Control of Food Intake and Body Weight Through Oral Administration of Leptin

Special Article - Oral Administration of Leptin

Austin J Endocrinol Diabetes. 2016; 3(3): 1049.

Control of Food Intake and Body Weight Through Oral Administration of Leptin

Bendayan M* and Cammisotto PG

Department of Pathology and Cell Biology, University of Montreal, Canada

*Corresponding author: Bendayan M, Department of Pathology and Cell Biology, University of Montreal, C.P. 6128 Succ. Centre Ville, 2900 Edouard Mont Petit Montreal, Quebec, H3C 3J7, Canada

Received: May 19, 2016; Accepted: August 11, 2016; Published: August 26, 2016


Upon demonstrating that leptin is secreted by gastric chief cells into the gastric juice, vehiculated towards the intestine, internalized by the duodenal epithelial cells to be transferred to circulation, we put forward the hypothesis that oral administration of leptin may be appropriate for the control of food intake and management of body weight. Oral leptin should follow the same path as the endogenous one. Leptin dissolved in an appropriate vehicle, was administered orally to ob/ob mice that lack leptin becoming rapidly obese. Oral leptin reached blood circulation very efficiently. When receiving regularly oral leptin twice a day, the animals experienced a drastic decrease in food intake and consequently in body weight. These changes were correlated to daily amounts of oral leptin. Adjusting these amounts was able to stabilize the body weight of the animals. Stopping leptin treatment led to increase in food intake and body mass. Experiments performed on normal C57 mice revealed that these animals, with normal endogenous circulating leptin, are by far more sensitive to oral leptin than the leptin-lacking ob/ob mice. On the other hand, db/db mice lacking the leptin receptors were non-responsive to the oral leptin. Long-term daily treatment of mice with oral leptin stabilized their body weight and demonstrated no morphological alterations of their gastric and duodenal mucosa and liver tissue. Oral administration of leptin thus appears as a promising avenue for the management of food intake and the control of body weight as well as for pathologies linked to leptin deficiency.

Keywords: Obesity; Leptin; Oral administration; Weight loss


Understanding regulation of food intake has become increasingly complex. Several hormones, both orexigenic and anorexigenic, have been identified. Once crossing the blood brain barrier they reach their main hypothalamic target sites to balance satiety and hunger. Among others, leptin plays fundamental roles in the control of appetite and in regulating energy expenditure [1-16]. Originally discovered in white adipose tissue [5,6,9,12], leptin is also expressed by other tissues and mainly by the gastric mucosa that secretes large amounts [2,7,12]. Leptin secretion is controlled by a wide range of factors such as food intake, certain hormones as insulin as well as nutrients like amino acids and glucose [12].

While adipose tissue secretes leptin through a slow constitutive endocrine pathway [5,6,9], the gastric mucosa releases leptin into the gastric juice through the classical RER-Golgi-secretory granule regulated exocrine pathway [7,12]. The gastric mucosa has been shown to contain both endocrine and exocrine leptin secreting cells [7]. Indeed, light and electron microscopy immunocytochemistry has revealed the presence of a number of isolated endocrine leptinsecreting cells within its connective tissue while all chief cells lining the gastric epithelium express and release leptin into the gastric juice [7]. The exocrine secretion of leptin by the gastric chief cells is carried out concomitantly with other products such as lipase and pepsinogen [12]. The question was raised on the capability for leptin, a small peptide of 17kD, to survive the harsh conditions of the gastric juice. This was answered by a series of studies demonstrating that within the chief cell secretory pathway, the small leptin peptide gets associated to a large protective chaperon that corresponds to the soluble isoform of the leptin-receptor [8,10]. This soluble receptor is synthesized by the gastric chief cells in parallel with leptin. From the RER, both molecules get transferred to the Golgi where maturation occurs, generating leptin on the one hand and, through furin and pro-convertase 7 converting enzyme actions, the soluble isoform of the leptin-receptor [12]. The leptin gets associated to this soluble leptin receptor isoform in the trans-Golgi network to form a complex which is packed in large secretory granules and discharged into the gastric lumen by exocytosis. The leptin-leptin receptor complex, highly resistant to hydrolysis from the gastric juice, is channelled to the duodenal lumen [12].

Levels of plasma leptin in rodents, rise within 15 min after the onset of food intake and was demonstrated to be the result of the gastric secretion since adipose tissue secretes leptin in a slow and constitutive manner [12]. We have demonstrated that the increase in postprandial circulating leptin is the result of the rapid transfer of gastric-secreted leptin across the duodenal wall to blood [7,10,12]. A complicated but highly efficient transcytotic pathway takes place within duodenal enterocytes that express transmembrane leptin receptor at both their luminal and baso-lateral membranes [9,10,12].

