Cellular immunodeficiency associated with nucleoside phosphorylase deficiency. Immunologic and biochemical studies

The First Purine Nucleoside Phosphorylase Deficiency Patient Resembling IgA Deficiency and a Review of the Literature

Purine nucleoside phosphorylase (PNP) deficiency is a rare autosomal recessive primary immunodeficiency disorder characterized by decreased numbers of T-cells, variable B-cell abnormalities, decreased amount of serum uric acid and PNP enzyme activity. The affected patients usually present with recurrent infections, neurological dysfunction and autoimmune phenomena. In this study, whole-exome sequencing was used to detect mutation in the case suspected of having primary immunodeficiency. We found a homozygous mutation in PNP gene in a girl who is the third case from the national Iranian registry. She had combined immunodeficiency, autoimmune hemolytic anemia and a history of recurrent infections. She developed no neurological dysfunction. She died at the age of 11 after a severe chicken pox infection. PNP deficiency should be considered in late-onset children with recurrent infections, autoimmune disorders without typical neurologic impairment.

Purine enzymes in patients with rheumatoid arthritis treated with methotrexate

OBJECTIVES

To study (a) purine metabolism during treatment with methotrexate (MTX) in patients with rheumatoid arthritis (RA) and (b) the relation of purine metabolism with efficacy and toxicity of MTX treatment.

METHODS

One hundred and three patients with active RA who started treatment with MTX were included. The initial MTX dosage was 7.5 mg/week and raised to a maximum of 25 mg weekly if necessary. The purine enzymes 5'-nucleotidase (5'NT), purine-nucleoside-phosphorylase (PNP), hypoxanthine-guanine-phosphoribosyltransferase (HGPRT), and adenosine-deaminase (ADA) were measured before the start, after six weeks, and after 48 weeks or at study withdrawal. The laboratory results were related to measures of efficacy and toxicity of MTX treatment.

RESULTS

Baseline values of 5'NT and PNP (16.9 and 206.8 nmol/10(6) mononuclear cells/h, respectively) were similar to those in former studies. Activities of HGPRT and ADA were relatively low at the start (8.7 and 80.3 nmol/10(6) mononuclear cells/h, respectively). After six weeks purine enzyme activities showed no important changes from baseline. After 48 weeks of MTX treatment a decrease of the enzyme activities of ADA (-21.6 nmol/10(6) mononuclear cells/h; 95% CI -28.6 to -14.7), PNP (-78.9 nmol/10(6) mononuclear cells/h; 95% CI -109.0 to -48.7), and HGPRT (-2.0 nmol/10(6) mononuclear cells/h; 95% CI -3.1 to -0.9) was found. No association was shown between the enzyme activities of ADA, PNP, and HGPRT, and the efficacy or toxicity of MTX treatment. In contrast, enzyme activity of 5'NT showed a decrease in the subgroup of patients discontinuing MTX treatment because of hepatotoxicity.

CONCLUSION

MTX treatment in patients with RA leads to a significant decrease of the purine enzyme activities of ADA, PNP, and HGPRT that is not related to the anti-inflammatory efficacy or toxicity of MTX. Hepatotoxicity was related to a decrease in the enzyme activity of 5'NT. These changes may be explained by direct or indirect (via purine de novo and salvage metabolism and the homocysteine pathway) effects of MTX.

Mitochondrial basis for immune deficiency. Evidence from purine nucleoside phosphorylase-deficient mice

We generated purine nucleoside phosphorylase (PNP)-deficient mice to gain insight into the mechanism of immune deficiency disease associated with PNP deficiency in humans. Similar to the human disease, PNP deficiency in mice causes an immunodeficiency that affects T lymphocytes more severely than B lymphocytes. PNP knockout mice exhibit impaired thymocyte differentiation, reduced mitogenic and allogeneic responses, and decreased numbers of maturing thymocytes and peripheral T cells. T lymphocytes of PNP-deficient mice exhibit increased apoptosis in vivo and higher sensitivity to gamma irradiation in vitro. We propose that the immune deficiency in PNP deficiency is a result of inhibition of mitochondrial DNA repair due to the accumulation of dGTP in the mitochondria. The end result is increased sensitivity of T cells to spontaneous mitochondrial DNA damage, leading to T cell depletion by apoptosis.

