El esqueleto como órgano endocrino: funciones metabólicas de la osteocalcina / The skeleton as an endocrine organ: metabolic functions of osteocalcin

El esqueleto es uno de los sistemas más grandes de un vertebrado y, como tal, es razonable especular que no puede funcionar aislado del resto del organismo. De hecho, sabemos que existen sistemas complejos de regulación cruzada entre el esqueleto y muchos otros órganos. Hoy poseemos herramientas que nos permiten realizar supresión genética en células o tejidos específicos. Esto nos ha permitido comprender cómo los órganos se comunican entre sí y ha revitalizado el concepto de fisiología del organismo como un todo. Efectivamente, los últimos años han sido testigos del descubrimiento de funciones inesperadas que ejerce el esqueleto y que afectan al organismo en su totalidad. Una de tales funciones reconocidas recientemente es el control del metabolismo energético, a través de la secreción de osteocalcina. La osteocalcina es una hormona producida por los osteoblastos que regula la secreción de insulina, la sensibilidad a esta hormona y el metabolismo energético. Los hallazgos iniciales suscitaron varias preguntas fundamentales sobre la naturaleza de la acción de la insulina sobre el hueso. Pero esto solo fue la punta del iceberg. Efectivamente, más adelante se descubrió, mediante el análisis de ratones que carecen del receptor de insulina (Ins R) solamente en osteoblastos, que la acción de la insulina sobre estas células favorecía la homeostasis de la glucosa en todo el cuerpo. Es importante destacar que esta función de la insulina en los osteoblastos opera mediante la regulación negativa de la carboxilación y la biodisponibilidad de la osteocalcina. Más aún, se observó que las vías de señalización de la insulina en los osteoblastos regulan positivamente no solo la formación sino también la resorción del hueso. Curiosamente, parece que las vías de señalización de la insulina en osteoblastos pueden inducir la activación de la osteocalcina mediante la estimulación de la actividad de los osteoclastos. De hecho, el bajo pH generado durante la resorción ósea es suficiente para desencadenar la descarboxilación (y subsiguiente activación) de la osteocalcina. En breve discutiremos dos nuevas proposiciones: 1) los osteoblastos son un blanco utilizado por la insulina para controlar la homeostasis de la glucosa en todo el organismo y 2) la resorción ósea desempeña un papel fundamental en la regulación de la activación de la osteocalcina. (AU)

The skeleton is one of the biggest systems in a vertebrate animal and, as such, it is reasonable to speculate that it cannot function isolated from the rest of the organism. In fact, we know that complex systems exist for the cross-regulation between the skeleton and several other organs. Today, we have the tools that allow us to perform genetic suppression in specific cells or tissues. This has allow us understand the mechanisms by which the organs communicate with each other and has revitalized the concept of organismal physiology as a whole. Studies conducted in recent years have uncovered unexpected functions performed by the skeleton. One of these is the control of global energy metabolism, through the secretion of osteocalcin, a protein produced by osteoblasts that acts as a hormone regulating insulin secretion, insulin sensitivity and energy expenditure. The evidence comes from the analysis of mice lacking insulin receptor (InsR) exclusively in osteoblasts. These mice have a global metabolic phenotype demonstrating that the action of insulin in osteoblasts promotes the homeostasis of glucose throughout the body. This action of insulin in osteoblasts is mediated by the negative regulation of the carboxylation (and bioavailability) of osteocalcin. The decarboxylation (and activation) of osteocalcin, in turn, occurs in the osteoclastic resorption pit. Briefly: the osteoblast is a target used by insulin to control the homeostasis of glucose throughout the body and bone resorption is the mechanism that regulates the activation of osteocalcin. (AU)

El papel del riñón en la homeostasis de la glucosa y drogas de acción renal en el tratamiento de la diabetes mellitus tipo 2 / Kidney role in the glucose's homeostasis and drugs of renal action in the treatment of type 2 diabetes mellitus

