Efeito de polimorfismos genéticos no metabolismo do ácido fólico e sua relação com as concentrações de folato, vitamina b12 e homocisteína total em indivíduos submetidos à fortificação e/ou terapêutica com ácido fólico
Data
2015-11-27
Autores
Lucena, Maylla Rodrigues 
Orientadores
Shinohara, Elvira Maria Guerra
Tipo
Dissertação de mestrado
Título da Revista
ISSN da Revista
Título de Volume
Resumo
O ácido fólico (AF) é um micronutriente importante para diversas reações no organismo, como a síntese de ácidos nucleicos e reações de metilação. Várias enzimas participam destas reações como a glutamato carboxipeptidase II (GCPII), metilenotetraidrofolato redutase (MTHFR), diidrofolato redutase (DHFR) e metilenotetraidrofolato desidrogenase (MTHFD1), além do carreador de folato reduzido (RFC1) sendo importantes para a absorção e metabolização do AF. Alguns polimorfismos genéticos nestas enzimas (MTHFR c.677C>T, MTHFR c.1298A>C, RFC1 c. 80G>A, GCP2 c. 1561C>T, MTHFD1 c. 1958G>A) associam-se à redução nas concentrações desta vitamina em humanos, e o polimorfismos DHFR del 19 pb está relacionado ao aparecimento de ácido fólico não metabolizado na circulação. A deficiência de AF é fator de risco para defeito de fechamento de tubo neural (DFTN), e outras malformações fetais, um problema de saúde pública no mundo. Na intenção de reduzir casos de DFTN, alguns países adotaram políticas de fortificação dos alimentos com AF. No Brasil, desde 2004 as farinhas de trigo e milho são fortificadas com 150 ug/AF para 100g de farinha. Estudos realizados após este período revelam alta incidência de indivíduos com concentrações suprafisiológicas de AF nas populações submetidas ao consumo de alimentos fortificados, sendo desconhecidos os possíveis efeitos destas concentrações na população. Objetivos: Avaliar o efeito de polimorfismos genéticos no metabolismo do AF e sua relação com as concentrações de folato, vitamina b12 e homocisteína total (tHcy) em indivíduos submetidos à fortificação e/ou terapêutica com AF. Métodos: Foram incluídos 27 pacientes com esferocitose hereditária e 50 indivíduos com ? talassemia heterozigota em uso ou não de AF. Também foram recrutados a participar do estudo 145 indivíduos saudáveis expostos apenas a fortificação obrigatória de farinhas de milho e trigo. Adicionalmente, foi realizado um estudo de intervenção com 5mg/dia de AF com 30 indivíduos saudáveis, com coleta de sangue e dados antes da intervenção e após 45 e 90 dias. A avaliação do consumo alimentar foi feita por meio de dois recordatórios de 24 horas e analisada utilizando o software Nutrition Data System for Research ? NDSR. Foram determinadas as concentrações séricas de folato e vitamina B12 (métodos microbiológicos), ácido fólico não metabolizado (UMFA), tetraidrofolato, 5-metil-tetraidrofolato, 5-formil- tetraidrofolato, 5,10-metenil-tetrahidrofolato, MeFox e folato total (LCMS), e as concentrações plasmáticas tHcy (quimiluminescência). Os polimorfismos MTHFR c. 677C>T, MTHFR c. 1298 A>C, MTHFD1 c. 1958G>A, DHFR del 19-pb, RFC1 c. 80G>A e GCPII c. 1561C>T foram determinados por técnicas de PCR, PCR-RFLP e PCR em tempo real. Resultados: Os valores das concentrações AF foram maiores em indivíduos que estavam em uso de AF (pacientes com EH e indivíduos saudáveis submetidos a intervenção com 5mg/dia de AF). Não foi encontrada relação entre os polimorfismos genéticos e as concentrações de AF, vitamina B12 e tHcy, quando analisados isoladamente nos grupos estudados. Entretanto, quando analisamos os polimorfismos em associação, houve efeito da interação entre genótipo para MTHFR c.677C>T, MTHFD1 c.1958G>A e RFC1.c.80G>A e a intervenção no grupo submetido a 5mg/dia de AF. A frequência de concentrações suprafisiológicas de AF (sérico e UMFA) foi alta, porém não foi encontrada associação entre altas concentrações de AF e a deleção no gene da DHFR (DHFR del 19-pb) nos indivíduos submetidos a fortificação e/ou intervenção com 5mg/dia de AF. Conclusões: As concentrações de folato sérico, eritrocitário e UMFA foram maiores nos indivíduos que estavam submetidos a terapêutica e/ou intervenção com 5mg/dia de AF. Os polimorfismos genéticos estudados não foram associados a menores concentrações de AF, nem tampouco a maiores concentrações de tHcy nos indivíduos saudáveis. Este achado sugere que a fortificação e/ou terapêutica com AF pode compensar o efeito dos polimorfismos, especialmente para o MTHFR c.677C>T, que é comprovadamente associado a menores concentrações de AF e maiores de tHcy.
