High density lipoprotein and cardiovascular diseases

Several epidemiological studies have clearly shown that low plasma levels of high density lipoprotein cholesterol (HDL-C) represent a cardiovascular disease (CVD) risk factor. However, it is unclear if there is a causal association between HDL-C concentration and CVD. A recent study published in the Lancet, which performed two Mendelian randomization analyses, showed that increased HDL-C levels were not associated with a decreased risk of myocardial infarction. These findings, together with the termination of the niacin-based AIM-HIGH trial and the discontinuation of cholesteryl ester transfer protein inhibitor dalcetrapib, challenge the concept that raising of plasma HDL-C will uniformly translate into reductions in CVD risk. HDL particles exhibit several anti-atherosclerotic properties, such as anti-inflammatory and anti-oxidative activities and cellular cholesterol efflux activity. Furthermore, HDL particles are very heterogeneous in terms of size, structure, composition and metabolism. HDL functionality may be associated more strongly with CVD risk than the traditional HDL-C levels. More research is needed to assess the association of the structure of HDL particle with its functionality and metabolism.     

Sitagliptin promotes macrophage-to-faeces reverse cholesterol transport through reduced intestinal cholesterol absorption in obese insulin resistant CETP-apoB100 transgenic mice

Dipeptidyl peptidase-4 inhibitors (DPP-4i) improve glycaemic control in type 2 diabetes, but their benefits on reverse cholesterol transport (RCT) remain unknown. We evaluated the effects of DPP-4i sitagliptin 500 mg/kg/day on RCT in obese insulin-resistant CETP-apoB100 transgenic mice. Metformin 300 mg/kg/day orally was used as a reference compound. Both metformin and sitagliptin showed the expected effects on glucose parameters. Although no significant effect was observed on total cholesterol and high-density lipoprotein (HDL) cholesterol levels, sitagliptin, but not metformin, increased faecal cholesterol mass excretion by 132% (p < 0.001 vs. vehicle), suggesting a potent effect on cholesterol metabolism. Mice were then injected i.p. with (3) H-cholesterol labelled macrophages to measure RCT over 48 h. Compared with vehicle, sitagliptin significantly increased macrophage-derived (3) H-cholesterol faecal excretion by 39%. Administration of (14) C-cholesterol labelled olive oil orally showed a significant reduction of (14) C-tracer plasma appearance over time with sitagliptin, indicating that this drug promotes RCT through reduced intestinal cholesterol absorption.     

Treatment with suboptimal doses of raltegravir leads to aberrant HIV-1 integrations

Integration of the DNA copy of the HIV-1 genome into a host chromosome is required for viral replication and is thus an important target for antiviral therapy. The HIV-encoded enzyme integrase (IN) catalyzes two essential steps: 3′ processing of the viral DNA ends, followed by the strand transfer reaction, which inserts the viral DNA into host DNA. Raltegravir binds to IN and blocks the integration of the viral DNA. Using the Rous sarcoma virus-derived vector RCAS, we previously showed that mutations that cause one viral DNA end to be defective for IN-mediated integration led to abnormal integrations in which the provirus had one normal and one aberrant end, accompanied by rearrangements in the host genome. On the basis of these results, we expected that suboptimal concentrations of IN inhibitors, which could block one of the ends of viral integration, would lead to similar aberrant integrations. In contrast to the proviruses from untreated cells, which were all normal, ∼10–15% of the proviruses isolated after treatment with a suboptimal dose of raltegravir were aberrant. The aberrant integrations were similar to those seen in the RCAS experiments. Most of the aberrant proviruses had one normal end and one aberrant end and were accompanied by significant rearrangements in the host genome, including duplications, inversions, deletions and, occasionally, acquisition of sequences from other chromosomes. The rearrangements of the host DNA raise concerns that these aberrant integrations might have unintended consequences in HIV-1–infected patients who are not consistent in following a raltegravir-containing treatment regimen.     

