In vivo blockade of tumor necrosis factor-alpha accelerates functional endothelial recovery after balloon angioplasty.

BACKGROUND: Tumor necrosis factor-alpha (TNF) is expressed locally in arteries at sites of balloon injury. In vitro studies have shown that TNF inhibits cell cycle progression and induces apoptosis in endothelial cells. Accordingly, we performed a series of experiments to test the hypothesis that inhibiting TNF could accelerate endothelial recovery after angioplasty. METHODS AND RESULTS: TNF soluble receptor (TNFsr) has been shown to neutralize the actions of TNF in vitro and in vivo. Sprague-Dawley rats received TNFsr versus control IgG through an intraperitoneal injection. De-endothelializing balloon injury was then performed, and animals were killed after 1 week to evaluate re-endothelialization (Evans blue dye staining) and after 2 weeks to evaluate re-endothelialization and endothelial function. At both time points, blockade of TNF using TNFsr resulted in an increase in re-endothelialization, as measured as absolute area and percent area re-endothelialized. TNFsr also accelerated functional endothelial recovery, which manifest as an increase in nitric oxide production. Neointimal thickening was also shown inhibited. CONCLUSIONS: In vivo blockade of TNF accelerates functional endothelial recovery after barotraumatic de-endothelializing injury. These findings suggest that locally expressed TNF acts to inhibit functional endothelial recovery after angioplasty and that transient blockade of TNF may improve the long-term success of angioplasty.

Prevalence of the T215Y mutation in human immunodeficiency virus type 1-infected pregnant women in a New York cohort, 1995--1999.

From 1997 through 1999, the prevalence of the zidovudine resistance mutation T215Y was 9.7% among pregnant women, and the human immunodeficiency virus type 1 (HIV-1) load in those with resistant virus was higher than that measured in women with wild-type HIV-1. All mutations were noted in women with zidovudine experience, which suggests that monotherapy may not be adequate prophylaxis for vertical transmission of HIV-1 infection in the current era.

Prevalence of methicillin-resistant and methicillin-susceptible Staphylococcus aureus in the community.

Recent reports indicate that community-acquired methicillin-resistant Staphylococcus aureus (MRSA) infections are increasing and may now involve persons without risk factors predisposing for acquisition. To estimate the extent of community MRSA in New York City, the prevalence of S. aureus and MRSA nasal colonization in a well-patient population of 500 children and guardians was determined. The prevalence of S. aureus nasal carriage was 35% for children and 28% for guardians. One person with predisposing risk factors was colonized with an MRSA, which was identified as the predominant clone found in New York City hospitals. A high degree of methicillin-susceptible S. aureus strain diversity was noted, with no apparent selection for specific clonal types. Thus, MRSA colonization is not ubiquitous in persons without predisposing risk outside of the health care environment. Bacterial competition and a lack of strong selection may limit the community spread of MRSA and can account for its sporadic distribution.

Adenovirus-encoded hammerhead ribozyme to Bcl-2 inhibits neointimal hyperplasia and induces vascular smooth muscle cell apoptosis.

OBJECTIVE: The balance between apoptosis and cell proliferation is vital for cellular homeostasis, yet little is known about the mechanisms that coordinate these two cell fates, particularly in the vessel wall. It is well established that the members of Bcl-2-gene family are regulators of apoptosis, but their role in cellular proliferation is less clear. METHODS: We analyzed the effects of disrupting Bcl-2 expression in vascular smooth muscle cells (VSMCs) by adenoviral-mediated delivery of a hammerhead ribozyme against bcl-2 mRNA (Ad-Rbz-Bcl-2). RESULTS: Forced ablation of Bcl-2 in balloon-injured rat carotid arteries reduced cell number and inhibited neointimal hyperplasia. In vitro, VSMCs transduced with the Ad-Rbz-Bcl-2 underwent apoptosis as indicated by a reduction in cell number and DNA fragmentation. Ad-Rbz-Bcl-2-transduced cells also exhibited aberrations in both G1- and S-phases of the cell cycle. However, forced perturbations in cell cycle activity by serum-stimulation or treatment with chemical inhibitors did not affect Ad-Rbz-Bcl-2-induced cell death, indicating that these cell cycle changes are not essential for apoptosis. CONCLUSION: These data show that physiological levels of Bcl-2 are essential for VSMC viability and that ablation of Bcl-2 alters cell cycle activity through the execution of the apoptotic process.

