Oral anticoagulation self-management and management by a specialist anticoagulation clinic: a randomised cross-over comparison.

BACKGROUND: Vitamin K antagonist treatment is effective for prevention and treatment of thromboembolic events but frequent laboratory control and dose-adjustment are essential. Small portable devices have enabled patient self-monitoring of anticoagulation and self-adjustment of the dose. We compared this self-management of oral anticoagulant therapy with conventional management by a specialist anticoagulation clinic in a randomised cross-over study. METHODS: 50 patients on long-term oral anticoagulant treatment were included in a randomised controlled crossover study. Patients were self-managed or were managed by the anticoagulation clinic for a period of 3 months. After this period the alternative strategy was followed for each patient. Prothrombin time (expressed as international normalised ratio [INR]) were measured at intervals of 1-2 weeks in both periods without knowledge of type of management. The primary endpoint was the number of measurements within the therapeutic range (therapeutic target value +/-50.5 INR units). FINDINGS: There was no significant difference in the overall quality of control of anticoagulation between the two study periods. Patients were for 55% and for 49% of the treatment period within a range of +/-0.5 from the therapeutic target INR during self-management and anticoagulation clinic management, respectively (p=0.06). The proportion of patients who spent most time in the therapeutic target range was larger during self-management than during anticoagulation clinic-guided management. The odds ratio for a better control of anticoagulation (defined as the period of time in the therapeutic target range) during self-management compared with anticoagulation clinic-guided management was 4.6 (95% CI 2.1-10.2). A patient-satisfaction assessment showed superiority of self-management over conventional care. INTERPRETATION: Self-management of INR in the population in this study is feasible and appears to result in control of anticoagulation that is at least equivalent to management by a specialist anticoagulation clinic. It is also better appreciated by patients. Larger studies are required to assess the effect of this novel management strategy on the incidence of thromboembolic or bleeding complications.

Diseases of captive cheetahs (Acinonyx jubatus jubatus) in South Africa: a 20-year retrospective survey.

As part of an ongoing study to determine the basis for high prevalences of veno-occlusive disease, glomerulosclerosis, and chronic lymphoplasmacytic gastritis in cheetahs, a retrospective pathology survey of captive cheetahs in the Republic of South Africa (RSA) was conducted. The RSA population was selected because its genetic composition and captive management were similar to those of the cheetah population in U.S. zoos, in which these diseases are common. For this study, archived pathology materials at the University of Pretoria Faculty of Veterinary Sciences in Onderstepoort and the Faculty of Veterinary Science, MEDUNSA, from 69 cheetahs that died between 1975 and 1995 were reviewed, and prevalences of common lesions were compared with those in the U.S. population. Gastritis associated with Helicobacter-like organisms was the most prevalent disease, accounting for close to 40% of the mortalities, including several cheetahs < 3 yr old. Glomerulosclerosis and veno-occlusive disease also were major causes of mortality in RSA cheetahs. RSA cheetahs also had adrenal cortical hyperplasia, cardiac fibrosis, lymphocytic depletion of the spleen, systemic amyloidosis, and splenic myelolipomas. The presence in the captive RSA cheetah population of the same unusual diseases that are common in U.S. cheetahs suggests a species predilection to develop these diseases in captivity.

Risk of venous thrombosis with use of current low-dose oral contraceptives is not explained by diagnostic suspicion and referral bias.

BACKGROUND: The magnitude of the relative risk of venous thrombosis caused by low-dose oral contraceptive use is still debated because previous studies might have been affected by diagnostic suspicion and referral bias. METHODS: We conducted a case-control study in which the effect of diagnostic suspicion and referral bias was excluded. The study was performed in 2 diagnostic centers to which patients with clinically suspected deep vein thrombosis of the leg were referred. History of oral contraceptive use was obtained before objective testing for thrombosis. Young females with an objective diagnosis of deep vein thrombosis were considered case patients, and those who were referred with the same clinical suspicion but who had no thrombosis served as control subjects. Participants were seen between September 1, 1982, and October 18, 1995: 185 consecutive patients and 591 controls aged 15 to 49 years with a first episode of venous thrombosis and without malignant neoplasms, pregnancy, or known inherited clotting defects. RESULTS: The overall odds ratio for oral contraceptive use was 3.2 (95% confidence interval [CI], 2.3-4.5); after adjustment for age, family history of venous thrombosis, calendar time, and center, the odds ratio was 3.9 (95% CI, 2.6-5.7). In the idiopathic group (120 patients and 413 controls, excluding recent surgery, trauma, or immobilization), the odds ratio for oral contraceptive use was 3.8 (95% CI, 2.5-5.9); after adjustment, the odds ratio was 5.0 (95% CI, 3.1-8.2). CONCLUSIONS: In this study, in which patients and controls were subj ect to the same referral and diagnostic procedures, we found similar relative risk estimates for oral contraceptive use as in previous studies. We conclude that diagnostic suspicion and referral bias did not play an important role in previous studies and that the risk of venous thrombosis with use of current brands of oral contraceptives still exists.

