Masamitsu Ichihashi

Involvement of pigment globules containing multiple melanosomes in the transfer of melanosomes from melanocytes to keratinocytes

The mechanism of melanosome transfer from melanocytes to keratinocytes has not been fully clarified. We now show a route of melanosome transfer using co-cultures of normal human melanocytes and keratinocytes. Substantial levels of melanosome transfer were elicited in co-cultures of melanocytes and keratinocytes separated by a microporous membrane filter. The melanocyte dendrites penetrated into the keratinocyte layer through the filter and many pigment globules were observed in keratinocytes. Electron microscopic observations revealed that melanosomes incorporated in keratinocytes were packed in clusters enclosed by a double membrane. Numerous pigment globules budded off from melanocyte dendrites and were released into the culture medium. Those pigment globules were filled with multiple melanosomes and a few mitochondria but no nuclei. When those globules were added to the culture medium of keratinocytes, they were incorporated and showed double membrane-enclosed melano-phagolysosomes consistent with the structures obtained from the co-culture system. In contrast, when individual naked melanosomes isolated from melanocytes were added to keratinocytes, they were also phagocytosed by keratinocytes but were enclosed by a single membrane in a manner distinct from the co-culture system. These results suggest a novel mechanism of melanosome transfer, wherein melanosomes are packed in membrane globules that bud off from melanocyte dendrites, where they are released into the extracellular space and then phagocytosed by keratinocytes.

Keratinocytes in culture accumulate phagocytosed melanosomes in the perinuclear area

There are many techniques for evaluating melanosome transfer to keratinocytes but the spectrophotometric quantification of melanosomes incorporated by keratinocyte phagocytosis has not been previously reported. Here we describe a new method that allows the spectrophotometric visualization of melanosome uptake by normal human keratinocytes in culture. Fontana‐Masson staining of keratinocytes incubated with isolated melanosomes showed the accumulation of incorporated melanosomes in the perinuclear areas of keratinocytes within 48u2003h. Electron microscopic observations of melanosomes ingested by keratinocytes revealed that many phagosomes containing clusters of melanosomes or their fragments were localized in the perinuclear area. A known inhibitor of keratinocyte phagocytosis which inhibits protease‐activated receptor‐2, i.e., soybean trypsin inhibitor, decreased melanosome uptake by keratinocytes in a dose‐dependent manner. These data suggest that our method is a useful model to quantitate keratinocyte phagocytosis of melanosomes visually in vitro.

Omeprazole, a Gastric Proton Pump Inhibitor, Inhibits Melanogenesis by Blocking ATP7A Trafficking

Omeprazole is a proton pump inhibitor used in the treatment of peptic ulcer disease and gastrosophageal reflux disease and acts by irreversibly blocking ATP4A, a P-type H+/K+ ATPase in gastric parietal cells. We found that omeprazole and its closely related congeners inhibited melanogenesis at micromolar concentrations in B16 mouse melanoma cells, normal human epidermal melanocytes, and in a reconstructed human skin model. Omeprazole topically applied to the skin of UV-irradiated human subjects significantly reduced pigment levels after 3 weeks compared with untreated controls. Omeprazole had no significant inhibitory effect on the activities of purified human tyrosinase or on the mRNA levels of tyrosinase, dopachrome tautomerase, Pmel17, or MITF mRNA levels. Although melanocytes do not express ATP4A, they do express ATP7A, a copper transporting P-type ATPase in the trans-Golgi network that is required for copper acquisition by tyrosinase. ATP7A relocalization from the trans-Golgi network to the plasma membrane in response to elevated copper concentrations in melanocytes was inhibited by omeprazole. Omeprazole treatment increased the proportion of EndoH sensitive tyrosinase, indicating that tyrosinase maturation was impaired. In addition, omeprazole reduced tyrosinase protein abundance in the presence of cycloheximide, suggestive of increased degradation. Our findings are consistent with the hypothesis that omeprazole reduces melanogenesis by inhibiting ATP7A and by enhancing degradation of tyrosinase.

