Sphingolipids are present in all eukaryotic cells. The backbone of all sphingolipids is ceramide. It is composed of a long chain sphingoid base and a fatty acid residue. Complex sphingolipids contain also other residues. Ceramide is located on the crossroads of sphingolipid metabolism. It is formed either from sphingomyelin or on de novo synthesis pathway. Ceramide may be converted either back to sphingomyelin, or to ceramide1-phosphate, glucosylceramide and galactosylceramide. The first step of ceramide catabolism is its deacylation and release of free sphingosine. Sphingosine can be phosphorylated to form sphingosine-1-phosphate (1, 2). A scheme of sphingolipid metabolism including names of the enzymes is presented in Fig. 1.

Fig. 1. Schematic outline of sphingolipid metabolism. Names of the intermediates and abbreviations of the enzymes involved are included. Single arrows denote one way reactions. Double arrows indicate two-way reactions. In the latter case each direction is catalyzed by a specific enzyme. SPT – serine palmitoyltransferase; KSR – 3-keto-sphinganine reductase; CS – ceramide synthase; CD – ceramidase; DD – dihydroceramide desaturase; SM – sphingomyelinase; SMS – sphingomyelin synthase; CK – ceramide kinase; C1PP – ceramide-1-phosphate phosphatase; GCS – glucosylceramide synthase; GCD – glucosylceramidase; GaCS – galactosylceramide synthase; GaCD – galactosylceramidase; SH – sphingosine kinase; SPP – sphingoid base-1-phosphate phosphatase; S1PL – sphingosine-1-phosphate lyase.

Certain sphingolipids, mainly ceramide, sphingosine-1-phosphate, sphingosine, sphinganine and ceramide-1-phosphate exert broad biological effects (3-5). In recent years, many data have been collected indicating the role of some bioactive sphingolipids, namely sphingosine-1-phosphate, sphingosine and ceramide in cardioprotection. Sphingosine-1-phosphate (S1P) exerts very strong cardioprotective effect.


SOURCES OF SPHINGOSINE-1-PHOSPHATE IN PLASMA
Erythrocytes are the main source of S1P in the plasma. Other sources of S1P in the plasma are platelets and endothelial cells (6, 7). The concentration of S1P in human plasma ranges from 200 to 1000 nM (8-11). 50–70% of total S1P in the plasma is transported by high density lipoproteins (HDL), about 30% by albumin and <10% by low density lipoproteins (LDL) and very low density lipoproteins (VLDL) (9-11).


SPHINGOSINE-1-PHOSPHATE RECEPTORS
S1P acts in two ways, namely, inside the cells where it was formed and from the outside binding to the plasma membrane receptors. It is important to note that the extracellular S1P can bind to the receptors present on the plasma membrane both of the cells from which it was released (autocrine action) and neighboring cells (paracrine action) as well as on remote cells when carried by the blood plasma (6, 12). Five plasma membrane S1P receptors have been identified. They have been numbered from 1 to 5. Localization of the particular receptors depends on the tissue. In the heart, three receptors, namely S1P1, 2 and 3 are present (6, 13). The complex S1P-receptor acts through protein G (6, 13).


EFFECTS OF SPHINGOSINE-1-PHOSPHATE
Extracellular S1P exerts very broad effects. It activates proliferation, differentiation, angiogenesis and carcinogenesis but inhibits apoptosis. It is also involved in inflammation and immunological processes, regulation of vascular tone and permeability of vessels (12-15). It is also claimed, that the antiatherogenic effect of HDL is mediated by S1P bound to this lipoprotein fraction (7, 10). The role of the intracellular S1P has only been poorly recognized, as yet. Methodologically, it is very difficult to exclude the action of an “inside-out effect” of undetectable amounts of S1P released from the cell and bound to its S1P receptors. Also, the targets of the intracellular S1P remain uncertain. It is suggested that its action depends on place of its synthesis inside the cell. E.g. it may directly act in the nucleus and influence gene expression. Results obtained so far indicate that the intracellular S1P may release calcium independently of inositol trisphosphate, enhance cell proliferation and inhibit apoptosis independently of S1P receptors (15, 16).


ROLE OF SPHINGOSINE-1-PHOSPHATE IN CARDIOPROTECTION
So far, there are no data on a role of the intracellular S1P in cardioprotection. Therefore the results presented in this review will concern only the cardioprotective role of extracellular S1P.

