Genotype-Guided Hydralazine Therapy

<b><i>Background:</i></b> Despite its approval in 1953, hydralazine hydrochloride continues to be used in the management of resistant hypertension, a condition frequently managed by nephrologists and other clinicians. Hydralazine hydrochloride undergoes metabolism by the N-acetyltransferase 2 (NAT2) enzyme. NAT2 is highly polymorphic as approximately 50% of the general population are slow acetylators. In this review, we first evaluate the link between NAT2 genotype and phenotype. We then assess the evidence available for genotype-guided therapy of hydralazine, specifically addressing associations of NAT2 acetylator status with hydralazine pharmacokinetics, antihypertensive efficacy, and toxicity. <b><i>Summary:</i></b> There is a critical need to use hydralazine in some patients with resistant hypertension. Available evidence supports a significant link between genotype and NAT2 enzyme activity as 29 studies were identified with an overall concordance between genotype and phenotype of 92%. The literature also supports an association between acetylator status and hydralazine concentration, as fourteen of fifteen identified studies revealed significant relationships with a consistent direction of effect. Although fewer studies are available to directly link acetylator status with hydralazine antihypertensive efficacy, the evidence from this smaller set of studies is significant in 7 of 9 studies identified. Finally, 5 studies were identified which support the association of acetylator status with hydralazine-induced lupus. Clinicians should maintain vigilance when prescribing maximum doses of hydralazine. <b><i>Key Messages:</i></b> NAT2 slow acetylator status predicts increased hydralazine levels, which may lead to increased efficacy and adverse effects. Caution should be exercised in slow acetylators with total daily hydralazine doses of 200 mg or more. Fast acetylators are at risk for inefficacy at lower doses of hydralazine. With appropriate guidance on the usage of <i>NAT2</i> genotype, clinicians can adopt a personalized approach to hydralazine dosing and prescription, enabling more efficient and safe treatment of resistant hypertension.

Establishing the Genotyping Method for NAT2 Polymorphism in Vietnamese Tuberculoma Patients

The metabolism of Isoniazid, one of the first-line antituberculosis drugs for TB treatment and prophylaxis, depends on the acetyltransferase 2 acetylation (NAT2) phenotype. Different phenotypes of NAT2 will lead to differences in drug concentration and the risk of uncontrolled side effects, such as hepatitis, peripheral neuropathy, gastrointestinal disorders (nausea, vomiting, and stomach pain). These risks are related to the presence of mutant NAT2 alleles such as NAT2*5 (c.341T> C), *6 (c.590G> A) and *7 (c.857G> A), that reduce the N- acetyltransferase activity. Therefore, the genotyping method for NAT2 polymorphism using RFLP and Sanger sequencing was established. The method was successfully applied to determine the polymorphism of 84 TB patients. This study provides a better tool for analyzing NAT2 gene to assist clinicians in treating isoniazid. Keywords Enzyme NAT2, isoniazid, single nucleotide polymorphism, RFLP, Sanger sequencing. References [1] U.A. Boelsterli, K.K. Lee, Mechanisms of isoniazid-induced idiosyncratic liver injury: emerging role of mitochondrial stress, J. Gastroenterol. Hepatol. 29 (2014) 678–687.[2] A. Zabost, S. Brzezinska, M. Kozinska, M. Blachnio, J. Jagodzinski, Z. Zwolska, E. Augustynowicz-Kopec, Correlation of N-acetyltransferase 2 genotype with isoniazid acetylation in Polish tuberculosis patients, Biomed Res Int. 2013 (2013) 1-5.[3] M. Kinzig-Schippers, D. Tomalik-Scharte, A. Jetter, B. Scheidel, V. Jakob, M. Rodamer, I. Cascorbi, O. Doroshyenko, F. Sorgel, U. Fuhr, Should we use N-acetyltransferase type 2 genotyping to personalize isoniazid doses? Antimicrob Agents Chemother. 49 (2005) 1733-8[4] K. Walker, G. Ginsberg, D. Hattis, D.O. Johns, K.Z. Guyton, B. Sonawane, Genetic polymorphism in N-Acetyltransferase (NAT): Population distribution of NAT1 and NAT2 activity, J Toxicol Environ Health B Crit Rev. 12 (2009) 440-472. [5] G. Ramachandran, S. Swaminathan, Role of pharmacogenomics in the treatment of tuberculosis: a review, Pharmgenomics Pers Med. 5 (2012) 89-98.[6] J. Azuma, M. Ohno, R. Kubota, S. Yokota, T. Nagai, K. Tsuyuguchi, Y. Okuda, T. Takashima, S. Kamimura, Y. Fujio, I. Kawase, Pharmacogenetics-based tuberculosis therapy research group, NAT2 genotype guided regimen reduces isoniazid-induced liver injury and early treatment failure in the 6-month four-drug standard treatment of tuberculosis: a randomized controlled trial for pharmacogenetics-based therapy, Eur J Clin Pharmacol. 69 (2013) 1091-1101.[7] P.S. Adole, P.S. Kharbanda, S. Sharma, N-acetyltransferase 2 (NAT2) gene polymorphism as a predisposing factor for phenytoin intoxication in tuberculous meningitis or tuberculoma patients having seizures - A pilot study, Indian J Med Res. 143 (2016) 581-590.[8] WHO Scientific Group on Pharmacogenetics and World Health Organization, Pharmacogenetics: report of a WHO scientific group,World Health Organization Technical Report Series. (1973)[9] T.D. Da Silva, A.V. Felipe, J.M. De Lima, C.T. Oshima, N.M. Forones, N-Acetyltransferase 2 genetic polymorphisms and risk of colorectal cancer, World J Gastroenterol. 17 (2011) 760-765. [10] E.Y. Lau, J.S. Felton, F.C. Lightstone, Insights into the o-acetylation reaction of hydroxylated heterocyclic amines by human arylamine N-acetyltransferases: a computational study, Chem Res Toxicol. 19 (2006) 182-1190.[11] Ensembl - EBI, http://asia.ensembl.org/Homo_sapiens/Variation/Population?db=core;r=8:18399844-18400844;v=rs1801280;vdb=variation;vf=1243314,2019 (Ensembl release 96 - April 2019).[12] I.B. Kuznetsov, M. McDuffie, R. Moslehi, A web server for inferring the human N-acetyltransferase-2 (NAT2) enzymatic phenotype from NAT2 genotype, Bioinformatics. 25 (2009) 1185-1186. [13] P. Wang, K. Pradhan, X.B. Zhong, X. Ma, Isoniazid metabolism and hepatotoxicity, Acta Pharm Sin B. 6 (2016) 384-392.[14] M. Ohno, I. Yamaguchi, I. Yamamoto, T. Fukuda, S. Yokota, Slow N-acetyltransferase 2 genotype affects the incidence of isoniazid and rifampicin-induced hepatotoxicity, Int J Tuberc Lung Dis. 4 (2000) 256-261. [15] G.M. Lower, T. Nilsson, C.E. Nelson, H. Wolf, T.E. Gamsky, G.T. Bryan, N-acetyltransferase phenotype and risk in urinary bladder cancer: approaches in molecular epidemiology. Preliminary results in Sweden and Denmark, Int J Epidemiol. 36 (2007) 11-18.

