Dynamics of alanine aminotransferase during hepatitis C virus treatment

Effect of Peg-IFN on the viral kinetics of patients with HDV infection treated with bulevirtide

Background & Aims

Bulevirtide is a first-in-class entry inhibitor antiviral treatment for chronic hepatitis D. The viral kinetics during bulevirtide therapy and the effect of combining bulevirtide with pegylated-interferon (Peg-IFN) are unknown.

Methods

We used mathematical modelling to analyze the viral kinetics in two French observational cohorts of 183 patients receiving bulevirtide with or without Peg-IFN for 48 weeks.

Results

The efficacy of bulevirtide in blocking cell infection was estimated to 90.3%, whereas Peg-IFN blocked viral production with an efficacy of 92.4%, albeit with large inter-individual variabilities. The addition of Peg-IFN to bulevirtide was associated with a more rapid virological decline, with a rate of virological response (>2 log of decline or undetectability) at week 48 of 86.9% (95% prediction interval [PI] = [79.7-95.0]), compared with 56.1% (95% PI = [46.4-66.7]) with bulevirtide only. The model was also used to predict the probability to achieve a cure of viral infection, with a rate of 8.8% (95% PI = [3.5-13.2]) with bulevirtide compared with 18.8% (95% PI = [11.6-29.0]) with bulevirtide + Peg-IFN. Mathematical modelling suggests that after 144 weeks of treatment, the rates of viral cure could be 42.1% (95% PI = [33.3-52.6]) with bulevirtide and 66.7% (95% PI = [56.5-76.8]) with bulevirtide + Peg-IFN.

Conclusions

In this analysis of real-world data, Peg-IFN strongly enhanced the kinetics of viral decline in patients treated with bulevirtide. Randomized clinical trials are warranted to assess the virological and clinical benefit of this combination, and to identify predictors of poor response to treatment.

Impact and implications

Bulevirtide has been approved for chronic HDV infection by regulatory agencies in Europe based on its good safety profile and rapid virological response after treatment initiation, but the optimal duration of treatment and the chance to achieve a sustained virological response remain unknown. The results presented in this study have a high impact for clinicians and investigators as they provide important knowledge on the long-term virological benefits of a combination of Peg-IFN and bulevirtide in patients with CHD. Clinical trials are now warranted to confirm those predictions.

A multiscale model of the action of a capsid assembly modulator for the treatment of chronic hepatitis B

Chronic hepatitis B virus (HBV) infection is strongly associated with increased risk of liver cancer and cirrhosis. While existing treatments effectively inhibit the HBV life cycle, viral rebound occurs rapidly following treatment interruption. Consequently, functional cure rates of chronic HBV infection remain low and there is increased interest in a novel treatment modality, capsid assembly modulators (CAMs). Here, we develop a multiscale mathematical model of CAM treatment in chronic HBV infection. By fitting the model to participant data from a phase I trial of the first-generation CAM vebicorvir, we estimate the drug's dose-dependent effectiveness and identify the physiological mechanisms that drive the observed biphasic decline in HBV DNA and RNA, and mechanistic differences between HBeAg-positive and negative infection. Finally, we demonstrate analytically and numerically that HBV RNA is more sensitive than HBV DNA to increases in CAM effectiveness.

Biomarkers of Hepatic Toxicity: An Overview

Background

Hepatotoxicity is the foremost issue for clinicians and the primary reason for pharmaceutical product recalls. A biomarker is a measurable and quantifiable attribute used to evaluate the efficacy of a treatment or to diagnose a disease. There are various biomarkers which are used for the detection of liver disease and the intent of liver damage.

Objective

This review aims to investigate the current state of hepatotoxicity biomarkers and their utility in clinical settings. Using hepatic biomarkers, the presence of liver injury, its severity, prognosis, causative agent, and type of hepatotoxicity can all be determined.

Methods

Relevant published articles up to 2022 were systematically retrieved from MEDLINE/PubMed, SCOPUS, EMBASE, and WOS databases using keywords such as drug toxicity, hepatotoxicity biomarkers, biochemical parameters, and nonalcoholic fatty liver disease.

Results

In clinical trials and everyday practice, biomarkers of drug-induced liver injury are essential for spotting the most severe cases of hepatotoxicity. Hence, developing novel biomarker approaches to enhance hepatotoxicity diagnosis will increase specificity and/or identify the person at risk. Importantly, early clinical studies on patients with liver illness have proved that some biomarkers such as aminotransferase, bilirubin, albumin, and bile acids are even therapeutically beneficial.

Conclusions

By assessing the unique signs of liver injury, health care professionals can rapidly and accurately detect liver damage and evaluate its severity. These measures contribute to ensuring prompt and effective medical intervention, hence reducing the risk of long-term liver damage and other major health concerns.

Modelling HDV kinetics under the entry inhibitor bulevirtide suggests the existence of two HDV-infected cell populations

Background & Aims

Bulevirtide (BLV) was approved for the treatment of compensated chronic hepatitis D virus (HDV) infection in Europe in 2020. However, research into the effects of the entry inhibitor BLV on HDV-host dynamics is in its infancy.

Methods

Eighteen patients with HDV under nucleos(t)ide analogue treatment for hepatitis B, with compensated cirrhosis and clinically significant portal hypertension, received BLV 2 mg/day. HDV RNA, alanine aminotransferase (ALT), and hepatitis B surface antigen (HBsAg) were measured at baseline, weeks 4, 8 and every 8 weeks thereafter. A mathematical model was developed to account for HDV, HBsAg and ALT dynamics during BLV treatment.

Results

Median baseline HDV RNA, HBsAg, and ALT were 4.9 log IU/ml [IQR: 4.4-5.8], 3.7 log IU/ml [IQR: 3.4-3.9] and 106 U/L [IQR: 81-142], respectively. During therapy, patients fit into four main HDV kinetic patterns: monophasic (n = 2), biphasic (n = 10), flat-partial response (n = 4), and non-responder (n = 2). ALT normalization was achieved in 14 (78%) patients at a median of 8 weeks (range: 4-16). HBsAg remained at pre-treatment levels. Assuming that BLV completely (∼100%) blocks HDV entry, modeling indicated that two HDV-infected cell populations exist: fast HDV clearing (median t1/2 = 13 days) and slow HDV clearing (median t1/2 = 44 days), where the slow HDV-clearing population consisted of ∼1% of total HDV-infected cells, which could explain why most patients exhibited a non-monophasic pattern of HDV decline. Moreover, modeling explained ALT normalization without a change in HBsAg based on a non-cytolytic loss of HDV from infected cells, resulting in HDV-free HBsAg-producing cells that release ALT upon death at a substantially lower rate compared to HDV-infected cells.

