N-Acetyltransferase 2 genotype correlates with sulfasalazine pharmacokinetics after multiple dosing in healthy Japanese subjects

Determination and occurrence of sulfonamide transformation products in surface waters

The transformation products of sulfonamides (SAs) have raised increasing environmental and health concerns in recent years, but information on their analysis and environmental fates remains limited. In this study, an analytical method using liquid chromatography with tandem mass spectrometry (LC-MSMS) was optimized to simultaneously analyze 9 SA transformation products and 14 SAs in water samples. This method was applied to investigate the occurrence of antibiotics in three urban rivers in Beijing, and all of the target compounds were detected. N-acetylsulfamethoxazole, N-acetylsulfapyridine, and N-acetylsulfamethazine were found to be the predominant acetyl SAs in the aquatic environment, and high frequencies of hydroxylated SA (5-hydroxysulfapyridine) and glucuronide-conjugated SA (sulfamethoxazole β-D-glucuronide) were also detected. The SA transformation products accounted for 22-32% of the total concentrations of SAs and their transformation products in the water samples. The pollution levels of the compounds exerted only minor effects on the proportions of the SA transformation products. The compound-specific transformation of sulfamethoxazole, sulfapyridine, and sulfadiazine in the water samples was consistent with their acetylation efficiencies in metabolic processes in organisms, which suggests that the SA-acetylated products were derived mainly from biological metabolism in humans or animals. This finding was supported by the fact that environmental degradation exerts a weak effect on SA profiles in the water samples.

Arylamine N-acetyltransferase polymorphisms in Han Chinese patients with ankylosing spondylitis and their correlation to the adverse drug reactions to sulfasalazine

BACKGROUND

Polymorphisms of Arylamine N-acetyltransferase (NAT) that contribute to diverse susceptibilities of some autoimmune diseases are also linked to the metabolism of several drugs including sulfasalazine (SSZ). The aim of this study was to investigate the distribution of NAT polymorphisms in Han Chinese patients with ankylosing spondylitis (AS) and their correlation to sulfasalazine-induced adverse drug reactions (ADRs).

METHODS

Arylamine N-acetyltransferase 1 (NAT1) and arylamine N-acetyltransferase 2 (NAT2) genotypes were determined in 266 AS patients who received SSZ treatment and 280 healthy controls. The correlation between NAT polymorphisms and SSZ-induced ADRs was analyzed.

RESULTS

The co-occurrence frequency of NAT2 fast acetylator genotype and NAT1*10/NAT1*10 genotype was lower in AS patients than in controls. No positive correlations were detected between NAT polymorphisms and AS clinical features. The prevalence of SSZ-induced ADRs and drug withdrawal was 9.4% and 7.1%, respectively. The frequencies of overall ADRs, dose-related ADRs, and termination of drug treatment because of intolerance were higher in the NAT2 slow acetylator genotype carriers than in the fast-type carriers and in those with co-existence of NAT1 and NAT2 slow acetylator genotypes. Furthermore, the ADRs emerged earlier in the AS cases carrying both NAT1 and NAT2 slow acetylator genotypes.

CONCLUSIONS

The prevalence of co-occurring NAT2 fast acetylator genotype and NAT1*10/NAT1*10 genotype was lower in AS patients than in controls. The NAT2 slow acetylator genotype and co-existing NAT1 and NAT2 slow acetylator genotypes appear to be associated with higher risks of SSZ-induced ADRs.

The anthelmintic triclabendazole and its metabolites inhibit the membrane transporter ABCG2/BCRP

