nitric oxide in human myocytes, and the stimulatory effect of estrogen on channel activity and NO production was reversed by inhibiting NO synthase with 10 microM N(G)-monomethyl-L-arginine.

CONCLUSIONS

Our cellular and molecular studies identify the BK(Ca) channel as a target of estrogen action in human coronary artery smooth muscle. This response to estrogen involves cGMP-dependent phosphorylation of the BK(Ca) channel or a closely associated regulatory molecule, and further evidence suggests involvement of the NO/cGMP signaling system in coronary smooth muscle. These findings are the first to provide direct evidence for a molecular mechanism that can account for endothelium-independent effects of estrogen on human arteries, and may also help explain why estrogens reduce myocardial ischemia and stimulate coronary blood flow in patients with diseased coronary arteries.

Estrogen and vascular function

The effects of estrogen on the female reproductive system are well known. In contrast, comparatively recent research has demonstrated that estrogen also exerts specific effects on the cardiovascular system--particularly the vasculature. This review summarizes some of the current ideas of how estrogen regulates and modulates vascular function, and focuses primarily on potential mechanisms of estrogen-induced vasodilation. Although many studies indicate estrogen exerts beneficial effects on the circulatory system, the overall conclusions from clinical studies remain somewhat equivocal. In contrast, it is clear that estrogen reduces atherosclerosis by reducing low-density lipoproteins (LDL) and inflammatory processes in the vasculature, and may also act as an antioxidant; however, these effects account for only a portion of the total cardiovascular benefit of estrogen. Estrogen is also a vasodilator and hypotensive agent, and can induce vascular relaxation by stimulating release of endothelium-derived vasodilatory substances (e.g., nitric oxide [NO]) or by acting directly on the vascular smooth muscle (VSM). Recent evidence indicates that calcium and potassium channels in VSM cells play an important role in mediating estrogen-induced relaxation of many vascular beds, but elucidating the signal transduction mechanisms coupling estrogen receptor (ER alpha and/or ER beta) activation to generation of second messengers and effector mechanisms remains an area of intense study. Not surprisingly, it is becoming apparent that the molecular basis of estrogen's influence on vascular function is multifactorial. A better understanding of these signaling mechanisms should lead to the development of powerful therapeutic agents which can maximize the many beneficial effects of estrogen action, while helping minimize the harmful (and sometimes lethal) side effects.

Effect of posterior capsular repair on early dislocation in primary total hip replacement

Formal repair of the posterior capsule and short external rotator tendons has been described as a surgical approach to reduce the incidence of posterior dislocation after posterolateral surgical approach to primary total hip replacement. The purpose of the current study was to compare the incidence of early posterior dislocation (within the first 6 months after surgery) using a complete posterior capsulectomy versus a formal posterior capsular repair. In patients with a complete posterior capsulectomy, 52 of 1078 primary total hip replacements (4.8%) had an early posterior dislocation. In patients with posterior capsular repair, three of 437 primary total hip replacements (0.7%) had an early posterior dislocation. This difference was statistically significant. The only complication in the capsular repair group was an avulsion fracture of the greater trochanter in four of 437 total hip replacements (0.9%).

Direct simultaneous analysis of plasma samples for a drug discovery compound and its hydroxyl metabolite using mixed-function column liquid chromatography-tandem mass spectrometry

A polymer-coated mixed-function (PCMF) column was evaluated for direct plasma injection for the simultaneous determination of a drug candidate and its hydroxyl metabolite by high-performance liquid chromatography (HPLC) with tandem mass spectrometry (MS-MS) in support of pharmacokinetic studies. Each diluted monkey plasma sample containing internal standard was directly injected on to the PCMF column for sample clean-up, enrichment and chromatographic separation. The proteins and macromolecules were first eluted from the column while the drug molecules were retained on the bonded hydrophobic phase. The analytes retained on the column were then eluted with a strong mobile phase using a gradient separation technique at a constant flow rate of 1.0 ml min(-1). When not diverted, the column effluent was connected either to the atmospheric pressure chemical ionization (APCI) source or the electrospray ionization (ESI) source as part of the mass spectrometer system used for quantification. The calibration curve was linear over the range 5-2500 ng ml(-1) for both analytes. The retention times for the analytes and the internal standard were both consistent and no column deterioration was observed for at least 500 injections. The recovery through the column and reproducibility of the dosed compound and its hydroxyl metabolite in monkey plasma samples were > 90% (RSD < 6%). The total analysis time was < 8 min per sample. The analytical results obtained by the proposed direct plasma injection method were in good agreement with those obtained by the conventional LC-MS-MS method.

