Topical treatment with thiazolidinediones, activators of peroxisome proliferator-activated receptor-?, normalizes epidermal homeostasis in a murine hyperproliferative disease model

Molecular mechanisms and drug therapy of metabolism disorders in psoriasis

Psoriasis is a prevalent skin disease affecting approximately 1%-3% of the population and imposes significant medical, social and economic burdens. Psoriasis involves multiple organs and is often complicated with obesity, diabetes, dyslipidemia, and hypertension. Because of the benefits of lipid-lowering agents and antidiabetic medications for psoriasis, metabolic abnormalities possibly play a pathogenic role in psoriasis.

This review focuses on the impacts of a variety of metabolic disorders on psoriasis and the underlying mechanisms.

In psoriasis, enhanced glycolysis, glutamine metabolism and altered fatty acid composition in the psoriatic lesion and plasma result in the excessive proliferation of keratinocytes and secretion of inflammatory cytokines. Altered metabolism is associated with the activation of MTORC signaling pathway and transcription factors such as HIF and S6K1. Therefore, MTORC1 can be a target for the treatment of psoriasis. Additionally, there are diabetes drugs and lipid-lowering drugs including TZDs, GLP-1 RAs, Metformin, statins and fibrates, which improve both metabolic levels and psoriasis symptoms.

The Effect of Polynucleotide-Hyaluronic Acid Hydrogel in the Recovery After Mechanical Skin Barrier Disruption

BACKGROUND

The epidermal barrier acts as a defense against external agents as well as helps to maintain body homeostasis. Polynucleotides (PN), exogenous DNA fragments, promote wound repair through their stimulatory and anti-inflammatory effects. Recent findings indicate a synergistic effect of PN and hyaluronic acid (HA) combinations in regulating inflammation and promoting cell proliferation. This study aims to elucidate the effects of PN and HA on repairing the epidermal barrier following its disruption by tape stripping (TS) in a mouse model.

MATERIALS AND METHODS

After disrupting the epidermal barrier using TS, a formulation containing PN (14 mg/mL) and HA (6 mg/mL) was applied. Trans-epidermal water loss (TEWL) was measured at 0, 3, 6, 24, 48, and 72 h. Mice were euthanized after the final application at 72 h, and tissue samples were analyzed for epidermal/dermal thickness, neutrophil infiltration, and filaggrin expression.

RESULTS

We observed a significant reduction in TEWL in the PN+HA group compared to that in the control group (20.8 ± 0.5 vs. 43.7 ± 0.5 g/m2h at 72 h, p < 0.05), indicating an improvement in barrier function. Histological evaluation showed decreased epidermal and dermal thickening in the PN+HA group compared to that in the control group (epidermal: 29.4 ± 2.2 vs. 57.9 ± 3.5 μm; dermal: 464.8 ± 25.9 vs. 825.9 ± 44.8 μm, both p < 0.05). Additionally, neutrophil infiltration in the dermis was significantly reduced, and filaggrin protein levels were significantly higher in the PN+HA group compared to those in the control group (4.8 ± 0.4 vs. 21.1 ± 3.3 for neutrophils; 0.84 ± 0.04 vs. 0.42 ± 0.03 for filaggrin, both p < 0.05).

CONCLUSION

These results suggest that PN+HA may be an effective therapeutic strategy for repairing skin barrier damage.

New Insights into the Role of PPARγ in Skin Physiopathology

Peroxisome proliferator-activated receptor gamma (PPARγ) is a transcription factor expressed in many tissues, including skin, where it is essential for maintaining skin barrier permeability, regulating cell proliferation/differentiation, and modulating antioxidant and inflammatory responses upon ligand binding. Therefore, PPARγ activation has important implications for skin homeostasis. Over the past 20 years, with increasing interest in the role of PPARs in skin physiopathology, considerable effort has been devoted to the development of PPARγ ligands as a therapeutic option for skin inflammatory disorders. In addition, PPARγ also regulates sebocyte differentiation and lipid production, making it a potential target for inflammatory sebaceous disorders such as acne. A large number of studies suggest that PPARγ also acts as a skin tumor suppressor in both melanoma and non-melanoma skin cancers, but its role in tumorigenesis remains controversial. In this review, we have summarized the current state of research into the role of PPARγ in skin health and disease and how this may provide a starting point for the development of more potent and selective PPARγ ligands with a low toxicity profile, thereby reducing unwanted side effects.

Thermal imprinting during embryogenesis modifies skin repair in juvenile European sea bass (Dicentrarchus labrax)

Fish skin is a multifunctional tissue that develops during embryogenesis, a developmental stage highly susceptible to epigenetic marks. In this study, the impact of egg incubation temperature on the regeneration of a cutaneous wound caused by scale removal in juvenile European sea bass was evaluated. Sea bass eggs were incubated at 11, 13.5 and 16 °C until hatching and then were reared at a common temperature until 9 months when the skin was damaged and sampled at 0, 1 and 3 days after scale removal and compared to the intact skin from the other flank. Skin damage elicited an immediate significant (p < 0.001) up-regulation of pcna in fish from eggs incubated at higher temperatures. In fish from eggs incubated at 11 °C there was a significant (p < 0.001) up-regulation of krt2 compared to fish from higher thermal backgrounds 1 day after skin damage. Damaged epidermis was regenerated after 3 days in all fish irrespective of the thermal background, but in fish from eggs incubated at 11 °C the epidermis was significantly (p < 0.01) thinner compared to other groups, had less goblet cells and less melanomacrophages. The thickness of the dermis increased during regeneration of wounded skin irrespective of the thermal background and by 3 days was significantly (p < 0.01) thicker than the dermis from the intact flank. The expression of genes for ECM remodelling (mmp9, colXα, col1α1, sparc, and angptl2b) and innate immunity (lyg1, lalba, sod1, csf-1r and pparγ) changed during regeneration but were not affected by egg thermal regime. Overall, the results indicate that thermal imprinting of eggs modifies the damage-repair response in juvenile sea bass skin.

Impact of ROS-Dependent Lipid Metabolism on Psoriasis Pathophysiology

Psoriasis is the most common autoimmune disease, yet its pathophysiology is not fully understood. It is now believed that psoriasis is caused by the increased activation of immune cells, especially Th1 lymphocytes. However, in psoriasis, immune cells interfere with the metabolism of keratinocytes, leading to their increased activation. Therefore, the pathophysiology of psoriasis is currently associated with the overproduction of ROS, which are involved in the activation of immune cells and keratinocytes as well as the modulation of various signaling pathways within them. Nevertheless, ROS modulate the immune system by also boosting the increasing generation of various lipid mediators, such as products of lipid peroxidation as well as endocannabinoids and prostaglandins. In psoriasis, the excessive generation of ROS and lipid mediators is observed in different immune cells, such as granulocytes, dendritic cells, and lymphocytes. All of the above may be activated by ROS and lipid mediators, which leads to inflammation. Nevertheless, ROS and lipid mediators regulate lymphocyte differentiation in favor of Th1 and may also interact directly with keratinocytes, which is also observed in psoriasis. Thus, the analysis of the influence of oxidative stress and its consequences for metabolic changes, including lipidomic ones, in psoriasis may be of diagnostic and therapeutic importance.

The Role of Transcription Factor PPAR-γ in the Pathogenesis of Psoriasis, Skin Cells, and Immune Cells

The peroxisome proliferator-activated receptor PPAR-γ is one of three PPAR nuclear receptors that act as ligand-activated transcription factors. In immune cells, the skin, and other organs, PPAR-γ regulates lipid, glucose, and amino acid metabolism. The receptor translates nutritional, pharmacological, and metabolic stimuli into the changes in gene expression. The activation of PPAR-γ promotes cell differentiation, reduces the proliferation rate, and modulates the immune response. In the skin, PPARs also contribute to the functioning of the skin barrier. Since we know that the route from identification to the registration of drugs is long and expensive, PPAR-γ agonists already approved for other diseases may also represent a high interest for psoriasis. In this review, we discuss the role of PPAR-γ in the activation, differentiation, and proliferation of skin and immune cells affected by psoriasis and in contributing to the pathogenesis of the disease. We also evaluate whether the agonists of PPAR-γ may become one of the therapeutic options to suppress the inflammatory response in lesional psoriatic skin and decrease the influence of comorbidities associated with psoriasis.

