Dear Sir, Heme oxygenase (HO) is a microsomal enzyme that catalyzes the first, rate-limiting step in the degradation of heme, and plays an important role in its recycling (Maines, 1997). It cleaves the a-meso carbon bridge of heme, yielding equimolar quantities of carbon monoxide, Fe, and biliverdin (Tenhunen et al., 1968). The enzymatic activity of HO results in decreased oxidative stress, an attenuated inflammatory response, and a lower rate of apoptosis. Three distinct mammalian HO isoforms (HO-1, HO-2, and HO-3) have been identified. They are the products of three different genes (Maines, 1988). Heme oxygenase-1, the inducible 32-kDa isoform, also known as heat shock protein 32, is highly expressed in liver and spleen, but can also be detected in many other tissues. It can be induced strongly in response to cellular stress and diverse oxidative stimuli, including its heme substrate, heat shock, ultraviolet (UV) irradiation, reactive oxygen species (ROS), nitric oxide (NO), inflammatory cytokines, prostaglandins, ethanol, heavy metals, and hypoxia (Applegate et al., 1991; Choi and Alam, 1996). Most of the known HO-1 inducers stimulate the production of ROS or lead to the depletion of glutathione levels, suggesting the involvement of HO-1 activity in cellular protection against oxidative stress (Ryter and Choi, 2002). Heme oxygenase-1 is known to play an important role in resistance to apoptosis and in the rapid growth of several solid tumors. It is often up-regulated in tumor tissues, and its expression can be further increased in response to therapy (Jozkowicz et al., 2007). Induction of HO-1 has been recognized as one of the most promising targets for chemoprevention and chemoprotection research (Prawan et al., 2005). Few studies of HO-1 expression in melanoma have been reported. Okamoto et al. (2006) suggested that HO-1 is an important candidate gene in the pathogenesis and growth of melanomas. Was et al. (2006) found that overexpression of HO-1 increased the viability, proliferation, and angiogenic potential of melanoma cells, augmented metastasis, and decreased survival of melanoma-bearing mice. In this study, we examined the expression of HO-1 in melanocytic nevi and melanomas by immunohistochemical staining, and in cultured normal human melanocytes and melanoma cell lines. We enrolled 38 patients, 20 with melanocytic nevi and 18 with melanomas. Patient characteristics are shown in Table S1. The mean age of the patients was 42 ± 23 yr (range 6–80). The diagnoses of the 20 melanocytic nevi were as follows: compound nevi (12; 60%), junctional nevi (4; 20%), intradermal nevus (1; 5%), and Spitz nevi (3; 15%). The histopathological types of the 18 melanomas were superficial spreading type (7; 39%), acral lentiginous type (7; 39%), lentigo maligna type (3; 17%), and metastatic melanoma (1; 6%). Immunohistochemical staining was performed using formalin-fixed, paraffin-embedded tissue specimens from 20 patients with melanocytic nevi and 18 with melanomas, using the LSAB2 System-HRP (DakoCytomation, Carpenteria, CA, USA). The intensity of HO-1 immunoreactivity was graded using the following scale: 0 = negative (no staining of melanocytic cells, but staining of the epidermis); 1 = weakly positive (staining intensity was markedly weaker than that of the epidermis); 2 = moderately positive (staining intensity was mildly weaker than that of the epidermis); and 3 = strongly positive (staining intensity was at least equal to that of the epidermis). The Mann–Whitney test (performed using SPSS version 12.0; SPSS Inc., Chicago, IL, USA) was used to analyze differences in HO-1 staining intensity between melanocytic nevi and melanomas. Additionally, HO-1 expression in melanocytic nevi and melanomas from sun-exposed and sun-protected areas was compared. Expression of HO-1 was detected in 19 of 20 melanocytic nevi (95%) and in 11 of 18 melanomas (61%). Of melanomas, one superficial spreading type, four acral lentiginous type, one lentigo maligna type, and one metastatic type did not express HO-1. Note that the intensity of HO-1 expression was markedly different between melanocytic nevi and melanomas (Figure 1). The mean intensity in melanocytic nevi was 1.82 ± 0.86. There was no difference in staining intensity among the types of melanocytic nevi. The intensity of HO-1 expression in the nearby epidermis in melanocytic nevi was 2.30 ± 0.64 (Figure S1). Only 13 of 20
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