RESUMEN

Recently, there have been efforts to use ultraviolet-B radiation (UV-B) as a biotechnological tool in greenhouses. Leafy Brassica species are mainly considered for their ability to synthesize glucosinolates and are valued as baby salads. They also have a remarkable concentration of chemically diverse flavonoid glycosides. In this study, the effect of short-term UV-B radiation at the end of the production cycle was investigated without affecting plant growth. The aim was to verify which exposure and adaptation time was suitable and needs to be further investigated to use UV as a biotechnological tool in greenhouse production of Brassica species. It is possible to modify the flavonoid glycoside profile of leafy Brassica species by increasing compounds that appear to have potentially high antioxidant activity. Exemplarily, the present experiment shows that kaempferol glycosides may be preferred over quercetin glycosides in response to UV-B in Brassica rapa ssp. chinensis, for example, whereas other species appear to prefer quercetin glycosides over kaempferol glycosides, such as Brassica oleracea var. sabellica or Brassica carinata. However, the response to short-term UV-B treatment is species-specific and conclusions on exposure and adaptation time cannot be unified but must be drawn separately for each species.

Asunto(s)

Adaptación Fisiológica , Brassica/metabolismo , Flavonoides/metabolismo , Glicósidos/metabolismo , Hojas de la Planta/metabolismo , Rayos Ultravioleta/efectos adversos , Brassica/clasificación , Brassica/crecimiento & desarrollo , Brassica/efectos de la radiación , Flavonoides/análisis , Flavonoides/efectos de la radiación , Glicósidos/análisis , Glicósidos/efectos de la radiación , Hojas de la Planta/crecimiento & desarrollo , Hojas de la Planta/efectos de la radiación , Especificidad de la Especie , Factores de Tiempo

RESUMEN

Context: Depending on its lipolytic activity, glucagon plays a promising role in obesity treatment. Glucagon-induced growth hormone (GH) release can promote its effect on lipid metabolism, although the underlying mechanisms have not been well-defined. Objective: The present study highlights the glucagon effect on the GH/insulinlike growth factor 1 (IGF-1)/IGF-binding protein (IGFBP) axis in vivo and in vitro, taking into consideration insulin as a confounding factor. Materials and Methods: In a double-blind, placebo-controlled study, we investigated changes in GH, IGFBP, and IGF-1 bioactivity after intramuscular glucagon administration in 13 lean controls, 11 obese participants, and 13 patients with type 1 diabetes mellitus (T1DM). The effect of glucagon on the transcription factor forkhead box protein O1 (FOXO1) translocation, the transcription of GH/IGF-1 system members, and phosphorylation of protein kinase B (Akt) was further investigated in vitro. Results: Despite unchanged total IGF-1 and IGFBP-3 levels, glucagon decreased IGF-1 bioactivity in all study groups by increasing IGFBP-1 and IGFBP-2. The reduction in IGF-1 bioactivity occurred before the glucagon-induced surge in GH. In contrast to the transient increase in circulating insulin in obese and lean participants, no change was observed in those with T1DM. In vitro, glucagon dose dependently induced a substantial nuclear translocation of FOXO1 in human osteosarcoma cells and tended to increase IGFBP-1 and IGFBP-2 gene expression in mouse primary hepatocytes, despite absent Akt phosphorylation. Conclusions: Our data point to the glucagon-induced decrease in bioactive IGF-1 levels as a mechanism through which glucagon induces GH secretion. This insulin-independent reduction is related to increased IGFBP-1 and IGFBP-2 levels, which are most likely mediated via activation of the FOXO/mTOR (mechanistic target of rapamycin) pathway.

