Plasma reduced homocysteine concentrations are increased in end-stage renal disease

Homocysteine Solution-Induced Response in Aerosol Jet Printed OECTs by Means of Gold and Platinum Gate Electrodes

Homocysteine (Hcy) is a non-protein, sulfur-containing amino acid, which is recognized as a possible risk factor for coronary artery and other pathologies when its levels in the blood exceed the normal range of between 5 and 12 μmol/L (hyperhomocysteinemia). At present, standard procedures in laboratory medicine, such as high-performance liquid chromatography (HPLC), are commonly employed for the quantitation of total Hcy (tHcy), i.e., the sum of the protein-bound (oxidized) and free (homocystine plus reduced Hcy) forms, in biological fluids (particularly, serum or plasma). Here, the response of Aerosol Jet-printed organic electrochemical transistors (OECTs), in the presence of either reduced (free) and oxidized Hcy-based solutions, was analyzed. Two different experimental protocols were followed to this end: the former consisting of gold (Au) electrodes' biothiol-induced thiolation, while the latter simply used bare platinum (Pt) electrodes. Electrochemical impedance spectroscopy (EIS) analysis was performed both to validate the gold thiolation protocol and to gain insights into the reduced Hcy sensing mechanism by the Au-gated OECTs, which provided a final limit of detection (LoD) of 80 nM. For the OECT response based on Platinum gate electrodes, on the other hand, a LoD of 180 nM was found in the presence of albumin-bound Hcy, with this being the most abundant oxidized Hcy-form (i.e., the protein-bound form) in physiological fluids. Despite the lack of any biochemical functionalization supporting the response selectivity, the findings discussed in this work highlight the potential role of OECT in the development of low-cost point-of-care (POC) electronic platforms that are suitable for the evaluation, in humans, of Hcy levels within the physiological range and in cases of hyperhomocysteinemia.

A simple and accurate HFCF-UF method for the analysis of homocysteine, cysteine, cysteinyl-glycine, and glutathione in human blood

The presence of reduced aminothiols, including homocysteine (Hcy), cysteine (Cys), cysteinyl-glycine (CG), and glutathione (GSH), is significantly increased in the pathological state. However, there have been no reports on the relationship between reduced aminothiols (Hcy, Cys, CG, and GSH) and different genders, ages, and drug combinations in human blood. The accurate quantification of these reduced thiols in biological fluids is important for monitoring some special pathological conditions of humans. However, the published methods typically not only require cumbersome and technically challenging processing procedures to ensure reliable measurements, but are also laborious and time-consuming, which may disturb the initial physiological balance and lead to inaccurate results. We developed a hollow fiber centrifugal ultrafiltration (HFCF-UF) method for sample preparation coupled with a high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) method and used it to determine four reduced aminothiols (Hcy, Cys, CG, and GSH) in human blood for the first time. A total of 96 clinical patients were enrolled in our study. The influence of different genders, ages, and drug combinations on the levels of four reduced thiols in human blood was also discussed by SPSS 24.0. The sample preparation was simplified to a single 5 min centrifugation step in a sealed system that did not disturb the physiological environment. The validation parameters for the methodological results were excellent. The procedure was successfully applied to monitoring the concentrations of four reduced aminothiols (Hcy, Cys, CG, and GSH) in 96 clinical blood samples. There were no significant differences in Hcy, Cys, CG, or GSH for the different genders, ages, or combinations with methotrexate or vancomycin (P > 0.05). However, there was a significant increase in Hcy concentration in patients treated with valproic acid who were diagnosed with epilepsy (p=0.0007). It is advisable to measure reduced Hcy level in patients taking valproic acid. The developed HFCF-UF method was simple and accurate. It can be easily applied in clinical research to evaluate oxidative stress in further study.

Diet-induced hyperhomocysteinemia impairs vasodilation in 5/6-nephrectomized rats

Plasma homocysteine is elevated in patients with impaired renal function, and markedly so at end-stage renal disease. As chronic kidney disease and hyperhomocysteinemia are also independent risk factors for cardiovascular disease, the latter is hypothesized to accelerate vascular abnormalities following renal failure. This study aimed to investigate the combined effect of impaired renal function and hyperhomocysteinemia on vascular function. We show that in 5/6-nephrectomized rats, a model of chronic kidney disease, a methionine-rich diet for 8 weeks induces moderate hyperhomocysteinemia, exacerbates hypertension, and attenuates the vascular response to acetylcholine, sodium nitroprusside, 8-bromo-cGMP, and isoprenaline. However, plasma nitrate/nitrite and total NOS activity in the thoracic aorta were not affected. Collectively, the data imply that hyperhomocysteinemia and end-stage renal disease synergistically impair endothelium-dependent and endothelium-independent vasodilatation by blocking the cGMP/protein kinase G and/or cAMP/protein kinase A pathways. 5/6-Nephrectomized rat with hyperhomocysteinemia induced by a methionine-rich diet would be a useful model for elucidating the pathogenesis of vascular impairment in patients with end-stage renal disease.

