International Journal of Drug Development and Research

Keywords

Simvastatin, Lovastatin, BDNF, Depression

INTRODUCTION

Mental disorders are common in medical practice and may present either as a primary disorder or as a co morbid condition.1 Depression is the commonest mood disorder characterized by feelings of sadness, despair and discouragement.2 In India, the morbidity rate due to mental illness is not less than 18-20 per 1000, and the types of illnesses and their prevalence are very much as in other parts of the world.1 Approximately 10-15% of those with severe depression attempt suicide at some time.3 Thus, it is important that symptoms of depression should be recognized and treated in timely manner.

The monoamine hypothesis of depression is increasingly called into question by newer theories that revolve around changes in neuronal plasticity, primarily in the hippocampus and cortex at both the structural and functional levels. Both stress and depression have been shown to affect levels of brainderived neurotrophic factor (BDNF) whose transcription is dependent on cAMP response element binding protein (CREB). BDNF itself has anti depressant like actions and can induce transcription of a number of molecules.4, 5, 15 One class of genes regulated by both BDNF and serotonin (5-HT) are neuropeptides including VEGF which has a novel role in depression.4 Recent theoretical mechanisms for depression pertaining to immune mediated alterations in serotonergic functions would be another possible explanation.6

More depression could also be secondary to a number of physical disorders like hypertension, myocardial infarction, stroke, dementia, epilepsy and endocrinal disorders like diabetes, hyperthyroidism (anxiety) and hypothyroidism (depression).7,8 Pharmacological treatment of such co-morbidities at times may include two drugs, one for physical or metabolic and the other for associated mental disorder. Under such circumstances, naturally a drug-drug or a drug-disease interaction could be expected.

Surprisingly, statins ( i.e 3 – hydroxyl – 3 methyl glutaryl [HMG] – co A reductase inhibitors) like simvastatin, lovastatin which are potent inhibitors of cholesterol synthesis have been reported to possess pleiotropic effects like anti- inflammatory, antioxidant, antiplatelet, antithrombotic etc. these effects extend beyond their lipid lowering effect.9 Certain other studies have reported that statins possess neuroprotective property by means of increasing the proteolytic cleavage of pro BDNF to BDNF10 and to prevent or limit effect of ischemia (stroke)5 on brain vasculature and parenchyma.

However there is scarcity of information regarding direct effect of statins on depression paradigms in animal models. Therefore the present study was planned to explore antidepressant activity, in any of these clinically used lipophilic statins viz Lovastatin, Simvastatin and atorvastatin in their clinically equivalent doses using paradigms of depression in male swiss mice.

Objectives:

• To investigate the effect of simvastatin, lovastatin and atorvastatin for their antidepressant activity using forced swim test and tail suspension test on behavioral models of depression in male swiss mice.

• To compare their antidepressant activity if any with that of standard drug Amitriptyline.

Subjects and Methods:

Animals: Adult male healthy mice weighing 20-30g were obtained from the central animal house, J. N. Medical College, Belgaum and were acclimatized to 12:12 h light - dark cycle for 10 days prior to the day of experimentation. They were maintained on standard chow pellet (Amrut Brand) and water ad libitum. The study was approved by Institutional Animal Ethical Committee formed as per the guidelines of CPSCEA, New Delhi.

Drugs and doses (Table-1): Considering the maximum therapeutic dose mice equivalent dose were calculated with the help of converting table devised by Paget and Barnes.11 Mice were divided into several groups of six each (n=6). Control group received 0.5ml of 1% gum acacia suspension, orally, while the other groups received calculated clinical equivalent doses of simvastatin, lovastatin, atorvastatin, amitriptyline in 1% gum acacia suspension, orally. Amitriptyline is taken as standard antidepressant drug. Antidepressant activity was assessed with the help of following paradigms.

The tests were conducted one hour after administration of drugs. Forced swim test: 12, 13, 14

It consists of a vertical Plexiglass cylinder measuring 21cms in height with diameter being 12cms, containing 10cms of water column maintained at 25’ C.

When a mouse is forced to swim in a situation from which there is no escape, it will, after an initial period of vigorous activity, eventually cease to move altogether making only those movements necessary to keep its head above water. This characteristic behavior of immobility indicates a state of despair in which the mouse resigns itself to the experimental conditions and such behavior is said to be equivalent to clinical depression. Obviously drugs that decrease immobility would be antidepressants.

Procedure: Adult healthy mice weighing 20-30g were plunged vertically into the cylinder and left for 15mins. The duration of immobility is scored. Each mouse was judged to be immobile when it ceased struggling and remained floating motionless in the water making only those movements necessary to keep its head above water. The animals were subjected to test after 24hrs.

