Omega-3 Polyunsaturated Fatty Acids and Pulmonary Arterial Hypertension: insights and perspectives

Abstract

Pulmonary arterial hypertension (PAH) is a rare and progressive disorder that affects the pulmonary vasculature. Although recent developments in pharmacotherapy have extended the life expectancy of PAH patients, their 5-year survival remains unacceptably low, underscoring the need for multitarget and more comprehensive approaches to managing the disease. This should incorporate not only medical, but also lifestyle interventions, including dietary changes and the use of nutraceutical support. Among these strategies, n-3 polyunsaturated fatty acids (n-3 PUFAs) are emerging as promising agents able to counteract the inflammatory component of PAH.

In this narrative review, we aim at analyzing the preclinical evidence for the impact of n-3 PUFAs on the pathogenesis and the course of PAH. Although evidence for the role of n-3 PUFAs deficiencies in the development and progression of PAH in humans is limited, preclinical studies suggest that these dietary components may influence several aspects of the pathobiology of PAH.

Further clinical research should test the efficacy of n-3 PUFAs on top of approved clinical management. These studies will provide evidence on whether n-3 PUFAs can genuinely serve as a valuable tool to enhance the efficacy of pharmacotherapy in the treatment of PAH.

Graphical Abstract

Introduction

The term “Pulmonary Arterial Hypertension” (PAH) describes a disease in a subpopulation of patients with Pulmonary Hypertension (PH) hemodynamically characterized by the presence of precapillary PAH, defined as a mean pulmonary artery pressure >20 mmHg at rest, a pulmonary capillary wedge pressure (PCWP) >15 mmHg, and pulmonary vascular resistance (PVR) >2 Wood units ¹. It is a severe and progressive disease with a high prevalence in certain risk groups ² such as in patients healthy carriers with the bone morphogenetic protein receptor (BMPR)2 gene mutation (prevalence ~20%) ², connective tissue diseases (prevalence ~15%) ³, congenital heart disease with systemic-pulmonary shunt (prevalence ~11%) ⁴, severe chronic liver disease (prevalence ~5%) ⁵, and HIV infection (prevalence ~0,5%) ^6,7.

From a pathogenetic point of view, PAH is primarily characterized by a remodeling of the precapillary tract of the pulmonary arterial circulation due to excessive vascular cell proliferation, involving both endothelial and smooth muscle cells (SMCs) with a certain degree of venous remodeling, depending on the clinical type of PAH. In idiopathic PAH (IPAH) the prevalence of pulmonary vein involvement is low (around 5%) ⁸, while in PAH associated with connective diseases, this is higher ⁹. At the other extreme, pure pulmonary veno-occlusive disease is characterized predominantly by venous remodeling ¹⁰. Over time, this pathological progression ultimately results in right ventricular failure and premature mortality ¹¹.

Significant advances in the management of PAH have been achieved through the utilization of drugs that specifically target the pathways associated with endothelin (ET), prostacyclin (prostaglandin I₂, PGI₂) or nitric oxide (NO) ¹². The inherently complex and chronic nature of this disease strongly provides the rationale for embracing a multitargeted approach with combination therapy ¹³. Ongoing clinical trials are also actively exploring novel therapeutic interventions that target alternative disease-related pathways ¹⁴. However, the chronic nature of this condition and the current absence of fully effective treatments also suggest the need and the opportunity to better emphasize broader supportive measures, including nutritional and nutraceutical supports ¹⁵.

N-3 polyunsaturated fatty acids (PUFAs) are one of the most notable nutraceutical classes displaying substantial promise for their utilization as pharmaceuticals in cardiovascular clinical practice ¹⁶. Interestingly, their vasodilatory effects on the pulmonary vasculature are also progressively gaining recognition ¹⁵.

Against this background, in this narrative review, we provide a concise, yet comprehensive, overview of the preclinical evidence pertaining to the impact of n-3 PUFAs on the development and treatment of PAH.