Osteopontin, Cardiovascular Risk Factors and Carotid Intima-Media Thickness in Chronic Kidney Disease

The pleiotropic cytokine osteopontin (OPN) is found to be involved in the pathogenesis of both kidney and cardiovascular disease (CVD). We evaluated the relationship between OPN, other cardiovascular risk factors and carotid intima-media thickness (CIMT) in chronic kidney disease (CKD) (predialysis) patients. This is a 2-year cross-sectional prospective study involving 75 patients with CKD from stage 1 to stage 5 attending the nephrology outpatient department and 25 healthy controls. Routine biochemical parameters were analyzed on clinical chemistry Autoanalyzer Beckman Coulter DXC 600 Synchron, USA. OPN was estimated by ELISA method. Carotid intima-media wall thickness was estimated by Doppler of carotid vessels. Serum OPN and other nontraditional cardiovascular risk factors such as CIMT, lipoprotein (a) Lp(a), fibrinogen, and homocysteine were significantly increased in patients of CKD compared to controls. OPN, Lp(a), fibrinogen, CIMT, parathyroid hormone, and homocysteine progressively increased from early stages of CKD and increased further with progression of the disease, but nitric oxide (NO) level progressively decreased with progression of CKD. OPN showed a positive correlation with CIMT, Lp(a), fibrinogen, and homocysteine and negative correlation with estimated glomerular filtration rate and NO. There was a close direct association between circulating levels of OPN and the presence of atherosclerotic plaques in carotid arteries of patients with CKD. Osteopontin and nontraditional CVD risk factors are altered in early stages of CKD and might predict adverse outcomes in these patients.

Disulfide Bonds as Regulators of Integrin Function in Thrombosis and Hemostasis

SIGNIFICANCE

Disulfide bonds are generally viewed as structure-stabilizing elements in proteins, but some display an alternative functional role as redox switches. Functional disulfide bonds have recently emerged as important regulators of integrin function in thrombosis and hemostasis.

RECENT ADVANCES

Functional disulfide bonds were identified in the β subunit of the major platelet integrin αIIbβ3 and in other integrins involved in thrombus formation that is, αvβ3 and α2β1. Most of these functional bonds are located in the four epidermal growth factor-like domains of the integrins. Redox agents such as glutathione and nitric oxide and enzymatic thiol isomerase activity were shown to regulate the function of these integrins by disulfide bond reduction and thiol/disulfide exchange.

CRITICAL ISSUES

Increasing evidence suggests that thiol isomerases such as protein disulfide isomerase (PDI) and Erp57 directly bind to the β3 subunit of αIIbβ3 and αvβ3 and regulate their function during thrombus formation. αIIbβ3 also exhibits an endogenous thiol isomerase activity. The specific functional disulfide bonds identified in the β3 subunit might be the targets for both exogenous and endogenous thiol isomerase activity.

FUTURE DIRECTIONS

Targeting redox sites of integrins or redox agents and enzymes that regulate their function can provide a useful tool for development of anti-thrombotic therapy. Hence, inhibitors of PDI are currently studied for this purpose.

Determination of reduced homocysteine in human serum by elemental labelling and liquid chromatography with ICP-MS and ESI-MS detection

Analytical methods allowing sensitive determination of reduced homocysteine (rHcy), one of the so-called biothiols, in human serum is a topic of growing interest due to its close relation to several human disorders, mainly cardiovascular diseases. Although most widely used analytical strategies to determine total Hcy involve derivatization by means of fluorescent labels, this work proposes the use of ebselen, a Se-containing labelling agent to derivatize the reactive sulfhydryl group of the Hcy molecule in its "free" reduced form, which is more likely to play different roles in disease pathogenesis. Optimization of the derivatization and separation conditions by high-performance liquid chromatography (HPLC) to isolate the excess of derivatizing reagent is carried out here using UV/VIS detection. Further, the study of the Se labelling reaction by electrospray ionization tandem mass spectrometry (ESI-MS/MS) provides a stoichiometry of the derivative of 1:1. The main advantage of using ebselen as a labelling agent is the presence of the Se atom in the molecule that allows the use of inductively coupled plasma mass spectrometry (ICP-MS) as a sensitive and selective Se detector. The coupling of HPLC with ICP-MS provided excellent features for the determination of Se-derivatized rHcy (detection limit of 9.6 nM) in real samples. Quantification was accomplished by using post-column isotope dilution (ID) of Se in serum samples, after precipitation of the main serum proteins. Quantitative results for "free" rHcy turned out to be around 0.18-0.22 μM in serum samples from healthy individuals that could be directly analyzed without sample preconcentration.

