The novel PPAR α/γ dual agonist MHY 966 modulates UVB-induced skin inflammation by inhibiting NF-κB activity

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.

The Activation of PPARγ by (2Z,4E,6E)-2-methoxyocta-2,4,6-trienoic Acid Counteracts the Epithelial–Mesenchymal Transition Process in Skin Carcinogenesis

Cutaneous squamous cell carcinoma (cSCC) is the most common UV-induced keratinocyte-derived cancer, and its progression is characterized by the epithelial–mesenchymal transition (EMT) process. We previously demonstrated that PPARγ activation by 2,4,6-octatrienoic acid (Octa) prevents cutaneous UV damage. We investigated the possible role of the PPARγ activators Octa and the new compound (2Z,4E,6E)-2-methoxyocta-2,4,6-trienoic acid (A02) in targeting keratinocyte-derived skin cancer. Like Octa, A02 exerted a protective effect against UVB-induced oxidative stress and DNA damage in NHKs. In the squamous cell carcinoma A431 cells, A02 inhibited cell proliferation and increased differentiation markers’ expression. Moreover, Octa and even more A02 counteracted the TGF-β1-dependent increase in mesenchymal markers, intracellular ROS, the activation of EMT-related signal transduction pathways, and cells’ migratory capacity. Both compounds, especially A02, counterbalanced the TGF-β1-induced cell membrane lipid remodeling and the release of bioactive lipids involved in EMT. In vivo experiments on a murine model useful to study cell proliferation in adult animals showed the reduction of areas characterized by active cell proliferation in response to A02 topical treatment. In conclusion, targeting PPARγ may be useful for the prevention and treatment of keratinocyte-derived skin cancer.

Atractylodin Ameliorates Colitis via PPARα Agonism

Atractylodin is a major compound in the rhizome of Atractylodes lancea, an oriental herbal medicine used for the treatment of gastrointestinal diseases, including dyspepsia, nausea, and diarrhea. Recent studies have shown that atractylodin exerts anti-inflammatory effects in various inflammatory diseases. Herein, we investigated the anti-colitis effects of atractylodin and its molecular targets. We determined the non-cytotoxic concentration of atractylodin (50 μM) using a cell proliferation assay in colonic epithelial cells. We found that pretreatment with atractylodin significantly inhibits tumor necrosis factor-α-induced phosphorylation of nuclear factor-κ-light-chain-enhancer of activated B in HCT116 cells. Through docking simulation analysis, luciferase assays, and in vitro binding assays, we found that atractylodin has an affinity for peroxisome proliferator-activated receptor alpha (PPARα). Daily administration of atractylodin (40 mg/kg) increased the survival rate of mice in a dextran sodium sulfate-induced colitis mouse model. Thus, atractylodin can be a good strategy for colitis therapy through inducing PPARα-dependent pathways.

Shedding Light on the Effects of Calorie Restriction and its Mimetics on Skin Biology

During the aging process of an organism, the skin gradually loses its structural and functional characteristics. The skin becomes more fragile and vulnerable to damage, which may contribute to age-related diseases and even death. Skin aging is aggravated by the fact that the skin is in direct contact with extrinsic factors, such as ultraviolet irradiation. While calorie restriction (CR) is the most effective intervention to extend the lifespan of organisms and prevent age-related disorders, its effects on cutaneous aging and disorders are poorly understood. This review discusses the effects of CR and its alternative dietary intake on skin biology, with a focus on skin aging. CR structurally and functionally affects most of the skin and has been reported to rescue both age-related and photo-induced changes. The anti-inflammatory, anti-oxidative, stem cell maintenance, and metabolic activities of CR contribute to its beneficial effects on the skin. To the best of the author’s knowledge, the effects of fasting or a specific nutrient-restricted diet on skin aging have not been evaluated; these strategies offer benefits in wound healing and inflammatory skin diseases. In addition, well-known CR mimetics, including resveratrol, metformin, rapamycin, and peroxisome proliferator-activated receptor agonists, show CR-like prevention against skin aging. An overview of the role of CR in skin biology will provide valuable insights that would eventually lead to improvements in skin health.

