Different regulation of lipogenesis in sebocytes and subcutaneous preadipocytes in hamsters in vitro.

Sebaceous gland cells (sebocytes) differentiate to intracellularly accumulate lipid droplets - a phenomenon similar to that found in adipocytes. In the present study, we examined whether the regulation of lipogenesis in sebocytes is the same as that in preadipocytes. When sebocytes and preadipocytes, prepared from auricle and subcutaneous adipose tissues from the inguinal region of hamsters, respectively, were treated with a common differentiation inducer, insulin, intracellular lipid-droplet formation and triacyglycerol (TG) production were dose- and time-dependently augmented in both. Insulin increased the production of perilipin, a differentiation marker in both sebocytes and adipocytes. Insulin-like growth factor 1 (IGF-1) augmented the intracellular level of TG in sebocytes and preadipocytes. In addition, the action of 1α,25-dihydroxyvitamin D3 [1,25(OH2)D3] on TG production was the opposite between sebocytes and preadipocytes. Furthermore, 5α-dihydrotestosterone (5α-DHT) augmented the TG level in sebocytes, whereas it did not alter TG production in preadipocytes. Moreover, insulin-augmented TG production in sebocytes was enhanced by IGF-1 and 5α-DHT, while diminished by 1,25(OH2)D3. In preadipocytes, the insulin-augmented production of TG was decreased by IGF-1, 1,25(OH2)D3, and 5α-DHT. These results suggest that sebocytic lipogenesis is partially similar to but substantially different from adipocyte lipogenesis due to the forementioned hormones and growth factors in the skin under physiological conditions.

Involvement of adenosine triphosphate-binding cassette subfamily B member 1 in the augmentation of triacylglycerol excretion by Propionibacterium acnes in differentiated hamster sebocytes.

An onset of acne, a common inflammatory skin disease, is associated with excess sebum production and secretion in sebaceous glands. Because Propionibacterium acnes has been reported to augment intracellular sebum accumulation in sebaceous glands in hamsters, it remains unclear whether P. acnes influences sebum secretion from differentiated sebocytes. Both P. acnes culture media (Acnes73-CM) and formalin-killed P. acnes (F-Acnes73) dose-dependently increased the extracellular levels of triacylglycerol (TG), a major sebum component, and Rhodamine 123, a substrate of adenosine triphosphate-binding cassette (ABC) transporter, from differentiated hamster sebocytes (DHS). In addition, the gene expression of the ABC subfamily B member 1 (ABCB1) was dose-dependently augmented by adding Acnes73-CM and F-Acnes73 into DHS. Furthermore, the F-Acnes73-induced increase of TG excretion was suppressed by PSC833, a selective ABCB1 inhibitor. On the other hand, peptidoglycan (PGN), which is a Toll-like receptor 2 (TLR2) ligand in P. acnes, increased extracellular TG levels, transporter activity and ABCB1 mRNA expression in DHS. The PGN-augmented TG excretion was suppressed by PSC833. Thus, these results provide novel evidence that P. acnes facilitates sebum secretion due to the activation of ABCB1 concomitantly with the increased ABCB1 expression, which may result from the activation of the TLR2 pathway in DHS. Therefore, the ABCB1 inhibitor is likely to become a candidate as a possible therapeutic for the treatment of acne.

Triptolide suppresses ultraviolet B-enhanced sebum production by inhibiting the biosynthesis of triacylglycerol in hamster sebaceous glands in vivo and in vitro.

