Ceramide is often considered a metabolic center because it is critical in sphingolipid formation and catabolism (74). It is also considered the simplest sphingolipid, consisting of a sphingosine backbone and a fatty acid chain. Ceramides are involved in various cellular processes, including inflammation, apoptosis and cell differentiation (75). De novo synthesis is one of the three metabolic pathways leading to ceramide formation controlled by ceramide synthase (76). It is generated in the endoplasmic reticulum and then transported to the Golgi (70, 77). Ceramide can be produced in the cell via the hydrolytic pathway in addition to de novo biosynthesis. Sphingomyelin is degraded into phosphocholine and ceramide by sphingomyelinase (78). Lastly, in the salvage pathway, ceramide can be synthesized from sphingosine by sphinganine N-acyltransferase (ceramide synthase) (79). Ceramide can be metabolized into complex sphingolipids (sphingomyelins and glycosphingolipids) or converted to C1P (11, 80, 81).

Sphingomyelin is the most common sphingolipid and a main component of the plasma membrane, consisting of ceramide, a polar phosphorylcholine head group, sphingosine, and a hydrophobic fatty acid chain (82, 83). Sphingomyelin synthesis involves the conversion of serine and palmitoyl-CoA to 3-ketosphinganine, which is reduced to sphinganine, acylated with a fatty acid to form dihydroceramide, desaturated to ceramide, and then converted to sphingomyelin by sphingomyelin synthase (84). Sphingomyelin synthesis mainly occurs in the Golgi apparatus and plasma membrane, and its metabolism creates several products that play major roles in the cells and participate in various signaling pathways (85). The different levels and compositions of sphingomyelin in the cell are regulated by the enzymes of its metabolic pathways, which create a balance between synthesis and degradation. The activity of these enzymes may modify various diseases that eventually bring to the degradation of sphingomyelin and the overproduction of ceramides (84). Sphingomyelin plays a significant role in the formation and maintenance of cell membranes and participates in various signaling pathways. Different fatty acid chains can create unique compositions of binding cholesterol, forming lipid rafts (86). The sphingomyelin level is crucial for cell function (84), especially in nervous tissue and red blood cells, where it contributes to the formation of myelin, acting as an electrical insulator on nerve impulses along the axon.

Glycosphingolipids are complex lipids that contain one or more sugar residues attached to the ceramide backbone, in addition to the fatty acid and sphingosine (87). They are produced in the Golgi from glucosylceramide that was transported and glycosylated by specific Golgi-resident enzymes (87–89), located mainly on the outer layer of the cell membrane where the sugar residue is exposed to the cell surface and the ceramide part is inserted in the membrane's external surface (90). Specific enzymes are responsible for the modification and addition of the various sugar molecules resulting in different structures and functions that have an essential role in cell adhesion, molecular signaling, cellular cross-talk (91), and overall membrane organization function (92, 93). However, excessive buildup of glycosphingolipids can cause a range of symptoms such as developmental delay, organ dysfunction, and neurodegeneration (94).

Two other types of sphingolipids are S1P and C1P which are involved in cell proliferation, differentiation, migration, inflammation and survival (95). S1P is produced in the plasma membrane by sphingosine kinase 1 (SphK1) and sphingosine kinase 2 (SphK2) sphingosine kinase isoenzymes by phosphorylation of sphingosine in the cell (96, 97). S1P acts as a signaling molecule by binding to five specific cell surface sphingosine-1-phosphate receptors (S1PR1-5) located on various cell types, including smooth muscle cells, immune cells, and endothelial cells. These S1RP1-5 are involved in various biological processes, such as regulating vascular tone, lymphocyte trafficking, and wound healing (98). In addition to its physiological roles, S1P has been recognized as a probable therapeutic target for several diseases, including cancer, autoimmune disorders, and cardiovascular disease (99–101). C1P is presumed to occur intracellularly through ceramide phosphorylation by CerK (77, 102, 103). Similarly to S1P, C1P functions as a signaling molecule by engaging specific cell surface receptors and is found in immune cells, epithelial cells, and smooth muscle cells (104). These specific signaling receptors regulate inflammation and immunological responses, as well as cell proliferation and survival, and have been discovered as a possible therapeutic target for diseases (105).

