The hyaluronan metabolism in the UV-irradiated human epidermis and the relevance of in vitro epidermal models.

Exposure to the sun affects the skin and may eventually result in UV-induced skin damage. It is generally known that hyaluronan (HA) is one of the main structural and functional components of the skin. However, UV-related changes in the HA metabolism in the skin have not yet been elucidated. Using qRT-PCR, confocal microscopy and LC-MS/MS we compared the naturally sun-exposed (SE), sun-protected, experimentally repeatedly UVA + UVB-exposed and acutely (once) UVA + UVB irradiated skin of Caucasian women. The epidermis was harvested by means of suction blistering 24 h after the acute irradiation. In addition, the epidermis was compared with a UV-irradiated in vitro reconstituted 3D epidermis (EpiDerm) and an in vitro 2D culture of normal human keratinocytes (NHEK). The amount of HA was found to be statistically significantly enhanced in the acutely irradiated epidermis. The acute UV evinced the upregulation of HA synthases (HAS2 and HAS3), hyaluronidases (HYAL2 and HYAL3), Cluster of differentiation 44 (CD44), and Cell Migration Inducing Proteins (CEMIP and CEMIP2), while only certain changes were recapitulated in the 3D epidermis. For the first time, we demonstrated the enhanced gene and protein expression of CEMIP and CEMIP2 following UV irradiation in the human epidermis. The data suggest that the HA metabolism is affected by UV in the irradiated epidermis and that the response can be modulated by the underlying dermis.

Comprehensive Physicochemical Characterization, In Vitro Membrane Permeation, and In Vitro Human Skin Cell Culture of a Novel TOPK Inhibitor, HI-TOPK-032.

Nonmelanoma skin cancers (NMSC) are the most common skin cancers, and about 5.4 million people are diagnosed each year in the United States. A newly developed T-lymphokine-activated killer cell-originated protein kinase (TOPK) inhibitor, HI-TOPK-032, is effective in suppressing colon cancer cell growth, inducing the apoptosis of colon cancer cells and ultraviolet (UV) light-induced squamous cell carcinoma (SCC). This study aimed to investigate the physicochemical properties, permeation behavior, and cytotoxicity potential of HI-TOPK-032 prior to the development of a suitable topical formulation for targeted skin drug delivery. Techniques such as scanning electron microscopy (SEM), energy-dispersive X-ray (EDX) spectroscopy, differential scanning calorimetry (DSC), hot-stage microscopy (HSM), X-ray powder diffraction (XRPD), Karl Fisher (KF) coulometric titration, Raman spectrometry, confocal Raman microscopy (CRM), attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR), and Fourier transform infrared microscopy were used to characterize HI-TOPK-032. The dose effect of HI-TOPK-032 on in vitro cell viability was evaluated using a 2D cell culture of the human skin keratinocyte cell line (HaCaT) and primary normal human epidermal keratinocytes (NHEKs). Transepithelial electrical resistance (TEER) at the air-liquid interface as a function of dose and time was measured on the HaCAT human skin cell line. The membrane permeation behavior of HI-TOPK-032 was tested using the Strat-M® synthetic biomimetic membrane with an in vitro Franz cell diffusion system. The physicochemical evaluation results confirmed the amorphous nature of the drug and the homogeneity of the sample with all characteristic chemical peaks. The in vitro cell viability assay results confirmed 100% cell viability up to 10 µM of HI-TOPK-032. Further, a rapid, specific, precise, and validated reverse phase-high performance liquid chromatography (RP-HPLC) method for the quantitative estimation of HI-TOPK-032 was developed. This is the first systematic and comprehensive characterization of HI-TOPK-032 and a report of these findings.

Innovative Rocuronium Bromide Topical Formulation for Targeted Skin Drug Delivery: Design, Comprehensive Characterization, In Vitro 2D/3D Human Cell Culture and Permeation.

Cutaneous squamous cell carcinoma (cSCC) is the second-most common type of non-melanoma skin cancer and is linked to long-term exposure to ultraviolet (UV) radiation from the sun. Rocuronium bromide (RocBr) is an FDA-approved drug that targets p53-related protein kinase (PRPK) that inhibits the development of UV-induced cSCC. This study aimed to investigate the physicochemical properties and in vitro behavior of RocBr. Techniques such as thermal analysis, electron microscopy, spectroscopy and in vitro assays were used to characterize RocBr. A topical oil/water emulsion lotion formulation of RocBr was successfully developed and evaluated. The in vitro permeation behavior of RocBr from its lotion formulation was quantified with Strat-M® synthetic biomimetic membrane and EpiDerm™ 3D human skin tissue. Significant membrane retention of RocBr drug was evident and more retention was obtained with the lotion formulation compared with the solution. This is the first systematic and comprehensive study to report these findings.

