Dra. Mardones-Leiva, Lorena

The liver has an extraordinary regenerative capacity in response to partial hepatectomy (PHx), which develops with neither tissue inflammation response nor alterations in the whole organism. This process is highly coordinated and it has been associated with changes in glutathione (GSH) metabolism. However, there are no reports indicating ascorbic acid (AA) levels after partial hepatectomy. AA and GSH act integrally as an antioxidant system that protects cells and tissues from oxidative damage and imbalance observed in a variety of diseases that affect the liver. Although rat hepatocytes are able to synthesize AA and GSH, which are the providers of AA for the whole organism, they also acquire AA from extracellular sources through the sodiumcoupled ascorbic acid transporter-1 (SVCT1). Here, we show that hepatocytes from rat livers subjected to PHx increase their GSH and AA levels from 1 to 7 days post hepatectomy, whose peaks precede the peak in cellproliferation observed at 3 days post-hepatectomy. The increase in both antioxidants was associated with higher expression of the enzymes involved in their synthesis, such as the modifier subunit of enzyme glutamine cysteine ligase (GCLM), glutathione synthetase (GS), gulonolactonase (GLN) and gulonolactone oxidase (GULO). Importantly, rat hepatocytes, that normally exhibit kinetic evidence indicating only SVCT1-mediated transport of AA, lost more than 90% of their capacity to transport it at day 1 after PHx without evidence of recovery at day 7. This observation was in agreement with loss of SVCT1 protein expression, which was undetectable in hepatocytes as early as 2 h after PHx, with partial recovery at day 7, when the regenerated liver weight returns to normal. We conclude that after PHx, rat hepatocytes enhance their antioxidant capacity by increasing GSH and AA levels prior to the proliferative peak. GSH and AA are increased by de novo synthesis, however paradoxically hepatocytes from rat subjected to PHx also suppress their capacity to acquire AA from extracellular sources through SVCT1.

Background: Genetic variants within the FTO gene have been associated with increased adiposity and metabolic markers; however, there is limited evidence regarding the association of FTO gene variants with physical activity-related variables. The authors aimed to investigate the association of the rs17817449 single-nucleotide polymorphism of FTO with physical activity, sedentary time, and cardiorespiratory fitness in Chilean adults. Methods: A total of 409 participants from the GENADIO study were included and genotyped for the rs17817449 single-nucleotide polymorphism of FTO in this cross-sectional study. Physical activity and sedentary time were measured with ActiGraph accelerometers. Cardiorespiratory fitness was assessed using the Chester step test. The associations were assessed by using multivariate regression analyses. Results: No associations were found for FTO variant with physical activity levels and cardiorespiratory fitness. The risk allele (G) of the FTO was found to be associated with sedentary time in the minimally adjusted model (β = 19.7 min/d; 95% confidence interval, 4.0 to 35.5, per each copy of the risk allele; P = .006), but the association was no longer significant when body mass index was included as a confounder (P = .211). Conclusion: The rs17817449 single-nucleotide polymorphism of the FTO gene was not associated with the level of physical activity, cardiorespiratory fitness, and sedentary behaviors in Chilean adults.

Antecedentes. El receptor de melanocortina 4 (MC4R) participa en el control del apetito a nivel del sistema nervioso central, a través de la vía de la leptina-melanocortina. Se ha reportado asociación entre diferentes polimorfismos del gen MC4R y la obesidad; sin embargo, existen escasos estudios del polimorfismo de nucleótido simple (SNP) rs483145 de este gen. Objetivo. Investigar su prevalencia y asociación con marcadores de adiposidad en adultos chilenos. Métodos. La prevalencia del SNP rs483145, del gen MC4R, fue determinada en 259 participantes del estudio Genes, Ambiente, Diabetes y Obesidad (GENADIO) mediante reacción en cadena de la polimerasa (PCR) en tiempo real. La asociación del alelo de riesgo de MC4R (A) con marcadores de adiposidad (peso corporal, índice de masa corporal, porcentaje de masa grasa, perímetro de cadera, perímetro de cintura e índice cintura/cadera), se realizó mediante análisis de regresión lineal y fue ajustada por variables de confusión (sociodemográficas y de actividad física) mediante 3 modelos estadísticos. Resultados. Se determinó que la prevalencia del alelo de riesgo (A) del SNP rs483145 del gen MC4R es del 24,5% en la población adulta chilena incluida en este estudio, sin encontrar asociación con ninguno de los marcadores de adiposidad estudiados, tanto en modelos ajustados como sin ajustar.

