Christiana D. Ingram

Pharmacogenetics of Nevirapine-Associated Hepatotoxicity: An Adult AIDS Clinical Trials Group Collaboration

Associations have been reported between an MDR1 variant and responses to nonnucleoside reverse-transcriptase inhibitors. We explored associations between MDR1, CYP2B6, and CYP3A polymorphisms and nevirapine hepatotoxicity. Among participants in a randomized study in South Africa (FTC-302), MDR1 3435C-->T was significantly associated with decreased risk of hepatotoxicity (risk ratio, 0.30; P=.016).

A Large Candidate Gene Survey Identifies the KCNE1 D85N Polymorphism as a Possible Modulator of Drug-Induced Torsades de Pointes

Background— Drug-induced long-QT syndrome (diLQTS) is an adverse drug effect that has an important impact on drug use, development, and regulation. We tested the hypothesis that common variants in key genes controlling cardiac electric properties modify the risk of diLQTS. Methods and Results— In a case-control setting, we included 176 patients of European descent from North America and Europe with diLQTS, defined as documented torsades de pointes during treatment with a QT-prolonging drug. Control samples were obtained from 207 patients of European ancestry who displayed <50 ms QT lengthening during initiation of therapy with a QT-prolonging drug and 837 control subjects from the population-based KORA study. Subjects were successfully genotyped at 1424 single-nucleotide polymorphisms (SNPs) in 18 candidate genes including 1386 SNPs tagging common haplotype blocks and 38 nonsynonymous ion channel gene SNPs. For validation, we used a set of cases (n=57) and population-based control subjects of European descent. The SNP KCNE1 D85N (rs1805128), known to modulate an important potassium current in the heart, predicted diLQTS with an odds ratio of 9.0 (95% confidence interval, 3.5–22.9). The variant allele was present in 8.6% of cases, 2.9% of drug-exposed control subjects, and 1.8% of population control subjects. In the validation cohort, the variant allele was present in 3.5% of cases and in 1.4% of control subjects. Conclusions— This high-density candidate SNP approach identified a key potassium channel susceptibility allele that may be associated with the rare adverse drug reaction torsades de pointes.

Characterization of HETEs and related conjugated dienes by UV spectroscopy

Three distinct pairs of HETEs can be distinguished on the basis of their UV spectra. We used hydroxy-linoleates (hydroxy-octadeca-cis-trans-dienoates) as a base for comparisons; both the 9- and 13-hydroxy isomers have identical chromophores with λmax near 234 nm. The presence of a double bond three carbons removed from the conjugated diene (the chromophore of 9- and 11-HETE) causes a shift in the observed λmax to near 235 nm. A double bond β to the chromophore (5- and 15-HETE) gives a further shift of 1.5 nm, giving a λmax between 236–236.5 nm. With double bonds in both these positions (8- and 12-HETE), the λmax is observed near 237 nm. It is apparent that the exact λmax of thecis-trans diene chromophore is influenced in a consistent way by the adjacent methylene interruptedcis double bonds.

A secondary isotope effect in the lipoxygenase reaction

Fatty acids containing a prochiral tritium label have often been used in the study of enzymatic reactions which involve an obligatory step of hydrogen abstraction. In the lipoxygenase reaction, the primary isotope effect associated with this approach is detected as an isotopic enrichment of the substrate. Herein we characterize a previously unrecognized secondary isotope effect which changes the specific activity of both the substrate and product. The 12-lipoxygenase of human platelets removes the 10-LS hydrogen of arachidonic acid in the formation of 12-hydroperoxyeicosatetraenoic acid. We studied the specific activity changes associated with conversion of the enantiomerically labeled [10-DR-3H]arachidonic acid to 12-[10-3H]hydroxyeicosatetraenoic acid in aspirin-treated platelets. [3-14C]Arachidonic acid served as internal standard. The most pronounced change in 3H/14C ratio in the early stages of reaction was a 15-20% deficiency of tritium in the product. Later, the remaining arachidonate showed a marked increase in 3H/14C ratio. The changes in specific activity closely matched those predicted for a secondary isotope effect. Comparison of these data with the theoretical equations for a secondary isotope effect indicated the 10-DR-3H substrate reacted at about 84% of the rate of unlabeled molecules. Interestingly, this secondary isotope effect is similar in magnitude to the secondary isotope effect in autoxidation reactions, a finding compatible with a basic similarity in reaction mechanisms in enzymatic and non-enzymatic oxygenation of lipids.

Multiplex ligation-dependent probe amplification copy number variant analysis in patients with acquired long QT syndrome

AIMS Thirteen genetic loci map to families with congenital long QT syndrome (cLQT) and multiple single nucleotide mutations have been functionally implicated in cLQT. Studies have investigated copy number variations (CNVs) in the cLQT genes to ascertain their involvement in cLQT. In these studies 3-12% of cLQT patients who were mutation negative by all other methods carried CNVs in cLQT genes. Prolongation of the QT interval can also be acquired after exposure to certain drugs [acquired LQT (aLQT)]. Single nucleotide mutations in cLQT genes have also been associated with and functionally implicated in aLQT, but to date no studies have explored CNVs as an additional susceptibility factor in aLQT. The aim of this study was to explore the contribution of CNVs in determining susceptibility to aLQT. METHODS AND RESULTS In this study we screened the commonest cLQT genes (KCNQ1; KCNH2; SCN5A; KCNE1, and KCNE2) in a general population of healthy volunteers and in a cohort of subjects presenting with aLQT for CNVs using the multiplex ligation-dependent probe amplification method. Copy number variants were detected and confirmed in 1 of 197 of the healthy volunteers and in 1 of 90 subjects with aLQT. The CNV in the aLQT subject was functionally characterized and demonstrated impaired channel function. CONCLUSION Copy number variation is a possible additional risk factor for aLQT and should be considered for incorporation into pharmacogenetic screening of LQTS genes in addition to mutation detection to improve the safety of medication administration.