Investigation into the effects of the novel antipsychotic ziprasidone on weight gain and reproductive function in female rats

Atypical antipsychotics and effects on feeding: from mice to men

RATIONALE

So-called atypical antipsychotics (AAPs) are associated with varying levels of weight gain and associated metabolic disturbances, which in patients with serious mental illness (SMI) have been linked to non-compliance and poor functional outcomes. Mechanisms underlying AAP-induced metabolic abnormalities are only partially understood. Antipsychotic-induced weight gain may occur as a result of increases in food intake and/or changes in feeding.

OBJECTIVE

In this review, we examine the available human and preclinical literature addressing AAP-related changes in feeding behavior, to determine whether changes in appetite and perturbations in regulation of food intake could be contributing factors to antipsychotic-induced weight gain.

RESULTS

In general, human studies point to disruption by AAPs of feeding behaviors and food consumption. In rodents, increases in cumulative food intake are mainly observed in females; however, changes in feeding microstructure or motivational aspects of food intake appear to occur independent of sex.

CONCLUSIONS

The findings from this review indicate that the varying levels of AAP-related weight gain reflect changes in both appetite and feeding behaviors, which differ by type of AAP. However, inconsistencies exist among the studies (both human and rodent) that may reflect considerable differences in study design and methodology. Future studies examining underlying mechanisms of antipsychotic-induced weight gain are recommended in order to develop strategies addressing the serious metabolic side effect of AAPs.

Recent evidence and potential mechanisms underlying weight gain and insulin resistance due to atypical antipsychotics

OBJECTIVE

Atypical antipsychotics (AAPs) promote obesity and insulin resistance. In this regard, the main objective of this study was to present potential mechanisms and evidence concerning side effects of atypical antipsychotics in humans and rodents.

METHOD

A systematic review of the literature was performed using the MEDLINE database. We checked the references of selected articles, review articles, and books on the subject.

RESULTS

This review provides consistent results concerning the side effects of olanzapine (OL) and clozapine (CLZ), whereas we found conflicting results related to other AAPs. Most studies involving humans describe the effects on body weight, adiposity, lipid profile, and blood glucose levels. However, it seems difficult to identify an animal model replicating the wide range of changes observed in humans. Animal lineage, route of administration, dose, and duration of treatment should be carefully chosen for the replication of the findings in humans.

CONCLUSIONS

Patients undergoing treatment with AAPs are at higher risk of developing adverse metabolic changes. This increased risk must be taken into account when making decisions about treatment. The influence of AAPs on multiple systems is certainly the cause of such effects. Specifically, muscarinic and histaminergic pathways seem to play important roles.

Modelling olanzapine-induced weight gain in rats

The second-generation antipsychotic drug olanzapine has become a widely prescribed drug in the treatment of schizophrenia and bipolar disorder. Unfortunately, its therapeutic benefits are partly outweighed by significant weight gain and other metabolic side effects, which increase the risk for diabetes and cardiovascular disease. Because olanzapine remains superior to other antipsychotic drugs that show less weight gain liability, insight into the mechanisms responsible for olanzapine-induced weight gain is crucial if it is to be effectively addressed. Over the past few decades, several groups have investigated the effects of olanzapine on energy balance using rat models. Unfortunately, results from different studies have not always been consistent and it remains to be determined which paradigms should be used in order to model olanzapine-induced weight gain most accurately. This review summarizes the effects of olanzapine on energy balance observed in different rat models and discusses some of the factors that appear to contribute to the inconsistencies in observed effects. In addition it compares the effects reported in rats with clinical findings to determine the predictive validity of different paradigms.