Methotrexate in rheumatoid arthritis: an update with focus on mechanisms involved in toxicity

OBJECTIVES

To provide an update of the current knowledge of the mechanism of action of low-dose methotrexate (MTX) in the treatment of patients with rheumatoid arthritis (RA), with an emphasis on the mechanisms involved in toxicity. We also considered strategies currently used to prevent or decrease toxicity of MTX.

METHODS

We reviewed the literature dealing with the subjects of MTX treatment of RA, the mechanisms of action of low-dose MTX regarding efficacy and toxicity, and strategies used to prevent or decrease MTX toxicity.

RESULTS

MTX is a fast working and effective second-line antirheumatic agent (SLA). Its use is limited mainly because of side effects. The mechanisms of action regarding efficacy and toxicity are probably determined by different metabolic pathways. Recent data indicate that the antiinflammatory effect of MTX is mediated by adenosine. However, MTX side effects can only partly be explained by folate antagonism and may also depend on its action on other related metabolic pathways. The latter include the homocysteine-methionine-polyamine pathway and purine metabolism. Variants in these metabolic routes (ie, the C677T mutation in the methylene-tetrahydrofolate reductase [MTHFR] gene), may predispose to the development of side effects. Currently the most promising strategy to decrease or prevent toxicity of MTX is concomitant prescription of folic acid or folinic acid. Other strategies are currently under investigation.

CONCLUSIONS

MTX benefits a majority of RA patients. Approximately 30% of patients, however, abandon treatment because of drug-related side effects. Folic acid or folinic acid likely reduces MTX toxicity. More data, however, are needed to evaluate a potential detrimental effect on the antirheumatic efficacy of MTX.

Correction of purine nucleoside phosphorylase deficiency by transplantation of allogeneic bone marrow from a sibling

Deficiency of the purine salvage pathway enzyme purine nucleoside phosphorylase causes a combined immunodeficiency and neurologic abnormalities and is usually fatal in childhood. We report the first successful transplantation of bone marrow from a sibling with identical class II human leukocyte antigens in this condition, demonstrating correction of both lymphocyte metabolic and functional abnormalities.

Enzymes as agents for the treatment of disease

The replacement of genetically deficient enzymes in patients with inherited metabolic disorders by infusion of purified enzymes or by organ transplantation has had very limited success, although good results with bone marrow transplantation have been obtained in some patients with mucopolysaccharidosis, Gaucher disease and inherited immunodeficiency diseases. Genetic engineering of the patient's lymphocytes may ultimately render these approaches redundant, at least for some of these diseases. Treatment of chronic pancreatic insufficiency and of disaccharidase deficiency with oral enzymes can be very effective; therapy can be monitored in the latter by measuring the breath hydrogen excretion and in the former by a range of tests of which stool chymotrypsin assay is the most convenient. Treatment of acute myocardial infarction by intracoronary perfusion of thrombolytic enzymes can improve both cardiac function and long-term survival if given early enough. Successful reperfusion can be identified by changes in the kinetics of serum enzyme release and clearance, especially for the isoenzymes and isoforms of creatine kinase. In cancer chemotherapy, L-asparaginase has long been a useful adjunct in the treatment of acute lymphoblastic leukemia, but recent experience suggests a role in acute nonlymphoblastic leukemia as well.

Expression of intracellular biochemical defects of lymphocytes in aging: proposal of a general aging mechanism which is not cell-specific

There is a decline in immune capacity with age which is expressed on the organismic level by association with numerous immune-related diseases, on the cellular level by impaired mitogenesis, on the biochemical level by impaired metabolic pathways, and on the molecular level by decreased protein synthesis and degradation. Defects in various cofactors such as calcium and several nucleotides also occur and may be related to the impaired enzyme function during mitogenesis in the aged. The central cause for decreased mitogenesis in the aged could be a decrease in protein synthesis which appears to cause impaired enzyme induction. This impaired enzyme induction accounts in part for the decreased glycolytic flux and DNA synthesis in these cells. Decreased protein synthesis also has been associated with a decreased synthesis of lymphokines which help these cells to proliferate. Numerous other intracellular age-related defects of lymphocytes also occur which may collectively play important interdependent roles in the impaired lymphocyte function of the aged. A potential general underlying mechanism of cellular senescence is proposed based on a genetic "slowing-cycle" effect of transcription, translation, and enzyme induction with immunosenescence presented as an example of an expression of these basic defects.

