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J A Agúndez

Publications and source records attributed to J A Agúndez.

At least 19 recordsLinked to original sources
PubMed2001

High frequency of mutations related to impaired CYP2C9 metabolism in a Caucasian population.

OBJECTIVE: To search for ethnic variability in the impact of cytochrome P450 2C9 (CYP2C9) polymorphism. METHODS: CYP2C9 allelic variants related to impaired CYP2C9 metabolism were analysed in genomic DNA from 157 Spanish healthy subjects using amplification-restriction and sequencing procedures. RESULTS: The frequency for CYP2C9 mutated alleles is higher among the Spanish subjects analysed than that reported for other Caucasian individuals: CYP2C9*2, 0.143 and CYP2C9*3, 0.162 (P = 0.0001). Nearly 10% of the individuals studied are expected to metabolise deficiently CYP2C9 substrates. CONCLUSION: In some Caucasian populations the impact of the CYP2C9 polymorphism may be much higher than that estimated from genotyping studies published to date.

Adult↗
PubMed2001

Association of CYP2C9 genotypes leading to high enzyme activity and colorectal cancer risk.

CYP2C9 enzyme activity is involved in the metabolism of substances related to colorectal cancer, and it is functionally linked to a genetic polymorphism. Two allelic variants of the CYP2C9 gene, namely CYP2C9*2 and CYP2C9*3, differ from wild-type CYP2C9*1 by single amino acid substitutions. These mutated alleles encode enzymes with altered properties that are associated with impaired metabolism. The present study evaluates the impact of CYP2C9 genotypes leading to high enzyme activity on colorectal cancer risk. For this, the frequency of allelic variants of the CYP2C9 gene was analysed in genomic DNA from 129 patients with colorectal cancer and in 150 healthy controls. Patients with colorectal cancer showed a statistically significant increase in the frequency of genotypes homozygous for the active CYP2C9*1 gene, as compared with healthy individuals. Such a high frequency is more significant among patients with cancer in proximal segments of the colon (P < 0.025; odds ratio 2.36 95% CI 1.18-4.72), and decreases in more distal tumour locations. We conclude that CYP2C9 polymorphism can be considered as a secondary risk factor for colorectal cancer in the studied population: those individuals with genotypes leading to high enzyme activity were at increased risk. The association of the CYP2C9 polymorphism to colorectal cancer risk could be related to CYP2C9-mediated metabolic activation of polycyclic aromatic hydrocarbons and heterocyclic aromatic amines. In addition, the key role of CYP2C9 in the metabolic inactivation of non-steroidal anti- inflammatory drugs could diminish the protective effect of these drugs against colorectal cancer.

Alleles↗
PubMed2001

Inhibition of cytochrome P450 2C9 activity in vitro by 5-hydroxytryptamine and adrenaline.

In the present study, the occurrence of a modulatory effect of 14 neurotransmitters, precursors and metabolites on the cytochrome P450 2C9 (CYP2C9) enzyme activity, as determined by diclofenac 4-hydroxylation, was studied in human liver microsomes. Two indoleamines, 5-hydroxytryptamine (5-HT) and adrenaline, showed a non-competitive-type inhibitory effect of approximately 90% of the diclofenac 4-hydroxylase activity, with Ki values of 63.5 (0.7 and 156 (89.3 microM, respectively. The rest of substances analysed were weak inhibitors or had no inhibitory effect. CYP2C subfamily is present in human brain, although CYP2C9 isozyme has not yet been identified in this tissue, and CYP2C9 is involved in the metabolism of psychoactive drugs. Therefore, the fact that endogenous compounds could modulate the CYP2C9 activity, suggests that an hypothetical local activity of brain CYP2C9 might be susceptible to regulatory mechanisms. The possible clinical implications of this modulation are discussed.

Aryl Hydrocarbon Hydroxylases↗
PubMed2001

Functionally active duplications of the CYP2D6 gene are more prevalent among larynx and lung cancer patients.