Conclusion

The entry inhibitor BLV provides a unique opportunity to understand HDV, HBsAg, ALT, and host dynamics.

Impact and implications

Mathematical modeling of hepatitis D virus (HDV) treatment with the entry inhibitor bulevirtide (BLV) provides a novel window into the dynamics of HDV RNA and alanine aminotransferase. Kinetic data from patients treated with BLV monotherapy can be explained by hepatocyte populations with different basal HDV clearance rates and non-cytolytic clearance of infected cells. While further studies are needed to test and refine the kinetic characterization described here, this study provides a new perspective on viral dynamics, which could inform evolving treatment strategies for HDV.

A Semi-mechanistic Model to Characterize the Long-Term Dynamics of Hepatitis B Virus Markers During Treatment With Lamivudine and Pegylated Interferon

Antiviral treatments against hepatitis B virus (HBV) suppress viral replication but do not eradicate the virus, and need therefore to be taken lifelong to avoid relapse. Mathematical models can be useful to support the development of curative anti-HBV agents; however, they mostly focus on short-term HBV DNA data and neglect the complex host-pathogen interaction. This work aimed to characterize the effect of treatment with lamivudine and/or pegylated interferon (Peg-IFN) in 1,300 patients (hepatitis B envelope antigen (HBeAg)-positive and HBeAg-negative) treated for 1 year. A mathematical model was developed incorporating two populations of infected cells, namely I 1 , with a high transcriptional activity, that progressively evolve into I 2 , at a rate δ tr , representing cells with integrated HBV DNA that have a lower transcriptional activity. Parameters of the model were estimated in patients treated with lamivudine or Peg-IFN alone (N = 894), and the model was then validated in patients treated with lamivudine plus Peg-IFN (N = 436) to predict the virological response after a year of combination treatment. Lamivudine had a larger effect in blocking viral production than Peg-IFN (99.4-99.9% vs. 91.8-95.1%); however, Peg-IFN had a significant immunomodulatory effect, leading to an enhancement of the loss rates of I 1 (×1.7 in HBeAg-positive patients), I 2 (> ×7 irrespective of HBeAg status), and δ tr (×4.6 and ×2.0 in HBeAg-positive and HBeAg-negative patients, respectively). Using this model, we were able to describe the synergy of the different effects occurring during treatment with combination and predicted an effect of 99.99% on blocking viral production. This framework can therefore support the optimization of combination therapy with new anti-HBV agents.

HCV direct acting antiviral treatment leads to highly durable rates of ALT and AST lower than 30/19 criteria and improved APRI and FIB-4 scores

Direct acting antiviral treatment (DAA) has been the standard of care for hepatitis C virus (HCV) infection, but its long-term benefits in alanine aminotransferase (ALT) and aspartate aminotransferase (AST) improvement and hepatic fibrosis assessed by aspartate aminotransferase-to-platelet ratio index (APRI) and Fibrosis-4 index (FIB-4) scores remain unknown. The purpose of the present study was to assess DAA's long-term benefits, including frequencies of posttreatment week 96 ALT/AST < 30 (males)/19 (females) (<30/19), improvement of APRI and FIB-4 scores, and the associated factors. This was a single-center, retrospective study on 157 patients with HCV with DAA-mediated sustained virological response (SVR) 12. At posttreatment week (post-Rx wk) 96, 75.4% had ALT < 30/19; 62.7%, AST < 30/19; and 60.1%, both ALT/AST < 30/19. ALT/AST < 30/19 at post-Rx wk 96 was associated with ALT/AST < 30/19 at post-Rx wk 12 (p = 0.026), independently of Child-Turcotte-Pugh < 6 (p = 0.862), platelets ≤ 120 × 10⁹ /L (p = 0.343). Improvement rates of APRI < 0.5 and FIB-4 < 1.45 from baseline to post-Rx wk 96 were from 30.9% to 80.5%, and from 23% to 37.8%, respectively. Both APRI and FIB-4 improvement was associated with both ALT/AST < 30 (males)/19 (females) at post-Rx wk 12 (p = 0.012 and 0.011, respectively). Conclusion: The present study showed that DAA-mediated SVR12 in patients with HCV resulted in (1) high and durable rates of ALT (75.4%), AST (62.7%), and both ALT/AST (60.1%) < 30/19, and (2) high rates of APRI < 0.5 (80.5%) and FIB-4 < 1.45 (37.8%) at post-Rx wk 96, demonstrated clinical value of ALT/AST < 30/19 and excellent long-term outcomes of DAA-mediated SVR12 in these patients.

Some stability results for a model of Hepatitis C including alanine aminotransferase and immune system

In clinical practice, many cirrhosis scores based on alanine aminotransferase (ALT) levels exist. Although the most recent direct acting antivirals (DAAs) reduce fibrosis and ALT levels, the Hepatitis C virus (HCV) is not always removed. In this paper, we study a mathematical model of the HCV virus, which takes into account the role of the immune system, to investigate the ALT behavior during therapy. We find five equilibrium points and analyze their stability. A sufficient condition for global asymptotical stability of the infection-free equilibrium is obtained and local asymptotical stability conditions are given for the immune-free infection and cytotoxic T lymphocytes (CTL) response equilibria. The stability of the infection equilibrium with the full immune response is numerically performed.

Modeling Favipiravir Antiviral Efficacy Against Emerging Viruses: From Animal Studies to Clinical Trials

In 2014, our research network was involved in the evaluation of favipiravir, an anti-influenza polymerase inhibitor, against Ebola virus. In this review, we discuss how mathematical modeling was used, first to propose a relevant dosing regimen in humans, and then to optimize its antiviral efficacy in a nonhuman primate (NHP) model. The data collected in NHPs were finally used to develop a model of Ebola pathogenesis integrating the interactions among the virus, the innate and adaptive immune response, and the action of favipiravir. We conclude the review of this work by discussing how these results are of relevance for future human studies in the context of Ebola virus, but also for other emerging viral diseases for which no therapeutics are available.