Studies with isolated cardiomyocytes

The first paper on the protective role of exogenous S1P against hypoxia of isolated cardiomyocytes was published in 2001 (17). The cardiomyocytes were isolated from the heart of a neonatal (one-day old) rat and were incubated in either normoxic or hypoxic conditions. Around 90% of cardiomyocytes were viable in normoxia, whereas 61.3% of the cells survived hypoxia. Pre-incubation of cardiomyocytes with S1P preserved their viability under hypoxic conditions (17). In other studies (18, 19) cardiomyocytes isolated from mouse and rat were also exposed to hypoxia and then to normoxia (this procedure is similar to the procedure of ischemia followed by reperfusion in experiments ex vivo and in vivo; I/R). Additionally, they were exposed to a few cycles of hypoxia/normoxia (this procedure is similar to the ischemic preconditioning ex vivo or in vivo, IPC) before I/R procedure. I/R resulted in the death of 35–40% of cardiomyocytes. IPC preceding the I/R increased the viability of the cells up to 93%. S1P added to the incubation medium before I/R increased the survival of the cells to a degree similar (93.8%) to IPC. It was also shown that IPC increases releasing of S1P from cardiomyocytes into the incubation medium. These data confirmed the former (17) data on the cardioprotective role of S1P against hypoxia. They also indicate on a role of S1P in the protective effect of IPC.

Studies on isolated, perfused heart

The experiments performed on isolated, perfused mouse and rat heart provided very strong data on the cardio protective effect of S1P (20). It was shown that infusion of TNF-, ceramide and S1P reduces the infarct size after ligation of the coronary artery to similar degree as IPC. The presence of N-oleoylethanolamine, an inhibitor of ceramidase (Fig. 1) in the perfusion medium considerably reduces the protective role of IPC, TNF- and ceramide on the infarct size and left ventricular developed pressure (LVDP) after I/R. Inhibition of ceramide catabolism results, most likely, in elevation of its content in the heart. Contrary to ceramide itself, the protective effect ceramide + the inhibitor was very weak. It strongly indicates that the cardioprotective effect of TNF- was finally mediated by S1P, the product of ceramide catabolism and not by ceramide itself. Also, adding of S1P to the perfusion medium during reperfusion after ischemia increases the recovery of LVDP to over 80% of the control value and reduces the infarct size of the left ventricle to 8%. In comparison, the respective values with S1P-free perfusion medium are ~8 and ~45% (21). Lower dose of the compound was less effective (22). The results obtained on isolated, perfused mouse heart (23) were also similar to the results obtained in isolated cardiomyocytes (18). The hearts were perfused before I/R either with S1P or GM-1 (it is a ganglioside activating sphingosine kinase and increasing the content of S1P). Each compound reduced the infarct size by about 50%, accelerated the recovery of LVDP and reduced left ventricular end diastolic pressure (LVEDP). Additionally, they reduced the liberation of creatine kinase from the heart after I/R. More data on an involvement of S1P in the cardioprotection of isolated, perfused heart are presented below in the section describing a role of particular enzymes and receptors in the cardioprotection induced by S1P.


INVOLVEMENT OF PARTICULAR SPHINGOSINE-1-PHOSPHATE RECEPTORS IN CARDIOPROTECTION
As it has already been mentioned (6, 13), there exist three S1P receptors in the heart, namely S1P1, S1P2 and S1P3. It raises a question on the role of the particular receptors in the process of cardioprotection. However, the present data regarding this question are rather incomplete. In mouse, either S1P2 or S1P3 or both receptors were knocked out and the animals were subjected to I/R procedure in vivo. Knocking out only one receptor (either S1P2 or S1P3) did not affect the infarct size after I/R. However knocking out the two receptors increased the infarct size by over 50%. Knocking out S1P1 receptor is lethal at the embryonic stage of life so that S1P1 knockout mice were unavailable for the experiment (24). Theilmeier et al. (25) showed in the mice that intravenous infusion of S1P before I/R reduced the infarct size by 32-40%, depending on a dose of the compound. Knocking out of S1P3 receptor blocks this protective action of intravenous S1P on the infarct size. Another approach to study the role of S1P receptors was to use their agonists and blockers. It was shown that blockade of S1P1 and 3 receptors by means of a compound VPC23019 (VPC) markedly reduced the protective effect of both IPC and IPOST (ischemic postconditioning) on the infarct size as well on LVDP after I/R in isolated, perfused rat heart. The compound also reduced the protective effect of IPC on viability of isolated rat cardiomyocytes after in vitro I/R (19). Both unspecific S1P receptor agonist (FTY720, FTY; in the heart it binds to S1P1 and 3 receptors) and specific agonist of the S1P1 (SEW2871, SEW) exerted a protective action similar to S1P in isolated cardiomyocytes subjected to the I/R procedure. These effects of the agonists were blocked by VPC (18, 26). The results obtained with the use of agonists in isolated, perfused rat heart are somewhat puzzling. FTY added at the beginning of reperfusion, after a period of ischemia, did not influence the infarct size but accelerated recovery of LVDP, reduced the level of LVEDP and the number of apoptotic cardiomyocytes. SEW added under the same conditions did not affect either the infarct size, the hemodynamic parameters or the level of apoptosis (26). FTY introduced during reperfusion additionally accelerated the recovery of contractility of isolated human atria stripes (SEW was not studied in this case) (26). In vivo study confirmed the lack of influence of FTY on the infarct size in rat heart after I/R. It was further shown that the compound increased the mortality of the animals as a consequence of fatal arrhythmias (27). The above data indicate that the outcome of stimulation of particular S1P receptors during I/R may depend on the type of receptor. The particular receptors bind to different G proteins and it may be a reason for the differences between the effect of particular agonists (28). Certainly, much more data are needed to get broader knowledge on this topic. Nevertheless, it is clear that specific functions played by particular heart S1P receptors should be taken into account in the prospective studies.


