Various forms of plasma cysteine and its metabolites in patients undergoing hemodialysis

The Diagnostic and Prognostic Roles Played by Homocysteine and Other Aminothiols in Patients with Chronic Kidney Disease

We examined standard clinical and laboratory biochemical parameters, as well as the levels of aminothiols in the blood and urine (homocysteine (Hcy), cysteine (Cys), S-adenosylmethionine (SAM), and S-adenosylhomocysteine (SAH)) via capillary electrophoresis in patients with CKD at stages II-V. Patient outcomes were assessed after five years. To complete forecasting, correlation and ROC analysis were performed. It was found that the levels of Cys and Hcy in blood plasma were earlier markers of CKD starting from stage II, while the levels of SAM and SAM/SAH in urine made it possible to differentiate between CKD at stages II and III. Blood plasma Hcy and urinary SAM and SAM/SAH correlated with mortality, but plasma Hcy concentrations were more significant. Thus, plasma Hcy, urine SAM, and SAM/SAH can be considered to be potential diagnostic and prognostic markers in patients with CKD.

A New Lysosome-Targeted NIR Fluorescent Probe for Specific Detection of Cysteine over Homocysteine and Glutathione

In this paper, by modifying the thioxanthene-benzothiozolium fluorophore, BCy-Cys, a lysosome-targeted near-infrared (NIR) fluorescent probe was synthesized for the detection of cysteine (Cys) from homocysteine (Hcy)/glutathione (GSH). As expected, BCy-Cys exhibited high selectivity and high sensitivity for detection of Cys over Hcy/GSH, with an extremely low limit of detection at 0.31 μM, marked by obvious color changes. HRMS was conducted to confirm that the fluorescence intensity at 795 nm was significantly enhanced by the enhancement of intramolecular charge transfer (ICT). Importantly, BCy-Cys could be used to visualize both exogenous and endogenous lysosomal Cys, signifying its potential application in complex organismal systems.

Mice kidney biometabolic process analysis after cantharidin exposure using widely-targeted metabolomics combined with network pharmacology

Cantharidin (CTD) is a principal bioactive component of traditional Chinese medicine Mylabris used in cancer treatment. However, CTD clinical application is limited due to nephrotoxicity, and the mechanism is unknown. The present study used widely-targeted metabolomics, network pharmacology, and cell experiments to investigate the nephrotoxicity mechanism after CTD exposure. In mice exposed to CTD, serum creatinine and urea nitrogen levels increased with renal injury. Then, 74 differential metabolites were detected, including 51 up-regulated and 23 down-regulated metabolites classified as amino acids, small peptides, fatty acyl, arachidonic acid metabolite, organic acid, and nucleotides. Sixteen metabolic pathways including tyrosine, sulfur, and pyrimidine metabolism were all disrupted in the kidney. Furthermore, network pharmacology revealed that 258 metabolic targets, and pathway enrichment indicated that CTD could activate oxidative phosphorylation and oxidative stress (OS). Subsequently, HK-2 cell experiments demonstrated that CTD could reduce superoxide dismutase while increasing malondialdehyde levels. In conclusion, after CTD exposure, biometabolic processes may be disrupted with renal injury in mice, resulting in oxidative phosphorylation and OS.

Blood Thiol Redox State in Chronic Kidney Disease

Thiols (sulfhydryl groups) are effective antioxidants that can preserve the correct structure of proteins, and can protect cells and tissues from damage induced by oxidative stress. Abnormal levels of thiols have been measured in the blood of patients with moderate-to-severe chronic kidney disease (CKD) compared to healthy subjects, as well as in end-stage renal disease (ESRD) patients on haemodialysis or peritoneal dialysis. The levels of protein thiols (a measure of the endogenous antioxidant capacity inversely related to protein oxidation) and S-thiolated proteins (mixed disulphides of protein thiols and low molecular mass thiols), and the protein thiolation index (the molar ratio of the S-thiolated proteins to free protein thiols in plasma) have been investigated in the plasma or red blood cells of CKD and ESRD patients as possible biomarkers of oxidative stress. This type of minimally invasive analysis provides valuable information on the redox status of the less-easily accessible tissues and organs, and of the whole organism. This review provides an overview of reversible modifications in protein thiols in the setting of CKD and renal replacement therapy. The evidence suggests that protein thiols, S-thiolated proteins, and the protein thiolation index are promising biomarkers of reversible oxidative stress that could be included in the routine monitoring of CKD and ESRD patients.

A novel quinoline-based fluorescent probe for real-time monitoring of Cys in glioma

The highly selective fluorescent probe ZS-C1 for imaging Cys in living cells and 3D tumor cell sphere.