Metabolism of purine nucleosides in human and ovine lymphocytes and rat thymocytes and their influence on mitogenic stimulation

1. Phosphorolysis and phosphorylation rates of inosine, guanosine and deoxyguanosine were determined in disrupted and intact human and ovine lymphocytes and rat thymocytes and related with their effect on mitogenic stimulation. 2. Activity of purine nucleoside phosphorylase (EC 2.4.2.1) was about 10 times higher in extracts of human lymphocytes than in those of ovine lymphocytes and rat thymocytes. Apparent Km values for inosine and guanosine were higher in human lymphocytes (about 100 microM) than in ovine lymphocytes (50 microM). Apparent Km values for deoxyguanosine were about 100 microM in the extracts of all three cell types. 3. In extracts of human and ovine lymphocytes the presence of guanosine kinase activity was established. Deoxyguanosine kinase activity was detected in all three cell types. 4. The rate of phosphorylation of deoxyguanosine was much lower than the rate of phosphorolysis both in extracts and in intact cells. 5. Deoxyguanosine, guanosine and inosine were incorporated by intact cells into nucleotides and nucleic acids. This incorporation of deoxyguanosine and guanosine was only partially due to phosphorolysis and subsequent conversion by hypoxanthine-guanine phosphoribosyltransferase (EC 2.4.2.8). The incorporation of inosine appeared to be due completely to this route. 6. Inosine (0.5 mM) did not inhibit thymidine incorporation of phytohemagglutinin-stimulated human and ovine lymphocytes. At the same concentration deoxyinosine caused 50% inhibition, but guanosine and deoxyguanosine inhibited almost completely. Thymidine incorporation of concanavalin A-stimulated rat thymocytes was hardly inhibited by 0.5 mM inosine, deoxyinosine and guanosine, but 50 microM and 0.5 mM deoxyguanosine caused 25% and complete inhibition, respectively.

Adenosine deaminase and purine nucleoside phosphorylase activities in peripheral lymphocytes from patients with solid tumours

Adenosine deaminase (ADA) and purine nucleoside phosphorylase (PNP) levels of peripheral blood mononuclear cells were measured in 34 patients with various types of solid tumours. The mean ADA activity was found to be significantly lower than in controls (P less than 0.005). Patients with nonresectable tumour or with recurrence after radical surgery showed low ADA levels, while patients operated upon and without recurrence had enzymatic activity not different from that of normal controls. The mean value of PNP activity was similar to that of normal controls; no differences were observed between operated patients without recurrence and cases with nonresectable tumour or with recurrence after surgical treatment. No effects on ADA and PNP levels appeared to be induced by chemotherapy.

Adenosine deaminase and purine nucleoside phosphorylase activity in spleen cells of aged mice

The activities of two enzymes of purine metabolism, adenosine deaminase (ADA) and purine nucleoside phosphorylase (PNP), were determined in spleen lymphocytes from mice of various ages. We found that in the older animals, which have depressed responses to concanavalin A and phytohemagglutinin, there is a decrease in the activity of PNP but normal activity of ADA. The decline of PNP activity was seen at 7.5 months of age and appears to be concurrent with a decline in T-cell function. These results suggest that a decrease in PNP activity may be a contributing factor in the immunodeficient state of the aged.

Nucleoside phosphorylase 2 (Np-2) of mice

Isozyme patterns of nucleoside phosphorylase (NP) in 16 inbred strains, two recombinant inbred, one congenic, and three species of wild mice were studied. Evidence is provided for a genetic locus, Np-2, encoding an electrophoretic variant which is expressed exclusively in erythrocytes of certain inbred strains. This finding establishes the occurrence of genetic polymorphism of NP among inbred strains of mice. In addition, the Npla allele previously reported only in inbred strains has been observed in one of the species of wild mice (Mus musculus castaneus) studied.