Olanzapine promotes fat accumulation in male rats by decreasing physical activity, repartitioning energy and increasing adipose tissue lipogenesis while impairing lipolysis

Abstract

Olanzapine and other atypical antipsychotics cause metabolic side effects leading to obesity and diabetes; although these continue to be an important public health concern, their underlying mechanisms remain elusive. Therefore, an animal model of these side effects was developed in male Sprague-Dawley rats. Chronic administration of olanzapine elevated fasting glucose, impaired glucose and insulin tolerance, increased fat mass but, in contrast to female rats, did not increase body weight or food intake. Acute studies were conducted to delineate the mechanisms responsible for these effects. Olanzapine markedly decreased physical activity without a compensatory decline in food intake. It also acutely elevated fasting glucose and worsened oral glucose and insulin tolerance, suggesting that these effects are adiposity independent. Hyperinsulinemic-euglycemic clamp studies measuring (14)C-2-deoxyglucose uptake revealed tissue-specific insulin resistance. Insulin sensitivity was impaired in skeletal muscle, but either unchanged or increased in adipose tissue depots. Consistent with the olanzapine-induced hyperglycemia, there was a tendency for increased (14)C-2-deoxyglucose uptake into fat depots of fed rats and, surprisingly, free fatty acid (FFA) uptake into fat depots was elevated approximately twofold. The increased glucose and FFA uptake into adipose tissue was coupled with increased adipose tissue lipogenesis. Finally, olanzapine lowered fasting plasma FFA, and as it had no effect on isoproterenol-stimulated rises in plasma glucose, it blunted isoproterenol-stimulated in vivo lipolysis in fed rats. Collectively, these results suggest that olanzapine exerts several metabolic effects that together favor increased accumulation of fuel into adipose tissue, thereby increasing adiposity.

Figure 1

Effects of chronic olanzapine on body weight, food intake, adiposity, oral glucose tolerance and insulin tolerance. Animals were trained to eat drug-free cookie dough and then allocated to experimental groups for chronic olanzapine or vehicle treatment as indicated (see ‘methods’ for detailed dosing protocol). Data represent the mean ± S.E. (n = 8-10). Asterisks indicate a significant difference (*P<0.05, **P<0.01, ***P<0.001) in the olanzapine group compared to the control group for each measurement. (A-B) Body weight and 24h food intake were measured daily and data represent the mean ± S.E. (C) Percent total body adiposity was measured weekly by ¹H-NMR for 5 weeks. (D-E) On day 28 of olanzapine or vehicle treatment an oral glucose tolerance test was performed. Animals were food-restricted for 14h and administered a half-dose of olanzapine (6 mg/kg) or vehicle 1h prior to beginning the OGTT. Baseline blood samples were collected 1h after the gavage and then a glucose solution (1.5 g/kg) administered orally. Serial blood samples were collected at 30-min intervals for 2h following glucose gavage for measurement of (D) blood glucose and (E) plasma insulin. Data represent the mean ± S.E. (n = 5-10). (F) On day 42 of olanzapine treatment, an insulin tolerance test was performed. Animals were food-restricted for 14h prior to the test and given a half-dose of olanzapine (6 mg/kg) or vehicle one hour prior to the challenge. The response to injected insulin was measured for 120 min as the change in baseline blood glucose.

Figure 2

Energy expenditure and locomotor activity following acute olanzapine administration. Animals were placed in specialized chambers to measure locomotor activity and energy expenditure using indirect calorimetry. Following acclimation, olanzapine (10 mg/kg) or vehicle solution was administered by oral gavage (indicated by arrows). Animals retained ad libitum access to food and water for the duration of the experiment. (A) VO₂ and (B) VCO₂ were measured at 15-minute intervals for 24h. (C) 24h locomotor activity was measured as an indicator of physical activity. Background shading or lack thereof indicates the dark and light cycles, respectively. Locomotor activity was significantly different from control in each dimension during the dark and light cycles (P<0.001). (D) Average VO₂ and (E) Average VCO₂ for the dark and light cycles were calculated. All data represent the mean ± S.E. (n = 12), asterisks indicate significant differences (***P<0.001, **P<0.01).

