Responses of insulin to oral glucose and fructose loads in marginally copper-deficient rats fed starch or fructose

Copper-Fructose Interactions: A Novel Mechanism in the Pathogenesis of NAFLD

Compelling epidemiologic data support the critical role of dietary fructose in the epidemic of obesity, metabolic syndrome and nonalcoholic fatty liver disease (NAFLD). The metabolic effects of fructose on the development of metabolic syndrome and NAFLD are not completely understood. High fructose intake impairs copper status, and copper-fructose interactions have been well documented in rats. Altered copper-fructose metabolism leads to exacerbated experimental metabolic syndrome and NAFLD. A growing body of evidence has demonstrated that copper levels are low in NAFLD patients. Moreover, hepatic and serum copper levels are inversely correlated with the severity of NAFLD. Thus, high fructose consumption and low copper availability are considered two important risk factors in NAFLD. However, the causal effect of copper-fructose interactions as well as the effects of fructose intake on copper status remain to be evaluated in humans. The aim of this review is to summarize the role of copper-fructose interactions in the pathogenesis of the metabolic syndrome and discuss the potential underlying mechanisms. This review will shed light on the role of copper homeostasis and high fructose intake and point to copper-fructose interactions as novel mechanisms in the fructose induced NAFLD.

Effect of dietary copper addition on lipid metabolism in rabbits

The present study was conducted to investigate the effect of copper supplementation on lipid metabolism in rabbits. Our study showed dietary copper addition (5-45 mg/kg) increased body mass gain, but decreased fat and liver weights compared with those in the control group (P < 0.05). Copper (45 mg/kg) addition significantly increased the skeletal muscle weight, but inhibited cytoplasmic lipid accumulation in liver, skeletal muscle and adipose tissue (P < 0.05). Compared with the control group, dietary copper addition (45 mg/kg) significantly increased plasma triglyceride levels but decreased very low density lipoprotein levels (P < 0.05). Copper treatment significantly increased gene expression of carnitine palmitoyltransferase (CPT) 1, CPT2 and peroxisome proliferator-activated receptor (PPAR) a in liver (P < 0.05). In skeletal muscle, CPT1, CPT2, fatty acid transport protein, fatty acid-binding protein, and PPARa mRNA as well as phosphorylated AMP-activated protein kinase (AMPK) levels were significantly up-regulated by copper treatment (P < 0.05). Rabbits receiving copper supplementation had higher CPT1, CPT2, PPARa and hormone-sensitive lipase mRNA levels in adipose tissue (P < 0.05). In conclusion, copper promoted skeletal muscle growth and reduced fat accretion. PPARa signaling in liver, skeletal muscle and adipose tissues and AMPK signaling in skeletal muscle tissue were involved in the regulation of lipid metabolism by copper.

Non-alcoholic fatty liver disease following liver transplantation: a clinical review

Non-alcoholic steatohepatitis (NASH) is rapidly becoming the leading indication for liver transplantation (LT) in the United States. While post-transplantation outcomes are similar to other indications for transplant, recent evidence has suggested that reduction in risk factors for post-transplant metabolic syndrome may impose a significant survival benefit in this patient population. Cardiovascular mortality is the leading cause of death following transplantation for NASH. While pre-transplant pharmacologic and surgical approaches have been utilized to reduce cardiovascular risk factors following transplantation, the effectiveness of these treatment approaches in the post-transplant setting is poorly defined. Studies are urgently needed in the treatment of this rapidly growing population.

Management of nonalcoholic steatohepatitis: an evidence-based approach

Nonalcoholic fatty liver disease (NAFLD) and its progressive form, nonalcoholic steatohepatitis (NASH), are an increasingly common cause of chronic liver disease in the developed world, with NASH projected to be the leading cause of liver transplantation in the United States by 2020. This review of NASH management addresses current data from the perspective of levels of evidence for therapeutic options in NASH, including lifestyle modification, drug therapies, and bariatric surgery. In particular, behavioral therapies to assist patients in adopting lifestyle changes are highlighted and a research agenda for future NASH management is presented.

High fructose feeding induces copper deficiency in Sprague-Dawley rats: a novel mechanism for obesity related fatty liver

BACKGROUND & AIMS

Dietary copper deficiency is associated with a variety of manifestations of the metabolic syndrome, including hyperlipidemia and fatty liver. Fructose feeding has been reported to exacerbate complications of copper deficiency. In this study, we investigated whether copper deficiency plays a role in fructose-induced fatty liver and explored the potential underlying mechanism(s).