Paclitaxel-Induced Epidermal Alterations: An In Vitro Preclinical Assessment in Primary Keratinocytes and in a 3D Epidermis Model.

Paclitaxel is a microtubule-stabilizing chemotherapeutic agent approved for the treatment of ovarian, non-small cell lung, head, neck, and breast cancers. Despite its beneficial effects on cancer and widespread use, paclitaxel also damages healthy tissues, including the skin. However, the mechanisms that drive these skin adverse events are not clearly understood. In the present study, we demonstrated, by using both primary epidermal keratinocytes (NHEK) and a 3D epidermis model, that paclitaxel impairs different cellular processes: paclitaxel increased the release of IL-1α, IL-6, and IL-8 inflammatory cytokines, produced reactive oxygen species (ROS) release and apoptosis, and reduced the endothelial tube formation in the dermal microvascular endothelial cells (HDMEC). Some of the mechanisms driving these adverse skin events in vitro are mediated by the activation of toll-like receptor 4 (TLR-4), which phosphorylate transcription of nuclear factor kappa B (NF-κb). This is the first study analyzing paclitaxel effects on healthy human epidermal cells with an epidermis 3D model, and will help in understanding paclitaxel's effects on the skin.

Cytotoxic, genotoxic, and toxicogenomic effects of dihydroxyacetone in human primary keratinocytes.

PURPOSE: Dihydroxyacetone (DHA) is the only ingredient approved by the U.S. FDA as a colour additive in sunless tanning (self-tanning) products. Consumer sunless tanning products available for retail purchase contain 1-15% DHA. Although originally thought to only interact with the stratum corneum, more recent research has shown that DHA penetrates beyond the stratum corneum to living keratinocytes indicating a possible route of exposure in the epidermis. MATERIALS AND METHODS: Normal Human Epidermal Keratinocytes (NHEK) were used to determine any potential in vitro toxicological effects of DHA in the epidermis. NHEK cells exposed to DHA concentrations up to 0.90% (100 mM) in dosing media were evaluated for viability, genotoxicity (Comet Assay), and gene expression changes by microarray analysis. RESULTS: Cell viability significantly decreased ∼50% after 3-h exposure to 50 and 100 mM DHA. DNA damage was only found to be significantly increased in cells exposed to cytotoxic DHA concentrations. A subtoxic dose of DHA induced significant gene expression changes. Particularly, expression of cyclin B1, CDK1, and six other genes associated with the G2/M cell cycle checkpoint was significantly decreased which correlates well with a G2/M block reported in the existing literature. Advanced Glycation End Product (AGE) formation significantly increased after 24 h of DHA exposure at and above 10 mM. In summary, these data show that DHA is cytotoxic above 25 mM in primary keratinocytes. Genotoxicity was detected only at cytotoxic concentrations, likely indicative of non-biologically relevant DNA damage, while subtoxic doses induce gene expression changes and glycation. CONCLUSION: DHA treatment had a significant and negative effect on primary keratinocytes consistent with in vitro cultured cell outcomes; however, more information is needed to draw conclusions about the biological effect of DHA in human skin.

The Establishment of an Assay to Measure DNA Polymerase-Catalyzed Repair of UVB-Induced DNA Damage in Skin Cells and Screening of DNA Polymerase Enhancers from Medicinal Plants.

An in vitro assay method was established to measure the activity of cellular DNA polymerases (Pols) in cultured normal human epidermal keratinocytes (NHEKs) by modifying Pol inhibitor activity. Ultraviolet (UV) irradiation enhanced the activity of Pols, especially DNA repair-related Pols, in the cell extracts of NHEKs. The optimal ultraviolet B (UVB) exposure dose and culture time to upregulate Pols activity was 100 mJ/cm² and 4-h incubation, respectively. We screened eight extracts of medicinal plants for enhancement of UVB-exposed cellular Pols activity using NHEKs, and found that rose myrtle was the strongest Pols enhancer. A Pols' enhancement compound was purified from an 80% ethanol extract of rose myrtle, and piceatannol was isolated by spectroscopic analysis. Induction of Pol activity involved synergy between UVB irradiation and rose myrtle extract and/or piceatannol. Both the extract and piceatannol reduced UVB-induced cyclobutane pyrimidine dimer production, and prevented UVB-induced cytotoxicity. These results indicate that rose myrtle extract and piceatannol, its component, are potential photo-protective candidates for UV-induced skin damage.