Figure 3

Effects of acute olanzapine on oral glucose tolerance, insulin tolerance and whole-body insulin sensitivity. Asterisks indicate significant differences compared to control (*P<0.05, ***P<0.001). (A, B) An oral glucose tolerance test was conducted on the second treatment day after acute olanzapine (4 mg/kg) gavage (see ‘Methods’ for dosing protocol). Animals were food-restricted for 5h prior to the OGTT and received a final olanzapine or vehicle gavage 1h prior to the start of the OGTT. Baseline blood samples were collected at 1h following gavage and then glucose solution (2.5 g/kg) administered orally. Serial blood samples were collected at 30-min intervals for 2h following glucose gavage for measurement of (A) blood glucose and (B) plasma insulin. Data represent the mean ± S.E. (n = 12). (C) An insulin tolerance test was performed in another group of animals on the second treatment day. Animals received high dose olanzapine (10 mg/kg), low dose olanzapine (4 mg/kg) or vehicle solution by oral gavage 1h prior to beginning the tolerance test. Baseline blood samples were collected and then insulin (0.75 U/kg, i.p.) injected. Blood glucose was measured for 120 min as an indicator of insulin sensitivity. Data represent the mean ± S.E. (n = 18-20). (D-E) Hyperinsulinemic-euglycemic clamp studies were conducted after acute olanzapine administration (10 mg/kg) (D) Hepatic glucose output was measured during basal (14h food-restricted) and clamp conditions. Basal hepatic glucose output (HGO) was equal to the total glucose turnover during the basal period, while the clamp was the residual HGO during the final 40 minutes of the clamp. (E) Whole-body glucose disposal, a measure of whole-body insulin action, was measured during hyperinsulinemic-euglycemic clamp conditions and compared to basal glucose turnover. Data represent the mean ± S.E. of glucose turnover during the last 40 minutes of the clamp experiment (n = 10-14). (F) Adipose tissue glucose uptake in ad libitum fed animals was measured after acute olanzapine administration (10 mg/kg). Data represent the mean ± S.E. (n = 8).

Figure 4

Acute effects of olanzapine on circulating and adipose tissue FFA uptake, lipogenesis, and mobilization of FFA and glucose in response to an isoproterenol challenge. (A) Plasma FFAs were measured in 14h food-restricted animals following olanzapine (10 mg/kg) gavage. (B) In a separate cohort, FFA uptake into adipose tissue was measured on the second day of olanzapine treatment using a non-metabolizable FFA analog (¹²⁵I-BMIPP) in animals that had ad libitum access to food and water. Two hours after the final olanzapine dose (10 mg/kg), an intravenous bolus of the FFA tracer was given and blood samples were collected during a 40-min in vivo labeling period. Epididymal, pararenal and subcutaneous fat pads were harvested and measured for tracer uptake, an index of adipocyte FFA uptake. (C) In another cohort of animals adipose tissue lipogenesis was measured in the well-fed state after acute olanzapine (10 mg/kg). Following final administration of olanzapine, ³H₂O was administered via i.p. injection and tissue samples were collected after a 120-min in vivo labeling period. Epididymal, retroperitoneal and subcutaneous adipose tissues were excised, extracted for total lipid and then counted for ³H content as an index of lipogenesis. (D-F) An isoproterenol challenge test was conducted to assess the effects of olanzapine (10 mg/kg) on isoproterenol-stimulated lipolysis and hepatic glucose output. Animals had ad libitum access to food and water. Baseline blood samples were collected and then isoproterenol (0.01 mg/kg) administered. Serial blood samples at 30-min intervals for 2h were collected to measure the lipolytic response, as measured by the change in (C) FFA and (D) glycerol from isoproterenol-stimulated lipolysis, as well as the (E) hepatic glycolytic response. Data represent the mean ± S.E. (n = 8-10). Asterisks indicate significant differences compared to time-matched control values (*P<0.05, ***P<0.001, ****P<0.0001).