Inosine triphosphate protects against ribavirin-induced adenosine triphosphate loss by adenylosuccinate synthase function

Inosine triphosphate pyrophosphatase: A guardian of the cellular nucleotide pool and potential mediator of RNA function

Inosine triphosphate pyrophosphatase (ITPase), encoded by the ITPA gene in humans, is an important enzyme that preserves the integrity of cellular nucleotide pools by hydrolyzing the noncanonical purine nucleotides (deoxy)inosine and (deoxy)xanthosine triphosphate into monophosphates and pyrophosphate. Variants in the ITPA gene can cause partial or complete ITPase deficiency. Partial ITPase deficiency is benign but clinically relevant as it is linked to altered drug responses. Complete ITPase deficiency causes a severe multisystem disorder characterized by seizures and encephalopathy that is frequently associated with fatal infantile dilated cardiomyopathy. In the absence of ITPase activity, its substrate noncanonical nucleotides have the potential to accumulate and become aberrantly incorporated into DNA and RNA. Hence, the pathophysiology of ITPase deficiency could arise from metabolic imbalance, altered DNA or RNA regulation, or from a combination of these factors. Here, we review the known functions of ITPase and highlight recent work aimed at determining the molecular basis for ITPA-associated pathogenesis which provides evidence for RNA dysfunction. This article is categorized under: RNA in Disease and Development > RNA in Disease RNA in Disease and Development > RNA in Development.

Effect of ITPA Polymorphism on Adverse Drug Reactions of 6-Mercaptopurine in Pediatric Patients with Acute Lymphoblastic Leukemia: A Systematic Review and Meta-Analysis

6-Mercaptopurine (6-MP) is a cornerstone of the maintenance regimen for pediatric acute lymphoblastic leukemia (ALL). Inosine triphosphate pyrophosphatase (ITPA) is considered a candidate pharmacogenetic marker that may affect metabolism and 6-MP-induced toxicities; however, the findings are inconsistent. Therefore, we attempted to evaluate the effect of ITPA 94C>A polymorphism on 6-MP-induced hematological toxicity and hepatotoxicity through a systematic review and meta-analysis. A literature search for qualifying studies was conducted using the PubMed, Web of Science, and Embase databases until October 2021. Overall, 10 eligible studies with 1072 pediatric ALL patients were included in this meta-analysis. The results indicated that ITPA 94C>A was significantly associated with 6-MP-induced neutropenia (OR 2.38, 95% CI: 1.56−3.62; p = 0.005) and hepatotoxicity (OR 1.98, 95% CI: 1.32−2.95; p = 0.0009); however, no significant association was found between the ITPA 94C>A variant and 6-MP-induced leukopenia (OR 1.75, 95% CI: 0.74−4.12; p = 0.20). This meta-analysis demonstrated that ITPA 94C>A polymorphism could affect 6-MP-induced toxicities. Our findings suggested that ITPA genotyping might help predict 6-MP-induced myelosuppression and hepatotoxicity.

Novel variant in glycophorin c gene protects against ribavirin-induced anemia during chronic hepatitis C treatment

BACKGROUND

The current use of ribavirin in difficult-to-cure chronic hepatitis C patients (HCV) and patients with severe respiratory infections is constrained by the issue of ribavirin-induced hemolytic anemia that affects 30% of treated patients, requiring dosage modification or discontinuation. Though some genetic variants have been identified predicting this adverse effect, known clinical and genetic factors do not entirely explain the risk of ribavirin-induced anemia.

METHODS

We assessed the associations of previously identified variants in inosine triphosphatase (ITPA), solute carrier 28A2 (SLC28A2) and vitamin D receptor (VDR) genes with ribavirin-induced anemia defined as hemoglobin decline of ≥30 g/L on treatment, followed by a staged discovery (n = 114), replication (n = 74), and combined (n = 188) genome-wide association study to uncover potential new predictive variants.

RESULTS

We identified a novel association in the gene coding glycophorin C (rs6741425; OR:0.12, 95%CI:0.04-0.34, P = 2.94 × 10^-6) that predicts protection against ribavirin-induced anemia. We also replicated the associations of ITPA and VDR genetic variants with the development of ribavirin-induced anemia (rs1127354; OR:0.13, 95%CI:0.04-0.41, P = 8.66 ×10^-5; and rs1544410; OR:1.65, 95%CI:1.01-2.70, P = 0.0437).

CONCLUSIONS

GYPC variation affecting erythrocyte membrane strength is important in predicting risk for developing ribavirin-induced anemia. ITPA and VDR genetic variants are also important predictors of this adverse reaction.

Viral inosine triphosphatase: A mysterious enzyme with typical activity, but an atypical function

Plant viruses typically have highly condensed genomes, yet the plant-pathogenic viruses Cassava brown streak virus, Ugandan cassava brown streak virus, and Euphorbia ringspot virus are unusual in encoding an enzyme not yet found in any other virus, the "house-cleaning" enzyme inosine triphosphatase. Inosine triphosphatases (ITPases) are highly conserved enzymes that occur in all kingdoms of life and perform a house-cleaning function by hydrolysing the noncanonical nucleotide inosine triphosphate to inosine monophosphate. The ITPases encoded by cassava brown streak virus and Ugandan cassava brown streak virus have been characterized biochemically and are shown to have typical ITPase activity. However, their biological role in virus infection has yet to be elucidated. Here we review what is known of viral-encoded ITPases and speculate on potential roles in infection with the aim of generating a greater understanding of cassava brown streak viruses, a group of the world's most devastating viruses.

Pharmacogenomics with red cells: a model to study protein variants of drug transporter genes

The PharmacoScan pharmacogenomics platform screens for variation in genes that affect drug absorption, distribution, metabolism, elimination, immune adverse reactions and targets. Among the 1,191 genes tested on the platform, 12 genes are expressed in the red cell membrane: ABCC1, ABCC4, ABCC5, ABCG2, CFTR, SLC16A1, SLC19A1, SLC29A1, ATP7A, CYP4F3, EPHX1 and FLOT1. These genes represent 5 ATP-binding cassette proteins, 3 solute carrier proteins, 1 ATP transport protein and 3 genes associated with drug metabolism and adverse drug reactions. Only ABCG2 and SLC29A1 encode blood group systems, JR and AUG, respectively. We propose red cells as an ex vivo model system to study the effect of heritable variants in genes encoding the transport proteins on the pharmacokinetics of drugs. Altered pharmacodynamics in red cells could also cause adverse reactions, such as haemolysis, hitherto unexplained by other mechanisms.

An efficient protection-free chemical synthesis of inosine 5'-nucleotides

A facile, straightforward, reliable, and efficient chemical synthesis of inosine nucleotides such as inosine-5'-monophosphate, inosine-5'-diphosphate, and inosine-5'-triphosphate, starting from inosine is delineated. The inosine-5'-monophosphate is achieved by the highly regioselective monophosphorylation of inosine using the Yoshikawa procedure. The inosine-5'-diphosphate is obtained by the coupling reaction of tributylammonium phosphate with an activated inosine-5'-monophosphate using zinc chloride as a catalyst. The inosine-5'-triphosphate is efficiently achieved by the improved "one-pot, three-step" Ludwig synthetic strategy. In all the cases, the resulting final product is isolated in good yields with high purity (>99.5%).

Inosine triphosphate pyrophosphatase polymorphisms are predictors of anemia in Chinese patients with chronic hepatitis C during therapy with ribavirin and interferon

BACKGROUND AND AIM

Polymorphisms of inosine triphosphate pyrophosphatase (rs1127354 and rs6051702) and interferon lambda 4 (IFLN4) (rs12979860) are indicators of anemia and/or sustained virological response (SVR) in patients with chronic hepatitis C on ribavirin/interferon. The study aims to investigate the associations of rs1127354, rs6051702, and rs12979860 with hemoglobin levels and SVR in patients on ribavirin/interferon.