Inflammation in the pathogenesis of PAH: role of endothelial dysfunction

The entire process of arterial remodeling in PAH begins with early signs of endothelial dysfunction, including vasoconstriction and inflammation. The initial increase in PVR is the result of disruption in the delicate balance between endogenous vasoconstrictors/mitogens, such as ET and thromboxane(TX)A₂, and vasodilators/antimitotic substances, such as PGI₂ and NO ¹⁷. High pulmonary blood pressure and increased pulsatile flow resulting from reduced vascular compliance simultaneously trigger a pro-inflammatory response in endothelial cells (ECs) ¹⁸. In animal models of PH, ECs exhibit heightened production of inflammatory cytokines and chemoattractants, such as interleukin (IL)-1β ¹⁹, IL-6 ^19,20, and macrophage migratory inhibitory factor (MIF) ²¹. Additionally, they feature increased expression of leukocyte cell adhesion molecules, including vascular cell adhesion molecule (VCAM)-1, intercellular adhesion molecule (ICAM)-1, and P-selectin ¹⁹. These molecules collectively contribute to the recruitment, infiltration, and accumulation of monocytes/macrophages in the perivascular adventitial space ^22,23, actively contributing to disease progression ²⁴. At the same time, other resident vascular cells, such as SMCs and fibroblasts, also respond to these biomechanical changes by altering their secretion of immune factors, including the release of inflammatory cytokines and mitogenic factors such as monocyte chemoattractant protein (MCP)-1, stromal cell-derived factor (SDF)-1, and transforming growth factor (TGF)β ^25,26.

A wide array of transcription factors are implicated in the dysregulated gene expression underlying the onset and progression of PAH ²⁷. Among these factors, hypoxia-inducible factors (HIFs) play a central role as key regulators of the molecular response to hypoxia and controls the expression of genes involved in cell proliferation and migration ²⁸. Under the same hypoxic conditions, an increase in Forkhead Box M1 (FOX-M1) expression is also present. FOX-M1 is a critical transcription factor for G1-S and G2-M cell cycle progression and the repair of DNA damage caused by reactive oxygen species (ROS). Studies in rodent model of PH have shown that blocking FOX-M1 expression can both prevent and reverse hypoxia-induced PH ¹⁸. In addition, inhibition of Nuclear Factor of Activated T Cells (NFATc)1 and -3, also activated by increased levels of ROS, has been shown to prevent hypoxia-induced PH in mice ^29,30. In the context of proinflammatory cell responses, increased activations of Signal Transducer and Activator of Transcription (STAT)3 ³¹ and Nuclear Factor (NF)-κB have been consistently observed in both animal models of PAH and PAH patients ³². Several lines of evidence suggest, in fact, that NF-κB may play a key role in PAH pathogenesis ³³. NF-κB is activated in the monocrotaline (MCT) model of PAH in rats, where its blockade improves the disease progression ³³. Increased activation of NF-κB has been demonstrated in alveolar macrophages obtained from bronchoalveolar lavage of PAH patients ³⁴ and, recently, clearly demonstrated activation of NF-κB directly in lung tissue of PAH patients ³⁵.

n-3 PUFAs docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA): New options for treating PAH

Structure and metabolism of PUFAs

Although inflammation appears to be crucial in development of the disease, the current therapeutic approaches to PAH are essentially based on the administration of vasodilator and anti-remodeling drugs, the action of which is limited to calcium channel blockage and a rebalancing of ET, NO and PGI₂ pathways, without acting on the inflammatory process in the lung tissue ³⁶. Against this background, n-3 PUFAs are one of the new strategies to counteract inflammation in PAH.

Fatty acids are long organic acids that can be classified into three main categories: saturated fatty acids (SFA), monounsaturated fatty acids (MUFAs), and PUFA (Figure 1). SFA are characterized by a carbon chain saturated with the maximum possible number of hydrogen atoms, containing no double bonds. In contrast, when one or more double bonds are present, these fatty acids are termed MUFAs and PUFAs, respectively. PUFAs play a crucial role in mammalian biology, with the most biologically significant families being n-6 and n-3 PUFAs. N-3 and n-6 refer to the position of the double bond nearest to the methyl terminus of the acyl chain, starting to count from the methyl carbon end of the fatty acid structure. Mammals lack the enzyme machinery required to introduce double bonds at the n-6 or n-3 positions. Therefore, PUFAs, such as linoleic acid (LA, n-6) and alpha-linolenic acid (ALA, n-3), are classified as “essential nutrients”. There is a conversion, yet limited, of these fatty acids to longer-chain PUFAs through desaturation and elongation reactions ³⁷. Specifically, LA can undergo conversion into arachidonic acid (AA, 20:4 n-6), whereas ALA can be transformed into eicosapentaenoic acid (EPA) (20:5 n-3) and, to an even lesser extent, into docosahexaenoic acid (DHA) (22:6 n-3) ^37,38.