The cytochrome P450 CYP2D6 is a polymorphic drug-metabolizing enzyme that is involved in the metabolism of several drugs and xenobiotics. Several independent studies indicate that the CYP2D6 metabolic status is a secondary factor in the risk of developing lung cancer, with individuals with high activity being at increased risk. The occurrence of functionally active duplications of the CYP2D6 gene is a phenomenon that affects 3-8% of Caucasians and up to 30% in some ethnic groups. These duplications cause ultrarapid metabolism of CYP2D6 substrates. In order to establish whether the highest CYP2D6 enzyme activity is associated with an increased risk of cancer, we analyzed the frequency of CYP2D6 gene duplications and enzyme-inactivating mutations in 199 Caucasian patients with lung or larynx cancer and in 335 healthy controls. A significantly increased frequency of carriers of the CYP2D6 gene duplication were found among lung and larynx cancer patients (13%), as compared with healthy controls (6.9%; p < 0.02). The frequency of the mutated active CYP2D6*9 allele was increased in lung cancer patients (p < 0.01) but not in larynx cancer patients. Global findings indicate that over 20% patients with lung or larynx cancer show CYP2D6 genotypes leading to ultrarapid metabolism or to the expression of an enzyme with altered kinetics (p < 0.01 vs. healthy controls). This may influence the metabolism of CYP2D6 substrates, including antineoplastic drugs and opioid derivatives used for pain relief in cancer patients. These patients would require higher doses than those considered as standard. We conclude that dosages for CYP2D6 substrates should be adapted to lung and larynx cancer patients.

Adult↗
PubMed2000

Modulation of midazolam 1-hydroxylation activity in vitro by neurotransmitters and precursors.

OBJECTIVE: The aim of this study was to find whether endogenous substances could modulate CYP3A activity. There is evidence that CYP3A, a major phase-I xenobiotic metabolizing enzyme, is present in human brain but, at the present time, endogenous substrates for such an enzyme remain to be identified. A possible linkage between the CYP2D6 enzyme and serotonergic transmission has been recently reported by our group. In the same manner, structurally related enzymes such as CYP3A could also be related to endogenous compounds. METHODS: CYP3A activity was measured using the enzyme-specific substrate midazolam in human liver microsomes. Several neurotransmitters, precursors, and their metabolites, corresponding to three different metabolic routes, were assayed as putative modulators of CYP3A enzyme activity. These comprised serotonergic, catecolaminergic, and GABAergic transmitters and precursors. The inhibitory capacity of ketoconazole, a competitive inhibitor of CYP3A, was also analyzed for comparison. RESULTS: The kinetic analysis of the midazolam 1-hydroxylase activity measured in microsomes from five human liver samples indicated Km values (mean +/- SD) of 5.8 +/- 4.9 microM, and Vmax values of 1.7 +/- 1.4 nmol min(-1) per mg microsomal protein in all the samples used in the study. Of the 14 substances analyzed, adrenaline, serotonin, and 5-hydroxytriptofol were full inhibitors of CYP3A enzyme activity (Ki values of 42.3, 26.4, and 43 microM, respectively). The remaining substances were weak inhibitors or had no inhibitory effect. CONCLUSION: Brain CYP3A activity could be modulated by some neurotransmitters and precursors.

Aryl Hydrocarbon Hydroxylases↗
PubMed1999

Identification and characterisation of novel polymorphisms in the CYP2A locus: implications for nicotine metabolism.

The polymorphic human cytochrome P450 2A6 (CYP2A6) metabolises a number of drugs, activates a variety of precarcinogens and constitutes the major nicotine C-oxidase. A relationship between CYP2A6 genotype and smoking habits, as well as incidence of lung cancer, has been proposed. Two defective alleles have hitherto been identified, one of which is very common in Asian populations. Among Caucasians, an additional defective and frequently distributed allele (CYP2A6*3) has been suggested to play a protective role against nicotine addiction and cigarette consumption. Here, we have re-evaluated the genotyping method used for the CYP2A6*3 allele and found that a gene conversion in the 3' flanking region of 30-40% of CYP2A6*1 alleles results in genotype misclassification. In fact, no true CYP2A6*3 alleles were found among 100 Spaniards and 96 Chinese subjects. In one Spanish poor metaboliser of the CYP2A6 probe drug coumarin, we found two novel defective alleles. One, CYP2A6*5, encoded an unstable enzyme having a G479L substitution and the other was found to carry a novel type of CYP2A6 gene deletion (CYP2A6*4D). The results imply the presence of numerous defective as well as active CYP2A6 alleles as a consequence of CYP2A6/CYP2A7 gene conversion events. We conclude that molecular epidemiological studies concerning CYP2A6 require validated genotyping methods for accurate detection of all known defective CYP2A6 alleles.

Apoproteins↗
PubMed1999

Comparative in vitro and in vivo inhibition of cytochrome P450 CYP1A2, CYP2D6, and CYP3A by H2-receptor antagonists.

