Nordihydroguaiaretic acid-mediated inhibition of ultraviolet B-induced activator protein-1 activation in human keratinocytes

Transcriptome characterization of Larrea tridentata and identification of genes associated with phenylpropanoid metabolic pathways

Larrea tridentata (Sesse and Moc. ex DC.) Coville (family: Zygophyllaceae) is an aromatic evergreen shrub with resin-covered leaves, known to use in traditional medicine for diverse ailments. It also has immense pharmacological significance due to presence of powerful phenylpropanoids antioxidant, nordihydroguaiaretic acid (NDGA). The RNA sequence/transcriptome analyses connect the genomic information into the discovery of gene function. Hence, the acquaint analysis of L. tridentata is in lieu to characterize the transcriptome, and to identify the candidate genes involved in the phenylpropanoid biosynthetic pathway. To gain molecular insight, the bioinformatics analysis of transcriptome was performed. The total bases covered 48,630 contigs of length greater than 200 bp and above came out to 21,590,549 with an average GC content of 45% and an abundance of mononucleotide, SSR, including C3H, FAR1, and MADS transcription gene families. The best enzyme commission (EC) classification obtained from the assembled sequences represented major abundant enzyme classes e.g., RING-type E3 ubiquitin transferase and non-specific serine/threonine protein kinase. The KEGG pathway analysis mapped into 377 KEGG different metabolic pathways. The enrichment of phenylpropanoid biosynthesis pathways (22 genes i.e., phenylalanine ammonia-lyase, trans-cinnamate 4-monooxygenase, 4-coumarate-CoA ligase, cinnamoyl-CoA reductase, beta-glucosidase, shikimate O-hydroxycinnamoyl transferase, 5-O-(4-coumaroyl)-D-quinate 3'-monooxygenase, cinnamyl-alcohol dehydrogenase, peroxidase, coniferyl-alcohol glucosyltransferase, caffeoyl shikimate esterase, caffeoyl-CoA O-methyltransferase, caffeate O-methyltransferase, coniferyl-aldehyde dehydrogenase, feruloyl-CoA 6-hydroxylase, and ferulate-5-hydroxylase), and expression profile indicated antioxidant, anti-arthritic, and anticancer properties of L. tridentata. The present results could provide an important resource for squeezing biotechnological applications of L. tridentata.

Plant Secondary Metabolites against Skin Photodamage: Mexican Plants, a Potential Source of UV-Radiation Protectant Molecules

Human skin works as a barrier against the adverse effects of environmental agents, including ultraviolet radiation (UVR). Exposure to UVR is associated with a variety of harmful effects on the skin, and it is one of the most common health concerns. Solar UVR constitutes the major etiological factor in the development of cutaneous malignancy. However, more than 90% of skin cancer cases could be avoided with appropriate preventive measures such as regular sunscreen use. Plants, constantly irradiated by sunlight, are able to synthesize specialized molecules to fight against UVR damage. Phenolic compounds, alkaloids and carotenoids constitute the major plant secondary metabolism compounds with relevant UVR protection activities. Hence, plants are an important source of molecules used to avoid UVR damage, reduce photoaging and prevent skin cancers and related illnesses. Due to its significance, we reviewed the main plant secondary metabolites related to UVR protection and its reported mechanisms. In addition, we summarized the research in Mexican plants related to UV protection. We presented the most studied Mexican plants and the photoprotective molecules found in them. Additionally, we analyzed the studies conducted to elucidate the mechanism of photoprotection of those molecules and their potential use as ingredients in sunscreen formulas.

