[Weight loss in a patient with morbid obesity under treatment with oleoyl-estrone]

Estrogens and the regulation of glucose metabolism

The main estrogens: estradiol, estrone, and their acyl-esters have been studied essentially related to their classical estrogenic and pharmacologic functions. However, their main effect in the body is probably the sustained control of core energy metabolism. Estrogen nuclear and membrane receptors show an extraordinary flexibility in the modulation of metabolic responses, and largely explain gender and age differences in energy metabolism: part of these mechanisms is already sufficiently known to justify both. With regard to energy, the estrogen molecular species act essentially through four key functions: (1) Facilitation of insulin secretion and control of glucose availability; (2) Modulation of energy partition, favoring the use of lipid as the main energy substrate when more available than carbohydrates; (3) Functional protection through antioxidant mechanisms; and (4) Central effects (largely through neural modulation) on whole body energy management. Analyzing the different actions of estrone, estradiol and their acyl esters, a tentative classification based on structure/effects has been postulated. Either separately or as a group, estrogens provide a comprehensive explanation that not all their quite diverse actions are related solely to specific molecules. As a group, they constitute a powerful synergic action complex. In consequence, estrogens may be considered wardens of energy homeostasis.

Gut-Brain Endocrine Axes in Weight Regulation and Obesity Pharmacotherapy

In recent years, the obesity epidemic has developed into a major health crisis both in the United States as well as throughout the developed world. With current treatments limited to expensive, high-risk surgery and minimally efficacious pharmacotherapy, new therapeutic options are urgently needed to combat this alarming trend. This review focuses on the endogenous gut-brain signaling axes that regulate appetite under physiological conditions, and discusses their clinical relevance by summarizing the clinical and preclinical studies that have investigated manipulation of these pathways to treat obesity.

Regulation of appetite to treat obesity

Obesity has escalated into a pandemic over the past few decades. In turn, research efforts have sought to elucidate the molecular mechanisms underlying the regulation of energy balance. A host of endogenous mediators regulate appetite and metabolism, and thereby control both short- and long-term energy balance. These mediators, which include gut, pancreatic and adipose neuropeptides, have been targeted in the development of anti-obesity pharmacotherapy, with the goal of amplifying anorexigenic and lipolytic signaling or blocking orexigenic and lipogenic signaling. This article presents the efficacy and safety of these anti-obesity drugs.

Oleoyl-estrone

Oleoyl-estrone (OE) is a powerful slimming agent that is also present in plasma and adipose tissue, where it is synthesized. It acts through the formation of a derivative W. OE effects (and W levels) are proportional to the dose. OE reduces food intake but maintains energy expenditure (thermogenesis). The energy gap is fulfilled with adipose tissue fat, sparing body protein and maintaining glycemia (and glycogen) with lower insulin and leptin levels. OE (in fact W) acts through specific receptors, different from those of estrogen. OE increases cholesterol catabolism, reducing hypercholesterolemia in obese rats. The main metabolic effect on adipose tissue is lowering of lipid synthesis, maintaining unchanged the intracellular lipolytic processes; the imbalance favors the progressive loss of fat, which is largely used by the muscle. OE administration induces additive effects with other antiobesity agents, such as β(3)-adrenergic agonists, forcing a massive loss of lipid. Corticosteroids markedly limit OE action by altering the liver control of lipogenesis. OE also inhibits the action of 17β-hydroxysteroid dehydrogenase, decreasing the synthesis of β-estradiol and testosterone. Discontinuous treatment allows for maximal efficacy both in rats and humans. OE has the advantage that the loss of fat is maintained and does not require additional dietary limitations.

Current trends in targeting the hormonal regulation of appetite and energy balance to treat obesity

With the eruption of the obesity pandemic over the past few decades, much research has been devoted to understanding the molecular mechanisms by which the human body regulates energy balance. These studies have revealed several mediators, including gut/pancreatic/adipose hormones and neuropeptides that control both short- and long-term energy balance by regulating appetite and/or metabolism. These endogenous mediators of energy balance have been the focus of many anti-obesity drug-development programs aimed at either amplifying endogenous anorexigenic/lipolytic signaling or blocking endogenous orexigenic/lipogenic signaling. Here, we discuss the efficacy and safety of targeting these pathways for the pharmacologic treatment of obesity.

