Comparison of endothelial shear stress between ultrathin strut bioresorbable polymer drug-eluting stent vs durable-polymer drug-eluting stent post-stent implantation: An optical coherence tomography substudy from BIOFLOW II.

BACKGROUND: Recent clinical data indicate a different performance of biodegradable polymer (BP)-drug eluting stent (DES) compared to durable polymer (DP)-DES. Whether this can be explained by a beneficial impact of BP-DES stent design on the local hemodynamic forces distribution remains unclear. OBJECTIVES: To compare endothelial shear stress (ESS) distribution after implantation of ultrathin (us) BP-DES and DP-DES and examine the association between ESS and neointimal thickness (NIT) distribution in the two devices at 9 months follow up. METHODS AND RESULTS: We retrospectively identified patients from the BIOFLOW II trial that had undergone OCT imaging. OCT data were utilized to reconstruct the surface of the stented segment at baseline and 9 months follow-up, simulate blood flow, and measure ESS and NIT in the stented segment. The patients were divided into 3 groups depending on whether DP-DES (N = 8, n = 56,160 sectors), BP-DES with a stent diameter of >3 mm (strut thickness of 80 µm, N = 6, n = 36,504 sectors), or BP-DES with a stent diameter of ≤3 mm (strut thickness of 60 µm, N = 8, n = 50,040 sectors) were used for treatment. The ESS, and NIT distribution and the association of these two variables were estimated and compared among the 3 groups. RESULTS: In the DP-DES group mean NIT was 0.18 ± 0.17 mm and ESS 1.68 ± 1.66 Pa; for the BP-DES ≤3 mm group the NIT was 0.17 ± 0.11 mm and ESS 1.49 ± 1.24 Pa and for the BP-DES >3 mm group 0.20 ± 0.23 mm and 1.42 ± 1.24 Pa respectively (p < 0.001 for both NIT and ESS comparisons across groups). A negative correlation between NIT and baseline ESS was found, the correlation coefficient for all the stented segments was -0.33, p < 0.001. CONCLUSION: In this OCT sub-study of the BIOFLOW II trial, the NIT was statistically different between groups of patients treated with BP-DES and DP-DES. In addition, regions of low ESS were associated with increased NIT in all studied devices.

Temporal changes in coronary plaque as assessed by an artificial intelligence-based optical coherence tomography: from the first-in-human trial on DREAMS 3G scaffold.

AIMS: The aim of the study is to assess the impact of the baseline plaque composition on the DREAMS 3G luminal late loss and to compare the serial plaque changes between baseline and 6 and 12 months (M) follow-up. METHODS AND RESULTS: A total of 116 patients were enrolled in the BIOMAG-I trial. Patients were imaged with optical coherence tomography (OCT) pre- and post-DREAMS 3G implantation and at 6 and 12 M. OCTPlus software uses artificial intelligence to assess composition (i.e. lipid, calcium, and fibrous tissue) of the plaque. The differences between the OCT-derived minimum lumen area (MLA) post-percutaneous coronary intervention and 12 M were grouped into three terciles. Patients with larger MLA differences at 12 M (P = 0.0003) had significantly larger content of fibrous tissue at baseline. There was a reduction of 24.8% and 20.9% in lipid area, both P < 0.001, between the pre-DREAMS 3G OCT and the 6 and 12 M follow-up. Conversely, the fibrous tissue increased by 48.4% and 36.0% at 6 and 12 M follow-up, both P < 0.001. CONCLUSION: The larger the fibrous tissue in the lesion at baseline, the larger the luminal loss seen at 6 and 12 M. Following the implantation of DREAMS 3G, favourable healing of the vessel coronary wall occurs as shown by a decrease in the lipid area and an increase in fibrous tissue.

Optical coherence tomography assessment of acute thrombogenicity at bifurcation sites using different stenting techniques: A porcine arteriovenous shunt study.