Disentangling the lifespans of hepatitis C virus-infected cells and intracellular vRNA replication-complexes during direct-acting anti-viral therapy

The decay rate of hepatitis C virus (HCV)-infected cells during therapy has been used to determine the duration of treatment needed to attain a sustained virologic response, but with direct-acting anti-virals (DAA), this rate has been difficult to estimate. Here, we show that it is possible to estimate it, by simultaneously analysing the viral load and alanine aminotransferase (ALT) kinetics during combination DAA therapy. We modelled the HCV RNA and ALT serum kinetics in 26 patients with chronic HCV genotype 1b infection, under four different sofosbuvir-based combination treatments. In all patients, ALT decayed exponentially to a set point in the normal range by 1-3 weeks after initiation of therapy. The model indicates that the ALT decay rate during the first few weeks after initiation of therapy reflects the death rate of infected cells, with an estimated median half-life of 2.5 days in this patient population. This information allows independent estimation of the rate of loss of intracellular replication complexes during therapy. Our model also predicts that the final ALT set point is not related to the release of ALT by dying HCV-infected cells. Using ALT data, one can separately obtain information about the rate of 'cure' of HCV-infected cells versus their rate of death, something not possible when analysing only HCV RNA data. This information can be used to compare the effects of different DAA combinations and to rationally evaluate their anti-viral effects.

Interferon at the cellular, individual, and population level in hepatitis C virus infection: Its role in the interferon-free treatment era

The advent of powerful direct-acting antiviral agents (DAAs) has revolutionized the treatment of hepatitis C. DAAs cure nearly all patients with short duration, oral treatments. Significant efforts are now underway to optimize DAA-based treatments. We discuss the potential role of interferon in this optimization. Clinical studies present compelling evidence that DAAs perform better in treatment-naive individuals than in individuals who previously failed treatment with interferon, a surprising correlation because interferon and DAAs are thought to act independently. Recent mathematical models explore a mechanistic hypothesis underlying this correlation. The hypothesis invokes the action of interferon at the cellular, individual, and population levels. Strong interferon responses prevent the productive infection of cells, reduce viral replication, and impede the development of resistance to DAAs in infected individuals and improve cure rates elicited by DAAs in treated populations. The models develop descriptions of these processes, integrate them into a comprehensive framework, and capture clinical data quantitatively, providing a successful test of the hypothesis. Individuals with strong endogenous interferon responses thus present a promising subpopulation for reducing DAA treatment durations. This review discusses the conceptual advances made by the models, highlights the new insights they unravel, and examines their applicability to optimize DAA-based treatments.

A New Age-Structured Multiscale Model of the Hepatitis C Virus Life-Cycle During Infection and Therapy With Direct-Acting Antiviral Agents

The dynamics of hepatitis C virus (HCV) RNA during translation and replication within infected cells were added to a previous age-structured multiscale mathematical model of HCV infection and treatment. The model allows the study of the dynamics of HCV RNA inside infected cells as well as the release of virus from infected cells and the dynamics of subsequent new cell infections. The model was used to fit in vitro data and estimate parameters characterizing HCV replication. This is the first model to our knowledge to consider both positive and negative strands of HCV RNA with an age-structured multiscale modeling approach. Using this model we also studied the effects of direct-acting antiviral agents (DAAs) in blocking HCV RNA intracellular replication and the release of new virions and fit the model to in vivo data obtained from HCV-infected subjects under therapy.

Peginterferon alfa-2a is associated with elevations in alanine aminotransferase at the end of treatment in chronic hepatitis C patients with sustained virologic response

Background

The purpose of this study was to investigate the incidence and demographic/clinical factors of alanine aminotransferase (ALT) abnormalities at the end of treatment (EOT) in chronic hepatitis C (CHC) patients with sustained virologic response (SVR).

Methods and Findings

Seven hundred naïve CHC patients who underwent combination treatment between January 2003 and December 2010 were included in the study. The patients with SVR and serum ALT>upper limit of normal (ULN) at the EOT were further analyzed. The effects of clinical characteristics, treatment regimen, and virologic variables were evaluated by logistic regression. Of the 700 included patients, 488 (69.7%) achieved an SVR after treatment, and 235 (33.6%) had serum ALT levels>ULN at the EOT. Of those 488 patients, 137 (28.1%) had abnormal ALT values at the EOT. A multivariate analysis showed that the occurrence of ALT abnormalities at the EOT was significantly associated with pegylated interferon (PEG-IFN) alfa-2a (odds ratio [OR], 2.24; 95% confidence interval [CI], 1.45–3.45; P<0.001), baseline fatty liver (OR, 1.76; 95% CI, 1.16–2.76; P = 0.007), and baseline liver cirrhosis (OR, 2.35; 95% CI, 1.35–4.09; P = 0.002).

Conclusions

Use of PEG-IFN-alfa-2a, fatty liver, and cirrhosis are important factors associated with EOT-ALT abnormality in CHC patients receiving combination therapy that achieve an SVR. PEG-IFN-alfa-2a-related EOT-ALT elevation will become normal at the end of follow-up, but fatty liver and cirrhosis-related ALT elevation will not be resolved.

Emergent properties of the interferon-signalling network may underlie the success of hepatitis C treatment

Current interferon alpha-based treatment of hepatitis C virus (HCV) infection fails to cure a sizeable fraction of patients treated. The cause of this treatment failure remains unknown. Here using mathematical modelling, we predict treatment failure to be a consequence of the emergent properties of the interferon-signalling network. HCV induces bistability in the network, creating a new steady state where it can persist. Cells that admit the new steady state alone are refractory to interferon. Using a model of viral kinetics, we show that when the fraction of cells refractory to interferon in a patient exceeds a critical value, treatment fails. Direct-acting antivirals that suppress HCV replication can eliminate the new steady state, restoring interferon sensitivity and improving treatment response. Our study thus presents a new conceptual basis of HCV persistence and treatment response, elucidates the origin of the synergy between interferon and direct-acting antivirals, and facilitates rational treatment optimization.

Circulating extracellular vesicles as a potential source of new biomarkers of drug-induced liver injury

Like most cell types, hepatocytes constantly produce extracellular vesicles (EVs) such as exosomes and microvesicles that are released into the circulation to transport signaling molecules and cellular waste. Circulating EVs are being vigorously explored as biomarkers of diseases and toxicities, including drug-induced liver injury (DILI). Emerging data suggest that (a) blood-borne EVs contain liver-specific mRNAs and microRNAs (miRNAs), (b) the levels can be remarkably elevated in response to DILI, and (c) the increases correlate well with classical measures of liver damage. The expression profile of mRNAs in EVs and the compartmentalization of miRNAs within EVs or other blood fractions were found to be indicative of the offending drug involved in DILI, thus providing more informative assessment of liver injury than using alanine aminotransferase alone. EVs in the urine and cell culture medium were also found to contain proteins or mRNAs that were indicative of DILI. However, major improvements in EV isolation methods are needed for the discovery, evaluation, and quantification of possible DILI biomarkers in circulating EVs.