Reversible voltammograms and a Pourbaix diagram for a protein tyrosine radical

Reversible voltammograms and a voltammetry half-wave potential versus solution pH diagram are described for a protein tyrosine radical. This work required a de novo designed tyrosine-radical protein displaying a unique combination of structural and electrochemical properties. The α₃Y protein is structurally stable across a broad pH range. The redox-active tyrosine Y32 resides in a desolvated and well-structured environment. Y32 gives rise to reversible square-wave and differential pulse voltammograms at alkaline pH. The formal potential of the Y32-O^•/Y32-OH redox couple is determined to 918 ± 2 mV versus the normal hydrogen electrode at pH 8.40 ± 0.01. The observation that Y32 gives rise to fully reversible voltammograms translates into an estimated lifetime of ≥30 ms for the Y32-O^• state. This illustrates the range of tyrosine-radical stabilization that a structured protein can offer. Y32 gives rise to quasireversible square-wave and differential pulse voltammograms at acidic pH. These voltammograms represent the Y32 species at the upper edge of the quasirevesible range. The square-wave net potential closely approximates the formal potential of the Y32-O^•/Y32-OH redox couple to 1,070 ± 1 mV versus the normal hydrogen electrode at pH 5.52 ± 0.01. The differential pulse voltammetry half-wave potential of the Y32-O^•/Y32-OH redox pair is measured between pH 4.7 and 9.0. These results are described and analyzed.     

Cholesterol, C-reactive protein, and cerebrovascular events following intensive and moderate statin therapy

Background: While statins have been shown to reduce cerebrovascular events (CVE), the relationship between cholesterol, C-reactive protein (CRP), and CVE in patients treated with different statin strategies is still being explored. Methods: PROVE IT-TIMI 22 was a randomized trial of intensive (atorvastatin 80 mg/day) and moderate (pravastatin 40 mg/day) statin therapy in 4,162 patients with acute coronary syndromes followed for an average of 24 months; serial biomarkers allowed for an assessment of the lipid and non-lipid effects of statins as they relate to CVE. Results: In this study, 45 patients on intensive statin therapy and 40 patients on moderate statin therapy had a CVE during the study period (2.1% v. 1.9%, P = 0.62). While the lipid profiles of patients with and without CVE were similar, those with CVE had higher CRP levels at 30 days and 4 months (2.7 v. 1.9, 2.4 v. 1.7 mg/L; P = 0.012, P = 0.005). Day 30 CRP remained an independent predictor of CVE after adjusting for age, development of atrial fibrillation, diabetes, and prior CVE. Patients with low density lipoprotein (LDL) levels < 70 mg/dL and ≥ 70 mg/dL had similar rates of CVE, while patients with CRP < 2 mg/L tended to have lower event rates when compared to those with higher levels. The lowest rates of CVE were seen in patients who had LDL < 70 mg/dL and CRP < 2 mg/L. Conclusion: In PROVE IT - TIMI 22, achieved LDL levels did not appear to independently impact the rate of CVE. In contrast, patients with elevated CRP levels were at higher risk of stroke or transient ischemic attack, reinforcing the link between inflammation and CVE. Condensed abstract The goal of this PROVE IT-TIMI 22 sub-study was to examine the relationship between cholesterol, CRP, and CVE in patients on intensive and moderate statin therapy. The achieved lipid levels were similar in patients with and without a CVE; however, the achieved levels of CRP were higher in patients who subsequently developed a stroke or TIA. These findings further support the relationship between inflammation and CVE.     

C反应蛋白与冠状动脉粥样硬化性心脏病

冠状动脉粥样硬化性心脏病中炎症扮演了重要的角色,而炎症的重要标记物C反应蛋白与冠心病的关系正逐渐成为研究的热潮。现综述C反应蛋白的来源、特性、代谢等问题,并通过临床试验、药物试验、细胞分子水平实验及动物实验几个方面的论述来认识C反应蛋白与冠心病的关系,试图了解目前的证据能支持C反应蛋白在冠状动脉疾病发生发展中所起的作用。     

Human plasma phospholipid transfer protein activity is decreased by acute hyperglycaemia: studies without and with hyperinsulinaemia in Type 1 diabetes mellitus.

