Enzymes of the purine interconversion system in chronic lymphatic leukemia: decreased purine nucleoside phosphorylase and adenosine deaminase activity

Imbalance in the ribonucleotide pools of lymphoid cells from acute lymphoblastic leukemia patients

The intracellular purine and pyrimidine ribonucleotide concentrations were determined in the lymphoid cells from peripheral blood and/or bone-marrow of 29 patients with acute lymphoblastic leukemia (ALL), as well as in the mononuclear cells from peripheral blood of 12 patients with ALL in remission. The lymphoid cells of ALL patients showed an imbalance in the nucleotide pool compared with normal lymphocytes, whereas the nucleotide pool of mononuclear cells from patients with ALL in remission had normal values. The imbalance in the lymphoid cells from ALL patients involved decreased ratios of purine:pyrimidine, adenine:guanine and uracil:cytosine nucleotides, and an increased amount, together with a changed composition, of the UDP sugars. When compared with tonsil-derived B lymphocytes and thymocytes, ALL lymphoid cells have an increased amount (absolute and relative) and a change composition of the UDP sugars. Significant differences were found between the mean values for the immunologically defined subgroups of ALL and between the mean values for patients with a high or a low percentage of blast cells. However, individual patients cannot be classified according to their nucleotide pattern, because of the overlapping ranges. The results of this study may be useful for the design of new therapeutic regimens.

Plasminogen-dependent fibrinolytic activity in normal human lymphocytes: diminished lymphocyte plasminogen activator in chronic lymphocytic leukemia

Discrepancies in correlations between fibrinolytic activity and metastatic potential of malignant cells has resulted in speculation on the putative role of plasminogen activators (PA) in cancer. In this report we have compared lymphocyte PA from 40 patients with chronic lymphocytic leukemia (CLL) to normal human B- and T-lymphocytes. Lymphocytes were isolated from peripheral blood by Ficoll-Hypaque centrifugation. The B- and T-cells were further separated on nylon wool columns. Cell PA activity and cell membrane PA were determined using 3H-fibrin-coated plates with added human plasminogen. Lymphocytes did not lyse 3H-fibrin in the absence of plasminogen. Plasminogen-dependent fibrinolytic activities of normal B- and T-lymphocytes were comparable. The addition of protease inhibitors with trypsin or plasmin specificity to lymphocytes significantly inhibited normal PA, thus substantiating the serine protease spectrum of lymphocyte PA. Examination of lymphocytes from greater than 95% of patients with chronic lymphocytic leukemia revealed a marked decrease in lymphocyte and cell membrane PA as compared to normals. No correlation between Stage of CLL and lymphocyte PA was observed. Likewise, an inhibitor of PA in CLL lymphocytes was not detected. The function of PA in normal B-lymphocyte physiology and the potential pathogenetic role of diminished PA in CLL lymphocytes remain to be explored.

Enzymatic differences between chronic lymphocytic leukemia and prolymphocytic leukemia

Chronic lymphocytic leukemia and prolymphocytic leukemia of the B-cell immunophenotype are closely related disorders, but differ in their cytomorphologic and clinical features. In an attempt to differentiate further between these two forms of leukemia, we measured adenosine deaminase and purine nucleoside phosphorylase activities by using a linked-enzyme spectrophotometric assay on peripheral-blood leukemic cells from seven patients with chronic lymphocytic leukemia, three patients with prolymphocytic leukemia, and one patient with prolymphocytoid transformation of chronic lymphocytic leukemia. By using discriminant analysis, we were able to distinguish the two groups only on the basis of purine nucleoside phosphorylase activity (F1,9; p less than 0.001). The purine nucleoside phosphorylase activity in leukemic cells with prolymphocytic cytomorphology was significantly elevated (mean = 58.6 nM/min/mg protein) compared to the activity in leukemic cells with lymphocytic cytomorphology (mean = 25.6 nM/min/mg protein). There was only one patient with chronic lymphocytic leukemia who was assigned to the prolymphocytic leukemia group on the basis of her purine nucleoside phosphorylase activity. Our study suggests that purine nucleoside phosphorylase activity in leukemic cells may be useful in the distinction of prolymphocytic leukemia from chronic lymphocytic leukemia, and that it may be an enzymatic marker for the early detection of prolymphocytoid transformation of chronic lymphocytic leukemia.

Enzymes of purine metabolism in B-chronic lymphocytic leukemia

In order to study if enzymes of purine metabolism could be used as cell markers in B-chronic lymphocytic leukemia (B-CLL), the activities of adenosine deaminase (ADA), purine nucleoside phosphorylase (PNP), and 5'-nucleotidase (5'N) were repeatedly measured in blood mononuclear cells from B-CLL patients and were compared to those obtained in normal controls. Enzyme activities in patients were also compared to other biological parameters indicative of B-CLL to activities of ADA and PNP in erythrocytes. Results show that B-leukemic cells display abnormal enzyme patterns: subnormal ADA activity is characteristic; 5'N activity is depressed in 60% of the cases but increased in 15%. An inverse relationship between PNP activity and corresponding lymphocytosis is observed in leukemic but not in normal cells. The enzymatic anomalies seem to be linked to the presence of an unusual peripheral lymphocytic population, induced by the leukemic process. Indeed, ADA and PNP are not abnormal in erythrocytes. In untreated nonevolutive patients, the enzyme profile tends to remain stable throughout the course of the illness; normalization of enzyme patterns in treated patients occurs only when therapy induces improvement in T and B cell distribution.