ABCG2/BCRP is an ATP-binding cassette transporter that extrudes compounds from cells in the intestine, liver, kidney, and other organs, such as the mammary gland, affecting pharmacokinetics and milk secretion of antibiotics, anticancer drugs, and other compounds and mediating drug-drug interactions. In addition, ABCG2 expression in cancer cells may directly cause resistance by active efflux of anticancer drugs. The development of ABCG2 modulators is critical in order to improve drug pharmacokinetic properties, reduce milk secretion of xenotoxins, and/or increase the effective intracellular concentrations of substrates. Our purpose was to determine whether the anthelmintic triclabendazole (TCBZ) and its main plasma metabolites triclabendazole sulfoxide (TCBZSO) and triclabendazole sulfone (TCBZSO(2)) inhibit ABCG2 activity. ATPase assays using human ABCG2-enriched membranes demonstrated a clear ABCG2 inhibition exerted by these compounds. Mitoxantrone accumulation assays using murine Abcg2- and human ABCG2-transduced MDCK-II cells confirmed that TCBZSO and TCBZSO(2) are ABCG2 inhibitors, reaching inhibitory potencies between 40 and 55% for a concentration range from 5 to 25 μM. Transepithelial transport assays of ABCG2 substrates in the presence of both TCBZ metabolites at 15 μM showed very efficient inhibition of the Abcg2/ABCG2-mediated transport of the antibacterial agents nitrofurantoin and danofloxacin. TCBZSO administration also inhibited nitrofurantoin Abcg2-mediated secretion into milk by more than 2-fold and increased plasma levels of the sulfonamide sulfasalazine by more than 1.5-fold in mice. These results support the potential role of TCBZSO and TCBZSO(2) as ABCG2 inhibitors to participate in drug interactions and modulate ABCG2-mediated pharmacokinetic processes.

Effects of NAT2 polymorphism on SASP pharmacokinetics in Chinese population

BACKGROUND

Sulfasalazine (SASP) pharmacologic actions are widely applied in clinical therapy. The role of N-Acetyltransferase 2 (NAT2) in the pharmacokinetics of SASP and its metabolites has not been clarified. We investigated the effects of genetic polymorphism of NAT2 on pharmacokinetic profiles of SASP and its two metabolites, sulfapyridine (SP) and N-acetylsufapyridine (AcSP).

METHODS

Eighteen subjects were recruited and divided into 3 groups by NAT2 genotype: wild type (w/w), heterozygous variant (w/m), homozygous variant (m/m). After taking 1000mg SASP tablets, the plasma concentrations of SASP, SP and AcSP were measured with HPLC method and pharmacokinetic parameters were calculated by using the computing program 3P97.

RESULTS

The AUC(0)(-)(72) and Cmax of SP in m/m subjects were significantly higher than those in w/m and w/w subjects, with the values of 172.57+/-49.42, 103.38+/-39.85, 71.37+/-17.52mg h/l, and 9.65+/-2.34, 6.10+/-1.79, 4.55+/-1.38mg/l, respectively. In contrast, the AUC(0)(-)(72) of AcSP was significantly lower in m/m subjects. The Cmax of AcSP in w/w, w/m and m/m subjects was 12.67+/-3.32, 9.07+/-2.29 and 4.22+/-0.93mg/l, respectively, with significant differences among groups. However, there was no significant difference in any pharmacokinetic parameter of SASP among groups.

CONCLUSION

Different NAT2 genotypes, leading to functional heterogeneity of NAT2, may affect pharmacokinetics of SP and AcSP. Therefore, genotyping NAT2 gene before administration would be important in SASP therapy.

Pharmacogenetic characterization of sulfasalazine disposition based on NAT2 and ABCG2 (BCRP) gene polymorphisms in humans

The role of breast cancer resistance protein (BCRP), an efflux ABC transporter, in the pharmacokinetics of substrate drugs in humans is unknown. We investigated the impact of genetic polymorphisms of ABCG2 (421C>A) and NAT2 on the pharmacokinetics of sulfasalazine (SASP), a dual substrate, in 37 healthy volunteers, taking 2,000 mg of conventional SASP tablets. In ABCG2, SASP AUC(0-48) of C/C, C/A, and A/A subjects was 171 +/- 85, 330 +/- 194, and 592 +/- 275 microg h/ml, respectively, with significant differences among groups. In contrast, AUC(0-48) of sulfapyridine (SP) tended to be lower in subjects with the ABCG2-A allele as homozygosity. In NAT2, AUC(AcSP)/AUC(SP) was significantly higher in rapid than in intermediate and slow acetylator (SA) genotypes. We successfully described the pharmacokinetics of SASP, SP, and N -acetylsulfapyridine (AcSP) simultaneously by nonlinear mixed-effects modeling (NONMEM) analysis with regard to both gene polymorphisms. The data indicate that SASP is a candidate probe of BCRP, particularly in its role in intestinal absorption.

Can NF-κB be a target for novel and efficient anti-cancer agents?