Ultraviolet B (UVB) irradiation causes alterations in cutaneous barrier function, including excessive production of sebum in sebaceous glands, which is associated with the aggravation of acne. This study aimed to evaluate the inhibitory effects of triptolide, a diterpenoid triepoxide from Tripterygium wilfordii Hook F, on sebocytic lipogenesis in UVB-irradiated hamster skin in vivo and in vitro. Topical application of triptolide decreased the UVB-enhanced sebum accumulation in the sebaceous glands of hamster skin. The level of triacylglycerol (TG), a major sebum component, on the skin surface was reduced by triptolide treatment in UVB-irradiated hamsters, whereas there was no change in that of free-fatty acids and cholesterol, which are minor sebum components. UVB irradiation significantly enhanced TG production (P<0.01 in extracellular lipids, P<0.05 in intracellular lipids), and the activity of acyl coenzyme A/diacylglycerol acyltransferase (DGAT), a rate-limiting enzyme of TG synthesis, in differentiated hamster sebocytes (P<0.05 at 6 h and UVB of 0.62 kJ/m2, P<0.001 at 24 h and UVB 0.37 or 0.62 kJ/m2). Furthermore, triptolide significantly inhibited UVB-enhanced TG production (P<0.05 at 28 nM and P<0.01 at 56 and 112 nM triptolide) and DGAT activity (P<0.01 at 28 nM and P<0.001 at 56 and 112 nM triptolide) in differentiated hamster sebocytes. These results provide novel evidence that triptolide decreases UVB-enhanced sebum production by inhibiting DGAT-dependent TG biosynthesis in differentiated hamster sebocytes. These findings may be applicable to the prevention of acne aggravation.

Adapalene suppresses sebum accumulation via the inhibition of triacylglycerol biosynthesis and perilipin expression in differentiated hamster sebocytes in vitro.

BACKGROUND: Acne is a chronic inflammatory disease in sebaceous glands and pilosebaceous units where excess sebum production and follicular hyperkeratinization are observed. Adapalene, which exerts comedolytic and anti-inflammatory effects, is used for the topical treatment of mild to moderate acne. OBJECTIVE: We examined the effect of adapalene on sebum production and accumulation in sebaceous gland cells (sebocytes). METHODS: The regulation of sebum production was examined by oil red O and nile red staining and the measurement of triacylglycerols (TGs) in differentiated hamster sebocytes. The gene expression and production of diacylglycerol acyltransferase-1 (DGAT-1) and perilipin 1 (PLIN1) were analyzed using real-time PCR and Western blotting, respectively. RESULTS: Adapalene suppressed sebum accumulation as lipid droplets in spontaneously and insulin-differentiated hamster sebocytes. The TG production, and the gene expression and production of DGAT-1, a rate-limiting enzyme of TG biosynthesis, were dose-dependently inhibited by adapalene in insulin-, 5α-dihydrotestosterone- or a peroxisome proliferator activating receptor γ agonist, troglitazone-differentiated hamster sebocytes. In addition, the inhibition of TG production by adapalene interfered with antagonists against nuclear retinoic acid and retinoid X receptors (CD2665 and UVI3006, respectively) in the differentiated sebocytes. Furthermore, the production of PLIN1, a lipid storage droplet protein, was transcriptionally inhibited by adapalene in the differentiated sebocytes. CONCLUSIONS: These results suggest that adapalene exerts an inhibitory action for sebum accumulation due to the suppression of TG and PLIN1 production in differentiated hamster sebocytes. Furthermore, these findings may contribute to a novel understanding of the molecular mechanisms of adapalene for acne treatment and prevention.

Differentiated hamster sebocytes exhibit apoptosis-resistant phenotype by the augmentation of intracellular calcium level in vitro.

Sebaceous glands play important roles in the maintenance of the skin barrier function by secreting sebum onto the skin surface. In our study, we demonstrated that differentiated hamster sebocytes (DHS) exhibited apoptosis resistance and the loss of Ca(2+) influx against a calcium ionophore, A23187 treatment, which induced both apoptosis and Ca(2+) influx in undifferentiated hamster sebocytes (unDHS). The Fluo-3-related signal of intracellular Ca(2+) in the DHS was higher than that in unDHS and was sustained even though there was a depletion of Ca(2+) from the culture medium. Furthermore, the intracellular Ca(2+) chelator, BAPTA-AM, was found to decrease the Ca(2+) signal in the DHS, which induced apoptosis. Thus, these results provide novel evidence that the cell differentiation-dependent increase in store-operated Ca(2+) release is associated with apoptosis resistance in the DHS. Moreover, these findings should accelerate the understanding of the mechanisms of sebogenesis and/or sebum production and secretion under physiological conditions.