METHODS

Polymorphisms were detected by pyrosequencing. Levels of hemoglobin and hepatitis C virus (HCV) RNA were measured at weeks 2, 4, 12, 24, 36, 48, and 72 of treatment.

RESULTS

A total of 351 patients (median age, 50 years; male, 71.2%) were recruited and had HCV genotypes 1b (55.8%) or 2a (37.0%). Vedian baseline hemoglobin and HCV RNA were 155 g/dL and 6.07 log₁₀ IU/mL. Major allele homozygosity was observed in 76.3% for rs1127354 (CC), 70.9% for rs6051702 (AA), and 89.7% for rs12979860 (CC). At 4 weeks of ribavirin/interferon treatment, a more significant reduction in hemoglobin was observed with rs112754 CC than with AC/AA (P < 0.05). A decline ≥3 g/dL was more common in patients with the rs112754 CC than with the other two polymorphisms. No significant change was observed regarding rs6051702 and rs12979860 variants. In the multivariable analysis, rs1127354 AA/AC (vs CC) were independently associated with lower odds of hemoglobin decline of > 3 g/dL at 4 weeks (odds ratio, 0.21; 95% CI, 0.09-0.46; P < 0.0001). In 258 patients with 72-week outcome data available, rs1127354, rs6051702, and rs12979860 were not associated with SVR (all P > 0.05).

CONCLUSION

rs1127354 polymorphisms are associated with hemoglobin levels in Chinese patients with chronic hepatitis C treated with ribavirin/interferon.

Inosine Triphosphate Pyrophosphatase Dephosphorylates Ribavirin Triphosphate and Reduced Enzymatic Activity Potentiates Mutagenesis in Hepatitis C Virus

A third of humans carry genetic variants of the ITP pyrophosphatase (ITPase) gene (ITPA) that lead to reduced enzyme activity. Reduced ITPase activity was earlier reported to protect against ribavirin-induced hemolytic anemia and to diminish relapse following ribavirin and interferon therapy for hepatitis C virus (HCV) genotype 2 or 3 infections. While several hypotheses have been put forward to explain the antiviral actions of ribavirin, details regarding the mechanisms of interaction between reduced ITPase activity and ribavirin remain unclear. The in vitro effect of reduced ITPase activity was assessed by means of transfection of hepatocytes (Huh7.5 cells) with a small interfering RNA (siRNA) directed against ITPA or a negative-control siRNA in the presence or absence of ribavirin in an HCV culture system. Low ribavirin concentrations strikingly depleted intracellular GTP levels in HCV-infected hepatocytes whereas higher ribavirin concentrations induced G-to-A and C-to-U single nucleotide substitutions in the HCV genome, with an ensuing reduction of HCV RNA expression and HCV core antigen production. Ribavirin triphosphate (RTP) was dephosphorylated in vitro by recombinant ITPase to a similar extent as ITP, a naturally occurring substrate of ITPase, and reducing ITPA expression in Huh 7.5 cells by siRNA increased intracellular levels of RTP in addition to increasing HCV mutagenesis and reducing progeny virus production. Our results extend the understanding of the biological impact of reduced ITPase activity, demonstrate that RTP is a substrate of ITPase, and may point to personalized ribavirin dosage according to ITPA genotype in addition to novel antiviral strategies.IMPORTANCE This study highlights the multiple modes of action of ribavirin, including depletion of intracellular GTP and increased hepatitis C virus mutagenesis. In cell culture, reduced ITP pyrophosphatase (ITPase) enzyme activity affected the intracellular concentrations of ribavirin triphosphate (RTP) and augmented the impact of ribavirin on the mutation rate and virus production. Additionally, our results imply that RTP, similar to ITP, a naturally occurring substrate of ITPase, is dephosphorylated in vitro by ITPase.

Pharmacogenetics and the treatment of HIV-/HCV-coinfected patients

This review will summarize the role of pharmacogenetics in the natural history of hepatitis C, particularly in patients with HIV/HCV and will take the perspective of pharmacogenetics and its influence on the response to antiviral therapy and the susceptibility to develop adverse effects. This review will also devote a section to host genetics in other clinical situations, such as disease progression and acute HCV infection, which may determine whether treatment of HIV-/HCV-coinfected patients is implemented or deferred.

Induction of inosine triphosphatase activity during ribavirin treatment for chronic hepatitis C

BACKGROUND

Ribavirin (RBV) is an antiviral agent and the primary component for chronic hepatitis C (CHC) therapy. Hemolytic anemia is limitation for RBV treatment. Inosine triphosphatase (ITPA) activity has been associated with severity of RBV-induced anemia. However, changes in ITPA activity during CHC therapy are unknown. The aim of this study was to measure the time-dependent change in ITPA activity over the RBV treatment.

METHODS

Forty-two patients with CHC were evaluated for ITPA activity over the course of RBV treatment.

RESULTS

The median value of ITPA activity at start of RBV treatment was 134.2 μmol/h/g hemoglobin (Hb; range, 26.3-251.0 μmol/h/g Hb). The ITPA activity values at 4, 8, and 12 weeks during RBV treatment were 143.2, 202.2, and 225.7 μmol/h/g Hb, respectively, and these ITPA values were significantly elevated compared with the start of treatment (p < 0.001). In patients with ITPA variants, patients with anemia (Hb < 10 g/dL) had greater elevated ITPA activities compared with patients without anemia at 12 weeks.

CONCLUSION

Our findings indicate that ITPA activities are elevated with RBV therapy, and this elevation may be a risk of anemia in late therapeutic phase in patients that began with low ITPA activity.

Reduced ITPase activity and favorable IL28B genetic variant protect against ribavirin-induced anemia in interferon-free regimens

BACKGROUND

Genetic variants of inosine triphosphatase (ITPA) that confer reduced ITPase activity are associated with protection against ribavirin(RBV)-induced hemolytic anemia in peginterferon(IFN)/RBV-based treatment of hepatitis C virus (HCV). Patients with reduced ITPase activity showed improved treatment efficacy when treated with IFN/RBV. In addition, a genetic polymorphism near the IL28B gene is associated with an improved response to IFN/RBV treatment. RBV has been an important component of IFN-containing regimens, and is currently recommended in combination with several IFN-free regimens for treatment of harder to cure HCV infections.

AIM

To evaluate whether genetic variations that reduce ITPase activity impact RBV-induced anemia in IFN-free/RBV regimens.

METHODS

In this study, genetic analyses were conducted in the PEARL-IV trial to investigate the effect of activity-reducing ITPA variants as well as IL28B polymorphism on anemia, platelet (PLT) counts, and virologic response in HCV genotype1a-infected patients treated with the direct-acting antiviral (DAA) regimen of ombitasvir/paritaprevir/ritonavir and dasabuvir±RBV.

RESULTS

Reduction in ITPase activity and homozygosity for the IL28Brs12979860 CC genotype protected against RBV-induced anemia. In patients receiving RBV, reduced ITPase activity was associated with reduced plasma RBV concentration and higher PLT counts. ITPase activity had no impact on response to DAA treatment, viral kinetics, or baseline IP-10 levels.

CONCLUSIONS

Our study demonstrates that genetics of ITPA and IL28B may help identify patients protected from RBV-induced anemia when treated with IFN-free regimens. Our work demonstrates for the first time that IL28B genetics may also have an impact on RBV-induced anemia. This may be of particular significance in patients with difficult-to-cure HCV infections, such as patients with decompensated cirrhosis where RBV-containing regimens likely will continue to be recommended.

A facile PCR-RFLP method for genotyping of ITPA rs1127354 and rs7270101 polymorphisms

BACKGROUND

Inosine triphosphate pyrophosphatase (ITPA) gene single nucleotide polymorphisms (SNPs), rs1127354 and rs7270101, may cause a functional impairment in ITPase enzyme, resulting anemia protection in patients with chronic hepatitis C virus (HCV) infection undergoing ribavirin (RBV)-dependent regimens. The main purpose of this study was to provide and validate a simple, rapid, and inexpensive polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) technique for genotyping of ITPA rs1127354 and rs7270101 polymorphisms in chronic HCV-infected patients.