The isozymes CYP1A2, CYP2D6, and CYP3A4/5 are involved in the majority of all cytochrome P450-mediated drug biotransformations. In this study we investigated the inhibition profiles of CYP1A2 (substrate: caffeine) CYP2D6 (substrate: dextromethorphan), and CYP3A4/5 (substrate: dextrorphan) by cimetidine, ranitidine, and the novel H2-receptor antagonist ebrotidine in human liver microsomes. The inhibitory effect of the drugs on the enzymes activities were as follows: CYP1A2: cimetidine >> ranitidine = ebrotidine; CYP2D6: cimetidine >>> ranitidine = ebrotidine; CYP3A4/5: ebrotidine > cimetidine >>> ranitidine. The inhibition of CYP3A4/5 enzyme activity by ebrotidine was competitive. To test whether the inhibitory effect of ebrotidine in CYP3A activity was also found in vivo, we analyzed the biodisposition of midazolam in 8 healthy volunteers. Midazolam biodisposition was significantly reduced when administered together with cimetidine (P < .05), whereas no significant inhibition was observed with ebrotidine or ranitidine compared with placebo. Psychomotor performance analysis revealed no significant effect of the observed reduction on midazolam biodisposition. We concluded that patients who are receiving treatment with drugs metabolized through CYP3A may experience enhanced drug effects as a result of pharmacokinetic interaction when treated concomitantly with cimetidine. In contrast, the effect of ranitidine or ebrotidine on CYP3A activity in vivo seems to have little clinical significance.

Adult↗
PubMed1998

Influence of genetic admixture on polymorphisms of drug-metabolizing enzymes: analyses of mutations on NAT2 and C gamma P2E1 genes in a mixed Hispanic population.

OBJECTIVES AND STUDY DESIGN: The genetic basis of two polymorphisms of drug- and carcinogen-metabolizing enzymes, NAT2 (arylamine N-acetyltransferase-2) and CYP2E1 (cytochrome P450 2E1), was studied in genomic deoxyribonucleic acid from 137 healthy, unrelated subjects from a mixed Nicaraguan population. RESULTS: Six point mutations were identified at the coding region of the NAT2 gene, including the most common alleles NAT2*4 (41.6%), NAT2*5B (31.4%), and NAT2*6A (16.8%). The percentage of carriers of two defective genes was 49.6%. The Nicaraguan population studied was in Hardy-Weinberg's disequilibrium for the NAT2 genotype (p < 0.01) and the allele frequencies were significantly different from those of other populations, being intermediate between those of pure Central American Indians and Spanish persons. The frequency of CYP2E1 alleles mutated at the RsaI site (c2 allele; 16.5%) was intermediate between that of Spanish white and Asian subjects. About 5% of the subjects were homozygous for the c2 allele. CONCLUSIONS: These findings indicate a high impact of genetic admixture of populations of Asian origin (Central American Indians) and white persons (Spaniards) on the genetic polymorphisms studied here and suggest that among mixed Hispanics a high heterogeneity of genotypes and phenotypes can be expected depending on the degree of genetic admixture of every subgroup. Therefore different subgroups of mixed Hispanic subjects can exhibit different results when treated with drugs that are inactivated through polymorphic enzymes.

Arylamine N-Acetyltransferase↗
PubMed1998

Expression in human prostate of drug- and carcinogen-metabolizing enzymes: association with prostate cancer risk.

The role of two common polymorphisms of enzymes involved in the metabolism of drugs and carcinogens was studied in relation to prostate cancer. The gene encoding one of these enzymes (NAT2) is located in an area where frequent allelic loss occurs in prostate cancer. Mutations at the genes CYP2D6 and NAT2 were analysed by allele-specific polymerase chain reaction and restriction mapping in DNA from 94 subjects with prostate cancer and 160 male healthy control subjects. Eleven prostate specimens were analysed for genotype and enzymatic activities NAT2, CYP2D6 and CYP3A by using the enzyme-specific substrates sulphamethazine and dextromethorphan. Enzyme activities with substrate specificities corresponding to NAT2, CYP2D6 and CYP3A are present in human prostate tissue, with mean +/-s.d. activities of 4.8+/-4.4 pmol min(-1) mg(-1) protein, 156+/-91 and 112+/-72 nmol min(-1) mg(-1) protein respectively. The Km values for the prostate CYP2D6 and CYP3A enzyme activities corresponded to that of liver CYP2D6 and CYP3A activities, and the CYP2D6 enzyme activity is related to the CYP2D6 genotype. The N-acetyltransferase, in contrast, had a higher Km than NAT2 and was independent of the NAT2 genotype. The CYP2D6 and CYP3A enzymes, and an N-acetyltransferase activity that is independent of the regulation of the NAT2 gene, are expressed in human prostate tissue. The presence of carcinogen-metabolizing enzymes in human prostate with a high interindividual variability may be involved in the regulation of local levels of carcinogens and mutagens and may underlie interindividual differences in cancer susceptibility.

