Bernadette E. Grayson

Maternal high-fat diet triggers lipotoxicity in the fetal livers of nonhuman primates

Maternal obesity is thought to increase the offsprings risk of juvenile obesity and metabolic diseases; however, the mechanism(s) whereby excess maternal nutrition affects fetal development remain poorly understood. Here, we investigated in nonhuman primates the effect of chronic high-fat diet (HFD) on the development of fetal metabolic systems. We found that fetal offspring from both lean and obese mothers chronically consuming a HFD had a 3-fold increase in liver triglycerides (TGs). In addition, fetal offspring from HFD-fed mothers (O-HFD) showed increased evidence of hepatic oxidative stress early in the third trimester, consistent with the development of nonalcoholic fatty liver disease (NAFLD). O-HFD animals also exhibited elevated hepatic expression of gluconeogenic enzymes and transcription factors. Furthermore, fetal glycerol levels were 2-fold higher in O-HFD animals than in control fetal offspring and correlated with maternal levels. The increased fetal hepatic TG levels persisted at P180, concurrent with a 2-fold increase in percent body fat. Importantly, reversing the maternal HFD to a low-fat diet during a subsequent pregnancy improved fetal hepatic TG levels and partially normalized gluconeogenic enzyme expression, without changing maternal body weight. These results suggest that a developing fetus is highly vulnerable to excess lipids, independent of maternal diabetes and/or obesity, and that exposure to this may increase the risk of pediatric NAFLD.

Chronic Consumption of a High-Fat Diet during Pregnancy Causes Perturbations in the Serotonergic System and Increased Anxiety-Like Behavior in Nonhuman Primate Offspring

Childhood obesity is associated with increased risk of behavioral/psychological disorders including depression, anxiety, poor learning, and attention deficient disorder. As the majority of women of child-bearing age are overweight or obese and consume a diet high in dietary fat, it is critical to examine the consequences of maternal overnutrition on the development of brain circuitry that regulates offspring behavior. Using a nonhuman primate model of diet-induced obesity, we found that maternal high-fat diet (HFD) consumption caused perturbations in the central serotonergic system of fetal offspring. In addition, female infants from HFD-fed mothers exhibited increased anxiety in response to threatening novel objects. These findings have important clinical implications as they demonstrate that exposure to maternal HFD consumption during gestation, independent of obesity, increases the risk of developing behavioral disorders such as anxiety.

A role for central nervous system PPAR-γ in the regulation of energy balance

The peroxisome proliferator–activated receptor-γ (PPAR-γ) is a nuclear receptor that is activated by lipids to induce the expression of genes involved in lipid and glucose metabolism, thereby converting nutritional signals into metabolic consequences. PPAR-γ is the target of the thiazolidinedione (TZD) class of insulin-sensitizing drugs, which have been widely prescribed to treat type 2 diabetes mellitus. A common side effect of treatment with TZDs is weight gain. Here we report a previously unknown role for central nervous system (CNS) PPAR-γ in the regulation of energy balance. We found that both acute and chronic activation of CNS PPAR-γ, by either TZDs or hypothalamic overexpression of a fusion protein consisting of PPAR-γ and the viral transcriptional activator VP16 (VP16–PPAR-γ), led to positive energy balance in rats. Blocking the endogenous activation of CNS PPAR-γ with pharmacological antagonists or reducing its expression with shRNA led to negative energy balance, restored leptin sensitivity in high-fat-diet (HFD)-fed rats and blocked the hyperphagic response to oral TZD treatment. These findings have implications for the widespread clinical use of TZD drugs and for understanding the etiology of diet-induced obesity.

Changes in Melanocortin Expression and Inflammatory Pathways in Fetal Offspring of Nonhuman Primates Fed a High-Fat Diet

The hypothalamic melanocortin system, which controls appetite and energy expenditure, develops during the third trimester in primates. Thus, maternal nutrition and health may have a profound influence on the development of this system. To study the effects of chronic maternal high-fat diet (HFD) on the development of the melanocortin system in the fetal nonhuman primate, we placed adult female macaques on either a control (CTR) diet or a HFD for up to 4 yr. A subgroup of adult female HFD animals was also switched to CTR diet during the fifth year of the study (diet reversal). Third-trimester fetuses from mothers on HFD showed increases in proopiomelanocortin mRNA expression, whereas agouti-related protein mRNA and peptide levels were decreased in comparison with CTR fetuses. Proinflammatory cytokines, including IL-1beta and IL-1 type 1 receptor, and markers of activated microglia were elevated in the hypothalamus, suggesting an activation of the local inflammatory response. Fetuses of diet-reversal mothers had normal melanocortin levels. These results raise the concern that chronic consumption of a HFD during pregnancy, independent of maternal obesity and diabetes, can lead to widespread activation of proinflammatory cytokines that may alter the development of the melanocortin system. The abnormalities in the fetal POMC system, if maintained into the postnatal period, could impact several systems, including body weight homeostasis, stress responses, and cardiovascular function. Indeed, the HFD offspring develop early-onset excess weight gain. These abnormalities may be prevented by healthful nutrient consumption during pregnancy even in obese and severely insulin-resistant individuals.

