Involvement of excitatory amino acid mechanisms in gamma-hydroxybutyrate model of generalized absence seizures in rats.

gamma-Hydroxybutyric acid (GHB), a naturally occurring compound which is synthesized from gamma-aminobutyric acid (GABA), induces bilaterally synchronous spike wave discharges, associated with behavioral changes, reminiscent of petit mal or generalized absence seizures in rats. In the present study, possible involvement of excitatory amino acids (EAAs) in GHB-induced spike wave discharges was investigated. The noncompetitive antagonist of NMDA receptors, MK-801, attenuated GHB-induced spike wave discharges at all doses tested (0.025-1.0 mg/kg) but dose-dependently induced suppression of EEG bursts in GHB-treated animals. The suppression of bursts was never observed with GHB in control experiments. N-Methyl-D-aspartate (NMDA) had a similar effect on GHB-induced spike wave discharges, when it was administered prior to GHB. This effect of NMDA was partially reversed by MK-801. The competitive antagonists of NMDA receptors, (+/-)CPP and CGP 43487 and the antagonist at the strychnine-insensitive glycine site, HA-966, also suppressed GHB-induced spike wave discharges with the EEG progressing to suppression of bursts but were weaker in this regard than MK-801 or NMDA. These data raise the possibility of involvement of excitatory amino acids in the GHB model of absence seizures.     

Animal model for theophylline--cimetidine drug interaction

Cimetidine (300 mg I.V.) and theophylline (15 mg/kg I.V.) were studied in Beagle dogs for possible drug interaction. The drugs were administered alone and in combination using a crossover design. Although none of the determined pharmacokinetic parameters for theophylline changed significantly in the presence of cimetidine, a trend towards significance was found for the terminal half-life, area under the curve, and mean residence time. The magnitude in changes found in Beagles is representative of the changes reported in man.     

Identification of trypanosomatid PEX19: functional characterization reveals impact on cell growth and glycosome size and number

Glycosomes are peroxisome-like organelles present in trypanosomatid pathogens. These organelles compartmentalize glycolysis, among other reactions, and are essential in both bloodstream and procyclic form Trypanosoma brucei. Peroxins (PEXs) are proteins necessary for biogenesis of peroxisomes and glycosomes. In each assembled trypanosomatid genome, we identified a predicted protein with approximately 20% sequence identity to human PEX19, a protein required for insertion of peroxisomal membrane proteins (PMPs) into the membrane. Functional analysis demonstrated that these proteins are indeed PEX19 orthologues. Like other PEX19s, T. brucei and Leishmania major PEX19 GFP fusion proteins are predominantly cytosolic. We further showed that LmPEX19 interacts with the glycosomal membrane protein PEX2 in the yeast two-hybrid system. Partial knockdown of TbPEX19 slowed parasite growth, particularly when glucose was present. Immunofluorescence and electron microscopic studies revealed biogenesis defect as evidenced by a sharp reduction in the number of glycosomes. Surprisingly, a four-fold increase in the size of the remaining glycosomes was observed. We propose that this phenotype of fewer but larger glycosomes results from the reduction in import of glycosomal membrane proteins.     

Elucidating the protective and pathologic T cell species in the virus-induced corneal immunoinflammatory condition herpetic stromal keratitis

Herpetic stromal keratitis (HSK) results in postinfection with Herpes simplex virus type 1 (HSV-1). The pathogenesis involves tissue damage by the host immune system, classifying HSK as an immunopathological disease. The crucial disease orchestrating cells is thought to be the T lymphocytes. The present study elucidates pathogenic and protective T cell subsets involved in the development of HSK using the gBT mice, which possess a monoclonal population of CD8+ T cells reactive to a HSV immunodominant epitope. Results show that HSV-reactive CD8+ T cells enter infected corneas during the acute but not the chronic phase of the disease during which the predominant population is CD4+ T cells. Adoptive transfer experiments in T and B cell-deficient recombination-activating gene knockout mice revealed that HSV-reactive CD8+ T cells are capable of ocular virus clearance, possibly through a combination of corneal and peripheral nervous system antiviral effects, but are not involved in lesion development. CD4+ T cells of the virus-specific or nonspecific species emerged as the pathogenic T cells capable of precipitating disease. These observations have the potential to yield important treatment strategies by targeting specific cell types in HSK.     

Insights from studies of blood substitutes in trauma

Most authorities believe that the greatest need for blood substitutes is in patients with unanticipated acute blood loss, and trauma is the most likely scenario. The blood substitutes reaching advanced clinical trials today are red blood cell (RBC) substitutes, derived from hemoglobin. The hemoglobin-based oxygen carriers (HBOCs) tested currently in FDA Phase III clinical trials are polymerized hemoglobin solutions. The standard approach to restoring oxygen delivery in hemorrhagic shock has been crystalloid administration to expand intravascular volume, followed by stored RBCs for critical anemia. However, allogenic RBCs may have adverse immunoinflammatory effects that increase the risk of postinjury multiple organ failure (MOF). Phase II clinical trials, as well as in vitro and in vivo work, suggest that resuscitation with a HBOC--in lieu of stored RBCs--attenuates the systemic inflammatory response invoked in the pathogenesis of MOF. Specifically, an HBOC has been shown to obviate stored RBC provoked neutrophil priming, endothelial activation, and systemic release of interleukins 6, 8, and 10. Based on this background and work by others, we have initiated a multicenter prehospital trial in which severely injured patients with major blood loss (systemic blood pressure <90 mmHg) are randomized to initial field resuscitation with crystalloid versus HBOC. During the hospital phase, the control group is further resuscitated with stored RBCs, whereas the study group receives HBOC (up to 6 units) in the first 12 h. The primary study endpoint is 30-day mortality, and secondary endpoints include reduction in allogenic RBCs, hemoglobin levels <5 g/dL, uncrossmatched RBCs, and MOF. The potential efficacy of HBOCs extends beyond the temporary replacement for stored RBCs. Hemoglobin solutions might ultimately prove superior in delivering oxygen to ischemic or injured tissue. The current generation of HBOCs can be lifesaving for acute blood loss today, but the next generation might be biochemically tailored for specific clinical indications.