Inflammation leads to an increase in the production of S1P and C1P (70). While S1P can be released by activated cells as a normal response, C1P is only released when the membrane is damaged or ruptured. Therefore, C1P is considered a damage-associated molecular pattern since it rapidly and exponentially accumulated at the site of injury (106, 107). Sphingolipids are an essential family of lipids found in all eukaryotes and provide a variety of roles in cellular processes. Ceramide, sphingomyelin, glycosphingolipids, S1P, and C1P are the most frequent forms, distinguished by their chemical structure and function. Each type performs unique and vital roles in various pathways, contributing to cell function and regulation in physiological and therapeutic settings. Understanding sphingolipid metabolism and regulation is critical for treating or preventing CVDs.

Worldwide, hypertension is responsible for a significant number of premature deaths and cases of cardiovascular disease, accounting for approximately 7.5 million deaths and 57 million disability-adjusted life years (DALYS) (110). The cause-and-effect relationship between sphingolipids and hypertension is not well understood, despite several clinical and experimental studies reporting alterations in sphingolipid metabolism in hypertension diseases (108). The dysregulation of sphingolipid metabolism has been linked to hypertension, with studies demonstrating an increase in total ceramide in SHR and sphingosine levels in hypertension-induced human umbilical vein endothelial cells (HUVECs) (116, 117). Deficiency or inhibition of SphK1 and SphK2, the rate-limiting enzymes in S1P generation, led to decreased blood pressure in mice (118). SphK1 was shown to be upregulated in patients with pulmonary arterial hypertension (PAH) and its genetic deletion and pharmacologic inhibition protected against the development of hypoxia-mediated pulmonary hypertension (HPH) in mice (doi: 10.1164/rccm.201401-0121OC). In addition, SphK1 overexpression in human pulmonary artery smooth muscle cells (PASMCs) resulted in an increase of pro-inflammatory cytokines such as the interleukin family cytokine and the TNF super ligand family (DOI: 10.1007/s12013-021-01006-8) (119). Additionally, elevated levels of circulating S1P have been found to be strongly associated with high blood pressure and inflammation in human and mouse models, making it a powerful biomarker for hypertension (120). Yogi et al. (121) have found that in vascular smooth muscle cells (VSMCs) isolated from rats, S1P induces the activation of pro-inflammatory mediators, and can serve as a biomarker to identify hypertensive rats at high risk of developing cardiovascular diseases. Furthermore, the protein sortilin was found to modulate sphingolipid levels in a way that impaired endothelial function and led to hypertension through an oxidative-stress-dependent mechanism in HUVEC and mice models (and increased the infiltration of inflammatory cells in mesenteric arteries) (117).

The immune system and chronic inflammation have a significant role in the development of hypertension (122). S1P plays a significant role in the regulation of adaptive immune responses as it is crucial for lymphocyte trafficking (123, 124). S1PR1 expression on T cells and the S1P gradient, low in lymphoid organs compared to their exit sites, are required for lymphocyte egress from the thymus and from secondary lymphatic organs to the blood and lymphatic circulation. Deletion of S1PR1 in hematopoietic cells displays disturbed lymphocyte egress from the thymus and secondary lymphoid organs. Meissner et al. (125) showed that inhibition of S1PR1 caused peripheral lymphopenia and prevented the development of hypertension in mice models, thus demonstrating the protentional role of T-cells in hypertension. This study has also demonstrated that SphK2 modulates markers of endothelial activation and inflammation (such as TNF-α, IL-1β and IL-6) in the mesenteric arteries of hypertensive mice.

Atherosclerosis is an inflammatory condition that can be life-threatening and is characterized by the formation of atheromatous plaques containing cholesterol and other lipids in medium- and large-sized arteries (108). The development of the atherosclerotic lesion is associated with activated macrophages and the presence of various pro-inflammatory cytokines such as TNF-α and IL-1β in mice (126). It has also been shown that macrophages are involved in cholesterol accumulation and plaque formation and promote atherosclerosis by creating foam cells (126). ApoE knockout mice demonstrated that deletion of Akt1/Akt3 is associated with activated macrophages producing pro-inflammatory cytokines leading to the progression of atherosclerotic lesions (127–129). Activated macrophages and pro-inflammatory cytokines can trigger sphingomyelin hydrolysis and ceramide production in conjunction with oxidized low-density lipoprotein (OxLDL) promoting atherogenesis and the formation of atherosclerotic plaques (108).