Saikosaponin a attenuates hyperlipidemic pancreatitis in rats via the PPAR-γ/NF-κB signaling pathway

The therapeutic effect of saikosaponin a (SSa) on hyperlipidemic pancreatitis (HP) is not completely understood. The aim of the present study was to investigate the therapeutic effect and the underlying mechanism of SSa using a rat model of HP. Following successful establishment of the HP rat model, different doses of SSa (low dose group, 10 mg/kg or high dose group, 20 mg/kg) were administrated. Histopathological examination, the wet/dry (W/D) ratio and myeloperoxidase (MPO) activity of the pancreatic tissues were assessed. The lipid, amylase (AMY), lipase and proinflammatory cytokine profiles in serum, as well as the expression of peroxisome proliferator-activated receptor (PPAR)-γ and the NF-κB signaling pathway-related proteins in pancreatic tissues were evaluated. The results showed that SSa effectively attenuated pancreatic pathological injury and reduced both the W/D ratio and MPO activity compared to the HP model rats. SSa also improved lipid metabolism by significantly decreasing the serum levels of total cholesterol and triglycerides (P<0.05). Following the administration of SSa, the activity of AMY and lipase, as well as the levels of the proinflammatory cytokines tumor necrosis factor-α, interleukin (IL)-1β and IL-6 were reduced, particularly in the high dosage group (P<0.05). Furthermore, SSa activated PPAR-γ expression and suppressed the NF-κB signaling pathway in pancreatic tissues. The present study suggested that SSa attenuated HP in rats by increasing lipid metabolism and inhibiting the release of proinflammatory cytokines via the NF-κB inflammatory pathway. The results from the present study indicated that SSa might be a promising therapeutic agent for the treatment of HP.

Asiatic Acid Glucosamine Salt Alleviates Ultraviolet B-induced Photoaging of Human Dermal Fibroblasts and Nude Mouse Skin

Herbal extracts including asiatic acid (AA) have become popular candidates of anti-photoaging agents due to their anti-inflammatory and antioxidant properties and minimal side effect. Nevertheless, low bioavailability due to poor solubility limits their practical application. In this study, a highly bioavailable form of AA called AAGS (compounded by asiatic acid and glucosamine) was investigated for its anti-photoaging effect using both in vitro and in vivo models along with UVB irradiation. The results showed that AAGS alleviated UVB-induced cell proliferation inhibition by reducing G2 phase arrest and cell apoptosis rate as well as the gene expressions of P53, BAX, CASPASE 3 and CASPASE 9, but enhancing BCL-2 expression. It also reduced the production of reactive oxygen species along with increased gene expression of GPX-1 and downregulated the gene expression of IL-1β, IL-6, IL-8, IL-17 and TNF-α compared to nontreated cells. In vivo results demonstrated the antiphotodamaging effects by restoring skin thickness, collagen content and reducing MMPs expression, which are also supported by reduced MMPs gene expression and enhanced collagen I and TGF-β1 gene expression in vitro. Thus, AAGS may become a potential anti-photoaging agent for topical use due to its capability of self-assembling into a water gel.

ETAS®50 Attenuates Ultraviolet-B-Induced Interleukin-6 Expression by Suppressing Akt Phosphorylation in Normal Human Dermal Fibroblasts

