Toxicologic studies of a conjugate of asparaginase and polyethylene glycol in mice, rats, and dogs.

A conjugate of asparaginase and monomethoxypolyethylene glycol was evaluated in acute, subacute, and subchronic toxicologic studies in mice, rats, and dogs. The drug induced low-grade toxicosis. The appearance and behavior of rats and dogs were not affected by the treatment. Only large doses produced inactivity, loss of appetite, and loss of weight. The LD50 could not be established. The drug retarded slightly body weight gains in dogs and female rats and produced mild anemia in 30% of the female rats. Urinalysis and blood chemical determinations in rats and dogs were generally not affected by the treatment. Monomethoxypolyethylene glycol-asparaginase was detectable in the plasma of mice 13 days after IV, intraperitoneal, or IM administration, and in dogs for 3 to 4 weeks.

beta-Receptor influence on lung vasoconstrictor responses to hypoxia and humoral agents.

The role of the adrenergic receptor in mediating pulmonary vascular responses to gaseous and humoral agents was investigated by use of epinephrine injections in the perfused feline pulmonary circulation. Alteration of the balance between alpha- and beta-adrenergic activity was quantified by measurement of decreasing vasoconstrictor activity to epinephrine and rising lobar tissue 3',5'-adenosine cyclic monophosphate (cAMP) levels. The increased beta-adrenergic activity thus generated was associated with marked reductions in the pulmonary vasoconstrictor responses to hypoxia, hypercapnic acidosis, and histamine, but not to serotonin. Repeated pulmonary vasodilations or increases in blood, but not pulmonary tissue, levels of cAMP induced by theophylline doses, which would not necessarily affect the beta-adrenergic activity, did not alter the pulmonary vasoconstrictor responses to hypoxia, hypercapnia, or histamine. These data support the significant role which the adrenergic system plays in mediating pulmonary vasoconstrictor responses to certain specific gaseous and humoral agents, and the specificity with which this mediation occurs serves to link hypoxia and histamine together so that the latter could serve as a mediator of the former.

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.

Alterations in norepinephrine, serotonin, c-AMP, and transsynaptic induction of tyrosine hydroxylase after spinal cord transection in the rat.

Tyrosine hydroxylase (TH) activity and the concentrations of norepinephrine (NE), serotonin (5-HT), and cyclic adenosine 3',5'-monophosphate (c-AMP) were measured in the heart, adrenals, and brain stem of paraplegic rats. Following spinal cord transection NE concentration in the heart dropped to 30% within 24 hours and that of 5-HT decreased to 60% of control. Tyrosine hydroxylase activity in the adrenals reached a peak at five days and was still twice that of sham-operated controls thirty days later. Five days following transection the TH activity and c-AMP levels in the brain stem were elevated while NE concentration remained low. At seven days, however, NE and 5-HT levels were higher than in controls while TH activity and c-AMP concentration dropped to control levels. The increase in TH activity in the brain stem may be due to curtailed end-product feedback inhibition and to reduced receptor activation. The sustained induction of the adrenal TH is probably a consequence of a continual stimulation of splanchnic nerves.

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.

Spinal cord injury: effect of thyrocalcitonin on periarticular bone formation in three subjects.

Sodium fluoride 18F scintimetry was performed before and after 1 month of salmon thyrocalcitonin treatment of 3 spinal cord injured patients with periarticular ossification of the hips and knees. Thyrocalcitonin therapy caused a marked diminution of 18F uptake in 1 patient with long-standing periarticular bone of both hips. Clinically, the range of motion in this subject increased by 25 degrees and there was a marked decrease in pain locally. The results were, however, not duplicated in the 2 patients with periarticular bone formation of short duration.

A preliminary study on the evaluation of asparaginase. Polyethylene glycol conjugate against canine malignant lymphoma.

Thirty-seven dogs with malignant lymphoma were treated with either polyethylene glycol conjugated (PEG) asparaginase alone (10-30 IU/kg intraperitoneally [IP] weekly--20 dogs) or PEG-asparaginase combined with one cycle of chemotherapy (vincristine, cyclophosphamide, methotrexate, and prednisone), followed by maintenance PEG-asparaginase (30 IU/kg, IP weekly--17 dogs). In the 20 dogs (eight were chemotherapy resistant) treated with PEG-asparaginase alone, seven had a complete response (CR), seven had a partial response (PR), five had no response (NR), and one was not evaluable (NE). The duration of response (CR + PR) ranged from 14 to 102 days (median, 48 days). In the eight chemotherapy-resistant dogs (seven were previously resistant to L-asparaginase) four had responses (one CR and three PR). In the 17 dogs treated with combined PEG-asparaginase and chemotherapy, 13 had a CR, two had a PR, and two had NR. None of the dogs had had prior chemotherapy, and the duration of response (CR + PR) ranged from 7 to 840+ days, with a median of 126+ days. Four dogs are still on maintenance PEG-asparaginase at 16+, 21+, 26+, and 28+ months. Toxicity consisted of death due to massive tumor breakdown (two dogs), disseminated intravascular coagulation (DIC--one dog), hypersensitivity reaction (one dog), vomiting (three dogs) and soft stools (three dogs). Four normal dogs were given very high doses of PEG-asparaginase (200 IU/kg and 1200 IU/kg) once weekly for two treatments without any significant toxicity. These results indicate that PEG-asparaginase has antitumor activity in dog with spontaneously occurring malignant lymphoma.

