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

Authors


Abstract

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 μg pegylated interferon α-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 (δ) (P = .13) but no differences in efficacy of blocking virus production (ϵ) and infected cell loss during treatment () compared with patients with elevated ALT levels. Differences were significant for ϵ (P = .02) and δ (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 ϵ, δ, and mδ was observed in patients with elevated γ-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. (HEPATOLOGY 2004;40:1442–1449.)

Approximately 20% to 40% of patients with chronic hepatitis C virus (HCV) infection have persistently normal alanine aminotransferase (ALT) levels.1–4 Patients with persistently normal ALT levels generally have mild degrees of liver inflammation and fibrosis and exhibit a lower disease progression rate compared with patients with elevated ALT levels.5 Nevertheless, some patients with persistently normal ALT levels have marked fibrosis, and in rare cases these patients may develop cirrhosis.6

The current standard therapy for patients with chronic hepatitis C and elevated ALT levels is the combination of pegylated interferon α (PEG IFN-α) with ribavirin.7, 8 Conflicting data regarding response to antiviral therapy, long-term benefits, and safety concerns have led to controversy over the treatment of patients with chronic hepatitis C and persistently normal ALT levels.9 However, a recent large international randomized trial in patients with chronic hepatitis C and persistently normal ALT levels showed that PEG IFN-α2a plus ribavirin has a similar efficacy, tolerability, and safety profile as in patients with elevated ALT levels.10

Patients with chronic hepatitis C and persistently normal ALT levels have lower rates of hepatocyte apoptosis and hepatocyte proliferation,11 less intrahepatic CD4+ T-lymphocytes, a reduced antigen-specific CD4+ T-cell proliferation, a lower in vitro T-helper 1 (interferon γ) cytokine production,12 and a lower HCV quasispecies heterogeneity than patients with elevated ALT levels.13, 14 Together, these studies indicate that patients with chronic hepatitis C and persistently normal ALT levels have an altered immunoreactivity against HCV associated with a lower hepatocellular turnover.

Mathematical approaches allow the estimation of the effectiveness of blocking virus production by antiviral therapy and the clearance of productively infected cells from a viral decay model.15–17 Therefore, in the present study, viral kinetics were analyzed in patients with chronic hepatitis C and persistently normal ALT levels to obtain information about the efficacy of combination therapy in blocking viral production (ϵ), the clearance rate (c), the pretreatment infected cell loss (δ), and the infected cell loss during therapy (mδ).15 Viral kinetic parameters were compared with data obtained from patients with chronic hepatitis C and elevated ALT levels.

Abbreviations:

ALT, alanine aminotransferase; GGT, γ-glutamyltranspeptidase; HCV, hepatitis C virus; PEG IFN-α, pegylated interferon α; SVR, sustained virological response; ULN, upper limit of normal.

Patients and Methods

Patients.

Adult patients with chronic hepatitis C who had not been previously treated with IFN-α were eligible for enrollment in the present study. In all patients the diagnosis of chronic hepatitis C was based on the consistent detection of HCV RNA (≥6 months), positive anti-HCV antibodies via third-generation enzyme immunoassay, and histological examination. Histological examination was performed by an experienced local pathologist, and grading and staging were semiquantitatively assessed according to Knodell et al.18 Patients had to be negative for hepatitis B surface antigen and antibodies to human immunodefiency virus types 1 and 2. Patients with alcohol consumption of more than 20 g/d, intravenous drug abuse within 1 year, decompensated liver disease, an organ transplant, neoplastic disease, severe cardiac or chronic pulmonary disease, autoimmune disease (except well-controlled thyroid disease), psychiatric disorders, seizure disorders, severe retinopathy, or unwillingness to practice contraception were excluded.

The present kinetic study was an investigator-initiated substudy within two global phase III randomized, multicenter, controlled trials.10, 19 Both trials as well as the kinetic study were approved by the local Ethics Committee and performed according to the Declaration of Helsinki. All patients gave written informed consent before enrollment.