Early changes in quasispecies repertoire in HIV-infected infants: correlation with disease progression.

The evolution of HIV-1 quasispecies in patients during the first year of life was investigated in 10 vertically infected infants, using heteroduplex analysis of the V3-V5 region of env. Four subjects, who showed little viral evolution during the period of the study, had rapid progression of disease and early loss of CD4(+) cells. The remaining six subjects, who were slow progressors, evolved new viral variants within 6 months, and in one case by 1 month of age. Of the four patients who were PCR positive at birth, one was infected with multiple HIV-1 variants. These results show that in HIV-infected children, multiple variants may initiate infection and early quasispecies diversification is associated with a favorable clinical outcome.

Adenovirus-mediated delivery of the Gax transcription factor to rat carotid arteries inhibits smooth muscle proliferation and induces apoptosis.

Adenovirus-mediated gene delivery in animal models of vascular injury has provided insights into the mechanisms underlying vessel wall pathologies. We have previously demonstrated that overexpression of the Gax transcription factor inhibits neointimal formation in rat and rabbit models of arterial injury. Here, we evaluate potential mechanisms for the reduction in stenotic lesion size due to Gax overexpression. At 3, 7 and 14 days after injury the Ad-Gax-infected arteries displayed a marked decrease in medial vascular smooth muscle cell number (3 days, 54% reduction P < 0.01; 7 days, 41% reduction P < 0.003; 14 days, 49% reduction P < 0.02). At 3 days after injury, PCNA expression was attenuated in the Ad-Gax-treated vessels compared with control vessels (65% reduction P < 0.02), indicating a reduction in cellular proliferation. At 7 days and 14 days after injury Ad-Gax-infected arteries exhibited elevated number of TUNEL-positive medial VSMCs compared with control-treated arteries (7 days, 9.2-fold increase P < 0.03; 14 days, 17.2-fold increase P < 0.03), indicating an induction of apoptotic cell death. These data suggest that deregulated Gax expression induces first cell cycle arrest and then apoptosis in the vascular smooth muscle cells that contribute to the neointimal layer. Therefore, the efficacy of this therapeutic strategy appears to result from the ability of the Gax transcriptional regulator to modulate multiple cellular responses.

Antibody blockade of thrombospondin accelerates reendothelialization and reduces neointima formation in balloon-injured rat carotid artery.

BACKGROUND: Remodeling of the extracellular matrix plays an important role during the pathogenesis of atherosclerosis and restenosis. The matrix glycoprotein thrombospondin-1 (TSP1) inhibits endothelial cell proliferation and migration in vitro. In contrast, TSP1 facilitates the growth and migration of cultured vascular smooth muscle cells. Accordingly, we investigated the hypothesis that administration of anti-TSP1 antibody could facilitate reendothelialization and inhibit neointimal thickening in balloon-injured rat carotid artery. METHODS AND RESULTS: Sprague-Dawley rats were subjected to left common carotid artery denudation, after which arteries were treated with C6.7 anti-TSP1 or control antibody. Evans blue dye staining 2 weeks after injury disclosed significantly increased reendothelialization in arteries treated with C6.7 antibody compared with the control group, and this effect was associated with increased number of proliferating cell nuclear antigen-positive endothelial cells. In contrast, treatment with C6.7 antibody decreased the number of proliferating cell nuclear antigen-positive vascular smooth muscle cells in the injured arterial wall. Neointimal thickening was correspondingly attenuated to a statistically significant degree in arteries receiving C6.7 antibody versus the control group at both the 2-week and 4-week time points. CONCLUSIONS: Intra-arterial delivery of antibody against TSP1 facilitated reendothelialization and reduced neointimal lesion formation after balloon denudation.