A Case for Hydrogen Sulfide Metabolism as an Oxygen Sensing Mechanism

The ability to detect oxygen availability is a ubiquitous attribute of aerobic organisms. However, the mechanism(s) that transduce oxygen concentration or availability into appropriate physiological responses is less clear and often controversial. This review will make the case for oxygen-dependent metabolism of hydrogen sulfide (H₂S) and polysulfides, collectively referred to as reactive sulfur species (RSS) as a physiologically relevant O₂ sensing mechanism. This hypothesis is based on observations that H₂S and RSS metabolism is inversely correlated with O₂ tension, exogenous H₂S elicits physiological responses identical to those produced by hypoxia, factors that affect H₂S production or catabolism also affect tissue responses to hypoxia, and that RSS efficiently regulate downstream effectors of the hypoxic response in a manner consistent with a decrease in O₂. H₂S-mediated O₂ sensing is then compared to the more generally accepted reactive oxygen species (ROS) mediated O₂ sensing mechanism and a number of reasons are offered to resolve some of the confusion between the two.

A selective fluorescent sensor for cysteine detection with potential as a white light emitting fluorophore in living cell imaging

A novel fluorescent sensor CysW-1 was introduced for cysteine detection via the cleavage reaction of two fluorophores. Then a relatively steady and practical white light emitting system was successfully generated. The biocompatibility ensured the living cell imaging and further pre-clinical applications.

Development of a mitochondria targetable ratiometric time-gated luminescence probe for biothiols based on lanthanide complexes

A mitochondria targetable ratiometric luminescence probe based on a mixture of Eu³⁺ and Tb³⁺ complexes has been developed for the specific recognition and ratiometric time-gated luminescence detection of biothiols in aqueous and living samples.

Total Sulfur Amino Acid Requirements Are Not Altered in Children with Chronic Renal Insufficiency, but Minimum Methionine Needs Are Increased

Background: The total sulfur amino acid (TSAA) and minimum Met requirements have been previously determined in healthy children. TSAA metabolism is altered in kidney disease. Whether TSAA requirements are altered in children with chronic renal insufficiency (CRI) is unknown.Objective: We sought to determine the TSAA (Met in the absence of Cys) requirements and minimum Met (in the presence of excess Cys) requirements in children with CRI.Methods: Five children (4 boys, 1 girl) aged 10 ± 2.6 y with CRI were randomly assigned to receive graded intakes of Met (0, 5, 10, 15, 25, and 35 mg · kg^-1 · d^-1) with no Cys in the diet. Four of the children (3 boys, 1 girl) were then randomly assigned to receive graded dietary intakes of Met (0, 2.5, 5, 7.5, 10, and 15 mg · kg^-1 · d^-1) with 21 mg · kg^-1 · d^-1 Cys. The mean TSAA and minimum Met requirements were determined by measuring the oxidation of l-[1-¹³C]Phe to ¹³CO₂ (F¹³CO₂). A 2-phase linear-regression crossover analysis of the F¹³CO₂ data identified a breakpoint at minimal F¹³CO₂ Urine samples collected from all study days and from previous studies of healthy children were measured for sulfur metabolites.Results: The mean and population-safe (upper 95% CI) intakes of TSAA and minimum Met in children with CRI were determined to be 12.6 and 15.9 mg · kg^-1 · d^-1 and 7.3 and 10.9 mg · kg^-1 · d^-1, respectively. In healthy school-aged children the mean and upper 95% CI intakes of TSAA and minimum Met were determined to be 12.9 and 17.2 mg · kg^-1 · d^-1 and 5.8 and 7.3 mg · kg^-1 · d^-1, respectively. A comparison of the minimum Met requirements between healthy children and children with CRI indicated significant (P < 0.05) differences.Conclusion: These results suggest that children with CRI have a similar mean and population-safe TSAA to that of healthy children, suggesting adequate Cys synthesis via transsulfuration, but higher minimum Met requirement, suggesting reduced remethylation rates.

