Prolonged changes in hepatic mitochondrial activity and insulin sensitivity by high fructose intake in adolescent rats

Persistence of damage induced by unhealthy diets during youth has been little addressed. Therefore, we investigated the impact of a short-term fructose-rich diet on liver metabolic activity in adolescent rats and the putative persistence of alterations after removing fructose from the diet. Adolescent rats were fed a fructose-rich diet for three weeks and then switched to a control diet for further three weeks. Body composition and energy balance were not affected by fructose-rich diet, while increased body lipids and lipid gain were found after the rescue period. Switching to a control diet reversed the upregulation of plasma fructose, uric acid, lipocalin, and haptoglobin, while plasma triglycerides, alanine aminotransferase, lipopolysaccharide, and tumor necrosis factor alpha remained higher. Hepatic steatosis and ceramide were increased by fructose-rich diet, but reversed by returning to a control diet, while altered hepatic response to insulin persisted. Liver fatty acid synthase and stearoyl-CoA desaturase (SCD) activities were upregulated by fructose-rich diet, and SCD activity remained higher after returning to the control diet. Fructose-induced upregulation of complex II-driven mitochondrial respiration, peroxisome proliferator-activated receptor-gamma coactivator 1 alpha, and peroxisome proliferator activated receptor alpha also persisted after switching to control diet. In conclusion, our results show prolonged fructose-induced dysregulation of liver metabolic activity

Prolonged changes in hepatic mitochondrial activity and insulin sensitivity by high fructose intake in adolescent rats

Persistence of damage induced by unhealthy diets during youth has been little addressed. Therefore, we investigated the impact of a short‐term fructose‐rich diet on liver metabolic activity in adolescent rats and the putative persistence of alterations after removing fructose from the diet. Adolescent rats were fed a fructose‐rich diet for three weeks and then switched to a control diet for further three weeks. Body composition and energy balance were not affected by fructose‐rich diet, while increased body lipids and lipid gain were found after the rescue period. Switching to a control diet reversed the upregulation of plasma fructose, uric acid, lipocalin, and haptoglobin, while plasma triglycerides, alanine aminotransferase, lipopolysaccharide, and tumor necrosis factor alpha remained higher. Hepatic steatosis and ceramide were increased by fructose‐rich diet, but reversed by returning to a control diet, while altered hepatic response to insulin persisted. Liver fatty acid synthase and stearoyl‐CoA desaturase (SCD) activities were upregulated by fructose‐rich diet, and SCD activity remained higher after returning to the control diet. Fructose‐induced upregulation of complex II‐driven mitochondrial respiration, peroxisome proliferator‐activated receptor‐gamma coactivator 1 alpha, and peroxisome proliferator activated receptor α also persisted after switching to control diet. In conclusion, our results show prolonged fructose‐induced dysregulation of liver metabolic activity

Assignment of the binding site for Haptoglobin on Apolipoprotein A-I

Haptoglobin (Hpt) was previously found binding the high-density lipoprotein (HDL) Apolipoprotein A-I (ApoA-I) and able to inhibit the ApoA-I-dependent activity of the enzyme Lecithin:Cholesterol Acyl-Transferase (LCAT), which plays a major role in the reverse cholesterol transport. The ApoA-I structure was analyzed for detecting the site bound by Hpt. ApoA-I was treated by cyanogen bromide or hydroxylamine and the resulting fragments, separated by electrophoresis or gel filtration, were tested by Western blotting or ELISA for their ability to bind Hpt. The ApoA-I sequence from Glu113 to Asn184 harbored the binding site for Hpt. Biotinylated peptides were synthesized overlapping such a sequence, and their Hpt binding activity was determined by avidin-linked peroxidase. The highest activity was exhibited by the peptide P2a, containing the ApoA-I sequence from Leu141 to Ala164. Such a sequence contains an ApoA-I domain required for binding cells, promoting cholesterol efflux, and stimulating LCAT. The peptide P2a effectively prevented both binding of Hpt to HDL-coated plastic wells and Hpt-dependent inhibition of LCAT, measured by anti-Hpt antibodies and cholesterol esterification activity respectively. The enzyme activity was not influenced, in the absence of Hpt, by P2a. Differently from ApoA-I or HDL, the peptide did not compete with Hemoglobin for Hpt binding in ELISA experiments. The results suggest that Hpt might mask the ApoA-I domain required for LCAT stimulation, thus impairing the HDL function. Synthetic peptides, able to displace Hpt from ApoA-I without altering its property of binding Hemoglobin, might be used for treatment of diseases associated with defective LCAT function

Fructose removal from the diet reverses inflammation, mitochondrial dysfunction, and oxidative stress in hippocampus

Young age is often characterized by high consumption of processed foods and fruit juices rich in fructose, which, besides inducing a tendency to become overweight, can promote alterations in brain function. The aim of this study was therefore to (a) clarify brain effects resulting from fructose consumption in juvenile age, a critical phase for brain development, and (b) verify whether these alterations can be rescued after removing fructose from the diet. Young rats were fed a fructose-rich or control diet for 3 weeks. Fructose-fed rats were then fed a control diet for a further 3 weeks. We evaluated mitochondrial bioenergetics by high-resolution respirometry in the hippocampus, a brain area that is critically involved in learning and memory. Glucose transporter-5, fructose and uric acid levels, oxidative status, and inflammatory and synaptic markers were investigated by Western blotting and spectrophotometric or enzyme-linked immunosorbent assays. A short-term fructose-rich diet induced mitochondrial dysfunction and oxidative stress, associated with an increased concentration of inflammatory markers and decreased Neurofilament-M and post-synaptic density protein 95. These alterations, except for increases in haptoglobin and nitrotyrosine, were recovered by returning to a control diet. Overall, our results point to the dangerous effects of excessive consumption of fructose in young age but also highlight the effect of partial recovery by switching back to a control diet

