Mechanism of action of 6-mercaptopurine (6-MP) and 6thioguanine (6-TG) were investigated in cultured L-1210mouse leukemia cells and human leukemic leukocytes. In L-1210 cells,6-MP and 6-TG were catalyzed by HGPRTase to 6-TIMP and 6-TGMP, respectively.6-TG was a competitive inhibitor of hypoxanthine in the presence of PRPP as fixed substrate and the inhibition coefficient (Ki) was 240μM. Also,6-TG inhibition was competitive against guanine with the Ki value of 60μM. The inhibitory effect of 0.2 mM of 6-TG on the IMP synthesis was similar to that of 2.5mM of 6-MP in human leukemic leukocytes. The HGPRTase activity of leukocytes obtained from 10 normal subjects,8 patients with chronic leukemia and 9 patients with acute leukemia were determined. When the HGPRTase activity was expressed as the μmole of synthesized IMP/hr/2×107 cells, the HGPRTase activity of normal leukocytes, chronic leukemia cells and acute leukemia cells were 0.193 ± 0.114,0.230 ± 0.086and 0.172 ± 0.068μmoles, respectively. The mean value of HGPRTase activity of chronic leukemia cells was significantly increased than that of acute leukemia cells. The inhibitory effect of 6-MP on IMP synthesis correlated to the HGPRTase activity significantly in both types of leukemias. The inhibitory effect of 6-TG correlated to the HGPRTase activity significantly in acute leukemia but not in chronic leukemia. The correlation between the inhibitory effect of drugs and percentage of immature leukemia cells was not obtained. It appeared that the HGPRTase activity played an important role in inhibitory effect of 6-MP and 6-TG as well as the concentration of intracellular PRPP.
Uric acid contents and xanthine dehydrogenase (XDH) activities in viscera of Fayoumi chickens which had been selected for animal model of hereditary gout were assayed to observe the distribution of the uric acid in viscera, when normal or high protein diets were fed for 2 weeks in the adult stage. Uric acid contents in viscera were increased by feeding a high protein diet. The interaction of genotype (gouty or non-gouty) and protein (a normal protein diet composed of 17% crude protein and a high protein diet composed of 40% crude protein) were observed. The interaction of genotype and protein level were different among organs. Especially, in the liver and the aorta, the multiplicative interactions were observed. The increase of the uric acid in the aorta of the gouty chicken fed on a high protein diet may suggest some relationship to the atherosclerosis. XDH activity levels in viscera of adult chickens were as follows: liver> kidney> spleen, irrespective to the diets. That in the heart was not able to be detected by the present method. XDH activities in the liver and the kidney were increased when fed on a high protein diet.
A simple and practical method for estimating the character of drugs, which may clinically cause hyperuricemia, was devised using rats with a catheterized aorta loaded with an urate oxidase inhibitor, potassium oxonate. The method was so simple and economical for detecting the increase of plasma uric acid with drug administration that we could use it as a routine assay for investigating the characteristics of drugs with experimental animals. This report introduces the method together with some examples showing its utility. Potassium oxonate, administered i.p.at 250 mg/kg, effectively inhibited the action of urate oxidase for at least two hours, and prolonged inhibition of the enzyme was maintained by successive treatment with the agent every two hours. Under such conditions, we could easily detect an obvious increase of plasma uric acid upon treatment with some test drugs such as uric acid, isoproterenol, fructose, xylitol and diuretic antihypertensives. Potassium oxonate showed an apparent diuretic and hyperuricosuric action by itself, and hence the method could not be used to estimate the main action of uricosuric agents, while an obvious increase of plasma uric acid was also detected with a high dose of tienilic acid or probenecid. Of course, although we should further investigate whether the increase of plasma uric acid demonstrated by this method truly displays the character of drugs inducing clinical hyperuricemia, the simplicity of the method should greatly aid solving many problems concerning drug-induced hyperurlcemia.
Microcephaly literally means “small head” or head circumference 2 SD below the mean, and is usually associated with a generalized reduction of the brain mass (micrencephaly). It was presented by the authors at the Eighteenth Annual Meeting of the Japanese Society of Neurology in Nagoya, May 18,1977, that CSF uric acid concentrations were decreased in most of the infants and the children with microcephaly. The purpose of this paper is to find out the difference between microcephaly of hypoplastic type and that of atrophic type. The concentrations of uric acid, cAMP and cGMP in CSF were investigated in 10 cases of normal control from 2 months to 2 years and in 22 cases of microcephaly from 3months to 4 years. The mean values and standard deviations in normal controls were as follows: Uric acid concentrations in CSF(n=10): 0.30±0.11mg/dl cAMP concentrations in CSF(n=5): 9.96±3.84 pmol/ml cGMP concentrations in CSF(n=5): 7.32±4.00 pmol/ml CSF uric acid concentrations were decreased in the microcephalies of genetic etiology with DQ below 50. The responsible factor is thought to be decreased turnover of the nucleic acid due to hypoplasia of the brain. On the contrary, CSF uric acid concentrations were increased in the microcephalies of postnatal etiology with DQ below 50. The responsible factors are thought to be (1) increased permeability of blood-CSF barrier and (2) cerebral cell necrosis, due to progressive atrophy of the brain secondary to trauma or infection. CSF cAMP and cGMP concentrations were decreased in the microcephalies of postnatal etiology with DQ below 50. The responsible factors for the decreased concentrations in the microcephalies of postnatal etiology are thought to be (1)damage to the cyclase enzymes, (2) inadequate delivery of cyclase-activating hormons, and (3) deficiency of the enzyme's substrates such as ATP and GTP. Finally, it should be kept in mind that the concentrations of uric acid, cAMP and cGMP were all normal in the CSF of 2microcephalies of genetic etiology without mental retardation.
We observed previously that allopurinol, which is used for the treatment of gout, had a life saving effect on account of the better survival rate of experimental traumatic shock rats and hemorrhagic shock rabbits. Fifteen patients undergoing open heart surgery which was considered to have the metabolic derangement similar to that of patients in shock state were investigated to evaluate the effect of allopurinol. Allopurinol was given orally 2mg/kg body weight twice before the start of nitrous oxide, oxygen and halothane anesthesia. In the control group containing ten patients who were not treated with allopurinol, serum uric acid increased, the lactate/pyruvate ratio rose and β-glucuronidase activity increased respectively after open heart surgery like in shock. While the metabolic changes of the fifteen patients pretreated with allopurinol were prohibited significantly although same tendency was observed. The heart beat of patients in the allopurinol group started spontaneously after extracorporeal circulation without using DC counter shock. We concluded that allopurinol is effective in preventive damage of cellular structures and derangements of metabolism of the patients performed open heart surgery.