Tomohiro Hakozaki

The effect of niacinamide on reducing cutaneous pigmentation and suppression of melanosome transfer

Summary Background Cutaneous hyperpigmentation occurs in multiple conditions. In addition, many Asian women desire a lighter skin colour. Thus, there is a need for the development of skin lightening agents. Niacinamide is a possible candidate.

Effective inhibition of melanosome transfer to keratinocytes by lectins and niacinamide is reversible.

Abstract:  Skin pigmentation results in part from the transfer of melanized melanosomes synthesized by melanocytes to neighboring keratinocytes. Plasma membrane lectins and their glycoconjugates expressed by these epidermal cells are critical molecules involved in this transfer process. In addition, the derivative of vitamin B3, niacinamide, can inhibit melanosome transfer and induce skin lightening. We investigated the effects of these molecules on the viability of melanocytes and keratinocytes and on the reversibility of melanosome‐transfer inhibition induced by these agents using an in vitro melanocyte–keratinocyte coculture model system. While lectins and neoglycoproteins could induce apoptosis in a dose‐dependent manner to melanocytes or keratinocytes in monoculture, similar dosages of the lectins, as opposed to neoglycoproteins, did not induce apoptosis to either cell type when treated in coculture. The dosages of lectins and niacinamide not affecting cell viability produced an inhibitory effect on melanosome transfer, when used either alone or together in cocultures of melanocytes–keratinocytes. Cocultures treated with lectins or niacinamide resumed normal melanosome transfer in 3 days after removal of the inhibitor, while cocultures treated with a combination of lectins and niacinamide demonstrated a lag in this recovery. Subsequently, we assessed the effect of niacinamide on facial hyperpigmented spots using a vehicle‐controlled, split‐faced design human clinical trial. Topical application of niacinamide resulted in a dose‐dependent and reversible reduction in hyperpigmented lesions. These results suggest that lectins and niacinamide at concentrations that do not affect cell viability are reversible inhibitors of melanosome transfer.

Reduction in the appearance of facial hyperpigmentation by topical N-acetyl glucosamine.

Glucosamine has been reported to inhibit melanin production in melanocyte culture. It thus has a potential to reduce hyperpigmentation via topical use. Due to stability limitations of glucosamine, we chose to clinically evaluate the stable derivative N‐acetyl glucosamine (NAG). Based on in vitro Franz cell testing, NAG is a good skin penetrant. In an 8‐week, double‐blind, placebo‐controlled, left‐right randomized, split‐face clinical test, topical 2% NAG reduced the appearance of facial hyperpigmentation. In a second clinical study involving the topical combination of 2% NAG with 4% niacinamide, an agent previously shown to be clinically active, the effect on hyperpigmentation was greater. Both of these agents are well tolerated by the skin. This high tolerance coupled with relative ease of formulation and stability in solution make NAG, especially in combination with niacinamide, a suitable cosmetic ingredient for use in skin care products dealing with issues of skin hyperpigmentation.

Epidermal Keratinocytes from Light vs. Dark Skin Exhibit Differential Degradation of Melanosomes

Modification of skin complexion coloration has traditionally been accomplished by interruption or attenuation of melanogenesis and/or melanosome transfer. Post-transfer modification of pigmented melanosomes provides an attractive and distinct avenue of modulating skin pigmentation. The processing of melanosomes during keratinocyte (KC) terminal differentiation and the degradative variability observed between light and dark skin (LS and DS) remains enigmatic. To evaluate this, we developed a model system to investigate the loss of fluorescently labeled and isolated melanosomes by cultured human KCs. The extent of melanosome loss has been qualitatively assessed using transmission electron microscopy and indirect immunofluorescence with confocal microscopy, and quantitatively assessed using flow cytometry analysis. Results show that melanosomes are incorporated into the cytoplasm of both light and dark keratinocytes (LKCs and DKCs) and trafficked to a perinuclear region. Within 48  hours, confocal microscopy images suggest that LKCs display accelerated melanosome loss. This time-dependent decrease in carboxyfluorescein diacetate (CFDA) fluorescence was then quantitatively analyzed using flow cytometry. Consistent with the results of the confocal analysis, over a 48-hour time frame, LKCs appear to lose melanosomes more efficiently than DKCs. These experiments show that melanosomes are more rapidly lost in KCs derived from LS as opposed to DS.

Ultrasound enhanced skin‐lightening effect of vitamin C and niacinamide

Background/purpose: Cutaneous hyperpigmentation occurs in multiple conditions. There is a strong need for the improvement of hyperpigmentation especially among Asian women. However, the effect of existing skin‐lightening agents is not sufficient. One reason attributes to the limited capability of active agents to be delivered transepidermally. Ultrasound is one promising approach to enhance transepidermal transport. In this work, we investigate the effect of the use of high‐frequency ultrasound together with coupling gel containing skin‐lightening agents (ascorbyl glucoside and niacinamide) on facial hyperpigmentation in vivo in Japanese women.

