The current clinical, biochemical and imaging parameters to monitor the progression of PAD and AAA exhibit limited predictive value and are poorly efficient. Thus, the identification of specific molecular markers able to provide both an early diagnosis during the asymptomatic stages of the disease and monitorization of disease progression after surgical intervention is imperative. Given the multifactorial nature of AAA and PAD, single biomarker determination may not fully capture the complex pathophysiological processes underlying vascular remodelling [60]. Therefore, adopting a multimarker panel could aid clinicians in decision-making regarding the management of AAA and PAD. Given the association of dyslipidaemia and altered lipid metabolism with these diseases, circulating lipids emerge as valuable targets in the quest for a molecular signature suitable for assessing and managing these conditions in clinical settings [2].

High-throughput lipidomics enables the detection of lipid variations at a molecular level, providing valuable insights into several chronic diseases [61]. Presently, clinical lipidomics has emerged as a reliable and consistent approach for understanding and identifying lipid diagnostic biomarkers and lipid therapeutic targets [62].

In this review, we aimed to gather lipidomic investigations in AAA and PAD. For that, English language publications were identified through a computerized search of PubMed database until January 2024, using the following keywords: “abdominal aortic aneurysm(s)” [MESH] OR “peripheral artery disease” [MESH] AND “lipidom*” OR “lipid profile” OR “phospholipid(s)” OR “fatty acid(s)” OR “sphingomyelin(s)” OR “ceramide(s)” OR (“spectrometry” AND “lipid”). A total of 14 papers (6 for AAA and 8 for PAD) were selected according to the eligibility criteria. Specifically, we focused on lipidomic research studies that used mass spectrometry (MS) approaches on any type of sample, excluding those that did not report the use of such approaches or were review papers. The data extracted from these studies were integrated to provide deeper insights into the pathogenesis of AAA and PAD.

Lipidome profiling in AAA

To the best of our knowledge, only six studies [63,64,65,66,67,68] applied MS-based lipidomics to study AAA in clinical settings (Table 2). These studies applied an untargeted approach using either liquid chromatography coupled with mass spectrometry (LC–MS) techniques or imaging mass spectrometry (IMS) approaches using matrix-assisted laser desorption ionization (MALDI). Lipidomic analysis was done in samples from both human and murine models of the disease. Murine models of AAA have been used for many years; however, they do not fully replicate human disease. Still, mice models can reproduce inflammation, extracellular matrix destruction and aortic dilatation, all of which are observed in human aortic aneurysms. The angiotensin II (Ang II)-induced mouse AAA model in the atherosclerotic-susceptible strain (apolipoprotein E deficient (ApoE−/−)) is the most common model to study AAA due to its simplicity and similarity to the human disease. Males are more prone to develop the disease in the setting of mild hypertension with an enhanced incidence when hyperlipidaemia is promoted [69,70,71,72]. In this model, there is a stimulation of an inflammatory response, macrophage accumulation and thrombosis [73, 74]. Nonetheless, only two lipidomic studies on AAA reported the use of the murine model of this disease (although, comparing with human samples) [63, 64].

Table 2 Main lipid variations observed in murine models of AAA and in AAA human patients reported in published lipidomic studies, available in PubMed database, using MS approachesLipidome profiling in murine models of AAA

A global lipidomic profiling of plasma samples from human AAA patients and ApoE−/− mice (Ang II-driven disease model) was performed by Xie and co-workers [63] to better understand alterations in the lipid metabolism with the disease. It was determined that the main differences between AAA and control samples resided in the behaviour of lyso-PC (LPC) class species that were found to be significantly reduced in AAA. A special reference should be made to LPC(16:0) and LPC(18:0), which were found even more reduced in samples of ruptured AAA, compared with non-rupture AAA and controls, indicating a possible role as predictive biomarkers of aneurysm rupture. This study also revealed that plasma levels of LPC are inversely correlated with AAA diameter which might indicate that the biosynthesis of LPC may be impaired in AAA patients compared to controls [63]. The results of the murine model followed the same trend as the human cohort, with significantly decreased abundances of LPC in the mice administered with Ang II. LPC are well-established pro-inflammatory molecules linked to the development of atherosclerotic plaques [75] and endothelial cell dysfunction [76], hallmarks of AAA development. The increased levels of AA in both AAA patients and mice plasma are associated with an enhancement of the pro-inflammatory prostaglandin E2 formation and inhibition of leukotriene B4 synthesis [77].