ROLE OF ENZYMES OF SPHINGOSINE-1-PHOSPHATE METABOLISM IN CARDIOPROTECTION
The level of S1P in most cells is regulated by the activity of two enzymes: sphingosine kinase (SK) and sphingosine-1-phosphate lyase (S1PL) (Fig. 1).

Sphingosine kinase

Sphingosine kinase (SK) catalyzes the conversion of sphingosine to S1P. There are two isoforms of SK: 1 and 2. Isoform 1 prevails in the heart muscle (30). Preincubation of isolated neonatal rat cardiomyocytes with N,N-dimethylsphingosine (DMS, an inhibitor of SK) markedly increases the number of dead cardiomyocytes cultured under normoxic conditions. This action of DMS is counteracted by S1P and ganglioside GM-1, an activator of SK (17). IPC activates SK1, increases the level of S1P and reduces the infarct size after I/R in isolated, perfused mouse heart. Inhibition of SK by DMS and in consequence the inhibition of elevation in the level of S1P by IPC eliminates the beneficial effect of IPC on the infarct size as well as LVDP and LVEDP after I/R (31). In further studies, DMS used in a much lower dose showed a cardioprotective effect in isolated perfused mouse heart. This effect was absent in PKC knockout mice. It was speculated that DMS, at low dose, activates PKC which in turn activates cytosolic SK1 and increases intracellular content of S1P (32). In the isolated, perfused heart of the rat ischemia was shown to inhibit SK1 activity by 61% and it remained on this level after subsequent reperfusion. IPC reduced this drop in the enzyme activity by half and partially prevented the reduction in the S1P level in the heart after I/R. It also reduced the infarct size and accelerated the recovery of LVDP. Also, adding S1P to the perfusion medium during reperfusion improved the recovery of LVDP (22). Knocking out SK1 gene in mice reduces the viability of isolated cardiomyocytes incubated under hypoxic conditions. Also, it increases the amount of cytochrome C released from mitochondria. Adding S1P to the incubation medium under the same conditions increased the viability of cardiomyocytes obtained both from wild and SK1 knockout mice. However, the effective dose of the compound in case of cardiomyocytes obtained from the wild animals was lower than in case of cardiomyocytes obtained from SK1 knockout mice. GM-1 also increases the survival of cardiomyocytes obtained from the wild mice but it does not have an effect in cardiomyocytes obtained from the SK1 knockout mice. Both VPC and inactivation of G1 protein (by means of the pertussis toxin) eliminates the influence of GM-1. These data indicate that S1P generated by GM-1 leaves the cell and acts either in autocrine or paracrine way (33). The results obtained in isolated, perfused heart of the mouse confirmed these observations (34). Also, SK1 knockout mice did not respond to the cardioprotective impact of either IPC or IPOST during I/R studied in isolated, perfused heart (35). On the other hand, in rats, overexpression of SK1 gene attenuated the reduction in LVDP and elevation in LVEDP after ligation of the left coronary artery (36). Taken together, the data on a role of SK1 in cardioprotection clearly show that formation of S1P from sphingosine by this enzyme plays a crucial role in the process.

Sphingosine-1-phosphate lyase

Sphingosine-1-phosphate lyase (S1PL) catalyzes the irreversible breakdown of S1P (Fig. 1). Recently, the data were presented showing that S1PL is involved in cardioprotection. The experiments were carried out on isolated, perfused hearts of wild and S1PL knockout mice. Ischemia increased the activity of the enzyme in the heart of wild mice. This elevation was prevented by IPC. In the S1PL gene knockout mice, the heart S1P content was elevated compared to the controls. Knocking out the gene reduced the infarct size and accelerated the LVDP recovery after I/R. Inhibition of S1PL by means of THI (tetrahydroxybutylimidazole) additionally increased the level of S1P. It also reduced the infarct size and accelerated the recovery of LVDP after I/R. These data indicate that the reduced activity of S1PL, same as the increased activity of SK1, elevates S1P content and exerts cardioprotective action against I/R (37). It is suggested that manipulation in the activity of the two enzymes may to be a promising therapeutic target (38).