Figure 1:

The position of the ω/n double bond from the methyl end is shown in blue. The position of the double bond at the carboxyl end is shown in red. The last column shows the primary food sources for FA.

Both DHA and to a lesser extent, EPA, are rapidly incorporated into various tissue phospholipids, also at the expense of AA, in various membrane tissues, including the lungs ^{39 40}. When in the membranes, EPA and DHA exert different influences on lipid structure and membrane fluidity, both crucial factors for receptor binding activities ^41,42, with DHA exhibiting more pronounced profluidic activity compared to EPA ⁴³. In addition to their membrane effects, PUFAs esterified in phospholipids play a central role in cell signaling pathways. After release by phospholipase A₂ activation, these fatty acids undergo oxygenation by various metabolic pathways through enzyme activities such as cyclooxygenase (COX)-1 and -2, lipoxygenase (LOX) and cytochrome P450 (CYP450). The resulting lipid signaling derivatives include 3-series prostaglandins (PGs), thromboxanes (TXs), 5-series leukotrienes (LTs), 5-series lipoxins (LXs), epoxyeicosatetraenoic acids (EEQs) and epoxydocosapentaenoic acids (EDPs) ⁴⁴. N-3 PUFAs derivatives, which have similar structures, often contribute to inflammation resolution and play a crucial role in the resolution of vascular inflammation ⁴⁵. DHA, in particular, is converted to 17-peroxidocoapentaenoic acid (17-HPDHA) by the corresponding LOX. The subsequent metabolization leads to the formation of protectin D1 (PD1), resolvins of the D-series (RvD1-D6), maresins (MaR1-MaR2) and aspirin-triggered resolving D (AT-RvD1-6). On the other hand, EPA can be converted to 18-hydroxy-eicosapentaenoic acid (18-HEPE) by acetylation through COX-2 or CYP450, which is then metabolized to E-series resolvins (RvE1-3) ⁴⁶. The broad spectrum of structural properties and the diversity in the production of lipid mediators may help explain the different functional activities of these fatty acids.

Cardiovascular benefits of n-3 PUFAs

The health effects of n-3 PUFAs have long been recognized ⁴⁷. Many clinical trials have assessed the benefits of dietary supplementation with fish oils in several inflammatory and autoimmune diseases in humans, including cardiovascular diseases (CVD), rheumatoid arthritis, Crohn’s disease, ulcerative colitis, psoriasis, systemic lupus erythematosus, multiple sclerosis and migraine headaches ^48,49.

The epidemiological association between dietary n-3 PUFAs and protection from CVD can be attributed, at least in part, to a lower degree in the development of atherosclerosis ⁴⁷. A number of studies have shown that n-3 PUFAs have a favorable impact on a number of intermediate determinants of CV risk ^50,51. They also favorably influence the development of atheromatous lesions in animal models of atherosclerosis ^52,53, as well as in humans ^54,55. Both EPA and DHA, as well as their derivatives, can modulate the expression and synthesis of various pro-inflammatory cytokines such as tumor necrosis factor-alpha(TNF)-α, IL-1β, IL-6, and IL-8 ⁵⁶. Many of these cytokines are implicated in inflammation and arterial wall remodeling in PAH, two events that significantly increase the severity of this lung disease ⁵⁷.