Well-being and symptoms in relation to insulin therapy in type 2 diabetes.

OBJECTIVE: To determine the influence of insulin therapy on physical symptoms, emotional and general well-being, and treatment satisfaction in patients with type 2 diabetes. RESEARCH DESIGN AND METHODS: A descriptive prospective 2-year cohort study was performed. The study population consisted of 272 eligible NIDDM patients of Dutch origin > or = 40 years of age who had a known diabetes duration > or = 3 months and who were treated with diet and/or oral hypoglycemic agents. Dependent variables in the logistic regression analysis were scores on the Type 2 Diabetes Symptom Checklist, the Profile of Mood States, and questions regarding general well-being and treatment satisfaction. Potential determinants under study were age, sex, known diabetes duration, insulin dose, duration of insulin therapy, comorbidity, baseline and change in metabolic parameters and cardiovascular risk factors. RESULTS: A baseline and 2-year questionnaire were available for 157 patients (58%). During follow-up, 39 of them (24.8%) were treated with insulin. Initiation of insulin therapy was significantly associated with improved glycemic control (mean HbA1c 8.2 +/- 1.4 [SD] to 7.4 +/- 0.9%, P = 0.001) and weight gain (BMI 27.1 +/- 3.9 to 28.6 +/- 4.3 kg/m2, P = 0.000). Of all symptom and well-being scores, only feelings of emotional fatigue worsened significantly, although modestly (0.4-1.7 on a scale of 0.0-10.0, P = 0.02). Although diabetes management with insulin was experienced as more demanding (P = 0.04), treatment satisfaction scores were not adversely influenced (2.5-1.9, P = 0.39). High insulin doses were significantly and independently associated with high symptom scores (total score, hypoglycemic score) and with low mood (displeasure score, anger, tension, emotional fatigue) and perceived state of health. CONCLUSIONS: Initiation of insulin therapy in type 2 diabetes improves glycemic control effectively, has little influence on physical and psychological well-being dimensions, and does not affect treatment satisfaction.

Sustained good glycaemic control in NIDDM patients by implementation of structured care in general practice: 2-year follow-up study.

In primary care it is difficult to treat the growing number of non-insulin-dependent diabetic (NIDDM) patients according to (inter)national guidelines. A prospective, controlled cohort study was designed to assess the intermediate term (2 years) effect of structured NIDDM care in general practice with and without 'diabetes service' support on glycaemic control, cardiovascular risk factors, general well-being and treatment satisfaction. The 'diabetes service', supervised by a diabetologist, included a patient registration system, consultation facilities of a dietitian and diabetes nurse educator, and protocolized blood glucose lowering therapy advice which included home blood glucose monitoring and insulin therapy. In the study group (SG; 22 general practices), 350 known NIDDM patients over 40 years of age (206 women; mean age 65.3 +/- SD 11.9; diabetes duration 5.9 +/- 5.4 years) were followed for 2 years. The control group (CG; 6 general practices) consisted of 68 patients (28 women; age 64.6 +/- 10.3; diabetes duration 6.3 +/- 6.4 years). Mean HbA1c (reference 4.3-6.1%) fell from 7.4 to 7.0% in SG and rose from 7.4 to 7.6% in CG during follow-up (p = 0.004). The percentage of patients with poor control (HbA1c > 8.5%) shifted from 21.4 to 11.7% in SG, but from 23.5 to 27.9% in CG (p = 0.008). Good control (HbA1c < 7.0%) was achieved in 54.3% (SG; at entry 43.4%) and 44.1% (CG; at entry 54.4%) (p = 0.013). Insulin therapy was started in 29.7% (SG) and 8.8% (CG) of the patients (p = 0.000) with low risk of severe hypoglycaemia (0.019/patient year). Mean levels of total and HDL-cholesterol (SG), triglycerides (SG) and diastolic blood pressure (SG + CG) and the percentage of smokers (SG) declined significantly, but the prevalence of these risk factors remained high. General well-being (SG) did not change during intensified therapy. Treatment satisfaction (SG) tended to improve. Implementation of structured care, including education and therapeutic advice, results in sustained good glycaemic control in the majority of NIDDM patients in primary care, with low risk of hypoglycaemia. Lowering cardiovascular risk requires more than reporting results and referral to guidelines.

