Resistance of male Sprague-Dawley rats to sucrose-induced obesity: effects of 18-methoxycoronaridine

[Effect of a multivitamin on insulin resistance, inflammation, and oxidative stress in a Wistar rat model of induced obesity]

Introduction

Introduction: excessive accumulation of adipose tissue is accompanied by alterations in the inflammatory state and increased oxidative stress, and these variables are associated with insulin resistance and increased glucose and insulin levels. On the other hand, vitamins and minerals reinforce the antioxidant and inflammatory capacity, for this reasons we propose that they could contribute to the control of insulin resistance, glucose and lipid metabolism in a rat model of obesity. Objective: to analyze the effect of a multivitamin supplement on markers of insulin resistance, inflammation, and oxidative stress in obese rats on a cafeteria diet. Methods: thirty-five 28-day-old male Wistar rats were randomly divided into four groups: 1, standard diet control; 2, standard diet plus multivitamin; 3, obese on a cafeteria diet; and 4, obese on a cafeteria diet plus multivitamin. After the treatments, glucose levels, HbA1c, insulin, TNF-α, IL-6, oxidative stress and lipid profile were analyzed by colorimetric methods, as well as the percentage of adipose tissue, Homeostasis Model Assessment (HOMA) index y Quantitative Insulin Sensitivity Check Index (QUICKI). Results: multivitamin supplementation significantly decreased visceral adipose tissue, HOMA index, glucose, HbA1c, oxidant stress, and inflammatory markers in the obese plus multivitamin rat group, compared with the obese cafeteria diet rat group and the standard diet rat control group. However, the group that was administered only the multivitamin without the cafeteria diet had increased levels of total adipose tissue, glucose, and oxidative stress, as well as the QUICKI index relative to the control group with the standard diet. Conclusion: co-administration of a multivitamin supplement may improve insulin sensitivity, glucose metabolism and lipid profile; strengthen antioxidant status; and decrease inflammation during weight gain. However, it was not expected that added sugars in multivitamin supplement can also increase total adipose tissue, oxidative stress and glucose levels, so it is suggested to use sugar-free multivitamins in the future.

Sex and Species Differences in the Development of Diet-Induced Obesity and Metabolic Disturbances in Rodents

Prevalence and health consequences of obesity differ between men and women. Yet, most preclinical studies investigating the etiology of obesity have, to date, been conducted in male rodents. Notably, diet is a major determinant of obesity, but sex differences in rodent models of diet-induced obesity, and the mechanisms that underlie such differences, are still understudied. Here, we aim to determine whether time course and characteristics of diet-induced obesity differ between sexes in rats and mice, and to investigate the potential causes of the observed divergence. To achieve this, we offered the most commonly tested rodents of both sexes, SD rats and C57BL/6 mice, a free choice of 60 % high-fat diet (HFD) and regular chow; body weight, food intake, fat mass, brown adipose responses, locomotor activity and glucose tolerance were assessed in a similar manner in both species. Our results indicate that overall diet-induced hyperphagia is greater in males but that females display a higher preference for the HFD, irrespective of species. Female rats, compared to males, showed a delay in diet-induced weight gain and less metabolic complications. Although male rats increased brown adipose tissue thermogenesis in response to the HFD challenge, this was not sufficient to counteract increased adiposity. In contrast to rats, female and male mice presented with a dramatic adiposity and impaired glucose tolerance, and a decreased energy expenditure. Female mice showed a 5-fold increase in visceral fat, compared to 2-fold increase seen in male mice. Overall, we found that male and female rodents responded very differently to HFD challenge, and engaged different compensatory energy expenditure mechanisms. In addition, these sex differences are divergent in rats and mice. We conclude that SD rats have a better face validity for the lower prevalence of overweight in women, while C57BL/6 mice may better model the increased prevalence of morbid obesity in women.

An overview of energy and metabolic regulation

The physiology and behaviors related to energy balance are monitored by the nervous and humoral systems. Because of the difficulty in treating diabetes and obesity, elucidating the energy balance mechanism and identifying critical targets for treatment are important research goals. Therefore, the purpose of this article is to describe energy regulation by the central nervous system (CNS) and peripheral humoral pathway. Homeostasis and rewarding are the basis of CNS regulation. Anorexigenic or orexigenic effects reflect the activities of the POMC/CART or NPY/AgRP neurons within the hypothalamus. Neurotransmitters have roles in food intake, and responsive brain nuclei have different functions related to food intake, glucose monitoring, reward processing. Peripheral gut- or adipose-derived hormones are the major source of peripheral humoral regulation systems. Nutrients or metabolites and gut microbiota affect metabolism via a discrete pathway. We also review the role of peripheral organs, the liver, adipose tissue, and skeletal muscle in peripheral regulation. We discuss these topics and how the body regulates metabolism.

Can We Selectively Reduce Appetite for Energy-Dense Foods? An Overview of Pharmacological Strategies for Modification of Food Preference Behavior

Excessive intake of food, especially palatable and energy-dense carbohydrates and fats, is largely responsible for the growing incidence of obesity worldwide. Although there are a number of candidate antiobesity drugs, only a few of them have been proven able to inhibit appetite for palatable foods without the concurrent reduction in regular food consumption. In this review, we discuss the interrelationships between homeostatic and hedonic food intake control mechanisms in promoting overeating with palatable foods and assess the potential usefulness of systemically administered pharmaceuticals that impinge on the endogenous cannabinoid, opioid, aminergic, cholinergic, and peptidergic systems in the modification of food preference behavior. Also, certain dietary supplements with the potency to reduce specifically palatable food intake are presented. Based on human and animal studies, we indicate the most promising therapies and agents that influence the effectiveness of appetite-modifying drugs. It should be stressed, however, that most of the data included in our review come from preclinical studies; therefore, further investigations aimed at confirming the effectiveness and safety of the aforementioned medications in the treatment of obese humans are necessary.

Effects of 18-methoxycoronaridine on ghrelin-induced increases in sucrose intake and accumbal dopamine overflow in female rats

RATIONALE

18-methoxycoronaridine (18-MC), a selective antagonist of α3β4 nicotinic receptors, has been previously shown, in rats, to reduce the self-administration of several drugs of abuse, reduce operant responding for sucrose, and prevent the development of sucrose-induced obesity. It has become increasingly apparent that there is a significant overlap between the systems regulating drug reward and food intake, therefore, we investigated whether 18-MC might modulate the effects of ghrelin, one of several orexigenic peptides recently implicated in both feeding and drug reward.

OBJECTIVES

In female Sprague-Dawley rats, we determined whether acute 18-MC treatment would reduce both ghrelin-induced increases in sucrose intake and ghrelin-elicited increases in accumbal dopamine levels.

RESULTS

Pretreatment with 18-MC (20 mg/kg, i.p.), given prior to the administration of ghrelin (1 μg, lateral ventricle), blocked ghrelin-induced increases in sucrose (5%) intake in a two-bottle open access paradigm. Using in vivo microdialysis, 18-MC (both 20 and 40 mg/kg) prevented ghrelin (2 μg, intraventral tegmental area)-induced increases in extracellular dopamine in the nucleus accumbens. 18-MC had no effect on deposition of fat or on serum levels of glucose, triglycerides, and cholesterol in ghrelin-treated rats.

CONCLUSIONS

The present results suggest that one potential mechanism by which 18-MC exerts its effects on palatable food consumption is via modulation of ghrelin's effects.