INTRACELLULAR PATHWAYS OF SPHINGOSINE-1-PHOSPHATE ACTION IN CARDIOPROTECTION
The intracellular pathways of the cardioprotective action of S1P are only poorly investigated. Available data indicates that Akt kinase plays a key role in mediating the cardioprotective action of S1P. It was shown that hypoxia itself as well as I/R activates very strongly Akt both in cultured cardiomyocytes and in isolated, perfused hearts of mice. This activation of Akt is accompanied by reduction in the number of apoptotic cardiomyocytes, reduction of infarct size, acceleration of recovery in LVDP and reduction in LVEDP in the mouse heart after I/R (18, 25, 39, 40). S1P and an antibody named 4B5.2, a selective activator of S1P1 receptor, markedly increase the activity of the enzyme in isolated mice cardiomyocytes (18, 25). Knocking out either S1P2 or S1P3 in the mice is accompanied only by a minor reduction in the activation of Akt by S1P. However, knockout of both receptors attenuates the process (25). Knocking out both receptors also blocks activation of Akt by I/R (25). Also, blockade of S1P1 receptors (by VPC at concentration of 100 nmol/l at which it does not interfere with S1P3 receptors) blocks activation of Akt by S1P in isolated mice cardiomyocytes (18). Inactivation of protein G1 (by pertussis toxin) or inhibition of PI3K (by wortmannin) blocks activation of Akt both by S1P and hypoxia (18). These data confirm the key role of S1P in activation of Akt in the process of cardioprotection. They also indicate that the ways of activation of Akt through S1P receptors are different. It is certainly due to the activation of different G proteins by particular S1P receptors (41). Hypoxia, S1P and 4B5.2 also block the elevation in the activity of glycogen synthase kinase-3ß (they cause its phosphorylation) which has protective effect on mitochondria. These data suggest the following sequence of events: activation of S1P receptors activates protein G1 which in turn activates PI3K. Activated PI3K activates Akt and inactivates glycogen synthase kinase-3ß (18). Inhibition of protein kinase C (by chelethyrine) blocks the protective action of S1P in cultured neonatal rat cardiomyocytes against hypoxia (17). Other studies showed that it is the PKC isoform of protein kinase C which is responsible for cardioprotection (23). However, knocking out PKC gene did not affect the cardioprotective impact of S1P. It indicates that S1P exerts its action independently of PKC (23). It was suggested, that the previously (17) observed effect of protein kinase C blockade by chelethyrine was a result of an unspecific action of this compound. I/R also activates ERK, JNK and p38 MAP kinases. However, removal of both S1P2 and S1P3 receptors did not affect the heart response to I/R. It indicates that the S1P receptors are not involved in the activation of the kinases by I/R (25). The data collected by Boengler et al. (42) clearly show that activation (phosphorylation) of the signal transducer and activator of transcription 3 (Stat3) exerts strong cardioprotective action against I/R injury The mechanism of Stat3 activation during I/R was elucidated by Frias et al. (43). They showed in isolated neonatal rat cardiomyocytes that S1P as well as reconstituted HDL (rHDL) enriched in S1P activates Stat3. They further showed using agonists and antagonists of different S1P receptor types that S1P activates Stat3 mainly though the S1P2 receptor. The latter data further support the role of S1P in cardioprotection and show that the compound exerts its effect not only by activation of Akt but also Stat3.


A ROLE OF OTHER BIOACTIVE SPHINGOLIPIDS IN ISCHEMIA/REPERFUSION INJURY
So far, two other sphingolipids, namely sphingosine and ceramide, were shown to be involved in I/R injury.

Sphingosine

Sphingosine (SPH) is a product of hydrolysis of ceramide and a precursor of S1P (Fig. 1). Ischemia of isolated, perfused rabbit heart as well as hypoxia of isolated cardiomyocytes obtained from an adult rat results in a several-fold elevation in the content of SPH (44). Vessey et al. (45) showed, that SPH in a high dose (5 µM) in a perfusion medium increases the infarct size after I/R in isolated, perfused rat heart. It indicates that elevation in the content of sphingosine during I/R may be cardiotoxic. However, it should be added that physiological concentration (0.4 µM) of SPH added either before ischemia or during reperfusion reduced the infarct size from over 45% to only 6% of the left ventricle. It also markedly accelerated the recovery of LVDP. However, blockade of S1P1 and 3 receptors with the VPC does not prevent the cardioprotective action of this compound (contrary to S1P) in the perfused rat heart. Also, inhibition of the PKC does not block the cardioprotective action of SPH. However, this effect is blocked by inhibition of protein kinase A or G. It clearly indicates that SPH is acting on a different pathway than S1P, namely on the pathway involving cyclic nucleotides and not the S1P receptors (45).