La vitamina C es el antioxidante más conocido, debido a su asociación con la prevención del resfrío común. Esta vitamina también participa en la síntesis de colágeno y de catecolaminas, actuando como cofactor de hidrolasas. Se han evidenciado efectos benéficos del consumo de vitamina C en la prevención del cáncer, del envejecimiento y de enfermedades cardiovasculares y neurodegenerativas, debido a que estas patologías presentan un componente oxidativo en su origen y propagación. En particular, la acción anti-cancerígena de la vitamina C resulta ser bastante compleja de analizar, y ha sido debatida por décadas. Actualmente, se sabe que los niveles plasmáticos de esta vitamina son finamente regulados, alcanzando un valor cercano a 50 μM al consumir la dosis diaria recomendada (60 mg/día), gracias a su absorción intestinal y a su reabsorción renal. La administración de dosis mayores a 500 mg/día por vía oral permite alcanzar una concentración plasmática máxima de 150 μM 1 . La vitamina C ingerida es absorbida a nivel intestinal en su forma reducida (ascorbato, AA) por el co-transportador sodio-ascorbato (SVCT1), y en su forma oxidada (deshidroascorbato, DHA), por los transportadores facilitativos de glucosa (GLUT2 preferentemente). Por otro lado, la administración por vía endovenosa de dosis mayores a 0,4 g/kg permite alcanzar niveles plasmáticos estables cercanos a 1,5 mM, con un máximo de hasta 30 mM. Diversos estudios prospectivos observacionales revelaron que la suplementación con AA oral disminuye en 20% la mortalidad asociada al desarrollo de cáncer de mama y que mega-dosis de vitamina C endovenosa actúan como co-adyudantes en distintas terapias anti-cancerígenas (radioterapia, quimioterapia con carbioplatino o paclitaxel) y reducen el riesgo de progresión de cáncer de hígado posterior a hepatectomía parcial 2−3 . La administración de DHA también presentó efectividad como terapia complementaria en el caso del tratamiento con doxoribucina, metotrexato y cisplatino 2 . Lamentablemente, la mayoría de estos estudios clínicos carecieron de la rigurosidad requerida o involucraban un número muy pequeño de pacientes. Por otro lado, dado que estos estudios se realizaron sin conocer el mecanismo de acción de la vitamina C, no se monitoreó relación entre dosis, tiempo de aplicación y efectividad de la respuesta. Además, hay que considerar que algunos de estos agentes anti-cancerígenos son oxidantes, por lo que la vitamina C podría intervenir con su mecanismo de acción.

