Does hepatitis C cause liver injury by pathways associated with mitochondrial dysfunction?

Mitochondrial abnormalities in patients with HIV-HCV co-infection as compared to patients with HCV mono-infection

INTRODUCTION

Mitochondrial dysfunction is a classic complication of HIV infection and its treatment and has also been reported in hepatitis C virus (HCV)-infected patients. Little is known about interactions between both viruses on mitochondrial metabolism.

METHODS

We performed a cross-sectional study of HCV-infected patients who underwent liver biopsy as part of their routine care. Mitochondrial function was assessed by (a) liver morphological (histology) and functional (spectro-photometry) studies, and (b) serum lactate kinetics, oxygen uptake, and anaerobic threshold measurement during standardized incremental exercise. Three predefined groups of patients were compared.

RESULTS

Thirty-eight HCV-infected patients were included: 13 not HIV infected (group 1), 7 with HIV co-infection and low nucleoside reverse transcriptase inhibitor (NRTI) exposure (none over the last 2 years; group 2), and 18 with HIV co-infection and high NRTI exposure (group 3). On liver biopsies, respiratory chain complex IV activity was impaired, at 5 (2-7) nmol/min/mg substrates in group 1, 5 (3-8) in group 2, and 8 (2-13) in group 3 (normal values, 20-56). Maximal power output was diminished and anaerobic threshold occurred earlier in HIV-infected patients, regardless of NRTI exposure.

CONCLUSION

HCV has deleterious effects on liver mitochondrial metabolism, notably on respiratory chain complex IV. No significant interaction with HIV was observed.

Possible effects of interferon-alpha on Fas-induced renal apoptosis in mouse

Fas (APO-1/CD95) is a cell surface receptor that initiates apoptotic pathway. Fas-stimulated ROS generation may play important role in Fas-mediated apoptosis. The aim of this study was to evaluate the influence of interferon-alpha on oxidative stress parameters in Fas-induced renal apoptosis in mice kidney.

SUBJECTS AND METHODS

One-month-old Balb C male mice were used for the study. The animals were divided in four groups: group 1 were the controls, group 2 mice were treated with anti-Fas antibody i.p., group 3 mice were treated with IFN-alpha, and group 4 mice were treated with both agents simultaneously. The mice were killed 48 h afterwards, and kidneys were homogenized. TBA reactive substances (TBARS), glutathione content, and reactive carbonyl group (RCG) were measured.

RESULTS

The results showed a statistically significant increase of TBARS (p < 0.05) and RCG (p < 0.05) concentration in the group treated with anti-Fas antibody versus control. IFN-alpha decreased the concentration of TBARS and RCG after anti-Fas antibody administration (p < 0.05). There is no significant difference in glutathione content between investigated groups.

CONCLUSION

IFN-alpha might be considered as a new target for therapeutic intervention in FasL/Fas induced renal injury.

Alteration of cytochrome oxidase subunit I labeling is associated with severe mitochondriopathy in NRTI-related hepatotoxicity in HIV patients

Liver mitochondrial toxicity induced by nucleoside reverse transcriptase inhibitors (NRTI) in human immunodeficiency virus (HIV) patients has been associated with a wide range of liver involvement ranging from low-grade hepatotoxicity, asymptomatic lactacidemia to severe liver insufficiency, with massive steatosis and life-threatening lactic acidosis. Considerable efforts have been made in the last few years to establish clinical guidelines to avoid life-threatening NRTI-associated lactic acidosis. However, the important issue of low-grade NRTI-associated hepatotoxicity still needs to be unravelled since its natural history is largely unknown. We have recently reported a series of 13 monoinfected HIV patients with low-grade NRTI-associated toxicity. Our results outlined the heterogeneity of NRTI-induced hepatotoxicity and raised the question of its diagnosis. The present study evaluates the expression of cytochrome oxidase (COX) subunits I and IV, encoded by mitochondrial and nuclear DNA, respectively, in NRTI hepatotoxicity. The aim of our study was to compare the detection rate of mitochondrial abnormalities of immunohistochemistry for COX subunit I with electron microscopy. COX subunit I and IV labeling was performed together with light microscopy and ultrastructural analysis in a series of 55 liver biopsies from HIV monoinfected and HIV-hepatitis C virus coinfected patients. Clinical data were also recorded. Our major findings were: (i) decreased COX subunit I labeling is associated with severe ultrastructural mitochondrial alterations and may represent overt NRTI-induced mitochondrial cytopathy; (ii) mild ultrastructural damage associated with normal COX subunit I labeling is of unknown clinical significance. The results of the study suggest that COX subunit I labeling may be a valuable tool for the diagnosis of mitochondrial liver disease in HIV patients.