Ceramide

Ceramide plays very important role in the heart pathology. Accumulation of ceramide was claimed to be responsible for lipoapoptosis, cardiomyopathy and loss of myocardial function in obese rats (46). In LpLGPI mice (mice with overexpression of a glycosylphosphatidylinositol membrane- anchored form of lipoprotein lipase in cardiomyocytes) the heart ceramide content is elevated and dilated cardiomyopathy develop. Inhibition of de novo ceramide synthesis is accompanied with improved cardiac function, reduction in utilization of fatty acids, increased oxidation of glucose as well with reduced mortality (47). Myocardial ceramide metabolism is much regulated by PPAR. Cardiac-specific overexpression of this receptor in high-fat fed mice results in accumulation of ceramide in the myocardium (48). Also, in high-fat fed rats, pharmacological stimulation of PPAR (with WY-14643, a selective PPAR agonist) resulted in elevation in the content of the heart of ceramide (49). It should also be added, that the content of ceramide in myocardium of obese and diabetic human subjects did not differ from that in the lean ones. (50). It was repeatedly shown that I/R increased the concentration of ceramide in vivo in the hearts of rats and rabbits (51, 52), in the perfused rat heart (53, 54) and in isolated cardiomyocytes (55). It was also shown in isolated rat heart that I/R did not elevate each of the 14 identified ceramides but only 7 of them. The ceramides differ in the fatty acid residues (53). Biological importance of this fact has not been explained so far. Inhibition of sphingomyelinase, the enzyme which hydrolyzes sphingomyelin to ceramide (Fig. 1), reduces the increase in the content of ceramide after I/R (51, 54). Ceramide is a potent activator of apoptosis of different cell types including cardiomyocytes (3, 4, 5, 55). The elevation in the content of ceramide is accompanied by augmentation of apoptosis in the ischemic area of the isolated heart (51, 54) as well as in the hypoxic isolated cardiomyocytes (55). It suggests that elevation in the content of ceramide could contribute to the augmentation of apoptosis after I/R. IPC reduces the content of ceramide during I/R and it may add to the mechanisms of cardioprotection by IPC (54). Dear et al. (56) put forward a possibility of another mechanism of the action of ceramide. They examined the effect of IR and IPC/IR on the level of ceramide, S1P and the expression of endothelial isoform of nitric oxide synthase (eNOS) in calveolae isolated from ex vivo perfused rat heart. I/R increased several fold the content of ceramide and the expression of eNOS bound to protein named caveolin-1 and did not increase the content of S1P in the calveolae. IPC reduced the elevation in the content of ceramide and the expression of eNOS bound to caveolin-1 after I/R but elevated manifold the content of S1P in the calveolae. It would suggest that I/R inactivates the eNOS in calveolae by increasing the binding of the enzyme with calveolin 1. This binding is augmented by ceramide. Subsequently, the availability of active eNOS and as result production of nitric oxide are diminished. Reduction in the content of ceramide and elevation in the content of S1P by IPC prevents the binding of eNOS to calveolin 1 and in consequence increases the production of cardioprotective nitric oxide.


BIOACTIVE SPHINGOLIPIDS IN THE HEART INFARCT IN HUMAN BEINGS
In patients, early after the myocardial infarction the concentration of SIP in the plasma decreases by about 50% and of sphinganine-1-phosphate by about 40% whereas the concentration of ceramide, sphinganine and sphingosine remains stable. In most patients, further reduction in the concentration of S1P and sphinganine-1-phosphate was observed on the fifth day after the infarction. As already mentioned, platelets are a source of S1P. Treatment of the patients with aspirin, which has antiplatelet effect, could be at least one reason responsible for the reduction in the concentration of S1P. The reduction in the concentration of S1P in the plasma after the infarction reduces, undoubtedly, its cardioprotective action (8). To date, there are no data on a role of sphinganine-1-phosphate present in the plasma in cardioprotection.


CONCLUDING REMARKS AND FUTURE PERSPECTIVES
Sphingosine-1-phosphate (S1P) has emerged as a very powerful cardioprotective factor. Exogenous S1P increases viability of cardiomyocytes incubated under hypoxic conditions and reduces the infarct size in isolated, perfused rat heart after I/R. It also mediates the beneficial effect of pre- and post-conditioning in the heart subjected to I/R. Formation of S1P in the heart is catalyzed by the enzyme sphingosine kinase 1 and its catabolism by the enzyme sphingosine-1-phosphate lyase. Reduction in the activity of sphingosine kinase 1 or knocking out its gene eliminates cardioprotective effect of ischemic preconditioning in mice. Knocking out the sphingosine-1-phosphate lyase gene has a very potent cardioprotective effect against I/R injury in the mouse heart. It is postulated that S1P exerts its cardioprotective action by activation of Akt kinase and Stat3.

