Efficacy of antioxidants as an adjunct to photochemotherapy in vitiligo: A case study of 30 patients

Introduction

Vitiligo is an acquired melanocytopenic disorder that affects 0.5-4% of the world′s population.[1] Exact etiology of vitiligo is not known. Autoimmune hypothesis of vitiligo is most widely accepted since autoantibodies to melanocytes and tyrosinase have been demonstrated and due to the association of vitiligo with other autoimmune diseases.[2]

Research at the molecular level has demonstrated a deficiency of antioxidant substances in the vitiliginous skin. A defective antioxidant defence is postulated to lead to the unhindered cytotoxic action of reactive oxygen species such as superoxide anion, hydroxyl radical etc. These reactive oxygen apecies are generated following UV induced damage to the epidermis and are cytotoxic to melanocytes and also inhibit tyrosinase. Low levels of catalase enzyme which is a key enzyme in scavenging reactive oxygen species has been demonstrated in the epidermal suction grafts of vitiliginous skin.[3] The presence of autoantibodies to melanocytes and iyrosinase may be a secondary phenomenon to the cytokines released due to free radical damage.

Photochemotherapy with psoralens is an established first-line treatment for stable vitiligo. Psoralens (8-methoxypsoralen, TMP) cause photosensitivity and on subsequent UV exposure of the affected skin, repigmentation results after many treatments.[4]

Antioxidant supplementation in vitiligo Is postulated to boost the antioxidant defence mechanism and prevent melanocyte damage by reactive oxygen species.

Materials and Methods

Thirty patients with stable vitiligo, not on any treatment for 1 month, were included in the trial after obtaining informed consent. Patients under 12 years of age, or those with photosensitive disorders or eye problems were excluded from the study. Patients were randomly allocated to two treatment groups.

Fifteen patients (group A) received photochemotherapy alone (M:F-7:8, 18-67 years, disease duration-3 months-20 years) and another 15 (group B) were treated with photochemotherapy and oral antioxidants, 1 capsule ad (M:F-10:5, 18-65 years, disease duration 6 months-30 years).

The clinical types of vitiligo in the two regimes were comparable.

The antioxidant formulation used contained vitamin E acetate 25 mg, beta-carotene 30% dispersion 10 mg, vitamin C 100mg, selenium 75 mcg, copper 1 mg, zinc 27.5 mg and manganese 1.5 mg.

In each patient, two lesions were chosen as index lesions and tracings were taken on polyethene sheets using a felt-tip marker using a bony prominence as landmark. The index lesions were then traced 1 month and 3 months after treatment. The area of the index lesions was assessed by Computer Aided Design.

The area of the index lesion was calculated in square centimetres and percentage decrease in the area after 1 month and 3 months of treatment was determined. The percentage decrease in the area of the index lesion after 3 months of treatment was taken as the parameter of efficosy of treatment.

Patients were monitored for side-effects to (erythema, burning sensation, vesicles, photophobia) and to oral antioxidant therapy.

Results

Percentage decrease in the area of index lesion after 3 months of treatment in the two groups was assessed. At the end of 3 months, in group A, except 3 lesions, all lesions showed decrease in area. At the end of 3 months, in group B, except for 4 lesions all lesions showed decrease in area. The percentage decrease in the area of the index lesions is summarized in the table given below [Figure - 1], [Figure - 2] [Table - 1].

Statistical analysis of the results by Fisher exact test showed that the difference between the two treatment groups was not statistically significant (p>0.05).

Overall, patients in both groups did not experience significant adverse effects. 2 patients of group A developed erythema, 1 patient developed blisters. 1 patient of group B developed transient blurring of vision and 2 patients developed erythema. No adverse effect which could be attributed to oral antioxidant therapy was observed.

Discussion

The evidence for the role of antioxidants in vitiligo is mainly from molecular studies demonstrating low levels of antioxidants (such as catalase). Catalase is an enzyme that effectively scavenges the toxic reactive oxygen species.

