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H A Simmonds

Publications and source records attributed to H A Simmonds.

At least 37 records · Page 2Linked to original sources
PubMed1994

Identification of a 7-basepair deletion in the adenine phosphoribosyltransferase gene as a cause of 2,8-dihydroxyadenine urolithiasis.

We describe a family of Turkish origin with adenine phosphoribosyltransferase (APRT) deficiency and renal stone disease. The proband had 2,8-dihydroxyadenine urolithiasis but an older sister, who was also deficient in enzyme activity, is so far asymptomatic. The proband was homozygous for a 7-bp deletion in exon 3 of the APRT gene. One allele from each of the parents also contained this deletion. The patient and her father were homozygous for an intragenic TaqI RFLP (1.25-kb fragment) whereas the mother was heterozygous (1.25- and 1.91-kb fragments), indicating that the mutation was present on the allele carrying the 1.25 kb TaqI fragment. The deletion alters the reading frame downstream of codon 93 and would be expected to abolish enzyme activity.

Adenine↗
PubMed1994

Nicotinic acid phosphoribosyltransferase activity in human erythrocytes: studies using a new HPLC method.

A non-radiochemical method linked to reverse-phase high-performance liquid chromatography was developed to determine the activity of nicotinic acid phosphoribosyltransferase (EC 2.4.2.11) in crude lysates of human red blood cells. The method is accurate and easily reproducible in different chromatographic systems. The enzyme activity was determined in erythrocytes of healthy subjects and in patients with different purine disorders showing altered NAD levels. Very low enzyme activity was found in a boy hemizygous for phosphoribosylpyrophosphate synthetase superactivity, consistent with the low erythrocyte NAD concentration.

Adenine Phosphoribosyltransferase↗
PubMed1994

Polynesian women are also at risk for hyperuricaemia and gout because of a genetic defect in renal urate handling.

The prevalence of asymptomatic hyperuricaemia among Polynesian women (Maoris, Cook Islanders, Samoans, Tongans) was high--44%. This hyperuricaemia resulted from a reduced fractional uric acid clearance (FEur: uric acid clearance factored by creatinine clearance x 100--6.7 +/- 1.5%) compared with the FEur in healthy UK women (12.8 +/- 2.9%). This reduction in FEur was not as great as that in young UK women with familial juvenile hyperuricaemic nephropathy (FJHN: 5.1 +/- 1.5%) and was not associated with impaired renal function. The FEur in the normouricaemic Polynesians (9.7 +/- 1.9%) was also lower than that in healthy UK women (12.8 +/- 2.9%). The reduced FEur in these Polynesian women supports the hypothesis that indigenous Pacific races share a similar genetic defect in renal urate handling to that reported as the basis for the susceptibility to hyperuricaemia in Maori men. Neither alcohol nor hypertension contributed to this. This study also confirmed that, compared with their European counterparts, Polynesian women have a high purine intake and a strong tendency to obesity which increases with age. These factors, together with the reduced FEur, put them at added risk for gout. However, the reduction in FEur was not as great as that reported for the normouricaemic or asymptomatic hyperuricaemic Maori male (4.9 +/- 1.5% and 3.9 +/- 1.4%, respectively), confirming the same sex difference in renal urate handling in adult Polynesians as in caucasians.

Adult↗
PubMed1993

HPLC determination of oxidized and reduced pyridine coenzymes in human erythrocytes.

The nucleotide concentrations in acid and alkaline erythrocyte extracts have been measured by RP-HPLC in healthy controls and in patients bearing different inherited disorders, with altered erythrocyte NAD(P) levels. The objective was the simultaneous determination of the nucleotide profile and of the oxidative state of pyridine coenzymes by the most suitable extraction method. Both alkaline and acid extractions were necessary to obtain the complete pattern, due to defective recovery of the oxidized or reduced coenzymes, respectively, during the extraction procedures. Purine nucleotide quantification seemed to be reliable by all methods. High NADP+ levels were confirmed in two glucose-6-phosphate dehydrogenase deficient patients, coupled with raised NAD levels, lowered NADPH/NADP+ ratio and increased NADH/NAD+ ratio. Higher NAD+ and normal or lower NADH/NAD+ ratios were found in two hypoxanthine-phosphoribosyltransferase deficient patients, while a patient with superactive phosphoribosylpyrophosphate synthetase showed a decreased NADH level in addition to the low NAD+ level previously found.

