Transient relaxation of rat mesenteric microvessels by ceramides

Metabolic profiling reveals new serum signatures to discriminate lupus nephritis from systemic lupus erythematosus

Background

Lupus nephritis (LN) occurs in 50% of patients with systemic lupus erythematosus (SLE), causing considerable morbidity and even mortality. Previous studies had shown the potential of metabolic profiling in the diagnosis of SLE or LN. However, few metabonomics studies have attempted to distinguish SLE from LN based on metabolic changes. The current study was designed to find new candidate serum signatures that could differentiate LN from SLE patients using a non-targeted metabonomics method based on ultra high performance liquid chromatography tandem mass spectrometry (UPLC-MS/MS).

Method

Metabolic profiling of sera obtained from 21 healthy controls, 52 SLE patients and 43 LN patients. We used SPSS 25.0 for statistical analysis. Principal component analysis (PCA), partial least squares discriminant analysis (PLS-DA) and metabolic pathway analysis were used to analyze the metabolic data.

Results

Upon comparison of SLE and LN groups, 28 differential metabolites were detected, the majority of which were lipids and amino acids. Glycerolphospholipid metabolism, pentose and glucuronate interconversions and porphyrin and chlorophyll metabolism were obviously enriched in LN patients versus those with SLE. Among the 28 characteristic metabolites, five key serum metabolites including SM d34:2, DG (18:3(9Z,12Z,15Z)/20:5(5Z,8Z,11Z,14Z,17Z)/0:0), nervonic acid, Cer-NS d27:4, and PC (18:3(6Z,9Z,12Z)/18:3(6Z,9Z,12Z) performed higher diagnostic performance in discriminating LN from SLE (all AUC > 0.75). Moreover, combined analysis of neuritic acid, C1q, and CysC (AUC = 0.916) produced the best combined diagnosis.

Conclusion

This study identified five serum metabolites that are potential indicators for the differential diagnosis of SLE and LN. Glycerolphospholipid metabolism may play an important role in the development of SLE to LN. The metabolites we screened can provide more references for the diagnosis of LN and more support for the pathophysiological study of SLE progressed to LN.

Protective effects and mechanisms of Rehmannia glutinosa leaves total glycoside on early kidney injury in db/db mice

The spontaneous db/db mice were used to elucidate the biological effects and mechanisms of Rehmannia glutinosa leaves total glycoside (DHY) on kidney injury through biochemical indicators, kidney pathological section analysis, metabolic profiling, intestinal flora analysis and in vitro Human renal tubular epithelial (HK-2) cell model induced by high glucose. It was found that DHY can decrease the blood sugar level (insulin, INS; fasting blood glucose, FBG), blood lipid level (Total Cholesterol, T-CHO; Triglyceride, TG) significantly and improve kidney injury level (blood urea nitrogen, BUN; urine microalbumin, mALB; serum creatinine, Scr). It can also alleviate kidney tubular epithelial cell oedema and reduce interstitial connective tissue hyperplasia of the injury kidney induced by high glucose. 13 endogenous metabolites were identified in serum, which involved of ether lipid metabolism, sphingolipid metabolism, glyoxylic acid and dicarboxylic acid metabolism and arachidonic acid metabolism. High glucose can also lead to the disorder of intestinal flora, especially Firmicutes and Bacteroides. Meanwhile, DHY also inhibited the expression of α-SMA, TGF- β1, Smad3 and Smad4 in the kidney tissues of db/db mice and HK-2 cells. To sum up, DHY may restore the dysfunctional intestinal flora to normal and regulate glycolipid level of db/db mice as well as TGF-β/Smad signalling pathway regulation to improve early kidney damage caused by diabetes.