AIMS: Little is known about the regulation of phospholipid transfer protein (PLTP), that plays a key role in lipoprotein metabolism. PLTP secretion may be up-regulated by glucose in vitro, whereas plasma PLTP activity is decreased by exogenous hyperinsulinaemia and glucose-induced hyperinsulinaemia in vivo. In the present study, we evaluated the separate effects of hyperglycaemia and hyperinsulinaemia in C-peptide-negative Type 1 diabetic patients. METHODS: The protocol was carried out in 16 patients (eight females). In each individual, plasma PLTP mass and activity (measured by enzyme-linked immuno-sorbent assay and liposome-high density lipoprotein system, respectively) as well as plasma cholesteryl ester transfer protein (CETP) activity, lipids and apolipoprotein levels were determined at the end of four different glucose clamps, each lasting 210 min: standard insulin (30 mU/kg/h) and standard glucose (glucose 5.0 mmol/l) (SI-SG), standard insulin and high glucose (glucose 12 mmol/l) (SI-HG), high insulin (150 mU/kg/h) and standard glucose (HI-SG), and high insulin and high glucose (HI-HG). RESULTS: Plasma lipids and (apo)lipoproteins, measured at the end of the SI-HG, HI-SG and HI-HG clamps, were not significantly different compared with the levels obtained at the end of the SI-SG clamp. Median plasma PLTP mass and activity at the end of the SI-SG clamp were 12.8 mg/l and 13.2 micromol/ml/h, respectively. Median plasma PLTP mass decreased by 9.1% at the end of the HI-HG clamp (P < 0.01), whereas the changes at the end of the SI-HG and HI-SG clamps were not significant. Median plasma PLTP activity decreased by 5.7, 4.6 and 8.6% at the end of the SI-HG, HI-SG and HI-HG clamps, respectively (all P < 0.05). Median plasma CETP activity was 177 nmol/ml/h at the end of the SI-SG clamp, and decreased by 4.9% (P < 0.05) and by 8.3% (P < 0.05) at the end of the HI-SG and the HI-HG clamps, respectively. Plasma CETP activity did not change significantly at the end of the SI-HG clamp. CONCLUSIONS: The present study demonstrates that plasma PLTP activity is independently decreased by acute hyperglycaemia and hyperinsulinaemia in humans in vivo. These data do not support a direct role of short-term hyperglycaemia in up-regulating plasma PLTP levels.     

Reciprocal regulation of NO signaling and TXNIP expression in humans: Impact of aging and ramipril therapy

Background

Impaired tissue responsiveness to nitric oxide (NO) occurs in many cardiovascular diseases as well as with advanced age and is a correlate of poor outcomes. This phenomenon results from oxidative stress, with NO “scavenging” and dysfunction of soluble guanylate cyclase (sGC). Thioredoxin-interacting protein (TXNIP) is a major intracellular regulator of inflammatory activation and redox stress, but its interactions with NO/sGC are poorly understood. We have now evaluated the relationship between platelet TXNIP expression and function of the NO/sGC axis in subjects of varying age and during therapy with ramipril.

Methods & results

Young (n = 42) and aging (n = 49) subjects underwent evaluation of platelet TXNIP content. Aging subjects additionally had measurements of platelet NO responsiveness and routine biochemistry. Platelet TXNIP content was greater (376 ± 33 units) in the aging compared to younger subjects (289 ± 13 units; p < 0.05). In the aging subjects there was a significant negative correlation (r = − 0.50, p < 0.001) between platelet TXNIP content and NO responsiveness. In a separate cohort of 15 subjects two week treatment with ramipril, which reversed platelet NO resistance and potentiated sGC activity, also decreased platelet TXNIP content by 40% (p = 0.011).

Conclusions

Platelet TXNIP content increases with aging, varies inversely with responsiveness to NO, and diminishes rapidly following treatment with ramipril. These data suggest that TXNIP-induced oxidative stress may be a critical modulator of tissue resistance to NO, a fundamental basis for cardiovascular disease. Analogously suppression of TXNIP expression can potentially be utilized as an index of restoration of cardiovascular homeostasis.     

