51
|
Abstract
The lipoprotein HDL has two important roles: first, it promotes reverse cholesterol transport, and second, it modulates inflammation. Epidemiological studies show that HDL-cholesterol levels are inversely correlated with the risk of cardiovascular events. However, many patients who experience a clinical event have normal, or even high, levels of HDL cholesterol. Measuring HDL-cholesterol levels provides information about the size of the HDL pool, but does not predict HDL composition or function. The main component of HDL, apolipoprotein A-I (apo A-I), is largely responsible for reverse cholesterol transport through the macrophage ATP-binding cassette transporter ABCA1. Apo A-I can be damaged by oxidative mechanisms, which render the protein less able to promote cholesterol efflux. HDL also contains a number of other proteins that are affected by the oxidative environment of the acute-phase response. Modification of the protein components of HDL can convert it from an anti-inflammatory to a proinflammatory particle. Small peptides that mimic some of the properties of apo A-I have been shown in preclinical models to improve HDL function and reduce atherosclerosis without altering HDL-cholesterol levels. Robust assays to evaluate the function of HDL are needed to supplement the measurement of HDL-cholesterol levels in the clinic.
Collapse
|
52
|
Vergeer M, Korporaal SJA, Franssen R, Meurs I, Out R, Hovingh GK, Hoekstra M, Sierts JA, Dallinga-Thie GM, Motazacker MM, Holleboom AG, Van Berkel TJC, Kastelein JJP, Van Eck M, Kuivenhoven JA. Genetic variant of the scavenger receptor BI in humans. N Engl J Med 2011; 364:136-45. [PMID: 21226579 DOI: 10.1056/nejmoa0907687] [Citation(s) in RCA: 257] [Impact Index Per Article: 19.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
BACKGROUND In mice, the scavenger receptor class B type I (SR-BI) is essential for the delivery of high-density lipoprotein (HDL) cholesterol to the liver and steroidogenic organs. Paradoxically, elevated HDL cholesterol levels are associated with increased atherosclerosis in SR-BI-knockout mice. It is unclear what role SR-BI plays in human metabolism. METHODS We sequenced the gene encoding SR-BI in persons with elevated HDL cholesterol levels and identified a family with a new missense mutation (P297S). The functional effects of the P297S mutation on HDL binding, cellular cholesterol uptake and efflux, atherosclerosis, platelet function, and adrenal function were studied. RESULTS Cholesterol uptake from HDL by primary murine hepatocytes that expressed mutant SR-BI was reduced to half of that of hepatocytes expressing wild-type SR-BI. Carriers of the P297S mutation had increased HDL cholesterol levels (70.4 mg per deciliter [1.8 mmol per liter], vs. 53.4 mg per deciliter [1.4 mmol per liter] in noncarriers; P<0.001) and a reduced capacity for efflux of cholesterol from macrophages, but the carotid artery intima-media thickness was similar in carriers and in family noncarriers. Platelets from carriers had increased unesterified cholesterol content and impaired function. In carriers, adrenal steroidogenesis was attenuated, as evidenced by decreased urinary excretion of sterol metabolites, a decreased response to corticotropin stimulation, and symptoms of diminished adrenal function. CONCLUSIONS We identified a family with a functional mutation in SR-BI. The mutation carriers had increased HDL cholesterol levels and a reduction in cholesterol efflux from macrophages but no significant increase in atherosclerosis. Reduced SR-BI function was associated with altered platelet function and decreased adrenal steroidogenesis. (Funded by the European Community and others.).
Collapse
Affiliation(s)
- Menno Vergeer
- Department of Vascular Medicine, Academic Medical Center, University of Amsterdam, Amsterdam, The Netherlands
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | |
Collapse
|
53
|
Modulators of Protein Kinase C Affect SR-BI-Dependent HDL Lipid Uptake in Transfected HepG2 Cells. CHOLESTEROL 2011; 2011:687939. [PMID: 21490774 PMCID: PMC3065880 DOI: 10.1155/2011/687939] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 08/30/2010] [Accepted: 12/02/2010] [Indexed: 11/17/2022]
Abstract
SR-BI is a cell surface HDL receptor that mediates selective uptake of the lipid cargo of HDL, an important process in hepatocytes, driving reverse cholesterol transport from cells in the artery wall. To facilitate examination of factors that modulate SR-BI activity in hepatocytes, we have generated fluorescent protein-tagged versions of SR-BI that allow for facile monitoring of SR-BI protein levels and distribution in transfected cells. We show that deletion of the C-terminal cytosolic tail does not affect the distribution of SR-BI in HepG2 cells, nor is the C-terminal cytosolic tail required for SR-BI-mediated uptake of HDL lipids. We also demonstrate that the phorbol ester, PMA, increased, while protein kinase C inhibitors reduced SR-BI-mediated HDL lipid uptake in HepG2 cells. These data suggest that protein kinase C may modulate selective uptake of HDL lipids including cholesterol in hepatocytes, thereby influencing hepatic HDL cholesterol clearance and reverse cholesterol transport.