Interestingly, the role of S1P and its receptors such as S1PR1 in the development of atherosclerosis is multifaceted (Figure 2). Some studies have suggested that S1P can promote atherosclerosis and some indicate that it can mitigate it. S1P can affect lymphocyte circulation, activation and plaque formation contributing to the progression of atherosclerosis in mice, and enhance the expression of adhesion molecules (130). On the contrary some studies have shown S1P suppresses the process of monocyte adhesion (131).

In addition, HDL-bound-S1P was shown to exerts anti-inflammatory effects in HUVECs (132, 133). HDL-bound-S1P was shown to inhibit inducible NO synthase (iNOS) and matrix metalloproteinase 9 (MMP9), both of which promote the inflammatory-related process of atherosclerosis in rat VSMCs (134). In addition, Feuerborn et al. (135). found that HDL-bound-S1P inhibits macrophage apoptosis by activating STAT3 and promoting surviving expression through S1PR2/S1PR3 signaling (in mice and human cell cultures). Additionally, HDL-bound-S1P boosted the formation of the S1PR1-β-arrestin 2 complex and reduced the ability of TNF-α to activate NF-κB and ICAM-1 thus reducing inflammation in HUVECs (133, 134).

Gonzalez et al. (136) have indicated that myeloid-specific S1PR1 deficiency accelerated the development of atherosclerosis as well as the necrotic core formation and the appearance of apoptotic cells within the atherosclerotic plaques of LDL receptor gene (Ldlr) deficient mice. On the contrary, S1PR1 selective agonist SEW2871 imparted the protection of macrophages from apoptotic damage through the activation of the PI3K/Akt signaling by endoplasmic reticulum (ER) stress or oxidized LDL. Studies also demonstrated that Increased plasma S1P is helpful in reducing monocyte adhesion and transport across the endothelial layer and minimizing endothelial cell permeability in human cells (137).

Studies have shown that ceramide promotes foam cell formation in mice (138), induces pro-inflammatory cytokine expression in human fibroblasts (139), promotes subendothelial infiltration of OxLDL into the vessel wall in HUVECs (140) And can act as a biomarker for atherosclerosis (Figure 2) (141). Deficiency or inhibition of neutral SMase2 lead to a reduction in atherosclerotic lesions, macrophage infiltration, and lipid deposition, as well as a reduction in IL-1β, IL-6, TNF-α and MCP-1 (monocyte chemoattractant protein-1) in Apolipoprotein E (ApoE)-null mouse models (used as a model of atherosclerosis) (Figure 2) (142). Studies have also found increased plasma concentrations of ceramides, sphingomyelins, sphinganine, and sphingosine in patients with CAD (which is caused by atherosclerosis) (143), and specific ceramide species were associated with increased thrombotic risk, adverse CAD incidents (144), and all-cause mortality, highlighting their potential as biomarkers for improving risk stratification (108, 145).

Vascular calcification refers to the deposition of calcium in the walls of blood vessels, particularly arteries. It is a process that occurs as a result of various factors, including aging, chronic inflammation, and certain medical conditions such as atherosclerosis and chronic kidney disease (146). Arterial stiffness, on the other hand, refers to the loss of elasticity or flexibility in the arterial walls, and is also associated with inflammation (147, 148). Arterial stiffness and vascular calcification frequently coincide, implying a strong association between the two. Studies have proposed that vascular calcification may have a contributory role in the development of arterial stiffness (149, 150). Both vascular calcification and arterial stiffness are associated with an increased risk of cardiovascular diseases, including coronary artery disease, stroke and myocardial infraction (151–153). Furthermore, emerging new evidence proposes a connection between sphingolipids and the development of these conditions.

Many studies researched sphingolipids’ involvement in vascular calcification. For instance, transgenic mice overexpressing SphK1 were shown to develop cardiac fibrosis and irregular calcification in the fibrotic area (154). Morris et al. (155) demonstrated that exogenous S1P elevated phosphate-induced VSMCs (isolated from bovine aortic explants) mineralization, whereas C2-ceramide (a ceramide analog) reduced the mineralization. Additionally, the mineralization and S1P levels were decreased by ceramidase and acid SMase inhibition. In the contrary, Luong et al. (156). Have reported that exogenous C2-cermaide elevated the mineralization of human aortic smooth muscle cells (HAOSMCs) which was induced by calcification medium. Bhat et al. (157). Demonstrated that lysosomal Ac (acid ceramidase) deficiency contributes to the development of AMC in the aorta and coronary arteries to smooth muscle-specific acid ceramidase gene knockout mice (Asah1^fl/fl/SM^Cre). The same group also revealed that high doses of vitamin D-induced calcification in mice with overexpression of lysosomal acid SMase, resulted in elevated aortic and coronary arterial medial calcification (AMC), and an acid SMase inhibitor decreased this calcification (158). In addition, acid SMase deficiency was shown to inhibit phosphate-induced calcification in culture, mouse model end ex vivo isolated-perfused arteries. Neutral SMase/ceramide pathway was also shown to trigger vascular calcification of human VSMCs (159).

