Sphingolipids and the orchestration of endothelium-derived vasoactive factors: when endothelial function demands greasing

Integrated metabolomics analysis reveals mechanistic insights into variability in blood pressure response to thiazide diuretics and beta blockers

Hypertensive patients with a higher proportion of genetic West African ancestry (%GWAA) have better blood pressure (BP) response to thiazide diuretics (TDs) and worse response to β-blockers (BBs) than those with lower %GWAA, associated with their lower plasma renin activity (PRA). TDs and BBs are suggested to reduce BP in the long term through vasodilation via incompletely understood mechanisms. This study aimed at identifying pathways underlying ancestral differences in PRA, which might reflect pathways underlying BP-lowering mechanisms of TDs and BBs. Among hypertensive participants enrolled in the Pharmacogenomics Evaluation of Antihypertensive Responses (PEAR) and PEAR-2 trials, we previously identified 8 metabolites associated with baseline PRA and 4 metabolic clusters (including 39 metabolites) that are different between those with GWAA <45% versus ≥45%. In the current study, using Ingenuity Pathway Analysis (IPA), we integrated these signals. Three overlapping metabolic signals within three significantly enriched pathways were identified as associated with both PRA and %GWAA: ceramide signaling, sphingosine 1- phosphate signaling, and endothelial nitric oxide synthase signaling. Literature indicates that the identified pathways are involved in the regulation of the Rho kinase cascade, production of the vasoactive agents nitric oxide, prostacyclin, thromboxane A2, and endothelin 1; the pathways proposed to underlie TD- and BB-induced vasodilatation. These findings may improve our understanding of the BP-lowering mechanisms of TDs and BBs. This might provide a possible step forward in personalizing antihypertensive therapy by identifying patients expected to have robust BP-lowering effects from these drugs.

Influence of Genetic West African Ancestry on Metabolomics among Hypertensive Patients

Patients with higher genetic West African ancestry (GWAA) have hypertension (HTN) that is more difficult to treat and have higher rates of cardiovascular diseases (CVD) and differential responses to antihypertensive drugs than those with lower GWAA. The mechanisms underlying these disparities are poorly understood. Using data from 84 ancestry-informative markers in US participants from the Pharmacogenomic Evaluation of Antihypertensive Responses (PEAR) and PEAR-2 trials, the GWAA proportion was estimated. Using multivariable linear regression, the baseline levels of 886 metabolites were compared between PEAR participants with GWAA < 45% and those with GWAA ≥ 45% to identify differential metabolites and metabolic clusters. Metabolites with a false discovery rate (FDR) < 0.2 were used to create metabolic clusters, and a cluster analysis was conducted. Differential clusters were then tested for replication in PEAR-2 participants. We identified 353 differential metabolites (FDR < 0.2) between PEAR participants with GWAA < 45% (n = 383) and those with GWAA ≥ 45% (n = 250), which were used to create 24 metabolic clusters. Of those, 13 were significantly different between groups (Bonferroni p < 0.002). Four clusters, plasmalogen and lysoplasmalogen, sphingolipid metabolism and ceramide, cofactors and vitamins, and the urea cycle, were replicated in PEAR-2 (Bonferroni p < 0.0038) and have been previously linked to HTN and CVD. Our findings may give insights into the mechanisms underlying HTN racial disparities.

Ceramide-Induced Lysosomal Biogenesis and Exocytosis in Early-Onset Preeclampsia Promotes Exosomal Release of SMPD1 Causing Endothelial Dysfunction

Aberrant ceramide build-up in preeclampsia, a serious disorder of pregnancy, causes exuberant autophagy-mediated trophoblast cell death. The significance of ceramide accumulation for lysosomal biogenesis in preeclampsia is unknown. Here we report that lysosome formation is markedly increased in trophoblast cells of early-onset preeclamptic placentae, in particular in syncytiotrophoblasts. This is accompanied by augmented levels of transcription factor EB (TFEB). In vitro and in vivo experiments demonstrate that ceramide increases TFEB expression and nuclear translocation and induces lysosomal formation and exocytosis. Further, we show that TFEB directly regulates the expression of lysosomal sphingomyelin phosphodiesterase (L-SMPD1) that degrades sphingomyelin to ceramide. In early-onset preeclampsia, ceramide-induced lysosomal exocytosis carries L-SMPD1 to the apical membrane of the syncytial epithelium, resulting in ceramide accumulation in lipid rafts and release of active L-SMPD1 via ceramide-enriched exosomes into the maternal circulation. The SMPD1-containing exosomes promote endothelial activation and impair endothelial tubule formation in vitro. Both exosome-induced processes are attenuated by SMPD1 inhibitors. These findings suggest that ceramide-induced lysosomal biogenesis and exocytosis in preeclamptic placentae contributes to maternal endothelial dysfunction, characteristic of this pathology.

