Arachidonic acid metabolism in skin health and disease

Murine Alox8 versus the human ALOX15B ortholog: differences and similarities

Human arachidonate 15-lipoxygenase type B is a lipoxygenase that catalyzes the peroxidation of arachidonic acid at carbon-15. The corresponding murine ortholog however has 8-lipoxygenase activity. Both enzymes oxygenate polyunsaturated fatty acids in S-chirality with singular reaction specificity, although they generate a different product pattern. Furthermore, while both enzymes utilize both esterified fatty acids and fatty acid hydro(pero)xides as substrates, they differ with respect to the orientation of the fatty acid in their substrate-binding pocket. While ALOX15B accepts the fatty acid "tail-first," Alox8 oxygenates the free fatty acid with its "head-first." These differences in substrate orientation and thus in regio- and stereospecificity are thought to be determined by distinct amino acid residues. Towards their biological function, both enzymes share a commonality in regulating cholesterol homeostasis in macrophages, and Alox8 knockdown is associated with reduced atherosclerosis in mice. Additional roles have been linked to lung inflammation along with tumor suppressor activity. This review focuses on the current knowledge of the enzymatic activity of human ALOX15B and murine Alox8, along with their association with diseases.

WFDC12-overexpressing contributes to the development of atopic dermatitis via accelerating ALOX12/15 metabolism and PAF accumulation

Atopic dermatitis (AD) is a chronic inflammatory skin disease characterized by eczema-like skin lesions, dry skin, severe itching, and recurrent recurrence. The whey acidic protein four-disulfide core domain gene WFDC12 is highly expressed in skin tissue and up-regulated in the skin lesions of AD patients, but its role and relevant mechanism in AD pathogenesis have not been studied yet. In this study, we found that the expression of WFDC12 was closely related to clinical symptoms of AD and the severity of AD-like lesions induced by DNFB in transgenic mice. WFDC12-overexpressing in the epidermis might promote the migration of skin-presenting cells to lymph nodes and increase Th cell infiltration. Meanwhile, the number and ratio of immune cells and mRNA levels of cytokines were significantly upregulated in transgenic mice. In addition, we found that ALOX12/15 gene expression was upregulated in the arachidonic acid metabolism pathway, and the corresponding metabolite accumulation was increased. The activity of epidermal serine hydrolase decreased and the accumulation of platelet-activating factor (PAF) increased in the epidermis of transgenic mice. Collectively, our data demonstrate that WFDC12 may contribute to the exacerbation of AD-like symptoms in DNFB-induced mouse model by enhancing arachidonic acid metabolism and PAF accumulation and that WFDC12 may be a potential therapeutic target for human atopic dermatitis.

Analysis of Massaciuccoli Peat after Maturation in Sodium Chloride Water of Undulna Thermae

In Italy, peat extracted from the peat bogs of Lake Massaciuccoli is the only peat used for therapeutic purposes. Massaciuccoli peat (M-peat) soaked in the salty bromine-iodine water of Undulna Thermae has given positive results in various pathological situations, mainly in dermatological, rheumatological, and traumatological conditions. Morphological and biochemical analysis were performed using base M-peat samples matured in the salty bromine-iodine water of the Undulna Thermae for different times, to evaluate whether maturation time modifies peat chemico-physical properties. The maturation process induced particle aggregation, with an increase in the fractions with larger particle size. The presence of a high number of proteins derived from organic degradation was observed; after 6 months of maturation, a significant increase in proteins was found, suggesting that salty bromine-iodine water plays a role in the clinical action of the peat. The presence of lipids in M-peat was also confirmed, allowing us to draw important considerations on its therapeutic properties possibly deriving from the relevant interactions between lipids and humic acids. Finally, from our observations, it could be reasonably argued that longer periods of maturation do not result in additional advantages regarding clinical activity.