Half an hour after a single dose of the test drug/vehicle, mice were placed in the cylinder and left for 6mins to note the duration of immobility (in seconds). The animals were then allowed to dry before returning them to their individual cages. Tail suspension test : 12,13,14

It consist of 2 metallic rods 35 cms apart connected with a horizontal rod to suspend a nylon thread from its centre. A hook was attached to the free end of the thread to enable suspension of the animal by its tail. The thread length was adjusted to provide a distance of 35cms from the ground to hook. A normal animal submitted to an aversive situation alternates between two kinds of behaviors: agitation and immobility. These can be named as Searching behavior (characterized by intense motor activity and expense of energy) and Waiting behavior (immobility and energy saving). It is named as searching-waiting strategy. Antidepressant drugs modify the balance between these forms of behavior in the favor of searching.

Procedure: The mouse pretreated with drug/vehicle was suspended from the hook hanging at the centre of a horizontal rod by an adhesive tape stuck 2 cm proximal to the tail tip. The mouse is said to be immobile when it stops moving and hangs motionless. Immobility time in seconds was recorded over a period of 6 min.

Statistical Analysis: The results presented here are the means+/- SD of 6 mice in each group. The results were analyzed using one-way analysis of variance (ANOVA) followed by Bonferroni’s multiple comparison test. P M 0.05 was considered statistically significant. All data was analyzed using statistical software SPSS (version 17.0).

RESULTS

In the present study the statins viz. simvastatin, lovastatin, atorvastatin are investigated for their antidepressant activity in male swiss albino mice. Amitriptyline as a standard antidepressant was used for the sake of comparison.

Antidepressant activity study: This was carried out employing two models viz. forced swim test and tail suspension test.

Forced swim test: The duration of immobility time in seconds was noted over a period of 6 minutes. The mean duration of immobility in the control group was 175.3 ± 5.09 while it was 142±3.19, 150.3±3.21, 159.3±3.40 and 170.5±4.64 in the amitriptyline, simvastatin, lovastatin, and atorvastatin groups respectively. There was statistically significant difference (p < 0.01) in the duration of immobility with amitriptyline and simvastatin, treated groups when compared to that of control groups. It was also found that there was no statistically significant difference between (p>0.05) amitriptyline and simvastatin groups indicating comparable antidepressant activity. (Table-2 , graph-1).

Tail suspension test: The duration of immobility time in seconds was noted over a period of 6 minutes. The mean duration of immobility in the control group was 217.8±11.14 while it was 159.8±1.85, 176.8±2.71, 183.7±2.25 and 202.7±3.71 in the amitriptyline, simvastatin, lovastatin, atorvastatin groups respectively. There was statistically significant difference (p<0.05) in the duration of immobility with amitriptyline and simvastatin, and lovastatin groups when compared to that of control groups. It was also found that there was no statistically significant difference (p> 0.05) between simvastatin, lovastatin groups when compared to amitriptyline indicating comparable anti-depressant activity. (Table-3, graph-2).

DISCUSSION:

In the present study, hydroxymethylglutaryl coenzyme A (HMG CoA) reductase inhibitors viz simvastatin, and lovastatin were investigated for their antidepressant effects using different behavioral models of depression in male swiss mice.

The findings of the present study in both the models of depression viz. forced swim test and tail suspension test clearly indicate that simvastatin and lovastatin have significant anti depressant activities that could be compared to that of amitryptyline.

Both stress and anti depressants have been shown to affect levels of BDNF whose transcription is dependent on cAMP response element binding protein (CREB). BDNF itself has anti depressant like actions and can induce transcription of a number of molecules.4 Statins can up-regulate the activity of the tissue type plasminogen activator (tPA)– plasminogen system, which is needed for the proteolytic cleavage of pro-BDNF (precursor of BDNF) to mature BDNF.10

Current immune mediated concepts on the etiology of depression may cause a reduction of serotonergic neurotransmission in depression. Considering the anti inflammatory and immuno modulatory properties of statins, they may block or reverse a cascade of immune mediated serotonin depletion in depression.6

Lack of antidepressant activity of atorvastatin on mice could be explained on the basis of its poor lipophilicity compared to other statins used in the present study.

The present study was not planned to probe into the anti depressant mechanism of statins. Based on the earlier reports , it could be hypothesized that restoration of dysregulated HPA axis, blockade of immune mediated depletion of serotonin and increasing cortical and hippocampal BDNF and VEGF levels. By these, statins could be contributing for their anti depressant activity observed in the present study.13

The present finding, that antidepressant activity of simvastatin as well as lovastatin, could be of therapeutic potential for patients with major depression, especially those that have dyslipidaemia or comorbidities relating to cardiovascular diseases. Statins have been found to be of clinical benefit in stroke16,5 and degenerative diseases, such as Alzheimer’s disease.3 It would be interesting to consider whether statins mediate any of their therapeutic effect in these diseases through the tPA– plasminogen–BDNF pathway, specifically. Furthermore, it may warrant further investigation to explore whether statins can also be of benefit in the treatment of other neuropsychiatric diseases associated with disturbed BDNF signaling, such as attention-deficit hyperactivity disorder 10,11 and Rett syndrome.

In conclusion, the antidepressant activity of simvastatin as well as lovastatin, could be of therapeutic potential for patients with major depression, especially those who have dyslipidaemia or comorbidities relating to cardiovascular diseases.

Tables at a glance

Table 1 Table 2 Table 3

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