Aged↗
PubMed1998

Slow allotypic variants of the NAT2 gene and susceptibility to early-onset Parkinson's disease.

OBJECTIVE: To determine the frequency and the linkage distribution of seven mutations at the polymorphic gene coding for the arylamine N-acetyl transferase (NAT2; EC 2.3.1.5) in 121 unrelated patients with sporadic PD and in 121 unrelated healthy volunteers. METHODS: The study was performed with mutation-specific PCR using genomic DNA obtained from blood of the probands. RESULTS: Comparison of the NAT2 genotypes of the overall PD patients and control subjects did not indicate statistically significant differences. However, patients with early-onset PD (onset before the age of 50 years, n=37) showed a higher frequency of slow-acetylation genotypes (78.4% patients) compared with both healthy control subjects (55.4%) and with late-onset (onset after 51 years of age, n=84) PD patients (54.8%). Such a difference was statistically significant (p < 0.015) and was the result of a homogeneous increase in the frequency of slow-acetylation alleles. All subgroups analyzed in the study were in Hardy-Weinberg equilibrium for mutations at the NAT2 gene. CONCLUSIONS: Slow-acetylation-mutated alleles may be considered low-penetrance genes in early-onset PD pathogenesis, with a relative risk ratio for individuals with slow-acetylation genotype of 2.92 (95% CI, 1.26 to 6.78). This study provides evidence for the interaction of genetic and environmental factors in the etiology of sporadic PD.

Adult↗
PubMed1998

Modulation of CYP1A2 enzyme activity by indoleamines: inhibition by serotonin and tryptamine.

Recent evidence supports a role for the CYP2D6 enzyme in the metabolism of tryptamine. Because of the partial overlapping between substrate and inhibitor specificities that characterize some cytochrome P450 enzymes, these finding raise the possibility that other cytochrome P450 enzymes may be modulated by endogenous compounds. In the present study, the occurrence of modulatory effect of 17 neurotransmitters, precursors and metabolites on the cytochrome P450 1A2 (CYP1A2) enzyme activity was studied in human liver microsomes. Two indoleamines, serotonin and tryptamine, showed a competitive inhibitory effect on the high-affinity component of the phenacetin O-de-ethylase activity. Both substances induced an inhibition of 100% of the activity, with Ki values of 35 and 45 microns for serotonin and tryptamine, respectively. The inhibitors did not affect the microsomal NADPH-reductase activity. Other substances, which were either poor or partial inhibitors, were dopamine, L-tyrosine, tryptophol, 5-hydroxytryptophol, adrenaline, indole-3-acetaldehyde, 5-hydroxytryptophan, noradrenaline, vanillylmandelic acid, indole-3-acetic acid, dihydroxyphenylacetic acid, and homovanillic acid. L-tryptophan, dihydroxyphenylalanine and 5-hyroxyindole acetic acid induced very low or no inhibitory effect. Tryptamine and serotonin metabolism in human liver microsomes was studied after inhibition of monoamine oxidase activity with the unspecific MAO inhibitor pargyline. Both serotonin and tryptamine were metabolized in human liver microsomes. However, the metabolism of both indoleamines was not significantly inhibited with the CYP1A2-specific inhibitor furafylline, thus indicating that the inhibition of CYP1A2 was not related to metabolic activity of the CYP1A2 enzyme on serotonin or tryptamine. The CYP1A2 enzyme is expressed in brain and is involved in the metabolism of psychoactive drugs. Therefore, the fact that endogenous compounds could modulate the CYP1A2 activity suggests that local activity of brain CYP1A2 might be susceptible to local regulatory mechanisms. This may have important clinical implications, one of them being that CYP1A2 activity in brain tissue might correlate poorly with that of liver, as observed in vivo. In addition, the influence of indoleamines on CYP1A2 activity might be partly responsible for a number of associations of CYP1A2 activity with nutritional and environmental factors.

Brain↗
PubMed1997

CYP2D6, NAT2 and CYP2E1 genetic polymorphisms in nonagenarians.