Los riñones contribuyen a la homeostasis de la glucosa a través de varios mecanismos, incluyendo la gluconeogénesis, utilización y reabsorción de la glucosa a partir del filtrado glomerular. Bajo condiciones fisiológicas normales, la glucosa filtrada es casi totalmente reabsorbida en el epitelio de las células tubulares; en consecuencia, no aparece glucosa en la orina. El transporte de glucosa dentro de las células epiteliales del túbulo se cumple gracias a cotransportadores activos glucosa-sodio (SGLT), una familia de proteínas dependientes de adenosin trifosfato (ATP) involucradas en el transporte de glucosa contra un gradiente de concentración con carga simultánea de sodio, igualmente en contra gradiente. La mayoría de la glucosa filtrada es reabsorbida por medio del SGLT2, un transportador de baja afinidad pero elevada capacidad localizado, predominantemente, en el segmento S1 del tubo contorneado proximal. Por largo tiempo la inhibición del SGLT2 ha sido considerada como un abordaje terapéutico potencial de la hiperglucemia en la diabetes mellitus tipo 2 (DM2), ya que al prevenir la reabsorción de glucosa por los túbulos renales promueven su excreción renal y descienden los valores de la glucemia. Los datos en humanos indican que los inhibidores de SGLT2 representan una estrategia novedosa y efectiva para controlar las cifras de glucemia en los pacientes con DM2. El recién publicado estudio EMPA-REG OUTCOME diseñado para examinar los desenlaces cardiovasculares con empagliflozina en sujetos con DM2 y enfermedad ardiovascular coexistente mostró beneficios tempranos, los cuales se mantuvieron durante el período de observación(AU)

The kidneys contribute to glucose homeostasis through several mechanisms, including gluconeogenesis, glucose use, and glucose reabsorption from the glomerular filtrate. Under normal physiological conditions, this filtered glucose is almost completely reabsorbed by renal tubular epithelial cells; thus, there is no glucose in urine. The transport of glucose into renal tubular epithelial cells is mediated by active cotransporters, the SGLT, a family of ATP-dependent proteins involved in the transport of glucose against a concentration gradient with simultaneous transport of Na+ down a concentration gradient. Most of the filtered glucose is reabsorbed through SGLT2, a low-affinity high-capacity transporter located predominantly in the S1 segment of the renal proximal tubule. Inhibition of SGLT2 has long been regarded as a potential treatment approach for hyperglycemia during T2DM, as they prevent glucose reabsorption from renal tubules, thereby promoting urinary glucose excretion and decreasing plasma glucose levels. Current data in humans indicate that SGLT2 inhibitors represent an effective and novel strategy to control the plasma glucose concentration in patients with T2DM. The recently published EMPA-REG OUTCOME trial, which assessed cardiovascular outcomes with empagliflozin therapy in persons with type 2 diabetes mellitus and coexisting cardiovascular disease showed that the benefits were noted early and continued throughout the study(AU)

Metabolic networks and bioenergetics of Aurantiochytrium sp. B-072 during storage lipid formation

Baffled shake flask cultivation of Aurantiochytrium sp. B-072 was carried out at in a glucose-monosodium glutamate mineral medium at different C/N-ratios (30-165) with glucose fixed at 90 g/L. With increasing C/N-ratio, a modest increase in lipid content (60 to 73 % w/w) was observed whereas fat-free biomass decreased but overall biomass showed little variation. FA-profiles were not affected to a large extent by C/N-ratio and absolute docosahexaenoic (DHA)-levels fell in narrow range (5-6 g/L). However at C/N > 64 a rapid decrease in lipid synthetic rate and/or incomplete glucose utilization occurred. Glucose and FA-fluxes based on fat-free biomass peaked at a C/N ratio of 56. This condition was chosen for calculation of the redox balance (NAD(P)H) and energy (ATP) requirement and to estimate the in vivo P/O ratio during the main period of fatty acid biosynthesis. Several models with different routes for NADPH, acetyl-CoA formation and re-oxidation of OAA formed via ATP-citrate lyase were considered as these influence the redox- and energy balance. As an example, using a commonly shown scheme whereby NADPH is supplied by a cytosolic "transhydrogenase cycle" (pyruvate-OAA-malate-pyruvate) and OAA formed by ATP-citrate lyase is recycled via import into the mitochondria as malate, the calculated NADPH-requirement amounted to 5.5 with an ATP-demand of 10.5 mmol/(g fat-free biomass x h) and an in vivo P/O-ratio (not including non-growth associated maintenance) of 1.6. The lowest ATP requirement is found when acetyl-CoA would be transported directly from the mitochondria to the cytosol by carnitine acetyltransferase. Assay of some enzymes critical for NADPH supply indicates that activity of glucose-6-phosphate dehydrogenase, the first enzyme in the HMP pathway, is far insufficient for the required NADPH-flux and malic enzyme must be a major source. Activity of the latter (ca. 300 mU/mg protein) far exceeds that in oleaginous fungi and yeast.