Mechanisms underlying Eugenia mattosii D. Legrand leaves extract, fractions and compounds induce relaxation of the aorta from normotensive and hypertensive rats

The present study aimed to verify the effect of methanolic extract, fractions, and phenolic compounds of Eugenia mattosii D. Legrand leaves on the aorta relaxation. Isometric tensions were measured on the aorta of normotensive (NTR) and spontaneously hypertensive rats (SHR). The results showed that both methanolic extracts of leaves and stems, as well as, fractions obtained from leaves were able to induce a concentration-dependent relaxation in both endothelium-intact and -denuded aortas. The methanolic extract of leaves (ME-leaves) was the most effective since the maximal relaxation (≈ 83%) obtained was at the concentration of 300 μg/mL. As the endothelium-dependent relaxation was more significant, we investigated the mechanisms by which ME-leaves induced this effect. After the pretreatment with LNAME, ME-leaves-induced relaxation was decreased in the aorta of NTR and SHR. However, the pretreatment with methylene blue only reduced the relaxation in the aorta of NTR. Furthermore, pretreatment with ME-leaves decreased phenylephrine-induced contraction in preparation Ca²⁺-free only in aortic rings from NTR. This study also reveals that both compounds, cryptostrobin isolated from chloroform fraction and catechin from the ethyl acetate fraction induced a marked relaxation in endotheliumintact aortic rings of NTR. In conclusion, ME-leaves induces relaxation in the rat aorta involves the modulation of NO/cGMP dependent signaling pathway, this mechanism may at least, in part, explain the endothelium-dependent relaxation. Furthermore, cryptostrobin and catechin also induced relaxation, which may contribute synergistically to the vasorelaxation effect of the ME-leaves.

Plasma glucosylceramides and cardiovascular risk in incident hemodialysis patients

BACKGROUND

Recent population-based studies identified plasma sphingolipids as independent predictors of increased cardiovascular disease (CVD) morbidity and mortality. Understanding the impact of sphingolipids on CVD outcomes in patients on dialysis, who suffer from higher risk of these conditions, is important for risk assessment and treatment.

OBJECTIVE

To measure plasma sphingolipid levels and determine their associations with CVD in adults initiating maintenance hemodialysis.

METHODS

To evaluate associations of plasma sphingolipids with intermediate cardiovascular outcomes (hypertension, left ventricular hypertrophy, and decreased ejection fraction), cardiovascular mortality, and all-cause mortality in patients with end-stage renal disease, we measured plasma levels of ceramides, glucosylceramides, and lactosylceramides from the family of sphingolipids in 368 incident hemodialysis patients enrolled in the Predictors of Arrhythmic and Cardiovascular Risk in End-Stage Renal Disease study.

RESULTS

Glucosylceramide C16GC (per 1 log μM increase) was associated with higher odds of having uncontrolled hypertension (odds ratio [OR]: 1.34; 95% confidential interval [CI]: 1.01-1.76), left ventricular hypertrophy (OR: 1.53; 95% CI: 1.11-2.13), and reduced ejection fraction (OR: 1.05; 95% CI: 1.00-1.11) in fully adjusted models. During a median 2.5 years of follow-up, there were 78 deaths from all causes, of which 33 were from CVD. Mortality was higher among those in the highest tertile of C16GC for all causes (HR: 1.81; 95% CI: 1.02-3.22) and CVD (HR: 2.63, 95% CI: 1.08-6.55).

CONCLUSIONS

These results suggest that abnormal glycosphingolipid metabolism might contribute to increased CVD risk in end-stage renal disease.