Indomethacin, a non-steroidal anti-inflammatory drug, induces skin dryness via PPARγ in mice

Cyclooxygenase (COX)-1-selective inhibitors have side effects such as itching and dryness of the skin. In this study, the degree of skin dryness and the onset mechanism of this condition were investigated by comparing the effects of three non-steroidal anti-inflammatory drugs (NSAIDs) in mice. Mice were orally administered either indomethacin, loxoprofen sodium, or celecoxib (n = 5 per group) once daily for four consecutive days, and blood samples as well as skin and jejunal tissues were isolated on day 5. In the mice treated with indomethacin, transepidermal water loss was significantly increased, and dry skin was observed. In addition, the expression of matrix metalloproteinase (MMP)-I, mast cells, CD163, CD23, CD21, histamine, and peroxisome proliferation-activated receptor (PPAR)γ in the skin and jejunum was increased, and the blood levels of interleukin-10 and immunoglobulin E were also increased. In contrast, the expression of collagen type I in the skin was decreased. These results show that indomethacin activates PPARγ in the skin and jejunum, changes the polarity of macrophages, increases the secretion of MMP-1 from mast cells, and decomposes collagen type I, leading to dry skin.

Keratinocyte-derived IL-1β induces PPARG downregulation and PPARD upregulation in human reconstructed epidermis following barrier impairment

Peroxisome proliferator-activated receptors (PPARs) are a family of nuclear hormone receptors. In skin, PPARs modulate inflammation, lipid synthesis, keratinocyte differentiation and proliferation and thus are important for skin barrier homeostasis. Accordingly, PPAR expression is altered in various skin conditions that entail epidermal barrier impairment, that is atopic dermatitis (AD) and psoriasis. Using human epidermal equivalents (HEEs), we established models of acute epidermal barrier impairment devoid of immune cells. We assessed PPAR and cytokine expression after barrier perturbation and examined effects of keratinocyte-derived cytokines on PPAR expression. We show that acetone or SDS treatment causes graded impairment of epidermal barrier function. Furthermore, we demonstrate that besides IL-1β and TNFα, IL-33 and TSLP are highly relevant markers for acute epidermal barrier impairment. Both SDS- and acetone-mediated epidermal barrier impairment reduce PPARG expression levels, whereas only SDS enhances PPARD expression. In line with findings in IL-1β and TNFα-treated HEEs, abrogation of IL-1 signalling restores PPARG expression and limits the increase of PPARD expression in SDS-induced epidermal barrier impairment. Thus, following epidermal barrier perturbation, keratinocyte-derived IL-1β and partly TNFα modulate PPARG and PPARD expression. These results emphasize a role for PPARγ and PPARβ/δ in acute epidermal barrier impairment with possible implications for diseases such as AD and psoriasis.

Biological action of docosahexaenoic acid in a 3D tissue-engineered psoriatic skin model: Focus on the PPAR signaling pathway

N-3 polyunsaturated fatty acids (n-3 PUFAs), and in particular docosahexaenoic acid (DHA), have many beneficial metabolic effects, including reducing epidermal thickness in patients with psoriasis. The positive impacts of DHA in psoriasis could be mediated by its interactions with the PPAR signaling pathway, as well as by its secretion of anti-inflammatory bioactive metabolites, but the detailed metabolism is still not understood. In the present study, we evaluated the influence of DHA on the main features of psoriasis and its effects on the PPAR signaling pathway, in a psoriatic in vitro skin model. Healthy and psoriatic skin substitutes were produced according to the tissue-engineered self-assembly method, using culture media supplemented with 10 μM of DHA. The presence of DHA led to a reduction in the abnormal cell differentiation of psoriatic keratinocytes, seen in the increased expression of filaggrin and keratin 10. DHA was incorporated into the membrane phospholipids of the epidermis and transformed principally into eicosapentaenoic acid (EPA). Furthermore, the addition of DHA into the culture medium led to a decrease in the levels of lipid mediators derived from n-6 PUFAs, mainly prostaglandin E₂ (PGE₂) and 12-hydroxyeicosatetraenoic acid (12-HETE). Finally, DHA supplementation rebalanced the expression of PPAR receptors and caused a decrease in the secretion of TNF-α. Altogether, our results show that DHA possesses the ability to attenuate the psoriatic characteristics of psoriatic skin substitutes, mostly by restoring epidermal cell differentiation and proliferation, as well as by reducing inflammation.

Analysis of PPARγ Signaling Activity in Psoriasis

In our previous work, we built the model of PPARγ dependent pathways involved in the development of the psoriatic lesions. Peroxisome proliferator-activated receptor gamma (PPARγ) is a nuclear receptor and transcription factor which regulates the expression of many proinflammatory genes. We tested the hypothesis that low levels of PPARγ expression promote the development of psoriatic lesions triggering the IL17-related signaling cascade. Skin samples of normally looking and lesional skin donated by psoriasis patients and psoriatic CD3⁺ Tcells samples (n = 23) and samples of healthy CD3⁺ T cells donated by volunteers (n = 10) were analyzed by real-time PCR, ELISA and immunohistochemistry analysis. We found that the expression of PPARγ is downregulated in human psoriatic skin and laser treatment restores the expression. The expression of IL17, STAT3, FOXP3, and RORC in psoriatic skin before and after laser treatment were correlated with PPARγ expression according to the reconstructed model of PPARγ pathway in psoriasis.In conclusion, we report that PPARγ weakens the expression of genes that contribute in the development of psoriatic lesion. Our data show that transcriptional regulation of PPARγ expression by FOSL1 and by STAT3/FOSL1 feedback loop may be central in the psoriatic skin and T-cells.

Magnolol may contribute to barrier function improvement on imiquimod-induced psoriasis-like dermatitis animal model via the downregulation of interleukin-23

Psoriasis is a chronic, recurrent, immune-mediated disease involving the skin and joints. Epidermal hyperproliferation, abnormal keratinocyte differentiation, angiogenesis with blood vessel dilatation, and excess T helper type-1 (Th-1) and Th-17 cell infiltration are the main histopathological features of psoriasis. Magnolol is a polyphenolic compound that exerts its biological properties through a variety of mechanisms such as the NF-κB/MAPK, Nrf2/HO-1 and PI3K/Akt pathways. Magnolol has been demonstrated to exert a number of therapeutic effects on dermatological processes, including acting as an anti-inflammation, antiproliferation and antioxidation agent. However, few studies have been published on the effect of magnolol on psoriasis. Therefore, the present study aimed to elucidate the mechanism of action of magnolol on psoriasis. BALB/c mice were treated topically with imiquimod (IMQ) to induce psoriasis-like dermatitis, and were randomly assigned to the control, vehicle control, low- and high-dose magnolol, and 0.25% desoximetasone ointment treatment groups in order to investigate skin barrier function, any changes in the levels of cytokines and for the histological assessment. High doses of magnolol were indicated to be able to improve the barrier function following IMQ-induced barrier disruption. Magnolol activated peroxisome proliferator-activated receptor-γ, and also significantly inhibited the protein expression of interleukin (IL)-23, IL-1β, IL-6, tumor necrosis factor-α and interferon-γ. However, administering a high dose of magnolol did not lead to any improvement in the clinical and pathological features of the psoriasis severity Taken together, these results demonstrated that downregulation of IL-23 may contribute to barrier function improvement in a psoriatic skin model.