The Effects of Different Garlic-Derived Allyl Sulfides on Anaerobic Sulfur Metabolism in the Mouse Kidney

Diallyl sulfide (DAS), diallyl disulfide (DADS) and diallyl trisulfide (DATS) are major oil-soluble organosulfur compounds of garlic responsible for most of its pharmacological effects. The present study investigated the influence of repeated intraperitoneally (ip) administration of DAS, DADS and DATS on the total level of sulfane sulfur, bound sulfur (S-sulfhydration) and hydrogen sulfide (H₂S) and on the activity of enzymes, which catalyze sulfane sulfur formation and transfer from a donor to an acceptor in the normal mouse kidney, i.e., γ-cystathionase (CSE) and rhodanese (TST). The activity of aldehyde dehydrogenase (ALDH), which is a redox-sensitive protein, containing an –SH group in its catalytic center, was also determined. The obtained results indicated that all tested compounds significantly increased the activity of TST. Moreover, DADS and DATS increased the total sulfane sulfur level and CSE activity in the normal mouse kidney. ALDH activity was inhibited in the kidney after DATS administration. The results indicated also that none of the studied allyl sulfides affected the level of bound sulfur or H₂S. Thus, it can be concluded that garlic-derived DADS and DATS can be a source of sulfane sulfur for renal cells but they are not connected with persulfide formation.

A near-infrared fluorescent probe for the detection of hydrogen polysulfides biosynthetic pathways in living cells and in vivo

We present a new NIR fluorescent probe for the biosynthetic pathways of H₂S_nin living cells andin vivo.

The effect of lipoate on anaerobic cysteine metabolism in erythrocytes of patients treated with peritoneal dialysis

BACKGROUND

The studies aimed to evaluate the changes in cysteine sulfur metabolism in erythrocytes of end-stage renal failure (ESRF) patients treated with continuous ambulatory peritoneal dialysis (CAPD) caused by a one-month lipoate (LA) supplementation at a daily dose of 600 mg.

METHODS

The level of sulfane sulfur and activity of sulfurtransferases were determined in erythrocytes of CAPD patients and in the control group.

RESULTS

The sulfane sulfur level in erythrocytes of CAPD patients did not differ compared with healthy volunteers but LA supplementation increased the reactive sulfur concentration. LA elevated also cystathionase activity.

CONCLUSIONS

LA supplementation in ESRF patients treated with CAPD increases the sulfane sulfur level which indicates the augmentation of its antioxidant and regulatory properties.

A native-chemical-ligation-mechanism-based ratiometric fluorescent probe for aminothiols

Thiol-containing amino acids (aminothiols) such as cysteine (Cys) and homocysteine (Hcy) play a key role in various biological processes including maintaining the homeostasis of biological thiols. However, abnormal levels of aminothiols are associated with a variety of diseases. The native chemical ligation (NCL) reaction has attracted great attention in the fields of chemistry and biology. NCL of peptide segments involves cascade reactions between a peptide-α-thioester and an N-terminal cysteine peptide. In this work, we employed the NCL reaction mechanism to formulate a Förster resonance energy transfer (FRET) strategy for the design of ratiometric fluorescent probes that were selective toward aminothiols. On the basis of this new strategy, the ratiometric fluorescent probe 1 for aminothiols was judiciously designed. The new probe is highly selective toward aminothiols over other thiols and exhibits a very large variation (up to 160-fold) in its fluorescence ratio (I(458)/I(603)). The new fluorescent probe is capable of ratiometric detection of aminothiols in newborn calf and human serum samples and is also suitable for ratiometric fluorescent imaging of aminothiols in living cells.

An investigation into possible xenobiotic-endobiotic inter-relationships involving the amino acid analogue drug, S-carboxymethyl-L-cysteine and plasma amino acids in humans

The amino acid derivative, S-carboxymethyl-L-cysteine, is an anti-oxidant agent extensively employed as adjunctive therapy in the treatment of human pulmonary conditions. A major biotransformation route of this drug, which displays considerable variation in capacity in man, involves the oxidation of the sulfide moiety to the inactive S-oxide metabolite. Previous observations have indicated that fasted plasma L-cysteine concentrations and fasted plasma L-cysteine/free inorganic sulfate ratios were correlated with the degree of sulfoxidation of this drug and that these particular parameters may be used as endobiotic biomarkers for this xenobiotic metabolism. It has been proposed also that the enzyme, cysteine dioxygenase, was responsible for the drug sulfoxidation. Further in this theme, the degree of S-oxidation of S-carboxymethyl-L-cysteine in 100 human volunteers was investigated with respect to it potential correlation with fasted plasma amino acid concentrations. Extensive statistical analyses showed no significant associations or relationships between the degree of drug S-oxidation and fasted plasma amino acid concentrations, especially with respect to the sulfur-containing compounds, methionine, L-cysteine, L-cysteine sulfinic acid, taurine and free inorganic sulfate, also the derived ratios of L-cysteine/L-cysteine sulfinic acid and L-cysteine/free inorganic sulfate. It was concluded that plasma amino acid levels or derived ratios cannot be employed to predict the degree of S-oxidation of S-carboxymethyl-L-cysteine (or vice versa) and that it is doubtful if the enzyme, cysteine dioxygenase, has any involvement in the metabolism of this drug.