We recently reported that ETAS 50, a standardized extract from the Asparagus officinalis stem, exerted anti-inflammatory effects on ultraviolet-B- (UV-B-) irradiated normal human dermal fibroblasts (NHDFs) by inhibiting nuclear factor-κB p65 nuclear import and the resulting interleukin-1β (IL-1β) expression. To further elucidate the antiphotoaging potency of ETAS 50, we examined the anti-inflammatory effects on UV-B-irradiated NHDFs by focusing on the stress-activated mitogen-activated protein kinase (MAPK) and Akt signaling pathways. NHDFs were treated with 1 mg/mL of ETAS 50 or dextrin (vehicle control) after UV-B irradiation (20 mJ/cm2) for different time periods. Phosphorylation levels of c-Jun N-terminal kinase (JNK), p38 MAPK, and Akt were analyzed by western blotting. IL-6 mRNA levels were analyzed by real-time polymerase chain reaction. UV-B-irradiated NHDFs showed increased phosphorylation levels of JNK, p38 MAPK, and Akt, as well as increased mRNA levels of IL-6. ETAS 50 treatment after UV-B irradiation suppressed the increased phosphorylation levels of Akt without affecting those of JNK and p38 MAPK. ETAS 50 as well as Akt inhibitor Perifosine repressed UV-B irradiation-induced IL-6 mRNA expression. These results suggest that ETAS 50 treatment represses UV-B irradiation-induced IL-6 expression by suppressing Akt phosphorylation. The present findings demonstrate the potential of ETAS 50 to prevent photoaging by attenuating UV-B irradiation-induced proinflammatory responses in skin fibroblasts.

Anti-Inflammatory Effect of ETAS®50 by Inhibiting Nuclear Factor-κB p65 Nuclear Import in Ultraviolet-B-Irradiated Normal Human Dermal Fibroblasts

Ultraviolet (UV) irradiation induces proinflammatory responses in skin cells, including dermal fibroblasts, accelerating premature skin aging (photoaging). ETAS 50, a standardized extract from the Asparagus officinalis stem, is a novel and unique functional food that suppresses proinflammatory responses of hydrogen peroxide-stimulated skin fibroblasts and interleukin- (IL-) 1β-stimulated hepatocytes. To elucidate its antiphotoaging potencies, we examined whether ETAS 50 treatment after UV-B irradiation attenuates proinflammatory responses of normal human dermal fibroblasts (NHDFs). UV-B-irradiated NHDFs showed reduced levels of the cytosolic inhibitor of nuclear factor-κB α (IκBα) protein and increased levels of nuclear p65 protein. The nuclear factor-κB nuclear translocation inhibitor JSH-23 abolished UV-B irradiation-induced IL-1β mRNA expression, indicating that p65 regulates transcriptional induction. ETAS 50 also markedly suppressed UV-B irradiation-induced increases in IL-1β mRNA levels. Immunofluorescence analysis revealed that ETAS 50 retained p65 in the cytosol after UV-B irradiation. Western blotting also showed that ETAS 50 suppressed the UV-B irradiation-induced increases in nuclear p65 protein. Moreover, ETAS 50 clearly suppressed UV-B irradiation-induced distribution of importin-α protein levels in the nucleus without recovering cytosolic IκBα protein levels. These results suggest that ETAS 50 exerts anti-inflammatory effects on UV-B-irradiated NHDFs by suppressing the nuclear import machinery of p65. Therefore, ETAS 50 may prevent photoaging by suppressing UV irradiation-induced proinflammatory responses of dermal fibroblasts.

The implication of neuronimmunoendocrine (NIE) modulatory network in the pathophysiologic process of Parkinson's disease

Parkinson's disease (PD) is a progressive neurodegenerative disorder implicitly marked by the substantia nigra dopaminergic neuron degeneration and explicitly characterized by the motor and non-motor symptom complexes. Apart from the nigrostriatal dopamine depletion, the immune and endocrine study findings are also frequently reported, which, in fact, have helped to broaden the symptom spectrum and better explain the pathogenesis and progression of PD. Nevertheless, based on the neural, immune, and endocrine findings presented above, it is still difficult to fully recapitulate the pathophysiologic process of PD. Therefore, here, in this review, we have proposed the neuroimmunoendocrine (NIE) modulatory network in PD, aiming to achieve a more comprehensive interpretation of the pathogenesis and progression of this disease. As a matter of fact, in addition to the classical motor symptoms, NIE modulatory network can also underlie the non-motor symptoms such as gastrointestinal, neuropsychiatric, circadian rhythm, and sleep disorders in PD. Moreover, the dopamine (DA)-melatonin imbalance in the retino-diencephalic/mesencephalic-pineal axis also provides an alternative explanation for the motor complications in the process of DA replacement therapy. In conclusion, the NIE network can be expected to deepen our understanding and facilitate the multi-dimensional management and therapy of PD in future clinical practice.

