Metabolic effects of intermittent access to caloric or non-caloric sweetened solutions in mice fed a high-caloric diet

The environmental pollutant, polychlorinated biphenyl 126, alters liver function in a rodent model of alcohol-associated liver disease

BACKGROUND

The prevalence of alcohol-associated liver disease (ALD), a subtype of fatty liver disease (FLD), continues to rise. ALD is a major cause of preventable death. Polychlorinated biphenyl (PCB) 126 is an environmentally relevant, dioxin-like pollutant whose negative metabolic effects have been well documented. In human and animal studies, PCB has been associated with the severity of nonalcoholic fatty liver disease (NAFLD). However, few studies have investigated whether exposures to environmental toxicants can worsen ALD. Thus, the objective of the current study was to develop an alcohol-plus-toxicant model to study how an environmental pollutant, PCB 126, impacts rodent ALD pathology.

METHODS

Briefly, male C57BL/6J mice were exposed to 0.2 mg/kg PCB 126 or corn oil vehicle four days prior to ethanol feeding using the chronic-binge (10-plus-one) model.

RESULTS

Concentrations of macromolecules, including hepatic lipids, carbohydrates, and protein (albumin) were impacted. Exposure to PCB 126 exacerbated hepatic steatosis and hepatomegaly in mice exposed to the chemical and fed an ethanol diet. Gene expression and the analysis of blood chemistry showed a potential net increase and retention of hepatic lipids and reductions in lipid oxidation and clearance capabilities. Depletion of glycogen and glucose was evident, which contributes to disease progression by generating systemic malnutrition. Granulocytic immune infiltrates were present but driven solely by ethanol feeding. Hepatic albumin gene expression and plasma levels were decreased by ~50% indicating a potential compromise of liver function. Finally, gene expression analyses indicated that the aryl hydrocarbon receptor and constitutive androstane receptor were activated by PCB 126 and ethanol, respectively.

CONCLUSIONS

Various environmental toxicants are known to modify or enhance FLD in high-fat diet models. Findings from the present study suggest that they interact with other lifestyle factors such as alcohol consumption to reprogram intermediary metabolism resulting in exacerbated ethanol-associated systemic malnutrition in ALD.

Prolonged Consumption of glucose syrup enhances glucose tolerance in mice

There is debate about the metabolic impact of sugar-sweetened beverages. Here, we tested the hypothesis that ad lib consumption of glucose (Gluc) or high-fructose (HiFruc) syrups improves glucose tolerance in mice. We provided C57BL/6 mice with a control (chow and water) or experimental (chow, water and sugar solution) diet across two consecutive 28-day exposure periods, and monitored changes in body composition, glucose tolerance, cephalic-phase insulin release (CPIR) and insulin sensitivity. The sugar solutions contained 11% concentrations of Gluc or HiFruc syrup; these syrups were derived from either corn starch or cellulose. In Experiment 1, consumption of the Gluc diets reliably enhanced glucose tolerance, while consumption of the HiFruc diets did not. Mice on the Gluc diets exhibited higher CPIR (relative to baseline) by the end of exposure period 1, whereas mice on the control and HiFruc diets did not do so until the end of exposure period 2. Mice on the Gluc diets also exhibited higher insulin sensitivity than control mice at the end of exposure period 2, while mice on the HiFruc diets did not. In Experiment 2, we repeated the previous experiment, but limited testing to the corn-based Gluc and HiFruc syrups. We found, once again, that consumption of the Gluc (but not the HiFruc) diet enhanced glucose tolerance, in part by increasing CPIR and insulin sensitivity. These results show that mice can adapt metabolically to high glucose diets, and that this adaptation process involves upregulating at least two components of the insulin response system.

Effects of Saccharin Consumption on Operant Responding for Sugar Reward and Incubation of Sugar Craving in Rats

Repeated experience with artificial sweeteners increases food consumption and body weight gain in rats. Saccharin consumption may reduce the conditioned satiety response to sweet-tasting food. Rats were trained to press a lever to obtain sucrose for five days. A compound cue (tone + light) was presented with every sucrose delivery. On the following day, each lever press produced only the compound cue (cue-reactivity test). Subjects were then provided with yogurt for three weeks in their home cages. The rats were divided into two groups. Rats in the saccharin group received yogurt sweetened with saccharin on some days and unsweetened yogurt on others. For the plain group, only unsweetened plain yogurt was provided. Subsequently, the cue-reactivity test was conducted again. On the following day, the rats underwent a consumption test in which each lever press was reinforced with sucrose. Chow consumption and body weight gain were larger in the saccharin group than in the plain group. Lever responses increased from the first to the second cue-reactivity tests (incubation of craving) in both groups. During the consumption test, lever responses were higher in the saccharin group than in the plain group, suggesting that the conditioned satiety response was impaired in the saccharin group.