Pituitary-testicular axis dysfunction in spinal cord injury.

Concentrations of testosterone, luteinizing hormone (LH), and follicle-stimulating hormone (FSH) in serum and 17-ketosteroids (17-KS) in urine of 10 paraplegic and 10 quadriplegic subjects were measured from onset of injury and followed once a week for 4 months. Compared with age-matched normal controls, paraplegic subjects showed significantly lower serum levels of LH and FSH for 2 weeks and of testosterone for 6 weeks after spinal cord trauma, following which periods of time these hormones attained normal levels. By contrast, in quadriplegic subjects, serum testosterone concentrations remained significantly lower than those of the controls during the entire 4-month testing period. Furthermore, in another group of 10 chronic (1 to 6 years after onset of injury) paraplegic and 10 chronic quadriplegic subjects, serum testosterone and FSH concentrations were comparable to those of the normal controls. Serum LH concentrations were at control levels in chronic paraplegic but significantly depressed in chronic quadriplegic subjects. The concentrations of urinary 17-KS exhibited sharp fluctuations over the 4-month period and were below control levels in paraplegic but within control limits in quadriplegic subjects. The results indicate that the function of the hypothalamic-pituitary-gonadal axis is disturbed for at least 4 months in quadriplegic subjects.

Alterations of cyclic AMP in cerebral ischemia.

Cyclic AMP levels were measured in brains of 21 cats after occlusion of a middle cerebral artery by a transorbital approach. Brain samples for determination of cAMP by a protein binding radioassay were obtained from the ischemic and contralateral temporal lobes before sacrifice, 1, 3, and 24 hours after occlusion of the right middle cerebral artery. At 1 hour, no difference between the 2 sides was observed; a mean of 17.4 pmoles/mg protein was observed from the side of the occlusion and 18.9 pmoles/mg protein from the contralateral side. At 3 hours, a mean value of 8.9 pmoles/mg protein on the ischemic side and a level of 21.7 pmoles/mg protein on the contralateral side were observed. At 24 hours, the cAMP level on the ischemic side remained below the nonischemic side; the values obtained were 13.7 pmoles/mg protein compared to 27.9 pmoles/mg protein compared to 27.9 pmoles/mg protein. These changes in cAMP as early as 3 hours after the onset of ischemia, when such a lesion is reversible, may indicate that in initial step in the alteration of cellular metabolism following ischemia is due to membrane perturbation and altered production of this second messenger.

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.

Use of polyethylene glycol-modified uricase (PEG-uricase) to treat hyperuricemia in a patient with non-Hodgkin lymphoma.

Modification by covalent attachment of monomethoxypolyethylene glycol (PEG) can reduce the immunogenicity and prolong the circulating life of injected enzymes, making their use as therapeutic agents feasible. We report the first clinical use of PEG-modified Arthrobacter protoformiae uricase (PEG-uricase) to treat hyperuricemia in a patient with non-Hodgkin lymphoma and renal insufficiency who was allergic to allopurinol. Two intramuscular injections totaling 3 U/kg body weight during the first 30 hours of treatment lowered the plasma urate level from 910 to 190 mumol/L (15.3 to 3.2 mg/dL), after which a dose of 2 U/kg every 5 to 6 days maintained the plasma urate level at 540 mumol/L (9 mg/dL) or lower. After the injection of PEG-uricase, uricase activity appeared in plasma rapidly, peaking within 24 hours and persisting for approximately 5 days; an inverse relation between plasma uricase activity and plasma urate concentration was noted. The agent was nontoxic and well tolerated. No antibody to either PEG-uricase or unmodified uricase developed over a 3-week period, during which four doses of PEG-uricase were administered. Because of its long circulating life, PEG-uricase is probably a more effective hypouricemic agent than unmodified uricase, which has previously had limited use. As an adjunct to cytolytic therapy for hematologic malignancies when protection from hyperuricemia is needed rapidly, PEG-uricase deserves further study.

Bone mineralization in the distal forearm of hemiplegic patients.