Modification of skin discoloration by a topical treatment containing an extract of Dianella ensifolia: a potent antioxidant

Skin hyperpigmentation, and the reactions that precipitate it, have been linked to free radicals by the fact that free radical scavengers or antioxidants can slow that hyperpigmentation. We have screened several hundred plant extracts for antioxidants and discovered one that is both a strong antioxidant and can reduce skin hyperpigmentation. Extracts of Dianella ensifolia contain 1‐(2,4‐dihydrophenyl)‐3‐(2,4‐dimethoxy‐3‐methylphenyl) propane (DP), which was found to inhibit the free radical 1‐1‐diphenyl‐2‐picryl‐hydrazyl (DPPH) with an EC50 value of 78u2003μm. DP was also found to inhibit Ultraviolet (UV)C‐induced lipid oxidation with an EC50 of about 30u2003μm. We next investigated the effects of this antioxidant on skin hyperpigmentation. The reduction of discoloration by different topical treatments has been assessed in human volunteers using an in vivo assay for the rate of fading of UVB‐induced tan. Two pharmaceutical formulas containing 4% hydroquinone (HQ) were used as positive controls, and we tested the ability of DP, a plant‐derived amphoteric antioxidant, to increase performance of non‐HQ cosmetic formulations. We found that the cosmetic formula containing DP produced an increase in the rate of fading compared to the two pharmaceutical treatments containing HQ.

1-(2,4-Dihydroxyphenyl)-3-(2,4-dimethoxy-3-methylpheny)propane inhibits melanin synthesis by dual mechanisms

BACKGROUNDn1-(2,4-Dihydroxyphenyl)-3-(2,4-dimethoxy-3-methylpheny)propane (DP) was reported as a novel tyrosinase inhibitor by Nesterov et al. In previous study, we showed that DP is an antioxidant and accelerates the fading of UVB-induced tan in human skin but details of inhibiting mechanism of DP in melanogenesis remain incomplete.nnnOBJECTIVEnTo clarify additional mechanisms of DP inhibition of melanogenesis, we studied the effect of DP on tyrosinase processing and degradation.nnnMETHODSnTyrosinase inhibition was assessed using mushroom and human tyrosinase. The effect of DP on mRNA and protein levels as well as glycosylation and degradation of tyrosinase was examined using normal human epidermal melanocytes (NHEM).nnnRESULTSnDP was 200 times more potent than that of kojic acid in inhibiting mushroom tyrosinase activity. In contrast, DP (IC(50)=200μM) was significantly less effective at inhibiting tyrosinase from NHEM. DP decreased melanin content in cultured NHEM after 7th day (IC(50)=10μM). The IC(50) for DP against human tyrosinase activity was found to be at least 20 times higher than that of melanin synthesis. At a non-cytotoxic concentration DP did not decrease tyrosinase mRNA however protein level decreased by 46% after 48h treatment. DP did not alter the ratio of mature and immature tyrosinase assayed by endo H cleavage. Tyrosinase degradation assays revealed that DP accelerated tyrosinase degradation in NHEM.nnnCONCLUSIONSnWe found that DP acts through dual mechanisms to reduce melanin synthesis; by inhibition of tyrosinase activity via an anti-oxidant effect, and, more importantly, by the acceleration of tyrosinase degradation.

Establishment of Photoaging In Vitro by Repetitive UVA Irradiation: Induction of Characteristic Markers of Senescence and its Prevention by PAPLAL with Potent Catalase Activity†

To understand a role of UVA radiation in photoaging of the skin, we established a model of photoaging cells using cultured human dermal fibroblasts. Repeated low‐dose UVA radiation for 10 consecutive days induced senescence in fibroblasts, characterized with (1) increased level of senescence‐associated β‐galactosidase, (2) flattened large cell shape, (3) accumulation of reactive oxygen species, (4) yellowish coloration and (5) expression of p16. These were also observed in chronologically aged fibroblasts (doubling times >20), whereas none of these were detected in young cells (doubling times <10). Collectively, we propose that fibroblasts exposed to repetitive UVA radiation may be a good model of aged cells to study the mechanism of aging and photoaging and further to search for novel agents preventing cellular senescence. In addition, H2O2 was produced in the culture medium by a single low dose of UVA irradiation. Further, PAPLAL, a nanoparticle of platinum and palladium having potent catalase‐like activity, significantly delayed the onset of H2O2‐induced cell senescence. The present study strongly indicates that repetitive short‐term UVA irradiation induces aging of cells possibly via H2O2 and may be suppressed by potent anti‐H2O2 agents.

Effects of platinum and palladium nanocolloid on macrophage polarization in relevance to repigmentation of vitiligo

Elevated oxidative stress is accepted to be the initial event in vitiligo leading to the final pathological regulation of immune systems known as autoimmune reaction, which destroys melanin‐forming cells, melanocytes. Recently, we reported an efficient topical use of PAPLAL, nanocolloid of platinum and palladium, having intense catalase‐like activity to vitiligo patients. In addition, we found that PAPLAL has dual effects on the AhR and Nrf‐2 pathways in keratinocytes, and suggested its contribution to the recovery of immune state in vitiligo. The precise mechanism developing autoimmune reaction in vitiligo, however, remains to be clarified. It is important to clarify what kinds of cells play an essential role in the development of vitiligo.