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

Tolerability of Erythrocyte Ribavirin Triphosphate Concentrations Depends on the ITPA Genotype

BACKGROUND

Ribavirin (RBV) is an antiviral drug that is part of the current standard therapy for chronic hepatitis C (CHC). It is enzymatically converted to ribavirin triphosphate (RTP) that inhibits the activity of viral RNA polymerase, thereby preventing viral replication. However, one of its adverse effects includes hemolytic anemia that limits its application. The variant of ITPA (inosine triphosphatase), which dephosphorylates inosine triphosphate to inosine monophosphate, is a protective factor for RBV-induced anemia. RTP is an important metabolite required for ribavirin action. This study evaluated the time-dependent association of RTP concentrations in erythrocytes, RBV-induced toxicity, and virological response to RBV treatment for hepatitis C.

METHODS

A total of 28 Japanese patients with CHC were treated with RBV/peg-interferon/simeprevir or RBV/sofosbuvir and were genotyped for ITPA variants (rs1127354 and rs7270101). We measured RTP concentrations in erythrocytes in a total of 76 samples collected at 4, 8, and 12 weeks from the initiation of treatment.

RESULTS

The ITPA rs1127354 variant was found in 7 patients. This was associated with significantly higher RTP concentrations in erythrocytes than in the wild-type patients (P < 0.001). Moreover, a significant correlation was observed between RTP concentrations and decline in hemoglobin (Hb) levels from baseline values in ITPA wild type and rs1127354 variant 12 weeks after treatment initiation (P < 0.01; r = -0.618 and -0.967, respectively). Multiple regression analysis revealed that ITPA genotype and erythrocyte RTP concentrations were major factors associated with reduced Hb levels in RBV therapy for CHC. However, we did not find any association between erythrocyte concentrations and virological response.

CONCLUSIONS

The increased tolerability to RTP concentrations in erythrocytes in the ITPA variant rs1127354 plays a role in preventing RBV-induced severe anemia in this ITPA variant.

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.

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.

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.