A novel functional site of extracellular matrix metalloproteinase inducer (EMMPRIN) that limits the migration of human uterine cervical carcinoma cells.

EMMPRIN (extracellular matrix metalloproteinase inducer)/CD147, a membrane-bound glycoprotein with two extracellular loop domains (termed loops I and II), progresses tumor invasion and metastasis by increasing the production of matrix metalloproteinase (MMP) in peritumoral stoma cells. EMMPRIN has also been associated with the control of migration activity in some tumor cells, but little is known about how EMMPRIN regulates tumor cell migration. In the present study, EMMPRIN siRNA suppressed the gene expression and production of EMMPRIN in human uterine cervical carcinoma SKG-II cells. An in vitro scratch wound assay showed enhancement of migration of EMMPRIN-knockdown SKG-II cells. In addition, the SKG-II cell migration was augmented by adding an E. coli-expressed human EMMPRIN mutant with two extracellular loop domains (eEMP-I/II), which bound to the cell surface of SKG-II cells. However, eEMP-I/II suppressed the native EMMPRIN-mediated augmentation of proMMP-1/procollagenase-1 production in a co-culture of the SKG-II cells and human uterine cervical fibroblasts, indicating that the augmentation of SKG-II cell migration resulted from the interference of native EMMPRIN functions by eEMP-I/II on the cell surface. Furthermore, a systematic peptide screening method using nine synthetic EMMPRIN peptides coding the loop I and II domains (termed EM1-9) revealed that EM9 (170HIENLNMEADPGQYR184) facilitated SKG-II cell migration. Moreover, SKG-II cell migration was enhanced by administration of an antibody against EM9, but not EM1 which is a crucial site for the MMP inducible activity of EMMPRIN. Therefore, these results provide novel evidence that EMMPRIN on the cell surface limits the cell migration of human uterine cervical carcinoma cells through 170HIENLNMEADPGQYR184 in the loop II domain. Finally, these results should provide an increased understanding of the functions of EMMPRIN in malignant cervical carcinoma cells, and could contribute to the development of clinical strategies for cervical cancer therapy.

Identification and characterization of ABCB1-mediated and non-apoptotic sebum secretion in differentiated hamster sebocytes.

Sebaceous glands secrete sebum onto the skin surface in a holocrine manner and as such a thin lipid layer is formed as a physiological barrier. In the present study, extracellular level of triacylglycerols (TG), a major sebum component, as well as intracellular TG accumulation was augmented in insulin-differentiated hamster sebocytes (DHS). The DHS exhibited phosphatidylserine exposure in an apoptosis-independent manner. In addition, intracellular ATP level and membrane-transporter activity using a substrate, Rhodamine 123, were highly detectable in the DHS rather than in the undifferentiated hamster sebocytes. A membrane-transporter activating reagent, 2'(3')-O-(4-benzoylbenzoyl) adenosine 5'-triphosphate (BzATP), enhanced transporter activity, extracellular TG level, and phosphatidylserine exposure in the DHS. Both transporter activity and TG secretion were suppressed by R-verapamil, a potent membrane-transporter inhibitor, in the BzATP-treated and untreated DHS. Furthermore, the gene expression and production of ATP-binding cassette subfamily B member 1 (ABCB1) were augmented in the DHS. ABCB1 was also detectable in sebaceous glands in the skin of hamsters. Moreover, the cell-differentiation- and BzATP-augmented transporter activity and TG secretion were dose-dependently inhibited by adding not only an ABCB1 antibody but also a selective inhibitor of ABCB1, PSC833. Thus, these results provide novel evidence that ABCB1 is involved in sebum secretion in the DHS, which is associated with non-apoptotic phosphatidylserine exposure and the increased level of intracellular ATP. These findings should accelerate the understanding of sebum secretion occurring in a holocrine-independent manner in sebaceous glands, and may contribute to the development of therapies for sebaceous gland disorders such as acne, seborrhea, and xerosis.

