[Osteoid osteoma in children: 5 cases treated with electrocoagulation]. / L'ostéome ostéoïde de l'enfant : à propos de 5 cas traités par électrocoagulation.

Osteoid osteoma is a benign bone tumor. Its diagnosis is often delayed despite typical symptoms: severe pain mainly situated on the lower limbs and characteristically worse at night. Once diagnosed, an antalgic treatment by aspirin is well known to be very effective in relieving pain. Osteoid osteoma will resolve spontaneously. If symptoms persist despite the use of aspirin, surgery can be performed to remove the tumor. Percutaneous electrocoagulation can be performed instead of surgical resection as a less invasive procedure. The success rate of surgery and percutaneous electrocoagulation is comparable. We reviewed the cases of 5 patients who were hospitalized in our institution for percutaneous electrocoagulation of an osteoid osteoma. We compared them to the literature.

[Nontuberculous mycobacterial epitrochlear adenitis]. / Adénite épitrochléenne à mycobactérie non tuberculeuse.

We report the case of a 2-year-old girl referred for unilateral epitrochlear lymphadenitis caused by Mycobacterium avium. Adenitis is the most frequent presentation of non tuberculous mycobacteria in children. Typical locations are the cervical, submandibular, axillar, inguinal, mediastinal, and parotid regions. To our knowledge, this is the first observation of an epitrochlear location. The diagnosis was made by evidencing the causal bacterium but also by the exclusion of other causes such as Bartonella henselae and Mycobacterium tuberculosis infections. Treatment is based on surgical excision, which provides a cure rate of 90%. Macrolides are reserved for extended lesions and/or relapsing lesions despite surgical management.

Prevention of chronic anthracycline cardiotoxicity in the adult Fischer 344 rat by dexrazoxane and effects on iron metabolism.

PURPOSE: Anthracyclines, such as doxorubicin and daunorubicin, continue to be widely used in the treatment of cancer, although they share the adverse effect of chronic, cumulative dose-related cardiotoxicity. The only approved treatment in prevention of anthracycline cardiotoxicity is dexrazoxane, a putative iron chelator. Previous in vitro studies have shown that disorders of iron metabolism, including altered IRP1-IRE binding, may be an important mechanism of anthracycline cardiotoxicity. METHODS: This study examined the role of IRP1-IRE binding ex vivo in a chronic model of daunorubicin cardiotoxicity in the Fischer 344 rat and whether dexrazoxane could prevent any daunorubicin-induced changes in IRP1 binding. Young adult (5-6 months) Fischer 344 rats received daunorubicin (2.5 mg/kg iv once per week for 6 weeks) with and without pretreatment with dexrazoxane (50 mg/kg ip). Other groups received saline (controls) or dexrazoxane alone. Rats were killed either 4 h or 2 weeks after the last dose of daunorubicin to assess IRP1-IRE binding. RESULTS: Contractility (dF/dt) of atrial tissue, obtained from rats 2 weeks after the last dose of daunorubicin, was significantly reduced in daunorubicin-treated compared to control rats. Dexrazoxane pretreatment protected against the daunorubicin-induced decrease in atrial dF/dt. However, left ventricular IRP1/IRE binding was not affected by daunorubicin treatment either 4 h or 2 weeks after the last dose of daunorubicin. CONCLUSIONS: IRP1 binding may not be altered in the rat model of chronic anthracycline cardiotoxicity.

Kinetic cooperativity of human liver alcohol dehydrogenase gamma(2).

Previous studies showed that natural human liver alcohol dehydrogenase gamma exhibits negative cooperativity (substrate activation) with ethanol. Studies with the recombinant gamma(2) isoenzyme now confirm that observation and show that the saturation kinetics with other alcohols are also nonhyperbolic, whereas the kinetics for reactions with NAD(+), NADH, and acetaldehyde are hyperbolic. The substrate activation with ethanol and 1-butanol are explained by an ordered mechanism with an abortive enzyme-NADH-alcohol complex that releases NADH more rapidly than does the enzyme-NADH complex. In contrast, high concentrations of cyclohexanol produce noncompetitive substrate inhibition against varied concentrations of NAD(+) and decrease the maximum velocity to 25% of the value that is observed at optimal concentrations of cyclohexanol. Transient kinetics experiments show that cyclohexanol inhibition is due to a slower rate of dissociation of NADH from the abortive enzyme-NADH-cyclohexanol complex than from the enzyme-NADH complex. Fluorescence quenching experiments confirm that the alcohols bind to the enzyme-NADH complex. The nonhyperbolic saturation kinetics for oxidation of ethanol, cyclohexanol, and 1-butanol are quantitatively explained with the abortive complex mechanism. Physiologically relevant concentrations of ethanol would be oxidized predominantly by the abortive complex pathway.

