Metabolism of 4-pyridone-3-carboxamide-1-beta-D-ribonucleoside triphosphate and its nucleoside precursor in the erythrocytes.

We recently discovered new nucleotides (4-pyridone-3-carboxamide-1-beta -D-ribonucleoside phosphates) in human erythrocytes. To establish the precursor compound and pathways of nucleotide derivative formation and breakdown, human erythrocytes were incubated for 3 hours with 0.3 mM 4-pyridone-3-carboxamide-1-beta-D-ribonucleoside (4PYR) and erythrocyte concentrations of 4PYR and adenine nucleotides were followed. 4PYR triphosphate increased from 16.1 +/- 0.6 micro M to 74.9 +/- 9.17 and 4PYR monophosphate increased from 5 micro M to 254.7 +/- 13.9 micro M. Conversely, incubation with 0.3 mM 4-pyridone-3-carboxamide (4PY) did not lead to additional 4PYR nucleotide formation. 4PYR nucleotides were catabolized to 4PYR. We conclude that 4PYR nucleotides are formed in erythrocytes by nucleoside kinase-mediated 4PYR phosphorylation and catabolized by 5'nucleotidase-mediated dephosphorylation.

4-pyridone-3-carboxamide ribonucleoside triphosphate accumulating in erythrocytes in end stage renal failure originates from tryptophan metabolism.

We recently identified an erythrocyte nucleotide accumulating in end-stage renal disease as 4-pyridone-3-carboxamide ribonucleotide triphosphate (4PYTP), a nucleotide never described previously. Plasma tryptophan concentration has been previously reported to be reduced in patients in chronic renal failure that is in turn associated with elevated precursors of tryptophan metabolism, including L -kynurenine and quinolinic acid, both of which have been implicated in the neurotoxic manifestations of chronic renal failure. Here we compare mean erythrocyte 4PYTP, and plasma tryptophan concentrations, in controls and four patient groups with renal impairment (10 per group) and confirmed a reduction in plasma tryptophan in patients on dialysis that corrected with renal transplantation. We found: An inverse correlation between plasma tryptophan and red cell 4PYTP concentrations (R(2)=0.44, P<0.001) when all patients were grouped together. Restoration of both tryptophan and 4PYTP concentrations to control values was only achieved following renal transplantation. 4PYTP was absent from erythrocytes in Molybdenum cofactor (MoCF) deficiency implicating aldehyde oxidase/dehydrogenase, a Molybdenum requiring enzyme. High 4PYTP erythrocyte concentrations in adenine or hypoxanthine-phosphoribosyltransferase deficient patients in severe uremia (113 microM and 103 microM), confirmed the lack of involvement of either enzyme in 4PYTP formation. We propose that 4PYTP is formed by a novel route involving the oxidation of the intermediates of NAD turnover from quinolinic acid by aldehyde oxidase.

The novel nucleotide 4KNTP, in high concentrations in erythrocytes of renal failure children: a comparison with accumulation of other putative precursors in the plasma.

We have measured the concentrations of metabolites related to the turnover of NAD, which accumulate in the blood of children with renal failure. One is a novel nucleotide, identified as the N1-riboside triphosphate of 4-pyridone-3-carboxamide (4PYTP), also described as 4KNTP, which accumulates in the erythrocytes in parallel with renal failure.

Familial juvenile hyperuricaemic nephropathy is not such a rare genetic metabolic purine disease in Britain.

Renal disease is rare today in classic adult gout, and gout is rare in renal disease--especially in the young. Here we summarise studies in 158 patients from 31 kindreds diagnosed with familial juvenile hyperuricaemic nephropathy FJHN from a total of 230 kindred members studied in Great Britain. Some patients have been followed for up to 30 years, and allopurinol has ameliorated the progression of the renal disease in all 113 surviving members provided: They have been diagnosed and treated sufficiently early. Compliance with allopurinol treatment and diet has been as important as early recognition. Hypertension has been rigorously controlled. The use of oral contraceptives has been avoided, as has pregnancy in any female with a Glomelar Filtration Rate GFR <70 ml/min. The question arising is: Why is FJHN the most prevalent genetic purine disorder diagnosed in Britain? Is it a lack of awareness which needs to be improved Europe-wide?

The neuroleptic chlorpromazine inhibits the cationic and stimulates the anionic phospholipid precursor synthesis in human lymphocytes.