Enzymological aspects of disorders in purine metabolism

Congenital enzyme defects of purine synthesis de novo and the salvage pathway are responsible for excessive uric acid production and are often associated with hyperuricemia and gout. On the other hand, defects of enzymes essential for the purine nucleotide cycles are the biochemical basis of dysfunction of the immune system. The influence of several congenital enzyme deficiencies on the regulation of biosynthesis de novo, on the regulation of purine nucleotide concentrations, and on adenosine concentration, as well as the effect on purine transport through cell membranes are discussed. The determination of enzymes involved in purine metabolism in noncongenital diseases seems to be of diagnostic importance. As examples, enzyme activities in lymphocytes of leukemic patients, and the determination of serum guanase activity in patients with liver dysfunction are described.

Enzyme alterations in leukemic cells

Recently, much attention has been focused on various enzyme alterations found in leukemic cells. Most of the data generated thus far has involved the study of terminal deoxynucleotidyl transferase, the purine pathway enzymes, and hexosaminidase and other lysosomal enzymes. Differences in both total enzyme activities and isoenzyme patterns have been found to occur among the various leukemia types and subtypes. These changes may prove to be useful aids in diagnosing, classifying, detecting subclinical recurrent or residual disease, and as therapeutic determinants in hematopoietic neoplasia, especially in the lymphoid malignancies.

Purine and pyrimidine activities in acute and chronic lymphocytic leukaemia: relation to cellular proliferative status

The cellular levels of the purine catabolic enzymes adenosine deaminase (ADA) and purine nucleoside phosphorylase (PNP) and those for the pyrimidine activities thymidine phosphorylase and thymidine kinase isozymes have been measured concurrently in peripheral blood nucleated cells of patients with acute lymphoblastic leukaemia, chronic lymphocytic or prolymphocytic leukaemia and correlated with the spontaneous tritiated thymidine uptake of the isolated cells. Highest ADA levels occurred in T-ALL cells but considerable overlap of individual activities occurred for non-T, non-BALL, B-CLL and T-CLL cells. The levels of PNP showed no distinct discriminatory trend in cells of the lymphoid proliferative disorders examined. Thymidine phosphorylase activity was markedly reduced in T-ALL and T-CLL cells with a stepwise increase in the level of mean activities for non-T, non-B ALL, B-CLL and B-PLL cells to that of isolated normal peripheral blood lymphocytes. Spontaneous tritiated thymidine uptake of the abnormal lymphoid cells exhibited a correlation between cellular thymidine kinase isozyme 1 and elevated ADA levels. The use of ADA inhibitors together with thymidine infusion for the treatment of lymphoproliferative disorders is discussed.

Enzyme and membrane markers in leukaemia: recent developments

Terminal deoxynucleotidyl transferase (TdT) assay has proved a valuable test for distinguishing lymphoblastic from myeloblastic leukaemias, particularly in adults whose blast cells are often negative for the c-ALL antigen. The immunofluorescence assay, particularly when used in combination with antisera to surface membrane antigens, has proved a sensitive technique for detecting small numbers of lymphoblasts in extramedullary sites, for example, testis or cerebrospinal fluid, or of residual Thy-ALL blasts in the marrow, which might otherwise be difficult to recognise. Differences in concentration of several enzymes concerned in purine metabolism have been detected between the blast cells in the various acute leukaemias. Adenosine deaminase (ADA) concentrations tend to be higher in Thy-ALL than in other forms of leukaemia, but the wide overlap reduces the diagnostic value of this assay. Thy-ALL blasts, however, appear to be selectively and exquisitely susceptible to inhibition of ADA by the drug deoxycoformycin, which has now been used sucessfully in a number of other wise resistant patients with Thy-ALL to obtain a complete remission. The recently introduced technique for the production of monoclonal antibodies has substantially widened the reagents available for analysing the membrane characteristics of bone marrow stem cells and of cell lineages derived from them. These have revealed previously unsuspected heterogeneity among different cases of acute lymphoblastic leukaemia, for example, among Thy-ALL blasts from different patients, and they have also delineated minor populations of immature thymocytes from which these leukaemic cells are derived. The potential use of these antibodies to prevent graft-versus-host disease by selective removal of T-lymphocytes from donor bone marrow before allogeneic bone marrow transplantation, or to prevent recurrence of Thy-ALL and other lymphoblastic leukaemias or lymphomas by selective removal of leukaemic or lymphoma malignant cells before autologous transplantation, is reviewed.