The relevance of pathophysiological alterations in redox signaling of 4-hydroxynonenal for pharmacological therapies of major stress-associated diseases

Modern analytical methods combined with the modern concepts of redox signaling revealed 4-hydroxy-2-nonenal (4-HNE) as particular growth regulating factor involved in redox signaling under physiological and pathophysiological circumstances. In this review current knowledge of the relevance of 4-HNE as "the second messenger of reactive oxygen species" (ROS) in redox signaling of representative major stress-associated diseases is briefly summarized. The findings presented allow for 4-HNE to be considered not only as second messenger of ROS, but also as one of fundamental factors of the stress- and age-associated diseases. While standard, even modern concepts of molecular medicine and respective therapies in majority of these diseases target mostly the disease-specific symptoms. 4-HNE, especially its protein adducts, might appear to be the bioactive markers that would allow better monitoring of specific pathophysiological processes reflecting their complexity. Eventually that could help development of advanced integrative medicine approach for patients and the diseases they suffer from on the personalized basis implementing biomedical remedies that would optimize beneficial effects of ROS and 4-HNE to prevent the onset and progression of the illness, perhaps even providing the real cure.

The evaluation of efficacy and safety of methotrexate and pioglitazone in psoriasis patients: A randomized, open-labeled, active-controlled clinical trial

OBJECTIVES

Psoriasis is a chronic inflammatory disease showing co-existence with metabolic syndrome (MS), as has been confirmed by numerous epidemiologic studies in recent times. In this study, the aim was to ascertain the beneficial effects of pioglitazone in psoriasis, simultaneously targeting the improvement of MS parameters.

MATERIALS AND METHODS

We conducted a prospective randomized open-labeled parallel-group interventional study in patients of moderate-to-severe chronic plaque psoriasis. A total of 90 patients were inducted in study and divided into three groups of standard treatment (methotrexate 7.5 mg/week for 12 weeks), active treatment (pioglitazone 15 mg tablets once daily for 12 weeks), and their combination. Primary outcome was taken as percentage Psoriasis Area and Severity Index (PASI) improvement from baseline; secondary outcomes were PASI-75, safety profile, and MS parameters.

RESULTS

Intergroup evaluation of PASI score showed that standard treatment methotrexate and active treatment pioglitazone were comparable. Combination of methotrexate and pioglitazone proved superior in efficacy from both standard and active treatment in 8 and 12 weeks. Adverse drug reactions were mild and treated symptomatically. Pioglitazone and combination group also demonstrated beneficial efficacy in parameter of MS hence establishing it as a potential therapy in psoriasis with MS.

CONCLUSIONS

Pioglitazone alone or in combination with standard treatment may be a safe alternative drug for psoriasis coexisting with MS proving beneficial for both.

Evidence that peroxisome proliferator-activated receptor γ suppresses squamous carcinogenesis through anti-inflammatory signaling and regulation of the immune response

A variety of evidence suggests that peroxisome proliferator-activated receptor (PPAR)γ agonists may represent a potential pharmacologic target in the prevention or treatment of skin cancer. In particular, recent reports suggest that PPARγ activation may exert at least some of its anti-neoplastic effects through the suppression of tumor promoting chronic inflammation as well as by strengthening antitumor immune responses. This activity is thought to occur through a distinct mode of ligand interaction with PPARγ that causes transrepression of transcription factors that are involved in inflammatory and immunomodulatory signaling. However, current thiazolidinedione (TZD)-type PPARγ agonists have significant safety concerns that limit their usefulness as a preventive or therapeutic option. Due to the relatively large ligand binding pocket of PPARγ, a diverse group of ligands can be seen to interact with distinct modes of binding to PPARγ, leading to the phenomenon of partial agonist activity and selective PPARγ modulators (SPPARγM). This has led to the development of ligands that are tailored to deliver desired pharmacologic activity, but lack some of the negative side effects associated with full agonists, such as the currently utilized TZD-type PPARγ agonists. In addition, there is evidence that a number of phytochemicals that are currently being touted as antineoplastic nutraceuticals also possess PPARγ activity that may partially explain their pharmacologic activity. We propose that one or more of these partial agonists, SPPARγMs, or putative phytochemical PPARγ ligands could presumably be used as a starting point to design more efficacious anti-neoplastic PPARγ ligands that lack adverse pharmacological effects.

Inhibition of tumorigenesis by peroxisome proliferator-activated receptor (PPAR)-dependent cell cycle blocks in human skin carcinoma cells

To examine the functional role of peroxisome proliferator-activated receptor-β/δ (PPARβ/δ) and PPARγ in skin cancer, stable cell lines were created in the A431 human squamous cell carcinoma cell line. Expression of PPAR target genes was greatly enhanced in response to ligand activation of PPARβ/δ or PPARγ in A431 cells expressing these receptors. PPARβ/δ expression blocked the cell cycle at the G2/M phase, and this effect was increased by ligand activation. Ligand activation of PPARβ/δ markedly inhibited clonogenicity as compared to vehicle-treated controls. Similarly, ligand activation of PPARγ in A431 cells expressing PPARγ resulted in reduced clonogenicity. Expression of either PPARβ/δ or PPARγ markedly reduced tumor volume in ectopic xenografts, while ligand activation of these receptors had little further influence on tumor volume. Collectively, these studies demonstrate that stable expression and activation of PPARβ/δ or PPARγ in A431 cells led to reduced tumorigenicity. Importantly, PPAR expression or ligand activation had major impacts on clonogenicity and/or tumor volume. Thus, PPARβ/δ or PPARγ could be therapeutically targeted for the treatment of squamous cell carcinomas.

Thiazolidinedione drugs in the treatment of type 2 diabetes mellitus: past, present and future

Thiazolidinedione (TZD) drugs used in the treatment of type 2 diabetes mellitus (T2DM) have proven effective in improving insulin sensitivity, hyperglycemia, and lipid metabolism. Though well tolerated by some patients, their mechanism of action as ligands of peroxisome proliferator-activated receptors (PPARs) results in the activation of several pathways in addition to those responsible for glycemic control and lipid homeostasis. These pathways, which include those related to inflammation, bone formation, and cell proliferation, may lead to adverse health outcomes. As treatment with TZDs has been associated with adverse hepatic, cardiovascular, osteological, and carcinogenic events in some studies, the role of TZDs in the treatment of T2DM continues to be debated. At the same time, new therapeutic roles for TZDs are being investigated, with new forms and isoforms currently in the pre-clinical phase for use in the prevention and treatment of some cancers, inflammatory diseases, and other conditions. The aims of this review are to provide an overview of the mechanism(s) of action of TZDs, a review of their safety for use in the treatment of T2DM, and a perspective on their current and future therapeutic roles.

Nuclear receptor function in skin health and disease: therapeutic opportunities in the orphan and adopted receptor classes

The skin forms a vital barrier between an organism's external environment, providing protection from pathogens and numerous physical and chemical threats. Moreover, the intact barrier is essential to prevent water and electrolyte loss without which terrestrial life could not be maintained. Accordingly, acute disruption of the skin through physical or chemical trauma needs to be repaired timely and efficiently as sustained skin pathologies ranging from mild irritations and inflammation through to malignancy impact considerably on morbidity and mortality. The Nuclear Hormone Receptor Family of transcriptional regulators has proven to be highly valuable targets for addressing a range of pathologies, including metabolic syndrome and cancer. Indeed members of the classic endocrine sub-group, such as the glucocorticoid, retinoid, and Vitamin D receptors, represent mainstay treatment strategies for numerous inflammatory skin disorders, though side effects from prolonged use are common. Emerging evidence has now highlighted important functional roles for nuclear receptors belonging to the adopted and orphan subgroups in skin physiology and patho-physiology. This review will focus on these subgroups and explore the current evidence that suggests these nuclear receptor hold great promise as future stand-alone or complementary drug targets in treating common skin diseases and maintaining skin homeostasis.