Changes in frequency of HIV-1-specific cytotoxic T cell precursors and circulating effectors after combination antiretroviral therapy in children.

Combination antiretroviral therapy has had a major role in reducing human immunodeficiency virus type 1 (HIV-1) plasma viral loads in HIV-1-infected adults but a variable effect in infants, in whom complete viral suppression appears to be less readily achieved. In adults, after the reduction in plasma viremia, there is a decrease in the numbers of circulating cytotoxic T cell (CTL) effectors and precursors in the majority of patients. This longitudinal study assessed the effect of combination drug therapy on the frequency of HIV-1-specific CTL responses in 8 HIV-1-infected children. Following treatment, the frequency of HIV-1-specific CTL responses initially increased, especially in children with incomplete viral suppression but with increasing CD4+ cell counts. In children with complete viral suppression, the frequency of HIV-1-specific CTL responses decreased, suggesting that viral replication is required to maintain CTL responses in the systemic circulation.

Immunologic and virologic responses to HAART in severely immunocompromised HIV-1-infected children.

OBJECTIVE: To determine the long-term immunologic and virologic effects of highly active antiretroviral therapy (HAART) in children with AIDS. DESIGN: A prospective observational study. SETTING: Two pediatric HIV clinics. PARTICIPANTS: Twenty-five protease-inhibitor naive HIV-infected children (aged 2-18 years) with advanced disease (CD4 < or =6%). INTERVENTION: HAART (one protease inhibitor and one or more nucleoside analogs). Diphtheria and tetanus immunization in six patients after 18 months of therapy. MAIN OUTCOME MEASURES: Changes in percentage of CD4 cells and plasma HIV-1 RNA levels; post-treatment assays of lymphoproliferative responses to recall antigens; CD4 cell memory phenotype. RESULTS: Median duration of follow-up was 18.8 months (range, 7.5-28 months). At baseline the CD4 cell percentage was 2% (range, 0-6%), this increased significantly to 16% (range, 3-48%) above baseline at 12 months (P = 0.002). The mean maximum CD4 cell increase was 20.7% (range 4-48%) which corresponds to 657x10(6) cells/l (range, 30-2240x10(6) cells/l) above baseline. By contrast, the median viral load was not significantly lower at 12 months than at baseline (P = 0.34), and only 25% of the patients had sustained undetectable viral load. Of the reconstituted CD4 cells 70% were naive, and none of the subjects had lymphoproliferative responses to tetanus and diphtheria although 40% did develop responses to Candida, an environmental antigen. A single immunization with diphtheria and tetanus toxoid produced lymphoproliferative responses to tetanus in three out of six patients. CONCLUSIONS: HAART was associated with sustained increases in CD4 cell counts, despite a high incidence of 'virologic failure'. CD4 counts and the proportion of naive cells were higher than have been reported in adults, which may be a reflection of greater thymic activity in children. Memory cell clones for antigens encountered in the past which are not prevalent before therapy could not be expanded without additional antigenic exposure.

Restoration of E2F expression rescues vascular endothelial cells from tumor necrosis factor-alpha-induced apoptosis.