The widely used neuroleptic drug chlorpromazine (CPZ) influences membrane functions at the levels of ionic channels and receptors as shown. Here we show the effect of short term treatments by CPZ (30 microM), on the nucleotide-containing phospholipid precursors in human lymphocyte primary cultures. During 60 minutes incubation of the cells, the CDP-ethanolamine (CDP-EA) content was only slightly reduced (87 to 76 pmol/10(6) cells), the amount of CDP-choline (CDP-Ch) was inhibited totally (from 25 to 0 pmol) upon the treatment with 30 microM CPZ under the same conditions. It has been shown earlier, that dCTP can be used as well as CTP for biosynthesis of phospholipids. Thus, the separation of the corresponding ribo- and deoxyribo-liponucleotides was developed. CPZ almost completely inhibited the synthesis of both dCDP-EA and dCDP-Ch under the same conditions The synthesis of the activated liponucleotide precursors, can be measured by incorporation of extracellular 14C-dCyt into both dCDP-EA and dCDP-Ch, as shown earlier. While the cationic deoxyribo-liponucleotide content (dCDP-Ch, dCDP-EA) was decreased, the labelling of the anionic phospholipid precursor dCDP-diacylglycerol (dCDP-DAG) was enhanced several times, it could be labelled only in the presence of CPZ from 14C-dCyd. Thus, a principal disturbance of the membrane phospholipid synthesis is presented (i.e., inhibition of the cationic and enhancement of the anionic dCDP-DAG synthesis). This profound influence on the membrane phospholipids by chlorpromazine, might be the primary effect that contributes to the wide spectrum of CPZ effects on neuronal cells.

HPRT deficiency as the cause of ESRD in a 24-year-old patient: a very rare presentation of the disorder.

A 24-year-old male with end-stage renal disease (ESRD) and disproportionately high uric acid plasma concentration was admitted to our unit. After studying the patient's medical history, as well as that of the entire family, hyperuricemia was discovered in his brother, while microscopic examination of his brother's and mother's urine revealed abundant uric acid crystals. After performing purine metabolic studies, it was determined that the two siblings suffered from partial hypoxanthine-guanine phosphoribosyltransferase (HPRT) deficiency (Kelley-Seegmiller syndrome). This report highlights the importance of clinical awareness and a thorough examination of the patient's medical history for establishing an early diagnosis and commencing treatment for such rare inherited metabolic disorders to prevent renal failure.

An unusual pyridine nucleotide accumulating in erythrocytes: its identity and positive correlation with degree of renal failure.

We have investigated an unusual nucleotide that accumulates, with precursors, in the erythrocytes of patients in uraemia. This nucleotide is related chemically to the NAD breakdown product, N1-methyl-2-pyridone-5-carboxamide (Me2Py), found in high concentrations in the plasma of uraemic patients. Both Me2Py and the nucleotide accumulate to high concentrations in the blood during uraemia: our investigations of samples from renal out-patients have provided information on a plausible link between the two compounds.

Nucleotide degradation products in cerebrospinal fluid (CSF) in inherited and acquired pathologies.

CSF purines were grossly elevated compared with controls only in adenylosuccinate lyase (ADSL) deficiency and TB meningitis. The former representing low permeability, the latter severe damage to the normal blood/brain barrier. By contrast, the similarity to controls, with no difference between Lesch-Nyhan disease (LND) or LND variants, would exclude hypoxia as a factor in the severe neurological deficits in LND. Similar findings in purine nucleoside phosphorylase (PNP) deficiency (although nucleosides replace the normal bases) likewise exclude hypoxia in the aetiology of the albeit milder neurological deficits.

Adenylosuccinate lyase deficiency--first British case.

A deficiency of adenylosuccinate lyase (ASDL) is characterised by the accumulation of SAICAriboside (SAICAr) and succinyladenosine (S-Ado) in body fluids. The severity of the clinical presentation correlates with a low S-Ado/SAICAr ratio in body fluids. We report the first British case of ADSL deficiency. The patient presented at 14 days with a progressive neonatal encephalopathy and seizures. There was marked axial and peripheral hypotonia. Brain MRI showed widespread white matter changes. She died at 4 weeks of age. Concentrations of SAICAr and SAdo were markedly elevated in urine, plasma and CSF and the SAdo/SAICAr ratio was low, consistent with the severe phenotype. The patient was compound heterozygous for 2 novel ADSL mutations; c.9 G>C (A3P) and c.572 C>T (R190X).