Ceramide and Regulation of Vascular Tone

In addition to playing a role as a structural component of cellular membranes, ceramide is now clearly recognized as a bioactive lipid implicated in a variety of physiological functions. This review aims to provide updated information on the role of ceramide in the regulation of vascular tone. Ceramide may induce vasodilator or vasoconstrictor effects by interacting with several signaling pathways in endothelial and smooth muscle cells. There is a clear, albeit complex, interaction between ceramide and redox signaling. In fact, reactive oxygen species (ROS) activate different ceramide generating pathways and, conversely, ceramide is known to increase ROS production. In recent years, ceramide has emerged as a novel key player in oxygen sensing in vascular cells and mediating vascular responses of crucial physiological relevance such as hypoxic pulmonary vasoconstriction (HPV) or normoxic ductus arteriosus constriction. Likewise, a growing body of evidence over the last years suggests that exaggerated production of vascular ceramide may have detrimental effects in a number of pathological processes including cardiovascular and lung diseases.

Decreased serum concentrations of sphingosine-1-phosphate in sepsis

Introduction

Sphingosine-1-phosphate (S1P) is a signaling lipid that regulates pathophysiological processes involved in sepsis progression, including endothelial permeability, cytokine release, and vascular tone. The aim of this study was to investigate whether serum-S1P concentrations are associated with disease severity in patients with sepsis.

Methods

This single-center prospective-observational study includes 100 patients with systemic inflammatory response syndrome (SIRS) plus infection (n = 40), severe sepsis (n = 30), or septic shock (n = 30) and 214 healthy blood donors as controls. Serum-S1P was measured by mass spectrometry. Blood parameters, including C-reactive protein (CRP), procalcitonin (PCT), interleukin-6 (IL-6), lactate, and white blood cells (WBCs), were determined by routine assays. The Sequential Organ Failure Assessment (SOFA) score was generated and used to evaluate disease severity.

Results

Serum-S1P concentrations were lower in patients than in controls (P < 0.01), and the greatest difference was between the control and the septic shock groups (P < 0.01). Serum-S1P levels were inversely correlated with disease severity as determined by the SOFA score (P < 0.01) as well as with IL-6, PCT, CRP, creatinine, lactate, and fluid balance. A receiver operating characteristic analysis for the presence or absence of septic shock revealed equally high sensitivity and specificity for S1P compared with the SOFA score. In a multivariate logistic regression model calculated for prediction of septic shock, S1P emerged as the strongest predictor (P < 0.001).

Conclusions

In patients with sepsis, serum-S1P levels are dramatically decreased and are inversely associated with disease severity. Since S1P is a potent regulator of endothelial integrity, low S1P levels may contribute to capillary leakage, impaired tissue perfusion, and organ failure in sepsis.

Involvement of neutral sphingomyelinase in the angiotensin II signaling pathway

The possibility that angiotensin II (ANG II) exerts its effects through the activation of neutral sphingomyelinase (nSMase) has not been tested in kidneys. The results of the present study provide evidence for the activity and expression of nSMase in rat kidneys. In isolated perfused rat kidney, ANG II-induced renal vasoconstriction was inhibited by GW4869, an inhibitor of nSMase. We used nSMase for investigating the signal transduction downstream of ceramide. nSMase constricted the renal vasculature. An inhibitor of ceramidase (CDase), N-oleoylethanolamine (OEA), enhanced either ANG II- or nSMase-induced renal vasoconstriction. To demonstrate the interaction between the nSMase and cytosolic phospholipase A2 (cPLA2) signal transduction pathways, we evaluated the response to nSMase in the presence and absence of inhibitors of arachidonic acid (AA) metabolism: arachidonyl trifluoromethyl ketone (AACOCF3), an inhibitor of cPLA2; 5,8,11,14-eicosatetraynoic acid (ETYA), an inhibitor of all AA pathways; indomethacin, an inhibitor of cyclooxygenase (COX); furegrelate, a thromboxane A2 (TxA2)-synthase inhibitor; and SQ29548 , a TxA2-receptor antagonist. In these experiments, the nSMase-induced renal vasoconstriction decreased. ANG II or nSMase was associated with an increase in the release of thromboxane B2 (TxB2) in the renal perfusate of isolated perfused rat kidney. In addition, the coexpression of the ceramide with cPLA2, was found in the smooth muscle layer of intrarenal vessels. Our results suggest that ANG II stimulates ceramide formation via the activation of nSMase; thus ceramide may indirectly regulate vasoactive processes that modulate the activity of cPLA2 and the release of TxA2.

