High Adenosine Deaminase Activity Research Articles

The levels of adenosine and its metabolites in the guinea pig and rat brain during complete ischemia—in vivo study

Changes in levels of adenosine, inosine, hypoxanthine and ATP during complete ischemia after decapitation were determined in various areas of the guinea pig and rat brain using an HPLC method. These results were compared with levels in brains fixed by microwave irradiation. The levels of adenosine during 60 min of complete ischemia were extremely high and unevenly distributed while levels in the microwaved brains were very low and evenly distributed. The ratios of inosine plus hypoxanthine levels to adenosine which indicate the rate of metabolic degradation from adenosine into inosine and hypoxanthine, were also unevenly distributed during complete ischemia in the cerebellum, superior colliculus, cerebral cortex and hippocampus of the guinea pig and rat, and the highest ratio was observed in the cerebellum of the guinea pig and the superior colliculus of the rat. The activities of adenosine deaminase (ADA), one of the enzymes involved in adenosine metabolism, were measured in the four regions of the guinea pig. The ADA activities were unevenly distributed and the highest ADA activity was found in the cerebellum. These regional differences in ADA activities are in good agreement with the regional differences in the ratio of inosine plus hypoxanthine levels to adenosine during complete ischemia. Furthermore, the administration of EHNA [ erythro-9-(2-hydroxy-3-nonyl)adenine hydrochloride] (10 mg/kg, i.p.), an ADA inhibitor, caused a significant increase of adenosine and decrease of inosine formation in all four regions and a drastic effect on the cerebellum with high ADA activity compared with the other regions in the guinea pig brain. These results indicate that the changes in concentrations of adenosine and its metabolites (inosine and hypoxanthine) during complete ischemia depend on ADA activity in each brain region.

Insights into thymic purine metabolism and adenosine deaminase deficiency revealed by transgenic mice overexpressing ecto-5'-nucleotidase (CD73).

The adenosine producing enzyme ecto-5'-nucleotidase (5'-NT) is not normally expressed during thymocyte development until the medullary stage. To determine whether earlier expression would lead to adenosine accumulation and/or be deleterious for thymocyte maturation, thymic purine metabolism, and T cell differentiation were studied in lckNT transgenic mice overexpressing 5'-NT in cortical thymocytes under the control of the lck proximal promoter. In spite of a 100-fold elevation in thymic 5'-NT activity, transgenic adenosine levels were unchanged and T cell immunity was normal. Inosine, the product of adenosine deamination, was elevated more than twofold, however, indicating that adenosine deaminase (ADA) can prevent the accumulation of adenosine, even with a dramatic increase in 5'-NT activity, and demonstrating the availability of 5'-NT substrates in the thymus for the first time. Thymic adenosine concentrations of mice treated with the ADA inhibitor 2'-deoxycoformycin (dCF) were elevated over 30-fold, suggesting that high ADA activity, rather than an absence of 5'-NT, is mainly responsible for low thymic adenosine levels. The adenosine concentrations in dCF-treated mice are sufficient to cause adenosine receptor-mediated thymocyte apoptosis in vitro, suggesting that adenosine accumulation could play a role in ADA-deficient severe combined immunodeficiency.

Activities of adenosine deaminase, 5'-nucleotidase, guanase, and cytidine deaminase enzymes in cancerous and non-cancerous human breast tissues.

We measured activities of some DNA turnover enzymes in 9 breast tissues with stage II cancer, 6 breast tissues with stage IIIa cancer, and 9 non-cancerous adjacent breast tissues from the same patients with stage II cancer. We found higher Adenosine Deaminase (ADA) and 5'-Nucleotidase (5'NT) and lower Guanase (GUA) activities in the cancerous tissues compared with the non-cancerous ones. No meaningful differences were however found between Cytidine Deaminase (CD) activities. Regarding the correlation analysis, positive correlations were established between ADA and 5'NT activities of the cancerous tissues (r = 0.45 for the tissues with stage II and r = 0.60 for the tissues with stage IIIa cancer). No meaningful correlations were however found between other enzyme activities. Relating to activity ratios, no meaningful differences were found between ADA/5'NT values in the tissues. GUA/CD ratios were however lower and the other ratios higher in the cancerous tissues. Results indicated that ADA and 5'NT activities increased and GUA activity decreased in the cancerous breast tissues but CD activities did not change in the tissues affected. It has been suggested that increased ADA and 5'NT together with decreased GUA activities might be a physiologic attempt of the cancer cells to provide more substrates needed by cancer cells to accelerate the salvage pathway activity. Furthermore, high ADA activity might also play part in the detoxication process of high amounts of toxic adenosine and deoxyadenosine substrates produced from accelerated purine metabolism in the cancerous tissues.