Chromatography, High Pressure Liquid↗
PubMed1993

Low-dose allopurinol plus azathioprine/cyclosporin/prednisolone, a novel immunosuppressive regimen.

Early rejection can still complicate renal transplantation even with cyclosporin. We added low-dose allopurinol (25 mg on alternative days) to "triple" immunosuppression with cyclosporin, prednisolone, and azathioprine for twelve recipients of cadaver renal grafts. The controls were fifteen patients on triple therapy alone. Only one rejection episode occurred among the allopurinol-treated patients, whereas eleven controls had rejections (seven with more than one episode). Allopurinol may be toxic when combined with azathioprine, yet the bone marrow tolerated the new regimen well. As expected, reduction of the azathioprine dose was necessary in the treated group.

Allopurinol↗
PubMed1993

Fast and slow methylators: do racial differences influence risk of allograft rejection?

A catabolic route for azathioprine involving methylation by thiopurine methyltransferase has been directly implicated in the drug's immunosuppressive efficacy. Since ethnic differences in thiopurine methyltransferase activity have been reported in a study of Lapps, this study compared the distribution of thiopurine methyltransferase activity in erythrocyte lysates from 134 healthy, randomly selected subjects living in Brazil, comprising 39 blacks (i.e. Afro-Brazilians), 33 white subjects, 30 mixed-race subjects, and 32 Brazilian-residing Japanese subjects. The results demonstrated bimodality of thiopurine methyltransferase activity compatible with genetic polymorphism in the white, black and mixed-race groups, but not in the Japanese, who were homogeneously 'fast methylators' (high thiopurine methyltransferase activity). Thiopurine methyltransferase activity was generally higher in Brazilian males than females, and some individuals in the black and mixed-race groups had very high activity. Azathioprine-immunosuppressed transplant patients with thiopurine methyltransferase activity above 35 pmol/h/mgHb have previously been shown to have significantly poorer outcomes. Using this thiopurine methyltransferase value as the cut-off point between 'poor responders' and 'good responders' to azathioprine, 65% of the Japanese, 59% of the black subjects, and 63% of the mixed-race subjects fell into the 'poor responder' category, compared with only 42% of the white group. Interestingly, this approximately 20% difference in azathioprine response corresponds to the racial differences seen in allograft survival.

Adult↗
PubMed1993

Depressed adenosine and total purine catabolite production in the postischemic rat heart.

The influence of global ischemia on myocardial nucleotide catabolite production and contraction was studied in Langendorff-perfused rat hearts. Hearts in the "ischemic" group were subjected to a 25 minute period of global ischemia at 30 minutes from the start of perfusion, and to two 30 s periods of global ischemia at 20 and 80 minutes of perfusion. Control hearts were subjected to three 30 s periods of ischemia at 20, 45 and 80 minutes of perfusion. Left ventricular developed pressure and concentrations of total nucleotide catabolites and adenosine in the coronary effluent were measured throughout. The concentration of nucleotide catabolites increased transiently by 2.1 +/- 0.5 microM in the control group and 2.2 +/- 0.8 microM in the "ischemic" group, immediately after 30 s ischemia at 20 minutes; while the concentration of adenosine increased transiently by 0.17 +/- 0.08 microM in the control group and 0.13 +/- 0.09 microM in the "ischemic" group. The next 30 s ischemic period in control hearts caused nucleotide catabolites to increase by 1.7 +/- 0.5 microM and adenosine by 0.12 +/- 0.06 microM. In the "ischemic" group, massive purine release was observed after 25 minutes of ischemia, the release decreasing to below pre-ischemic levels after 10 minutes of reperfusion. The increases in effluent nucleotide catabolites and adenosine in response to 30 s ischemia at 80 minutes were 1.4 +/- 0.4 microM and 0.13 +/- 0.1 microM, respectively, in the control group. In contrast, in the "ischemic" group, nucleotide catabolites increased by only 0.3 +/- 0.2 microM and adenosine by 0.011 +/- 0.008 microM after 30 s ischemia at the same time.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenosine↗
PubMed1992