The purpose of this study was to investigate healthy lifestyle behaviours across age categories in the older population in Chile. Data from 1390 older adults (≥60 years), in the 2009–2010 Chilean National Health Survey were analyzed. We derived the following age categories: 60–65, 66–70, 71–75, 76–80 and >80 years. The associations between age and compliance with healthy lifestyle behaviours (smoking, sitting time, physical activity, sleep duration and intake of salt, alcohol, fruit and vegetables) were investigated using logistic regression. The probability of meeting the guidelines for alcohol intake (OR trend: 1.35 [95% CI: 1.11; 1.64], p = 0.001) and smoking (OR trend: 1.23 [95% CI: 1.13; 1.33], p < 0.0001) increased with age, whereas spending <4 h per day sitting time or engaging in at least 150 min of physical activity per week or sleep on average between 7 and 9 h per day were less likely to be met with increasing age (OR trend: 0.77 [95% CI: 0.71; 0.83], p < 0.000; OR trend: 0.73 [95% CI: 0.67; 0.79], p < 0.0001, and OR trend: 0.89 [95% CI: 0.82; 0.96], p = 0.002, respectively). No significant trend across age categories was observed for fruit and vegetables, and salt intake. The probability of meeting at least 3 out of 7 healthy lifestyle behaviours across the age categories was also lower in older age categories compared to those aged 60 to 65 years. Overall, in older adults the probability of having the healthy lifestyle behaviours of physical activity, sitting time and sleeping behaviours was low but not for smoking or alcohol consumption. With an increasingly ageing population, these findings could inform stakeholders on which lifestyle behaviours could be targeted in the older adults and therefore which interventions should take place to promote healthy ageing.

Differentiated mammary epithelial cells are responsible for milk synthesis during lactation, supporting early postnatal life in mammals. These cells are found in the terminal alveoli of a secretory epithelium, which is surrounded by myoepithelial cells and a stroma rich in fatty tissue. The aim of this study was to explore the cell-specific expression of the glucose transporter GLUT8 in mammary gland and evaluate its functionality for glucose transport, in order to confirm its role in lactose synthesis. Our histological results revealed that GLUT8 is expressed in adipocytes and the epithelial and myoepithelial cells in mammary gland, with a predominant intracellular granular pattern. Colocalization studies of endogenous and green fluorescent protein fused GLUT8 revealed their expressions in lysosome and Golgi, respectively, with Pearson's coefficient correlations of 0.82 ± 0.05 and 0.68 ± 0.16. Functional studies of dileucine to dialanine mutant of GLUT8 showed a fructose-sensitive 2-deoxy glucose uptake at a rate of 83.3 pmoles/(min∗106 cells), 7 folds over empty vector, with a 60 ± 4 and 72 ± 6% decline in 2-deoxy glucose in the presence of 20 and 50 mM fructose, respectively. We concluded that functional GLUT8 is expressed in mammary gland, localizing in mammary epithelial and myoepithelial cells, and adipocytes. In lactation, GLUT8 is expressed mainly in luminal epithelial cells, at the compartments of the endomembrane system. It is necessary to explore the physiological/pathological functions of GLUT8 in mammary gland, including its role in lactation.

The mammary gland increases energy requirements during pregnancy and lactation to support epithelial proliferation and milk nutrients synthesis. Lactose, the principal carbohydrate of the milk, is synthetized in the Golgi of mammary epithelial cells by lactose synthase from glucose and UPD galactose. We studied the temporal changes in the expression of GLUT1 and GLUT8 in mammary gland and their association with lactose synthesis and proliferation in BALB/c mice. Six groups were used: virgin, pregnant at 2 and 17 days, lactating at 2 and 10 days, and weaning at 2 days. Temporal expression of GLUT1 and GLUT8 transporters by qPCR, western blot and immunohistochemistry, and its association with lactalbumin, Ki67, and cytokeratin 18 within mammary tissue was studied, along with subcellular localization. GLUT1 and GLUT8 transporters increased their expression during mammary gland progression, reaching 20-fold increasing in GLUT1 mRNA at lactation (p < 0.05) and 2-fold at protein level for GLUT1 and GLUT8 (p < 0.05 and 0.01, respectively). The temporal expression pattern was shared with cytokeratin 18 and Ki67 (p < 0.01). Endogenous GLUT8 partially co-localized with 58 K protein and α-lactalbumin in mammary tissue and with Golgi membrane–associated protein 130 in isolated epithelial cells. The spatial-temporal synchrony between expression of GLUT8/GLUT1 and alveolar cell proliferation, and its localization in cis-Golgi associated to lactose synthase complex, suggest that both transporters are involved in glucose uptake into this organelle, supporting lactose synthesis.