Adenosine triphosphate (ATP) is the universal energy currency within cells. The main sources of ATP for macrophages and lymphocytes involve glucose metabolism via glycolysis and the pentose phosphate pathway (PPP). Under normal oxygen conditions, cells generate 36 ATP molecules through the citric acid cycle and oxidative phosphorylation (OXPHOS) pathway in the mitochondria. In an anaerobic environment, pyruvate is reduced as a hydrogen acceptor to lactate, resulting in a decrease in ATP production (two molecules) but an increase in ATP production rate. In the 1920s, the German scientist Warburg observed that, even in the presence of sufficient oxygen, tumour cells suppress aerobic respiration through a series of molecular mechanisms and promote efficient glycolysis reactions. This metabolic shift leads to the production of a large amount of ATP, creating a microenvironment suitable for the survival of tumour cells. This unique form of energy metabolism is known as the “Warburg effect”. In recent years, several research groups have observed that the metabolic profile of activated macrophages, induced by phagocytosis or inflammatory stimulation, undergoes reprogramming. This reprogramming involves a transition from oxidative metabolism to “Warburg metabolism” (5), enabling the rapid supply of energy required for the inflammatory process and the essential metabolic intermediates needed for biosynthesis ( Figure 1 ).

During atherosclerosis, apolipoprotein A1 (ApoA1) indirectly affects T cell responses during inflammation. ApoA1 is the major protein component of high-density lipoprotein (HDL) and is produced in hepatocytes. Before being released into the plasma, it interacts with pre-HDL particles and ATP-binding cassette transporter A1 (ABCA1), acquiring phospholipids and cholesterol to form new HDL or ABCA1 (73). The formation of pre-HDL promotes the efflux of cholesterol from cells, resulting in a reduction in plaque volume. Research has shown that treating ApoE ^−/− mice with ApoA1 increased ABCA1 expression in Treg cells and restored cholesterol levels in these cells to normal (74). The anti-inflammatory properties of ApoA1 are also associated with changes in the lipid raft composition. Lipid rafts are microdomains on the cell membrane that are rich in sphingolipids and cholesterol, serving as enriched sites for IL-2 receptors. Lipid raft components regulate immune cell signalling and proliferation. Several studies have demonstrated that ApoA1 exerts regulatory effects on cholesterol levels, IL-2 receptor expression, and IL-6 expression in Treg cells during the progression of atherosclerosis, thereby impeding the transition from exTregs to Tfh cells and ultimately reducing atherosclerosis (73, 74).

Notably, diet-induced disruption of intracellular cholesterol metabolism is a significant factor affecting the differentiation and function of Tregs in atherosclerotic lesions. Maganto-García et al. (75) found that diet-induced hypercholesterolemia promoted the differentiation and migration of Treg cells in mouse splenic and prevented atherosclerosis. The classification of fatty acids into saturated, monounsaturated, and polyunsaturated forms is determined by the saturation level of their hydrocarbon chains. They can also be categorised as short-chain (SCFAs), medium-chain, or long-chain fatty acids (LCFAs) based on their carbon chain length. Fatty acids play a crucial role in regulating specific aspects of the body’s innate immunity and cholesterol metabolism within atherosclerotic plaques. The innate immune system relies on a diverse group of pattern-recognition receptors called toll-like receptors (TLRs) (76, 77). TLR4 is highly expressed in atherosclerosis and has multiple functions. It activates cell adhesion, enhancing the uptake of oxidized lipids by macrophages and foam cell formation (78, 79). It also influences cholesterol metabolism and its impact on atherosclerosis development (80). In contrast to saturated fatty acids, polyunsaturated acids do not activate the TLR4 signalling pathway (81–83) and instead inhibit NACHT-, leucine-rich repeat (LRR)-, and pyrin domain (PYD)-containing protein 3 (NLRP3) activity (84, 85). This is significant because NLRP3 may contribute to the pathogenesis of atherosclerosis through a signalling pathway that triggers PCSK9 secretion via IL-1β stimulation (86). LCFAs and SCFAs also play different roles in arteriosclerotic lesions. LCFAs can enhance the proliferation and differentiation of Teff cells into Th1 and Th17 cells, aggravating the progression of atherosclerosis (87). Conversely, dietary SCFAs affect Treg differentiation, which in turn improves and treats autoimmune-related diseases (87, 88).

