Antioxidant status of segmental and non-segmental vitiligo
Sir,
Vitiligo is a depigmenting disorder resulting from the loss of melanocytes in the skin and affects 1–2% of the world population. Several hypotheses are proposed about the pathogenesis of vitiligo and oxidative stress hypothesis considers a systemic involvement during the course of the disease. We have earlier reported impairment of systemic antioxidant status of Baroda vitiligo patients (Agrawal et al., 2004) and we now show analysis of the blood antioxidant status of segmental and non-segmental clinical types of vitiligo.
Blood samples were collected from 124 vitiligo patients without any other associated diseases and also from 126 age and sex matched healthy consenting volunteers without any disease for the estimation of antioxidant parameters. Vitiligo patients were further classified into segmental and non-segmental vitiligo. We have analyzed the blood antioxidant enzymes such as catalase (CAT), superoxide dismutase (SOD), glutathione peroxidase (GPx); non-enzymatic antioxidants like reduced glutathione (GSH), vitamin E; erythrocyte lipid peroxidation levels (LPO) and glucose-6-phosphate dehydrogenase (G6PDH) activity in segmental and non-segmental vitiligo patients and controls according to the standard established methods (Agrawal et al., 2004) and the results are shown in Table 1. A significant increase in erythrocyte SOD activity was observed in both the types of vitiligo patients compared with controls (Table 1). However, no significant change was observed in segmental vitiligo compared with non-segmental vitiligo. There are no specific reports available on the SOD levels in different clinical types of vitiligo. However, an increase in SOD activity was reported (Chakraborty et al., 1996; Agrawal et al., 2004). Catalase activity was found to be significantly lower in segmental vitiligo, while no significant change in the catalase activity was observed in non-segmental vitiligo. Also, no significant change was observed in segmental vitiligo compared to non-segmental vitiligo (Table 1). There is no report on the catalase levels in different clinical types of vitiligo. No significant change in the erythrocyte catalase activity was reported (Beazley et al., 1999). A significant decrease in GPx levels was observed in non-segmental and no change was observed in segmental vitiligo. Segmental vitiligo showed no significant change compared with non-segmental vitiligo (Table 1). Beazley et al. (1999) reported low levels of GPx in the blood of generalized vitiligo patients compared with controls and there are no reports on other clinical types of vitiligo. We observed significant decrease in G6PDH activity in both the types of vitiligo, however, no significant change is observed in segmental vitiligo compared with non-segmental vitiligo (Table 1). There is no report on the G6PDH levels in different clinical types of vitiligo. However, Agrawal et al. (2004) and Saha et al. (1982) reported a decrease in G6PDH levels in vitiligo patients compared with controls. Significantly, lower GSH levels were observed non-segmental vitiligo compared with controls, however, no change is observed in segmental vitiligo compared with non-segmental vitiligo (Table 1). There are no reports on the GSH levels in different clinical types of vitiligo. Passi et al. (1998) showed that epidermal GSH levels of active vitiligo patients were significantly lower compared with controls. Agrawal et al. (2004) and Yildirim et al. (2003) have also shown a significant decrease in the erythrocyte GSH levels in non-segmental vitiligo patients compared with controls. However, Picardo et al. (1994) found no change in the erythrocyte GSH activity of vitiligo patients. Changes in plasma vitamin E levels were non-significant in both the types of vitiligo and among segmental and non-segmental vitiligo (Table 1). There are no reports on the vitamin E levels in different clinical types of vitiligo. Agrawal et al. (2004) and Picardo et al. (1994) showed no change in the plasma vitamin E levels in vitiligo patients compared to controls. Significant increase in LPO levels was observed in both the clinical types of vitiligo, however, no change is observed in segmental vitiligo compared to non-segmental vitiligo (Table 1). Non-significant changes in plasma lipoperoxides of vitiligo patients were reported by Picardo et al. (1994).
Type of vitiligo | Antioxidant parametersa | ||||||
---|---|---|---|---|---|---|---|
SOD | CAT | GPx | G6PDH | GSH | VIT E | LPO | |
Control (n = 126) | 1830 ± 51.33 | 266.4 ± 4.59 | 17.28 ± 0.40 | 14.14 ± 0.48 | 34.47 ± 0.66 | 7.913 ± 0.1709 | 184.5 ± 2.71 |
Non-segmental (n = 94) | 2885 ± 55.41*** | 252.0 ± 6.450 NS | 15.89 ± 0.2611* | 7.444 ± 0.3033*** | 31.52 ± 0.7020** | 7.654 ± 0.1873 NS | 201.8 ± 3.769*** |
Segmental (n = 30) | 2892 ± 99.75*** | 233.7 ± 11.22** | 15.28 ± 0.5578 NS | 7.712 ± 0.5223*** | 31.99 ± 1.268 NS | 7.718 ± 0.3359 NS | 204.9 ± 5.518 ** |
- SOD is expressed as U/g Hb; CAT as k/g Hb; GPx as μmoles of GSH utilized/s/g Hb; G6PDH as mmoles of nicotinamide adenine dinucleotide phosphate (NADP) reduced to NADPH/min/g Hb; GSH as mg GSH/dl blood; Vitamin E as μg Vit E/ml of plasma and LPO is expressed as nmoles of malonaldehyde formed/g Hb.
- NS, non-significant; SOD, superoxide dismutase; CAT, catalase; GSH, glutathione; G6PDH, glucose-6-phosphate dehydrogenase; LPO, lipid peroxidation levels; GPx, glutathione peroxidase.
- aValues are expressed as mean ± SE.
- *P < 0.05; **P < 0.02, ***P < 0.01.
From the above, it is clear that the status of enzymatic and non-enzymatic antioxidants is altered in both the clinical types of vitiligo compared with controls. Increased levels of erythrocyte SOD could enhance the systemic production of H2O2. The downstream antioxidant enzymes that neutralize H2O2, i.e. catalase, is found to be significantly decreased in segmental vitiligo patients, whereas significantly lowered GPx and GSH levels are found in non-segmental vitiligo patients. Plasma vitamin E levels of these patients remain unchanged, however, with significantly lower nicotinamide adenine dinucleotide phosphate (reduced) (NADPH) levels (because of reduced levels of G6PDH), the non-enzymatic cycle may not proceed to completion. Hence, the free radicals may accumulate and contribute to the build up of oxidative stress in the system. Thus high levels of SOD, low levels of catalase and G6PDH could contribute to oxidative stress in segmental vitiligo; while high levels of SOD, low levels of GPx, G6PDH and GSH could contribute to oxidative stress in non-segmental vitiligo as is evident by high LPO levels in vitiligo patients. Elevated LPO levels in both the clinical types of vitiligo (Table 1) suggest that systemic oxidative stress is the hallmark feature of all these patients. Nevertheless, there are minor changes in the antioxidant status among different clinical types of vitiligo. The difference between the generation of oxidative stress in segmental and non-segmental seems to lie in the levels of catalase and GPx. The low levels of catalase may contribute for the generation of oxidative stress in segmental vitiligo while the generation of oxidative stress in non-segmental vitiligo may be attributed to the lower levels of GPx and GSH. In conclusion, impairment of the systemic antioxidant system resulting in oxidative stress in both the clinical types of vitiligo is observed in this study indicating that melanocyte damage in vitiligo may be linked to generalized oxidative stress.