Rol de las isoenzimas del Citocromo P450 en el desencadenamiento y la severidad de la Porfiria Cutánea Tardía
Porphyrias are metabolic disorders caused by deficiency in one of the enzymes of heme biosynthesis. Porphyria Cutanea tarda (PCT), the most common of all Porphyrias, results from a decrease in the activity of uroporphyrinogen decarboxylase (URO-D) at the liver level (A-PCT) or in all organs (H-PCT)....
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| Formato: | Tesis doctoral acceptedVersion |
| Lenguaje: | Español |
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Facultad de Farmacia y Bioquímica
2020
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| Acceso en línea: | http://repositoriouba.sisbi.uba.ar/gsdl/cgi-bin/library.cgi?a=d&c=posgraafa&cl=CL1&d=HWA_6325 http://repositoriouba.sisbi.uba.ar/gsdl/collect/posgraafa/index/assoc/HWA_6325.dir/6325.PDF |
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| Sumario: | Porphyrias are metabolic disorders caused by deficiency in one of the enzymes of heme biosynthesis. Porphyria Cutanea tarda (PCT), the most common of all Porphyrias, results from a decrease in the activity of uroporphyrinogen decarboxylase (URO-D) at the liver level (A-PCT) or in all organs (H-PCT). A-PCT is the most common (75 to 80%) of this type of Porphyria, H-PCT has autosomal dominant inheritance and URO-D has an activity of about 50% than normal value. When its character is homozygous or heterozygous compound is called Hepatoerythropoietic Porphyria (HEP). PCT is a low-penetrance disease, appears in adulthood at approximately 40 years and the ratio male:woman is 4:1. There are various agents that are able to trigger it such as alcohol, estrogen, iron overload, polyhalogenated hydrocarbons, nitrosamines from tobacco smoke and hepatotropic viruses.\nOur hypothesis is based on the assumption that the presence of SNPs in CYPs would play a role in the triggering of Porphyria by increasing the metabolizing capacity of CYPs by generating metabolites that would inhibit URO-D. The overall objective was to provide additional evidence on the possibilities of PCT manifestation and to expand our knowledge of the CYP system's involvement in the clinical expression of PCT.\nTo get our objective, the following variants were genotyped: CYP1A1 (*4 or m4, *2C or m2, *2A or m1), CYP1A2 (*1F) and CYP2E1 (*5B and *7B), which were selected based on previous report about their relationship with the development of cancer but with respect to Porphyria the results are conflictive. In this context we decided to study its genotype and allele frequencies and its relationship with this disease in the Argentine population. The following population was studied: 36 H-PCT patients, 76 A-PCT and 89 controls. In all cases the individuals signed the informed consent and the project was approved by the CIPYP Ethics Committee. The RFLP-PCR technique was used, sequencing was used when the pattern of bands obtained was not clear.\nGenotype and allele frequencies were estimated by direct count for each SNP. Risk genotypes and alleles were calculated by bioinformatics methods through VCCStats using the parameters: Odd Ratio, confidence intervals and Fisher p; results were reported only when the differences were statistically significant (pf<0.05). For the study of risk haplotypes, 64 samples from the 112 studied were used: 24 Controls, 23 H-PCT and 17 A-PCT, using the SNPStats program. With the SNP predict program the effect of the amino acid change on the structure of the enzyme and its role in triggering the PCT was estimated.\nCYP1A2*1F (C/A) is an atypical case in which the reference allele is the least common, the same trend was observed in our population. The genotype containing A allele, was a risk factor to trigger the PCT.\nFor our population the CYP1A1*4 (C/A) variant showed that the frequency of the alternative homozygous genotype was significantly higher in H-PCT than in controls; this genotype was non-existent in A-PCT. The frequency of A allele was higher in hereditary than in acquired. For groups: H-PCT vs Control and A-PCT the A/A genotype and A allele result to be of risk. The effect of this alternative variant is not clearly reported but it would be a risk factor for H-PCT in our population.\nIn the case of CYP1A1*2C (A/G) for genotype frequency the profiles were different from those expected. Alternative homozygous usually occurs in low proportion or is non-existent. The genotype containing the G allele in heterozygous turned out to be risky for H-PCT vs A-PCT.\nFor CYP1A1*2A (T/C) in H-PCT vs A-PCT the T/T genotype was found in the higher proportion in this first group and for T/C the frequency was higher in the latter. Our results do not show significant risk association by contrasting porphyric with controls and hereditary with acquired ones.\nThe study of risk haplotypes yielded significant differences for H-PCT vs Control being in this order m4-m2-m1-1A2: C-G-C-C.\nIn CYP2E1*5B (C/T) allele C was the most common, reference homozygous frequencies were like to those of heterozygous, no alternative homozygous was found. There were no significant differences in any of the contrasted groups for each genotype and allele. No association between the alternative variable and the PCT was found in our population.\nFor CYP2E1*7B (G/T) the ancestral allele was the most frequent and each variant has a similar frequency for different groups. The T allele in homozygous is at a low frequency. In our results for H-PCT vs A-PCT G/T vs G/G gave significant risk association.\nThe CYP2E1 risk haplotype study found that T-T was the risk haplotype for all groups of PCTs contrasted with controls. |
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