Treatment With PEG IFN-α2a and Ribavirin.

Patients were randomized for 24 or 48 weeks of treatment with PEG IFN-α2a (PEGASYS; Hoffmann-La Roche, Basel, Switzerland) 180 μg once weekly in combination with ribavirin.10 All patients with persistently normal ALT levels were treated with 800 mg/d ribavirin, while patients with elevated ALT levels were randomized to receive 800 mg/d ribavirin at a fixed dose or 1,000 or 1,200 mg/d according to body weight (<75 kg body weight and ≥75 kg body weight, respectively).19

Serum samples for HCV RNA quantification were collected 30 minutes before the first injection and were subsequently collected 1, 2, 3, 4, 7, and 10 days and 2, 4, 8, 12, and 24 weeks after the injection. The primary efficacy end point for this study was defined as undetectable serum HCV RNA via reverse-transcriptase–polymerase chain reaction 24 weeks after the end of treatment (sustained virological response).

Detection and Quantification of HCV RNA.

Serum HCV RNA was determined using a quantitative reverse-transcriptase–polymerase chain reaction assay (Cobas Amplicor HCV Monitor 2.0; Roche Diagnostic Systems, Branchburg, NJ) with a lower detection limit of 600 IU/mL. Serum samples at the end of therapy and the end of the follow-up period were also tested for HCV RNA using a qualitative assay (Amplicor HCV; Roche Diagnostic Systems) with a lower detection limit of 50 IU/mL. End-of-treatment virological response and sustained virological response (SVR) were defined as undetectable HCV RNA for both assays at the end of treatment and 24 weeks after discontinuation of therapy, respectively. HCV genotyping was performed by reverse hybridization assay (Inno LiPA HCV II; Innogenetics, Gent, Belgium).

Definition of Normal Ranges for Serum ALT and γ-Glutamyltranspeptidase.

ALT and γ-glutamyltranspeptidase (GGT) levels were quantified in the local laboratory. The upper limit of normal (ULN) for ALT was 40 U/L in male and 30 U/L in female patients. The ULN for GGT was 52 U/L in male and 33 U/L in female patients.

Inclusion criteria for patients with chronic hepatitis C and persistently normal ALT levels were three ALT values below the ULN in serum samples taken at least 4 weeks apart, with one value within a 42-day screening period and another between 6 and 12 months before the study onset. Any documented ALT value above the ULN within 18 months before the onset of the study led to exclusion.10 Patients with chronic hepatitis C and elevated ALT values had to have two ALT values above the ULN which were taken at least 4 weeks apart during the preceding 6 months before the onset of combination therapy.19

The current definition of normal ranges for serum ALT levels fails to identify many patients with hepatic injury. Prati et al.20 recently defined 0.75 times the standard ULN for male and 0.63 times the standard ULN for female patients as an updated “healthy” ULN for ALT. According to the reference ranges of our local laboratory, a “healthy” ULN for ALT refers to 30 U/L and 19 U/L for male and female patients, respectively.

Viral Kinetic Model.

Viral kinetics were calculated according to the kinetic model described by Herrmann et al.15 Compartments were used for the free viral load, productively infected, and uninfected hepatocytes. Constant rates were assumed for clearance of free virus (c), infected cell loss (δ), virus production, and de novo infection. Antiviral effects were modeled by efficiency factors ϵ and η on virus production and on de novo infection, respectively, where η was fixed to 0.5. A possible immunological effect on the infected cell loss was modeled by an inflation factor m ≥ 1, which started at some delayed time point t1 > t0. We derived estimates for c, δ, mδ, ϵ, the delay time t1, and the viremia levels V0 = V(t0) and V1 = V(t1) from a nonlinear least squares approach of the logarithmic viral load. All parameters were estimated simultaneously with a general multivariate minimization procedure. To include data below the detection limit, the Tobit approach was used as described previously.17 Numeric minimization and solution of the differential equations was performed using Matlab software (Math Works Inc., Natick, MA).