Sequences adjacent to oriP improve the persistence of Epstein-Barr virus-based episomes in B cells

Epstein-Barr virus (EBV) oriP and the EBV nuclear antigen 1 (EBNA-1) protein allow persistence of EBV-based episomes. A nuclear matrix attachment region (MAR) spans oriP and the adjacent region of the EBV genome containing the EBV-expressed RNAs. Here, we show that episomes with the MAR are retained significantly more efficiently in EBV-positive B cells than episomes containing oriP alone.

Epoxyeicosatrienoic acid-induced relaxation is impaired in insulin resistance

We assessed the effect of epoxyeicosatrienoic acids (EETs) in intact mesenteric arteries and Ca(2+)-activated K(+) (BK(Ca)) channels of isolated vascular smooth muscle cells from control and insulin-resistant (IR) rats. The response to 11,12-EET and 14,15-EET was assessed in small mesenteric arteries from control and IR rats in vitro. Mechanistic studies were performed in endothelium intact or denuded arteries and in the presence of pharmacological inhibitors. Moreover, EET-induced activation of the BK(Ca) channel was assessed in myocytes in both the cell-attached and the inside-out (I/O) patch-clamp configurations. In control arteries, both EET isomers induced relaxation. Relaxation was impaired by endothelium denudation, N(omega)-nitro-L-arginine, or iberiotoxin (IBTX), whereas it was abolished by IBTX + apamin or charybdotoxin + apamin. In contrast, the EETs did not relax IR arteries. In control myocytes, the EETs increased BK(Ca) activity in both configurations. Conversely, in the cell-attached mode, EETs had no effect on BK(Ca) channel activity in IR myocytes, whereas in the I/O configuration, BK(Ca) channel activity was enhanced. EETs induce relaxation in small mesenteric arteries from control rats through K(Ca) channels. In contrast, arteries from IR rats do not relax to the EETs. Patch-clamp studies suggest impaired relaxation is due to altered regulatory mechanisms of the BK(Ca) channel.

Testosterone relaxes coronary arteries by opening the large-conductance, calcium-activated potassium channel

Cardiovascular diseases are often considered to be a predominantly male health problem, and it has been suggested that testosterone exerts deleterious effects on cardiovascular function; however, few experimental studies support this suggestion. Moreover, the cellular and molecular mechanism(s) underlying vascular responses to testosterone is unknown. The present study has investigated the acute effects of testosterone on porcine coronary artery smooth muscle at the tissue and cellular levels. Contractile studies demonstrated that testosterone or dihydrotestosterone (a nonaromatizable metabolite) relaxed these arteries by an endothelium-independent mechanism involving potassium efflux. Direct evidence from patch-clamp studies confirmed that testosterone opened K(+) channels in single coronary myocytes, and further analysis identified this protein as the large-conductance, calcium- and voltage-activated potassium (BK(Ca)) channel. Moreover, inhibiting BK(Ca) channel activity significantly attenuated testosterone-induced coronary relaxation. These findings indicate that testosterone relaxes porcine coronary arteries predominantly by opening BK(Ca) channels in coronary myocytes, and this response may be associated with accumulation of cGMP. This novel mechanism may provide a better understanding of testosterone-induced vasorelaxation reported in recent experimental and early clinical studies.

Pharmacokinetic theory of cassette dosing in drug discovery screening

Cassette dosing is a procedure for higher-throughput screening in drug discovery to rapidly assess pharmacokinetics of large numbers of candidate compounds. In this procedure, multiple compounds are administered simultaneously to a single animal. Blood samples are collected, and the plasma samples obtained are analyzed by means of an assay method such as liquid chromatography coupled to tandem mass spectrometry that permits concurrent assay of many compounds in a single sample. Consequently, the pharmacokinetics of multiple compounds can be assessed rapidly with a small number of experimental animals and with shortened assay times. However, coadministration of multiple compounds may result in pharmacokinetic drug-drug interactions. This paper describes a pharmacokinetic description for cassette dosing derived from pharmacokinetic theory. The most important finding from this theoretical treatment is that the potential for drug-drug interactions leading to altered clearances of coadministered drugs depends on both the relative K(M) values for the metabolic enzymes and the total number of drugs coadministered. However, the theory predicts that the potential for drug-drug interactions is only a weak function of the dose size. Finally, it is also shown that including a benchmark compound within the set of coadministered compounds cannot ensure the detection of errors due to drug-drug interactions. Thus, neither the absolute values of pharmacokinetic parameters nor the rank order obtained from cassette dosing can be accepted without independent confirmation. These theoretical predictions are evaluated with data taken from the literature.

Resection arthroplasty for nonseptic failure of total hip arthroplasty

Although resection arthroplasty is a well-recognized salvage procedure for septic total hip arthroplasty, the nonseptic complications of total hip arthroplasty are customarily handled by revision and replacement of a new total hip implant. Some of the severe forms of failure of total hip arthroplasty in the absence of infection may require resection arthroplasty. The indication is massive loss of available bone stock for the revision operation. This may result from technical errors or progressive and extensive destruction of bone associated with loosened components. Concern for this outcome is important for assessing the probabilities of long-term success of the use of total hip arthroplasty in young patients.