Disruption of sphingolipid metabolism augments ceramide-induced autophagy in preeclampsia

Bioactive sphingolipids including ceramides are involved in a variety of pathophysiological processes by regulating cell death and survival. The objective of the current study was to examine ceramide metabolism in preeclampsia, a serious disorder of pregnancy characterized by oxidative stress, and increased trophoblast cell death and autophagy. Maternal circulating and placental ceramide levels quantified by tandem mass spectrometry were elevated in pregnancies complicated by preeclampsia. Placental ceramides were elevated due to greater de novo synthesis via high serine palmitoyltransferase activity and reduced lysosomal breakdown via diminished ASAH1 expression caused by TGFB3-induced E2F4 transcriptional repression. SMPD1 activity was reduced; hence, sphingomyelin degradation by SMPD1 did not contribute to elevated ceramide levels in preeclampsia. Oxidative stress triggered similar changes in ceramide levels and acid hydrolase expression in villous explants and trophoblast cells. MALDI-imaging mass spectrometry localized the ceramide increases to the trophophoblast layers and syncytial knots of placentae from pregnancies complicated by preeclampsia. ASAH1 inhibition or ceramide treatment induced autophagy in human trophoblast cells via a shift of the BOK-MCL1 rheostat toward prodeath BOK. Pharmacological inhibition of ASAH1 activity in pregnant mice resulted in increased placental ceramide content, abnormal placentation, reduced fetal growth, and increased autophagy via a similar shift in the BOK-MCL1 system. Our results reveal that oxidative stress-induced reduction of lysosomal hydrolase activities in combination with elevated de novo synthesis leads to ceramide overload, resulting in increased trophoblast cell autophagy, and typifies preeclampsia as a sphingolipid storage disorder.

Dietary fish oil improves endothelial function and lowers blood pressure via suppression of sphingolipid-mediated contractions in spontaneously hypertensive rats

OBJECTIVE

Long-chain n-3 polyunsaturated fatty acids from oily fish reduce blood pressure (BP) in hypertension. Previously, we demonstrated that hypertension is associated with marked alterations in sphingolipid biology and elevated ceramide-induced vasoconstriction. Here we investigated in spontaneously hypertensive rats (SHRs) whether fish oil improves endothelial function including reduced vascular contraction induced via the sphingolipid cascade, resulting in reduced BP.

METHODS

Twelve-week-old SHRs were fed a control or fish oil-enriched diet during 12 weeks, and BP was recorded. Plasma sphingolipid levels were quantified by mass spectrometry and the response of isolated carotid arteries towards different stimuli was measured. Furthermore, erythrocyte membrane fatty acid composition, thromboxane A2 formation and cytokine secretion in ex-vivo lipopolysaccharide-stimulated thoracic aorta segments were determined.

RESULTS

The fish oil diet reduced the mean arterial BP (P < 0.001) and improved endothelial function, as indicated by a substantially increased relaxation potential towards ex-vivo methacholine exposure of the carotid arteries (P < 0.001). The long-chain n-3 polyunsaturated fatty acid diet resulted in altered levels of specific (glucosyl)ceramide subspecies (P < 0.05), reduced membrane arachidonic acid content (P < 0.001) and decreased thromboxane concentrations in plasma (P < 0.01). Concomitantly, the fish oil diet largely reduced ceramide-induced contractions (P < 0.01), which are predominantly mediated by thromboxane. Furthermore, thromboxane A2 and interleukin-10 were reduced in supernatants of lipopolysaccharide-stimulated thoracic aorta of SHRs fed the fish oil diet while RANTES (regulated on activation, normal T-cell expressed and secreted) was enhanced. This may contribute to reduced vasoconstriction in vivo.

CONCLUSIONS

Dietary fish oil lowers BP in SHRs and improves endothelial function in association with suppression of sphingolipid-dependent vascular contraction.

Selective intrauterine growth restriction in monochorionic twin pregnancies: markers of endothelial damage and metabolomic profile

The aim of this study was to assess the aorta-intima thickness (aIT) and serum metabolomic profile in selective intrauterine growth-restricted (sIUGR) monochorionic diamniotic (MCDA) twin fetuses presenting Doppler velocimetry alterations. Fetal abdominal aIT was measured by ultrasound at 32 weeks of gestation, enrolling 24 MCDA twin fetuses (8 sIUGR and 16 controls). sIUGR twin fetuses were classified into two groups: Group 1 consisted of sIUGR with abnormal umbilical artery (UA) Doppler waveforms and Group 2 included sIUGR with normal UA Doppler. Group 3 were control fetuses appropriate for gestational age (AGA). Fetal blood samples were obtained from the umbilical vein immediately after fetal extraction. A non-targeted metabolomic profiling investigated fetal metabolism alterations by using liquid chromatography-high-resolution mass spectrometry (LC-HRMS). Median fetal aIT was significantly larger in Group 1 (median value = 0.9 mm; range = 0.8-1.0 mm; p < .002) and Group 2 (median value = 0.8 mm; range = 0.7-0.8 mm; p < .002) than in AGA Group 3 (median value = 0.5 mm; range = 0.4-0.6 mm; p < .002). Metabolomic analyses, performed on four sIUGR cases (Group 1) compared with four AGA co-twins, showed an upregulation of phenylalanine, sphingosine, glycerophosphocholine, and choline, and a downregulation of valine, tryptophan, isoleucine, and proline sIUGR Group 1 compared with AGA. Although for metabolomics data only a statistical tendency (and not a statistical significance) was reached due to the small sample size, we believe that our results represent a valid starting point for further in-depth metabolomic and proteomic investigations of sIUGR in MCDA fetuses.