These findings suggest the potential of using fat-free ApoA1 therapy and dietary adjustments to regulate the conversion between Treg and Tfh cells, offering potential benefits to patients with atherosclerosis and other inflammatory diseases.

Although glucose is generally considered the most important nutrient for inflammatory cells, amino acid metabolism also plays a crucial role in inflammatory cell proliferation and activation. Abnormal amino acid metabolism contributes to the occurrence and development of atherosclerotic lesions (89). Relevant studies mainly focus on monocytes and macrophages, with relatively fewer studies on lymphocytes.

Glutamine is one of the most widely studied amino acids involved in inflammation. It enters cell mitochondria through amino acid transporters and is converted to glutamic acid by the action of glutaminase. It also provides nutrients for the synthesis of other amino acids and NADPH and is an important energy source (90, 91). Glutamine, a non-essential amino acid in plasma, exerts intracellular effects on macrophage polarisation. Glutamine undergoes conversion to alpha-ketoglutaric acid (α-KG) through the enzymatic actions of glutaminase (GLS) and glutamate dehydrogenase (GDH/GLUD1). α-KG plays a crucial role in the tricarboxylic acid cycle, and its deficiency disrupts normal metabolic processes, thereby promoting the polarisation of macrophages towards the M1 phenotype and enhancing pro-inflammatory cytokine secretion. Conversely, active glutamine metabolism can stimulate macrophages to polarise towards the M2 type and secrete anti-inflammatory factors (9). Activated T cells exhibit increased glutamine uptake and metabolism, similar to cancer cells (90, 92). Depletion or deficiency of glutamine can disrupt T cell activation and proliferation (92). Rapid extracellular glutamine uptake depends on the amino acid transport weight group solute carrier family 1, member 5 (Slc1a5, also known as ASCT2). In mouse immune and autoimmune models, Slc1a5 defects impair Th1 and Th17 cell differentiation and thus affect inflammatory T cell responses (93). Under these circumstances, targeted therapy with glutamine hydrolase holds promise in preclinical models of cardio-cerebral vascular disease (94).

Leucine is an essential amino acid that affects the differentiation of Teff cells. Leucine entry into activated T cells requires the involvement of the L-leucine transporter (LAT1) (95). T cells lacking LAT1 cannot differentiate into Th1 or Th17 cells, even with appropriate polarising cytokines (96). Genetic defects in the leucine sensor sestrin 2 also limit T-cell activation and differentiation (97).

There is growing evidence that tryptophan metabolism is also involved in inflammatory responses. Overexpression of aminophenamide 2,3 dioxygenase 1 (IDO1) during inflammation can drive tryptophan consumption, produce bioactive metabolites, and control the interaction between general control non-derepressible 2 and specific receptors, thereby shifting cytokine production toward an anti-inflammatory phenotype. Conversely, the ablation of IDO1 promotes the pro-inflammatory effect of immune cells. The induction of IDO1 is associated with protection against atherosclerosis and increased plaque stability (98, 99). Other studies suggest that in addition to IDO1, other enzymes involved in tryptophan degradation, such as kynurenine 3-hydroxylase, are also involved in inflammation regulation, potentially increasing the instability of atherosclerotic plaques (100).

Arginine metabolism and its byproduct, nitric oxide (NO), play crucial roles in the early stages of atherosclerosis (101), such as involvement in immunity and affect the phenotypic polarisation of macrophages (102). Under inflammatory conditions, macrophages exhibit overexpression of inducible nitric oxide synthase (iNOS), thereby promoting arginine metabolism and subsequent NO production. Elevated NO levels can impede the repolarisation process from M1 to M2 by interfering with the electron transport chain (103). Additionally, arginine inhibits T-cell proliferation and impairs their ability to migrate to related chemokines, possibly contributing to its protective effect against atherosclerosis (104) ( Table 3 ).