Changes in Appetite Regulation-Related Signaling Pathways in the Brain of Mice Supplemented with Non-nutritive Sweeteners

Non-nutritive sweeteners (NNSs) are commonly used to prevent weight gain and development of metabolic diseases associated with consumption of high-energy diets. Recent studies have demonstrated that these compounds may have unwanted detrimental effects under specific circumstances in vivo. In particular, an association between NNS consumption and changes in signaling pathways involved in the hunger-satiety system in the brain has been reported. Nonetheless, the extent of alterations in brain signaling pathways associated with consumption of these compounds has not been determined. The objective of this study was to determine the effect of frequent consumption of NNSs on the expression of proteins involved in signaling pathways related to appetite control in the brain in vivo. Eight-week-old BALB/c mice were supplemented with sucrose, sucralose, or steviol glycosides in their daily drinking water for 6 weeks. Subsequently, total brain protein extracts were used to analyze the expression of total and phosphorylated JAK2, STAT5, ERK 1/2, JNK, as well as SHP-2 and POMC, by western blot. Serum concentrations of leptin and α-MSH were quantified by ELISA. Results show that consumption of NNSs promotes significant changes in these signaling pathways, reducing the expression of pSTAT5/STAT5, pERK 1/2, SHP-2, and pJNK/JNK in male mice supplemented with steviol glycosides. Furthermore, consumption of steviol glycosides induced a decrease of α-MSH in male mice. In contrast, steviol glycosides induced overexpression of pSTAT5, pERK, and SHP-2 in females. These data suggest that chronic consumption of NNSs promotes sex-specific changes in signaling pathways related to the central hunger-satiety system in vivo.

Added sugar intake is associated with pericardial adipose tissue volume

AIM

The purpose of this study was to determine the relationships of pericardial adipose tissue and visceral adipose tissue volume with added sugar and sugar-sweetened beverage intakes. We hypothesized that both added sugar and sugar-sweetened beverages were positively associated with pericardial adipose tissue and visceral adipose tissue volumes in black and white men and women enrolled in the prospective Coronary Artery Risk Development in Young Adults study.

METHODS AND RESULTS

Dietary intake was assessed by diet history at baseline, year 7 and year 20 examinations in 3070 participants aged 18-30 and generally healthy at baseline. After 25 years follow-up, participants underwent a computed tomography scan of chest and abdomen; the computed tomography scans were read, and pericardial adipose tissue, visceral adipose tissue, and subcutaneous adipose tissue volumes were calculated. Quintiles were created for the average of baseline, year 7 and year 20 added sugar and for the average of sugar-sweetened beverages. General linear regression analysis evaluated the associations of pericardial adipose tissue and visceral adipose tissue volumes across quintiles of added sugar and across quintiles of sugar-sweetened beverage intakes adjusted for potential confounding factors. In a multivariable model, pericardial adipose tissue volume was higher across increasing quintiles of added sugar and sugar-sweetened beverage intakes (p_trend = 0.001 and p_trend < 0.001, respectively). A similar relation was observed for visceral adipose tissue (p_trend < 0.001 for both added sugar and sugar-sweetened beverages).

CONCLUSIONS

Long-term intakes of added sugar and sugar-sweetened beverages were associated with higher pericardial adipose tissue, visceral adipose tissue, and subcutaneous adipose tissue volumes. Because these ectopic fat depots are associated with greater risk of disease incidence, these findings support limiting intakes of added sugar and sugar-sweetened beverages.

Endogenous opiates and behavior: 2017

This paper is the fortieth consecutive installment of the annual anthological review of research concerning the endogenous opioid system, summarizing articles published during 2017 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides and receptors as well as effects of opioid/opiate agonists and antagonists. The review is subdivided into the following specific topics: molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors (1), the roles of these opioid peptides and receptors in pain and analgesia in animals (2) and humans (3), opioid-sensitive and opioid-insensitive effects of nonopioid analgesics (4), opioid peptide and receptor involvement in tolerance and dependence (5), stress and social status (6), learning and memory (7), eating and drinking (8), drug abuse and alcohol (9), sexual activity and hormones, pregnancy, development and endocrinology (10), mental illness and mood (11), seizures and neurologic disorders (12), electrical-related activity and neurophysiology (13), general activity and locomotion (14), gastrointestinal, renal and hepatic functions (15), cardiovascular responses (16), respiration and thermoregulation (17), and immunological responses (18).

