Hypoxanthine-guanine phosphoribosyltransferase mutant glioma cells: diminished monamine oxidase activity.

A defective capability of cultured rat glioma cells to reutilize purine bases (hypoxanthine-guanine phosphoribosyltransferase deficiency) was associated with a reduced capacity to oxidatively deaminate serotonin and tryptamine. The mutant glioma cells were also more sensitive to the cytotoxic effects of serotonin than were normal cells

Increased cystine in leukocytes from individuals homozygous and heterozygous for cystinosis.

In patients with cystinosis, the concentration of free cystine in leukocytes was 80 times greater than normal, and six times the normal content for their parents. This is the first demonstration of an abnormality in heterozygotes for this rare inherited disease of childhood. Three-quarters of the cystine was recovered in the granular fraction of cystinotic leukocytes.

Substrate stabilization: genetically controlled reciprocal relationship of two human enzymes.

5-Phosphoribosyl-l-pyrophosphate, a substrate shared by adenine phosphoribosyltransferase and hypoxanthine-guanine phosphoribosyltransferase, accumulates in human erythrocytes lacking hypoxanthine-guanine phosphoribosyltransferase. 5-Phosphoribosyl-l-pyrophosphate added to purified adenine phosphoribosyltransferase stabilizes it against heat inactivation. The increased activity of adenine phosphoribosyltransferase seen in erythrocytes deficient in hypoxanthine-guanine phosphoribosyltransferase may result from substrate stabilization of this enzyme in vivo.

Enzyme defect associated with a sex-linked human neurological disorder and excessive purine synthesis.

A sex-linked familial neurological disease consisting of cerebral palsy, mental retardation, choreoathetosis, and compulsive aggressive behavior is associated with a loss of an enzyme that participates in purine metabolism, namely, hypoxanthine-guanine phosphoribosyltransferase. The production of excessive uric acid in this disorder implies that the enzyme is involved in the normal regulation of purine biosynthesis. This is the first example of a relation between a specific enzyme defect and abnormal compulsive behavior. It is also the first enzyme defect in purine metabolism demonstrated in a neurological disease.

Adenine and adenosine are toxic to human lymphoblast mutants defective in purine salvage enzymes.

Mutants deficient in adenosine kinase or adenine phosphoribosyltransferase activities were selected from the WI-L2 line of human lymphoblasts. The adenosine kinase-deficient mutant was still as sensitive as its parent to growth inhibition caused by adenosine deaminase was inhibited. Similarly, the adenine phosphoribosyltransferase mutant remained sensitive to growth inhibition caused by adenine. Thus, the toxicity of adenine and adenosine to human lymphoblasts is not mediated by nucleotides to which they may be converted.

Cholera toxin-peroxidase: changes in surface labeling of glioblastoma cells with increased time in tissue culture.

Cholera toxin coupled to peroxidase yielded a highly specific ultrastructural marker of plasma membrane monosialogangliosides. Studies with cultures of brain and brain tumors suggested that long-term culture of tissue in monolayers results in eventual loss of surface monosialogangliosides.

Cystine: compartmentalization within lysosomes in cystinotic leukocytes.

The large amount of cystine compartmentalized in cystinotic leukocytes cosediments in isopycnic sucrose density gradients with dense lysosomal particles, within which it is presumably contained. Such cystine appears to be primarily noncrystalline in these organelles.

Increased pyrophosphate in fibroblasts and lymphoblasts from patients with hereditary diffuse articular chondrocalcinosis.

The metabolic and genetic factors leading to deposition of calcium pyrophosphate crystals in cartilage of patients with chondrocalcinosis are not well understood. Analysis of cultured fibroblasts and lymphoblasts from 12 affected members of a large kindred showed a mean concentration of intracellular inorganic pyrophosphate two times greater than that in cells from unaffected family members or normal, unrelated volunteers. Increased intracellular pyrophosphate may, therefore, be a biochemical marker for the heterozygous expression of the chondrocalcinosis gene.

Purine overproduction in man associated with increased phosphoribosylpyrophosphate synthetase activity.

In hemolyzates from red cells of two brothers with purine overproduction and gout, activity of phosphoribosylpyrophosphate synthetase is more than twofold greater than that measured in normal or other gouty individuals. The increased enzyme activity, which is also demonstrable in fibroblasts of the one patient tested, is associated with increased production of 5-phosphoribosyl-1-pyrophosphate by intact cells, an indication that the enzyme abnormality is the basis for the purine overproduction. This genetic abnormality is an example of an increased enzyme activity producing a disease state.