Plasma vitamins, amino acids, and renal function in postexercise hyperhomocysteinemia

Several studies have assessed the effect of the physical activity on plasma homocysteine (Hcy) concentrations, although the findings have been contradictory, and the exact mechanism by which plasma Hcy concentrations varied after an acute intense exercise remains unknown.

PURPOSE

We studied the effect of different acute aerobic intense exercises on plasma, reduced, and total Hcy (rHcy, tHcy) and cysteine (rCys, tCys) and on its metabolically related vitamins and amino acids. Parallel effects on renal function were assessed by plasma creatinine.

METHODS

Fifteen cyclists and 14 kayakers were examined before and 30 +/- 5 min after a specific test to exhaustion during a low-intensity training period.

RESULTS

After a bout of specific exercise, the concentrations of aminothiols were increased regardless of the group considered. Plasma concentrations were higher than baseline values in tHcy (17.7 +/- 1.5%; P < 0.001), rHcy (10.6 +/- 1.6%; P < 0.001), tCys (9.9 +/- 1.6%; P < 0.001), and rCys (7.6 +/- 2.2%; P < 0.01). Both groups showed significant elevations of pyridoxal-5'-phosphate (PLP; P < 0.01), vitamin B12 (P < 0.001), and creatinine concentrations (P < 0.001) after acute exercises, but no changes were seen in folate. Changes in plasma aminothiols after exercise did not reach significant correlation with changes in free amino acids or baseline vitamins, but significant and positive correlations were observed with changes in plasma PLP, vitamin B12, and creatinine concentrations, when the pooled data were considered.

CONCLUSIONS

Our results show that higher plasma concentrations of tHcy after an acute intense exercise are associated to higher concentrations of rHcy, and this effect is independent of the type of exercise, vitamin status, or amino acid metabolic stress but could be related to potential changes in the renal function.

Redox control of platelet function

There has recently been a dramatic expansion in research in the area of redox biology with systems that utilize thiols to perform redox chemistry being central to redox control. Thiol-based reactions occur in proteins involved in platelet function, including extracellular platelet proteins. The alphaIIbbeta3 fibrinogen receptor contains free thiols that are required for the activation of this receptor to a fibrinogen-binding conformation. This process is under enzymatic control, with protein disulfide isomerase playing a central role in the activation of alphaIIbbeta3. Other integrins, such as the alpha2beta1 collagen receptor on platelets, are also regulated by protein disulfide isomerase and thiol metabolism. Low molecular weight thiols that are found in blood regulate these processes by converting redox sensitive disulfide bonds to thiols and by providing the appropriate redox potential for these reactions. Additional mechanisms of redox control of platelets involve nitric oxide that inhibits platelet responses, and reactive oxygen species that potentiate platelet thrombus formation. Specific nitrosative or oxidative modifications of thiol groups in platelets may modulate platelet function. Since many biologic processes are regulated by redox reactions that involve surface thiols, the extracellular redox state can have an important influence on health and disease status and may be a target for therapeutic intervention.

Administration of minor polar compound-enriched extra virgin olive oil decreases platelet aggregation and the plasma concentration of reduced homocysteine in rats