The formation of functional blood vessels and vascular plexuses, including processes like EC junction reorganisation, tip cell migration, stem cell proliferation, and phagocytosis (108–112), requires a substantial amount of energy in the form of ATP (108). Vascular sprouting relies on the differentiation of ECs into specialised subtypes, each with a specific function. Once the blood vessels are perfused, ECs transition into a quiescent state while being firmly anchored in the extracellular matrix. Blood vessels in which ECs germinate are regulated by genetic signalling and metabolic factors. ECs prefer to rely on glycolytic metabolism to minimise the production of ROS and rapidly produce ATP (95). Glycolytic enzymes and ATP are concentrated within the lamellar and filamentous pseudopods of ECs, facilitating their rapid motility (111).

Pfkfb3, the most prominent member of the Pfkfb family, plays a pivotal role in glycolysis by serving as the key enzyme (111). Conversely, the isozyme Pfkfb4 exhibits diminished kinase activity and can either stimulate or inhibit glycolysis (113). Signalling molecules known to induce germination in tip and stem cells, such as VEGF and FGF2 have been found to upregulate Pfkfb3 expression, subsequently promoting glycolysis. Furthermore, Pfkb3 also governs EC proliferation and influences their motility. In vitro and in vivo experiments have demonstrated that deactivating Pfkfb3 leads to reduced EC proliferation, impaired formation of filopodia/lamellipodia, and compromised directional migration, ultimately resulting in impaired vascular growth and branching in mice deficient in endothelial Pfkfb3 (114).

Alternatively, the Pfkfb3 blockade may reduce angiogenesis through other mechanisms. For example, in the context of tumour angiogenesis, lactic acid can activate HIF1α, upregulating vascular endothelial growth factor receptor 2 (VEGFR2) and promoting angiogenesis, or activate proangiogenic nuclear factors by inhibiting oxygen sensor PHD2 κB/IL-8 (115, 116). Reduced lactate levels after the Pfkfb3 blockade may inhibit angiogenesis through these mechanisms. Additionally, it has been proposed that Pfkfb3 may regulate cell proliferation through nuclear activity independent of glycolysis (117). However, further research is required to ascertain whether targeting Pfkfb3 can effectively reduce pathological angiogenesis.

Pyruvate kinases, which are involved in the production of pyruvate and ATP, are crucial for regulating glycolytic flux (109). PKM2, one of the PK isoenzymes located at the junctions of ECs expressing VE-cadherin, provides the material and energy required for promoting EC binding dynamics, migration, and proliferation through hyperactive glycolysis (118). Silencing PKM2 reduces ATP levels near EC junctions, affects the dynamics and internalisation of VE-cadherin at EC junctions, reduces the number of filopodia in endothelial tip cells, and ultimately disrupts EC junction remodelling, collective migration, and angiogenic germination.

ECs serve as gatekeepers for fatty acid transport. The fatty acids at atherosclerotic sites are associated with alterations in biophysical properties and membrane protein function within EC membranes. Polyunsaturated fatty acids not only serve as carbon sources for cultured ECs but are also regulated by ECs for transport to metabolically active tissues (119). Circulating fatty acids can be locally released from triglyceride-rich lipoproteins in the lumen of ECs via lipoprotein lipase-mediated lipolysis. Subsequently, they can enter ECs via passive diffusion or fatty acid transporters (120). The silencing or deletion of fatty acid-related genes can affect various EC functions, including migration capacity, vascular sprouting ability, and permeability regulation. Additionally, it can impact the activity of endothelial nitric oxide synthase (eNOS), leading to the production of excessive NO, an important vasodilator. Therefore, dysregulation of eNOS and excessive NO production can lead to pathological dysfunction and contribute to the progression of atherosclerosis (121).

Vascular ECs undergo different flow patterns depending on their location. For instance, the aortic arch, near the branching of the large ductal artery, and the tip of the coronary artery are exposed to oscillating shear stress known as disturbed flow (d-flow). In contrast, the larger curvature of the aorta and thoracic aorta experience high shear stress known as steady flow (s-flow). Exposure to d-flow increases the susceptibility of ECs to intima-media thickening and atherosclerosis (122). Among the numerous mechanosensitive transcription factors that differentially regulate vascular pathophysiology, our focus lies on KLF2 and YAP/TAZ.