Regional localization of the gene for human phosphoribosylpyrophosphate synthetase on the X chromosome.

Sixty-eight independent hybrid clones were isolated after irradiated normal human lymphocytes were fused with Chinese hamster fibroblasts lacking hypoxanthine-guanine phosphoribosyltransferase activity. The cells were grown under selective conditions requiring retention of the X chromosome-linked locus for human hypoxanthine-guanine phosphoribosyltransferase. The frequency and patterns of cotransference of human phosphoribosylpyrophosphate synthetase with the selected marker and with additional X-linked enzymatic markers confirm X linkage of the structural gene for human phosphoribosylpyrophosphate synthetase and support assignment of this gene to a position on the long arm of the X, between the loci for alpha-galactosidase and hypoxanthine-guanine phosphoribosyltransferase.

Lesch-Nyhan syndrome: preventive control by prenatal diagnosis.

The Lesch-Nyhan syndrome was detected in a fetus at a time sufficiently early to allow termination of the pregnancy. The feasibility of a preventive program for control of a severe sex-linked neurological disease through prenatal diagnosis is thus demonstrated.

Retroviral vector-mediated gene transfer into human hematopoietic progenitor cells.

The transfer of the human gene for hypoxanthine phosphoribosyltransferase (HPRT) into human bone marrow cells was accomplished by use of a retroviral vector. The cells were infected in vitro with a replication-incompetent murine retroviral vector that carried and expressed a mutant HPRT complementary DNA. The infected cells were superinfected with a helper virus and maintained in long-term culture. The production of progeny HPRT virus by the bone marrow cells was demonstrated with a colony formation assay on cultured HPRT-deficient, ouabain-resistant murine fibroblasts. Hematopoietic progenitor cells able to form colonies of granulocytes or macrophages (or both) in semisolid medium in the presence of colony stimulating factor were present in the nonadherent cell population. Colony forming units cloned in agar and subsequently cultured in liquid medium produced progeny HPRT virus, indicating infection of this class of hematopoietic progenitor cell.

Effect of adenosine deaminase inhibition upon human lymphocyte blastogenesis.

The biochemical mechanisms by which a genetically determined deficiency of adenosine deaminase leads to immunodeficiency are still poorly understood and prompted this study. We have examined the effects of the adenosine deaminase inhibitor erythro-9-(2-hydroxy-3-nonyl) adenine hydrochloride (EHNA) upon the response of human peripheral blood mononuclear cells to the mitogen concanavalin A (Con A). Cells isolated from normal volunteers were incubated in microtiter plates in the presence of various inhibitors, and the incorporation of tritrated thymidine or leucine into macromolecular material was measured after 64 h. EHNA at a concentration of 0.3 muM, which inhibited 90% of the adenosine deaminase (ADA) activity in a mononuclear preparation, impaired the incorporation of tritrated leucine into protein; 100 muM EHNA was the minimal concentration that inhibited thymidine uptake. The addition of 15 muM adenosine or 10 muM cyclic AMP to Con A-stimulated lymphocytes inhibited leucine uptake, while millimolar concentrations were required to inhibit thymidine uptake. Lower doses of adenosine and cyclic AMP stimulated thymidine incorporation. The inhibition of thymidine uptake observed with millimolar concentrations of adenosine was independent of the type of mitogen (pokeweed or Con A), the concentration of mitogen, or the medium used, but could be increased if the cells were cultured in a serum with reduced levels of adenosine deaminase. Washout experiments failed to demonstrate a critical period early in immune induction during which adenosine exerted its inhibitory effects. Noninhibitory doses of EHNA potentiated the effects of adenosine and cyclic AMP on leucine and thymidine uptake. EHNA at a concentration of 50 muM also potentiated the inhibitory effects on thymidine uptake of dibutyryl cyclic AMP, butyric acid, norepinephrine, and isoproterenol, but not theophylline. When mitogenesis was assayed by leucine incorporations, no synergy between EHNA and these compounds was apparent. Uridine relieved to some extent the inhibition of blastogenesis produced by adenosine and cyclic AMP, but not by dibutyryl cyclic AMP, norepinephreine, isoproterenol, or theophylline. Neither uridine alone nor uridine plus adenosine protected lymphocytes from the inhibitory effects of EHNA.

Adenosine metabolism in phytohemagglutinin-stimulated human lymphocytes.

