Deactivation of mitochondrial complex I after hypoxia-ischemia in the immature brain

Mortality from perinatal hypoxic-ischemic (HI) brain injury reached 1.15 million worldwide in 2010 and is also a major factor for neurological disability in infants. HI directly influences the oxidative phosphorylation enzyme complexes in mitochondria, but the exact mechanism of HI-reoxygenation response in brain remains largely unresolved. After induction of HI-reoxygenation in postnatal day 10 rats, activities of mitochondrial respiratory chain enzymes were analysed and complexome profiling was performed. The effect of conformational state (active/deactive (A/D) transition) of mitochondrial complex I on H₂O₂ release was measured simultaneously with mitochondrial oxygen consumption. In contrast to cytochrome c oxidase and succinate dehydrogenase, HI-reoxygenation resulted in inhibition of mitochondrial complex I at 4 h after reoxygenation. Immediately after HI, we observed a robust increase in the content of deactive (D) form of complex I. The D-form is less active in reactive oxygen species (ROS) production via reversed electron transfer, indicating the key role of the deactivation of complex I in ischemia/reoxygenation. We describe a novel mechanism of mitochondrial response to ischemia in the immature brain. HI induced a deactivation of complex I in order to reduce ROS production following reoxygenation. Delayed activation of complex I represents a novel mitochondrial target for pathological-activated therapy.

Stroke in the immature brain: review of pathophysiology and animal models of pediatric stroke

Pediatric stroke research presents many challenges. Relatively low incidence, need for age stratification, diverse etiologies, delays in diagnosis, lack of an established age-based stroke severity scale and outcome measures are only some of the issues that have prevented the implementation of clinical trials in infants and children with stroke. Experimental animal models of pediatric stroke, therefore, are critical to understanding the pathophysiology and management of ischemic brain damage in the immature brain, and provide the necessary platform for future clinical trials. In this review we discuss the pertinent clinical aspects of pediatric stroke, the pathophysiology of stroke in the developing brain and the animal models established to study basic mechanisms as well as translational issues in pediatric stroke.

Mercury exposure and cutaneous disease

Human contact with mercury has been ongoing for centuries and was previously considered a legitimate means of treating different cutaneous and systemic conditions. Toxicity from this heavy metal may occur from exposure to elemental, inorganic, and organic forms of mercury. This article outlines the signs and symptoms of mercury poisoning and the different clinical conditions with assorted cutaneous findings.

Kinetics of GLUT1 and GLUT4 glucose transporters expressed in Xenopus oocytes

The predominant mechanism by which insulin activates glucose transport in muscle and adipose tissue is by affecting the redistribution of the facilitated hexose carriers, GLUT1 and GLUT4, from an intracellular site to the plasma membrane. A quantitative analysis of this process has been hampered by the lack of reliable determinations for kinetic constants catalyzed by each of these isoforms. In order to obtain such information, each transporter was expressed in Xenopus oocytes by the injection of mRNA encoding rat GLUT1 or GLUT4. Equilibrium exchange 3-O-methylglucose uptake was measured and the data fitted to a two-compartment model, yielding Km = 26.2 mM and Vmax = 3.5 nmol/min/cell for GLUT1 and Km = 4.3 mM and Vmax = 0.7 nmol/min/cell for GLUT4. Measurement of the abundance of cell surface transporters was accomplished by two independent protocols: photolabeling with the impermeant hexose analog 2-N-4-(1-azi-2,2,2-trifluoroethyl)benzoyl-1,3-bis(D-mannos-4 -yloxy)-2-propylamine and subcellular fractionation of oocytes. Data obtained by either technique revealed that the ratio of plasma membrane GLUT1 to GLUT4 was about 4; this paralleled the relative maximal velocities for hexose transport, indicating that the turn-over numbers for the two isoforms were the same. Moreover, measurement of the concentration of exofacially disposed transporters with 2-N-4-(1-azi-2,2,2-trifluoroethyl)benzoyl-1,3-bis(D-mannos-4 -yloxy)-2-propylamine allowed calculation of the turnover number to be about 20,000 min-1. These data indicate that, at low substrate concentrations, the catalytic efficiency of GLUT4 is significantly greater than GLUT1. Extrapolation to mammalian systems suggests that GLUT4 is responsible for virtually all of the hexose uptake in insulin-responsive targets, particularly in the presence of hormone.

Expression of mouse-GLUT3 and human-GLUT3 glucose transporter proteins in brain

Polyclonal anti-peptide antisera were raised to the C-terminal sequence of mouse- and human-GLUT3 glucose transporter isoforms. GLUT3 protein and mRNA expression were investigated by Western blot and Northern blot assays, in a range of tissues and cell lines. Mouse-GLUT3 protein was detected only in rat brain, where it was present in most regions except adenohypophysis and pineal gland. Mouse-GLUT3 was also detected in primary cultured rat cerebellar neurons and the neuronal cell lines PC12 and NG108-15, but not in cultured astroglia. Human-GLUT3 protein was detected in CHO cells transfected with the human-GLUT3 cDNA and in human brain, but not in human placenta or fat. The expression of GLUT3 in rat brain and neurons indicates it is a major neuronal glucose transporter.

Substrates of energy metabolism of the pituitary and pineal glands

The capability of the neurohypophysis, the adenohypophysis, and the pineal gland to oxidize nonesterified fatty acids and glucose as energy sources was studied in vivo. Fed and 48-h-starved rats had catheters placed in their femoral vessels. After they became conscious, an intravenous injection of one of the following was given: [1-14C]acetate, [1-14C]octanoate, [1-14C]-palmitate, or [2-14C]glucose. After 5 min the rats were sacrificed. These metabolites produce [14C]acetyl-CoA within the mitochondria when they are oxidized as metabolic fuels. On passage through the Krebs cycle a considerable portion of the 14C is trapped in large amino acid pools closely associated with the Krebs cycle; the appearance of 14C in these amino acids was taken as evidence of oxidation. As expected, brain structures behind the blood-brain barrier (cerebral cortex and caudate) showed considerable labeling of Krebs cycle-associated amino acids in both nutritional states when [2-14C]glucose was the substrate. Surprisingly, however, no label was detected in amino acids of the neurohypophysis or the pineal gland in starved rats and very little in fed rats. On the other hand, 14C from acetate and palmitate was extensively incorporated into amino acids of the pineal gland and the neurohypophysis, while little 14C labeling was found in the cerebral cortex and the caudate. Octanoate, which passes the blood-brain barrier readily, labeled amino acids of all tissues. The experiments demonstrated conclusively that the neural structures studied, which have no blood-brain barrier, do not rely heavily upon glucose as a fuel for oxidative energy metabolism, in contrast to the rest of the brain. The results also showed that nonesterified fatty acids may supply at least some of their energy requirements.