Lipoproteins and the endothelium: insights from clinical research

Elevated plasma levels of atherogenic lipoproteins such as low-density lipoprotein (LDL) and remnant lipoproteins and low levels of HDL cholesterol constitute major risk factors for the development of atherothrombotic disease. In addition to their role in the initiation and propagation of atherosclerosis, hyperlipidemia also causes endothelial dysfunction. In addition, hyperlipidemia has an influence on thrombosis by modulating levels of prothrombotic and fibrinolytic factors, thus promoting the final step in the atherosclerotic process, vascular occlusion. In the last 5 years, randomized, prospective, placebo-controlled studies aimed at reducing plasma levels of atherogenic lipoproteins have demonstrated a significant effect on cardiovascular morbidity and all-cause mortality in both primary and secondary prevention. Although the mechanisms underlying the clinical benefit of lipid-lowering therapy remain uncertain, the lowering of lipids has been associated with improved endothelial function and a less thrombotic state, two factors that could play a role in the benefit of lipid lowering. This review focuses on recent clinical research related to the impact of lipoproteins and lipid-lowering therapy on endothelial function and plasma levels of prothrombotic and fibrinolytic factors.     

The endothelium and lipoproteins: insights from recent cell biology and animal studies

Both lipoproteins and the endothelium play critical roles in the initiation and progression of atherosclerosis. An understanding of the interactions between lipoproteins and the endothelium facilitates our understanding of atherogenesis and could suggest new therapeutic targets. Lipoproteins have important effects on endothelial cells. Atherogenic lipoproteins such as remnants, low-density lipoprotein (LDL), and oxidized LDL act on endothelial cells to cause upregulation of endothelial adhesion molecules and selectins, promotion of oxygen radicals, increased apoptosis, and reduced endothelium-dependent relaxation. Antiatherogenic lipoproteins such as HDL protect endothelial cells from oxidative stress and apoptosis and reduce adhesion molecule expression. Conversely, the endothelium has major effects on lipoprotein metabolism and function. Several lipases, including lipoprotein lipase, hepatic lipase, endothelial lipase, and secretory phospholipase A2, are bound to the endothelial cell matrix and have the ability to hydrolyze lipoprotein triglycerides and phospholipids. Furthermore, endothelial cells express a variety of lipoprotein receptors including the VLDL receptor, scavenger receptor A, SR-BI, CD36, and LOX-1, although little is known about their function on endothelial cells. Although a great deal is known about endothelial-lipoprotein interactions, more research is needed in this important area.     

Effect of adrenomedullin on the cerebral circulation: relevance to primary headache disorders

Adrenomedullin (ADM) is closely related to calcitonin gene-related peptide, which has a known causative role in migraine. Animal studies have strongly suggested that ADM has a vasodilatory effect within the cerebral circulation. For these reasons, ADM is also likely to be involved in migraine. However, the hypothetical migraine-inducing property and effect on human cerebral circulation of ADM have not previously been investigated. Human ADM (0.08 µg kg⁻¹ min⁻¹) or placebo (saline 0.9%) was administered as a 20-min intravenous infusion to 12 patients suffering from migraine without aura in a crossover double-blind study. The occurrence of headache and associated symptoms were registered regularly 24 h post infusion. Cerebral blood flow (CBF) was measured by ¹³³Xenon single-photon emission computed tomography, mean blood flow velocity in the middle cerebral artery (V_MCA) by transcranial Doppler and the diameter of peripheral arteries by transdermal ultrasound (C-scan). ADM did not induce significantly more headache or migraine compared with placebo ( P  = 0.58). CBF was unaffected by ADM infusion (global CBF, P  = 0.32 and rCBF_MCA, P  = 0.38) and the same applied for the V_MCA ( P  = 0.18). The superficial temporal artery dilated compared with placebo ( P  < 0.001), and facial flushing was seen after ADM administration ( P  = 0.001). In conclusion, intravenous ADM is not a mediator of migraine headache and does not dilate intracranial arteries.     