Sphingolipids were also shown to be linked with arterial stiffness. Habibi et al. (160) has demonstrated that while Western diet (WD) increases aortic stiffness in mice models, GW4869, a neutral SMase inhibitor, suppressed the WD-induced increase in neutral SMase activation and pulse wave velocity (PWV), an arterial stiffness marker. Additionally, GW4869 attenuated the WD-induced increased mRNA expression of inflammatory molecules MCP-1, intercellular adhesion molecule 1 (ICAM-1) and vascular CAM-1 (VCAM-1). Several additional sphingolipids were associated with arterial stiffness. Metabolomics profiling among participants of the Bogalusa Heart Study has revealed that metabolites related to sphingomyelin metabolism were correlated with PWV (161). Inhibition of lactosylceramide synthase (LCS) and GCS, two enzymes involved in the synthesis of glycosphingolipids (lactosylceramide and glucosylceramide respectively) improved the PWV of ApoE−/− mice fed a high fat and cholesterol diet (162). Jung et al. (163) has also reported that lactosylceramide served as an independent indicator of elevated arterial stiffness in individuals with impaired fasting glucose.

Stroke is a major cause of mortality globally, and there is a pressing need for effective therapies for both ischemic and hemorrhagic stroke, as well as post-stroke repair. Sphingolipid activities have been found to change after stroke and are closely linked to stroke outcomes, leading to investigations on whether targeting the sphingolipid pathway could be a viable therapeutic approach for stroke (164). Several studies investigated the role of sphingolipids in stroke and cerebral injury. Following ischemic stroke, regulation of S1PR2 antagonist and knockout of S1PR2, which is involved in endothelial activation during acute vascular inflammation injury and increases pro-inflammatory cytokines (165), led to a decrease in infarct ratio and cerebral edema ratio, and better neurological scores in mice cell models of stroke (108, 166). Inhibition of SphK1, a kinase involved in S1P generation and has an essential role in regulating inflammation, also reduced infarct volumes and improved neurological deficits after stroke in mice model by reducing the expression of TRAF2 and NF-κB (108, 167). Mouse brain tissue and human patients with acute ischemic stroke showed a marked increase in long-chain ceramides and specific ceramide species, which correlated with poor functional outcomes (168). The potential use of chloroquine, which usually prevents and treats malaria, for ganglioside dysregulation prevention as a treatment for stroke was also discussed and was associated with decrease in inflammation at the site of injury in stroke-injured rats, but the efficacy of this treatment remains uncertain (108, 169).