The effect of ziprasidone on body weight and energy expenditure in female rats

Ziprasidone, a novel antipsychotic agent with a unique receptor-binding profile, has been reported to have lower propensity for weight gain compared with other atypical antipsychotics. Here, we examined the effects of ziprasidone on resting energy expenditure, physical activity, thermogenesis, food intake, and weight gain in female Sprague-Dawley rats. Ziprasidone (20 mg/kg) or vehicle was administered once daily for 7 weeks; and body weight, food intake, resting energy expenditure, locomotor activity, colonic temperature on cold exposure, and abdominal fat were measured. Compared with control animals, ziprasidone-treated rats gained significantly less weight (P = .031), had a lower level of physical activity (P = .016), showed a higher resting energy expenditure (P < .001), and displayed a greater capacity for thermogenesis when subjected to cold (P < .001). In addition, ziprasidone-treated rats had a lower level of abdominal fat than did controls, although the difference was not significant. Ziprasidone had no effect on food intake. Our results indicate that, in female Sprague-Dawley rats, a 7-week treatment regimen of ziprasidone induces a significant decrease in weight gain by increasing resting energy expenditure without decreasing food intake and even with a lower level of physical activity. Further studies are needed to elucidate the precise mechanism of lower propensity of weight gain of ziprasidone.

Metabolic consequences of antipsychotic therapy: preclinical and clinical perspectives on diabetes, diabetic ketoacidosis, and obesity

Antipsychotic drugs, particularly second-generation antipsychotics (SGAs), have reduced the burden to society of schizophrenia, but many still produce excessive weight gain. A significant number of SGAs also act directly to impair glycemic control causing insulin resistance, impaired glucose tolerance and type 2 diabetes, and also rarely diabetic ketoacidosis (DKA). Schizophrenia itself is almost certainly causal in many endocrine and metabolic disturbances, making this population especially vulnerable to the adverse metabolic consequences of treatment with SGAs. Hence, there is an urgent need for a new generation of antipsychotic drugs that provide efficacy equal to the best of the SGAs without their liability to cause weight gain or type 2 diabetes. In the absence of such safe and effective alternatives to the SGAs, there is a substantial clinical need for the introduction of new antipsychotics without adverse metabolic effects and new antiobesity drugs to combat these metabolic side effects. We discuss the adverse metabolic consequences of schizophrenia, its exacerbation by a lack of social care, and the additional burden placed on patients by their medication. A critical evaluation of the animal models of antipsychotic-induced metabolic disturbances is provided with observations on their strengths and limitations. Finally, we discuss novel antipsychotic drugs with a lower propensity to increase metabolic risk and adjunctive medications to mitigate the adverse metabolic actions of the current generation of antipsychotics.

Differential effects of ziprasidone and haloperidol on immobilization stress-induced mRNA BDNF expression in the hippocampus and neocortex of rats

Recent in vivo and in vitro experiments have demonstrated that second-generation antipsychotic drugs (SGAs) might have neuroprotective effects. Ziprasidone is a SGA that is efficacious in the treatment of schizophrenia. In this study, we sought to analyze the effects of ziprasidone on the expression of the neuroprotective protein brain-derived neurotrophic factor (BDNF) in the rat hippocampus and neocortex, with or without immobilization stress. The effect of ziprasidone (2.5mg/kg) on the expression of BDNF mRNA was determined by in situ hybridization in tissue sections from the rat hippocampus and neocortex. Haloperidol (1.0mg/kg) was used for comparison. Haloperidol strongly decreased the expression of BDNF mRNA in both the hippocampal and cortical regions, with or without immobilization stress (p<0.01). In contrast, the administration of ziprasidone significantly attenuated the immobilization stress-induced decrease in BDNF mRNA expression in the rat hippocampus and neocortex (p<0.01). Ziprasidone exhibited differential effects on BDNF mRNA expression in the rat hippocampus and neocortex. These results suggest that ziprasidone might have a neuroprotective effect by recovering stress-induced decreases in BDNF mRNA expression.

