Hepatitis C: Overview of Recent Therapeutic Advances

David E. Kaplan, M.D.

Introduction

Hepatitis C infection represents a major threat to public health in the United States and worldwide. It is a leading cause of cirrhosis, end-stage liver disease and hepatocellular carcinoma. This article will briefly discuss the nature of the virus, the clinical course of the disease and the scope of the epidemic. Recent advances in treatment and candidacy for therapy will be addressed, as will costs and side effects. Potential adjuncts to current therapy will be introduced. An attempt will be made to provide recommendations on whom and how to treat patients in the clinical setting, although certain controversies regarding these issues continue to exist.

Epidemiology and Virology

Presently, Hepatitis C affects over 4 million Americans. Approximately 36,000 more annually become infected with 8-10,000 deaths annually attributable to this virus  Anti-Hepatitis C Virus antibodies are present in 1.8% of the population with higher prevalence in intravenous drug users, hemodialysis patients and alcoholics . Hepatitis C is responsible for 20% of cases of acute hepatitis, 70% of chronic hepatitis in the U.S., and is the most common etiology leading to liver transplant in U.S

Hepatitis C is a RNA virus of the family Flaviviridae, genus hepacivirus (Figure 1). This 50 nm, positive-sense single-stranded RNA virus possesses a 9.5 kB genome with a 5' non-coding region, a single open reading frame with at least 3 structural and 6 non-structural genes, and a 3' non-coding region. The non-structural genes include a Hepatitis C Virus-specific serine protease, a RNA helicase, and a RNA-dependent RNA polymerase

Hepatitis C is a heterogenous virus with at least 6 genotypes and more than 50 subtypes. By cDNA analysis, these genotypes diverged 300 years ago  In the United States, genotype I comprises 70-80% of cases.

Individual isolates exist as a quasispecies. In any individual patient, dozens of separate variants with unique RNA sequences may co-exist . Viral heterogeneity is fostered by a viral RNA polymerase which errs every 10⁴ to 10⁵ base-pairs without a proofreading mechanism . A highly mutable 81 base-pair hypervariable region (HVR1) is found at the 5' end of Envelope 2 gene. Genotype Ib strains, which are the most common in the U.S., possess a second 7 base-pair hypervariable region (HVR2) just 3' to HVR1. The envelope proteins encoded by HVR1 and HVR2 are thought to be important neutralization epitopes, whose variability precludes protective antibody formation  The host immune system exerts a high selection pressure on these epitopes, as does therapy with Interferon-alpha  Conversely, agammaglobulinemic patients demonstrate less complex quasispeciation. The 5' and 3' non-coding and capsid genes, are more conserved. The most important clinical implication of viral heterogeneity has been the failure of efforts to develop an effective vaccine secondary to immunologic escape . Increased viral heterogeneity, as measured by PCR techniques, predicts poorer response to Interferon therapy

Intravenous drug use, exposure to incompletely sterilized hemodialysis tubing, and sexual contact are well defined modes of transmission of the virus. Perinatal transmission rates have been estimated at 5% but breast feeding does not appear to be a method of transmission  Household contact, presumably with minor amounts of blood or serum on toothbrushes or shared razors, has been postulated. Intranasal cocaine users are at high risk due to exposure to body fluids from sharing straws, or other coincident high-risk behaviors. Health-care workers are at risk from percutaneous needle sticks which carry approximately a 2% risk of transmission  At least one ocular exposure leading to infection has been reported. Tattooing and piercing with inadequately sterilized needles has been implicated  A high rate of Hepatitis C Virus infection, 6-49% in some series, has been documented in alcoholics with an unclear mechanism of exposure  Even with careful history, no identifiable risk factors can be ascertained in up to 10%-40 patients

Diagnosis

Hepatitis C Virus diagnosis can be made with up to 97% sensitivity with anti-Hepatitis C Virus antibody testing by enzyme immunoassay (EIA) with subsequent confirmation by recombinant immunoblot assay (RIBA) [. Seroconversion occurs in 80% of patients at 15 weeks, 90% at 5 months, and greater than 97% at 6 months after exposure. Antibody positivity cannot differentiate acute from chronic or resolved infections. Quantification of serum viral RNA, also known as "viral load" via reverse transcriptase-polymerase chain reaction (RT-PCR) or branched-chain DNA (bDNA) can make a diagnosis of acute hepatitis C within 1-2 weeks of exposure, prior to detection of anti-Hepatitis C Virus antibody. RT-PCR assays are not FDA approved, and should not be used exclusively in the diagnosis of Hepatitis C Virus . Hepatitis C Virus genotyping may have prognostic implications, but routine testing for genotype has not been widely advocated.