Regulation of gastric emptying rate and its role in nutrient-induced GLP-1 secretion in rats after vertical sleeve gastrectomy

Roux-en-Y gastric bypass (RYGB) and vertical sleeve gastrectomy (VSG) are effective weight loss surgeries that also improve glucose metabolism. Rapid, early rises of circulating insulin and glucagon-like peptide-1 (GLP-1) concentrations following food ingestion are characteristic of these procedures. The purpose of the current study was to test the hypothesis that postprandial hormone release is due to increased nutrient emptying from the stomach. Radioscintigraphy and chemical and radiolabeled tracers were used to examine gastric emptying in rat models of VSG and RYGB surgery. Intraduodenal nutrient infusions were used to assess intestinal GLP-1 secretion and nutrient sensitivity in VSG rats compared with shams. Five minutes after a nutrient gavage, the stomachs of RYGB and VSG rats were completely emptied, whereas only 6.1% of the nutrient mixture had emptied from sham animals. Gastric pressure was increased in VSG animals, and rats with this procedure did not inhibit gastric emptying normally in response to increasing caloric loads of dextrose or corn oil, and they did not respond to neural or endocrine effectors of gastric motility. Finally, direct infusion of liquid nutrients into the duodenum caused significantly greater GLP-1 release in VSG compared with shams, indicating that increases in GLP-1 secretion after VSG are the result of both greater gastric emptying rates and altered responses at the level of the intestine. These findings demonstrate greatly accelerated gastric emptying in rat models of RYGB and VSG. In VSG this is likely due to increased gastric pressure and reduced responses to inhibitory feedback from the intestine.

Wired on sugar: the role of the CNS in the regulation of glucose homeostasis.

Obesity and type 2 diabetes mellitus (T2DM) — disorders of energy homeostasis and glucose homeostasis, respectively — are tightly linked and the incidences of both conditions are increasing in parallel. The CNS integrates information regarding peripheral nutrient and hormonal changes and processes this information to regulate energy homeostasis. Recent findings indicate that some of the neural circuits and mechanisms underlying energy balance are also essential for the regulation of glucose homeostasis. We propose that disruption of these overlapping pathways links the metabolic disturbances associated with obesity and T2DM. A better understanding of these converging mechanisms may lead to therapeutic strategies that target both T2DM and obesity.

Gastric Bypass Surgery Attenuates Ethanol Consumption in Ethanol-Preferring Rats

BACKGROUND Roux-en-Y gastric bypass (RYGB) surgery is an effective weight loss strategy employed to treat obesity and associated complications. Importantly, the RYGB procedure has been reported to attenuate reward-related consummatory behaviors. The present work examined the hypothesis that RYGB surgery attenuates ethanol intake and reward in the context of frequent ethanol consumption. METHODS To do this, self-report of ethanol intake was examined in human bariatric patients (n = 6165) before and following the RYGB procedure. In addition, we utilized a rodent model of RYGB and examined ethanol consumption and ethanol reward in male ethanol-preferring (P) rats, which are selectively bred to consume large volumes of ethanol. RESULTS Patients that reported frequent consumption of ethanol before RYGB reported decreased consumption following RYGB surgery. Moreover, the RYGB procedure decreased ethanol intake and the reinforcing properties of ethanol in P rats. Notably, the attenuating effect of RYGB surgery on ethanol consumption was associated with ethanol-induced increases in the gut hormone glucagon-like peptide-1 (GLP-1). Pharmacologic administration of GLP-1 agonists attenuated ethanol consumption in sham P rats. In addition, pharmacologic replacement of the gut hormone ghrelin restored drinking behavior in P rats following RYGB. CONCLUSIONS Collectively, these findings unveil the potential of RYGB surgery to attenuate ethanol consumption in some humans and rats. Furthermore, our data indicate that this regulation is achieved, in part, through reduction of reward and is modified by the gut hormones GLP-1 and ghrelin.

