A new chromatographic method for the determination of cysteine, glutathione, homocysteine and Nɛ-homocysteinyllysine isopeptide in human plasma

Cysteine and glutathione can be applied as therapeutic targets in civilization diseases such as diabetes mellitus and cancers. On the other hand, an elevated concentration of homocysteine, and its metabolites such as homocysteine thiolactone and Nɛ-homocysteinyllysine result in health problems and has been indicated as an independent risk factor for cardiovascular disease and accelerated atherosclerosis. This work describes the first simplified HPLC-UV method that allows simultaneous determination of Nɛ-homocysteinyllysine isopeptide, cysteine, glutathione and homocysteine in human plasma. The assay is based on reversed-phase high performance liquid chromatography with UV detection and simultaneous reduction of disulfide bound with tris(2-carboxyethyl)phosphine and the selective pre-column derivatization of the thiol group with 1-benzyl-2-chloropyridinium bromide. Linearities of the detector responses for plasma samples were observed in ranges: 0.1-10.0 nmol/mL for Nɛ-homocysteinyllysine, 2.0-60.0 nmol/mL for glutathione and homocysteine, 20.0-600.0 nmol/mL for cysteine. The proposed method reduces the number of steps, shortens the total time of sample preparation, and limits the amount of single-use polypropylene laboratory materials.

Homocysteine Modification in Protein Structure/Function and Human Disease

Epidemiological studies established that elevated homocysteine, an important intermediate in folate, vitamin B₁₂, and one carbon metabolism, is associated with poor health, including heart and brain diseases. Earlier studies show that patients with severe hyperhomocysteinemia, first identified in the 1960s, exhibit neurological and cardiovascular abnormalities and premature death due to vascular complications. Although homocysteine is considered to be a nonprotein amino acid, studies over the past 2 decades have led to discoveries of protein-related homocysteine metabolism and mechanisms by which homocysteine can become a component of proteins. Homocysteine-containing proteins lose their biological function and acquire cytotoxic, proinflammatory, proatherothrombotic, and proneuropathic properties, which can account for the various disease phenotypes associated with hyperhomocysteinemia. This review describes mechanisms by which hyperhomocysteinemia affects cellular proteostasis, provides a comprehensive account of the biological chemistry of homocysteine-containing proteins, and discusses pathophysiological consequences and clinical implications of their formation.

Fluorescent Probes with Multiple Binding Sites for the Discrimination of Cys, Hcy, and GSH

Biothiols such as cysteine (Cys), homocysteine (Hcy), and glutathione (GSH) play crucial roles in maintaining redox homeostasis in biological systems. This Minireview summarizes the most significant current challenges in the field of thiol-reactive probes for biomedical research and diagnostics, emphasizing the needs and opportunities that have been under-investigated by chemists in the selective probe and sensor field. Progress on multiple binding site probes to distinguish Cys, Hcy, and GSH is highlighted as a creative new direction in the field that can enable simultaneous, accurate ratiometric monitoring. New probe design strategies and researcher priorities can better help address current challenges, including the monitoring of disease states such as autism and chronic diseases involving oxidative stress that are characterized by divergent levels of GSH, Cys, and Hcy.

Nonstenotic bicuspid aortic valve is associated with elevated plasma asymmetric dimethylarginine

BACKGROUND

Recently, it has been reported that nonstenotic bicuspid aortic valve (BAV) with dilated proximal aorta is linked with increased matrix metalloproteinase-2 (MMP-2) and endothelial dysfunction.

OBJECTIVE

We wondered whether asymmetric dimethylarginine (ADMA), a nitric oxide synthase inhibitor, might be altered and associated with MMP-2 in BAV patients. We assessed the relation between ADMA levels and aortic diameters and hypothesized that elevated ADMA might be an independent predictor of progressive aortic dilatation in BAV patients.

METHODS

We studied 20 patients with nonstenotic BAV (17 men and 3 women, median age 27, range 24-33 years). Twenty age-matched patients with tricuspid aortic valves served as controls. Plasma levels of ADMA, symmetric dimethylarginine (SDMA), L-arginine, serum MMP-2, MMP-9, and plasma total homocysteine (tHcy), together with parameters of aortic elasticity, were measured.

RESULTS

ADMA and MMP-2 levels were higher in the BAV group compared with controls (medians, 0.55 vs. 0.43 μmol/l, P < 0.001 and 1.25 vs. 1.00 μmol/l, P < 0.001, respectively). The BAV patients also had higher SDMA and tHcy levels than controls (0.39 vs. 0.35 μmol/l, P < 0.001 and 11.5 vs. 9.7 μmol/l, P = 0.006). ADMA levels in BAV patients correlated with aortic annulus (r = 0.4, P = 0.043), peak aortic velocity (r = 0.6, P = 0.001), aortic distensibility (r = 0.6, P = 0.004), aortic stiffness index (r = 0.7, P < 0.001), and aortic strain (r = 0.7, P < 0.001) as well as with MMP-2 (r = 0.6, P = 0.002) and tHcy (r = 0.4, P = 0.042).