Statistical Analysis.

Individual parameters from different groups were compared using the Mann-Whitney U test. Here, one-sided P values less than .05 were considered to be significant. Fisher's exact test, χ2 test, and Spearman rank correlation were calculated where two-sided P values less than .05 were considered to be significant.

Results

Baseline Characteristics.

We investigated 20 patients with chronic hepatitis C and persistently normal ALT levels and 19 patients with elevated ALT levels (Table 1). Age, body mass index, distribution of HCV genotypes, and median serum HCV RNA levels were similar in patients with persistently normal and elevated ALT levels. Five patients who fulfilled the enrollment criteria for the group of patients with persistently normal ALT levels during the screening phase had ALT values slightly above the ULN at baseline (1.05, 1.06, 1.06, 1.19, and 1.52 times ULN). Only 6 (30%) of 20 patients with persistently normal ALT levels had “healthy” ALT levels according to an updated ULN for ALT (0.75 times ULN for males and 0.63 times ULN for females).20 Three of these patients were infected with HCV genotype 1, and 3 were infected with HCV genotype 3.

Table 1. Clinical, Biochemical, Molecular, and Histological Characteristics of Patients With Chronic Hepatitis C
CharacteristicsPatients With Chronic Hepatitis C and Persistently Normal ALT (n = 20)Patients With Chronic Hepatitis C and Elevated ALT (n = 19)
  • NOTE. Normal reference ranges: males ≤ 40 U/L, females ≤ 30 U/L for ALT; males ≤ 29 U/L, females ≤ 23 U/L for AST; males ≤ 52 U/L, females ≤ 33 U/L for GGT.

  • Abbreviation: AST, aspartate aminotransferase.

  • *

    Data expressed as median (range).

Age (yr)*44 (33–68)42 (24–73)
Sex (M/F)9/1112/7
Body mass index (kg/m2)*24 (20–34)24 (18–31)
ALT 6–18 months before therapy (U/L)*28 (17–40) 
ALT 1–6 months before therapy (U/L)*28 (13–40)96 (44–233)
ALT 1 month before therapy (U/L)*28 (15–40)112 (45–202)
Baseline ALT (U/L)*28 (15–61)108 (51–324)
Baseline AST (U/L)*26 (13–66)62 (28–157)
Baseline GGT (U/L)*25 (12–144)52 (13–302)
Genotype HCV (1/2/3)12/5/312/1/6
HCV-RNA (log10 IU/mL)*5.4 (4.7–6)5.2 (1–6)
Histological activity index according to Knodell et al.18  
 I–III (grading)*4.5 (2–9)5 (3–10)
 IV (staging)*1 (0–3)3 (1–4)
 Total histology activity index score6 (2–12)6 (4–14)
 Treatment duration (24/48 weeks)12/86/13
 Ribavirin (800/1,000–1,200 mg)20/07/12

Previous studies have identified a baseline ALT level 3 times above the ULN and a normal baseline serum GGT level as independent predictive factors for SVR in multivariate logistic regression analyses.21, 22 Baseline ALT levels 3 times the ULN were present in 9 (47%) of 19 patients with chronic hepatitis C and elevated ALT levels. Normal GGT levels were observed in 15 (75%) of 20 patients with persistently normal ALT levels and in 7 (37%) of 19 patients with elevated ALT levels. The GGT level was correlated with the ALT level (r = 0.58, P < .001), the necroinflammatory score (r = 0.36, P = .03), and the fibrosis score (r = 0.37, P = .03) according to Knodell et al.18 No correlation with body mass index was observed (r = 0.08, P > .2).

Patients with chronic hepatitis C and persistently normal ALT levels tended to have lower histological necroinflammatory and fibrosis scores than patients with chronic hepatitis C and elevated ALT levels. Fibrosis was absent in only 2 (10%) of 20 patients with chronic hepatitis C and persistently normal ALT levels and in none of the patients with chronic hepatitis C and elevated ALT levels. Among the 6 patients with “healthy” ALT levels according to the updated ULN, fibrosis was absent in 1 patient. One patient with “healthy” ALT levels according to the updated ULN had fibrous portal expansion (F2), and 4 patients presented with bridging fibrosis (F3).