Low levels of catalase have been demonstrated in the epidermis of patients with vitiligo.[3] UV irradiation of the skin is known to trigger free radical generation and resultant melanocyte damage. Human melanocytes in cell culture are especially sensitive to exygen radicals and melanocytes from vitiliginous skin require the addition of catalase to the culture medium to grow. The melanocytes from healthy skin proliferate without addition of catalase enzyme. Histological examination of involved and uninvolved epidermis in vitiligo revealed evidence for peroxidative damage to both keratinocytes and melanocytes. Superoxide dismutase is important for the generation and disproportionation of superoxide anion. As a consequence of UV irradiation, superoxide anion and reactive oxygen species are generated in the skin.

In patients with vitiligo, abnormally high concentrations of catecholamine have been demonstrated in the epidermis and dermis.[5] Increased levels of norepinephrine in the keratinocytes and plasma leads to ischaemia of the skin. This leads to the over- production of reactive exygen species and accumulation of 6 and 7 tetrahydrobiopterins.[5] These molecules are extremely cytotoxic to melanocytes and also inhibit tyrosinase activity.

Defective calcium transport in vitiligo has been demonstrated and it interferes with the distribution of melanin from melanocytes to keratinocytes by preventing the activation of protein kinase C.[6] Cyclic AMP modulators such as alpha MSH, beta-adrenergic receptors, melatonin receptors depend on the stimulation of calcium uptake by inosine triphosphate as a prerequisite for protein kinase C activation. A defect in calcium acquisition could prevent processes.

The decrease of catalase in epidermis of patients with vitiligo highlitghts the backup role of thioprotiens, thioredoxin reductase and glutathione peroxidase.[7] These enzymes reduce superoxide anion to water and the glutathione reductase/glutathione peroxidase system can also catalyze this reaction. The dermis contains high levels of gluathione reductase and low levels of thioredoxin reductase with a pH range of 7.8 to 8.2. Therefore, the induction of glutathione reductase in the epidermis of vitiligo patients could be caused by a increase in pH based on hydroxyl radical released in the Haber-Weiss reaction. Alternatively, the highly significant induction of glutathione reductase in uninvolved skin compared to involved skin in vitiligo could reflect a replacement of catalase by the backup of glutathione reductase/glutathione peroxidase system of superxide anion reduction. This mechanism does of directly account for structural defects in melanocytes or the autommune hypothesis for vitiligo. Both these processes could occur as a secondary response to the proposed breakdown of antioxidant defence. Also epidermal suction blister extracts used in these studies reflect changes in metabolism of reactive exygen species by keratinocytes with little contribution from melanocytes. In this respect, it appears that both involved and uninvolved epidermis of patients with vitiligo show abnormalities in antioxidant defense enzyme levels primarily in the keratinocyte, indicating that vitiligo could be a disorder of keratinocytes.

Thus, bulk of the evidence for the role of antioxidants in vitiligo is from molecular and in vitro studies. A case study of 33 patients with vitiligo who were treated with a topical application of pseudocatalase and calcium in cimbination with short-term UVB exposure showed good results.[4] Pseudocatalase is a low molecular weight coordination complex which is more active in the production of oxygen and hydrogen peroxide than catalase itself.

In another study, it was found that antioxidants (alpha tocopherol, butylated hydroxytoluene etc) selectively inhibited the photochemical stage of erythema and hyperpigmentation, but had no impact on the postirradiation stages of the processes.[7] Evidently, the basis of these processes is the reaction of the psoralen-photosensitized oxidation of unsaturated lipids and the impairment of barrier functions of biomembranes, since the photochemical stage of these reactions is inhibited by the antioxidant. Thus, antioxidants can be used as a tool for improvement of psoralen photochemotherapy.

Studies have demonstrated that topical application of alpha-tocopherol modulates the antioxidant network and diminishes UV induced oxidative damage in murine skin.[8] Vitamin A, C and E are believed to protect the skin from UV induced free radical damage and hence prevent melanocyte toxicity.[9]

In our study, 30 patients of stable vitiligo were included. Fifteen patients received photochemotherapy alone while 15 patients received photochemotherapy and oral antioxidant therapy. Percentage decrease in the area of index lesion at the end of 3 months of therapy was taken as the parameter of efficacy. No statistically significant difference was found between the two groups. No adverse effects specific to antioxidant therapy were observed. Thus, antioxidants as an adjunct to photochemotherapy offer no distinct advantage in the management of stable vitiligo. However, a larger study of a similar design is required before drawing a definite conclusion.