Long-term neurobehavioral and histological damage in brain of mice induced by L-cysteine

The mechanism of action of N-acetylcysteine (NAC): The emerging role of H2S and sulfane sulfur species

Initially adopted as a mucolytic about 60 years ago, the cysteine prodrug N-acetylcysteine (NAC) is the standard of care to treat paracetamol intoxication, and is included on the World Health Organization's list of essential medicines. Additionally, NAC increasingly became the epitome of an "antioxidant". Arguably, it is the most widely used "antioxidant" in experimental cell and animal biology, as well as clinical studies. Most investigators use and test NAC with the idea that it prevents or attenuates oxidative stress. Conventionally, it is assumed that NAC acts as (i) a reductant of disulfide bonds, (ii) a scavenger of reactive oxygen species and/or (iii) a precursor for glutathione biosynthesis. While these mechanisms may apply under specific circumstances, they cannot be generalized to explain the effects of NAC in a majority of settings and situations. In most cases the mechanism of action has remained unclear and untested. In this review, we discuss the validity of conventional assumptions and the scope of a newly discovered mechanism of action, namely the conversion of NAC into hydrogen sulfide and sulfane sulfur species. The antioxidative and cytoprotective activities of per- and polysulfides may explain many of the effects that have previously been ascribed to NAC or NAC-derived glutathione.

Hollow POM@MOF-derived Porous NiMo6 @Co3 O4 for Biothiol Colorimetric Detection

Developing highly active and sensitive peroxidase mimics for _L -cysteine (_L -Cys) colorimetric detection is very important for biotechnology and medical diagnosis. Herein, polyoxometalate-doped porous Co₃ O₄ composite (NiMo₆ @Co₃ O₄ ) was designed and prepared for the first time. Compared with pure and commercial Co₃ O₄ , NiMo₆ @Co₃ O₄ (n) composites exhibit the enhanced peroxidase-mimicking activities and stabilities due to the strong synergistic effect between porous Co₃ O₄ and multi-electron NiMo₆ clusters. Moreover, the peroxidase-mimicking activities of NiMo₆ @Co₃ O₄ (n) composites are heavily dependent on the doping mass of NiMo₆ , and the optimized NiMo₆ @Co₃ O₄ (2) exhibits the superlative peroxidase-mimicking activity. More importantly, a sensitive _L -Cys colorimetric detection is developed with the sensitivity of 0.023 μM^-1 and the detection limit at least 0.018 μM in the linear range of 1-20 μM, which is by far the best enzyme-mimetic performances, to the best our knowledge.

Real-time effects of insulin-induced hypoglycaemia on hippocampal glucose and oxygen

The hippocampus plays a vital role in learning and memory and is susceptible to damage following hypoglycaemic shock. The effect of an acute administration of insulin on hippocampal function has been described in terms of behavioural deficits but its effect on hippocampal oxygen and glucose is unclear. Glucose oxidase biosensors (detecting glucose) and carbon paste electrodes (detecting oxygen) were implanted into the hippocampus of Sprague Dawley rats. Animals were allowed to recover and real-time recordings were made in order to determine the effects of fasting, insulin administration (15 U/kg; i.p.) and reintroduction of food on hippocampal oxygen and glucose. Fasting caused a significant decrease in hippocampal glucose over the course of 24h. Insulin administration produced a significant decrease in hippocampal glucose along with a significant increase in hippocampal oxygen. Finally, the reintroduction of food resulted in glucose levels significantly increasing along with a transient but significant increase in oxygen levels. The findings presented here suggest that even a single acute period of hypoglycaemia may substantially disrupt hippocampal oxygen and glucose and therefore affect hippocampal function.

"Red-to-blue" colorimetric detection of cysteine via anti-etching of silver nanoprisms