Bone mineral content was measured by single photon absorptiometry using a modified bone densitometer (Packard) with 125I as the source. In 42 hemiplegic subjects, matched for sex and age, the bone density was compared bilaterally on the radius and ulna 2 cm and 4 cm above the wrist. The nonparalyzed side served as a control for the paralyzed side. The results indicate a consistent, general loss of bone mineral on the paralyzed side compared with the nonparalyzed side. The extent of demineralization in females was greater than in male subjects. Right-dominant left-paralyzed patients showed a greater loss of bone density than right-dominant right-paralyzed subjects. The absorption ratio of the paralyzed vs the nonparalyzed sides revealed that there was a 5.3% and 7.4% decrease in the average bone density at 4 and 2 cm above the wrist, respectively. There was a progressive loss of bone mineral content relative to time after the onset of paralysis, amounting to an average of 6.4% approximately three months after the onset of injury. It was estimated that before the onset of paralysis there was an excess of bone mineral on the dominant vs the nondominant side of +5.4% and +3.2% for males and females, respectively.

Mitigation of pulmonary oxygen toxicity in premature lambs with intravenous antioxidants.

Deficiencies of antioxidants and increased free radical generation may explain the high incidence of bronchopulmonary dysplasia in premature infants. Long-acting antioxidants such as polyethylene glycol (PEG) conjugated superoxide dismutase (SOD), and catalase might modify this process. We delivered 32 premature lambs, 16 pairs of twins, by cesarean section at 125-141 days of gestation (term 146 days) and stabilized them on ventilators in normocapnic hyperoxia for a period of 8 h. One lamb of each twin pair received an intravenous dose of 7,500-50,000 IU/kg of PEG-SOD and of 37,500-1,000,000 IU/kg of PEG-catalase at birth. Their siblings acted as controls. Mean airway pressure, arterial pressure, and heart rate were recorded continuously. Arterial blood gases and pH were obtained every 30 min. After sacrifice, standardized lung biopsies were prepared for quantitative morphometrics and electron microscopy. Administration of PEG antioxidants at birth reduced the influx of neutrophils and macrophages into the lung and damage to arterioles, bronchiolar mucosa, and type II pneumocytes without major changes in alveolar surface area or pulmonary function. These effects were dose-related and detectable even at the lowest doses of PEG antioxidants administered.

The physiological and histopathological response of dogs to exchange transfusion with polyethylene glycol-modified bovine hemoglobin (PEG-Hb).

The performance of polyethylene glycol-modified bovine hemoglobin (PEG-Hb) was evaluated in dogs following the replacement of 30% or 50% of their blood volume with PEG-Hb or lactated Ringer's solution (LRS). Dogs fully instrumented with catheters and blood pressure probes were transfused by simultaneous bleeding from the jugular vein and infusion of PEG-Hb or LRS via the cephalic vein. Animals were monitored for abnormal behavior and clinical signs for fourteen days. No mortalities, overt toxicity, changes in body weight, food consumption or ophthalmology, or discernable trends in hematology, blood chemistry coagulation, urinalysis or hemodynamic parameters that could be attributed to PEG-Hb were noted. Blood gas analyses were steady and within physiological ranges. Dose-related histopathological findings of vacuolated histiocytes in the femoral bone marrow, splenic parenchyma, the medulla of the mesenteric and mandibular lymph nodes, and vacuolated sinusoidal cells in the liver and the renal tubular epithelial cells were believed to be related to the phagocytosis and degradation of PEG-Hb by the reticulo-endothelial system. The maintenance of high oxygen levels in the circulation for the two-week treatment period, as well as the insignificant physiological and histopathological findings indicate that PEG-Hb could be a successful blood substitute.

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.

Prevention of oxygen toxicity with superoxide dismutase and catalase in premature lambs.

The use of high oxygen concentrations and high mean airway pressures during mechanical ventilation of premature newborn infants with respiratory distress syndrome leads in 20%-30% of the survivors to chronic lung disease. This study explores if exogenous polyethylene glycol conjugated superoxide dismutase (PEG-SOD) and catalase (PEG-CAT) mitigate oxygen toxicity in premature lambs with respiratory distress syndrome. Six pairs of premature lambs were delivered by cesarean section and treated by tracheal instillation of 60 mg natural sheep surfactant/kg/body weight. After birth, all lambs were ventilated with 100% oxygen, and one of each pair received a single intravenous injection of 1 million U/kg PEG-CAT and 50,000 U/kg PEG-SOD. At 8 h of age or after respiratory failure was established, the lambs were killed and the lungs were removed intact. Lung damage was assessed by microscopy. The arterial blood gases, pH, and mean airway pressures of the lambs treated with PEG-SOD/PEG-CAT did not differ from those of the controls. Mean PaO2 was greater than 140 mmHg during the first 4 h of the experiments. In the lambs treated with PEG-SOD/PEG-CAT, SOD and CAT levels were very high during the study period and less bronchiolar epithelial damage and lung hemorrhages were found at microscopy.