Antisense overlapping long non-coding RNA regulates coding arachidonate 12-lipoxygenase gene by translational interference

The arachidonate 12-lipoxygenase (ALOX12) enzyme catalyzes polyunsaturated fatty acids and facilitates generation of bioactive lipid mediators associated with various biological processes and disease pathologies. The human genome assembly revealed that the ALOX12 gene overlaps an antisense non-coding gene designated as ALOX12-antisense 1 (ALOX12-AS1). This arrangement indicates that the uncharacterized ALOX12-AS1 long non-coding RNA (lncRNA) may bind to the sense coding ALOX12 mRNA to form an antisense-sense duplex providing the basis of a novel ALOX12 regulatory mechanism. Therefore, this study was designed to determine whether the interaction of ALOX12-AS1 with ALOX12 mRNA functions as an anti-sense/sense duplex-mediated regulatory mechanism controlling the cellular content of ALOX12. Our findings indicate that two major isoforms of ALOX12-AS1 lncRNA are ubiquitously expressed in a variety of primary adult human tissues and different transformed cell types. RNA-FISH revealed cell-type-specific cytosolic as well as nuclear and nucleolar localization of the lncRNA. Interestingly, phorbol ester-induced nucleo-cytoplasmic translocation of the lncRNA in monocytic THP-1 cells resulted in a reduction of ALOX12 protein without a concomitant change in its mRNA level. This indicated ALOX12-AS1 operates via an antisense-sense duplex-mediated translational downregulation mechanism. This deduction was validated by demonstrating sense/antisense duplex formation and an association of the duplex with ribosomal proteins in HEK293 cells. Overall, this study revealed a hitherto unknown mechanism of antisense lncRNA-mediated translational downregulation of ALOX12 that adds to the existing regulatory mechanisms for the modulation of potent bioactive lipid mediators that contribute to both health and disease.

Gene Size Matters: An Analysis of Gene Length in the Human Genome

While it is expected for gene length to be associated with factors such as intron number and evolutionary conservation, we are yet to understand the connections between gene length and function in the human genome. In this study, we show that, as expected, there is a strong positive correlation between gene length, transcript length, and protein size as well as a correlation with the number of genetic variants and introns. Among tissue-specific genes, we find that the longest transcripts tend to be expressed in the blood vessels, nerves, thyroid, cervix uteri, and the brain, while the smallest transcripts tend to be expressed in the pancreas, skin, stomach, vagina, and testis. We report, as shown previously, that natural selection suppresses changes for genes with longer transcripts and promotes changes for genes with smaller transcripts. We also observe that genes with longer transcripts tend to have a higher number of co-expressed genes and protein-protein interactions, as well as more associated publications. In the functional analysis, we show that bigger transcripts are often associated with neuronal development, while smaller transcripts tend to play roles in skin development and in the immune system. Furthermore, pathways related to cancer, neurons, and heart diseases tend to have genes with longer transcripts, with smaller transcripts being present in pathways related to immune responses and neurodegenerative diseases. Based on our results, we hypothesize that longer genes tend to be associated with functions that are important in the early development stages, while smaller genes tend to play a role in functions that are important throughout the whole life, like the immune system, which requires fast responses.

Plant-Based Diet, Serum Fatty Acid Profile, and Free Radicals in Postmenopausal Women: The Diet and Androgens (DIANA) Randomized Trial

High calorie and fat consumption and the production of free radicals are two major mechanistic pathways between diet and disease. In this study we evaluated the effect of a plant-based diet poor in animal fat and rich in (n-3) fatty acids on fatty acids of serum phospholipids and on the production of reactive oxygen metabolites (ROMs). One hundred and four healthy female postmenopausal volunteers were recruited and randomized to a dietary intervention or a control group. Dietary intervention included a program of food education and biweekly common meals for 18 weeks. When the intervention and control groups were compared, it was seen that dietary intervention resulted in a significant reduction of saturated fatty acids (-1.5%) and a significant increase in (n-3) fatty acids (+20.6%), in particular docosahexaenoic acid (+24.8%). We observed that arachidonic acid decreased (–7.7%), while (n-6) fatty acids did not, and the (n-3)/(n-6) polyunsaturated ratio increased significantly (+24.1%). As expected, ROMs decreased significantly in the intervention group (-6%). The results indicated that a plant-based diet can improve the serum fatty acid profile and decrease ROMs production. These results suggest that a plant-based diet may reduce the body's exposure to oxidative stress.