Extensive basic research has recently uncovered a wealth of potential mechanistic explanations for the cardiovascular preventive and therapeutic utilization of n-3 PUFAs ⁴⁷. According to evidence from the literature ⁵⁸, using cytokine-activated adult human saphenous vein ECs (HSVEC) or human umbilical vein ECs (HUVEC) as in vitro models of inflammation, we observed that DHA and EPA, when added to endothelial culture hours to days before stimulation with cytokines, early enough to allow significant incorporation into cell membrane phospholipids, significantly inhibited events associated with endothelial activation and inflammation, including a reduction in ROS production and NF-κB activation, with a consequent downregulation of the related surface expression of adhesion molecules and of the release of pro-inflammatory mediators ^59–61. Interestingly, in a recent meta-analysis of randomized controlled trials evaluating the effects of EPA and DHA on blood pressure and inflammatory factors, EPA significantly reduced systolic blood pressure while DHA exerted a significant reduction in diastolic blood pressure. On the other hand, both EPA and DHA significantly reduced the concentrations of C-reactive protein (CRP) ⁶². The anti-hypertensive effect exerted by EPA and DHA may be due to general downregulation in the synthesis of pro-inflammatory prostaglandins and to the inhibition of vasoconstrictor TXs ⁶³ as well as to lipid and structural changes occurring in caveolae, plasma membrane microdomains acting as regulators of vasodilatory activity of eNOS, as shown in ECs supplemented with both EPA ^64,65 and DHA alone ^66–68 or in combination with drugs (statins) ⁶⁹, suggesting that these fatty acids may favor vasodilation.

From a more clinical perspective, among the latest robust trials, the GISSI-Prevenzione study, conducted now about 25 years ago, demonstrated a striking reduction in all-cause mortality, and - particularly - sudden death in patients after an acute myocardial infarction randomly assigned to 1 g of a concentrated preparation of EPA + DHA ethyl esters or control ⁷⁰. Subsequent studies, however, did not confirm those data, and some recent, robust meta-analysis have even concluded for the absence of significant cardioprotection ^71,72, possibly due to the changed background therapies of such patients and the increased use of myocardial revascularization. As a consequence, the European Medicinal Agency (EMA) issued a statement that such preparations, at the dose of 1 g/day are ineffective in preventing the recurrence of cardiovascular events in patients after a myocardial infarction (https://www.ema.europa.eu/en/medicines/human/referrals/omega-3-acid-ethyl-esters-containing-medicinal-products-oral-use-secondary-prevention-after-myocardial-infarction). However, the recent completion of the REDUCE-IT trial has reopened the question of cardiovascular efficacy of these preparations in a more contemporary context ⁷³. The REDUCE-IT study involved 8179 patients from 11 countries who were at elevated cardiovascular risk: had a previous cardiovascular event or diabetes with one additional risk factor and had raised triglyceride levels ⁷³. All participants already taking a statin were randomized to receive either 4 g of pure EPA (icosapent ethyl, 2 g twice daily) or a placebo. The median EPA concentration in plasma was 26 μg/ml (approximatively 85 μmol/L) at the start of the study and increased to 144 μg/ml (approximatively 476 μmol/L) after one year ⁷⁴. After a median follow-up of 4.9 years, there was an approximately 25% relative risk reduction in the primary endpoint of first occurrence of a major adverse cardiovascular event - any one of cardiovascular death, nonfatal myocardial infarction, nonfatal stroke, coronary revascularization, or unstable angina requiring hospitalization - in the EPA group, which was highly significant (P < .001) ⁷³. Results from REDUCE-IT study confirm data previously obtained in the Japan EPA Lipid Intervention Study (JELIS) trial conducted on 8645 Japanese hypercholesterolemic patients ⁷⁵ randomly assigned to receive statin plus 1.8 g of EPA daily or statin therapy alone. Here the risk of major coronary events was lowered by 19% in the group that received EPA plus statin therapy compared to the control group on statin therapy alone. These data have raised the hypothesis that EPA might be, per se, more efficient in reducing the cardiovascular risk than EPA + DHA in combinations ⁷⁶. However, mechanistic data collected up to now for both EPA and DHA activities do not support such hypothesis ⁷⁷ as confirmed in a head-to-head comparison of EPA and DHA supplementation in men and women at risk of cardiovascular disease ⁷⁸. Furthermore, although the REDUCE-IT trial has been designed to evaluate a high dose of EPA (4 g/day) in patients with elevated triglycerides, the selection of a population purely on the basis of high triglycerides does not apparently explain the findings, in that an analysis reported dividing patients with higher than median and lower than median triglyceride values showed apparently similar efficacy ⁷³. Mechanisms responsible for the benefit of EPA observed in REDUCE-IT have not be not exhaustively disclosed yet. Although antiplatelet and/or anticoagulant effects, as well as membrane stabilizing effects, might also explain part of the observed benefits ⁷⁷