Alanine aminotransferase normalization at week 8 predicts viral response during hepatitis C treatment

AIM: To investigate alanine aminotransferase (ALT) and sustained virological response (SVR) in chronic hepatitis C (CHC) during peginterferon-ribavirin treatment.

METHODS: One hundred and fifty-one genotype 1 CHC patients underwent treatment for 48 wk with peginterferon and ribavirin, and were retrospectively divided into two groups as having a rapid virological response (RVR) (Group 1, n = 52) and not having an RVR (Group 2, n = 99). We also subdivided each group into two according to the initial ALT level being high (Group 1h and Group 2h) or normal (Group 1n and Group 2n). HCV RNA and ALT levels were measured at baseline; at 4, 12, 24 and 48 wk during the treatment period; and at 24 wk follow-up. ALT levels were also obtained at 8 wk. According to the results of ALT, patients were enrolled in either the follow-up abnormal or follow-up normalized ALT groups at each interval. Patients with high and normal ALT levels were compared for each interval in terms of SVR.

RESULTS: The SVR rates were 83% vs 40% (P = 0.000), 82% vs 84% (P = 0.830), and 37% vs 44% (P = 0.466) when comparing Group 1 with 2, 1h with 1n, and 2h with 2n, respectively. In Group 2h, the SVR rates were 34% vs 40% (P = 0.701), 11% vs 52% (P = 0.004), 12% vs 50% (P = 0.007), 7% vs 50% (P = 0.003), 6% vs 53% (P = 0.001), and 0% vs 64% (P = 0.000) when comparing patients with high and normalized ALT levels at week 4, 8, 12, 24, 48 and 72, respectively. The multiple logistic regression analysis revealed that RVR (OR = 7.05; 95%CI: 3.1-16.05, P = 0.000), complete early virological response (cEVR) (OR = 17.55; 95%CI: 6.32-48.76, P = 0.000), normalization of ALT at 8 wk (OR = 3.04; 95%CI: 1.31-7.06, P = 0.008), and at 12 wk (OR = 4.21; 95%CI: 1.65-10.76, P = 0.002) were identified as independent significant predictive factors for SVR.

CONCLUSION: Normalization of ALT at 8 wk may predict viral response during peginterferon-ribavirin treatment in genotype-1 CHC patients especially without RVR.

Analysis and simulation of an Adefovir anti-hepatitis B virus infection therapy immune model with alanine aminotransferase

Hepatitis B virus (HBV) infection models and anti-HBV infection therapy models have been set up to understand and explain clinical phenomena. Many of these models have been proposed based on Zeuzem et al. and Nowak et al.'s basic virus infection model (BVIM). Some references have pointed out that the basic infection reproductive number of the BVIM is biologically questionable and gave the modified models with standard mass action incidences. This study describes one anti-HBV therapy immune model with alanine aminotransferase (ALT) based on standard mass action incidences. There are two basic infection reproductive numbers R0 and R1 in the model. It is proved that if R0 < 1 and R1 < 1, the disease free equilibrium is locally and globally asymptotically stable, respectively. For the endemic equilibrium, simulation shows that if R1 > 1, it may be also globally asymptotically stable. Simulations based on clinical data of HBV DNA and ALT can explain some clinical phenomena. Simulations of the correlation between liver cells, HBV DNA, cytotoxic T lymphocytes and ALT are also given.

Hepatitis C viral kinetics: the past, present, and future

Mathematical modeling of hepatitis C viral kinetics has been an important tool in understanding hepatitis C virus (HCV) infection dynamics and in estimating crucial in vivo parameters characterizing the effectiveness of HCV therapy. Because of the introduction of direct-acting antiviral agents, there is a need to extend previous models so as to understand, characterize, and compare various new HCV treatment regimens. Here we review recent modeling efforts in this direction.

Mathematical modelling of HCV infection: what can it teach us in the era of direct-acting antiviral agents?

HCV infection is a major cause of chronic liver disease and affects nearly 170 million people worldwide. Whereas the previous standard of care with pegylated interferon and ribavirin had a modest effectiveness, the recent approval of two highly potent protease inhibitors and the ongoing development of dozens of direct-acting antiviral agents (DAAs) constitute a major milestone for HCV therapy. Mathematical modelling of viral kinetics under treatment has played an instrumental role in improving our understanding of virus pathogenesis and in guiding drug development. Here, we review the current state of HCV kinetic modelling, and challenges to the standard biphasic viral decline model that arise when fitting viral kinetic models to data obtained with DAAs.

A review of mathematical models of influenza A infections within a host or cell culture: lessons learned and challenges ahead

Most mathematical models used to study the dynamics of influenza A have thus far focused on the between-host population level, with the aim to inform public health decisions regarding issues such as drug and social distancing intervention strategies, antiviral stockpiling or vaccine distribution. Here, we investigate mathematical modeling of influenza infection spread at a different scale; namely that occurring within an individual host or a cell culture. We review the models that have been developed in the last decades and discuss their contributions to our understanding of the dynamics of influenza infections. We review kinetic parameters (e.g., viral clearance rate, lifespan of infected cells) and values obtained through fitting mathematical models, and contrast them with values obtained directly from experiments. We explore the symbiotic role of mathematical models and experimental assays in improving our quantitative understanding of influenza infection dynamics. We also discuss the challenges in developing better, more comprehensive models for the course of influenza infections within a host or cell culture. Finally, we explain the contributions of such modeling efforts to important public health issues, and suggest future modeling studies that can help to address additional questions relevant to public health.

Noninvasive monitoring of hepatic damage from hepatitis C virus infection

The mathematical model for the dynamics of the hepatitis C proposed in Avendaño et al. (2002), with four populations (healthy and unhealthy hepatocytes, the viral load of the hepatitis C virus, and T killer cells), is revised. Showing that the reduced model obtained by considering only the first three of these populations, known as basic model, has two possible equilibrium states: the uninfected one where viruses are not present in the individual, and the endemic one where viruses and infected cells are present. A threshold parameter (the basic reproductive virus number) is introduced, and in terms of it, the global stability of both two possible equilibrium states is established. Other central result consists in showing, by model numerical simulations, the feasibility of monitoring liver damage caused by HCV, avoiding unnecessary biopsies and the undesirable related inconveniences/imponderables to the patient; another result gives a mathematical modelling basis to recently developed techniques for the disease assessment based essentially on viral load measurements.