Isoniazid Concentration and NAT2 Genotype Predict Risk of Systemic Drug Reactions during 3HP for LTBI

Weekly rifapentine and isoniazid therapy (known as 3HP) for latent tuberculosis infection (LTBI) is increasingly used, but systemic drug reactions (SDR) remain a major concern. Methods: We prospectively recruited two LTBI cohorts who received the 3HP regimen. In the single-nucleotide polymorphism (SNP) cohort, we collected clinical information of SDRs and examined the NAT2, CYP2E1, and AADAC SNPs. In the pharmacokinetic (PK) cohort, we measured plasma drug and metabolite levels at 6 and 24 h after 3HP administration. The generalised estimating equation model was used to identify the factors associated with SDRs. Candidate SNPs predicting SDRs were validated in the PK cohort. A total of 177 participants were recruited into the SNP cohort and 129 into the PK cohort, with 14 (8%) and 13 (10%) in these two cohorts developing SDRs, respectively. In the SNP cohort, NAT2 rs1041983 (TT vs. CC+CT, odds ratio [OR] [95% CI]: 7.00 [2.03–24.1]) and CYP2E1 rs2070673 (AA vs. TT+TA, OR [95% CI]: 3.50 [1.02–12.0]) were associated with SDR development. In the PK cohort, isoniazid level 24 h after 3HP administration (OR [95% CI]: 1.61 [1.15–2.25]) was associated with SDRs. Additionally, the association between the NAT2 SNP and SDRs was validated in the PK cohort (rs1041983 TT vs. CC+CT, OR [95% CI]: 4.43 [1.30–15.1]). Conclusions: Isoniazid played a role in the development of 3HP-related SDRs. This could provide insight for further design of a more optimal regimen for latent TB infection.

Dietary Carcinogens and Cancer Risk: Findings From Japanese Studies

Background: Red meat and processed meat consumption are established risk factors for colorectal cancer. One hypothesized mechanism for this association is through exposure to heterocyclic aromatic amines (HAAs), which are formed when meat is cooked at high temperature for a long duration. Although they are mutagenic and carcinogenic in nonhuman primates, the findings of epidemiologic studies that have specifically examined the association between HAA intake and colorectal cancer risk have been inconsistent. Moreover, since N-acetyltransferase 2 (NAT2) has been shown to play a critical role in the bioactivation of HAAs, an interaction between HAA intake and NAT2 on colorectal cancer has been hypothesized and the findings in the previous studies have been inconsistent. Aim: To investigate the association of meat- and fish-derived HAA intake, which were estimated by our validated food frequency questionnaire and population-specific data on HAA contents in meat and fish items with the risk of colorectal adenoma, precursor of colorectal cancer, among middle-aged and elderly Japanese in Japan and Japanese Brazilians in Sao Paulo. In addition, to test the modifying effect of NAT2 on the association of HAA intake on colorectal adenoma risk. Methods: Tokyo adenoma study includes 738 patients with adenoma and 697 controls who underwent total colonoscopy in National Cancer Center, Japan. Brazil adenoma study includes 316 patients with adenoma and 403 controls who underwent total colonoscopy in 2 hospitals in Sao Paulo. HAA intake was estimated from meat and fish intake based on an HAA database that was validated against 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) values measured in human hair. NAT2 acetylation genotype was inferred using 2 SNPs in the NAT2 gene. Logistic regression models were used to calculate odds ratios (ORs) and 95% confidence interval (CI) for the association between HAA intake and colorectal adenoma risk after adjusting for potential confounders. Results: Tokyo adenoma study showed that high intake of 2-amino-3,4-dimethylimidazo[4, 5-f]quinoline (MeIQ) and total HAA was significantly associated with an increased risk of colorectal adenoma in women but not in men. No clear association with PhIP or 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx) intakes and no effect modification by NAT2 genotype was observed. Brazil adenoma study found no association for HAAs and no effect modification by NAT2 genotype. Conclusion: Tokyo Adenoma Study suggests that high MeIQ and total HAA intakes are positively associated with colorectal adenoma risk among Japanese women in Japan. However, Brazil adenoma study failed to observe positive associations. The possible explanations of inconsistent findings and the difficulty of the studies will be discussed.