We have carried out a series of studies to comprehend the mechanism by which leptin is synthesized and secreted by the gastric chief cells, transported by the gastric juice without being degraded and the pathway taken by this gastric leptin to cross the intestinal barrier to reach circulation [12].

Exocrine-secreted gastric leptin thus belongs to a physiological axis, independent in terms of time of secretion and regulation from that of adipose tissue-secreted leptin in order to rapidly adjust food intake and nutrient absorption. Adipocytes and gastric epithelial cells are two cell types the metabolism of which is closely linked to food intake and energy storage. The coordinated secretion of adipose and gastric leptin ensures proper management of food processing and energy storage.

In view of the facts 1- that leptin is normally present in the gastric lumen, 2- that there is an efficient protective configuration to ensure survival of leptin in the gastric lumen 3- and that there is a well-organized transport system responsible for the transfer of leptin from the intestinal lumen to blood circulation, we put forward the hypothesis that exogenous leptin given orally could reach blood circulation and act upon the hypothalamic cells for the control of food intake.

Studies to support such hypothesis were carried out in vivo using various animal models such the normal mouse, the ob/ob mouse, the db/db mouse, other normal rodents and larger animals. The work was carried out in various steps and convey as a series of reports. In this first one, we have designed an optimal vehicle to administer oral leptin and then force-fed ob/ob, db/db and C57 control mice with leptin to evaluate the efficiency of the approach.

Material & Methods and Results

Based on previous studies [3,4,22,23], we designed a vehicle able to dissolve leptin, to protect it while in the gastric juice and to promote its transfer to the blood across the duodenal wall upon its oral administration to animals.

Normal, ob/ob and db/db mice were acquired from Jackson Laboratories (Maine, USA). Normal mice were about 6 weeks old and weight ~20g. Ob/b mice were also young animals, about 6 weeks old and weight 40g while the db/db mice were 8 weeks old and weight about 40g. Work was carried out following the guidelines of the Canadian Committee of Animal Care and those of the Animal Facility of the University of Montreal, Several recipes and concentrations of reagents were tested by force-feeding the animals with a constant amount of leptin and varying the composition of our vehicle. Upon leptin administration, we assessed circulating levels of leptin at different time points. In order to facilitate the experiments, we decided to work with ob/ob mice since they are totally devoid of leptin. Indeed due to genetic mutations, the ob/ob gene, responsible for leptin expression, is not active in these animals and circulating plasma levels of leptin are undetectable. Because of their lack of leptin, these animals have no satiety feelings and upon having food ad libitum, they very rapidly become obese [14,15].

Different recipes of the vehicle were assessed by force-feeding the animals with 50 μg of mouse recombinant leptin (R&D Systems Inc. Minneapolis, MN, USA) dissolved in 0.5 ml of vehicle. Blood (0.1 ml) was sampled at time 0 and at each hour for five hours upon leptin administration. Plasma levels of leptin were determined using the Elisa kit (R&D Systems Inc. Minneapolis, MN, USA). Recipes of vehicle #1 and vehicle #2 used in the present study, are: Vehicle #1 contains leptin mixed with 2000 Kallikrein inhibitor units (KIU) of aprotinin (Trasylol, Bayer, Leverkusen, FRG) dissolved in 0.5ml of bicarbonate buffer pH 9. While in vehicle #2, we added 5 mg of sodium deoxycholate (22mmol/l) (Sigma St-Louis, Mo, USA). Addition of aprotinin was required to reduce leptin degradation, while the addition of sodium deoxycholate was found to enhance duodenal absorption [3,4,22,23]. Circulating levels of leptin were assessed using the Leptin Elisa kit (R&D Systems Inc. Minneapolis, MN, USA). This kit displays <0.5% cross reactivity with available related human leptin molecules and no cross-reactivity with rodent leptin. Detection of human leptin is carried out with a Minimum Detectable Dose (MDD) of less that 7.8pg/mL.

Figure 1 shows the results obtained upon force-feeding the animals with 50μg of leptin dissolved in buffer (PBS), in vehicle #1 and in vehicle #2. Very small amounts of leptin reach circulation when oral leptin was dissolved in buffer (Figure 1). However, upon dissolving it in vehicle #1 or #2 the amounts of leptin detected in plasma during the first hours after its oral administration are quite significant (Figure 1). The levels reach a pick at 60 minutes and decrease gradually thereafter. Vehicle #2 appears to be significantly more efficient, circulating levels of leptin reaching about three times the amounts observed with vehicle #1 (Figure 1).