Suppression of proto-oncogene (AP-1) in a model of skin epidermal hyperproliferation is reversed by topical application of 13-hydroxyoctadecadienoic acid and 15-hydroxyeicosatrienoic acid

Oral Administration of Linoleic Acid Induces New Vessel Formation and Improves Skin Wound Healing in Diabetic Rats

Introduction

Impaired wound healing has been widely reported in diabetes. Linoleic acid (LA) accelerates the skin wound healing process in non-diabetic rats. However, LA has not been tested in diabetic animals.

Objectives

We investigated whether oral administration of pure LA improves wound healing in streptozotocin-induced diabetic rats.

Methods

Dorsal wounds were induced in streptozotocin-induced type-1 diabetic rats treated or not with LA (0.22 g/kg b.w.) for 10 days. Wound closure was daily assessed for two weeks. Wound tissues were collected at specific time-points and used to measure fatty acid composition, and contents of cytokines, growth factors and eicosanoids. Histological and qPCR analyses were employed to examine the dynamics of cell migration during the healing process.

Results

LA reduced the wound area 14 days after wound induction. LA also increased the concentrations of cytokine-induced neutrophil chemotaxis (CINC-2αβ), tumor necrosis factor-α (TNF-α) and leukotriene B₄ (LTB₄), and reduced the expression of macrophage chemoattractant protein-1 (MCP-1) and macrophage inflammatory protein-1 (MIP-1). These results together with the histological analysis, which showed accumulation of leukocytes in the wound early in the healing process, indicate that LA brought forward the inflammatory phase and improved wound healing in diabetic rats. Angiogenesis was induced by LA through elevation in tissue content of key mediators of this process: vascular-endothelial growth factor (VEGF) and angiopoietin-2 (ANGPT-2).

Conclusions

Oral administration of LA hastened wound closure in diabetic rats by improving the inflammatory phase and angiogenesis.

Assessment of inflammatory resilience in healthy subjects using dietary lipid and glucose challenges

BACKGROUND

Resilience or the ability of our body to cope with daily-life challenges has been proposed as a new definition of health, with restoration of homeostasis as target resultant of various physiological stress responses. Challenge models may thus be a sensitive measure to study the body's health. The objective of this study was to select a dietary challenge model for the assessment of inflammatory resilience. Meals are a challenge to metabolic homeostasis and are suggested to affect inflammatory pathways, yet data in literature are limited and inconsistent.

METHOD

The kinetic responses of three different dietary challenges and a water control challenge were assessed on various metabolic and inflammatory markers in 14 healthy males and females using a full cross-over study design. The dietary challenges included glucose (75 g glucose in 300 ml water), lipids (200 ml whipping cream) and a mix of glucose and lipids (same amounts as above), respectively. Blood samples were collected at baseline and at 0.5, 1, 2, 4, 6, 8 and 10 h after consumption of the treatment products. Inflammation (IFNγ, IL-1β, IL-6, IL-8, IL-10, IL-12p70, TNF-α CRP, ICAM-1, VCAM-1, SAA, E-selectin, P-selectin, thrombomodulin, leukocytes, neutrophils, lymphocytes) and clinical (e.g. glucose, insulin, triglycerides) markers as well as gene expression in blood cells and plasma oxylipin profiles were measured.

RESULTS

All three dietary challenges induced changes related to metabolic control such as increases in glucose and insulin after the glucose challenge and increases in triglycerides after the lipid challenge. In addition, differences between the challenges were observed for precursor oxylipins and some downstream metabolites including DiHETrE's and HODE's. However, none of the dietary challenges induced an acute inflammatory response, except for a modest increase in circulating leukocyte numbers after the glucose and mix challenges. Furthermore, subtle, yet statistically significant increases in vascular inflammatory markers (sICAM-1 and sVCAM-1) were found after the mix challenge, when compared to the water control challenge.

CONCLUSIONS

This study shows that dietary glucose and lipid challenges did not induce a strong acute inflammatory response in healthy subjects, as quantified by an accurate and broad panel of parameters.

Eicosanoids in skin inflammation

Eicosanoids play an integral part in homeostatic mechanisms related to skin health and structural integrity. They also mediate inflammatory events developed in response to environmental factors, such as exposure to ultraviolet radiation, and inflammatory and allergic disorders, including psoriasis and atopic dermatitis. This review article discusses biochemical aspects related to cutaneous eicosanoid metabolism, the contribution of these potent autacoids to skin inflammation and related conditions, and considers the importance of nutritional supplementation with bioactives such as omega-3 and omega-6 polyunsaturated fatty acids and plant-derived antioxidants as means of addressing skin health issues.

Bioactive lipid mediators in skin inflammation and immunity

The skin is the primary barrier from the outside environment, protecting the host from injury, infectious pathogens, water loss and solar ultraviolet radiation. In this role, it is supported by a highly organized system comprising elements of innate and adaptive immunity, responsive to inflammatory stimuli. The cutaneous immune system is regulated by mediators such as cytokines and bioactive lipids that can initiate rapid immune responses with controlled inflammation, followed by efficient resolution. However, when immune responses are inadequate or mounted against non-infectious agents, these mediators contribute to skin pathologies involving unresolved or chronic inflammation. Skin is characterized by active lipid metabolism and fatty acids play crucial roles both in terms of structural integrity and functionality, in particular when transformed to bioactive mediators. Eicosanoids, endocannabinoids and sphingolipids are such key bioactive lipids, intimately involved in skin biology, inflammation and immunity. We discuss their origins, role and influence over various cells of the epidermis, dermis and cutaneous immune system and examine their function in examples of inflammatory skin conditions. We focus on psoriasis, atopic and contact dermatitis, acne vulgaris, wound healing and photodermatology that demonstrate dysregulation of bioactive lipid metabolism and examine ways of using this insight to inform novel therapeutics.

