Disrupted Binding of Cystathionine γ-Lyase to p53 Promotes Endothelial Senescence

BACKGROUND

Advanced age is unequivocally linked to the development of cardiovascular disease; however, the mechanisms resulting in reduced endothelial cell regeneration remain poorly understood. Here, we investigated novel mechanisms involved in endothelial cell senescence that impact endothelial cell transcription and vascular repair after injury.

METHODS

Native endothelial cells were isolated from young (20±3.4 years) and aged (80±2.3 years) individuals and subjected to molecular analyses to assess global transcriptional and metabolic changes. In vitro studies were conducted using primary human and murine endothelial cells. A murine aortic re-endothelialization model was used to examine endothelial cell regenerative capacity in vivo.

RESULTS

RNA sequencing of native endothelial cells revealed that aging resulted in p53-mediated reprogramming to express senescence-associated genes and suppress glycolysis. Reduced glucose uptake and ATP contributed to attenuated assembly of the telomerase complex, which was required for endothelial cell proliferation. Enhanced p53 activity in aging was linked to its acetylation on K120 due to enhanced activity of the acetyltransferase MOZ (monocytic leukemic zinc finger). Mechanistically, p53 acetylation and translocation were, at least partially, attributed to the loss of the vasoprotective enzyme, CSE (cystathionine γ-lyase). CSE physically anchored p53 in the cytosol to prevent its nuclear translocation and CSE absence inhibited AKT (Protein kinase B)-mediated MOZ phosphorylation, which in turn increased MOZ activity and subsequently p53 acetylation. In mice, the endothelial cell-specific deletion of CSE activated p53, induced premature endothelial senescence, and arrested vascular repair after injury. In contrast, the adeno-associated virus 9-mediated re-expression of an active CSE mutant retained p53 in the cytosol, maintained endothelial glucose metabolism and proliferation, and prevented endothelial cell senescence. Adenoviral overexpression of CSE in native endothelial cells from aged individuals maintained low p53 activity and reactivated telomerase to revert endothelial cell senescence.

CONCLUSIONS

Aging-associated impairment of vascular repair is partly determined by the vasoprotective enzyme CSE.

Endothelial-dependent S-Sulfhydration of tissue factor pathway inhibitor regulates blood coagulation

Tissue factor pathway inhibitor (TFPI) is an important regulator of coagulation and a link between inflammation and thrombosis. Here we investigated whether endothelial cell-driven oxidative post-translational modifications could have an impact on TFPI activity. We focused on S-sulfhydration, which is a hydrogen sulfide-dependent post-translational modification that, in endothelial cells, is regulated by the enzyme cystathionine γ-lyase (CSE). The study made use of human primary endothelial cells and blood from healthy individuals or subjects with atherosclerosis as well as from mice lacking endothelial CSE. TFPI was S-sulfhydrated in endothelial cells from healthy individuals and mice, while the loss of endothelial CSE expression/activity reduced its modification. Non-S-sulfhydrated TFPI was no longer able to interact with factor Xa, which facilitated the activation of tissue factor. Similarly, non-S-sulfhydratable TFPI mutants bound less protein S, while supplementation with hydrogen sulfide donors, preserved TFPI activity. Phenotypically, loss of TFPI S-sulfhydration increased clot retraction, suggesting that this post-translational modification is a new endothelial cell-dependent mechanism that contributes to the regulation of blood coagulation.

Mapping the Endothelial Cell S-Sulfhydrome Highlights the Crucial Role of Integrin Sulfhydration in Vascular Function

BACKGROUND

In vascular endothelial cells, cysteine metabolism by the cystathionine γ lyase (CSE), generates hydrogen sulfide-related sulfane sulfur compounds (H₂S_n), that exert their biological actions via cysteine S-sulfhydration of target proteins. This study set out to map the "S-sulfhydrome" (ie, the spectrum of proteins targeted by H₂S_n) in human endothelial cells.

METHODS

Liquid chromatography with tandem mass spectrometry was used to identify S-sulfhydrated cysteines in endothelial cell proteins and β3 integrin intraprotein disulfide bond rearrangement. Functional studies included endothelial cell adhesion, shear stress-induced cell alignment, blood pressure measurements, and flow-induced vasodilatation in endothelial cell-specific CSE knockout mice and in a small collective of patients with endothelial dysfunction.

