Nutritional Composition of Infant Cereal Prototypes Can Precisely Predict Their Glycemic Index

Designing cereal-based products with appropriate metabolic responses is of high interest to the food industry in view of the potential health impact of the product. The objective of this study was to test whether a model that used the nutrient composition of breakfast cereals to predict their glycemic index (GI) and glycemic load (GL) could also accurately predict the GI and GL for complete (containing protein, reconstituted in water) infant cereal prototypes. Four independent studies measured the postprandial glucose response of 20 complete infant cereal prototypes (51−76 g/100 g glycemic carbohydrates) in healthy adults. The predictions were strongly correlated with the measured values for both the GI (r = 0.93, p-value < 0.01) and GL (r = 0.98, p-value < 0.01). The in vivo incremental area under the curve (iAUC) for glucose showed a strong linear relationship with the predicted GL (r = 0.99, p < 0.01). In summary, the model previously developed to predict the GI and GL of breakfast cereals was both accurate and precise for infant cereals and could be considered a simple tool to support nutritionally responsible product development.

Assessment of Glycemic Response to Model Breakfasts Varying in Glycemic Index (GI) in 5-7-Year-Old School Children

Reduced Glycemic Index (GI) of breakfast has been linked to improved cognitive performance in both children and adult populations across the morning. However, few studies have profiled the post-prandial glycemic response (PPGR) in younger children. The aim of this study was to assess PPGR to breakfast interventions differing in GI in healthy children aged 5-7 years. Eleven subjects completed an open-label, randomized, cross-over trial, receiving three equicaloric test beverages (260 kcal) consisting of 125 mL semi-skimmed milk and 50 g sugar (either glucose, sucrose, or isomaltulose). On a fourth occasion, the sucrose beverage was delivered as intermittent supply. PPGR was measured over 180 min using Continuous Glucose Monitoring (CGM). The incremental area under the curve (3h-iAUC) was highest for the glucose beverage, followed by intermittent sucrose (-21%, p = 0.288), sucrose (-27%, p = 0.139), and isomaltulose (-48%, p = 0.018). The isomaltulose beverage induced the smallest Cmax (7.8 mmol/L vs. >9.2 mmol/L for others) and the longest duration with moderate glucose level, between baseline value and 7.8 mmol/L (150 vs. <115 min for others). These results confirm that substituting mid-high GI sugars (e.g., sucrose and glucose) with low GI sugars (e.g., isomaltulose) during breakfast are a viable strategy for sustained energy release and glycemic response during the morning even in younger children.

Predicting Glycemic Index and Glycemic Load from Macronutrients to Accelerate Development of Foods and Beverages with Lower Glucose Responses

Low glycemic index (GI) and/or low glycemic load (GL) are associated with decreased risks of type-2 diabetes and cardiovascular disease. It is therefore relevant to consider GI and GL in the early phases of the development of packaged foods and beverages. This paper proposes a model that predicts GI and GL from macronutrient composition, by quantifying both the impact of glycemic carbohydrates and the GI-lowering effects of nutrients such as proteins, fats and fibers. The precision of the model is illustrated using data on 42 breakfast cereals. The predictions of GI (r = 0.90, median residual = 2.0) and GL (r = 0.96, median residual = 0.40 g) compete well with the precision of the underlying in-vivo data (Standard Error SE = 3.5 for GI). This model can guide product development towards lowering GI and GL, before final confirmation by in vivo testing.

The scientific basis for healthful carbohydrate profile

Dietary guidelines indicate that complex carbohydrates should provide around half of the calories in a balanced diet, while sugars (i.e., simple carbohydrates) should be limited to no more than 5-10% of total energy intake. To achieve this public health goal a collective effort from different entities including governments, food & beverage industries and consumers is required. Some food companies have committed to continually reduce sugars in their products. Different solutions can be used to replace sugars in food products but it is important to ensure that these solutions are more healthful than the sugars they replace. The objectives of this paper are, (1) to identify carbohydrates and carbohydrates sources to promote and those to limit for dietary intake and food product development, based on current knowledge about the impact of carbohydrates on the development of dental caries, obesity and cardio-metabolic disorders (2) to evaluate the impact of food processing on the quality of carbohydrates and (3) to highlight the challenges of developing healthier products due to the limitations and gaps in food regulations, science & technology and consumer education.

Whole grain intake, determined by dietary records and plasma alkylresorcinol concentrations, is low among pregnant women in Singapore

BACKGROUND AND OBJECTIVES

To quantify whole grain intake in pregnant women in Singapore in order to provide the first detailed analysis of whole grain intake in an Asian country and in pregnant women.

METHODS AND STUDY DESIGN

Analysis of 24-h diet recalls in a cross-sectional cohort study and analysis of a biomarker of whole grain intake (plasma alkylresorcinols) in a subset of subjects. The Growing Up in Singapore Towards healthy Outcomes-mother offspring cohort study based in Singapore. 998 pregnant mothers with complete 24-h recalls taken during their 26-28th week of gestation. Plasma samples from a randomly select subset of 100 subjects were analysed for plasma alkylresorcinols.

RESULTS

Median (IQR) whole grain intake for the cohort and the 30% who reported eating whole grains were 0 (IQR 0, 9) and 23.6 (IQR 14.6, 44.2) g/day respectively. Plasma alkylresorcinol concentrations were very low [median (IQR)=9 (3, 15) nmol/L], suggesting low intake of whole grain wheat in this population. Plasma alkylresorcinols were correlated with whole grain wheat intake (Spearman's r=0.35; p<0.01).

CONCLUSIONS

Whole grain intake among pregnant mothers in Singapore was well below the 2-3 (60-95 g) servings of whole grains per day recommended by the Singapore Health Promotion Board. Efforts to increase whole grain intake should be supported to encourage people to choose whole grains over refined grains in their diet.

Effect of a mixture of bovine milk oligosaccharides, Lactobacillus rhamnosus NCC4007 and long-chain polyunsaturated fatty acids on catch-up growth of intra-uterine growth-restricted rats

AIM

To investigate the effect of a nutritional mixture (bovine milk oligosaccharides, Lactobacillus rhamnosus NCC4007, arachidonic and docosahexaenoic acid) on growth of intrauterine growth-restricted (IUGR) rats.

METHODS

IUGR was induced by maternal food restriction. The offspring (males and females) were assigned to: REF (non-IUGR, no mixture), IUGRc (IUGR, no mixture), or IUGRmx (IUGR, mixture). The mixture was given from day 7 to day 58, when tissues and plasma from half of the animals were collected for hormones, metabolites and microarray analysis. The rest received a high-fat diet (HFD) until day 100. Glucose tolerance was measured at 56 and 98 days, and body fat content at 21, 52 and 97 days.

RESULTS

IUGRmx had the greatest growth during lactation, but from day 22 to day 54, both IUGR groups gained less body weight than the REF (P < 0.05). In the short-term (58 days), IUGRmx tended to be longer (P = 0.06) and had less body fat (P = 0.03) than IUGRc. These differences were not seen after HFD. Microarray analysis of hepatic mRNA expression at 58 and 100 days revealed a gender-dependent treatment effect, and expression of genes related to lipid metabolism was the most affected. Twelve of these genes were selected for studying differences in DNA methylation in the promoter region, for some, we observed age- and gender-related differences but none because of treatment.

CONCLUSION

The nutritional intervention promoted catch-up growth and normalized excessive adiposity in IUGR animals at short-term. The benefits did not extend after a period of HFD. IUGR and early diet had gender-dependent effects on hepatic gene expression.

Use of dicarboxylic acids in type 2 diabetes

Even-number, medium-chain dicarboxylic acids (DAs), naturally occurring in higher plants, are a promising alternative energy substrate. Unlike the homologous fatty acids, DAs are soluble in water as salts. They are β-oxidized, providing acetyl-CoA and succinyl-CoA, the latter being an intermediate of the tricarboxylic acid cycle. Sebacic acid and dodecanedioic acid, DAs with 10 and 12 carbon atoms respectively, provide 6.6 and 7.2 kcal g⁻¹ each; therefore, their energy density is intermediate between glucose and fatty acids. Dicarboxylic acids have been proved to be safe in both experimental animals and humans, and their use has recently been proposed in diabetes. Studies in animals and humans with type 2 diabetes showed that oral administration of sebacic acid improved glycaemic control, probably by enhancing insulin sensitivity, and reduced hepatic gluconeogenesis and glucose output. Moreover, dodecanedioic acid intake reduced muscle fatigue during exercise in subjects with type 2 diabetes, suggesting an improvement of energy utilization and 'metabolic flexibility'. In this article, we review the natural sources of DAs, their fate in animals and humans and their effect in improving glucose metabolism in type 2 diabetes.