酪氨酸激酶信号级联与支气管哮喘发病的关系

支气管哮喘的发病机制涉及炎症细胞和气道结构细胞、细胞因子、趋化因子、生长因子和炎症介质的相互作用.酪氨酸激酶信号级联在变应性气道炎症中起重要作用,活化的酪氨酸激酶激活了多重下游信号转导途径如磷酯酰肌醇3激酶、丝裂原活化蛋白激酶和核因子κB,导致细胞的分化、存活、增殖、脱颗粒和趋化.     

Characterization of apoptosis induced by protein kinase C inhibitors and its modulation by the caspase pathway in acute promyelocytic leukaemia

Acute promyelocytic leukaemia (APL;M3) is a unique form of acute myelogenous leukaemia characterized by t(15;17) translocation. The induction of apoptosis via inhibiting protein kinase C (PKC) has been recently viewed as a promising tool for the eradication of several malignant disorders. In the present study, we investigated the effect of two different protein kinase C inhibitors, Gö6976 and safingol, on the induction of apoptosis in the APL cell line NB4 and its all trans retinoic acid (ATRA)‐resistant variant NB4.306. The effect of the PKC inhibitors on leukaemic cells obtained from three APL patients was also studied. We also evaluated the possible involvement of the caspases in apoptosis induced by PKC inhibitors. Significant time‐ and concentration‐dependent apoptotic changes were demonstrated using Gö6976 and safingol. In addition, our results demonstrated that the caspases were involved in the apoptosis induced by the PKC inhibitors. In conclusion, our study illustrates that the PKC inhibitors Gö6976 and safingol induce apoptosis in APL and hence could be potential therapeutic agents for the treatment of this disease.     

Inhibitors of signaling in myelodysplastic syndrome

Treatment of myelodysplastic syndrome (MDS) has been hampered by the lack of understanding of the molecular and biological abnormalities associated with this disease. Biological abnormalities may lead to typical phenotypic changes in more differentiated cells. Recent developments in the natural history and underlying molecular mechanisms of MDS and acute myeloid leukemia (AML) have identified new molecular therapeutic targets. Several new classes of drugs have shown promise in early clinical trials and may alter the standard of care of these patients. Among these new drugs are farnesyltransferase inhibitors, receptor tyrosine kinase inhibitors, protein kinase C inhibitors, and VEGF inhibitors. These agents have been tested in patients with solid tumors and hematological malignancies such as AML and MDS. Most of the studies in MDS are in early stages of development, where doses are being determined based on the experience in refractory or relapsed AML or solid tumors. Future therapies in MDS will attempt to resolve cytopenias, eliminate malignant clones and allow differentiation by attacking specific mechanisms of the disease.     

Structural basis for membrane binding and catalytic activation of the peripheral membrane enzyme pyruvate oxidase from Escherichia coli

The thiamin- and flavin-dependent peripheral membrane enzyme pyruvate oxidase from E. coli catalyzes the oxidative decarboxylation of the central metabolite pyruvate to CO₂ and acetate. Concomitant reduction of the enzyme-bound flavin triggers membrane binding of the C terminus and shuttling of 2 electrons to ubiquinone 8, a membrane-bound mobile carrier of the electron transport chain. Binding to the membrane in vivo or limited proteolysis in vitro stimulate the catalytic proficiency by 2 orders of magnitude. The molecular mechanisms by which membrane binding and activation are governed have remained enigmatic. Here, we present the X-ray crystal structures of the full-length enzyme and a proteolytically activated truncation variant lacking the last 23 C-terminal residues inferred as important in membrane binding. In conjunction with spectroscopic results, the structural data pinpoint a conformational rearrangement upon activation that exposes the autoinhibitory C terminus, thereby freeing the active site. In the activated enzyme, Phe-465 swings into the active site and wires both cofactors for efficient electron transfer. The isolated C terminus, which has no intrinsic helix propensity, folds into a helical structure in the presence of micelles.     