Changes in adiponectin multimer distribution in response to atorvastatin treatment in patients with type 2 diabetes

Objective  Multimeric high molecular weight (HMW) forms of adiponectin were previously shown to be inversely associated with the extent of atherosclerosis in males and are down-regulated in patients with the metabolic syndrome and type 2 diabetes. In this study, potential influences of atorvastatin therapy on adiponectin multimer distribution were studied in patients with type 2 diabetes.
Design, patients and measurements  The effect of 40 mg atorvastatin on HMW, medium molecular weight (MMW), and low molecular weight (LMW) isoforms of adiponectin were investigated in 75 patients (23 females; 52 males) with type 2 diabetes in an 8-week-long, placebo-controlled and randomized study. Adiponectin multimeric isoforms were detected by Western blot analysis.
Results  After atorvastatin therapy the median serum concentration of HMW adiponectin increased significantly by 42·3% (1·68 vs. 2·39 µg/ml; P  < 0·001), while concentrations of MMW adiponectin and LMW adiponectin significantly decreased by 20·8% and 23·2%, respectively (MMW: 3·31 vs. 2·62 µg/ml, P  = 0·047; LMW: 0·56 vs. 0·43 µg/ml, P  = 0·033). Median total adiponectin levels were not significantly altered by atorvastatin treatment (6·0 vs. 6·2 µg/ml, P  = 0·898). Consequently, the HMW : total-adiponectin ratio significantly increased by 25·0% (0·40 vs. 0·50; P  = 0·013).
Conclusions  Atorvastatin therapy is associated with significant changes in adiponectin multimer distribution in patients with type 2 diabetes. Since total adiponectin levels were not affected by intervention, atorvastatin may shift adiponectin size towards the HMW form.     

六味五灵片联合替比夫定治疗活动性慢性乙型肝炎肝硬化临床疗效观察

目的观察六味五灵片联合替比夫定治疗活动性慢性乙型肝炎（CHB）肝硬化的临床疗效。方法将72例HBV DNA、HBeAg阳性的CHB肝硬化患者随机分为治疗组和对照组,两组均为36例。治疗组给予六味五灵片联合替比夫定治疗,对照组单用替比夫定治疗,疗程均为24周。治疗前后分别检测患者肝功能、慢性HBV标志物、HBV DNA低于检测下限的比率。结果治疗组血清ALT、AST下降明显,与对照组比较,差异有统计学意义（P〈0.05）,治疗组HBeAg低于检测下限的比率及HBeAg/抗-HBe血清转换率均高于对照组,治疗组总有效率高于对照组,差异有统计学意义（P〈0.05）。结论六味五灵片联合替比夫定治疗活动性CHB肝硬化疗效显著,不良反应发生率小,疗效优于单一用药组,是治疗活动性CHB肝硬化的有效方法。     

Reduction of serum matrix metalloproteinase 1 and matrix metalloproteinase 3 in rheumatoid arthritis patients following anti- tumour necrosis factor-alpha (cA2) therapy

Matrix metalloproteinase (MMP)-1 and MMP-3 levels were measured in serum samples from rheumatoid arthritis (RA) patients undergoing a double-blinded placebo-controlled trial with the chimaeric anti-tumour necrosis factor (TNF)-alpha antibody cA2. Both MMP-1 (P < 0.015), but to a larger extent MMP-3 (P < 0.001) levels were elevated in all RA patients prior to the commencement of the trial compared with normal control sera. Following cA2 therapy, MMP-1 and MMP-3 levels were assessed in the placebo, and 1 and 10 mg/kg cA2-treated groups at 7, 14, 21 and 28 days. In both the 1 and the 10 mg/kg cA2-treated groups, a significant decrease in serum MMP-3 levels at all time points was observed, reducing maximally to 41% of pre-infusion values at day 7. MMP-1 levels were also reduced, but less dramatically than MMP-3, to 85% of pre-infusion values after 14 days in the 10 mg/kg cA2 treated group. In a separate non-placebo-controlled study, we also evaluated the tissue inhibitor of metalloproteinase (TIMP)-1 levels in plasma following cA2 infusion. Pre-infusion TIMP-1 levels were above the normal control range, but were significantly reduced (P < 0.035) 14 days after infusion to 72% of pre-infusion values. This study confirms previous reports that MMP-3 levels are elevated and correlate with measures of inflammation in RA, and furthermore demonstrate that serum MMP-3 and MMP-1 levels are downmodulated following anti-TNF-alpha antibody therapy. Whilst serum MMP-3 levels correlated with C-reactive protein (CRP) both prior to and following anti-TNF-alpha antibody therapy, it remains to be demonstrated that serum MMP-3 and/or MMP-1 levels reflect the cartilage and bone resorptive processes which are evident in this disease.      