Consequences of exchanging carbohydrates for proteins in the cholesterol metabolism of mice fed a high-fat diet

Consumption of low-carbohydrate, high-protein, high-fat diets lead to rapid weight loss but the cardioprotective effects of these diets have been questioned. We examined the impact of high-protein and high-fat diets on cholesterol metabolism by comparing the plasma cholesterol and the expression of cholesterol biosynthesis genes in the liver of mice fed a high-fat (HF) diet that has a high (H) or a low (L) protein-to-carbohydrate (P/C) ratio. H-P/C-HF feeding, compared with L-P/C-HF feeding, decreased plasma total cholesterol and increased HDL cholesterol concentrations at 4-wk. Interestingly, the expression of genes involved in hepatic steroid biosynthesis responded to an increased dietary P/C ratio by first down-regulation (2-d) followed by later up-regulation at 4-wk, and the temporal gene expression patterns were connected to the putative activity of SREBF1 and 2. In contrast, Cyp7a1, the gene responsible for the conversion of cholesterol to bile acids, was consistently up-regulated in the H-P/C-HF liver regardless of feeding duration. Over expression of Cyp7a1 after 2-d and 4-wk H-P/C-HF feeding was connected to two unique sets of transcription regulators. At both time points, up-regulation of the Cyp7a1 gene could be explained by enhanced activations and reduced suppressions of multiple transcription regulators. In conclusion, we demonstrated that the hypocholesterolemic effect of H-P/C-HF feeding coincided with orchestrated changes of gene expressions in lipid metabolic pathways in the liver of mice. Based on these results, we hypothesize that the cholesterol lowering effect of high-protein feeding is associated with enhanced bile acid production but clinical validation is warranted. (246 words).

Effect of different protein sources on satiation and short-term satiety when consumed as a starter

BACKGROUND

Because the source of protein may play a role in its satiating effect, we investigated the effect of different proteins on satiation and short-term satiety.

METHODS

Two randomized single-blind cross-over studies were completed. In the first study, we investigated the effect of a preload containing 20 g of casein, whey, pea protein, egg albumin or maltodextrin vs. water control on food intake 30 min later in 32 male volunteers (25 ± 4 yrs, BMI 24 ± 0.4 kg/m(2)). Subjective appetite was assessed using visual analogue scales at 10 min intervals after the preload. Capillary blood glucose was measured every 30 min during 2 hrs before and after the ad libitum meal. In the second study, we compared the effect of 20 g of casein, pea protein or whey vs. water control on satiation in 32 male volunteers (25 ± 0.6 yrs, BMI 24 ± 0.5 kg/m(2)). The preload was consumed as a starter during an ad libitum meal and food intake was measured. The preloads in both studies were in the form of a beverage.

RESULTS

In the first study, food intake was significantly lower only after casein and pea protein compared to water control (P = 0.02; 0.04 respectively). Caloric compensation was 110, 103, 62, 56 and 51% after casein, pea protein, whey, albumin and maltodextrin, respectively. Feelings of satiety were significantly higher after casein and pea protein compared to other preloads (P < 0.05). Blood glucose response to the meal was significantly lower when whey protein was consumed as a preload compared to other groups (P < 0.001). In the second study, results showed no difference between preloads on ad libitum intake. Total intake was significantly higher after caloric preloads compared to water control (P < 0.05).

CONCLUSION

Casein and pea protein showed a stronger effect on food intake compared to whey when consumed as a preload. However, consuming the protein preload as a starter of a meal decreased its impact on food intake as opposed to consuming it 30 min before the meal.

The guinea pig as a model for metabolic programming of adiposity

BACKGROUND

The human infant accumulates body fat during intrauterine life. The guinea pig shares this characteristic and is born with similar adiposity; thus, it may be a relevant model to study obesity programming.

OBJECTIVE

The objective of this study was to evaluate guinea pig adipose tissue (AT) development and the effect of a maternal high-fat diet on the offspring's body composition.

DESIGN

In experiment 1, adipogenesis dynamics were evaluated at 3, 10, 21, and 136 d in epididymal and retroperitoneal AT with the use of (2)H(2)O labeling. In experiment 2, dams received a control or high-fat diet from mating to 21 d after delivery. The offspring received a high-fat diet from 22 to 105 d; adiposity was measured at 2, 21, 54, and 97 d.

RESULTS

The fractional proliferation rate (FPR) of cells in epididymal AT was 25.2% of cells synthesized in 5 d at 3 d of age and decreased over time (P < 0.001). Age had no effect on retroperitoneal FPR (P = 0.179). In both depots, the fractional synthesis rate (FSR) of palmitate decreased extensively from day 3 to day 10, increasing by day 21 and declining by day 136 (P < 0.001). The FSR of triglycerides decreased with age (P < 0.001). A maternal high-fat diet increased the offspring's adiposity at 2 d and 21 d (P < 0.05) but had no effect on body composition later in life.

CONCLUSIONS

Adipogenesis in the guinea pig is very active during early life and was altered by a maternal high-fat diet; thus, it is an adequate model for intrauterine fat deposition. However, there were no effects of maternal diet later in life.

The fat:carbohydrate energy ratio of the weaning diet programs later susceptibility to obesity in male sprague dawley rats

Dietary fat intake, which is high during suckling, is markedly reduced when food and drinks are introduced into the diet. We investigated whether alterations in the fat:carbohydrate (CHO) content of the weaning diet influenced the later development of adiposity and insulin sensitivity. Three groups of male rats (24/group) were fed from age 16-37 d (phase I) with weaning diets varying in their fat:CHO energy (E) ratios, 10:70 low-fat, high-CHO (LFHC); 30:50 medium-fat, medium-CHO (MFMC), and 60:30 high-fat, high-CHO (HFLC), on an isocaloric basis. Then, all groups consumed ad libitum first a low-fat diet (13% fat E) for 30 wk (phase II) and subsequently a high-fat diet (45% fat E) for another 18 wk (phase III). At the end of phase I, the group fed the HFLC diet demonstrated higher plasma glucose and insulin responses to an oral glucose tolerance test (P < 0.05), but this effect was transient and did not persist into adulthood (phases II and III). By contrast, when challenged with a high-fat diet later in life (age 35.3-53.3 wk), the LFHC group had greater gains in weight (as percent initial weight) and body fat (as absolute and percent body weight) than the other 2 groups that had been weaned with diets higher in fat (P < 0.04 for all). These results provide evidence that metabolic programming by altering the dietary fat:CHO ratio can occur during the weaning period and emphasizes the importance of the fat:CHO ratio of the complementary diet and its relation to the susceptibility to develop adiposity later in life.

Effect of oral sebacic Acid on postprandial glycemia, insulinemia, and glucose rate of appearance in type 2 diabetes

OBJECTIVE

Dicarboxylic acids are natural products with the potential of being an alternate dietary source of energy. We aimed to evaluate the effect of sebacic acid (a 10-carbon dicarboxylic acid; C10) ingestion on postprandial glycemia and glucose rate of appearance (Ra) in healthy and type 2 diabetic subjects. Furthermore, the effect of C10 on insulin-mediated glucose uptake and on GLUT4 expression was assessed in L6 muscle cells in vitro.

RESEARCH DESIGN AND METHODS

Subjects ingested a mixed meal (50% carbohydrates, 15% proteins, and 35% lipids) containing 0 g (control) or 10 g C10 in addition to the meal or 23 g C10 as a substitute of fats.

RESULTS

In type 2 diabetic subjects, the incremental glucose area under the curve (AUC) decreased by 42% (P<0.05) and 70% (P<0.05) in the 10 g C10 and 23 g C10 groups, respectively. At the largest amounts used, C10 reduced the glucose AUC in healthy volunteers also. When fats were substituted with 23 g C10, AUC of Ra was significantly reduced on the order of 18% (P<0.05) in both healthy and diabetic subjects. The insulin-dependent glucose uptake by L6 cells was increased in the presence of C10 (38.7±10.3 vs. 11.4±5.4%; P=0.026). This increase was associated with a 1.7-fold raise of GLUT4.

CONCLUSIONS

Sebacic acid significantly reduced hyperglycemia after a meal in type 2 diabetic subjects. This beneficial effect was associated with a reduction in glucose Ra, probably due to lowered hepatic glucose output and increased peripheral glucose disposal.