Possible new therapeutic strategy to regulate atopic dermatitis through upregulating filaggrin expression.

BACKGROUND: Nonsense mutations in filaggrin (FLG) represent a significant genetic factor in the cause of atopic dermatitis (AD). OBJECTIVE: It is of great importance to find drug candidates that upregulate FLG expression and to determine whether increased FLG expression controls the development of AD. METHODS: We screened a library of bioactives by using an FLG reporter assay to find candidates that promoted FLG mRNA expression using a human immortalized keratinocyte cell line (HaCaT). We studied the effect of the compound on keratinocytes using the human skin equivalent model. We examined the effect of the compound on AD-like skin inflammation in NC/Nga mice. RESULTS: JTC801 promoted FLG mRNA and protein expression in both HaCaT and normal human epidermal keratinocytes. Intriguingly, JTC801 promoted the mRNA and protein expression levels of FLG but not the mRNA levels of other makers for keratinocyte differentiation, including loricrin, keratin 10, and transglutaminase 1, in a human skin equivalent model. In addition, oral administration of JTC801 promoted the protein level of Flg and suppressed the development of AD-like skin inflammation in NC/Nga mice. CONCLUSION: This is the first observation that the compound, which increased FLG expression in human and murine keratinocytes, attenuated the development of AD-like skin inflammation in mice. Our findings provide evidence that modulation of FLG expression can be a novel therapeutic target for AD.

Ligand Activation of the Aryl Hydrocarbon Receptor Upregulates Epidermal Uridine Diphosphate Glucose Ceramide Glucosyltransferase and Glucosylceramides.

Ligand activation of the aryl hydrocarbon receptor (AHR) accelerates keratinocyte differentiation and the formation of the epidermal permeability barrier. Several classes of lipids, including ceramides, are critical to the epidermal permeability barrier. In normal human epidermal keratinocytes, the AHR ligand, 2,3,7,8-tetrachlorodibenzo-p-dioxin, increased RNA levels of ceramide metabolism and transport genes: uridine diphosphate glucose ceramide glucosyltransferase (UGCG), ABCA12, GBA1, and SMPD1. Levels of abundant skin ceramides were also increased by 2,3,7,8-tetrachlorodibenzo-p-dioxin. These included the metabolites synthesized by UGCG, glucosylceramides, and acyl glucosylceramides. Chromatin immunoprecipitation-sequence analysis and luciferase reporter assays identified UGCG as a direct AHR target. The AHR antagonist, GNF351, inhibited the 2,3,7,8-tetrachlorodibenzo-p-dioxin-mediated RNA and transcriptional increases. Tapinarof, an AHR ligand approved for the treatment of psoriasis, increased UGCG RNA, protein, and its lipid metabolites hexosylceramides as well as increased the RNA expression of ABCA12, GBA1, and SMPD1. In Ahr-null mice, Ugcg RNA and hexosylceramides were lower than those in the wild type. These results indicate that the AHR regulates the expression of UGCG, a ceramide-metabolizing enzyme required for ceramide trafficking, keratinocyte differentiation, and epidermal permeability barrier formation.

Protective Effect of Hydroxygenkwanin against Hair Graying Induced by X-Ray Irradiation and Repetitive Plucking.

Hair graying in mice is caused by various injuries such as X-ray radiation and repeated plucking that ultimately damage melanocytes and their stem cells (melanocyte stem cells). In X-ray‒induced hair graying, injuries first manifest as a loss-of-niche function of hair follicular keratinocyte stem cells to maintain melanocyte stem cells. Thus, we hypothesized that hair follicular keratinocyte stem cells could be a practical target to prevent hair graying. In this study, we investigated the in vivo effect of the flavonoid hydroxygenkwanin, which has been shown to exert the best protection on human epidermal keratinocytes against in vitro X-ray‒induced cytological effects, using X-ray‒induced and repeated hair plucking‒induced hair graying mice models. We found that hydroxygenkwanin exerted a remarkable effect in preventing hair graying; however, when receptor Y kinase Kit-mutant mice were used, no prevention effect was observed. Therefore, we propose that Kit signaling might be involved in the hydroxygenkwanin-induced protective effect against hair graying.