METHODS

In the current study, 100 Iranian patients with chronic hepatitis C were examined and genotyped for ITPA rs1127354 and rs7270101 gene polymorphisms. To genotype rs1127354 and rs7270101 polymorphisms, PCR-RFLP technique and sequencing technique were performed on these samples. To validate the PCR-RFLP method, the PCR-RFLP genotyping results should be 100% concordant with the PCR-sequencing results.

RESULTS

The rs1127354 and rs7270101 polymorphisms of ITPA gene were genotyped by PCR-RFLP technique and sequencing simultaneously, and the results of both techniques were 100% concordant in all 100 patients. Both PCR-RFLP and sequencing techniques indicated that the genotypic frequency of rs7270101 was 80% AA, 19% AC and 1% CC, and for rs1127354 was 79% CC, 20% CA and 1% AA, respectively.

CONCLUSION

We developed and validated a rapid and inexpensive PCR-RFLP technique for the detection of ITPA rs1127354 and rs7270101 gene polymorphisms.

Single Nucleotide rs760370 Polymorphism at the Main Ribavirin Transporter Gene Detection by PCR-RFLP Assay Compared with the TaqMan Assay and Its Relation to Sustained Virological Response in Chronic HCV Patients Treated with Pegylated Interferon-Ribavirin Therapy

Ribavirin clearly plays a role in chronic hepatitis C treatment response. The equilibrative nucleoside transporter-1 codified by SLC29A1 gene has been associated with ribavirin uptake into hepatocytes and erythrocytes. rs760370A>G single nucleotide polymorphism (SNP) at the SLC29A1 gene may have a role in ribavirin-based regimen treatment response. Accuracy of the polymerase-chain reaction-restriction fragment length polymorphism (PCR-RFLP) assay compared with the TaqMan assay for the detection of the SNP rs760370 at the main ribavirin transporter gene and its relation to sustained virological response in chronic hepatitis C virus (HCV) patients treated with pegylated interferon-ribavirin therapy. The study included 100 chronic HCV patients who were treated with pegylated interferon-ribavirin therapy. The patients were categorized according to the treatment response into responders (50 patients) and null responders (50 patients). rs760370 SNP was measured using TaqMan 5-nuclease assay and by the newly developed PCR-based RFLP assay. The overall accuracy of the newly developed PCR-RFLP assay compared with the TaqMan assay for rs760370 polymorphism detection was 100%. Allelic frequencies at rs760370 were as follows: A/A genotype (28%), A/G genotype (58%), and G/G genotype (14%). Treatment response was not significantly related with rs760370 polymorphism (P = 0.5). Ribavirin-induced anemia was good predictor of sustained virological response (P = 0.001), but was not related to rs760370 polymorphism (P = 0.92). PCR-RFLP assay is an accurate, cost-effective method in the detection of rs760370 compared with TaqMan assay. rs760370 SNP cannot serve as predictor of response in chronic HCV patients treated with interferon ribavirin therapy.

A systematic review and meta-analysis of HCV clearance

While hepatitis C exemplifies the role of host genetics in infectious diseases outcomes, there is no comprehensive overview of polymorphisms influencing spontaneous and/or treatment-induced hepatitis C virus clearance. We performed a systematic review and meta-analysis of host polymorphisms associated with these phenotypes. Literature search was conducted using combinations of keywords in three databases. Studies were reviewed and relevant data systematically extracted for subsequent meta-analyses. Polymorphisms from candidate gene studies were tested in two cohorts of HCV-infected patients with available genomic data. The literature search yielded 8'294 citations, among which 262 studies were selected. In the meta-analysis of 27 HLA studies, the most significant associations with spontaneous hepatitis C virus clearance included DQB1*02, DQB1*03, DRB1*04 and DRB1*11. In the meta-analysis of 16 studies of KIR genes and their HLA-ligands, KIR2DS3 was associated with both spontaneous and treatment-induced clearance, and the HLA-C2 ligand with failure to spontaneously clear the virus. In a pooled analysis of 105 candidate genes and two genome-wide association studies, we observed associations of single nucleotide polymorphisms from nine genes (EIF2AK2, IFNAR2, ITPA, MBL2, MX1, OASL, SPP1, TGFB1, TNK2) with response to interferon-based therapy. Meta-analysis of 141 studies confirmed the association of IFNL3/4 polymorphisms with spontaneous and treatment-induced hepatitis C virus clearance, even in previously underpowered groups, such as hepatitis C virus genotypes 2/3-infected patients. This study may contribute to a better understanding of hepatitis C virus immunopathogenesis and highlights the complex role of host genetics in hepatitis C virus clearance.

The relationship between ITPA rs1127354 polymorphisms and efficacy of antiviral treatment in Northeast Chinese CHC patients

This prospective study investigated the relationship between 2 inosine triphosphatase (ITPA) polymorphisms (rs7270101 and rs1127354) and the efficacy of ribavirin-based antiviral therapy in hepatitis C virus (HCV)-infected Chinese patients.A total of 906 patients diagnosed with chronic hepatitis C receiving pegylated interferon (PEG-IFN) plus ribavirin combination therapy between January 2011 and January 2014 from 5 hepatitis centers in Northeast China were enrolled. The patients were divided into genotype 1 and non-genotype 1 groups according to the genotype of infected HCV. ITPA single nucleotide polymorphism (SNP) genotyping was performed for all patients. Ribavirin-induced hemolytic anemia and virological response (VR) were monitored during treatment and follow-up. Multivariate regression analysis was used to analyze the predictors for sustained virological response (SVR).IPTA rs7270101 variants were not detected. IPTA rs1127354 variants were detected and showed no difference between the genotype 1 and non-genotype 1 groups. IPTA rs1127354 genotype CC was related to a higher incidence of ribavirin-induced hemolytic anemia. For patients who received >80% of the planned ribavirin dose, rs1127354 variants and related ITPase were related to better SVR. Multivariate analysis showed that IPTA rs1127354 non-genotype CC, HCV genotype, a baseline HCV RNA level <4 × 10 IU/mL, IL-28B rs12979860 genotype CC, and low liver fibrosis were independent predictors for SVR during the combination therapy.IPTA rs1127354 variants and related ITPase were not only related with ribavirin-induced hemolytic anemia but also directly affected the SVR to PEG-IFN plus ribavirin combination therapy in Chinese HCV-infected patients.

ITPA gene polymorphism (94C>A) effects on ribavirin-induced anemia during therapy in Egyptian patients with chronic hepatitis C

Inosine triphosphatase (ITPA) gene variants can protect against ribavirin (RBV)-induced anemia in patients treated for chronic hepatitis C. The aim of this study was to determine the relationship between genetic variants of ITPA polymorphism, anemia, RBV dose reduction, and treatment response in hepatitis C virus (HCV)-infected patients. This study was conducted on 97 Egyptian chronic HCV patients who were scheduled for pegylated-interferon (PEG-INF) /RBV therapy. ITPA genotypes rs1127354 were determined by Real Time PCR melting curve analysis. Effects of ITPA polymorphism on hemoglobin (Hb) levels, RBV dose reduction and treatment response were analyzed. The homozygous wild genotype (CC) was associated with Hb reduction at week 4 (P = 0.004). The minor allele protected against Hb reduction. No association with sustained virological response was observed (P = 0.492). Female gender; lower baseline Hb and higher baseline WBC were associated with week 4 anemia (P = 0.04; P = 0.023; 0.033, respectively). The ITPA gene polymorphism rs1127354 heterozygous genotype (CA) may influence Hb levels and protect against hemolytic anemia during RBV-containing regimens for HCV. However, such findings were not significantly related to treatment outcomes. Patients with wild ITPA genotype (CC) experienced a more Hb drop and RBV dose reductions more frequently.

