Carriage of the apolipoprotein E-epsilon4 allele and histologic outcome of recurrent hepatitis C after antiviral treatment

Putative Survival Advantages in Young Apolipoprotein ɛ4 Carriers are Associated with Increased Neural Stress

Inheritance of a single copy of the apolipoprotein E (APOE) ɛ4 allele increases risk of Alzheimer’s disease (AD) by 3-4-fold, with homozygosity associated with a 12-16-fold increase in risk, relative to ɛ3 allele homozygosity. There is a decreased risk associated with the APOE ɛ2 allele. The pathological consequence of APOE genotype has led to intense efforts to understand the mechanistic basis of the interplay between APOE status and loss of synapses. Numerous ɛ4 allele-related associations have been reported with the potential relevance of these associations to the pathogenesis of AD unknown at this time. In primarily young subjects, we have reviewed a representative body of literature on ɛ4 allele-associations related to the following: cardiovascular responses; impacts on reproduction and fetal development; co-morbidities; resistance to infectious disease; responses to head injury; biochemical differences possibly related to neural stress; and brain structure-function differences. In addition, the literature on the association between the ɛ4 allele and cognitive performance has been reviewed comprehensively. The weight-of-the-evidence supports the hypothesis that possession of the ancestral ɛ4 allele in youth is associated with improved fitness during fetal development, infancy, and youth relative to the more recently appearing ɛ3 allele, at the expense of decreased fitness in old age, which is substantially improved by the ɛ3 allele. However, possession of the ɛ4 allele is also associated with higher levels of synaptic macromolecular turnover, which likely stresses basic cellular neuroplasticity mechanisms. Clinical trials of potential AD therapeutics should consider APOE status as an enrollment criterion.

Beyond the CNS: The many peripheral roles of APOE

Apolipoprotein E (APOE) is a multifunctional protein synthesized and secreted by multiple mammalian tissues. Although hepatocytes contribute about 75% of the peripheral pool, APOE can also be expressed in adipose tissue, the kidney, and the adrenal glands, among other tissues. High levels of APOE production also occur in the brain, where it is primarily synthesized by glia, and peripheral and brain APOE pools are thought to be distinct. In humans, APOE is polymorphic, with three major alleles (ε2, ε3, and ε4). These allelic forms dramatically alter APOE structure and function. Historically, the vast majority of research on APOE has centered on the important role it plays in modulating risk for cardiovascular disease and Alzheimer's disease. However, the established effects of this pleiotropic protein extend well beyond these two critical health challenges, with demonstrated roles across a wide spectrum of biological conditions, including adipose tissue function and obesity, metabolic syndrome and diabetes, fertility and longevity, and immune function. While the spectrum of biological systems in which APOE plays a role seems implausibly wide at first glance, there are some potential unifying mechanisms that could tie these seemingly disparate disorders together. In the current review, we aim to concisely summarize a wide breadth of APOE-associated pathologies and to analyze the influence of APOE in the development of several distinct disorders in order to provide insight into potential shared mechanisms implied in these various pathophysiological processes.

Expression Cloning of Host Factors Required for the HCV Replication Cycle

Chronic infection with the hepatitis C virus (HCV) is a common cause of chronic liver disease, cirrhosis, and liver cancer. Like most viruses, HCV depends of a number of factors encoded by its host cell to execute its replication cycle and create. Expression cloning is one of several possible approaches that have been employed to identify novel host factors essential for the HCV replication cycle. It involves generation of a cDNA library from a cell type with a desired trait (such as ability to bind E2 or being susceptible to HCV infection), expression of that library in a different cell type missing the trait of interest, and selection for cell clones that have acquired that trait through expression of a specific cDNA. This chapter describes an expression cloning approach similar to the one that was used to identify the tight junction component claudin-1 as an essential HCV cell entry factor.