Mitochondrial DNA depletion in liver tissue of patients infected with hepatitis C virus: contributing effect of HIV infection?

OBJECTIVES

It has been suggested that chronic hepatitis C virus (HCV) infection depletes mitochondrial DNA (mtDNA) in the liver. Because decreased mtDNA levels were also found in humans infected with HIV, we investigated whether HIV may have aggravated hepatic mtDNA depletion in individuals with HCV infection.

METHODS

In this cross-sectional study, liver biopsies were performed in a total of 40 individuals prior to any antiviral therapy. The individuals were recruited from the Hospital Clinic, Barcelona and the HIV Centre, Dusseldorf. Seventeen patients were negative for HIV and HCV and were biopsied for liver enzyme elevation of unknown cause (controls), 14 individuals had chronic HCV but no HIV infection, and nine subjects were coinfected with both viruses. mtDNA and liver histology were centrally assessed.

RESULTS

The groups did not differ with respect to age, gender, liver function tests and HCV viral load, where applicable. mtDNA levels were decreased by 19% in the HCV-monoinfected group (P=0.03) and by 27% in the HIV/HCV-coinfected subjects (P=0.02) compared to controls. The mtDNA content, however, did not differ between individuals with HCV monoinfection and HCV/HIV coinfection (P=0.75). The degrees of liver fibrosis, inflammatory activity or steatosis did not correlate with mtDNA content.

CONCLUSIONS

Liver mtDNA content is reduced in both HCV-monoinfected and HIV/HCV-coinfected patients. Under the limitations of our study, we could demonstrate only a slight trend towards more pronounced mtDNA depletion in HIV/HCV-coinfected subjects.

Improvement of mitochondrial function evaluated by ketoisocaproic acid breath test in patients with HCV infection undergoing albumin dialysis

BACKGROUND AND AIM

Oxidative injury occurs as a direct result of hepatitis C virus (HCV) core protein expression both in vitro and in vivo, and may be due to a direct effect on mitochondria. The ketoisocaproic acid (KICA) breath test is a simple, reliable, and noninvasive test to evaluate hepatic mitochondrial function. Albumin dialysis (MARS) is an effective bridge treatment for patients with acute failure superimposed on chronic liver disease. The aim of our study was to evaluate the improvement of mitochondrial function measured by KICA in patients undergoing MARS for acute-on-chronic HCV liver failure.

MATERIALS AND METHODS

Five patients with HCV chronic infection undergoing MARS treatment for acute decompensation were enrolled. Before and after each MARS treatment, patients underwent blood testing for the main hematochemical parameters as well as for mitochondrial function by the KICA breath test and the arterial ketone bodies ratio (AKBR).

RESULTS

MARS treatment effectively decreased the serum level of total bilirubin, bile acids, urea, and ammonium. Moreover, MARS treatment produced an increase in AKBR and in the cumulative percentage of (13)CO(2) recovered in exhaled air 2 hours after KICA ingestion.

CONCLUSION

Liver mitochondrial function appears to be beneficially affected by MARS treatment.

Special considerations in the initiation and management of antiretroviral therapy in individuals coinfected with HIV and hepatitis C

BACKGROUND

Although hepatitis C (HCV) treatment efficacy has improved in recent years, the majority of HIV/HCV-coinfected individuals may not enjoy the full benefits of these treatments and appropriate HIV management is crucial. Evidence is accumulating regarding the impact of HIV/HCV coinfection on the response to, and safety and tolerability of, antiretroviral therapy (ART) in this population.

METHODS

Computerized, English-language literature searches of MEDLINE and PubMed databases (January 1985 to May 2004) for studies of HIV and HCV infection in humans to examine critically (a) the impact of HCV on the HIV virologic and immunologic response to ART; (b) the safety and tolerability of ART in coinfected individuals; and (c) the relationship between immune suppression and immune restoration on hepatic injury.

RESULTS

Three key messages emerged regarding the use of ART in HIV/HCV-coinfected individuals: (a) although HCV appeared to have no impact on HIV virologic response, the data are equivocal regarding immunologic response; (b) morbidities associated with HCV infection, such as insulin resistance, diabetes, mitochondrial dysfunction, and liver inflammation, are also associated toxicities of ART, and (c) both immune suppression and restoration can contribute to the onset and acceleration of HCV-related liver disease.