OBJECTIVES: We aimed to compare bare-metal stents (BMS), durable-polymer everolimus-eluting stents (DP-EES), and abluminal biodegradable-polymer sirolimus-eluting stents (ABP-SES) in the bifurcation model setup. BACKGROUND: The mechanism of thrombogenicity, which differs among second-generation stents implanted using double-kissing (DK) crush or culotte stenting techniques, remains unclear. We have shown previously that setting up a porcine arteriovenous shunt model is feasible and useful to assess thrombogenicity at vessel bifurcation points. METHODS: Six porcine shunt models were prepared for the comparison between DK crush and culotte stenting techniques using BMS, DP-EES, and ABP-SES. Intracoronary imaging with high-resolution optical coherence tomography (OCT) was performed to evaluate the thrombogenicity in different stent types in the bifurcation stenting model and was evaluated by a core lab. RESULTS: Culotte stenting demonstrated more thrombogenicity at the proximal main branch (MB) with DP-EES, side branch (SB) with BMS, and the bifurcation site irrespective of the stent type, while DK crush technique exhibited thrombogenicity only at SB with BMS and ABP-SES. OCT analysis revealed malapposition of DP-EES in the proximal MB with culotte stenting. Stent expansion was generally larger in ABP-SES than BMS and DP-EES. CONCLUSIONS: The study provides hypothesis-generating findings in distinct thrombogenicity of bifurcation stenting with DP- or ABP-coated drug-eluting stents.

A prospective, first-in-human use of the NeVa mechanical thrombectomy device for patients with acute coronary syndromes.

BACKGROUND: There is no established technique for managing large thrombus burden (LTB) in patients with acute coronary syndrome (ACS). AIMS: The aim of this study was to assess the safety and efficacy of the NeVa (Vesalio) mechanical thrombectomy device (MTD) in ACS patients with LTB. METHODS: Consecutive patients with ACS and LTB were treated with the NeVa MTD as the primary vessel recanalisation and thrombus removal modality, followed by conventional intervention. We further developed a bench model and applied to a subset of patients, a vacuum-assisted aspiration technique, exploiting 6 Fr-compatible conventional guiding catheter extensions, as an adjudicative manoeuvre to the use of stent-based MTD. A core laboratory reviewed the angiographic images for procedural complications, Thrombolysis In Myocardial Infarction (TIMI) flow, myocardial blush grade (MBG) and TIMI thrombus grade (TTG). RESULTS: Between November 2019 and March 2021, 61 patients underwent thrombectomy with the NeVa device. Non-flow limiting and reversible coronary spasm occurred in 14 (23%) patients. One patient (#10) suffered from side branch embolisation, which was successfully treated with the NeVa, triggering the development of a vacuum-assisted aspiration technique in a bench model, which was then applied to the subsequent 51 patients. No other device-related complications occurred. After NeVa use, TIMI flow <3 decreased from 68.3% at baseline to 10.3% (p<0.001), MBG <2 from 65% to 27.6% (p<0.001), TTG ≥3 from 96.7% to 43.2% (p<0.001), respectively. CONCLUSIONS: In patients with LTB, the NeVa MTD was safe and associated with high rates of vessel recanalisation and thrombus removal. The concomitant use of vacuum-assisted aspiration has potential to improve the effectiveness and safety of the technique.

Comparison of Angiographic and Intravascular Ultrasound Vessel Measurements in Infra-Popliteal Endovascular Interventions: The Below-the-Knee Calibration Study.