Efecto del oxígeno y la glucosa en la metanogénesis y mineralización de resinas poliméricas / The effect of oxygen and glucose on polymeric resin methanogenesis and mineralisation

The effect of dissolved oxygen concentration and glucose on polymeric resin compounds’ methanogenesisand mineralisation was examined in batch cultures. They were inoculated with sludge from an upflow anaerobicsludge blanket reactor fed with polymeric resin compounds and 1.0 mg L-1 steady-state dissolved oxygen.All tests were carried out with 1,500 mg L-1 chemical oxygen demand (COD), at 30±2ºC, with 23.8 g L-1 volatile suspended solids (VSS) as inoculum and 1:1 COD/VSS ratio. The effect of different dissolved oxygen concentrations showed that COD efficiently removed glucose whilst methanogenic activity remained constant at low concentrations (0.6 and 1.0 mg L-1), but polymeric resin compounds’ COD removal efficiency increased 58.1±1% whilst methane yield decreased, due to the higher aerobic mineralisation of carbon to carbon dioxide. The result of different glucose/polymeric resin compound ratios in the presence of 0.6 mg L-1 dissolved oxygen showed that glucose did not improve polymeric resin compound removal. However, methanogenic activity decreased by 75% with polymeric resin compounds as substrate compared to methanogenic activity with glucose as sole carbon source, suggesting that the presence of glucose promotes conditions for highertolerance to oxygen. The presence of low dissolved oxygen concentrations therefore promotes polymeric resin compounds’ methanogenesis and mineralisation.

En el presente trabajo se evaluó el efecto de la concentración de oxígeno disuelto (OD) y la presencia de laglucosa en la metanogénesis y mineralización de los compuestos de resinas poliméricas, mediante cultivos en lote. El inóculo utilizado para los cultivos fueron lodos procedentes de un reactor de lecho de lodos con flujoascendente UASB (por sus siglas en inglés), alimentado con glucosa y aguas residuales de resinas poliméricas,y 1,0 mg L-1 d-1 de oxígeno disuelto en estado estacionario. Todas las pruebas fueron realizadas con 1500 mgL-1 de demanda química de oxígeno, a 30±2° C, con 23,8 g L-1 de sólidos suspendidos volátiles como inóculoy una relación demanda química de oxígeno / sólidos suspendidos volátiles de 1. El efecto de diferentesconcentraciones de oxígeno disuelto mostró que, para la glucosa, con bajas concentraciones (0,6 y 1,0 mgL-1) la eficiencia de remoción de la demanda química de oxígeno y la actividad metanogénicas permanecieronconstantes, pero la eficiencia de remoción de la demanda química de oxígeno para los compuestos de resinaspoliméricas aumentó 58,1±1% y el rendimiento de metano disminuyó, debido a que una mayor fracción delcarbono alimentado fue mineralizada a dióxido de carbono, posiblemente por una ruta aerobia. Los resultadoscon diferentes proporciones de glucosa / compuestos de resinas poliméricas (CRP) en presencia de 0,6 mg L-1 de oxígeno disuelto mostraron que la presencia de glucosa no mejoró la eliminación de los compuestosde resinas poliméricas. Sin embargo, la actividad metanogénica disminuyó en un 75% cuando solamente se usó a los compuestos de resinas poliméricas como sustrato, al compararla con la actividad metanogénica con glucosa como única fuente de carbono, sugiriendo que la glucosa no favorece la eliminación de los compuestosde resinas poliméricas, pero proporciona una mejor tolerancia al oxígeno..

Simultaneous effects of pH and substrate concentration on hydrogen production by acidogenic fermentation / Efectos simultáneos del pH y la concentración de sustrato en la producción de hidrógeno mediante fermentación acidogénica

The present research examined the effects of initial substrate concentration and pH on the yield and productivity of hydrogen production by acidogenic fermentation. Assays were carried out at three different initial pH levels (5.5, 6.5 and 7.5) and three initial substrate concentrations (3, 5 and 10 g COD/L). Glucose was used as carbon source and the experiments were conducted at 37°C in batch tests, after a thermal pretreatment to eliminate methanogenic microorganisms. Conversions of glucose into hydrogen were between 16.75 and 27.25 percent of theoretical maximum, and high values of hydrogen productivity were obtained. An optimum value for the yield of glucose between initial pH of 6.3 and 3.7 g COD/L and productivity of the 5.95 H2/gVSS h and initial pH of 6.7 and 10 g COD/L were obtained from the response surface.