Oxidized phospholipid (OxPL) species were detected in AAA lesions of aortic tissue from male ApoE−/− mice (Ang II-driven disease model) (thrombus and AAA wall) [64]. The authors found that mice with Alox12−/− and Alox15−/− (murine isoforms of LOX) are able to generate smaller venous thrombi and bleed excessively when challenged, which were reverted by injecting OxPL into damaged tissue [78, 79]. However, they could not clearly define which OxPL molecular species are formed upon clotting, or the predominant forms that contribute to haemostasis/thrombosis: it was not reported how OxPL may interact with the coagulation factors and influence vascular inflammation. Additionally, the procoagulant role of the surface of circulating blood cells, required for haemostasis, has not been investigated in the context of human AAA. With that in mind, in this study, the authors also evaluated the lipidome of aortic tissue from humans (undergoing open AAA repair) and detected, in both human and mice samples, a significant number of OxPL species belonging to the classes of phosphatidylethanolamine (PE) and phosphatidylcholine (PC), namely hydroxyoctadecadienoic acid (HODE), hydroxydocosahexanoic acid (HDOHE) and 5-, 11-, 12- and 15-hydroxyeicosatetraenoic acid (HETE)-PL [64]. These oxidized species were not found in the aortic wall from control samples. Additionally, OxPL containing truncated PUFA were found in AAA wall and thrombi. It is most likely that OxPL deposit on the surface of the vessel wall, providing a localized surface to enable coagulation factor binding and activation. Furthermore, Alox12 and Alox15 gene products (12-LOX and 12/15-LOX) generate similar OxPL isomers in mice, specifically the abundant 12-HETE-PLs, which is in agreement with the findings of this study, suggesting these are the most likely candidates for driving AAA in the vessel wall [80,81,82]. OxPL have also been considered pro-inflammatory agents and can contribute to aggravate AAA [58, 83, 84]. Thus, this study shows that OxPL may play an important role in the development of thrombus and AAA due to their presence in both angiotensin II/ApoE mice model and human AAA tissue [64].

Lipidome profiling in human studies of AAA

AAA-associated lipid species were assessed on serum samples of AAA patients by Moxon and partners [65]. The study compared AAA patients with individuals with PAD as controls. The results showed that sphingosine 1-phosphate was significantly decreased in AAA samples compared with PAD, revealing a negative association with AAA. These results are in agreement with the findings of previous studies [85]. On the other side, AAA presented significantly higher levels of three diglycerides (DG) and seven triglycerides (TG) species, all bearing fatty acid 18:2, which were found to be positively correlated with the presence of AAA. Increased circulating TG may contribute to endothelial dysfunction through generation of ROS in patients with diabetes mellitus [86]; however, TG do not directly participate in vascular damage in PAD.

Human tissue from the aneurysmal wall was examined by MALDI imaging by Tanaka et al. [66]. to clarify the role of lipids in the pathobiology of AAA. The study revealed significantly high intensities of cholesteryl esters (CE) CE(18:1), CE(18:2), TG(52:2), TG(52:3), PC(16:0/18:0) and PC(16:0/18:1) in the aneurysmal tissue of AAA patients compared with the non-aneurysmal one. As expected, CE were identified around atherosclerotic legions. Additionally, it was found that the distribution of TG in the aneurysmal wall was similar to the distribution found in cells with morphological characteristics similar to adipocytes, revealing the potential role of adipocytes in the reduction of aortic wall strength. Thus, the authors hypothesize that local adipocytes may suffer from hypertrophy due to changes in the TG levels in tissues located in the abdominal aorta [66]. In this sense, the hypertrophic adipocytes may influence the progression of AAA.

AAA is abundantly surrounded by perivascular adipose tissue (PVAT), and its sphingolipid profile was analyzed by Folkesson and colleagues [67]. The study intended to establish a correlation between sphingolipid metabolites and pro-inflammatory factors in AAA. It was determined that C16-ceramides were strongly negatively correlated with macrophages but positively correlated with T-cell infiltration in PVAT of AAA. Moreover, sphingosine 1-phosphate was found to be positively associated with neutrophils in PVAT. It has been described that the abnormal vessel wall of AAA contains abundant immune cells [87, 88], and the results of this study serve to show that some sphingolipid species are directly associated with the pro-inflammatory state of this pathology [67].