Viral and host factors associated with outcomes of hepatitis C virus infection (Review)

Hepatitis C virus (HCV) infection is a major health issue globally. Owing to the progress made in host genetics and HCV molecular virology, emerging data have suggested that the natural course and treatment response in patients with HCV infection are largely determined by complex host‑viral interactions. HCV genotype is the most important viral factor predicting the response to pegylated interferon‑α plus ribavirin therapy. The subtype of HCV genotype 1 is the key viral factor that predicts the efficacy of direct‑acting antiviral therapy. HCV genome heterogeneity and baseline viral load are additionally associated with the treatment response. Multiple host genetic variants localized in genes associated with the immune response have been identified as predictors of spontaneous disease course and therapy outcome in chronic HCV. However, most findings from candidate gene association studies have not been proven universal for all investigated populations and independent studies. Previous findings in independent large genome wide association studies confirmed that interferon‑λ3 gene polymorphisms are associated with spontaneous clearance and treatment responsiveness. A polymorphism of the inosine triphosphatase gene has been identified as a protective factor against ribavirin‑induced anemia and dose reductions. Another genetic variant in the patatin‑like phospholipase domain containing 3 genes is associated with hepatic steatosis and fibrosis in patients with HCV. The present review focused on the identified viral and host factors associated with outcomes of patients with HCV, and assessed the involvement of viral and host genetics in the natural history and treatment outcomes of HCV infection. This will provide novel ideas concerning personalized prevention and individualized clinical management.

The impact of rare and low-frequency genetic variants in common disease

Despite thousands of genetic loci identified to date, a large proportion of genetic variation predisposing to complex disease and traits remains unaccounted for. Advances in sequencing technology enable focused explorations on the contribution of low-frequency and rare variants to human traits. Here we review experimental approaches and current knowledge on the contribution of these genetic variants in complex disease and discuss challenges and opportunities for personalised medicine.

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.

Effects of ribavirin/sofosbuvir treatment and ITPA phenotype on endogenous purines

Ribavirin (RBV), a purine analog, causes hemolytic anemia in some patients. In vitro, anemia appears to result from depletion of endogenous purines, but there are limited data in vivo. Single nucleotide polymorphisms in the gene encoding the inosine triphosphatase (ITPA) enzyme have been associated with protection against RBV-induced anemia and may mediate the effect of RBV treatment on endogenous purines. The purpose of this work was to determine the effect of RBV treatment on endogenous purine concentrations in individuals being treated for chronic hepatitis C virus (HCV) infection. Adenosine triphosphate (ATP), guanosine triphosphate (GTP), inosine triphosphate (ITP) and ribavirin triphosphate (RTP) were measured in whole blood obtained from 47 HCV-infected individuals at day zero (baseline), day three, day 28 and day 84 of RBV/sofosbuvir (SOF) treatment. ATP decreased -35.1% and -38.6% (p < 0.0001) at day 28 and day 84 of treatment, respectively compared to baseline. The decrease in ATP was greater in patients with ≤60% ITPA activity compared to those with 100% ITPA activity (-29.4% vs. -9.6%). GTP did not change during treatment but was 16.5% (p = 0.01) higher per 100 pmol/106 cells RTP in those with 100% ITPA activity. No significant change or effect of RTP or ITPA phenotype was noted for ITP. In summary, only ATP was reduced by RBV/SOF treatment and ITPA variants had larger reductions in ATP suggesting RBV-induced anemia is due to a different mechanism than predicted from in-vitro studies. These data emphasize the importance of characterizing the effect of nucleos(t)ide analog treatment on endogenous purines in-vivo.

Rapidity and Severity of Hemoglobin Decreasing Associated with Erythrocyte Inosine Triphosphatase Activity and ATP Concentration during Chronic Hepatitis C Treatment

The purpose of this study was to evaluate the association between therapy-induced hemoglobin (Hb) decreasing rapidity and severity with erythrocyte inosine triphosphatase (ITPase) activity and ATP concentration in chronic hepatitis C patients receiving chronic hepatitis C (HCV) treatment. Forty-three Japanese patients were included in the study. Erythrocyte ITPase activity before therapy was determined by HPLC-UV. Erythrocyte ATP concentrations before and during therapy were determined by luciferase assay. Genotyping for ITPA 94C>A (rs1127354) and IVS2+21 A>C (rs7270101) was conducted using TaqMan probes. The median ITPase activity (µmol/h/g hemoglobin) of ITPA 94 CC, CA, and AA genotypes was 136.8 (range, 80.4-289.6), 41.1 (24.3-93.1), and 11.8, respectively. ITPase activity and Hb decreasing showed a significantly inverse relationship at therapeutic weeks 2, 4, and 6 (p<0.01). Erythrocyte ATP concentration was decreased by therapy, and Hb decreasing was significantly and inversely correlated with erythrocyte ATP concentration at week 4 and after week 8 (p<0.001 and 0.05, respectively). ATP concentration for patients with ITPA 94CA was significantly lower than ITPA 94CC at week 4 (p=0.045). We concluded that ITPase activity plays an important function and that ATP concentration changes due to therapy are related to the Hb decreasing mechanism in the early period of therapy with HCV treatment.

Variant Inosine Triphosphatase Phenotypes Are Associated With Increased Ribavirin Triphosphate Levels

Individuals with lower inosine triphosphatase (ITPA) enzyme activity have a reduced likelihood of experiencing hemolytic anemia during hepatitis C virus (HCV) treatment containing ribavirin (RBV). Because ITPA degrades purines and RBV is a purine analogue, it is conceivable that ITPA activity may affect intracellular RBV concentrations. Here we assessed the association between ITPA activity phenotype and concentrations of RBV triphosphate (RBV-TP) in red blood cells (RBCs) during HCV treatment. RBV-TP was quantified in the RBCs of 177 HCV-infected individuals at a median (range) of 84 (19 to 336) days into HCV treatment that included RBV. Mean (SD) RBV-TP concentrations were 92.8 (51.6), 101.3 (53.5), 184.8 (84.5), and 197.7 (64.6) pmol/106 cells for 100%, 60%, 30%, and ≤10% ITPA activity groups, respectively. Overall, RBV-TP was approximately 2-fold higher in patients with ≤30% ITPA activity compared to 100% activity (P < .0001). Despite higher RBV-TP levels, individuals with variant ITPA phenotypes had less anemia. The 100% activity group had, on average, a -2.20 g/dL drop in hemoglobin vs -1.43 g/dL (P = .04) for 60% activity, -1.14 g/dL (P = .008) for 30% activity, and -0.70 g/dL (P = .06) for ≤10% activity. This finding of higher RBV-TP concentrations in RBCs in ITPA variants was unexpected given that ITPA activity-deficient individuals have a reduced likelihood of RBV-induced anemia. It also refutes the hypothesis that the mechanism by which ITPA variants are protected against anemia is due to lower RBV-TP levels in RBCs.

A LC-MS/MS Method for Quantifying Adenosine, Guanosine and Inosine Nucleotides in Human Cells

PURPOSE

To develop and validate a method for the simultaneous measurement of adenosine, guanosine, and inosine derived from mono (MP) and triphosphate (TP) forms in peripheral blood mononuclear cells (PBMCs), red blood cells (RBCs) and dried blood spots (DBS).

METHODS

Solid phase extraction of cell lysates followed by dephosphorylation to molar equivalent nucleoside and LC-MS/MS quantification.

RESULTS

The assay was linear for each of the three quantification ranges: 10-2000, 1.0-200 and 0.25-50 pmol/sample for adenosine, guanosine, and inosine, respectively. Intraassay (n = 6) and interassay (n = 18) precision (%CV) were within 1.7 to 16% while accuracy (%deviation) was within -11.5 to 14.7% for all three analytes. Nucleotide monophosphates were less concentrated than triphosphates (except for inosine) and levels in PBMCs were higher than RBCs for all three nucleotides (10, 55, and 5.6 fold for ATP, GTP and ITP, respectively). DBS samples had an average (SD) of -26% (22.6%) lower TP and 184% (173%) higher MP levels compared to paired RBC lysates, suggesting hydrolysis of the TP in DBS.