Design, Physicochemical Characterization, and In Vitro Permeation of Innovative Resatorvid Topical Formulations for Targeted Skin Drug Delivery.

Nonmelanoma skin cancers (NMSCs) are the most common malignancies worldwide and affect more than 5 million people in the United States every year. NMSC is directly linked to the excessive exposure of the skin to solar ultraviolet (UV) rays. The toll-like receptor 4 (TLR4) antagonist, resatorvid (TAK-242), is a novel prototype chemo preventive agent that suppresses the production of inflammation mediators induced by UV exposure. This study aimed to design and develop TAK-242 into topical formulations using FDA-approved excipients, including DermaBaseTM, PENcreamTM, polyethylene glycol (PEG)-400, propylene glycol (PG), carbomer gel, hyaluronic acid (HA) gel, and Pluronic® F-127 poloxamer triblock copolymer gel for the prevention of skin cancer. The physicochemical properties of raw TAK-242, which influence the compatibility and solubility in the selected base materials, were confirmed using X-ray powder diffraction (XRPD), differential scanning calorimetry (DSC), hot-stage microscopy (HSM), Raman spectroscopy, and attenuated total reflectance Fourier-transform infrared (ATR-FTIR) spectroscopic analysis. The permeation behavior of TAK-242 from the prepared formulations was determined using Strat-M® transdermal diffusion membranes, and 3D cultured primary human-derived epidermal keratinocytes (EpiDermTM). Despite TAK-242's high molecular weight and hydrophobicity, it can permeate through reconstructed human epidermis from all formulations. The findings, reported for the first time in this study, emphasize the capabilities of the topical application of TAK-242 via these multiple innovative topical drug delivery formulation platforms.

Identification of compounds in red wine that effectively upregulate aquaporin-3 as a potential mechanism of enhancement of skin moisturizing.

In a previous clinical study, the moisture content in the stratum corneum of healthy Japanese women who consumed a beverage rich in oligomeric proanthocyanidins (OPCs) made from red wine extract was found to be higher than that in the control group. This finding suggested that OPCs can increase skin moisture content. In this study, we determined the expression level of aquaporin-3 (AQP3) in keratinocytes to elucidate the mechanism by which compounds in red wine grape increase moisture content in stratum corneum. Through in vitro studies, we confirmed that normal human epidermal keratinocytes (NHEK) incubated with red wine induced AQP3 expression. Furthermore, the supplementation of red wine fractions enriched in OPC was shown to increase AQP3 expression. Besides, the component of OPC-rich fractions that upregulated AQP3 expression was found to be a gallic acid (GA)-binding flavan-3-ol, particularly oligomeric compounds. We found that GA-binding OPC were able to upregulate AQP3 expression and that these compounds were enriched in red wine. Our findings might suggest that the mechanism of enhancement of moisture content in stratum corneum by red wine might be via the upregulation of AQP3 expression in the epidermal keratinocytes.

Evaluation of selective and non-selective cyclooxygenase inhibitors on sulfur mustard-induced pro-inflammatory cytokine formation in normal human epidermal keratinocytes.

Sulfur mustard (SM) is a highly toxic chemical warfare agent, which produces blisters after skin contact. Treatment of SM-induced adverse health effects, such as cutaneous blistering, ulceration, and inflammation remains a challenging task. Antidotes or specific therapeutic measures are lacking. Some drugs (e.g. cyclooxygenase (COX) inhibitors) exhibited beneficial effects after SM poisoning in vivo. However, in vitro studies that evaluate and compare the potency of COX inhibitors are missing. In the presented study, non-specific (acetylsalicylic acid, ibuprofen, diclofenac, indomethacin, and piroxicam), COX-2-specific (celecoxib and parecoxib) inhibitors and COX-independent drugs (paracetamol and tofacitinib) were compared regarding anti-inflammatory and cytoprotective effects after SM exposure in post-exposure treatment settings. Normal human epidermal keratinocytes (NHEK) were used as a surrogate model. Prostaglandin E2 (PGE2) formation, a direct indicator for COX activity, was determined by ELISA. Changes in pro-inflammatory cytokine levels after SM exposures were assessed by quantitative determination of 27 inflammatory cytokines using a multiplex method. Cytotoxicity was determined using an XTT viability assay. The results demonstrated that SM highly increased PGE2 production and release of pro-inflammatory cytokines, predominantly IL-6, IL-8 and TNF-α. In general, all COX inhibitors and paracetamol were able to reduce the PGE2 formation, while tofacitinib, an inhibitor of Janus kinase, had no influence on PGE2 levels. In addition, IL-6, IL-8, and TNF-α formation were also inhibited, but sometimes independently of PGE2. The COX-2 specific celecoxib was identified as the most potent drug to reduce IL-6, IL-8 and TNF-α formation after SM exposures in vitro. However, cell viability was not improved significantly by any of the investigated drugs in our experiments.