Rosemary (Rosmarinus officinalis L.) leaf extract limits weight gain and liver steatosis in mice fed a high-fat diet

The objective of this study was to investigate the effects of rosemary (Rosmarinus officinalis L.) leaf extract (RE) on the prevention of weight gain and associated metabolic disorders in mice fed a high-fat diet. For this purpose, RE was administered for 50 days at 20 or 200 mg/kg body weight (BW) to mice fed a high-fat diet. Body weight was monitored during the study and body composition was measured before and at the end of the intervention. Glucose tolerance, assessed by an intraperitoneal glucose tolerance test (IPGTT), and hepatic and faecal lipid contents were determined at the end of the study. Treatment with 200 mg/kg BW of RE induced a significant reduction of weight and fat mass gain (-64% and -57%, respectively) associated with an increase of faecal lipid excretion. This effect appears to be related to the inhibition of pancreatic lipase activity induced by RE, as demonstrated IN VITRO. While glucose tolerance and fasting glycaemia were not affected by RE treatment, hepatic triglyceride levels were decreased by 39% in RE-treated mice. Administration of the lower dose of RE (20 mg/kg BW) was ineffective on all the parameters measured. In conclusion, our results demonstrate that consumption of 200 mg/kg BW of RE can limit weight gain induced by a high-fat diet and protect against obesity-related liver steatosis.

A low alpha-linolenic intake during early life increases adiposity in the adult guinea pig

Background

The composition of dietary fatty acids (FA) during early life may impact adult adipose tissue (AT) development. We investigated the effects of α-linolenic acid (ALA) intake during the suckling/weaning period on AT development and metabolic markers in the guinea pig (GP).

Methods

Newborn GP were fed a 27%-fat diet (w/w %) with high (10%-ALA group), moderate (2.4%-ALA group) or low (0.8%-ALA group) ALA content (w/w % as total FA) until they were 21 days old (d21). Then all animals were switched to a 15%-fat diet containing 2% ALA (as total FA) until 136 days of age (d136).

Results

ALA and docosapentaenoic acid measured in plasma triglycerides (TG) at d21 decreased with decreasing ALA intake. Total body fat mass was not different between groups at d21. Adipose tissue TG synthesis rates and proliferation rate of total adipose cells, as assessed by ²H₂O labelling, were unchanged between groups at d21, while hepatic de novo lipogenesis was significantly 2-fold increased in the 0.8%-ALA group. In older GP, the 0.8%-ALA group showed a significant 15-%-increased total fat mass (d79 and d107, p < 0.01) and epididymal AT weight (d136) and tended to show higher insulinemia compared to the 10%-ALA group. In addition, proliferation rate of cells in the subcutaneous AT was higher in the 0.8%-ALA (15.2 ± 1.3% new cells/5d) than in the 10%-ALA group (8.6 ± 1.7% new cells/5d, p = 0.021) at d136. AT eicosanoid profiles were not associated with the increase of AT cell proliferation.

Conclusion

A low ALA intake during early postnatal life promotes an increased adiposity in the adult GP.

Comparison of two models of intrauterine growth restriction for early catch-up growth and later development of glucose intolerance and obesity in rats

Two models of intrauterine growth restriction, maternal food restriction (FR), and dexamethasone (DEX) exposure were compared for early postnatal catch-up growth and later development of glucose intolerance and obesity in Sprague-Dawley rats. Mated dams were randomly divided into three groups at 10 days gestational age. Group FR was food restricted (50% of nongestating rats) during the last 11 days of gestation; Group DEX received DEX injections during the last week of gestation, and Group CON, the control group, had no intervention. Birth weight, catch-up growth, body weight, and food intake were measured in male offspring for 22 wk. Body composition, blood glucose, and plasma insulin in response to a glucose load were assessed at 8, 16, and 22 wk. Pups from both FR and DEX dams had similarly lower birth weights than CON (22% and 25%, P < 0.0001), but catch-up growth, which occurred during the suckling period, was much more rapid in FR than DEX offspring (6 vs. 25 days, 95% CI). Postweaning, there were no significant differences between groups in food intake, body weight, body fat, and plasma insulin, but baseline plasma glucose at 22 wk and 2-h glucose area-under-the-curve at 8 and 22 wk were greater only in FR vs. CON offspring ( P < 0.05), thereby contrasting with the lack of significant differences between DEX and CON. These results suggest that prenatal food restriction is a more sensitive model than DEX exposure for studies aimed at investigating the link between low birth weight, early postnatal catch-up growth, and later development of glucose intolerance.

Interleukin-18 protein level is upregulated in adipose tissue of obese mice

In this study, we investigated the regulation of Interleukin-18 (IL-18) and caspase-1 mRNA and protein levels in adipose and liver tissue of obese (ob/ob) mice compared with ob/+ mice. In ob/ob mice, which have a twofold higher IL-18 plasma level as compared with lean mice, IL-18 mRNA expression was significantly reduced by 1.6-fold in adipose tissue, whereas protein level was enhanced fourfold as compared with ob/+ mice. However, caspase-1 mRNA expression and activity were significantly enhanced in adipose tissue of ob/ob mice. Conversely, both IL-18 mRNA and protein levels were slightly enhanced, but caspase-1 activity was reduced in liver of ob/ob mice as compared with lean mice. In conclusion, we show that adipose and hepatic IL-18 protein expressions are increased in obese mice. However, in contrast to liver, the adipose IL-18 protein level appears to be upregulated through a post-transcriptional mechanism probably involving caspase-1.

Impact of intrauterine growth retardation and early protein intake on growth, adipose tissue, and the insulin-like growth factor system in piglets

Small birth weight and excess of early protein intake are suspected to enhance later adiposity. The present study was undertaken to determine the impact of diets differing in protein content on short-term growth, adipose tissue development, and the insulin-like growth factor (IGF) system in piglets. Normal (NW) and small (SW) birth weight piglets were fed milk-replacers formulated to provide an adequate (AP) or a high protein (HP) supply between 7 and 28 d of age. The fractional growth rate was higher (p < 0.01) in SW than in NW piglets. At 7 d of age, the lower (p < 0.05) weight of perirenal adipose tissue relative to body mass in SW than in NW piglets did not involve significant changes in plasma IGF-I, leptin, or insulin-like growth factor binding protein levels, but involved differences (p < 0.05) in the expression of IGF-I and leptin in adipose tissue. Growth rates did not differ between AP and HP piglets. At 28 d of age, HP piglets had lower (p < 0.001) relative perirenal adipose tissue weight but did not differ clearly from AP piglets with regard to the IGF system. It remains to be determined whether piglets fed such a high protein intake will stay subsequently with a low adiposity.

Neonatal dietary supplementation of arachidonic acid increases prostaglandin levels in adipose tissue but does not promote fat mass development in guinea pigs

The role of arachidonic acid (AA) on the development of adipose tissue is still controversial since its metabolites, i.e., prostaglandins, can either stimulate or inhibit preadipocyte differentiation in vitro. In the present study, we evaluated the effects of early postnatal supplementation of AA on body weight and adipose tissue development in guinea pigs. Male newborn guinea pigs were fed for 21 days ( day 21) with diets (milk and pellet) supplemented (+AA) or not (−AA) with 1.2% (total fatty acids) AA. From day 21 to day 105 both groups were fed a chow diet. The 21-days-old +AA pups showed a twofold higher AA accretion in phospholipids associated with a two- to sixfold increase in several prostaglandins, such as 6-keto PGF1α(the stable hydrolysis product of PGI2), PGF2α, PGE2, and PGD2in adipose tissue, compared with the −AA group. No difference in fat pad and body weight, aP2, and leptin gene expression in adipose tissue, fasting plasma glucose, free-fatty acids, and triglyceride concentration was observed between groups at day 21 or day 105. These results show that dietary supplementation of AA during the suckling/weaning period increases prostaglandin levels in adipose tissue but does not influence early fat mass development in the guinea pig.

Contribution of mesothelial cells in the expression of inflammatory-related factors in omental adipose tissue of obese subjects

OBJECTIVE

The objective of this study was to determine the contribution of mesothelial cells, present in human omental adipose tissue (OAT) but not in the subcutaneous depot (SAT), on the expression of inflammation-related factors.

DESIGN

Comparison of the expression profiles of inflammation-related genes in mesothelial cells with those in the adipocyte-enriched (AEF) and stromal vascular fractions (SVF) and localization of interleukin-18 (IL-18) expression in adipose depots.

SUBJECTS

Eleven obese Caucasian female subjects undergoing gastric bypass surgery (body mass index: 43.6+/-1.3 kg/m(2); age: 41.6+/-2.3 years).

MEASUREMENTS

The expression profiles of cytokine and chemokine-related genes in mesothelial cells and in cell fractions prepared from OAT were assessed by the microarray technique. The differential expression of IL-18 was confirmed by real-time PCR and the protein was localized in adipose depots by immunohistochemistry.