BACKGROUND: enzymatic polymorphisms affecting the metabolic disposition of xenobiotics may modulate the rate of activation or deactivation of carcinogens and other toxic environmental chemicals. Hence, these polymorphisms may influence the risk of suffering some types of cancer and other degenerative diseases that are incompatible with extreme longevity. AIMS: to establish the distribution of three well known enzymatic polymorphisms that affect the CYP2D6, NAT-2 and CYP2E1 genes and the activity of their enzymatic gene products, involved in the disposition of many xenobiotics, in a group of nonagenarians and in much younger controls. PATIENTS: the three genotypes were determined in 41 nonagenarians (10 males, mean age 92.2 years, range 90-98) free of known malignancies or neurodegenerative diseases. The control groups comprised 217 healthy volunteers (128 males, mean age 36.3 years; SD, 12.7) for the CYP2D6 and NAT2 genotypes and 137 (116 males, mean age 32 years; SD, 18.8) for the CYP2E1 genotype. METHODS: after extraction of DNA from white blood cells, polymerase chain reaction and restriction fragment polymorphism methods were used to identify the allelic variants of the three genotypes. RESULTS: we found no qualitative or quantitative difference in the mutations underlying the three genetic polymorphisms studied, nor in the expected enzymatic phenotypes. Instead, a close parallelism exists between advanced age and younger groups. CONCLUSION: longevity does not seem to be related to any special configuration of these three polymorphic traits. Comparisons with younger controls may be adequate when studying the distribution of these polymorphisms in diseases affecting old people. No genetically determined differences in the activation of drugs metabolized by these enzymes are to be expected in very old people.

Aged↗
PubMed1997

CYP2D6 polymorphism is not associated with essential tremor.

Recent reports have shown an association between cytochrome P450IID6 (CYP2D6) polymorphism and Parkinson's disease. We investigated the association between this polymorphism and the risk for developing essential tremor (ET). Leukocytic DNA from 91 unrelated ET patients and a control group of 258 unrelated healthy individuals was studied for the occurrence of eight different CYP2D6 allelic variants by using allele-specific PCR amplification Xbal and EcoRI-RFLP's analyses. The prevalence for these allelic variants in the ET and control groups were, respectively: CYP2D6*1 76.9 and 78.7%, CYP2D6*2 0.5 and 0.2%, CYP2D6*3 0 and 1%, CYP2D6*4 12.1 and 12.2%, CYP2D6*5 1.6 and 1.7%, CYP2D6*9 4.4 and 2.9%, CYP2D6*2x2 4.4 and 3.2%. The prevalence of subjects with absent CYP2D6 activity (those carrying two defect genes) was 1.1 and 3.1% in ET and control groups, respectively. Both groups studied were in Hardy-Weinberg equilibrium. These results indicate that mutations at the CYP2D6 gene do not seem to be a major factor in determining susceptibility to ET, and reinforces the view that ET and parkinsonism are distinct conditions.

Adolescent↗
PubMed1997

Tryptamine: a possible endogenous substrate for CYP2D6.

The fact that CYP2D6 is not only expressed in liver but also in brain and the clinical association of this cytochrome with Parkinson's disease suggests the possibility of existence of some endogenous substrate, and among these perhaps one or more neurotransmitters could be metabolized by CYP2D6. In this study we explored such a possibility by studying the modulation of CYP2D6 activity by several neurotransmitters. Our findings confirm the occurrence of a competitive inhibition of dextromethorphan O-demethylation in the presence of tryptamine, with a Ki value of 44.6 microM. Tryptamine was metabolized in human liver microsomes by an enzyme activity with a K(m) of 3.6 +/- 0.9 microM. Such activity is NADPH dependent and is inhibited by quinidine and CYP2D6-specific substrates. The product of the reaction is tryptophol. These results suggest that tryptamine may be an endogenous substrate of CYP2D6.

Cytochrome P-450 CYP2D6↗
PubMed1996

CYP2D6 genotypes in Spanish women with breast cancer.

Wild type and three mutated alleles of the polymorphic CYP2D6 gene were studied in genomic DNA samples from 187 women with breast carcinoma and 151 healthy women by a mutation-specific polymerase chain reaction. The prevalence of the enzyme-inactivating CYP2D6(B) allele was higher among patients (18.2%) than in controls (11.6%; OR = 1.7; 95% c.i. = 1.14-3.13; P = 0.018). This excess was more marked in postmenopausal patients (19.8%, P = 0.0086) and in patients with non-ductal infiltrating carcinomas (25.8%, P = 0.003). The percentage of carriers of only one active gene (heterozygote extensive metabolizers) was higher in patients (31% vs. 19.9%; OR = 1.81; 95% c.i. = 1.06-3.11; P = 0.02). The CYP2D6(B)-carrier state may be related to a greater risk of breast cancer in women.

Adult↗