[Reversible cerebral vasoconstriction syndrome associated with anastrozole: an unusual cause of high impact]. / Sindrome de vasoconstriccion cerebral reversible asociado a anastrozol: una causa inusual de alto impacto.

INTRODUCTION: Reversible cerebral vasoconstriction syndrome (RCVS) is a low incidence disability with a multifactorial etiology and a wide array of symptoms. The main symptom is a thunderclap headache, accompanied sometimes with various neurological deficits that can lead to death. RCVS is usually diagnosed through radiological imaging technology. The treatment includes adopting general measures of monitoring, symptomatic management, identifying the etiology and acting on it to avoid recurrence. CASE REPORT: A 71-year-old woman with a history of breast cancer originally treated with tamoxifen. Due to urticaria, the anastrozole management was staggered. She was admitted for aphasia, drowsiness and a thunderclap headache. The patient reported a similar event two weeks prior admission. In brain resonance, there was evidence of small sub-arachnoidal haemorrhage (SAH) of the left parietal temporal convexity and cerebral angiography. As well as documented vasospasm in the posterior parietal region confirming the diagnosis of RCVS plus SAH. During the stay, she presented three events with the same characteristics, requiring intensive monitoring and two therapeutic panangiographies with intra-arterial nimodipine with subsequent resolution of the vessel spasm. The patient remains asymptomatic six months later. CONCLUSION: RCVS is difficult to diagnose given its wide array of symptoms and multifactorial etiology. In this case, RCVS plus SAH is associated with the use of anastrozole. So far there are no reported cases of aromatase inhibitors associated with this pathology and should be reported in the literature for pharmacovigilance.

TITLE: Sindrome de vasoconstriccion cerebral reversible asociado a anastrozol: una causa inusual de alto impacto.Introduccion. El sindrome de vasoconstriccion cerebral reversible (SVCR) es una entidad de baja incidencia, de etiologia multifactorial y amplio espectro de presentacion. El principal sintoma es la cefalea de tipo trueno. Puede estar acompañado de focalizacion neurologica y cursar con desenlaces clinicos variable que incluso pueden llevar a la muerte. El diagnostico es clinico e imaginologico, y el tratamiento incluye adoptar medidas generales de monitorizacion, manejo sintomatico, identificar la etiologia y actuar sobre ella para evitar recurrencia. Caso clinico. Mujer de 71 años con antecedente de cancer de seno, tratada inicialmente con tamoxifeno; por presentar urticaria, se escalono tratamiento con anastrozol. Ingreso por cefalea de tipo trueno, afasia anterior y somnolencia. La paciente refirio un evento similar una semana antes del ingreso. En la resonancia magnetica cerebral evidencio una hemorragia subaracnoidea (HSA) pequeña de la convexidad temporoparietal izquierda, y la panangiografia documento vasoespasmo en la region parietal posterior, lo que confirmo el diagnostico de SVCR mas HSA. Durante el ingreso presento tres eventos de iguales caracteristicas, que requirieron monitorizacion intensiva y dos panangiografias terapeuticas con nimodipino intraarterial, con posterior resolucion del vasoespasmo. Permanece asintomatica seis meses despues. Conclusion. El SVCR constituye un reto diagnostico dada su presentacion variable y su etiologia multifactorial. En este caso, el SVCR mas HSA esta asociado al uso de anastrozol. Hasta el momento no hay casos descritos de inhibidores de la aromatasa asociados a esta patologia, que debe comunicarse para su farmacovigilancia.

Kinetics of inactivation of glutamate decarboxylase by cysteine-specific reagents.

Mercuric chloride, p-chloromercuribenzoate and 5,5'-dithiobis(2-nitrobenzoic acid) irreversibly inhibited the activity of Escherichia coli glutamate decarboxylase. Their second order rate constants for inactivation are 0.463 microM(-1) min(-1), 0.034 microM(-1) min(-1), 0.018 microM(-1) min(-1), respectively. The characteristics of the inhibition by the three thiol-group reagents supports the idea that cysteinyl residues at the binding sites for the cofactor and/or the substrate are important for enzyme activity in E. coli.

Despite structural similarities between gp91phox and FRE1, flavocytochrome b558 does not mediate iron uptake by myeloid cells.