Nordihydroguaiaretic Acid in Therapeutics: Beneficial to Toxicity Profiles and the Search for its Analogs

Nordihydroguaiaretic acid (NDGA) is a plant lignan obtained from creosote bush, Larrea tridentata and is known to possess antioxidant, anticancer activities and is used in traditional medicine in North America and Mexico. However, its prolonged consumption leads to liver damage and kidney dysfunction. Despite its toxicity and side effects, there is little awareness to forbid its consumption and its use in the treatment of medical ailments has continued over the years. Several reports discuss its therapeutic efficiency and its medical applications have tremendously been on the rise to date. There has been a recent surge of interest in the chemical synthesis of NDGA derivatives for therapeutic applications. NDGA derivatives have been developed as better alternatives to NDGA. Although several NDGA derivatives have been chemically synthesized as evidenced by recent literature, there is a paucity of information on their therapeutic efficacies. This review is to highlight the medicinal applications of NDGA, its toxicity evaluations and discuss the chemical derivatives of NDGA synthesized and studied so far and suggest to continue research interests in the development of NDGA analogs for therapeutic applications. We suggest that NDGA derivatives should be investigated more in terms of chemical synthesis with preferred conformational structures and exploit their biological potentials with future insights to explore in this direction to design and develop structurally modified NDGA derivatives for potential pharmacological properties.

Topical delivery of nordihydroguaretic acid for attenuating cutaneous damage caused by arsenicals

This study evaluated the topical delivery of nordihydroguaretic acid (NDGA), a molecule that can potentially alleviate cutaneous damage caused by exposure to arsenic warfare chemicals. N-acetylcysteine (NAC 0.2% w/v) was added as an antioxidant, preventing the oxidation of NDGA to toxic quinones. A 24 h study was performed to arrive at a minimum concentration of NDGA needed to deliver maximum drug. A solution of 3% w/v delivered the maximum amount of drug at the end of 24 h (37.45 ± 4.32 μg). Short duration studies were carried out to determine the time needed to saturate skin with NDGA. There was no significant difference in the skin concentrations for 24 h and 8 h (14.89 ± 2.36 μg), due to skin saturation. However, there was significant difference in the amount of drug delivered to the epidermis (12.29 ± 1.87 μg) and dermis (2.54 ± 0.56 μg) at the end of 8 h. Solution of NDGA was applied on UV treated skin to assess changes in drug delivery. In vivo studies revealed that 3% NDGA was non-toxic for topical administration.

12-lipoxygenase: a potential target for novel anti-platelet therapeutics

Platelets play an essential role in the regulation of hemostasis and thrombosis and controlling their level of activation is central to prevention of occlusive clot formation and stroke. Although a number of anti-platelet targets have been identified to address this issue including COX-1, the P2Y(12) receptor, the integrin αIIbβ3, and more recently the protease-activated receptor-1, these targets often result in a significant increased risk of bleeding which may lead to pathologies as serious as the thrombosis they were meant to treat including intracranial hemorrhage and gastrointestinal bleeding. Therefore, alternative approaches to treat uncontrolled platelet activation are warranted. Platelet-type 12-lipoxygenase is an enzyme which oxidizes the free fatty acid in the platelet resulting in the production of the stable metabolite 12-hydroxyeicosatetraenoic acid (12-HETE). The role of 12-HETE in the platelet has been controversial with reports associating its function as being both anti- and pro-thrombotic. In this review, the role of 12-lipoxygenase and its bioactive metabolites in regulation of platelet reactivity, clot formation, and hemostasis is described. Understanding the mechanisms by which 12-lipoxygenase and its metabolites modulate platelet function may lead to the development of a novel class of anti-platelet therapies targeting the enzyme in order to attenuate injury-induced clot formation, vessel occlusion and pathophysiological shifts in hemostasis.