Augmentation of gene expression and production of promatrix metalloproteinase 2 by Propionibacterium acnes-derived factors in hamster sebocytes and dermal fibroblasts: a possible mechanism for acne scarring.

Aberrant extracellular matrix (ECM) remodeling in sebaceous glands and pilosebaceous units in the skin is associated with scar formation under acne conditions. To investigate the involvement of Propionibacterium acnes (P. acnes), a Gram-positive anaerobic microbial species, in ECM remodeling in sebaceous glands and pilosebaceous units, we examined the effects of P. acnes culture media, formalin-fixed P. acnes, and peptidoglycan (PGN) from Gram-positive bacteria walls on the production of promatrix metalloproteinase 2 (proMMP-2)/progelatinase A in hamster sebocytes and dermal fibroblasts. When hamster sebocytes (1.8×10(5) cells) and dermal fibroblasts (1×10(5) cells) were treated with P. acnes culture media and formalin-fixed P. acnes (corresponding to 1×10(6) and 1×10(7) bacterial cells), the production of proMMP-2 was augmented. In addition, PGN (5-50 µg/ml) dose-dependently augmented the production of proMMP-2 in both cells. Furthermore, the PGN (50 µg/ml)-augmented proMMP-2 production was resulted from an increase of its transcript. In contrast, there were no changes in cell proliferative activity in either the P. acnes or PGN-treated sebocytes and dermal fibroblasts, indicating that the augmented proMMP-2 production was not due to an increase in cell numbers. Therefore, these results provide novel evidence that PGN transcriptionally up-regulates the production of proMMP-2 in hamster sebocytes and dermal fibroblasts. Given an increase in the quantity of Gram-positive bacteria, including P. acnes in acne lesions, the aberrant ECM degradation may progress in sebaceous glands and pilosebaceous units, which is associated with acne scar formation.

Adiponectin resides in mouse skin and upregulates hyaluronan synthesis in dermal fibroblasts.

Adipose tissue is a hormonally active tissue that produces adipokines that influence the activity of other tissues. Adiponectin is an adipocyte-specific adipokine involved in systemic metabolism. We detected the expression of adiponectin receptors (AdipoR1 and AdipoR2) mRNA in cultured dermal fibroblasts. The full-length adiponectin (fAd), but not the globular adiponectin (gAd), increased hyaluronan (HA) production and upregulated HA synthase (HAS) 2 mRNA expression. AdipoR1 and AdipoR2 mRNAs were also expressed in keratinocytes, though neither fAd nor gAd had any effect on HA synthesis. In mouse skin, we found that adiponectin was present and decreased markedly with aging. The age-dependent pattern of adiponectin decrease in skin, correlated well with that of HA in skin. Our experiments were also the first to identify adiponectin production in cultured mouse sebocytes, a finding that suggests that skin adiponectin may derive not only from plasma and/or subcutaneous adipose tissue, but also from the sebaceous gland. These results indicated that adiponectin plays an important role in the HA metabolism of skin.

Induction of inflammatory reactions by lipopolysaccharide in hamster sebaceous glands and pilosebaceous units in vivo and in vitro.

