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Biomedical subjects

J Benítez

Publications and source records attributed to J Benítez.

At least 19 recordsLinked to original sources
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↗
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↗
PubMed2000

Suspected sexual abuse: an unusual presentation form of congenital myotonic dystrophy.

UNLABELLED: In children, anal abnormalities due to various causes may be confused with sexual abuse. We present the case of a child in whom the suspicion of abuse due to anal dilatation led to the previously unknown diagnosis of myotonic dystrophy. Myopathic involvement of the perianal musculature is a known feature of congenital myotonic dystrophy that usually appears in late childhood or adolescence. CONCLUSION: We stress the importance of considering an underlying myopathic condition in the differential diagnosis of anal laxity. Further studies, such as anal ultrasonography, may help when the diagnosis of abuse is not clear.

Child↗
PubMed2000

Identification by comparative genomic hybridization of genetic changes involved in tumoral progression of a T-cell non-Hodgkin lymphoma.

Comparative genomic hybridization (CGH) was used to detect chromosomal imbalances in tumor DNA from two relapsed samples obtained in stages II and IV of a T-cell non-Hodgkin lymphoma in order to identify genetic mechanisms involved in tumor progression of this neoplasm. With conventional cytogenetic techniques (CCT), a complex hyperdiploid karyotype was obtained in stage IV. Using CGH analysis, a normal profile was observed in stage II, whereas gains of 6p11.2, 7q11.2, 7q21-->q32, 7q34, 10p13, Xp11.4, and loss of 4q33-->qter chromosomal regions were detected in stage IV.

Humans↗
PubMed2000

Molecular analysis of the BRCA1 and BRCA2 genes in 32 breast and/or ovarian cancer Spanish families.

It is estimated that about 5-10% of breast cancer cases may be due to inherited predisposition. Until now, two main susceptibility genes have been identified: BRCA1 and BRCA2. The first linkage and mutational studies suggested that mutations in these two genes would account for the majority of high-risk breast cancer families, but recent studies show how the proportion of families due to BRCA1 or BRCA2 mutations strongly depends on the population and the types of family analyzed. It is now clear that, in the context of families with a modest cancer profile, which are the most commonly found in the clinical practice, the percentage of mutations found is much lower than that suggested by the first studies. In the present study, we analyze a group of 32 Spanish families, which contained at least three cases of female breast cancer (at least one of them diagnosed before the age of 50 years), for the presence of mutations in the BRCA genes. The total proportion of mutations was low (25%), although the percentage of mutations in the BRCA1 and BRCA2 genes was higher, considering the breast and ovarian cancer families and the male breast cancer families respectively. Our results are in agreement with the idea that a great proportion of moderate-risk cancer families could be due to low penetrance susceptibility genes distinct from BRCA1 or BRCA2.

Adult↗
PubMed2000

N-acetyltransferase 2 (NAT2) genotype and colorectal carcinoma: risk variability according to tumour site?

BACKGROUND: Dietary heterocyclic aromatic amines (HAAs) are members of a family of chemicals that comprise highly mutagenic compounds related to colon cancer. The polymorphic N-acetyltransferase 2 enzyme (NAT2, E.C. 2.3.1.5) plays a key role in the transformation of HAAs to ultimate carcinogens. NAT2 enzyme activity is expressed in a genotype-dependent manner in colon epithelium. Therefore local activation of HAAs in colon, and hence increased risk to develop colon cancer, is likely to be related to high NAT2 enzyme activity. This study is aimed at analysing the association between genotypes leading to high NAT2 activity and colorectal cancer risk. METHODS: Genomic DNA from 120 colorectal cancer patients and 258 healthy individuals were analysed for enzyme-inactivating mutations at the coding region of the NAT2 gene by means of a mutation-specific polymerase chain reaction. RESULTS: Among patients with sigmoid colon cancer, a significant excess of individuals with genotypes leading to high NAT2 activity was observed as compared both to controls and to the rest of patients with colorectal cancer (P < 0.05). CONCLUSIONS: Our findings, which require independent confirmation, suggest that the NAT2 genotype constitutes a secondary risk factor to develop sigmoid colon cancer.