Roux-en-Y Gastric Bypass Surgery But Not Vertical Sleeve Gastrectomy Decreases Bone Mass in Male Rats

The most effective treatment for obesity is bariatric surgery. However, there is increasing concern that bariatric surgery can cause nutrient deficiencies that translate into metabolic bone disease. Whether this is true for all surgery types is not yet clear. We therefore investigated the effects of 2 commonly applied bariatric surgeries (Roux-en-Y gastric bypass [RYGB] and vertical sleeve gastrectomy) on energy and bone metabolism in rats 60 days after surgery. Both surgeries resulted in similar reductions of body weight, body fat, and food intake. Glucose tolerance was improved to a similar extent after both surgeries and was accompanied by increased postprandial secretion of glucose-dependent insulinotropic peptide. Using microcomputed tomography, we found that, relative to sham-operated rats, bone volume was significantly reduced after RYGB but not vertical sleeve gastrectomy. RYGB rats also had markedly reduced lipid absorption from the intestine and significantly lower serum 25-hydroxyvitamin D and calcium levels. Importantly, dietary supplementation with calcium and vitamin D could not fully rescue the reduced bone volume after RYGB surgery. Both surgeries resulted in a significant increase in stomach pH, which may have worsened the malabsorption in RYGB rats. Our findings suggest that bone loss in RYGB rats is not exclusively driven by calcium and vitamin D malabsorption but also by additional factors that may not be rescuable by dietary supplementation. These data point toward important similarities and differences between bariatric procedures that should be considered in clinical settings as guidance for which procedure will be best for specific patient populations.

Effect of vertical sleeve gastrectomy on food selection and satiation in rats

Vertical sleeve gastrectomy (VSG) is a restrictive procedure that reduces food intake to produce weight loss. Here we assess volume and nutrient effects on the ingestive behavior of VSG and sham surgery animals. Rats given access to Ensure or pelleted chow were used to determine if liquid foods would adversely affect weight loss after surgery. Volume effects were studied by altering the caloric density of Ensure, and dietary preferences for fat and carbohydrate (sucrose) were assessed using a two-bottle test. c-Fos was used to measure neuronal activation in the nucleus of the solitary tract and area postrema in response to intragastric infusions of water, sucrose, or Intralipid. The degree of colocalization with catecholaminergic neurons was also assessed. VSG rats did not show the expected preference for a liquid diet over chow and lacked dietary preferences for fat seen in shams. Preferences for carbohydrate/sucrose solutions were unaffected by surgery. Meal size was reduced by VSG; however, VSG rats were able to alter their volume of intake to compensate for changes in caloric density, and intragastric infusions of water produced similar levels of neuronal activation among VSG, sham, and pair-fed rats. In comparison, nutrient-induced c-Fos activation was substantially increased by VSG. Colocalization between c-Fos and catecholaminergic-expressing neurons was similar among rats treated with water, sucrose, or Intralipid. VSG alters nutrient sensing in a manner that lowers the threshold for satiety and reduces fat preference to induce and maintain weight loss.

High Fat Diet Alters Lactation Outcomes: Possible Involvement of Inflammatory and Serotonergic Pathways

Delay in the onset of lactogenesis has been shown to occur in women who are obese, however the mechanism altered within the mammary gland causing the delay remains unknown. Consumption of high fat diets (HFD) has been previously determined to result decreased litters and litter numbers in rodent models due to a decrease in fertility. We examined the effects of feeding a HFD (60% kcal from fat) diet versus a low-fat diet (LFD; 10% kcal from fat) to female Wistar rats on lactation outcomes. Feeding of HFD diet resulted in increased pup weights compared to pups from LFD fed animals for 4 d post-partum. Lactation was delayed in mothers on HFD but they began to produce copious milk volumes beginning 2 d post-partum, and milk yield was similar to LFD by day 3. Mammary glands collected from lactating animals on HFD diet, displayed a disrupted morphologies, with very few and small alveoli. Consistently, there was a significant decrease in the mRNA expression of milk protein genes, glucose transporter 1 (GLUT1) and keratin 5 (K5), a luminobasal cell marker in the mammary glands of HFD lactating animals. Expression of tryptophan hydroxylase 1 (TPH1), the rate-limiting enzyme in serotonin (5-HT) biosynthesis, and the 5-HT7 receptor (HTR7), which regulates mammary gland involution, were significantly increased in mammary glands of HFD animals. Additionally, we saw elevation of the inflammatory markers interleukin-6 (IL-6) and tumor necrosis factor-α (TNF- α). These results indicate that consumption of HFD impairs mammary parenchymal tissue and impedes its ability to synthesize and secrete milk, possibly through an increase in 5-HT production within the mammary gland leading to an inflammatory process.