Resolvins and aliamides: lipid autacoids in ophthalmology - what promise do they hold?

The therapeutic potential of resolvins in pulmonary diseases

Uncontrolled inflammation leads to nonspecific destruction and remodeling of tissues and can contribute to many human pathologies, including pulmonary diseases. Stimulation of inflammatory resolution is considered an important process that protects against the progression of chronic inflammatory diseases. Resolvins generated from essential omega-3 polyunsaturated fatty acids have been demonstrated to be signaling molecules in inflammation with important pro-resolving and anti-inflammatory capabilities. By binding to specific receptors, resolvins can modulate inflammatory processes such as neutrophil migration, macrophage phagocytosis and the presence of pro-inflammatory mediators to reduce inflammatory pathologies. The discovery of these pro-resolving mediators has led to a shift in drug research from suppressing pro-inflammatory molecules to investigating compounds that promote resolution to treat inflammation. The exploration of inflammatory resolution also provided the opportunity to further understand the pathophysiology of pulmonary diseases. Alterations of resolution are now linked to both the development and exacerbation of diseases such as asthma, chronic obstructive pulmonary disease, cystic fibrosis, acute respiratory distress syndrome, cancer and COVID-19. These findings have resulted in the rise of novel design and testing of innovative resolution-based therapeutics to treat diseases. Hence, this paper reviews the generation and mechanistic actions of resolvins and investigates their role and therapeutic potential in several pulmonary diseases that may benefit from resolution-based pharmaceuticals.

Dysregulation of Resolvin E1 Metabolism and Signaling in a Light-Damage Model of Age-Related Macular Degeneration

Resolvin E1 (RvE1) is an eicosapentaenoic acid-derived lipid mediator involved in the resolution of inflammation. Here, we investigated whether RvE1 alterations may occur in an animal model of age-related macular degeneration (AMD). To this end, Sprague Dawley albino rats underwent light damage (LD), and retinas and serum were analyzed immediately or seven days after treatment. Western blot of retinas showed that the RvE1 receptor ChemR23 and the RvE1 metabolic enzymes 5-LOX and COX-2 were unchanged immediately after LD, but they were significantly up-regulated seven days later. Instead, the RvE1 receptor BLT1 was not modulated by LD, and neither was the RvE1 degradative enzyme 15-PGDH. Moreover, ChemR23, 5-LOX, COX-2 and BLT1 were found to be more expressed in the inner retina under all experimental conditions, as observed through ImageJ plot profile analysis. Of note, amacrine cells highly expressed BLT1, while ChemR23 was highly expressed in the activated microglia of the outer retina. ELISA assays also showed that LD rats displayed significantly higher circulating levels and reduced retinal levels of RvE1 compared to controls. Altogether, our data indicate that RvE1 metabolism and signaling are modulated in the LD model, suggesting a potentially relevant role of this pathway in AMD.

Major structure-activity relationships of resolvins, protectins, maresins and their analogues

Resolvins, protectins and maresins are a series of polyunsaturated fatty acid-derived molecules which play important roles in the resolution of inflammation. They are termed specialized proresolving mediators and facilitate a return to homeostasis following an inflammatory response. These molecules are currently the focus of intensive investigation, primarily for their ability to suppress inflammation in chronic disease states. Researchers have employed different synthetic approaches to assess whether various structural modifications of these compounds could provide access to future therapeutics. This review summarizes the modifications made thus far and focuses on the key structure-activity relationships which have been uncovered for resolvins, protectins, maresins and their analogues.

Resolvins' Obesity-Driven Deficiency: The Implications for Maternal-Fetal Health

Since pregnancy is already characterized by mild but significant inflammatory activity in physiological conditions, when complicated by obesity the probability of a persistent inflammatory state increases, with consequent multiple repercussions that add up to the complications associated with acute inflammation. In this context, the role of resolvins, specialized pro-resolving mediators (SPMs), deriving from omega-3 essential fatty acids, may be crucial. Indeed, differential production in numerous high-risk conditions associated with both childbirth and neonatal health, the correlation between maternal omega-3 intake and resolvin concentrations in maternal blood and at the placental level, and the high values found in breast milk in the first month of breastfeeding, are some of the most important hallmarks of these autacoids. In addition, a growing body of scientific evidence supports the lack of SPMs, at the level of immune-metabolic tissues, in the case of obesity. Furthermore, the obesity-related lack of SPMs seems to be decisive in the context of the current outbreak of COVID-19, as it appears to be one of the causes associated with the higher incidence of complications and negative outcomes of SARS-CoV-2 infection. The usefulness of metabolomics in this field appears clear, given that through the metabolome it is possible to observe the numerous and complex interactions between the mother, the placenta and the fetus in order to identify specific biomarkers useful in the prediction, diagnosis and monitoring of the various obstetric conditions. However, further investigations are needed in order to evaluate the possible use of some resolvins as biomarkers of maternal–fetal outcomes but also to establish adequate integration values in pregnant women with omega-3 fatty acids or with more active derivatives that guarantee optimal SPM production under risky conditions.