Asunto(s)

Diabetes Mellitus Tipo 1/metabolismo , Glucagón/administración & dosificación , Hormona del Crecimiento/efectos de los fármacos , Proteínas de Unión a Factor de Crecimiento Similar a la Insulina/efectos de los fármacos , Factor I del Crecimiento Similar a la Insulina/efectos de los fármacos , Adulto , Western Blotting , Diabetes Mellitus Tipo 1/diagnóstico , Diabetes Mellitus Tipo 1/tratamiento farmacológico , Relación Dosis-Respuesta a Droga , Método Doble Ciego , Esquema de Medicación , Ensayo de Inmunoadsorción Enzimática , Femenino , Proteína Forkhead Box O1/efectos de los fármacos , Proteína Forkhead Box O1/metabolismo , Hormona del Crecimiento/metabolismo , Humanos , Inyecciones Intramusculares , Proteínas de Unión a Factor de Crecimiento Similar a la Insulina/metabolismo , Factor I del Crecimiento Similar a la Insulina/metabolismo , Masculino , Obesidad/metabolismo , Obesidad/fisiopatología , Estadísticas no Paramétricas

RESUMEN

SCOPE: Nasturtium plants contain the glucosinolate glucotropaeolin and its corresponding breakdown product benzyl isothiocyanate (BITC), the latter being intensively studied with regard to cancer chemoprevention and anti-inflammatory properties. In addition, recent research has shown that isothiocyanates are able to activate the release of several gut hormones in vitro and in rodent studies. Here, we tested the effects of a dietary nasturtium administration on circulating levels of gut hormones in humans. METHODS AND RESULTS: Metabolically healthy males (n = 15) received a single oral dose of 10 g freeze-dried nasturtium leaf material suspended in water or only water (control). Blood samples were taken every hour and serum concentrations of insulin, C-peptide, glucagon-like peptide 1 (GLP-1), glucose-dependent insulinotropic peptide (GIP), and peptide (PYY) were analyzed. Oral nasturtium intake resulted in an increased release of PYY over a time period of 6 h whereas circulating levels of other hormones were not changed. CONCLUSION: Given the finding that nasturtium consumption enhances secretion of PYY, a key hormone involved in energy regulation, special diets containing nasturtium, or supplementation with nasturtium or BITC might be considered in the treatment of obesity.

Asunto(s)

Suplementos Dietéticos , Nasturtium , Péptido YY/sangre , Administración Oral , Adulto , Glucemia/metabolismo , Péptido C/sangre , Polipéptido Inhibidor Gástrico/sangre , Variación Genética , Péptido 1 Similar al Glucagón/sangre , Humanos , Insulina/sangre , Masculino , Persona de Mediana Edad , Receptores Acoplados a Proteínas G/genética

RESUMEN

Nasturtium (Tropaeolum majus L.) contains high concentrations of benzylglcosinolate. We found that a hydrolysis product of benzyl glucosinolate-the benzyl isothiocyanate (BITC)-modulates the intracellular localization of the transcription factor Forkhead box O 1 (FOXO1). FoxO transcription factors can antagonize insulin effects and trigger a variety of cellular processes involved in tumor suppression, longevity, development and metabolism. The current study evaluated the ability of BITC-extracted as intact glucosinolate from nasturtium and hydrolyzed with myrosinase-to modulate i) the insulin-signaling pathway, ii) the intracellular localization of FOXO1 and, iii) the expression of proteins involved in gluconeogenesis, antioxidant response and detoxification. Stably transfected human osteosarcoma cells (U-2 OS) with constitutive expression of FOXO1 protein labeled with GFP (green fluorescent protein) were used to evaluate the effect of BITC on FOXO1. Human hepatoma HepG2 cell cultures were selected to evaluate the effect on gluconeogenic, antioxidant and detoxification genes and protein expression. BITC reduced the phosphorylation of protein kinase B (AKT/PKB) and FOXO1; promoted FOXO1 translocation from cytoplasm into the nucleus antagonizing the insulin effect; was able to down-regulate the gene and protein expression of gluconeogenic enzymes; and induced the gene expression of antioxidant and detoxification enzymes. Knockdown analyses with specific siRNAs showed that the expression of gluconeogenic genes was dependent on nuclear factor (erythroid derived)-like2 (NRF2) and independent of FOXO1, AKT and NAD-dependent deacetylase sirtuin-1 (SIRT1). The current study provides evidence that BITC might have a role in type 2 diabetes T2D by reducing hepatic glucose production and increasing antioxidant resistance.

