Pharmacogenetics of ribavirin-induced anemia in hepatitis C

Inosine Triphosphate Pyrophosphatase (ITPase): Functions, Mutations, Polymorphisms and Its Impact on Cancer Therapies

Inosine triphosphate pyrophosphatase (ITPase) is an enzyme encoded by the ITPA gene and functions to prevent the incorporation of noncanonical purine nucleotides into DNA and RNA. Specifically, the ITPase catalyzed the hydrolysis of (deoxy) nucleoside triphosphates ((d) NTPs) into the corresponding nucleoside monophosphate with the concomitant release of pyrophosphate. Recently, thiopurine drug metabolites such as azathioprine have been included in the lists of ITPase substrates. Interestingly, inosine or xanthosine triphosphate (ITP/XTP) and their deoxy analogs, deoxy inosine or xanthosine triphosphate (dITP/dXTP), are products of important biological reactions such as deamination that take place within the cellular compartments. However, the incorporation of ITP/XTP, dITP/dXTP, or the genetic deficiency or polymorphism of the ITPA gene have been implicated in many human diseases, including infantile epileptic encephalopathy, early onset of tuberculosis, and the responsiveness of patients to cancer therapy. This review provides an up-to-date report on the ITPase enzyme, including information regarding its discovery, analysis, and cellular localization, its implication in human diseases including cancer, and its therapeutic potential, amongst others.

Impact of comorbidities on patient outcomes after interferon-free therapy-induced viral eradication in hepatitis C

BACKGROUND & AIMS

Patients with advanced liver fibrosis remain at risk of cirrhosis-related outcomes and those with severe comorbidities may not benefit from hepatitis C (HCV) eradication. We aimed to collect data on all-cause mortality and relevant clinical events within the first two years of direct-acting antiviral therapy, whilst determining the prognostic capability of a comorbidity-based model.

METHODS

This was a prospective non-interventional study, from the beginning of direct-acting antiviral therapy to the event of interest (mortality) or up to two years of follow-up, including 14 Spanish University Hospitals. Patients with HCV infection, irrespective of liver fibrosis stage, who received direct-acting antiviral therapy were used to build an estimation and a validation cohort. Comorbidity was assessed according to Charlson comorbidity and CirCom indexes.

RESULTS

A total of 3.4% (65/1,891) of individuals died within the first year, while 5.4% (102/1,891) died during the study. After adjusting for cirrhosis, platelet count, alanine aminotransferase and sex, the following factors were independently associated with one-year mortality: Charlson index (hazard ratio [HR] 1.55; 95% CI 1.29-1.86; p = 0.0001), bilirubin (HR 1.39; 95% CI 1.11-1.75; p = 0.004), age (HR 1.06 95% CI 1.02-1.11; p = 0.005), international normalized ratio (HR 3.49; 95% CI 1.36-8.97; p = 0.010), and albumin (HR 0.18; 95% CI 0.09-0.37; p = 0.0001). HepCom score showed a good calibration and discrimination (C-statistics 0.90), and was superior to the other prognostic scores (model for end-stage liver disease 0.81, Child-Pugh 0.72, CirCom 0.68) regarding one- and two-year mortality. HepCom score identified low- (≤5.7 points: 2%-3%) and high-risk (≥25 points: 56%-59%) mortality groups, both in the estimation and validation cohorts. The distribution of clinical events was similar between groups.

CONCLUSIONS

The HepCom score, a combination of Charlson comorbidity index, age, and liver function (international normalized ratio, albumin, and bilirubin) enables detection of a group at high risk of one- and two-year mortality, and relevant clinical events, after starting direct-acting antiviral therapy.

LAY SUMMARY

The prognosis of patients with severe comorbidities may not benefit from HCV viral clearance. An algorithm to decide who will benefit from the treatment is needed to manage the chronic HCV infection better.