Toward isolating reward changes in diet-induced obesity: A demand analysis

Although hormonal and metabolic factors are well known to influence obesity, recent evidence suggests that obesity may be influenced also by changes in reward sensitivity akin to that seen in other 'reward pathologies', like substance use disorders. The current study sought to isolate changes in reward that may occur after the onset of diet-induced obesity by characterizing the economic demand for caloric (sucrose) and non-caloric (saccharin) reinforcers in a preclinical model of diet-induced obesity (DIO). We utilized economic demand analysis to measure baseline demand intensity (Q₀) and demand elasticity (α) for sucrose and saccharin reinforcers in rats. After baseline measures were collected, rats were assigned randomly to a high-fat (HF) diet or low-fat (LF) control diet. After 8-weeks of diet exposure, HF rats were divided into obesity-resistant (OR) or obesity-prone (OP) groups based on weight after the 8-week HF diet exposure. Post-DIO demand data for each reinforcer were reassessed. At baseline, rats had higher demand intensity and lower elasticity for sucrose compared to saccharin. After 8-weeks of the high-fat diet, OP rats had significantly greater weight gain and lower demand elasticity for sucrose and saccharin and higher demand intensity for saccharin. The changes in sucrose and saccharin elasticity suggest that DIO-induced changes in food-related behavior are associated with changes in reward processes. The changes in demand intensity for saccharin suggest that demand intensity, as a measure of 'set point', is not directly linked to metabolic processes. The current study shows that microeconomic theory and demand analysis is able to isolate independent aspects of diet-induced reward changes related to caloric and non-caloric reinforcers.

Effect of a high sucrose and high fat diet in BDNF (+/-) mice on oxidative stress markers in adipose tissues

The purpose of this study was to investigate the effects of a high fat and a high sucrosediet in wild type and BDNF (+/-) mice on oxidative stress in epididymal and subcutaneousadipose tissues by measuring different markers of oxidative stress and antioxidant enzymes. Wild type (WT) and BDNF (+/-) male mice were divided into six groups receiving fed control diet (CD), high sucrose diet (HSD), or high fat diet (HFD) for four months. Levels of 3-nitrotyrosine (3-NT) increased in the HFD-fed BDNF (+/-) mice, while 4-hydroxynonenal (4-HNE) levels increased in the CD and HFD-fed BDNF (+/-) groups. Malondialdehyde (MDA) levels decreased in subcutaneous tissue compared to epididymal adipose tissue, independently of diet type. Superoxide dismutase (SOD) activity was reduced by HFD (p < 0.05), butglutathione peroxidase (GSH-Px) activity was increased by HSD in epididymal adipose tissuein BDNF (+/-) mice (p < 0.05). GSH-Px activities was increased by CD and HFD in subcutaneous adipose tissue of BDNF (+/-) (p < 0.05). SOD2 and GSH-Px3 expressions were only decreased by HSD in epididymal and subcutaneous adipose tissues of BDNF (+/-) mice (p < 0.05). In conclusion, reduced BDNF may increase OS in epididymal adipose tissue, but not in subcutaneous adipose tissue following HSD and HFD.

Rodent Models of Alcoholic Liver Disease: Role of Binge Ethanol Administration

Both chronic and acute (binge) alcohol drinking are important health and economic concerns worldwide and prominent risk factors for the development of alcoholic liver disease (ALD). There are no FDA-approved medications to prevent or to treat any stage of ALD. Therefore, discovery of novel therapeutic strategies remains a critical need for patients with ALD. Relevant experimental animal models that simulate human drinking patterns and mimic the spectrum and severity of alcohol-induced liver pathology in humans are critical to our ability to identify new mechanisms and therapeutic targets. There are several animal models currently in use, including the most widely utilized chronic ad libitum ethanol (EtOH) feeding (Lieber–DeCarli liquid diet model), chronic intragastric EtOH administration (Tsukamoto–French model), and chronic-plus-binge EtOH challenge (Bin Gao—National Institute on Alcohol Abuse and Alcoholism (NIAAA) model). This review provides an overview of recent advances in rodent models of binge EtOH administration which help to recapitulate different features and etiologies of progressive ALD. These models include EtOH binge alone, and EtOH binge coupled with chronic EtOH intake, a high fat diet, or endotoxin challenge. We analyze the strengths, limitations, and translational relevance of these models, as well as summarize the liver injury outcomes and mechanistic insights. We further discuss the application(s) of binge EtOH models in examining alcohol-induced multi-organ pathology, sex- and age-related differences, as well as circadian rhythm disruption.