Folic acid (FA) is an essential micronutrient for several functions of the organism, such as nucleic acids synthesis and methylation reactions. Several important enzymes participate of folate metabolism such as glutamate carboxypeptidase II (GCPII), methylenetetrahydrofolate reductase (MTHFR), dihydrofolate reductase (DHFR) and methylenetetrahydrofolate dehydrogenase (MTHFD1), and also the reduced folate carrier (RFC1), being important for FA absorption and metabolism. Some genetic polymorphisms in these enzymes (MTHFR c.677C>T, MTHFR c.1298A>C, RFC1 c.80G>A, GCP2 c.1561C>T, MTHFD1 c.1958G>A) are associated with the reduction in the concentration of this vitamin human and polymorphism DHFR del 19 pb is related to the appearance of unmetabolized folic acid in circulation. Folic acid deficiency is a risk factor for neural tube defects (NTDs), and other birth defects, in an attempt to reduce NTDs cases, some countries have adopted food fortification with FA. Wheat and corn flour are fortified with 150 ug/AF for 100g of wheat in Brazil since 2004. Studies carried out after this period revealed high incidence of individuals with FA supraphysiological concentrations in populations subjected to the consumption of fortified foods,the possible effects of these concentrations in the population are unknown. Objectives: To evaluate the effect of polymorphisms in genes related to concentrations of FA, vitamin B12 and homocysteine (tHcy) metabolism in subjects submitted to fortification or/and therapeutics with 5mg of FA daily. Methods: Twenty seven patients with hereditary spherocytosis (HS) and 50 subjects with ? thalassemia heterozygote (BTH) were included, using or not 5 mg / day of FA. Also, 145 healthy subjects exposed only to the mandatory fortification of corn and wheat flours were recruited to participate in the study. Additionally, we performed an intervention study with 5 mg / day of AF with 30 healthy subjects, with blood and data collection before the intervention and after 45 and 90 days. Food intake was assessed by 24 hour recalls and analyzed using the software is Nutrition Data System for Research - NDSR. Serum concentrations of folate and vitamin B12 (microbiological method), unmetabolized folic acid (UMFA), tetrahydrofolate, 5-methyl-tetrahydrofolate, 5-formyl-tetrahydrofolate, 5,10-methenyl-tetrahydrofolate, MeFox and Total folate (LCMS) and plasma concentrations of total homocysteine (tHcy) were determined. The polymorphisms MTHFR c. 677C> T, MTHFR c. 1298 A> C MTHFD1 c. 1958G> A, DHFR del 19-bp RFC1 c. 80G> A and c GCPII. 1561C> T were determined by PCR techniques, PCR-RFLP and PCR in real time. Results: The folate levels (serum and erythrocyte) were higher in subjects that were using FA (patients with HS and healthy subjects subjected to intervention with 5mg/day of FA). No associations were found among genetic polymorphisms and FA, vitamin B12 and tHcy levels when analyzed separately in groups. However, when we analyzed the polymorphisms in combination, there was interaction effect among genotype for MTHFR c.677C>T, MTHFD1 c.1958G>A e and RFC1.c.80G>A and the intervention group submitted to 5mg / day of FA. The frequency of supraphysiological concentrations of FA (serum and UMFA) was high, but no association was found between high concentrations of FA and the deletion in the DHFR gene (DHFR del 19 bp) of individuals subjected to fortification and / or intervention with 5mg per day of FA. Conclusions: Serum folate levels and erythrocyte UMFA were higher in patients who were submitted to treatment and / or intervention with 5mg per day of FA. Genetic polymorphisms were not associated with lower serum and erythrocyte folate concentrations, and neither with higher concentrations of tHcy in healthy subjects. This finding suggests that fortification and / or therapy with FA can offset the effect of the polymorphisms, especially for the MTHFR c.677C> T, which is demonstrably associated with lower concentrations of FA and higher tHcy.