Adenosine deaminase isozymes in tuberculous pleural effusion

Total adenosine deaminase (ADA) activity and its isozyme (ADA 1 and ADA 2) activities were measured in pleural effusions and serum samples from patients with tuberculosis and in those from patients with lung cancer as controls. To analyze the cellular source of ADA isozymes in tuberculous pleural effusions, ADA isozyme activities in CD2 + T lymphocytes purified from tuberculous pleural effusions and cultured human cell lines derived from hematopoietic tumors were measured. Tuberculous pleural effusions had a much higher ADA activity than cancerous effusions, and high ADA activity mainly originated from the increase in ADA 2 activity. Further, total ADA activity in tuberculous pleural effusions decreased after antituberculosis treatment, because of the decrease in ADA 2 activity. On the other hand, measurement of ADA and ADA isozyme activities in T lymphocytes purified from tuberculous pleural effusions and human hematopoietic cell lines showed dominant expression of ADA 1 in total ADA activity. In conclusion, we found that ADA 2 is a dominant component of tuberculous pleural effusions and that ADA, is a major component of lymphoid cells. These results suggest that elevation of ADA activity in tuberculous pleural effusions does not always reflect the activation of cell-mediated immunity.

Adenosine deaminase (ADA) isoenzyme analysis in pleural effusions: diagnostic role, and relevance to the origin of increased ADA in tuberculous pleurisy.

The rise in adenosine deaminase (ADA) activity in the pleural fluid of tuberculous pleurisy patients, though used for diagnosis, is of unknown origin. In this work, we determined ADA activity and the activities of 2'-deoxyadenosine deaminase and ADA-2 in 350 patients. We also considered whether the results throw light on the origin of high pleural fluid ADA in tuberculous pleurisy and estimated the diagnostic efficiency of 2'-deoxyadenosine deaminase, ADA-2 and total ADA activities with and without the inclusion of the 2'-deoxyadenosine deaminase/ADA activity ratio in a combined criterion. The 350 pleural effusions were classified by previously established criteria as transudates (60 males/18 females) or as tuberculous (49 males/27 females), neoplastic (50 males/39 females), parapneumonic (36 males/19 females), empyematous (11 males/3 females), or miscellaneous (25 males/13 females) exudates. Total ADA, ADA-2 and 2'-deoxyadenosine deaminase activities were, respectively, 127.5 +/- 2.9, 103 +/- 29.5 and 42.8 +/- 14 U.L-1 in tuberculous exudates. With diagnostic thresholds of 47, 40 and 22 U.L-1 respectively, the sensitivities of ADA, ADA-2 and 2'-deoxyadenosine deaminase for tuberculosis were 100, 100 and 95%; their specificities 91, 96 and 92%; and their efficiencies 93, 97 and 93%, respectively. One hundred and one effusions (all 76 tuberculous, 12 neoplastic, 4 parapneumonic and 9 empyematous exudates) had total ADA levels > 47 U.L-1; of these, 8 neoplastic, 1 parapneumonic and all the tuberculous exudates had a 2'-deoxyadenosine deaminase/ADA activity ratio < 0.49. The criterion of simultaneously having ADA > 47 U.L-1, ADA-2 > 40 U.L-1 and a 2'-deoxyadenosine deaminase/ADA activity ratio < 0.49 was satisfied by all the tuberculous effusions but only eight others (all neoplastic) (sensitivity 100%, specificity 97%, efficiency 98%). We conclude that: 1) high total ADA activity in tuberculous pleural effusions is due mainly to an increase in ADA-2, and, therefore, originated from the only known source monocytes and macrophages; 2) ADA-2 was a more efficient diagnostic marker of tuberculous pleurisy than total ADA activity, although the difference was not statistically significant; and 3) among effusions with high total ADA the 2'-deoxyadenosine deaminase/ADA activity ratio differentiates tuberculous effusions from empyemas and parapneumonic effusions, but fails to discriminate well between tuberculous and neoplastic effusions.

