Therapeutic Potential of Modulating microRNAs in Atherosclerotic Vascular Disease

Atherosclerosis (also known as arteriosclerotic vascular disease) is a chronic inflammatory disease of the arterial wall, characterized by the formation of lipid-laden lesions. The activation of endothelial cells at atherosclerotic lesion-prone sites in the arterial tree results in the up-regulation of cell adhesion molecules and chemokines, which mediate the recruitment of circulating monocytes. Accumulation of monocytes and monocyte-derived phagocytes in the wall of large arteries leads to chronic inflammation and the development and progression of atherosclerosis. The lesion experiences the following steps: foam cell formation, fatty streak accumulation, migration and proliferation of vascular smooth muscle cells, and fibrous cap formation. Finally, the rupture of the unstable fibrous cap causes thrombosis in complications of advanced lesions that lead to unstable coronary syndromes, myocardial infarction and stroke. MicroRNAs have recently emerged as a novel class of gene regulators at the post-transcriptional level. Several functions of vascular cells, such as cell differentiation, contraction, migration, proliferation and inflammation that are involved in angiogenesis, neointimal formation and lipid metabolism underlying various vascular diseases, have been found to be regulated by microRNAs and are described in the present review as well as their potential therapeutic application.

Malaria in a Liver Transplant Recipient: A Case Report

Malaria is an exotic complication in liver transplants patients. It can be acquired either by transfusion of blood products or through the transplanted organ. Infections caused by Plasmodium spp are unusual in liver transplants; to date, only four cases have been reported in the literature. Herein we have presented a case of Plasmodium vivax in a liver transplant patient. This diagnosis must be excluded in febrile transplant patients in endemic areas, especially during the first 2 months. An epidemiological history relevant for malaria both in the donor and in the recipient must be routinely included with screening tests.

Aplidin® induces JNK-dependent apoptosis in human breast cancer cells via alteration of glutathione homeostasis, Rac1 GTPase activation, and MKP-1 phosphatase downregulation

Aplidin is an antitumor agent in phase II clinical trials that induces apoptosis through the sustained activation of Jun N-terminal kinase (JNK). We report that Aplidin alters glutathione homeostasis increasing the ratio of oxidized to reduced forms (GSSG/GSH). Aplidin generates reactive oxygen species and disrupts the mitochondrial membrane potential. Exogenous GSH inhibits these effects and also JNK activation and cell death. We found two mechanisms by which Aplidin activates JNK: rapid activation of Rac1 small GTPase and downregulation of MKP-1 phosphatase. Rac1 activation was diminished by GSH and enhanced by L-buthionine (SR)-sulfoximine, which inhibits GSH synthesis. Downregulation of Rac1 by transfection of small interfering RNA (siRNA) duplexes or the use of a specific Rac1 inhibitor decreased Aplidin-induced JNK activation and cytotoxicity. Our results show that Aplidin induces apoptosis by increasing the GSSG/GSH ratio, a necessary step for induction of oxidative stress and sustained JNK activation through Rac1 activation and MKP-1 downregulation.

High amino acid variability within the NS5A of hepatitis C virus (HCV) is associated with hepatocellular carcinoma in patients with HCV-1b-related cirrhosis

Interferon therapy may decrease the risk of hepatocellular carcinoma in patients with hepatitis C virus (HCV)-related liver cirrhosis. Interaction of the cellular protein kinase PKR with the PKR-binding domain (PKR-bd) of HCV-NS5A protein may affect cellular growth control and viral resistance to interferon therapy. Mutations within the PKR-bd, which comprises the interferon sensitivity determining region (ISDR), have been associated with interferon sensitivity. To determine whether or not there is an association between HCV heterogeneity and the presence of hepatocellular carcinoma, HCV-1b genomic regions were amplified and directly sequenced from serum samples obtained from 82 patients with liver cirrhosis, 53 with, and 29 without hepatocellular carcinoma. None of them had received antiviral therapy. When compared with the deduced consensus sequence, the median number of amino acid changes in the PKR-bd was higher among samples from patients with (4.22) than from those without hepatocellular carcinoma (1.62; P <.001), and isolates with 3 or more amino acid changes were significantly more common among the former (60%) than among the later (6%, P <.001). No such differences were observed in other viral regions, including Core, E2-HVR-1, E2-PePHD, NS3, and the 5' and 3' PKR-bd flanking regions. In addition, amino acid variation in viral regions other than HVR-1 did not accumulate over time in the analyzed sequential serum samples obtained from patients with or without hepatocellular carcinoma. Therefore, a mutated HCV-PKR-bd phenotype is very common in cirrhotic patients with hepatocellular carcinoma.