Nordihydroguaiaretic acid inhibits transforming growth factor beta type 1 receptor activity and downstream signaling

It has been well documented that nordihydroguaiaretic acid (NDGA), a phenolic lignan isolated from the creosote bush, Larrea tridentate, has anti-cancer activity in vitro and in vivo. Several mechanisms have been identified that could contribute to these actions, as NDGA directly inhibits metabolic enzymes and receptor tyrosine kinases that are established anti-cancer targets. In the present study, we show that NDGA inhibits the transforming growth factor beta (TGF-beta) type I receptor, a serine threonine kinase receptor. In cultured cells, NDGA treatment repressed Smad2 phosphorylation induced by TGF-beta treatment and by a constitutively active mutant of TGF-beta type I receptor (T202D). NDGA also inhibited downstream transcriptional activation mediated by both TGF-beta treatment and the constitutively active mutant receptor. In vitro, NDGA inhibited TGF-beta type I receptor mediated Smad2 phosphorylation in crude cell lysates and in a purified preparation. Importantly, screening select analogs demonstrated that modification of NDGA's structure resulted in altered potency against the receptor. These results indicated that the structure of NDGA can be modified to achieve increased potency. Together our data provide a novel mechanism for NDGA activity which could help explain its anti-cancer activity, and suggest that NDGA could serve as a structural motif for developing serine/threonine kinase inhibitors with selectivity for TGF-beta type I receptor.

Long-range enhancer associated with chromatin looping allows AP-1 regulation of the peptidylarginine deiminase 3 gene in differentiated keratinocyte

Transcription control at a distance is a critical mechanism, particularly for contiguous genes. The peptidylarginine deiminases (PADs) catalyse the conversion of protein-bound arginine into citrulline (deimination), a critical reaction in the pathophysiology of multiple sclerosis, Alzheimer's disease and rheumatoid arthritis, and in the metabolism of the major epidermal barrier protein filaggrin, a strong predisposing factor for atopic dermatitis. PADs are encoded by 5 clustered PADI genes (1p35-6). Unclear are the mechanisms controlling the expression of the gene PADI3 encoding the PAD3 isoform, a strong candidate for the deimination of filaggrin in the terminally differentiating epidermal keratinocyte. We describe the first PAD Intergenic Enhancer (PIE), an evolutionary conserved non coding segment located 86-kb from the PADI3 promoter. PIE is a strong enhancer of the PADI3 promoter in Ca2+-differentiated epidermal keratinocytes, and requires bound AP-1 factors, namely c-Jun and c-Fos. As compared to proliferative keratinocytes, calcium stimulation specifically associates with increased local DNase I hypersensitivity around PIE, and increased physical proximity of PIE and PADI3 as assessed by Chromosome Conformation Capture. The specific AP-1 inhibitor nordihydroguaiaretic acid suppresses the calcium-induced increase of PADI3 mRNA levels in keratinocytes. Our findings pave the way to the exploration of deimination control during tumorigenesis and wound healing, two conditions for which AP-1 factors are critical, and disclose that long-range transcription control has a role in the regulation of the gene PADI3. Since invalidation of distant regulators causes a variety of human diseases, PIE results to be a plausible candidate in association studies on deimination-related disorders or atopic disease.

ERK and JNK signaling pathways are involved in the regulation of activator protein 1 and cell death elicited by three isothiocyanates in human prostate cancer PC-3 cells

Many isothiocyanates (ITCs) such as sulforaphane (SFN), phenethyl isothiocyanate (PEITC) and allyl isothiocyanate (AITC) are highly effectively in chemoprevention or reduction of the risk of cancer and possess antitumor activities in vitro and in vivo. The activator protein 1 (AP-1) and MAPK signaling pathways are believed to play an important role in cancer chemoprevention and chemotherapy due to their involvement in tumor cell growth, proliferation, apoptosis and survival. In the present study, we determined the effects of SFN, PEITC and AITC on AP-1 activation, and investigated the roles of extracellular signal-regulated protein kinase (ERK) and c-Jun N-terminal kinase (JNK) signaling pathways in the regulation of AP-1 activation and cell death elicited by these ITCs in human prostate cancer PC-3 cells. SFN, PEITC and AITC each induced AP-1 activity potently and caused a significant elevation in the phosphorylation of ERK1/2, JNK1/2, Elk-1 and c-Jun. Transfection with ERK2 and upstream kinase DNEE-MEK1 activated AP-1 activity, and transfection with dominant-negative mutant ERK2 (dnERK2) potently decreased AP-1 activation induced by SFN, PEITC and AITC. Transfection with JNK1 and upstream kinase MKK7 activated AP-1 activity, and transfection with dominant-negative mutant JNK1-APF significantly attenuated AP-1 activation induced by SFN, PEITC and AITC. Pretreatment with MEK1-ERK inhibitor U0126 and JNK inhibitor SP600125 substantially attenuated the decrease in cell viability induced by SFN, PEITC and AITC. Transfection with dnERK2 and JNK1-APF significantly reversed the decrease of Bcl-2 expression elicited by these ITCs. Furthermore, transfection with dnERK2 and JNK1-APF blocked the apoptosis induced by these ITCs in PC-3 cells. Taken together, our results indicate that the activation of the ERK and JNK signaling pathways is important for transcriptional activity of AP-1 and is involved in the regulation of cell death elicited by ITCs in PC-3 cells.