Insulin resistance following continuous, chronic olanzapine treatment: an animal model

Some atypical antipsychotics have been linked to an increased propensity for weight gain and metabolic disturbances, including type II diabetes. The objective of this study was to investigate an animal model to help understand the mechanisms underlying this phenomenon. Female, Sprague-Dawley rats were treated with olanzapine (2.0 or 7.5 mg/kg, via osmotic mini-pump) for 4 weeks, followed by the hyperinsulinemic/euglycemic and hyperglycemic clamp procedures to assess insulin sensitivity and secretion in vivo. Changes in body weight, visceral fat, food intake and locomotor activity were also assessed. Hepatic glucose production (R(A)) was increased in the hyperinsulinemic/euglycemic clamp for both treatment groups compared to control rats, while the high-dose olanzapine group had decreased peripheral glucose utilization (R(D)). No changes in insulin secretion were detected in the hyperglycemic clamp. Olanzapine did not change body weight or food intake, but did result in significant accumulation of visceral fat and decreases in locomotor activity. Like others, we found that a rodent model for antipsychotic-related weight gain per se is not tenable. However, chronic treatment with olanzapine was found to confer both hepatic and peripheral insulin resistance independent of weight gain, indicating a direct effect on glucose dysregulation.

Ziprasidone and aripiprazole attenuate olanzapine-induced hyperphagia in rats

Weight gain induced by some second-generation anti-psychotics such as olanzapine has emerged as a most debilitating side-effect. This study investigates whether co-administration with either ziprasidone or aripiprazole, which have little propensity to induce weight gain, can attenuate the hyperphagic effect of olanzapine. Female hooded-Lister rats (n=8 per group) were treated acutely with either vehicle, olanzapine (1 mg/kg), ziprasidone (1 mg/kg), aripiprazole (2 mg/kg) or olanzapine in combination with ziprasidone or aripiprazole and placed in automated locomotor activity (LMA) boxes with preweighed palatable mash. Food intake and LMA were measured for 60 min postdrug treatment. All olanzapine-treated groups demonstrated significant increases in food intake (P<0.001). This effect was attenuated following co-administration of olanzapine with either ziprasidone or aripiprazole (P<0.001), neither of which affected food intake alone. The lack of hyperphagia induced by aripiprazole and ziprasidone may reflect an inherent pharmacological mechanism preventing weight gain.

Investigation into the influence of a high fat diet on antipsychotic-induced weight gain in female rats

Atypical antipsychotic drug therapy may result in substantial weight gain, increased adiposity and the promotion of metabolic abnormalities. The mechanism(s) which underlie such effects remain unclear. Previous studies in our laboratory have demonstrated significant weight gain in female rats maintained on a standard laboratory diet after sub-chronic administration of olanzapine and risperidone, but not ziprasidone. The aim of this paper is to investigate the effect of antipsychotic drugs on body weight, ingestive behaviour and adiposity in female rats with access to a high fat diet. Adult female rats given free access to a high fat diet received either olanzapine (2 mg/kg), risperidone (0.5 mg/kg), ziprasidone (2.5 mg/kg) or vehicle for 28 days. Body weight, food and water intake in addition to intra-abdominal fat deposition were assessed. Olanzapine initially increased body weight but by the end of the study olanzapine animals appeared to have lost weight compared to the vehicle-treated group. Olanzapine-induced reductions in body weight were accompanied by a significant hypophagia during weeks 3 and 4. Risperidone increased body weight during week 1 only and reduced intake of a high fat diet during weeks 3 and 4. Ziprasidone was without effect on indices of body weight and ingestive behaviour. There were no effects of antipsychotic drugs on intra-abdominal fat deposition. Access to a diet high in fat attenuated weight gain induced by olanzapine and risperidone in female rats.

Chronic clozapine treatment in female rats does not induce weight gain or metabolic abnormalities but enhances adiposity: implications for animal models of antipsychotic-induced weight gain