CONCLUSION

This method was accurate and precise for physiologically relevant concentrations of adenosine, guanosine and inosine nucleotides in mono- and triphosphate forms, providing a bioanalytical tool for quantitation of nucleotides for clinical studies.

Significance of functional disease-causal/susceptible variants identified by whole-genome analyses for the understanding of human diseases

Human genome variation may cause differences in traits and disease risks. Disease-causal/susceptible genes and variants for both common and rare diseases can be detected by comprehensive whole-genome analyses, such as whole-genome sequencing (WGS), using next-generation sequencing (NGS) technology and genome-wide association studies (GWAS). Here, in addition to the application of an NGS as a whole-genome analysis method, we summarize approaches for the identification of functional disease-causal/susceptible variants from abundant genetic variants in the human genome and methods for evaluating their functional effects in human diseases, using an NGS and in silico and in vitro functional analyses. We also discuss the clinical applications of the functional disease causal/susceptible variants to personalized medicine.

Impact of ITPA gene polymorphisms on the risk of ribavirin-induced haemolytic anaemia using interferon-free antivirals for chronic hepatitis C

BACKGROUND

Single nucleotide polymorphisms (SNPs) at the ITPA gene are associated with haemolytic anaemia in chronic hepatitis C patients treated with pegylated interferon-ribavirin (RBV). Information in patients treated with interferon-free, direct-acting antivirals (DAA) is scarce.

METHODS

Median haemoglobin (Hb) levels were compared at baseline and at week 4, when ribavirin concentration achieves steady state, in all consecutive chronic hepatitis C patients treated with oral DAA plus RBV at our clinic.

RESULTS

Median Hb drop in 55 patients was greater in rs1127354-CC than -CA/AA (1.8 versus 0.7 g/dl; P=0.029), and in rs6051702-AA than -AC/CC carriers (2.2 versus 1.1 g/dl; P=0.016). Eleven (20%) patients experienced severe anaemia, defined as Hb drop >3 g/dl or to <10 g/dl. All of them were rs6051702-AA.

CONCLUSIONS

Baseline testing of rs6051702 may identify the subset of patients at greatest risk for RBV-induced anaemia using interferon-free hepatitis C therapies.

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.

ITPA deficiency and ribavirin level are still predictive of anaemia in HCV-HIV-coinfected patients receiving ribavirin combined with a first-generation DAA (ANRS HC27 study)

BACKGROUND

We aimed to determine the impact of inosine triphosphatase (ITPA) deficiency on ribavirin (RBV)-induced anaemia in HIV-HCV-coinfected patients receiving a triple therapy including the haematotoxic direct-acting antiviral agent boceprevir (BOC).

METHODS

Patients of the ANRS HC27 BocepreVIH study were genotyped for two ITPA single nucleotide polymorphisms involved in ITPA deficiency. RBV trough concentration (Ctrough) was determined at week (W)4 and W8. Impact of ITPA deficiency on anaemia, RBV Ctrough, response and haematotoxicity (grade 3/4 anaemia, erythropoietin [EPO] use, RBV dose reduction or transfusion between day [D]0 and W8) was evaluated. Impact of RBV Ctrough on anaemia was also studied.

RESULTS

Among the 63 genotyped patients, 33% had a predicted ITPA deficiency. ITPA deficiency was associated with a lower haemoglobin (Hb) decline both at W4 (-1.0 g/dl versus -2.1 g/dl; P=0.02) and W8 (-2.7 g/dl versus -4.1 g/dl; P=0.05). None of the patients with ITPA deficiency received EPO between D0-W8 versus 26% of patients without ITPA deficiency (P=0.01). RBV Ctrough was associated with Hb decrease both at W4 and W8 and an RBV Ctrough cutoff value of 2 µg/ml was significantly associated with a W4 Hb decline >2 g/dl. Haematotoxicity was significantly associated with a lower W4 Hb level (P=0.017), absence of ITPA deficiency (P=0.018) and higher RBV Ctrough (P=0.012). ITPA deficiency, W4 RBV Ctrough and gender were independent predictors of anaemia at W4. ITPA deficiency was not associated with virological response.

CONCLUSIONS

ITPA deficiency and RBV Ctrough are still predictive of RBV-induced anaemia in HIV-HCV-coinfected patients treated with RBV combined with a first-generation direct antiviral agent.

Pharmacogenetics of ribavirin-induced anemia in hepatitis C

Pharmacogenetics assesses inherited genetic differences in drug metabolic pathways and its role in medicine is growing. Ribavirin (RBV) and peginterferon were the standard of care therapy in hepatitis C virus infection during 15 years, with the addition of first-generation protease inhibitors at the beginning of 2010s. New direct-acting agents are the new standard of care, but RBV remains important in some scenarios. The main adverse effect of RBV is anemia, which requires dose reduction and even stopping treatment in some patients. Pharmacogenetics has identified ITPA and SLC28/29 genes to be closely related to RBV-induced anemia. The routine evaluation of these genes could help to identify those patients at risk of developing anemia during the hepatitis C virus treatment.

Adenosine monophosphate deaminase 3 activation shortens erythrocyte half-life and provides malaria resistance in mice

The factors that determine red blood cell (RBC) lifespan and the rate of RBC aging have not been fully elucidated. In several genetic conditions, including sickle cell disease, thalassemia, and G6PD deficiency, erythrocyte lifespan is significantly shortened. Many of these diseases are also associated with protection from severe malaria, suggesting a role for accelerated RBC senescence and clearance in malaria resistance. Here, we report a novel, N-ethyl-N-nitrosourea-induced mutation that causes a gain of function in adenosine 5'-monophosphate deaminase (AMPD3). Mice carrying the mutation exhibit rapid RBC turnover, with increased erythropoiesis, dramatically shortened RBC lifespan, and signs of increased RBC senescence/eryptosis, suggesting a key role for AMPD3 in determining RBC half-life. Mice were also found to be resistant to infection with the rodent malaria Plasmodium chabaudi. We propose that resistance to P. chabaudi is mediated by increased RBC turnover and higher rates of erythropoiesis during infection.

Pharmacogenetics of ribavirin-induced anemia in HCV patients

Dual therapy (pegylated interferon plus ribavirin) was considered the standard of care for hepatitis C virus (HCV) treatment until 2011, when the first-wave direct-acting antivirals were added to this regimen for HCV genotype-1 patients to increase the sustained virological response rate. The second-wave direct-acting antivirals entered the clinical use also in some ribavirin (RBV)- and/or interferon-free combinations. Nevertheless, since some of the new therapeutic regimens also include RBV and its use results still associated with hemolytic anemia, this requires countermeasures to be prevented. These include the identification of several host predictive factors involved in RBV absorption, distribution, metabolism, elimination and many others that might influence this toxic effect. For this reason, we provided an overview of the potential role of pharmacogenomics in predisposing RBV-treated HCV patients to anemia.

The ITPA and C20orf194 Polymorphisms and Hematological Changes During Treatment With Pegylated-Interferon Plus Ribavirin in Patients With Chronic Hepatitis C

BACKGROUND

It has been found that ITPase deficiency is caused by ITPA gene polymorphisms. It was observed that ITPA polymorphisms have impact on hematological changes, including hemoglobin (Hb)-decline during treatment of chronic hepatitis C (CHC) patients with pegylated-interferon (PEG-IFN) plus ribavirin (RBV).

OBJECTIVES

This study aimed to assess the effect of ITPA and C20orf194 polymorphisms on hematological changes at week 4 of treatment with PEG-IFN plus RBV in patients with CHC.

PATIENTS AND METHODS

In this retrospective study, 168 patients with CHC (56% HCV genotype-1 and 44% HCV genotype-3) under the treatment of PEG-IFN plus RBV were genotyped for rs1127354, rs7270101 and rs6051702 polymorphisms by the polymerase chain reaction-restriction fragment length polymorphism. Hematological changes including Hb-, platelet (Plt)- and white blood cell-decline at week 4 of the treatment were assessed.

