Brain injury after neonatal hypoxia-ischemia in rats: a role of cysteine?

A Near-Infrared Fluorescent Dye with Tunable Emission Wavelength and Stokes Shift as a High-Sensitivity Cysteine Nanoprobe for Monitoring Ischemic Stroke

Sulfur-substituted dicyanomethylene-4H-chromene (DCM) derivatives based on the intramolecular charge transfer (ICT) mechanism were designed as near-infrared (NIR) fluorescent dyes. Using the Knoevenagel condensation method, the S-DCM-OH(835) fluorescence dye was synthesized, which had an emission wavelength exceeding 800 nm and 220 nm of a Stokes shift. Compared to commercial ICG, S-DCM-OH(835) was not only synchronized in emission wavelength but also far superior in Stokes shifts. These advantages made the design of S-DCM-NIR(835) based on this dye potentially valuable for biological applications. Based on this chemical structure, a fluorescent S-DCM-NIR(835) nanoprobe with a mean diameter of 17.69 nm was fabricated as the NIR imaging nanoprobe. Results showed that the nanoprobe maintained the high-specificity identification of cysteine (Cys) via the Michael addition reaction, with the detection limitation of 0.11 μM endogenous Cys. More importantly, in an ischemic stroke mouse model, the S-DCM-NIR(835) nanoprobe could monitor the Cys concentration change at stroke lesion due to the disruption of Cys metabolism under the ischemic stroke condition. Such a S-DCM-NIR(835) nanoprobe could not only differentiate the severity of the ischemic stroke using response time but also quantify the concentration of Cys in real-time in vivo.

Biochemical tissue monitoring during hypoxia and reoxygenation

Oxygen deficiency during critical illness may cause profound changes in cellular metabolism and subsequent tissue and organ dysfunction. Clinical treatment in these cases targets rapid reoxygenation to avoid a prolonged impaired synthesis of cellular high-energy phosphates (ATP). However, the effect of this therapeutic intervention on tissue metabolism has not been determined yet. Thus the present study was designed to determine the effects of hypoxia and reoxygenation with either room air or 100% oxygen on variables of interstitial metabolism in different tissues using in vivo microdialysis. Twenty-seven adult, male CD-rats (407-487 g; Ivanovas, Kisslegg, Germany) were studied during general anesthesia. Following preparation and randomization, rats were normoventilated for 45 min (FiO(2) 0.21), followed by induction of hypoxia (FiO(2) 0.1, 40 min) and reoxygenated for 50 min either with FiO(2) 1.0 (group 1, n=10) or FiO(2) 0.21 (group 2, n=10). Control animals (n=7) were ventilated with 21% oxygen during the observation period. Additional to invasive haemodynamic parameters, biochemical tissue monitoring was performed using CMA 20 microdialysis probes, inserted into muscle, subcutaneous space, liver, and the peritoneal cavity allowing analyses of lactate and pyruvate at short intervals. Hypoxia induced a significant reduction in mean arterial pressure (MAP) in group 1 and 2 compared with the control group (P<0.05) without any significant differences between both treatment groups. This was accompanied by a significant increase in blood lactate (10.5+/-3.1 mM (group 1) and 12.3+/-4.1 mM (group 2) vs. 1.5+/-0.3 mM (control); P<0.05) and severe metabolic acidosis (base excess (BE): -18.3+/-5 mM (1) and -17.3+/-7 mM (2) vs. -2.6+/-1.8 mM (control), P<0.05). During hypoxia, the interstitial lacate/pyruvate ratio in groups 1 and 2 increased to 455+/-199% (muscle), 468+/-148% (intraperitoneal), 770+/-218% (hepatic) and 855+/-432% (subcutaneous) (P<0.05 vs. control, respectively). No significant inter-organ or inter-group differences in interstitial dialysates were observed in the treatment groups, neither during hypoxia nor during reoxygenation. Our data suggest, that hypoxia induces comparable metabolic alterations in various tissues and that reoxygenation with 100% oxygen is not superior to 21% oxygen in restoring tissue metabolism after critical hypoxia.

Glutathione efflux induced by NMDA and kainate: implications in neurotoxicity?

Neurotoxicity in acute as well as chronic neurological diseases may be partly mediated by oxidative stress caused by overactivation of glutamate receptors. A key component of the cellular defense against oxidative stress is reduced glutathione. In our earlier work, we have shown that ischemia in brain induces increased efflux, elevated metabolism, and decreased tissue concentrations of glutathione. In this study, we have evaluated the effect of glutamate receptor activation on the efflux of glutathione from hippocampus in vitro. NMDA and kainate induced a delayed increase in glutathione, taurine, and phosphoethanolamine efflux. Extracellular glutathione was recovered mainly in the reduced form (85-95%); the efflux was dependent on extracellular calcium but unrelated to dantrolene-sensitive intracellular calcium release and independent of glutathione or NO synthesis. The NMDA-induced efflux of glutathione was enhanced by blockage of gamma-glutamyl transpeptidase, indicating an increased transpeptidation of glutathione after NMDA receptor activation. Our results suggest that increased efflux of glutathione could be a factor in initiating nerve cell death via a change in intracellular redox potential and/or a decrease in the intracellular capacity for inactivation of reactive oxygen species.