Obesity & Addiction

InterVivo Solutions offers a capability for assessment of NCEs in chronic models of Obesity: the Diet Induced Obesity model (DIO) and the genetic Zucker rat model. NCE’s may be evaluated at multiple levels of analysis from the behavioural to whole body imaging using QMR. Measurement of blood lipids and glucose/insulin content is feasible. NCE’s may also be evaluated in acute feeding tests to study specific factors which may contribute to anorectic efficacy such as motivation and satiety.

There is considerable overlap between obesity and drug addiction: for example overlapping CNS circuitries and pharmacological mechanisms are implicated in each behaviour. Indeed, it has been proposed that obesity, or at least the behaviour that causes it, be recognised as a mental disorder and included in the upcoming DSM-V with diagnostic criteria modelled on those identified for substance abuse 1 (Volkow and O'Brien, 2007).

InterVivo Solutions therefore offers services to integrate evaluation of an NCE across these two therapeutic areas.

1 Volkow ND, O'Brien CP (2007) Issues for DSM-V: should obesity be included as a brain disorder? Am. J. Psychiatry 164: 708-710.

Both the Zucker fa/fa rat and Diet induced obesity models provide a means to study effect of an NCE on multiple endpoints important for determining its potential as an anti-obesity therapy. A brief overview of endpoints that InterVivo can measure and how these compare between the two models is presented below.

Zucker model DIO model
Body mass ~50% > vs. lean controls ~30% > vs. controls
Body composition (QMR) Fat mass ~35% vs. ~7% lean controls
Lean mass ~56% vs. 80% lean controls
Fat mass ~20% vs. ~10% controls
Lean mass ~59% vs. 75% controls
Food and water intake Food and water intake elevated vs. lean controls. Food and water intake actuall reduced vs. lean controls (based on high fat diet).
Lipid profile TG's + Cholesterol elevated vs. lean controls TG's + Cholesterol modestly elevated vs. lean controls
Blood insulin levels Severe hyperinsulinaemia Hyperinsulinaemia
Blood glucose levels Hyperglycemia Normal blood glucose levels
Glucose tolerance test Elevated blood [glucose] following load - 2x AUC vs. lean controls. Elevated blood [glucose] following load - 1.5x AUC vs. controls.
Behavioural profile Hypoactive, allodynia to a tactile stimulus vs. lean conrols Hypoactive vs. controls.

Acute feeding models provide a means to assess the effect of an NCE on specific factors that may contribute to anorectic efficacy or unwanted side effect of an NCE. Acute feeding tests may also assist with dose finding necessary for chronic studies.

Rats are trained either to consume their daily food ration over a specific time period each day, i.e. feeding induced by deprivation, or given access to a sweetened diet in a specific location and time each day without restriction to standard food, i.e feeding induced by palatability. Enables the administration of an NCE to be precisely timed to feeding.

Validation Data: Effect of lorcaserin (Belviq) on feeding induced by palatability or deprivation
% change in food intake

Percentage change in food intake following lorcaserin (0.3-3 mg/kg SC) compared to vehicle pretreatment in rats trained to consume food over a limited access period under conditions of 22h food deprivation, or palatability-induced feeding in non-deprived rats. Data modified from: Higgins et al (2012) Neuropsychopharmacology 37: 1177-1191.

Typically rats given access to food will display a sequence of behaviours as they feed to satiation, i.e feed>active/groom>rest. Provides the means to study effect of an NCE on this behavioural sequence to measure specificity of any anorectic effect.

Validation Data: Effect of lorcaserin (Belviq) on the behavioural satiety sequence

Effect of lorcaserin (1 mg/kg) on the behavioural satiety sequence measured during the palatability-induced feeding experiment. Note in the vehicle controls and lorcaserin (1 mg/kg) groups, the predominant behaviours are feeding and active/grooming over the first 15-20min, before ‘inactive’ predominates from 20-25 min onwards. At this dose, lorcaserin is therefore reducing food intake with minimal effect on the behavioural satiety sequence. Data modified from: Higgins et al (2012) Neuropsychopharmacology 37: 1177-1191.

Effect of lorcaserin

Rats may be trained to respond for food reward under a variety of schedules to study factors such as effect of an NCE on motivation for food. Because animals are typically well trained in these tasks, baseline performance can be tightly controlled and performance becomes predictable enabling robust baselines with which to study effects of an NCE.

Validation Data: Effect of lorcaserin (Belviq) on operant responding for food under a progressive ratio schedule of reinforcement
Effect of lorcaserin pretreatment on behaviours motivated by food
Effect of lorcaserin (0.3-1 mg/kg SC) pretreatment on behaviours motivated by food made available under a progressive ratio schedule of reinforcement. In this test the response requirement for food reward is increased with each successive reward. The critical measure is the break point, i.e at which response level will the animal cease to work for food. Lorcaserin reduced the break point for food under a progressive schedule of reinforcement consistent with a reduced motivation for food. The effect of lorcaserin wasreversed by the selective 5-HT2C receptor antagonist SB-242084 (SB). Data modified from: Higgins et al (2012) Neuropsychopharmacology 37: 1177-1191.

