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O Sperling

Publications and source records attributed to O Sperling.

At least 19 recordsLinked to original sources
PubMed1995

Metabolism of guanine and guanine nucleotides in primary rat cardiomyocyte cultures.

The metabolic fate of labeled guanine and of prelabeled guanine nucleotides (GuRN) was studied in cultured rat cardiomyocytes. Special attention was given to guanine salvage in comparison to degradation; to the contribution of GuRN to adenine nucleotides (AdRN); to the fluxes from GMP to IMP and from IMP to GMP; and to the degradation pathways of GuRN. In accordance with the 3- to 4-fold higher activity of guanine deaminase (guanase), in comparison to that of hypoxanthine-guanine phosphoribosyltransferase (HGPRT), the rate of guanine deamination to xanthine exceeded that of guanine incorporation into nucleotides (at 4 microM) by 13.2-fold. The label from guanine incorporated into nucleotides was found mainly (81%) in GuRN, but also in IMP and AdRN. The prelabeled GuRN lost 43% of the label in 4 h, reflecting mainly degradation to xanthine (and uric acid) and synthesis of nucleic acids. Blocking nucleoside degradation was associated with a marked accumulation of label in guanosine and inosine (guanosine/inosine labeling ratio is 1.25). The results indicate that in the myocardium guanine is a poor substrate for salvage synthesis of GuRN and that its contribution to the homeostasis of adenine nucleotides is negligible; that GMP degradation to xanthine proceeds through both guanosine and IMP; and that the cardiomyocytes contain the activity of GMP reductase and of the enzymes converting IMP to GMP.

Animals↗
PubMed1995

Role of cellular ribose-5-phosphate content in the regulation of 5-phosphoribosyl-1-pyrophosphate and de novo purine synthesis in a human hepatoma cell line.

5-Phosphoribosyl-1-pyrophosphate (PRPP) is an important regulator of de novo purine synthesis. However, the role of ribose-5-phosphate (R5P), the precursor for PRPP, in the regulation of PRPP and de novo purine synthesis has not yet been clarified conclusively. This study was designed to clarify interrelationships between R5P content, PRPP availability, and the rate of de novo purine synthesis in the cultured human hepatoma cell line (HepG2), a plausible model for normal human hepatocytes. Increasing glucose concentration in the culture media from 0 to 10 mmol/L resulted in a 2.9-fold elevation of cellular R5P content (from 107 +/- 31 to 311 +/- 57 nmol/g protein), associated with a correlated increase of 7.14-fold in cellular PRPP availability (from 4.76 +/- 3.4 to 34 +/- 8.4 pmol/mg protein/min) and of 149-fold in the rate of de novo purine synthesis (from 55 to 8,204 dpm/mg protein/h). Plotting the rate of de novo purine synthesis versus R5P content indicates that at a wide range of R5P content, including that prevailing in hepatocytes under physiological conditions, the rate of purine synthesis depends on R5P content. A similar dependence was also demonstrated for PRPP availability. The rate of de novo purine synthesis exhibited a sigmoidal dependence on PRPP availability. The demonstration in human hepatocytes of dependence of the rate of purine synthesis on R5P content has implications concerning the pathogenesis of purine overproduction associated with several inborn and acquired conditions in man.

Carcinoma, Hepatocellular↗
PubMed1995

Use of ECFMG certifying examinations for national comparisons: performance of graduates of Israeli medical schools in basic and clinical science examinations.

Examinations were used for comparison of Israeli medical school graduates. The two schools with traditional curricula had higher pass rates for first takers of Day 1 (68% and 61%, mean scores 76.6 and 76.4) than the community-based school (44%, mean score 74.5) and the technologically oriented school (40%, mean score 72.5). There were similar pass rates for traditional school first takers of Day 2 (97% and 91%, mean scores 82.4 and 80.4) as for community-based school first takers (94%, mean score 80.1). The traditional schools and the community-based school demonstrated higher pass rates and mean scores for first takers of Day 2 than the technologically oriented school. Analysis of the time lapse between the basic science curriculum and taking the basic science examination reveals no trend in scores or pass rates. While the likelihood of better performance on Day 1 seems enhanced by traditional curricula, there is an equivalent performance on Day 2 by graduates of schools with traditional curricula.