BACKGROUND: Endovascular revascularization (ER) via percutaneous transluminal angioplasty (PTA) and stenting are viable options for revascularization in below-the-knee (BTK) peripheral arterial disease. Two-dimensional angiography has been the standard of practice for estimating vessel size and selecting treatment devices during ER. However, in other vascular territories, intravascular ultrasound (IVUS) offers better visualization of the lumen dimensions. PURPOSE: To compare angiographic and intravascular ultrasound reference vessel (lumen) measurements in below-the-knee peripheral artery interventions. METHODS: Twenty consecutive patients were enrolled in the BTK Calibration study from 2 sites in the United States and Australia. Patients with at least one diseased segment in a native infra-popliteal artery (below-the-knee) and a clinical indication for endovascular therapy (EVT) were included with no limitations with regard to vessel diameter or lesion length. Digital subtraction angiography and IVUS imaging were collected pre- and post-PTA and images were sent to an independent core lab for standardized quantitative analysis of the normal-looking reference vessel dimensions when available. The results were presented as least square means with 95% confidence intervals and a p-value of <0.05 was considered significant. RESULTS: The overall (N = 19) mean reference vessel diameter for QVA was 2.98 ± 1.24 mm vs. 3.47 ± 0.72 mm for IVUS (mean difference was -0.50 mm, (95% CI: -0.80, -0.20; p = 0.14). As expected, in the proximal segments (N = 12), the mean reference vessel diameters were larger: for QVA, it was 3.17 ± 1.34 mm vs. 3.55 ± 0.76 mm in IVUS, (mean difference was -0.38 mm, (95% CI: -0.79, 0.03; p = 0.40); while in the distal segments (N = 7), mean reference vessel diameters were smaller: for QVA, it was 2.64 ± 1.06 mm vs. 3.33 ± 0.67 mm in IVUS, (mean difference was -0.69 mm, (95% CI: -1.04, 0.34; p = 0.17). We observed a greater degree of acute gain in cases where the treatment balloon size correlated with the IVUS measured reference size. CONCLUSION: Angiography underestimates infrapopliteal reference vessel lumen size even when quantitatively assessed. Adjunctive IVUS imaging use in guiding BTK procedures could help ensure adequate sizing and possibly impact immediate post-procedure indices.

Diagnostic comparison of automatic and manual TIMI frame-counting-generated quantitative flow ratio (QFR) values.

Quantitative flow ratio (QFR) is a computational measurement of FFR (fractional flow reserve), calculated from coronary angiography. Latest QFR software automates TIMI frame counting (TFC), which occurs during the flow step of QFR analyses, making the analysis faster and more reproducible. The objective is to determine the diagnostic performance of QFR values obtained from analyses using automatic TFC compared to those obtained from analyses using manual TFC. This was a single-arm clinical trial that used the prospective analysis of the coronary angiographic image series of 97 patients who underwent evaluation of stable coronary artery disease with FFR/iFR at MedStar Washington Hospital Center in Washington, DC, USA. Automatic and manual TFC QFR values were obtained from the analyses of each of the 97 patients' image series, with manual TFC QFR values as the current gold standard for comparison. The diagnostic performance of automatic TFC QFR values was measured as follows: sensitivity was 0.87 (95% CI 0.66-0.97) and specificity was 1.00 (95% CI 0.9514-1.00), positive predictive value (PPV) was 1.00 (95%CI 1.00-1.00), while the NPV was 0.96 (95% CI 0.96-0.99). Overall accuracy was 96.91% (95% CI 91.23%-99.36%). The agreement as illustrated by the Bland-Altman plot shows a bias of 0.0023 (SD 0.0208) and narrow limits of agreement (LOA): Upper LOA 0.0573 and Lower LOA - 0.0528. The area under curve (AUC) was 0.996. QFR values generated from automatic TFC are comparable to those generated from manual TFC in diagnostic capability. The most recent software update produces values equivalent to those of the previous manual option, and can therefore be used interchangeably.

Comparison of Quantitative Flow Ratio and Invasive Physiology Indices in a Diverse Population at a Tertiary United States Hospital.

BACKGROUND: Quantitative flow ratio (QFR) is a technology to evaluate the coronary stenosis significance on 3-dimensional quantitative coronary angiography. The aim of this study is to evaluate and compare the QFR versus fractional flow reserve (FFR) and/or instantaneous free-wave ratio (iFR) in a US population with a fair African American population representation. METHODS AND RESULTS: This was a retrospective, observational and single-center study that enrolled 100 patients who underwent coronary angiography. The diagnostic performance of QFR in terms of sensitivity was 0.80 (95%CI 0.64-0.97) and specificity was 0.95 (95% CI 0.90-1.00), the positive predictive value (PPV) was 0.83 (0.68-0.98), while the negative predictive value (NPV) was 0.94 (0.88-0.99). The overall accuracy was 0.91 and area under the curve (AUC) was 0.92 (95% CI 0.87-0.97). The R-squared was 0.54 and the Bland-Altman plot showed a bias of 0.0016 (SD 0.063) and limits of agreement (LOA): Upper LOA 0.13 and Lower LOA -0.12. In African Americans (n = 33), accuracy, AUC, sensitivity, specificity (94%; 0.90 [0.80-1.00]; 0.90 [0.71-1.00]; 0.96 [0.87-1.00], respectively) were better than those for the overall population. CONCLUSIONS: In a US-based representative population, vessel QFR accuracy and agreement with FFR as reference is high. Diagnostic performance of QFR in African Americans is also excellent.