We investigated the effect of extra virgin olive oil (EVOO) on platelet aggregation and plasma concentrations of homocysteine (Hcy) redox forms in rats in relation to the minor polar compound (MPC) concentration of EVOO. We used 3 olive oil samples with similar fatty acid but different MPC concentrations: refined olive oil (RF) with traces of MPC (control oil), native EVOO with low MPC concentration (LC), and EVOO with high MPC concentration (HC) enriching LC with its own MPC. Oil samples were administered to rats by gavage (1.25 mL/kg body weight) using 2 experimental designs: acute (24-h food deprivation and killed 1 h after EVOO administration) and subacute (12-d treatment, a daily dose of oil for 12 d, and killed after 24 h of food deprivation). Platelet aggregation was induced by ADP (ex vivo tests) and a reduction in platelet reactivity occurred in cells from rats given LC in the subacute study and in cells from rats administered HC in both studies as indicated by an increase in the agonist half maximal effective concentration. HC inhibited platelet aggregation induced by low ADP doses (reversible aggregation) in cells of rats in both the acute and subacute studies, whereas LC had this effect only in the subacute experiment. Moreover, in rats administered HC in both experiments, the plasma concentration of free reduced Hcy (rHcy) was lower and Hcy bound to protein by disulfide bonds (bHcy) was greater than in RF-treated rats. bHcy was also greater in rats given LC than in RF-treated rats in the subacute experiment. Plasma free-oxidized Hcy was greater in rats given LC and HC than in those administered RF only in the subacute experiment. In conclusion, these results show that MPC in EVOO inhibit platelet aggregation and reduce the plasma rHcy concentration, effects that may be associated with cardiovascular protection.

Detrimental role of homocysteine in renal ischemia-reperfusion injury

Ischemia followed by reperfusion is a major cause for renal injury in both native kidney and renal allografts. Hyperhomocysteinemia, a condition of elevated plasma homocysteine (Hcy) level, is associated with cardiovascular diseases. Recent evidence suggests that Hcy, at higher levels, may be harmful to other organs such as the kidney. In this study, we investigated the role of Hcy in ischemia-reperfusion-induced renal injury. The left kidney of a Sprague-Dawley rat was subjected to either 30-min or 1-h ischemia followed by 1- or 24-h reperfusion. Ischemia-reperfusion caused a significant increase in peroxynitrite formation and lipid peroxidation in kidneys, which reflected oxidative stress. The number of apoptotic cells in those kidneys was also markedly increased. Hcy levels were elevated 2.9- and 1.5-fold in kidneys subjected to ischemia alone or ischemia-reperfusion, respectively. Further investigation revealed that elevation of Hcy level in the kidney upon ischemia-reperfusion was due to reduced activity of cystathionine-beta-synthase, a key enzyme in Hcy metabolism. Administration of anti-Hcy antibodies into the kidney not only abolished ischemia-reperfusion-induced oxidative stress and cell death in the kidneys but also restored renal function after 1 h of reperfusion. However, such a protective effect was not sustained after 24 h of reperfusion. In conclusion, ischemia-reperfusion impairs Hcy metabolism in the kidney. Hcy, at elevated levels, is capable of inducing oxidative stress and renal injury. Neutralization of Hcy with antibodies offers transient functional benefit against ischemia-reperfusion-induced oxidative stress and renal injury. These results suggest that Hcy may play a detrimental role in the kidney during ischemia-reperfusion.

Increased plasma protein homocysteinylation in hemodialysis patients

Hyperhomocysteinemia, an independent cardiovascular risk factor, is present in the majority of hemodialysis patients. Among the postulated mechanisms of toxicity, protein homocysteinylation is potentially able to cause significant alterations in protein function. Protein homocysteinylation occurs through various mechanisms, among which is the post-translational acylation of free amino groups (protein-N-homocysteinylation, mediated by homocysteine (Hcy) thiolactone). Another type of protein homocysteinylation occurs through the formation of a covalent -S-S- bond, found primarily with cysteine residues (protein-S-homocysteinylation). Scant data are available in the literature regarding the extent to which alterations in protein homocysteinylation are present in uremic patients on hemodialysis, and the effects of folate treatment are not known. Protein homocysteinylation was measured in a group of hemodialysis patients (n=28) compared to controls (n=14), with a new method combining protein reduction, gel filtration and Hcy derivatization. Chemical hydrolysis was performed, followed by high-pressure liquid chromatography separation. The effects of folate treatment on protein homocysteinylation, as well as in vitro binding characteristics were evaluated. Plasma Hcy, protein-N-homocysteinylation and protein-S-homocysteinylation were significantly higher in patients vs controls. Plasma Hcy and protein-S-homocysteinylation were significantly correlated. After 2 months of oral folate treatment, protein-N-homocysteinylation was normalized, and protein-S-homocysteinylation was significantly reduced. Studies on albumin-binding capacity after in vitro homocysteinylation show that homocysteinylated albumin is significantly altered at the diazepam-binding site. In conclusion, increased protein homocysteinylation is present in hemodialysis patients, with possible consequences in terms of protein function. This alteration can be partially reversed after folate treatment.