Randomized placebo control study of insulin sensitizers (Metformin and Pioglitazone) in psoriasis patients with metabolic syndrome (Topical Treatment Cohort)

Background

Increased prevalence of metabolic syndrome (MS) is observed in psoriasis. Metformin has shown improvement in cardiovascular risk factors while pioglitazone demonstrated anti proliferative, anti-inflammatory and anti angiogenic effects. Study objective is to evaluate the efficacy and safety of Insulin sensitizers (metformin and pioglitazone) in psoriasis patients with metabolic syndrome (MS).

Methods

Single centre, parallel group, randomized, study of metformin, pioglitazone and placebo in psoriasis patients with MS.

Results

Statistically significant improvement was observed in Psoriasis Area and Severity Index (PASI), Erythema, Scaling and Induration (ESI) and Physician global assessment (PGA) scores in pioglitazone (p values – PASI = 0.001, ESI = 0.002, PGA = 0.008) and metformin groups (p values – PASI = 0.001, ESI = 0.016, PGA = 0.012) as compared to placebo. There was statistically significant difference in percentage of patients achieving 75 % reduction in PASI and ESI scores in metformin (p value – PASI = 0.001, ESI = 0.001) and pioglitazone groups (p vaue – PASI = 0.001, ESI = 0.001). Significant improvement was observed in fasting plasma glucose (FPG) and triglycerides levels in metformin and pioglitazone arms. Significant improvement was noted in weight, BMI, waist circumference, FPG, triglycerides and total cholesterol after 12 weeks of treatment with metformin while pioglitazone showed improvement in FPG, triglyceride levels, systolic blood pressure (SBP), diastolic blood pressure (DBP), total cholesterol and LDL cholesterol levels. There was no difference in pattern of adverse drug reaction in three groups.

Conclusion

Insulin sensitizers have shown improvement in the parameters of MS as well as disease severity in psoriasis patients.

Trial registration

CTRI Registration Number: CTRI/2011/12/002252. Registered on 19/12/2011.

Topical Administration of Acylated Homoserine Lactone Improves Epithelialization of Cutaneous Wounds in Hyperglycaemic Rats

Clinicians often experience delayed epithelialization in diabetic patients, for which a high glucose condition is one of the causes. However, the mechanisms underlying delayed wound closure have not been fully elucidated, and effective treatments to enhance epithelialization in patients with hyperglycaemia have not been established. Here we propose a new reagent, acylated homoserine lactone (AHL), to improve the delayed epithelialization due to the disordered formation of a basement membrane of epidermis in hyperglycaemic rats. Acute hyperglycaemia was induced by streptozotocin injection in this experiment. Full thickness wounds were created on the flanks of hyperglycaemic or control rats. Histochemical and immunohistochemical analyses were performed to identify hyperglycaemia-specific abnormalities in epidermal regeneration by comparison between groups. We then examined the effects of AHL on delayed epithelialization in hyperglycaemic rats. Histological analysis showed the significantly shorter epithelializing tissue (P < 0.05), abnormal structure of basement membrane (fragmentation and immaturity), and hypo- and hyperproliferation of basal keratinocytes in hyperglycaemic rats. Treating the wound with AHL resulted in the decreased abnormalities of basement membrane, normal distribution of proliferating epidermal keratinocytes, and significantly promoted epithelialization (P < 0.05) in hyperglycemic rats, suggesting the improving effects of AHL on abnormal epithelialization due to hyperglycemia.

Genetic Basis of Irritant Susceptibility in Health Care Workers

OBJECTIVE

The aim of this study was to investigate the association of single nucleotide polymorphisms (SNPs) within genes involved in inflammation, skin barrier integrity, signaling/pattern recognition, and antioxidant defense with irritant susceptibility in a group of health care workers.

METHODS

The 536 volunteer subjects were genotyped for selected SNPs and patch tested with three model irritants: sodium lauryl sulfate (SLS), sodium hydroxide (NaOH), and benzalkonium chloride (BKC). Genotyping was performed on genomic DNA using Illumina Goldengate custom panels.

RESULTS

The ACACB (rs2268387, rs16934132, rs2284685), NTRK2 (rs10868231), NTRK3 (rs1347424), IL22 (rs1179251), PLAU (rs2227564), EGFR (rs6593202), and FGF2 (rs308439) SNPs showed an association with skin response to tested irritants in different genetic models (all at P < 0.001). Functional annotations identified two SNPs in PLAU (rs2227564) and ACACB (rs2284685) genes with a potential impact on gene regulation. In addition, EGF (rs10029654), EGFR (rs12718939), CXCL12 (rs197452), and VCAM1 (rs3917018) genes showed an association with hand dermatitis (P < 0.005).

CONCLUSIONS

The results demonstrate that genetic variations in genes related to inflammation and skin homeostasis can influence responses to irritants and may explain inter-individual variation in the development of subsequent contact dermatitis.

The role of PPARγ-mediated signalling in skin biology and pathology: new targets and opportunities for clinical dermatology

Peroxisome proliferator-activated receptors (PPARs) are ligand-activated transcription factors that modulate the expression of multiple different genes involved in the regulation of lipid, glucose and amino acid metabolism. PPARs and cognate ligands also regulate important cellular functions, including cell proliferation and differentiation, as well as inflammatory responses. This includes a role in mediating skin and pilosebaceous unit homoeostasis: PPARs appear to be essential for maintaining skin barrier permeability, inhibit keratinocyte cell growth, promote keratinocyte terminal differentiation and regulate skin inflammation. They also may have protective effects on human hair follicle (HFs) epithelial stem cells, while defects in PPARγ-mediated signalling may promote the death of these stem cells and thus facilitate the development of cicatricial alopecia (lichen planopilaris). Overall, however, selected PPARγ modulators appear to act as hair growth inhibitors that reduce the proliferation and promote apoptosis of hair matrix keratinocytes. The fact that commonly prescribed PPARγ-modulatory drugs of the thiazolidine-2,4-dione class can exhibit a battery of adverse cutaneous effects underscores the importance of distinguishing beneficial from clinically undesired cutaneous activities of PPARγ ligands and to better understand on the molecular level how PPARγ-regulated cutaneous lipid metabolism and PPARγ-mediated signalling impact on human skin physiology and pathology. Surely, the therapeutic potential that endogenous and exogenous PPARγ modulators may possess in selected skin diseases, ranging from chronic inflammatory hyperproliferative dermatoses like psoriasis and atopic dermatitis, via scarring alopecia and acne can only be harnessed if the complexities of PPARγ signalling in human skin and its appendages are systematically dissected.

Cellular metabolism and macrophage functional polarization

Macrophages are a functionally heterogeneous cell population that is mainly shaped by a variety of microenvironmental stimuli. Interferon γ (IFN-γ), interleukin-1β (IL-1β), and lipopolysaccharide (LPS) induce a classical activation of macrophages (M1), whereas IL-4 and IL-13 induce an alternative activation program in macrophages (M2). Reprogramming of intracellular metabolisms is required for the proper polarization and functions of activated macrophages. Similar to the Warburg effect observed in tumor cells, M1 macrophages increase glucose consumption and lactate release and decreased oxygen consumption rate. In comparison, M2 macrophages mainly employ oxidative glucose metabolism pathways. In addition, fatty acids, vitamins, and iron metabolisms are also related to macrophage polarization. However, detailed metabolic pathways involved in macrophages have remained elusive. Understanding the bidirectional interactions between cellular metabolism and macrophage functions in physiological and pathological situations and the regulatory pathways involved may offer novel therapies for macrophage-associated diseases.

Protective effects of pioglitazone against immunoglobulin deposition on heart of streptozotocin-induced diabetic rats

AIM

Peroxisome proliferator-activated receptor-γ (PPAR-γ) agonists have immunomodulatory and anti-inflammatory effects. The study investigated the autoimmune injuries of diabetic cardiomyopathy (DCM) and tested the hypothesis that PPAR-γ agonists suppress disordered immune responses in diabetic heart, thereby preventing evolution of DCM.