During the development of atherosclerotic plaques, VSMCs transition from their contractile state to a more synthetic state, involving proliferation and migration from the tunica media to the intima. This phenotypic alteration is closely linked to alterations in glucose metabolism, particularly glycolysis (131). One key driver of VSMC proliferation in atherosclerosis is the upregulation of GLUT1, a glucose transporter. This upregulation results in a substantial increase (44%) in the intracellular glucose concentration within these cells (132–134). The higher glucose levels provide ample energy and lactic acid for further VSMC proliferation. Therefore, modulating glycolysis presents a promising therapeutic avenue for treating atherosclerosis.

Inhibition of the glycosylation pathway rate-limiting enzyme PKM2 leads to a decrease in extracellular and intracellular lactate production (135). Lactate dehydrogenase A (LDHA) converts pyruvate to lactic acid, which affects the survival, proliferation, migration, and invasion of human and rat aortic SMCs (133, 134). Additionally, LDHA down-regulates adenosine monophosphate-activated protein kinase (AMPK), which is involved in the vascular injury pathway. Furthermore, pyruvate can be oxidized to form acetyl-CoA by the PDH enzyme complex in the mitochondria of SMCs, entering the TCA cycle (136). Therefore, inhibition of PDK1 weakens the TCA cycle and shifts glucose metabolism from OXPHOS to glycolytic pathways (137).

In summary, the regulation of glycolysis is a key factor influencing VSMC proliferation. Additionally, VSMCs possess functional mitochondria, which not only produce energy but also provide metabolites necessary for biomass synthesis. Targeting mitochondrial complex I activity may reduce neointimal hyperplasia by inhibiting VSMC proliferation and migration (138). Furthermore, the presence of ox-LDL induces oxidative stress and ROS production in human VSMCs. High levels of ox-LDL exacerbate VSMC apoptosis, resulting in matrix and collagen loss and the thinning of the fibrous cap (139). These intricate metabolic processes play critical roles in the development of atherosclerotic plaques and offer potential therapeutic targets for intervention.

In addition to glucose, VSMCs can also derive energy from fatty acids. FAO yields a higher amount of energy compared to glucose metabolism but requires higher oxygen levels. The presence of fatty acids can impact the utilisation of glucose and glycogen in both resting and contracting VSMCs (140). During the phenotypic transformation of VSMCs, there is a decrease in glucose oxidation and an increase in FAO. This elevation in FAO may provide VSMCs with additional energy for rapid proliferation, migration, synthesis, and secretion of the extracellular matrix (141, 142). The Randall cycle plays a pivotal role in altering the preference for utilising either glucose or fatty acids as fuel sources. This shift towards increased FAO impedes the oxidation of glucose (143). The Randall cycle has been implicated in regulating oxidative metabolism in muscle tissue, adipose tissue (143, 144), and brain energy balance (145). However, its influence on VSMC metabolism remains unclear. Exploring this aspect could present an intriguing avenue for future research.

Notably, dysfunctional FAO has been observed in plaques within the carotid artery of humans (146). This impaired FAO capacity may limit the functions of VSMCs, such as proliferation and migration, which are essential for plaque stability and vascular health.

Currently, there is a growing body of research focusing on the role of amino acid metabolism in VSMCs. Glutamine, the primary non-essential amino acid in plasma, plays a pivotal role in this process. Recent findings indicate that Slc1a5 plays a pivotal role in the efficient transportation of L-glutamine, and this transport mechanism has the potential to enhance VSMC proliferation (147). Moreover, glutamine is utilised to produce glutathione (γ-glutamyl-L-cysteinylglycine, GSH), an essential component involved in combating free radicals. Within VSMCs, both reduced GSH and its oxidized form (glutathione disulfide, GSSG) play critical roles in maintaining cellular redox balance (148). Depletion of GSH and increased DNA damage have been shown to inhibit growth and induce cell death in human VSMCs (149–151). Nitric oxide, a free radical in VSMCs, induces p53 expression and triggers programmed cell death by consuming intracellular GSH, making it a potent initiator of apoptosis (152). Additionally, it impedes mitochondrial respiration by suppressing the functions of complexes I and II; thereby affecting the relaxation of vascular smooth muscle (107). Furthermore, L-arginine effectively suppresses the proliferation and migration of VSMCs, even in the absence of NOS (153–155). Tryptophan, an essential amino acid serving as a substrate for serotonin synthesis, significantly enhances both proliferative and migratory tendencies of rat VSMCs under laboratory conditions (156). Elevated cysteine levels cause inflammation, oxidative stress, and increased proliferation and migration of VSMCs (157, 158). Notably, endogenous synthesis of hydrogen sulphide (H₂S) from cysteine has protective effects on blood vessels. It inhibits NADPH oxidase, ROS production, glutathione disulfide formation, glutathione synthesis, and cysteine uptake (159, 160).