Does Treating Subclinical Hypothyroidism Improve Markers of Cardiovascular Risk?

Subclinical hypothyroidism is defined as an elevated serum thyroid-stimulating hormone (TSH) level in the face of normal free thyroid hormone values. The overall prevalence of subclinical hypothyroidism is 4-10% in the general population and up to 20% in women aged >60 years. The potential benefits and risks of therapy for subclinical hypothyroidism have been debated for 2 decades, and a consensus is still lacking. Besides avoiding the progression to overt hypothyroidism, the decision to treat patients with subclinical hypothyroidism relies mainly on the risk of metabolic and cardiovascular alterations. Subclinical hypothyroidism causes changes in cardiovascular function similar to, but less marked than, those occurring in patients with overt hypothyroidism. Diastolic dysfunction both at rest and upon effort is the most consistent cardiac abnormality in patients with subclinical hypothyroidism, and also in those with slightly elevated TSH levels (>6 mIU/L). Moreover, mild thyroid failure may increase diastolic blood pressure as a result of increased systemic vascular resistance. Restoration of euthyroidism by levothyroxine replacement is generally able to improve all these abnormalities. Early clinical and autopsy studies had suggested an association between subclinical hypothyroidism and coronary heart disease, which has been subsequently confirmed by some, but not all, large cross-sectional and prospective studies. Altered coagulation parameters, elevated lipoprotein (a) levels, and low-grade chronic inflammation are regarded to coalesce with the hypercholesterolemia of untreated patients with subclinical hypothyroidism to enhance the ischemic cardiovascular risk. Although a consensus is still lacking, the strongest evidence for a beneficial effect of levothyroxine replacement on markers of cardiovascular risk is the substantial demonstration that restoration of euthyroidism can lower both total and low-density lipoprotein-cholesterol levels in most patients with subclinical hypothyroidism. However, the actual effectiveness of thyroid hormone substitution in reducing the risk of cardiovascular events remains to be elucidated. In conclusion, the multiplicity and the possible reversibility of subclinical hypothyroidism-associated cardiovascular abnormalities suggest that the decision to treat a patient should depend on the presence of risk factors, rather than on a TSH threshold. On the other hand, levothyroxine replacement therapy can always be discontinued if there is no apparent benefit. Levothyroxine replacement therapy is usually safe providing that excessive administration is avoided by monitoring serum TSH levels. However, the possibility that restoring euthyroidism may be harmful in the oldest of the elderly population of hypothyroid patients has been recently raised, and should be taken into account in making the decision to treat patients with subclinical hypothyroidism who are aged >85 years.

Plasma Reduced Homocysteine and Other Aminothiol Concentrations in Patients With CKD

BACKGROUND

Hyperhomocysteinemia, a risk factor for cardiovascular disease, is present in the majority of patients with chronic kidney disease (CKD). Several studies indicated that the moiety of homocysteine (Hcy) with an unbound -SH group (reduced Hcy [rHcy]) is the atherogenic molecule. This study is designed to examine the relation between different forms of Hcy and other aminothiols in hemodialysis (HD) patients, peritoneal dialysis (PD) patients, and nondialyzed patients with CKD.

METHODS

rHcy, free Hcy (fHcy), and total Hcy (tHcy), as well as different forms of cysteine, cysteinyl-glycine, and glutathione, were studied by using a high-performance liquid chromatography technique in 19 HD patients, 12 PD patients, 47 patients with CKD, and 15 control subjects.

RESULTS

In PD patients, tHcy levels were 2.8 times greater compared with controls, and in HD patients and those with CKD, 2.1 and 1.9 times greater, respectively. Mean rHcy/tHcy ratios were significantly greater in both HD (P < 0.05) and PD patients (P < 0.01), but did not differ in patients with CKD compared with controls. The decrease in rHcy levels during 1 HD treatment was smaller than that in tHcy and fHcy levels, and rHcy/tHcy ratio increased (before HD, 1.25% +/- 0.44%; after HD, 1.44% +/- 0.66%; P < 0.05).

CONCLUSION

Levels of rHcy and other aminothiols are markedly increased in patients with impaired renal function. In dialysis patients, rHcy/tHcy ratio is markedly elevated and shows greater variability than in patients with CKD and controls. We conclude that because rHcy is believed to induce endothelial dysfunction and may be part of the accelerated atherogenic process in patients with CKD, plasma rHcy level could be a more relevant marker of cardiovascular disease risk than tHcy level.