The lipidomic signatures of the aortic media from patients with thoracic nonatherosclerotic aortic aneurysm (TNAA), thoracic atherosclerotic aortic aneurysm (TAAA) and abdominal atherosclerotic aortic aneurysm (AAAA) were determined by Saito and co-workers [68]. The study showed several findings worth mentioning. Considering TNAA, it was observed lower levels of plasmalogen PE, TG, 12- and 15-LOX metabolites and increased levels of LPC, glucosylceramides (GlcCer), prostaglandin PGD2 and 5-LOX metabolites during the development of thoracic aortic aneurysms. In TAAA, there was a significant decrease of plasmalogen PE and an increase in PC, sphingomyelin (SM), CE and TG species and prostaglandin PGD2 and 15-LOX metabolites. Regarding AAA, it was also found a reduction of plasmalogen PE and an increase of 12-LOX metabolites. LOX metabolites are usually pro-inflammatory mediators contributing to the increase of ROS generation via NADPH oxidase stimulation [89]. Plasmalogen PE are well-known endogenous antioxidants, and their reduction in the aortic media of both TAAA and AAAA may have a pivotal role in atherosclerotic aortic aneurysm development [68]. The authors concluded that the reduction of plasmalogen PE species may be associated with lower antioxidant effects contributing to enhance the oxidative stress environment generated during atherosclerotic events, thus aggravating these conditions. Additionally, the increase of prostaglandin PGD2 in the aortic media may counteract TAAA development since it has been found that the inhibition of lipocalin-type PGD2 synthase accelerates aortic lipid accumulation and development of atherosclerosis in murine models [90].

Overall, the studies previously mentioned suggest that the alterations in lipid metabolism that occur during AAA can be evaluated through plasma/tissue lipidomic analysis. Phospholipids, TG, oxylipins and products of lipid oxidation were found to be significantly modified in this disease, confirming the high impact of oxidative stress in the pathogenesis of AAA. Furthermore, besides the already reported lipid peroxidation products like MDA and 4-HNE, oxidized phospholipids may play important roles in haemostasis and vascular cell behaviour.

Lipidome profiling in PAD

Up to date and to the best of our knowledge, lipidomic analysis on PAD [91,92,93,94,95,96,97,98] was performed using gas chromatography-mass spectrometry (GC–MS) for fatty acids profiling (FA), using MALDI imaging to visualize individual molecules on tissue sections and LC–MS techniques for lipidomic signatures (Table 3). Lipidomic analysis was performed also on both murine and human samples of PAD. The human studies gathered in this review report lipidomic analysis on different types of samples.

Table 3 Main lipid variations observed in murine models of PAD and in PAD human patients reported in published lipidomic studies, available in PubMed database, using MS approachesLipidome profiling in murine models of PAD

Identification and visualization of specific lipid markers for aortic atherosclerotic lesions were made by Zaima and partners [95]. The study analyzed tissue from aortic roots of ApoE−/− mice (C57BL/6 genetic background) by IMS and identified CE(18:1), CE(18:2), PC(16:0/20:4) and PC(18:0/20:4) to be significantly increased in the atherosclerotic aortic tissue. These species were not found in nonatherosclerotic lesions, revealing an atherosclerotic site-specificity and their potential undesirable role in the formation of atherosclerotic plaques. The authors also collected perivascular adipose tissue from human patients with PAD and performed the same analysis, determining the increase of the same species found for mice samples, plus the lipid species TG(18:0/18:1/18:2). Even though TG involvement in the development of atherosclerosis remains unknown, this lipid class may play an important role in the evolution of atherosclerosis since TG deposits were found in aortic atherosclerotic lesions, while cholesterol levels were within the normal range [99].

A direct comparison of murine and human atherosclerotic plaques was performed by Khamehgir-Silz et al. to determine lipid markers able to differentiate disease progression and medication [98]. The aortic tissue of ApoE−/− mice was initially studied to identify possible lipid markers for the subsequent evaluation of human atherosclerotic vessel samples. The study found that the levels of 7 ketocholesterol CE(18:2), CE(20:4), LPC(18:2) and lyso-PE (LPE(22.0)) were significant to differentiate murine atherosclerotic tissue from the nonatherosclerotic one, being identified as ApoE-specific plaque biomarkers. Then, in the analysis of atherosclerotic vessel samples from PAD patients, the levels of cholesteryl acetate, LPE(18:0), LPC(16:1), LPC(22:5), LPC(22:6) and the glucosylated cholesterol species (Glc-cholesterol) esterified with 16:0, 16:3, 18:3 and 22:0 were identified as significant human atherosclerotic markers due to their increased abundances [98]. The dissimilarity of the markers found for mice and human samples may be explained by the fact that human vascular specimens present a more diverse patient-dependent lipid distribution, which differ from the vascular specimens derived from the monogenetic ApoE−/− mice. This could also be explained by the different stages of atherosclerosis progression that reflect in different lipid profiles. Additionally, diet, lifestyle, smoking habits [100] as well medication of the patients with cholesterol-lowering drugs [101] influence the lipid profile.