Lipopolysaccharide (LPS) from Gram-negative bacteria has been reported to exert inflammatory reactions in epidermis, dermis, and sebaceous glands. Here, we demonstrated that the intradermal administration of Escherichia coli-derived LPS, three times a week for 4 weeks, to hamster auricle skin did not influence sebaceous morphology or sebum accumulation in sebaceous glands but in fact induced epidermal thickness. In addition, the administration of LPS, once a day for 2 days, augmented the production of cyclooxygenase 2 (COX-2) in sebaceous glands. Furthermore, LPS increased the production of prostaglandin F(2α) (PGF(2α) ) in hamster sebocytes. Moreover, the production of progelatinase A/promatrix metalloproteinase 2 (proMMP-2) was transcriptionally augmented by LPS and PGF(2α) in hamster sebocytes. Therefore, these results suggest that LPS directly increases inflammation by augmenting COX-2, PGF(2α) , and the PGF(2α) -mediated proMMP-2 production in sebaceous glands as well as epidermal inflammatory events in skin disorders including acne and folliculitis.

Involvement of Propionibacterium acnes in the augmentation of lipogenesis in hamster sebaceous glands in vivo and in vitro.

Propionibacterium acnes is considered to be involved in the aggravation of acne vulgaris, but it remains unclear whether P. acnes directly influences lipogenesis in sebaceous glands. In this study, we showed that a culture medium of P. acnes (acnes-CM) and formalin-killed P. acnes (F-acnes) prepared from P. acnes strains, JCM6473 and JCM6425, intracellularly augmented lipid droplet formation and triacylglycerol (TG) synthesis in undifferentiated and insulin-differentiated hamster sebocytes. Acnes-CM and F-acnes prepared from four clinical P. acnes strains elicited the same lipogenesis augmentation. The augmented TG production resulted from an increase in the diacylglycerol acyltransferase activity. Topical application of acnes-CM to the skin of hamster auricles every day for 4 weeks revealed that sebum accumulation was augmented in sebaceous glands and ducts. Furthermore, both acnes-CM and F-acnes increased the production of 15-deoxy-Delta(12,14)-prostaglandin J(2) (15d-PGJ(2)), a cytochrome P450 (CYP)-linked sebaceous lipogenic factor, in differentiated sebocytes. A CYP inhibitor, SKF-525A, decreased the acnes-CM- and F-acnes-augmented production of TG and 15d-PGJ(2). Thus, to our knowledge these results provide previously unreported evidence that P. acnes directly participates in the augmentation of sebaceous lipogenesis through a proposed mechanism in which an increase of 15d-PGJ(2) production through the CYP pathway is closely associated with the enhancement of TG production.

Augmentation of sebaceous lipogenesis by an ethanol extract of Grifola frondosa (Maitake mushroom) in hamsters in vivo and in vitro.

Grifola frondosa (Maitake mushroom) is an edible and medicinal mushroom with versatile effects such as antitumor and immunomodulating actions. Here, we demonstrated that an ethanol extract of G. frondosa fruiting body (Maitake extract) augmented intracellular lipid droplet formation and the production of triacylglycerols (TG), a major component of sebum, along with the activation of diacylglycerol acyltransferase, a rate-limiting enzyme of TG synthesis in cultured hamster sebocytes. The topical treatment of Maitake extract on the skin of hamster auricles augmented sebum accumulation in sebaceous glands and ducts. However, in comparison with the Maitake extract, another ethanol extract prepared from Agaricus blazei Murill showed less activity in sebaceous lipogenesis in hamsters in vivo and in vitro. These results provide novel evidence that Maitake extract augments sebaceous lipogenesis in hamsters in vivo and in vitro. Thus, Maitake extract is likely to be a unique agent leading to the remission of dry skin.

A citrus polymethoxy flavonoid, nobiletin inhibits sebum production and sebocyte proliferation, and augments sebum excretion in hamsters.