Elevated erythrocyte CDP-choline levels associated with beta-thalassaemia in patients with transfusion independent anaemia.

The accumulation of CDP-ethanolamine as well as CDP-choline in a small cohort of patients with normal UMPH1 and no defined cause for their anaemia suggested a defect in both phosphotransferases. Here we report 10 patients with transfusion independent beta-thalassaemia; 8 being pure heterozygotes and 2 heterozygotes also for Hb E. Mean CDP-choline (86.xxx +/- 48 microM) and CDP-ethanolamine (34.6 microM +/- 34.5 microM), mean control <3 microM. Elevated CDP-choline in patients with no defined cause for their haemolytic anaemia was previously suggested as a possible indicator of CDP-choline phosphotransferase deficiency. Here we associate it with transfusion independent beta-thalassaemia.

Severe impairment of nucleotide synthesis through inhibition of mitochondrial respiration.

Since de-novo synthesis of pyrimidine nucleotides is coupled to the mitochondrial respiratory chain (RC) via dehydroorotic acid dehydrogenase (DHODH), respiratory chain dysfunction should impair pyrimidine synthesis. To investigate this, we used specific RC inhibitors, Antimycin A and Rotenone, to treat primary human keratinocytes and 143B cells, a human osteosarcoma cell line, in culture. This resulted in severe impairment of de novo pyrimidine nucleotide synthesis. The effects of RC inhibition were not restricted to pyrimidine synthesis, but concerned purine nucleotides, too. While the total amount of purine nucleotides was not diminished, they were significantly broken down from triphosphates to monophosphates, reflecting impaired mitochondrial ATP regeneration. The effect of Rotenone was similar to that of Antimycin A. This was surprising since Rotenone inhibits complex I of the respiratory chain, which is upstream of ubiquinone where DHODH interacts with the RC. In order to avoid unspecific effects of Rotenone, we examined the consequences of a mitochondrial DNA mutation that causes a specific complex I defect. The effect was much less pronounced than with Rotenone, suggesting that complex I inhibiton cannot fully explain the marked effect of Rotenone on pyrimidine nucleotide synthesis.

GTP concentrations are elevated in erythrocytes of renal transplant recipients when conventional immunosuppression is replaced by the inosine monophosphate dehydrogenase inhibitor mycophenolic acid mofetil (MMF).

We show that GTP concentrations rise in the erythrocytes of renal transplant recipients receiving the immunosuppressant MMF, and demonstrate that this effect is not caused by poor renal function after engraftment. We propose a model that is consistent with our observations.

Early treatment with allopurinol in familial juvenile hyerpuricaemic nephropathy (FJHN) ameliorates the long-term progression of renal disease.

BACKGROUND: The efficacy of allopurinol in autosomal dominant familial juvenile hyperuricaemic nephropathy (FJHN) has been disputed. AIM: To address this question, in the absence of controlled trials. DESIGN: Retrospective long-term follow-up study. METHODS: All kindreds were biochemically screened. Measurements included uric acid clearance, creatinine clearance, serum creatinine, and glomerular filtration rate (GFR). We used five siblings who had died or progressed to transplantation, ten other deceased relatives, and two index cases (one untreated, one non-compliant) as controls to assess the effects of allopurinol. RESULTS: Of eight families with FJHN, six had a strong history of renal disease and early parental death (mean age 41 years, n=10). Of 27 patients started immediately on allopurinol and treated uninterruptedly, 21 responded well, including three children born subsequently. Eight siblings (mean age 19 years) with a normal plasma creatinine at start (<120 micromol/l, mean GFR 80 ml/min/1.73 m(2)) retained stable renal function (mean 14.5 years, mean age 34 years, GFR 85 ml/min/1.73 m(2)). Of the 13 other responders, treated for up to 34 years, 10 with a creatinine <200 micromol/l at diagnosis (mean age 28 years, mean creatinine 137 micromol/l at start) now have a mean creatinine of 210 micromol/l. In contrast, five patients (mean age 26 years) with a creatinine >200 micromol/l (GFR <35 ml/min/1.73 m(2)) when allopurinol commenced, plus one untreated index case, all progressed rapidly (mean 6 years) to end-stage renal failure. In two others (one non-compliant, one initially untreated), GFR fell by >50% in 7 years. Introduction of allopurinol in the latter has stabilized GFR. DISCUSSION: Allopurinol reduced the morbidity and mortality from renal failure seen in untreated siblings and previous generations of these families. Early diagnosis of FJHN is important, so that treatment can begin before irreversible renal damage has developed.