Heart failure is a prevalent disease caused by various factors, including sphingolipids such as ceramides, which contribute to impaired cardiomyocyte function. The accumulation of ceramides in mitochondria and their increased permeability to cytochrome c can lead to apoptosis, a significant mechanism in the development and progression of cardiovascular diseases like heart failure and atherosclerosis (108). Multiple studies have highlighted the significant role that sphingolipids play in the development and progression of this condition. Further understanding of the impact of ceramides on mitochondrial function and apoptosis may lead to the development of more effective treatments for these conditions. Experimental studies in patients with heart failure have shown that there is a decrease in S1P and an increase in ceramide levels in the myocardium, which can directly affect the metabolism and function of the failing heart and inflammatory response (11). Meissner et al. (170) identified the cystic fibrosis transmembrane conductance regulator (CFTR) as a vital control site for S1P signaling in mice models. In heart failure, its TNF-α-dependent reduction underlies an increase in microvascular tone. This research shows that CFTR dysregulation could shift S1P signaling and could represent a unique and important therapeutic target for inflammatory cardiovascular diseases. Dysregulated sphingolipid metabolism genes were observed in human cardiac tissue affected by heart failure, with changes in the gene's expression involved in both the de novo and salvage pathways, which are responsible for producing a third of the ceramides in a healthy heart and are activated during inflammation (171, 172). Additionally, an extensive clinical trial involving over 4,000 adults found that higher levels of sphingomyelin and ceramide, which stimulate the production of reactive oxygen species (ROS) in endothelial cells, were associated with an increased risk of heart failure and elevated pro-inflammatory cytokines. These associations were observed independently of other factors. Conversely, higher levels of certain sphingomyelin species were linked to a lower risk of heart failure (108, 173). Inhibition of serine palmitoyltransferase (SPT) with myriocin has shown the ability to reduce adverse cardiac remodeling and improving outcomes in both mice and human studies by inhibiting the initial step of sphingolipids biosynthesis and ceramide accumulation with reduction in very long-chain ceramide species (108, 172). Low-density lipoprotein receptor knockout mice showed elevation in S1P levels that considerably decreased atherosclerosis development due to reduced recruitment of inflammatory activated macrophages and monocytes into the peritoneal cavity, leucocyte adhesion to blood capillary walls and endothelial permeability and plaque formation (174). Furthermore, the severity of heart failure was negatively correlated with plasma S1P levels in patients with ischemic heart disease reducing the inflammatory cytokines and activating reparative markers (175, 176). Additionally, SphK1/S1P/S1PR1 axis was shown to regulate the pro-inflammatory response in mice cardiomyocyte following the induction β1-adrenergic receptor (β1-AR), a chronic inflammatory process caused by myocadiac infraction (177).

Sphingolipids have been found to regulate critical cellular processes, such as inflammation, apoptosis, and oxidative stress, which are all important contributors to the development and progression of cardiovascular diseases. While significant progress has been made in recent years, there are still many unanswered questions that warrant further investigation, such as the role of specific sphingolipid species in different types of cardiovascular diseases. A better understanding of the mechanisms by which sphingolipids contribute to cardiovascular diseases could lead to the development of novel therapeutic strategies for the prevention and treatment of these diseases.

S1PR drugs target the S1PRs that are involved in the regulation of immune cell trafficking and vascular tone. Some S1PR agonists have been shown to be effective in the treatment of multiple sclerosis. They have also been studied for their potential use in the treatment of CVDs such as hypertension and heart failure (190). Fingolimod (FTY720), for instance, indirectly affects sphingolipid metabolism and ceramide synthesis (191). It was shown to prevent ischemia/reperfusion injury-associated arrhythmias in rat heart model (179), inhibit the development of cardiac hypertrophy in stress-induced hypertrophic mice (180), increase anti-inflammatory cytokines in blood concentration and diminish development of atherosclerosis in mice (178). In addition, Imeri et al. (192) showed that fingolimod and its two derivatives (ST-968 and ST-1071) reduce the expression of adhesion molecules of immune cells by activating the S1PR3-PI3K/AKT signaling pathway in human cell lines. However, other studies have shown that multiple sclerosis patients using fingolimod failed to reduce disease progression (193) or have an increased risk of cardiac events (194).

The selective S1PR1 agonist, amiselimod (MT-1303), could pose an alternative since it was shown to have a better cardiac safety profile in a clinical trial (195). Amiselimod binds immune cells inside lymph nodes in multiple sclerosis, stopping them from moving to the brain and spinal cord and creating the inflammation that drives the disease (196). However, additional investigations are required to validate its effectiveness in the treatment of CVDs. SEW2871, an additional S1PR1 selective agonist, reduced systolic blood pressure of hypertensive mice (181). In mice, SEW2817 has been also reported to have anti-inflammatory effects including reducing pro-inflammatory cytokine levels in peritoneal macrophages (197), as well as inhibiting dendritic cell chemotaxis and migration to lymph nodes in vivo (198).

In addition, S1P plasma concentrations are related to cardiovascular diseases, including heart rate change, atherosclerosis, heart failure and myocardial infarction. The S1P-lyase inhibitor, 6-[(2R)-4-(4-benzyl-7-chlorophthalazin-1-yl)-2-methylpiperazin-1-yl] pyridine-3-carbonitrile, prevents the degradation of S1P, increase S1P plasma concentrations and slow down the heart rate and consequently improve heart function in rats (189). Furthermore, it was shown to downregulate pro-inflammatory cytokines and reduce inflammatory infiltrates in IBD mice model (199). These targets may prove to be novel treatment avenue for CVDs though further research is needed.