NCEs may reduce feeding behaviour by non-specific means such as malaise. InterVivo Solutions offer a variety of techniques to study malaise in rats, including measurement of pica, certain spontaneous behaviours and conditioned behaviours such as place aversion and conditioned disgust. Nausea and vomiting are one of the primary dose limiting side effects of CNS drugs in the clinic. Certain drug classes such as PDE4 inhibitors, e.g rolipram are associated with induction of nausea in humans.

Validation Data: Assessing the aversive properties of rolipram

Effect of rolipram (0.3 – 1 mg/kg) pretreatment on various measures which may reflect malaise in rats. Rolipram produced a dose related incidence of checked signs such as chin rubbing, flat body posture and chewing. These were aggregated to give a ‘malaise score’. In a separate experiment, equivalent doses of rolipram increased the amount of clay eaten over a 4h time period. Rolipram (1 mg/kg) also produced a significant place aversion for a distinct compartment it was paired to (unbiased procedure).

Effect of rolipram

In addition to providing a platform to study the potential for an NCE to reduce a specific aspect of a drug, known to contribute to its liability for abuse, i.e efficacy based study, these same tests may be applied to investigate abuse potential of an NCE, i.e safety based study. InterVivo Solutions has experience in either approaches to study an NCE.

Most drugs of abuse have locomotor stimulant effects which can be readily measured in open field activity chambers. The total distance travelled within unit time will give a reliable measure of any motor stimulant/depressant effect of an NCE. Alternatively an NCE may be tested for its ability to inhibit the stimulant property of a drug of abuse.

Validation Data: Motor stimulant effects of nicotine

Rats were habituated to test apparatus and over a 1h time period the total distance travelled following treatment with either saline vehicle, or nicotine (0.05-0.4 mg/kg) was measured by an automated tracking system. Nicotine produced a robust increase in total distance travelled consistent with its known stimulant property.

Motor stimulant effects of nicotine

All drugs of abuse, as well as certain non-abused drug classes, will produce an internal state that the rat can be trained to discriminate from a neutral stimulus such as saline injection. Drug discrimination procedures typically rely on a two-lever operant procedure. NCE’s may be tested for (a) their ability to either substitute (generalise) to a known drug cue (i.e suggestive of a similar interoceptive state) or (b) their ability to antagonise a known drug cue (i.e suggestive of an ability to block the interoceptive state of a known drug). Alternatively rats may be trained with an NCE to see if it can support a discrimination opening up opportunities to identify which known drugs may generalise. InterVivo Soluions has experience in each of these areas.

Validation Data: Cross generalisation between a nicotine and diazepam cue
Separate groups of rats were trained to discriminate either nicotine (0.3 mg/kg) from saline (Nicotine), or Diazepam (2 mg/kg) from saline (DZP). As expected Nicotine trained rats showed a dose related generalisation to the nicotine lever, and DZP trained rats showed a dose related generalisation to the diazepam lever. However diazepam administered to Nicotine group, and nicotine administered to DZP group produced only at best a very weak (~25%) generalisation, thus showing the specificity of each cue type.

Many drugs of abuse following chronic treatment will produce adaptive changes in the animal which may lead to tolerance, i.e higher dose of drug to produce an equivalent pharmacological response, and/or dependence, i.e cessation of drug may lead to an aversive withdrawal state, which may also be precipitated by an acute pharmacological challenge (precipitated withdrawal). Avoidance of an aversive withdrawal state is a contributory factor in continued drug taking of certain abused drugs.

Validation Data: Nicotine dependence
Adult, male rats were implanted with minipumps primed to deliver nicotine at 6 mg/kg/day or 9 mg/kg/day. Body weight gain was reduced in the animals receiving the 9 mg/kg/day dose. At day 7 post implant, rats injected with the nicotine antagonist mecamylamine (1 mg/kg SC). Somatic withdrawal signs, e.g ptosis, tremor, muscle jerks, chewing were manifest. Mecamylamine-induced W/D signs not evident in rats implanted with saline minipumps.

Many drugs of abuse will produce a preference for a specific location to which it has been paired, i.e the drug will produce a conditioned place preference based on the appetitive properties of that drug. Alternatively drugs which may elicit an aversive state, may produce an aversion for a specific location to which it has been paired, i.e the drug will produce a conditioned place aversion. This procedure may therefore be of value in determining an appetitive vs. an aversive interoceptive state generated by an NCE. Alternatively the procedure may be used to see if an NCE may modify a conditioned place preference/aversion produced by a known drug. InterVivo Solutions has experience with each approach.

The majority of abused drugs will support their self-administration, which defines their reinforcing property. InterVivo Solutions has access to intravenous self-administration procedures through sub-contract.