In summary, amino acid metabolism in atherosclerotic lesions affects smooth muscle proliferation and migration. These processes have profound implications for vascular health and the development of conditions such as atherosclerosis ( Figure 4 ) ( Table 4 ).

Statins exert their pharmacological effects through a multi-faceted approach. Primarily, they act on hepatocytes and inhibit the activity of HMG-CoA reductase, a critical enzyme responsible for the synthesis of mevalonate, a precursor to cholesterol. This leads to a decrease in cellular cholesterol levels. Moreover, statins promote the removal of sterol regulatory element-binding proteins (SREBPs) from the endoplasmic reticulum by inducing protease activity. SREBPs are responsible for increasing LDL receptor expression when they translocate to the cell nucleus. The decreased cholesterol levels in liver cells lead to an increase in the number of LDL receptors on their membranes, which facilitates the efficient clearance of LDL cholesterol particles from the bloodstream. Recent research suggests that statins may also enhance the expression of PCSK9, an enzyme involved in LDL receptor breakdown, potentially affecting their effectiveness in reducing LDL-C levels and preventing coronary heart disease risk (180).

Several mechanisms underlie the antioxidant properties of statins (1): Statins reduce cholesterol levels, leading to decreased lipoprotein cholesterol and oxidative substrate levels (181). (2) They inhibit superoxide production in macrophages, thereby reducing cellular oxygen production. Additionally, statins inhibit the isopentenylation process of the p21 Rac protein in ECs, thereby impeding the formation of superoxide anions (182). This preserves the functionality of the endogenous antioxidant system, counteracting LDL oxidation (183). (3) By binding with phospholipids on lipoprotein surfaces, statins obstruct the penetration of free radicals generated during oxidative stress into the core region of lipoproteins. (4) Metabolites resulting from statin usage exhibit potent antioxidant capabilities that effectively protect against lipoprotein oxidation.

Ox-LDL promotes the activation of the NLRP3 inflammasome and its receptor pathway in plaques. The first signal is triggered by pattern recognition receptors such as TLR, which activates the NF-κB pathway, leading to the transcription of NLRP3 and other pro-inflammatory cytokines. The second signal involves the oligomerisation of activated NLRP3, ultimately forming the inflammasome, which activates pro-inflammatory cytokines. Statins exert a pleiotropic effect on the NLRP3 complex. They cause a reduction in TLR agonists and inhibit the TLR4/MyD88/NF-κB pathway. Additionally, statins inhibit the NLRP3 inflammatory response via the LOX-1/NF-κB pathway (184).

The development of endothelial dysfunction due to elevated cholesterol levels is an early event in the progression of atherosclerosis. Hindered by hypercholesterolemia, the capacity of ECs to generate NO, a pivotal regulator of anti-atherosclerotic functions, is compromised. Research has demonstrated that statins effectively enhance endothelial function by reducing cholesterol levels. In 2002, Simionescu et al. (185) discovered that simvastatin alleviated the intracellular effects of LDL and restored endothelium-dependent relaxation, possibly due to increased NO synthesis. In 2018, Geng et al. (186) demonstrated that rosuvastatin protects endothelial cells in an in vitro model of human umbilical vein endothelial cells induced by ox-LDL, through its antioxidant function and up-regulation of the expression of eNOS, an endothelial protective factor. These findings confirm the advantageous impact of statins on promoting eNOS expression and preventing LDL-induced suppression of eNOS expression (187).