CONCLUSIONS

This study is the first to show that circulating ADMA together with MMP-2 is a marker of proximal ascending aortic dilatation and impaired aortic elastic properties in nonstenotic BAV patients. It might be speculated that plasma ADMA could be helpful in identifying BAV patients at a higher risk of aortic aneurysm.

Nɛ-homocysteinyl-lysine isopeptide is associated with progression of peripheral artery disease in patients treated with folic acid

OBJECTIVE

Folic acid (FA) administration can reduce plasma total homocysteine (tHcy); however, it fails to decrease cardiovascular events and progression of peripheral artery disease (PAD). Nɛ-homocysteinyl-lysine isopeptide (Nɛ-Hcy-Lys) is formed during catabolism of homocysteinylated proteins. We sought to investigate factors that determine the presence of Nɛ-Hcy-Lys in PAD patients with hyperhomocysteinemia receiving FA.

PATIENTS AND METHODS

We studied 131 consecutive PAD patients with tHcy > 15 μmol l(-1) taking FA 0.4 mg d(-1) for 12 months. Serum Nɛ-Hcy-Lys was determined by high-performance liquid chromatography (HPLC). We also measured interleukin-6 (IL-6), plasminogen activator inhibitor-1 (PAI-1), asymmetric dimethylarginine (ADMA) and 8-iso-prostaglandin F(2α) (8-iso-PGF(2α)).

RESULTS

FA administration resulted in a 70.5% decrease in tHcy (p < 0.0001). However, serum Nɛ-Hcy-Lys was detectable in 28 (21.4%) patients on FA who were more frequently current smokers and survivors of ischaemic stroke (p < 0.001). They had higher tHcy by 46.0%, PAI-1 by 51.7%, 8-iso-PGF(2α) by 59.1% and ADMA by 26.4% (all, p < 0.0001). The presence of Nɛ-Hcy-Lys was associated with lower ankle-brachial index (ABI) values (p < 0.001) and higher prevalence of cardiovascular events (p < 0.001) following therapy.

CONCLUSION

The presence of Nɛ-Hcy-Lys in one-fifth of hyperhomocysteinemic individuals with PAD despite FA treatment is associated with progression of PAD and with increased ADMA formation, oxidative stress and hypofibrinolysis.

Metabolism and neurotoxicity of homocysteine thiolactone in mice: protective role of bleomycin hydrolase

Genetic or nutritional disorders in homocysteine (Hcy) metabolism elevate Hcy-thiolactone and cause heart and brain diseases. Hcy-thiolactone has been implicated in these diseases because it has the ability to modify protein lysine residues and generate toxic N-Hcy-proteins with auto-immunogenic, pro-thrombotic, and amyloidogenic properties. Bleomycin hydrolase (Blmh) has the ability to hydrolyze L-Hcy-thiolactone (but not D-Hcy-thiolactone) to Hcy in vitro, but whether this reflects a physiological function has been unknown. Here, we show that Blmh (-/-) mice excreted in urine 1.8-fold more Hcy-thiolactone than wild-type Blmh (+/+) animals (P = 0.02). Hcy-thiolactone was elevated 2.3-fold in brains (P = 0.004) and 2.0-fold in kidneys (P = 0.047) of Blmh (-/-) mice relative to Blmh (+/+) animals. Plasma N-Hcy-protein was elevated in Blmh (-/-) mice fed a normal (2.3-fold, P < 0.001) or hyperhomocysteinemic diet (1.5-fold, P < 0.001), compared with Blmh (+/+) animals. More intraperitoneally injected L-Hcy-thiolactone was recovered in plasma in Blmh (-/-) mice than in wild-type Blmh (+/+) animals (83.1 vs. 39.3 μM, P < 0.0001). In Blmh (+/+) mice injected intraperitoneally with D-Hcy-thiolactone, D,L-Hcy-thiolactone, or L-Hcy-thiolactone, 88, 47, or 6.3%, respectively, of the injected dose was recovered in plasma. The incidence of seizures induced by L-Hcy-thiolactone injections (3,700 nmol/g body weight) was higher in Blmh (-/-) than in Blmh (+/+) mice (93.8 vs. 29.5%, P < 0.001). Using the Blmh null mice, we provide the first direct evidence that a specific Hcy metabolite, Hcy-thiolactone, rather than Hcy itself, is neurotoxic in vivo. Taken together, our findings indicate that Blmh protects mice against L-Hcy-thiolactone toxicity by metabolizing it to Hcy and suggest a mechanism by which Blmh might protect against neurodegeneration associated with hyperhomocysteinemia and Alzheimer's disease.