A novel route of ATP synthesis.

Incorporation of the adenine moiety of 2'-deoxyadenosine (dAdo) into ATP, consistently observed in human erythrocytes, is a phenomenon which cannot be explained by the operation of any known pathway. We reported previously that this effect was not observed in adenine phosphoribosyltransferase-deficient erythrocytes showing that adenine must be an obligatory intermediate. However, generation of adenine from dAdo was difficult to reconcile with the operation of any known process in human cells, and involvement of S-adenosylhomocysteine hydrolase (SAH-hydrolase) was postulated. The present studies with intact human erythrocytes demonstrate that nucleoside analogues which inhibit SAH-hydrolase caused substantial attenuation of adenine transfer from dAdo into ATP. It was confirmed that dAdo is not a substrate of 5'deoxy-5'methylthioadenosine (5'MT-adenosine) phosphorylase. Inhibition of the transfer of the adenine moiety of dAdo into ATP did not correlate with inhibition of 5'MT-adenosine phosphorylase by nucleoside analogues. This report provides further evidence that the pathway involving nucleoside (adenosine) analogue binding to SAH-hydrolase, release of base and subsequent phosphoribosylation can operate in intact cells. The metabolic significance of this process relates to the possible generation of free bases (adenine) in the human body, ATP synthesis and nucleoside drug interconversions.

Adenosine Triphosphate↗
PubMed1992

Determination of nicotinamide phosphoribosyltransferase activity in human erythrocytes: high-performance liquid chromatography-linked method.

A radiochemical reverse-phase-high-performance liquid chromatography-linked method to measure the activity of nicotinamide phosphoribosyltransferase (EC 2.4.2.12) in crude lysates of human red blood cells is described. The apparent Km for nicotinamide was in the micromolar range, much lower than that described in human erythrocytes in the past. The enzyme activity in crude hemolysates was found to be extremely low (21 +/- 3.5 nmol x h-1 x g-1 Hb); nevertheless, the low Km for nicotinamide might account for the production of pyridine nucleotides reported by us for intact erythrocytes incubated at low, physiological concentrations of this substrate.

Carbon Radioisotopes↗
PubMed1992

The importance of thiopurine methyltransferase activity for the use of azathioprine in transplant recipients.