Virological Response.

End-of-treatment and SVR rates were not different between patients with persistently normal or elevated ALT levels (Table 2). SVR rates tended to be lower in patients receiving 800 mg/d ribavirin compared with patients receiving 1,000 or 1,200 mg/d ribavirin (two-sided P = .07). Furthermore, significantly lower SVR rates were observed in patients with HCV genotype 1 infection randomized to be treated for 24 weeks compared with patients randomized to be treated for 48 weeks (two-sided P = .007).

Table 2. Virological Response in Patients With Chronic Hepatitis C and Persistently Normal or Elevated ALT Levels
 Patients With Persistently Normal ALT Levels (n = 20)Patients With Elevated ALT Levels (n = 19)
  1. NOTE. Two patients (both HCV genotype 1) with persistently normal ALT levels and 1 patient (HCV genotype 3) with elevated ALT levels prematurely discontinued therapy (weeks 6, 8, and 4, respectively). One patient was HCV RNA–positive at the end of therapy; 2 patients were HCV RNA–negative at the end of therapy and relapsed thereafter.

End-of-treatment virological response (% of total)16/20 (80)15/19 (79)
 HCV 1 (% of HCV 1)9/12 (75)9/12 (75)
 HCV 2, 3 (% of HCV 2, 3)7/8 (88)6/7 (86)
Sustained virological response (of total)10/20 (50)13/19 (68)
 HCV 1 (% of HCV 1)5/12 (42)7/12 (58)
 HCV 2, 3 (% of HCV 2, 3)5/8 (63)6/7 (86)

Viral Kinetics in Patients With Chronic Hepatitis C and Persistently Normal or Elevated ALT Levels.

The first-phase decline is mainly determined by the clearance rate of free viral particles c and the effectiveness of blocking virus production ϵ. The clearance rate of free viral particles c was not different between patients with chronic hepatitis C and persistently normal ALT levels and those patients with elevated ALT levels (P > .2). The efficacy factor ϵ of blocking virus production was associated with HCV genotype (P = .03) and SVR to antiviral therapy (P = .03) but not ribavirin dosage (P > .2). When stratifying for HCV genotype, no difference was found between patients with chronic hepatitis C and persistently normal ALT levels and those patients with elevated ALT levels (P > .2; Figs. 1A, 2A); however, ϵ was significantly lower in patients with “healthy” ALT levels compared with patients with elevated ALT levels (P = .02; Fig. 1B).

Figure 1.

(A) Mean log decay of HCV RNA during the first 6 weeks of antiviral therapy is shown for patients with persistently normal ALT levels who were infected with HCV genotype 1 (solid black line, n = 12) or HCV genotypes 2 and 3 (solid gray line, n = 8) and those with elevated ALT levels infected with HCV genotype 1 (dashed black line, n = 12) or HCV genotypes 2 and 3 (dashed gray line, n = 7). (B) Mean log decay of HCV RNA during the first 6 weeks of antiviral therapy is shown for patients with “healthy” ALT levels according to an updated ULN20 who were infected with HCV genotype 1 (solid black line, n = 3) or HCV genotypes 2 and 3 (solid gray line, n = 3) and those patients with elevated ALT levels who were infected with HCV genotype 1 (dashed black line, n = 12) or HCV genotypes 2 and 3 (dashed gray line, n = 7). Error bars indicate standard deviation. HCV, hepatitis C virus.

Figure 2.