Vascular effects of sphingolipids

The sphingomyelin metabolites ceramide, sphingosine 1-phosphate (S1P) and sphingosylphosphorylcholine (SPC) are emerging modulators of vascular tone. While ceramide appears to act primarily intracellularly, S1P and SPC appear to mainly work via specific receptors, although those for SPC have not yet been defined unequivocally. Each of the sphingomyelin metabolites can induce both vasoconstriction and vasodilatation and, in some cases--ceramide on the one hand, and S1P and SPC on the other hand--have opposite effects on vascular tone. The differences in effects between vessels may relate to the relative roles of endothelial and smooth muscle cells in mediating them, as well as to the distinct expression patterns of S1P receptors among vascular beds and among endothelial and smooth muscle cells. Recent evidence suggests that vascular tone is not only modulated by sphingomyelin metabolites which are exogenously added or reach the vessel wall via the bloodstream but also by those formed locally by cells in the vessel wall. Such local formation can be induced by known vasoactive agents such as angiotensin II and may serve a signalling function.

CONCLUSION

We conclude that sphingomyelin metabolites are important endogenous modulators of vascular function, which may contribute to the pathophysiology of some diseases and be targets for therapeutic interventions.

Sphingosine kinase-dependent activation of endothelial nitric oxide synthase by angiotensin II

OBJECTIVE

In addition to their role in programmed cell death, cell survival, and cell growth, sphingolipid metabolites such as ceramide, sphingosine, and sphingosine-1-phosphate have vasoactive properties. Besides their occurrence in blood, they can also be formed locally in the vascular wall itself in response to external stimuli. This study was performed to investigate whether vasoactive compounds modulate sphingolipid metabolism in the vascular wall and how this might contribute to the vascular responses.

METHODS AND RESULTS

In isolated rat carotid arteries, the contractile responses to angiotensin II are enhanced by the sphingosine kinase inhibitor dimethylsphingosine. Endothelium removal or NO synthase inhibition by N(omega)-nitro-L-arginine results in a similar enhancement. Angiotensin II concentration-dependently induces NO production in an endothelial cell line, which can be diminished by dimethylsphingosine. Using immunoblotting and intracellular calcium measurements, we demonstrate that this sphingosine kinase-dependent endothelial NO synthase activation is mediated via both phosphatidylinositol 3-kinase/Akt and calcium-dependent pathways.

CONCLUSIONS

Angiotensin II induces a sphingosine kinase-dependent activation of endothelial NO synthase, which partially counteracts the contractile responses in isolated artery preparations. This pathway may be of importance under pathological circumstances with reduced NO bioavailability. Moreover, a disturbed sphingolipid metabolism in the vascular wall may lead to reduced NO bioavailability and endothelial dysfunction.

C2-ceramide induces vasodilation in phenylephrine-induced pre-contracted rat thoracic aorta: role of RhoA/Rho-kinase and intracellular Ca2+ concentration

