A new strategy to decrease N-methyl-D-aspartate (NMDA) receptor coactivation: inhibition of D-serine synthesis by converting serine racemase into an eliminase

Serine racemase is a brain-enriched enzyme that synthesizes d-serine, an endogenous modulator of the glycine site of N-methyl-d-aspartate (NMDA) receptors. We now report that serine racemase catalyzes an elimination reaction toward a nonphysiological substrate that provides a powerful tool to study its neurobiological role and will be useful to develop selective enzyme inhibitors. Serine racemase catalyzes robust elimination of l-serine O-sulfate that is 500 times faster than the physiological racemization reaction, generating sulfate, ammonia, and pyruvate. This reaction provides the most simple and sensitive assay to detect the enzyme activity so far. We establish stable cell lines expressing serine racemase and show that serine racemase can also be converted into a powerful eliminase in cultured cells, while the racemization of l-serine is inhibited. Likewise, l-serine O-sulfate inhibits the synthesis of d-serine in primary astrocyte cultures. We conclude that the synthetic compound l-serine O-sulfate is a better substrate than l-serine as well as an inhibitor of d-serine synthesis. Inhibition of serine racemase provides a new strategy to selectively decrease NMDA receptor coactivation and may be useful in conditions in which overstimulation of NMDA receptors plays a pathological role.

Kinetics of cytokine gene expression in experimental chagasic cardiomyopathy: tissue parasitism and endogenous IFN-gamma as important determinants of chemokine mRNA expression during infection with Trypanosoma cruzi

We investigated the kinetics of parasite replication, leukocyte migration, and cytokine/chemokine mRNA expression in the heart tissue from animals infected with the Colombiana strain of Trypanosoma cruzi. Cardiac tissue parasitism was noticeable at 15 days, peaked around 30 days and was dramatically reduced at 120 days postinfection (p.i.). Kinetic studies showed that the inflammatory infiltrate was dominated by the presence of alphabetaT CD3(+ )CD4(+ )CD8(-), alphabetaT CD3(+ )CD4(-)CD8(+ )lymphocytes and macrophages. The mRNA expression of the monokines IL-1beta and IL-12(p40) was elevated at 15 days p.i. and controlled at later time points. In contrast, TNF-alpha mRNA was expressed throughout the infection. Interestingly, we found that at 15 and 30 days p.i. cytokine expression was dominated by the presence of IFN-gamma mRNA, whereas at 60 days or later time points the balance of type 1 and type 2 cytokines was switched in favor of IL-4 and IL-10 mRNAs. The chemokine mRNAs encoding JE, MIP-1alpha, MIP-1beta, KC, and MIP-2 were all mainly expressed at 15 and/or 30 days p.i. and diminished thereafter. In contrast, the expression of RANTES, MIG and IP-10 mRNAs was augmented at 15 days p.i. and persisted at high levels up to 120 days p.i. Taken together, our results indicate that regulation of IFN-gamma and chemokine expression, associated with decreased tissue parasitism, may be largely responsible for the control of inflammation and immunopathology observed in the cardiac tissue of animals infected with T. cruzi.

[Foreign-body aspiration in adults]

Proximal airway obstruction and acute life-threatening asphyxia is the most important complication of foreign body aspiration. Small foreign bodies that transverse the larynx may be initially asymptomatic appearing serious respiratory disturbances only later. Three patients with different clinical evolutions are reported and the diagnostic and therapeutic approaches, discussed.