Causal effects of fatty acids on atopic dermatitis: A Mendelian randomization study

Assessment of causal relationships between omega-3 and omega-6 polyunsaturated fatty acids in autoimmune rheumatic diseases: a brief research report from a Mendelian randomization study

Background

Currently, the association between the consumption of polyunsaturated fatty acids (PUFAs) and the susceptibility to autoimmune rheumatic diseases (ARDs) remains conflict and lacks substantial evidence in various clinical studies. To address this issue, we employed Mendelian randomization (MR) to establish causal links between six types of PUFAs and their connection to the risk of ARDs.

Methods

We retrieved summary-level data on six types of PUFAs, and five different types of ARDs from publicly accessible GWAS statistics. Causal relationships were determined using a two-sample MR analysis, with the IVW approach serving as the primary analysis method. To ensure the reliability of our research findings, we used four complementary approaches and conducted multivariable MR analysis (MVMR). Additionally, we investigated reverse causality through a reverse MR analysis.

Results

Our results indicate that a heightened genetic predisposition for elevated levels of EPA (ORIVW: 0.924, 95% CI: 0.666-1.283, P IVW = 0.025) was linked to a decreased susceptibility to psoriatic arthritis (PsA). Importantly, the genetically predicted higher levels of EPA remain significantly associated with an reduced risk of PsA, even after adjusting for multiple testing using the FDR method (P IVW-FDR-corrected = 0.033) and multivariable MR analysis (P MV-IVW < 0.05), indicating that EPA may be considered as the risk-protecting PUFAs for PsA. Additionally, high levels of LA showed a positive causal relationship with a higher risk of PsA (ORIVW: 1.248, 95% CI: 1.013-1.538, P IVW = 0.037). It is interesting to note, however, that the effects of these associations were weakened in our MVMR analyses, which incorporated adjustment for lipid profiles (P MV-IVW > 0.05) and multiple testing using the FDR method (P IVW-FDR-corrected = 0.062). Moreover, effects of total omega-3 PUFAs, DHA, EPA, and LA on PsA, were massively driven by SNP effects in the FADS gene region. Furthermore, no causal association was identified between the concentrations of other circulating PUFAs and the risk of other ARDs. Further analysis revealed no significant horizontal pleiotropy and heterogeneity or reverse causality.

Conclusion

Our comprehensive MR analysis indicated that EPA is a key omega-3 PUFA that may protect against PsA but not other ARDs. The FADS2 gene appears to play a central role in mediating the effects of omega-3 PUFAs on PsA risk. These findings suggest that EPA supplementation may be a promising strategy for preventing PsA onset. Further well-powered epidemiological studies and clinical trials are warranted to explore the potential mechanisms underlying the protective effects of EPA in PsA.

A systematic review and meta-analysis of nutritional and dietary interventions in randomized controlled trials for skin symptoms in children with atopic dermatitis and without food allergy: An EAACI task force report

This systematic review and meta-analysis aimed to consolidate evidence on dietary interventions for atopic eczema/dermatitis (AD) skin symptoms in children without food allergies, following PRISMA 2020 guidelines. Systematic review updates were conducted in May 2022 and June 2023, focusing on randomized placebo-controlled trials (RCTs) involving children with AD but without food allergies. Specific diets or supplements, such as vitamins, minerals, probiotics, prebiotics, symbiotics, or postbiotics, were explored in these trials. Exclusions comprised descriptive studies, systematic reviews, meta-analyses, letters, case reports, studies involving elimination diets, and those reporting on food allergens in children and adolescents. Additionally, studies assessing exacerbation of AD due to food allergy/sensitization and those evaluating elimination diets' effects on AD were excluded. Nutritional supplementation studies were eligible regardless of sensitization profile. Evaluation of their impact on AD clinical expression was performed using SCORAD scores, and a meta-analysis of SCORAD outcomes was conducted using random-effect models (CRD42022328702). The review encompassed 27 RCTs examining prebiotics, Vitamin D, evening primrose oil, and substituting cow's milk formula with partially hydrolyzed whey milk formula. A meta-analysis of 20 RCTs assessing probiotics, alone or combined with prebiotics, revealed a significant reduction in SCORAD scores, suggesting a consistent trend in alleviating AD symptoms in children without food allergies. Nonetheless, evidence for other dietary interventions remains limited, underscoring the necessity for well-designed intervention studies targeting multiple factors to understand etiological interactions and propose reliable manipulation strategies.