Properties of BK(Ca) channels in oral keratinocytes

Keratinocytes are important for epithelial antimicrobial barrier function. The activity of ion channels can affect the proliferation of keratinocytes. Little is known about Ca2+-activated K+ currents in these cells. Ion currents in normal human oral keratinocytes were characterized with a patch-clamp technique. In whole-cell configuration, depolarizing pulses evoked K+ outward currents (I(K)) in oral keratinocytes. Iberiotoxin (200 nM) and paxilline (1 microM) suppressed I(K); however, neither apamin (200 nM) nor 5-hydroxydecanoate (30 microM) had any effects on it. Caffeic acid phenethyl ester, a compound of honeybee propolis, increased I(K) with an EC50 value of 12.8 +/- 1.2 microM. In inside-out patches, a BK(Ca) channel was observed in keratinocytes, but not in oral squamous carcinoma (OCE-M1) cells. Caffeic acid phenethyl ester or cinnamyl-3,4-dihydroxy-alpha-cyanocinnamate applied to the intracellular surface of a detached patch increased BK(Ca)-channel activity. The results demonstrate that the properties of BK(Ca) channels in normal human oral keratinocytes are similar to those described in other types of cells. Caffeic acid derivatives can also stimulate BK(Ca)-channel activity directly.

Larrea tridentata (Creosote bush), an abundant plant of Mexican and US-American deserts and its metabolite nordihydroguaiaretic acid

Although controversial, Creosote bush, Larrea tridentata (Sesse and Moc. ex DC) Coville, is used to treat a variety of illnesses including infertility, rheumatism, arthritis, diabetes, gallbladder and kidney stones, pain and inflammation. Recently, it has been used as a nutritional supplement. The primary product extracted from this common plant of the arid regions of northern Mexico and Southwestern United States is the potent antioxidant nordihydroguaiaretic acid (NDGA). It was widely used during the 1950s as a food preservative and to preserve naturals fibers. Later it was banned after reports of toxicity during the early 1960s. Renal and hepatotoxicity are also reported for chronic use of creosote bush and NDGA. This article reviews traditional and contemporary uses and pharmacology, including toxicology of this plant widely used in Mexican traditional medicine.

Regulation of Ultraviolet B Radiation-Mediated Activation of AP1 Signaling by Retinoids in Primary Keratinocytes