Asunto(s)

Gluconeogénesis/efectos de los fármacos , Gluconeogénesis/genética , Tiocianatos/farmacología , Tioglucósidos/farmacología , Tropaeolum/química , Acetilcisteína/farmacología , Transporte Activo de Núcleo Celular/efectos de los fármacos , Antioxidantes/farmacología , Línea Celular , Supervivencia Celular/efectos de los fármacos , Diabetes Mellitus Tipo 2/tratamiento farmacológico , Diabetes Mellitus Tipo 2/genética , Diabetes Mellitus Tipo 2/metabolismo , Proteína Forkhead Box O1/antagonistas & inhibidores , Proteína Forkhead Box O1/genética , Proteína Forkhead Box O1/metabolismo , Expresión Génica/efectos de los fármacos , Técnicas de Silenciamiento del Gen , Gluconeogénesis/fisiología , Glucosa-6-Fosfatasa/genética , Células Hep G2 , Humanos , Hipoglucemiantes/química , Hipoglucemiantes/farmacología , Isotiocianatos/química , Isotiocianatos/farmacología , Factor 2 Relacionado con NF-E2/antagonistas & inhibidores , Factor 2 Relacionado con NF-E2/genética , Fosfoenolpiruvato Carboxiquinasa (ATP)/genética , Plantas Medicinales/química , Transporte de Proteínas/efectos de los fármacos , Proteínas Proto-Oncogénicas c-akt/antagonistas & inhibidores , Proteínas Proto-Oncogénicas c-akt/genética , ARN Interferente Pequeño/genética , Proteínas Recombinantes de Fusión/genética , Proteínas Recombinantes de Fusión/metabolismo , Sirtuina 1/antagonistas & inhibidores , Sirtuina 1/genética , Tiocianatos/química , Tioglucósidos/química

RESUMEN

The flavones apigenin (4',5,7,-trihydroxyflavone) and luteolin (3',4',5,7,-tetrahydroxyflavone) are plant secondary metabolites with antioxidant, antiinflammatory, and anticancer activities. We evaluated their impact on cell signaling pathways related to insulin-resistance and type 2 diabetes. Apigenin and luteolin were identified in our U-2 OS (human osteosarcoma) cell screening assay for micronutrients triggering rapid intracellular translocation of the forkhead box transcription factor O1 (FOXO1), an important mediator of insulin signal transduction. Insulin reversed the translocation of FOXO1 as shown by live cell imaging. The impact on the expression of target genes was evaluated in HepG2 (human hepatoma) cells. The mRNA-expression of the gluconeogenic enzymes phosphoenolpyruvate carboxykinase (PEPCK) and glucose-6-phosphatase (G6Pc), the lipogenic enzymes fatty-acid synthase (FASN) and acetyl-CoA-carboxylase (ACC) were down-regulated by both flavones with smaller effective dosages of apigenin than for luteolin. PKB/AKT-, PRAS40-, p70S6K-, and S6-phosphorylation was reduced by apigenin and luteolin but not that of the insulin-like growth factor receptor IGF-1R by apigenin indicating a direct inhibition of the PKB/AKT-signaling pathway distal to the IGF-1 receptor. N-acetyl-L-cysteine did not prevent FOXO1 nuclear translocation induced by apigenin and luteolin, suggesting that these flavones do not act via oxidative stress. The roles of FOXO1, FOXO3a, AKT, sirtuin1 (SIRT1), and nuclear factor (erythroid-derived2)-like2 (NRF2), investigated by siRNA knockdown, showed differential patterns of signal pathways involved and a role of NRF2 in the inhibition of gluconeogenic enzyme expression. We conclude that these flavones show an antidiabetic potential due to reduction of gluconeogenic and lipogenic capacity despite inhibition of the PKB/AKT pathway which justifies detailed investigation in vivo.