Effect of Procedural Technique on Cardiovascular Outcomes Following Second-Generation Drug-Eluting Resorbable Magnesium Scaffold Implantation.

BACKGROUND: This study sought to assess target lesion failure (TLF) and clinically driven target lesion revascularization (CD-TLR) through 1 year following second-generation drug-eluting magnesium scaffold (Magmaris) implantation using a dedicated technique (so-called "4 P's" strategy). METHODS AND RESULTS: The 4 P's strategy stands for: correct patient selection, proper scaffold sizing, pre-dilatation (<20% residual stenosis), post-dilatation. All the patient and lesion characteristics, preparation, and sizing of the device were compared in patients with TLF and CD-TLR through 1-year follow-up. We analyzed 315 patients for this study. At 1 year, there were 14 TLFs and 10 CD-TLRs. The TLF rates were 7.7%, 4.9%, and 4.1%; while the CD-TLR rates were 7.7%, 2.5%, and 3.2% in the undersized, properly sized, and oversized vessel groups, correspondingly. Diameter stenosis (DS) after pre-dilatation in patients with TLF and CD-TLR was significantly greater than in those without TLF and CD-TLR. In patients with a properly sized scaffold, DS after pre-dilatation was similar in patients with and without TLF and CD-TLR. However, in patients with non-properly sized scaffolds, greater post-balloon DS was observed in patients with TLF and CD-TLR. CONCLUSIONS: Improper sizing and poor lesion preparation before Magmaris implantation appear to be related to TLF during 1-year follow-up.

Optical Coherence Tomography based treatment approach for patients with Acute Coronary Syndrome.

INTRODUCTION: Areas covered:In this review, we outline the underlying causes of acute coronary syndrome (ACS) as evaluated by optical coherence tomography (OCT). We report both the definitions of each mechanism and its frequency as reported in the literature to date. Finally, we present an algorithm based on the findings in the review that gives an outlined approach to perform intervention on ACS patients.Expert opinion:Although the most common and most accepted intervention in ACS cases is stent implantation, data suggest a stentless approach in cases of plaque erosion, which generally occurs in younger patients presenting with an acute coronary syndrome that have TIMI flow of 2/3 and either a small or large burden of thrombus and underlying stenosis of less than 50%.

Comparison of Patterns of Coronary Artery Disease in Patients With Heart Failure by Cardiac Amyloidosis Status.

BACKGROUND/PURPOSE: The aim of this study is to characterize the pattern and the severity of coronary artery lesions in cardiac amyloidosis. METHODS: We retrospectively compared patients with heart failure who tested positive (i.e., biopsy or gene tests - HF/CA+) against those who tested negative (HF/CA-) for cardiac amyloidosis. Groups were compared demographically and angiographically for qualitative and quantitative variables to determine patterns of involvement in the major epicardial coronary vessels. RESULTS: The study included 110 heart failure patients, of whom 55 patients (88 lesions) were in the HF/CA+ group, and 55 patients (66 lesions) were HF/CA-. Despite the advanced age of HF/CA+ patients (74.5 ± 11.0 years vs. 54.1 ± 15.0 years; p = 0.05), no severe calcification was found in the HF/CA+ group (0.0% vs. 4.5%; p = 0.018). The HF/CA+ group also had fewer ostial lesions (3.4% vs. 15.1%; p = 0.0095) and a higher, albeit not significant, Thrombolysis in Myocardial Infarction frame count (30.4 ± 12.6 vs. 26.6 ± 11 frames; p = 0.06). In the HF/CA+ group, men had a significant number of tandem lesions compared to women (14.5% vs 0.0%, p = 0.02). CONCLUSIONS: Overall, heart failure patients with cardiac amyloidosis were older but were found to have less calcified lesions, less ostial involvement, and a reduced anterograde coronary blood flow. This is the first report examining coronary lesions in heart failure patients with cardiac amyloidosis.