Folic acid (FA) is an essential micronutrient for several functions of the organism, such as nucleic acids synthesis and methylation reactions. Several important enzymes participate of folate metabolism such as glutamate carboxypeptidase II (GCPII), methylenetetrahydrofolate reductase (MTHFR), dihydrofolate reductase (DHFR) and methylenetetrahydrofolate dehydrogenase (MTHFD1), and also the reduced folate carrier (RFC1), being important for FA absorption and metabolism. Some genetic polymorphisms in these enzymes (MTHFR c.677C>T, MTHFR c.1298A>C, RFC1 c.80G>A, GCP2 c.1561C>T, MTHFD1 c.1958G>A) are associated with the reduction in the concentration of this vitamin human and polymorphism DHFR del 19 pb is related to the appearance of unmetabolized folic acid in circulation. Folic acid deficiency is a risk factor for neural tube defects (NTDs), and other birth defects, in an attempt to reduce NTDs cases, some countries have adopted food fortification with FA. Wheat and corn flour are fortified with 150 ug/AF for 100g of wheat in Brazil since 2004. Studies carried out after this period revealed high incidence of individuals with FA supraphysiological concentrations in populations subjected to the consumption of fortified foods,the possible effects of these concentrations in the population are unknown. Objectives: To evaluate the effect of polymorphisms in genes related to concentrations of FA, vitamin B12 and homocysteine (tHcy) metabolism in subjects submitted to fortification or/and therapeutics with 5mg of FA daily. Methods: Twenty seven patients with hereditary spherocytosis (HS) and 50 subjects with ? thalassemia heterozygote (BTH) were included, using or not 5 mg / day of FA. Also, 145 healthy subjects exposed only to the mandatory fortification of corn and wheat flours were recruited to participate in the study. Additionally, we performed an intervention study with 5 mg / day of AF with 30 healthy subjects, with blood and data collection before the intervention and after 45 and 90 days. Food intake was assessed by 24 hour recalls and analyzed using the software is Nutrition Data System for Research - NDSR. Serum concentrations of folate and vitamin B12 (microbiological method), unmetabolized folic acid (UMFA), tetrahydrofolate, 5-methyl-tetrahydrofolate, 5-formyl-tetrahydrofolate, 5,10-methenyl-tetrahydrofolate, MeFox and Total folate (LCMS) and plasma concentrations of total homocysteine (tHcy) were determined. The polymorphisms MTHFR c. 677C> T, MTHFR c. 1298 A> C MTHFD1 c. 1958G> A, DHFR del 19-bp RFC1 c. 80G> A and c GCPII. 1561C> T were determined by PCR techniques, PCR-RFLP and PCR in real time. Results: The folate levels (serum and erythrocyte) were higher in subjects that were using FA (patients with HS and healthy subjects subjected to intervention with 5mg/day of FA). No associations were found among genetic polymorphisms and FA, vitamin B12 and tHcy levels when analyzed separately in groups. However, when we analyzed the polymorphisms in combination, there was interaction effect among genotype for MTHFR c.677C>T, MTHFD1 c.1958G>A e and RFC1.c.80G>A and the intervention group submitted to 5mg / day of FA. The frequency of supraphysiological concentrations of FA (serum and UMFA) was high, but no association was found between high concentrations of FA and the deletion in the DHFR gene (DHFR del 19 bp) of individuals subjected to fortification and / or intervention with 5mg per day of FA. Conclusions: Serum folate levels and erythrocyte UMFA were higher in patients who were submitted to treatment and / or intervention with 5mg per day of FA. Genetic polymorphisms were not associated with lower serum and erythrocyte folate concentrations, and neither with higher concentrations of tHcy in healthy subjects. This finding suggests that fortification and / or therapy with FA can offset the effect of the polymorphisms, especially for the MTHFR c.677C> T, which is demonstrably associated with lower concentrations of FA and higher tHcy.
Descrição
Citação
LUCENA, Maylla Rodrigues. Efeito de polimorfismos genéticos no metabolismo do ácido fólico e sua relação com as concentrações de folato, vitamina b12 e homocisteína total em indivíduos submetidos à fortificação e/ou terapêutica com ácido fólico. 2015. 117 f. Dissertação (Mestrado em Hematologia) - Escola Paulista de Medicina, Universidade Federal de São Paulo (UNIFESP), São Paulo, 2015.