The immunosuppressive efficacy of azathioprine is related to its rapid metabolism in vivo to 6-mercaptopurine (6MP), with subsequent conversion to thioguanine nucleotides by an anabolic route involving hypoxanthine-guanine phosphoribosyltransferase. Two alternative catabolic routes exist: oxidation to 6-thiouric acid via xanthine oxidase and methylation to 6-methylmercaptopurine via the enzyme thiopurine methyltransferase (TPMT). Catabolism via either route would restrict formation of the active metabolites. We analyzed TPMT activity in erythrocyte lysates of 25 controls, 25 uremic patients on dialysis, and 68 transplanted patients. Median activity was lower in controls (31.0 pmol/hr/mg Hb, range 16.2-43.0) and transplanted patients receiving only cyclosporine and prednisolone (31.7 pmol/hr/mg Hb, range 12.7-43.5) than in the azathioprine treated group, (36.1 pmol/hr/mg Hb, range 16.1-71.3), or the uremic group on dialysis, (35.5 pmol/hr/mg Hb, range 18.6-62.6) suggesting that both azathioprine and uremia induce the enzyme, but CsA does not. Only 3 patients demonstrated total intolerance to azathioprine, 2 of whom had very low TPMT activity (zero and 12.7 pmol/hr/mg Hb). The intolerance of the third patient, despite high TPMT activity, was attributed to concomitant cotrimoxazole therapy. Patients with intermediate activity (15-26 pmol/hr/mg Hb) could tolerate azathioprine well. Of 29 cadaver recipients given only azathioprine plus prednisolone, 24 with a better clinical outcome had a significantly lower activity (33.1 pmol/hr/mg Hb, range 16.1-46.1) than 5 with reduced allograft function (42.5 pmol/hr/mg Hb, range 33.8-51.5). TPMT activity in these 24 patients was also significantly lower than the general group of azathioprine-treated recipients. This inverse association between TPMT activity and allograft function was again found among 30 patients receiving triple therapy (azathioprine, CsA, prednisolone). Self-selection of the best recipients for azathioprine immunosuppression apparently occurred, based on low catabolism of the drug. We conclude that total intolerance to azathioprine is rare and usually appears in patients with very low TPMT activities. Our results also suggest that the wide range of TPMT activity may be an important factor in determining long-term graft survival in azathioprine-treated patients; those with high activity might benefit from doses near the upper limit generally recommended.

Adolescent↗
PubMed1991

Effects of adenosine analogues on ATP concentrations in human erythrocytes. Further evidence for a route independent of adenosine kinase.

Adenosine derivatives are frequently used in chemotherapy because of their potent antitumor, antiviral and antiparasitic activity. We investigated the metabolism of some adenosine analogues in adenosine deaminase inhibited normal and adenine phosphoribosyltransferase (APRT) deficient human erythrocytes. The ATP and GTP concentrations and the formation of unusual nucleotides were measured. Some of the analogues studied (tubercidin, 9 beta-D-arabinofuranosyladenine, 2'-deoxyadenosine, 2-chloroadenosine, neplanocin A) were phosphorylated to the corresponding nucleoside triphosphates and this process was abolished by iodotubercidin--an adenosine kinase inhibitor. With the exception of 2'-deoxyadenosine, nucleotide analogue formation was accompanied by ATP depletion. ATP decrease was not observed after adenosine kinase inhibition and ATP concentration even increased in the presence of 2'-deoxyadenosine, neplanocin A and 5'-iodo-5'-deoxyadenosine. However, the latter increment was not observed in APRT deficient erythrocytes. Bredinin, S-adenosylhomocysteine, deoxycoformycin and adenosine dialdehyde did not form nucleotide derivatives or exert any effects on ATP concentration. It is concluded that adenosine analogues can either enter the nucleotide pool via phosphorylation mechanisms, or may be converted to ATP by the pathways involving the intermediate formation of adenine.

Adenine Phosphoribosyltransferase↗
PubMed1991

A high performance liquid chromatographic assay for AMP-deaminase activity in the erythrocytes of healthy subjects and patients with inherited purine disorders.

A novel method for measuring AMP-deaminase activity in human erythrocytes is presented, based on the determination of the reaction product, IMP, using high performance liquid chromatography. IMP formation was found to be proportional both to the incubation time and the amount of haemolysate over a wide range. The minimal detectable AMP-deaminase activity was more than 1000 times lower than the mean activity found in healthy controls (1083 nmol/h/mg Hb). No marked difference of activity was found in the patients with the following inherited purine disorders: familial juvenile gouty nephropathy and deficiencies of adenosine deaminase, hypoxanthine-guanine phosphoribosyltransferase or adenine phosphoribosyltransferase. The activity in the erythrocytes of patients with chronic renal failure was also similar to controls. The existence of subjects with low erythrocyte AMP-deaminase activity in the population has been confirmed.

AMP Deaminase↗