Adolescent↗
PubMed2000

Use of the mesoridazine/thioridazine ratio as a marker for CYP2D6 enzyme activity.

Thioridazine is metabolized in humans by CYP2D6 to mesoridazine, which is an active metabolite. Two or more CYP2D6 substrates are seldom given simultaneously to elderly patients because potentially dangerous metabolic interactions may occur. It may be valuable to know the CYP2D6 metabolic capacity of such patients to avoid drug interactions, which depend on the metabolic phenotype. The goal of this study was to evaluate the use of the mesoridazine/thioridazine ratio for the estimation of CYP2D6 enzyme capacity. A sensitive and reliable method has been developed for the determination of thioridazine and its metabolites, mesoridazine and sulforidazine. Commonly used central nervous system (CNS) comedications do not interfere with the method. A group of 27 chronic patients with mental illness receiving monotherapy with thioridazine were studied. There were 23 men and 4 women between 37 and 80 years old (mean +/- SD: 61.2 +/- 10.2). The thioridazine/mesoridazine ratio correlated with the debrisoquine metabolic ratio (r = 0.74, p < 0.001). Therefore, the authors suggest that the measurement of thioridazine and its metabolite might be a useful tool to assess CYP2D6 activity during treatment.

Adult↗
PubMed2000

Construction and characterization of a nonproliferative El Tor cholera vaccine candidate derived from strain 638.

In recent clinical assays, our cholera vaccine candidate strain, Vibrio cholerae 638 El Tor Ogawa, was well tolerated and immunogenic in Cuban volunteers. In this work we describe the construction of 638T, a thymidine auxotrophic version of improved environmental biosafety. In so doing, the thyA gene from V. cholerae was cloned, sequenced, mutated in vitro, and used to replace the wild-type allele. Except for its dependence on thymidine for growth in minimal medium, 638T is essentially indistinguishable from 638 in the rate of growth and morphology in complete medium. The two strains showed equivalent phenotypes with regard to motility, expression of the celA marker, colonization capacity in the infant mouse cholera model, and immunogenicity in the adult rabbit cholera model. However, the ability of this new strain to survive environmental starvation was limited with respect to that of 638. Taken together, these results suggest that this live, attenuated, but nonproliferative strain is a new, promising cholera vaccine candidate.

Amino Acid Sequence↗
PubMed2000

Pharmacokinetic-Pharmacodynamic Modelling of the antipyretic effect of two oral formulations of ibuprofen.

OBJECTIVE: To analyse the population pharmacokinetic-pharmacodynamic relationships of racemic ibuprofen administered in suspension or as effervescent granules with the aim of exploring the effect of formulation on the relevant pharmacodynamic parameters. DESIGN: The pharmacokinetic model was developed from a randomised, cross-over bioequivalence study of the 2 formulations in healthy adults. The pharmacodynamic model was developed from a randomised, multicentre, single dose efficacy and safety study of the 2 formulations in febrile children. PATIENTS AND PARTICIPANTS: Pharmacokinetics were studied in 18 healthy volunteers aged 18 to 45 years, and pharmacodynamics were studied in 103 febrile children aged between 4 and 16 years with bodyweight 225kg. METHODS: The pharmacokinetic study consisted of two 1-day study occasions, each separated by a 1-week washout period. On each occasion ibuprofen 400mg was administered orally as suspension or granules. The time course of the antipyretic effect was evaluated in febrile children receiving a single oral dose of 7 mg/kg in suspension or 200 or 400mg as effervescent granules. During the pharmacodynamic analysis, the predicted typical pharmacokinetic profile (based on the pharmacokinetic model previously developed) was used. RESULTS: The disposition of ibuprofen was described by a 2-compartment model. No statistical differences (p > 0.05) were found between the 2 formulations in the distribution and elimination parameters. Absorption of ibuprofen from suspension was adequately described by a first-order process; however, a model with 2 parallel first-order input sites was used for the drug given as effervescent granules, leading to time to reach maximum drug concentration (tmax) values of 0.9 and 1.9 hours for suspension and granules, respectively. The time course of the antipyretic effect was best described using an indirect response model. The estimates (with percentage coefficients of variation in parentheses) of Emax (maximum inhibition of the zero-order synthesis rate of the factor causing fever), EC50 (plasma concentration eliciting half of Emax), n (slope parameter) and k(out) (first order rate constant of degradation) were 0.055 (10), 6.16 (14) mg/L, 2.71 (18) and 1.17 (23) h(-1), respectively, where To is the estimate of the basal temperature, 38.8 (1) degrees C. No significant (p > 0.05) covariate effects (including pharmaceutical formulation) were detected in any of the pharmacodynamic parameters. CONCLUSIONS: Because of the indirect nature of the effect exerted by ibuprofen, the implications of differences found in the plasma drug concentration profiles between suspension and effervescent granules are less apparent in the therapeutic response.