Gas chromatography-mass spectrometry analysis of effects of dietary fish oil on total fatty acid composition in mouse skin

Altering the fatty acid (FA) composition in the skin by dietary fish oil could provide therapeutic benefits. Although it has been shown that fish oil supplementation enhances EPA (eicosapentaenoic acid) and DHA (docosahexaenoic acid) abundance in the skin, comprehensive skin FA profiling is needed. We established a gas chromatography-mass spectrometry method, which allows precise quantification of FA profile using small (<24 mm² for mice and <12 mm² for humans) skin specimens that can be readily obtained from live mice and humans. We determined mouse skin FA composition after 2, 4 and 8 weeks of consuming a control diet or a diet supplemented with fish oil. Fish oil markedly enhanced EPA and DHA in mouse skin within 2 weeks, and this increase plateaued after 4 weeks. The FA composition in mouse skin was different from that of serum, indicating that skin has homeostatic control of FA metabolism. Mice fed the control diet designed to simulate Western human diet displayed similar skin FA composition as that of humans. The present study presents a validated method for FA quantification that is needed to investigate the mechanisms of actions of dietary treatments in both mouse and human skin.

Modulation of Cox-1, 5-, 12- and 15-Lox by popular herbal remedies used in southern Italy against psoriasis and other skin diseases

Acanthus mollis (Acanthaceae), Achillea ligustica, Artemisia arborescens and Inula viscosa (Asteraceae) are used in Southern Italy against psoriasis and other skin diseases that occur with an imbalanced production of eicosanoids. We here assessed their in vitro effects upon 5-, 12-, 15-LOX and COX-1 enzymes as well as NFκB activation in intact cells as their possible therapeutic targets. All methanol crude extracts inhibited both 5-LOX and COX-1 activities under 200 µg/mL, without significant effects on the 12-LOX pathway or any relevant in vitro free radical scavenging activity. NFκB activation was prevented by all extracts but A. mollis. Interestingly, A. ligustica, A. arborescens and A. mollis increased the biosynthesis of 15(S)-HETE, an anti-inflammatory eicosanoid. A. ligustica (IC50 =49.5 µg/mL) was superior to Silybum marianum (IC50 =147.8 µg/mL), which we used as antipsoriatic herbal medicine of reference. Its n-hexane, dichloromethane and ethyl acetate fractions had also inhibitory effects on the LTB4 biosynthesis (IC50 s=9.6, 20.3 and 68 µg/mL, respectively) evidencing that the apolar extracts of A. ligustica are promising active herbal ingredients for future phytotherapeutical products targeting psoriasis.

Regulation of human microsomal prostaglandin E synthase-1 by IL-1β requires a distal enhancer element with a unique role for C/EBPβ

The studies of PGE2 (prostaglandin E2) biosynthesis have focused primarily on the role of cyclo-oxygenases. Efforts have shifted towards the specific PGE2 terminal synthases, particularly mPGES-1 (microsomal PGE synthase 1), which has emerged as the crucial inducible synthase with roles in pain, cancer and inflammation. mPGES-1 is induced by pro-inflammatory cytokines with studies focusing on the proximal promoter, mediated specifically through Egr-1 (early growth-response factor 1). Numerous studies demonstrate that the mPGES-1 promoter (PTGES) alone cannot account for the level of IL-1β (interleukin 1β) induction. We identified two DNase I-hypersensitive sites within the proximal promoter near the Egr-1 element and a novel distal site near −8.6 kb. Functional analysis of the distal site revealed two elements that co-operate with basal promoter expression and a stimulus-dependent enhancer. A specific binding site for C/EBPβ (CCAAT/enhancer-binding protein β) in the enhancer was directly responsible for inducible enhancer activity. ChIP (chromatin immunoprecipitation) analysis demonstrated constitutive Egr-1 binding to the promoter and induced RNA polymerase II and C/EBPβ binding to the promoter and enhancer respectively. Knockout/knockdown studies established a functional role for C/EBPβ in mPGES-1 gene regulation and the documented interaction between Egr-1 and C/EBPβ highlights the proximal promoter co-operation with a novel distal enhancer element in regulating inducible mPGES-1 expression.