Detection of omega-3 oxylipins in human plasma and response to treatment with omega-3 acid ethyl esters

The long-chain omega-3 fatty acids (n-3 FA) eicosapentaenoic acid (EPA) and docosahexaenoic acids (DHA) have beneficial health effects, but the molecular mediators of these effects are not well characterized. Oxygenated n-3 FAs (oxylipins) may be an important class of mediators. Members of this chemical class include epoxides, alcohols, diols, and ketones, many of which have bioactivity in vitro. Neither the presence of n-3 oxylipins in human plasma nor the effect of n-3 FA ingestion on their levels has been documented. We measured plasma oxylipins derived from both the n-3 and n-6 FA classes in healthy volunteers (n = 10) before and after 4 weeks of treatment with prescription n-3 FA ethyl esters (4 g/day). At baseline, EPA and DHA oxylipins were detected in low (1-50 nM) range, with alcohols > epoxides >or= diols. Treatment increased n-3 oxylipin levels 2- to 5-fold and reduced selected n-6 oxylipins by approximately 20%. This is the first documentation that endogenous n-3 oxylipin levels can be modulated by n-3 FA treatment in humans. The extent to which the beneficial cardiovascular effects of n-3 FAs are mediated by increased n-3 and/or reduced n-6 oxylipin levels remains to be explored.

Detection of omega-3 oxylipins in human plasma and response to treatment with omega-3 acid ethyl esters

The long-chain omega-3 fatty acids (n-3 FA) eicosapentaenoic acid (EPA) and docosahexaenoic acids (DHA) have beneficial health effects, but the molecular mediators of these effects are not well characterized. Oxygenated n-3 FAs (oxylipins) may be an important class of mediators. Members of this chemical class include epoxides, alcohols, diols, and ketones, many of which have bioactivity in vitro. Neither the presence of n-3 oxylipins in human plasma nor the effect of n-3 FA ingestion on their levels has been documented. We measured plasma oxylipins derived from both the n-3 and n-6 FA classes in healthy volunteers (n = 10) before and after 4 weeks of treatment with prescription n-3 FA ethyl esters (4 g/day). At baseline, EPA and DHA oxylipins were detected in low (1-50 nM) range, with alcohols > epoxides >or= diols. Treatment increased n-3 oxylipin levels 2- to 5-fold and reduced selected n-6 oxylipins by approximately 20%. This is the first documentation that endogenous n-3 oxylipin levels can be modulated by n-3 FA treatment in humans. The extent to which the beneficial cardiovascular effects of n-3 FAs are mediated by increased n-3 and/or reduced n-6 oxylipin levels remains to be explored.

Activation of peroxisome proliferator-activated receptor (PPAR)-gamma by 15S-hydroxyeicosatrienoic acid parallels growth suppression of androgen-dependent prostatic adenocarcinoma cells

Although dietary gamma-linolenic acid (GLA) and its 15-lipoxygenase metabolite, 15S-hydroxyeicosatrienoic acid (15S-HETrE), have been reported to exert antiproliferative activities in other systems, their role in prostatic carcinogenesis is unknown. To evolve a possible mechanism for the suppressive effect on growth of prostatic cells, we incubated GLA and 15S-HETrE with androgen-dependent prostatic adenocarcinoma cells. 15S-HETrE but not GLA markedly inhibited [(3)H]thymidine uptake in parallel with the upregulation of peroxisome proliferator-activated receptor-gamma expression (a growth modulating nuclear receptor). The data, taken together, suggest that dietary GLA via its in vivo metabolite 15S-HETrE could serve as an endogenous adjunct to attenuate prostatic tumorigenesis.

Biological significance of essential fatty acids/prostanoids/lipoxygenase-derived monohydroxy fatty acids in the skin

The skin displays a highly active metabolism of polyunsaturated fatty acids (PUFA). Dietary deficiency of linoleic acid (LA), an 18-carbon (n-6) PUFA, results in characteristic scaly skin disorder and excessive epidermal water loss. Although arachidonic acid (AA), a 20-carbon (n-6) PUFA, is metabolized via cyclooxygenase pathway into predominantly prostaglandin E2 (PGE2) and PGF2alpha, the metabolism of AA via the 15-lipoxygenase (15-LOX) pathway, which is very active in skin epidermis and catalyzes the transformation of AA into predominantly 15S-hydroxyeicosatetraenoic acid (15S-HETE). Additionally, the 15-LOX also metabolizes the 18-carbon LA into 13S-hydroxyoctadecadienoic acid (13S-HODE), respectively. Interestingly, 15-LOX catalyzes the transformation of dihomo-gamma-linolenic acid (DGLA), derived from dietary gamma-linolenic acid, to 15S-hydroxyeicosatrienoic acid (15S-HETrE). These monohydroxy fatty acids are incorporated into the membrane inositol phospholipids which undergo hydrolytic cleavage to yield substituted-diacylglycerols such as 13S-HODE-DAG from 13S-HODE and 15S-HETrE-DAG from 15S-HETrE. These substituted-monohydroxy fatty acids seemingly exert anti-inflammatory/antiproliferative effects via the modulation of selective protein kinase C as well as on the upstream/down-stream nuclear MAP-kinase/AP-1/apoptotic signaling events.