胆固醇酯转运蛋白与血脂、血糖的关系

目的　研究胆固醇酯转运蛋白 (CETP)与各种类型的血脂异常和血糖异常的关系。方法　 1999年 9月至 10月 ,在北京市自然人群中采用分层随机抽样方法进行危险因素的横断面调查。分析了 719名 4 5～ 6 4岁的男女两性的血浆CETP浓度与血脂、血糖的关系。结果　 (1)在正常甘油三酯 (TG)组 ,CETP低于第 2 5百分位数与高于第 75百分位数时低高密并脂蛋白胆固醇 (HDL C)的患病率分别为 7 4 %和 5 3%。在高TG组 ,CETP低于第 2 5百分位数时低HDL C的患病率也仅为3 6 % ,与正常TG组相似 ;但CETP大于第 75百分位数时低HDL C的患病率为 35 7% ,是CETP低于第 2 5百分位数组的 10倍 ,且高低密度脂蛋白胆固醇 (LDL C)和高极低密度脂蛋白胆固醇 (VLDL C)的患病率也最高。 (2 )高TG合并低HDL C组 ,CETP高于第 75百分位数者占 5 0 0 % ,明显高于其他各组(P <0 0 5 )。 (3)采用Logistic回归模型调整了年龄、性别、吸烟、饮酒、肥胖、血糖和总胆固醇后 ,CETP大于第 75百分位数组与小于第 2 5百分位数组相比患高TG低HDL C型血脂异常的危险显著增加 ,OR =10 94 ,P =0 0 2 5。 (4 )高TG和 (或 )低HDL C者合并高血糖的患病率亦较高 (P <0 0 0 1) ,但仅在CETP较高者中 ,高血糖患病率增加有显著性 (P <0 0 0 1)。结论　CETP     

Measuring thrombin generation based sensitivity to activated protein C using an automated coagulometer (ACL 9000)

Increased thrombin generation in the presence of activated protein C (APC) is known to be an independent risk factor for thrombosis. Although commercially available methods for measuring thrombin generation are available, none measure sensitivity to APC. We have developed an automated thrombin generation based APC sensitivity test, for use with defibrinated plasma using the automated coagulometer (ACL9000). A chromogenic substrate that is cleaved by thrombin at a slow rate, 7 pm tissue factor and 20 mum phospholipid (DOPC : DOPE : DOPS, 60 : 20 : 20) with and without 5 nm APC. Thrombin generation with [endogenous thrombin potential (ETP)(+APC)] and without APC (ETP), was expressed as a ratio relative to pooled normal plasma. Normal reference ranges were established in 30 normal subjects: ETP 0.73-1.06; ETP(+APC) 0.42-1.07. ETP(+APC) was found to be sensitive to factor V Leiden, oral contraceptive use, low levels of protein S and tissue factor pathway inhibitor and increased plasma factor VIII.     

Apoptosis in leukemia: from molecular pathways to targeted therapies

Knowledge about apoptosis pathways developed in the last few years is already being translated into novel targeted therapies. Two illustrative approaches to this process are the development of small molecule BCL2 inhibitors and X-linked inhibitors of apoptosis proteins (XIAP) inhibitors. This work demonstrates both the development of new agents based on molecular mechanisms and how these agents further our understanding of the biology of apoptosis.     

Early events in the folding of four-helix-bundle heme proteins

Topologically homologous four-helix-bundle heme proteins exhibit striking diversity in their refolding kinetics. Cytochrome b562 has been reported to fold on a sub-millisecond time scale, whereas cytochrome c' refolding requires 10 s or more to complete. Heme dissociation in cytochrome b562 interferes with studies of folding kinetics, so a variant of cytochrome b562 (cytochrome c-b562) with a covalent c-type linkage to the heme has been expressed in Escherichia coli. Early events in the electron transfer-triggered folding of Fe(II)-cytochrome c-b562, along with those of Fe(II)-cytochrome c556, have been examined by using time-resolved absorption spectroscopy. Coordination of S(Met) to Fe(II) occurs within 10 mus after reduction of the denatured Fe(III)-cytochromes, and shortly thereafter (100 micros) the heme spectra are indistinguishable from those of the folded proteins. Under denaturing conditions, carbon monoxide binds to the Fe(II)-hemes in approximately 15 ms. By contrast, CO binding cannot compete with refolding in the Fe(II)-cytochromes, thereby confirming that the polypeptide encapsulates the heme in <10 ms. We suggest that Fe-S(Met) ligation facilitates refolding in these four-helix-bundle heme proteins by reducing the conformational freedom of the polypeptide chain.