To determine the effects of aging on myocyte cell death, Fischer 344 rats at 3, 7, 12, 16, and 24 mo of age were injected with myosin monoclonal antibody for the localization and quantification of necrotic myocyte cell death in the left ventricle, interventricular septum, and right ventricle. Conversely, the presence of DNA strand breaks in myocyte nuclei, indicative of programmed cell death, was evaluated by the terminal deoxynucleotidyl transferase assay and confirmed by DNA laddering. Myocyte necrosis, which involved nearly 1,000 myocytes in the left ventricular free wall at 3 mo, progressively increased with aging, reaching a value of 13,600 myocytes at 24 mo. Corre- sponding values in the interventricular septum were 300 and 9,400 myocytes. In the right ventricle, there were 270 necrotic myocytes at 3 mo and 9,000 at 24 mo. Programmed myocyte cell death was restricted to the left ventricular free wall and included 140 cells at 3 mo. This form of myocyte cell death increased at the subsequent age intervals, resulting in the involvement of 874 cells at 24 mo. The combination of necrosis and apoptosis in the left ventricular free wall was associated with 1,150 cells dying at 3 mo and 14,500 at 24 mo. In conclusion, myocyte cell death, apoptotic and necrotic in nature, constitutes an important determinant of the aging process, possibly mediating the occurrence of ventricular dysfunction and failure in the old heart.

Patients with Hermansky-Pudlak syndrome type 2 (HPS-2) have mutations in the beta 3A subunit of adaptor complex-3 (AP-3) and functional deficiency of this complex. AP-3 serves as a coat protein in the formation of new vesicles, including, apparently, the platelet's dense body and the melanocyte's melanosome. We used HPS-2 melanocytes in culture to determine the role of AP-3 in the trafficking of the melanogenic proteins tyrosinase and tyrosinase-related protein-1 (TRP-1). TRP-1 displayed a typical melanosomal pattern in both normal and HPS-2 melanocytes. In contrast, tyrosinase exhibited a melanosomal (i.e., perinuclear and dendritic) pattern in normal cells but only a perinuclear pattern in the HPS-2 melanocytes. In addition, tyrosinase exhibited a normal pattern of expression in HPS-2 melanocytes transfected with a cDNA encoding the beta 3A subunit of the AP-3 complex. This suggests a role for AP-3 in the normal trafficking of tyrosinase to premelanosomes, consistent with the presence of a dileucine recognition signal in the C-terminal portion of the tyrosinase molecule. In the AP-3-deficient cells, tyrosinase was also present in structures resembling late endosomes or multivesicular bodies; these vesicles contained exvaginations devoid of tyrosinase. This suggests that, under normal circumstances, AP-3 may act on multivesicular bodies to form tyrosinase-containing vesicles destined to fuse with premelanosomes. Finally, our studies demonstrate that tyrosinase and TRP-1 use different mechanisms to reach their premelanosomal destination.

Reactive oxygen species are the intermediates that are formed during the normal metabolic process which are effectively neutralized by the antioxidant system of the body. Any imbalance in this neutralization process causes oxidative stress which has been implicated as one of the cause in diseases such as Alzheimer's disease, cardiovascular disorders, cancer etc. Research has enabled the use of antioxidants as therapeutic agents in the treatment of various diseases. Literature also puts forth the negative effects of using antioxidants in the treatment of diseases. This review is a compilation of both the beneficial and detrimental effects of use of antioxidants in the treatment of diseases such as cancer, cardiovascular diseases, diabetes and oral diseases.

addition to its role in eumelanin synthesis, Tyrp1 is involved in Tyrosinase-related protein 1 (Tyrp1) is a melanocyte-specific maintaining stability of tyrosinase protein and modulating its gene product involved in eumelanin synthesis. Mutations in the catalytic activity. Tyrp1 is also involved in maintenance of mouse Tyrp1 gene are associated with brown pelage, and in the human TYRP1 gene with oculocutaneous albinism type 3 melanosome ultrastructure and affects melanocyte prolifera-(OCA3). In the murine system, Tyrp1 expresses significant tion and melanocyte cell death. The current review is an dihydroxyindole carboxylic acid oxidase (i.e. DHICA oxattempt to consolidate our understanding of the role of Tyrp1 idase) activity. However, in humans, TYRP1 is enigmatic in in the melanocyte. that despite extensive efforts focused on the study of its Key words: Pigmentation, Tyrosine hydroxylase, Brown/Rufunction, its actual role in the human melanocyte is still fous Albinism, Brown locus, Protein trafficking unclear. There is mounting evidence demonstrating that in Mutations in the genes encoding some of the enzymes and regulatory proteins involved in melanin synthesis result in various forms of oculocutaneous albinism (OCA). OCA1 correlates with mutations in the tyrosinase (TYR) gene (7). Most individuals with OCA1 have completely amelanotic skin, hair and eyes with the inability to tan (i.e. OCA1A). However, some nucleotide lesions of the TYR gene result in a partially functional enzyme so that individuals with this subtype of OCA1 can exhibit moderate levels of skin and hair pigmentation and the ability to tan (i.e. OCA1B). OCA2 correlates with mutations in the P gene (8). Individuals with OCA2 present with minimal to moderate amounts of pigment remaining in the skin, hair and eyes, many of whom can develop pigmented freckles, lentigines and/or nevi with age. OCA3 correlates with mutations in the TYRP1 gene (9). Individuals with OCA3 present with minimal pigment reduction in the skin, hair and eyes. This form of albinism was previously referred to as Rufous and possibly some forms of Brown albinism.

It has been known for several decades that cutaneous depigmentation, i.e., contact/occupational vitiligo, can be caused by some phenolic derivatives that have a similar structure to tyrosine. Among these phenolic depigmenting agents, 4-tertiary butylphenol is the most potent. The cutaneous depigmentation induced by phenolic derivatives results from the loss of functional melanocytes. Tyrosinase is a melanocyte specific copper-containing enzyme that catalyzes the conversion of the amino acid tyrosine, through a complex series of intermediates, to melanin. In this study we tested the hypothesis that the cytotoxicity induced by 4-tertiary butylphenol is mediated by tyrosinase and occurs via an apoptotic process. Melanocyte cultures derived from African-American and Caucasian donors exhibiting a 3-fold difference in tyrosinase activity and 14-fold difference in melanin content demonstrate comparable concentration-dependent sensitivity to 4-tertiary butylphenol. In addition, cultures of dermal fibroblasts and epidermal keratinocytes exhibited similar and reduced sensitivity, respectively, to 4-tertiary butylphenol compared with autologous melanocytes. Two melanoma cell lines, one melanotic and one amelanotic lacking the expression of both tyrosinase protein and activity, when transfected with the tyrosinase cDNA, exhibited no alteration in its sensitivity to 4-tertiary butylphenol. These data suggest that 4-tertiary butylphenol cytotoxicity is not mediated via tyrosinase. Melanocytes treated with 4-tertiary butylphenol, however, did exhibit plasma membrane blebbing, DNA fragmentation, and phosphatidylserine relocalization indicating that 4-tertiary butylphenol induced melanocyte destruction occurs by an apoptotic process.