The prevalence and determinants of foot ulceration in type II diabetic patients in a primary health care setting.

The purpose of the study was to assess the prevalence of foot (pre-)ulcers and their determinants in type II diabetic patients in a primary health care setting. Six hundred and nine patients (246 men, mean age 64.8 (range, 40-94) years, diabetes duration, 4.3 (0-44.9) years) from 22 general practices attended a regional shared care project in Amsterdam. At first visit all patients were examined by a podiatrist. Amputations, active fool ulcers (Wagner stage 1 or 2) and pre-ulcers (Wagner stage 0, hard skin with or without macerating changes) were recorded in 0 (0%), 11 (1.8%) and 79 (12.9%) patients, respectively. In multivariate logistic regression analysis, after adjustment for age and gender, diabetes duration, cigarette smoking, peripheral vascular disease (assessed by calculating ankle/brachial index), sensory neuropathy (by Semmes-Weinstein monofilament 5.07), dry feet and severe hammer toes were independently and significantly associated (pre-)ulceration. In conclusion, one of every seven type II diabetic patients in primary health care has a foot (pre-)ulcer. Patients at risk for foot ulceration can be identified by inspection and the use of simple instruments.

Special challenges of maintaining wild animals in captivity: a southern African perspective.

The authors summarise the issues of concern in game ranching, and the challenges involved in maintaining and utilising wild animals. The more intensive farming of ostriches and crocodiles is discussed. An indication of regulatory controls on the movement and possession of wild animals is given. Institutions concerned with aspects of wildlife care, rehabilitation and research are described.

Protein C deficiency in a controlled series of unselected outpatients: an infrequent but clear risk factor for venous thrombosis (Leiden Thrombophilia Study)

A deficiency of protein C (PC), antithrombin, or protein S is strongly associated with deep-vein thrombosis in selected patients and their families. However, the strength of the association with venous thrombosis in the general population is unknown. This study was a population-based, patient-control study of 474 consecutive outpatients, aged less than 70 years, with a first, objectively diagnosed, episode of venous thrombosis and without an underlying malignant disease, and 474 healthy controls who matched for age and sex. Relative risks were estimated as matched odds ratios. Based on a single measurement, there were 22 (4.6%) patients with a PC deficiency (PC activity, less than 0.67 U/mL or PC antigen, less than 0.33 U/mL when using coumarins). Among the controls, the frequency was 1.5% (seven subjects). Thus, there is a threefold increase in risk of thrombosis in subjects with PC levels below 0.67 or 0.33 U/mL [matched odds ratio, 3.1; 95% confidence interval (CI), 1.4 to 7.0]. When a PC deficiency was based on two repeated measurements, the relative risk for thrombosis increased to 3.8 (95% CI, 1.3 to 10); when it was based on DNA-confirmation, the relative risk increased further to 6.5 (95% CI, 1.8 to 24). In addition, there was a gradient in thrombosis risk, according to PC levels. The results for antithrombin are similar to those for PC, although less pronounced (relative risk, 2.2; 95% CI, 1.0 to 4.7). We could not find an association between reduced total protein S (relative risk, 0.7; 95% CI, 0.3 to 1.8) or free protein S levels (relative risk, 1.6; 95% CI, 0.6 to 4.0) and thrombosis risk. Although not very frequent, PC and antithrombin deficiency are clearly associated with an increase in thrombosis risk.

A comparison of real-time compression ultrasonography with impedance plethysmography for the diagnosis of deep-vein thrombosis in symptomatic outpatients.