Modelling Hepatitis C virus Kinetics: The Relationship between the Infected Cell Loss rate and the Final Slope of Viral Decay

Background

Patients infected with hepatitis C virus (HCV) who respond to treatment with interferon-α plus ribavirin exhibit biphasic or triphasic viral load decreases. While the rapid first phase is indicative of the effectiveness of therapy in blocking viral production (e), the slope of the final phase ( X), that is, the second phase in biphasic decreases and the third phase in triphasic decreases, depends on the infected cell loss rate (δ). In standard models, X is approximately εδ when the viral clearance rate c>>δ, as has been previously estimated.

Methods

The relationship among e, S, X and the baseline fraction of HCV-infected hepatocytes (π) was investigated in a model that included proliferation of hepatocytes.

Results

We found that X was not proportional to e, but rather obeyed a complex relationship that could lead to dramatic increases in estimates of 8 as e increased. In particular, when ε<99%, X moderately underestimated 8 in patients with a small π, whereas δ might be up to 10-fold larger than λ in patients with a large π. Interestingly, when ε>99%, δ∼λ regardless of π.

Conclusions

Our results indicated that in patients undergoing therapy who achieved a 2 log10 reduction in viral load (ε<99%), previously estimated δ values might represent only a minimal estimate of the infected cell loss rate. Moreover, combining interferon-α with new antiviral agents to achieve ε>99% should allow for a more accurate estimate of 8 in HCV RNA kinetic studies. This might be important when using viral kinetics to estimate the effect of the immune response on viral elimination and the attainment of sustained virological response.

Antinuclear antibody positivity in patients with chronic hepatitis C: clinically relevant or an epiphenomenon?

BACKGROUND

Serum autoantibodies such as antinuclear antibody (ANA) are frequently detected in patients with chronic hepatitis C virus (HCV) infection, but its relevance is a matter of discussion.

AIM

To assess the association of ANA positivity with clinical and histological features, and with the outcome of antiviral therapy in patients with HCV infection.

METHODS

Baseline samples from patients with hepatitis C treated with interferon and ribavirin were tested for ANA positivity by indirect immunofluorescence.

RESULTS

The mean age was 48.3+/-11.1 years and 56% were men. Among 234 included patients, 22 patients (9.4%) were positive for ANA. These patients showed significantly higher median alanine aminotransferase level (3.52 vs. 2.39 x upper limit of normal, P=0.009) when compared with ANA-negative patients. Fibrosis stage and necroinflammatory grading were not influenced by ANA positivity. Sustained virological response (SVR) rates were similar between ANA-positive and ANA-negative patients (27 vs. 29%, P=0.882). Alanine aminotransferase flares (> or = 1.5-fold the baseline) during treatment were observed in 28 patients (12%), irrespective of the presence of ANA and without any clinical significance.

CONCLUSION

Among HCV patients, ANA positivity seems to represent an immunological epiphenomenon. It neither influences clinical, biochemical, and histological features of chronic hepatitis C nor predicts response to antiviral treatment.

Bio-mathematical models of viral dynamics to tailor antiviral therapy in chronic viral hepatitis

The simulation of the dynamics of viral infections by mathematical equations has been applied successfully to the study of viral infections during antiviral therapy. Standard models applied to viral hepatitis describe the viral load decline in the first 2-4 wk of antiviral therapy, but do not adequately simulate the dynamics of viral infection for the following period. The hypothesis of a constant clearance rate of the infected cells provides an unrealistic estimation of the time necessary to reach the control or the clearance of hepatitis B virus (HBV)/hepatitis C virus (HCV) infection. To overcome the problem, we have developed a new multiphasic model in which the immune system activity is modulated by a negative feedback caused by the infected cells reduction, and alanine aminotransferase kinetics serve as a surrogate marker of infected-cell clearance. By this approach, we can compute the dynamics of infected cells during the whole treatment course, and find a good correlation between the number of infected cells at the end of therapy and the long-term virological response in patients with chronic hepatitis C. The new model successfully describes the HBV infection dynamics far beyond the third month of antiviral therapy under the assumption that the sum of infected and non-infected cells remains roughly constant during therapy, and both target and infected cells concur in the hepatocyte turnover. In clinical practice, these new models will allow the development of simulators of treatment response that will be used as an “automatic pilot” for tailoring antiviral therapy in chronic hepatitis B as well as chronic hepatitis C patients.

ANALYSIS OF HEPATITIS C VIRUS INFECTION MODELS WITH HEPATOCYTE HOMEOSTASIS

Recently, we developed a model for hepatitis C virus (HCV) infection that explicitly includes proliferation of infected and uninfected hepatocytes. The model predictions agree with a large body of experimental observations on the kinetics of HCV RNA change during acute infection, under antiviral therapy, and after the cessation of therapy. Here we mathematically analyze and characterize both the steady state and dynamical behavior of this model. The analyses presented here are important not only for HCV infection but should also be relevant for modeling other infections with hepatotropic viruses, such as hepatitis B virus.

Hepatitis C Viral Kinetics in Special Populations

Mathematical models of hepatitis C viral (HCV) kinetics provide a means of estimating the antiviral effectiveness of therapy, the rate of virion clearance and the rate of loss of HCV-infected cells. They have also proved useful in evaluating the extrahepatic contribution to HCV plasma viremia and they have suggested mechanisms of action for both interferon-α and ribavirin. Viral kinetic models can explain the observed HCV RNA profiles under treatment, e.g., flat partial response, biphasic and triphasic viral decay and viral rebound. Current therapy with (pegylated) interferon-α and ribavirin has a poorer success in patients having insulin resistance, hepatic fibrosis, African American ethnicity, HCV/HIV-coinfection, HCV genotype-1 and high baseline viral load. The use of mathematical modeling and statistical analysis of experimental data have been useful in understanding some of these treatment obstacles.