The effect of uremic toxin cyanate (OCN–) on anaerobic sulfur metabolism and prooxidative processes in the rat kidney: a protective role of lipoate

Cyanate and its active form isocyanate are formed mainly in the process of nonenzymatic urea biodegradation. Cyanate is capable of protein S- and N-carbamoylation, which can affect their activity. The present studies aimed to demonstrate the effect of cyanate on activity of the enzymes implicated in anaerobic cysteine metabolism and cyanide detoxification and on glutathione (GSH) level and peroxidative processes in the kidney. In addition, we examined whether a concomitant treatment with lipoate, a dithiol that may act as a target of S-carbamoylation, can prevent these changes. The studies were conducted in Wistar rats. The animals were assigned to four groups, which received injections of physiological saline, cyanate (200 mg/kg), cyanate (200 mg/kg) + lipoate (100 mg/kg) and lipoate alone (100 mg/kg). The animals were killed 2 h after the first injection, the kidneys were isolated and kept at -80°C until biochemical assays were performed. Cyanate inhibited rhodanese (TST) and mercaptopyruvate sulfotransferase (MPST) activity, decreased GSH level and enhanced peroxidative processes in the kidney. All these changes were abolished by cyanate treatment in combination with lipoate.

A sensitive and selective fluorescent thiol probe in water based on the conjugate 1,4-addition of thiols to alpha,beta-unsaturated ketones

Compound 1 was designed and synthesized as a new fluorescent thiol probe. Probe 1 was constructed on the basis of the conjugate 1,4-addition of thiols to alpha,beta-unsaturated ketones. Notably, probe 1 has suitable water solubility, which allows the sensing assay to be performed in water. Probe 1 is highly sensitive for thiols with a 211-fold fluorescence dynamic range and a low detection limit of 9.25x10(-7) M. The major features of probe 1 also include a high selectivity for thiols over other relevant biological species, excitation and emission in the visible region, rapid functioning at pH 7.4, and a good linear relationship between the fluorescence signal and the thiol concentration. Accordingly, these desirable characteristics may render probe 1 as potentially useful for biological applications.

Disruption of thiol homeostasis in plasma of terminal renal failure patients

BACKGROUND

The aim of the present studies was to investigate the changes in concentrations of different forms of thiols in plasma of terminal renal failure patients before and after hemodialysis.

METHODS

Total concentrations of thiols, their free forms and the level of their mixed disulfides with proteins were determined with HPLC.

RESULTS

In terminal renal failure patients before dialysis, total concentrations of cysteine, homocysteine and cysteinylglycine and their free and protein-bound fractions increased while level of all such forms of glutathione dropped. A single dialysis session caused short-lasting return of concentrations of all forms of thiols to the level equal or close to the control group. The changes observed in non-dialyzed patients were similar to those observed in dialyzed patients before single dialysis procedure.

CONCLUSIONS

The obtained results showed severe disturbance of thiol homeostasis in plasma of terminal renal failure patients. The following changes have to be emphasized: (1) high level of free cysteine (cystine) fraction, (2) strong tendency of homocysteine to form mixed disulfides with proteins, (3) drop of glutathione level. These observations confirm a suggestion that atherogenic action of homocysteine can be a result of S-homocysteinylation and N-homocysteinylation reactions, whereas toxic action of cysteine can result from auto-oxidation reaction.

Redox Imbalance in Cystine/Glutamate Transporter-deficient Mice

Cystine/glutamate transporter, designated as system x(-)(c), mediates cystine entry in exchange for intracellular glutamate in mammalian cells. This transporter consists of two protein components, xCT and 4F2 heavy chain, and the former is predicted to mediate the transport activity. This transporter plays a pivotal role for maintaining the intracellular GSH levels and extracellular cystine/cysteine redox balance in cultured cells. To clarify the physiological roles of this transporter in vivo, we generated and characterized mice lacking xCT. The xCT(-/-) mice were healthy in appearance and fertile. However, cystine concentration in plasma was significantly higher in these mice, compared with that in the littermate xCT(-/-) mice, while there was no significant difference in plasma cysteine concentration. Plasma GSH level in xCT(-/-) mice was lower than that in the xCT(-/-) mice. The embryonic fibroblasts derived from xCT(-/-) mice failed to survive in routine culture medium, and 2-mercaptoethanol was required for survival and growth. When 2-mercaptoethanol was removed from the culture medium, cysteine and GSH in these cells dramatically decreased, and cells started to die within 24 h. N-Acetyl cysteine also rescued xCT(-/-)-derived cells and permitted growth. These results demonstrate that system x(-)(c) contributes to maintaining the plasma redox balance in vivo but is dispensable in mammalian development, although it is vitally important to cells in vitro.