The activation of PPARγ by 2,4,6-Octatrienoic acid protects human keratinocytes from UVR-induced damages

Increasing attention is addressed to identify products able to enhance skin photoprotection and to prevent skin carcinogenesis. Several studies have demonstrated that the α-melanocyte stimulating hormone (αMSH), acting on a functional MC1R, provides a photoprotective effect by inducing pigmentation, antioxidants and DNA repair. We discovered a link between αMSH and the nuclear receptor Peroxisome Proliferator-Activated Receptor-γ (PPARγ), suggesting that some of the αMSH protective effects may be dependent on PPARγ transcriptional activity. Moreover, we demonstrated that the activation of PPARγ by the parrodiene 2,4,6-octatrienoic acid (Octa) induces melanogenesis and antioxidant defence in human melanocytes and counteracts senescence-like phenotype in human fibroblasts. In this study, we demonstrate that the activation of PPARγ by Octa exerts a protective effect against UVA- and UVB-induced damage on normal human keratinocytes (NHKs), the major target cells of UV radiation. Octa promotes the antioxidant defence, augments DNA repair and reduces the induction of proteins involved in UV-induced DNA damage response. Our results contribute to deepen the analysis of the αMSH/PPARγ connection and suggest perspectives for the development of new molecules and formulations able to prevent cutaneous UV damage by acting on the different skin cell populations through PPARγ activation.

Arjunolic acid, a peroxisome proliferator-activated receptor α agonist, regresses cardiac fibrosis by inhibiting non-canonical TGF-β signaling

Cardiac hypertrophy and associated heart fibrosis remain a major cause of death worldwide. Phytochemicals have gained attention as alternative therapeutics for managing cardiovascular diseases. These include the extract from the plant Terminalia arjuna, which is a popular cardioprotectant and may prevent or slow progression of pathological hypertrophy to heart failure. Here, we investigated the mode of action of a principal bioactive T. arjuna compound, arjunolic acid (AA), in ameliorating hemodynamic load-induced cardiac fibrosis and identified its intracellular target. Our data revealed that AA significantly represses collagen expression and improves cardiac function during hypertrophy. We found that AA binds to and stabilizes the ligand-binding domain of peroxisome proliferator-activated receptor α (PPARα) and increases its expression during cardiac hypertrophy. PPARα knockdown during AA treatment in hypertrophy samples, including angiotensin II-treated adult cardiac fibroblasts and renal artery-ligated rat heart, suggests that AA-driven cardioprotection primarily arises from PPARα agonism. Moreover, AA-induced PPARα up-regulation leads to repression of TGF-β signaling, specifically by inhibiting TGF-β-activated kinase1 (TAK1) phosphorylation. We observed that PPARα directly interacts with TAK1, predominantly via PPARα N-terminal transactivation domain (AF-1) thereby masking the TAK1 kinase domain. The AA-induced PPARα-bound TAK1 level thereby shows inverse correlation with the phosphorylation level of TAK1 and subsequent reduction in p38 MAPK and NF-κBp65 activation, ultimately culminating in amelioration of excess collagen synthesis in cardiac hypertrophy. In conclusion, our findings unravel the mechanism of AA action in regressing hypertrophy-associated cardiac fibrosis by assigning a role of AA as a PPARα agonist that inactivates non-canonical TGF-β signaling.