Early and accurate prediction of Peg-IFNs/ribavirin therapy outcome in the individual patient with chronic hepatitis C by modeling the dynamics of the infected cells

A novel biomathematical model that analyzes the combined alanine transaminase (ALT) and viral-load kinetics during the first month of pegylated interferon (Peg-IFN) plus ribavirin (RBV) therapy was successfully applied in 90 of 97 (93%) chronic hepatitis C patients in order to compute the number of infected cells at the end of therapy (I(eot)). The I(eot) indices were lower in sustained virological responders than in relapsers (RELs) and nonresponders (NRs) (median values: 31 vs. 2,190 vs. 1,090,000; P < 0.001), and were independently associated with treatment outcomes (P = 0.003). A threshold of 250 I(eot) was shown to identify sustained virological response (SVR) with high positive predictive value (93%) and good diagnostic accuracy (81%). The time taken to attain 250 I(eot) ranged from 3 to 11 months in patients with hepatitis C virus (HCV) genotypes 2 or 3 and from 3 to 18 months in those with HCV genotypes 1 or 4. Overall, the duration of therapy would have been 49 months less than that suggested by the most recent algorithms based on a rapid virological response (RVR) at week 4.

Dynamics of Apoptotic Activity during Antiviral Treatment of Patients with Chronic Hepatitis C

Introduction

Cell death during antiviral therapy of patients with chronic hepatitis C is not well understood.

Methods

In the present study, apoptotic activity was monitored by quantification of apoptotic cytokeratin-18 neoepitopes in serum from patients with chronic hepatitis C before and 4, 12, 24 and 48 weeks after initiation of antiviral therapy with pegylated interferon-α2a and ribavirin and was compared with viral kinetic parameters.

Results

After 4 weeks of treatment apoptotic activity decreased significantly compared with baseline. Later during treatment, however, apoptotic activity increased again to levels similar to baseline. Alanine aminotransferase (ALT) activity also showed a significant decrease at week 4 compared with baseline but, in contrast to apoptotic activity, ALT remained at a reduced level during the treatment period. Baseline apoptotic activity was inversely correlated with the infected cell loss while an increase of apoptotic activity within the first 4 treatment weeks compared with baseline was positively correlated with the infected cell loss.

Conclusions

Apoptosis appears to be an important form of cell death during interferon-α-based treatment and is associated with infected cell loss and underestimated by ALT activity.

Immunopathogenesis of hepatitis B virus infection

Hepatitis B virus (HBV) infection is a non-cytopathic hepatotropic virus that can lead to severe liver disease including acute hepatitis, cirrhosis and hepatocellular carcinoma. Successful clearance of the virus as well as the establishment of liver disease is largely driven by a complex interaction between the virus and the host immune response. In this review, the immunological events, including both the innate and adaptive immune response are discussed in the setting of both acute and chronic HBV infection and liver disease.

Estimation of dynamical model parameters taking into account undetectable marker values

Background

Mathematical models are widely used for studying the dynamic of infectious agents such as hepatitis C virus (HCV). Most often, model parameters are estimated using standard least-square procedures for each individual. Hierarchical models have been proposed in such applications. However, another issue is the left-censoring (undetectable values) of plasma viral load due to the lack of sensitivity of assays used for quantification. A method is proposed to take into account left-censored values for estimating parameters of non linear mixed models and its impact is demonstrated through a simulation study and an actual clinical trial of anti-HCV drugs.

Methods

The method consists in a full likelihood approach distinguishing the contribution of observed and left-censored measurements assuming a lognormal distribution of the outcome. Parameters of analytical solution of system of differential equations taking into account left-censoring are estimated using standard software.

Results

A simulation study with only 14% of measurements being left-censored showed that model parameters were largely biased (from -55% to +133% according to the parameter) with the exception of the estimate of initial outcome value when left-censored viral load values are replaced by the value of the threshold. When left-censoring was taken into account, the relative bias on fixed effects was equal or less than 2%. Then, parameters were estimated using the 100 measurements of HCV RNA available (with 12% of left-censored values) during the first 4 weeks following treatment initiation in the 17 patients included in the trial. Differences between estimates according to the method used were clinically significant, particularly on the death rate of infected cells. With the crude approach the estimate was 0.13 day^-1 (95% confidence interval [CI]: 0.11; 0.17) compared to 0.19 day^-1 (CI: 0.14; 0.26) when taking into account left-censoring. The relative differences between estimates of individual treatment efficacy according to the method used varied from 0.001% to 37%.

Conclusion

We proposed a method that gives unbiased estimates if the assumed distribution is correct (e.g. lognormal) and that is easy to use with standard software.

Pharmacodynamics of PEG-IFN alpha differentiate HIV/HCV coinfected sustained virological responders from nonresponders

Pegylated interferon (PEG-IFN) has become standard therapy for hepatitis C virus (HCV) infection. We evaluated whether PEG-IFN pharmacodynamics and pharmacokinetics account for differences in treatment outcome and whether these parameters might be predictors of therapeutic outcome. Twenty-four IFN-naïve, HCV/human immunodeficiency virus-coinfected patients received PEG-IFN alpha-2b (1.5 microg/kg) once weekly plus daily ribavirin (1000 or 1200 mg) for up to 48 weeks. HCV RNA and PEG-IFN alpha concentrations were obtained from samples collected frequently after the first 3 PEG-IFN doses. We modeled HCV kinetics incorporating pharmacokinetic and pharmacodynamic parameters. Although PEG-IFN concentrations and pharmacokinetic parameters were similar in sustained virological responders (SVRs) and nonresponders (NRs), the PEG-IFN alpha-2b concentration that decreases HCV production by 50% (EC50) was lower in SVRs compared with NRs (0.04 vs. 0.45 microg/L [P = .014]). Additionally, the median therapeutic quotient (i.e., the ratio between average PEG-IFN concentration and EC50 [C/EC50]), and the PEG-IFN concentration at day 7 divided by EC50 (C(7)/EC50) were significantly increased in SVRs compared with NRs after the first (10.1 vs. 1.0 [P = .012], 2.8 vs. 0.3 [P = .007], respectively) and second (14.0 vs. 1.1 [P = .016], 5.4 vs. 0.4 [P = .02], respectively) PEG-IFN doses. All 3 parameters may be used to identify NRs. In conclusion, PEG-IFN concentrations and pharmacokinetic parameters do not differ between SVRs and NRs. In contrast, pharmacodynamic measurements-namely EC50, the therapeutic quotient, and C(7)/EC50--are different in coinfected SVRs and NRs. These parameters might be useful predictors of treatment outcome during the first month of therapy.