RESULTS

In univariate analysis, rs1127354 and HCV genotypes were found to influence the Hb-decline at week 4 of the treatment. In multivariate analysis, rs1127354 CA + AA and HCV genotype-3 were found to have a great role on prevention of Hb-decline. Furthermore, rs1127354 and HCV RNA levels were found to influence the Plt-decline at week 4 of the treatment in the univariate analysis. In multivariate analysis, rs1127354 CA + AA and HCV RNA levels less than 600,000 IU/mL were found to be associated with a higher level of Plt-decline.

CONCLUSIONS

In patients with CHC, who were treated with PEG-IFN plus RBV, Hb-decline was affected by rs1127354 and HCV genotypes. However, Plt-decline may be altered by rs1127354 and baseline HCV RNA levels.

Modeling Ribavirin-Induced Anemia in Patients with Chronic Hepatitis C Virus

Ribavirin remains an important component of hepatitis C treatment in certain clinical scenarios, but it causes hemolytic anemia. A quantitative understanding of the ribavirin exposure-anemia relationship is important in dose individualization/optimization. We developed a model relating ribavirin triphosphate (RTP) exposure in red blood cells (RBCs), RBC lifespan, feedback regulation of RBC production when anemia occurs, and the resulting hemoglobin decline. Inosine triphosphatase (ITPA) and interleukin 28B (IL28B) genetics were found to be significant covariates. Clinical trial simulations predicted that anemia is least severe in IL28B non-CC (rs12979860, CT or TT), ITPA variant subjects, followed by IL28B non-CC, ITPA wild-type, IL28B CC, ITPA variant, and IL28B CC, ITPA wild-type subjects (most severe). Reducing the ribavirin dose from 1,200/1,000 mg to 800/600 mg could reduce the proportions of grade 2 anemia by about half. The resulting model framework will aid the development of dosing strategies that minimize the incidence of anemia in treatment regimens that include ribavirin.

Low-dose ribavirin potentiates the antiviral activity of favipiravir against hemorrhagic fever viruses

Favipiravir is approved in Japan to treat novel or re-emerging influenza viruses, and is active against a broad spectrum of RNA viruses, including Ebola. Ribavirin is the only other licensed drug with activity against multiple RNA viruses. Recent studies show that ribavirin and favipiravir act synergistically to inhibit bunyavirus infections in cultured cells and laboratory mice, likely due to their different mechanisms of action. Convalescent immune globulin is the only approved treatment for Argentine hemorrhagic fever caused by the rodent-borne Junin arenavirus. We previously reported that favipiravir is highly effective in a number of small animal models of Argentine hemorrhagic fever. We now report that addition of low dose of ribavirin synergistically potentiates the activity of favipiravir against Junin virus infection of guinea pigs and another arenavirus, Pichinde virus infection of hamsters. This suggests that the efficacy of favipiravir against hemorrhagic fever viruses can be further enhanced through the addition of low-dose ribavirin.

ITPA Genotypes Predict Anemia but Do Not Affect Virological Response with Interferon-Free Faldaprevir, Deleobuvir, and Ribavirin for HCV Infection

Background & Aim

Whether inosine triphosphatase (ITPA) gene polymorphisms predict anemia during interferon-free therapy in chronic hepatitis C virus (HCV)-infected patients is unknown. We examined the relationship between two ITPA polymorphisms, anemia, and sustained virological response 12 weeks post-treatment (SVR12) in patients receiving the NS3/4A protease inhibitor faldaprevir, the non-nucleoside polymerase inhibitor deleobuvir, and ribavirin.

Methods

HCV genotype 1-infected, treatment-naïve patients (N = 362) were randomized and treated in one of five treatment arms with faldaprevir and deleobuvir with or without ribavirin. Two ITPA polymorphisms (rs1127354 and rs6051702) were genotyped and defined as ITPA-deficient (rs1127354 AA or AC; rs6051702 CC or CA) or ITPA-non-deficient (rs1127354 CC; rs6051702 AA) according to their association with ITPA deficiency. Baseline and on-treatment variables associated with anemia and SVR12 were identified using logistic regression.

Results

In the pooled ribavirin-containing arms, 10.1% (32/316) of patients experienced on-treatment hemoglobin <10 g/dL, and 32.6% (103/316) experienced on-treatment hemoglobin <10 g/dL or a change from baseline ≥3.5 g/dL. Of the latter group, 99% (102/103) had the ITPA-non-deficient rs1127354 genotype. Other variables associated with on-treatment hemoglobin <10 g/dL or a decrease ≥3.5 g/dL were age, baseline hemoglobin, rs6051702 genotype, and plasma ribavirin concentration. In a multivariate analysis, high plasma ribavirin concentration, low baseline hemoglobin, HCV genotype 1b, and IL28B genotype CC were associated with higher SVR12.

Conclusions

The ITPA rs1127354 CC and rs6051702 AA genotypes may predict ribavirin-induced anemia during treatment with interferon-free, ribavirin-containing regimens. With this interferon-free regimen, SVR was associated with ribavirin levels, but not with anemia or ITPA genotypes.

Trial Registration

ClinicalTrials.gov: NCT01132313

Association between IPTA gene polymorphisms and hematological abnormalities in hepatitis C virus-infected patients receiving combination therapy

Background/Aims

Hematological abnormalities during hepatitis C virus (HCV) combination therapy with pegylated interferon α and ribavirin often necessitate dose reduction. Variants of the ITPA gene have been reported to protect against anemia during the early stages of HCV combination treatments but have also been associated with larger decreases in platelet counts. We aimed to identify the association between specific ITPA gene polymorphisms and hematological abnormalities in patients undergoing HCV combination therapy.

Methods

In this retrospective study, 175 patients treated with HCV combination therapy were enrolled at St. Martin De Porres Hospital in Taiwan between 2006 and 2012. Two single nucleotide polymorphisms (SNP) within or adjacent to the ITPA gene (rs1127354, rs6051702) were genotyped. We investigated the effect of ITPA gene variants on hematological abnormalities during the therapy.

Results

The ITPA rs1127354 minor variants were significantly associated with protection against anemia at week 4 (p=1.86×10⁻⁶) and with more severe decreases in platelet counts during HCV combination therapy. SNP rs6051702 was not associated with the hemoglobin decline to >3 g/dL at week 4 in our study (p=0.055).

Conclusions

The ITPA SNP rs1127354 is a useful predictor of ribavirin-induced anemia in Taiwanese patients and may be related to more severe decreases in platelet counts during the early stage of HCV combination therapy.

VDR gene polymorphisms impact on anemia at 2 weeks of anti-HCV therapy: a possible mechanism for early RBV-induced anemia

OBJECTIVES

Vitamin D receptors (VDR) bind calcitriol and modulate several physiological systems through genomic and nongenomic pathways. Calcitriol stimulates store-operated channels Ca²⁺ influx by translocation of the caveolar VDR to the plasma membrane. Intracellular Ca²⁺ levels in erythrocytes control biophysical properties and an increase in its concentration can deregulate membrane composition, cell volume, glycolytic enzymes regulation, redox state, and cell clearance.We evaluated the role of single nucleotide polymorphisms in ITPA, CYP27B1, CYP24A1, and VDR genes in the prediction of ribavirin-induced anemia in HCV-1/2/3/4 patients at 2 and 4 weeks of treatment.

PATIENTS AND METHODS

Two hundred and twenty-five patients treated with ribavirin and pegylated interferon-α were genotyped by real-time PCR.

RESULTS

BMI at baseline more than 30 kg/m² [P=0.013, odds ratio (OR): 10.95, 95% confidence interval (CI): 1.66-74.21], alanine aminotransferase at baseline more than 37 IU/l (P=0.020, OR: 0.26, 95% CI: 0.09-0.81), and the VDR BsmI AA profile (P=0.003, OR: 5.09, 95% CI: 1.72-15.05) were anemia-predictive factors at 2 weeks of therapy. At week 4, the ITPA rs6051702 AC/CC profile (P=0.001, OR: 0.19, 95% CI: 0.07-0.51) was the only factor that could predict this side effect.