Extracellular Interactions between Hepatitis C Virus and Secreted Apolipoprotein E

Interactions between hepatitis C virus (HCV) and lipoproteins in humans play an important role in the efficient establishment of chronic infection. Apolipoprotein E (ApoE) on the HCV envelope mediates virus attachment to host cells as well as immune evasion. This interaction is thought to occur in hepatocytes, as ApoE plays dual functions in HCV assembly and maturation as well as cell attachment. In the present study, we found that secreted ApoE (sApoE) can also bind to viral particles via its C-terminal domain after HCV is released from the cell. Furthermore, the binding affinity of interactions between the sApoE N terminus and cell surface receptors affected HCV infectivity in a dose-dependent manner. The extracellular binding of sApoE to HCV is dependent on HCV envelope proteins, and recombinant HCV envelope proteins are also able to bind to sApoE. These results suggest that extracellular interactions between HCV and sApoE may potentially complicate vaccine development and studies of viral pathogenesis.IMPORTANCE End-stage liver disease caused by chronic HCV infection remains a clinical challenge, and there is an urgent need for a prophylactic method of controlling HCV infection. Because host immunity against HCV is poorly understood, additional investigations of host-virus interactions in the context of HCV are important. HCV is primarily transmitted through blood, which is rich in lipoproteins. Therefore, it is of interest to further determine how HCV interacts with lipoproteins in human blood. In this study, we found that secreted ApoE (sApoE), an exchangeable component found in lipoproteins, participates in extracellular interactions with HCV virions. More significantly, different variants of sApoE differentially affect HCV infection efficiency in a dose-dependent manner. These findings provide greater insight into HCV infection and host immunity and could help propel the development of new strategies for preventing HCV infection.

Apolipoprotein E allele frequencies in chronic and self-limited hepatitis C suggest a protective effect of APOE4 in the course of hepatitis C virus infection

BACKGROUND & AIMS

Infectious hepatitis C virus (HCV) particles bind to host lipoproteins such as low-density lipoproteins (LDLs). Low-density lipoprotein receptors (LDLR) have been termed candidate receptors for HCV-LDL complexes. Functional host genetic single nucleotide polymorphisms (SNPs) in the apolipoprotein E (APOE) gene encoding apolipoprotein E (apoE) - a major structural LDL component and natural ligand of LDLR - likely influence the course of HCV infection. We investigated the prevalence of APOE SNPs in two large and independent cohorts of patients with chronic HCV infection compared to respective controls.

METHODS

We genotyped 996 chronically HCV-infected patients; 179 patients with spontaneous HCV clearance; 283 individuals with non-HCV-associated liver disease; and 2 234 healthy controls.

RESULTS

APOE genotype proportions in patients with persistent HCV infection significantly differed from healthy controls (P = 0.007) primarily because of a substantial under-representation of APOE4 alleles in chronically HCV-infected patients (10.2%) compared to 13.0% in healthy controls (P = 0.001). The distribution of APOE4 allele positive genotypes (ε2ε4, ε3ε4, ε4ε4) also significantly differed between chronically HCV-infected patients and healthy controls (1.4%, 17%, 1% vs. 2.4%, 20.5%, 1.7%; P = 0.001), suggesting a protective effect of the APOE4 allele in HCV infection. This was confirmed by a significant over-representation of the APOE4 allele in patients with spontaneous HCV clearance (17.6%; P = 0.00008). The APOE4 allele distribution in patients with non-HCV-associated liver disease (14.0%) was very similar to healthy controls and also differed from chronically HCV-infected patients (P = 0.012), suggesting HCV specificity.

CONCLUSIONS

Our findings suggest that the APOE4 allele may confer a protective effect in the course of HCV infection.

Apolipoprotein E-ε4 deficiency and cognitive function in hepatitis C virus-infected patients

Hepatitis C virus (HCV) causes not only liver damage in certain patients but can also lead to neuropsychiatric symptoms. Previous studies have shown that the type 4 allele of the gene for apolipoprotein E (APOE) is strongly protective against HCV-induced damage in liver. In this study, we have investigated the possibility that APOE genotype is involved in the action of HCV in brain. One hundred HCV-infected patients with mild liver disease underwent a neurological examination and a comprehensive psychometric testing of attention and memory function. In addition, patients completed questionnaires for the assessment of fatigue, health-related quality of life and mood disturbances. Apolipoprotein E gene genotyping was carried out on saliva using buccal swabs. The APOE-ε4 allele frequency was significantly lower in patients with an impairment of working memory, compared to those with a normal working memory test result (P = 0.003). A lower APOE-ε4 allele frequency was also observed in patients with definitely altered attention ability (P = 0.008), but here, the P-value missed the level of significance after application of the Bonferroni correction. Our data suggest that the APOE-ε4 allele is protective against attention deficit and especially against poor working memory in HCV-infected subjects with mild liver disease. Considering the role of apolipoprotein E in the life cycle of the virus, the findings shed interesting new light upon possible pathomechanisms behind the development of neuropsychiatric symptoms in hepatitis C infection.