A correlation study between serum adenosine deaminase activities and peripheral lymphocyte subsets in Parkinson's disease

Adenosine deaminase (ADA) and its isozyme activities in serum were measured together with peripheral lymphocyte subsets in 42 patients with idiopathic Parkinson's disease. The total and ADA 2 activities were significantly higher than normal controls ( p < 0.01). As regards the peripheral lymphocyte subsets, the proportion of OKT 10+ cells (activated T lymphocytes) and the proportions of interleukin-2 receptor+ and HLA-DR+ cells (mainly activated T lymphocytes) were significantly higher than normal controls ( p < 0.05, 0.01, 0.01, respectively). On the other hand, OKT 10+ cells demonstrated a significant correlation not only with total ADA but also with ADA 2 activity. These results suggest that high serum ADA activity may be involved in the pathogenesis of Parkinson's disease through peripheral T lymphocyte activation.

Adenosine deaminase activity in the CSF of patients with aseptic meningitis: utility in the diagnosis of tuberculous meningitis or neurobrucellosis.

We assayed 229 CSF samples from 180 adults with meningitis of different etiologies for adenosine deaminase activity (ADA) and evaluated the usefulness of this assay in the differential diagnosis of aseptic meningitis. Cases of meningitis were classified as tuberculous meningitis (TBM), pyogenic meningitis, viral meningitis, self-resolving aseptic meningitis without a specific diagnosis, meningitis associated with other infections, and neoplastic meningitis. We also tested 117 CSF specimens for which parameters were normal. We chose a cutoff point of 10 IU/L on the basis of our results and found elevated ADA levels in 50% of the patients with TBM (no differences between patients with AIDS and those who did not have AIDS were observed). Among samples from patients with aseptic meningitis, we observed high ADA levels in only two of five of the patients with neurobrucellosis. Therefore, we concluded that in cases of aseptic meningitis, a CSF ADA level of > or = 10 IU/L has a sensitivity of 48%, a specificity of 100%, a positive predictive value of 1, and a negative predictive value of 0.91 as a diagnostic criterion for TBM or neurobrucellosis. ADA levels were also > 10 IU/L in 30% of the patients with pyogenic meningitis, but this diagnosis was easily excluded on other grounds.

Isozyme analysis of the high serum adenosine deaminase activity in patients with myasthenia gravis.

The serum activities of adenosine deaminase (ADA) and its isozymes (ADA 1 and ADA 2) were measured in 31 patients with myasthenia gravis (MG). As compared with 50 normal controls, in MG the total activity and ADA 1 were significantly high (p < 0.01, respectively), and ADA 2 tended to be high. The total activity and ADA 2 were higher in generalized MG than in ocular MG. ADA 2 was significantly higher in grade IIB patients as compared with grade I patients divided by Osserman's classification (p < 0.05). Patients with bulbar signs showed a significantly high total ADA (p < 0.05) with an increasing tendency for ADA 2. There was a significant elevation of the total activity and ADA 2 in patients with positive anti-acetylcholine-receptor antibody as compared to those of the negative antibody (p < 0.05). It was concluded that total ADA, reflecting the increase of both ADA 1 and ADA 2, is high in MG; and the measurement of ADA 2 is more important because ADA 2 was increased with advancing clinical MG grade.

Enhanced oral bioavailability of DDI after administration of 6-Cl-ddP, an adenosine deaminase-activated prodrug, to chronically catheterized rats.

