Impact of Orexin-A Treatment on Food Intake, Energy Metabolism and Body Weight in Mice

Abstract

Orexin-A and -B are hypothalamic neuropeptides of 33 and 28-amino acids, which regulate many homeostatic systems including sleep/wakefulness states, energy balance, energy homeostasis, reward seeking and drug addiction. Orexin-A treatment was also shown to reduce tumor development in xenografted nude mice and is thus a potential treatment for carcinogenesis. The aim of this work was to explore in healthy mice the consequences on energy expenditure components of an orexin-A treatment at a dose previously shown to be efficient to reduce tumor development. Physiological approaches were used to evaluate the effect of orexin-A on food intake pattern, energy metabolism body weight and body adiposity. Modulation of the expression of brain neuropeptides and receptors including NPY, POMC, AgRP, cocaine- and amphetamine related transcript (CART), corticotropin-releasing hormone (CRH) and prepro-orexin (HCRT), and Y2 and Y5 neuropeptide Y, MC4 (melanocortin), OX1 and OX2 orexin receptors (Y2R, Y5R, MC4R, OX1R and OX2R, respectively) was also explored. Our results show that orexin-A treatment does not significantly affect the components of energy expenditure, and glucose metabolism but reduces intraperitoneal fat deposit, adiposity and the expression of several brain neuropeptide receptors suggesting that peripheral orexin-A was able to reach the central nervous system. These findings establish that orexin-A treatment which is known for its activity as an inducer of tumor cell death, do have minor parallel consequence on energy homeostasis control.

Fig 1. Effect of orexin-A injection on body weight evolution.

Data are shown as mean ± SEM, n = 8. A two-factor repeated measures anova was performed to compare both groups and no significant difference was reported.

Fig 2

Components of caloric intake: total caloric intake (A), meal number (B) meal size (C) and Injestion speed (D). Data are presented as box and whiskers, n = 8. Significant differences are indicated: * P<0.05 (t-test).

Fig 3. Effect of orexin-A injection on body composition evaluated immediatly after sacrifice.

Data are presented as box and whiskers, n = 8. Significant differences are indicated *P<0.05, ** P<0.01, *** P<0.001 (Student-t test).

Fig 4. Components of energy expenditure: energy expenditure.

TEE: total energy expenditure, REE: resting energy expenditure, EE-Act: energy expenditure spent in response to spontaneous motor activity, Activity: spontaneous motor activity, Act-Cost: energy cost of spontaneous activity. Data are presented as box and whiskers, n = 8. A t-test was performed and no significant differences are reported.

Fig 5

Blood glucose (A) and insulin (B) concentrations during the oral glucose tolerance test in control or orexin-A injected mice. Data are shown as mean ± SD, n = 8. A t-test was performed to compare both groups and no significant difference was reported. Insulin AUC were calculated using the trapezoidal rule (C). Data are presented as box and whiskers, n = 8. A t-test was performed and no significant differences are reported.

Fig 6. Histology of pancreas.

Panel A and B, representative Hematoxylin and Eosin staining (H&E) of pancreas from control (A) and orexin-A-treated (B) mice. Panel C and D, representative OX1R immunostaining of pancreas from control (C) and Orexin-A-treated (D) mice. Arrows highlight the islets. Figures were taken at the same magnification (20x). Scale bar = 50 μm.