It is known that ceramide may play an important regulatory role in vascular tone although its effect on vascular tone and the mechanisms involved are controversial. The present study was designed to investigate the effects of ceramide and its key initial regulators, TNF-alpha and neutral sphingomyelinase (SMase), on vascular tone of isolated rat thoracic aortic rings and elucidate the mechanisms involved in the changes in vascular tone induced by ceramide. Contractile responses and Fura-2 Ca2+ signals were measured in rat thoracic aortic rings or strips. 10(-5) M C2-ceramide, 0.1 U/ml neutral sphingomyelinase (SMase), and 5x10(-7) g/ml TNF-alpha had no effect on resting tone in rat thoracic aortic rings. However, in phenylephrine-induced pre-contracted rings, treatment with ceramide, SMase, and TNF-alpha evoked a gradual but sustained vasodilation. Vasodilation effect in response to 10(-5) M C2-ceramide was not significantly changed by the absence or presence of endothelium, a cyclooxygenase pathway inhibitor (10(-6) M indomethacin), or PKC inhibitors (10(-5) M H-7 & 5x10(-7) M calphostin-C). Pretreatment with 1 microM Y-27632, a RhoA/Rho-kinase inhibitor, significantly inhibited the phenylephrine-induced contraction itself as well as the C2-ceramide-induced vasodilation. Pre-treatment with 10(-5) M C2-ceramide had no effect on phasic rise in [Ca2+]i and tension evoked by stimulation with 10(-8) M phenylephrine, but post-treatment of C2-ceramide significantly reduced the phenylephrine-induced secondary tonic [Ca2+]i and tension plateau. Our results indicate that C2-ceramide induces vasodilation in phenylephrine-induced pre-contracted rat thoracic aorta. Furthermore, inhibition of phenylephrine-induced activation of RhoA/Rho-kinase pathway as well as phenylephrine-induced elevations in [Ca2+]i are clearly a key factors in C2-ceramide-induced vasodilation.

Involvement of cyclic AMP-dependent and -independent mechanisms in the relaxation of rat detrusor muscle via beta-adrenoceptors

We investigated the cAMP-dependent and -independent mechanisms of relaxation via beta-adrenoceptor in rat detrusor muscle with and without pre-contraction. A microdialysis technique was used to measure detrusor tension and cAMP level on the same detrusor tissue. In non-contracted tissue, isoproterenol, clenbuterol (beta2-adrenoceptor agonist) and FR165101, ((8S)-8-{[(2R)-2-(3-chlorophenyl)-2-hydroxyethyl]amino}-6,7,8,9-tetrahydro-5H-benzocyclohepten-2-yl)oxy]acetic acid hydrochloride (beta3-adrenoceptor agonist) relaxed detrusor muscle and cAMP levels also increased in a concentration dependent manner. SQ22536 (adenylyl cyclase inhibitor) markedly suppressed relaxation, suggesting that beta-adrenoceptor-mediated relaxation may be attributed mainly to cAMP-dependent mechanism. In high K+ pre-contracted tissue, although relaxation advanced in a concentration dependent manner, cAMP production reached a plateau at concentrations of more than 10(-7) M. SQ22536 had only a small inhibitory effect. However, large-conductance, Ca2+-activated K+ (BK(Ca)) channel inhibitors, charybdotoxin and iberiotoxin markedly suppressed relaxation. These results suggest that in addition to cAMP-dependent pathway, BK(Ca) channels are involved in the beta-adrenoceptor agonists-induced relaxation in pre-contracted detrusor muscle.

Does cyclic AMP mediate rat urinary bladder relaxation by isoproterenol?

Cyclic AMP is the prototypical second messenger of beta-adrenergic receptors, but recent findings have questioned its role in mediating smooth muscle relaxation upon beta-adrenergic receptor stimulation. We have investigated the signaling mechanisms underlying beta-adrenergic receptor-mediated relaxation of rat urinary bladder. Concentration-response curves for isoproterenol-induced bladder relaxation were generated in the presence or absence of inhibitors, with concomitant experiments using passive tension and KCl-induced precontraction. The adenylyl cyclase inhibitor 9-(tetrahydro-2-furanyl)-9H-purin-6-amine (SQ 22,536; 1 microM), the protein kinase A inhibitors 1-(5-isoquinolinesulfonyl)-2-methylpiperazine (H7; 10 microM), N-[2-(p-bromocinnamylamino)ethyl]-5-isoquinolinesulfonamide (H89; 1 microM), and Rp-adenosine 3',5'-cyclic monophosphorothioate (Rp-cAMPS; 30 microM), and the guanylyl cyclase inhibitor 1H-[1,2,4]oxadiazolo-[4,3-a]quinoxalin-1-one (ODQ; 3 microM) produced only minor if any inhibition of relaxation against passive tension or KCl-induced precontraction. Among various potassium channel inhibitors, BaCl2 (10 microM), tetraethylammonium (3 microM), apamin (300 nM), and glibenclamide (10 microM) did not inhibit isoproterenol-induced relaxation. Some inhibition of the isoproterenol effects against KCl-induced tone but not against passive tension was seen with inhibitors of calcium-dependent potassium channels such as charybdotoxin and iberiotoxin (30 nM each). A combination of SQ 22,536 and ODQ significantly inhibited relaxation against passive tension by about half, but not that against KCl-induced tone. Moreover, the combination failed to enhance inhibition by charybdotoxin against KCl-induced tone. We conclude that cAMP and cGMP each play a minor role in beta-adrenergic receptor-mediated relaxation against passive tension, and calcium-dependent potassium channels play a minor role against active tension.