Systemic lupus erythematosus, thrombocytopenia, microangiopathic haemolytic anaemia and anti-CD36 antibodies [clinical conference]

Thrombocytopenia in patients with acute systemic lupus erythematosus (SLE) frequently presents the clinician with considerable diagnostic and therapeutic difficulties. In this Grand Round, we present a 48-yr- old woman with a 7 yr history of lupus, who presented with acute proliferative glomerulonephritis and nephrotic syndrome, pneumonia, profound hypocomplementaemia and a severe microangiopathic haemolytic anaemia with associated thrombocytopenia. Her thrombocytopenia proved initially refractory to conventional immunosuppressive therapy, and corticosteroids, and resolved only with plasma exchange and repeated fresh frozen plasma infusions. Serological testing revealed high-titre antinuclear antibodies (ANA) and markedly raised antibodies to double- stranded (ds) DNA, but no significant elevation in anticardiolipin antibodies. Platelet-associated IgG and IgM and antibodies to the CD36 glycoprotein antigen, expressed on platelets and endothelium, were detected in the serum. We address some of the difficult diagnostic and management issues raised by this complex patient and the possible immunopathological links between antibodies to CD36, immune-mediated red cell destruction, thrombocytopenia and thrombotic microangiopathic haemolytic anaemia.      

Recombinant rat stem cell factor synergizes with recombinant human granulocyte colony-stimulating factor in vivo in mice to mobilize peripheral blood progenitor cells that have enhanced repopulating potential

Splenectomized mice treated for 7 days with pegylated recombinant rat stem cell factor (rrSCF-PEG) showed a dose-dependent increase in peripheral blood progenitor cells (PBPC) that have enhanced in vivo repopulating potential. A dose of rrSCF-PEG at 25 micrograms/kg/d for 7 days produced no significant increase in PBPC. However, when this dose of rrSCF-PEG was combined with an optimal dose of recombinant human granulocyte colony-stimulating factor (rhG-CSF; 200 micrograms/kg/d), a synergistic increase in PBPC was observed. Compared with treatment with rhG-CSF alone, the combination of rrSCF-PEG plus rhG-CSF resulted in a synergistic increase in peripheral white blood cells, in the incidence and absolute numbers of PBPC, and in the incidence and absolute numbers of circulating cells with in vivo repopulating potential. These data suggest that low doses of SCF, which would have minimal, if any, effects in vivo, can synergize with optimal doses of rhG-CSF to enhance the mobilization of PBPC stimulated by rhG-CSF alone.     

Transfected leukocyte integrin CD11b/CD18 (Mac-1) mediates phorbol ester-activated, homotypic cell:cell adherence in the K562 cell line

The CD11b/CD18 leukocyte integrin molecule mediates diverse neutrophil adherence-related functions, including cell:cell and cell:extracellular matrix attachments. To study the individual role of this leukocyte integrin in cell adherence in hematopoietic cells, we expressed the CD11b/CD18 complex on the surface of K562 cells, a cell line derived from an individual with chronic myelogenous leukemia in blast crisis. We used an amphotrophic retroviral vector designated LCD18SN, harboring the complete coding sequence for the CD18 subunit, to transfer the CD18 cDNA into K562 cells and select stable cell lines. The CD11b subunit in the expression plasmid pREP4 was transfected into these K562/CD18 cells by electroporation and stable cell clones were selected. These K562 cells possessed RNA and intracellular protein for each subunit, and they expressed the CD11b/CD18 heterodimer on the cell surface. When CD11b/CD18 expressing K562 cells were stimulated with phorbol myristate acetate (50 ng/mL) for 24 to 48 hours, these K562 cells formed dense cell:cell aggregates. This homotypic aggregation required both activation of the CD11b/CD18 complex and the induction of the counter- receptor for CD11b/CD18 on the conjugate cell. This cell line will (1) enable the structure-function relationships between cell activation and homotypic adherence to be assessed, (2) provide the opportunity to identify accessory molecules required for activation of the CD11b/CD18 complex, and (3) facilitate the identification of novel ligands for the CD11b/CD18 complex.