Role of n-3 PUFAs in pulmonary hypertension

In the context of pulmonary dysfunctions, n-3 PUFAs are likewise emerging as promising agents for promoting and preserving lung health ⁷⁹. Recent clinical data have demonstrated a relative deficiency of n-3 PUFAs, compared with n-6 PUFAs and a higher ω6/ω3 ratio in a cohort of newly diagnosed PAH patients ⁸⁰. In support of a protective role for n-3 PUFA intake in terms of pulmonary health status, low levels of DHA have been found to predict poor survival in PAH patients ⁸¹. These findings collectively suggest that n-3 PUFAs may play a role in preventing and potentially restoring pulmonary dysfunction. From a mechanistic perspective, the potential protective effects of n-3 PUFAs, including DHA, EPA and DPA and their source, fish oils, have been investigated in various PH animal models, including the MCT and hypoxia rat models ⁸² as well as in human organ culture and in vitro disease models (Table 1), providing a comprehensive, although not yet exhaustive, description of the possible mechanisms of n-3 PUFA effects. Earlier studies tested fish oils effects in MCT and hypoxia models ^83,84 with encouraging results indicating a reduction in mortality, an improvement in some hemodynamic parameters, and a reduction in pulmonary fibrosis and inflammation associated with decreased recruitment of inflammatory cell infiltrates ^83,84. Subsequent investigations confirmed the initial outcomes for DHA in both MCT- and hypoxia-models ^85,86. Notably, these studies provided additional insights, revealing specific anti-inflammatory and anti-fibrotic effects associated with DHA administration. These effects were characterized by a reduction in the activation of pro-inflammatory transcription factors NF-κB and Activator Protein (AP)-1 and even in the endoplasmic reticulum stress. This, in turn, led to a consequential decrease in the expression of pro-inflammatory genes, including COX-2 and MCP-1, alongside a parallel suppression of anti-fibrotic genes such as matrix metalloproteinases (MMPs) and interference with pro-fibrotic signaling pathways. These molecular responses were correlated with a simultaneous amelioration of right ventricular hypertrophy (RVH) and a reduction in pulmonary arteriole thickness ^85,86. The administration of DHA yielded comparable effects in hypoxia model of PH ⁸⁷ and, notably, this corrective effect extended to arterial tissues derived from patients with idiopathic PAH ⁸⁸. In close parallel to DHA, EPA administration showed a comparable protective effect in MCT models, in which this fatty acid significantly improved animal survival and RVH ⁸⁹. In addition, EPA showed significant vasodilatory and anti-inflammatory effects in inflamed human pulmonary arteries ⁹⁰; and in sheep pulmonary arteries, EPA caused vasorelaxation by increasing endothelium-mediated production of NO and inhibiting the influx of extracellular Ca²⁺ via L-type calcium channels ⁹¹. Elucidating the exact mechanisms underlying the reduction of inflammation in MCT and hypoxia models by fish oil or its specific components DHA and EPA remains a fascinating and unresolved research area. When administered exogenously, the accumulation of both DHA and EPA within membrane phospholipids induces deep modifications in membrane fluidity ⁴³. This alteration may subsequently influence the binding activities of cytokine receptors, such as those involved in the signaling pathway of TNF-α ⁹². However, the accumulation of DHA and EPA may also act through the activities of related lipid signaling derivatives ⁴⁴. Some of the sequelae associated with the development of MCT-PH appear to involve prostaglandin and/or leukotriene metabolites of AA ⁹³. Under these experimental conditions, levels of the pro-inflammatory, pro-fibrotic and chemoattractant LTB₄ are elevated in the lung ⁹⁴. In contrast, fish oil strongly decreased the production of LTB₄ in alveolar macrophages ⁹⁵ and in bronchoalveolar lavage fluid ³⁹, as well as the production of the pro-inflammatory and vasoconstrictor LTC4/D4, TXB₂ and PGE₂, while the production of 6-keto-PGF1α (the stable metabolite of PGI₂) was not completely suppressed ⁹⁵, possibly allowing the maintenance of its protective vasodilatory effect ^96,97. Among the other n-3 lipid signaling derivatives, a vasodilatory effect of 17(18) Ep-ETA, ⁹⁸, as well as of RvE1, RvD1 and RvD2 was recognized ⁹⁹. Interestingly, plasma levels of MaR1 and RvE1 (derived from DHA and EPA, respectively) are reduced in the plasma of patients with IPAH and in the lungs of experimental animal models ^100,101. Administration of RvE1 and MaR1 has been shown to improve both MCT and hypoxia PAH ^{100 101 89}, suppressed the proliferation of PASMC and restored mitochondrial function by affecting Wnt7a/β-catenin and TGFβ2 signal transduction ^89,101.