Superoxide (O2-) generated by the phagocyte reduced nicotinamide adenine dinucleotide phosphate oxidase is dependent on electron transfer by flavocytochrome b558 (flavocytochrome b), a transmembrane heterodimer that forms the redox center of the oxidase at the plasma or phagosomal membrane. The larger of its two subunits, gp91phox, is homologous to the yeast iron reductase subunit FRE1, and these two proteins share many structural and functional characteristics. Because FRE1 is required for iron uptake in yeast, we hypothesized that flavocytochrome b might serve a similar function in human phagocytes and thus provide a mechanism for the transferrin-independent iron acquisition observed in myeloid cells. To determine whether flavocytochrome b was required for iron uptake, we compared iron acquisition by polymorphonuclear neutrophils (PMNs) or Epstein-Barr virus (EBV)-transformed B lymphocytes derived from individuals with X-linked chronic granulomatous disease (CGD) with iron acquisition by normal cells. Our results indicate that all cells acquired iron to the same extent and that uptake could be significantly enhanced in the presence of the trivalent metal gallium. The gallium enhancement of iron uptake observed in PMNs or in EBV-transformed B lymphocytes derived from healthy individuals was mirrored by those derived from individuals deficient in flavocytochrome b. Furthermore, both normal and CGD-derived EBV-transformed B lymphocytes had similar iron reductase activity, suggesting that flavocytochrome b is not a biologically significant iron reductase. In contrast to previously suggested hypotheses, these results show conclusively that flavocytochrome b is not necessary for cellular iron acquisition, despite structural and functional similarities between yeast iron reductases and flavocytochrome b.

A novel form of hereditary myeloperoxidase deficiency linked to endoplasmic reticulum/proteasome degradation.

Myeloperoxidase (MPO) deficiency is a common inherited disorder linked to increased susceptibility to infection and malignancy. We identified a novel missense mutation in the MPO gene at codon 173 whereby tyrosine is replaced with cysteine (Y173C) that is associated with MPO deficiency and assessed its impact on MPO processing and targeting in transfectants expressing normal or mutant proteins. Although the precursor synthesized by cells expressing the Y173C mutation (MPOY173C) was glycosylated, associated with the molecular chaperones calreticulin and calnexin, and acquired heme, it was neither proteolytically processed to mature MPO subunits nor secreted. After prolonged association with calreticulin and calnexin in the endoplasmic reticulum, MPOY173C was degraded. Furthermore, the 20S proteasome inhibitor N-acetyl-L-leucinyl-L-leucinyl-L-norleucinyl inhibited its degradation, suggesting that the proteasome mediates proteolysis of MPOY173C and, thus, participates in quality control in this novel form of hereditary MPO deficiency.

Coordinated participation of calreticulin and calnexin in the biosynthesis of myeloperoxidase.

Myeloperoxidase (MPO) is a neutrophil lysosomal hemeprotein essential for optimal oxygen-dependent microbicidal activity. We have demonstrated previously that calreticulin, a luminal endoplasmic reticulum protein, functions as a molecular chaperone during myeloperoxidase biosynthesis, associating reversibly with the heme-free precursor apopro-MPO. Because the membrane-bound endoplasmic reticulum protein calnexin is structurally and functionally related to calreticulin, we assessed the role of calnexin in myeloperoxidase biosynthesis. Like calreticulin, calnexin coprecipitated exclusively with glycosylated MPO precursors and with apopro-MPO but, in contrast to calreticulin, also with the enzymatically active, heme-containing precursor pro-MPO. To determine if calnexin participated in heme insertion into MPO, we compared the kinetics of chaperone association with MPO precursors using stable transfectants expressing cDNA encoding wild type MPO or mutated forms that do not acquire heme. Transfectants expressing mutant cDNA had prolonged association of MPO-related precursors with calreticulin and especially with calnexin. These studies demonstrate that 1) both calreticulin and calnexin associated with glycosylated apopro-MPO; 2) only calnexin associated selectively with the enzymatically active, heme-containing precursor pro-MPO; and 3) mutants unable to incorporate heme had prolonged association with calnexin. These findings represent the first evidence of a specialized role for calnexin in facilitating protein maturation in the endoplasmic reticulum of myeloid cells.

Calreticulin functions as a molecular chaperone in the biosynthesis of myeloperoxidase.

Myeloperoxidase (MPO), a lysosomal heme protein found exclusively in neutrophils and monocytes, is necessary for efficient oxygen-dependent microbicidal activity. Acquisition of heme by the heme-free MPO precursor apopro-MPO appears to be a prerequisite for its subsequent proteolytic processing and advancement along the biosynthetic pathway to mature MPO. We present data indicating that calreticulin (CRT), a high capacity calcium-binding protein residing in the lumen of the endoplasmic reticulum of a wide variety of cells, interacts specifically with fully glycosylated apopro-MPO. Biosynthetically radiolabeled CRT (60 kDa) and apopro-MPO (90 kDa) were coprecipitated from PLB 985 cells by monospecific antiserum against CRT when the immunoprecipitations were performed either under nondenaturing conditions or following reversible crosslinking. Nonglycosylated MPO precursors synthesized in the presence of tunicamycin did not interact with CRT. The CRT-apopro-MPO interaction was restricted to an early phase of MPO biosynthesis, and CRT did not interact with the later appearing, heme-containing species of MPO, i.e. pro-MPO or the heavy subunit of mature MPO. These data show that CRT participates in the post-translational processing of MPO, perhaps by maintaining apopro-MPO in a conformation competent to accommodate insertion of the heme group. In this general way, CRT shares certain functional properties with the structurally homologous transmembrane calcium-binding endoplasmic reticulum protein calnexin. Both interact with glycosylated biosynthetic precursors of proteins selectively expressed in specialized cells.