Adolescent↗
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↗
PubMed1999

Prevalence of BRCA1 and BRCA2 Jewish mutations in Spanish breast cancer patients.

We screened the 185delAG and 5382insC (BRCA1) and the 6174delT (BRCA2) mutation in 298 Spanish women with breast cancer. Two women (one with Sephardic ancestors) presented the 185delAG mutation and the same haplotype reported in Ashkenazim with this mutation. This suggests a common origin of the 185delAG in both Sephardic and Ashkenazi populations.

Adult↗
PubMed1999

Genetic and clinical analysis in 10 Spanish patients with multiple endocrine neoplasia type 1.

Multiple endocrine neoplasia type 1 (MEN 1) is characterised by the combination of tumours of the parathyroid, endocrine pancreas and anterior pituitary glands. In 1988 the MEN 1 gene was mapped to chromosome 11q13 and it was cloned in 1997. This gene contains 10 exons and extends across 9 Kb of genomic DNA; it encodes for a product of 610 amino acid named menin whose function is unknown. We have studied 10 unrelated MEN 1 kindreds by a complete sequencing analysis of the entire gene; mutations were identified in nine of them: five deletions, one insertion, two nonsense mutation and a complex alteration consisting of a deletion and an insertion that can be explained by a hairpin loop model. Two of the mutations have been previously described; the other seven were novel, and they were scattered throughout the coding sequence of the gene. As in previous series, no correlation was found between phenotype and genotype.

Base Sequence↗
PubMed1999

Pharmacokinetic interaction of fluvoxamine and thioridazine in schizophrenic patients.

This study investigated to what extent fluvoxamine affects the pharmacokinetics of thioridazine (THD) in schizophrenic patients under steady-state conditions. Concentrations of THD, mesoridazine, and sulforidazine were measured in plasma samples obtained from 10 male inpatients, aged 36 to 78 years, at three different time points: A, during habitual monotherapy with THD at 88 +/-54 mg/day; B, after addition of a low dosage of fluvoxamine (25 mg twice a day) for 1 week; and C, 2 weeks after fluvoxamine discontinuation. After the addition of fluvoxamine, THD concentrations relative to time point A significantly increased approximately threefold from 0.40 to 1.21 micromol/L (225%) (p < 0.002), mesoridazine concentrations increased from 0.65 to 2.0 micromol/L (219%) (p < 0.004), and sulforidazine levels increased from 0.21 to 0.56 micromol/L (258%) (p < 0.004). The THD-mesoridazine and THD-sulforidazine ratios remained unchanged during the study. Mean plasma THD, mesoridazine, and sulforidazine levels decreased at time point C, but despite fluvoxamine discontinuation for 2 weeks, three patients continued to exhibit elevated concentrations of THD and its metabolites. In conclusion, fluvoxamine markedly interferes with the metabolism of THD, probably at the CYP2C19 and/or CYP1A2 enzyme level. Therefore, clinicians should be aware of the potential for a clinical drug interaction between both compounds, and careful monitoring of THD levels is valuable to prevent the accumulation of the drug and resulting toxicity.