Rat liver responsiveness to gluconeogenic substrates during insulin-induced hypoglycemia

Hepatic responsiveness to gluconeogenic substrates during insulin-induced hypoglycemia was investigated. For this purpose, livers were perfused with a saturating concentration of 2 mM glycerol, 5 mM L-alanine or 5 mM L-glutamine as gluconeogenic substrates. All experiments were performed 1 h after an ip injection of saline (CN group) or 1 IU/kg of insulin (IN group). The IN group showed higher (P<0.05) hepatic glucose production from glycerol, L-alanine and L-glutamine and higher (P<0.05) production of L-lactate, pyruvate and urea from L-alanine and L-glutamine. In addition, ip injection of 100 mg/kg glycerol, L-alanine and L-glutamine promoted glucose recovery. The results indicate that the hepatic capacity to produce glucose from gluconeogenic precursors was increased during insulin-induced hypoglycemia.

Time sequence of changes in the responsiveness of glycogen breakdown to adrenergic agonists in perfused liver of rats with insulin-induced hypoglycemia

The time-course changes of the responsiveness of glycogen breakdown to a- and Beta-adrenergic agonists during insulin-induced hypoglycemia (IIH) were investigated. Blood glucose levels were decreased prior to the alteration in the hepatic responsiveness to adrenergic agonists. The activation of hepatic glucose production and glycogenolysis by phenylephrine (2 µM) and isoproterenol (20 µM) was decreased in IIH. The changes in the responsiveness of glycogen catabolism were first observed for isoproterenol and later for phenylephrine. Hepatic ß-adrenergic receptors showed a higher degree of adrenergic desensitization than did a-receptors. Liver glycogen synthase activity, glycogen content and the catabolic effect of dibutyryl cyclic AMP (the Beta-receptor second messenger) were not affected by IIH.

The metabolic effects of estriol in female rat liver

The effects of estriol on oxygen uptake, glucose release, lactate and pyruvate production, beta-hydroxybutyrate and acetoacetate production in perfused rat liver as well as, carbon uptake in rat liver and intracellular calcium in isolated Kupffer cells were investigated. Basal oxygen consumption of perfused liver increased significantly in estriol or ethanol-treated rats. But these increased effects were blocked by gadolinium chloride pretreatment. In a metabolic study, pretreatment with estriol resulted in a decrease in glucose production and in glycolysis while an increase in ketogenesis. A more oxidized redox state of the mitochondria was indicated by increased ratios of perfusate [lactate]/[pyruvate] and decreased ratios of perfusate [beta-hydroxybutyrate]/[acetoacetate]. Carbon uptake of Kupffer-cell increased significantly in estriol-treated rats. But these increased uptake were not shown in rats pre-treated by gadolinium chloride blocking phagocytosis. In isolated Kupffer cells from estriol-treated rats, intracellular calcium was more significantly increased after addition of lipopolysaccharide (LPS) than in controls. These findings suggest that the metabolic effects of estriol (two mg per 100 mg body wt) can be summarized to be highly toxic in rat liver, and these findings suggest that oral administration of estrogens may induce hepatic dysfunctions and play a role in the development of liver disease.

Inhibición de la glicosilación no enzimática de la hemoglobina en la diabetes mellitus / Inhibition of non-enzymatic glycosilation of hemoglobin in diabetes mellitus

Se estudió el efecto inhibidor del aminoácido glicina sobre la glicosilación no enzimática de la hemoglobina en la diabetes experimental de ratas Wistar con estreptozotocina. La hemoglobina glicosilada de las ratas diabéticas fue de 4.2 ñ 0.38 por ciento y la de las diabéticas que tomaron glicina al 1 por ciento en el agua de bebida ad libitum fue de 2.90 ñ 0.37 por ciento (p = 0.00005). Un grupo de 30 personas diabéticas tipo II y 8 de tipo I tomaron glicina disuelta en agua: 20 gramos diarios (4 tomas de 5 g cada 6 horas) durante tiempos variables: de 3 hasta 56 meses. La hemoglobina glicosilada promedio de los diabéticos antes de tomar la clicina fue de 12.8 ñ 3.3 por ciento y después fue de 8.3 ñ 2.2 por ciento con un valor de p= 7 x 10-12 (prueba de rangos señalados de Wilcoxon)