RESULTS

Three paired sample sets were compared: (1) native human endothelial cells isolated from plaque-free mesenteric arteries (CSE activity high) and plaque-containing carotid arteries (CSE activity low); (2) cultured human endothelial cells kept under static conditions or exposed to fluid shear stress to decrease CSE expression; and (3) cultured endothelial cells exposed to shear stress to decrease CSE expression and treated with solvent or the slow-releasing H₂S_n donor, SG1002. The endothelial cell "S-sulfhydrome" consisted of 3446 individual cysteine residues in 1591 proteins. The most altered family of proteins were the integrins and focusing on β3 integrin in detail we found that S-sulfhydration affected intraprotein disulfide bond formation and was required for the maintenance of an extended-open conformation of the β leg. β3 integrin S-sulfhydration was required for endothelial cell mechanotransduction in vitro as well as flow-induced dilatation in murine mesenteric arteries. In cultured cells, the loss of S-sulfhydration impaired interactions between β3 integrin and Gα13 (guanine nucleotide-binding protein subunit α 13), resulting in the constitutive activation of RhoA (ras homolog family member A) and impaired flow-induced endothelial cell realignment. In humans with atherosclerosis, endothelial function correlated with low H₂S_n generation, impaired flow-induced dilatation, and failure to detect β3 integrin S-sulfhydration, all of which were rescued after the administration of an H₂S_n supplement.

CONCLUSIONS

Vascular disease is associated with marked changes in the S-sulfhydration of endothelial cell proteins involved in mediating responses to flow. Short-term H₂S_n supplementation improved vascular reactivity in humans highlighting the potential of interfering with this pathway to treat vascular disease.

Soluble epoxide hydrolase promotes astrocyte survival in retinopathy of prematurity

Polyunsaturated fatty acids such as docosahexaenoic acid (DHA) positively affect the outcome of retinopathy of prematurity (ROP). Given that DHA metabolism by cytochrome P450 and soluble epoxide hydrolase (sEH) enzymes affects retinal angiogenesis and vascular stability, we investigated the role of sEH in a mouse model of ROP. In WT mice, hyperoxia elicited tyrosine nitration and inhibition of sEH and decreased generation of the DHA-derived diol 19,20-dihydroxydocosapentaenoic acid (19,20-DHDP). Correspondingly, in a murine model of ROP, sEH-/- mice developed a larger central avascular zone and peripheral pathological vascular tuft formation than did their WT littermates. Astrocytes were the cells most affected by sEH deletion, and hyperoxia increased astrocyte apoptosis. In rescue experiments, 19,20-DHDP prevented astrocyte loss by targeting the mitochondrial membrane to prevent the hyperoxia-induced dissociation of presenilin-1 and presenilin-1-associated protein to attenuate poly ADP-ribose polymerase activation and mitochondrial DNA damage. Therapeutic intravitreal administration of 19,20-DHDP not only suppressed astrocyte loss, but also reduced pathological vascular tuft formation in sEH-/- mice. Our data indicate that sEH activity is required for mitochondrial integrity and retinal astrocyte survival in ROP. Moreover, 19,20-DHDP may be more effective than DHA as a nutritional supplement for preventing retinopathy in preterm infants.

Shear stress regulates cystathionine γ lyase expression to preserve endothelial redox balance and reduce membrane lipid peroxidation

Cystathionine γ lyase (CSE) is the major source of hydrogen sulfide-derived species (H₂S_n) in endothelial cells and plays an important role in protecting against atherosclerosis. Here we investigated the molecular mechanisms underlying the regulation of CSE expression in endothelial cells by fluid shear stress/flow. Fluid shear stress decreased CSE expression in human and murine endothelial cells and was negatively correlated with the transcription factor Krüppel-like factor (KLF) 2. CSE was identified as a direct target of the KLF2-regulated microRNA, miR-27b and high expression of CSE in native human plaque-derived endothelial cells, was also inversely correlated with KLF2 and miR-27b levels. One consequence of decreased CSE expression was the loss of Prx6 sulfhydration (on Cys47), which resulted in Prx6 hyperoxidation, decamerization and inhibition, as well as a concomitant increase in endothelial cell reactive oxygen species and lipid membrane peroxidation. H₂S_n supplementation in vitro was able to reverse the redox state of Prx6. Statin therapy, which is known to activate KLF2, also decreased CSE expression but increased CSE activity by preventing its phosphorylation on Ser377. As a result, the sulfhydration of Prx6 was partially restored in samples from plaque containing arteries from statin-treated donors. Taken together, the regulation of CSE expression by shear stress/disturbed flow is dependent on KLF2 and miR-27b. Moreover, in murine and human arteries CSE acts to maintain endothelial redox balance at least partly by targeting Prx6 to prevent its decamerization and inhibition of its peroxidase activity.