Since the discovery of the NF-kappaB transcription factor in 1986 and the cloning of the genes coding for NF-kappaB and IkappaB proteins, many studies demonstrated that this transcription factor can, in most cases, protect transformed cells from apoptosis and therefore participate in the onset or progression of many human cancers. Molecular studies demonstrated that ancient widely used drugs, known for their chemopreventive or therapeutic activities against human cancers, inhibit NF-kappaB, usually among other biological effects. It is therefore considered that the anti-cancer activities of NSAIDs (non-steroidal anti-inflammatory drugs) or glucocorticoids are probably partially related to the inhibition of NF-kappaB and new clinical trials are being initiated with old compounds such as sulfasalazine. In parallel, many companies have developed novel agents acting on the NF-kappaB pathway: some of these agents are supposed to be NF-kappaB specific (i.e. IKK inhibitors) while others have wide-range biological activities (i.e. proteasome inhibitors). Today, the most significant clinical data have been obtained with bortezomib, a proteasome inhibitor, for the treatment of multiple myeloma. This review discusses the preclinical and clinical data obtained with these various drugs and their putative future developments.

Unified Pharmacogenetics-Based Parent–Metabolite Pharmacokinetic Model Incorporating Acetylation Polymorphism for Talampanel in Humans

The N-acetylation of the noncompetitive AMPA antagonist talampanel (TLP) represents a route of varying significance in various species. For a detailed analysis in humans, plasma concentrations of TLP and its N-acetyl metabolite (NAc-TLP) were measured for up to 48 h after administration of a single oral dose of 75 mg in 28 healthy volunteers following genotyping for the N-acetyltansferase NAT2 isozymes (alleles NAT2*4, *5, *6, and *7). Unified parent-metabolite pharmacokinetic (PK) models that allowed three different rates of acetylation were used to simultaneously fit plasma levels for both the parent drug and its metabolite following genotype-based classification as slow, intermediate, or fast acetylator. A perfect correspondence was found between the phenotype inferred from genotyping and the phenotype determined by using plasma metabolite-to-parent molar ratios indicating that this route of metabolism is indeed mediated by NAT2. Linear parent-metabolite PK models (first-order input, first-order elimination through two parallel routes one of which is through a metabolite with polymorphic rate of formation) gave adequate and sufficiently consistent fit. Parameters obtained suggest that for TLP in humans, N-acetylation represents only about 1/4th of the total elimination even in true (*4/*4 homozygous) fast acetylators, acetylation is about 8-12 times faster in fast and 3-6 times faster in intermediate acetylators than in slow acetylators, and the N-acetyl metabolite is eliminated faster than the parent drug. Such PK models can provide quantitative estimates of relative in vivo metabolism rates for routes catalyzed by functionally polymorphic enzymes.

N-acetyltransferase 2 genotype-related efficacy of sulfasalazine in patients with rheumatoid arthritis

PURPOSE

For the individual optimization of drug therapy with sulfasalazine (SASP), we studied the influence of the N-acetyltransferase 2 (NAT2) genotype on the pharmacokinetics, efficacy, and incidence of adverse reactions of SASP in patients.

METHODS

Ninety-six rheumatoid arthritis (RA) patients were treated or had been treated with 0.5 and/or 1.0 g/day of SASP. The wild-type allele (NAT2*4) and three variant alleles (NAT2*5B, *6A, and *7B) of NAT2 were determined by the polymerase chain reaction-restriction fragment length polymorphism method. Plasma concentrations of SASP and its two metabolites, sulfapyridine (SP) and N-acetylsulfapyridine (AcSP), were estimated by HPLC. Therapeutic efficacy and incidence of adverse reactions were also monitored as recommended by the American College of Rheumatology.

RESULTS

Patients were classified into three groups by NAT2 genotyping: Rapid Type (homozygote for NAT2*4), Intermediate Type (heterozygote for NAT2*4 and variant alleles), and Slow Type (homozygote for variant alleles). There was no clear difference in the genotype frequencies between RA patients and healthy subjects. NAT2 genotypes significantly affected both the plasma concentration ratios of SP to AcSP (SP/AcSP) and the efficacy of SASP (p < 0.05). Adverse reactions to SASP were found in 26 (27.1%) out of 96 patients, and there was no difference among the three genotype groups.

CONCLUSIONS

NAT2 gene polymorphism is related to the plasma SP/AcSP ratio and the efficacy of SASP.