Sufficient therapeutic effect of cryopreserved frozen adipose-derived regenerative cells on burn wounds.

INTRODUCTION: The purpose of this study was to evaluate whether cryopreserved (frozen) adipose-derived regenerative cells (ADRCs) have a therapeutic effect on burn wound healing as well as freshly isolated (fresh) ADRCs. METHODS: Full thickness burns were created on dorsum of nude mice and burn wound was excised. The wound was covered by artificial dermis with; (i) fresh ADRCs, (ii) frozen ADRCs, and (iii) PBS (control). The assessment for wound healing was performed by morphological, histopathological and immunohistochemical analyses. RESULTS: In vivo analyses exhibited the significant therapeutic effect of frozen ADRCs on burn wound healing up to the similar or higher level of fresh ADRCs. There were significant differences of wound closure, epithelized tissue thickness, and neovascularization between the treatment groups and control group. Although there was no significant difference of therapeutic efficacy between fresh ADRC group and frozen ADRC group, frozen ADRCs improved burn wound healing process in dermal regeneration with increased great type I collagen synthesis compared with fresh ADRCs. CONCLUSIONS: These findings indicate that frozen ADRCs allow us to apply not only quickly but also for multiple times, and the cryopreserved ADRCs could therefore be useful for the treatment of burn wounds in clinical settings.

Light-activated phenalen-1-one bactericides: efficacy, toxicity and mechanism compared with benzalkonium chloride.

AIM: Five photoactive compounds with variable elongated alkyl-substituents in a phenalen-1-one structure were examined in view of structural similarity to the antimicrobial agent benzalkonium chloride (BAC). METHODS: All phenalen-1-ones and BAC were evaluated for their antimicrobial properties against Staphylococcus aureus, methicillin-resistant S. aureus, Escherichia coli, Pseudomonas aeruginosa and for their eukaryotic toxicity against normal human epidermal keratinocyte (NHEK) cells to narrow down the BAC-like effect and the photodynamic effect depending on the chemical structure. All compounds were investigated for effective concentration ranges, where a bacterial reduction of 5 log10 is achieved, while an NHEK survival of 80% is ensured. RESULTS: Effective concentration ranges were found for four out of five photoactive compounds, but not for BAC and the compound with BAC-like alkyl chain length. CONCLUSION: Chain length size and polar area of the respective head-groups of phenalen-1-one compounds or BAC showed an influence on the incorporation inside lipid membranes and thus, head-groups may have an impact on the toxicity of antimicrobials.

Analysis of aquaporin 9 expression in human epidermis and cultured keratinocytes.

Aquaporin 9 (AQP9) is a member of the aquaglyceroporin family that transports glycerol, urea and other small solutes as well as water. Compared to the expression and function in epidermal keratinocytes of AQP3, another aquaglyceroporin, our knowledge of epidermal AQP9 remains elusive. In this study, we investigated the expression of AQP9 in the human epidermis and cultured keratinocytes. Immunofluorescence studies revealed that AQP9 expression is highly restricted to the stratum granulosum of the human epidermis, where occludin is also expressed at the tight junctions. Interestingly, the AQP3 staining decreased sharply below the cell layers in which AQP9 is expressed. In cultured normal human epidermal keratinocytes (NHEK), knock-down of AQP9 expression in the differentiated cells induced by RNA interference reduced glycerol uptake, which was not as pronounced as was the case with AQP3 knock-down cells. In contrast, similar reduction of urea uptake was detected in AQP9 and AQP3 knock-down cells. These findings suggested that AQP9 expression in NHEK facilitates at least the transport of glycerol and urea. Finally, we analyzed the effect of retinoic acid (RA), a potent stimulator of keratinocyte proliferation, on AQP3 and AQP9 mRNA expression in differentiated NHEK. Stimulation with RA at 1 µM for 24 h augmented AQP3 expression and down-regulated AQP9 expression. Collectively, these results indicate that AQP9 expression in epidermal keratinocytes is regulated in a different manner from that of AQP3.

Reduction of CC-chemokine ligand 5 by aryl hydrocarbon receptor ligands.