Visualization and characterization of UVB-induced reactive oxygen species in a human skin equivalent model

Reactive oxygen species (ROS) play important roles in the process of ultraviolet-induced skin damage or photoaging. Although many enzymatic and chemical methods have been developed for evaluating ROS, evaluation methods for ROS generation in living systems are quite limited. Here we propose a unique system to visualize UVB-induced ROS and investigate the biological impact of ROS. In brief, a human skin equivalent model (HSEM) was exposed to UVB. Emitted luminescence from the HSEM was visualized and semi-quantified by using a chemiluminescent probe (CLA) and an ultra low-light imaging apparatus. The effects of anti-oxidative compounds such as ascorbate, β-carotene, superoxide dismutase (SOD), and yeast ferment filtrate (YFF) on the HSEM were evaluated by semi-quantification of emitted chemiluminescence (CL) intensities, MTT assay and 8-hydroxy-2′-deoxyguanosine (8-OHdG) staining. Visualization of time- and space-dependent dynamics of ROS generation in the HSEM was successfully achieved by utilizing a sensitive two-dimensional ultra-low light luminograph. Treatments with β-carotene and SOD effectively suppressed CL intensity, indicating the generation of 1O2 and O2·− in the HSEM under UVB exposure. Tested anti-oxidative compounds also attenuated UVB-induced CL and ameliorated the induced skin damages in terms of 8-OHdG formation and cell death. As a conclusion, this model is useful for not only visualizing the production of UVB-induced ROS in real-time but also evaluating the efficacy of topically applied anti-oxidative compounds to suppress ROS generation and attenuate sequential chemical and biological responses.

Reduction in the appearance of facial hyperpigmentation by topical N-undecyl-10-enoyl-l-phenylalanine and its combination with niacinamide

Objectives  N‐undecyl‐10‐enoyl‐l‐phenylalanine (Sepiwhite®, N‐undecylenoyl phenylalanine), a reported alpha‐melanocyte‐stimulating hormone (MSH) receptor antagonist, has been observed to reduce melanin production in cultured melanocytes. In other testing, niacinamide has been found to inhibit melanosome transfer in cultured cells and to reduce the appearance of hyperpigmented spots in clinical studies. Since these two agents function by different mechanisms, we conducted two studies to determine if their combination is more effective than niacinamide alone in reducing facial hyperpigmentation.

Application of genomics to breakthroughs in the cosmetic treatment of skin ageing and discoloration.

The use of global gene expression profiling, also known as transcriptomics or genomics, provides a means to identify key pathways affected in ageing skin that can be improved with appropriate cosmetic compounds. Aspects of skin ageing that can be addressed include matrix production, barrier, lipid synthesis, antioxidant capacity and hyperpigmentation. Gene expression profiling together with in vitro human skin cell cultures for compound screening and verification have led to the identification of cosmetic compounds and an understanding of the biological effects of compounds such as niacinamide, Pal‐KTTKS, hexamidine, retinyl propionate and sodium dehydroacetate. In addition, understanding of the decreased antioxidant capacity of aged skin has led to the identification of new antiageing ingredients, olive‐derived fatty acid ethoxylates, which have been shown to restore antioxidant enzymes in skin keratinocytes and fibroblasts. Gene expression profiling of age spots has also provided an understanding of the role of undecylenoyl phenylalanine in reducing melanin production by an adrenergic receptor mechanism in melanocytes. The use of these compounds in cosmetic formulations for skin care can aid improvements in the appearance of aged skin, including the improved appearance of fine lines, wrinkles and age spots.

Hydrolytic enzymes of the interfollicular epidermis differ in expression and correlate with the phenotypic difference observed between light and dark skin

Degradation of melanosomes in light skin (LS, i.e. phototype I/II) appears to occur more rapidly than dark skin (DS, i.e. phototype IV/V). Hydrolytic enzymes known to reside and be expressed in a differential pattern within the interfollicular epidermis are implicated in playing a role in epidermal differentiation and potentially melanosome degradation. The aim of this present study was to evaluate the differential expression of hydrolytic enzymes that may correlate with physiological and phenotypic differences seen between DS and LS. Expression of six hydrolytic enzymes was confirmed by microarray analysis of the suprabasal epidermis from LS and DS. Specific lysosomal hydrolases identified by microarray analysis were analyzed by indirect immunofluorescence (IIF) and immunoblot analysis. Immunogold electron microscopy (IEM) was completed to visualize cellular expression of the hydrolytic enzyme cathepsin L2 (Cath L2) and biochemical assay was performed to ascertain Cath L2 activity. Immunoblotting of light and dark epidermal lysates demonstrated that of the six enzymes initially analyzed, both prostatic acid phosphatase (ACPP) and Cath L2 were reproducibly upregulated in DS and LS, respectively. IIF and IEM analyses of Cath L2 in tissue confirmed this differential expression. Biochemical analysis of Cath L2 in light and dark epidermal lysates displays increased activity of Cath L2 in LS. The results of this study confirm differential expression of ACPP and Cath L2 in DS and LS at gene and protein level. Additionally, Cath L2 displays increased activity in LS‐derived epidermal lysates. This study indentified two acid hydrolases that may play a role in melanosome degradation and pigment processing.

A regulator of ubiquitin-proteasome activity, 2-hexyldecanol, suppresses melanin synthesis and the appearance of facial hyperpigmented spots.

2‐Hexyldecanol has long been used in skin‐care products, but has not previously been reported as an active ingredient for skin benefits.