Pleiotropy and allelic heterogeneity in the TOMM40-APOE genomic region related to clinical and metabolic features of hepatitis C infection

Hepatitis C virus (HCV) modulates host lipid metabolism as part of its lifecycle and is dependent upon VLDL for co-assembly and secretion. HCV dyslipidemia is associated with steatosis, insulin resistance, IL28B genotype and disease progression. Apolipoprotein E (ApoE) is an important lipid transport protein, a key constituent of VLDL, and is involved in immunomodulation. Our aims were to determine the role of APOE regional polymorphisms on host lipids, IL28B genotype and disease severity in chronic HCV (CHC) patients. The study cohort included 732 CHC patients with available DNA for genotype determination of four polymorphisms in the chromosome 19 region that encompasses the TOMM40, APOE and APOC1 genes. Serum lipid analysis and apolipoproteins levels were measured using an immunoturbidimetric assay. APOE rs7412 polymorphism (capturing the ε2 isoform) was significantly associated with serum ApoE levels in both Caucasians and African-American patients (p = 2.3 × 10(-11)) and explained 7 % of variance in serum ApoE. Among IL28B-CC patients (n = 196), the rs429358 (defines ε4 isoform) and TOMM40 '523' S polymorphisms were associated with 12 % of variance in ApoB levels. Patients homozygous for the APOE ε3 isoform had a greater than twofold increased odds of F2-F4 fibrosis (p = 1.8 × 10(-5)), independent of serum lipid and lipoprotein levels. There were no associations between APOE polymorphisms and serum HDL-C, APO-CIII and triglycerides. In CHC patients, genetic heterogeneity in the APOE/TOMM40 genomic region is significantly associated with variation in serum ApoE and ApoB levels, and also with fibrosis suggesting a pleiotropic attribute of this genomic region.

Apolipoprotein E genotypes modulate fibrosis progression in patients with chronic hepatitis C and persistently normal transaminases

BACKGROUND AND AIM

Carriage of the apolipoprotein E (Apo E) variants, E2, E3 and E4, affects cholesterol metabolism and may be involved in the persistence of hepatitis C virus (HCV) infection. Our aim was to verify whether carriage of specific Apo E variants modulates the course of hepatitis C.

METHODS

We studied a cohort of 116 HCV-positive patients (49 male subjects) with persistently normal transaminases and an Ishak staging score ≤ 2 at an initial biopsy. These untreated patients underwent regular clinical monitoring (median histological follow up: 10 years). Apo E variants were genotyped and results were related to the histological outcome.

RESULTS

The mean ± standard deviation staging scores were 0.9 ± 0.7 at entry versus 1.9 ± 1.2 at the end of follow up, P < 0.0001. Initial and final staging scores in the E3/E3 homozygotes (n = 74) were 1.0 ± 0.7 versus 2.1 ± 1.3, P < 0.0001, while in the remaining patients (n = 42) they were 0.9 ± 0.6 versus 1.5 ± 1.0, P < 0.002. A synergistic effect was observed between Apo E polymorphisms and baseline serum cholesterol values: patients not carrying any E3 allele, as well as carriers of a single E3 allele with serum cholesterol concentration > 190 mg/dL were more likely to have a favorable outcome (final vs initial staging score increased in 7/66, did not change in 10/46, and decreased in 3/4, P <0.005).

CONCLUSIONS

Some of the variability in the natural history of patients with persistently normal transaminases with initially mild hepatitis C can be related to their Apo E genetic background.