BACKGROUND: Normally, quiescent endothelial cells (EC) line the inner surface of arteries and protect against thrombosis and neointimal growth. A variety of noxious stimuli, including balloon angioplasty, may compromise EC integrity, thereby initiating proliferation and triggering the local release of cytokines, including tumor necrosis factor-alpha (TNF-alpha). METHODS AND RESULTS: In vivo blockade of TNF-alpha using a soluble receptor molecule results in accelerated reendothelialization at sites of balloon angioplasty, suggesting an important physiological role of TNF-alpha in attenuating regrowth of endothelium after balloon angioplasty. Our studies reveal that TNF-alpha, an apoptosis-inducing cytokine, induces G1 cell-cycle arrest in proliferating EC. Quiescent EC are relatively immune to TNF-induced apoptosis versus proliferating EC, which display repression of the E2F transcription factor coincident with TNF-induced apoptosis and cell-cycle arrest. We also show that in this setting, E2F overexpression exerts a survival effect in proliferating EC and restores cell-cycle progression, in direct contrast to results of prior reports, which revealed that deregulated expression of E2F in normally cycling cells induces apoptosis. CONCLUSIONS: These data demonstrate that TNF-induced apoptosis is highly dependent on cell-cycle activity and that E2F can function as survival factor under certain conditions.

Increased transmission of vertical hepatitis C virus (HCV) infection to human immunodeficiency virus (HIV)-infected infants of HIV- and HCV-coinfected women.

The transmission of perinatal hepatitis C virus (HCV) infection was studied retrospectively in 62 infants born to 54 HCV- and human immunodeficiency virus (HIV)-coinfected women enrolled in a prospective natural history study of HIV transmission. Infant HCV infection was assessed by nested RNA polymerase chain reaction. The overall rate of vertical HCV transmission was 16.4% (9/62). Most HCV-infected children did not develop antibodies to HCV. The rate of HCV infection was higher among HIV-infected infants (40%) than among HIV-uninfected infants (7.5%; odds ratio, 8.2; P = .009). This difference in transmission was not related to differences in maternal HCV load, as measured by branched DNA assay, or mode of delivery. Why HIV-infected infants of HCV- and HIV-coinfected women have significantly higher rates of perinatal HCV transmission remains to be elucidated. The rate of HCV transmission in HIV-uninfected infants of HCV- and HIV-coinfected women is similar to that reported for infants born to HIV-seronegative mothers.

Characteristics of acute pneumonia in human immunodeficiency virus-infected children and association with long term mortality risk. National Institute of Child Health and Human Development Intravenous Immunoglobulin Clinical Trial Study Group.

OBJECTIVE: To describe the epidemiologic, clinical, radiologic, laboratory and treatment characteristics of acute pneumonia and its association with mortality in HIV-infected children. METHODS: Data were collected during a trial of intravenous immunoglobulin (IVIG) for infection prophylaxis (1988 to 1991); CD4+ percentage was measured and HIV RNA was assessed on stored sera collected at baseline and every 3 months. Mortality was recorded during the trial and updated through 1996. All reported physician-diagnosed pneumonia episodes underwent blinded review for trial endpoint classification as acute (new radiologic findings and presence of clinical symptoms) or nonacute. RESULTS: On blinded clinical trial endpoint review of all reported pneumonia episodes (n = 281), only 47% were classified as acute. One hundred thirty-one episodes of acute pneumonia were reported in 93 children (47 in 31 IVIG and 84 in 62 placebo patients, P < 0.01). The incidence of acute pneumonia was 24 episodes per 100 patient years. Findings associated with an acute bacterial process were uncommon (leukocytosis > or =15000/mm3 in 21% and fever > or =103 degrees F in 32% of episodes). Multiple acute episodes occurred in 34% of the children and were associated with increased risk of mortality in a univariate analysis (risk ratio, 2.1; 95% confidence interval, 1.3 to 3.4, P = 0.002), but in a multivariate model only baseline HIV RNA copy number and CD4+ percentage remained independently associated with mortality (relative risk, 2.0 and 1.4, respectively, P < 0.001). CONCLUSION: Acute pneumonia was a common occurrence in HIV-infected children and was associated with long term mortality risk. Multiple episodes of acute pneumonia likely represent a marker of progressive disease and immunologic dysfunction rather than being causally associated with increased long term mortality.