Preliminary Results of the Effect of Treatment of Hyperhomocysteinemia and Its Relationship With Inflammation, Coagulation Status, and Endothelial Function After Renal Transplantation

The aim of this study was to assess the relationship between total plasma homocysteine (tHC) and several markers of endothelial function, coagulation, and pro-inflammatory status in renal transplant recipients. Our own previous study demonstrated the efficacy of folic acid (FA) and vitamin B(12) (B(12)) treatment to reduce tHC. Using 70 stable recipients, 56 of whom showed hyperhomocisteinemia (HHC) (tHC > or = 14 micromol/L) and a control group (n = 14, tHC < 14 micromol/L), we treated 29 patients in the HHC group (10 mg FA and 500 mg B(12) daily) and determined their endothelial function, inflammatory activity, and coagulation status. We assessed plasma levels of von Willebrand Factor and fibrinogen as the prothrombotic profile and C-reactive protein and plasma albumin as inflammation markers. We performed Doppler sonography of the brachial artery to assess endothelial function. The mean value of plasma tHC of 19.05 +/- 3.70 micromol/L before treatment decreased to 13.45 +/- 3.25 micromol/L after 3 months of treatment (P < .001). The vWF was significantly correlated with tHC (P < .05) and was higher in the HHC patients (P < .05). The fibrinogen mean level was also significantly higher in HHC patients (P < .05). The C-reactive protein level was significantly higher and the albumin level was lower among patients with HHC. The endothelium-dependent dilation (EDD) correlated with baseline tHC (P < .05). In preliminary data we observed that homocysteine-lowering therapy may provide cardiovascular protection by enhancing endothelial function, limiting oxidative stress, and reducing procoagulation status.

Various forms of homocysteine and oxidative status in the plasma of ischemic-stroke patients as compared to healthy controls

OBJECTIVES

We compared various forms of plasma homocysteine (Hcy) including total Hcy (tHcy), free reduced Hcy (reHcy), free oxidized Hcy (oxHcy) and reHcy plus oxHcy between patients with acute/subacute-ischemic stroke and healthy controls. We also investigated whether the patients have increased oxidative stress.

DESIGN AND METHODS

Using an in-tube derivatization method, we measured plasma levels of tHcy, reHcy and oxHcy in 55 ischemic-stroke patients (14 females and 41 males, median age 64) and 52 age-matched healthy subjects (15 females and 37 males, median age 60). We also measured plasma malondialdehyde (MDA, as lipid peroxidation marker) and oxygen-radical absorbance capacity (ORAC, as total antioxidant activity).

RESULTS

The plasma levels of reHcy and reHcy plus oxHcy and the ratio of reHcy to oxHcy were significantly higher in the patients than in the age-matched controls, whereas tHcy and oxHcy levels were not significantly different. The patients had a significantly higher level of MDA but a lower value of ORAC than that of controls. A significantly positive correlation was found in the levels of reHcy vs. MDA (r = 0.19, P < 0.03), whereas significant negative correlations were found for reHcy vs. ORAC (r = -0.30, P < 0.001) and free Hcy vs. ORAC (r = -0.30, P < 0.001).

CONCLUSIONS

reHcy and reHcy plus oxHcy Hcy, rather than tHcy, are significantly elevated in patients with acute/subacute ischemic stroke. The elevated reHcy along with elevated MDA level and lowered ORAC value in the plasma of the stroke patients indicates an imbalance of antioxidant-prooxidant status in acute ischemic stroke.

The role of thiols and disulfides in platelet function

Disulfide bonds formed in newly synthesized proteins in the endoplasmic reticulum of cells are important for protein structure and stability. Recent research, however, emphasizes a role for thiol-disulfide reactions with disulfide bond rearrangement as a dynamic process in cell and protein function, and in platelet function in particular. Protein disulfide isomerase was found on the platelet surface where it appears to play an important role in the platelet responses of aggregation and secretion, as well as activation of the platelet fibrinogen receptor, the alphaIIbbeta3 integrin. Additionally, sulfhydryl groups in alphaIIbbeta3 have been implicated in the activation of this integrin. Physiologic concentrations of reduced glutathione generate sulfhydryls in alphaIIbbeta3 and potentiate sulfhydryl-dependent reactions in alphaIIbbeta3. Sulfhydryl labeling in alphaIIbbeta3 is inhibited by phenylarsine oxide, a reagent that binds to vicinal thiols. As vicinal thiols are in equilibrium with disulfide bonds, they provide redox-sensitive sites in alphaIIbbeta3 able to respond to external or cytoplasmic reducing equivalents. Furthermore, protein disulfide isomerase and sulfhydryls are now implicated in platelet adhesion by a second platelet integrin, the alpha2beta1 collagen receptor. Most recently, extracellular sulfhydryls in the P2Y12 ADP receptor were found to be required for platelet activation by this receptor. We here provide an overview of this field with a focus on recent developments, and conclude with a working model.