Testing for hepatitis C is recommended in all patients with histories of intravenous drug use, those that received clotting factors prior to 1987, patients with histories of long-term hemodialysis, and those with persistently elevated aminotransferase levels. Children born to Hepatitis C Virus infected mothers should be tested. Post-exposure testing is also indicated. Routine testing of health care workers, pregnant women, and household contacts has not been recommended by the CDC. Transplant recipients, non-injection illegal drug users, tattoo or body-piercing recipients, promiscuous persons or long-term steady sexual partners of Hepatitis C Virus-infected patients should be approached on an individual basis

Clinical Course

Acute Hepatitis C Virus hepatitis occurs after an incubation period averaging 7 weeks (range 3-20 weeks). Followed prospectively, approximately 33% of newly-infected patients develop icterus although 90% of patients will not recall this retrospectively. Acute hepatitis C lasts 2-12 weeks. During this time, up to 15% of patients will have normalization of their aminotransferase levels and subsequently become aviremic. However, 85% of patients become chronically viremic and 65-80% develop evidence of chronic active hepatocellular damage with persistently elevated aminotransferase levels  Chronic infection is rarely symptomatic. Fewer than 20% of patients develop protean symptoms such as fatigue, abdominal pain, fever and arthralgias. A subset of roughly 30% of patients have chronic active hepatitis with mild histologic changes with normal aminotransferase levels. Long-term prognosis in these patients is less well defined.

Extrahepatic manifestations of hepatis C include essential mixed cryoglobulinemia, membranoproliferative glomerulonephritis, porphyria cutanea tarda and cryoglobulinemic vasculitis. Keratoconjunctivitis sicca and lichen planus have been reported but the causality has not been proven

Approximately 20-30% of patients with chronic hepatitis C will develop cirrhosis usually after 10 to 30 years. Risk factors for progression to cirrhosis include advanced age (>55yo), male gender, and concomitant alcohol abuse  Most studies show that Genotype I virus is associated with higher serum Hepatitis C Virus RNA levels. Higher RNA levels independently increase the risk of progression  Immunocompromised patients, such as HIV or transplant patients, also have an increased risk of developing cirrhosis  Once cirrhosis develops, patients have a 30% 10-year risk of decompensation, as evidenced by ascites, variceal bleeding, encephalopathy and/or jaundice . Once cirrhosis develops, patients have a 1.4-7% annual incidence of hepatocellular carcinoma.

Treatment

Agents

Interferons are a heterogenous class of cytokines produced in vivo by fibroblasts and other immune cells. Alpha interferons upregulate antiviral functions of cells through diverse mechanisms such as by direct inhibition of viral uncoating and penetration, reduction of viral mRNA synthesis, activation of cytokine synthesis and cellular immune responses, and up-regulation of HLA Class-I molecule expression. Four commercially available alpha interferons have been used in a majority of clinical trials: Interferon a 2b (Intron Aâ), Interferon a 2a (Roferon Aâ ), consensus Interferon (Infergenâ ), and Interferon a n1  The standard doses of Interferon a 2a and a 2b are 3 million units administered subcutaneously or intramuscularly three times per week for 6 months.

Ribavirin is a nucleoside analogue that has been used in the treatment of several RNA virus infections. Ribavirinís mechanism of action is unclear but it may reduce intracellular GTP, and thus indirectly inhibit the Hepatitis C Virus-genomic RNA polymerase. Early attempts were made to treat Hepatitis C Virus with Ribavirin monotherapy. High rates of biochemical responses were produced by therapy, but were not sustained after cessation of therapy  75% of Interferon non-responders treated with Ribavirin monotherapy for 6 to 9 months demonstrated improved ALT levels, with complete normalization in 50%; however no patients became aviremic on therapy and all relapsed after treatment cessation  Ribavirin does not reduce Hepatitis C Virus RNA levels and thus has no potential to "cure" patients  As such, Ribavirin is used only in combination with Interferon.

Recently, the FDA approved the marketing of Rebetron^Ç, a pre-packaged combination of Interferon a2b (Intron A^Ç) and Ribavirin (Rebetol^Ç), for the treatment of Hepatitis C following relapse after Interferon monotherapy. The approved regimen is Interferon-alpha 3 million units three times weekly for a duration of 6 months, in combination with Ribavirin 1000 mg/d (3 pills in AM, 2 in PM) for patients under 75 kg and 1200 mg/d (3 pills BID) for those heavier than 75 kg.