Asunto(s)

Apigenina/farmacología , Regulación de la Expresión Génica/efectos de los fármacos , Hipoglucemiantes/farmacología , Luteolina/farmacología , Osteoblastos/efectos de los fármacos , Acetil-CoA Carboxilasa/genética , Acetil-CoA Carboxilasa/metabolismo , Proteínas Adaptadoras Transductoras de Señales/genética , Proteínas Adaptadoras Transductoras de Señales/metabolismo , Línea Celular Tumoral , Acido Graso Sintasa Tipo I/genética , Acido Graso Sintasa Tipo I/metabolismo , Proteína Forkhead Box O1 , Factores de Transcripción Forkhead/genética , Factores de Transcripción Forkhead/metabolismo , Glucosa-6-Fosfatasa/genética , Glucosa-6-Fosfatasa/metabolismo , Células HEK293 , Células Hep G2 , Humanos , Insulina/farmacología , Factor 2 Relacionado con NF-E2/genética , Factor 2 Relacionado con NF-E2/metabolismo , Osteoblastos/citología , Osteoblastos/metabolismo , Fosfoenolpiruvato Carboxiquinasa (ATP)/genética , Fosfoenolpiruvato Carboxiquinasa (ATP)/metabolismo , Proteínas Proto-Oncogénicas c-akt/genética , Proteínas Proto-Oncogénicas c-akt/metabolismo , Receptor IGF Tipo 1/genética , Receptor IGF Tipo 1/metabolismo , Transducción de Señal , Sirtuina 1/genética , Sirtuina 1/metabolismo

RESUMEN

Signaling through the mammalian target of rapamycin complex 1 (mTORC1) and its effectors the S6-kinases (S6K) in the hypothalamus is thought to be involved in nutrient sensing and control of food intake. Given the anatomical proximity of this pathway to circuits for the hormone ghrelin, we investigated the potential role of the mTORC1/S6K pathway in mediating the metabolic effects of ghrelin. We found that ghrelin promoted phosphorylation of S6K1 in the mouse hypothalamic cell line N-41 and in the rat hypothalamus after intracerebroventricular administration. Rapamycin, an inhibitor of mTORC1, suppressed ghrelin-induced phosphorylation of hypothalamic S6K1 and increased food intake and insulin in rats. Chronic peripheral administration of ghrelin induced a significant increase in body weight, fat mass and food efficiency in wild-type and S6K2-knockout but not in S6K1-knockout mice. We therefore propose that ghrelin-induced hyperphagia, adiposity and insulin secretion are controlled by a central nervous system involving the mTORC1/S6K1 pathway.

Asunto(s)

Adiposidad/fisiología , Ingestión de Energía , Ghrelina/fisiología , Proteínas Quinasas S6 Ribosómicas/metabolismo , Serina-Treonina Quinasas TOR/metabolismo , Tejido Adiposo Pardo/fisiología , Animales , Línea Celular , Insulina/sangre , Canales Iónicos/metabolismo , Masculino , Diana Mecanicista del Complejo 1 de la Rapamicina , Ratones , Ratones Noqueados , Proteínas Mitocondriales/metabolismo , Complejos Multiproteicos/antagonistas & inhibidores , Complejos Multiproteicos/metabolismo , Ratas , Ratas Wistar , Sirolimus/farmacología , Serina-Treonina Quinasas TOR/antagonistas & inhibidores , Proteína Desacopladora 1