The great variety of biological effects of S1P tempted to develop specific compounds acting on the activity of SK1 or SPL or binding to particular S1P receptors with an idea to introduce them to therapy (57). So far, a compound called Fingolimod (FTY720) was shown to have strong immunomodulating properties and has been approved by US Food and Drug Administration as a drug for treatment of multiple sclerosis (58, 59). It is to believe that development new drugs mimicking the cardiprotective properties of S1P is under the way.

Conflict of interests: None declared.


REFERENCES

1. Gault CR, Obeid LM, Hannun YA. An overview of sphingolipid metabolism: from synthesis to breakdown. Adv Exp Med Biol 2010; 688: 1-23.
2. Riboni L, viani P, Bassi R, Prinetti A, Tettamanti G. The role of sphingolipids in the process of signal transduction. Prog Lipid Res 1997; 36: 153-195.
3. Gangoiti P, Camacho L, Arana L, et al. Control of metabolism and signaling of simple bioactive sphingolipids: implications in disease. Prog Lipid Res 2010; 49: 316-334.
4. Huwiler A, Kotler T, Pfeilschifter J, Sandhoff K. Physiology and pathophysiology of sphingolipid metabolism and signaling. Biochem Biophys Acta 2000; 1485: 63-69.
5. Bartke N, Hannun YA. Bioactive sphingolipids: metabolism and function. J Lipid Res 2009; 50(Suppl.): S91-S96.
6. Takabe K, Paugh SW, Milstien S, Spiegel S. ”Inside-out” signaling of sphingosine-1-phosphate: therapeutic targets. Pharmacol Rev 2008; 60: 181-195.
7. Argraves KM, Argraves WS. HDL serves as a S1P signaling platform mediating a multitude of cardiovascular effects. J Lipid Res 2007; 48: 2325-2333.
8. Knapp M, Baranowski M, Czarnowski D, et al. Plasma sphingosine-1-phosphate concentration is reduced in patients with myocardial infraction. Med Sci Monit 2009; 15: CR490-CR493.
9. Murata N, Sato K, Kon J, et al. Interaction of sphingosine 1-phosphate with plasma components, including lipoproteins, regulates the lipid-mediated actions. Biochem J 2000; 352: 809-815.
10. Sattler K, Levkau B. Sphingosine-1-phosphate as a mediator of high-density lipoprotein effects in cardiovascular protection. Cardiovasc Res 2009; 82: 201-211.
11. Zhang B, Tomura H, Kuwabara A, et al. Correlation of high density lipoprotein (HDL)-associated spingosine 1-phosphate with serum levels of HDL-cholesterol and apoproteins. Atherosclerosis 2005; 178: 199-205.
12. Alvarez SE, Milstien S, Spiegel S. Autocrine and paracrine roles of sphingosine-1- phosphate. Trends Endocr Metab 2007; 18: 300-307.
13. Means CK, Brown JH. Sphingosine-1-phosphate receptor signalling in the heart. Cardiovasc Res 2009; 82: 193-200.
14. Fyrst H, Saba JD. An update on sphingosine-1-phosphate and other sphingolipid mediators. Nat Chem Biol 2010; 6: 489-497.
15. Strub GM, Maceyka M, Hait NC, Milstien, S, Spiegel S. Extracellular and intracellular actions of sphingosine-1-phosphate. Adv Exp Med Biol 2010; 688: 141-155.
16. Spiegel S, Milstien S. Sphingosine 1-phosphate, a key cell signaling molecule. J Biol Chem 2002; 277: 25851-25854.
17. Karliner JS, Honbo N, Summers K, Gray MO, Goetzl EJ. The lysophospholipids sphingosine-1-phosphate and lysophosphatidic acid enhance survival during hypoxia in neonatal rat cardiac myocytes. J Mol Cell Cardiol 2001; 33: 1713-1717.
18. Zhang J, Honbo N, Goetzl EJ, Chatterjee K, Karliner JS, Gray MO. Signals from type 1 sphingosine 1-phosphate receptors enhance adult mouse cardiac myocyte survival during hypoxia. Am J Physiol Heart Circ Physiol 2007; 293: H3150-H3158.
19. Vessey DA, Li L, Honbo N, Karliner JS. Sphingosine 1-phosphate is an important endogenous cardioprotectant released by ischemic pre- and postconditioning. Am J Physiol Circ Physiol 2009; 297: H1429-H1435.