METHODS

STZ-induced diabetic rats were assigned to five groups: DM group, given no treatment; INS group, given insulin (4 U kg(-1) d(-1)); PIL group, given low dose pioglitazone (4 mg kg(-1) d(-1)); PIL/INS group, given both low dose pioglitazone and insulin; PIH group, given high dose pioglitazone (20 mg kg(-1) d(-1)). Normal rats (CON group) were also monitored as control. The pathologic abnormalities of hearts were observed. The immunoglobulin deposition was examined by immunohistochemistry and immunofluorescence.

RESULTS

At 16 weeks, interstitial fibrosis was shown in diabetic heart which was accompanied by plenty of inflammatory cells infiltrated. Pioglitazone therapy could ameliorate the cardiac injuries. Shown by immunohistochemistry, the difference of integrated optical density (IOD) of immunoglobulin deposition among each group had statistic significance. No obvious immunoglobulins were deposited in the intercellular substance of heart in CON group (IgA 290.8 ± 88.1, IgG 960.4 ± 316.0 and IgM 341.3 ± 67.9). But the deposition of immunoglobulins increased significantly in DM group (IgA 7,047.5 ± 1,328.3, P < 0.05; IgG 28,945.9 ± 5,160.7, P < 0.05 and IgM 8,580.8 ± 1,336.8, P < 0.05). Administration of pioglitazone greatly reduced the increased deposition in a dose-dependent fashion. Moreover, the statistical significance was the same with immunofluorescence analysis as with immunohistochemical examination.

CONCLUSIONS

The data suggest that disordered immune responses play an important role in the pathogenesis of DCM. Pioglitazone showed protective effects by inhibiting the immunoglobulin deposition on diabetic myocardium.

Role of PPAR, LXR, and PXR in epidermal homeostasis and inflammation

Epidermal lipid synthesis and metabolism are regulated by nuclear hormone receptors (NHR) and in turn epidermal lipid metabolites can serve as ligands to NHR. NHR form a large superfamily of receptors modulating gene transcription through DNA binding. A subgroup of these receptors is ligand-activated and heterodimerizes with the retinoid X receptor including peroxisome proliferator-activated receptor (PPAR), liver X receptor (LXR) and pregnane X receptor (PXR). Several isotypes of these receptors exist, all of which are expressed in skin. In keratinocytes, ligand activation of PPARs and LXRs stimulates differentiation, induces lipid accumulation, and accelerates epidermal barrier regeneration. In the cutaneous immune system, ligand activation of all three receptors, PPAR, LXR, and PXR, has inhibitory properties, partially mediated by downregulation of the NF-kappaB pathway. PXR also has antifibrotic effects in the skin correlating with TGF-beta inhibition. In summary, ligands of PPAR, LXR and PXR exert beneficial therapeutic effects in skin disease and represent promising targets for future therapeutic approaches in dermatology. This article is part of a Special Issue entitled The Important Role of Lipids in the Epidermis and their Role in the Formation and Maintenance of the Cutaneous Barrier. Guest Editors: Kenneth R. Feingold and Peter Elias.

sPLA2 and the epidermal barrier

The mammalian epidermis provides both an interface and a protective barrier between the organism and its environment. Lipid, processed into water-impermeable bilayers between the outermost layers of the epidermal cells, forms the major barrier that prevents water from exiting the organism, and also prevents toxins and infectious agents from entering. The secretory phospholipase 2 (sPLA2) enzymes control important processes in skin and other organs, including inflammation and differentiation. sPLA2 activity contributes to epidermal barrier formation and homeostasis by generating free fatty acids, which are required both for formation of lamellar membranes and also for acidification of the stratum corneum (SC). sPLA2 is especially important in controlling SC acidification and establishment of an optimum epidermal barrier during the first postnatal week. Several sPLA2 isoforms are present in the epidermis. We find that two of these isoforms, sPLA2 IIA and sPLA2 IIF, localize to the upper stratum granulosum and increase in response to experimental barrier perturbation. sPLA2F(-/-) mice also demonstrate a more neutral SC pH than do their normal littermates, and their initial recovery from barrier perturbation is delayed. These findings confirm that sPLA2 enzymes perform important roles in epidermal development, and suggest that the sPLA2IIF isoform may be central to SC acidification and barrier function. This article is part of a Special Issue entitled The Important Role of Lipids in the Epidermis and their Role in the Formation and Maintenance of the Cutaneous Barrier. Guest Editors: Kenneth R. Feingold and Peter Elias.

Capsaicin delivery into the skin with lipidic nanoparticles for the treatment of psoriasis

The study aims to explore the potential of solid lipid nanoparticles (SLNs) and nanostructured lipid carriers (NLCs) in improving the topical delivery of capsaicin (CAP) by in vitro and in vivo studies. The lipidic nanoparticles were prepared by solvent diffusion method and were characterized for average particle size, zeta potential and entrapment efficiency. TEM photomicrographs revealed that the particles were nanometric in size. Higher amount of CAP can be encapsulated in the NLCs (87.4 ± 3.28) as compared with SLNs (79.7 ± 2.93%). The cumulative amounts of CAP permeated through the skin and retained in the SC were higher in the case of NLCs as compared with plain drug solution and SLNs. SLNs and NLCs exhibited minimum to no irritation. All the results concluded that NLCs and SLNs have shown a good ability to increase drug accumulation in the various skin layers but NLCs may be a more potential carrier for topical delivery of CAP for an effective therapy of psoriasis.

Peptidoglycan induced expression of peroxisome proliferator-activated receptor γ in mouse peritoneal macrophages: role of ERK and JNK MAP kinases

The peroxisome proliferator-activated receptor (PPAR) γ plays an important role in macrophage inflammatory homeostasis. Here we investigate the cross talk between PPARγ and TLR2 signaling pathway in mouse peritoneal macrophages. Real time RT-PCR and immunoblot analysis revealed that peptidoglycan (PGN) treatment of macrophages leads to biphasic effect on PPARγ expression i.e. an early upregulation and a late suppression. Inhibition of ERK MAP kinase by PD98059 abolished the early and rapid induction of PPARγ, while the inhibition of JNK MAP kinase by SP600125 nullifies the late inhibitory effect on the PPARγ expression in a dose-dependent manner. Furthermore, PPARγ knockdown macrophages showed enhanced NF-κB activity after PGN treatment. PGN treatment also enhances PPARγ interaction with p65 as observed by immunoprecipitation. This interaction may inhibit NF-κB (p65) activity as increased nuclear localization of p65 was observed in PPARγ knockdown macrophages after PGN treatment. PPARγ knockdown also increased the PGN-induced inflammatory cytokines (TNF-α, IL-1β, IL-12p40) production. Thus, our observations suggest that PGN induces PPARγ expression which is regulated by MAPKs activation and this enhanced PPARγ in turn attenuate NF-κB activity probably via enhancing p65 nuclear export. These results provide insight into how these pathways could be modulated in inflammatory diseases.

Topical hesperidin improves epidermal permeability barrier function and epidermal differentiation in normal murine skin

Orange peel extract appears to exhibit beneficial effects on skin whitening, inflammation, UVB protection, as well as keratinocyte proliferation. In the present study, we determine whether topical hesperidin influences epidermal permeability barrier function and its underlying mechanisms. Hairless mice were treated topically with 2% hesperidin or 70% ethanol alone twice daily for 6 days. At the end of treatment, basal transepidermal water loss (TEWL) was measured 2 and 4 h post barrier disruption. Epidermal proliferation and differentiation were evaluated by immunohistochemical staining and Western blot analysis. Additionally, lamellar body density and secretion were assessed by electron microscopy. Although there were no significant differences in basal barrier function, in comparison with control animals, topical hesperidin significantly accelerated barrier recovery at both 2 and 4 h after acute barrier abrogation. Enhanced barrier function in hesperidin-treated skin correlated with stimulation of both epidermal proliferation and differentiation, as well as enhanced lamellar body secretion. These results indicate that topical hesperidin enhances epidermal permeability barrier homeostasis at least in part due to stimulation of epidermal proliferation, differentiation, as well as lamellar body secretion.

