Human arsenic methyltransferase pharmacogenetics: functional studies of common polymorphisms and its impact on medicine
Over the past years the clinical research has rapidly advanced towards the direction of pharmacogenetics, which is defined as the study of the role of inherited variation in drug response. It appeared that individuals respond significantly different to the same drug dose; the answer lies in our gene...
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|Summary:||Over the past years the clinical research has rapidly advanced towards the direction of pharmacogenetics, which is defined as the study of the role of inherited variation in drug response. It appeared that individuals respond significantly different to the same drug dose; the answer lies in our genes, the differences in our genes. However, we are not talking about inconspicuous differences in the reactions to the same drug dose, the range varies between death and no effect level.
These differences are due to polymorphisms within the gene. When describing genetic polymorphisms, it is easiest to imagine two strands of DNA that differ in sequence rather than in shape.
Single nucleotide polymorphisms involve only the change of single bases in the sequence. This type of polymorphism is the most common and extremely studied form of polymorphisms in genetic research. In our studies the existence of a variable number tandem repeat plays also an important role, the variation involves individual alleles that have different numbers of repeats.
Arsenic is present in the drinking water in many parts of the world. In humans, arsenic is absorbed in the gastrointestinal tract, but it is not known as a trace element. Inorganic arsenic is methylated, and methylconjugation has been shown to be an important pathway for biotransformation of many drugs and neurotransmitters.
In this study, our goal was to analyze the genetic variations of the human arsenic methyltransferase gene with the impacts on protein function. Inorganic arsenic is methylated during biotransformation, the enzyme catalyzing this process is the arsenic methyltransferase.
We followed the model of the drug-metabolizing enzyme thiopurine methyltransferase The activity of this enzyme is known to be in human red blood cells and controlled by a common genetic polymorphism that also regulates the enzyme activity in all other tissues which have been analyzed.
The studies in which I participated involved testing the hypothesis that individual variation in the sequence or structure of the arsenic methyltransferase gene might contribute to individual differences in arsenic methylation in vivo and result in individual variation in arsenic toxicity and carcinogenesis. To test this hypothesis, a genotype-to-phenotype, rather than a phenotype-to-genotype strategy was used to study arsenic methyltransferase pharmacogenetics. This study initially focused on the 5’-flanking region and the single nucleotide polymorphisms in the open reading frame of this gene. However, the project started with resequencing the human arsenic methyltransferase gene. When that was done, 26 polymorphisms were observed, 3 of which were nonsynonymous coding single nucleotide polymorphisms in the open reading frame. An enzyme assay was then optimized to test the possible functions of the coding single nuclotide polymorphisms and its expressed proteins. A variable number tandem repeat was also observed in the 5‘-untranslated region. A series of reporter gene constructs, incorporating portions of the 5’-flanking region as well as the 5‘-untranslated region, were used to identify the promotor of the gene and to study the possible functional implications of the variable number tandem repeat.
In conclusion, we were able to prove that the differences in the methylation level are due to the polymorphisms in the arsenic methyltransferase gene. Furthermore, we showed that not only the open reading frame but also the region within the flanking region and untranslated region had an impact on the protein activity.
A major challenge for the future will be to develop ways to translate the pharmacogenetic information of the human arsenic methyltransferase gene into meaningful clinical reality and individual patient treatment.|
|Physical Description:||75 Pages|