Postnatal overfeeding induces hepatic microRNA-221 expression and impairs the PI3K/AKT pathway in adult male rats

BACKGROUND

Increasing evidence suggests that postnatal overfeeding induces childhood obesity, which is strongly associated with metabolic syndrome. Insulin resistance is a risk factor for metabolic syndrome. MicroRNA-221 (miR-221) is involved in the development of obesity and has been reported to negatively regulate insulin sensitivity. However, the underlying mechanism remains unclear.

METHODS

Rats raised in small litters (SLs, three pups/dam, n = 10) and normal litters (NLs, 10 pups/dam, n = 10) were used to model early postnatal overfeeding and act as controls, respectively. miR-221 and proteins related to the phosphoinositide 3-kinases (PI3K)/protein kinase B (AKT) pathway were assessed in the liver.

RESULTS

Early postnatal overfeeding significantly increased body weight, visceral fat index, blood glucose, serum triglycerides, and the homeostasis model assessment of insulin resistance at 9 weeks. Real-time polymerase chain reaction (PCR) and western blot analysis revealed that postnatal overfeeding induced insulin receptor and insulin receptor substrate 2 expression, but decreased PI3K and AKT phosphorylation in the liver. Quantitative real-time PCR showed that hepatic miR-221 was significantly overexpressed in the SL group.

CONCLUSIONS

These results indicate that postnatal overfeeding induces hepatic miR-221 overexpression and impairs the PI3K/AKT signal pathway, which may cause insulin resistance.

IMPACT

We first report postnatal overfeeding induces hepatic miR-221 expression. Postnatal overfeeding impairs PI3K/AKT pathway in the liver of adult rats. Postnatal overfeeding induces obesity and high blood glucose. Avoidance of overfeeding during early postnatal life may prevent obesity and T2DM.

11 beta-hydroxysteroid dehydrogenase type 1 induction in the arcuate nucleus by high-fat feeding: A novel constraint to hyperphagia?

11 beta-Hydroxysteroid dehydrogenase type 1 (11 beta-HSD1) catalyzes regeneration of active intracellular glucocorticoids in fat, liver, and discrete brain regions. Although overexpression of 11 beta-HSD1 in adipose tissue causes hyperphagia and the metabolic syndrome, male 11 beta-HSD1 null (11 beta-HSD1-/-) mice resist metabolic disease on high-fat (HF) diet, but also show hyperphagia. This suggests 11 beta-HSD1 may influence the central actions of glucocorticoids on appetite and perhaps energy balance. We show that 11 beta-HSD1-/- mice express lower hypothalamic mRNA levels of the anorexigenic cocaine and amphetamine-regulated transcript and melanocortin-4 receptor, but higher levels of the orexigenic melanin-concentrating hormone mRNAs than controls (C57BL/6J) on a low-fat diet (11% fat). HF (58% fat) diet promoted transient ( approximately 8 wk) hyperphagia and decreased food efficiency in 11 beta-HSD1-/- mice and decreased melanocortin-4 receptor mRNA expression in control but not 11 beta-HSD1-/- mice. 11 beta-HSD1-/- mice showed a HF-mediated up-regulation of the orexigenic agouti-related peptide (AGRP) mRNA in the arcuate nucleus which paralleled the transient HF hyperphagia. Conversely, control mice showed a rapid (48 h) HF-mediated increase in arcuate 11 beta-HSD1 associated with subsequent down-regulation of AGRP. This regulatory pattern was unexpected because glucocorticoids increase AGRP, suggesting an alternate hyperphagic mechanism despite partial colocalization of 11 beta-HSD1 and AGRP in arcuate nucleus cells. One major alternate mechanism governing selective fat ingestion and the AGRP system is endogenous opioids. Treatment of HF-fed mice with the mu opioid agonist DAMGO recapitulated the HF-induced dissociation of arcuate AGRP expression between control and 11 beta-HSD1-/- mice, whereas the opioid antagonist naloxone given with HF induced a rise in arcuate AGRP and blocked HF-diet induction of 11 beta-HSD1. These data suggest that 11 beta-HSD1 in brain plays a role in the adaptive restraint of excess fat intake, in part by increasing inhibitory opioid tone on AGRP expression in the arcuate nucleus.