Certification↗
PubMed1994

Effects of differentiation-inducing agents on purine nucleotide metabolism in an ovarian cancer cell line.

The effects of the differentiation-inducing agents sodium butyrate (NaOBt), dimethylsulfoxide (DMSO) and mycophenolic acid (MA), on purine nucleotide metabolism, was studied in an ovarian carcinoma cell line (GZL-8). Exposure to these agents inhibited cell proliferation, but did not affect cell viability. Three hours following exposure, NaOBt and DMSO moderately decelerated purine synthesis de novo, but MA accelerated it three-fold, this being associated with a two-fold increase in the excretion of hypoxanthine and xanthine into the incubation medium. NaOBt and DMSO did not affect the cellular nucleotide content, but MA caused a 73% decrease in GTP content and about a 50% increase in the cellular content of UTP. The following alterations in cellular enzyme activity were observed 72 h following exposure: NaOBt decreased the activity of hypoxanthine-guanine phosphoribosyltransferase and increased the activity of IMP and of AMP 5'-nucleotidases, DMSO increased the activity of IMP 5'-nucleotidase, and MA increased the activity of the two nucleotidases. The results suggest that, in the carcinoma cell line studied, the differentiation process induced by NaOBt and DMSO may be associated with a general shift in the direction of purine metabolism from anabolism to catabolism, whereas that induced by MA is associated with a specific decrease in the production of GTP.

Butyrates↗
PubMed1994

Uric acid nephrolithiasis.

Uric acid is the end-product of purine nucleotide metabolism in man. The renal handling of urate is a complicated process, resulting in a fractional clearance of 8.2-10.3%. The anhydrous form is thermodynamically the most stable uric acid crystal. Uric acid is a weak acid that ionizes with a Pka at pH 5.75. At the normal acidic region, uric acid solubility is strongly increased by urinary pH. The prevalence of uric acid stones varies between countries, reflecting climatic, dietary, and ethnical differences, ranging from 2.1% (in Texas) to 37.7% (in Iran). The risk for uric acid stone formation correlates with the degree of uric acid supersaturation in the urine, depending on uric acid concentration and urinary pH. Hyperuricosuria is the major risk factor, the most common cause being increased purine intake in the diet. Acquired and hereditary diseases accompanied by hyperuricosuria and stone disease include: gout, in strong correlation with the amount of uric acid excreted, myelo- and lymphoproliferative disorders, multiple myeloma, secondary polycythemia, pernicious anemia and hemolytic disorders, hemoglobinopathies and thalassemia, the complete or partial deficiency of HGPRT, superactivity of PRPP synthetase, and hereditary renal hypouricemia. A common denominator in patients with idiopathic and gouty stone formers is a low urinary pH. Uric acid nephrolithiasis is indicated in the presence of a radiolucent stone, a persistent undue urine acidity and uric acid crystals in fresh urine samples. A radiolucent stone in combination with normal or acidic pH should raise the possibility of urate stones.(ABSTRACT TRUNCATED AT 250 WORDS)

Allopurinol↗
PubMed1992

Metabolic fate of hypoxanthine and inosine in cultured cardiomyocytes.