BACKGROUND: The aryl hydrocarbon receptor (AhR) is a ligand-activated transcription factor that recognizes a large number of xenobiotics, such as polycyclic aromatic hydrocarbons (PAHs), dioxins, and some endogenous ligands. Despite numerous investigations targeting AhR ligands, the precise physiological role of AhR remains unknown. OBJECTIVE: We explored novel AhR target genes, especially focused on inflammatory chemokine. METHODS: We treated (1) HaCaT, a human keratinocyte cell line, (2) normal human epidermal keratinocytes (NHEKs), and (3) mouse primary keratinocytes with AhR ligands, such as 6-formylindolo[3,2-b]carbazole (FICZ; endogenous ligand) and benzo[a]pyrene (BaP; exogenous ligand). Then, we detected mRNA and protein of chemokine using quantitative RT-PCR and ELISA. We next clarified the relationship between AhR and chemokine expression using AhR siRNA. In addition, we measured serum chemokine levels in patients with Yusho disease (oil disease), who were accidentally exposed to dioxins in the past. RESULTS: We identified CC-chemokine ligand 5 (CCL5), a key mediator in the development of inflammatory responses, as the AhR target gene. AhR ligands (FICZ and BaP) significantly reduced CCL5 mRNA and protein expression in HaCaT cells. These effects were observed in NHEKs and mouse primary keratinocytes. AhR knockdown with siRNA restored CCL5 inhibition by AhR ligands. In addition, AhR ligands exhibited a dose-dependent suppression of CCL5 production induced by Th1-derived cytokines. Finally, serum levels of CCL5 in patients with Yusho disease, were significantly lower than in controls. CONCLUSION: Our findings indicate that CCL5 is a target gene for AhR, and might be associated with the pathology of dioxin exposure.

In vitro human skin irritation test for evaluation of medical device extracts.

The aim of this study was to determine if the EpiDerm™ reconstructed human skin model (MatTek Corp.) could be an acceptable alternative to the ISO 10993-required rabbit skin irritation test for assessing medical device biocompatibility. Eleven medical device polymers were tested. Four extracts were prepared per polymer, two each with saline and sesame oil; half were spiked with two R-38 irritants, lactic acid for saline extracts and heptanoic acid for the sesame oil extracts. Tissue viability was assessed by MTT reduction and the proinflammatory response was assessed by IL-1α release. LOAELs of 2% for lactic acid in saline and 0.7% for heptanoic acid in sesame oil were determined. A cell viability reduction of >50% was indicative of skin irritation. Cells exposed to saline extracts spiked with 3.25% lactic acid had significantly reduced mean cell viabilities (12.6-17.2%). Cells exposed to sesame oil extracts spiked with 1.25% heptanoic acid also exhibited reduced mean cell viabilities (25.5%-41.7%). All spiked cells released substantial amounts of IL-1α (253.5-387.4pg/ml) signifying a proinflammatory response. These results indicate that the EpiDerm™ model may be a suitable in vitro replacement for the assessment of the irritation potential of medical device extracts.

Cytokine regulation by MAPK activated kinase 2 in keratinocytes exposed to sulfur mustard.

Uncontrolled inflammation contributes to cutaneous damage following exposure to the warfare agent bis(2-chloroethyl) sulfide (sulfur mustard, SM). Activation of the p38 mitogen activated protein kinase (MAPK) precedes SM-induced cytokine secretion in normal human epidermal keratinocytes (NHEKs). This study examined the role of p38-regulated MAPK activated kinase 2 (MK2) during this process. Time course analysis studies using NHEK cells exposed to 200µM SM demonstrated rapid MK2 activation via phosphorylation that occurred within 15 min. p38 activation was necessary for MK2 phosphorylation as determined by studies using the p38 inhibitor SB203580. To compare the role of p38 and MK2 during SM-induced cytokine secretion, small interfering RNA (siRNA) targeting these proteins was utilized. TNF-α, IL-1ß, IL-6 and IL-8 secretion was evaluated 24h postexposure, while mRNA changes were quantified after 8h. TNF-α, IL-6 and IL-8 up regulation at the protein and mRNA level was observed following SM exposure. IL-1ß secretion was also elevated despite unchanged mRNA levels. p38 knockdown reduced SM-induced secretion of all the cytokines examined, whereas significant reduction in SM-induced cytokine secretion was only observed with TNF-α and IL-6 following MK2 knockdown. Our observations demonstrate potential activation of other p38 targets in addition to MK2 during SM-induced cytokine secretion.