CONCLUSION

The BsmI AA genotype is a predictive factor of 2-week anemia and it could be related to a VDR-enhanced activity, and thus an increased calcium influx, resulting in the deregulation of the Ca²⁺-dependent signaling, which can lead to erythrocytes hemolysis. This rapid mechanism could be responsible for the development of early anemia.These results indicate for the first time the strong, significant, and independent role of VDR in the early development of ribavirin-induced anemia and confirm the ITPA function in the prediction of anemia at week 4.

ITPA Polymorphisms Are Associated with Hematological Side Effects during Antiviral Therapy for Chronic HCV Infection

Background/Objective

Genetic polymorphisms in the inosine triphosphatase (ITPA) gene have been associated with the protection from early ribavirin(RBV)-induced hemolytic anemia among patients with chronic hepatitis C virus (HCV) infection. The aim of the present study was to investigate the association between the functional ITPA variants and hematological side effects during antiviral therapy with pegylated interferon (PegIFN) and RBV.

Patients and Methods

This cohort study included all consecutive Caucasian patients treated for chronic HCV infection with PegIFN and RBV between 2000 and 2009 for whom a serum sample was available for genetic testing. The predicted inosine triphosphate pyrophosphatase (ITPase) activity was based on the genotypes of the SNPs rs1127354 and rs7270101. Decline in hemoglobin (Hb) during antiviral therapy, as well as dose reductions, blood transfusions and use of erythropoietin were assessed.

Results

In total, 213 patients were included. The predicted ITPase activity was normal among 152 (71%) patients; 61 (29%) patients had ITPase deficiency. By multivariable linear regression, RBV dose in mg per kilogram (Beta 0.09, 95%CI 0.04–0.13, p<0.001) and normal ITPase activity (Beta 0.89, 95%CI 0.64–1.14, p<0.001) were associated with more Hb decline at week 4 of treatment. Patients with normal ITPase activity underwent more dose adjustments of RBV than patients with ITPase deficiency (19(13%) vs 1(2%),p = 0.014) and received erythropoietin more frequently (12 (8%) vs 0 (0%),p = 0.024).

Conclusion

Genetic variants in the ITPA gene protected against RBV treatment-induced anemia among Caucasian patients with chronic HCV infection. Patients with normal ITPase activity underwent more dose reductions of RBV and received erythropoietin more frequently.

Relationship between ITPA polymorphisms and hemolytic anemia in HCV-infected patients after ribavirin-based therapy: a meta-analysis

BACKGROUND

There is growing evidence that variations in the gene encoding inosine triphosphate pyrophosphohydrolase (ITPase), known as inosine triphosphatase (ITPA), are related to hemolytic anemia, which is frequently observed among hepatitis C virus (HCV)-infected patients receiving ribavirin (RBV)-based therapy. We performed a meta-analysis of all eligible studies assessing ITPA gene polymorphisms related to RBV-induced hemolytic anemia in HCV-infected patients published in PubMed, Embase and the Cochrane library prior to the end of 2014.

METHODS

Three outcomes were evaluated: (1) hemoglobin decline, (2) severe anemia, and (3) RBV dose reduction or treatment discontinuation. Pooled odds ratio (OR) and 95 % confidence interval (95 % CI) were estimated by either fixed or random effects models.

RESULTS

Twenty-nine studies were selected from the literature search: 20 references involving 6533 individuals for hemoglobin decline, 13 references on 3764 patients for severe anemia, and 16 references on 3918 patients for RBV dose reduction or discontinuation. Significant associations with hemoglobin decline were found for rs1127354 CC [OR = 12.84 (95 % CI 7.44; 22.17)], rs7270101 AA [OR = 3.41 (95 % CI 2.08; 5.59)] and rs6051702 AA [OR = 4.43 (95 % CI 2.80; 7.00)] genotypes. Moreover, significant associations with hemoglobin decline were also found for absent [OR = 6.01 (95 % CI 4.84; 7.46)] and mild [OR = 4.68 (95 % CI 2.83; 7.74)] ITPase deficiency haplotypes. The ITPA rs1127354 CC genotype and absent ITPase deficiency haplotype were also associated with severe anemia {[OR = 7.77 (95 % CI 5.03; 12.00)] and [OR = 4.79 (95 % CI 1.69; 13.56)], respectively}. Additionally, the rs1127354 CC genotype showed significant association with RBV dose reduction or stopping treatment (OR = 2.24; 95 % CI 1.79; 2.81).

CONCLUSIONS

ITPA polymorphisms increase the likelihood of developing hemolytic anemia for HCV-infected patients on RBV-based therapy, particularly rs1127354 CC and rs7270101 AA genotypes, suggesting the utility of screening for ITPA polymorphisms to avoid hematological toxicity and increase adherence to RBV-based therapy.

Role of genetic polymorphisms in hepatitis C virus chronic infection

AIM: To analyze the host genetics factors influencing the clinical course and the response to antiviral treatment in patients with chronic hepatitis C (CHC).

METHODS: We conducted an electronic search on the PubMed and MEDLINE (2000-2014) databases and Cochrane library (2000-2014). A total of 73 articles were retrieved and their data were extensively evaluated and discussed by the authors and then analyzed in this review article.

RESULTS: Several studies associated polymorphisms in the interleukin 28B gene on chromosome 19 (19q13.13) with a spontaneous viral clearance in acute hepatitis C and with the response to pegylated interferon (Peg-IFN)-based treatment in chronic hepatitis C patients. Other investigations demonstrated that inosine triphosphate pyrophosphatase genetic variants protect hepatitis C virus-genotype-1 CHC patients from ribavirin-induced anemia, and other studies that a polymorphism in the patatin-like phospholipase domain-containing protein 3 was associated with hepatic steatosis in CHC patients. Although not conclusive, some investigations suggested that the vitamin D-associated polymorphisms play an important role in the achievement of sustained virologic response in CHC patients treated with Peg-IFN-based antiviral therapy. Several other polymorphisms have been investigated to ascertain their possible impact on the natural history and on the response to treatment in patients with CHC, but the data are preliminary and warrant confirmation.

CONCLUSION: Several genetic polymorphisms seem to influence the clinical course and the response to antiviral treatment in patients with CHC, suggesting individualized follow up and treatment strategies.

Pharmacogenomics of antimicrobial agents

Antimicrobial efficacy and toxicity varies between individuals owing to multiple factors. Genetic variants that affect drug-metabolizing enzymes may influence antimicrobial pharmacokinetics and pharmacodynamics, thereby determining efficacy and/or toxicity. In addition, many severe immune-mediated reactions have been associated with HLA class I and class II genes. In the last two decades, understanding of pharmacogenomic factors that influence antimicrobial efficacy and toxicity has rapidly evolved, leading to translational success such as the routine use of HLA-B*57:01 screening to prevent abacavir hypersensitivity reactions. This article examines recent advances in the field of antimicrobial pharmacogenomics that potentially affect treatment efficacy and toxicity, and challenges that exist between pharmacogenomic discovery and translation into clinical use.

Impact of IL28B, ITPA and PNPLA3 genetic variants on therapeutic outcome and progression of hepatitis C virus infection

Chronic HCV infection comprises a broad spectrum of liver disease, ranging from no or minimal activity to active hepatitis that in time may progress to severe liver fibrosis, cirrhosis and hepatocellular carcinoma if left untreated. This review describes the impact of genetic variants of interleukin 28B (IL28B; also known as interferon-lambda 3), inosine triphosphate pyrophosphatase (ITPA) and patatin-like phospholipase domain-containing 3 (PNPLA3) on therapeutic outcome and liver disease severity in HCV-infected patients.