The ability of clozapine to induce weight gain in female rats was investigated in three studies with progressively lowered doses of clozapine. In an initial preliminary high dose study, clozapine at 6 and 12 mg/kg (i.p., b.i.d.) was found to induce weight loss. In a subsequent intermediate dose study, we obtained no evidence for clozapine-induced weight gain despite using identical procedures and doses of clozapine (1-4 mg/kg, i.p., b.i.d.) with which we have observed olanzapine-induced weight gain, hyperphagia, enhanced adiposity and metabolic changes [Cooper G, Pickavance L, Wilding J, Halford J, Goudie A (2005). A parametric analysis of olanzapine-induced weight gain in female rats. Psychopharmacology; 181: 80-89.]. Instead, clozapine induced weight loss without alteration in food intake and muscle mass or changes in levels of glucose, insulin, leptin and prolactin. However, these intermediate doses of clozapine enhanced visceral adiposity and elevated levels of adiponectin. In a final study, low doses of clozapine (0.25-0.5 mg/kg, i.p, b.i.d.) induced weight loss. These data demonstrate that clozapine-induced weight gain can be much more difficult to observe in female rats than olanzapine-induced weight gain. Moreover, these findings contrast with clinical findings with clozapine, which induces substantial weight gain in humans. Clozapine-induced enhanced adiposity appears to be easier to observe in rats than weight gain. These findings, along with other preclinical studies, suggest that enhanced adiposity can be observed in the absence of antipsychotic-induced weight gain and hyperphagia, possibly reflecting a direct drug effect on adipocyte function independent of drug-induced hyperphagia [e.g. Minet-Ringuet J, Even P, Valet P, Carpene C, Visentin V, Prevot D, Daviaud D, Quignard-Boulange A, Tome D, de Beaurepaire R (2007). Alterations of lipid metabolism and gene expression in rat adipocytes during chronic olanzapine treatment. Molecular Psychiatry; 12: 562-571.]. These and other findings which show that the results of studies of antipsychotic treatment in animals do not always mimic clinical findings have important implications for the use of animal models of antipsychotic-induced weight gain. With regard to weight gain the results obtained appear to depend critically on the experimental procedures used and the specific drugs studied. Thus such models are not without limitations. However, they do consistently demonstrate the ability of various antipsychotics to enhance adiposity.

The distinct effects of subchronic antipsychotic drug treatment on macronutrient selection, body weight, adiposity, and metabolism in female rats

INTRODUCTION

Treatment with some antipsychotic drugs may result in excessive body weight gain which can have detrimental effects on patient compliance, morbidity and mortality. The aim of the present study was to investigate the effect of atypical antipsychotic drugs on dietary macronutrient selection, body weight, body composition and biochemical parameters related to obesity in female rats.

MATERIALS AND METHODS

Forty pair-housed, adult female hooded-Lister rats (250 +/- 5 g) were habituated to three diets containing principally protein, fat, or carbohydrate in a home cage self-selection paradigm. Olanzapine (2 mg/kg), risperidone (0.5 mg/kg), ziprasidone (2.5 mg/kg), or vehicle was injected intraperitoneally once daily for 22 days; food selection, water intake, and body weight were recorded daily, while body composition and plasma hormones (insulin, glucose, nonesterified free fatty acid, total cholesterol, glycerol, triacylglycerol, leptin, and prolactin) were analyzed at the end of the study.

RESULTS

Only olanzapine significantly increased body weight and food intake. Macronutrient selection was significantly altered after olanzapine and risperidone treatment (increased protein and decreased fat preference). Only olanzapine increased carcass fat content. Locomotor activity was significantly reduced in all treatment groups. Both olanzapine and risperidone significantly increased plasma prolactin. Olanzapine was without effect on any other biochemical parameter measured. Ziprasidone significantly reduced plasma leptin and nonsignificantly reduced NEFA, while risperidone significantly reduced fasting plasma glucose.

CONCLUSION

This study supports our previous work demonstrating weight gain and increased feeding behavior induced by olanzapine and could have important implications for enhancing our understanding of the mechanisms by which olanzapine and other atypical antipsychotics induce weight gain in the clinic.

Effects of olanzapine in male rats: enhanced adiposity in the absence of hyperphagia, weight gain or metabolic abnormalities