RESULTS

Microarray data analysis demonstrated that, of the 16 cytokine and chemokine-related genes that were upregulated in mesothelial cells compared with the AEF, IL-18 was the cytokine with the highest differential expression. IL-18 expression was similar in mesothelial cells and the SVF. In both SAT and OAT, IL-18 was immunolocalized in neutrophils and mast cells, but not in macrophages nor adipocytes. This cytokine was also detected in mesothelial cells in OAT. This additional source of expression may explain the higher IL-18 expression levels in OAT than SAT (+5.9-fold).

CONCLUSION

By their capacity to express inflammatory-related factors, and in particular the proinflammatory cytokine IL-18 in OAT, mesothelial cells appear as a new player in the process of low-grade inflammation associated with obesity.

Administration of Cyperus rotundus tubers extract prevents weight gain in obese Zucker rats

Cyperus rotundus L. (Cyperaceae; C. rotundus) is an Indian medicinal plant demonstrated to exert multiple health benefits. The purpose of the present study was to test the biological efficacy of C. rotundus tubers extract on weight control in obese Zucker rats. It was demonstrated that administration of 45 or 220 mg/kg/day of C. rotundus tubers hexane extract for 60 days in Zucker rats induced a significant reduction in weight gain without affecting food consumption or inducing toxicity. In vitro, 250 microg/mL of this extract was able to stimulate lipolysis in 3T3-F442 adipocytes suggesting that this medicinal plant contains activators of beta-adrenoreceptors (AR). The binding assay performed on the rat beta3-AR isoform, known to induce thermogenesis, demonstrated that C. rotundus tubers extract can consistently and effectively bind to this receptor. These data suggest that the effect on weight gain exerted by C. rotundus tubers extract may be mediated, at least partially, through the activation of the beta3-AR. In conclusion, C. rotundus tubers extract prove to be a new herbal supplement for controlling body weight preferentially in beta3-AR sensitive species.

Effect of a thermogenic beverage on 24-hour energy metabolism in humans

OBJECTIVE

To test whether consumption of a beverage containing active ingredients will increase 24-hour energy metabolism in healthy, young, lean individuals.

RESEARCH METHOD AND PROCEDURES

Thirty-one male and female subjects consumed 3 x 250-mL servings of a beverage containing green tea catechins, caffeine, and calcium for 3 days in a single-center, double-blind, placebo-controlled, cross-over design study. On the 3rd day, 23-hour energy metabolism, extrapolated to 24-hour, was measured in a calorimeter chamber. Blood pressure and heart rate were measured, and total day and night urines were analyzed for urea and catecholamine excretion.

RESULTS

Twenty-four-hour energy expenditure (EE) and 24-hour fat oxidation were lower in women than in men (p < 0.0001 and p < 0.015, respectively). Although there were no treatment or treatment/gender effects on substrate oxidation, treatment increased 24-hour EE by 106 +/- 31 kcal/24 hours (p = 0.002), equivalent to 4.7 +/- 1.6 kcal/h (day; p = 0.005) and 3.3 +/- 1.5 kcal/h (night; p = 0.04). No significant differences were observed in hemodynamic parameters.

DISCUSSION

The present study provides evidence that consumption of a beverage containing green tea catechins, caffeine, and calcium increases 24-hour EE by 4.6%, but the contribution of the individual ingredients cannot be distinguished. Although this increase is modest, the results are discussed in relation to proposed public health goals, indicating that such modifications are sufficient to prevent weight gain. When consumed regularly as part of a healthy diet and exercise regime, such a beverage may provide benefits for weight control.

Dietary fat and fat types as early determinants of childhood obesity: a reappraisal

BACKGROUND

The growing prevalence of childhood overweight and obesity has renewed interest in determining the influence of the maternal and infant diet on the risk of developing excess fat mass later in life.

APPROACH

Review of available human and animal data reporting the effects of dietary fat and fat types early in life on adipose development.

RESULTS

Rodent studies tend to show that maternal high-fat feeding during pregnancy and lactation results in increased adiposity of the offspring. Nevertheless, today there is a lack of population-based studies investigating this potential detrimental effect of maternal high-fat intake. Most epidemiological studies, performed so far, do not find any association between the level of dietary fat intake of infants and children and body weight and/or fatness. Regarding fat types exposure to high levels of dietary n-6 fatty acids during gestation and post-natal life, has been shown to promote obesity in mice. Nevertheless, other rodent studies do not demonstrate such an effect.

CONCLUSION

There is no evidence supporting a restriction of fat intake during the first two post-natal years but the potential detrimental effects of maternal high-fat intake during gestation should be further investigated. The role of dietary fat types as early determinants of childhood obesity has so far been poorly studied. Robust evidence to support the adipogenic effects of n-6 fatty acids enriched-diets is currently lacking but this hypothesis is of importance and should be further evaluated in different animal models as well as in longitudinal human studies.

Long-term cultured human myotubes decrease contractile gene expression and regulate apoptosis-related genes

The present study examined time-dependent changes in the gene expression profile of long-term cultured human myotubes. Microarray transcriptional analysis was performed in a primary culture of differentiated myotubes from one subject over seven weeks. This analysis showed a main gradual fall in genes of the contractile apparatus, and a broad upregulation of genes involved in cell development and growth, followed by stress response and signal transduction. Glucose metabolism was also monitored, but no significant alterations in glucose uptake, oxidation or glycogen storage were observed. Mitochondrial membrane potential, or the amount of membrane lipid peroxides, remained similarly unchanged, nor was lactate dehydrogenase leakage observed. Time-dependent changes in eight genes were validated by real-time RT-PCR in primary cultured myotubes from four subjects, of similar age and isolated after equivalent replication cycles in vitro and differentiated over seven weeks. Insulin-like growth factor-binding protein 2 (IGFBP2), a modulator of the IGF signal, was upregulated. The antiapoptotic gene heat-shock 70-kd protein 2 (HSPA2) was induced, whereas the proapoptotic tumor necrosis factor receptor superfamily, member 25 (WSL-1) was suppressed. A decline in the muscle-specific gene M-cadherin and contraction genes, such as slow-twitch troponin I (TNNI1) and myosin heavy chain 2 (MYH2), myosin light chain 1 (MYL1) and myosin-binding protein H (MYBPH), which are expressed in adult fast-twitch muscle, was shown. In summary, these data demonstrate extensive downregulation of contractile genes and modulation of apoptosis-related genes, in favour of cell survival, during maintenance of cultured human myotubes.

Effect of sucrose and saturated-fat diets on mRNA levels of genes limiting muscle fatty acid and glucose supply in rats

In this study, we examined whether the increased availability of lipids in blood resulting from two types of diet manipulation regulated metabolic gene expression in the skeletal muscle of rats. Feeding for 4 wk on an isocaloric-sucrose or a hypercaloric-fat diet increased plasma TAG in the fed condition by increments of 70 and 40%, respectively, and increased fasting insulinemia (approximately 3-fold) compared with a starch diet. The fat diet impaired glucose tolerance and caused obesity, whereas sucrose-fed rats maintained their normal weight. We analyzed the expression of genes that regulate the exogenous FA supply (LPL, FAT/CD36, FATP1), synthesis (ACC1), glucose (GLUT4, GLUT1, HK2, GFAT1, glycogen phosphorylase) or glycerol (glycerol kinase) provision, or substrate choice for oxidation (PDK4) in gastrocnemius and soleus muscles at the end of the glucose tolerance test. LPL, FAT/CD36, FATP1, PDK4, and GLUT4 mRNA as well as glycogen phosphorylase and glycerol kinase activity levels in both muscles were unchanged by the diets. Increased mRNA levels of GLUT1 (1.6- and 2.6-fold, respectively) and GFAT1 (about 1.7-fold) in gastrocnemius, and of ACC1 (about 1.5-fold) in soleus, were found in both the sucrose and fat groups. In the fat group, HK2 mRNA was also higher (1.8-fold) in the gastrocnemius. Both sucrose and saturated-fat diets prompted hyperinsulinemia and hyperlipemia in rats. These metabolic disturbances did not alter the expression of LPL, FAT/CD36, FATP1, PDK4, and GLUT4 genes or glycogen phosphorylase and glycerol kinase activity levels in either analyzed muscle. Instead, they were linked to the coordinated upregulation in gastrocnemius of genes that govern glucose uptake and the hexosamine pathway, namely, GLUT1 and GFAT1, which might contribute to insulin resistance.