Mice lacking epidermal PPARγ exhibit a marked augmentation in photocarcinogenesis associated with increased UVB-induced apoptosis, inflammation and barrier dysfunction

Recent studies suggest that peroxisome proliferator-activated receptor gamma (PPARγ) agonists may have cancer chemopreventive activity. Other studies have shown that loss of epidermal PPARγ results in enhanced chemical carcinogenesis in mice via unknown mechanisms. However, ultraviolet B (UVB) exposure represents the primary etiological agent for skin cancer formation and the role of PPARγ in photobiology and photocarcinogenesis is unknown. In previous studies, we demonstrated that UVB irradiation of cells results in the formation of oxidized glycerophosphocholines that exhibit PPARγ ligand activity. We therefore hypothesized that PPARγ would prove to be a chemopreventive target in photocarcinogenesis. We first showed that UVB irradiation of mouse skin causes generation of PPARγ agonist species in vivo. We then generated SKH-1 hairless, albino mice deficient in epidermal Pparg (Pparg-/-(epi)) using a cytokeratin 14 driven Cre-LoxP strategy. Using a chronic model of UVB photocarcinogenesis, we next showed that Pparg-/-(epi) mice exhibit an earlier onset of tumor formation, increased tumor burden and tumor progression. Increased tumor burden in Pparg-/-(epi) mice was accompanied by a significant increase in epidermal hyperplasia and p53 positive epidermal cells in surrounding skin lacking tumors. After acute UVB irradiation, Pparg-/-(epi) mice exhibited an augmentation of both UVB-induced Caspase 3/7 activity and inflammation. Increased apoptosis and inflammation was also observed after treatment with the PPARγ antagonist GW9662. With chronic UVB irradiation, Pparg-/-(epi) mice exhibited a sustained increase in erythema and transepidermal water loss relative to wildtype littermates. This suggests that PPARγ agonists could have possible chemopreventive activity in non-melanoma skin cancer.

Peroxisome proliferator-activated receptors (PPARs) in dermatology: Challenge and promise

Since their discovery it has become clear that peroxisome proliferator-activated receptors (PPARs) are ligand-activated transcription factors involved in the genetic regulation of the lipid metabolism and energy homoeostasis. Subsequently, accumulating evidence suggests a role of PPARs in genomic pathways including the regulation of cell growth, apoptosis and differentiation. These findings indicate that PPARs and PPAR agonists play an important role in inflammatory responses and tumor promotion. Because of their diverse biologic activities on keratinocytes and other skin cells, PPARs represent a major research target for the understanding and treatment of many skin pathologies, such as hyperproliferative and inflammatory diseases. Overmore recent clinical trials identified PPARs as promising drug targets for the prevention and treatment of various diseases in the field of dermatology. The present review summarizes the current knowledge of PPAR functions in various skin disorders particularly those involving inflammation and epidermal hyperproliferation (i.e., psoriasis, atopic dermatitis, acne, scleroderma, skin malignancies).

Laser-assisted topical drug delivery by using a low-fluence fractional laser: imiquimod and macromolecules

The aim of this study was to evaluate the ability of a low-fluence fractional erbium:yttrim-aluminum-garnet (Er:YAG) laser, with a wavelength of 2940 nm, for enhancing and controlling the skin permeation of imiquimod and macromolecules such as polypeptides and fluorescein isothiocyanate (FITC)-labeled dextran (FD). The in vitro permeation has been determined using a Franz diffusion cell, with porcine skin and nude mouse skin as the barriers. Hyperproliferative and ultraviolet (UV)-irradiated skins were also used as barrier models to mimic the clinical therapeutic conditions. Confocal laser scanning microscopy (CLSM) was used to examine the in vivo nude mouse skin uptake of peptide, FITC, and FD. Both in vitro and in vivo results indicated an improvement in permeant skin delivery by the laser. The laser fluence and number of passes were found to play important roles in controlling drug transport. Increases of 46- and 127-fold in imiquimod flux were detected using the respective fluences of 2 and 3 J/cm(2) with 4 pulses. An imiquimod concentration of 0.4% from aqueous vehicle with laser treatment was sufficient to approximate the flux from the commercial cream with an imiquimod dose of 5% without laser treatment, indicating a reduction of the drug dose by 125-fold. The enhancement of peptide permeation was size and sequence dependent, with the smaller molecular weight (MW) and more-hydrophilic entities showing greater enhancing effect. Skin permeation of FD with an MW of at least 150 kDa could be achieved with fractional laser irradiation. CLSM images revealed intense green fluorescence from the permeants after exposure of the skin to the laser. The follicular pathway was significant in laser-assisted permeation.

PPARγ mediates innate immunity by regulating the 1α,25-dihydroxyvitamin D3 induced hBD-3 and cathelicidin in human keratinocytes

BACKGROUND

Production of antimicrobial peptides (AMPs) is the primary mechanism by which skin innate immunity protects against infection. Hormonally active vitamin D3 (1α,25-dihydroxyvitamin D3; 1,25D₃) is a vital regulator of skin innate immunity, and has been shown to increase the expression and function of AMPs.

OBJECTIVE

PPARγ is a ligand-activated nuclear receptor and plays a role in keratinocyte differentiation and cutaneous homeostasis. In this study, we investigate whether 1,25D₃-activated PPARγ signaling regulates AMP expression in keratinocytes.

METHODS

Subconfluent keratinocytes were treated with 1,25D₃ for the indicated times. The mRNA and protein levels of AMPs were detected by RT-PCR and Western blot, and the DNA binding activation of PPARγ, VDRE and AP-1 was investigated by EMSA. To examine the role of PPARγ, the recombinant adenovirus carrying a dominant-negative form of PPARγ (dn-PPARγ) was constructed and transfected into keratinocytes.

RESULTS

We show here that 1,25D₃ significantly enhances hBD-3 and cathelicidin expression in keratinocytes. Expression of dn-PPARγ did not affect binding to the vitamin D-responsive element (VDRE), which is crucial for cathelicidin induction by VD3; however, it did decrease 1,25D₃ induction of both hBD-3 and cathelicidin. Inhibition of the p38, ERK, and JNK signaling pathways blocked hBD-3 expression, whereas only p38 inhibition suppressed cathelicidin induction. dn-PPARγ had no effect on ERK and JNK activity, but inhibited p38 phosphorylation and suppressed 1,25D₃-induced AP-1 activation via effects on Fra1 and c-Fos proteins.

CONCLUSIONS

In conclusion, PPARγ regulates the 1,25D₃-induced hBD-3 and cathelicidin expression in keratinocytes through the regulation of AP-1 and p38 activity.

Healing fats of the skin: the structural and immunologic roles of the omega-6 and omega-3 fatty acids

Linoleic acid (18:2omega6) and alpha-linolenic acid (18:3omega3) represent the parent fats of the two main classes of polyunsaturated fatty acids: the omega-6 (n-6) and the omega-3 (n-3) fatty acids, respectively. Linoleic acid and alpha-linolenic acid both give rise to other long-chain fatty acid derivatives, including gamma-linolenic acid and arachidonic acid (omega-6 fatty acids) and docosahexaenoic acid and eicosapentaenoic acid (omega-3 fatty acids). These fatty acids are showing promise as safe adjunctive treatments for many skin disorders, including atopic dermatitis, psoriasis, acne vulgaris, systemic lupus erythematosus, nonmelanoma skin cancer, and melanoma. Their roles are diverse and include maintenance of the stratum corneum permeability barrier, maturation and differentiation of the stratum corneum, formation and secretion of lamellar bodies, inhibition of proinflammatory eicosanoids, elevation of the sunburn threshold, inhibition of proinflammatory cytokines (tumor necrosis factor-alpha, interferon-gamma, and interleukin-12), inhibition of lipoxygenase, promotion of wound healing, and promotion of apoptosis in malignant cells, including melanoma. They fulfill these functions independently and through the modulation of peroxisome proliferator-activated receptors and Toll-like receptors.