Dose-dependent effects of lovastatin on cell cycle progression. Distinct requirement of cholesterol and non-sterol mevalonate derivatives

The mevalonate pathway is tightly linked to cell proliferation. The aim of the present study is to determine the relationship between the inhibition of this pathway by lovastatin and the cell cycle. HL-60 and MOLT-4 human cell lines were cultured in a cholesterol-free medium and treated with increasing concentrations of lovastatin, and their effects on cell proliferation and the cell cycle were analyzed. Lovastatin was much more efficient in inhibiting cholesterol biosynthesis than protein prenylation. As a result of this, lovastatin blocked cell proliferation at any concentration used, but its effects on cell cycle distribution varied. At relatively low lovastatin concentrations (less than 10 microM), cells accumulated preferentially in G(2) phase, an effect which was both prevented and reversed by low-density lipoprotein cholesterol. At higher concentrations (50 microM), the cell cycle was also arrested at G(1) phase. In cells treated with lovastatin, those arrested at G(1) progressed through S upon mevalonate provision, whereas cholesterol supply allowed cells arrested at G(2) to traverse M phase. These results demonstrate the distinct roles of mevalonate, or its non-sterol derivatives, and cholesterol in cell cycle progression, both being required for normal cell cycling.

Hydroxymethylglutaryl-coenzyme A reductase inhibition stimulates caspase-1 activity and Th1-cytokine release in peripheral blood mononuclear cells

T cells are prominent components of both early and late atherosclerotic lesions and the role of Th1/Th2 cells subsets in the evolution and rupture of the plaque is currently under investigation. Statins, which are inhibitors of 3-hydroxy-3-methylglutaryl CoA (HMG-CoA) reductase, exert actions beyond that of simply lowering cholesterol levels, and some effects on immune function have been reported. We studied in vitro the effects of fluvastatin on Th1/Th2 cytokine release in relation to caspase-1 activation, in human peripheral-blood mononuclear cells (PBMC) stimulated or not with Mycobacterium tuberculosis. Fluvastatin treatment resulted in the activation of caspase-1 and in a small secretion of interleukin (IL)-1beta, IL-18, and IFNgamma (Th1). In the presence of bacteria, the release of these cytokines was highly increased by the statin in a synergistic way. By contrast, production of IL-12, IL-10 and IL-4 were unaffected by the statin. Not only did mevalonate abolish the effects of the statin but it also prevented the caspase-1 activation induced by the bacteria, suggesting the involvement of isoprenoids in the response to M. tuberculosis. It is proposed that inhibition of HMG-CoA reductase may be immunoprotective by enhancing the Th1 response, which has therapeutical potential not only in atherosclerosis but also in infectious diseases.

Cholesterol starvation decreases p34(cdc2) kinase activity and arrests the cell cycle at G2

As a major component of mammalian cell plasma membranes, cholesterol is essential for cell growth. Accordingly, the restriction of cholesterol provision has been shown to result in cell proliferation inhibition. We explored the potential regulatory role of cholesterol on cell cycle progression. MOLT-4 and HL-60 cell lines were cultured in a cholesterol-deficient medium and simultaneously exposed to SKF 104976, which is a specific inhibitor of lanosterol 14-alpha demethylase. Through HPLC analyses with on-line radioactivity detection, we found that SKF 104976 efficiently blocked the [(14)C]-acetate incorporation into cholesterol, resulting in an accumulation of lanosterol and dihydrolanosterol, without affecting the synthesis of mevalonic acid. The inhibitor also produced a rapid and intense inhibition of cell proliferation (IC(50) = 0.1 microM), as assessed by both [(3)H]-thymidine incorporation into DNA and cell counting. Flow cytometry and morphological examination showed that treatment with SKF 104976 for 48 h or longer resulted in the accumulation of cells specifically at G2 phase, whereas both the G1 traversal and the transition through S were unaffected. The G2 arrest was accompanied by an increase in the hyperphosphorylated form of p34(cdc2) and a reduction of its activity, as determined by assaying the H1 histone phosphorylating activity of p34(cdc2) immunoprecipitates. The persistent deficiency of cholesterol induced apoptosis. However, supplementing the medium with cholesterol, either in the form of LDL or free cholesterol dissolved in ethanol, completely abolished these effects, whereas mevalonate was ineffective. Caffeine, which abrogates the G2 checkpoint by preventing p34(cdc2) phosphorylation, reduced the accumulation in G2 when added to cultures containing cells on transit to G2, but was ineffective in cells arrested at G2 by sustained cholesterol starvation. Cells arrested in G2, however, were still viable and responded to cholesterol provision by activating p34(cdc2) and resuming the cell cycle. We conclude that in both lymphoblastoid and promyelocytic cells, cholesterol availability governs the G2 traversal, probably by affecting p34(cdc2) activity.