The sesquiterpene caulerpenyne from Caulerpa spp. is a lipoxygenase inhibitor

Many algae contain secondary metabolites with the potential to gain importance as pharmaceutically active secretions. Caulerpa racemosa var. cylindracea and Caulerpa prolifera are very abundant on the Mediterranean coastlines. The methanolic extracts of C. racemosa and C. prolifera were tested for inhibitory effects on soybean lipoxygenase. The extract of C. prolifera showed potent inhibitory effect in a lipoxygenase enzyme activity assay. HPLC comparison revealed that C. racemosa extract contained less caulerpenyne, the major secondary metabolite of both algae. In accordance with these findings, purified caulerpenyne inhibited lipoxygenase with an IC(50) of 5.1 μM. The enzyme kinetic studies indicated that both K (M) and V (max) decreased from 0.041 to 0.019 mM and 312.5 to 151.5 U mL(-1) in the presence of 5 µM caulerpenyne, revealing an un-competitive type of inhibition kinetics. The major secondary metabolite of Caulerpa species, caulerpenyne, is thus a novel lipoxygenase inhibitor that can be easily obtained in high quantities from the abundant algae.

Inhibition of 12-LOX and COX-2 reduces the proliferation of human epidermoid carcinoma cells (A431) by modulating the ERK and PI3K-Akt signalling pathways

Eicosanoids, the oxygenated metabolites of arachidonic acid (AA), mediate a variety of human diseases, such as cancer, inflammation and arthritis. To evaluate the role of eicosanoids in epidermoid carcinoma, the expression of AA metabolizing enzymes, such as lipoxygenases (LOXs) and cyclooxygenases (COXs), was analysed in a human epidermoid carcinoma cell line (A431). These studies revealed overexpression of 12-R-LOX and COX-2 in A431 cells. Baicalein (a 12-LOX inhibitor) and celecoxib (a COX-2 inhibitor) significantly reduced thymidine incorporation, whereas 12-(R)-HETE and 12-(S)-HETE (12-LOX metabolites) and PGE(2) (COX-2 metabolite) significantly enhanced thymidine incorporation, suggesting a role for these enzymes in the regulation of A431 cell proliferation. Further studies on the mechanism of cell death by baicalein and celecoxib revealed that the induction of apoptosis in A431 cells was associated with reduction in the Bcl-2/Bax ratio, release of cytochrome c, activation of caspase-3 and PARP cleavage. The apoptosis induced by baicalein and celecoxib was mediated by down regulation of ERK and PI3K-Akt pathways. Further, 12-(R)-HETE, 12-(S)-HETE and PGE(2) upregulated the p-ERK and p-Akt levels, suggesting the involvement of ERK and Akt pathways in the 12-LOX- and COX-2-mediated regulation of growth in A431 cells. Our findings suggest that 12-R-LOX and COX-2 play a critical role in the regulation of growth in epidermoid carcinoma and that their inhibitors may be of potential therapeutic importance.

Glucocorticoid-regulated crosstalk between arachidonic acid and endocannabinoid biochemical pathways coordinates cognitive-, neuroimmune-, and energy homeostasis-related adaptations to stress

Arachidonic acid and its derivatives constitute the major group of signaling molecules involved in the innate immune response and its communication with all cellular and systemic aspects involved on homeostasis maintenance. Glucocorticoids spread throughout the organism their influences over key enzymatic steps of the arachidonic acid biochemical pathways, leading, in the central nervous system, to a shift favoring the synthesis of anti-inflammatory endocannabinoids over proinflammatory metabolites, such as prostaglandins. This shift modifies local immune-inflammatory response and neuronal activity to ultimately coordinate cognitive, behavioral, neuroendocrine, neuroimmune, physiological, and metabolic adjustments to basal and stress conditions. In the hypothalamus, a reciprocal feedback between glucocorticoids and arachidonate-containing molecules provides a mechanism for homeostatic control. This neurochemical switch is susceptible to fine-tuning by neuropeptides, cytokines, and hormones, such as leptin and interleukin-1beta, assuring functional integration between energy homeostasis control and the immune/stress response.