A selective and sensitive method for quantification of endogenous polysulfide production in biological samples

Hydrogen sulfide (H₂S) is a gasotransmitter that regulates cellular homeostasis and impacts on multiple physiological and pathophysiological processes. However, it exerts many of its biological actions indirectly via the formation of H₂S-derived sulfane sulfur species/polysulfides. Because of the high reactivity of sulfur species, the detection of H₂S-derived polysulfides in biological systems is challenging and currently used methods are neither sensitive nor quantitative. Herein, we describe a LC-MS/MS-based method that makes use of Sulfane Sulfur Probe 4 to detect endogenously generated polysulfides in biological samples in a selective, sensitive and quantitative manner. The results indicate a large variability in the activity of the H₂S-generating enzymes in different murine organs, but the method described was able to detect intracellular levels of polysulfides in the nanomolar range and identify cystathionine γ-lyase as the major intracellular source of sulfane sulfur species/polysulfides in murine endothelial cells and hearts. The protocol described can be applied to a variety of biological samples for the quantification of the H₂S-derived polysulfides and has the potential to increase understanding on the control and consequences of this gaseous transmitter.

Pharmacokinetics and Bioavailability of Quercetin Glycosides in Humans

Due to its potentially beneficial impact on human health, the polyphenol quercetin has come into the focus of medicinal interest. However, data on the bioavailability of quercetin after oral intake are scarce and contradictory. Previous investigations indicate that the disposition of quercetin may depend on the sugar moiety of the glycoside or the plant matrix. To determine the influence of the sugar moiety or matrix on the absorption of quercetin, two isolated quercetin glycosides and two plant extracts were administered to 12 healthy volunteers in a four-way crossover study. Each subject received an onion supplement or quercetin-4'-O-glucoside (both equivalent to 100 mg quercetin), as well as quercetin-3-O-rutinoside and buckwheat tea (both equivalent to 200 mg quercetin). Samples were analyzed by HPLC with a 12-channel coulometric array detector. In human plasma, only quercetin glucuronides, but no free quercetin, could be detected. There was no significant difference in the bioavailability and pharmacokinetic parameters between the onion supplement and quercetin-4'-O-glucoside. Peak plasma concentrations were 2.3 +/- 1.5 microg x mL(-1) and 2.1 +/- 1.6 microg x mL(-1) (mean +/- SD) and were reached after 0.7 +/- 0.2 hours and 0.7 +/- 0.3 hours, respectively. After administration of buckwheat tea and rutin, however, peak plasma levels were--despite the higher dose-only 0.6 +/- 0.7 microg x mL(-1) and 0.3 +/- 0.3 microg x mL(-1), respectively. Peak concentrations were reached 4.3 +/- 1.8 hours after administration of buckwheat tea and 7.0 +/- 2.9 hours after ingestion of rutin. The terminal elimination half-life was about 11 hours for all treatments. Thus, the disposition of quercetin in humans primarily depends on the sugar moiety. To a minor extent, the plant matrix influences both the rate and extent of absorption in the case of buckwheat tea administration compared with the isolated compound. The site of absorption seems to be different for quercetin-4'-O-glucoside and quercetin-3-O-rutinoside. The significance of specific carriers on the absorption of quercetin glycosides, as well as specific intestinal beta-glucosidases, needs to be further evaluated.