Review article: predicting response in hepatitis C virus therapy

The introduction of combination therapy with ribavirin and of pegylated interferons has improved treatment results in patients with chronic hepatitis C. However, overall rates of sustained virologic response following antiviral therapy of chronic hepatitis C still do not exceed 54-63%. Because of several virus- and patient-related factors, treatment is even less successful in some patient subpopulations. The major viral factors associated with impaired response are hepatitis C virus genotype 1 infection and a high viral load. Among patient-related factors cirrhosis is of special importance. Baseline predictive factors for sustained virologic response become less important for prediction of treatment outcome when quantifications of hepatitis C virus RNA during early therapy are taken into account. This article provides a summary of virus- and patient-related parameters, which are prognostic for response to antiviral therapy in chronic hepatitis C and focuses on the prediction of treatment response by quantification of hepatitis C virus RNA concentration during therapy.

A Multiphase Model of the Dynamics of HBV Infection in Hbeag-Negative Patients during Pegylated Interferon-α2A, Lamivudine and Combination Therapy

Using a multiphase bio-mathematical model, we studied the dynamics of hepatitis B virus (HBV) infection in 72 HBeAg-negative patients who received 48 weeks of either lamivudine (3TC; 25 patients); pegylated interferon-α2a (peg-IFN-α2a) 180 mg weekly plus 3TC (23 patients), or peg-IFN-α2a 180 mg weekly plus placebo (24 patients).

During the first month of therapy most of the 3TC -/+ peg-IFN-α2a treated patients showed a multiphase decay of viral load: during the first two phases, where we hypothesized a direct inhibition of virus production, the mean viral production per infected cell was reduced by 2.22 log10 and 2.36 log10, respectively. At variance, peg-IFN-α2a treated patients had a biphasic profile: the first phase HBV DNA decline was slower than that observed in 3TC patients (mean HBV DNA t1/2=1.6 ±1.1 days and 9.5 ±3.0 h, respectively) and the direct antiviral effect reduced virus production by 1.14 log10 From day 14 onwards (third or second phase according to multi- or biphasic patterns), HBV DNA declined mainly because of the infected hepatocyte clearance that slowed down in approximately 50% of the patients from day 35, possibly because of a negative feedback on the immune system activity. Computing the number of infected cells at the end of therapy we found that peg-IFN-α2a and 3TC monotherapy determined a similar reduction of infected hepatocytes (mean: -3.3 log10), whereas there was a greater reduction in combination therapy patients (-5.0 versus -3.3 log10, P=0.039). In conclusion, peg-IFN-α2a, in spite of having direct antiviral activity lower than that of 3TC, achieved a comparable reduction of infected hepatocytes, possibly because of a higher infected cell clearance rate.

New kinetic models for the hepatitis C virus

Viral kinetic modeling has played an important role in the analysis of HCV RNA decay after the initiation of antiviral therapy. Models have provided a means of evaluating the antiviral effectiveness of therapy, of estimating parameters such as the rate of virion clearance and the rate of clearance of hepatitis C virus (HCV)-infected cells, and they have suggested mechanisms of action for both interferon and ribavirin. Nevertheless, the models that were originally formulated were unable to explain all of the observed HCV RNA profiles. We provide an update on the state of HCV kinetic modeling and discuss new models that have taken into consideration the different pharmacokinetics of standard and pegylated forms of interferon, allow for changes in drug effectiveness as drug concentrations fall between dosing intervals, and that have incorporated alanine aminotransferase kinetics and aspects of immune responses to provide a more comprehensive picture of the biology underlying changes in HCV RNA during therapy.

Replicative homeostasis II: influence of polymerase fidelity on RNA virus quasispecies biology: implications for immune recognition, viral autoimmunity and other "virus receptor" diseases

Much of the worlds' population is in active or imminent danger from established infectious pathogens, while sporadic and pandemic infections by these and emerging agents threaten everyone. RNA polymerases (RNA_pol) generate enormous genetic and consequent antigenic heterogeneity permitting both viruses and cellular pathogens to evade host defences. Thus, RNA_pol causes more morbidity and premature mortality than any other molecule. The extraordinary genetic heterogeneity defining viral quasispecies results from RNA_pol infidelity causing rapid cumulative genomic RNA mutation a process that, if uncontrolled, would cause catastrophic loss of sequence integrity and inexorable quasispecies extinction. Selective replication and replicative homeostasis, an epicyclical regulatory mechanism dynamically linking RNApol fidelity and processivity with quasispecies phenotypic diversity, modulating polymerase fidelity and, hence, controlling quasispecies behaviour, prevents this happening and also mediates immune escape. Perhaps more importantly, ineluctable generation of broad phenotypic diversity after viral RNA is translated to protein quasispecies suggests a mechanism of disease that specifically targets, and functionally disrupts, the host cell surface molecules – including hormone, lipid, cell signalling or neurotransmitter receptors – that viruses co-opt for cell entry. This mechanism – "Viral Receptor Disease (VRD)" – may explain so-called "viral autoimmunity", some classical autoimmune disorders and other diseases, including type II diabetes mellitus, and some forms of obesity. Viral receptor disease is a unifying hypothesis that may also explain some diseases with well-established, but multi-factorial and apparently unrelated aetiologies – like coronary artery and other vascular diseases – in addition to diseases like schizophrenia that are poorly understood and lack plausible, coherent, pathogenic explanations.

Viral kinetics in patients with lamivudine-resistant hepatitis B during adefovir-lamivudine combination therapy

BACKGROUND/AIMS

Mathematical analysis of viral kinetics during lamivudine-adefovir combination therapy has not yet been performed in patients with lamivudine-resistant hepatitis B.

METHODS

In 8 patients with lamivudine-resistant hepatitis B, adefovir dipivoxil (10 mg/day) was added to ongoing lamivudine. Viral decay during the first 8 weeks of combination therapy was described by a biphasic model to determine the efficacy: epsilon, of blocking viral production, the clearance: c, of free virus, and the loss of infected cells: delta.

RESULTS

Median epsilon was 98%, median c was 0.7/day, and median delta was 0.07/day. No significant association was found between viral kinetic and baseline parameters and virologic and biochemical treatment response. When compared with viral kinetic constants reported for higher dose adefovir dipivoxil monotherapy, epsilon was lower (P=0.026) and delta was higher (P=0.008) in this study whereas c did not differ between both studies.

CONCLUSIONS

Although a recent study did not show any differences in the reduction of HBV DNA comparing monotherapy with adefovir dipivoxil to adefovir-lamivudine combination therapy in patients with lamivudine-resistant chronic hepatitis B, mathematical analysis of early viral kinetics suggests an additional effect of lamivudine on the infected cell loss during adefovir-lamivudine combination therapy.