Site-related white adipose tissue lipid-handling response to oleoyl-estrone treatment in overweight male rats

BACKGROUND

Oleoyl-estrone (OE) decreases energy intake while maintaining glucose homeostasis, and energy expenditure at the expense of body fat. White adipose tissue (WAT) depots behave differently under starvation, postprandial state and pharmacologically induced lipolysis.

AIM OF THE STUDY

To understand the mechanism of massive lipid loss from WAT elicited by OE treatment.

METHODS

We used overweight male rats. Rats receiving OE (10 nmol/g) gavages were compared with controls and a pair-fed group. Whole fat pads from the mesenteric, retroperitoneal, epididymal and inguinal subcutaneous sites were excised and analyzed for lipid, DNA, mRNA and the expression of lipogenic, fatty acid transporters and lipase genes.

RESULTS

In OE and pair-fed rats, WAT weights decreased, with the limited loss of cells. Patterns of gene expression in most WAT sites were similar for OE and PF, suggesting a shared mechanism of fat mobilization, but in mesenteric WAT, PF increased lipogenic and fatty acid transporter gene expressions. However, OE inhibited lipogenic expressions more deeply than PF.

CONCLUSIONS

White adipose tissue sites showed different expression patterns, hinting at relatively specialized functions in fat storage; thus, single site analyses cannot be extrapolated to whole WAT. Differences between mesenteric and the other sites suggest that 'visceral fat' should be reserved for this site only, and not applied to other abdominal fat depots (epididymal, retroperitoneal).

Intestinal oleoyl-estrone esterase activity in the Wistar rat

Low-dose oral oleoyl-estrone (OE) (i.e. in dairy products) is hydrolysed to estrone, which promotes growth and fat deposition. However, pharmacological doses of OE are absorbed largely intact and elicit fat losses. Thus, in order to find out how the intestine handles OE, esterase activity (at pH 5, 7 or 8) was measured in rat stomach, duodenum, jejunum, ileum, cecum, large intestine, and liver using OE as substrate. There were no sex-related differences. Pure pancreatic cholesterol-ester esterase hydrolysed OE even in the absence of taurocholate. The differences in the pH-related activity distribution pattern and selective inhibition and taurocholate dependence show that, in addition to the luminal (i.e. pancreatic) cholesterol-ester esterase, other esterases hydrolyse OE; these combined activities may be sufficient to rapidly dispose of pharmacological doses of OE. Female rats received a tritium-labeled OE gavage; the luminal and tissue label content were measured up to 24 h. The high retention of label in the stomach suggest that this may be a significant site of absorption. The rapid decrease of label in intestinal lumen (and rat tissues) shortly after the administration, hint at rapid absorption and disposal. In conclusion, the high OE-esterase activity and early absorption of OE are indicative of upper gastro-intestinal tract absorption skipping most of the medium-tract esterases.

Short-term oleoyl-estrone treatment affects capacity to manage lipids in rat adipose tissue

BACKGROUND

Short-term OE (oleoyl-estrone) treatment causes significant decreases in rat weight mainly due to adipose tissue loss. The aim of this work was to determine if OE treatment affects the expression of genes that regulate lipid metabolism in white adipose tissue.

RESULTS

Gene expression in adipose tissue from female treated rats (48 hours) was analysed by hybridization to cDNA arrays and levels of specific mRNAs were determined by real-time PCR. Treatment with OE decreased the expression of 232 genes and up-regulated 75 other genes in mesenteric white adipose tissue. The use of real-time PCR validate that, in mesenteric white adipose tissue, mRNA levels for Lipoprotein Lipase (LPL) were decreased by 52%, those of Fatty Acid Synthase (FAS) by 95%, those of Hormone Sensible Lipase (HSL) by 32%, those of Acetyl CoA Carboxylase (ACC) by 92%, those of Carnitine Palmitoyltransferase 1b (CPT1b) by 45%, and those of Fatty Acid Transport Protein 1 (FATP1) and Adipocyte Fatty Acid Binding Protein (FABP4) by 52% and 49%, respectively. Conversely, Tumour Necrosis Factor (TNFalpha) values showed overexpression (198%).

CONCLUSION

Short-term treatment with OE affects adipose tissue capacity to extract fatty acids from lipoproteins and to deal with fatty acid transport and metabolism.