Boxplots of kinetic parameters in patients with chronic hepatitis C and persistently normal ALT levels and those with elevated ALT levels according to HCV genotype. The lower boundary of the boxes indicates the 25th percentile, and the upper boundary indicates the 75th percentile. The horizontal line shows the median of the respective kinetic parameter. The whiskers above and below the boxes indicate the 3-fold quartile distance. Dots indicate extreme values. (A) Efficacy of blocking virus production ϵ. (B) Pretreatment infected cell loss δ. (C) Infected cell loss during treatment mδ. ALT, alanine aminotransferase; HCV, hepatitis C virus.

The decay during the second phase corresponds to the pretreatment infected cell loss δ. A trend toward lower pretreatment infected cell loss δ was found in patients with HCV genotype 1 infection (P = .15), virological nonresponders (P = .06), and patients receiving 800 mg/d ribavirin (P = .08). When stratifying for HCV genotype, patients with persistently normal ALT levels showed a trend to lower pretreatment infected cell loss δ compared with patients with elevated ALT levels (P = .13; Fig. 2B). The difference in the pretreatment infected cell loss δ between patients with persistently normal and elevated ALT levels became most evident when using the updated “healthy” ULN for ALT (Fig. 1B). Patients with a “healthy” ALT level according to the updated ULN20 had a significantly lower δ than patients with elevated ALT levels when stratifying for HCV genotype (P = .04).

A pronounced third phase of viral decline due to treatment-enhanced infected cell loss with a delay (t1) was observed in 9 of 20 patients with chronic hepatitis C and persistently normal ALT levels and in 7 of 19 patients with chronic hepatitis C and elevated ALT levels. The putative treatment-enhanced infected cell loss (mδ), which equals δ in patients with a biphasic decay function, was associated with HCV genotype (P = .01) and SVR (P = .01) but showed only a trend association with ribavirin dosage (P = .09). Similar to the pretreatment infected cell loss, mδ was lower in patients infected with HCV genotype 1 (P = .02) and in virological nonresponders and relapsers (P = .01). Instead, mδ was not different between patients with chronic hepatitis C and persistently normal ALT levels and those with elevated ALT levels when stratifying for HCV genotype (P = .33; Fig. 2C). A trend toward a lower infected cell loss during treatment mδ was observed in patients with a “healthy” ALT level according to the updated ULN for ALT (P = .06), while a 3-fold elevation of baseline ALT was not associated with δ (P = .13) or mδ (P > .2).

Viral Kinetics in Patients According to Baseline GGT Levels.

Patients with normal baseline GGT levels had a significantly higher efficacy of blocking virus production ε than patients with elevated baseline GGT levels when stratifying for HCV genotype (P = .02; Fig. 3A-B). No association between GGT level and the clearance of free virus c was observed. In the second phase of viral decay, normal GGT levels were associated with higher pretreatment infected cell loss δ when stratifying for HCV genotype (P = .005, Fig. 3C). Besides, patients with normal baseline GGT levels showed a higher infected cell loss during treatment mδ compared with patients with elevated baseline GGT levels when stratifying for HCV genotype (P = .02; Fig. 3D).

Figure 3.

(A) Mean log decay of HCV RNA during the first 6 weeks of antiviral therapy is shown for patients with normal baseline GGT levels who were infected with HCV genotype 1 (solid black line, n = 11) or HCV genotypes 2 and 3 (solid gray line, n = 9) and elevated baseline GGT levels in patients who were infected with HCV genotype 1 (dashed black line, n = 13) or HCV genotypes 2 and 3 (dashed gray line, n = 4). Baseline GGT values for 2 patients were unavailable. Error bars indicate standard deviation. (B-D) Boxplots of kinetic parameters in patients with chronic hepatitis C and normal or elevated baseline GGT levels according to HCV genotype. The lower boundary of the boxes indicates the 25th percentile, and the upper boundary the 75th percentile. The horizontal line shows the median of the respective kinetic parameter. The whiskers above and below the boxes indicate the 3-fold quartile distance. Dots indicate extreme values. (B) Efficacy of blocking virus production ϵ. (C) Pretreatment infected cell loss δ. (D) Infected cell loss during treatment . HCV, hepatitis C virus; GGT, γ-glutamyltranspeptidase.