Impact of different low-density lipoprotein (LDL) receptor mutations on the ability of LDL to support lymphocyte proliferation

Based on the demand for cholesterol for membrane formation, we determined the ability of low-density lipoprotein (LDL) to support proliferation in lymphocytes bearing different LDL receptor mutations, which were treated "in vitro" with lovastatin to inhibit endogenous cholesterol synthesis. Peripheral lymphocytes were isolated from two patients with homozygous familial hypercholesterolemia (FH), one homozygote for the mutation N804K (FH(Colmenar)) in exon 17, herein described for the first time, and a compound heterozygote carrying the mutations D280G and G528V, which determine a transport-defective biochemical phenotype. Flow cytometric analysis with 1,1'-dioctadecyl-3,3,3,3'-tetramethylindocarbocyanineperchlorate (Dil)-LDL showed normal LDL binding but defective internalization in lymphocytes from case 1, whereas in lymphocytes from case 2 both LDL binding and internalization were affected. Studies with mitogen-stimulated lymphocytes demonstrated that despite the different phenotype, the ability of LDL to support proliferation was impaired in both cases to a similar extent. These results indicate that internalization of the LDL particle is required for expression of the mitogenic effect of LDL.

Induction of apoptosis in p53-null HL-60 cells by inhibition of lanosterol 14-alpha demethylase

To determine the role of cholesterol deprivation in cell proliferation and, eventually, in apoptosis, HL-60 promyelocytic cells were incubated in a cholesterol-depleted medium in the presence of SKF 104976, a specific inhibitor of lanosterol 14-alpha demethylase. As expected, SKF 104976 efficiently blocked the [14C]-acetate incorporation into cholesterol, whereas it induced the accumulation of both lanosterol and, especially, dihydrolanosterol. As a consequence, cell proliferation was greatly depressed at 24 h of treatment with the drug, and clear signs of apoptosis--annexin V binding, condensed and fragmented nuclei and DNA ladder--were observed thereafter. Provided that the HL-60 cell line does not express p53, it may be concluded that apoptosis induced by cholesterol deprivation is not dependent on this tumor suppressor protein. Supplementing the incubation medium with LDL-cholesterol or pure free cholesterol, fully prevented cell growth inhibition and apoptosis induction, whereas mevalonate was ineffective. These results indicate that cholesterol plays a specific role in cell proliferation, a function that is not shared by its precursors lanosterol and dihydrolanosterol.

Human CD36 is a high affinity receptor for the native lipoproteins HDL, LDL, and VLDL

Mouse and hamster SR-BI glycoproteins and their putative human counterpart CLA-I are so far the only scavenger receptors known to bind both native and modified lipoproteins. CD36, a multigland glycoprotein structurally related to SR-BI and CLA-1, has been reported to bind oxidized low density lipoprotein (OxLDL) and acetylated LDL (AcLDL). In this report, we have studied the ability of CD36 to bind native lipoproteins. By transient expression of human CD36 in mammalian and insect cells, we demonstrate that CD36 is a high affinity receptor for the native lipoproteins HDL, LDL, VLDL, and, as previously reported, for OxLDL and AcLDL. The specificity of these interactions is supported by the dose-dependent inhibiton, effect of a monoclonal antibody against CD36. Furthermore, at least for HDL, binding to CD36 does not require the presence of apoE. These findings, together with preferential expression of CD36 in tissues performing very active fatty acid metabolism (skeletal muscle, heart, mammary epithelium, and adipose tissue) and its involvement in foam cell formation (macrophages), suggest that binding of lipoproteins to CD36 might contribute to the regulation of lipid metabolism, and to the pathogenesis of atherosclerosis.