In the rat, estrone sulphate is the main serum metabolite of oral oleoyl-estrone

Two different oral doses of oleoyl-estrone: 1 and 10 nmol/g a day were given once to male Wistar rats. The serum levels of free estrone, estrone sulphate, estradiol, and acyl-estrone were measured at intervals up to 72 h after the gavage. Oleoyl-estrone was rapidly absorbed; with the 1 nmol/g dose no changes were observed in plasma acyl-estrone but levels increased dramatically with 10 nmol/g, peaking at 6 h; high acyl-estrone levels were maintained up to 24 h, returning to normalcy at 48 h. With the 10 nmol/g dose, free estrone at most doubled its levels but estrone sulphate concentrations rose by one order of magnitude; in both cases, the increases soon (2 h) reached a plateau that was maintained for almost two days. Estradiol levels remained unchanged except for a transient peak at 2 h at the 10 nmol/g dose. The relationship between free estrone and its sulphate was linear, and those of estrone and estrone sulphate versus acyl-estrone showed the existence of an upper serum concentration limit for both molecules. The results hint at estrone sulphate being an important metabolite of oleoyl-estrone disposal, confirm the limited estrogenic response to oleoyl-estrone administration and agree with a rapid absorption and disposal of oleoyl-estrone, nevertheless maintaining high circulating levels of the ester for a time after its oral administration.

Effects of Combined Oleoyl-Estrone and Rimonabant on Overweight Rats

Oleoyl-estrone (OE) decreases appetite, maintains energy expediture, induces lipolysis (sparing protein), and decreases cholesterolemia and insulin resistance. Rimonabant (SR141716) is a cannabinoid-receptor inhibitor that decreases appetite and mobilizes fat. We studied whether their combination improves their slimming effects. Male overweight rats received daily gavages of 5.3 mg/kg OE, 10 mg/kg rimonabant, or both drugs during 10 days. Body weight and composition, energy balance, adipose tissue weight, and serum hormones and metabolites were measured. OE halved food intake and maintained energy expenditure at the expense of body fat. Rimonabant effects on appetite and energy balance were less marked, resulting in lower lipid mobilization. OE and rimonabant followed the OE pattern, with no additive or synergic effects. Glycemia was maintained, but OE decreased insulin, GLP-1, and cholesterol, whilst rimonabant increased cholecystokinin and cholesterol, and decreased NEFA. Both drugs decreased leptin and triacylglycerols; ghrelin was unchanged. The results hint at different mechanisms of action of both drugs: we can assume that OE effects do not involve the cannabinoid pathway. OE does not seem to act, either, after 10 days, through the secretion of ghrelin or the intestinal appetite-controlling peptides tested.

Combined effects of oral oleoyl-estrone and limited food intake on body composition of young overweight male rats

OBJECTIVE

The combined effects of limited food intake and OE treatment have been analysed in order to determine whether hypocaloric diets enhance the slimming effects of OE on mature overweight male rats. Two levels of dietary limitation at 50 and 25% of a standard intake were established, roughly corresponding to the human LCDs and VLCDs.

DESIGN

Wistar male rats (6 weeks old) were made overweight by a cafeteria diet. After transition to standard diet, they were subjected to food restriction: down to 50 or 25% with respect to the transition period. Half the animals were given daily oral gavages of 10 nmol/g oleoyl-estrone (OE), and the rest received only the vehicle during 10 days.

MEASUREMENTS

Changes in weight and body composition: water, lipid, protein or gross energy were determined by comparing the final pool size with that of day 0, calculated from the initial body weight and the composition of untreated rats. Energy and nitrogen balances were estimated. Plasma levels of metabolites and hormones were also measured.

RESULTS

OE induced changes in body composition similar to those elicited by a 50% reduction in food, with massive loss of lipid and energy. OE-treated rats ate less than the controls, but additional effects on body composition on reduced diet were minimal. OE improved metabolic homoeostasis: better maintained glycaemia, lower cholesterol and shallower hormonal changes, but at the expense of slightly increased protein mobilisation.

CONCLUSIONS

The data presented suggest that no advantages are accomplished by combining OE treatment and hypocaloric diets compared with OE alone, at least under the experimental conditions tested, since the effects were not additive. Despite OE affecting food intake, mechanisms other than that are deemed responsible for the mobilisation of body fat, since intake alone cannot explain the effects on body weight, nor the metabolic and hormonal changes in OE-treated rats. It is concluded that the combination of food restriction and OE may result in unwanted increased protein mobilisation with no synergy between both slimming treatments.