Enhanced hypothalamic AMP-activated protein kinase activity contributes to hyperphagia in diabetic rats

AMP-activated protein kinase (AMPK) acts as a cellular energy sensor, being activated during states of low energy charge. Hypothalamic AMPK activity is altered by hormonal and metabolic signals and mediates the feeding response. To determine the effect of diabetes on hypothalamic AMPK activity, we assayed this activity in streptozotocin (STZ)-induced diabetic rats. Compared with control rats, STZ-induced diabetic rats had significant hyperphagia and weight loss. Hypothalamic AMPK phosphorylation and alpha2-AMPK activity were higher and acetyl-CoA carboxylase activity was lower in diabetic rats than in control rats. Chronic insulin treatment or suppression of hypothalamic AMPK activity completely prevented diabetes-induced changes in food intake as well as in hypothalamic AMPK activity and mRNA expression of neuropeptide Y and proopiomelanocortin. Plasma leptin and insulin levels were profoundly decreased in diabetic rats. Intracerebroventricular administration of leptin and insulin reduced hyperphagia and the enhanced hypothalamic AMPK activity in diabetic rats. These data suggest that leptin and insulin deficiencies in diabetes lead to increased hypothalamic AMPK activity, which contributes to the development of diabetic hyperphagia.

Analysis of energy expenditure at different ambient temperatures in mice lacking DGAT1

Mice lacking acyl-CoA:diacylglycerol acyltransferase 1 (DGAT1), a key enzyme in triglyceride synthesis, have increased energy expenditure and therefore are resistant to obesity. Because ambient temperature can significantly affect energy expenditure in mice, we undertook these studies to determine the effects of different ambient temperatures on energy expenditure, food intake, and thermoregulation in DGAT1-deficient [Dgat1(-/-)] mice. Dgat1(-/-) mice had increased energy expenditure irrespective of changes in the ambient temperature. Although core temperature was normal, surface temperature was increased in Dgat1(-/-) mice, most likely reflecting an active mechanism to dissipate heat from increased thermogenesis. Dgat1(-/-) mice had increased food intake at baseline, and this hyperphagia became more pronounced upon exposure to cold. When fasted in a cold environment, Dgat1(-/-) mice developed hypothermia, which was associated with hypoglycemia. These results suggest that the hyperphagia in Dgat1(-/-) mice is a secondary mechanism that compensates for the increased utilization of fuel substrates. Our findings offer insights into the mechanisms of hyperphagia and increased energy expenditure in a murine model of obesity resistance.

Nitric oxide mediates hyperphagia of obese Zucker rats: relation to specific changes in the microstructure of feeding behavior

The presence of a nitric oxide synthetase (NOS) was demonstrated in the rat brain. It has been demonstrated recently that NOS-inhibitors reduce food intake in mammals and this suggest that nitric oxide (NO) might be a physiological mediator involved in the mechanisms controlling feeding behavior. Actually, there is no information about the acute central and peripheral effects of NOS-inhibitors on feeding behavior in obese and lean Zucker rats. That is why we investigated the acute dose-dependent activity of NG-Nitro-Arginine-Methyl-Ester (L-NAME) on food intake and feeding behavior in these rats. When given peripherally in the obese rats, L-NAME produced a dose-dependent decrease in food intake (p<0.001). The calculated MED and the ED 50 were 0.50 mg/kg IP and 3.46 mg/kg IP, respectively. These effects could not be reproduced in the lean Zucker rats whatever the dose used (p=0.59). The anorectic properties of L-NAME were very well translated into the microstructure of the feeding behavior. Time spent to eat (p<0.001), meal duration (p<0.01) and meal number (p<0.01) were reduced in the obese rats. Interestingly, L-NAME produced the same effects in the lean rats, but meal size increased in a compensatory manner. Central administration of L-NAME reproduced the same effects in the obese rats, but lean rats still remained insensitive. Central aminergic and/or peptidergic defects associated with the expression of hyperphagia might explain the differences observed between these lean and the obese animals. These results indicate a role of nitric oxide in the expression of hyperphagia and show that it might be a physiological mediator involved in the mechanisms controlling feeding behavior.