In vitro and in vivo effects of Ranunculus peltatus subsp. baudotii methanol extract on models of eicosanoid production and contact dermatitis

Ranunculus (Crowfoot) species are numerous and they are all reputed to be counter-irritants and are used in several topical conditions. In order to study the pharmacological mechanisms of action underlying this popular use, a methanol extract of Ranunculus peltatus was tested in vitro in various assays involving eicosanoid and human elastase release by intact cells as well as in vivo, with models of delayed-type hypersensitivity (DTH) contact dermatitis. The extract proved to be a selective inhibitor of the cyclooxygenase-1 pathway, producing the total inhibition of 12-(S)-HHTrE release at 200 microg/mL, while leaving both 5-lipoxygenase and 12-lipoxygenase activities unaffected at the same dose. The n-hexane, chloroform and ethyl acetate fractions of the crude methanol extract inhibited LTB(4) release by intact rat peritoneal neutrophils, but more polar fractions were inactive and did not increase the 5-LOX activity as seen previously for extracts of other Ranunculus species. In the in vivo models, the methanol extract reduced the dinitrofluorobenzene (DNFB)-induced oedema by 40%, but failed to inhibit the oedema brought on by oxazolone. The results agree with the age-old assertion that Water Crowfoot species can be used as a topical antiinflammatory remedy without the prominent irritant action that accompanies the application of non-aquatic Ranunculus species.

Arachidonic acid metabolic pathways and pancreatic cancer

Arachidonic acid (AA), one of the essential fatty acids, refers to icosa-5, 8, 11, 14-tetraenoic acid constituting 20 carbon atoms and 4 double bonds. There are two major pathways including the lipoxygenase (LOX) pathway to hydroxy derivatives and leukotrienes and the cyclooxygenase (COX) pathway to prostaglandins. Members of the AA metabolizing enzymes have been reported to play a significant role in carcinogenesis, because the modulation of these pathways results in suppression of tumor growth. The both pathways were reported recently to be important in the growth regulation of human pancreatic cancer cells, and COX and LOX metabolic pathways are emerging as key regulators of cell proliferation and neo-angiogenesis. COX and LOX inhibitors are being investigated as potential anticancer drugs and results from clinical trials seem to be encouraging.

Glucocorticoids shift arachidonic acid metabolism toward endocannabinoid synthesis: a non-genomic anti-inflammatory switch

Glucocorticoids are capable of exerting both genomic and non-genomic actions in target cells of multiple tissues, including the brain, which trigger an array of electrophysiological, metabolic, secretory and inflammatory regulatory responses. Here, we have attempted to show how glucocorticoids may generate a rapid anti-inflammatory response by promoting arachidonic acid-containing endocannabinoids biosynthesis. According to our hypothesized model, non-genomic action of glucocorticoids results in the global shift of membrane lipid metabolism, subverting metabolic pathways toward the synthesis of the anti-inflammatory endocannabinoids, anandamide (AEA) and 2-arachidonoyl-glycerol (2-AG), and away from arachidonic acid production. Post-transcriptional inhibition of cyclooxygenase-2 (COX(2)) synthesis by glucocorticoids assists this mechanism by suppressing the synthesis of pro-inflammatory prostaglandins as well as endocannabinoid-derived prostanoids. In the central nervous system (CNS) this may represent a major neuroprotective system, which may cross-talk with leptin signaling in the hypothalamus allowing for the coordination between energy homeostasis and the inflammatory response.