Role of c-fos and E2F in the induction of cyclin A transcription and vascular smooth muscle cell proliferation.

Excessive proliferation of vascular smooth muscle cells (VSMCs) contributes to vessel renarrowing after angioplasty. Here we investigated the transcriptional regulation of the cyclin A gene, a key positive regulator of S phase that is induced after angioplasty. We show that Ras-dependent mitogenic signaling is essential for the normal stimulation of cyclin A promoter activity and DNA synthesis in VSMCs. Overexpression of the AP-1 transcription factor c-fos can circumvent this requirement via interaction with the cAMP-responsive element (CRE) in the cyclin A promoter. Moreover, c-fos overexpression in serum-starved VSMCs results in the induction of cyclin A promoter activity in a CRE-dependent manner, and increased binding of endogenous c-fos protein to the cyclin A CRE precedes the onset of DNA replication in VSMCs induced by serum in vitro and by angioplasty in vivo. We also show that E2F function is essential for both serum- and c-fos-dependent induction of cyclin A expression. Taken together, these findings suggest that c-fos and E2F are important components of the signaling cascade that link Ras activity to cyclin A transcription in VSMCs. These studies illustrate a novel link between the transcriptional and cell cycle machinery that may be relevant to the pathogenesis of vascular proliferative disorders.

Adenoviral constructs encoding phosphorylation-competent full-length and truncated forms of the human retinoblastoma protein inhibit myocyte proliferation and neointima formation.

BACKGROUND: The retinoblastoma (Rb) protein is a key cell-cycle regulator that controls entry into the S phase by modulating the activity of the E2F transcription factor. We analyzed the effects of full-length phosphorylation-competent and a mutant truncated form of human Rb for their effects on vascular smooth muscle cell (VSMC) proliferation and neointima formation. METHODS AND RESULTS: A number of mutant forms, both phosphorylation competent and incompetent, of human Rb protein were evaluated for their ability to inhibit E2F activity. The results of these assays indicated that a phosphorylation competent, amino-terminal-truncated Rb protein (Rb56) was a particularly potent inhibitor of E2F-mediated transcription relative to the full-length Rb construct (Rb110). Adenoviral constructs containing Rb56 or Rb110 expressed their respective Rb forms in VSMCs, as determined by Western immunoblot analysis, and were similar in their abilities to arrest the cell cycle, as determined by assays of 3H-thymidine incorporation and by flow cytometric analyses. When examined for their effect on neointima formation after balloon injury of the rat carotid artery, both full-length and truncated forms of Rb inhibited formation of this VSMC-derived lesion. CONCLUSIONS: These analyses revealed that the maintenance of high levels of phosphorylation-competent human Rb, either full-length or truncated forms, in VSMCs is an effective method of modulating the extent of intimal hyperplasia that occurs after balloon-induced vascular injury.

Low serum thiol levels predict shorter times-to-death among HIV-infected injecting drug users.

OBJECTIVES: To investigate whether serum thiol levels are altered by HIV disease, and whether low serum thiols predict time to death among HIV-infected injecting drug users (IDU). DESIGN: A cross-sectional study of serum thiol levels among 13 HIV-seronegative IDU, 116 HIV-seropositive IDU, and 17 HIV-seropositive IDU with a history of AIDS, and a cohort study of the 133 HIV-infected IDU who took part in the cross-sectional study. METHODS: Subjects were recruited from a methadone-maintenance treatment program during 1990-1991. Total serum thiols were determined spectrophotometrically at enrolment; low serum thiols were defined as those with an absorbance at 412 nm < or = 0.46. Deaths through 31 December 1993 were determined from the National Death Index (NDI). Twenty-six HIV-seropositive subjects died during follow up; death certificates, which were obtained for 23 subjects, indicated AIDS or HIV infection for 20. Product-limit estimation was used to calculate survival. Multivariate analyses employed Cox proportional-hazards regression. RESULTS: Analysis of cross-sectional data showed that serum thiols did not differ significantly among HIV-free subjects, HIV-infected subjects, and HIV-infected subjects with a history of AIDS. Cohort analysis, adjusted for age, revealed that persons with those with high serum thiols (relative hazard = 2.83; 95% confidence interval (CI), 1.15, 6.97); a significant interaction between low serum thiols and a history of AIDS was associated with a relative hazard of 5.65 (95% CI, 1.22-2.61). CONCLUSIONS: Among HIV-infected persons, low serum thiols, especially in concert with a history of AIDS, predict mortality risk. These findings support the hypothesis that oxidative stress is critical to the pathogenesis of HIV infection.