Collapse
|
54
|
Syder AJ, Lee H, Zeisel MB, Grove J, Soulier E, Macdonald J, Chow S, Chang J, Baumert TF, McKeating JA, McKelvy J, Wong-Staal F. Small molecule scavenger receptor BI antagonists are potent HCV entry inhibitors. J Hepatol 2011; 54:48-55. [PMID: 20932595 DOI: 10.1016/j.jhep.2010.06.024] [Citation(s) in RCA: 108] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/07/2010] [Revised: 06/10/2010] [Accepted: 06/14/2010] [Indexed: 12/27/2022]
Abstract
BACKGROUND AND AIMS ITX 5061 is a clinical stage small molecule compound that promotes high-density lipoprotein (HDL) levels in animals and patients by targeting the scavenger receptor BI protein pathway. Since SR-BI is a known co-receptor for HCV infection, we evaluated these compounds for their effects on HCV entry. METHODS We obtained ITX 5061 and related compounds to characterize their interaction with SR-BI and effects on HCV entry and infection. RESULTS We confirmed that a tritium-labeled compound analog (ITX 7650) binds cells expressing SR-BI, and both ITX 5061 and ITX 7650 compete for HDL-mediated lipid transfer in an SR-BI dependent manner. Both molecules inhibit HCVcc and HCVpp infection of primary human hepatocytes and/or human hepatoma cell lines and have minimal effects on HCV RNA replication. Kinetic studies suggest that the compounds act at an early post-binding step. CONCLUSIONS These results suggest that the ITX compounds inhibit HCV infection with a mechanism of action distinct from other HCV therapies under development. Since ITX 5061 has already been evaluated in over 280 patients with good pharmacokinetic and safety profiles, it warrants proof-of-concept clinical studies in HCV infected patients.
Collapse
Affiliation(s)
- Andrew J Syder
- iTherX Pharmaceuticals, Inc., San Diego, CA 92191-0530, USA
| | | | | | | | | | | | | | | | | | | | | | | |
Collapse
|
55
|
Tencate V, Sainz B, Cotler SJ, Uprichard SL. Potential treatment options and future research to increase hepatitis C virus treatment response rate. Hepat Med 2010; 2010:125-145. [PMID: 21331152 PMCID: PMC3039485 DOI: 10.2147/hmer.s7193] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
Hepatitis C virus (HCV) is a liver-tropic blood-borne pathogen that affects more than 170 million people worldwide. Although acute infections are usually asymptomatic, up to 90% of HCV infections persist with the possibility of long-term consequences such as liver fibrosis, cirrhosis, steatosis, insulin resistance, or hepatocellular carcinoma. As such, HCV-associated liver disease is a major public health concern. Although the currently available standard of care therapy of pegylated interferon α plus ribavirin successfully treats infection in a subset of patients, the development of more effective, less toxic HCV antivirals is a health care imperative. This review not only discusses the limitations of the current HCV standard of care but also evaluates upcoming HCV treatment options and how current research elucidating the viral life cycle is facilitating the development of HCV-specific therapeutics that promise to greatly improve treatment response rates both before and after liver transplantation.