6-Cl-2',3'-dideoxypurine (6-Cl-ddP), an adenosine deaminase (ADA) activated prodrug of ddI, may be an effective antiretroviral agent for the treatment of AIDS dementia due to its ability to deliver increased concentrations of ddI to brain tissue. To examine the feasibility of administering this drug orally, the oral and hepatic portal bioavailabilities of 6-Cl-ddP were determined. In addition, the oral and portal bioavailabilities of ddI after administration of the prodrug were compared to those from administration of ddI itself. Pharmacokinetic and bioavailability studies were conducted in fully conscious, chronically catheterized rats in a randomized crossover design. Plasma ddI and 6-Cl-ddP concentration-time profiles were determined by HPLC. 6-Cl-ddP has poor apparent oral bioavailability (7% +/- 3%, n = 3) but high bioavailability after portal administration (97% +/- 11%), suggesting either poor absorption or extensive gut wall metabolism. The appearance of > 50% of the dose as ddI in the systemic circulation after an oral dose of 6-Cl-ddP rules out poor absorption of the prodrug, and confirms expectations of high ADA activity in the gastrointestinal tract. Gastric administration of 6-Cl-ddP resulted in a > 10-fold increase in the oral bioavailability of ddI, from 3-7% to > 50%, and a significant decrease in the variability in apparent bioavailability. These data indicate that lipophilic adenosine deaminase activated prodrugs of dideoxypurine nucleosides may have limited utility for improving CNS delivery after oral administration but may be useful in enhancing the oral bioavailability of highly polar and therefore poorly absorbed dideoxynucleosides.

The effect of enzyme replacement on red cell adenine deoxyribonucleotides in adenosine deaminase-deficient erythrocytes of the opossum, Didelphis virginiana

1. 1. Polyethyleneglycol-modified bovine adenosine deaminase was administered (10–20 U/kg/week) intramuscularly to two opossums for 15 weeks and changes in red cell adenine ribo- and deoxyribonucleotides quantitated by HPLC. 2. 2. Only a moderate decline of erythrocyte dAXP was observed at the end of the study when compared to results of enzyme replacement seen in human adenosine deaminase deficient patients. 3. 3. Opossum red cells salvage substantial amounts of deoxyadenosine provided in physiologic (50 nM) concentration from plasma having either low or high adenosine deaminase activity.

Clinical significance of serum adenosine deaminase activity in patients with mycosis fungoides.

Adenosine deaminase is one of the key enzymes in purine nucleotide degradation. This enzyme exists in most of the human tissues and the activity is high in lymphatic tissues, especially in T lymphocytes. Elevated adenosine deaminase activity in T cell leukemia has been reported, and its inhibitor, deoxycoformycin, has been developed as an antitumor agent. In some types of leukemia, serum adenosine deaminase activity increases in accordance with the severity of the disease. Although mycosis fungoides rarely involves peripheral blood, tumor cells do invade the skin. In order to evaluate the clinical significance of adenosine deaminase in mycosis fungoides, adenosine deaminase activity was measured in sera of 15 patients with mycosis fungoides at various stages. The mean enzyme activity was 23.2 IU/l, which was high with statistical significance compared with healthy controls (P < 0.001). Nine of twelve patients in the plaque stage (T2N0M0, IB) showed higher adenosine deaminase activity than did the normal population. The mean adenosine deaminase activity in sera in the patients in the plaque stage (T2N0M0, IB) was as high as 19.0 IU/l (range 13.7-21.4) with statistical significance compared with healthy control (P < 0.001). Three tumor stage patients without visceral involvement (T3N0M0, IIB) showed higher levels of adenosine deaminase activity (19.7, 21.5, 24.4 IU/l). An erythrodermic patient (T4N0M0, III) also had a high adenosine deaminase activity 28.4 IU/l. Two tumor stage patients with organ involvement (T3N0M1, IVB) exhibited extremely high adenosine deaminase activity (60.9, 32.2 IU/l). The adenosine deaminase activity in sera showed a tendency to become higher with the extension of the stages.(ABSTRACT TRUNCATED AT 250 WORDS)