The metabolic fate of labeled hypoxanthine and inosine, degradation products of adenine nucleotides, was studied in cultured beating cardiomyocytes, in order to assess the physiological significance of their contribution to salvage nucleotide synthesis in the heart. Inosine and hypoxanthine were found to be incorporated into nucleotides by a similar rate, but in the presence of 8-aminoguanosine, a potent inhibitor of purine nucleoside phosphorylase (EC 2.4.2.1), the rate of inosine incorporation into nucleotides was markedly reduced (by 75%), indicating that inosine incorporation to IMP (inosinic acid) occurs following its degradation to hypoxanthine. The proportion of hypoxanthine converted to IMP by hypoxanthine-guanine phosphoribosyltransferase (EC 2.4.2.8) is markedly greater than that degraded to xanthine and uric acid by xanthine oxidase (EC 1.3.2.3). However, close to 50% of the IMP formed was degraded to inosine by IMP 5'-nucleotidase (EC 3.1.3.5). The results demonstrate the activity of the following futile cycle in the cardiomyocytes: hypoxanthine----IMP----inosine----hypoxanthine. The rational for the activity of this energy consuming cycle is yet unclear.

Cells, Cultured↗
PubMed1992

Metabolism of guanine and guanine nucleotides in primary rat neuronal cultures.

The metabolic fate of guanine and of guanine ribonucleotides (GuRNs) in cultured rat neurons was studied using labeled guanine. 8-Aminoguanosine (8-AGuo), an inhibitor of purine nucleoside phosphorylase, was used to clarify the pathways of GMP degradation, and mycophenolic acid, an inhibitor of IMP dehydrogenase, was used to assess the flux from IMP to GMP and, indirectly, the activity of the guanine nucleotide cycle (GMP----IMP----XMP----GMP). The main metabolic fate of guanine in the neurons was deamination to xanthine, but significant incorporation of guanine into GuRNs, at a rate of approximately 8.5-13.1% of that of the deamination, was also demonstrated. The turnover rate of GuRNs was fast (loss of 80% of the radioactivity of the prelabeled pool in 22 h), reflecting synthesis of nucleic acids (32.8% of the loss in radioactivity) and degradation to xanthine, guanine, hypoxanthine, guanosine, and inosine (49.3, 4.3, 4.1, 1.1, and 0.5% of the loss, respectively). Of the radioactivity in GuRNs, 7.9% was shifted to adenine nucleotides. The accumulation of label in xanthine indicates (in the absence of xanthine oxidase) that the main degradative pathway from GMP is that to xanthine through guanosine and guanine. The use of 8-AGuo confirmed this pathway but indicated the operation of an additional, relatively slower degradative pathway, that from GMP through IMP to inosine and hypoxanthine. Hypoxanthine was incorporated mainly into adenine nucleotide (91.5%), but a significant proportion (6%) was found in GuRNs.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1991

Stimulation of ribose-5-phosphate and 5-phosphoribosyl-1-pyrophosphate generation by pyrroline-5-carboxylate in mouse liver in vivo: evidence for a regulatory role of ribose-5-phosphate availability in nucleotide synthesis.

Pyrroline-5-carboxylase (P5C), a physiological stimulator of hexose-monophosphate-pentose pathway activity, was found before to increase 5-phosphoribosyl-1-pyrophosphate (PRPP) generation and nucleotide synthesis in human erythrocytes and cultured fibroblasts. We now report the stimulation of PRPP generation by P5C also in mouse liver in vivo. In addition we demonstrated a simultaneous elevation in ribose-5-phosphate (R5P) concentration, which was relatively smaller and transient. The demonstrated effect of P5C on liver R5P and PRPP content in vivo provides strong evidence for the physiological role of R5P availability in the regulation of PRPP and purine production.

Animals↗
PubMed1991

Acceleration of purine synthesis in mouse liver by glycogenolytic hormones.

Administration (ip) into fed mice of glucagon, epinephrine, vasopressin, oxytocin, angiotensin II, and dibutyryl cyclic AMP (dbcAMP) resulted in a rapid (within 2.5 to 15 min) elevation of PRPP content (two- to threefold) and in acceleration of the rate of de novo purine synthesis (twofold). Inhibition of the epinephrine-stimulated glycogenolysis by 2,5-anhydromannitol diminished markedly the acceleration effect of the hormone on the rate of purine synthesis. Administration of the hormones caused a rapid rise in the liver content of glucose 6-phosphate (G6P) by 15-70% but did not increase the ribose 5-phosphate (R5P) content. Liver ATP content was not affected. The hormones did not cause direct activation of PRPP synthetase, as gauged by the specific activity of the enzyme, its Km for substrates R5P and ATP, and its sensitivity to inhibition by ADP and GDP. The hormones did not increase the liver content of the enzyme activators Pi and Mg2+. The results suggest that the glycogenolytic hormones accelerate purine synthesis by a metabolic mechanism associated with the enhancement of glycogenolysis. PRPP synthesis is probably enhanced by the glycogenolysis-induced alterations in the cellular content of some metabolites other than R5P.