Table 1.

Effects of n-3 PUFAs administration in animal models of PH

Author, year, [ref]	PH model	n-3 PUFA tested and doses	FA concentration/variation in tissue or plasma	Results
Archer, 1989 83	Hypoxia/rat	Fish oil, 15% by weight	Lung EPA↑ by 50 times, lung DHA ↑ by 12 times; ND in plasma	↓ mPAP; ↓TXB2, 6ketoPGF1α, platelet aggregation; ↓ mortality
Baybutt, 2002 84	MCT/rat	Fish oil, 13% by weight of standard diet	Lung EPA↑ by 10 times, liver EPA ↑ by 115 times; ND in plasma	↓pneumonitis; ↓inflammatory cells; ↔ RVH
Morin, 2014 102	MCT/rat	DPA, (231 mg/kg equivalent to 3g/day)	DPA↑ by 4 times in lung and plasma	↓RVH; ↓pulmonary arterioles thickness; ↓pulmonary artery cell proliferation; ↓NF-κB and p38 MAPK activation; ↓MMP-2, MMP-9, and VEGF; ↑RvD5
Hiram, 2016 85	MCT/rat	DHA (231 mg/kg)	ND	↓RVH; ↓pulmonary arterioles thickness; ↓COX-2, HIF, STAT3; TNFα, NF-κB, C-Fos C-Jun
Chen, 2017 86	MCT/rat	DHA (100 mg/kg)	ND	↓RVH; ↓ mPAP; ↓pulmonary arterioles thickness; ↓pulmonary artery cell proliferation; ↓ ER stress; ↓ IL-1β, TNF-α, IL-6, and MCP-1; ↓inflammatory cells
Kurahara, 2020 89	MCT/rat	EPA, 1.5 g/day)	Plasma EPA↑ (≈ from 900 μM to 1200 μM)	↑ survival; ↓RVH; ↓pulmonary arterioles thickness; ↓ Src family kinase activation and vasoconstriction
Yan, 2013 87, 2013	Hypoxia/rat	DHA (100 mg/day)	ND	↓ RVSP; ↓pulmonary arterioles thickness; ↓ PASMC proliferation and migration; ↓ERK1/2 activation
Hiram, 2015 90	Inflamed human pulmonary arteries and human PASMC	EPA (resolvin E 1)	ND	↓ vasoconstriction; ↓ PASMC migration and inflammation, ↓ COX-2, NF-κB, C-Fos C-Jun, PPARγ
Nagaraj, 2016 88	Hypoxia/rat and arteries from idiopathic PAH patients	DHA (Ex-vivo, 10 μM)	ND	↓ vasoconstriction; ↓ RVSP; ↓ mPAP;

PH, pulmonary hypertension; PUFA, polyunsaturated fatty acids; DHA, docosahexaenoic acid; EPA, eicosapentaenoic acid; DPA, docosapentaenoic acid; RVH, right ventricular hypertrophy; DPA, docosapentaenoic acid; NF-κB, Nuclear Factor-κB; p38 MAPK p38 mitogen-activated protein kinases activation; ↓MMPs, metalloproteinase; VEGF, Vascular Endothelial Growth Factor; RvD5, Resolvin D5; mPAP, mean Pulmonary Arterial Pressure; ER stress, endoplasmic reticulum stress; ILs, Interleukins; TNF-α, Tumor Necrosis Factor-α; MCP-1, Monocyte Chemoattractant Protein-1; ERK, extracellular signal regulated kinase; PASMC, pulmonary artery smooth muscle cell; PAH, Pulmonary Arterial hypertension, MCT, monocrotaline; RVSP, right ventricular systolic pressure; ND, not determined.