Comprehensive assessment of coronary computed tomography angiography by using Leaman and Leiden score in overweight and obese patients.

Coronary computed tomography angiography (CCTA) is a non-invasive modality used to assess for coronary artery disease. The CT Leaman and Leiden scores utilize coronary plaque location, composition and severity of stenosis to risk stratify patients for cardiovascular events with remarkable precision. This study compares the CCTA Leaman and Leiden score between overweight and obese populations in addition to their associated baseline characteristics. All patients who underwent CCTA within the last 1 year from a single institution were included for initial analysis. Body mass index (BMI) was used to classify patients who were overweight (25.0 to < 30 kg/m2) or obese (≥ 30 kg/m2). Patients with a BMI of < 25 kg/m2 were excluded from further analysis. Patients were divided into overweight and obese groups. CT Leaman and Leiden scores, in addition to baseline characteristics were subsequently compared between the two groups. Overall, a strong correlation between CT Leaman and Leiden scores was found (R2 = 0.9831). Patients classified as obese have more coronary lesions 0.71 ± 0.12 vs 0.31 ± 0.50 in overweight patients (p = 0.02) and tended to have a higher positive CT Leiden (5.47 ± 4.10 vs 3.90 ± 1.36, p = 0.2) and Leaman (3.45 ± 2.58 vs 2.35 ± 0.90, p = 0.1). Furthermore, obese patients with a Leiden score > 5 had significantly higher scores compared to overweight patients (10.22 ± 2.54 vs 5.87 ± 0.64, p = 0.016). Obese patients had similar average CT Leaman and Leiden scores compared to overweight individuals but were more likely to have higher CT Leiden scores > 5 which may indicate a higher risk for adverse cardiovascular outcomes.

Impact of two formulas to calculate percentage diameter stenosis of coronary lesions: from stenosis models (phantom lesion model) to actual clinical lesions.

Percentage diameter stenosis (%DS) by angiography is still commonly used to determine luminal obstruction of coronary artery disease (CAD) lesions. While visual estimation of %DS is widespread, because of high inter-operator variability, quantitative coronary arteriography (QCA) analysis is the gold standard. There are two %DS formulas: %DS1 averages the proximal and distal reference vessel diameter (RVD); %DS2 interpolates the RVD. This study aims to evaluate the difference between %DS assessed by QCA in two datasets, phantom lesion models and CAD patients. Ten phantom lesion models (PLMs) and 354 CAD lesions from the FIRST trial were assessed by QCA. In the latter, two scenarios were assessed: Scenario A (worst view), the most common approach in the clinical setting; and Scenario B (average of two complementary views), the standard core-laboratory analysis. In the PLMs, %DS1 and %DS2 mean ± standard deviation (median) was 58.5 ± 21.7 (61.6) and 58.7 ± 21.6 (61.8), respectively, with a signed difference of - 0.2% ± 0.3% (- 0.1%). In Scenario A, the mean %DS1 was 43.8 ± 9.1 (43.3) and 44.0 ± 9.1 (42 .9) in %DS2. In Scenario B, the mean %DS1 was 45.3 ± 8.8 (45.1) and 45.5 ± 9.0 (45.1) in %DS2. The signed difference was - 0.2% ± 2.4% (0.0%) and - 0.2% ± 2.1% (0.0%) in Scenario A and B, respectively. These differences between formulas ranged from - 1.2 to 0.5% for the phantom cases compared to - 17.7% to 7.7% in Scenario A and to - 15.5% to 7.1% in Scenario B. Although the overall means of the formulas provide similar results, significant lesion-level differences are observed. The use of the worst view versus the average of two views provided similar results.