The reported strategies for cysteine (Cys) colorimetric detection based on noble metal nanomaterials include triggering aggregation, etching or fluorescence quenching of nanomaterials by Cys. In this study, we propose a new strategy for Cys colorimetric detection, i.e. anti-etching of silver nanoprisms (AgNPRs). In the absence of Cys, iodide ions (I(-)) could etch the corners and edges of AgNPRs and induce the morphology transition from nanoprism to nanodisk, which results in color change of the AgNPR dispersion from blue to red. In its presence, however, Cys can prevent the AgNPRs from I(-) attack. In that case, the color of the AgNPR dispersion containing I(-) and Cys remains blue. The mechanism is confirmed by using UV-vis spectra, TEM, DLS, Raman spectra and XPS spectra. According to the sensing effect of the Cys detection system, the concentration of I(-) incubated with AgNPRs, incubation time of AgNPRs and I(-), and pH of AgNPR dispersions are optimized to 5.0 μM, 10 min, and pH 6.2, respectively. Under the optimized conditions, the proposed Cys detection system has excellent selectivity and high sensitivity. The limit of detection (LOD) of our Cys detection system is 25 nM by the naked eye, which is much better than the reported lowest LOD by eye-vision (100 nM), and 10 nM by UV-vis spectroscopy. The results of Cys detection in rabbit urine or plasma samples reinforce that our Cys detection system is applicable for rapid colorimetric detection of Cys in real body fluid samples.

Changes of hippocampal beta-alanine and citrulline levels are paralleling early and late phase of retrieval in the Morris Water Maze

Although a series of amino acids (AA) have been associated with spatial memory formation, there is limited information on concentrations of beta-alanine and citrulline in rodent brains. Given the importance of AA metabolism in cognitive functions it was the aim of the study to determine hippocampal levels of beta-alanine and citrulline in rats during two different phases of memory retrieval in a spatial memory paradigm. Ten rats were used per group and the first group was trained and sacrificed five min, the second six hours following retrieval in the Morris Water Maze (MWM) and the third and fourth group were untrained, yoked controls. Hippocampi were taken and free AA were determined using a well-established HPLC protocol. Beta-alanine and citrulline levels were higher in trained rat hippocampi, during both, early and late phase of memory retrieval. Taurine, methionine, cysteine, lysine and ornithine levels were higher in yoked rats at the late phase while tyrosine was higher in yoked rats during the early phase. There were no significant correlations between time spent in the target quadrant and any of the AA levels. Herein, an AA pattern, different between yoked and trained animals at early and late phase of memory retrieval is shown, indicating probable involvement of different AA pathways in animals trained and untrained in the MWM. The results may be useful for the interpretation of previous studies and the design of future experiments to identify amino acids as possible targets for modulating spatial memory.

Inhibition of GTRAP3-18 may increase neuroprotective glutathione (GSH) synthesis

Glutathione (GSH) is a tripeptide consisting of glutamate, cysteine, and glycine; it has a variety of functions in the central nervous system. Brain GSH depletion is considered a preclinical sign in age-related neurodegenerative diseases, and it promotes the subsequent processes toward neurotoxicity. A neuroprotective mechanism accomplished by increasing GSH synthesis could be a promising approach in the treatment of neurodegenerative diseases. In neurons, cysteine is the rate-limiting substrate for GSH synthesis. Excitatory amino acid carrier 1 (EAAC1) is a neuronal cysteine/glutamate transporter in the brain. EAAC1 translocation to the plasma membrane promotes cysteine uptake, leading to GSH synthesis, while being negatively regulated by glutamate transport associated protein 3-18 (GTRAP3-18). Our recent studies have suggested GTRAP3-18 as an inhibitory factor for neuronal GSH synthesis. Inhibiting GTRAP3-18 function is an endogenous mechanism to increase neuron-specific GSH synthesis in the brain. This review gives an overview of EAAC1-mediated GSH synthesis, and its regulatory mechanisms by GTRAP3-18 in the brain, and a potential approach against neurodegeneration.

Decreased cholinergic receptor expression in the striatum: motor function deficit in hypoglycemic and diabetic rats

Hypoglycemic brain injury is a common and serious complication of insulin therapy associated with diabetes. This study evaluated the effect of insulin-induced hypoglycemia and STZ-induced diabetes on striatal cholinergic receptors and enzyme expression and on motor function. Cholinergic enzymes: AChE and ChAT gene expression, radioreceptor binding assay and immunohistochemistry of muscarinic M1, M3 receptors and α7nAChR were carried out. Motor performance on grid walk test was analysed. AChE and ChAT expression significantly downregulated in hypoglycemic and diabetic rats. Total muscarinic and Muscarinic M3 receptor binding decreased in hypoglycemic rats compared to diabetic rats whereas muscarinic M1 receptor binding increased in hypoglycemic rats compared to diabetic rats. Real-time PCR analysis and confocal imaging of muscarinic M1, M3 receptors confirmed the changes in muscarinic receptor binding in hypoglycemic and diabetic rats. In hypoglycemic rats, α7nAChR expression significantly up regulated compared to diabetic rats. Grid walk test demonstrated the impairment in motor function and coordination in hypoglycemic and hyperglycemic rats. Neurochemical changes along with the behavioral data implicate a role for impaired striatal cholinergic receptor function inducing motor function deficit induced by hypo and hyperglycemia. Hypoglycemia exacerbated the neurobehavioral deficit in diabetes which has clinical significance in the treatment of diabetes.