RESUMEN

BACKGROUND: Despite their beneficial effects on weight loss and blood lipids, high-protein (HP) diets have been shown to increase insulin resistance and diabetes risk, whereas high-cereal-fiber (HCF) diets have shown the opposite effects on these outcomes. OBJECTIVE: We compared the effects of isoenergetic HP and HCF diets and a diet with moderate increases in both cereal fibers and dietary protein (Mix diet) on insulin sensitivity, as measured by using euglycemic-hyperinsulinemic clamps with infusion of [6,6-(2)H(2)]glucose. DESIGN: We randomly assigned 111 overweight adults with features of the metabolic syndrome to 1 of 4 two-phased, 18-wk isoenergetic diets by group-matching. Per 3-d food protocols, the percentages of energy derived from protein and carbohydrates and the intake of cereal fiber per day, respectively, were as follows-after 6 wk: 17%, 52%, and 14 g (control); 17%, 52%, and 43 g (HCF); 28%, 43%, and 13 g (HP); 23%, 44%, and 26 g (Mix); after 18 wk: 17%, 51%, and 15 g (control); 17%, 51%, and 41 g (HCF); 26%, 45%, and 14 g (HP); and 22%, 46%, and 26 g (Mix). Eighty-four participants completed the study successfully and were included in the final analyses. Adherence was supported by the provision of tailored dietary supplements twice daily in all groups. RESULTS: Insulin sensitivity expressed as an M value was 25% higher after 6 wk of the HCF diet than after 6 wk of the HP diet (subgroup analysis: 4.61 ± 0.38 compared with 3.71 ± 0.36 mg · kg(-1) · min(-1), P = 0.008; treatment × time interaction: P = 0.005). Effects were attenuated after 18 wk (treatment × time interaction: P = 0.054), which was likely explained by lower adherence to the HP diet. HP intake was associated with a tendency to increased protein expression in adipose tissue of the translation initiation factor serine-kinase-6-1, which is known to mediate amino acid-induced insulin resistance. Biomarkers of protein intake indicated interference of cereal fibers with dietary protein absorption. CONCLUSION: Greater changes in insulin sensitivity after intake of an isoenergetic HCF than after intake of an HP diet might help to explain the diverse effects of these diets on diabetes risk. This trial is registered at clinicaltrials.gov as NCT00579657.

Asunto(s)

Fibras de la Dieta/administración & dosificación , Proteínas en la Dieta/administración & dosificación , Resistencia a la Insulina , Sobrepeso/metabolismo , Tejido Adiposo/metabolismo , Adulto , Anciano , Presión Sanguínea , Suplementos Dietéticos , Grano Comestible , Femenino , Humanos , Masculino , Persona de Mediana Edad , Transducción de Señal

RESUMEN

CONTEXT AND OBJECTIVE: Inactivating mutations in the calcium-sensing receptor (CaSR) gene cause neonatal severe hyperparathyroidism and familial hypocalciuric hypercalcemia (FHH). The aims of the present study were the functional characterization of novel mutations of the CaSR found in FHH patients, the comparison of in vitro receptor function with clinical parameters, and the effect of the allosteric calcimimetic NPS R-568 on the signaling of mutant receptors. METHODS: Wild-type and mutant CaSRs (W530G, C568Y, W718X, M734R, L849P, Q926R, and D1005N) were expressed in human embryonic kidney 293 cells. Receptor signaling was studied by measuring intracellular free calcium in response to different concentrations of extracellular calcium ([Ca(2+)](o)). RESULTS: Four CaSR mutations (C568Y, W718X, M734R, and L849P) demonstrated a complete lack of a [Ca(2+)](o)-induced cytosolic Ca(2+) response up to 30 mm [Ca(2+)](o), whereas the CaSR mutants W530G, Q926R, and D1005N retained some sensitivity to [Ca(2+)](o). There was no significant relation between the in vitro calcium sensitivity, serum calcium, and intact PTH levels in the patients. Patients with C-terminal CaSR mutations had a calcium to creatine ratio above the established diagnostic threshold of 0.01 for FHH. The calcimimetic NPS R-568 enhanced the responsiveness to [Ca(2+)](o) in CaSR mutants of the extracellular domain (W530G and C568Y) as well as the intracellular C-terminal domain (Q926R and D1005N). CONCLUSION: Therefore, calcimimetics might offer medical treatment for symptomatic FHH patients, and more important, for patients with neonatal severe hyperparathyroidism that harbor calcimimetic-sensitive CaSR mutants.