Liver X receptor preferentially activates de novo lipogenesis in human preadipocytes

The liver X receptor (LXR) was demonstrated to play a key role in cholesterol metabolism in liver, intestine and macrophage. However, its function on the regulation of preadipocyte differentiation remains unclear since contradictory results were reported. The objective of the present study was to unravel the functionality of LXR in human preadipocytes. We show that the LXR agonist T0901317 strongly stimulated the expression of SREBP-1c and the lipogenic enzymes ACC-1, FAS and SCD-1 in both the human preadipose cell line Chub-S7 as well as human primary stromal vascular fraction (SVF) cells. The effects on gene expression were associated with the stimulation of de novo lipogenesis in both cell models, resulting in the induction of lipid accumulation. In contrast with a PPARgamma agonist (BRL49653), T0901317 enhanced only slightly the expression of PPARgamma dependent genes (PPARgamma, aP2 and adiponectin) in Chub-S7 cells and failed to change their expression in human SVF cells. These results show that LXR stimulated preferentially triglyceride accumulation in human preadipocytes via the induction of de novo lipogenesis, rather than activating the differentiation process through PPARgamma activation.

Protein quality and quantity in cow's milk-based formula for healthy term infants: past, present and future

The development of infant formula with optimized protein quality and quantity has been, and still is, the subject of intense investigation. A better understanding of the protein composition of breast milk and infant needs in association with technological breakthroughs in cow's milk fractionation, has led to the development of infant formulas with a protein content that is closer to that of human milk. Today, infant formulas with a protein/energy ratio of 1.8 g/100 kcal are commercially available. These formulas have been shown to be safe and nutritionally adequate for term infants. However, the short-term and potentially long-term metabolic benefits of formulas with reduced protein content have still to be elucidated and are currently under investigation. In addition to providing amino acids as building blocks for growth, milk is the source of numerous bioactive factors/hormones which are involved in multiple physiological processes. Continuous efforts are being made to identify new bioactive compounds in human milk. However, a better understanding of their biological functions in suckling infants as well as a comparison with their bovine counterparts are needed. Technological processes, which preserve some bioactive factors in cow's milk already exist. These processes could be applied to infant formulas.

Aspergillus oryzae produces compounds inhibiting cholesterol biosynthesis downstream of dihydrolanosterol

The formation of cholesterol synthesis inhibiting molecules by five different strains of the koji mold Aspergillus oryzae was studied. After growing these strains on a complex liquid medium we found in crude organic phase extracts and specific fractions there from compounds inhibiting cholesterol synthesis in human hepatic T9A4 cells in vitro at enzyme sites downstream of dihydrolanosterol. This was evidenced by using different radioactively labeled precursors, namely acetate, mevalonate, 24,25-dihydro-[24,25-(3)H2]-lanosterol or [3-(3)H]-lathosterol.

Immortalization of human preadipocytes

Primary human preadipocytes in culture are characterized by a low proliferative capacity associated with a rapid decline of differentiation ability during subculturing; thereby limiting their use as cellular model. Cellular immortalization constitutes an interesting approach for establishing cell lines presenting an unlimited life span and a maintained differentiation capacity. Different procedures for developing immortalized human preadipocytes are discussed in this review. Transformation of human preadipocytes with the simian virus 40 large T-antigen (SV40 T-Ag) permitted the development of immortalized cells; however these cells could not maintain their capacity to differentiate into adipocytes. This limitation may be explained by the ability of SV40 T-Ag to inhibit transcriptional factors involved in the differentiation of preadipocyte. Reconstitution of the telomerase activity by stable expression of the hTERT (human telomerase catalytic subunit) gene was able to partially extend the lifespan of primary preadipocytes but not to promote cellular immortalization. However, a combined expression of hTERT and the E7 oncoprotein of human papillomavirus type 16, generated human preadipocytes with both an unlimited life span and a preserved adipogenic potential. This approach appears to be an effective method for establishing human preadipose cell lines for studying adipocyte differentiation and metabolism.

beta3-adrenoceptor agonist prevents alterations of muscle diacylglycerol and adipose tissue phospholipids induced by a cafeteria diet

Background

Insulin resistance induced by a high fat diet has been associated with alterations in lipid content and composition in skeletal muscle and adipose tissue. Administration of β3-adrenoceptor (β3-AR) agonists was recently reported to prevent insulin resistance induced by a high fat diet, such as the cafeteria diet. The objective of the present study was to determine whether a selective β3-AR agonist (ZD7114) could prevent alterations of the lipid profile of skeletal muscle and adipose tissue lipids induced by a cafeteria diet.

Methods

Male Sprague-Dawley rats fed a cafeteria diet were treated orally with either the β3-AR agonist ZD7114 (1 mg/kg per day) or the vehicle for 60 days. Rats fed a chow diet were used as a reference group. In addition to the determination of body weight and insulin plasma level, lipid content and fatty acid composition in gastronemius and in epididymal adipose tissue were measured by gas-liquid chromatography, at the end of the study.

Results

In addition to higher body weights and plasma insulin concentrations, rats fed a cafeteria diet had greater triacylglycerol (TAG) and diacylglycerol (DAG) accumulation in skeletal muscle, contrary to animals fed a chow diet. As expected, ZD7114 treatment prevented the excessive weight gain and hyperinsulinemia induced by the cafeteria diet. Furthermore, in ZD7114 treated rats, intramyocellular DAG levels were lower and the proportion of polyunsaturated fatty acids, particularly arachidonic acid, in adipose tissue phospholipids was higher than in animals fed a cafeteria diet.

Conclusions

These results show that activation of the β3-AR was able to prevent lipid alterations in muscle and adipose tissue associated with insulin resistance induced by the cafeteria diet. These changes in intramyocellular DAG levels and adipose tissue PL composition may contribute to the improved insulin sensitivity associated with β3-AR activation.

Fiber type- and fatty acid composition-dependent effects of high-fat diets on rat muscle triacylglyceride and fatty acid transporter protein-1 content

Intramuscular triacylglyceride (TAG) is considered an independent marker of insulin resistance in humans. Here, we examined the effect of high-fat diets, based on distinct fatty acid compositions (saturated, monounsaturated or n-6 polyunsaturated), on TAG levels and fatty acid transporter protein (FATP-1) expression in 2 rat muscles that differ in their fiber type, soleus, and gastrocnemius; the relationship to whole body glucose intolerance was also studied. Compared with carbohydrate-fed rats, the groups subjected to any one of the high-fat diets consistently exhibited enhanced body weight gain and adiposity, elevated plasma free fatty acids and TAG in the fed condition, hyperinsulinemia, and glucose intolerance. TAG content was consistently higher in soleus than in gastrocnemius, but was only significantly elevated by the n-6 polyunsaturated-based diet. FATP-1 levels in soleus were double those in gastrocnemius muscle in carbohydrate-fed animals. High-fat diets caused an elevation in FATP-1 protein content in soleus, but a reduction in gastrocnemius. In conclusion, the hyperinsulinemic hyperlipidemic condition upregulates FATP-1 expression in soleus and downregulates that of gastrocnemius. Hypercaloric saturated, monounsaturated, or n-6 polyunsaturated lipid diets cause equivalent whole body insulin resistance in rats, but only an n-6 polyunsaturated acid-based diet triggers intramuscular TAG accumulation.

Reconstitution of telomerase activity combined with HPV-E7 expression allow human preadipocytes to preserve their differentiation capacity after immortalization

Overexpression of SV40 T-antigen (SV40 T-Ag) has been widely used to overcome replicative senescence of human primary cells and to promote cell immortalization. However, in the case of certain cell types, such as preadipocytes, the differentiation process of immortalized cells is blocked by SV40 T-Ag expression. In this study, human telomerase reverse transcriptase (hTERT) and papillomavirus E7 oncoprotein (HPV-E7) genes were coexpressed in human preadipocytes to test whether this combination could maintain cell differentiation capacity after immortalization. We demonstrated that the HPV-E7/hTERT expressing preadipocytes displayed an indefinite life span. Interestingly, immortalized cells were diploid and presented no chromosomic alterations. These immortalized cells were able to accumulate and hydrolyze intracellular triglycerides and to express adipocyte markers. These data demonstrate, for the first time, that coexpression of hTERT and HPV-E7 in human preadipocytes allows cells not only to display an indefinite life span but also to retain their capacity to differentiate.