Clinical Evaluation of Efficacy

The current objective of therapy in chronic hepatitis C is the clearance of hepatitis C virus from the blood, with subsequent reduction of hepatocellular inflammation and prevention of cirrhosis. Early treatment trials attempted to treat hepatitis C used serum aminotransferases as markers of therapeutic efficacy. Unfortunately, their sensitivity and specificity are poor . Many patients with "biochemical" responses to therapy, as evidenced by normalization of aminotransferases, continue to have detectable Hepatitis C Virus viral RNA in their sera, which predicts subsequent relapse  Conversely, greater than 90% of patients who reach undetectable serum Hepatitis C Virus RNA levels during therapy remain free of detectable virus after one year of follow-up, and more than 90% maintain normal ALT levels and undetectable serum Hepatitis C Virus RNA in one to six years of follow-up  Although 82% of these long-term responders continue to demonstrate mild chronic hepatitis on biopsy at one-year post-treatment  progression to cirrhosis and development of hepatocellular carcinoma are dramatically reduced  Histologic evaluation is the gold standard for evaluating efficacy of therapy but requires serial liver biopsies with associated morbidity, mortality and expense. Quantitative RNA assays therefore provide the best non-invasive marker of both short and long term therapeutic success.

Response Rates

A recent meta-analysis of 20 randomized, placebo-controlled trials of standard- dose Interferon-a 2b demonstrated undetectable viral loads in 29 v. 5% at the end of therapy and in 8 v. 1% (p < 0.001) six months after cessation of therapy. These results are comparable with other large trials of IFN a2b  Extending therapy 12 to 18 months marginally improved biochemical sustained response rates, with a 23% undetectable viral load following 18 months of treatment as demonstrated by Poynard and colleagues . On average, sustained virologic response rates to Interferon monotherapy are on the order of 10% . Trials of Interferon a2a, Interferon an1, and Consensus interferon demonstrate similar efficacy

Although intensive daily and high dose induction regimens have to date not demonstrated improved response rates to Interferon , emerging data suggest that these approaches merit further investigation. For example, recent meta-analysis revealed that higher doses of Interferon a2b (6-10 million units) for 6 months demonstrated higher rates of biochemical response rates (28% v. 19% p< 0.01) versus standard therapy. Sustained virologic responses however have not resulted from dose intensification

Repeat treatment of patients who relapse following initial response to Interferon monotherapy is effective in normalizing aminotransferases levels in 79-85% of patients. Sustained responses may be seen in 40-51% when higher doses of interferon and/or longer duration of therapy (e.g.12 months) are employed  Only 10% of relapsers with genotype Ib respond to retreatment compared to 41% for non-Ib genotypes. Cirrhotic patients and patients in whom aminotransferases never normalized with initial therapy (non-responders) fare poorly with repeated monotherapy with 0-30% response rates

Although FDA approved only for treatment of relapse after failure of monotherapy, combination therapy with Interferon and Ribavirin has shown greatly improved therapeutic efficacy as first-line therapy. Long-term efficacy of combination therapy was first shown by Lai and colleagues in 1996, who demonstrated sustained aviremia at 96 weeks in 43% of Interferon-Ribavirin treated patients versus 6% of Interferon monotherapy patients (p=<0.05)  Pilot studies by Reichard and colleagues of combination therapy in Interferon-naive patients demonstrated sustained viral clearance rates of 42% compared to 20% with Interferon monotherapy cohort (p=0.03) (Figure 3). Subgroup analysis revealed that patients with Hepatitis C Virus viral loads greater than 3 x 10⁶ copies/ml had greater rates of sustained response rates to combination therapy (41%) compared to monotherapy (4%, p=0.009) (Figure 4). Patients with genotype Ib virus responded relatively poorly in both groups, in contrast to genotype IIIa patients who showed the highest response rates  These results compare with sustained virologic response rates of 33-47% for combination therapy in other small studies

These small trials have recently been corroborated by larger trials. McHutchinson and colleagues randomized 916 patients to 4 treatment groups: Monotherapy for 24 and 48 weeks compared with Combination therapy for 24 and 48 weeks (Figure 5). Baseline characteristics of each group were identical. Sustained virologic clearance was found in 6%, 13%, 31% and 38% respectively with similar sustained biochemical response rates. Histologic indices of inflammation improved most in patients treated with combination therapy for 48 weeks, although the degree of hepatic fibrosis on biopsy was not affected by therapy. Genotype I and Hepatitis C Virus RNA levels greater than 2 x 10⁶ predicted poorer response rates in all groups proportionately. Fibrosis at study entry did not affect response rates .