METHODS

Male weanling Sprague-Dawley rats were fed either an adequate copper or a marginally copper deficient diet for 4 weeks. Deionized water or deionized water containing 30% fructose (w/v) was also given ad lib. Copper and iron status, hepatic injury and steatosis, and duodenum copper transporter-1 (Ctr-1) were assessed.

RESULTS

Fructose feeding further impaired copper status and led to iron overload. Liver injury and fat accumulation were significantly induced in marginal copper deficient rats exposed to fructose as evidenced by robustly increased plasma aspartate aminotransferase (AST) and hepatic triglyceride. Hepatic carnitine palmitoyl-CoA transferase I (CPT I) expression was significantly inhibited, whereas hepatic fatty acid synthase (FAS) was markedly up-regulated in marginal copper deficient rats fed with fructose. Hepatic antioxidant defense system was suppressed and lipid peroxidation was increased by marginal copper deficiency and fructose feeding. Moreover, duodenum Ctr-1 expression was significantly increased by marginal copper deficiency, whereas this increase was abrogated by fructose feeding.

CONCLUSIONS

Our data suggest that high fructose-induced nonalcoholic fatty liver disease (NAFLD) may be due, in part, to inadequate dietary copper. Impaired duodenum Ctr-1 expression seen in fructose feeding may lead to decreased copper absorption, and subsequent copper deficiency.

Exercise counteracts fatty liver disease in rats fed on fructose-rich diet

BACKGROUND

This study aimed to analyze the effects of exercise at the aerobic/anaerobic transition on the markers of non-alcoholic fatty liver disease (NAFLD), insulin sensitivity and the blood chemistry of rats kept on a fructose-rich diet.

METHODS

We separated 48 Wistar rats into two groups according to diet: a control group (balanced diet AIN-93 G) and a fructose-rich diet group (60% fructose). The animals were tested for maximal lactate-steady state (MLSS) in order to identify the aerobic/anaerobic metabolic transition during swimming exercises at 28 and 90 days of age. One third of the animals of each group were submitted to swimming training at an intensity equivalent to the individual MLSS for 1 hours/day, 5 days/week from 28 to 120 days (early protocol). Another third were submitted to the training from 90 to 120 days (late protocol), and the others remained sedentary. The main assays performed included an insulin tolerance test (ITT) and tests of serum alanine aminotransferase [ALT] and aspartate aminotransferase [AST] activities, serum triglyceride concentrations [TG] and liver total lipid concentrations.

RESULTS

The fructose-fed rats showed decreased insulin sensitivity, and the late-exercise training protocol counteracted this alteration. There was no difference between the groups in levels of serum ALT, whereas AST and liver lipids increased in the fructose-fed sedentary group when compared with the other groups. Serum triglycerides concentrations were higher in the fructose-fed trained groups when compared with the corresponding control group.

CONCLUSIONS

The late-training protocol was effective in restoring insulin sensitivity to acceptable standards. Considering the markers here evaluated, both training protocols were successful in preventing the emergence of non-alcoholic fatty liver status disease.

Increased male offspring's risk of metabolic-neuroendocrine dysfunction and overweight after fructose-rich diet intake by the lactating mother

An adverse endogenous environment during early life predisposes the organism to develop metabolic disorders. We evaluated the impact of intake of an iso-caloric fructose rich diet (FRD) by lactating mothers (LM) on several metabolic functions of their male offspring. On postnatal d 1, ad libitum eating, lactating Sprague-Dawley rats received either 10% F (wt/vol; FRD-LM) or tap water (controls, CTR-LM) to drink throughout lactation. Weaned male offspring were fed ad libitum a normal diet, and body weight (BW) and food intake were registered until experimentation (60 d of age). Basal circulating levels of metabolic markers were evaluated. Both iv glucose tolerance and hypothalamic leptin sensitivity tests were performed. The hypothalamus was dissected for isolation of total RNA and Western blot analysis. Retroperitoneal (RP) adipose tissue was dissected and either kept frozen for gene analysis or digested to isolate adipocytes or for histological studies. FRD rats showed increased BW and decreased hypothalamic sensitivity to exogenous leptin, enhanced food intake (between 49-60 d), and decreased hypothalamic expression of several anorexigenic signals. FRD rats developed increased insulin and leptin peripheral levels and decreased adiponectinemia; although FRD rats normally tolerated glucose excess, it was associated with enhanced insulin secretion. FRD RP adipocytes were enlarged and spontaneously released high leptin, although they were less sensitive to insulin-induced leptin release. Accordingly, RP fat leptin gene expression was high in FRD rats. Excessive fructose consumption by lactating mothers resulted in deep neuroendocrine-metabolic disorders of their male offspring, probably enhancing the susceptibility to develop overweight/obesity during adult life.