3-methylindole-induced toxicity to human bronchial epithelial cell lines

Transfected BEAS-2B cells that express different cytochrome P450 enzymes were used to assess whether human bronchial epithelial cell lines are target cells for 3-methylindole (3MI)-induced damage. Four different transfected BEAS-2B lines overexpressing P450s 2A6, 3A4, 2F1, and 2E1 (B-CMV2A6, B-CMV3A4, B-CMV2F1, and B-CMV2E1), respectively, were compared. The B-CMV2F1 and B-CMV3A4 cells were the most susceptible to 3MI-mediated cytotoxicity, measured by leakage of lactate dehydrogenase into the medium after a 48-h incubation. The toxicity was ameliorated by pretreatment with 1-aminobenzotriazole (ABT). Depletion of glutathione with diethylmaleate decreased the onset and increased the extent of cell death with 3MI. Thus, 3MI is cytotoxic to immortalized bronchial epithelial cells overexpressing 2F1 without concomitant depletion of GSH, but depletion of GSH modestly enhances the cytotoxicity of 3MI to human lung cells. Additional studies clearly demonstrated that a low concentration of 3MI (10 micro M) induced apoptosis in BEAS-2B cells that was measured by DNA fragmentation, and apoptosis was inhibited by the presence of ABT. The B-CMV2F1 cells overexpressing 2F1 demonstrated increased apoptosis (measured by Annexin-V binding) at 24 h with 100 micro M 3MI. Therefore, CYP2F1 in human bronchial epithelial lung cells may bioactivate 3MI to 3-methyleneindolenine, which induces programmed cell death at relatively low concentrations. Human lung cells may be susceptible to this prototypical pneumotoxicant.

Chondroitin and keratan sulfates have opposing effects on attachment and outgrowth of ventral mesencephalic explants in culture

During rat brain development, striatal proteoglycan (PG) expression shows specific spatio-temporal modifications suggesting a possible role in the guidance of its dopaminergic afferents. The effects of individual glycosaminoglycans (GAGs) on dopaminergic (DA) neuronal adhesion and outgrowth were therefore studied. We tested the behavior of dissociated embryonic rat mesencephalic cells cultivated on substrate-bound GAGs. Neuronal attachment was very limited and quantitative morphometry revealed variations in DA fiber outgrowth depending on the type and the concentration of GAG used. Next, we developed a cryoculture system to examine how neurons react toward GAGs expressed in situ. Rat brain slices from different developmental stages were used as substrates for embryonic mesencephalic explants. Preferential regions of adherence and outgrowth were observed: the striatum was found to be the most permissive, whereas the cortex was inhibitory. Western blotting experiments confirmed quantitative and qualitative changes in chondroitin sulfate (neurocan, phosphacan) and keratan sulfate (KS) containing PGs in these substrates and enzymatic digestion of GAGs before cryoculture revealed a substantial involvement of PGs in DA neuron adhesion and outgrowth. In particular, CSPGs seemed to mediate the permissive effect of the striatum, whereas KS confers an inhibitory effect to the cortex. PGs may thus be important for limiting midbrain projections to the striatum during development and for maintaining topography in the adult.

Cyclosporin A-induced free radical generation is not mediated by cytochrome P-450

1. Reactive oxygen species (ROS) have been proposed to play a role in the side effects of the immunosuppressive drug cyclosporin A (CsA). 2. The aim of this study was to investigate whether cytochrome P-450 (CYP) dependent metabolism of CsA could be responsible for ROS generation since it has been suggested that CsA may influence the CYP system to produce ROS. 3. We show that CsA (1 -- 10 microM) generated antioxidant-inhibitable ROS in rat aortic smooth muscle cells (RASMC) using the fluorescent probe 2,7-dichlorofluorescin diacetate. 4. Using cytochrome c as substrate, we show that CsA (10 microM) did not inhibit NADPH cytochrome P-450 reductase in microsomes prepared from rat liver, kidney or RASMC. 5. CsA (10 microM) did not uncouple the electron flow from NADPH via NADPH cytochrome P-450 reductase to the CYP enzymes because CsA did not inhibit the metabolism of substrates selective for several CYP enzymes that do not metabolize CsA in rat liver microsomes. 6. CsA (10 microM) did not generate more radicals in CYP 3A4 expressing immortalized human liver epithelial cells (T5-3A4 cells) than in control cells that do not express CYP 3A4. 7. Neither diphenylene iodonium nor the CYP 3A inhibitor ketoconazole were able to block ROS formation in rat aortic smooth muscle or T5-3A4 cells. 8. These results demonstrate that CYP enzymes do not contribute to CsA-induced ROS formation and that CsA neither inhibits NADPH cytochrome P-450 reductase nor the electron transfer to the CYP enzymes.

Comparative aflatoxin B(1) activation and cytotoxicity in human bronchial cells expressing cytochromes P450 1A2 and 3A4

Some epidemiological evidence suggests a link between the inhalation of aflatoxin B(1) (AFB(1))-contaminated grain dusts and increased lung cancer risk. However, the mechanisms of AFB(1) activation and action in human lung are not well understood. We compared AFB(1) action in SV40 immortalized human bronchial epithelial cells (BEAS-2B) with two transfected cell lines that stably express human cytochromes P450 (CYPs) 1A2 (B-CMV1A2) and 3A4 (B3A4), the principal CYPs thought to activate this mycotoxin in human liver. All three cell types retained catalytically active glutathione S-transferase, the key phase II enzyme that detoxifies metabolically activated AFB(1). B-CMV1A2 and B3A4 cells expressed methoxyresorufin-O-demethylase (MROD) and nifedipine oxidase activities, respectively, and were 3000- and 70-fold more susceptible, respectively, to the cytotoxic effects of AFB(1) than the control cell line (BEAS-2B). When cultured with a range of low, environmentally relevant AFB(1) concentrations (0.02-1.5 microM), control cells formed barely detectable AFB(1)-DNA adducts, whereas B-CMV1A2 cells formed significantly more adducts than B3A4 cells. In B-CMV1A2 cells, formation of AFB(1)-DNA adducts was inhibited by the CYP 1A2 inhibitor 7,8-benzoflavone, whereas formation of AFB(1)-DNA adducts in B3A4 cells was inhibited by the CYP 3A4 inhibitor 17alpha-ethynylestradiol. Competitive reverse transcription-PCR analysis showed that only the CYP-transfected cell lines expressed CYP mRNA. When adjusted for CYP mRNA expression, B-CMV1A2 cells were more efficient in the formation of cytotoxic and DNA-alkylating species at low AFB(1) concentrations, whereas B3A4 cells were more efficient at high concentrations. Our results affirm the hypothesis that, as in human liver microsomes, CYP 1A2 in human lung cells appears to have a more important role than CYP 3A4 in the bioactivation of low AFB(1) concentrations associated with many human exposures. Therefore, it is possible that under conditions in which appropriate CYPs are expressed in lung, inhalation of AFB(1) may result in increased risk of lung cancer in exposed persons.

A human cellular model for studying the regulation of glucagon-like peptide-1 secretion

GLP-1 (glucagon-like peptide-1) is a potent insulin secretagogue released from L cells in the intestine. The regulation of GLP-1 secretion has been described both in vivo and in vitro in several animal species, but data from human cellular models are lacking. For this purpose, factors and cell-signaling pathways regulating GLP-1 secretion were investigated in the NCI-H716 human intestinal cell line. After differentiation, these cells homogeneously produced 16.8 pmol GLP-1/mg protein with a basal release of 4.2% during a 2-h incubation period. Nutrients, such as palmitic acid, oleic acid, and meat hydrolysate, stimulated GLP-1 secretion in a dose-dependent manner, as did the cholinergic agonist carbachol and the neuromediator gastrin-releasing peptide. Along with stimulating GLP-1 release, gastrin-releasing peptide, like ionomycin, increased intracellular calcium levels. Activators of PKA and PKC were able to increase GLP-1 secretion in NCI-H716 cells. However, neither PKA activators nor meat hydrolysate increased proglucagon mRNA levels. These findings indicate that the NCI-H716 cell line constitutes a unique model to study the cellular mechanism of GLP-1 secretion in humans and suggest potential interspecies divergence in the regulation of proglucagon gene expression in enteroendocrine cells.

Overexpression of UCP3 in cultured human muscle lowers mitochondrial membrane potential, raises ATP/ADP ratio, and favors fatty acid vs. glucose oxidation

The skeletal muscle mitochondrial uncoupling protein-3 (UCP3) promotes substrate oxidation, but direct evidence for its metabolic role is lacking. Here, we show that UCP3 overexpression in cultured human muscle cells decreased mitochondrial membrane potential (DYm). Despite this, the ATP content was not significantly decreased compared with control cells, whereas ADP content was reduced and thus the ATP/ADP ratio raised. This finding was contrasts with the effect caused by the chemical protonophoric uncoupler, CCCP, which lowered DYm, ATP, and the ATP/ADP ratio. UCP3-overexpression enhanced oxidation of oleate, regardless of the presence of glucose, whereas etomoxir, which blocks fatty acid entry to mitochondria, suppressed the UCP3 effect. Glucose oxidation was stimulated in UCP3-overexpressing cells, but this effect was inhibited by oleate. UCP3 caused weak increase of both 2-Deoxyglucose uptake and glycolytic rate, which differed from the marked stimulation by CCCP. We concluded that UCP3 promoted nutrient oxidation by lowering DYm and enhanced fatty acid-dependent inhibition of glucose oxidation. Unlike the uncoupler CCCP, however, UCP3 raised the ATP/ADP ratio and modestly increased glucose uptake and glycolysis. We propose that this differential effect provides a biological significance to UCP3, which is up-regulated in metabolic stress situations where it could be involved in nutrient partitioning.