The association of a human genetic deficiency of adenosine deaminase activity with combined immunodeficiency prompted a study of the effects of adenosine and of inhibition of adenosine deaminase activity on human lymphocyte transformation and a detailed study of adenosine metabolism throughout phytohemagglutinin-induced blastogenesis. The adenosine deaminase inhibitor, coformycin, at a concentration that inhibited adenosine deaminase activity more than 95%, or 50 muM adenosine, did not prevent blastogenesis by criteria of morphology or thymidine incorporation into acid-precipitable material. The combination of coformycin and adenosine, however, substantially reduced both the viable cell count and the incorporation of thymidine into DNA in phytohemagglutinin-stimulated lymphocytes. Incubation of lymphocytes with phytohemagglutinin for 72 h produced a 12-fold increase in the rate of deamination and a 6-fold increase in phosphorylation of adenosine by intact lymphocytes. There was no change in the apparent affinity for adenosine with either deamination or phosphorylation. The increased rates of metabolism, apparent as early as 3 h after addition of mitogen, may be due to increased entry of the nucleoside into stimulated lymphocytes. Increased adenosine metabolism was not due to changes in total enzyme activity; after 72 h in culture, the ratios of specific activities in extracts of stimulated to unstimulated lymphocytes were essentially unchanged for adenosine kinase, 0.92, and decreased for adenosine deaminase, 0.44. As much as 38% of the initial lymphocyte adenosine deaminase activity accumulated extracellularly after a 72-h culture with phytohemagglutinin. In phytohemagglutinin-stimulated lymphocytes, the principal route of adenosine metabolism was phosphorylation at less than 5 muM adenosine, and deamination at concentrations greater than 5 muM. In unstimulated lymphocytes, deamination was the principal route of adenosine metabolism over the range of adenosine concentrations studied (0.5-250 muM). These studies demonstrate the dependence of both the unstimulated and stimulated lymphocyte on adenosine and may account for the observed sensitivity of mitogen-stimulated lymphocytes to the toxic effects of exogenously supplied adenosine in the presence of the adenosine deaminase inhibitor coformycin. A single case of immunodeficiency disease has been reported in association with purine nucleoside phosphorylase deficiency. The catabolism of guanosine was also found to be enhanced in stimulated normal lymphocytes; phosphorolysis of guanosine to guanine by intact lymphocytes increased six fold after 72-h culture with phytohemagglutinin. The specific activity of purine nucleoside phosphorylase in extracts, with guanosine as substrate, was essentially the same in stimulated and unstimulated lymphocytes after 72 h of culture.

The effects of azathioprine (imuran) on purine synthesis in clinical disorders of purine metabolism.

Azathioprine, a purine analogue, significantly suppressed the purine synthesis de novo of two gouty patients manifesting overproduction of uric acid, as well as three of four gouty patients who showed normal uric acid production. This suppression is taken as evidence that phosphoribosyl-pyrophosphate amidotransferase, the rate-controlling step in purine synthesis de novo, has a normal sensitivity to feedback inhibitors in the patients who responded to the drug.Two children afflicted with the familial disorder of hyperuricemia, choreo-athetosis, and self-mutilation described by Lesch and Nyhan showed no reduction in the activity of the biosynthetic pathway in response to azathioprine. This inability to respond to azathioprine can be directly related to the absence in these patients of the enzyme hypoxanthine-guanine phosphoribosyltransferase which is required for conversion of the drug or its metabolites to the biochemically active ribonucleotide form.

Suppression of glycine-15N incorporation into urinary uric acid by adenine-8-13C in normal and gouty subjects.

Adenine inhibited the de novo synthesis of purines in both normal and gouty man as shown by inhibition of the incorporation of glycine-(15)N into urinary uric acid without altering the incorporation of glycine-(15)N into urinary creatinine. The diminished purine synthesis did not result in a diminution in the 24 hr excretion of uric acid. This observation was explainable in part by the prompt conversion of adenine to uric acid. In addition to this direct conversion, adenine-8-(13)C provided a slow and prolonged contribution to urinary uric acid.A feedback inhibition of purine synthesis by nucleotides derived from adenine provides the best interpretation of these results.

Variations in purine metabolism of cultured skin fibroblasts from patients with gout.

Purine metabolism was studied in fibroblasts cultured from three patients with gout in an attempt to determine the biochemical bases of their disease. The rate of purine biosynthesis de novo was normal in one line of cells, but the rate of catabolism of adenine nucleotides to hypoxanthine and inosine was greatly increased. The rate of purine biosynthesis de novo was increased in two lines of cells, and this was associated with increased concentrations of 5-phosphoribosyl 1-pyrophosphate. Purine synthesis was also less sensitive than normal to feedback inhibition. The catabolism of inosinate synthesized de novo was increased.