LCAT cholesterol esterification is associated with the increase of ApoE/ApoA-I ratio during atherosclerosis progression in rabbit

Apolipoprotein A-I and Apolipoprotein E promote different steps of reverse cholesterol transport, including lecithin-cholesterol acyltransferase stimulation. Our aim was to study the changes in the levels of Apolipoprotein A-I, Apolipoprotein E, and lecithin-cholesterol acyltransferase activity during atherosclerosis progression in rabbits. Quantitative echocardiographic parameters were analyzed in order to evaluate, for the first time, whether atherosclerosis progression in rabbit is associated to apolipoproteins changes and alteration of indices of cardiac function, such as systolic strain and strain rate of the left ventricle. Atherosclerosis was induced by feeding rabbits for 8 weeks with 2 % cholesterol diet. The HDL levels of cholesterol and cholesteryl esters were measured by HPLC. The lecithin-cholesterol acyltransferase activity was evaluated both ex vivo, as cholesteryl esters/cholesterol molar ratio, and in vitro. Apolipoproteins levels were analyzed by ELISA. The HDL levels of cholesterol and cholesteryl esters increased, during treatment, up to 3.7- and 2.5-fold, respectively, compared to control animals. The lecithin-cholesterol acyltransferase activity in vitro was halved after 4 weeks. During cholesterol treatment, Apolipoprotein A-I level significantly decreased, whereas Apolipoprotein E concentration markedly increased. The molar ratio Apolipoprotein E/Apolipoprotein A-I was negatively correlated with the enzyme activity, and positively correlated with both increases in the intima-media thickness of common carotid wall and cardiac dysfunction signs, such as systolic strain and strain rate of the left ventricle. © 2012 University of Navarra

LCAT cholesterol esterification is associated with the increase of ApoE/ApoA-I ratio during atherosclerosis progression in rabbit

Apolipoprotein A-I and Apolipoprotein E promote different steps of reverse cholesterol transport, including lecithin-cholesterol acyltransferase stimulation. Our aim was to study the changes in the levels of Apolipoprotein A-I, Apolipoprotein E, and lecithin-cholesterol acyltransferase activity during atherosclerosis progression in rabbits. Quantitative echocardiographic parameters were analyzed in order to evaluate, for the first time, whether atherosclerosis progression in rabbit is associated to apolipoproteins changes and alteration of indices of cardiac function, such as systolic strain and strain rate of the left ventricle. Atherosclerosis was induced by feeding rabbits for 8 weeks with 2 % cholesterol diet. The HDL levels of cholesterol and cholesteryl esters were measured by HPLC. The lecithin-cholesterol acyltransferase activity was evaluated both ex vivo, as cholesteryl esters/cholesterol molar ratio, and in vitro. Apolipoproteins levels were analyzed by ELISA. The HDL levels of cholesterol and cholesteryl esters increased, during treatment, up to 3.7- and 2.5-fold, respectively, compared to control animals. The lecithin-cholesterol acyltransferase activity in vitro was halved after 4 weeks. During cholesterol treatment, Apolipoprotein A-I level significantly decreased, whereas Apolipoprotein E concentration markedly increased. The molar ratio Apolipoprotein E/Apolipoprotein A-I was negatively correlated with the enzyme activity, and positively correlated with both increases in the intima-media thickness of common carotid wall and cardiac dysfunction signs, such as systolic strain and strain rate of the left ventricle. © 2012 University of Navarra

Glucose-6-phosphate dehydrogenase plays a crucial role in the protection from redox-stress induced apoptosis.

Glucose-6-phosphate dehydrogenase-deleted embryonic stem (ES) cells (G6pdD) proliferate in vitro without special requirements, but when challenged with oxidants fail to sustain glutathione disulphide reconversion to reduced glutathione (GSH), entering a condition of oxidative stress. Here, we investigate the signalling events downstream of GSH oxidation in G6pdD and wild-type (wt) ES cells. We found that G6pdD ES cells are very sensitive to oxidants, activating an apoptotic pathway at oxidant concentrations otherwise sublethal for wt ES cells. We show that the apoptotic pathway activated by low oxidant concentrations is accompanied by mitochondria dysfunction, and it is therefore blocked by the overexpression of Bcl-XL. Bcl-XL does not inhibit the decrease in cellular GSH and reactive oxygen species formation following oxidant treatment. We also found that oxidant treatment in ES cells is followed by the activation of the MEK/ extracellular signal-regulated kinase (ERK) pathway. Interest¬ingly, ERK activation has opposite outcomes in G6pdD ES cells compared to wt, which has a proapoptotic function in the first and a prosurvival function in the latter. We show that this phenomenon can be regulated by the cellular GSH level