Acne vulgaris is characterized by excess sebum production, and apart from all-trans retinoic acid (atRA) or 13-cis retinoic acid (13-cisRA), there are few effective agents for acne therapy that directly suppresses sebaceous lipogenesis. In this study, we demonstrated that topical application of a citrus polymethoxy flavonoid, nobiletin, to hamster auricles decreased skin surface triacylglycerols (TG) level and the size of sebaceous glands along with inhibition of diacylglycerol acyltransferase (DGAT)-dependent TG synthesis and sebocyte proliferation. The inhibitory actions were similar to that observed with atRA and 13-cisRA in hamster sebocytes. The antilipogenic and antiproliferative actions of nobiletin were also reproduced in UVB (5.4 kJ/m2)-irradiated hamsters, which showed aberrant enhancement of sebum accumulation and sebaceous enlargement. Furthermore, nobiletin, but not 13-cisRA, augmented sebum excretion along with increases in intracellular cAMP level, protein kinase A (PKA) activation, and apoptosis-independent phosphatidylserine (PS) externalization in cell membrane. These phenomena were reproduced by forskolin and inhibited by a PKA inhibitor, H-89. These results provide early evidence that nobiletin is an effective candidate for acne therapy through mechanisms that include the inhibition of DGAT-dependent TG synthesis and sebocyte proliferation, and the progression of apoptosis-independent and PS-externalization-dependent sebum excretion by PKA activation.

Augmentation of lipogenesis by 15-deoxy-Delta12,14-prostaglandin J2 in hamster sebaceous glands: identification of cytochrome P-450-mediated 15-deoxy-Delta12,14-prostaglandin J2 production.

Prostaglandins (PGs) play important roles in the regulation of cutaneous cell functions under physiological and pathological conditions. In this study, we examined the involvement of PGs in sebocyte lipogenesis using non-steroidal anti-inflammatory drugs in vivo and in vitro. Hamster auricle sebocytes spontaneously differentiated to accumulate intracellular triacylglycerol (TG), under which the relative levels of 15-deoxy-Delta(12,14)-PGJ2 (15d-PGJ2) to PGF(2alpha) and PGE2 increased. 15d-PGJ2 was found to augment the formation of lipid droplets, which was because of an increase of TG synthesis by diacylglycerol acyltransferase (DGAT). Furthermore, sebocytes constitutively produced cyclooxygenase 2 (COX-2), but not COX-1, in vivo and in vitro. When sebocytes were treated with COX inhibitors such as indomethacin, diclofenac, or NS-398, the production of PGF(2alpha) and PGE2 decreased. The production of 15d-PGJ2, however, was increased in these inhibitor-treated sebocytes. In addition, indomethacin, diclofenac, and NS-398 augmented the synthesis of TG along with the increase in DGAT activity. Similarly, topical administration of indomethacin to hamster auricles caused the development of sebaceous glands with the augmentation of sebum deposition in vivo. Furthermore, indomethacin and NS-398-augmented 15d-PGJ2 production and TG synthesis were suppressed by a non-selective cytochrome P-450 (CYP) inhibitor, SKF-525A. A ligand activator of peroxisome proliferation activating receptor gamma (PPARgamma), troglitazone-induced synthesis of TG, however, was not altered even in the presence of SKF-525A. These results suggest that 15d-PGJ2 is a crucial stimulator of sebocyte lipogenesis by augmenting DGAT-mediated synthesis of TG. In addition to the COX-2-dependent pathway of PG synthesis, our findings suggest a sebocyte-specific pathway of 15d-PGJ2 production by CYP, the activity of which may be evoked by inhibiting COX-2.

Expression of perilipin A on the surface of lipid droplets increases along with the differentiation of hamster sebocytes in vivo and in vitro.