A biosynthetic pathway generating 12-hydroxy-5,8,14-eicosatrienoic acid from arachidonic acid is active in mouse skin microsomes

The epidermis expresses cyclooxygenases, lipoxygenases, and cytochromes P450, which utilize arachidonic acid to generate a diverse array of lipid mediators affecting epidermal cellular differentiation and functions. Recent studies show that mouse epidermis expresses CYP2B19, a keratinocyte-specific epoxygenase that generates 11,12- and 14,15-epoxyeicosatrienoic (EET) acids from arachidonate. We studied CYP2B19-dependent metabolism in mouse epidermal microsomes, reconstituted in the presence of [1-(14)C]arachidonic acid. The majority of the (14)C products formed independently of NADPH, indicative of robust epidermal cyclooxygenase and lipoxygenase activities. We studied two NADPH-dependent products generated in a highly reproducible manner from arachidonate. One of these (product I) coeluted with the CYP2B19 product 14,15-EET on a reversed-phase high-performance liquid chromatography (HPLC) system; there was no evidence for other regioisomeric EET products. Further analyses proved that product I was not an epoxy fatty acid, based on different retention times on a normal-phase HPLC system and failure of product I to undergo hydrolysis in acidic solution. We analyzed purified epidermal (14)C products by liquid chromatography negative electrospray ionization mass spectrometry. Structures of the NADPH-dependent products were confirmed to be 12-oxo-5,8,14-eicosatrienoic acid (I) and 12-hydroxy-5,8,14-eicosatrienoic acid (II). This was the first evidence for a 12-hydroxy-5,8,14-eicosatrienoic acid biosynthetic pathway in mouse epidermis. Epidermal microsomes also generated 12-hydroperoxy, 12-hydroxy, and 12-oxo eicosatetraenoic acids from arachidonate, possible intermediates in the 12-hydroxy-5,8,14-eicosatrienoic acid biosynthetic pathway. These results predict that hydroxyeicosatrienoic acids are synthesized from arachidonate in human epidermis. This would have important implications for human skin diseases given the known pro- and anti-inflammatory activities of stereo- and regioisomeric hydroxyeicosatrienoic acids.

Immunolocalization of Low-Affinity Prostaglandin E2 Receptors, EP1 and EP2, in Adult Human Epidermis

Four prostaglandin (PG)E(2) receptors have been described, termed E-series prostaglandin receptors (EP(1)-EP(4)), that can be further subclassified as low-affinity (EP(1) and EP(2)) or high-affinity (EP(3) and EP(4)) receptors. Activation of the low-affinity PGE(2) receptors is likely to be important in mediating the actions of the high levels of PGE(2) found in various pathologic processes. The pattern of expression of these receptors in epidermis, however, is unknown. We therefore examined the immunolocalization of the EP(1) and EP(2) receptors in human epidermis. The EP(1) and EP(2) receptors demonstrated both plasma membrane and perinuclear or nuclear staining within the basal and spinous layers. Within the granular layer, both receptors were expressed in the cytoplasm with a grainy or granular appearance. The major differences were that the EP(2) receptor demonstrated a zone of decreased to absent plasma membrane staining in the superficial spinous layer and only scattered cellular staining within the granular layer. In contrast, the EP(1) receptor was prominently expressed throughout the stratum granulosum and the plasma membrane staining pattern was seen throughout the spinous layer. In cultured primary human keratinocytes, we also verified the presence of functional EP(1) receptor coupled to intracellular calcium mobilization and EP(2) receptor coupled to cAMP production.

Evidence that cytochrome P450 CYP2B19 is the major source of epoxyeicosatrienoic acids in mouse skin

CYP2B19 is an arachidonic acid monooxygenase highly expressed in the outer, differentiated cell layers of mouse epidermis. We aimed to establish whether CYP2B19 is the source of epidermal epoxyeicosatrienoic acids (EETs), which are implicated in mechanisms regulating epidermal cornification. We show that primary cultures of mouse epidermal keratinocytes expressed native CYP2B19, as determined by mass spectrometry. Differentiation upregulated CYP2B19 mRNA levels ( approximately 39-fold) detected by real-time PCR, CYP2B19 immunoreactivity detected by Western blotting, and cellular levels of the CYP2B19 product 11,12-EET. Cellular 11,12-EET formed from endogenous arachidonic acid increased preferentially (4- to 12-fold) at Day 4 or 5 of differentiation, compared with undifferentiated (Day 0) keratinocyte cultures. Temporally, these results concur with the maximal levels of CYP2B19 mRNA measured at Day 2 and CYP2B19 immunoreactivity at Day 4. We conclude that while mouse epidermis likely expresses multiple cytochrome P450 enzymes, existing evidence supports native CYP2B19 as being the major source of epidermal EET formation.

