Cellular and ultrastructural alterations of Arabidopsis thaliana roots in response to exogenous trans-aconitic acid

In this work, the responses of Arabidopsis thaliana (L.) Heynh to trans-aconitic acid (TAA) were investigated. A. thaliana was grown in the presence of TAA in a concentration range of 400–1200 µM for 7 or 15 days. Changes in the morphoanatomy, cellular ultrastructure, and micromorphology of the roots were evaluated by light and transmission electron (TEM) microscopy. At concentrations below 1000 µM, TAA reduced the length of the primary roots, but induced an early appearance of lateral roots and root hairs. At a concentration of 1200 µM, TAA suppressed the growth of seedlings. The images of longitudinal sections of root tips of seedlings treated with IC50 of TAA (684 µM) revealed a reduced elongation zone with an increased differentiation zone. TEM images showed an increase in the number and volume of vacuoles, an increase in vesicles containing electron-dense material derived from plasmalemma, and electron-dense granules attached to the cell wall. Trans-aconitic acid induced an early differentiation of A. thaliana seedlings suggesting an interference in the auxin action. Changes in the cellular ultrastructure may represent vacuolar and extracellular accumulation of TAA, to remove excess TAA in the cytosol and mitochondria. An inhibition of aconitase and the chelation of intracellular cations may have contributed to cytotoxicity of TAA at 1200 µM concentration.Ministerio de Economía y Competitividad | Ref. AGL2013-41281-RUniversidade de Vigo/CISU

A inibição do transporte de monossacarídeos no fígado pelo steviosídeo e seus derivados

Orientador: Prof. Dr. Adelar BrachtTese (Doutorado) -Universidade Federal do Paraná, Curso de Pós-Graduação em BioquímicaInclui referências: p. 107-116Resumo: Um estudo do efeito do steviosídeo e seus derivados sobre o transporte de monossacarídeos no fígado foi realizado. O transporte foi avaliado no fígado de rato perfundido isoladamente, pela técnica da diluição de indicadores múltiplos com análise matemática, de acordo com o modelo proposto por Goresky et al. (1973). A distribuição da D-glucose no espaço intra e extracelular, em condições de equilíbrio (steady-state), e as relações entre o transporte e a metabolismo das hexoses foram também investigadas. O Km encontrado para o transporte da D-glucose (troca de estado estacionário) no fígado foi de 38,9 ± 12 mM e a Vmax de 388 ± 61 umol.min-1 . g-1. A razão entre as concentrações intra e extracelular de D-glucose, nas mesmas condições, variou entre 0,6 e 0,7. Os produtos da Stevia rebaudiana inibiram o transporte de monossacarídeos. Dos compostos testados, o isosteviol foi o mais ativo, seguido pelo steviosídeo, sendo o steviolbiosídeo, o menos potente. O steviosídeo afetou tanto o Km quanto a Vmax do transporte da D-glucose, indicando uma inibição do tipo misto. Em baixas concentrações de D-glucose no perfusado, os produtos da Stevia rebaudiana testados, afetaram a razão Ci/Ce, em função da inibição sobre o transporte. Por outro lado, na faixa de concentração entre 10 e 100 mM, o steviosídeo não modificou a razão Ci/Ce. Isto foi consequência do fato de que o fluxo metabólico, nessas concentrações, é muito pequeno em comparação com os altos fluxos unidirecionais através da membrana. Em função da inibição sobre o transporte, o metabolismo de hexoses como a D-frutose e a D-galactose no fígado foi inibido pelo steviosídeo. O mesmo não foi observado com respeito ao metabolismo da D-glucose. Nas condições experimentais utilizadas no presente trabalho, o steviosídeo não parece ser hidrolisado em quantidades significativas pelo fígado. Derivados como o steviol, o glucosil-steviol e o steviolbiosídeo não foram identificados após recirculação do steviosídeo por períodos de até duas horas. O espaço de distribuição do steviosídeo, avaliado pela técnica da diluição de indicadores múltiplos, foi estimado em cerca de 5 a 6% do espaço celular total do fígado. O acesso do steviosídeo ao espaço aquoso celular não é livre, em uma simples passagem. Destes dados, pode-se concluir que o efeito do steviosídeo sobre o carreador de monossacarídeos é exercido do lado externo da membrana plasmática