Collapse
Affiliation(s)
- Veronica Tencate
- Department of Medicine, Section of Hepatology, University of Illinois at Chicago, Chicago, IL, USA
| | | | | | | |
Collapse
|
56
|
Baldick CJ, Wichroski MJ, Pendri A, Walsh AW, Fang J, Mazzucco CE, Pokornowski KA, Rose RE, Eggers BJ, Hsu M, Zhai W, Zhai G, Gerritz SW, Poss MA, Meanwell NA, Cockett MI, Tenney DJ. A novel small molecule inhibitor of hepatitis C virus entry. PLoS Pathog 2010; 6:e1001086. [PMID: 20838466 PMCID: PMC2936744 DOI: 10.1371/journal.ppat.1001086] [Citation(s) in RCA: 72] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/25/2010] [Accepted: 08/03/2010] [Indexed: 12/25/2022] Open
Abstract
Small molecule inhibitors of hepatitis C virus (HCV) are being developed to complement or replace treatments with pegylated interferons and ribavirin, which have poor response rates and significant side effects. Resistance to these inhibitors emerges rapidly in the clinic, suggesting that successful therapy will involve combination therapy with multiple inhibitors of different targets. The entry process of HCV into hepatocytes represents another series of potential targets for therapeutic intervention, involving viral structural proteins that have not been extensively explored due to experimental limitations. To discover HCV entry inhibitors, we utilized HCV pseudoparticles (HCVpp) incorporating E1-E2 envelope proteins from a genotype 1b clinical isolate. Screening of a small molecule library identified a potent HCV-specific triazine inhibitor, EI-1. A series of HCVpp with E1-E2 sequences from various HCV isolates was used to show activity against all genotype 1a and 1b HCVpp tested, with median EC50 values of 0.134 and 0.027 µM, respectively. Time-of-addition experiments demonstrated a block in HCVpp entry, downstream of initial attachment to the cell surface, and prior to or concomitant with bafilomycin inhibition of endosomal acidification. EI-1 was equally active against cell-culture adapted HCV (HCVcc), blocking both cell-free entry and cell-to-cell transmission of virus. HCVcc with high-level resistance to EI-1 was selected by sequential passage in the presence of inhibitor, and resistance was shown to be conferred by changes to residue 719 in the carboxy-terminal transmembrane anchor region of E2, implicating this envelope protein in EI-1 susceptibility. Combinations of EI-1 with interferon, or inhibitors of NS3 or NS5A, resulted in additive to synergistic activity. These results suggest that inhibitors of HCV entry could be added to replication inhibitors and interferons already in development.
Collapse
Affiliation(s)
- Carl J Baldick
- Bristol-Myers Squibb, Research and Development, Wallingford, Connecticut, United States of America.
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | |
Collapse
|
57
|
Wong-Staal F, Syder AJ, McKelvy JF. Targeting HCV entry for development of therapeutics. Viruses 2010; 2:1718-1733. [PMID: 21994703 PMCID: PMC3185726 DOI: 10.3390/v2081718] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/28/2010] [Revised: 08/05/2010] [Accepted: 08/16/2010] [Indexed: 01/11/2023] Open
Abstract
Recent progress in defining the molecular mechanisms of Hepatitis C Virus (HCV) entry affords the opportunity to exploit new viral and host targets for therapeutic intervention. Entry inhibitors would limit the expansion of the infected cell reservoir, and would complement the many replication inhibitors now under development. The current model for the pathway of entry involves the initial docking of the virus onto the cell surface through interactions of virion envelope and associated low density lipoproteins (LDL) with cell surface glycosaminoglycans and lipoprotein receptors, followed by more specific utilization with other hepatocyte membrane proteins: Scavenger Receptor Class B type 1 (SR-BI), CD81, Claudin 1 (CLDN1) and Occludin (OCLN). The use of blockers of these interactions, e.g. specific antibodies, suggests that inhibition of any one step in the entry pathway can inhibit infection. Despite this knowledge base, the tools for compound screening, HCV pseudoparticles (HCVpp) and cell culture virus (HCVcc), and the ability to adapt them to industrial use are only recently available and as a result drug discovery initiatives are in their infancy. Several therapies aiming at modulating the virus envelope to prevent host cell binding are in early clinical testing. The first test case for blocking a cellular co-receptor is an SR-BI modulator. ITX 5061, an orally active small molecule, targets SR-BI and has shown potent antiviral activity against HCVpp and HCVcc. ITX 5061 has exhibited good safety in previous clinical studies, and is being evaluated in the clinic in chronic HCV patients and patients undergoing liver transplantation. Entry inhibitors promise to be valuable players in the future development of curative therapy against HCV.
