Efficacy and Safety Pharmacological Evaluation of Histidine Decarboxylase Inhibitor in Combination with H1 Antihistamine in Treatment of Atopic Dermatitis

Abstract

Aim & Objective There have been many number of targets for treatment of allergic diseases and many drugs are available for treatment of the same, but due to various side effect these drugs are not satisfactory and there is a need to develop newer strategies for treatment and management of allergic disorders. In the present study we aim at developing better therapeutic regimen in treatment of allergic dermatitis using combination of plant derived histidine decarboxylase inhibitor and anti histaminic drug cetirizine, thereby reducing the side effect of anti histaminic drug and increasing the efficacy of the treatment. Materials and Methods Isolation of catechin from acacia catechu has been carried out and determination of amount of catechin isolated was carried out by HPTLC method. To study the effect of catechin on histamine synthesis in normal animals, Sprague Dowley rats were divided in to three groups 1) Normal control, 2)treated with catechin (100mg/kg) 3)treated with catechin (50mg/kg)orally for 14 days. On 14thday blood histamine content, release of histamine from mast cell and histidine decarboxylase assay from stomach was carried out. To study the effect catechin, cetirizine and combination of catechin and cetrizine on allergic dermatitis, Balb/c mice were divided into five groups: 1) normal control, 2) disease control, 3)disease treated with catechin (100mg/kg), 4) disease treated with cetirizine, 10mg/kg, 5) disease treated with combination of catechin and cetirizine, 50mg/kg & 5mg/kg respectively. Sensitization was carried out by applying 30 μl of 0.5% 2,4-dinitro-1-fluorobenzene dissolved in acetone : olive oil (4:1) onto the shaved abdominal skin on day 0, 1, 14 and 15. Simultaneously, catechin treatment was started from day 7. Cetirizine 10mg/kg and 5mg/kg, p.o was administered on 20th day. One hr after treatment 20 μl of 0.3% DNFB was applied onto both sides of the right ear. After 24 hr of last DNFB application, clinical scoring, ear weight measurement, determination of vascular permeability using evans blue dye, determination of histamine release from mast cell, skin histamine content, histidine decarboxylase assay of skin, histopathology study of ear , HDC enzyme mRNA expression was carried out. In order to study the CNS safety pharmacology of proposed drug, Balb/c mice were divided into four groups: 1) normal control, 2)treated with catechin (100mg/kg), 3) treated with cetirizine, 10mg/kg, 4) treated with combination of catechin (50mg/kg) and cetirizine (5mg/kg) orally. Catechin treatment was carried out fourteen days. At the end of treatment the behavioural changes in animals was observed, effect on locomotor activity using actophotometer, effect on exploratory activity by open field test, effect on muscle co-ordination using rota rod, and effect of drugs on barbiturate induced sleeping time was measured. To study the CVS safety pharmacology of proposed drug, Sprague Dowley rats were divided into previously mentioned groups. At the end of treatment ECG was recorded using I-worx and QT interval was measured. Results Catechin was isolated from acacia catechu and yield obtained was 22%. Treatment with catechin showed significant decrease (p<0.05) on blood histamine content, release of histamine from mast cells and histidine decarboxylase activity. In animal model allergic dermatitis treatment with catechin, cetirizine and their combination showed significant decrease(p<0.05) in the clinical scoring, ear weight, histamine content of skin and histamine release from mast cells as compared to disease control. Also significant decrease (p<0.05) in vascular permeability was observed. The histidine decarboxylase enzyme activity i.e conversion of l- histidine to histamine was also significantly decreased (p<0.05) in disease treatment groups as compared to disease control. Further histopathology study of ears showed decreased dermal thickness and decrease in size of mast cells. The gene expression of histidine decarboxylase enzyme in stomach was also found to be reduced in disease treatment groups as compared to disease control. The CNS safety studies showed there was no significant change in the behavior of animals, muscle co-ordination and barbiturates induced sleeping time in treatment groups as compared to normal control group. Although cetrizine (10mg/kg) and combination of catechin(50mg/kg) &cetirizine (5mg/kg) showed significant decrease(p<0.05) in locomotory activity as compared to normal control group and catechin(100mg/kg) had no significant change in locomotory activity as compared to normal control. Treatment with cetrizine (10mg/kg) showed significant decrease (p<0.05) in exploratory behavior compared to normal group while catechin (100mg/kg) & combination of catechin(50mg/kg) &cetirizine (5mg/kg) had no significant effect on exploratory behavior compared to normal group. Treatment with catechin, cetirizine and their combination had no significant effect on the QT interval of ECG compared to normal group. Conclusion Thus from the present study it can be concluded that by virtue of HDC enzyme inhibitory activity of catechin and histaminergic receptor antagonist activity of cetirizine, there combination is proved to be a better therapeutic regimen in treatment of allergic dermatitis as it minimizes CNS or CVS side effect of cetrizine by reducing the dose of cetrizine when used in combination with catechin.