Viral Kinetics in Patients with Chronic Hepatitis C Treated with the Serine Protease Inhibitor Biln 2061

We analysed viral kinetics from a 2-day treatment with BILN 2061, a serine protease inhibitor of hepatitis C virus, in patients chronically infected with genotype 1 hepatitis C virus. The efficiency (ε), describing inhibition of viral production, was above 99.45% in all patients with minor or moderate fibrosis receiving doses of 200 mg and 500 mg twice daily and larger than in previous studies for interferon-based treatments. However, ε was slightly smaller in patients with cirrhosis given 200 mg and markedly smaller in patients given 25 mg. Estimates of viral clearance and infected-cell loss support conclusions on these rates and on treatment mechanisms from previous studies on interferon-α-based treatments.

Mathematical modeling of primary hepatitis C infection: noncytolytic clearance and early blockage of virion production

BACKGROUND & AIMS

Although hepatitis C virus kinetics and immune determinants during primary infection have been described, the virus-host interplay is not fully understood. We used mathematical modeling to elucidate and quantify virus-host dynamics.

METHODS

Ten chimpanzees were infected intrahepatically with H77-RNA (n = 3) or intravenously with infected serum. Blood samples were taken 1-3 times per week for 6 months. A new model was fitted to the observed HCV RNA and alanine aminotransferase (ALT) kinetics.

RESULTS

After infection, viral levels increased in a biphasic manner with a transient decline in between. This can be explained by a partial block (mean, 91%) of virion production, possibly due to an endogenous type I interferon response. After reaching maximum levels, a long viral plateau (mean, 6.1 log cp/mL) can be explained by blind homeostasis and lack of susceptible cells. Modest elevations in ALT levels (21-93 IU/L) were concurrently observed, indicating a shorter half-life of infected versus noninfected hepatocytes (mean ratio, 2.6). Following the ALT flare, viral titers rapidly declined to a lower (mean, 4.5 log cp/mL; n = 6) or undetectable level (n = 4). This decline is compatible with increased cell death (mean minimal estimate half-life, 28.7 days) and noncytolytic clearance (mean maximal estimate half-life, 24.1 days) of infected cells.

CONCLUSIONS

Our results quantify virus-host dynamics during primary HCV infection and suggest that endogenous type I interferon slows virus production in the early acute phase. Partial or effective virus control correlates with the half-life of infected cells regulated by both cytolytic and noncytolytic mechanisms.

Dynamic decision analysis to determine optimal treatment duration in chronic hepatitis C

BACKGROUND

Current guidelines for stopping treatment of chronic hepatitis C are based on hepatitis C ribonucleic acid measurements at 12 and 24 weeks.

AIM

To explore an alternative approach for making individualized recommendations about treatment duration, based on simple alanine aminotransferase tests and on cost-per-cure.

METHODS

We analysed individual patient data from 13 randomized, controlled trials with interferon alone or combined with ribavirin. Using multiple logistic regression, we built a model that estimated the probability of sustained virological response for treatment durations of 24 and 48 weeks. Decisions to prolong treatment were based on an increase in probability of sustained virological response. If the increase was 10%, the cost-per-cure became decisive with a limit of 50,000.

RESULTS

Noncirrhotics with genotype 2 or 3 did not benefit when treatment was continued beyond 24 weeks. Sustained virological response rates in cirrhotic patients increased by 14-47% if treatment was continued up to 48 weeks. In noncirrhotic genotype 1 or 4 patients who had elevated alanine aminotransferase levels at week 4, the probability of sustained virological response increased by <10% if treatment was continued up to 48 weeks; the cost-per-cure for these patients would exceed 50,000.

CONCLUSION

The dynamics of alanine aminotransferase levels and cost-per-cure provides a useful alternative to determine the duration of therapy in chronic hepatitis C.

Replicative homeostasis: a fundamental mechanism mediating selective viral replication and escape mutation

Hepatitis C (HCV), hepatitis B (HBV), the human immunodeficiency viruses (HIV), and other viruses that replicate via RNA intermediaries, cause an enormous burden of disease and premature death worldwide. These viruses circulate within infected hosts as vast populations of closely related, but genetically diverse, molecules known as "quasispecies". The mechanism(s) by which this extreme genetic and antigenic diversity is stably maintained are unclear, but are fundamental to understanding viral persistence and pathobiology. The persistence of HCV, an RNA virus, is especially problematic and HCV stability, maintained despite rapid genomic mutation, is highly paradoxical. This paper presents the hypothesis, and evidence, that viruses capable of persistent infection autoregulate replication and the likely mechanism mediating autoregulation - Replicative Homeostasis - is described. Replicative homeostasis causes formation of stable, but highly reactive, equilibria that drive quasispecies expansion and generates escape mutation. Replicative homeostasis explains both viral kinetics and the enigma of RNA quasispecies stability and provides a rational, mechanistic basis for all observed viral behaviours and host responses. More importantly, this paradigm has specific therapeutic implication and defines, precisely, new approaches to antiviral therapy. Replicative homeostasis may also modulate cellular gene expression.

Viral kinetics during antiviral therapy in patients with chronic hepatitis C and persistently normal ALT levels

The aim of the present study was to compare viral kinetics between patients with chronic hepatitis C and persistently normal alanine aminotransferase (ALT) levels and those with elevated ALT levels. Kinetic parameters were derived from nonlinear, least square fitting of serum hepatitis C virus RNA quantifications collected from patients with chronic hepatitis C and persistently normal (n = 20) and elevated (n = 19) ALT levels before and during treatment with 180 mug pegylated interferon alpha-2a once weekly plus daily ribavirin. Patients with chronic hepatitis C and persistently normal ALT levels showed a trend to lower pretreatment infected cell loss (delta) (P = .13) but no differences in efficacy of blocking virus production (epsilon) and infected cell loss during treatment (mdelta) compared with patients with elevated ALT levels. Differences were significant for epsilon (P = .02) and delta (P = .04) when applying updated "healthy" levels for ALT (0.75 times and 0.63 times upper limit of normal for male and female patients, respectively). A significant reduction of the kinetic parameters epsilon, delta, and mdelta was observed in patients with elevated gamma-glutamyltranspeptidase (GGT) levels compared with patients with normal GGT levels (P = .02, P = .005, and P = .02, respectively). In conclusion, viral kinetics are similar in patients with chronic hepatitis C and persistently normal ALT levels and those with elevated ALT levels. However, in patients with elevated GGT levels, a major association with reduced efficacy of blocking virus production and lower infected cell loss was observed. These data show that virological response in patients with chronic hepatitis C is less associated with baseline ALT than with GGT levels.