Clinical outcomes of complete revascularization using either angiography-guided or fractional flow reserve-guided drug-eluting stent implantation in non-culprit vessels in ST elevation myocardial infarction patients: insights from a study based on a systematic review and meta-analysis.

Current guidelines recommend that percutaneous coronary intervention (PCI) should be restricted to the culprit vessel in ST elevation myocardial infarction (STEMI) patients with multi-vessel disease (MVD) and without cardiogenic shock. However, newer data suggests that performing complete revascularization (CR) in MVD patients may lead to better outcomes compared to intervention in the culprit vessel only. The aim of this meta-analysis is to examine the available data to determine if CR (using either angio- or fractional flow reserve guidance-FFR) following primary PCI in STEMI patients without cardiogenic shock impacts clinical outcomes. Meta-analysis was performed by conducting a literature search of PubMed from January 2004 to July 2017. Pooled estimates of outcomes, presented as odds ratios (OR) [95% confidence intervals], were generated using random-effect models. A total of 9 studies (3317 patients) were included. CR showed a significant MACE reduction (OR 0.49, 95% CI 0.36-0.66, p < 0.001); All-cause mortality (OR 0.69, 95% CI 0.48-0.98, p = 0.04) and repeat revascularization (OR 0.38, 95% CI 0.28-0.51, p < 0.001) at ≥ 12 months follow-up. The FFR-guiding CR group presented a MACE reduction (odds ratio 0.52, 95% CI 0.30-0.90, p = 0.02) due to a decrease of repeat revascularization (OR 0.41, 95% CI 0.21-0.80, p = 0.009). Overall, performing complete revascularization in STEMI patients showed a MACE reduction, all-cause death and repeat revascularization. Compared to culprit-only revascularization, treating multi-vessel disease in STEMI patients using FFR guidance is associated with decreased incidence of MACE, due to a decreased rate of revascularization.

Palliative care and support for persons with HIV/AIDS in 7 African countries: implementation experience and future priorities.

To combat morbidity and mortality from the worldwide epidemic of the human immunodeficiency virus (HIV), the United States Congress implemented a President's Emergency Plan for AIDS Relief (PEPFAR) in 30 resource-limited countries to integrate combination antiretroviral therapy (ART) for both prevention and cure. Over 35% of eligible persons have been successfully treated. Initial legislation cited palliative care as an essential aspect of this plan but overall health strengthening became critical to sustainability of programming and funding priorities shifted to assure staffing for care delivery sites; laboratory and pharmaceutical infrastructure; data collection and reporting; and financial management as individual countries are being encouraged to assume control of in-country funding. Given infrastructure requisites, individual care delivery beyond ART management alone has received minimal funding yet care remains necessary for durable viral suppression and overall quality of life for individuals. Technical assistance staff of one implementing partner representing seven African countries met to clarify domains of palliative care compared with the substituted term "care and support" to understand potential gaps in on-going HIV care. They prioritized care needs as: 1) mental health (depression and other mood disorders); 2) communication skills (age-appropriate disclosure of HIV status); 3) support of care-providers (stress management for sustainability of a skilled HIV workforce); 4) Tied Priorities: symptom management in opportunistic infections; end-of-life care; spiritual history-taking; and 5) Tied Priorities: attention to grief-related needs of patients, their families and staff; and management of HIV co-morbidities. This process can inform health policy as funding transitions to new priorities.

Contribution of epoxyeicosatrienoic acids to the hypoxia-induced activation of Ca2+ -activated K+ channel current in cultured rat hippocampal astrocytes.