Successful HLA-identical bone marrow transplantation in a patient with PNP deficiency using busulfan and fludarabine for conditioning.

PNP deficiency is an autosomal recessive metabolic disorder characterized by severe combined immunodeficiency and by complex neurological symptomatology including ataxia, developmental delay and spasticity. Patients usually die in the first or second decade of life due to recurrent infections. The only curative treatment is bone marrow transplantation (BMT). We describe a 22-month-old girl who underwent BMT from her HLA-identical brother. Conditioning consisted of busulfan and fludarabine only, resulting in low toxicity and prompt engraftment. At 18 months after BMT, the girl has developed normal immunological functions, and her neurological status has improved.

Genetic basis of hemolytic anemia caused by pyrimidine 5' nucleotidase deficiency.

Pyrimidine 5' nucleotidase (P5'N-1) deficiency is an autosomal recessive condition causing hemolytic anemia characterized by marked basophilic stippling and the accumulation of high concentrations of pyrimidine nucleotides within the erythrocyte. It is implicated in the anemia of lead poisoning and is possibly associated with learning difficulties. Recently, a protein with P5'N-1 activity was analyzed and a provisional complementary DNA (cDNA) sequence published. This sequence was used to study 3 families with P5'N-1 deficiency. This approach generated a genomic DNA sequence that was used to search GenBank and identify the gene for P5'N-1. It is found on chromosome 7, consists of 10 exons with alternative splicing of exon 2, and produces proteins 286 and 297 amino acids long. Three homozygous mutations were identified in this gene in 4 subjects with P5'N-1 deficiency: codon 98 GAT-->GTT, Asp-->Val (linked to a silent polymorphism codon 92, TAC-->TAT), codon 177, CAA-->TAA, Gln-->termination, and IVS9-1, G-->T. The latter mutation results in the loss of exon 9 (201 bp) from the cDNA. None of these mutations was found in 100 normal controls. The DNA analysis was complicated by P5'N-1 pseudogenes found on chromosomes 4 and 7. This study is the first description of the structure and location of the P5'N-1 gene, and 3 mutations have been identified in affected patients from separate kindreds. (Blood. 2001;97:3327-3332)

Mycophenolic acid-induced GTP depletion also affects ATP and pyrimidine synthesis in mitogen-stimulated primary human T-lymphocytes.

BACKGROUND: Mycophenolate mofetil (MMF) is an effective immunosuppressant developed for use in organ transplantation. It specifically targets lymphocyte purine biosynthesis. However, side effects do occur. Understanding how the active metabolite of MMF, mycophenolic acid (MPA) affects the normally integrated interaction between intracellular purine and pyrimidine pathways might aid the development of improved therapeutic regimes. METHODS: We used a primary human T-lymphocyte model to study how preincubation with MPA (0.1-50 microM) affected normal ribonucleotide pool responses to phytohemagglutinin using radiolabeled precursors. RESULTS: MPA not only restricted the mitogen-induced expansion of GTP pools, but actually induced a severe drop in both GTP (10% of unstimulated cells) and GDP-sugar pools, with a concomitant fall in ATP (up to 50%). These effects were concentration dependent. By contrast, uridine pools expanded whereas CTP pools remained at resting levels. These changes were confirmed by the altered incorporation of [14C]-bicarbonate and [14C]-glycine into nucleotides. Restriction of [14C]-hypoxanthine incorporation and reduction of [14C]-uridine uptake comparable to that of unstimulated cells indicated that MPA also inhibited both salvage routes of nucleotide synthesis. CONCLUSION: MPA affects pyrimidine as well as purine responses to mitogens in T-lymphocytes, but not in an integrated way. The molecular mechanisms underlying these disproportionate changes can best be explained by MPA-related inhibition of amidophosphoribosyltransferase, catalysing the first step in purine biosynthesis. This would increase phosphoribosylpyrophosphate availability, thereby stimulating UTP biosynthesis. Such imbalances, coupled with ATP-depletion, could underlie reported side effects and might be overcome by appropriate combination therapies.