The utilisation of resolvins in medicine and tissue engineering

Recent advances in the field of regenerative medicine and biomaterial science have highlighted the importance of controlling immune cell phenotypes at the biomaterial interface. These studies have clearly indicated that a rapid resolution of the inflammatory process, mediated by a switch in the macrophage population towards a reparative phenotype, is essential for tissue regeneration to occur. While various biomaterial surfaces have been developed in order to impart immunomodulatory properties to the resulting constructs, an alternative strategy involving the use of reparative biological cues, known as resolvins, is emerging in regenerative medicine. This review reports on the mechanisms via which resolvins participate in the resolution of inflammation and describes their current utilisation in pre-clinical and clinical settings, along with their effectiveness when combined with biomaterial constructs in tissue engineering applications. STATEMENT OF SIGNIFICANCE: The resolution of the inflammatory process is necessary for achieving tissue healing and regeneration. Resolvins are lipid mediators and play a key role in the resolution of the inflammatory response and can be used in as biological cues to promote tissue regeneration. This review describes the various biological inflammatory mechanisms and pathways involving resolvins and how their action results in a pro-healing response. The use of these molecules in the clinical setting is then summarised for various applications along with their limitations. Lastly, the review focuses on the emergence resolvins in tissue engineering products including the use of a more stable form which holds greater prospect for regenerative purposes.

Experimental Pharmacotherapy for Dry Eye Disease: A Review

Dry eye disease (DED) is a complex multifactorial disease showing heterogenous symptoms, including dryness, photophobia, ocular discomfort, irritation and burning but also pain. These symptoms can affect visual function leading to restrictions in daily life activities and reduction in work productivity with a consequently high impact on quality of life. Several pathological mechanisms contribute to the disease: evaporative water loss leads to impairment and loss of tear homeostasis inducing either directly or indirectly to inflammation, in a self-perpetuating vicious cycle. Dysregulated ocular immune responses result in ocular surface damage, which further contributes to DED pathogenesis. Currently, DED treatment is based on a flexible stepwise approach to identify the most beneficial intervention. Although most of the available treatments may control to a certain extent some signs and symptoms of DED, they show significant limitations and do not completely address the needs of patients suffering from DED. This review provides an overview of the emerging experimental therapies for DED. Several promising therapeutic strategies are under development with the aim of dampening inflammation and restoring the homeostasis of the ocular surface microenvironment. Results from early phase clinical trials, testing the effects of EnaC blockers, TRPM8 agonist or mesenchymal stem cells in DED patients, are especially awaited to demonstrate their therapeutic value for the treatment of DED. Moreover, the most advanced experimental strategies in the pipeline for DED, tivanisiran, IL-1R antagonist EBI-005 and SkQ1, are being tested in Phase III clinical trials, still ongoing. Nevertheless, although promising results, further studies are still needed to confirm efficacy and safety of the new emerging therapies for DED.

Stereoselective Synthesis and Structural Confirmation of the Specialized Pro-Resolving Mediator Resolvin E4

Herein, we report the stereoselective and convergent synthesis of resolvin E4, a newly identified specialized pro-resolving mediator. This synthesis proves the absolute configuration and exact olefin geometry. Key elements of the successful strategy include a highly stereoselective MacMillan organocatalytic oxyamination, a Midland Alpine borane reduction, and the use of a 1,4-pentadiyne unit as a linchpin building block. The application of reaction telescoping in several of the synthetic transformations enabled the preparation of the resolvin E4 methyl ester in 10% yield over 10 steps (longest linear sequence). The physical property (UV–Vis and LC–MS/MS) data of synthetic resolvin E4 matched those obtained from biologically produced material.