Mendelian Randomization Studies in Atopic Dermatitis: A Systematic Review

Prior studies have found associations between atopic dermatitis (AD) and comorbidities, including depression, obesity, asthma, and allergic rhinitis. Although observational studies often cannot establish robust causality between potential risk factors and AD, Mendelian randomization minimizes confounding when exploring causality by relying on random allelic assortment at birth. In this study, we systematically reviewed 30 Mendelian randomization studies in AD. Body mass index, gut microbial flora, the IL-18 signaling pathway, and gastroesophageal reflux disease were among the causal factors for AD, whereas AD was causal for several medical conditions, including heart failure, rheumatoid arthritis, and conjunctivitis. These insights may improve preventive counseling in AD.

Deficit of Omega-3 Fatty Acids in Acne Patients-A Cross-Sectional Pilot Study in a German Cohort

Omega-3 fatty acids (ω-3 FAs) exert anti-inflammatory effects, including the downregulation of pro-inflammatory cytokines, eicosanoids, and insulin-like growth factor-1. Therefore, they may improve acne severity as an adjunct treatment. However, there is a paucity of data regarding patients' existing deficits. The aim of this study was to determine ω-3 FA levels in acne patients in correlation with self-reported dietary preferences and clinical severity. A single-center, cross-sectional study of 100 acne patients was conducted. Patients' blood parameters, including ω-3 FAs levels, were assessed using the HS-omega-3 Index® in erythrocytes (Omegametrix® GmbH, Martinsried, Germany). Dietary preferences were assessed using a standardized food frequency questionnaire. Clinical dermatologic evaluation was performed using the Investigator Global Assessment (IGA) of acne. The values of the HS-omega-3 Index® were outside the recommended range of 8-11% in 96 patients (mean 5.15%), independent of the clinical severity or affected anatomic sites. A severe deficit (HS-omega-3 Index® < 4%) was seen more commonly in men than in women (p = 0.021). The regular consumption of legumes was significantly associated with higher ω-3 FA levels (p = 0.003), as was oral ω-3 FA supplementation (p = 0.006) and the lack of sunflower oil intake (p = 0.008). This pilot study demonstrated a deficit of ω-3 FAs in a German acne cohort. Higher ω-3 FAs levels were observed in patients with regular legume intake and oral ω-3 FAs supplementation. Further prospective studies are needed to investigate whether the clinical severity of acne improves in patients with normal HS-omega-3 Index®.

Causality of unsaturated fatty acids and psoriasis a Mendelian randomization study

Background

Many observational studies have identified a link between unsaturated fatty acids and psoriasis. However, they contain reverse causality and confounding factors, and there is no definite causal study between unsaturated fatty acids and psoriasis.

Objectives

Analysis of causality between unsaturated fatty acids and psoriasis by Mendelian randomization.

Methods

We used IEU Open GWAS Project, omega-3 PUFA and omega-6 PUFA data from 114,999 subjects, MUFA data from 13,535 subjects, and psoriasis data from 4,510 cases and 212,242 controls were included. We employed the inverse-variance weighted (IVW) method as the primary analytical approach and four additional MR methods. Moreover, we performed heterogeneity and horizontal pleiotropy assessments using Cochrane's Q and MR-Egger intercept tests, respectively. Finally, we performed sensitivity analyses to enhance our findings' precision and veracity.