These inhibitors are another class of sphingolipid-based drugs that have been studied for their potential use in the treatment of CVDs. Sphingosine kinase is an enzyme that is involved in the synthesis of S1P. Józefczuk et al. (182) have shown that PF543, a selective SphK1 inhibitor, improved the endothelial function of arteries of hypertensive mice. In another study, Wu et al. (200) showed that rats treated with an injection of two different concentrations of PF543 after myocardial infarction, had a reduced expression of the pro-inflammatory cytokines IL-1β, IL-6, and TNF-α. The higher concentration had a better inhibitory effect, and PF543 improved the cardiac function of rats. Shao et al. (201), on the contrary, revealed different results in Oxygen–Glucose Deprivation/Reoxygenation (OGDR)-induced cardiomyocyte injury. K6PC-5 (SphK1 activator) elevated intracellular S1P content in murine cell model and considerably hindered OGDR-induced cardiomyocyte death. Furthermore, SphK1 inhibitors, SKI-II and B-5354c (or SphK1-siRNA knockdown) aggravated OGDR-induced cytotoxicity and even reversed K6PC-5 cytoprotection in rat and murine cell lines. In addition, SKI-II was shown to produce pro-inflammatory cytokines and exacerbate atherosclerosis in low-density lipoprotein receptor-deficient mice on high cholesterol diet (202).

SphK2 antagonists ABC294640 or K-145 considerably decreased the blood pressure levels in Angiotensin-II (AngII)-induced hypertension model in mice (125). Studies have not yet revealed the anti-inflammatory effect of ABC294640 in CVDs. Nonetheless, a previous study in mice ulcerative colitis model, which is associated with an increased risk of CVDs (203), have found that ABC294640 inhibited the activation of NF-κB by TNF-α with some anti-inflammatory effect when administered in a therapeutic perspective with a better gastric safety compared to control NSAID (204). On the contrary, Ishimaru et al. (205) demonstrated that in SphK2-knockout mice, the formation of atherosclerotic lesions was exacerbated. Moreover, SphK2-deficient macrophages had increased lipid content and that could contribute to atherosclerotic plaque formation.

These intriguing and contradicting results regarding SphKs in CVDs require further research to better comprehend SphKs role.

Acid SMase is an enzyme that hydrolyzes sphingomyelin to generate ceramide, and dysregulation of acid SMase activity has been implicated in the development of atherosclerosis and other CVDs (206). Acid SMase inhibitors, such as the compound amitriptyline, have been shown in HUVEC cells to reduce endothelial inflammation and improve vascular endothelial function after preincubation with amitriptyline. The amitriptyline reduced TNF-a-induced Acid SMase/CER and MAPK activation, inhibiting TNF-induced monocyte/EC interactions while decreasing future endothelial inflammation and dysfunction which is linked to atherosclerosis. The preincubation also prevented the downregulation of endothelial nitric oxide synthase (which contributes to atherosclerosis) induced by TNF-α (183). Though, other reports are contradicting regarding the cardioprotective effect of acid SMase inhibition. In 2008, Devlin et al. (207) found that acid SMase deficient mice had reduced lipoprotein retention within early lesions of plaque formation, whereas Leger et al. (184) found that ApoE−/− mice with acid SMase overexpression did not accelerate or exacerbated lesions. Further research is needed to evaluate the efficacy and safety of acid SMase inhibitors in clinical trials.

SPT catalyzes the condensation of serine and palmitoyl CoA, the first step in the biosynthesis of numerous sphingolipids (184). Myriocin, a commonly used SPT inhibitor, was shown to inhibit atherosclerotic lesions progression, regress pre-existing plaques and lower plasma lipid levels such as ceramides and S1P in ApoE−/− mice (185, 208). In another mice therapeutic study of cystic fibrosis, myriocin was shown to reduce apoptosis and inflammation in vivo (209), and in a study conducted by the same group for myocardial reperfusion injury reduction, application of intraventricular administration of nanocarriers-myriocin in mice model during the beginning of reperfusion reduced effectively ceramide accumulation and inflammatory response (210). Though continued study is essential, myriocin and other SPT inhibitors could be potential therapeutic targets for CVDs.