Validated method for the determination of hydroquinone in human urine by high-performance liquid chromatography-coulometric-array detection

The paper describes the computer aided method development and validation for the determination of hydroquinone in human urine from a clinical study on renal excretion of hydroquinone metabolites and the release of free hydroquinone in the urinary tract in order to evaluate the proposed urine disinfecting concept. The presented method uses high-performance liquid chromatography on reversed-phase material with a polar endcapping (Aqua-C18, 250x4.6 mm). Selective and sensitive determination (LOQ= 12.5 ng on-column) of the target compound was achieved by electrochemical array detection (CoulArray). Gradient and parameter optimization were supported by DryLab software in order to minimize efforts of the expensive and time-consuming method development. Specificity and selectivity were carried out by separation experiments involving the prodrug arbutin and the metabolites hydroquinone, hydroquinone glucuronide, and hydroquinone sulfate, respectively. Hydroquinone glucuronide reference standard was obtained from in vitro glucuronidation in a rat liver microsomes assay. The method was validated according to the criteria for validation of pharmaceutical bioanalytical methods as drafted by the US Department of Health and Human Services, 1998.

Identification of quercetin glucuronides in human plasma by high-performance liquid chromatography-tandem mass spectrometry

After intake of food or herbal medicinal products containing quercetin glycosides, the systemic availability of the genuine glycoside, as well as the systemic occurrence of the aglycone or conjugates of this polyphenol has been a matter of dispute. Consequently, we designed this study to develop a reliable method for determination of quercetin and its metabolites. Following consumption of fried onions five different glucuronides of quercetin could be identified in human plasma samples by means of HPLC-UV-MS/MS. Selective determination of the target compounds was achieved by simultaneous UV (254 nm) and MS/MS detection with selected reaction monitoring experiments using positive mode electrospray ionisation. In contrast, neither the free flavonol nor the genuine glycoside could be detected in plasma. Identification of the quercetin glucuronides detected in vivo was confirmed by comparison with authentic reference compounds synthesised enzymatically using glucuronyl transferase from rabbit liver.

[The distribution of microorganisms in household kitchens. I. Problems, experiments, results]

Epidemiological investigations have demonstrated that insufficient hygiene in households results in increasing health hazards. In order to be able to recommend ways to disrupt infection chains it was necessary to explore the most important pathways of cross-contamination. Housewives without special training were instructed to prepare a complete meal, in the kitchen of a modern, vacant apartment. Among the raw products provided was minced meat, contaminated with Sarcinae (unbeknown to the housewives) in a quantitative manner. When cooking and cleaning procedures were completed we analysed household utensils and surfaces by Rodac impressions and swabs. The test organisms could be detected on all inspected surfaces and on the dining-table with albeit different frequencies. The following locations showed an especially high degree of cross-contamination: a) working-surfaces, especially boards of wood and plastics. b) cutting-machines, c) kitchen-machines. These results agree with literature data. By careful disinfection, i.e. by application of a 0.5% solution of hypochlorite, the contaminations could be removed. We assessed this when arranging the kitchen for the next test. Since it is impossible to practise disinfection procedures in a household kitchen on the same scale as in an operating room, we tried to achieve at least a limited disinfection by household cleansers with germicidal properties. In our opinion a minimum reduction of five log stages, demanded in the medical area, can not be achieved in a household kitchen and indeed it is not necessary. A reduction of the microbial counts to 10% of the original value would already be useful, as toxic levels of microbial counts will be reached later especially when there is simultaneous refrigeration. Correct dosage proved to be one of the main practical problems because a discrepancy exists between the low concentration of tensids, necessary for cleaning, and the relatively high dose necessary for germ-killing compounds. Diluted DOMESTOS proved to be a cleaning agent and germicide, but was, however, blamed for chlorine odour, especially when diluted with warm water. A greater acceptance level was reached with a peroxide-containing cleanser, which, however, was not sufficiently germicidal, when applied in diluted form. The concentrated formulation was more effective in everyday experience, but for this housewives had to wear rubber gloves. This was reported to be complicated and uncomfortable, and indeed the search for better formulations must be continued. (In communication II comparisons with the bibliography and hygienic consequences will be published.)