BACKGROUND: Impedance plethysmography performed serially over a one-week period has been shown to be an effective diagnostic strategy for patients with clinically suspected acute deep-vein thrombosis. Compression ultrasonography has a high sensitivity and specificity for the detection of proximal-vein thrombosis. The clinical value of repeated ultrasonography in the management of symptomatic deep-vein thrombosis is unknown. METHODS: We conducted a randomized trial in 985 consecutive outpatients with clinically suspected deep-vein thrombosis to compare the diagnostic value of serial impedance plethysmography (494 patients) and serial compression ultrasonography (491 patients). We compared the positive predictive values of both tests for the diagnosis of venous thrombosis, using contrast venography as a reference. The frequencies of venous thromboembolism during a six-month follow-up period were also compared in patients with repeatedly normal results in order to evaluate the safety of withholding anticoagulant therapy from such patients. RESULTS: The positive predictive value of an abnormal ultrasonogram was 94 percent (95 percent confidence interval, 87 to 98 percent), whereas the predictive value of impedance plethysmography was 83 percent (95 percent confidence interval, 75 to 90 percent) (P = 0.02). In patients with repeatedly normal results, the incidence of venous thromboembolism during the six-month follow-up period was 1.5 percent (95 percent confidence interval, 0.5 to 3.3 percent) for serial compression ultrasonography, as compared with 2.5 percent (95 percent confidence interval, 1.2 to 4.6 percent) for serial impedance plethysmography. CONCLUSIONS: In making the diagnosis of deep-vein thrombosis in symptomatic outpatients, serial compression ultrasonography is preferable to impedance plethysmography, in view of its superior performance in detecting venous thrombosis.

Involvement of the complement system in the pathogenesis of pulmonary leukostasis in experimental myelocytic leukemia.

The role of the complement system in the pathogenesis of pulmonary leukostasis in myelocytic leukemia was studied in a rat model. Acute myelocytic leukemia was induced in six Brown-Norway rats, and complement levels were assayed during the course of the disease. Whole complement activity (CH50) and hemolytic activity of C1q, C3, and C4 decreased from day 16 after induction of the leukemia, when the rats developed pulmonary leukostasis. In addition, local complement activation was established in the lung vessels by immunofluorescence microscopy in advanced stages of pulmonary leukostasis. Finally, following systemic activation of the complement system by injection of cobra venom factor (CVF), leukemic rats (n = 6) died of pulmonary leukostasis 4.5 days earlier than did leukemic controls (n = 6). These findings suggest that, in acute myelocytic leukemia in Brown-Norway rats, pulmonary leukostasis is induced by activation of the complement system. This finding could lead to new modes of treatment for a life-threatening complication of leukemia.

Increase in Ara-C sensitivity in Ara-C sensitive and -resistant leukemia by stimulation of the salvage and inhibition of the de novo pathway.

In this study the hypothesis that inhibition of the de novo pathway results in stimulation of salvage pathway activity was tested. The key enzyme in the balance between these two pathways is ribonucleotide reductase (RR), which can be inhibited by hydroxyurea (HU). The metabolism of 1-beta-D-arabinofuranosylcytosine and 5-Aza-2 deoxycytidine (Aza-dC), which are activated via the salvage pathway, was evaluated in cells from Ara-C-sensitive and -resistant myelocytic leukemia cell line (BNML-Cl/0 and BNML-Cl/Ara-C). The combination of HU and Ara-C caused as much as a threefold increase of Ara-CTP; it significantly increased the incorporation of Ara-C into DNA and induced synergistic cytotoxicity, as evaluated in a colony assay. Even in the deoxycytidine (CdR) kinase-deficient Ara-C-resistant cell line, HU was partially able to restore sensitivity to Ara-C and Aza-dC. dCTP levels are reduced during the first 10 h after incubation with HU, but this effect vanishes at the time when phosphorylation is maximal. Increased CdR kinase activity in cell-free extracts could explain the enhanced synthetic salvage pathway activity, which is likely due to the fact that more enzyme is present (Vmax has increased by Km unchanged). RR inhibition combined with Ara-C might provide a means of eliminating leukemic cells with suboptimal anabolic salvage pathway activity, which otherwise survive Ara-C chemotherapy.

The use of the D-dimer test in combination with non-invasive testing versus serial non-invasive testing alone for the diagnosis of deep-vein thrombosis.