Biochemical Response to Antiviral Therapy.

We observed two distinct patterns of ALT change during treatment resembling pattern 1 (ALT decline to a lower level) and pattern 3 (ALT increase to a higher level) according to Ribeiro et al.23 Pattern 2 showing an intermediate increase of the ALT level could not be differentiated from pattern 1 because of the frequency of the serum sampling. Patterns of ALT change during antiviral therapy were different among patients with persistently normal and elevated ALT levels (P = .02). An increase to higher ALT levels resembling pattern 323 was found in 5 (25) of 20 patients with persistently normal ALT levels but in none of the patients with elevated baseline ALT levels. Patterns of ALT change were not associated with kinetic parameters ϵ, δ, and mδ (P > .2, P > .2, P > .2). Nine (45%) of 20 patients with persistently normal ALT levels and 8 (42%) of 19 patients with elevated ALT levels showed a decline of ALT below the updated “healthy” ULN for ALT within 24 weeks of treatment, respectively.

At the end of the 24-week posttreatment follow-up period, low ALT levels were significantly associated with SVR (P = .001). Twenty-four weeks after the end of therapy, 11 (55%) of 20 patients with persistently normal baseline ALT levels and 7 (37%) of 19 patients with elevated pretreatment ALT levels showed ALT levels below the updated “healthy” ULN for ALT. In addition, GGT levels were significantly lower in sustained virological responders compared with nonresponders 24 weeks after the end of therapy (P = .002).

Discussion

Analysis of viral kinetics enables an efficient comparison of different groups even for relatively small sample sizes.15–17, 23, 25, 26 Here, viral kinetics in 20 patients with chronic hepatitis C and persistently normal ALT levels and 19 patients with elevated ALT levels were analyzed. The first-phase decline of the viral load is mainly determined by the clearance rate of free viral particles c and the effectiveness of blocking virus production ϵ. In the present study, no differences in the viral degradation rate c and for the efficacy of PEG IFN-α2a plus ribavirin to block virus production ϵ were observed between patients with chronic hepatitis C and persistently normal ALT levels and those with elevated ALT levels. A strong association of ϵ with HCV genotype, which was previously described for patients with chronic hepatitis C and elevated ALT levels, was confirmed in patients with persistently normal ALT levels.15, 17, 25

The decay of viral load in the second phase corresponds to the pretreatment infected cell loss δ. Patients with persistently normal ALT levels showed a trend to lower infected cell loss δ compared with patients with elevated ALT levels. These findings are in agreement with previous kinetic studies showing a positive correlation between baseline ALT levels and the infected cell loss δ17, 23 and with studies showing that patients with chronic hepatitis C and persistently normal ALT levels have lower levels of hepatocellular apoptosis and proliferation11 and a weaker immune response than patients with elevated ALT levels.12–14

The possibility of a treatment-induced enhancement of infected cell loss is included in a triphasic model.15 Such treatment effects on the infected cell loss can be explained in part by an enhanced immunological response and by the reduction of HCV particles with a putative suppressive effect on the immune system.15, 27 In the present study, approximately half of the patients with chronic hepatitis C and persistently normal or elevated ALT levels showed a third phase of viral kinetics. No differences in treatment-induced infected cell loss mδ were observed between patients with chronic hepatitis C and persistently normal ALT levels and those with elevated ALT levels. Thus, virus- or host-related factors leading to a reduced hepatocellular turnover in patients with chronic hepatitis C and persistently normal ALT levels may be less important for the elimination of infected cells during treatment with PEG IFN-α and ribavirin. We cannot exclude that differences in δ and achieve statistical significance when investigating larger cohorts. Nevertheless, the results of the present study are in line with SVR rates obtained in a recent multicenter, randomized, controlled trial.10