FTY720 (fingolimod) increases vascular tone and blood pressure in spontaneously hypertensive rats via inhibition of sphingosine kinase

BACKGROUND AND PURPOSE

FTY720 (Fingolimod) is a recently approved orally administered drug for the treatment of multiple sclerosis. Phase II and III clinical trials have demonstrated that this drug modestly increases BP. We previously showed that inhibition of sphingosine kinase increases vascular tone and BP in hypertensive, but not normotensive rats. Since FTY720 is reported to have inhibitory effects on sphingosine kinase, we investigated whether FTY720 increases vascular tone and BP only in hypertensive rats via this mechanism.

EXPERIMENTAL APPROACH

The contractile and BP modulating effects of FTY720 were studied in vivo and ex vivo (wire myography) in age-matched normotensive Wistar Kyoto (WKY) rats and spontaneously hypertensive rats (SHRs).

KEY RESULTS

Oral administration of FTY720 induced an increase in mean arterial pressure in SHR, whereas a decrease in BP was observed in WKY rats, as measured 24 h after administration. Similar to the sphingosine kinase inhibitor dimethylsphingosine (DMS), FTY720 induced large contractions in isolated carotid arteries from SHR, but not in those from WKY. In contrast, the phosphorylated form of FTY720 did not induce contractions in isolated carotid arteries from SHR. FTY720-induced contractions were inhibited by endothelium denudation, COX and thromboxane synthase inhibitors, and by thromboxane receptor antagonism, indicating that (like DMS-induced contractions) they were endothelium-dependent and mediated by thromboxane A₂.

CONCLUSIONS AND IMPLICATIONS

These data demonstrate that FTY720 increases vascular tone and BP only in hypertensive rats, most likely as a result of its inhibitory effect on sphingosine kinase.

Hypertension is associated with marked alterations in sphingolipid biology: a potential role for ceramide

Background

Hypertension is, amongst others, characterized by endothelial dysfunction and vascular remodeling. As sphingolipids have been implicated in both the regulation of vascular contractility and growth, we investigated whether sphingolipid biology is altered in hypertension and whether this is reflected in altered vascular function.

Methods and Findings

In isolated carotid arteries from spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto (WKY) rats, shifting the ceramide/S1P ratio towards ceramide dominance by administration of a sphingosine kinase inhibitor (dimethylsphingosine) or exogenous application of sphingomyelinase, induced marked endothelium-dependent contractions in SHR vessels (DMS: 1.4±0.4 and SMase: 2.1±0.1 mN/mm; n = 10), that were virtually absent in WKY vessels (DMS: 0.0±0.0 and SMase: 0.6±0.1 mN/mm; n = 9, p<0.05). Imaging mass spectrometry and immunohistochemistry indicated that these contractions were most likely mediated by ceramide and dependent on iPLA₂, cyclooxygenase-1 and thromboxane synthase. Expression levels of these enzymes were higher in SHR vessels. In concurrence, infusion of dimethylsphingosine caused a marked rise in blood pressure in anesthetized SHR (42±4%; n = 7), but not in WKY (−12±10%; n = 6). Lipidomics analysis by mass spectrometry, revealed elevated levels of ceramide in arterial tissue of SHR compared to WKY (691±42 vs. 419±27 pmol, n = 3–5 respectively, p<0.05). These pronounced alterations in SHR sphingolipid biology are also reflected in increased plasma ceramide levels (513±19 pmol WKY vs. 645±25 pmol SHR, n = 6–12, p<0.05). Interestingly, we observed similar increases in ceramide levels (correlating with hypertension grade) in plasma from humans with essential hypertension (185±8 pmol vs. 252±23 pmol; n = 18 normotensive vs. n = 19 hypertensive patients, p<0.05).

Conclusions

Hypertension is associated with marked alterations in vascular sphingolipid biology such as elevated ceramide levels and signaling, that contribute to increased vascular tone.