Animals↗
PubMed1990

Developmental changes in the activity of enzymes of purine metabolism in rat neuronal cells in culture and in whole brain.

The activities (Vmax) of several enzymes of purine nucleotide metabolism were assayed in premature and mature primary rat neuronal cultures and in whole rat brains. In the neuronal cultures, representing 90% pure neurons, maturation (up to 14 days in culture) resulted in an increase in the activities of guanine deaminase (guanase), purine-nucleoside phosphorylase (PNP), IMP 5'-nucleotidase, adenine phosphoribosyltransferase (APRT), and AMP deaminase, but in no change in the activities of hypoxanthine-guanine phosphoribosyltransferase (HGPRT), adenosine deaminase, adenosine kinase, and AMP 5'-nucleotidase. In whole brains in vivo, maturation (from 18 days of gestation to 14 days post partum) was associated with an increase in the activities of guanase, PNP, IMP 5'-nucleotidase, AMP deaminase, and HGPRT, a decrease in the activities of adenosine deaminase and IMP dehydrogenase, and no change in the activities of APRT, AMP 5'-nucleotidase, and adenosine kinase. The profound changes in purine metabolism, which occur with maturation of the neuronal cells in primary cultures in vitro and in whole brains in vivo, create an advantage for AMP degradation by deamination, rather than by dephosphorylation, and for guanine degradation to xanthine over its reutilization for synthesis of GMP. The physiological meaning of the maturational increase in these two ammonia-producing enzymes in the brain is not yet clear. The striking similarity in the alterations of enzyme activities in the two systems indicates that the primary culture system may serve as an appropriate model for the study of purine metabolism in brain.

Adenosine Monophosphate↗
PubMed1989

Thyroxine-induced redistribution of creatine kinase isoenzymes in rat cardiomyocyte cultures.

The present study demonstrates a change occurring in the creatine-kinase isoenzyme profile of cardiomyocyte cultures induced by a chronic administration of excessive amounts of thyroid hormones (TH). This change is manifested by an increased level of the CK-BB isoenzyme, generally at the expense of CK-MM isoenzyme. The elevation of CK-BB is probably a result of a specific effect of TH through activation of gene expression, rather than a contribution of an increased number of non-myocardial cells. The implications of these results in the diagnosis of heart failures are discussed.

Animals↗
PubMed1989

Prenatal diagnosis of Lesch-Nyhan syndrome: experience with three fetuses at risk.

Our experience with the prenatal detection of the Lesch-Nyhan syndrome (LNS; hypoxanthine-guanine phosphoribosyltransferase (HGPRT) deficiency) in three fetuses at risk is reported. Enzyme activities were measured in cultured amniocytes in two pregnancies, and in tissues and cultures obtained from chorionic villus sampling (CVS) in a third pregnancy. In all tissues the specific activities of HGPRT and adenine phosphoribosyltransferase (APRT) were determined and APRT/HGPRT ratios were calculated. In addition to the enzyme assays, the rate of purine synthesis de novo was assessed in the two amniocyte cultures, and the rate of [14C]hypoxanthine incorporation into nucleotides and sensitivity to azaguanine were measured in one of the amniocyte cultures. We report the diagnosis of normal fetuses by study of amniocytes in two pregnancies and of LNS using CVS in one pregnancy. In all three cases the diagnosis was confirmed.

Adenine Phosphoribosyltransferase↗