Metabolism of the beta-oxidized intermediates of N-nitrosodi-n-propylamine: N-nitroso-beta-hydroxypropylpropylamine and N-nitroso-beta-oxopropylpropylamine

The rat liver carcinogen N-nitrosodi-n-propylamine (NDPA) is metabolized to a propylating and methylating species in vivo. Metabolism to a methylating species is believed to require an initial hydroxylation by cytochrome P450s (P450s) to N-nitroso-beta-hydroxypropylpropylamine (NHPPA), which is oxidized to N-nitroso-beta-oxopropylpropylamine (NOPPA), followed by a P450-mediated depropylation to beta-oxopropyldiazotate, which non-enzymatically breaks down to the methylating agent. Purified rat liver P450 2B1 and rabbit liver 2E1 in the reconstituted system and liver microsomes from phenobarbital (PB) and pyridine (Pyr) treated rats readily metabolized NOPPA to a methylating species as determined by the in vitro formation of 7-methylguanine (m7Gua) in DNA. Exposure of cells derived from the human liver epithelium transfected with human 2E1 (T5-2E1) to NOPPA resulted in the formation of m7Gua DNA adducts and a dose dependent toxicity. In vitro incubation of NHPPA with microsomes from PB, Pyr and non-treated (NT) rats and a human microsomal sample also resulted in m7Gua formation. P450s 2B1 and 2E1 oxidized NHPPA to NOPPA, forming 16.5 +/- 3.1 and 20.0 +/- 4.4 pmol NOPPA/pmol P450 in 1 h, respectively. Rat liver cytosol, in the presence of NAD+, oxidized NHPPA to NOPPA at a rate of 13.7 +/- 3.0 pmol/min/mg protein while microsomes from NT rats catalyzed this reaction at 95.6 +/- 16.5 pmol/min/mg protein. Cells derived from hamster lung tissue (V79 control) and T5-neo cells oxidized NHPPA to NOPPA. This oxidation was about 15 fold higher in T5-2E1 or V79 cells transfected with human 2E1 or rat 2B1, respectively. The results are consistent with the putative sequential oxidation pathway and suggest that, at the concentrations tested, oxidation of NHPPA to NOPPA may be predominantly mediated by cytochrome P450s. In addition, it appears that rabbit, rat and human P450 2E1 can catalyze both oxidations.

DAG accumulation from saturated fatty acids desensitizes insulin stimulation of glucose uptake in muscle cells

The increased availability of saturated lipids has been correlated with development of insulin resistance, although the basis for this impairment is not defined. This work examined the interaction of saturated and unsaturated fatty acids (FA) with insulin stimulation of glucose uptake and its relation to the FA incorporation into different lipid pools in cultured human muscle. It is shown that basal or insulin-stimulated 2-deoxyglucose uptake was unaltered in cells preincubated with oleate, whereas basal glucose uptake was increased and insulin response was impaired in palmitate- and stearate-loaded cells. Analysis of the incorporation of FA into different lipid pools showed that palmitate, stearate, and oleate were similarly incorporated into phospholipids (PL) and did not modify the FA profile. In contrast, differences were observed in the total incorporation of FA into triacylglycerides (TAG): unsaturated FA were readily diverted toward TAG, whereas saturated FA could accumulate as diacylglycerol (DAG). Treatment with palmitate increased the activity of membrane-associated protein kinase C, whereas oleate had no effect. Mixture of palmitate with oleate diverted the saturated FA toward TAG and abolished its effect on glucose uptake. In conclusion, our data indicate that saturated FA-promoted changes in basal glucose uptake and insulin response were not correlated to a modification of the FA profile in PL or TAG accumulation. In contrast, these changes were related to saturated FA being accumulated as DAG and activating protein kinase C. Therefore, our results suggest that accumulation of DAG may be a molecular link between an increased availability of saturated FA and the induction of insulin resistance.

Evidence for cytochrome P4501A2-mediated protein covalent binding of thiabendazole and for its passive intestinal transport: use of human and rabbit derived cells

Thiabendazole (TBZ), an anthelmintic and fungicide benzimidazole, was recently demonstrated to be extensively metabolized by cytochrome P450 (CYP) 1A2 in man and rabbit, yielding 5-hydroxythiabendazole (5OH-TBZ), the major metabolite furtherly conjugated, and two minor unidentified metabolites (M1 and M2). In this study, exposure of rabbit and human cells to 14C-TBZ was also shown to be associated with the appearance of radioactivity irreversibly bound to proteins. The nature of CYP isoforms involved in this covalent binding was investigated by using cultured rabbit hepatocytes treated or not with various CYP inducers (CYP1A1/2 by beta-naphthoflavone, CYP2B4 by phenobarbital, CYP3A6 by rifampicine, CYP4A by clofibrate) and human liver and bronchial CYP-expressing cells. The covalent binding to proteins was particularly increased in beta-naphthoflavone-treated rabbit cells (2- to 4-fold over control) and human cells expressing CYP1A2 (22- to 42-fold over control). Thus, CYP1A2 is a major isoenzyme involved in the formation of TBZ-derived residues bound to protein. Furthermore, according to the good correlation between covalent binding and M1 or 5OH-TBZ production, TBZ would be firstly metabolized to 5OH-TBZ and subsequently converted to a chemically reactive metabolic intermediate binding to proteins. This metabolic activation could take place preferentially in liver and lung, the main biotransformation organs, rather than in intestines where TBZ was shown to be not metabolized. Moreover, TBZ was rapidly transported by passive diffusion through the human intestinal cells by comparison with the protein-bound residues which were not able to cross the intestinal barrier. Consequently, the absence of toxicity measured in intestines could be related to the low degree of TBZ metabolism and the lack of absorption of protein adducts. Nevertheless, caution is necessary in the use of TBZ concurrently with other drugs able to regulate CYP1A2, particularly in respect to liver and lung tissues, recognised as sites of covalent-binding.

Metabolism-dependent stimulation of reactive oxygen species and DNA synthesis by cyclosporin A in rat smooth muscle cells

The clinical use of the immunosuppressive drug cyclosporin A (CsA) is limited by its side effects, namely hypertension and nephrotoxicity. It has been proposed that reactive oxygen species (ROS) could be involved as mediators of the toxic effects of CsA. Here, we have studied the possible interrelationship between CsA metabolism and production of ROS. Using cultures of rat aortic smooth muscle cells (RASMC), CsA (1 microM) produced a rapid (within 10 min) increase in reactive oxygen species, detected by oxidation of the fluorescent probes 2,7-dichlorofluorescin and dihydrorhodamine-123. DNA synthesis was increased in the presence of CsA as assessed by [3H]thymidine incorporation. The superoxide dismutase inhibitor diethyldithiocarbamate (1 mM) and the iron chelator desferal (5 microM), as well as ketoconazole (1 microM) and troleandomycin (10 microM), inhibitors of the cytochrome P-450 3A, were able to block both effects. High-performance liquid chromatography analysis revealed that RASMC were capable to metabolize CsA to its primary metabolites (AM1, AM9 and AM4N), and that their formation was inhibited by ketoconazole and troleandomycin. Furthermore, mRNAs encoding cytochrome P-450 3A1 and 3A2 were detected in RASMC by reverse transcriptase-polymerase chain reaction. Our data suggest that CsA is metabolized by cytochrome P-450 3A in RASMC producing reactive oxygen species, most likely superoxide and the hydroxyl radical, known to damage lipids and DNA.