Asunto(s)

Compuestos de Anilina/farmacología , Mutación , Receptores Sensibles al Calcio/genética , Receptores Sensibles al Calcio/fisiología , Transducción de Señal/efectos de los fármacos , Transducción de Señal/genética , Western Blotting , Calcio/agonistas , Calcio/sangre , Línea Celular , Humanos , Hipercalcemia/genética , Hipercalcemia/fisiopatología , Hipoparatiroidismo/genética , Hipoparatiroidismo/fisiopatología , Mutagénesis Sitio-Dirigida , Fenetilaminas , Propilaminas

RESUMEN

The intracellular enzyme 11beta-hydroxysteroid dehydrogenase type 1 (11beta-HSD1) converts cortisone into the more active metabolite cortisol. Overexpression of 11beta-HSD1 was associated with features of the metabolic syndrome such as obesity or impaired glucose tolerance. Despite this considerable impact of 11beta-HSD1, the human 11beta-HSD1 promoter has not been described in detail yet. We therefore cloned eight different promoter fragments of the 5'-upstream region of the known transcription/translation-start up to -3034 bp into the luciferase-reporter vector pGL3. A low-cost in-house assay was developed and validated to detect firefly and renilla luciferase activity. Promoter fragments were analysed in human HepG2 and undifferentiated and differentiated murine 3T3-L1 cells. A differential regulation of the human 11beta-HSD1 promoter depending upon the cell type was observed. Specifically, a strong repressor of the basal promoter activity was found between -85 and -172 bp in HepG2 cells only, while an additional repressor appeared to be active between -342 and -823 bp in both, the hepatic and the adipose cell line. The presented data suggest a cell-type specific regulation of the 11beta-HSD1 promoter, which is in agreement with existing expression data from animal and human studies. The described promoter constructs will allow subsequent studies about the role of specific hormonal, metabolic and transcription factors to finally characterise the regulation of the human 11beta-HSD1-promoter in more detail.

Asunto(s)

11-beta-Hidroxiesteroide Deshidrogenasa de Tipo 1/genética , Regiones Promotoras Genéticas , Células 3T3-L1 , Tejido Adiposo/citología , Tejido Adiposo/enzimología , Animales , Secuencia de Bases , Línea Celular Tumoral , Cartilla de ADN , Humanos , Hígado/citología , Hígado/enzimología , Ratones

RESUMEN

Global gene expression profiles of livers from mice, fed diets differing in alpha-tocopherol content, were compared using DNA microarray technology. Three hundred and eighty nine genes were found to significantly differ in their expression level by a factor of 2 or higher between the high and the low alpha-tocopherol group. Functional clustering using the EASE software identified 121 genes involved in transport processes. Twenty-one thereof were involved in (synaptic) vesicular trafficking. Up-regulation of syntaxin 1C (Stx1c), vesicle-associated membrane protein 1 (Vamp1), N-ethylmaleimide-sensitive factor (Nsf) and syntaxin binding protein 1 (Stxbp1, Munc18-1) was verified by real time PCR. At a functional level, alpha-tocopherol increased the secretory response in RBL and PC12 cells. Although here detected in liver, the alpha-tocopherol-responsive pathways are also relevant to neurotransmission. A role of alpha-tocopherol in the vesicular transport might not only affect its own absorption and transport but also explain the neural dysfunctions observed in severe alpha-tocopherol deficiency.

Asunto(s)

Antioxidantes/administración & dosificación , Dieta , Perfilación de la Expresión Génica , Hígado/efectos de los fármacos , Vesículas Transportadoras/genética , alfa-Tocoferol/administración & dosificación , Animales , Antioxidantes/análisis , Transporte Biológico/genética , Hígado/metabolismo , Masculino , Ratones , Ratones Endogámicos C57BL , Análisis de Secuencia por Matrices de Oligonucleótidos , Reacción en Cadena de la Polimerasa , alfa-Tocoferol/análisis