Adenine phosphoribosyltransferase deficiency: a previously undescribed genetic defect in man.

A deficiency of adenine phosphoribosyltransferase (A-PRTase) is described in four members in three generations of one family. A-PRTase is coded by an autosome and the mutants described in this report are heterozygotes for this enzyme defect. The level of enzyme activity in these heterozygotes was inappropriately low, ranging from 21 to 37% of normal rather than the expected 50% of normal. Examination of various physical and chemical properties of the A-PRTase obtained from the mutant heterozygotes failed to reveal differences from the normal enzyme. These patients have no discernable abnormality in uric acid production despite the finding that patients with a deficiency of a closely related enzyme, hypoxanthine-guanine phosphoribosyltransferase, invariably produce excessive quantities of uric acid. A relationship of the A-PRTase deficiency to the disturbance in lipoprotein metabolism observed in the propositus has not been firmly established. Possible manifestations of the homozygous form of this enzyme deficiency will require identification of such individuals in the future.

Thymidine as a chemotherapeutic agent: pharmacologic, cytokinetic, and biochemical studies in a patient with T-cell acute lymphocytic leukemia.

Biochemical studies suggested that leukemia T-cells have low levels of TTP-catabolizing enzyme activity and are uniquely sensitive to thymidine (dThd). A child with T-cell acute lymphocytic leukemia (ALL), whose peripheral blood lymphoblasts manifested very low TTP catabolic capacity, was treated with 75 g dThd/m2/day by constant iv infusion for two courses of 5 and 8 days. The dThd caused an initial accumulation of peripheral blood blasts in S-phase at the expense of cells in G1, followed by a rapid reversal of this pattern consistent with a block in late G1 and/or early S. Concurrently, a prompt reduction of blasts was found in the peripheral blood. However, dThd treatment neither decreased the number of lymphoblasts in the cerebrospinal fluid (CSF) nor cleared the marrow. No major toxicity was observed, but the effect of dThd on normal marrow elements could not be evaluated in this patient. Blood concentrations of dThd were 1.4-3.0 mM, and concentrations of thymine were in the same range; beta half-life for dThd was 48 minutes. Steady-state CSF dThd was 9% of the simultaneous serum level. Clearance measurements demonstrated that catabolism of dThd was saturated and that renal clearance was a major determinant of total body clearance during high-dose dThd infusion. A good correlation was found between biochemical and cytokinetic parameters and response to dThd for the peripheral blood lymphoblasts. However, dThd did not produce a useful remission in this case of T-cell ALL.

Cytotoxic and metabolic effects of adenosine and adenine on human lymphoblasts.

The metabolic and growth inhibitory effects of adenosine toward the human lymphoblast line WI-L2 were potentiated by the adenosine deaminase inhibitors erythro-9-(2-hydroxy-3-nonyl) adenine (EHNA) and coformycin. EHNA, 5 micron, or coformycin, 3.5 micron, at concentrations that inhibited adenosine deaminase activity more than 90% had little effect on cell growth or the metabolic parameters studied. Adenosine, 50 micron, plus EHNA, 5 micron, arrested cell growth in both parent and adenosine kinase-deficient lymphoblasts, implicating the nucleoside as the mediator of the cytostatic effect. Adenosine, 50 micron, in combination with the adenosine deaminase inhibitors reduced 14CO2 generation from [1-14C]glucose by 38%, depleted 5-phosphoribosyl-1-pyrophosphate by more than 90%, and reduced pyrimidine ribonucleotide concentrations. Uridine, 10 or 100 micron, reversed adenosine plus EHNA growth inhibition in WI-L2 but not in adenosine kinase mutants. Adenine, 500 micron, which may be converted to the same intracellular nucleotides as adenosine, reduced the growth rate by 50% in both parent and adenine phosphoribosyltransferase-deficient lymphoblasts. Although adenine also depleted cells of 5-phosphoribosyl-1-pyrophosphate and reduced pyrimidine ribonucleotide by 50%, the mechanisms of adenine and adenosine toxicity differ. In contrast to the ability of uridine to reverse adenosine cytostasis, growth inhibition by adenine was not reversed by uridine, indicating that pyrimidine ribonucleotide depletion is not the primary mechanisms of adenine toxicity.