Cardiovascular effects of sphingosine-1-phosphate and other sphingomyelin metabolites

Upon various stimuli, cells metabolize sphingomyelin from the cellular plasma membrane to form sphingosylphosphorylcholine (SPC) or ceramide. The latter can be further metabolized to sphingosine and then sphingosine-1-phosphate (S1P). Apart from local formation, S1P and SPC are major constituents of blood plasma. All four sphingomyelin metabolites (SMM) can act upon intracellular targets, and at least S1P and probably also SPC can additionally act upon G-protein-coupled receptors. While the molecular identity of the SPC receptors remains unclear, several subtypes of S1P receptors have been cloned and their distribution in cardiovascular tissues is described. In the heart SMM can alter intracellular Ca(2+) release, particularly via the ryanodine receptor, and conductance of various ion channels in the plasma membrane, particularly I(K(Ach)). While the various SMM differ somewhat in their effects, the above alterations of ion homeostasis result in reduced cardiac function in most cases, and ceramide and/or sphingosine may be the mediators of the negative inotropic effects of tumour necrosis factor. In the vasculature, SMM mainly act as acute vasoconstrictors in most vessels, but ceramide can be a vasodilator. SMM-induced vasoconstriction involves mobilization of Ca(2+) from intracellular stores, influx of extracellular Ca(2+) via L-type channels and activation of a rho-kinase. Extended exposure to SMM, particularly S1P, promotes several stages of the angiogenic process like endothelial cell activation, migration, proliferation, tube formation and vascular maturation. We propose that SMM are an important class of endogenous modulators of cardiovascular function.

Evidence for a significant role of a Gs-triggered mechanism unrelated to the activation of adenylyl cyclase in the cyclic AMP-independent relaxant response of guinea-pig tracheal smooth muscle

Cyclic AMP is a key molecule in the regulation of airway smooth muscle tone. Increased cyclic AMP leads to relaxation of this smooth muscle and its inhibition results in the muscle contraction. A constitutive role for cyclic AMP in the contraction and relaxation of airway muscle is supported by the observations that direct activators of adenylyl cyclase, such as forskolin and membrane-permeable cyclic AMP analogues, relax this smooth muscle potently. This traditional view of the role for cyclic AMP is the basis for the idea that relaxation of airway smooth muscle mediated through adenylyl cyclase-linked, G(s)-coupled receptors, including the beta(2)-adrenoceptor, is achieved mainly by the elevation of cyclic AMP content [cyclic AMP-dependent mechanism(s)]. However, recent pharmacological and biochemical evidence raises a fundamental question concerning the role of cyclic AMP; can G(s)-coupled receptor-mediated relaxation of tracheal smooth muscle be attributed exclusively to cyclic AMP-dependent mechanism(s)? In the present study, we show that cholera toxin (CTX, 5 microg/ml), an activator of the heterotrimeric guanine-nucleotide-binding protein G(s), relaxes guinea-pig tracheal smooth muscle. CTX also elevates tissue cyclic AMP content by about 30-fold and this is practically abolished by an adenylyl cyclase inhibitor, SQ 22,536 (100 microM). However, unexpectedly, the relaxant response to CTX is not affected by SQ 22,536. These results firstly show that activation of G(s) is able to produce a relaxation in tracheal smooth muscle independently of the elevation of cyclic AMP. G(s)-triggered, cyclic AMP-unrelated cellular mechanism(s) seem(s) to play a substantial role in smooth muscle relaxation mediated through adenylyl cyclase-linked receptors. This mechanism may account in part for the cyclic AMP-independent relaxant response of tracheal smooth muscle.