Abdominal cyst formation following ventriculoperitoneal shunt in a case of hydrocephalus due to cryptococcal meningitis: Case report: Completely cured by surgical removal of the cyst and treatment with a newly developed anti-fungal drug (Difulcan)

A 54-year-old woman was admitted to the hospital for evaluation of meningitis. Tuberculous meningitis was suspected initially because of general findings and a high adenosine deaminase activity (ADA) value in the cerebrospinal fluid. Administration of antituberculous drugs was not effective. Computed tomography scanning revealed progression of ventricular enlargement. A ventriculo-peritoneal shunt was placed upon diagnosis of hydrocephalus due to meningitis. The presence of a large abdominal cyst formation was demonstrated. Cryptococcus was detected in the cyst fluid, leading to a diagnosis of cryptococcal meningitis. Intravenous administration of fluconazole (400 mg/day) was begun. Excision of the cyst was performed when Cryptococcus was no longer detected in the cyst fluid. The patient recovered uneventfully.

Adenosina deaminasa en fiebre tifoidea y otras enfermedades febriles

The contribution of serum adenosine deaminase (ADA) activity to the diagnosis of typhoid fever was assessed in 246 children and in 46 adults, by Giusti's original technique. Children included otherwise healthy patients admitted for elective surgical conditions or under follow up for epilepsy which were considered to be a control group (n: 81), presumptive viral diseases (n: 31), miscellaneous febrile diseases except for typhoid fever (n: 41), different kinds of bacteremia (n: 6), diarrhea due to Salmonella typhimurium (n: 14), viral hepatitis (n: 24), and culture proven typhoid fever (n: 49). Adult's group included 39 healthy controls and 7 patients with culture proven typhoid fever. Among children mean ADA activity was as follows: control group 28 +/- 7.8, viral disease 35.3 +/- 13.1, miscellaneous febrile disease 36.1 +/- 15.6, bacteremia group: 30.3 +/- 10.3, salmonellosis group 51.6 +/- 9, hepatitis group 68.3 +/- 34.5, typhoid fever group 124.4 +/- 40.8 U/I 37 degrees C. Among adults, values were 18.4 +/- 7.5 for controls and 112.8 +/- 19.2 U/I 37 degrees C in typhoid fever patients. In both adults and children ADA activity was significantly higher in the typhoid fever group (p < 0.0001). Untreated typhoid fever patients had their higher ADA activity between 10th and 15th day of illness. When ADA cut point was set at 80 U/I, sensitivity of the test was 91.8% and specificity was 91.4% as a preliminary clue to the recognition of typhoid fever.

High serum adenosine deaminase activity and its correlation with lymphocyte subsets in myasthenia gravis

Serum adenosine deaminase (ADA) activity and peripheral lymphocyte subsets of patients with myasthenia gravis (MG) were simultaneously measured. The ADA activity in MG (n = 30) was significantly higher as compared with normal control (n = 150) and multiple sclerosis (n = 12) (P less than 0.05). The ADA activity of generalized MG was higher than that of ocular MG, while a significant elevation of ADA activity was observed in grade IIB as compared with grade I of Osserman's classification (P less than 0.05). A trend of high ADA activity was demonstrated in those whose disease had advanced to a severe degree associated with unstable clinical features (P less than 0.05). In addition, there was a significant elevation of ADA activity in patients who disclosed positive anti-Ach-receptor-antibody as compared with negative one (P less than 0.05). There was no specific trend among the proportions of the subsets of peripheral lymphocytes which could reflect the severity of MG, however, the proportion of OK Ia1+ tended to be higher with advancing the grade of MG. Interestingly enough, a close correlation was found between the ADA activity and the proportion of OK Ia1+ cells (P less than 0.05). From the above results, it was concluded that high ADA may be responsible for the pathophysiology of MG through the alteration of peripheral lymphocyte function.

Selective adenosine release from human B but not T lymphoid cell line.