Patients who relapse after initial success with Interferon monotherapy tend to respond well to retreatment with combination therapy  Bellobuono, et al., randomized 24 non-responders and 24 relapsers to combination therapy versus interferon alpha monotherapy and demonstrated sustained virologic responses in 20.5% versus 4.2% . More recent data from a larger study revealed sustained virologic responses in 49% with combination therapy compared to 5% in monotherapy after primary treatment failures  Overall, sustained responses with combination therapy are seen in approximately 40% of naive patients, 20-50% of interferon-relapsers, and 21% interferon non-responders

One meta-analysis demonstrated that Interferon-alpha therapy reduced Hepatitis C Virus viral loads to undetectable levels in 41% of treated patients with Acute Hepatitis C  This compared with 4% of untreated controls. These results appear to validate therapy of acute hepatitis C with Interferon. Prophylaxis after needle-stick injuries has not been rigorously studied.

Who should be treated?

Several pretreatment variables correlate with response rates to Interferon monotherapy. Older patients, those with advanced disease, those with high Hepatitis C Virus viral loads, patients with pre-existing cirrhosis, those with co-infection with Hepatitis B and patients with genotype Ib virus tend to respond poorly to therapy  Virologic responses to therapy in cirrhotics range from 5-10% as compared to 20-35% in non-cirrhotics . More severe inflammation on biopsy, measured by Knodell histologic indices, correlates with poorer response  In contrast, patients with non-type I genotype, female gender and lower baseline Hepatitis C Virus RNA levels tend to have higher response rates to Interferon  Pretreatment variables such as Hepatitis C Virus viral load, genotype, and pre-existing cirrhosis, however, have not been proven to accurately predict response rates in individual patients  and therefore treatment decisions should be individualized.

Recommendations regarding candidacy for therapy should be interpreted with caution because all are based on retrospective data from Interferon monotherapy trials. With the recent approval of Rebetron, modifications may be needed.

There is consensus that young patients who are early in the course of chronic hepatitis C, who demonstrate persistent elevations of aminotransferase levels, and who do not have pre-existing cirrhosis have the best response rates to therapy. In the absence of contraindications, these patients should be offered treatment. Patients with chronic hepatitis C but persistently normal aminotransferase levels have not clearly been demonstrated to benefit from therapy  However, these patients may be early in the course of their disease, with lower viral loads, and therefore are more likely to respond to therapy and be potentially "cured." Treatment of patients with less favorable profiles, such as advanced age, cirrhosis or comorbidity, must be individualized.

Side Effects

Adverse effects force dose reduction in 10% and cessation of therapy in 5% of Interferon treated patients. (Figure 6) These effects of interferon include flu like symptoms such as myalgia, fever, and arthralgia, which occur in virtually 100% of patients. This often may be mitigated by nocturnal administration and with acetaminophen pretreatment. These symptoms frequently lessen in severity with subsequent doses. In contrast, depression, alopecia, and myelosuppression, if present, tend to persist. Myelosuppression, especially leukopenia may require treatment reduction or cessation. Specifically, doses are halved for absolute neutrophil counts (ANC) under 1000/m l and therapy discontinued for an absolute neutrophil count (ANC) less than 800/ml. Neuropsychiatric symptoms such as depression, irritability, and cognitive impairment are common. Some authors hold that previous suicide attempt ought to be an absolute contraindication to interferon therapy. Fewer than 2% of patients experience thyroid dysfunction but thyroid function tests should be monitored during therapy

Side effects of Ribavirin therapy include low grade hemolysis (decrease of hemoglobin by 1-3 g/dl) which occurs in nearly 100% of treated patients  Patients with underlying anemia, myelosuppression, renal failure, ischemic coronary or cerebrovascular diseases may poorly tolerate hemolysis. Dose reductions by 200 mg/day every 2 weeks are recommended when hemoglobin levels drop below 11 g/dl. Reductions should continue until hemoglobin levels remain above 11 g/dl. Fewer than 10% of patients have been unable to tolerate Ribavirin secondary to hemolysis. Ribavirin, a potent teratogen, requires contraception and pre-treatment pregnancy testing. In combination therapy trials. anemia, leukopenia, pruritis and hyperbilirubinemia have been more common in the combination therapy cohorts .

