Variant Inosine Triphosphatase Phenotypes Are Associated With Increased Ribavirin Triphosphate Levels

Abstract

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/10 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 facile PCR‐RFLP method for genotyping of ITPA rs1127354 and rs7270101 polymorphisms

“…This gene has 8 exons and 7 introns and is located on the short arm of human chromosome number 20, which, according to GRCh38.p2, is located from nucleotide 3208868 to nucleotide 3227449 . Two functional variants of ITPA gene, rs1127354 (NM_033453.3:c.94C>A), P32T (in exon 2) a missense variant and rs7270101 (NM_033453.3:c.124 + 21A>C) (in intron 2) a splice variant have been identified and associated with RBV‐induced anemia . ITPase promotes the hydrolysis of inosine triphosphate (ITP) and deoxy inosine triphosphate (dITP) to monophosphate and diphosphate nucleotides (IMP and IDP) .…”

“…This will lead to the resistance of those carrying the ITPA variant to anemia and severe hemoglobin decrease following RBV‐related treatments . Ribavirin is known as a purine nucleoside analogue and one of the fundamental treatments of chronic hepatitis C . The ITPase activity may lead to anemia induction via endogenous purines .…”

“…Ribavirin is known as a purine nucleoside analogue and one of the fundamental treatments of chronic hepatitis C . The ITPase activity may lead to anemia induction via endogenous purines . Hemolytic anemia, as one of the major side effects of pegylated‐interferon/RBV therapy, affects 30% of chronic HCV‐infected patients .…”

Ribavirin and cellular ribavirin‐triphosphate concentrations in blood and bronchoalveolar lavage fluid in two lung transplant patients with respiratory syncytial virus

“…Although these phosphorylated metabolites have been associated with ribavirin's in vitro antiviral properties, they concentrate in RBCs and are also thought to cause the major dose‐limiting toxicity of ribavirin, hemolytic anemia 8,13 . Several studies have determined the intracellular pharmacokinetics of ribavirin in patients with hepatitis C, but to our knowledge, no studies have evaluated the plasma, intracellular concentrations, and BAL fluid of oral and inhaled ribavirin in adult lung transplant patients with RSV 10‐12,19 . Without pharmacokinetic data, in vitro measurements of effective concentration that gives half maximal response (EC 50 ) minimally inform appropriate dosing.…”

“…Ribavirin undergoes intracellular phosphorylation by host enzymes to a mono‐ (iRMP), di‐ (iRDP), and triphosphate (iRTP). The phosphorylated forms of ribavirin have been characterized and associated with efficacy and toxicity in persons with Hepatitis C virus 10‐13 . However, studies to define the cellular pharmacology, pharmacokinetics, and pharmacodynamics of oral or inhaled ribavirin for RSV and other viruses are lacking.…”