Protective effects of Aloe sterols against UVB-induced photoaging in hairless mice

BACKGROUND

Aloe vera is a traditional medical plant whose gel has been widely used in skin care. Previously, we have identified Aloe sterols from Aloe vera as active ingredients. This study investigated the protective effects of Aloe sterols without polysaccharides, against ultraviolet B (UVB)-induced skin photoaging in mice using Aloe vera gel extract (AVGE) obtained by supercritical fluid extraction.

METHODS

Aloe vera gel extract was supplemented in the diet (12 or 120 ppm), and HR-1 hairless mice were exposed to UVB irradiation for 7 weeks. Skin measurements and histological and analytical studies were performed.

RESULTS

Repeated UVB irradiation induced rough wrinkling of skin with water content reduction and hyperkeratosis. AVGE administration resulted in the significant improvement of UVB-induced skin dryness, epidermal thickness, and wrinkle formation. The AVGE group also suppressed the degenerations of dermal collagen fibers and the appearance of cutaneous apoptosis cells induced by UVB. Furthermore, AVGE administration reduced the excess elevation of pro-inflammatory cytokines (IL-1β and TNF-α) and matrix metalloproteinases (MMP-2, MMP-9, MMP-12, and MMP-13) in UVB-exposed skin.

CONCLUSION

The dietary ingestion of Aloe sterols protected against chronic UVB damage in mouse skin, and our results suggest that Aloe sterols may prevent skin photoaging through the anti-inflammation and MMP regulation.

Enzyme-Treated Asparagus Extract Prevents Hydrogen Peroxide-Induced Pro-Inflammatory Responses by Suppressing p65 Nuclear Translocation in Skin L929 Fibroblasts

We recently reported that enzyme-treated asparagus extract (ETAS) attenuates hydrogen peroxide (H2O2)-stimulated matrix metalloproteinase-9 expression in skin fibroblast L929 cells. To further elucidate the anti-aging effects of ETAS on skin, we examined whether ETAS has preventive effects on H2O2-induced pro-inflammatory responses of skin fibroblasts. H2O2 induced Ser536 phosphorylation and nuclear accumulation of nuclear factor-κB (NF-κB) p65, and increased the mRNA levels of interleukin-12α (IL-12α) and inducible nitric oxide synthase (iNOS) in L929 cells. Pretreatment of the cells with JSH-23, an inhibitor of NF-κB nuclear translocation, abolished the H2O2-induced expression of IL-12α and iNOS, indicating that the increased transcription is regulated by p65. The H2O2-stimulated nuclear accumulation of p65 and induction of IL-12α and iNOS mRNA were significantly attenuated after pretreatment with ETAS for 3 h, and these responses were completely abolished when the duration was extended to 24 h. However, ETAS did not affect the H2O2-stimulated degradation of IκBα and phosphorylation of p65. On the other hand, ETAS treatment for 24 h resulted in decreased protein levels of importin-α. These results suggest that ETAS prevents pro-inflammatory responses by suppressing the p65 nuclear translocation in skin fibroblasts induced by H2O2.

Activation of Peroxisome Proliferator-Activated Receptor Alpha Improves Aged and UV-Irradiated Skin by Catalase Induction

Peroxisome proliferator-activated receptor alpha (PPARα) is a nuclear hormone receptor involved in the transcriptional regulation of lipid metabolism, fatty acid oxidation, and glucose homeostasis. Its activation stimulates antioxidant enzymes such as catalase, whose expression is decreased in aged human skin. Here we investigated the expression of PPARα in aged and ultraviolet (UV)-irradiated skin, and whether PPARα activation can modulate expressions of matrix metalloproteinase (MMP)-1 and procollagen through catalase regulation. We found that PPARα mRNA level was significantly decreased in intrinsically aged and photoaged human skin as well as in UV-irradiated skin. A PPARα activator, Wy14643, inhibited UV-induced increase of MMP-1 and decrease of procollagen expression and caused marked increase in catalase expression. Furthermore, production of reactive oxygen species (ROS) was suppressed by Wy14643 in UV-irradiated and aged dermal fibroblasts, suggesting that the PPARα activation-induced upregulation of catalase leads to scavenging of ROS produced due to UV irradiation or aging. PPARα knockdown decreased catalase expression and abolished the beneficial effects of Wy14643. Topical application of Wy14643 on hairless mice restored catalase activity and prevented MMP-13 and inflammatory responses in skin. Our findings indicate that PPARα activation triggers catalase expression and ROS scavenging, thereby protecting skin from UV-induced damage and intrinsic aging.