Melatonin: Implications for Ocular Disease and Therapeutic Potential

Melatonin, an indoleamine secreted mainly by the pineal gland, is known to modulate a wide range of circadian functions. However, this neurohormone is also synthesized within the eye and acts directly on ocular structures to mediate a variety of physiological processes. This review is focused on the role and therapeutic potential of melatonin in ocular diseases. We summarize data indicating that melatonin may represent a powerful tool to counteract ocular dysfunctions such as uveitis, glaucoma, age-related macular degeneration, and diabetic retinopathy. A search strategy was conducted to identify studies in PubMed (January 1990 to September 2017). In particular, we included experimental studies, clinical trials, and reviews to provide suitable insights and elucidations regarding the action of melatonin on age-related ocular disorders. Literature data suggest that melatonin could potentially protect ocular tissues by decreasing the production of free radicals and pro-inflammatory mediators. Additionally, melatonin appears to be safe and well-tolerated, even at high doses, and no adverse/side effects were reported. Although this topic remains under intense investigation, we can conclude that melatonin, as a single agent or in combination with other drugs, is an attractive pharmacological candidate for age-related ocular diseases.

Modulating Contact Lens Discomfort With Anti-Inflammatory Approaches: A Randomized Controlled Trial

Purpose

To assess the efficacy of anti-inflammatory approaches, comprising a topical corticosteroid and omega-3 supplements, for modulating the inflammatory overlay associated with contact lens discomfort (CLD).

Methods

This randomized controlled trial involved 72 adults with CLD, randomized (1:1:1:1) to one of the following: placebo (oral olive oil), oral fish oil (900 mg/d eicosapentaenoic acid [EPA] + 600 mg/d docosohexaenoic acid [DHA]), oral combined fish+flaxseed oils (900 mg/d EPA + 600 mg/d DHA + 900 mg/d alpha-linolenic acid), or omega-3 eye-drops (0.025% EPA + 0.0025% DHA four times per day [qid]) for 12 weeks, with visits at baseline, weeks 4 and 12. At week 12, participants who received placebo were assigned a low-potency corticosteroid (fluorometholone [FML] 0.1%, drops, three times per day [tid]) for 2 weeks (week 14).

Results

Sixty-five participants completed the primary endpoint. At week 12, contact lens dry-eye questionnaire (CLDEQ-8) score was reduced from baseline with oral fish oil (-7.3 ± 0.8 units, n = 17, P < 0.05), compared with placebo (-3.5 ± 0.9 units, n = 16). FML produced significant reductions in tear IL-17A (-71.1 ± 14.3%, n = 12) and IL-6 (-47.6 ± 17.5%, n = 12, P < 0.05) relative to its baseline (week 12). At week 12, tear IL-17A levels were reduced from baseline in the oral fish oil (-63.2 ± 12.8%, n = 12, P < 0.05) and topical omega-3 (-76.2 ± 10.8%, n = 10, P < 0.05) groups, compared with placebo (-3.8 ± 12.7%, n = 12). Tear IL-6 was reduced with all omega-3 interventions, relative to placebo (P < 0.05) at week 12.

Conclusions

CLD was attenuated by oral long-chain omega-3 supplementation for 12 weeks. Acute (2 week) topical corticosteroids and longer-term (12 week) omega-3 supplementation reduced tear levels of the proinflammatory cytokines IL-17A and IL-6, demonstrating parallels in modulating ocular inflammation with these approaches.

Nitro-fatty acids: New drug candidates for chronic inflammatory and fibrotic diseases

Nitrated oleic acid (NO₂-OA) was first identified in 2003, and after the characterization of its formation and thiol reactivity, it was used as a prototypical molecule to investigate the physiological actions of endogenous nitrated fatty acids (NO₂-FA). Based on in vitro observations showing significant activation of cytoprotective and anti-inflammatory signaling responses by NO₂-FA, experiments were designed to determine their pharmacological potential. Supported by strong intellectual protection and favorable pharmacokinetic and pharmacodynamic data, 10-NO₂-OA (CXA-10) underwent pharmaceutical development as a drug to treat fibrotic and inflammatory diseases. NO₂-FA are at the intersection of three unconventional drug candidate classes that include 1) fatty acids, 2) metabolic intermediates and 3) electrophilic molecules. These three groups use different scaffolds for drug development, are characterized by broad activities and are individually gaining traction as alternatives to mono-target drug therapies. In particular, NO₂-FA share key characteristics with currently approved pharmacological agents regarding reactivity, distribution, and mechanism of action. This review first presents the characteristics, liabilities, and opportunities that these different drug candidate classes display, and then discusses these issues in the context of current progress in the preclinical and clinical development of NO₂-FA as drugs. Lessons learned from the novel approaches presented herein were considered early on during development to structurally define and improve NO₂-FA and their disease targets.