Hepatic metabolism of diclofenac: role of human CYP in the minor oxidative pathways

The aim of this study was to re-examine the human hepatic metabolism of diclofenac, with special focus on the generation of minor hydroxylated metabolites implicated in the idiosyncratic hepatotoxicity of the drug. Different experimental approaches were used: human hepatocytes, human microsomes, and engineered cells expressing single human CYP (cytochromes P450). Human hepatocytes formed 3'-hydroxy-, 4'-hydroxy-, 5-hydroxy- 4',5-dihydroxy-, and N,5-dihydroxydiclofenac, as well as several lactams. Formation of 4'- and 5-hydroxydiclofenac by human liver microsomes followed a Michaelis-Menten kinetics (Km 9 +/- 1 microM; Vmax 432 +/- 15 pmol/min/mg and Km 43 +/- 5 microM; and Vmax 15.4 +/- 0.6 pmol/min/mg, respectively). Secondary metabolites were detected after incubation of 5-hydroxydiclofenac with human liver microsomes, yielding 4',5-dihydroxydiclofenac (Km 15 +/- 1 microM; Vmax 96 +/- 3 pmol/min/mg) and small amounts of N,5-dihydroxydiclofenac (non-Michaelis-Menten kinetics). Based on microsome studies and the incubations with human hepatocytes and engineered cells, we estimated that in vivo CYP2C9 would be exclusively responsible for the 4' hydroxylation of diclofenac (>99.5%) as well as 5-hydroxydiclofenac (>97%). CYP2C9 was exclusively responsible for the formation of 3'-hydroxydiclofenac. Multiple regression analysis evidenced that the rate of production of 5-hydroxydiclofenac in human microsomes followed the algorithm: 0.040 x S-mephenytoin 4'-hydroxylation + 0.083 x tolbutamide methylhydroxylation, (multiple correlation coefficient = 0.969). However, the incubation of diclofenac with cell lines expressing different human CYP suggested that 7 isoforms could be involved. Comparison of data obtained with CYP-expressing cells and human hepatocytes suggests that CYP2C8 > CYP2C19 approximately CYP2C18 >> CYP2B6 are the isoforms implicated in the 5-hydroxylation of diclofenac in vivo.

Immortalized human corneal epithelial cells for ocular toxicity and inflammation studies

PURPOSE

To develop a metabolically competent, human immortalized corneal epithelial cell line for use in toxicity and inflammation studies.

METHODS

Primary corneal epithelial cells (P-CEPI) were immortalized by a recombinant simian virus (SV)40 T antigen retroviral vector defective for viral replication. The cells were grown in serum-free medium with the addition of bovine pituitary extract, cloned at passage 15 and one of the best-growing clones, CEPI-17-CL4, was extensively characterized for differentiation and metabolic characteristics of the human corneal epithelium. Methods used were immunostaining, reverse transcription-polymerase chain reaction (RT-PCR), northern blot analysis, and enzyme assays.

RESULTS

The CEPI-17-CL4 cells showed a typical cobblestone morphology, grew to more than 200 passages and expressed the SV40 T antigen in the nucleus of every cell. Immunofluorescence staining for CEPI-17-CL4 cells was strongly positive for keratins (K)8, K18, and K19 and vimentin; weakly positive for K3, K13, and K17; and negative for K4, K7, and K14. Expression of cytokines (interleukin [IL]-1alpha, IL-1beta, IL-6, IL-8, tumor necrosis factor-alpha, and IL-ra), growth factors (transforming growth factor [TGF]-alpha, epidermal growth factors [EGF], EGF receptor [EGFR], TGF-beta1, TGF-beta2, and platelet-derived growth factor-beta) and cytochrome P450 enzymes (1A1, 2C, 2E1, and 3A5) was similar in CEPI-17-CL4 cells and human corneal epithelial samples obtained in biopsy. The CEPI-17-CL4 cells were metabolically competent for enzymes glutathione S-transferase, quinone reductase, aflatoxin aldehyde reductase, glutathione peroxidase, glutathione reductase, superoxide dismutase, and catalase.

CONCLUSIONS

The CEPI-17-CL4 cells are truly immortal and express an extensive array of cytokines, growth factors, and metabolic enzymes that resemble the original tissue. These characteristics, which remain stable up to high passage, will allow reproducible, mechanistic studies on toxicity, inflammation, and wound healing.

Production of DNA strand breaks by N-nitrosodimethylamine and 2-amino-3-methylimidazo[4,5-f]quinoline in THLE cells expressing human CYP isoenzymes and inhibition by sulforaphane

The production of DNA strand breaks by N-nitrosodimethylamine (NDMA) and 2-amino-3-methylimidazo[4,5-f]quinoline (IQ) has been observed in T5-2E1 (expressing human CYP2E1) and T5-1A2 (expressing human CYP1A2) human liver cells respectively, using the Comet assay. Responses were statistically significant (P<0.05) and concentration dependent (0.01-1 microg ml-1 NDMA and 0.1-10 microg ml-1 IQ) and were not observed in T5-neo cells devoid of cytochrome P450 activity. Sulforaphane (1-isothiocyanate-4-methylsulfinylbutane) (0.1-10 microM) gave a marked inhibition of DNA strand breakage by these carcinogens (P<0.05 linear regression). This was seen in the absence of cytotoxicity and in the absence of an inhibition of H2O2-induced DNA strand breakage. The ability of sulforaphane to inhibit both CYP2E1 and CYP1A2-mediated genotoxicity therefore is relevant to human isoforms of these enzymes and may contribute to a chemopreventative activity.

Identification of human and rabbit cytochromes P450 1A2 as major isoforms involved in thiabendazole 5-hydroxylation

This report characterized one of the major cytochrome P450 isozyme involved in thiabendazole metabolism. This study was undertaken by using both cultured rabbit hepatocytes treated or not with drugs known to specifically induced various cytochromes P450 isoenzymes (i.e., P450 1A1/2 by beta-naphthoflavone, P450 2B4 by phenobarbital, P450 3A6 by rifampicine and P450 4A by clofibrate) and human liver (THLE-5) and bronchial (BEAS-2B) epithelial cells expressing or not the major constitutive human cytochromes P450 (i.e., CYP1A2, 2A6, 2B6, 2C9, 2D6, 2E1 or 3A4). Only hepatocytes exposed to beta-naphthoflavone and clofibrate significantly metabolized thiabendazole to 5-hydroxythiabendazole. Extensive biotransformation of this anthelmintic only occurred in human cells expressing CYP1A2. Moreover, experiments performed on rabbit preparations showed good correlations between thiabendazole 5-hydroxylase activity and both ethoxyresorufin and methoxyresorufin O-dealkylase activities. Thus, CYP1A2 is a major isoenzyme involved in thiabendazole 5-hydroxylation.

Characterisation of xenobiotic-metabolising enzyme expression in human bronchial mucosa and peripheral lung tissues

The human respiratory epithelium is in direct contact with chemical carcinogens and toxins in inhaled air. Therefore, the activities of xenobiotic-metabolising enzymes in this epithelium could modulate respiratory toxicity and carcinogenesis. We determined the expression of several xenobiotic-metabolising enzymes, including phase I and phase II enzymes, in human bronchial mucosa and peripheral lung tissues. Reverse transcription-polymerase chain reaction (RT-PCR) analysis of phase I enzymes showed CYP1A1 and CYP2C (CYP2C8 and CYP2C18) mRNA expression in all of the 14 bronchial mucosa specimens. CYP2A6 and CYP2B6 mRNAs were found in 85% of the samples, whereas 50 and 90% of the tissues displayed CYP2E1 and CYP3A5 expression, respectively. However, CYP1A2, CYP2D6 and CYP3A4 mRNAs were not detected in all samples analysed. Normal human bronchial epithelial cells (NHBE cells) cultured in serum-free conditions showed reduced P450 expression in comparison with the bronchial mucosal samples. Similar to the bronchial mucosa, the peripheral lung tissues expressed CYP1A1, CYP2A6, CYP2B6, CYP2C (CYP2C8 and CYP2C18), CYP2E1 and CYP3A5 mRNAs, but did not show detectable levels of CYP2D6. Additional P450s, such as CYP1A2 and CYP3A4, were detected. The expression of CYP1A1, CYP1A2, CYP2B6, CYP2E1 and CYP3A4/5 in peripheral lung tissues was confirmed at the protein level, whereas CYP2A6 protein was undetectable. The use of specific primers for the detection of the phase II isoenzymes belonging to the glutathione S-transferase mu (GST mu) and N-acetyl transferase (NAT) families showed that GSTM1 was expressed in 40% of the bronchial mucosa and 25% of the peripheral lung tissues, whereas GSTM3 and NAT1 mRNAs were found in all bronchial and lung samples. Finally, NAT2 expression was detected in all peripheral lung tissues, but was not detected in the bronchus. In conclusion, these results describing the diversity of the xenobiotic-metabolising enzymes expressed in the bronchus and lung tissues indicate that the human respiratory system could significantly and specifically contribute to the activation and metabolism of several environmental procarcinogens.