We studied the usefulness of the determination of plasma D-dimer levels (using an ELISA) in combination with non-invasive testing with impedance plethysmography (IPG) or real-time ultrasonography (US) for the diagnosis of deep-vein thrombosis (DVT), in outpatients with clinically suspected DVT. This combined approach was compared to serial non-invasive testing alone in these patients. The sensitivity of a positive D-dimer test (greater than 300 micrograms/l) for the presence of DVT was 100% (70/70 patients; 95% C.I.: 95-100%), whereas the specificity was 29% (69/239 patients; 95% C.I.: 23-34%). The proportion of patients in which a definitive decision about the presence or absence of DVT could be made on the day of referral, was calculated for both approaches. When applying the combined approach, in 42% of all referred patients the diagnosis of DVT could either be established or refuted on entry, as opposed to only 19% of patients using serial non-invasive testing alone. Also, the costs per DVT diagnosed were calculated for the two diagnostic approaches. For the diagnosis of DVT the costs using serial IPG were comparable to the costs using the combination of IPG and the D-dimer test. The same conclusion holds for the comparison of serial US with the combination of US and D-dimer testing. We conclude that for the diagnosis of DVT in symptomatic outpatients the combination of non-invasive testing with the D-dimer test might be preferred over serial non-invasive testing alone, although the safety of such an approach remains to be established in future management studies.

Fatal acute babesiosis in a juvenile wild dog (Lycaon pictus).

Clinical examination of a 75-day-old captive juvenile wild dog suffering from lassitude revealed pale mucous membranes, icterus, laboured respiration, a "water-hammer" pulse and splenomegaly. A peripheral blood smear containing numerous Babesia-infected erythrocytes confirmed the diagnosis of babesiosis. Treatment was unsuccessful and the animal died shortly after receiving a blood transfusion. The findings at necropsy were typical for acute babesiosis and included anaemia, icterus, splenomegaly and haemoglobinuria. In addition, marked atrophy of the thymus and lymph nodes was evident. Microscopic and electron microscopic examination of selected tissues disclosed high parasitaemia with vascular stasis and injury to both endothelial and parenchymal components. It is speculated that vaccination-induced immune incompetence predisposed to development of clinical babesiosis.

Development of pulmonary leukostasis in experimental myelocytic leukemia in the Brown-Norway rat.

The pathogenesis of pulmonary leukostasis in leukemia was studied in a rat model by investigating the course of its development. Leukemia was induced by inoculating rats with leukemic cells. The earliest stage of leukostasis was found from day 14 onward, when leukemic cells appeared in the peripheral blood, and was characterized by accumulation of leukemic cells at the capillary level. Simultaneous with the increase of leukemic cell concentrations in the peripheral blood, accumulation in capillaries increased gradually over a period of several days. This was accompanied by increasing severity of tachypnea. Shortly before death, aggregates consisting almost solely of leukemic cells were found in medium-sized blood vessels. This stage was rapidly followed by the end-stage, characterized by complete obstruction of the lung vasculature--including the largest arteries and veins--by leukemic cell aggregates, giving rise to extensive hemorrhages and edema. The end-stage was considered to be the cause of death, which occurred 18-26 days after the inoculation. The histological and ultrastructural findings in this study suggest that besides the size and stiffness of individual leukemic cells, interactions not only between leukemic cells, but also between leukemic cells and the endothelium play a role in the pathogenesis of pulmonary leukostasis.

The antileukaemic activity of 5-Aza-2 deoxycytidine (Aza-dC) in patients with relapsed and resistant leukaemia.

In the present study we demonstrate that Aza-dC in combination with Amsacrine has major antileukaemic properties in patients who have not already received extensive Ara-C therapy. Eight out of 11 patients in their first relapse of acute leukaemia achieved complete remission. Cross resistance between Ara-C and Aza-dC was revealed by the lack of antileukaemic activity in five patients with with Ara-C resistant leukaemia. Combination therapy with Aza-dC/Ams-acrine induced a considerable period of a granulocytopenia (28-35 days), while the toxic effect on erythro- and megakaryopoiesis was comparable to that reported for high dose Ara-C/Amsacrine chemotherapy. Remarkable is the long disappearance time for leukaemic blast cells in bone marrow, i.e. 3-5 weeks in some cases. Analysis of cell membrane markers showed a loss of the early differentiation antigens CD34 and CD33 from leukaemic bone marrow cells after 7 days of Aza-dC treatment, which is suggestive of leukaemic cell differentiation. In the small group of patients tested for DNA hypomethylation no association existed between the degree of hypomethylation and clinical response. Non-haematologic side effects were considerable in patients receiving the highest dosages of Aza-dC and consisted of severe, although usually reversible, gastrointestinal and neurological complications. In comparison with Ara-C, Aza-dC causes less nausea and vomiting and is therefore better tolerated.

Substrate-specific deoxycytidine kinase deficiency in 1-beta-D-arabinofuranosylcytosine-resistant leukemic cells.