20. Lecour S, Smith RM, Woodward B, Opie LH, Rochette L, Sack MN. Identification of a novel role for sphingolipid signaling in TNFa and ischemic preconditioning mediated cardioprotection. J Mol Cell Cardiol 2002; 34: 509-518.
21. Vessey DA, Li L, Kelley M, Karliner JS. Combined sphingosine, S1P and ischemic postconditioning rescue the heart after protracted ischemia. Biochem Biophys Res Commun 2008; 375: 425-429.
22. Vessey DA, Kelley M, Li L, et al. Role of sphingosine kinase activity in protection of heart against ischemia reperfusion injury. Med Sci Monit 2006; 12: BR318-BR324.
23. Jin Z-Q, Zhou H-Z, Zhu P, et al. Cardioprotection mediated by sphingosine-1-phosphate and ganglioside GM-1 in wild-type and PKC epsilon knockout mouse hearts. Am J Physiol Heart Circ Physiol 2002; 282: H1970-H1977.
24. Means CK, Xiao Ch-Y, Li Z, et al. Sphingosine 1-phosphate S1P2 and S1P3 receptor-mediated Akt activation protects against in vivo myocardial ischemia-reperfusion injury. Am J Physiol Heart Circ Physiol 2007; 292: H2944-H2951.
25. Theilmeier G, Schmidt Ch, Herrmann J, et al. High-density lipoproteins and their constituent, sphingosine-1-phosphate, directly protect the heart against ischemia/reperfusion injury in vivo via the S1P3 lysophospholipid receptor. Circulation 2006; 114: 1403-1409.
26. Hofman U, Burkard N, Vogt C, et al. Protective effects of sphingosine-1-phosphate receptor agonist treatment after myocardial ischemia-reperfusion. Cardiovasc Res 2009; 83: 285-293.
27. Hofman U, Hu K, Walter F, et al. Pharmacological pre- and post-conditioning with the sphingosine-1-phosphate receptor modulator FTY720 after myocardial ischemia-reperfusion. Br J Pharmacol 2010; 160: 1243-1251.
28. Windh RT, Lee MJ, Hla T, An S, Barr AJ, Manning DR. Differential coupling of the sphingosine1-phosphate receptors Edg-1, Edg-3, and H218/Edg-5 to the Gi, Gq, and G12 families of heterotrimeric G proteins. J Biol Chem 1999; 274: 27351-27358.
29. Kennedy S, Kane KA, Pyne NJ, Pyne S. Targeting sphingosine-1-phosphate signalling for cardioprotection. Curr Opinion Pharmacol 2009; 9: 194-201.
30. Fukuda Y, Kihara A, Igarashi Y. Distribution of sphingosine kinase activity in mouse tissues: contribution of SPHK1. Biochem Biophys Res Commun 2003; 309: 155-160.
31. Jin Z-Q, Goetzl EJ, Karliner JS. Sphingosine kinase activation mediates ischemic preconditioning in murine heart. Circulation 2004; 110: 1980-1989.
32. Jin Z-Q, Karliner JS. Low dose N,N-dimethylsphingosine is cardioprotective and activates cytosolic sphingosine kinase by a PKC epsilon dependent mechanism. Cardiovasc Res 2006; 71: 725-734.
33. Tao R, Zhang J, Vessey DA, Honbo N, Karliner JS. Deletion of the sphingosine kinase-1 gene influences cell fate during hypoxia and glucose deprivation in adult mouse cardiomyocytes. Cardiovasc Res 2007; 74: 56-63.
34. Jin Z-Q, Zhang J, Huang Y, Hoover HE, Vessey DA, Karliner JS. A sphingosine kinase 1 mutation sensitizes the myocardium to ischemia/reperfusion injury. Cardiovasc Res 2007; 76: 41-50.
35. Jin Z-Q, Karliner JS, Vessey DA. Ischaemic postconditioning protects isolated mouse hearts against ischemia/reperfusion injury via sphingosine kinase isoform-1 activation. Cardiovasc Res 2008; 79: 134-140.
36. Duan HF, Wang H, Yi J, et al. Adenoviral gene transfer of sphingosine kinase 1 protects heart against ischemia/reperfusion-induced injury and attenuates its postischemic failure. Hum Gene Ther 2007; 18: 1119-1128.
37. Bandhuvula P, Honbo N, Wang G-Y, et al. S1P lyase (SPL): a novel therapeutic target for ischemia/reperfusion injury of the heart. Am J Physiol Heart Circ Physiol 2011; 300: H1753-H1761.
38. Billich A, Baumruker T. Sphingolipid metabolizing enzymes as novel therapeutic targets. Subcell Biochem 2008; 49: 487-522.