Efectos del acipimox sobre el metabolismo de la glucosa y de los lípidos, en pacientes con diabetes mellitus tipo II, obesos de difícil control con hiperlipoproteinemia tipo IIb y IV: resultados de un estudio multicéntrico / Acipimox affects in glucose metabolism in patients with diabetes mellitus type II and hyperlipidemia type IIb or IV

La interacción metabólica entre hidratos de carbono y lípidos, ha permitido considerar la hipótesis de que la corrección con hiperlipidemia en el diabético mal controlado, permite al paciente mejorar su control glucémico, posiblemente modificando la resistencia a la insulina. El objetivo de este trabajo multicéntrico fue evaluar la acción de un hipolipemiante, un análogo del ácido nicotínico acipimox en pacientes diabéticos no insulino dependientes con hiperlipoproteinemia tipo IIb y IV, que presentaban un descontrol metabólico aún recibiendo hipoglucemiantes orales a dosis máximas. La investigación incluyó 133 pacientes, de los que 67 tomaron acipimox por un periodo de tres meses (olbetam, *marca registrada) en dosis de 250 mg tres veces por vía oral; y 66 pacientes (grupo control) a quienes se les administró placebo. Se examinaron diversos parámetros bioquímicos antes de la administración del medicamento, a las cuatro, ocho y 12 semanas. En el grupo con acipimox se observó una disminución estadísticamente significativa de los niveles plasmáticos de triglicéridos, colesterol total, colesterol LDL, glucosa en ayuno y postprandial, hemoglobina glucosilada y un incremento de colesterol HDL. Estos resultados indican que el acipimox es un agente hipolipidemico con efecto sobre el control metabólico, tanto de los lípidos como de la glucosa, en pacientes diabéticos tipo II con hiperlipidemia tipo IIb o IV de difícil control

Effect of corticosteroids on carbohydrate metabolism in Bufo melanostictus (Schneider).

A single injection of corticosterone (1 or 5 micrograms/50 g body weight) produced a significant elevation in plasma glucose, liver and muscle glycogen contents of B. melanostictus. Single but identical doses of aldosterone had no effect on plasma glucose concentration. Liver and muscle glycogen contents were however significantly augmented. Administration of 1 or 5 micrograms corticosterone and 1 microgram or 200 ng aldosterone/50 g body weight, for 15 days, caused no change in plasma glucose concentration. In all the groups receiving corticosterone or aldosterone for 15 days, liver and muscle glycogen contents significantly increased. The magnitude of increase in liver and muscle glycogen by aldosterone was marginally greater than that by corticosterone. The results suggest that both the corticosteroids may be gluconeogenic in B. melanostictus.

Estudo cinético preliminar da decomposiçäo da glicose em sais de reidrataçäo oral / Preliminary kinetic study of glucose degradation in oral rehydration salts

Diversas formulaçöes de sais de reidrataçäo oral (SRO) foram submetidas a degradaçäo em diferentes temperaturas por períodos de tempo variáveis. A quantidade de glicose, contida nestas formulaçöes, foi determinada pelo método colorimétrico enzimático com a finalidade de se calcular as velocidades aparentes de decomposiçäo e os parâmetros cinéticos necessários para se obter os prazos de validade dos SRO. O aumento da umidade e a utilizaçäo do bicarbonato de sódio em lugar do citrato de sódio favorece a decomposiçäo dos SRO, diminuindo consequentemente os prazos de validade dos produtos. A quantificaçäo do t90, tempo necessário para que se observe degradaçäo de 10%, confirmou a importância da umidade e das características dos sais inorgânicos da formulaçäo, na determinaçäo do prazo de validade dos SRO. O aumento da umidade e a utilizaçäo do bicarbonato de sódio em lugar do citrato de sódio favorece a decomposiçäo dos SRO, diminuindo consequentemente os prazos de validade (t90)