Results

IVW results showed no causal effect of omega-3 PUFA on psoriasis (p = 0.334; OR, 0.909; 95% CI, 0.748-1.104), omega-6 PUFA cause psoriasis (p = 0.046; OR, 1.174; 95% CI, 1.003-1.374), MUFA cause psoriasis (p = 0.032; OR, 1.218; 95% CI, 1.018-1.457), no causal effect of omega-3 PUFA in psoriasis (p = 0.695; OR, 0.989; 95% CI, 0.937-1.044), no causal effect of omega-6 PUFA in psoriasis (p = 0.643; OR, 1.013; 95% CI, 0.960-1.068), psoriasis is not causal to MUFA (p = 0.986; OR, 1.000; 95% CI, 0.949-1.055). Heterogeneity, horizontal pleiotropy, and sensitivity analyses showed reliable results.

Conclusion

We found that circulating omega-6 PUFA and MUFA cause psoriasis, while omega-3 PUFA do not. Treatments that lower circulating omega-6 PUFA and MUFA are effective in psoriasis. After a better understanding of fatty acid intake and circulation, the population can be advised to regulate their diet.

Integrative polygenic analysis of the protective effects of fatty acid metabolism on disease as modified by obesity

Dysregulation of fatty acid metabolites can play a crucial role in the progression of complex diseases, such as cardiovascular disease, digestive diseases, and metabolic diseases. Metabolites can have either protective or risk effects on a disease; however, the details of such associations remain contentious. In this study, we demonstrate an integrative PheWAS approach to establish high confidence, causally suggestive of metabolite-disease associations for three fatty acid metabolites, namely, omega-3 fatty acids, omega-6 fatty acids, and docosahexaenoic acid, for 1,254 disease endpoints. Metabolite-disease associations were established if there was a concordant direction of effect and significance for metabolite level and genetic risk score for the metabolite. There was enrichment for metabolite associations with diseases of the respiratory system for omega-3 fatty acids, diseases of the circulatory system and endocrine system for omega-6 fatty acids, and diseases of the digestive system for docosahexaenoic acid. Upon performing Mendelian randomization on a subset of the outcomes, we identified 3, 6, and 15 significant diseases associated with omega-3 fatty acids, omega-6 fatty acids, and docosahexaenoic acid, respectively. We then demonstrate a class of prevalence-risk relationships indicative of (de)canalization of disease under high and low fatty acid metabolite levels. Finally, we show that the interaction between the metabolites and obesity demonstrates that the degree of protection afforded by fatty acid metabolites is strongly modulated by underlying metabolic health. This study evaluated the disease architectures of three polyunsaturated fatty acids (PUFAs), which were validated by several PheWAS modes of support. Our results not only highlight specific diseases associated with each metabolite but also disease group enrichments. In addition, we demonstrate an integrative PheWAS methodology that can be applied to other components of the human metabolome or other traits of interest. The results of this study can be used as an atlas to cross-compare genetic with non-genetic disease associations for the three PUFAs investigated. The findings can be explored through our R shiny app at https://pufa.biosci.gatech.edu.

Fatty Acids Profile and the Relevance of Membranes as the Target of Nutrition-Based Strategies in Atopic Dermatitis: A Narrative Review

Recently, the prevalence of atopic dermatitis has increased drastically, especially in urban populations. This multifactorial skin disease is caused by complex interactions between various factors including genetics, environment, lifestyle, and diet. In eczema, apart from using an elimination diet, the adequate content of fatty acids from foods (saturated, monounsaturated, and polyunsaturated fatty acids) plays an important role as an immunomodulatory agent. Different aspects regarding atopic dermatitis include connections between lipid metabolism in atopic dermatitis, with the importance of the MUFA levels, as well as of the omega-6/omega-3 balance that affects the formation of long-chain (C20 eicosanoic and C22 docosaenoic) fatty acids and bioactive lipids from them (such as prostaglandins). Impair/repair of the functioning of epidermal barrier is influenced by these fatty acid levels. The purpose of this review is to drive attention to membrane fatty acid composition and its involvement as the target of fatty acid supplementation. The membrane-targeted strategy indicates the future direction for dermatological research regarding the use of nutritional synergies, in particular using red blood cell fatty acid profiles as a tool for checking the effects of supplementations to reach the target and influence the inflammatory/anti-inflammatory balance of lipid mediators. This knowledge gives the opportunity to develop personalized strategies to create a healthy balance by nutrition with an anti-inflammatory outcome in skin disorders.