Adverse effects of direct acting antiviral-based regimens in chronic hepatitis C patients: a Brazilian experience

Background Direct-acting antivirals (DAA) are currently used for the treatment of chronic hepatitis C (HCV). However, few studies describe the adverse effects (AE) associated with DAA therapy in "real-word" cohorts. Aim To evaluate AE in Brazilian chronic HCV patients after DAA-therapy. Setting A reference center for hepatitis treatment in Rio de Janeiro, Brazil. Methods An observational "real-world" study was conducted with 102 chronic HCV patients undergoing DAA therapy for 12 or 24 weeks. The self-reported AE were correlated with cirrhosis status, genotype, age, current therapeutic schemes and comorbidities. Serious AE were also investigated. Main outcome measure Frequency of AE during DAA therapy. Results Overall, mean ± SD age was 60.9 ± 9.4 years, 67% were females, HCV-genotype 1 was the most prevalent (81%) and 74% were cirrhotic. Moreover, all patients reached sustained virological response. About 90% of patients reported at least one AE associated with current treatment, with a mean of 2.7 symptoms per patient. The most frequently reported AE were fatigue (43%), headache (42%), neuropsychiatric symptoms (30%) and nausea (26%). Furthermore, hemoglobin < 12 mg/dL was the most frequent (38%) laboratory abnormality observed. Neuropsychiatric symptoms were the only AE significantly different in treatment-experienced group when compared to naïve patients (41.7 vs. 12.5, P = 0.002). The higher frequency of AE did not correlate with the presence of previous treatment, cirrhosis, genotype, age, current therapeutic schemes with DAA or comorbidities. Conclusion DAA-based therapeutic regimens demonstrated safety in a Brazilian "real-world" cohort of chronic hepatitis C patients.

DHEA prevents ribavirin-induced anemia via inhibition of glucose-6-phosphate dehydrogenase

Ribavirin has been widely used for antiviral therapy. Unfortunately, ribavirin-induced anemia is often a cause of limiting or interrupting treatment. Our team has observed that dehydroepiandrosterone (DHEA) has a protective effect against in vitro and in vivo ribavirin-induced hemolysis. The aim of this study was to better understand this effect as well as the underlying mechanism(s). DHEA was able to reduce in vitro intraerythrocytic ATP depletion induced by ribavirin. Only 1% of ATP remained after incubation with ribavirin (2 mM) at 37 °C for 24 h vs. 37% if DHEA (200 μM) was added (p < 0.01). DHEA also helped erythrocytes conserve their size, with a shrinkage of only 10% vs 40% at 24 h with ribavirin alone (p < 0.01), and reduced phosphatidylserine exposure at the outer membrane, i.e. 27% vs 40% at 48 h, (p < 0.05). DHEA also inhibits ribavirin-induced hemolysis, i.e. 34% vs 46.5% at 72 h (p < 0.01). DHEA is an inhibitor of glucose-6-phosphate dehydrogenase (G6PD), a key enzyme in the hexose monophosphate shunt connected to the glycolytic pathway which is the only energy supplier of the red blood cell in the form of ATP. We have confirmed this inhibitory effect in the presence of ribavirin. All these observations suggest that ribavirin-induced hemolysis was initiated by ATP depletion, and that the inhibitory effect of DHEA on G6PD was able to rescue enough ATP to limit this hemolysis. This mechanism could be important for improving the therapeutic management of patients treated with ribavirin.

Improvement in Glycemic Control of Type 2 Diabetes After Successful Treatment of Hepatitis C Virus

OBJECTIVE

Hepatitis C virus (HCV) infection is associated with diabetes and may worsen glycemic control in patients with diabetes. We aimed to investigate whether eradication of HCV infection with direct-acting antiviral (DAA) agents is associated with improved glycemic control in patients with diabetes.

RESEARCH DESIGN AND METHODS

We identified 2,435 patients with diabetes who underwent interferon-free and ribavirin-free DAA-based antiviral treatment for HCV in the national Veterans Affairs health care system. Changes in average hemoglobin A_1c (HbA_1c) level and use of antidiabetic medications 1 year before and after antiviral treatment were compared between patients who achieved sustained virologic response (SVR) and those who did not.

RESULTS

Among patients with elevated baseline HbA_1c, the drop in HbA_1c associated with antiviral treatment was greater in those who achieved SVR (0.98%) than in those who sustained treatment failure (0.65%) (adjusted mean difference 0.34, P = 0.02). Use of antidiabetic medications decreased more in patients who achieved SVR than in those who sustained treatment failure, especially for the use of insulin, which dropped significantly from 41.3% to 38% in patients achieving SVR compared with a slight increase from 49.8% to 51% in those who sustained treatment failure.