Sulphasalazine-induced leucopenia in a patient with renal dysfunction

BACKGROUND

Sulphasalazine is used for the long-term maintenance therapy of ulcerative colitis to prevent the relapse of symptoms. However, its clinical use is often restricted by its serious adverse effects.

OBJECTIVE

Leucopenia occurred in a patient with severe renal dysfunction after administration of sulphasalazine. The present study was designed to examine whether the adverse event was associated with a disability in the metabolism of sulphasalazine.

SUBJECT

A 29-year-old male patient with ulcerative colitis, who underwent haemodialysis thrice a week because of severe renal dysfunction. The chief complaint was diarrhoea.

METHODS

Serum concentrations of three major metabolites of sulphasalazine, (5-aminosalicylic acid, sulphapyridine and N-acetyl-sulphapyridine), were measured. The polymorphism of N-acetyltransferase 2, an enzyme that metabolizes sulphapyridine, was also determined by polymerase chain reaction.

RESULTS

The trough levels of 5-aminosalicylic acid, sulphapyridine and N-acetyl-sulphapyridine were 0.77-1.45 microg/mL, 31.20-39.25 microg/mL and 14.19-15.03 microg/mL, respectively. The gene diagnosis of N-acetyltransferase 2 suggested that the type was classified as NAT2*6A/*7B, indicating that the patient was a slow acetylator.

CONCLUSION

The patient was a slow acetylator, which might lead to a rise in the serum sulphapyridine concentration. Moreover, the decrease in protein binding of sulphasalazine as a result of severe renal dysfunction might have potentiated the effect because of the extremely high protein binding of this compound. Thus, it is most likely that these two factors contributed to the sulphasalazine-induced leucopenia.

N-acetyltransferase 2 genotype-related sulfapyridine acetylation and its adverse events

Sulfapyridine (SP), one of the metabolites of sulfasalazine (SASP), is further metabolized into N-acetylsulfapyridine (AcSP) by polymorphic N-acetyltransferase 2 (NAT2). NAT2 activity has been diagnosed by phenotyping, that is, evaluating plasma concentrations or urinary excretions of tentatively administered test drugs for dose individualization and avoidance of serious adverse events. Herein, we investigated the relationship between NAT2 genotypes and the pharmacokinetics of SP in healthy Japanese subjects, as well as the adverse events of SASP in patients with inflammatory bowel disease (IBD). Eight healthy subjects and 13 IBD patients were classified into three groups by NAT2 genotyping; the homozygote for the wild-type allele (Rapid Types), the compound heterozygote for the wild-type and mutant alleles (Intermediate Types), and the homozygote for mutant alleles (Slow Types). A single oral dose of 40 mg/kg SASP was administered to each healthy subject, and plasma and urine samples were taken until 51 and 72 h after administration, respectively. Both the SP and AcSP concentrations in each sample were determined by the HPLC method. The NAT2 genotypes were well-correlated with the plasma concentrations or urinary excretions of SP and AcSP in 8 healthy subjects, except for one Slow Type. In patients with IBD, skin rash was seen in 3 of 6 Rapid Types and 1 of 6 Intermediate Types, consistent with the concept that hypersensitive reactions are independent of serum SP concentrations. In contrast, SASP dosing-related acute pancreatitis was found in the Slow Type patient. In this case, the NAT2 activity was diagnosed by genotyping in advance, and the medical staff could pay scrupulous attention, resulting in no serious subjective symptoms such as abdominal pain, anorexia or fever. Further investigations on the relationship between the NAT2 genotype and adverse events are required, although genotyping appeared to be a promising method to avoid such serious adverse events.

Arylamine N-acetyltransferases and drug response

Arylamine N-acetyltransferases (NATs) play an important role in the interaction of competing metabolic pathways determining the fate of and response to xenobiotics as therapeutic drugs, occupational chemicals and carcinogenic substances. Individual susceptibility for drug response and possible adverse drug reactions are modulated by the genetic predisposition (manifested for example, by polymorphisms) and the phenotype of these enzymes. For all drugs metabolized by NATs, the impact of different in vivo enzyme activities is reviewed with regard to therapeutic use, prevention of side effects and possible indications for risk assessment by phenotyping and/or genotyping. As genes of NATs are susceptibility genes for multifactorial adverse effects and xenobiotic-related diseases, risk prediction can only be made possible by taking the complexity of events into consideration.