Intracellular adenosine formation and release to extracellular space was studied in WI-L2-B and SupT1-T lymphoblasts under conditions which induce or do not induce ATP catabolism. Under induced conditions, B lymphoblasts but not T lymphoblasts, release significant amounts of adenosine, which are markedly elevated by adenosine deaminase inhibitors. In T lymphoblasts, under induced conditions, only simultaneous inhibition of both adenosine deaminase activity and adenosine kinase activities resulted in small amounts of adenosine release. Under noninduced conditions, neither B nor T lymphoblasts release adenosine, even in the presence of both adenosine deaminase or adenosine kinase inhibitors. Comparison of B and T cell's enzyme activities involved in adenosine metabolism showed similar activity of AMP deaminase, but the activities of AMP-5'-nucleotidase, adenosine kinase and adenosine deaminase differ significantly. B lymphoblasts release adenosine because of their combination of enzyme activities which produce or utilize adenosine (high AMP-5'-nucleotidase and relatively low adenosine kinase and adenosine deaminase activities). Accelerated ATP degradation in B lymphoblasts proceeds not only via AMP deamination, but also via AMP dephosphorylation into adenosine but its less efficient intracellular utilization results in the release of adenosine from these cells. In contrast, T lymphoblasts release far less adenosine, because they contain relatively low AMP-5'-nucleotidase and high adenosine kinase and adenosine deaminase activities. In T lymphoblasts, AMP formed during ATP degradation is not readily dephosphorylated to adenosine but mainly deaminated to IMP by AMP deaminase. Any adenosine formed intracellularly in T lymphoblasts is likely to be efficiently salvaged back to AMP by an active adenosine kinase. In general, these results may suggest that adenosine can be produced only by selective cells (adenosine producers) whereas other cells with enzyme combination similar to SupT1-T lymphoblasts can not produce significant amounts of adenosine even in stress conditions.

Detection by ELISA of Specific IgG to Mycobacterial Antigen 60 in a Tuberculous Exudate

A case of active multicavitary tuberculosis is reported. In the 3rd month of treatment, an X-ray film of the thorax showed right pleural effusion. The properties of the pleural fluid were those of an exudate with high adenosine deaminase activity. An ELISA was performed to detect specific IgG antibody to mycobacterial antigen 60 in serum before the treatment and on a two-monthly basis following the initiation of therapy until completion of the course. Values were all above 1,750 U. Moreover, an ELISA test using the same antigen was done on pleural fluid, and a high IgG titer was obtained (950 U). A cutoff for a positive ELISA test was established at 240 U in serum and 150 U in other biologic fluids.

Adenosine Deaminase and Porcine Meat Quality

The adenosine analogues 5'-(N-ethyl) carboxamidoadenosine (NECA) and N6-(phenylisopropyl) adenosine (R-PIA) were shown to differ in their effect on the plasma level of free fatty acids (FFA), glucose and lactate in pigs representing low (Ada 0) and high (Ada A) red cell adenosine deaminase activity. At the same dosage range (0.001-0.005 mg/kg) R-PIA produced a much stronger suppression of the FFA level than NECA, indicating that A1 adenosine receptors predominate in porcine adipose tissue. Pretreatment with 8-phenyltheophylline completely abolished the antilipolytic effect of both adenosine analogues. NECA in contrast to R-PIA elevated the blood glucose concentration, suggesting that A2 adenosine receptors are involved in the stimulation of glycogenolysis. This effect of NECA was not altered by a beta-adrenoceptor blockade providing evidence for a direct effect of adenosine on glycogenolysis. Whereas the changes in plasma FFA following NECA administration were of similar magnitude in Ada A and Ada 0 pigs, the changes in the blood glucose concentration were different in these two groups of pigs.