Many of olanzapine's (OLZ) actions in humans related to weight regulation can be modelled in female rats (Cooper et al., 2005). Such effects include weight gain, hyperphagia, enhanced visceral adiposity and elevated Levels of insulin and adiponectin. As sex differences have been reported in the effects of antipsychotic drugs, including OLZ, in rats, the current study extended our study in female rats by directly comparing the actions of OLZ in maLes using identical methodology. Individually housed male Han Wistar rats were administered OLZ twice daily (i.p.), at 0, 1, 2, and 4 mg/kg over 21 days. Both differences from, and simiLarities to, the data obtained in females were obtained. Males treated with OLZ showed reduced weight gain, enhanced visceral adiposity and reduced lean muscle mass. There were no accompanying changes in food or water intake. OLZ did not induce changes in plasma levels of insulin, leptin or glucose. Significant elevation of adiponectin was observed. OLZ-treated males displayed elevated prolactin and suppressed testosterone. OLZ's effects in humans can very clearly be most validly modelled in female rats, although the cause(s) of the sex difference in OLZ's actions in rats are not clear. However, the finding that significantly enhanced adiposity is seen in both male and female rats, in other animal species (mice and dogs) and in humans suggests that studies in male rats of OLZ's effects may be of value, by highlighting the consistent ability of OLZ to increase visceral adiposity. It is hypothesized that such adiposity is a key, clinically relevant, common component of OLZ's actions which may be, at Least partially, independent of both OLZinduced weight gain and hyperphagia, and which is induced reliably in male and female rats and other animal species. Possible mechanisms involved in the effects reported are discussed.

Body weights and plasma prolactin levels in female rats treated subchronically with ziprasidone versus olanzapine

In a putative animal model of antipsychotic drug-induced weight gain, female rats received either vehicle, ziprasidone (2.0, 6.0, 10 mg/kg) or olanzapine (2.0 mg/kg), orally, twice daily, for 7 days. Body weights were assessed daily and prolactin assayed at the end of the regimen. Ziprasidone caused significant weight gain, as did olanzapine, while stimulating distinct patterns of prolactin secretion. Thus, assessment of body weight provides only limited predictive validity in differentiating between weight gain-inducing and weight-neutral drugs.

A model for antipsychotic-induced obesity in the male rat

INTRODUCTION

Weight gain is a common and severe side effect of antipsychotic drugs. A usual tool to study the side effects of psychotropic drugs is animal models. However, attempts to create an animal model of antipsychotic-induced weight gain were not successful so far. Female rodents are sensitive to the effects of antipsychotics, but not males. This does not match the human clinical situation. Antipsychotics have different pharmacokinetic properties in rats and humans, and rats and humans have different spontaneous diets.

MATERIALS AND METHODS

In the present study, we tested the hypothesis that the insensitivity of male rats to the weight-promoting effects of antipsychotics could be related to the mode of administration of antipsychotics and to the animals' diet. Antipsychotics were mixed with the food, and rats were fed a diet resembling the human diet. Rats were treated with 0.01, 0.1, 0.5, and 2 mg/kg of olanzapine or with a control solution for 6 weeks. Their weight and food intake were recorded, and their body composition were analyzed. The effects on weight and food intake of olanzapine (1 mg/kg), haloperidol (1 mg/kg), and ziprasidone (10 mg/kg) were also compared in a 3-week treatment experiment.

RESULTS

The results showed that 0.5 and 2 mg of olanzapine, but not lower doses, increase body weight and subcutaneous fat deposition. After the 3-week treatment, olanzapine-treated rats, but not haloperidol- or ziprasidone-treated rats, had significantly increased their weight.

CONCLUSION

This study shows that a rat model of obesity induced by antipsychotics can be created under specific conditions of drug administration, diet, and dose.

Effects of the atypical antipsychotics olanzapine and risperidone on plasma prolactin levels in male rats: a comparison with clinical data

RATIONALE

Hyperprolactinaemia is a common side effect of antipsychotic treatment and the clinical consequences associated with this, e.g. sexual dysfunction, can have a negative impact on patient compliance.

OBJECTIVES

The aim of this study was to investigate the effect of the atypical antipsychotics olanzapine and risperidone on prolactin levels in rats using different treatment regimes and to compare these data with those reported clinically.

METHODS

All experiments were carried out in male CD rats. In separate studies, the effects of acute, sub-chronic (7 days) and chronic (28 days) olanzapine and risperidone administration on prolactin levels were determined. Further studies investigated the time course of the prolactin response following olanzapine and risperidone treatment over 24 h.