RESUMEN

Metabolism of vitamin E is initiated by cytochrome P450 (CYP) enzymes usually involved in the metabolism of xenobiotics. Like other CYP substrates, vitamin E induced a reporter gene under the control of the pregnane X receptor (PXR) which regulates the expression of CYPs including CYP3A4. gamma-Tocotrienol, the most effective PXR activator, also induced endogenous CYP3A4 mRNA in HepG2 cells. Since these findings imply an interference of vitamin E with drug metabolism it was deemed necessary to investigate their in vivo relevance. Therefore, mice were grown for 3 months with alpha-tocopherol-deficient, -adequate, and -supranutritional diet, i.e. 2, 20 and 200 mg RRR-alpha-tocopheryl acetate/kg diet, respectively. Half of them received 250 microg gamma-tocotrienol/day for the last 7 days. After 3 months, hepatic levels of Cyp3a11 mRNA, the murine homolog to human CYP3A4, were about 2.5-fold higher in the 20 and 200 mg alpha-tocopherol groups than in the 2 mg group. After feeding 200 mg alpha-tocopherol for 9 months, Cyp3a11 mRNA was 1.7-fold higher than after 3 months. In contrast, gamma-tocotrienol did not induce Cyp3a11 mRNA. This could be explained by its high metabolism as demonstrated by the 20- to 25-fold increase in the urinary excretion of gamma-CEHC, the final metabolite of gamma-tocotrienol degradation. In conclusion, alpha-tocopherol maintains an adequate level of xenobiotic-metabolizing enzymes. If fed in supranutritional dosages, especially for longer times, alpha-tocopherol induces Cyp3a11 to levels which might interfere with drug metabolism.

Asunto(s)

Regulación de la Expresión Génica/efectos de los fármacos , alfa-Tocoferol/farmacología , gamma-Tocoferol/farmacología , Animales , Masculino , Ratones , Ratones Endogámicos C57BL , ARN Mensajero/genética , ARN Mensajero/metabolismo , alfa-Tocoferol/metabolismo , gamma-Tocoferol/metabolismo

RESUMEN

Some 80 years after its discovery, vitamin E has experienced a renaissance which is as surprising as it is trivial. Although vitamin E is essential for reproduction, in rats at least, and deficiency causes neurological disorders in humans, the main interest in the last decades has concentrated on its antioxidant functions. This focus has highly underestimated the biological importance of vitamin E, which by far exceeds the need for acting as a radical scavenger. Only recently has it become clear that vitamin E can regulate cellular signaling and gene expression. Out of the eight different tocols included in the term vitamin E, alpha-tocopherol often exerts specific functions, which is also reflected in its selective recognition by proteins such as the alpha-tocopherol transfer protein and alpha-tocopherol-associated proteins. Vitamin E forms other than alpha-tocopherol are very actively metabolised, which explains their low biopotency. In vivo, metabolism may also attenuate the novel functions of gamma-tocopherol and tocotrienols observed in vitro. On the other hand, metabolites derived from individual forms of vitamin E have been shown to exert effects by themselves. This article focuses on the metabolism and novel functions of vitamin E with special emphasis on differential biological activities of individual vitamin E forms.

Asunto(s)

Antioxidantes/farmacología , Vitamina E/farmacología , Animales , Fertilidad , Humanos , Modelos Químicos , Oxidación-Reducción , Oxígeno/metabolismo , Factores de Tiempo , Tocotrienoles/química , Vitamina E/química , alfa-Tocoferol/metabolismo , gamma-Tocoferol/metabolismo