CONCLUSIONS

DAA-based eradication of HCV is associated with improved glycemic control in patients with diabetes as evidenced by decreased mean HbA_1c and decreased insulin use. These endocrine benefits of SVR provide additional justification for considering antiviral treatment in all patients with diabetes.

ITPase activity modulates the severity of anaemia in HCV-related cirrhosis treated with ribavirin-containing interferon-free regimens

BACKGROUND

To investigate the association between inosine triphosphatase (ITPase) activity and the degree of anaemia occurring during direct-acting antiviral (DAA)/ribavirin (RBV)-based therapy in patients with cirrhosis.

METHODS

In a multicentre, prospective study 227 patients with HCV-related cirrhosis treated with DAA and RBV were enrolled. All patients were screened for the rs1127354 and rs7270101 ITPA single nucleotide polymorphisms using direct sequencing.

RESULTS

150 (66.1%) patients had normal (100%) ITPase activity, 48 (21.1%) had moderate (60%) activity and 29 (12.8%) minimal (≤30%) activity. The ITPase activity significantly influenced the haemoglobin concentration: at day 15 it was -1.248 (sd ±0.978) in the 150 patients with an ITPase activity of 100% and -0.616 (±0.862) in the 77 patients with an ITPase activity less than 100% (P<0.000), and at day 30 it was -1.941 ±1.218 versus -1.11 ±1.218 (P<0.000). The 63 patients with a severe (at least 3/dl) haemoglobin decline, compared to those without, more frequently had an ITPase activity of 100% (82.1% versus 62.8%; P=0.021), were older (mean age ±sd: 66.7 ±8.2 versus 61.4 ±9.7 years; P=0.004) and were treated with a higher ribavirin dose (13.7 ±2.1 versus 12.8 ±2.5 mg/kg/day; P=0.008). At multivariate logistic regression analysis, the ITPase activity of 100% (OR: 2.83; 95% CI: 1.12, 7.10), male gender (OR: 3.22; 95% CI: 1.35, 7.66), body mass index (OR: 1.17; 95% CI: 1.03, 1.34) and dose of ribavirin (OR: 1.22; 95% CI: 1.06, 1.47) were independent predictors of a severe decline in haemoglobin (P<0.0001).

CONCLUSIONS

This study suggests that the polymorphisms in the ITPA gene influence the severity of anaemia during the first month of a DAA/RBV-based treatment in HCV-related cirrhosis.

A disease spectrum for ITPA variation: advances in biochemical and clinical research

Human ITPase (encoded by the ITPA gene) is a protective enzyme which acts to exclude noncanonical (deoxy)nucleoside triphosphates ((d)NTPs) such as (deoxy)inosine 5′-triphosphate ((d)ITP), from (d)NTP pools. Until the last few years, the importance of ITPase in human health and disease has been enigmatic. In 2009, an article was published demonstrating that ITPase deficiency in mice is lethal. All homozygous null offspring died before weaning as a result of cardiomyopathy due to a defect in the maintenance of quality ATP pools. More recently, a whole exome sequencing project revealed that very rare, severe human ITPA mutation results in early infantile encephalopathy and death. It has been estimated that nearly one third of the human population has an ITPA status which is associated with decreased ITPase activity. ITPA status has been linked to altered outcomes for patients undergoing thiopurine or ribavirin therapy. Thiopurine therapy can be toxic for patients with ITPA polymorphism, however, ITPA polymorphism is associated with improved outcomes for patients undergoing ribavirin treatment. ITPA polymorphism has also been linked to early-onset tuberculosis susceptibility. These data suggest a spectrum of ITPA-related disease exists in human populations. Potentially, ITPA status may affect a large number of patient outcomes, suggesting that modulation of ITPase activity is an important emerging avenue for reducing the number of negative outcomes for ITPA-related disease. Recent biochemical studies have aimed to provide rationale for clinical observations, better understand substrate selectivity and provide a platform for modulation of ITPase activity.