The main cause of skin cancer and photo-aging is chronic exposure to ultraviolet B (UVB) radiation. Such damage can be ameliorated by retinoid treatment. UVB-radiation-induced skin carcinogenesis is associated with the induction of activator protein 1 (AP1) signaling and factors, namely FOS and JUN family members. We investigated the effects of several retinoids, all-trans-retinoic acid (tRA), 9-cis-retinoic acid (cRA), and N-(4-hydroxyphenyl)-retinamide (HPR), on UVB-induced damage in primary mouse keratinocytes. In addition, the interplay between UVB radiation, retinoid receptors, and AP1 signaling was assessed using Western blot analysis and ribonuclease protection and gene reporter assays. Exposure of keratinocytes to UVB radiation caused a down-regulation of the retinoid receptor protein levels in a proteasome-mediated manner. In contrast, FOS and JUN proteins were transiently induced shortly after exposure to UVB radiation. Retinoid treatment caused a dose-dependent reduction in the levels of retinoid receptor proteins. When irradiated cells were treated with retinoids, no significant effects on AP1 protein expression were noted. Interestingly, pretreatments with tRA and cRA, but not HPR, suppressed UVB-radiation-induced AP1 activity by more than 50%, whereas post-treatment failed to produce similar effects. Our findings indicate that the inhibition of AP1 activity by retinoids explains, at least in part, the chemopreventive potential of retinoids in UV-radiation-associated epidermal damage.

Development of a high-throughput plate-based chemiluminescent transcription factor assay

Transcription factors are DNA-binding proteins that regulate the expression of specific genes by controlling transcription initiation. Two families of transcription factors, NFkappaB and AP-1, play pivotal roles in controlling important cellular processes ranging from normal cell growth and differentiation to apoptosis and cancer. Identifying changes in the DNA-binding activity of these factors is essential to understanding the regulation of these processes. We have developed a high-throughput DNA-based ELISA capable of monitoring activated levels of NFkappaB (p50 and p65) and AP-1 (c-Jun and c-Fos). This chemiluminescent assay utilizes a 96-well plate format, eliminating the throughput challenges imposed by traditional gel shift assays and exceeding the sensitivity and dynamic range of standard colorimetric detection systems. The sensitivity of this assay enables distinction between subtle as well as dramatic differences in the DNA-binding activity of these factors that result from the treatment of cells with various inhibitors or activating agents.

Phase II enzyme inducer, sulforaphane, inhibits UVB-induced AP-1 activation in human keratinocytes by a novel mechanism

Ultraviolet (UV) light-induced activation of activator protein-1 (AP-1), resulting at least in part from oxidative stress, promotes skin carcinogenesis. It has not yet been determined whether elevating cellular phase II enzymes and glutathione (GSH) levels inhibits the AP-1 activation. We have, therefore, examined the effects of two well-known inducers of phase II enzymes, sulforaphane (SF) and tert-butylhydroquinone (tBHQ), on UVB-induced AP-1 activation, with an AP-1-luciferase reporter plasmid that was stably transfected into human HaCaT keratinocytes (HCL14 cells). Exposure of HCL14 cells to SF or tBHQ led to the induction of quinone reductase-1 (QR-1), a marker of global cellular phase II enzymes, as well as elevation of cellular GSH levels. Incubation of the cells with 1-10 microM SF or 11-45 microM tBHQ for 24 h resulted in up to 1.4-fold and 1.7-fold increase of QR-1 activity, respectively, and up to 1.5-fold and 1.6-fold increases in cellular GSH levels, respectively. AP-1 activation was dramatically enhanced by irradiating HCL14 cells with 250 J/m(2) of UVB. While the above SF treatment dose-dependently reduced the UVB-induced AP-1 activation in HCL14 cells, the tBHQ treatment did not, suggesting that elevating cellular phase II enzymes and GSH levels may not lead to inhibition of UVB-induced AP-1 activation. Indeed, depleting cellular GSH by 80% did not affect UVB-induced AP-1 activation either. Subsequent electrophoretic mobility shift assays (EMSA) showed that SF added directly to the EMSAs inhibited AP-1 DNA binding activity, whereas tBHQ was ineffective. Taken together, our results indicated that elevating phase II enzymes and GSH levels in human keratinocytes does not lead to significant inhibition of UVB-induced AP-1 activation. The inhibitory effect of SF on UVB-induced AP-1 activation appears to be at least partly due to the direct inhibition of AP-1 DNA binding activity. This direct effect of SF on AP-1 DNA binding is a novel mechanism for the action of a drug inhibitor of AP-1 activation.