Recombinant urate oxidase for the prophylaxis or treatment of hyperuricemia in patients With leukemia or lymphoma.

PURPOSE: To improve the control of hyperuricemia in patients with leukemia or lymphoma, we tested a newly developed uricolytic agent, recombinant urate oxidase (SR29142; Rasburicase; Sanofi-Synthelabo, Inc, Paris, France), which catalyzes the oxidation of uric acid to allantoin, a highly water-soluble metabolite readily excreted by the kidneys. PATIENTS AND METHODS: We administered Rasburicase intravenously, at 0.15 or 0.20 mg/kg, for 5 to 7 consecutive days to 131 children, adolescents, and young adults with newly diagnosed leukemia or lymphoma, who either presented with abnormally high plasma uric acid concentrations or had large tumor cell burdens. Blood levels of uric acid, creatinine, phosphorus, and potassium were measured daily. The pharmacokinetics of Rasburicase, the urinary excretion rate of allantoin, and antibodies to Rasburicase were also studied. RESULTS: At either dosage, the recombinant enzyme produced a rapid and sharp decrease in plasma uric acid concentrations in all patients. The median level decreased by 4 hours after treatment, from 9.7 to 1 mg/dL (P =.0001), in the 65 patients who presented with hyperuricemia, and from 4.3 to 0.5 mg/dL (P =.0001) in the remaining 66 patients. Despite cytoreductive chemotherapy, plasma uric acid concentrations remained low throughout the treatment (daily median level, 0.5 mg/dL). The urinary excretion rate of allantoin increased during Rasburicase treatment, peaking on day 3. Serum phosphorus concentrations did not change significantly during the first 3 days of treatment, decreased significantly by day 4 in patients presenting with hyperuricemia (P =.0003), and fell within the normal range in all patients by 48 hours after treatment. Serum creatinine levels decreased significantly after 1 day of treatment in patients with or without hyperuricemia at diagnosis (P =.0003 and P =.02, respectively) and returned to normal range in all patients by day 6 of treatment. Toxicity was negligible, and none of the patients required dialysis. The mean plasma half-lives of the agent were 16.0 +/- 6.3 (SD) hours and 21.1 +/- 12.0 hours, respectively, in patients treated at dosages of 0.15 or 0.20 mg/kg. Seventeen of the 121 assessable patients developed antibodies to the enzyme. CONCLUSION: Rasburicase is safe and highly effective for the prophylaxis or treatment of hyperuricemia in patients with leukemia or lymphoma.

Cloning and characterization of the calreticulin gene from Ricinus communis L.

A full-length cDNA encoding a calreticulin-like protein was isolated by immune-screening a germinating castor bean endosperm cDNA library with antisera raised to the total lumenal fraction of purified plant endoplasmic reticulum. The calcium-binding properties of the recombinant protein were characterized and shown to be essentially identical to those reported for the mammalian calreticulin. Calcium overlays and immune blot analysis confirmed the endoplasmic lumenal identity of this reticuloplasmin. Probing protein blots of endoplasmic reticulum subfractions with radio-iodinated calreticulin showed specific associations with various polypeptides including one identified as the abundant reticuloplasmin protein disulfide isomerase. Characterization of the corresponding genomic clones revealed that calreticulin is encoded by a single gene of 3 kb in castor. The full genomic sequence reveals the presence of 12 introns, 12 translated exons, and one exon containing the last three amino acids of the translated sequence and the 3'-untranslated region of the gene. Northern blot analysis of RNA isolated from various organ tissues showed a basal constitutive level of expression throughout the plant, but more abundant mRNA being detected in tissues active in secretion. This was confirmed by analysis of transgenic tobacco plants containing 1.8 kb of 5'-untranslated genomic sequence fused to the beta-glucuronidase reporter gene (GUS) showed a more localized pattern of expression. Activity being localized to the vasculature (phloem, root hairs and root tip) in vegetative tissue, and being strongly expressed in the floral organs including the developing and germinating seed.

Molecular characterisation of plant endoplasmic reticulum. Identification of protein disulfide-isomerase as the major reticuloplasmin.

Purified endoplasmic reticulum devoid of contaminating endomembranes has been isolated from both germinating and developing castor bean endosperm by a modified two-step centrifugation procedure. These membranes have been characterised for protein and lipid composition, subfractionated into lumenal and integral membrane protein fractions, and antisera raised to these two components. A cDNA clone encoding a major lumenal protein of 55 kDa was cloned using affinity-purified antisera and shown to encode a protein with strong sequence similarity to the endoplasmic reticulum lumenal chaperone protein disulfide-isomerase. Northern and Southern blot analysis showed that the mRNA from a single-copy gene was constitutively expressed in all tissues investigated, but was preferentially expressed in developing seed where it was the most abundant lumenal protein. Expression of the recombinant protein in Escherichia coli yielded a homodimer with a molecular mass of 110 kDa with protein disulfide-isomerase catalytic activity, thus confirming identity of this protein.

Reduced aflatoxicosis in livers of hamsters fed a manganese sulfate supplement.

Male, weanling Syrian hamsters (Mesocricetus auratus) were given (for 10 weeks) diets supplemented with manganese sulfate, aflatoxin, or a combination of both. All animals were killed and a histopathologic evaluation was performed on each liver to assess the influence of a manganese-supplemented diet on aflatoxicosis. Serum cholesterol and liver glycogen levels were also analyzed to further study the interaction of manganese and aflatoxin. Characteristic aflatoxin-induced precancerous histopathologic changes were observed in animals receiving the toxin. These changes included bile duct cell hyperplasia, enlarged nuclei, nuclear inclusions, and megala-hepatocytes. The dietary manganese addition to aflatoxin animals caused a slight reduction in the bile duct cell hyperplasia and significantly reduced the enlarged nuclei and nuclear inclusions. The latter indicates that the manganese may be influencing membrane chemistry. Animals receiving aflatoxin alone showed significantly increased serum cholesterol and liver glycogen. The cholesterol levels were significantly increased over the aflatoxin-induced levels when manganese was given in combination with the aflatoxin. The manganese lowered the increased liver glycogen levels caused by the aflatoxin. Dietary manganese shows some potential in suppressing several, but not all, of the aspects of developing aflatoxicosis in the hamster. The specific mode and site of action of manganese requires additional study.