To clarify the involvement of perilipin, a lipid-droplet-surface protein associated with adipocytes and steroidogenic cells, in the differentiation of sebocytes, we investigated the expression of perilipin in sebaceous glands in vivo and in vitro. Perilipin was expressed in sebaceous glands of the hamster auricle in vivo and was localized at the surface of intracellular lipid droplets in differentiated hamster sebocytes in vitro. Western blot analysis showed that perilipin with a molecular weight of approximately 57 kDa, which was identical to that in differentiated mouse 3T3-L1 adipocytes, was detected in cultured sebocytes, indicating that sebaceous glands expressed perilipin A. In addition, the production of perilipin A in cultured sebocytes was transcriptionally augmented by sebocytic-lipogenesis stimulators, insulin, and 5alpha-dihydrotestosterone, whereas it was decreased by a suppressor of sebocytic differentiation, epidermal growth factor. Furthermore, hamster sebocytes were found to express peroxisome proliferation-activating receptor alpha and gamma1, the activation of which by WY14643 and troglitazone, respectively, caused the transcriptional augmentation of perilipin A expression along with an increase in levels of triacylglycerols in lipid droplets in sebocytes. Therefore, these results provide novel evidence that the expression of perilipin A increases on the surface of intracellular lipid droplets augmented along with the differentiation of hamster sebocytes.

Isolation and identification of histone H3 protein enriched in microvesicles secreted from cultured sebocytes.

Secretion of microvesicles, defined as sebosomes, containing lipid particles were discovered for the first time in cultured sebocytes. After reaching confluency, hamster-cloned sebocytes released bubble-like microvesicles with a diameter range of 0.5-5.0 microm. They had a complex structure containing multiple Oil Red O-stainable particles. The lipid components of the microvesicles were large amounts of squalene both of hamster-cloned and rat primary cultured sebocytes. The microvesicles contained a concentrated 17-kDa cationic protein, which was soluble in sulfate buffer including Nonidet P-40 at pH 1.5. As the protein bound tightly to heparin-Sepharose and eluted with 1.5 M NaCl, it was further purified from a SDS-PAGE gel. Peptide sequencing identified the protein to be histone H3. Polyclonal antibodies against the purified protein detected the antigen in the microvesicles both in the hamster-cloned and rat primary cultured sebocytes. The antibodies demonstrated a distribution of the protein within the nucleus, cytoplasm, and precursor microvesicles. When a gene construct encoding histone H3-enhanced green fluorescent protein was transfected to the sebocytes, fluorescence of the fusion proteins was detected within both the nucleus and the precursor microvesicles of the cytoplasm. The distribution of heparan sulfate was evident in the microvesicles, and it suggested the possibility that the histone H3 protein was recruited and then condensed to the secreted microvesicles by the molecules. In addition, the 14-3-3 protein, which was detected in the microvesicles, also may help incorporate the histone H3 protein in the microvesicles because it can bind to both histone and lipid particles.

Prevention of UVB-induced photoinflammation and photoaging by a polymethoxy flavonoid, nobiletin, in human keratinocytes in vivo and in vitro.

Exposure to ultraviolet B (UVB) irradiation induces acute skin inflammation such as erythema (sunburn) and edema, and prostaglandin (PG)E2 in the epidermis plays an important role as its prominent mediator. In the present study, we investigated the effect of nobiletin (5,6,7,8,3',4'-hexamethoxy flavone) from Citrus depressa, on the production of PGE2 in UVB-irradiated human keratinocytes. When keratinocytes were irradiated with 60mJ of UVB/cm2, the production and gene expression of cyclooxygenase (COX)-2, but not COX-1, were augmented along with an increase in PGE2 levels. The augmented COX-2 production was transcriptionally suppressed by nobiletin. In addition, neither the release of [14C]arachidonic acid from membrane phospholipids nor the gene expression of cytosolic phospholipase A2 (cPLA2) was altered in UVB-irradiated human keratinocytes. However, nobiletin was found to inhibit the release of [14C]arachidonic acid by decreasing the Ca2+ -dependent activity of cPLA2. Furthermore, topical treatment of nobiletin on the skin of the back prevented the UVB-induced increase of transepidermal water loss and hyperplasia of the epidermis in hairless mice. Therefore, these results suggest that nobiletin inhibits the UVB-induced production of PGE2 not only by suppressing the expression of COX-2 but also by decreasing the activity of cPLA2 in human keratinocytes. Furthermore, nobiletin may be useful as a novel sunscreen reagent to be applied for protection against photoinflammation and photoaging.