Paula M. Bozeman

Assay of the human leukocyte enzymes myeloperoxidase and eosinophil peroxidase

Conditions were optimized for measuring the activity of myeloperoxidase (MPO) and the eosinophil peroxidase (EPO) with tetramethylbenzidine (TMB) as the substrate. Detergents caused a small increase in the measured activity of the purified enzymes and were required when isolated neutrophils or eosinophils were assayed. Sharp concentration optima were observed with both ionic and non-ionic detergents. Activity was also influenced by halide ions. Bromide or iodide caused up to a 7-fold increase in EPO activity and a 1.5-fold increase in MPO activity. The effect of bromide is notable because the bromide-containing detergent CETAB is often used to extract the enzymes for assay and purification. Stimulation by bromide or iodide was consistent with peroxidase-catalyzed oxidation of the halides to hypohalous acids (HOBr and HOI), which oxidized TMB. MPO catalyzes the oxidation of chloride to hypochlorus acid (HOCl), which also oxidized TMB, but chloride up to 20 mM had little effect on the assay. Both MPO and EPO catalyze thiocyanate oxidation, but the product (HOSCN) was a poor oxidant for TMB, and thiocyanate inhibited the measured activities. Stimulation by bromide or iodide could be used to facilitate detection of EPO and to distinguish between MPO and EPO. Activities could also be distinguished based on the greater sensitivity of EPO to inhibition by thiocyanate, azide, aminotriazole, and dapsone. Methods reported here may prove useful for measuring leukocyte influx into inflamed tissues, detecting MPO or EPO deficiencies, and measuring enzyme synthesis and secretion.

Role of flexible bronchoscopy in the diagnosis of pulmonary infiltrates in pediatric patients with cancer

We reviewed 60 consecutive flexible bronchoscopies done during a 36-month period in 48 pediatric cancer patients with undiagnosed pulmonary infiltrates. Diagnostic procedures during bronchoscopy included 40 brushings, 50 bronchoalveolar lavages, and 6 transbronchial and mucosal biopsies. A total of 16 specific diagnoses were made by bronchoscopy (27% diagnostic yield), including infection (12), pulmonary leukemia (3), and lymphoma (1). The largest proportion of specific diagnoses came from lavage (14/50) and the smallest from brushings (1/40). Biopsies were also useful for selected patients. The low overall yield for bronchoscopy was probably due to the routine use of empiric broad-spectrum antibiotics and antifungal therapy, as well as trimethoprim-sulfamethoxazole prophylaxis for Pneumocystis carinii pneumonitis. Subsequent specific diagnoses were obtained by other procedures (open biopsy, needle aspiration, or autopsy) for 10 patients with negative bronchoscopy results and 3 patients with diagnostic bronchoscopies. These additional diagnoses included 7 infections (Pneumocystis carinii (1), Candida tropicalis (1), cytomegalovirus (1), and Aspergillus (4), and 6 other diagnoses with nonspecific histologic findings. A positive bronchoscopy result may be useful, but negative bronchoscopy findings do not justify delaying other diagnostic procedures or discontinuing antibiotic and antifungal therapy in children with cancer and pulmonary infiltrates.

Postsepsis bradycardia in children with leukemia

ObjectiveWe observed sinus bradycardia in a small number of children with hematologic malignancies who were recovering from sepsis. Our objective was to define this symptom complex and attempt to delineate its etiology. DesignRetrospective chart review. SettingA pediatric ICU in a childrens oncology hospital. PatientsChildren admitted to the ICU over a 24-month period who developed persistent bradycardia (heart rate <5% for age for >1 hr) after an episode of sepsis. Measurements and Main ResultsSeven children developed postsepsis bradycardia. Six patients had a primary diagnosis of acute myelogenous leukemia and one patient had acute lymphocytic leukemia. All patients had positive blood cultures (Streptococcus mitis, n = 4; Escherichia coli, n = 2; and Klebsiella pneumoniae, n = 1). All seven children were clinically recovering from sepsis when the bradycardia developed. Neither hypotension nor other symptom was associated with the bradycardia. No therapy was given for the bradycardia. Echocardiograms and ECGs were normal in all patients, except for the presence of bradycardia. Bradycardia persisted for 24 to 72 hrs. After that time, heart rates slowly increased to the normal range for age. ConclusionsWe speculate that this syndrome may result from alterations in β-adrenergic receptor function or an unidentified humoral factor produced by the invading organism or as part of the hosts response to sepsis. Prior drug therapy or the underlying illness may predispose to this condition, since all the patients had acute leukemia. As the bradycardia was clinically insignificant, invasive therapeutic or diagnostic strategies were not indicated.