RESUMEN

BACKGROUND: Glucocorticoids (GCs) are commonly used for long-term medication in immunosuppressive and anti-inflammatory therapy. However, the data describing gluco- and mineralo-corticoid (MC) properties of widely applied synthetic GCs are often based on diverse clinical observations and on a variety of in vitro tests under various conditions, which makes a quantitative comparison questionable. METHOD: We compared MC and GC properties of different steroids, often used in clinical practice, in the same in vitro test system (luciferase transactivation assay in CV-1 cells transfected with either hMR or hGRalpha expression vectors) complemented by a system to test the steroid binding affinities at the hMR (protein expression in T7-coupled rabbit reticulocyte lysate). RESULTS AND CONCLUSIONS: While the potency of a GC is increased by an 11-hydroxy group, both its potency and its selectivity are increased by the Delta1-dehydro-configuration and a hydrophobic residue in position 16 (16-methylene, 16alpha-methyl or 16beta-methyl group). Almost ideal GCs in terms of missing MC effects, as defined by our in vitro assay, are therefore prednylidene, budesonide, beclomethasone and betamethasone.The MC potency of a steroid is increased by a 9alpha- or a 6alpha-fluoro substituent. A hydrophilic substituent in position 16 (like 16-hydroxylation in triamcinolone) decreases both MC and GC properties. As no substituent that leads to an isolated reduction of GC activity could be characterized in our experiments, 9alpha-fluorocortisol, the most frequently used steroid for MC substitution, seems to be the best choice of available steroids for this purpose.

Asunto(s)

Glucocorticoides/farmacología , Prednisolona/farmacología , Receptores de Glucocorticoides/metabolismo , Receptores de Mineralocorticoides/metabolismo , Animales , Antiinflamatorios/química , Antiinflamatorios/farmacología , Células Cultivadas , Chlorocebus aethiops , Dexametasona/química , Dexametasona/farmacología , Glucocorticoides/química , Humanos , Hidrocortisona/química , Hidrocortisona/farmacología , Riñón/citología , Prednisolona/química , Pregnadienos/química , Pregnadienos/farmacología , Receptores de Glucocorticoides/genética , Receptores de Mineralocorticoides/genética , Transfección

RESUMEN

The 11beta-hydroxysteroid dehydrogenase (11beta-HSD) system plays a pivotal role in glucocorticoid (GC) and mineralocorticoid (MC) action. Although 11beta-HSD activities are important determinants for the efficacy of synthetic MCs and GCs, corresponding pharmacokinetic data are scanty. Therefore, we characterized 11beta-HSD profiles for a wide range of steroids often used in clinical practice. 11beta-HSD1 and 11beta-HSD2 were selectively examined in 1) human liver and kidney cortex microsomes, and 2) Chinese hamster ovarian cells stably transfected with 11beta-HSD1 or 11beta-HSD2 expression vectors. Both systems produced concordant evidence for the following conclusions. Oxidation of steroids by 11beta-HSD2 is diminished if they are fluorinated in position 6alpha or 9alpha (e.g. in dexamethasone) or methylated at 2alpha or 6alpha (in methylprednisolone) or 16alpha or 16beta, by a methylene group at 16 (in prednylidene), methyloxazoline at 16, 17 (in deflazacort), or a 2-chlor configuration. Whereas the methyl groups also decrease reductase activity (steric effects), fluorination increases reductase activity (negative inductive effect), leading to a shift to reductase activity. This may explain the strong MC activity of 9alpha-fluorocortisol and should be considered in GC therapy directed to 11beta-HSD2-expressing tissues (kidney, colon, and placentofetal unit). 11beta-HSD2 oxidation of prednisolone is more effective than that of cortisol, explaining the reduced MC activity of prednisolone compared with cortisol. Reduction by 11beta-HSD1 is diminished by 16alpha-methyl, 16beta-methyl, 2alpha-methyl, and 2-chlor substitution, whereas it is increased by the Delta(1)-dehydro configuration in prednisone, resulting in higher hepatic first pass activation of prednisone compared with cortisone. To characterize a GC or a MC as substrate for the different 11betaHSDs may be essential for an optimized steroid therapy.

Asunto(s)

Glucocorticoides/metabolismo , Hidroxiesteroide Deshidrogenasas/metabolismo , Mineralocorticoides/metabolismo , 11-beta-Hidroxiesteroide Deshidrogenasa de Tipo 1 , 11-beta-Hidroxiesteroide Deshidrogenasa de Tipo 2 , Animales , Células CHO , Cricetinae , Humanos , Corteza Renal/metabolismo , Microsomas/metabolismo , Microsomas Hepáticos/metabolismo , Mineralocorticoides/síntesis química , Oxidación-Reducción , Especificidad por Sustrato , Transfección