In line with an attenuation in the pro-fibrotic and pro-inflammatory stigmata underlying PAH, recent data from our laboratory also suggest another potential role for DHA in the clinical setting of PH ¹⁰³. Specifically, using a microarray-based analytic approach, a high-throughput genomic tool that allows the simultaneous comparison of the expression level of thousands of genes in a non-biased manner, not limited by a priori assumptions ¹⁰³, we observed that exposure of human endothelial cells to the proinflammatory cytokine IL-1β increased phosphodiesterase (PDE)5 expression. Under the same experimental conditions, the addition of DHA before stimulation with the cytokine blunted PDE5 expression, suggesting an additional interference by DHA in the NO-sGC-cGMP axis ^{103 30}. In particular, our data have highlighted that in human ECs, pro-inflammatory – but not proangiogenic – stimuli increased PDE5 expression. Under such experimental conditions, DHA reduced inflammation-mediated PDE5 protein and messenger RNA expression. Furthermore, under the same experimental conditions, DHA also reduced basal and upregulated expression of TGFβ₂, another recognized player in the pathogenesis of PAH ¹⁰⁴. Finally, under the same experimental conditions, we also observed that DHA reduced the activation of the pro-inflammatory transcription factors AP-1 and NF-κB, both recognized to be activated in the lung of PAH patients ³⁵ (Fig. 2), thus reinforcing the hypothesis of a potential role of fish oils as therapeutic tools in the treatment of PAH.

Figure 2.

When incorporated into the phospholipid bilayer, n-3 PUFAs modulate cell membrane properties and control membrane ion channels mediating vasodilatory effects, increasing eNOS activity and downregulating the expression of PDE5. Also, n-3 PUFAs exert anti-inflammatory and anti-fibrotic effects by modifying pro-inflammatory and pro-fibrotic prostaglandins and leukotrienes, NF-κB, NFATc1 and TGF-β signaling. Abbreviations: NF-κB, nuclear factor-κB; NFATc1, nuclear factor of activated T cells 1; PPARs: peroxisome proliferator-activated receptor α/γ; TGF-β: transforming growth factor-β; NO, nitric oxide; eNOS, endothelial nitric oxide synthase; PDE5, phosphodiesterase type 5; sGC, soluble guanylate cyclase; cGMP, Cyclic guanosine 3′–5′ monophosphate; GTP, guanosine 5′-trisphosphate; ROS, reactive oxygen species; prostaglandins (PGs); leukotrienes (LTs).

Overall, experimental evidence indicates a promising therapeutic potential for n-3 PUFAs, with DHA and EPA demonstrating shared mechanisms that yield anti-inflammatory and anti-fibrotic effects. Based on the existing literature on animal, ex vivo and cellular models of PH (see Table 1), it is difficult to establish a significant difference in the therapeutic efficacy of EPA versus DHA. To address this, more well-designed head-to-head comparisons of EPA with DHA are needed, as such studies are currently lacking. Furthermore, to our knowledge, there are no experimental studies investigating the effect of omega-3 ALA in cell and animal models of PH. However, in a recent observational study in PH patients, levels of the ALA eicosanoid derivative 13(S)-HOTrE(γ) were shown to be associated with a lower likelihood of PH ¹⁰⁵.

Conclusions

Addressing tissue inflammation, a key factor underlying human pulmonary artery dysfunctions leading to abnormal cell proliferation and vasoconstriction, may offer a more definitive and enduring solution for PAH in addition to acute vasodilatory therapies. While the evidence on the role of n-3 PUFA deficiency in the development and progression of clinical PAH is so far limited to sparse studies, it points to a potential preventive and therapeutic role for n-3 PUFAs. Literature data support the hypothesis of anti-inflammatory properties of n-3 PUFAs, including a stimulation of the NO/sGC/cGMP axis and the interference with the production of pro-inflammatory and pro-fibrotic PGs, LTs and TXs, potentially complementing the activities of currently prescribed medications. These encouraging data suggest that n-3-PUFAs may be listed as a beneficial nutritional supplement for the chronic management of PAH. This hypothesis merits further in-depth investigation in preclinical disease models to initially assess whether n-3-PUFAs, alone or in combination with approved medications, provide a favorable therapeutic effect. Such favorable interactions also have the potential to reduce daily medication doses in the treatment of PAH.

In conclusion, considering the influence of genetic predisposition to disease development ¹⁰⁶ and the need to distinguish between responders and non-responders, our findings advocate a further exploration of the effects of n-3 PUFAs in individuals with PAH as potential adjuncts to current clinical disease management.

Data availability:

there are no new data associated with this article