(Z)-5-(2,4-Dihydroxybenzylidene)thiazolidine-2,4-dione Prevents UVB-Induced Melanogenesis and Wrinkle Formation through Suppressing Oxidative Stress in HRM-2 Hairless Mice

Background. Uncontrolled melanogenesis and wrinkle formation are an indication of photoaging. Our previous studies demonstrated that (Z)-5-(2,4-dihydroxybenzylidene)thiazolidine-2,4-dione (MHY498) inhibited tyrosinase activity and melanogenesis in vitro. Objective. To examine in vivo effects of MHY498 as an antiaging compound on UVB-induced melanogenesis and wrinkle formation, we topically applied MHY498 on dorsal skin of HRM-2 hairless mice. Methods. Using histological analysis, we evaluated effects of MHY498 on melanogenesis and wrinkle formation after UVB exposure. In addition, related molecular signaling pathways were examined using western blotting, fluorometric assay, and enzyme-linked immunosorbent assay. Results. MHY498 suppressed UVB-induced melanogenesis by inhibiting phosphorylation of CREB and translocation of MITF protein into the nucleus, which are key factors for tyrosinase expression. Consistently, tyrosinase protein levels were notably reduced in the dorsal skin of the hairless mice by MHY498 treatment. Furthermore, MHY498 inhibited UVB-induced wrinkle formation and collagen fiber destruction by increasing type 1 procollagen concentration and decreasing protein expression levels of MMPs, which play an essential role in collagen fiber degradation. As a mechanism, MHY498 notably ameliorated UVB-induced oxidative stress and NF-κB activation in the dermal skin of the hairless mice. Conclusion. Our study suggests that MHY498 can be used as a therapeutic or cosmetic agent for preventing uncontrolled melanogenesis and wrinkle formation.

Upregulation of Collagen Expression via PPARβ/δ Activation in Aged Skin by Magnesium Lithospermate B from Salvia miltiorrhiza

This study investigated the agonistic activity of magnesium lithospermate B (1), isolated from Salvia miltiorrhiza, on peroxisome proliferator-activated receptor (PPARβ/δ) and the expressions of collagen genes (COL1A1 and COL3A1) and transforming growth factor-β1 (TGF-β1) in models of skin aging. The action of compound 1 as a PPARβ/δ agonist was determined by reporter gene assay, immunostaining, and Western blotting. To determine the antiaging effects of compound 1 on skin, aged Sprague-Dawley rat skin and ultraviolet B (UVB)-irradiated human skin fibroblasts were used. The results show that 1 presented a marked enhancement of both nuclear protein levels and activity of PPARβ/δ in fibroblasts. In addition, 1 prevented downregulation of PPARβ/δ activity in aged rat skin and UVB-induced fibroblasts. Furthermore, 1 increased the expressions of COL1A1, COL3A1, and TGF-β1 in vivo and in a cell culture system. Therefore, the present study shows that compound 1 prevents collagen degradation in aged rat skin and UVB-exposed fibroblasts through PPARβ/δ activation. The therapeutic and cosmetic applications of compound 1 need further investigation.