Combination of calcipotriol and methotrexate in nanostructured lipid carriers for topical delivery

The combination of calcipotriol with methotrexate can strengthen the topical therapy for psoriasis. The aim of the present study was to evaluate the potential of nanostructured lipid carriers (NLCs) loaded with lipophilic calcipotriol and hydrophilic methotrexate as topical therapy. NLCs composed of Precirol ATO 5 with various amounts of squalene as the liquid lipid were prepared. The particle size, surface charge, molecular environment, drug permeation, and skin irritation of the carriers were assessed. Hyperproliferative skin was also used as a permeation barrier in this study. It was found that variations in the Precirol/squalene ratio had profound effects on the physicochemical characteristics of the NLCs. The range of particle size of the NLC preparations was 270 to 320 nm, with vehicles containing a higher Precirol amount exhibiting a larger diameter. NLCs with a higher Precirol/squalene ratio also showed greater polarity in their molecular environment. Calcipotriol-loaded NLC systems provided drug fluxes of 0.62 to 1.08 microg/cm(2)/h, which were slightly higher or comparable to the 30% ethanol vehicle (control, 0.72 microg/cm(2)/h). The methotrexate amount permeating the skin was 2.4 to 4.4-times greater using NLCs compared to that with the control. Dual drug-loaded NLCs exhibited reduced skin permeation of calcipotriol but not methotrexate. The in vivo topical delivery examined by confocal laser scanning microscopy (CLSM) showed a good correlation with the in vitro results. These two drugs with extremely different polarities can successfully be combined in NLCs. Results suggest that NLCs may have the potential to serve as delivery carriers for antipsoriatic drugs because of enhanced drug permeation and limited skin irritation.

Murine atopic dermatitis responds to peroxisome proliferator-activated receptors alpha and beta/delta (but not gamma) and liver X receptor activators

BACKGROUND

Atopic dermatitis (AD) is a chronic inflammatory dermatosis now increasingly linked to mutations that alter the structure and function of the stratum corneum. Activators of peroxisome proliferator-activated receptors (PPARs) alpha, beta/delta, and gamma and liver X receptor (LXR) regulate epidermal protein and lipid production, leading to superior barrier function. Additionally, some of these activators exhibit potent antihyperplastic and anti-inflammatory activity in irritant contact dermatitis and acute allergic contact dermatitis murine models.

OBJECTIVE

We evaluated the efficacy of PPAR/LXR activation in a hapten (oxazolone [Ox])-induced AD-like model (Ox-AD) in hairless mice.

METHODS

Ox-AD was established with 10 Ox challenges (every other day) on the flank. After the establishment of Ox-AD, twice-daily topical application with individual PPAR/LXR activators was then performed for 4 days, with continued Ox challenges every other day. The efficacy of topical PPAR/LXR activators to reduce parameters of Ox-AD was assessed physiologically, morphologically, and immunologically.

RESULTS

Certain topical activators of PPARalpha, PPARbeta/delta, and LXR, but not activators of PPARgamma, reversed the clinical dermatosis, significantly improved barrier function, and increased stratum corneum hydration in Ox-AD mice. In addition, the same activators, but again not PPARgamma, largely reversed the immunologic abnormalities in Ox-AD mice, including the increased T(H)2 markers, such as tissue eosinophil/mast cell density, serum thymus and activation-related chemokine levels, the density of chemoattractant receptor-homologous molecule expressed on T(H)2-positive lymphocytes (but not serum IgE levels), and reduced IL-1alpha and TNF-alpha activation, despite ongoing hapten challenges.

CONCLUSION

These results suggest that topical applications of certain activators/ligands of PPARalpha, PPARbeta/delta, and LXR could be useful for the treatment of AD in human subjects.

Filaggrin deficiency confers a paracellular barrier abnormality that reduces inflammatory thresholds to irritants and haptens

BACKGROUND

Mutations in the human filaggrin gene (FLG) are associated with atopic dermatitis (AD) and are presumed to provoke a barrier abnormality. Yet additional acquired stressors might be necessary because the same mutations can result in a noninflammatory disorder, ichthyosis vulgaris.

OBJECTIVE

We examined here whether FLG deficiency alone suffices to produce a barrier abnormality, the basis for the putative abnormality, and its proinflammatory consequences.

METHODS

By using the flaky-tail mouse, which lacks processed murine filaggrin because of a frameshift mutation in the gene encoding profilaggrin that mimics some mutations in human AD, we assessed whether FLG deficiency provokes a barrier abnormality, further localized the defect, identified its subcellular basis, and assessed thresholds to irritant- and hapten-induced dermatitis.

RESULTS

Flaky-tail mice exhibit low-grade inflammation with increased bidirectional, paracellular permeability of water-soluble xenobiotes caused by impaired lamellar body secretion and altered stratum corneum extracellular membranes. This barrier abnormality correlates with reduced inflammatory thresholds to both topical irritants and haptens. Moreover, when exposed repeatedly to topical haptens at doses that produce no inflammation in wild-type mice, flaky-tail mice experience a severe AD-like dermatosis with a further deterioration in barrier function and features of a T(H)2 immunophenotype (increased CRTH levels plus inflammation, increased serum IgE levels, and reduced antimicrobial peptide [mBD3] expression).

CONCLUSIONS

FLG deficiency alone provokes a paracellular barrier abnormality in mice that reduces inflammatory thresholds to topical irritants/haptens, likely accounting for enhanced antigen penetration in FLG-associated AD.

Age-related changes in the meibomian gland

The purpose of this study was to characterize the age-related changes of the mouse meibomian gland. Eyelids from adult C57Bl/6 mice at 2, 6, 12 and 24 months of age were stained with specific antibodies against peroxisome proliferator activated receptor gamma (PPARgamma) to identify differentiating meibocytes, Oil Red O (ORO) to identify lipid, Ki67 nuclear antigen to identify cycling cells, B-lymphocyte-induced maturation protein-1 (Blimp1) to identify potential stem cells and CD45 to identify immune cells. Meibomian glands from younger mice (2 and 6 months) showed cytoplasmic and perinuclear staining with anti-PPARgamma antibodies with abundant ORO staining of small, intracellular lipid droplets. Meibomian glands from older mice (12 and 24 months) showed only nuclear PPARgamma localization with less ORO staining and significantly reduced acinar tissue (p < 0.04). Acini of older mice also showed significantly reduced (p < 0.004) numbers of Ki67 stained nuclei. While Blimp1 appeared to diffusely stain the superficial ductal epithelium, isolated cells were occasionally stained within the meibomian gland duct and acini of older mice that also stained with CD45 antibodies, suggesting the presence of infiltrating plasmacytoid cells. These findings suggest that there is altered PPARgamma receptor signaling in older mice that may underlie changes in cell cycle entry/proliferation, lipid synthesis and gland atrophy during aging. These results are consistent with the hypothesis that mouse meibomian glands undergo age-related changes similar to those identified in humans and may be used as a model for age-related meibomian gland dysfunction.