Effect of nutritional obesity on the induction of CYP2B enzymes following phenobarbital treatment

Human obesity is associated with a number of pathophysiologic processes, such as fatty infiltration and fibrosis of the liver. Although obesity has been shown to alter the metabolism of various xenobiotics, its effect on hepatic cytochromes P-450 is not known. In this study, the overfed rat was used as a model for examining the influence of obesity on the expression and regulation of hepatic cytochrome P-450 2B1/2B2. Sprague-Dawley rats were fed either a standard diet or an energy-dense diet for 32 weeks. The energy-dense diet resulted in a significant increase in body weight, serum triglyceride levels, and liver lipid content. Obesity did not influence baseline levels of spectral cytochrome P-450 content. Similar baseline activities of CYP2B1/2B2 (16 beta-testosterone hydroxylase and pentoxyresorufin O-dealkylation)--comparative protein levels of CYP2B1/2B2 (Western blot), and mRNA (slot blot)--were found in rats fed either diet. Half of the animals in each group were given 20 mg phenobarbital (intraperitoneal injection)/animal every 12 hr for three consecutive days. This resulted in similar phenobarbital plasma concentrations in both groups. Phenobarbital treatment increased the concentrations of cytochrome P-450 in both groups to the same extent. However, greater CYP2B1/2B2 activity was found in control rats following phenobarbital administration, whereas the amount of protein and mRNA was similar in each treated group. In conclusion, obesity did not affect the regulation of CYP2B1/2B2 enzymes. However, changes in the lipid environment associated with obesity may have affected the activity of these proteins.

Phosphatidate phosphohydrolases in liver, heart and adipose tissue of the JCR:LA corpulent rat and the lean genotypes: implications for glycerolipid synthesis and signal transduction

The activities of two distinct phosphatidate phosphohydrolases (PAP) were measured in livers, hearts and adipose tissues of the JCR:LA corpulent rat which is hyperphagic, hypertriglyceridaemic and insulin resistant. The specific activity of PAP-1, which requires Mg2+, was similar in the livers of lean and corpulent female rats and in male corpulent rats, but these activities were about 1.6-fold higher than in lean males. There was a correlation between the specific activity of PAP-1 and the concentrations of hepatic and serum triacylglycerols in the males, but not in the females. Chronic treatment of the corpulent rats with ethanol did not significantly alter the hepatic activity of PAP-1, or the concentrations of hepatic or serum triacylglycerols. Specific activities of PAP-1 in the heart were higher in the lean compared to the corpulent males. There was no significant difference for the females. Specific activities of PAP-1 were over 5-fold higher in the subcutaneous adipose tissue of the corpulent males and females compared to the lean genotypes. The differences were smaller (1.6-1.9-fold) in the gonadal adipose tissue of both sexes and in the peri-renal depot for the males. PAP-1 activity in the peri-renal depots of corpulent females was 23% lower than in lean females. PAP-2 activity was insensitive to N-ethylmaleimide and did not require Mg2+ for activity. Its activity was 1.5-2.0-fold higher in the livers and hearts of the lean male and female rats than in the corpulent genotypes. Chronic treatment with ethanol increased the activity of PAP-2 in the hearts of the corpulent males, but had no effect in the corpulent females. The specific activity of PAP-2 was higher in subcutaneous, gonadal and peri-renal adipose depots in the females and in the peri-renal depot of the corpulent males compared with the lean genotypes. Lean males had higher specific activities in all three depots compared to lean females. The tissue specificity and the sex differences in the specific activities of PAP-1 and PAP-2 are discussed in terms of their proposed functions in glycerolipid biosynthesis and signal transduction. It is proposed that a decreased activity of PAP-2 could be involved in the insulin insensitivity in the corpulent rats.

Selective increase in cytochrome P450 content in hepatic microsomes from rats with ventromedial hypothalamic lesions

Changes in the components of hepatic microsomal electron transport systems and in drug hydroxylase activities were investigated in ventromedial hypothalamus (VMH) lesioned obese rats. Eight weeks after electrolysis of the bilateral VMH, the content of cytochrome P450 per mg microsomal protein (0.79 +/- 0.07 nmol/mg protein) was significantly higher (P less than 0.02) than that in the sham-operated rats (0.59 +/- 0.02). Cytochrome P450 per whole liver in the VMH-lesioned obese rats had also significantly increased (87 +/- 9 nmol vs 56 +/- 3, P less than 0.02). No significant differences were found in the cytochrome b5 contents, and the activities of NADPH- and NADH-cytochrome c reductases between the VMH-lesioned obese and sham-operated rats. The demethylation activities of aminopyrine (1.04 +/- 0.02 nmol/mg protein/min vs 0.94 +/- 0.02, P less than 0.05) and p-nitroanisole (0.96 +/- 0.02 vs 0.89 +/- 0.02 , p less than 0.02) and the aniline hydroxylase activity (0.22 +/- 0.01 vs 0.16 +/- 0.01, P less than 0.01) were enhanced, but 7-ethoxycoumarin O-deethylase activity was unchanged in the VMH-lesioned obese rats. These results indicate a selective increase in the content of cytochrome P450 among the components of the P450-dependent mixed function oxidase system in the liver of VMH-lesioned obese rats. Our observations suggest that drug metabolism may be enhanced in the hypothalamic obesity.