Markedly different SVR rates were observed between HCV genotype 1–infected patients with persistently normal ALT levels and HCV genotype 1–infected patients with elevated ALT levels who were treated with PEG IFN-α2a and 800 mg/d ribavirin for 24 weeks (13% vs. 24%), while SVR rates were similar in those patients treated for 48 weeks (40% vs. 41%).10, 19 The low SVR rate in 13% of patients with persistently normal ALT levels treated for 24 weeks was due to a high relapse rate, because the end-of-treatment virological response in this group was as high as 68%.10 The lower infected cell loss δ as observed in the present study for HCV genotype 1–infected patients with persistently normal ALT levels provides a comprehensive explanation for the high virological relapse rate in this patient population after 24 weeks of combination treatment. Longer treatment duration apparently can compensate for a lower infected cell loss δ and possibly mδ and appears to be particularly important for patients with persistently normal ALT levels.

Current ULNs for ALT fail to identify many patients with hepatic injury.20 Based on a population of first-time blood donors at lowest risk for liver diseases, Prati et al.20 computed “healthy” ranges for ALT that are considerably lower than the current ULN for ALT. In the present study, only one third of patients with chronic hepatitis C and persistently normal ALT levels had “healthy” ALT levels according to these updated ULNs. “Healthy” ALT levels according to the updated ULNs were associated with a lower efficacy of blocking virus production ϵ and a lower pretreatment infected cell loss δ. However, the infected cell loss during treatment mδ was less affected, and a trend toward lower mδ was observed only in patients with “healthy” ALT levels. Whether lower mδ affects SVR cannot be answered with the small number of patients with “healthy” ALT levels in the present study, but this question should be addressed in future prospective trials.

The baseline GGT level in patients with chronic hepatitis C has been shown in multivariate analyses to be an independent predictor of virological response to antiviral therapy.21, 22 Although baseline GGT levels and ALT levels are correlated, the effects on viral kinetic parameters were different in the present study. While patients with persistently normal ALT levels tended to a lower efficacy of blocking virus production and reduced infected cell loss, a lower efficacy of blocking virus production ϵ, a lower infected cell loss δ, and a lower infected cell loss during treatment mδ was observed in patients with elevated baseline GGT levels compared with patients with normal baseline GGT levels. The results indicate that the underlying mechanisms leading to an elevated GGT level have a stronger and more sustained influence on the responsiveness to antiviral therapy than the mechanisms associated with normal ALT levels.

The mechanisms leading to elevation of the GGT level in chronic hepatitis C are not fully understood. In agreement with previous studies,22 we observed a correlation between the GGT level and the necroinflammation score and fibrosis. GGT elevations caused by toxic injury and obesity are unlikely due to strict inclusion criteria in the present study and a lack of correlation with body mass index. It is possible that GGT elevation is a result of HCV infection of biliary epithelial cells and/or HCV-induced bile duct damage.28, 29 Furthermore, the association between elevated GGT and insulin resistance30–32 may explain a reduced virological response to IFN-α.33

Patients with persistently normal baseline ALT levels showed a different distribution of ALT patterns during treatment than patients with elevated baseline ALT levels.23 An increase of ALT levels during treatment was more likely in patients with persistently normal baseline ALT levels, however, ALT patterns had no influence on viral kinetic parameters. In the majority of virological responders, irrespective of the pretreatment ALT level, ALT levels decreased below the updated “healthy” ULN20 and in sustained virological responders remained there throughout the follow-up period, indicating that successful antiviral therapy is associated with a reduction of hepatocellular turnover.

In conclusion, patients with persistently normal ALT levels show a trend to lower infected cell losses than patients with elevated ALT levels. The lower turnover rate of infected cells is typically overcome early during treatment, leading to similar kinetic profiles after the second week of treatment and comparable sustained response rates in both groups. Patients with chronic hepatitis C and elevated GGT levels but not persistently normal ALT levels showed a reduced efficacy of blocking virus production and lower infected cell loss before and during therapy with PEG IFN-α2a and ribavirin. These data show that virological response in patients with chronic hepatitis C is less associated with baseline ALT than with GGT.

Ancillary