Inhibition of different targets in the glycosphingolipid synthesis process has been explored as a possible therapeutic strategy for CVDs. Glucosylceramide synthase (GCS) catalyzes the first reaction of ceramide glycosylation in sphingolipid metabolism (87). Different studies were conducted examining different GSC inhibitors. Chatterjee et al. (162) demonstrated that D-thero-1-phenyl-2-decanoylamino-3-morpholino-1-propanol (D-PDMP), glucosylceramide analog, could mitigate atherosclerosis and vascular stiffness in both ApoE−/− mice. In another atherosclerosis mice study, D-PDMP was found to have anti-inflammatory properties by inhibiting ERK and NF-κB activation and have antioxidative properties as well (211). In addition, Baccam et al. (212) have shown that different GCS inhibitors protect against cardiac hypertrophy in chronic kidney disease in mouse models.

There are many more potential therapeutic targets to treat CVDs that need further investigations. One such example is sphingomyelin synthase (SMS). SMSs catalyze the final step in sphingomyelin biosynthesis. Overexpression of SMS2 (SMS homolog) was shown to promote atherogenesis and elevate plasma sphingomyelin levels in mice models (213). Additionally, inflammatory response and atherosclerotic lesions were reduced in SMS2 deficient mice (214). It's worth noting that the development of highly specific SMS2 inhibitors is crucial for effectively targeting the enzyme and avoiding cross-reactivity with less favorable homologs. The identification of SMS2 selective inhibitors, such as derivatives of 4-benzyloxybenzo[d]isoxazole-3-amine, highlights the therapeutic potential of such compounds, as a specific derivative was shown to reduce chronic inflammation in mice models (215). Ceramide synthases (CerSs) are another example. CerSs are enzymes required for both salvage pathway and de novo synthesis of ceramides and other sphingolipids (76). It was shown that CerS5 (a specific CerS) knockdown prevents induction of hypertrophic cardiomyopathy in mice model and inhibits palmitate-induced lipotoxicity in human cardiac progenitor cells (CPCs) (216, 217). In addition, CerS6 inhibition was shown to improve diabetes and obesity indexes in humans (218), thus posing a potential target for cardioprotective approaches. Another potential target is dihydroceramide desaturase (DES), an enzyme that catalyzes the final step in de novo ceramide synthesis (219). Heterozygous deletion of the dominant isoform DES1 has been found to avert diet-induced hypertension and vascular dysfunction in mice and reduce the expression of NF-κB in cells isolated from rats (220). Furthermore, CIN038, a selective DES1 inhibitor has been demonstrated to reduce hypertrophy in neonatal rat cardiomyocytes by effecting protein-bound uremic toxins which mediate sphingolipid imbalance and inflammatory responses in heart and kidney cells (187). Fenretinide, another DES1 inhibitor has been found to mitigate the plasma lipid levels mitigate in obese mice thus potentially alleviating diet-induced dyslipidemia (188). In addition, fenretinide has been found to inhibit LPS-induced pro-inflammatory cytokines secretion in mice macrophages cell line and decrease systolic pressure of spontaneously hypertensive rats (SHR) (221). Further studies are needed to better understand DES1's role.

In addition, there are several FDA-approved drugs that are used to treat various conditions and do not directly target sphingolipids metabolism or signaling pathways, while still having cardioprotective properties. Some of these drugs have been shown to reduce ceramide levels, providing a potential therapeutic approach for CVDs. Empagliflozin is a sodium-glucose transport protein 2 (SGLT2) inhibitor used for type 2 diabetes, that was shown to reduce the content of sphingomyelin and ceramide in the heart of type 2 diabetic rats (222). SGLT2 inhibition with empagliflozin, also affects cardiac inflammation by reducing cardiac mRNA levels of IL-6 and TNF-α in rats. In addition, empagliflozin reduces the risk of cardiovascular death or heart failure hospitalization in patients with heart failure, and improves clinical outcomes in these patients (223, 224). Further research is needed to elucidate whether empagliflozin's effect on CVDs is linked to ceramide inhibition.

Although there are currently no CVD drugs directly composed of sphingolipids, several classes of sphingolipid-based drugs are being developed, targeting different pathways involved in sphingolipid metabolism or signaling. These drugs can be grouped based on their targets such as S1PR agonists, sphingosine kinase inhibitors/agonists, acid sphingomyelinase inhibitors, serine palmitoyl transferase inhibitors, glycosphingolipid synthesis inhibitors, and sphingomyelin synthase inhibitors. Various studies indicate the potential of these drugs as therapeutic targets for CVDs, although further research and clinical trials are needed to validate their efficacy and safety.