Lipidome profiling in human studies of PAD

The variation of the FA profile of the plasma of PAD patients, compared with non-disease condition, was reported by Leng and collaborators. The FA profile of the TG, PL and CE classes separated by thin-layer chromatography showed differences in the disease state [93]. In the TG fraction, it was found significantly decreased levels of AA. Eicosapentaenoic acid (C20:5, EPA) and docosahexaenoic acid (C22:6, DHA) were significantly reduced in the PL and CE fractions. The ratio between EPA and AA (EPA/AA ratio) was markedly decreased in the CE fraction. Additionally, docosapentaenoic acid (C22:5, DPA) showed considerably lower levels in the PL fraction. EPA competes with AA for COX activity, leading to the formation of different prostacyclins and thromboxanes that contribute to a more vasodilatory state with lower platelet aggregation [102]. However, the results of this study regarding a lower EPA/AA ratio in the CE fraction of PAD patients suggest that EPA is being either less produced or more oxidized in PAD, possibly due to the increased inflammatory state.

The FA alterations in the sera of PAD patients were investigated by Gautam and colleagues [94]. The results showed significantly reduced levels of C18:3 n−6, EPA, DPA, DHA, EPA/AA ratio and DHA/AA ratio in PAD, in accordance with the study of Leng et al. [93]. It was also shown that the low levels of C18:3 n−6 and EPA:AA ratio were significantly associated with the presence and advanced status of the disease [94]. Studies with C18:3 n−6 supplementation support an anti-inflammatory or immunomodulatory role of C18:3 n−6 [103, 104], a vasodilatory [105], blood pressure-lowering [106] and even an inhibitory effect on smooth muscle cell proliferation associated with the progression of atherosclerosis. Thus, the authors suggest that C18:3 n−6 may have a potential role in inflammation mediating the development of peripheral atherosclerosis.

Connecting PAD with other CVD, the study conducted by Caligiuri et al. aimed to show that higher levels of eicosanoids derived from n−6 FA increase the probability of cardiovascular and cerebrovascular events in patients with PAD [96]. They analyzed plasma samples of PAD patients who have stable angina, acute coronary syndrome (ACS), transient ischemic attacks (TIA) and cerebrovascular accidents (CVA) and assessed their relationship with plasma FA and oxylipin concentrations. The authors found that the levels of four plasma oxylipins were changed in the presence of an event. Plasma 16-hydroxyeicosatetraenoic acid (16-HETE), thromboxane B2/6 keto prostaglandin F1α (TXB2/6KPGF1α) ratio and prostaglandin E2 (PGE2) were markedly higher in PAD patients with CVA, TIA and angina, respectively. Also, 8,9-dihydroxyeicosatrienoic acid (8,9-DiHETRE) was positively correlated with ACS in PAD individuals. This study identified specific inflammatory oxylipins that may be considered potential markers/therapeutic targets of cardiovascular/cerebrovascular events [96].

The correlations between the content of marine n−3 PUFA in adipose tissue and the risk of PAD incidence were also evaluated [92]. It was found that PAD patients had lower levels of EPA, DHA and EPA + DHA and higher levels of DPA. The study showed an inverse association between the marine n−3 PUFA, EPA and DHA, as well as between the combined content of EPA + DHA in adipose tissue and the risk of PAD. Marine n−3 PUFA were found to have a protective role against atherosclerotic diseases [107,108,109]; thus, the results of this study suggest that increased levels of marine n−3 PUFA are associated with a lower risk of developing the disease [92].

As PAD is a very common comorbidity of diabetes mellitus, Muradi and his research team investigated the relationship between short-chain FA (SCFA) levels and PAD in faecal samples of patients with diabetes [91]. SCFA are produced in the gut microbiota and are known to inhibit cholesterol synthesis and the inflammatory process of atherosclerosis, thereby preventing immune cells from migrating, proliferating and producing a variety of cytokines [110]. Additionally, some studies have discovered an inverse relationship between SCFA and the size of atherosclerotic plaques [111]. In Muradi’s study, it was reported increased levels of acetate, propionate, butyrate, valerate and total SCFA in PAD patients with diabetes. It was also shown that there is a significant positive correlation between the levels of propionate, butyrate, total SCFA and blood glucose. The SCFA acetate, propionate and valerate presented likewise a significant positive correlation with the diameter of the superficial femoral artery and dorsal pedis artery and with the peak systolic velocity of the posterior tibial, popliteal, common femoral and superficial femoral arteries. On the other side, valerate revealed an inverse correlation with TG levels [91]. Acetate is known to inhibit the production of oxalate, an atherogenic mediator that increases lipid oxidation and, thus, decreases the risk of fat accumulation in peripheral arteries [112].

The plasma oxylipidome, including oxylipins and oxidized PC, was characterized by Caligiuri and colleagues from PAD patients with a history of tobacco smoking [