Brief hypoxia differentially regulates the activities of Ca(2+)-activated K(+) channels (K(Ca)) in a variety of cell types. We investigated the effects of hypoxia (<2% O(2)) on K(Ca) channel currents and on the activities of cytochrome P450 2C11 epoxygenase (CYP epoxygenase) in cultured rat hippocampal astrocytes. Exposure of astrocytes to hypoxia enhanced macroscopic outward K(Ca) current, increased the open state probability (NPo) of 71 pS and 161 pS single-channel K(Ca) currents in cell-attached patches, but failed to increase the NPo of both the 71 pS and 161 pS K(Ca) channel currents recorded from excised inside-out patches. The hypoxia-induced enhancement of macroscopic K(Ca) current was attenuated by pretreatment with tetraethylammonium (TEA, 1 mM) or during recording using low-Ca(2+) external bath solution. Exposure of astrocytes to hypoxia was associated with generation of superoxide as detected by staining of cells with the intracellular superoxide detection probe hydroethidine (HE), attenuation of the hypoxia-induced activation of unitary K(Ca) channel currents by superoxide dismutation with tempol, and as quantitated by high-pressure liquid chromatography/fluorescence assay using HE as a probe. In cultured astrocytes in which endogenous CYP epoxygenase activity has been inhibited with either miconazole or N-methylsulfonyl-6-(2-propargyloxyphenyl) hexanamide (MSPPOH) hypoxia failed to increase the NPo of both the 71 pS and 161 pS K(Ca) currents and generation of superoxide. Hypoxia increased the level of P450 epoxygenase protein and production of epoxyeicosatrienoic acids (EETs) from cultured astrocytes, as determined by immunohistochemical staining and LC/MS analysis, respectively. Exogenous 11,12-EET increased the NPo of both the 71 pS and 161 pS K(Ca) single-channel currents only in cell-attached but not in excised inside-out patches of cultured astrocytes. These findings indicate that hypoxia enhances the activities of two types of unitary K(Ca) currents in astrocytes by a mechanism that appears to involve CYP epoxygenase-dependent generation of superoxide and increased production or release of EETs.

Production of 20-HETE and its role in autoregulation of cerebral blood flow.

In the brain, pressure-induced myogenic constriction of cerebral arteriolar muscle contributes to autoregulation of cerebral blood flow (CBF). This study examined the role of 20-HETE in autoregulation of CBF in anesthetized rats. The expression of P-450 4A protein and mRNA was localized in isolated cerebral arteriolar muscle of rat by immunocytochemistry and in situ hybridization. The results of reverse transcriptase-polymerase chain reaction studies revealed that rat cerebral microvessels express cytochrome P-450 4A1, 4A2, 4A3, and 4A8 isoforms, some of which catalyze the formation of 20-HETE from arachidonic acid. Cerebral arterial microsomes incubated with [(14)C]arachidonic acid produced 20-HETE. An elevation in transmural pressure from 20 to 140 mm Hg increased 20-HETE concentration by 6-fold in cerebral arteries as measured by gas chromatography/mass spectrometry. In vivo, inhibition of vascular 20-HETE formation with N-methylsulfonyl-12, 12-dibromododec-11-enamide (DDMS), or its vasoconstrictor actions using 15-HETE or 20-hydroxyeicosa-6(Z),15(Z)-dienoic acid (20-HEDE), attenuated autoregulation of CBF to elevations of arterial pressure. In vitro application of DDMS, 15-HETE, or 20-HEDE eliminated pressure-induced constriction of rat middle cerebral arteries, and 20-HEDE and 15-HETE blocked the vasoconstriction action of 20-HETE. Taken together, these data suggest an important role for 20-HETE in the autoregulation of CBF.

Peroxynitrite reversibly inhibits Ca(2+)-activated K(+) channels in rat cerebral artery smooth muscle cells.

Peroxynitrite (ONOO(-)) is a contractile agonist of rat middle cerebral arteries. To determine the mechanism responsible for this component of ONOO(-) bioactivity, the present study examined the effect of ONOO(-) on ionic current and channel activity in rat cerebral arteries. Whole cell recordings of voltage-clamped cells were made under conditions designed to optimize K(+) current. The effects of iberiotoxin, a selective inhibitor of large-conductance Ca(2+)-activated K(+) (BK) channels, and ONOO(-) (10-100 microM) were determined. At a pipette potential of +50 mV, ONOO(-) inhibited 39% of iberiotoxin-sensitive current. ONOO(-) was selective for iberiotoxin-sensitive current, whereas decomposed ONOO(-) had no effect. In excised, inside-out membrane patches, channel activity was recorded using symmetrical K(+) solutions. Unitary currents were sensitive to increases in internal Ca(2+) concentration, consistent with activity due to BK channels. Internal ONOO(-) dose dependently inhibited channel activity by decreasing open probability and mean open times. The inhibitory effect of ONOO(-) could be overcome by reduced glutathione. Glutathione, added after ONOO(-), restored whole cell current amplitude to control levels and reverted single-channel gating to control behavior. The inhibitory effect of ONOO(-) on membrane K(+) current is consistent with its contractile effects in isolated cerebral arteries and single myocytes. Taken together, our data suggest that ONOO(-) has the potential to alter cerebral vascular tone by inhibiting BK channel activity.