Enzyme association with PPARγ: evidence of a new role for 15-lipoxygenase type 2

Fatty acids have historically important structural roles in contributing to epidermal barrier function and therefore cutaneous health. Their metabolism to bioactive compounds is often up-regulated in response to cutaneous toxins thus providing them with functional roles. Some metabolites of arachidonic acid, such as 15S-hydroxyeicosatetraenoic acid (HETE), also serve functional roles as direct ligands for peroxisome proliferator activated receptors (PPARs). 15S-HETE, produced by 15-lipoxygenase type 2 (15-LOX-2), is an endogenous ligand for PPARgamma. This report demonstrates epidermal keratinocyte expression of both 15-LOX-2 and PPARgamma and provides evidence for a relationship beyond that of ligand-producer and -user, namely in vivo association of the two proteins at the molecular level making the enzyme a candidate nuclear receptor coregulator. Such close physical approximation of the 15S-HETE-producing enzyme and PPARgamma could potentiate the receptor response to a short-lived ligand. 15-LOX-2 may exemplify a class of enzymatically active nuclear receptor coactivator proteins distinct from those previously described but sharing their ability to promote expression from nuclear receptor-regulated promoters.

Cyclooxygenase-2 contributes to dysmotility and enhanced excitability of myenteric AH neurones in the inflamed guinea pig distal colon

We have previously demonstrated that trinitrobenzene sulphonic acid (TNBS)-induced colitis in guinea pig is associated with hyperexcitability of myenteric AH neurones, enhanced synaptic activity in the myenteric plexus, increased serotonin (5-HT) availability in the mucosa, and decreased propulsive motor activity. The current study tested the hypothesis that the activation of cyclooxygenase (COX) contributes to these alterations in bowel functions. DFU inhibition of COX-2, but not SC-560 inhibition of COX-1, restored to normal levels the electrical properties of myenteric AH neurones, the proportion of S neurones exhibiting slow EPSPs, and the rate of propulsive motor activity. Neither inhibitor was effective in altering the level of inflammation, the increased availability of mucosal 5-HT, or the enhanced fast EPSPs in myenteric AH and S neurones. COX-2 expression is enhanced in the myenteric plexus and cells within the smooth muscle layers during colitis, possibly reflecting the site at which COX-2 inhibition acts to allow recovery of motor function. In support of this concept, COX-1, but not COX-2, inhibition was effective in restoring normal mucosal prostaglandin levels. These results indicate that the various changes that occur in the motor neural pathways of the distal colon in TNBS-induced colitis do not involve a single neuroimmune mechanism. COX-2 activation is a critical step in the enhanced excitability of AH neurones as well as diminished propulsive motility in TNBS colitis, whereas other yet to be resolved pathways, that do not involve COX-1 or COX-2 activation, lead to altered 5-HT content in the mucosa and an augmentation of fast EPSPs.

Lipoxygenase and cyclooxygenase metabolism: new insights in treatment and chemoprevention of pancreatic cancer

The essential fatty acids, linoleic acid and arachidonic acid play an important role in pancreatic cancer development and progression. These fatty acids are metabolized to eicosanoids by cyclooxygenases and lipoxygenases. Abnormal expression and activities of both cyclooxygenases and lipoxygenases have been reported in pancreatic cancer. In this article, we aim to provide a brief summary of (1) our understanding of the roles of these enzymes in pancreatic cancer tumorigenesis and progression; and (2) the potential of using cyclooxygenase and lipoxygenase inhibitors for pancreatic cancer treatment and prevention.