Furthermore, ox-LDL induces ECs to generate adhesion molecules and selective proteins, thereby facilitating immune cell infiltration into the intima. Statin therapy inhibits EC adhesion and permeability while reducing white blood cell migration, ultimately mitigating the inflammatory response within plaques (188).

Cytokines released by macrophages and lymphocytes influence endothelial function and promote SMC proliferation, collagen degradation, and thrombosis. Statins act by inhibiting the expression and activity of these cytokines in the pathogenesis of atherosclerosis. In hypercholesterolemic rabbits, atorvastatin has been demonstrated to reduce the presence of macrophages, monocyte chemoattractant protein-1 (MCP-1), and nuclear factor NF-κB activation within the intima layer (189). Moreover, statins exhibit anti-inflammatory effects on monocytes and macrophages by downregulating intercellular adhesion molecule-1 expression induced by LPS and suppressing IL-6 secretion. The presence of crystalline cholesterol is widely acknowledged in the scientific community to play a significant role in arterial inflammation. This inflammatory response occurs due to the activation of NLRP3 (or cryopyrin) inflammasomes by cholesterol, subsequently triggering caspase-1 and leading to the release of IL-1 family cytokines (190). Additionally, studies have demonstrated that statins can effectively reduce hs-CRP levels and potentially mitigate adverse events in patients, even in the absence of evident hypercholesterolemia (191).

In atherosclerotic lesions, the proliferation, migration, and invasion of SMCs into the subendothelial layer can induce intimal hyperplasia, while the secretion of collagen fibres by SMCs can influence the thickness of fibrous caps within plaques. In 2000, Bellosta et al. (192) conducted a study using both in vitro and in vivo models. The findings suggest that fluvastatin, simvastatin, lovastatin, and atorvastatin exhibit dose-dependent inhibition of SMC migration and proliferation. Chandrasekar et al. (193) demonstrated that the pro-atherosclerotic cytokine IL-18 stimulates SMC migration in an MMP9-dependent manner, and atorvastatin inhibits this process. Zhou et al. (194) established a diabetic mouse model by utilising ApoE ^-/- mice and administered atorvastatin treatment. Subsequently, they quantified SMCs and collagen composition, revealing that atorvastatin effectively reduced the number of SMCs while promoting collagen fibre synthesis. Moreover, it resulted in diminished atherosclerotic plaque area and enhanced arterial plaque stability through modulation of the RAGE pathway. However, Palomino-Morales et al. (195) demonstrated that statins effectively attenuated the activity of RhoA in SMCs, consequently leading to a reduction in collagen expression. The differences among these findings may be attributed to the different animal models used. By 2021, Jo et al. (196) conducted experiments to elucidate the mechanism underlying the inhibitory effect of statins on SMC apoptosis. Upon stimulation by ox-LDL in atherosclerotic lesions, platelet-derived growth factors induce the proliferation and migration of VSMCs. Prolonged stimulation ultimately leads to VSMC apoptosis. Statins exert their inhibitory effects by suppressing p38 activation through autophagy, thereby attenuating intracellular ROS levels and preventing apoptosis.

In summary, statins can promote the stability of atherosclerotic plaques by inhibiting the proliferation, migration, and apoptosis of SMCs and by affecting the collagen secreted by SMCs.

Hyperlipidaemia and atherosclerotic plaque formation are associated with increased platelet activation and blood hypercoagulability. Elevated LDL levels promote an increase in thromboxane A2 production, which augments platelet responsiveness. Statin treatment leads to a reduction in collagen- and fibrinogen-induced platelet aggregation and thromboxane production. In a clinical trial, Barale et al. (197) assessed the impact of simvastatin treatment on platelet aggregation response and inflammatory cytokine expression in patients with hypercholesterolemia for a duration of 2 months. The findings demonstrated that in addition to ameliorating lipid distribution, simvastatin treatment also attenuated platelet aggregation rate and reduced circulating levels of pro-inflammatory factors, endothelial markers, and platelet markers. These results indicate that statins effectively reduce lipids, inhibit platelet activation, and improve inflammation levels and EC dysfunction within atherosclerotic plaques associated with primary hypercholesterolemia ( Table 5 ).