Renal insufficiency and mortality from acute coronary syndromes

BACKGROUND

Although there is accumulating evidence that renal insufficiency is an independent risk factor for mortality after acute myocardial infarction (AMI), it is not known whether renal dysfunction is associated with an increased mortality rate after a broad range of acute coronary syndromes, including unstable angina.

METHODS

We examined consecutive patients from 24 Veterans Affairs hospitals with confirmed AMI or unstable angina between March 1998 and February 1999, who were categorized into groups according to estimated glomerular filtration rate (GFR). Multivariable regression was used to assess the independent association between GFR and the 7-month mortality rate, adjusting for differences in patient characteristics and treatment.

RESULTS

Of the 2706 patients, 436 (16%) had normal renal function (GFR >90 mL/min/1.73 m(2)), 1169 (43%) had mild renal insufficiency (GFR 60-89 mL/min/1.73 m(2)), 864 (32%) had moderate renal insufficiency (GFR 30-59 mL/min/1.73 m(2)), and 237 (9%) had severe renal insufficiency (GFR <30 mL/min/1.73 m(2)). Patients with renal insufficiency were less likely to undergo coronary angiography or to receive aspirin or beta-blockers at discharge. In multivariable models, renal insufficiency was associated with a higher odds of death (mild renal insufficiency: odds ratio [OR] = 1.76; 95% CI, 0.93-3.33; moderate renal insufficiency: OR = 2.72; 95% CI, 1.43-5.15; and severe renal insufficiency: OR = 6.18; 95% CI, 3.09-12.36; all compared with normal renal function). The associations between renal insufficiency and mortality rate were similar in both the AMI and unstable angina subgroups (P value for interaction =.45).

CONCLUSIONS

Renal insufficiency is common and is associated with higher risks for death in patients with a broad range of ACS at presentation. Future efforts should be dedicated to determining whether more aggressive treatment will optimize outcomes in this patient population.

Free cysteine is increased in plasma from hemodialysis patients

BACKGROUND

Although only the total thiol concentration, which includes bound and free forms, has been determined in most previous clinical studies, the free form may be a better predictor of cardiovascular risk.

METHODS

We measured the apparent concentration of free homocysteine (Hcy) and cysteine (Cys) in filtered and acid-soluble fractions of plasma in healthy control subjects and in patients with chronic renal failure just before and after a hemodialysis session.

RESULTS

In control, filtered Hcy and acid-soluble Hcy were similar, while filtered Cys was much smaller than in acid-soluble Cys. In prehemodialysis samples, filtered Cys was more than 60 times as abundant (259.2 +/- 26.2 micromol/L) as in control samples (4.1 +/- 0.7 micromol/L ). Free-to-total ratios for filtered Cys were 1.6 +/- 0.3% in controls, but 40.9 +/- 2.7% in prehemodialysis patients.

CONCLUSIONS

The filtered fraction of thiols can be used to estimate solute transport across the dialysis membrane. In addition, the possible involvement of cysteine in the pathogenesis of atherosclerosis in hemodialysis patients should be reexamined.

Elevated C-reactive protein and homocysteine values: cardiovascular risk factors in hypothyroidism? A cross-sectional and a double-blind, placebo-controlled trial

Hypothyroidism is associated with premature atherosclerosis and cardiovascular disease. Recently, total homocysteine (tHcy) and C-reactive protein (CRP) emerged as additional cardiovascular risk factors. We first investigated CRP and tHcy in different severities of primary hypothyroidism and in a second study we evaluated the effect of L-thyroxine treatment in patients with subclinical hypothyroidism (SCH) in a double-blind, placebo-controlled trial. One hundred and twenty-four hypothyroid patients (63 with subclinical, 61 with overt hypothyroidism, OH) and 40 euthyroid controls were evaluated. CRP was measured using a latex-based high sensitivity immunoassay; tHcy was determined by a fluorescence polarization immunoassay. tHcy values were significantly elevated in OH (P=0.01). In SCH tHcy levels were not augmented as compared to controls. CRP values were significantly increased in OH (P=0.016) and SCH (P=0.022) as compared to controls. In a univariate analysis tHcy correlated significantly with fT4, vitamin B12, folic acid and creatinine levels. In multiple regression analysis only fT4 (beta=0.33) had a significant effect on tHcy. CRP did not correlate with thyroid hormones. In SCH, L-T4 replacement had no significant effect on either tHcy or CRP levels. This is the first paper to show that CRP values increase with progressive thyroid failure and may count as an additional risk factor for the development of coronary heart disease in hypothyroid patients. In contrast to overt disease, only CRP, but not tHcy values, are affected in SCH, yet without significant improvement after L-thyroxine therapy.