Inactivation of 3-hydroxy-3-methylglutaryl-CoA synthase and other Acyl-CoA-utilizing enzymes by 3-Oxobutylsulfoxyl-CoA.

3-Oxobutylsulfoxyl-CoA has been produced by oxidation of S-3-oxobutyl-CoA, the thioether analog of acetoacetyl-CoA. Avian hydroxymethylglutaryl-CoA (HMG-CoA) synthase is inactivated by oxobutylsulfoxyl-CoA in a time-dependent fashion. Protection against inactivation is afforded by the substrate, acetyl-CoA, suggesting that inactivation involves modification of the enzyme's active site. Pretreatment of HMG-CoA synthase with the inactivator blocks the enzyme's ability to form Michaelis and acetyl-S-enzyme intermediates, supporting the hypothesis that modification is active-site directed. Incubation of enzyme with oxobutylsulfoxyl-[32P]CoA followed by precipitation with trichloroacetic acid indicates that inactivation correlates with stoichiometric formation of a covalent adduct between enzyme and a portion of the inactivator that includes the CoA nucleotide. The observation of reagent partitioning suggests that HMG-CoA synthase catalyzes conversion of oxobutylsulfoxyl-CoA into a reactive species that modifies the protein. Treatment of inactivated enzyme with DTT or other mercaptans restores enzyme activity and reverses the covalent modification with release of CoASH. Oxobutylsulfoxyl-CoA inactivates beta-ketothiolase and HMG-CoA lyase in a process that is also reversed by DTT. These three enzymes all contain active site cysteines, suggesting that inactivation results from disulfide formation between a cysteine and the CoA moiety of the inhibitor. The data are consistent with the hypothesis that enzymatic cleavage of oxobutylsulfoxyl-CoA results in the transient formation of a sulfenic acid derivative of CoA which subsequently reacts to form a stable disulfide linkage to protein.

Avian cytosolic 3-hydroxy-3-methylglutaryl-CoA synthase: evaluation of the role of cysteines in reaction chemistry.

The pH dependence of avian cytosolic HMG-CoA synthase activity is fit by a titration curve with a pK = 8.6. The observation of optimal activity at alkaline pH and the insensitivity of pK to divalent cation concentration suggest that the pK reflects ionization of an amino-acid side chain (e.g., cysteinyl sulfhydryl) rather than substrate enolization. Upon reaction of 3-chloropropionyl-CoA with HMG-CoA synthase C129S, an enzyme variant lacking the sulfhydryl group normally targeted by this mechanism-based inhibitor, stoichiometric modification occurs. Amino-acid analysis indicates that cysteine is the principal target in C129S enzyme, demonstrating the presence of a second reactive cysteine within this enzyme. To test whether another cysteine functions in reaction chemistry, conserved cysteines were identified by sequence homology analysis. Five cysteine residues (C59, C69, C224, C232, C268), invariant in the nine sequences available for various eukaryotic HMG-CoA synthase isozymes, were individually replaced by alanine in a series of mutant enzymes. Kinetic analyses of the isolated mutant HMG-CoA synthases indicate that none of these is crucial to the chemistry that results in production of HMG-CoA. These results further distinguish the HMG-CoA synthase reaction from the related condensation of acyl-CoA substrates catalyzed by beta-ketothiolase.

Evidence supporting catalytic roles for aspartate residues in phosphoribulokinase.

The DNA encoding Rhodobacter sphaeroides phosphoribulokinase (PRK) has been modified to allow ligation into pET-3d. Using the resulting expression plasmid, PRK was overexpressed in Escherichia coli and isolated in milligram quantities. Homogeneous preparations of the enzyme exhibit properties comparable to those of PRK expressed using a previously described pUC19-derived construct [Sandbaken et al., Biochemistry 31, 3715-3719]. Mutagenesis experiments have been designed to produce conservative substitutions that eliminate the carboxyl groups of each of four conserved acidic residues (D42, E131, D169, and E178). Using the newly developed expression system, the resulting PRK variants have been expressed, isolated, and characterized. Expression levels and recoveries upon affinity chromatography purification are similar to the results obtained with wild-type PRK. Apparent substrate affinities of these mutant proteins do not differ greatly from values observed for wild-type PRK. In contrast, these PRK variants display a wide range of Vmax values, ranging from wild-type activity (approximately 200 units/mg; E178A) to levels that are diminished by 4 (D169A) to 5 (D42A, D42N) orders of magnitude. That the large diminutions in catalytic activity are significant and do not merely reflect gross perturbations in protein structure is suggested not only by the modest effects on substrate affinity but also by the allosteric properties of D169A, D42A, and D42N. The activities of these proteins, like that of wild-type PRK, are markedly stimulated by the positive effector NADH. The magnitude of the Vmax perturbations suggests that D42 and D169 are candidates for the role of active site base or activator cation ligand.(ABSTRACT TRUNCATED AT 250 WORDS)