Molecular mechanisms controlling nutritive blood flow: role of cytochrome P450 enzymes.

This short review summarizes the potential role of cytochrome P450 (P450) in regulating blood flow in the brain tissue and in the skeletal muscle. We provide data showing that pressure-induced myogenic activity in the brain is largely responsible for autoregulation of CBF. This myogenic response to pressure is maintained, in part, by 20-HETE formation in arterial muscle cells through a P450 omega-hydroxylase coded for by a P450 4A cDNA. Autoregulation of CBF is a hallmark of the cerebral circulation and provides adequate nutritive blood flow despite large fluctuations in arterial pressure. Given the importance of oxidative metabolism in the brain, support of neuronal activity is mediated by functional hyperaemia to active neurones providing adequate delivery of oxidative substrate. We provide data demonstrating that this functional hyperaemia in the brain is regulated by astrocytes which sense neural activity and release dilator metabolites which shunt blood flow to active neurones. One of the metabolites released by astrocytes in this regard are epoxygenated products of arachidonic acid (AA) formed by P450 enzymes. These AA metabolites of P450 enzymes are epoxyeicosatrienoic acid (EETs). One of these P450 enzymes is coded by a 2C11 cDNA present in astrocytes. Furthermore, astrocytes are capable of inducing capillary angiogenesis which appears to be mediated, in part, by P450-derived EETs.

Cannabinoid CB1 receptor of cat cerebral arterial muscle functions to inhibit L-type Ca2+ channel current.

The CB1 subtype of the cannabinoid receptor is present on neurons in the brain and mediates the perceptual effects of Delta9-tetrahydrocannabinol and other cannabinoids. We found that cat cerebral arterial smooth muscle cells (VSMC) contain the protein for the CB1 receptor and express a cDNA that has >98% amino acid homology to the CB1 cDNA expressed in rat and human neurons. Activation of the CB1 cannabinoid receptor has been shown to decrease the opening of N-type voltage-gated Ca2+ channels in neurons through a pertussis toxin-sensitive GTP-binding protein. In the present study we tested the hypothesis that activation of the cannabinoid CB1 receptor in cerebral VSMC inhibits voltage-gated Ca2+ channels and results in cerebral vasodilation. The predominant Ca2+ current identified in cat cerebral VSMC is a voltage-gated, dihydropyridine-sensitive, L-type Ca2+ current. The cannabimimetic drug WIN-55,212-2 (10-100 nM) induced concentration-dependent inhibition of peak L-type Ca2+ current, which reached a maximum of 82 +/- 4% at 100 nM (n = 14). This effect was mimicked by the putative endogenous CB1-receptor agonist anandamide, which produced a concentration-related reduction of peak L-type Ca2+ current with a maximum inhibition (at 300 nM) of 39 +/- 4% (n = 12). The inhibitory effects of both ligands on peak L-type Ca2+ currents were abolished by pertussis toxin pretreatment and application of the CB1-receptor antagonist SR-141716A (100 nM, n = 5). Both WIN-55,212-2 and anandamide produced concentration-dependent relaxation of preconstricted cerebral arterial segments that was abolished by SR-141716A. These results indicate that the CB1 receptor is expressed in cat cerebral VSMC and that the cerebral vasculature is one of the targets for endogenous cannabinoids. These findings suggest that the CB1 receptor and its endogenous ligand may play a fundamental role in the regulation of cerebral arterial tone and reactivity by modulating the influx of Ca2+ through L-type Ca2+ channels.