RESULTS

Both drugs significantly increased prolactin levels in a similar manner following acute administration, in keeping with clinically reported data. However, this elevation was still present following sub-chronic and chronic treatment, contrasting with clinical data with respect to olanzapine but not risperidone. Over 24 h, olanzapine demonstrated a more transient elevation of prolactin levels, whereas risperidone caused a robust and persistent increase in prolactin up to 24 h post-dose, closely mimicking clinical results.

CONCLUSIONS

The present study has demonstrated that olanzapine and risperidone display similar effects on prolactin levels in the rat following acute and chronic administration but differ in their prolactin response over a 24-h period. In conclusion, prolactin levels in rats following atypical antipsychotic treatment may not be fully predictive of the clinical situation.

Effects of sub-chronic antipsychotic drug treatment on body weight and reproductive function in juvenile female rats

RATIONALE

Weight gain caused by some antipsychotics is not only confined to adults but can also adversely affect both children and adolescents. Indeed, olanzapine and risperidone have been associated with extreme weight gain in adolescents even greater than that reported in adults. We have recently shown substantial weight gain in adult female rats following treatment with olanzapine and risperidone but not ziprasidone.

OBJECTIVES

The aim of the present study was to compare the effects of several antipsychotics on weight gain and reproductive function in juvenile (aged 7 weeks) female hooded Lister rats.

METHODS

Olanzapine (4 mg/kg), risperidone (0.5 mg/kg), ziprasidone (2.5 mg/kg), sulpiride (10 mg/kg), haloperidol (0.5 mg/kg) or vehicle was administered i.p. once per day for 21 days. Body weight, food and water intake were measured daily, in addition to the determination of stage of the oestrous cycle.

RESULTS

Sub-chronic administration of olanzapine, risperidone, sulpiride and haloperidol, but not ziprasidone, significantly increased body weight compared to vehicle-treated animals during weeks 1-3. Sulpiride significantly increased food and water intake. Significantly increased percentage intra-abdominal fat weight was observed in olanzapine, risperidone, sulpiride and haloperidol, but not ziprasidone-treated animals. Marked disruption of the oestrous cycle was observed in all but the ziprasidone-treated group, which continued to have regular 4-day oestrous cycles.

CONCLUSIONS

Weight gain observed in these juvenile animals was 1.5-2 times greater than that previously observed in adult rats. These findings have important implications for the use of antipsychotics in children and adolescent patients.

Characterisation of olanzapine-induced weight gain and effect of aripiprazole vs olanzapine on body weight and prolactin secretion in female rats

RATIONALE

Atypical antipsychotic drug (APD)-induced weight gain causes non-compliance, increasing the risk of relapse and medical complications.

OBJECTIVES

In an animal model, we assessed body weights, food intake, body fat/lean body mass contents and blood serum levels of glucose and lipids in female rats treated with olanzapine (Experiment 1). Also, we investigated the effect of aripiprazole vs olanzapine treatment on weight gain (WG) and plasma prolactin secretion in two strains (Wistar and Sprague-Dawley) and in two housing conditions (singly and group housed; Experiment 2).

METHODS

In Experiment 1, Wistar females received either vehicle or olanzapine (5.0 mg kg(-1), p.o.) twice daily for 14 days. In Experiment 2, female rats (Wistar or Sprague-Dawley), housed singly or in groups, received either vehicle, aripiprazole (2.0-8.0 mg kg(-1), p.o.), or olanzapine (1.0-10 mg kg(-1), p.o.) twice daily for 7 days. Body weights and food intake were assessed daily. Body composition and blood assays were analyzed at the end of the treatment.

RESULTS

WG induced by chronic olanzapine treatment was characterised by hyperphagia, increased body fat, and serum free fatty acid content and reduced lean tissue and serum glucose content. Subchronic aripiprazole treatment resulted in rapid and robust WG similar to those observed with olanzapine. In spite of similar effects on body weight, aripiprazole and olanzapine stimulated markedly different patterns of prolactin secretion. Body weight changes and prolactin secretion induced by these APDs were significantly modulated by housing and by strain.

CONCLUSION

Assessment of body weight in the present model may not have predictive validity, and other measures may be needed to differentiate between WG-inducing and weight-neutral drugs.