Overall, 81.6% of patients had undetectable serum HCV-RNA levels at the end of hepatitis C therapy, and 63.4% reached a sustained virological response, defined as negative serum HCV-RNA 6 months after HCV treatment discontinuation. After the initiation of hepatitis C therapy, there was an overall increase in the mean mtDNA amount in PBMC, which reached statistical significance in patients with baseline serum HCV-RNA levels greater than 6 log IU/ml compared with those with lower HCV-RNA levels (+61 versus –30 mtDNA copies/cell; P = 0.033) and in patients without antiretroviral therapy compared with those under HAART (+133 versus −13 mtDNA copies/cell; P = 0.021). Increases in mtDNA content in PBMC were recognized as soon as week 12 of anti-HCV therapy in patients who suppressed HCV-RNA and were not taking antiretroviral drugs.
As expected, patients on stavudine showed significantly lower median mtDNA at baseline than the rest of the patients on HAART (187 versus 338 mtDNA copies/cell; P = 0.004), whereas patients taking zidovudine had a higher baseline mtDNA content than the rest (424 versus 286 mtDNA copies/cell; P = 0.041). Changes in mtDNA during the course of hepatitis C therapy did not, however, differ significantly when comparing patients using distinct nucleoside analogues as part of HAART (data not shown).
The median ribavirin plasma trough concentrations during HCV therapy were 2.11 μg/ml [interquartile range (IQR) 1.56–3.14]. Serum ribavirin plasma levels tended to be inversely associated with the mtDNA content in PBMC at the end of hepatitis C therapy in the subset of patients on HAART (Spearman's rho −0.326; P = 0.074). Moreover, in the multivariate analysis, whatever combination of antiretroviral drugs taken along with HCV therapy was associated with a significant depletion in the mtDNA content in PBMC (Table 3), supporting a potential additive effect on mitochondrial toxicity of ribavirin and antiretroviral drugs.
This study shows that the level of HCV replication is associated with the extent of mtDNA depletion in PBMC of HIV-infected patients with chronic hepatitis C. Treatment of HCV infection was associated with an improvement in the mtDNA content in this population. This benefit was mainly seen in patients not taking antiretroviral drugs concomitantly, however, suggesting that there is a deleterious effect on mtDNA content when HCV therapy is taken along with antiretroviral drugs.
The recognition of a significant inverse relationship between HCV replication and mtDNA content in PBMC from HIV/HCV-co-infected patients is a remarkable finding. It may help to explain why there is a greater incidence of mitochondrial-related toxicities, such as insulin resistance, dyslipidemia and lipoatrophy, in HIV-infected patients with chronic hepatitis C compared with patients without HCV infection [9,10]. Interestingly, the mtDNA content (at least in PBMC) improved after the suppression of HCV replication with pegIFN plus ribavirin. This observation may allow us to hypothesize that the eradication of HCV infection with hepatitis C therapy might reduce the chances of developing or the severity of metabolic complications and morphological abnormalities frequently seen in HIV/HCV-co-infected patients. If confirmed by others, this observation could be a further argument to prioritize the treatment of hepatitis C in HIV-positive patients.
It should be noted, however, that this benefit of HCV therapy in the mid–long term must be balanced with its potential short-term complications. In the subset of co-infected patients taking antiretroviral drugs, a more profound mtDNA depletion was seen after the prescription of HCV medications, regardless of HCV suppression. Although the inhibition of mitochondrial function has been reported after the administration of interferon , our data favour a more important role for ribavirin, which could interact with some nucleoside analogues, enhancing mitochondrial damage. Accordingly, a trend towards increased mtDNA depletion was noticed in patients on antiretroviral drugs in whom plasma concentrations of ribavirin were greater. Altogether, it seems that a relative mtDNA depletion is associated with active HCV and HIV infections. The use of some nucleoside analogues to treat HIV infection might enhance mitochondral damage, which could be further aggravated by the concomitant prescription of ribavirin in a dose-dependent manner.
Discrepancies reported so far measuring mtDNA in HIV-infected patients with chronic hepatitis C and the effect of anti-HCV therapy with pegIFN plus ribavirin could be explained by the influence of antiretroviral drugs. In an earlier study we recognized an overall detrimental effect, which has not been confirmed in the current larger study; however, most patients in the former study were on antiretroviral therapy . Our current results support the belief that the deleterious effect of HCV replication on mtDNA may be reversed with successful anti-HCV therapy. When pegIFN plus ribavirin are provided in HIV-infected individuals along with antiretroviral drugs, however, this benefit is no longer apparent. We postulate that a synergistic detrimental effect of anti-HCV and anti-HIV drugs is the mechanism for this observation.
Reports of acute pancreatitis, lactic acidosis, hepatic decompensation and severe weight loss have all been described in HCV/HIV-co-infected patients on HAART after the initiation of HCV therapy [15,16,20–23]. Although most of these toxicities have been attributed to an enhancement of mitochondrial toxicity caused by anti-HIV nucleoside analogues, it was unclear whether ribavirin itself might also cause mtDNA damage. Given that the mtDNA content in PBMC uniformly increased during the course of HCV therapy in all our patients not taking antiretroviral drugs, our results suggest that ribavirin does not cause mtDNA depletion by itself. Therefore, HCV therapy should ideally be administered to HCV/HIV-co-infected patients before beginning antiretroviral therapy.
Another interesting observation in this study was that mtDNA depletion at baseline tended to be more pronounced in patients with chronic hepatitis C caused by HCV genotype 3 than in those carrying other HCV genotypes. The relatively low number of patients with HCV genotype 3 probably prevented the results from reaching statistical significance. HCV genotype 3 is particularly prevalent among intravenous drug users in Europe, and responds quite well to HCV therapy . Hepatic steatosis [25,26], liver fibrosis progression [27,28] and episodes of hepatotoxicity after the initiation of antiretroviral therapy [29,30] all seem to be more frequent in individuals infected with HCV genotype 3 than other HCV variants. Therefore, the treatment of chronic hepatitis C caused by HCV genotype 3 should be particularly prioritized in HIV-infected patients. Clearance of infection with this HCV variant in HIV-positive individuals will provide a benefit that is beyond chronic liver disease.
Finally, our data are in favour of a general mechanism of mtDNA depletion in chronic viral diseases, in which high levels of viral particles are produced per day in a given individual. The immunological stress driven by this rapid viral turnover is probably the main cause of this observation . Therefore, our findings may apply not only to HIV and HCV, but also to hepatitis B virus infection. Patients with active chronic hepatitis B may show mtDNA depletion, which could revert somewhat with effective antiviral therapy. Studies are currently ongoing to prove this hypothesis.
In conclusion, HCV replication is directly associated with mtDNA depletion in PBMC of HCV/HIV-co-infected patients, which may explain the higher incidence of mitochondrial-related toxicities seen in this population compared with either HIV or HCV-monoinfected individuals. More importantly, treatment of chronic hepatitis C seems to revert this deleterious effect on the amount of mtDNA. The concomitant administration of antiretroviral drugs during the course of HCV therapy seems to enhance mitochondrial damage further, probably because of a synergistic deleterious interaction between HCV and HIV medications. Long-term follow-up of HIV-infected patients who have cleared HCV with therapy is warranted, and will allow us to confirm whether the incidence of mitochondrial-related toxicities is reduced in this subset of patients.
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