The C-terminal alpha-helix domain of apolipoprotein E is required for interaction with nonstructural protein 5A and assembly of hepatitis C virus

We have recently demonstrated that human apolipoprotein E (apoE) is required for the infectivity and assembly of hepatitis C virus (HCV) (K. S. Chang, J. Jiang, Z. Cai, and G. Luo, J. Virol. 81:13783-13793, 2007; J. Jiang and G. Luo, J. Virol. 83:12680-12691, 2009). In the present study, we have determined the molecular basis underlying the importance of apoE in HCV assembly. Results derived from mammalian two-hybrid studies demonstrate a specific interaction between apoE and HCV nonstructural protein 5A (NS5A). The C-terminal third of apoE per se is sufficient for interaction with NS5A. Progressive deletion mutagenesis analysis identified that the C-terminal α-helix domain of apoE is important for NS5A binding. The N-terminal receptor-binding domain and the C-terminal 20 amino acids of apoE are dispensable for the apoE-NS5A interaction. The NS5A-binding domain of apoE was mapped to the middle of the C-terminal α-helix domain between amino acids 205 and 280. Likewise, deletion mutations disrupting the apoE-NS5A interaction resulted in blockade of HCV production. These findings demonstrate that the specific apoE-NS5A interaction is required for assembly of infectious HCV. Additionally, we have determined that using different major isoforms of apoE (E2, E3, and E4) made no significant difference in the apoE-NS5A interaction. Likewise, these three major isoforms of apoE are equally compatible with infectivity and assembly of infectious HCV, suggesting that apoE isoforms do not differentially modulate the infectivity and/or assembly of HCV in cell culture.

Genetic polymorphism at the apolipoprotein E locus affects the outcome of chronic hepatitis B

Apolipoprotein E (ApoE) and H (ApoH) genotypes are known to affect plasma lipoprotein concentrations. By modulating transport and entry of the hepatitis B virus into hepatocytes, apolipoproteins may influence the course of infection. To verify this hypothesis, 105 patients with chronic HBV infection were examined. Sixty-two of the patients were followed-up for a median time of 21 years. One hundred two controls were included. ApoE and ApoH genotypes were determined by the restriction fragment length polymorphism method. A trend was found for progressive overrepresentation of ApoE3/E3 among patients with advanced liver disease: 13/27 (48%) of inactive HBV carriers, 36/61 (59%) of chronic hepatitis B patients and 16/17 (94%) of patients who received liver transplants (P < 0.005). Being an E3/* carrier was associated with a lower probability of loss of HBsAg: 9/56 (16%) versus 3/6 (50%) (P < 0.05); it was also associated with a longer time before HBsAg loss (P < 0.05). No influence of ApoH genotypes on clinical outcomes was found. The probability of disease progression was higher, and that of loss of HBsAg was lower, among patients with the ApoE3 allelic variant. Downregulation and/or reduced binding of the LDL receptor may explain the more benign course of hepatitis B among carriers of ApoE2-E4.

Know your enemy: translating insights about the molecular biology of hepatitis C virus into novel therapeutic approaches

Identified in 1989 as the cause of what was then known as hepatitis non-A non-B, the hepatitis C virus (HCV) continues to be a significant global public health threat, given that an estimated 123 million individuals are chronically infected and, thus, at risk for cirrhosis and hepatocellular carcinoma. After 20 years of basic and clinical research into HCV infection, the backbone of therapy has remained interferon, a drug that - in a different formulation - was already being employed before HCV was even identified. Nonetheless, research has overcome many obstacles that stood in the way of studying this pre-eminent human pathogen. Hard-won insights into its molecular biology have identified promising therapeutic targets, and we are now on the verge of an era where rationally designed therapeutics, also referred to as specifically targeted antiviral therapy for HCV, will reshape the treatment of hepatitis C. This article describes recent insights on the molecular biology of HCV and the efforts to translate them into clinical applications.

Methylenetetrahydrofolate reductase C677T polymorphism and liver fibrosis progression in patients with recurrent hepatitis C

BACKGROUND/AIMS

Methylenetetrahydrofolate reductase (MTHFR) C677T polymorphism, being a putative steatogenic factor, may promote liver fibrosis progression in patients with chronic hepatitis C. This study aimed to verify the role of recipient MTHFR polymorphism in favouring graft fibrosis progression in patients with recurrent HCV after orthotopic liver transplantation (OLT).