Reciprocal relation between VEGF and NO in the regulation of endothelial integrity.

Balloon angioplasty disrupts the protective endothelial lining of the arterial wall, rendering arteries susceptible to thrombosis and intimal thickening. We show here that vascular endothelial growth factor (VEGF), an endothelial cell mitogen, is upregulated in medial smooth muscle cells of the arterial wall in response to balloon injury. Both protein kinase C (PKC) and tyrosine kinase pp60src mediate augmented VEGF expression. In contrast, nitric oxide (NO) donors inhibit PKC-induced VEGF upregulation by interfering with binding of the transcription factor activator protein-1 (AP-1) to the VEGF promoter. Inhibition of VEGF promoter activation suggests that NO secreted by a restored endothelium functions as the negative feedback mechanism that downregulates VEGF expression to basal levels. Administration of a neutralizing VEGF antibody impaired reendothelialization following balloon injury performed in vivo. These findings establish a reciprocal relation between VEGF and NO in the endogenous regulation of endothelial integrity following arterial injury.

Failure of Neutralizing gp120 Monoclonal Antibodies to Prevent HIV Infection of Choriocarcinoma-Derived Trophoblasts.

Although placental trophoblasts, the only fetal cells in direct contact with infectious maternal blood, can be infected with HIV, the precise cause for the low transmission rate of virus across the placental barrier is unknown. One of the most common conjectures is that maternal anti-HIV antibodies (Abs) contribute to the protection of the fetus. This hypothesis has been tested in vitro by infecting the CD4-negative placental trophoblast line, BeWo, with HIV-1(IIIB) in the presence of serial dilutions of neutralizing monoclonal Abs against the V3 loop (No. 694) or CD4-binding conformational domain (No. 588). The results, based on measurement of p24 production from virus-exposed cells, reveal that the titers of Abs, adequate in preventing the infection of control MT-4 T lymphocytes, were less effective in protecting trophoblasts. Furthermore, PCR analysis of HIV DNA formed after a single round of infection has shown no significant decrease in the number of viral copies in Ab-protected BeWo cells. An anti-HIV serum from a pregnant woman did also have no effect. Although our in vitro observations do not necessarily apply to the in vivo situation, the results suggest that the humoral immune response sustained by neutralizing Abs may be able to protect T lymphocytes, but not placental trophoblasts. The findings are consistent with recent clinical studies demonstrating a lack of correlation between the presence of neutralizing anti-HIV Abs in pregnant women and HIV transmission in utero. Copyright 1997 S. Karger AG, Basel

Impaired early growth of infants perinatally infected with human immunodeficiency virus: correlation with viral load.