Hypoglycemia induced behavioural deficit and decreased GABA receptor, CREB expression in the cerebellum of streptozoticin induced diabetic rats

Intensive glycemic control during diabetes is associated with an increased incidence of hypoglycemia, which is the major barrier in blood glucose homeostasis during diabetes therapy. The CNS neurotransmitters play an important role in the regulation of glucose homeostasis. In the present study, we showed the effects of hypoglycemia in diabetic and non- diabetic rats on motor functions and alterations of GABA receptor and CREB expression in the cerebellum. Cerebellar dysfunction is associated with seizure generation, motor deficits and memory impairment. Scatchard analysis of [(3)H]GABA binding in the cerebellum of diabetic hypoglycemic and control hypoglycemic rats showed significant (P<0.01) decrease in B(max) and K(d) compared to diabetic and control rats. Real-time PCR amplification of GABA receptor subunit GABA(Aα1) and GAD showed significant (P<0.001) down-regulation in the cerebellum of hypoglycemic rats compared to diabetic and control rats. Confocal imaging study confirmed the decreased GABA receptors in hypoglycemic rats. CREB mRNA expression was down-regulated during recurrent hypoglycemia. Both diabetic and non-diabetic hypoglycemic rats showed impaired performance in grid walk test compared to diabetic and control. Impaired GABA receptor and CREB expression along with motor function deficit were more prominent in hypoglycemic rats than hyperglycemic which showed that hypoglycemia is causing more neuronal damage at molecular level. These molecular changes observed during hypo/hyperglycemia contribute to motor and learning deficits which has clinical significance in diabetes treatment.

Label-free colorimetric assay for biological thiols based on ssDNA/silver nanoparticle system by salt amplification

We report a novel method for biological thiols detection using ssDNA/silver nanoparticles system. The adsorbing ssDNA supplies silver nanoparticles high density charge to rescue nanoparticles from aggregation induced by salt. However, homocysteine (cysteine or glutathione) is conjugated more powerfully than ssDNA to AgNPs via Ag-S bond, which holds back ssDNA binding to AgNPs surface. When salt is added, AgNPs aggregation occurs and the corresponding color changes from yellow to brown after these biological thiols is introduced. A high sensitivity can be achieved using salt as an amplifier to assay thiols. In our study, a favorable linear correlation between the A(0)/A(x) ratio and homocysteine concentration was obtained in the range of 10 to 500 nM with a low detection limit of 10 nM, indicating that homocysteine could be analyzed at low concentration. A concentration as low as 300 nM homocysteine caused a visible color change. As well as, cysteine and glutathione can be detected at a detection limit of 50 nM and 100 nM, respectively. In addition, study on the selectivity of this method shows that only homocysteine, cysteine and glutathione can generate signal response.

Simple and sensitive colorimetric detection of cysteine based on ssDNA-stabilized gold nanoparticles

In this paper, we demonstrate a simple and sensitive colorimetric detection of cysteine based on the cysteine-mediated color change of ssDNA-stabilized gold nanoparticles (AuNPs). Cysteine is capable of absorbing onto AuNPs surfaces via the strong interaction between its thiol group and gold. ssDNA molecules which stabilize AuNPs against salt-induced aggregation are removed away by cysteine encapsulation on the AuNPs surfaces, resulting in a characteristic color change of AuNPs from red to blue as soon as salt is added. The ratio of absorptions at 640 to 525 nm (A(640)/A(525)) is linear dependent on the cysteine concentration in the range from 0.1 to 5 microM. Furthermore, amino acids other than cysteine cannot mediate the color change under the identical conditions due to the absence of thiol groups, suggesting the selectivity of the proposed method toward cysteine. The employment of complicated protocols and sophisticated processes such as the preparation of modified AuNPs are successfully avoided in design to realize the simple and low-cost cysteine detection; and the high sensitivity and low cost of the method is favorable for practical applications.