Methods for measuring sulfur amino acid metabolism

PURPOSE OF REVIEW

The importance of sulfur amino acid metabolism has become increasingly apparent in recent years. Methionine and cysteine are precursors of glutathione, which plays an important role in intracellular antioxidant/free radical defenses. Homocysteine is a non-protein-bound sulfur amino acid strongly implicated in the pathogenesis of several diseases. Both glutathione and homocysteine are affected by abnormalities in sulfur amino acid metabolism that occur in the clinical setting.

RECENT FINDINGS

The Storch-Young model, which determines methionine turnover and homocysteine remethylation by means of a tracer methionine infusion, has been improved by using plasma homocysteine (rather than methionine) enrichment in the model. A complex new tracer method involving the use of tracer serine, methionine, and leucine has been described to determine the effects of folate or pyridoxine deficiency on sulfur amino acid-methyl transfer reactions in humans. The etiology of hyperhomocysteinemia in chronic renal failure is controversial; new concepts in this area are described. There is new interest in the subspecies of homocysteine in the circulation. A new method is described for measuring the extremely low plasma concentrations of reduced homocysteine, using gas chromatography-mass spectrometry. Plasma S-adenosylhomocysteine, measured by fluorescence high-performance liquid chromatography, has been suggested as being superior to homocysteine as a predictor of the risk of vascular disease.

SUMMARY

This review highlights and critiques the above recent developments, and points out some of the complexities and pitfalls in designing and interpreting human metabolic studies involving the sulfur amino acids.

Plasma aminothiol oxidation in chronic hemodialysis patients

BACKGROUND

Plasma aminothiols, including homocysteine, cysteine, and glutathione, function as an important extracellular redox system. We examined the plasma aminothiol concentration and redox status in ten chronic hemodialysis patients compared to ten age-matched healthy subjects.

METHODS

Plasma levels of reduced, free oxidized, and protein-bound homocysteine, cysteine, cysteinylglycine, and glutathione were determined using high-pressure liquid chromatography (HPLC).

RESULTS

Total plasma homocysteine, cysteine, and cysteinylglycine levels were significantly elevated in hemodialysis patients before dialysis compared to healthy subjects. Total plasma concentration of cysteine and homocysteine significantly decreased after hemodialysis. The ratio of free oxidized to free reduced homocysteine, cysteine, cysteinylglycine, and glutathione were each significantly elevated before dialysis compared to healthy subjects, and decreased significantly by the end of dialysis. The free oxidized to reduced ratio of cysteine and homocysteine were also significantly correlated with total plasma concentrations.

CONCLUSIONS

Plasma aminothiols are excessively oxidized in uremia, while the hemodialysis procedure is restorative of redox status. Oxidized aminothiols are candidate uremic toxins.

Pathophysiology and Treatment of Hyperhomocysteinemia in End-Stage Renal Disease Patients

The pathophysiology of hyperhomocysteinemia in end-stage renal disease (ESRD) patients includes impaired remethylation of homocysteine (Hcy) to methionine, inhibition of extrarenal Hcy metabolism by uremic solutes, a block in decarboxylation of cysteinesulfinic acid, impaired [adenosylmethionine]/[adenosylhomocysteine] ratio, and a probable impairment of renal Hcy metabolism and excretion. Treatment of hyperhomocysteinemia in ESRD patients includes administration of folic acid (1 - 15 mg per day). No additional effects have been observed with higher folic acid doses, folinic acid, or 5-methyltetrahydrofolate. Oral supplementation with vitamin B ₆ and vitamin B ₁₂ has no effect, but some studies reported a decrease of plasma Hcy with high intravenous vitamin doses. Effective reduction of plasma total Hcy (tHcy) in patients treated with super-flux hemodialyzers suggests the removal of uremic toxins with inhibitory activities against enzymes involved in the extrarenal Hcy metabolism.