OBJECTIVE: To evaluate the effect of viral load on the early growth of infants infected with human immunodeficiency virus (HIV). METHODS: Plasma concentrations of p24-antigen and HIV ribonucleic acid were measured retrospectively and correlated with growth parameters for the first 18 months of life in a cohort of 47 term infants born to HIV-infected mothers prospectively enrolled in a study of perinatal HIV transmission. Comparisons of the mean weight and length of the 18 HIV-infected and 29 uninfected infants for each interval and across intervals were made. Viral load was correlated with standard deviation scores. Infants were stratified by high and low viral load during the first 6 months of life. RESULTS: At birth, no difference in weight and length was observed between HIV-infected and uninfected infants. Between birth and 6 months of age, the infected infants grew less rapidly than the uninfected infants, a finding temporally associated with an exponential increase in HIV viremia. The linear growth of infected infants remained consistently less than that of the uninfected infants after 6 months of life, although the differences were no longer statistically significant and tended to decrease with age in parallel with declines in viral load. The median plasma concentration of HIV ribonucleic acid was significantly higher at 3, 6, 12, and 18 months in infected infants in whom growth failure developed. Infants who had a high viral load in the first 6 months of life were significantly more likely to have severe growth failure. Though the mean SD for weight of the infected infants was always less than that of the uninfected infants, the differences were small and not significant. CONCLUSIONS: Our results confirm the observation that stunting is an early frequent finding in perinatal HIV infection. The deleterious effect of HIV on linear growth appears to be correlated with the level of postnatal HIV viremia, although the exact mechanism of this association remains to be elucidated.

Downregulation of cyclin-dependent kinase 2 activity and cyclin A promoter activity in vascular smooth muscle cells by p27(KIP1), an inhibitor of neointima formation in the rat carotid artery.

Abnormal proliferation of vascular smooth muscle cells (VSMCs) contributes to intimal hyperplasia during atherosclerosis and restenosis, but the endogenous cell cycle regulatory factors underlying VSMC growth in response to arterial injury are not well understood. In the present study, we report that downregulation of cyclin-dependent kinase 2 (cdk2) activity in serum-deprived VSMCs was associated with the formation of complexes between cdk2 and its inhibitory protein p27(KIP1) (p27). Ectopic overexpression of p27 in serum-stimulated VSMCs resulted in the inhibition of cdk2 activity and repression of cyclin A promoter activity. Collectively, these findings indicate that p27 may contribute to VSMC growth arrest in vitro. Using the rat carotid model of balloon angioplasty, a marked upregulation of p27 was observed in injured arteries. High levels of p27 expression in the media and neointima correlated with downregulation of cdk2 activity at 2 wk after angioplasty, and adenovirus-mediated overexpression of p27 in balloon-injured arteries attenuated neointimal lesion formation. Thus, the inhibition of cdk2 function and repression of cyclin A gene transcription through the induction of the endogenous p27 protein provides a mechanism for the inhibition of VSMC growth at late time points after angioplasty.

Estradiol accelerates functional endothelial recovery after arterial injury.

BACKGROUND: The mechanisms of the established atheroprotective effects of estrogen have not been entirely clarified. Recent data suggest that agents that hasten the recovery of the endothelium after denuding injury will deter the development of neointimal lesions. Because estrogen has been shown to exert angiogenic effects in vitro and in vivo, we performed a series of experiments to evaluate whether estrogen was capable of accelerating reendothelialization. METHODS AND RESULTS: Ovariectomized Sprague-Dawley rats received estrogen replacement therapy in the form of subcutaneously implanted pellets designed to release 1.5 or 5.0 mg 17 beta-estradiol over 30 days. Deendothelializing balloon injury was performed 1 week after pellet implantation, and animals were euthanatized after 1 week for evaluation of reendothelialization (Evans blue staining) or 2 weeks for evaluation of reendothelialization and neointimal formation. At both time points, the use of estradiol caused a dose-dependent increase in reendothelialization, which was measured as absolute area and percentage of area that is reendothelialized. Estradiol accelerated functional endothelial recovery, manifested as an increase in nitric oxide production. Neointimal thickening was also shown to be inhibited in a dose-dependent fashion. CONCLUSIONS: Estrogen accelerates functional endothelial recovery after barotraumatic deendothelializing injury. These findings, along with the recent demonstration of estrogen receptor expression by endothelial cells, suggest that the antiatherogenic action of estrogen may be mediated in part through direct effects on endothelial cells.