CONCLUSIONS

The CD4 cell count threshold for initiating ART in HIV/HCV-coinfected patients may be higher because of the impact of immune suppression and restoration on the onset of HCV-associated liver disease and the possibility of a blunted immune response to ART at lower CD4 cell counts. Further, overlapping morbidity between HCV-related mitochondrial and metabolic disease manifestations and ART toxicities warrant careful attention by clinicians.

Depletion of mitochondrial DNA in liver under antiretroviral therapy with didanosine, stavudine, or zalcitabine

The "D drug" HIV reverse-transcriptase inhibitors zalcitabine, didanosine, and stavudine are relatively strong inhibitors of polymerase-gamma compared with the "non-D drugs" zidovudine, lamivudine, and abacavir. D drugs deplete mitochondrial DNA (mtDNA) in cultured hepatocytes. This mtDNA depletion is associated with an increased in vitro production of lactate. To investigate the origin of hyperlactatemia in HIV-infected patients and the effects of antiretroviral therapy on liver mtDNA, we biopsied liver tissue from 94 individuals with chronic hepatitis C virus (HCV) infection. Eighty subjects were coinfected with HIV. Serum lactate was measured at the time of biopsy. Hepatic mtDNA and liver histology were centrally assessed. Liver mtDNA content of HIV-infected patients receiving D drugs at the time of biopsy (n = 34) was decreased by 47% (P<.0001) compared with those without D drugs (n = 35). Aside from a possible association between HCV genotype I status and mtDNA depletion in multivariate analysis, there were no other virologic, immunologic, histologic, demographic or treatment-related variables that could explain the mtDNA depletion. Lactate was above the upper limit of normal in only three patients, all of whom were treated with D drugs. The mtDNA in each of them was lower than in any non-D drug patient and significantly (P =.017) depleted compared with D drug patients with normal lactate. In conclusion, D drug treatment is associated with decreased hepatic mtDNA in HIV-infected patients with chronic HCV infection. Moderate mtDNA depletion in liver does not necessarily lead to hyperlactatemia, but more pronounced decreases in hepatic mtDNA may be an important contributor to lactate elevation.

Clinical manifestations and management of antiretroviral nucleoside analog-related mitochondrial toxicity

OBJECTIVES

This article reviews the clinical manifestations of mitochondrial toxicity associated with the use of nucleoside analog reverse transcriptase inhibitors (NRTIs) and outlines strategies to manage these sequelae.

BACKGROUND

NRTIs are the key components of the antiretroviral combinations used in the management of patients infected with HIV. The available NRTIs differ in their convenience of administration, frequency of dosing, resistance profiles, and side-effect profiles. NRTIs act as competitive inhibitors of the RNA/DNA polymerase reverse transcriptase of HIV and cause chain termination in the growing viral DNA chain. Many of the important and treatment-limiting side effects of NRTIs may be related to the effect of these agents on human DNA polymerases, in particular, mitochondrial DNA polymerase gamma. Depletion of mitochondrial DNA during chronic NRTI therapy may lead to cellular respiratory dysfunction and generalized and tissue- and drug-specific toxicities, including myopathy, peripheral neuropathy, and lactic acidosis. Recently, it has been proposed that the fat redistribution syndrome, or lipodystrophy, reported during chronic antiretroviral therapy is a manifestation of the differential impact of at least some NRTIs on peripheral and visceral adipocytes. Management of potential mitochondrial toxicity during NRTI therapy remains a challenge. A range of nutritional supplements, both as treatments and prophylaxes, have been proposed, and some have been investigated in vitro; no in vivo studies have yet been conducted.

METHODS

The information in this review was compiled using MEDLINE and AIDSLINE searches of the literature, including conference abstracts.

CONCLUSIONS

At present, interruption of NRTI therapy or substitution of the probable causative agent with alternative NRTIs that appear to be better tolerated represents the mainstay of management for mitochondrial toxicity and its clinical manifestations.

Mitochondrial toxicity of nucleoside analogue reverse transcriptase inhibitors: a looming obstacle for long-term antiretroviral therapy?

Nucleoside reverse transcriptase inhibitors suppress HIV replication by blocking reverse transcriptase, an RNA-dependent DNA polymerase. These drugs can also affect cellular and mitochondrial DNA polymerases. Mitochondrial DNA polymerase gamma is particularly sensitive to nucleoside reverse transcriptase inhibitors, and the majority of adverse effects caused by nucleoside reverse transcriptase inhibitors are most likely caused by mitochondrial dysfunction. This article reviews the recent clinical implications of nucleoside reverse transcriptase inhibitor-induced mitochondrial toxicity and discusses options for management.