Topical delivery of 5-aminolevulinic acid-encapsulated ethosomes in a hyperproliferative skin animal model using the CLSM technique to evaluate the penetration behavior

Psoriasis, an inflammatory skin disease, exhibits recurring itching, soreness, and cracked and bleeding skin. Currently, the topical delivery of 5-aminolevulinic acid-photodynamic therapy (ALA-PDT) is an optional treatment for psoriasis which provides long-term therapeutic effects, is non-toxic and enjoys better compliance with patients. However, the precursor of ALA is hydrophilic, and thus its ability to penetrate the skin is limited. Also, little research has provided a platform to investigate the penetration behavior in disordered skin. We employed a highly potent ethosomal carrier (phosphatidylethanolamine; PE) to investigate the penetration behavior of ALA and the recovery of skin in a hyperproliferative murine model. We found that the application of ethosomes produced a significant increase in cumulative amounts of 5-26-fold in normal and hyperproliferative murine skin samples when compared to an ALA aqueous solution; and the ALA aqueous solution appeared less precise in terms of the penetration mode in hyperproliferative murine skin. After the ethosomes had been applied, the protoporphyrin IX (PpIX) intensity increased about 3.64-fold compared with that of the ALA aqueous solution, and the penetration depth reached 30-80 microm. The results demonstrated that the ethosomal carrier significantly improved the delivery of ALA and the formation of PpIX in both normal and hyperproliferative murine skin samples, and the expression level of tumor necrosis factor (TNF)-alpha was reduced after the ALA-ethosomes were applied to treat hyperproliferative murine skin. Furthermore, the results of present study encourage more investigations on the mechanism of the interaction with ethosomes and hyperproliferative murine skin.

Expression of the vanin gene family in normal and inflamed human skin: induction by proinflammatory cytokines

The vanin gene family encodes secreted and membrane-bound ectoenzymes that convert pantetheine into pantothenic acid and cysteamine. Recent studies in a mouse colitis model indicated that vanin-1 has proinflammatory activity and suggest that pantetheinases are potential therapeutic targets in inflammatory diseases. In a microarray analysis of epidermal gene expression of psoriasis and atopic dermatitis lesions, we identified vanin-3 as the gene showing the highest differential expression of all annotated genes that we studied (19-fold upregulation in psoriasis). Quantitative real-time PCR analysis confirmed the microarray data on vanin-3 and showed similar induction of vanin-1, but not of vanin-2, in psoriatic epidermis. Immunohistochemistry showed that vanin-3 is expressed in the differentiated epidermal layers. Using submerged and organotypic keratinocyte cultures, we found that vanin-1 and vanin-3 are induced at the mRNA and protein level by psoriasis-associated proinflammatory cytokines (Th17/Th1) but not by Th2 cytokines. We hypothesize that increased levels of pantetheinase activity are part of the inflammatory-regenerative epidermal differentiation program, and may contribute to the phenotype observed in psoriasis.

Activators of PPARs and LXR decrease the adverse effects of exogenous glucocorticoids on the epidermis

While glucocorticoids (GC) exert beneficial effects (anti-inflammatory), they also have adverse effects on the epidermis including decreased epidermal differentiation, decreased keratinocyte proliferation, and decreased cutaneous permeability barrier homeostasis. Thus, the purpose of this study was to develop strategies to prevent these GC toxicities using simultaneous topical treatments in clobetasol-treated mice. While a triple-lipid mixture of stratum corneum lipids (ceramide, free fatty acid and cholesterol) was previously shown to reverse the GC-induced abnormality in cutaneous barrier function [J Invest Dermatol, 120 (2003) 456], this lipid mixture did not prevent the GC-induced abnormalities in either keratinocyte proliferation or differentiation. As activators of PPARalpha, beta/delta, gamma and LXR, regulate keratinocyte proliferation and differentiation and improve permeability barrier homeostasis, we next assessed the effects of these activators during concurrent GC treatment. Co-application of either ciglitazone (PPARgamma activator), clofibrate (PPARalpha activator) or 22R (OH) cholesterol (LXR activator) with clobetasol prevented the decrease in involucrin, filaggrin and loricrin expression. By contrast, a PPARbeta/delta activator (GW501516) normalized only the expression of involucrin and filaggrin but not loricrin. Moreover, topical application of PPARalpha, beta/delta or LXR activators partially prevented the decrease in keratinocyte proliferation in GC-treated murine skin, as measured using PCNA, while no effect was seen after co-treatment with PPARgamma activators. Finally, PPARgamma and PPARbeta/delta activators but not PPARalpha and LXR activators improved permeability barrier homeostasis in GC-treated mice. Together, these studies demonstrate that PPAR and LXR activators can prevent several of the adverse effects of topical GC on the epidermis.

Maintenance of an acidic stratum corneum prevents emergence of murine atopic dermatitis

Neutralization of stratum corneum (SC) adversely impacts key epidermal functions, including permeability barrier homeostasis and SC integrity. Conversely, acidification of SC improves these functions in developmentally impaired (neonatal or aged) skin, and enhances function in normal skin. Hence, we hypothesized that acidification could alter the course of inflammatory dermatoses, which invariably exhibit an increased SC pH. Maintenance of a low pH by topical applications of the polyhydroxyl acid, lactobionic acid, during the repeated-challenge phase inhibited the development of oxazolone-induced atopic dermatitis (AD). Neither gross/histological dermatitis nor altered barrier function developed, and emergence of epidermal hyperplasia was prevented; however, cytokine generation decreased. Acidification also largely normalized the development of hapten-induced changes in eosinophil/mast cell densities, density of chemoattractant receptor-homologous molecule expressed on TH2-positive lymphocytes, and serum IgE levels. The pH-induced improvement in barrier function most likely accounts for the anti-inflammatory activity, which could be further attributed to normalization of both lamellar body secretion and lamellar bilayer formation. Acidification of SC alone substantially prevents development of barrier abnormalities and downstream immune abnormalities during the elicitation phase of murine AD. These results provide direct evidence for the "outside-inside" pathogenesis of AD and further suggest that maintenance of an acidic SC pH could prevent the emergence of AD in humans.

pH-regulated mechanisms account for pigment-type differences in epidermal barrier function

To determine whether pigment type determines differences in epidermal function, we studied stratum corneum (SC) pH, permeability barrier homeostasis, and SC integrity in three geographically disparate populations with pigment type I-II versus IV-V skin (Fitzpatrick I-VI scale). Type IV-V subjects showed: (i) lower surface pH (approximately 0.5 U); (ii) enhanced SC integrity (transepidermal water loss change with sequential tape strippings); and (iii) more rapid barrier recovery than type I-II subjects. Enhanced barrier function could be ascribed to increased epidermal lipid content, increased lamellar body production, and reduced acidity, leading to enhanced lipid processing. Compromised SC integrity in type I-II subjects could be ascribed to increased serine protease activity, resulting in accelerated desmoglein-1 (DSG-1)/corneodesmosome degradation. In contrast, DSG-1-positive CDs persisted in type IV-V subjects, but due to enhanced cathepsin-D activity, SC thickness did not increase. Adjustment of pH of type I-II SC to type IV-V levels improved epidermal function. Finally, dendrites from type IV-V melanocytes were more acidic than those from type I-II subjects, and they transfer more melanosomes to the SC, suggesting that melanosome secretion could contribute to the more acidic pH of type IV-V skin. These studies show marked pigment-type differences in epidermal structure and function that are pH driven.

PPARs Mediate Lipid Signaling in Inflammation and Cancer

Lipid mediators can trigger physiological responses by activating nuclear hormone receptors, such as the peroxisome proliferator-activated receptors (PPARs). PPARs, in turn, control the expression of networks of genes encoding proteins involved in all aspects of lipid metabolism. In addition, PPARs are tumor growth modifiers, via the regulation of cancer cell apoptosis, proliferation, and differentiation, and through their action on the tumor cell environment, namely, angiogenesis, inflammation, and immune cell functions. Epidemiological studies have established that tumor progression may be exacerbated by chronic inflammation. Here, we describe the production of the lipids that act as activators of PPARs, and we review the roles of these receptors in inflammation and cancer. Finally, we consider emerging strategies for therapeutic intervention.