[The distribution of microorganisms in household kitchens. II. Evaluation of results and hygienic inferences]

The very high morbidity rates of Enteritis infectiosa diseases demand improved prophylactic measures. An important indication of the source of these illnesses is the fact that infections in private households are about three times more frequent than in canteens. Indeed, the rise in morbidity is undoubtedly caused by inadequate treatment of raw products, of meal rests and by insufficient heating processes. Furthermore, in household kitchens no efforts are made to interrupt infection chains, and disinfections are considered as superfluous and housewives are content if their kitchens appear to be clean. The aim of our study performed in a normal household kitchen, was to investigate cross-contamination caused by pathogens, introduced into the kitchen from outdoors. A further aim was to establish the main sources of contamination in order to be able to recommend practical disinfection procedures. The main fields of contamination discovered when 55 meals prepared were: a) working surfaces (including boards of wood and plastics) b) kitchen- and cutting-machines. The amount of test organisms (Sarcinae), introduced into the kitchen (unbeknown to the housewives) by experimentally contaminated minced meat was only reduced by common cleaning procedures, in sofar as nearly half of the original contaminations could be demonstrated to be still present. However, when the normal cleanser was replaced by one containing hypochlorite, and with retention of the same working routines, about 90% bacteriologically clean surfaces were determined. In this way it could be demonstrated that infection chains can be interrupted. It is, however, not correct to compare the efficiency of these procedures with the efficiency of disinfection, according to the Federal Infectious Diseases Act (Bundesseuchengesetz). On practical application of these experiences it must be borne in mind that housewives should not be forced to apply medical disinfection procedures: indeed, traditional and practised cleaning methods should be retained, as far as possible. We recommend therefore that manufacturers supply household cleansers with an anti-bacterial additive, after its application in the kitchens working surfaces and machines are bacteriologically clean. Additionally housewives should be appropriately informed about the necessity of these manipulations. We consider minimization of toxicity and a thorough environmental compatibility of formulations to be self-evident.

Coronary artery bypass in hereditary factor XI deficiency

Hereditary factor XI deficiency is a disorder of coagulation that has been associated with postoperative bleeding. Because cardiopulmonary bypass itself induces transient abnormalities in hemostasis, the patient with factor XI deficiency could be at increased risk for bleeding after cardiac surgical procedures. We report the successful management of a 61-year-old man with hereditary factor XI deficiency who had coronary artery bypass. Treatment with low-dose aspirin, begun 24 hours postoperatively for graft patency, was well tolerated. Once recognized and aggressively treated, factor XI deficiency does not appear to be a contraindication to potentially life-saving procedures like coronary revascularization.

Adrenergic influences on the distal Purkinje system of the canine heart

The purpose of these experiments was to examine the effects of norepinephrine and propranolol on distal Purkinje fibers of the canine heart. Previous studies have indicated that action potential duration is normally greatest in distal Purkinje fibers 3-4 mm from the Purkinje-muscle junction. In such preparations, premature beats initiated either proximal or distal to the area of maximal action potential duration may propagate with delay or block. Our experiments were performed on the right bundle branch and the distal Purkinje fibers of dog hearts and used standard microelectrode techniques. Premature beats with a coupling interval comparable to the duration of action potentials at the area of maximal duration were conducted with delay. Earlier beats were confined to fibers proximal to the area of maximal action potential duration. Norepinephrine (1 x 10 -5 M ) increased action potential duration in some fibers, consistently prolonged the functional refractory period of distal Purkinje fibers, and produced a marked delay in the propagation of early premature beats. Propranolol (0.25-1.0 mg/liter) shortened action potential duration, shortened the functional refractory period of distal fibers, and reduced or abolished conduction delay and block of early premature beats. These observations suggest that the unique properties of the Purkinje-muscle junction may contribute to the genesis of arrhythmias and that this region is an important site of action of propranolol. The action of propranolol on the Purkinje-muscle junction was dose dependent.

Superconducting Phosphorus

Phosphorus, the element itself, becomes superconducting near 4.7 degrees K and at pressures exceeding 100 kilobars. This constitutes one of the four last missing links in the proof that superconductivity is normal behavior for every truly metallic sp element. The three remaining ones are arsenic, sulfur, and iodine.

Superconductivity of Metallic Aluminum Antimonide

The high-pressure metallic phase of aluminunm antimnonide is super conducting [critical temperature T(c) (P approximately 125 kilobars) = 2.8 degrees +/-0.2 degrees K]. This transition temperature is significantly lower than the transition temperature of metallic germanium under an equivalent high pressure. A similar result had been previously found for superconducting indiumantimonide in comparison to tin.