Consumption of sweetened beverages and intakes of fructose and glucose predict type 2 diabetes occurrence

The role of intakes of different sugars in the development of type 2 diabetes was studied in a cohort of 4,304 men and women aged 40-60 y and initially free of diabetes at baseline in 1967-1972. Food consumption data were collected using a dietary history interview covering the habitual diet during the previous year. The intakes of different sugars were calculated and divided in quartiles. During a 12-y follow-up, 177 incidents of type 2 diabetes cases were identified from a nationwide register. Combined intake of fructose and glucose was associated with the risk of type 2 diabetes but no significant association was observed for intakes of sucrose, lactose, or maltose. The relative risk between the highest and lowest quartiles of combined fructose and glucose intake was 1.87 (95% [CI] = 1.19, 2.93; P = 0.003). The corresponding relative risks between the extreme quartiles of consumption of food items contributing to sugar intakes were 1.69 (95% [CI] = 1.17, 2.43; P < 0.001) for sweetened berry juice and 1.67 (95% [CI] = 0.98, 2.87; P = 0.01) for soft drinks. Our findings support the view that higher intake of fructose and glucose and sweetened beverages may increase type 2 diabetes risk.

Carbohydrate metabolism in erythrocytes of copper deficient rats

Dietary copper deficiency is known to adversely affect the circulatory system of fructose-fed rats. Part of the problem may lie in the effect of copper deficiency on intermediary metabolism. To test this, weanling male Long-Evans rats were fed for 4 or 8 weeks on sucrose-based diets containing low or adequate copper content. Copper deficient rats had significantly lower plasma and tissue copper as well as lower plasma copper, zinc-superoxide dismutase activity. Copper deficient rats also had a significantly higher heart:body weight ratio when compared to pair-fed controls. Direct measurement of glycolysis and pentose phosphate pathway flux in erythrocytes using (13)C NMR showed no differences in carbon flux from glucose or fructose to pyruvate but a significantly higher flux through the lactate dehydrogenase locus in copper deficient rats (approximately 1.3 times, average of glucose and glucose + fructose measurements). Copper-deficient animals had significantly higher erythrocyte concentrations of glucose, fructose, glyceraldehyde 3-phosphate and NAD(+). Liver metabolite levels were also affected by copper deficiency being elevated in glycogen and fructose 1-phosphate content. The results show small changes in carbohydrate metabolism of copper deficient rats.

Fructose, weight gain, and the insulin resistance syndrome

This review explores whether fructose consumption might be a contributing factor to the development of obesity and the accompanying metabolic abnormalities observed in the insulin resistance syndrome. The per capita disappearance data for fructose from the combined consumption of sucrose and high-fructose corn syrup have increased by 26%, from 64 g/d in 1970 to 81 g/d in 1997. Both plasma insulin and leptin act in the central nervous system in the long-term regulation of energy homeostasis. Because fructose does not stimulate insulin secretion from pancreatic beta cells, the consumption of foods and beverages containing fructose produces smaller postprandial insulin excursions than does consumption of glucose-containing carbohydrate. Because leptin production is regulated by insulin responses to meals, fructose consumption also reduces circulating leptin concentrations. The combined effects of lowered circulating leptin and insulin in individuals who consume diets that are high in dietary fructose could therefore increase the likelihood of weight gain and its associated metabolic sequelae. In addition, fructose, compared with glucose, is preferentially metabolized to lipid in the liver. Fructose consumption induces insulin resistance, impaired glucose tolerance, hyperinsulinemia, hypertriacylglycerolemia, and hypertension in animal models. The data in humans are less clear. Although there are existing data on the metabolic and endocrine effects of dietary fructose that suggest that increased consumption of fructose may be detrimental in terms of body weight and adiposity and the metabolic indexes associated with the insulin resistance syndrome, much more research is needed to fully understand the metabolic effect of dietary fructose in humans.