Inosine triphosphatase allele frequency and association with ribavirin-induced anaemia in Brazilian patients receiving antiviral therapy for chronic hepatitis C

Inosine triphosphatase (ITPA) single nucleotide polymorphisms (SNPs) are strongly associated with protection against ribavirin (RBV)-induced anaemia in European, American and Asian patients; however, there is a paucity of data for Brazilian patients. The aim of this study was to evaluate the ITPA SNP (rs7270101/rs1127354) frequency in healthy and hepatitis C virus (HCV)-infected patients from Brazil and the association with the development of severe anaemia during antiviral therapy. ITPA SNPs were determined in 200 HCV infected patients and 100 healthy individuals by sequencing. Biochemical parameters and haemoglobin (Hb) levels were analysed in 97 patients who underwent antiviral therapy. A combination of AArs7270101+CCrs1127354 (100% ITPase activity) was observed in 236/300 individuals. Anaemia was observed in 87.5% and 86.2% of treated patients with AA (rs7270101) and CC genotypes (rs1127354), respectively. Men with AA (rs7270101) showed a considerable reduction in Hb at week 12 compared to those with AC/CC (p = 0.1475). In women, there was no influence of genotype (p = 0.5295). For rs1127354, men with the CC genotype also showed a sudden reduction in Hb compared to those with AC. Allelic distribution of rs7270101 and rs1127354 shows high rates of the genotypes AA and CC, respectively, suggesting that the study population had a great propensity for developing RBV-induced anaemia. A progressive Hb reduction during treatment was observed; however, this reduction was greater in men at week 12 than in women.

Non-immune Hemolysis: Diagnostic Considerations

Non-immune hemolytic anemia (NIHA) is characterized by positive routine hemolytic tests but negative anti-human immunoglobulin (Coombs) test. Hereditary non-immune hemolysis includes disorders of erythrocytic enzymes, membrane, hemoglobin (qualitative and quantitative disorders), as well as the rare hereditary forms of thrombotic microangiopathies. Acquired NIHA includes paroxysmal nocturnal hemolysis (PNH), infections, drug and metal intoxications with as a target red blood cells or endothelium of capillaries, the rare acquired forms of thalassemia or erythrocytic membrane disorders, and hemolysis secondary to a dysfunctioning artificial (prosthetic) cardiac valve. Identification of the specific cause of NIHA is sometimes difficult and requires not only a good knowledge of this entity but mainly a qualified specialized hematologic laboratory. An algorithm to be used in every new patient consulting for NIHA is proposed in the last part of this article.

Serum and cellular ribavirin pharmacokinetic and concentration-effect analysis in HCV patients receiving sofosbuvir plus ribavirin

OBJECTIVES

Ribavirin concentrations may impact hepatitis C virus (HCV) treatment outcome. We modelled ribavirin serum and intracellular ribavirin monophosphate (RBV-MP) and ribavirin triphosphate (RBV-TP) pharmacokinetics in red blood cells (RBC) using samples collected during the NIAID SPARE trial to explore associations with treatment outcome and the development of anaemia.

PATIENTS AND METHODS

Individuals infected with HCV genotype 1 (GT1) received 400 mg of sofosbuvir and either low-dose or weight-based ribavirin as part of the NIAID SPARE trial. Concentrations were modelled using NONMEM and associated with treatment outcomes using unpaired t-tests or Pearson's rho correlations.

RESULTS

Average day 14 RBV-MP concentrations were higher in subjects with haemoglobin nadir <10 g/dL relative to patients with haemoglobin nadir ≥10 g/dL (6.54 versus 4.48 pmol/10(6) cells; P = 0.02). Additionally, day 14 RBV-MP average concentrations trended towards being higher in subjects that achieved sustained virological response (SVR) as compared with patients who relapsed (4.97 versus 4.09 pmol/10(6) cells; P = 0.07). Receiver operating characteristic curves suggested day 14 RBV-MP concentration thresholds of 4.4 pmol/10(6) cells for SVR (P = 0.06) and 6.1 pmol/10(6) cells for haemoglobin nadir <10 versus ≥10 g/dL (P = 0.02), with sensitivity and specificity ≥60%. Dosing simulations showed that 800 mg of ribavirin once daily produced day 14 RBV-MP concentrations within the 4.4-6.1 pmol/10(6) cells range.

CONCLUSIONS

RBV-MP concentrations in RBC at day 14 were related to anaemia and SVR. A therapeutic range was identified for RBV-MP in persons with HCV GT1 disease receiving 24 weeks of sofosbuvir plus ribavirin, suggesting a potential pharmacological basis for individualized ribavirin dosing in IFN-free regimens.

Population pharmacokinetic modeling of plasma and intracellular ribavirin concentrations in patients with chronic hepatitis C virus infection

Ribavirin, a guanosine analog, is a broad-spectrum antiviral agent. Ribavirin has been a fundamental component of the treatment of hepatitis C virus (HCV) infection for decades, but there is a very limited understanding of the clinical pharmacology of this drug. Furthermore, it is associated with a major dose-limiting toxicity, hemolytic anemia. Ribavirin undergoes intracellular phosphorylation by host enzymes to ribavirin monophosphate (RMP), ribavirin diphosphate (RDP), and ribavirin triphosphate (RTP). The intracellular forms have been associated with antiviral and toxic effects in vitro, but the kinetics of these phosphorylated moieties have not been fully elucidated in vivo. We developed a model to characterize the plasma pharmacokinetics of ribavirin and the difference between intracellular phosphorylation kinetics in red cells (nonnucleated) and in peripheral blood mononuclear cells (nucleated). A time-independent two-compartment model with first-order absorption described the plasma data well. The cellular phosphorylation kinetics was described by a one-compartment model for RMP, with the formation rate driven by plasma concentrations and the first-order degradation rate. RDP and RTP rapidly reached equilibrium with RMP. Concomitant telaprevir use, inosine triphosphatase genetics, creatinine clearance, weight, and sex were significant covariates. The terminal ribavirin half-life in plasma and phosphorylated anabolites in cells was approximately 224 h. We found no evidence of time-dependent kinetics. These data provide a foundation for uncovering concentration-effect associations for ribavirin and determining the optimal dose and duration of this drug for use in combination with newer direct-acting HCV agents. (This study has been registered at ClinicalTrials.gov under registration no. NCT01097395.).

SLC29A1 polymorphism and prediction of anaemia severity in patients with chronic hepatitis C receiving triple therapy with telaprevir

OBJECTIVES

The equilibrative nucleoside transporter 1 (ENT1) is the main protein involved in ribavirin cellular uptake. Polymorphisms at the SLC29A1 gene, encoding ENT1, may influence ribavirin-associated anaemia, which is observed at a higher incidence with telaprevir in combination with pegylated-IFNα and ribavirin than with pegylated-IFNα and ribavirin alone. In this study, we investigated the role of the rs760370 SLC29A1 variant in ribavirin-induced anaemia in chronic hepatitis C patients treated with telaprevir-based triple therapy.

METHODS

Forty patients infected with hepatitis C virus (HCV) genotype 1 and starting anti-HCV therapy with telaprevir in combination with pegylated-IFN/ribavirin were prospectively evaluated for SNPs at the SLC29A1 gene and inosine triphosphatase (ITPA) genes using a real-time PCR system.

RESULTS

40% of patients developed severe anaemia with a haemoglobin (Hb) decline ≥ 5 g/dL from the pretreatment value. The SLC29A1 rs760370 GG genotype was associated with the severity of Hb decrease as expressed by the median (IQR) Hb nadir change from baseline [-5.4 (-5.6; -5.0) g/dL in GG versus -4.2 (-5.1; -3.4) in AA/AG genotype; P=0.05] and by the Hb decrease ≥ 5 g/dL by week 12 (77.8% of GG carriers versus 24% of AA/AG; P<0.01). In multivariate analysis, older age (P=0.03), lower baseline Hb concentration (P=0.02) and SLC29A1 rs760370 GG (P=0.02) were associated with the development of severe anaemia during treatment, whereas no association was found with ITPA SNPs in our population receiving telaprevir-based therapy.

CONCLUSIONS

In patients with chronic hepatitis C receiving telaprevir-based therapy, SNP rs760370A>G at the SLC29A1 gene influences the severity of ribavirin-induced anaemia, possibly mirroring the erythrocyte uptake of ribavirin.