Safety evaluation of free radical scavengers PEG-catalase and PEG-superoxide dismutase.

Treatment with catalase and SOD (superoxide dismutase) could diminish the damage due to oxygen free radical formation, but these enzymes are rapidly removed from circulation. The covalent attachment of monomethoxypolyethylene glycol (PEG) to catalase and SOD extended their plasma half-lives. Toxicity of PEG-catalase and PEG-SOD was evaluated in mice and rats prior to their use as free radical scavengers. Rodents used in acute, subacute, and subchronic toxicologic studies could tolerate large doses of PEG-catalase and PEG-SOD without developing toxic signs. The conjugates did not affect survival rate, appearance, behavior, food intake, blood chemistry, hematology, or urinalysis. In general, body weight gains, organ weights, and histomorphology were also unaffected. Massive doses of PEG-catalase caused slight weight loss, splenic hypertrophy, and generalized splenic stimulation in mice. Massive doses of PEG-SOD resulted in vacuolation in splenic macrophages in rats. PEG-catalase and PEG-SOD circulated for 3 days and 8 days, respectively, in mice following i.v. or i.m. administration.

Cancer therapy with chemically modified enzymes. I. Antitumor properties of polyethylene glycol-asparaginase conjugates.

The covalent attachment of monomethoxypolyethylene glycol (PEG) to asparaginases from Escherichia coli and Vibrio succinogenes by new coupling methodology produced conjugates that are active, stable, without significant immune response, and with greatly extended plasma half-lives in mice. Therapeutic efficacies were greater for the PEG-asparaginases than for the unmodified asparaginases in mice infected with the L5178Y lymphosarcoma or the 6C3HED tumor. Large single doses of native or modified enzymes were more effective against tumors than the same amount of enzyme given in smaller doses over several days.

Spinal cord injury: effect of thyrocalcitonin on calcium, magnesium and phosphorus in paraplegic rats.

Calcium, magnesium and phosphorus balances were studied in 20 paraplegic rats (T5) fed ad libitum an 18% casein diet. Ten of the paraplegic animals were treated daily with 4MRC (Medical Research Council) units of thyrocalcitonin. Ten sham-operated rats served as controls. Spinal cord transection caused an immediate increase in urinary excretion of calcium, 550 +/- 70 micrograms/24 hr, compared with controls levels, 257 +/- 85 micrograms/24 hr. Paraplegia also resulted in an elevated excretion of fecal calcium, 39 +/- 5 mg/24 hr, phosphorus, 42 +/- 7 mg/24 hr, and magnesium, 4.6 +/- 0.8 mg/24 hr, compared with that of controls, 26 +/- 6 mg/24 hr, 32 +/- 6 mg/24 hr and 2.7 +/- 0.8 mg/24 hr for calcium, phosphorus and magnesium, respectively. Administration of thyrocalcitonin to paraplegic rats further increased urinary excretion of calcium, 835 +/- 186 micrograms/24 hr. However, fecal losses of calcium, 19 +/- 5mg/24 hr, phosphorus, 31 +/- 6mg/24 hr, and magnesium, 2.6 +/- 0.4mg/24 hr, which were elevated following spinal cord transection, were markedly reduced after thyrocalcitonin treatment. As a result, balances of these compounds, which were depressed in rats following spinal cord transection, were "normalized" after treatment with thyrocalcitonin. It would seem, therefore, worthwhile to study the effect of thyrocalcitonin in spinal cord injured humans in an effort to determine whether or not it would be helpful in improving mineral balances.

Mineral metabolism in spinal cord injury.

In 10 paraplegic and 10 quadroplegic subjects, bone resorption was investigated by determining urinary excretion of hydroxyproline, calcium, and phosphorus. Measurements were performed weekly from the onset to 4 months after injury. During the first 7 weeks following injury, urinary excretion of calcium in paraplegic and quadriplegic subjects reached the highest level (380 +/- 180 mg/24hr). From 7 to 16 weeks after injury average urinary excretion of calcium (245 +/- 72 mg/24hr) remained significantly greater than that in controls (100 +/- 25 mg/24hr; p less than 0.05). Urinary hydroxyproline was elevated in paraplegic subjects (80 +/- 18 mg/24hr) for 8 weeks and in quadriplegic subjects (102 +/- 37 mg/24hr) for the entire 16 weeks following injury compared with that in controls (48 +/- 12 mg/24hr; p less than 0.05). Both paraplegic and quadriplegic subjects excreted more phosphorus (1.6 +/- 0.4 gm/24hr) than controls (0.85 +/- 0.2 gm/24hr; p less than 0.05) only during the first 2 weeks following spinal cord injury. During the acute phase of the injury (0-3 months), urinary excretion of calcium and magnesium was significantly higher (p less than 0.05) in subjects with complete compared with incomplete spinal cord lesions.