Platelet alpha 2-adrenoceptor and adenylate cyclase in patients with anorexia nervosa and bulimia

Platelets alpha 2-adrenoceptors were studied in 24 patients with anorexia nervosa shortly after admission to the hospital and after 10% weight gain. Twenty patients with bulimia and 24 healthy age- and sex-matched normal subjects also were studied. Receptor number was significantly increased in patients with bulimia and anorexia nervosa. After 10% weight gain, the receptor number almost normalized in anorexia nervosa patients. Kd values were increased in all patients groups at all times of study. In patients with bulimia or anorexia nervosa, both initially and after weight gain, the maximal effect of prostaglandin E1 (PGE1) on platelet cAMP production was greatly increased, while the half-maximally effective dose was unchanged. Also, the maximal inhibitory effects of epinephrine and clonidine on PGE1-stimulated platelet cAMP production were greater, while the half-maximal dose of both alpha 2-agonists was unchanged. Metabolic and endocrine indicators of starvation were present in both bulimic and anorexia nervosa patients initially. Blood beta-hydroxybutyric acid was elevated, and plasma T3 values and the orthostatic response of plasma norepinephrine (delta NA) were reduced, while cortisol was elevated (only in anorexia nervosa patients). Among these parameters, only delta NA significantly correlated with the actions of PGE1 and epinephrine on cAMP production. In conclusion, the activity of the sympathetic nervous system was reduced in patients with anorexia nervosa and bulimia. This reduction was accompanied by an increased capacity and a decreased affinity of platelet alpha 2-receptors and an increased PGE1 stimulatory and epinephrine inhibitory effects on cAMP production.

Medical complications of bulimia: a prospective evaluation

Recent increase in the identification and treatment of bulimia, an eating disorder characterised by excessive eating and often accompanied by some form of purging behaviour, has led to an interest in its proper medical evaluation. Although scattered reports describe a multitude of associated medical complications, their true incidence is not known. We describe our experience with 39 consecutive bulimic patients who underwent thorough medical evaluation. Serious disease was rarely encountered although a significant association was found between low body weight and hypokalaemia. Elevated serum amylase values were also noted in 15 of 24 patients (62 per cent). The potential utility of the latter in treating bulimic patients is discussed. A practical approach to the management of these patients is outlined.

Pancreatic hydrolases in cold-induced hyperphagia of rats fed a low or high-fat diet

Rats fed either a low (2p. 100) or high (40 p. 100)-fat diet were exposed to 22 or 5 degrees C. The resulting hyperphagia adequately compensated energy losses as judged from body weight. The cold-induced hyperphagia was accompanied by a non-parallel increase in pancreatic hydrolases. Amylase and lipase were not increased above the adaptive levels they had respectively reached in the heat with a high-starch or high-lipid diet. Chymotrypsinogen, on the contrary, responded to increased intake of both diets. It also responded to the higher protein concentration in the high-fat diet caused by isocaloric replacement of starch by fat. Colipase varied independently of lipase and was increased additively by fat and protein intakes. Consequently, although limiting for lipase in the warm, colipase rose to a 1:1 ratio in the cold. Increased intake had a consistent pleiotropic effect evidenced by an increase of amylase with the high-fat diet and of lipase with the low-fat diet. The net effect was a significant increase in the lipid-digesting potential of the organism of lipid-fed animals upon exposure to cold, while the starch-digesting potential remained unaffected in starch-fed animals.

Benign parotid enlargement in bulimia

Bulimia is an episodic compulsive urge to overeat often followed by recurrent attempts to lose weight by self-induced vomiting. Seven young women with this eating disorder and associated benign bilateral painless parotid enlargement are described. The glandular swelling was generally intermittent, with parotid enlargement usually developing 2 to 6 days after a binge overeating episode had stopped. Several had hypokalemic alkalosis and a moderate elevation in serum amylase levels. None had clinical evidence of pancreatitis, and a parotid gland biopsy in one patient was normal. The clinician should be alerted to the association of benign parotid enlargement with this syndrome.