METHODS

We studied 63 such patients, followed for >1 year. MTHFR allelic variants were determined by a polymerase chain reaction/restriction fragment length polymorphism method.

RESULTS

Recipients carrying the TT genotype had more frequently, 1-year post-OLT, homocysteine serum levels >23 micromol/L (P<0.05), serum triglycerides >180 mg/dL (P<0.02) and de novo diabetes mellitus (P<0.05) but not a higher frequency of graft steatosis. Time-to-event analysis in reaching an Ishak staging score >2 was performed by stratifying the recipients as follows: (a) patients with donor age < or =45 years, (b) patients with donor age >45 and C/(*) genotype, and (c) patients with donor age >45 years and TT genotype. A significant linear trend was observed, with increasing frequencies as follows: (a) 8/37, (b) 10/19 and (c) 6/7 (P=0.0005).

CONCLUSION

The MTHFR C677T polymorphism may play a role in influencing liver fibrosis progression in patients with recurrent hepatitis C, in conjunction with donor age, but not via steatosis promotion.

Apolipoprotein E alleles can contribute to the pathogenesis of numerous clinical conditions including HSV-1 corneal disease

Apolipoprotein E (ApoE) alleles have been reported to affect the clinical outcome of numerous cardiovascular, neurodegenerative, and viral infectious diseases, including atherosclerosis, Alzheimer's disease (AD), hepatitis C, and HIV. The major alleles of ApoE are 2, 3, and 4. ApoE genotypes have been hypothesized to regulate many biological functions, resulting in significant changes in the onset and/or outcome (severity and duration) of several clinical conditions. Based on genetic analyses in human and animal studies using knockout (ApoE -/-) mice and mice transgenic for human 3 and 4, we present evidence that strongly suggests that the ApoE alleles can regulate the pathogenesis of ocular herpes simplex virus type 1 (HSV-1) infections. This review will summarize the major studies that support this hypothesis. Significant gender based differences in HSV-1 pathogenesis have also been reported, suggesting that hormonal regulation combined with ApoE genotype plays a significant role in HSV-1 pathogenesis. Identification of specific mechanisms in ocular HSV-1 infections related to the ApoE alleles and gender could lead to therapeutic intervention based on the properties of the apoE isoforms. While many clinical investigations have been reported and, to a lesser extent, transgenic mouse studies have been conducted, no specific mechanisms of how ApoE induces or alters clinical disease are known.

Excess body weight, liver steatosis, and early fibrosis progression due to hepatitis C recurrence after liver transplantation

AIM: To investigate how weight gain after OLT affects the speed of fibrosis progression (SFP) during recurrent hepatitis C virus (HCV) infection of the graft.

METHODS: Ninety consecutive patients (63 males, median age 53 years; 55 with HCV-related liver disease), transplanted at a single institution, were studied. All were followed for at least 2 years after OLT and had at least one follow-up graft biopsy, performed not earlier than 1 year after the transplant operation. For each biopsy, a single, experienced pathologist gave an estimate of both the staging according to Ishak and the degree of hepatic steatosis. The SFP was quantified in fibrosis units/month (FU/mo). The lipid metabolism status of patients was summarized by the plasma triglycerides/cholesterol (T/C) ratio. Body mass index (BMI) was measured before OLT, and 1 and 2 years after it.

RESULTS: In the HCV positive group, the highest SFP was observed in the first post-OLT year. At that time point, a SFP ≤0.100 FU/mo was observed more frequently among recipients who had received their graft from a young donor and had a pre-transplant BMI value >26.0 kg/m². At completion of the first post-transplant year, a BMI value >26.5 kg/m² was associated with a T/C ratio ≤1. The proportion of patients with SFP >0.100 FU/mo descended in the following order: female recipients with a high T/C ratio, male recipients with high T/C ratio, and recipients of either gender with low T/C ratio. Hepatic steatosis was observed more frequently in recipients who, in the first post-transplant year, had increased their BMI ≥1.5 kg/m² in comparison to the pre-transplant value. Hepatic steatosis was inversely associated with the staging score.

CONCLUSION: Among HCV positive recipients, excess weight gain post-OLT does not represent a factor favoring early liver fibrosis development and might even be protective against it.