Effects of monocrotaline on energy metabolism in the rat liver

Monocrotaline (MCT) is a pyrrolizidine alkaloid present in the plants of the Crotalaria species that causes cytotoxicity and genotoxicity in animals and humans, and it is hepatically metabolized to the alkylating agent dehydromonocrotaline by cytochrome P-450. The exact cellular and molecular mechanisms of MCT- induced tissue injury remain unclear. We previously demonstrated that dehydromonocrotaline, but not monocrotaline, inhibits the activity of NADH-dehydrogenase at micromolar concentrations in isolated liver mitochondria, an effect associated with significantly reduced ATP synthesis. Impairment of energy metabolism is expected to lead to several alterations in cell metabolism. In this work, the action of different concentrations of monocrotaline (250, 500, and 750 mu M) on energy metabolism-linked parameters was investigated in isolated perfused rat livers. In the fed state, monocrotaline increased glycogenolysis and glycolysis, whereas in the livers of fasted Fats, it decreased gluconeogenesis and urea synthesis from L-alanine. These metabolic alterations were only found in livers of phenobarbital-treated rats, indicating that active metabolites including dehydromonocrotaline were responsible for the obsorved activity. Our findings indicate that hepatic metabolic changes may be implicated, partly at least, in the hepatotoxicity of monocrotaline in animals and humans. (C) 2008 Elsevier B.V. All rights reserved.Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq

Effect of fipronil on energy metabolism in the perfused rat liver

Fipronil is an insecticide used to control pests in animals and plants that can causes hepatotoxicity in animals and humans, and it is hepatically metabolized to fipronil sulfone by cytochrome P-450. The present study aimed to characterize the effects of fipronil (10-50 mu M) on energy metabolism in isolated perfused rat livers. In fed animals, there was increased glucose and lactate release from glycogen catabolism, indicating the stimulation of glycogenolysis and glycolysis. In the livers of fasted animals, fipronil inhibited glucose and urea production from exogenous L-alanine, whereas ammonia and lactate production were increased. In addition, fipronil at 50 mu M concentration inhibited the oxygen uptake and increased the cytosolic NADH/NAD(+) ratio under glycolytic conditions. The metabolic alterations were found both in livers from normal or proadifen-pretreated rats revealing that fipronil and its reactive metabolites contributed for the observed activity. The effects on oxygen uptake indicated that the possible mechanism of toxicity of fipronil involves impairment on mitochondrial respiratory activity, and therefore, interference with energy metabolism. The inhibitory effects on oxygen uptake observed at the highest concentration of 50 mu M was abolished by pretreatment of the rats with proadifen indicating that the metabolites of fipronil, including fipronil sulfone, acted predominantly as inhibitors of respiratory chain. The hepatoxicity of both the parent compound and its reactive metabolites was corroborated by the increase in the activity of lactate dehydrogenase in the effluent perfusate in livers from normal or proadifen-pretreated rats.Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP

The Influence of Ca2+ on Gluconeogenesis Stimulation by Glucagon in the Liver of Arthritic Rats

Ca2+ participates in the stimulation of hepatic gluconeogenesis by glucagon and there is evidence that Ca2+ fluxes are modified in arthritic rats. These findings raise the question whether hepatic gluconeogenesis in arthritic rats responds differently to glucagon and Ca2+. The experimental system was the isolated perfused rat liver. In the presence of Ca2+, stimulation of hepatic gluconeogenesis by glucagon in arthritic rats was equal to that in normal rats in absolute terms, but higher in relative terms (104.5 and 45.2%, respectively). In the absence of Ca2+, however, stimulation of hepatic gluconeogenesis by glucagon in arthritic rats was smaller in both absolute and relative terms (18.5 and 41.9%, respectively). It can be concluded that the Ca2+-dependent component of gluconeogenesis activation by glucagon is more important in arthritic than in normal rats