The role of specialized pro-resolving mediators in maternal-fetal health

Infants developing in a pro-inflammatory intrauterine environment have a significant risk for severe complications after birth. It has been shown that omega-3 fatty acids reduce inflammation, and also reduce early preterm births and decrease risk of infant admission to the neonatal intensive care unit. However, the mechanism for omega-3 fatty acids exerting these effects was previously unknown. Recent evidence has shown that downstream products of polyunsaturated fatty acids called specialized pro-resolving mediators may mediate inflammatory physiology, thus playing an important role in maternal-fetal health. In this review, current knowledge relating to specialized pro-resolving mediators in pregnancy, delivery, and perinatal disease states will be summarized.

Early treatment with Resolvin E1 facilitates myocardial recovery from ischaemia in mice

BACKGROUND AND PURPOSE

An appropriate inflammatory response is necessary for cardiac healing after acute myocardial infarction (MI). Resolvin E1 (RvE1) is an anti-inflammatory and pro-resolution lipid mediator derived from eicosapentaenoic acid. Here we have investigated the effects of RvE1 on the recovery of cardiac function after MI in mice.

EXPERIMENTAL APPROACH

Acute MI was induced by surgical ligation of the left anterior descending artery in male C57BL/6 mice. RvE1 (5 ng·g^-1 ·day^-1 ; i.p.) was given to mice at different times following MI. Cardiac function was monitored by transthoracic echocardiography at days 3, 7 and 14 after MI. Effects of RvE1 on the migration of subpopulations of monocytes/macrophages (Mos/Mps, Ly6C^hi and Ly6C^low ) were examined by flow cytometry and transwell assay.

KEY RESULTS

RvE1 administration from days 1 to 7 post-MI improved cardiac function, whereas treatment from days 7 to 14 markedly inhibited recovery of cardiac function. Early treatment with RvE1 post-MI suppressed the infiltration of dominant Ly6C^hi Mos/Mps and secretion of pro-inflammatory cytokines in injured hearts, which protected cardiomyocytes against apoptosis in the peri-infarct zones. Contrastingly, treatment with RvE1 1 week after MI decreased infiltration of Ly6C^low Mos/Mps and expression of pro-angiogenic factors in cardiac tissue, consequently reducing neovascularization in the peri-infarct zones. Additionally, RvE1 inhibited Mp migration by activating ChemR23 receptors.

CONCLUSION AND IMPLICATIONS

Treatment with RvE1 during the initial 7 days after MI facilitated cardiac healing by suppressing pro-inflammatory cytokine secretion, indicating that RvE1 may serve as an early therapeutic agent for acute MI.

LINKED ARTICLES

This article is part of a themed section on Spotlight on Small Molecules in Cardiovascular Diseases. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v175.8/issuetoc.

Fundamentals of and Critical Issues in Lipid Autacoid Medicine: A Review

The identification of a number of families of lipid signal molecules since the 1990s created new therapeutic possibilities for a great number of disorders characterized by chronic inflammation and pain. These lipid autacoids have been explored in a great variety of animal models related to inflammation, pain, (neuro-)protection, and repair. Based on the data from these models, as well as on a number of proof of principle studies in the clinic in indications such as neuropathic pain, a new chapter in medicine is about to begin. We would like to introduce the term “Autacoid Pain Medicine” for this chapter. There are, however, a number of methodological and strategic issues to overcome in this field. One of the roadblocks is related to patent strategies around families of these molecules. As this is not always recognized we will present a number of examples.

Skin matters! The role of keratinocytes in nociception: a rational argument for the development of topical analgesics

Treatment of neuropathic pain using topical formulations is still in its infancy. Only few topical analgesic formulations have become available for clinical use, and among these, analgesic creams are still rare. This is unfortunate because analgesic creams offer a number of advantages over patches, such as convenience, ease of adapting the frequency of application, and dose, and “rubbing cream where it hurts” involves the patient much more in the therapeutic process compared to patches and other localized treatment modalities. Although the literature supporting the efficacy and safety of analgesic creams (mostly compounded) is growing since the last decade, most pain physicians have not yet noticed and appreciated the therapeutic potential and clinical value of these creams. This is most probably due to a prejudice that topical application should need to act transdermally, more or less as a slow-release formulation, such as in patches delivering opioids. We will discuss this prejudice and show that there are multiple important targets in the skin to be reached by topical analgesic or anti-inflammatory compounds, and that the keratinocyte is one of those targets. By specifically targeting the keratinocyte, analgesia seems possible, effective, and safe, and thus topical analgesic creams may hold promise as a novel treatment modality for neuropathic pain.