Esophageal stent placement without fluoroscopy

BACKGROUND

Access to fluoroscopic equipment is limited in some regions where esophageal cancer is common. This report describes a simple method for placement of expandable esophageal stents without fluoroscopy.

METHODS

Patients with dysphagia due to unresectable esophageal cancer underwent esophageal stent placement under endoscopic control alone. A colored mark on the stent delivery catheter was used to properly position the undeployed stent with respect to the proximal end of the tumor.

RESULTS

Stent placement was attempted in 70 patients and was successful in every case. There were no immediate complications of stent placement. Mean dysphagia score decreased from 3.3 before stent placement to 0.5 at follow-up. There was a trend toward lower dysphagia scores in patients who received coated stents.

CONCLUSION

Expandable esophageal stents can be accurately and safely placed under direct endoscopic control, without fluoroscopy.

Angiotensin II relaxes microvessels via the AT(2) receptor and Ca(2+)-activated K(+) (BK(Ca)) channels

Angiotensin II (Ang II) is one of the most potent vasoconstrictor substances, yet paradoxically, Ang II may dilate certain vascular beds via an undefined mechanism. Ang II-induced vasoconstriction is mediated by the AT(1) receptor, whereas the relative expression and functional importance of the AT(2) receptor in regulating vascular resistance and blood pressure are unknown. We now report that Ang II induces relaxation of mesenteric microvessels and that this vasodilatory response was unaffected by losartan, an AT(1) receptor antagonist, but was inhibited by PD123,319, a selective antagonist of AT(2) receptors. In addition, reverse transcriptase-polymerase chain reaction studies revealed high amounts of AT(2) receptor mRNA in smooth muscle from these same microvessels. Ang II-induced relaxation was inhibited by either tetraethylammonium or iberiotoxin, suggesting involvement of the large-conductance, calcium- and voltage-activated potassium (BK(Ca)) channel. Subsequent whole-cell and single-channel patch-clamp studies on single myocytes demonstrated that Ang II increases the activity of BK(Ca) channels. As in our tissue studies, the effect of Ang II on BK(Ca) channels was inhibited by PD123,319, but not by losartan. In light of these consistent findings from tissue physiology, molecular studies, and cellular/molecular physiology, we conclude that Ang II relaxes microvessels via stimulation of the AT(2) receptor with subsequent opening of BK(Ca) channels, leading to membrane repolarization and vasodilation. These findings provide evidence for a novel endothelium-independent vasodilatory effect of Ang II.

Cassette-accelerated rapid rat screen: a systematic procedure for the dosing and liquid chromatography/atmospheric pressure ionization tandem mass spectrometric analysis of new chemical entities as part of new drug discovery

This report addresses the continuing need for increased throughput in the evaluation of new chemical entities (NCEs) in terms of their pharmacokinetic (PK) parameters by describing an alternative procedure for increasing the throughput of the in vivo screening of NCEs in the oral rat PK model. The new approach is called "cassette-accelerated rapid rat screen" (CARRS). In this assay, NCEs are dosed individually (n = 2 rats/compound) in batches of six compounds per set. The assay makes use of a semi-automated protein precipitation procedure for sample preparation in a 96-well plate format. The liquid chromatography/atmospheric pressure ionization tandem mass spectrometry (LC/API-MS/MS) assay is also streamlined by analyzing the samples as "cassettes of six". Using this new approach, a threefold increase in throughput was achieved over the previously reported "rapid rat screen".

Stable correction of a genetic deficiency in human cells by an episome carrying a 115 kb genomic transgene

Persistent expression of a transgene at therapeutic levels is required for successful gene therapy, but many small vectors with heterologous promoters are prone to vector loss and transcriptional silencing. The delivery of genomic DNA would enable genes to be transferred as complete loci, including regulatory sequences, introns, and native promoter elements. These elements may be critical to ensure prolonged, regulated, and tissue-specific transgene expression. Many studies point to considerable advantages to be gained by using complete genomic loci in gene expression. Large-insert vectors incorporating elements of the bacterial artificial chromosome (BAC) cloning system, and the episomal maintenance mechanisms of Epstein-Barr virus (EBV), can shuttle between bacteria and mammalian cells, allowing large genomic loci to be manipulated conveniently. We now demonstrate the potential utility of such vectors by stably correcting a human genetic deficiency in vitro. When the complete hypoxanthine phosphoribosyltransferase (HPRT) locus of 115 kilobases (kb) was introduced into deficient human cells, the transgene was both maintained as an episome and expressed stably for six months in rapidly dividing cell cultures. The results demonstrate for the first time that gene expression from an episomal genomic transgene can correct a cell culture disease phenotype for a prolonged period.