Alteration in plasma levels of nonprotein sulfhydryl compounds and S-nitrosothiols in chronic renal failure patients

BACKGROUND

Uremia is accompanied by the elevated nitric oxide (NO) synthesis, and it has not yet been established how this influences the levels of nonprotein sulfhydryl compounds (NPSH) and formation of S-nitrosothiols (SNT).

METHODS

Our study was designed to determine plasma levels of SNT and NPSH in chronic renal failure (CRF) patients, who were hemodialysed (HD) or were not on hemodialysis treatment (ND), and in the control group.

RESULTS

In ND patients, the plasma levels of SNT were significantly increased (11.25+/-2.08 nmol/ml, p<0.01), while NPSH levels were simultaneously decreased (66.67+/-15.0 nmol/ml, p<0.05) in comparison with the control subjects (SNT: 8.75+/-2.08 nmol/ml, NPSH: 86.66 nmol/ml). In HD patients, plasma concentration of SNT before hemodialysis was significantly lower than in the control group (0.150+/-0.042 nmol/mg protein vs. control: 0.175+/-0.075 nmol/mg protein), and no significant change was observed after dialysis (0.142+/-0.058 nmol/mg protein, p<0.05). The level of NPSH in HD patients before dialysis was significantly decreased in comparison with the control subjects, both, when the results were calculated per 1 ml of plasma (45.96+/-17.87 nmol/ml) and per 1 mg of protein (0.70+/-0.25 nmol/mg protein). In the postdialysis samples, NPSH rose (79.15+/-22.9 nmol/ml, p<0.001 which corresponds to 1.30+/-0.55 nmol/mg protein, p<0.001) as compared to the level before dialysis.

CONCLUSIONS

Firstly, plasma SNT level was found to be increased in CRF patients who were not treated with hemodialysis, while in HD patients, it dropped below the control values. It indicates that hemodialysis disturbs an equilibrium of reactions involved in S-nitrosothiols formation most probably by removing low molecular weight S-nitrosylating compounds. Secondly, the increased level of NPSH after each hemodialysis session indicates reestablished antioxidant capacity of plasma and suggests the existence of dialysable compounds, which via unknown mechanism become responsible for the decreased level of thiols.

Distribution of cystine/glutamate exchange transporter, system x(c)-, in the mouse brain

Mammalian cells express a transport system known as system x(c)-, which is an exchange agency specific for anionic forms of cystine and glutamate. System x(c)- activity is important to maintain both intracellular glutathione levels and the redox balance between cystine and cysteine in the extracellular milieu. We have shown that the cloned cDNAs encoding the transporter for system x(c)- consist of two components, xCT and the heavy chain of 4F2 antigen. In the present study, we have investigated the mRNA distribution for these components in the mouse brain by in situ hybridization. The xCT mRNA was expressed in the area postrema, subfornical organ, habenular nucleus, hypothalamic area, and ependymal cells of the lateral wall of the third ventricle in the adult mouse brain. A strong signal was also detected in the meninges in both adult and fetal mouse brains. The mRNA expression of the heavy chain of 4F2 antigen was detected in a more broad area, including all of the regions in which xCT mRNA was detected. These data are compatible with our biochemical evidence that xCT functions in combination with the heavy chain of 4F2 antigen to elicit system x(c)- activity. The expression of system x(c)- in meninges and some circumventricular organs may suggest that this transporter contributes to the maintenance of the redox state (i.e., cysteine/cystine ratio) in the CSF.

A simple, optimized method for the determination of sulphide in whole blood by GC-mS as a marker of bowel fermentation processes

Hydrogen sulphide is produced in human large intestine by anaerobic fermentation and may play a pathogenic role. An analytical method for determination of sulphide in whole blood using an extractive alkylation technique was optimised and validated for this purpose. The sample was mixed with organic phase containing pentafluorobenzyl bromide as an alkylating agent. The benzalkonium chloride was used as a phase-transfer catalyst. The quantitative determination was performed using GC-MS technique in selected ion monitoring mode. The blood levels of sulphide of healthy controls were measured (35-80 microM/l). The method is versatile, reproducible (RSD=2.7%) and suitable for research of anaerobic fermentation in vivo.