Collapse
Affiliation(s)
- Flossie Wong-Staal
- Author to whom correspondence should be addressed; E-Mail: ; Tel.: +1-858-824-1114; Fax: +1-858-824-1112
| | | | | |
Collapse
|
58
|
Fazio S, Linton MF. High-density lipoprotein therapeutics and cardiovascular prevention. J Clin Lipidol 2010; 4:411-9. [PMID: 21122685 DOI: 10.1016/j.jacl.2010.08.004] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2010] [Accepted: 08/07/2010] [Indexed: 01/30/2023]
Abstract
The field of cardiovascular prevention has long anticipated the evolution of high-density lipoprotein (HDL) therapy from unproven metabolic tweaking to pillar of risk reduction on par with low-density lipoprotein control. However, the convincing epidemiologic data linking HDL cholesterol (HDL-C) and cardiovascular disease risk in an inverse correlation has not yet translated into clinical trial evidence supporting linearity between HDL-C increases and risk reduction, or identifying obvious goals of therapy. Although HDL-C-increasing lifestyle maneuvers and established HDL drugs such as niacin and fibrates are likely to protect the vasculature, the negative results obtained in trials of a cholesteryl ester transfer protein inhibitor remind us that HDL-C increases are not always beneficial. It is becoming clear that a functional HDL is a more desirable target than simply increasing HDL-C levels. The larger objective of improving HDL functionality (with or without HDL-C level changes) is bound to become the guiding principle for pharmaceutical research in this area. Several new compounds currently being tested bridge the classical aim of increasing HDL-C levels with the novel target of improving HDL function.
Collapse
Affiliation(s)
- Sergio Fazio
- Division of Cardiovascular Medicine, Vanderbilt University Medical Center, Atherosclerosis Research Unit, 383 PRB-2220 Pierce Avenue, Nashville, TN 37232-6300, USA.
| | | |
Collapse
|
59
|
Uprichard SL. Hepatitis C virus experimental model systems and antiviral drug research. Virol Sin 2010; 25:227-45. [PMID: 20960298 DOI: 10.1007/s12250-010-3134-0] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/17/2010] [Accepted: 04/18/2010] [Indexed: 12/27/2022] Open
Abstract
An estimated 130 million people worldwide are chronically infected with hepatitis C virus (HCV) making it a leading cause of liver disease worldwide. Because the currently available therapy of pegylated interferon-alpha and ribavirin is only effective in a subset of patients, the development of new HCV antivirals is a healthcare imperative. This review discusses the experimental models available for HCV antiviral drug research, recent advances in HCV antiviral drug development, as well as active research being pursued to facilitate development of new HCV-specific therapeutics.
Collapse
Affiliation(s)
- Susan L Uprichard
- Department of Medicine, University of Illinois at Chicago, Chicago, IL 60612, USA.
| |
Collapse
|
60
|
Motazacker MM, Kastelein JJ, Kuivenhoven JA. Are high-density lipoprotein genes and their products targets for therapy? Curr Opin Lipidol 2010; 21:157-8. [PMID: 20616629 DOI: 10.1097/mol.0b013e3283376923] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
|
61
|
Delang L, Coelmont L, Neyts J. Antiviral therapy for hepatitis C virus: beyond the standard of care. Viruses 2010; 2:826-866. [PMID: 21994657 PMCID: PMC3185663 DOI: 10.3390/v2040826] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2009] [Revised: 03/09/2010] [Accepted: 03/17/2010] [Indexed: 02/06/2023] Open
Abstract
Hepatitis C virus (HCV) represents a major health burden, with an estimated 180 million chronically infected individuals worldwide. These patients are at increased risk of developing liver cirrhosis and hepatocellular carcinoma. Infection with HCV is the leading cause of liver transplantation in the Western world. Currently, the standard of care (SoC) consists of pegylated interferon alpha (pegIFN-α) and ribavirin (RBV). However this therapy has a limited efficacy and is associated with serious side effects. Therefore more tolerable, highly potent inhibitors of HCV replication are urgently needed. Both Specifically Targeted Antiviral Therapy for HCV (STAT-C) and inhibitors that are believed to interfere with the host-viral interaction are discussed.
Collapse
Affiliation(s)
| | | | - Johan Neyts
- Rega Institute for Medical Research, KULeuven, Minderbroedersstraat 10, 3000 Leuven, Belgium; E-Mails: (L.D.); (L.C.)
| |
Collapse
|