Costs

Interferon alpha costs approximately $5000 for a 6 month course. Bennet analyzed cost-effectiveness in 5 prospective trials of Interferon a2b and found that treatment cost $500 for each year of life saved in 20 year old patients, $1900 in 35 year old patients, and $62,000 in 70 year olds  To put this in context, the cost of interferon therapy per quality-of-life-year is comparable to that of cholesterol reduction therapy

Adjuncts to Therapy

It has been suggested that patients with relatively low ferritin levels have higher response rates to treatment. Iron depletion may have antiviral effect, improve immune reactivity, or reduce free-radical formation  The clinical efficacy of iron reduction therapy, in the form of phlebotomy or desferroxamine, has yet to be proven. Antiviral therapy with amantadine is under investigation with disappointing early results. N-acetyl-cysteine, Vitamin E, GM-CSF, levamisole, ursodiol and NSAIDs have no proven benefit as an adjunctive agents  Pentoxifylline may increase endogenous Interferon-alpha levels and decrease TNFa production. Early data suggests improved but non-sustained normalization of aminotransferases during pentoxiffyline treatment

Thymosin a-1, a cytokine derived from the human thymus, has shown promise in small studies with virologic responses in up to 73% of patients treated with Interferon-an1 combined with Thymosin a-1 for 12 months. Other studies reveal virologic end-treatment responses of 71% and sustained response rates of 29% with combination therapy for six months  Two multicenter randomized, placebo-controlled studies of this therapy are currently underway. Specific Hepatitis C Virus proteases inhibitors are in development, but are not yet in clinical testing.

Does Interferon reduce occurrence of Hepatocellular Carcinoma (HCC)?

The reported annual risk of development of HCC in cirrhotic patients with Hepatitis C Virus ranges from 1.4-7%. Co-infection with Hepatitis B, alcoholism, and porphyria cutanea tarda appear to increase the risk of malignancy in Chronic Hepatitis C  Alcoholics with Hepatitis C Virus and cirrhosis have a reported 81% 10-year risk of developing HCC .

Interferon may reduce the risk of hepatocellular carcinoma by improving immune surveillance, by initiating cellular differentiation, or by acting as an anti-mitotic agent

The benefit of Interferon therapy for preventing HCC was suggested in a study 90 patients with compensated cirrhosis randomized to treatment with Interferon-an1 versus no therapy. 4% of treated patient compared with 38% of untreated control patients (p=0.002) developed HCC after an average of 4.4 years (range 2-7y) of follow-up. All treated patient who developed HCC were biochemical and virologic non-responders to Interferon therapy. The relative risk of HCC in treated patients was 0.067 (p=0.01), a 93% relative reduction  Kasahara et al prospectively followed 1022 patients with compensated cirrhosis from six Interferon trials by serial ultrasound for 13-92 months (mean 30 months). Seven-year cumulative incidence of HCC was 4.3%, 4.7% and 26.1% respectively in sustained responders, relapsers, and non-responders (p=0.0009). Non-responders had a relative risk for HCC of 7.9 (p = 0.008) compared to sustained responders . HCC developed in 0.9% of responders, 6.1% in relapsers, 12.8% in non-responders, and in 13.2% of untreated historical controls (p<0.05)  No significant difference in HCC rates have been found between sustained-responders and non-sustained-responders, nor between non-responders and untreated patients, in these studies  In contrast, a retrospective study in a European consortium revealed no significant reduction in the 5 year estimated probability of HCC in treated versus untreated patients, although the rate of hepatic decompensation in treated patients was significantly reduced  At this time, consensus has yet to be reached whether or not interferon therapy truly reduces the risk of HCC, and whether or not this provides independent justification for initiating Interferon therapy in patients with pre-existing cirrhosis.

Summary

Hepatitis C represents a major threat to public health. Virological characteristics have to date thwarted efforts at developing a vaccine for primary prevention. Untreated, chronic hepatitis C results in high rates of progression to cirrhosis and hepatocellular carcinoma. Interferon alpha monotherapy appears to clear viral RNA in 10-20% of patients. Combination therapy with Interferon and Ribavirin produces markedly improved response rates in previously untreated patients, potentially curing 35-40%. FDA approval for this use is anticipated soon. Up to half of patients who relapse after initial response to Interferon may have sustained clearance with combination therapy. Further research is needed to define which patient groups should be treated, or if all patients with Hepatitis C should be treated in order to reduce development of hepatocellular carcinoma. Future therapy may include Iron reduction, thymosin a-1, and Hepatitis C Virus-specific helicase, protease or RNA polymerase inhibitors. The use of high-dose induction remains controversial. As data continues to be collected, further refinements in the treatment of chronic Hepatitis C promise to spare a large number of patients with chronic hepatitis C the morbidity and mortality from cirrhosis and hepatocellular carcinoma.

Special thanks to Dr. Paul J. Thuluvath for assisting me in the editing of this article