Resveratrol Derivative-Rich Melinjo Seed Extract Attenuates Skin Atrophy in Sod1-Deficient Mice

The oxidative damages induced by a redox imbalance cause age-related changes in cells and tissues. Superoxide dismutase (SOD) enzymes play a pivotal role in the antioxidant system and they also catalyze superoxide radicals. Since the loss of cytoplasmic SOD (SOD1) resulted in aging-like phenotypes in several types of murine tissue, SOD1 is essential for the maintenance of tissue homeostasis. Melinjo (Gnetum gnemon Linn) seed extract (MSE) contains trans-resveratrol (RSV) and resveratrol derivatives, including gnetin C, gnemonoside A, and gnemonoside D. MSE intake also exerts no adverse events in human study. In the present studies, we investigated protective effects of MSE on age-related skin pathologies in mice. Orally MSE and RSV treatment reversed the skin thinning associated with increased oxidative damage in the Sod1^−/− mice. Furthermore, MSE and RSV normalized gene expression of Col1a1 and p53 and upregulated gene expression of Sirt1 in skin tissues. In vitro experiments revealed that RSV significantly promoted the viability of Sod1^−/− fibroblasts. These finding demonstrated that RSV in MSE stably suppressed an intrinsic superoxide generation in vivo and in vitro leading to protecting skin damages. RSV derivative-rich MSE may be a powerful food of treatment for age-related skin diseases caused by oxidative damages.

Adaptive cellular stress pathways as therapeutic targets of dietary phytochemicals: focus on the nervous system

During the past 5 decades, it has been widely promulgated that the chemicals in plants that are good for health act as direct scavengers of free radicals. Here we review evidence that favors a different hypothesis for the health benefits of plant consumption, namely, that some phytochemicals exert disease-preventive and therapeutic actions by engaging one or more adaptive cellular response pathways in cells. The evolutionary basis for the latter mechanism is grounded in the fact that plants produce natural antifeedant/noxious chemicals that discourage insects and other organisms from eating them. However, in the amounts typically consumed by humans, the phytochemicals activate one or more conserved adaptive cellular stress response pathways and thereby enhance the ability of cells to resist injury and disease. Examplesof such pathways include those involving the transcription factors nuclear factor erythroid 2-related factor 2, nuclear factor-κB, hypoxia-inducible factor 1α, peroxisome proliferator-activated receptor γ, and forkhead box subgroup O, as well as the production and action of trophic factors and hormones. Translational research to develop interventions that target these pathways may lead to new classes of therapeutic agents that act by stimulating adaptive stress response pathways to bolster endogenous defenses against tissue injury and disease. Because neurons are particularly sensitive to potentially noxious phytochemicals, we focus on the nervous system but also include findings from other cell types in which actions of phytochemicals on specific signal transduction pathways have been more thoroughly studied.

Inhibition of peroxisome proliferator-activated receptor gamma prevents the melanogenesis in murine B16/F10 melanoma cells

The purpose of this study was to investigate if PPARγ plays a role in the melanogenesis. B16/F10 cells were divided into five groups: control, melanin stimulating hormone (α-MSH), α-MSH+retinol, α-MSH+GW9662 (PPARγ antagonist), and GW9662. Cells in the control group were cultured in the Dulbecco's modified Eagle's medium (DMEM) for 48 hrs. To initiate the melanogenesis, cells in all α-MSH groups were cultured in medium containing α-MSH (10 nM) for 48 hrs. Cells were treated simultaneously with retinol (5 μM) in the α-MSH+retinol group. Instead of retinol, GW9662 (10 μM) was cocultured in the α-MSH+GW9662 group. Cells in the final group were cultured in the DMEM with GW9662. All the analyses were carried out 48 hours after treatments. The α-MSH was able to increase cell number, melanin production, and the activity of tyrosinase, the limiting enzyme in melanogenesis. These α-MSH-induced changes were prevented either by retinol or by GW9662. Further analyses of the activities of antioxidant enzymes including glutathione, catalase, and the superoxide dismutase (SOD) showed that α-MSH treatment raised the activity of SOD which was dependent on PPARγ level. According to our results, the α-MSH-induced melanogenesis was PPARγ dependent, which also modulated the expression of SOD.

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.