39. Fujio Y, Nguyen T, Wencker D, Kitsis RN, Walsh K. Akt promotes survival of cardiomyocytes in vitro and protects against ischemia-reperfusion injury in mouse heart. Circulation 2000; 101: 660-667.
40. Matsui T, Tao J, Monte F, et al. Akt activation preserves cardiac function and prevents injury after transient cardiac ischemia in vitro. Circulation 2001; 104: 330-335.
41. Hla T, Lee M-J, Ancellin N, Paik JH, Kluk MJ. Lysophospholipids-receptor revelations. Science 2001; 294: 1875-1878.
42. Boengler K, Hilfiker-Kleiner D, Drexler H, Heusch G, Schulz R. The myocardial JAK/STAT pathway: from protection to failure. Pharmacol Therapeut 2008; 120: 172-185.
43. Frias MA, James RW, Gerber-Wicht Ch, Lang U. Native and reconstituted HDL activate Stat3 in ventricular cardiomyocytes via ERK1/2: role of sphingosine-1-phosphate. Cardiovasc Res 2009; 82: 313-323.
44. Cavalli AM, Ligutti JA, Gellings NM, et al. The role of TNFa and sphingolipid signaling in cardiac hypoxia: evidence that cardiomyocytes release TNFa and sphingosine. Basic Appl Myol 2002; 12: 167-175.
45. Vessey DA, Li L, Kelley M, Zhang J, Karliner JS. Sphingosine can pre- and post-condition heart and utilizes a different mechanism from sphingosine 1-phosphate. J Biochem Mol Toxicol 2008; 22: 113-118.
46. Unger RH, Orci L. Lipoapotosis: its mechanism and its diseases. Biochim Biophys Acta 2002; 1585: 202-212.
47. Park T-S, Hu Y, Noh H-L, et al. Ceramide is a cardiotoxin in lipotoxic cardiomyopathy. J Lipid Res 2008; 49: 2101-2112.
48. Finck BN, Han X, Courtois M, et al. Critical role for PPAR-alpha-mediated lipotoxicity in the pathogenesis of cardiac cardiomyopathy: modulation by dietary fat content. Proc Natl Acad Sci USA 2003; 100: 1226-1231.
49. Baranowski M, Blachnio A, Zabielski P, Gorski J. PPARa agonist induces the accumulation of ceramide in the heart of rats fed high-fat diet. J Physiol Pharmacol 2007; 58: 57-72.
50. Baranowski M, Blachnio-Zabielska A, Hinrle T, et al. Myocardium of type 2 diabetic and obese patients is characterized by alterations in sphingolipid metabolic enzymes but not by accumulation of ceramide. J Lipid Res 2010; 51: 74-80.
51. Argaud L, Prigent A-F, Chalabreysse L, Loufouat J, Lagarde M, Ovize M. Ceramide in the antiapoptotic effect of ischemic preconditioning. Am J Physiol Heart Circ Physiol 2004; 286: H246-H251.
52. Zhang DX, Fryer RM, Hsu AK, Gross GJ, Campbell WB, Li P-L. Production and metabolism of ceramide in normal and ischemic-repefused myocardium of rats. Basic Res Cardiol 2001; 96: 267-274.
53. Beresewicz A, Dobrzyn A, Gorski J. Accumulation of specific ceramides in ischemic/reperfused ceramides; effect of ischemic preconditioning. J Physiol Pharmacol 2002; 53: 371-382.
54. Cui J, Engelman RM, Maulik N, Das DK. Role of ceramide in ischemic preconditioning. J Am Coll Surg 2004; 198: 770-777.
55. Bielawska AE, Shapiro JP, Jiang L, et al. Ceramide is involved in triggering of cardiomyocyte apoptosis induced by ischemia and reperfusion. Am. J Pathol 1997; 151: 1257-1263.
56. Der P, Cui J, Das DK. Role of lipid rafts in ceramide and nitric oxide signaling in the ischemic and preconditioned hearts. J Mol Cell Cardiol 2006; 40: 313-320.
57. Huwiler A, Pfeilschifter J. New players on the center stage: sphingosine 1-phosphate and its receptors as drug targets. Biochem Pharmacol 2008; 75: 1893-1900.
58. Brinkmann V, Billich A, Baumruker T, et al. Fingolimod (FTY720): discovery and development of an oral drug to treat multiple sclerosis. Nature Rev Drug Discov 2010; 9: 883-897.
59. Singer B, Ross AP, Tobias K. Oral fingolimod for the treatment of patients with relapsing forms of multiple sclerosis. Int J Clin Pract 2011; 65: 887-895.