Adult↗
PubMed1999

[Stapedectomy versus stapedotomy. Our experience].

Otosclerosis surgery has seen three well-differentiated stages of development: a) SHC fenestration; b) stapes mobilization, and c) platinectomy, a procedure introduced in 1960 by Shea. Since then, only one variation has been proposed: platinotomy. After a comparative study of platinectomy versus platinotomy, we, like other authors, concluded that platinotomy was a better technique because of the ease of execution and good functional results.

Adolescent↗
PubMed1999

[Prevalence of Factor V Leiden and the G20210A mutation of the prothrombin gene in a random group of patients with thrombotic episodes].

UNLABELLED: Factor V Leiden and G20210A mutation of the prothrombin gene have been described as risk factors in thrombophilic pathologies. Our objective has been to know the prevalence of these two mutations in a group of patients with thrombophilic pathology and to compare it with its prevalence in a control group of Spanish population. PATIENTS AND METHODS: 64 patients were divided in two groups. First, 39 patients with deep venous thrombosis (DVT): 24 with an unique episode of DVT; 11 with more than one episode; 3 with DVT and pulmonary thromboembolism, and one with DVT and more than one episode of cerebral thrombosis. Second, 25 patients with other pathologies, such as pulmonary thromboembolism (9 patients), acute cerebrovascular accident (10 patients) and 6 who came to our Department because there were some carrier in their families. The 20210A allele was analyzed in 37 of the 64 patients. Some of the 64 patients had haematological determinations of the activated protein C resistance (APC resistance). As well, 103 unrelated subjects with unknown thrombotic pathologies were analyzed. RESULTS: We have found a prevalence of factor V Leiden in the group of patients of 14.1% (9 carriers in 64 patients, all of them in the first group of 39 patients with DVT) versus 1% in the control group (1 carrier in 103 controls). On the other hand, the difference between the prevalence of the 20210A allele was not statistically significant between the group of patients and the control group (2.7% vs 2.9%). In 75% of the patients no haematological results of APC resistance were obtained, generally because they were with anticoagulant treatment, and in 11.1% of the carriers the result of the determination was considered as ambiguous or false negative. CONCLUSION: Factor V Leiden is well established as risk factor in the thrombophilic pathology, but more studies are needed to know the meaning of the G20210A mutation of the prothrombin gene.

Alleles↗
PubMed1999

[Genetic bases in Huntington disease].

Huntington disease is a neurodegenerative syndrome of late appearance in 80% of the cases. Its clinical course shows motor and cognitive disorders which lead to total incapacity of the individual 10 to 15 years after the appearance of the first syndromes. From a genetic point of view, this disease is of autosomic dominant inheritance with complete penetration. The gene (IT15) is localized in the short arm of chromosome 4 in the telemaric region 4p16.3 and it is known that the mutation is produced by an increase in the number of trinucleotides CAG (glutamine) localized in the 5' end of the gene, in the first exon. In the general population these are repeated in a number of less than 30 repetitions and in the disease population in a number greater than 36 and, in some cases, even greater than 100 repetitions. These sequences are unstable from one generation to another and this fact may explain the phenomenon of genetic anticipation shown in this disease since there is an inversely proportional correlation between the number of repetitions and the age of appearance of the first symptoms. The gene codifies for a protein known as "huntingtina" which is expressed not only in brain but also in different tissues. Although the function remains unknown, it is known that it is bound to other proteins related to the transmission of neuron signals and to the regulation of neuron death (apoptosis) among others. The defect is produced by a gain in function closely related to the number of repetitions. At present, presymptomatic and prenatal diagnosis of the disease may be achieved since the reliability of the studies is practically 100%. Nonetheless, the demand is lower than expected and this may be due to psychologic, social and legal problems, together with the lack of adequate infrastructure for completely guaranteeing the performance of these studies.

Chromosome Aberrations↗