Mechanisms of hydrogen-peroxide-induced biphasic response in rat mesenteric artery

1. In phenylephrine (PHE) (1 micro M)-precontracted superior mesenteric arteries from adult rats, low concentration of hydrogen peroxide (H(2)O(2), 10-100 micro M) caused only contraction, while high concentration of H(2)O(2) (0.3-1 mM) caused a biphasic response: a transient contraction followed by a relaxation response. 2. Endothelium removal did not affect the biphasic response. 7,7-Dimethyl-(5Z,8Z)-eicosadienoic acid, diclofenac, furegrelate, or SQ 29548 greatly inhibited the contraction but did not affect the relaxation. 17-Octadecynoic acid, eicosatriynoic acid, ICI 198615, SQ 22536, or ODQ did not inhibit the biphasic response. 3. KCl at 40 mM inhibited the relaxation response to H(2)O(2) by 98+/-24%. 4-Aminopyridine (4-AP) inhibited while tetraethylammonium chloride (TEA), charybdotoxin, or glibenclamide attenuated the relaxation response. A combination of 4-AP, TEA and glibenclamide mimicked the effects of 40 mM KCl. Iberiotoxin, apamin, or barium chloride did not inhibit the relaxation response. 4. H(2)O(2) at 1 mM hyperpolarized membrane potential and reversibly augmented K(+) current in smooth muscle cells of mesenteric artery. These effects of H(2)O(2) were attenuated significantly by 4-AP. 5. In summary, in PHE-precontracted rat mesenteric artery: (1) the response to H(2)O(2) shifted qualitatively from contraction to a biphasic response as H(2)O(2) increased to 0.3 mM or higher; (2) the relaxation response is caused by the activation of K(+) channels, with voltage-dependent K(+) channels playing a primary role; and the contraction is likely to be mediated by thromboxane A(2); (3) the K(+) channel activation by H(2)O(2) is independent of phospholipase A(2), cyclooxygenase, lipoxygenase, cytochrome P450 monooxygenase, adenylate or guanylate cyclase.

Plant-derived, synthetic and endogenous cannabinoids as neuroprotective agents. Non-psychoactive cannabinoids, 'entourage' compounds and inhibitors of N-acyl ethanolamine breakdown as therapeutic strategies to avoid pyschotropic effects

There is good evidence that plant-derived and synthetic cannabinoids possess neuroprotective properties. These compounds, as a result of effects upon CB(1) cannabinoid receptors, reduce the release of glutamate, and in addition reduce the influx of calcium following NMDA receptor activation. The major obstacle to the therapeutic utilization of such compounds are their psychotropic effects, which are also brought about by actions on CB(1) receptors. However, synthesis of the endogenous cannabinoids anandamide and 2-arachidonoylglycerol, which also have neuroprotective properties, are increased under conditions of severe inflammation and ischemia, raising the possibility that compounds that prevent their metabolism may be of therapeutic utility without having the drawback of producing psychotropic effects. In this review, the evidence indicating neuroprotective actions of plant-derived, synthetic and endogenous cannabinoids is presented. In addition, the pharmacological properties of endogenous anandamide-related compounds that are not active upon cannabinoid receptors, but which are also produced during conditions of severe inflammation and ischemia and may contribute to a neuroprotective action are reviewed.