Adenosine Deaminase and Porcine Meat Quality

The effect of dipyridamole--an adenosine uptake inhibitor--on the plasma concentration of free fatty acids (FFA), glucose, lactate and cyclic adenosine monophosphate (cAMP) has been examined in 2 groups of Landrace pigs representing low (Ada 0) and high (Ada A) red cell adenosine deaminase (Ada) activity. Pigs fitted with a jugular vein catheter were given dipyridamole (0.16 mg/kg/min) over a period of 30 min. The infusions were performed 22 h after the last meal at a time where pigs were found to show steady increase and decline in rates of lipolysis and glycogenolysis, respectively. The results showed that lipid mobilization as identified by the plasma FFA concentration was markedly depressed. During the infusion of dipyridamole similar degree of inhibition was seen in Ada 0 and Ada A pigs, however, in the period following the infusion, a significantly stronger suppression persisted in the Ada 0 pigs. Both the blood glucose and lactate level rose distinctly as a result of the dipyridamole treatment. This stimulation of the glycolysis rate was significantly more expressed in Ada 0 pigs compared to that of the Ada A pigs. When theophylline, an antagonist of adenosine, was given together with dipyridamole, the rise in the lactate level was considerably diminished. Dipyridamole also produced a distinct rise in the plasma cAMP levels.

Potentiation of Growth‐inhibitory Activity of 9‐β‐d‐Arabinofuranosyladenine by 2′‐Deoxycoformycin in Human Cultured Cell Lines Derived from Leukemias and Lymphomas

Growth‐inhibitory activity of 2′‐deoxycoformycin (DCF) and 9‐β‐D‐arabinofuranosyladenine (Ara‐A) used either singly or in combination was assessed in 30 human cultured cell lines (seven T‐cell, nine B‐cell, five non‐T, non‐B, and nine myeloid cell lines) derived from leukemias and lymphomas. DCF had little activity even at 100 μM any of the cell lines, while Ara‐A had an obvious inhibitory effect on them, especially on non‐T, non‐B cell lines at 10 μM or less. Lymphoid cell lines were apparently more sensitive to the combined use of Ara‐A and DCF than myeloid cell lines. DCF potentiated the antiproliferative activity of Ara‐A not only in T‐cell lines with high adenosine deaminase (ADA) activity, but also in some other cell lines with low ADA activity. DCF was stable in the culture medium, but Ara‐A in the medium containing cultured cells was rapidly inactivated. DCF completely inhibited the inactivation of Ara‐A in the medium containing P12/ICH or NALM‐6, but not in the medium containing Daudi. This suggests that there is some unknown mechanism(s) of inactivation of Ara‐A other than ADA in Daudi, which was insensitive to Ara‐A in the presence of 1 μM DCF. The capacity of DCF to inhibit degradation of Ara‐A in the medium containing these cultured cells correlated with the level of Ara‐A sensitivity potentiated by DCF. In all seven T‐cell lines, seven of the nine B‐cell lines, all five non‐T, non‐B cell lines, and only three of nine myeloid cell lines, the IC50 value for Ara‐A decreased to 5 μM or less in the presence of 1 μM DCF. These results suggest that the combination of DCF and Ara‐A may be effective against various types of lymphoid malignancies and some myeloid leukemias.

Molecular forms of adenosine deaminase in pleural effusions.

The molecular forms of adenosine deaminase (ADA) were studied in pleural effusions with high ADA activity. The molecular forms were separated by polyacrylamide gel electrophoresis (PAGE), and the molecular masses estimated by gel filtration. Effusions investigated were: tuberculosis (TB) (20 cases), lymphoma (3 cases), chronic myelogenous leukemia (1 case) and empyema (6 cases). Two ADA forms were identified, a small form (Smf-ADA) and a large form (Lmf-ADA). Without exception, the tuberculous effusions have shown only Lmf-ADA. All the other effusions contained both forms, the Smf-ADA being predominant. This was also the ADA pattern seen in normal lymphocytes. These findings may indicate different mechanisms of ADA release or origins of ADA in the various effusions. The Lmf-ADA may be secreted by activated T cells in TB, which would confirm the notion that ADA activity reflects cellular immunity. In contrast, in the nontuberculous cases the ADA probably leaked from damaged lymphocytes or neutrophils, hence the reflection of the cellular ADA pattern. The PAGE pattern may also be of value in distinguishing between TB and these other causes of high pleural fluid ADA.