In this study we describe the establishment of a leukemic cell line (BNML-CL/ara-C), originating from the 1-beta-D-arabinofuranosylcytosine (ara-C)-resistant brown Norway rat myelocytic leukemia model (BNML/ara-C), that retains the in vivo generated ara-C resistance. Its biological and biochemical characteristics have been compared with a cell line, derived from the ara-C-sensitive BNML model (BNML-CL/O). Resistance to ara-C was attributed to a decrease in phosphorylation of ara-C. Deoxycytidine (dCyd) kinase activity in crude cell extracts with dCyd as substrate showed similar enzyme activities in both cell lines, whereas with ara-C as substrate no dCyd kinase activity was detectable in the ara-C-resistant cell line. Two isoenzymes of dCyd kinase with different substrate specificities have been described (Cheng, Y.C., Domin, B., and Lee, L.S. Biochim. Biophys. Acta, 481: 481-492, 1977), cytoplasmic (dCyd kinase I, substrates: dCyd and ara-C) and mitochondrial (dCyd kinase II, substrates: dCyd and thymidine). In the ara-C-sensitive BNML model, thymidine induced a reduction of dCyd kinase activity when dCyd was used as substrate. However, thymidine did not affect kinase activity with ara-C was used as substrate. In the BNML-CL/ara-C, thymidine even induces a dCyd kinase inhibition of 85% with dCyd as substrate. It is likely that the ara-C-specific dCyd kinase deficiency in BNML-CL/ara-C cells was due to a selective loss of dCyd kinase I, whereas dCyd kinase II activity remained intact.

Cell kinetics after high dose cytosine arabinoside in patients with acute myelocytic leukemia.

In this study 10 patients with acute myelocytic leukemia (AML) each received a rapid intravenous injection of high dose cytosine arabinoside (HD Ara-C; 1 g/m2). Bone marrow aspirates were obtained before and after Ara-C administration to determine the percentage of cells in S-phase measured by flow cytometry. In 5 out of 10 cases synchronization of the leukemic cells in S-phase of the cell cycle was observed. However, the time of maximum synchronization turned out to be difficult to predict. Therefore, the strong correlation between percentage of cells in S-phase at diagnosis and the time of maximal accumulation of S-phase cells after Ara-C administration, as observed by others in childhood AML, could not be confirmed for adult AML patients. Although synchronization of AML cells after in vivo Ara-C administration could be demonstrated in at least half of the patients, the practical consequences are such that clinical application was hampered.

A simplified assay for measurement of cytosine arabinoside incorporation into DNA in Ara-C-sensitive and -resistant leukemic cells.

The assays for the detection of unlabeled 1-beta-D-arabinofuranosylcytosine (cytosine arabinoside, Ara-C) incorporation into DNA was simplified. The procedure includes DNA isolation from leukemic cells, quantification of DNA concentrations, breakdown by enzymatic digestion of DNA to nucleosides and a radioimmunoassay (RIA) using an antibody against Ara-C. Different techniques for quantification of DNA concentrations are compared. A fluorimetric technique using Hoechst 33258 is preferred because it is the most specific method. Comparison of this RIA assay with measurement of [3H]-Ara-C/DNA formation under similar conditions in HL-60 cells showed a correlation of 0.99. Ara-C incorporation into DNA of leukemic cells was studied using two rat-leukemia cell lines, one of which is sensitive to Ara-C and the other is an Ara-C-resistant wild type: BNML-Cl/0 and BNML-Cl/Ara-C, respectively. The results showed that Ara-C is incorporated when the cells are incubated at concentrations equal to or higher than the Ara-C concentration that induces 50% growth inhibition after 48 h incubation (IC50). This implies that at lower Ara-C concentration, i.e. levels that do not induce cytotoxicity, Ara-C is not incorporated into DNA. Similar results were obtained with human HL-60 myeloid leukemia cells. The detection limit of this assay is 2 pmol/ml Ara-C; therefore, the assay is more sensitive than measurement of Ara-C triphosphate (Ara-CTP), the only metabolite that can be measured in leukemic cells from patients after in vivo Ara-C administration. On the basis of in vitro studies, the finding of detectable Ara-C/DNA levels in vivo is expected to correlate with cytotoxicity; whether or not the Ara-C/DNA level itself is informative remains to be evaluated.

Deoxycytidine kinase, thymidine kinase and cytidine deaminase and the formation of Ara-CTP in leukemic cells in different phases of the cell cycle.

In this study we investigated the Ara-CTP-forming capacity of leukemic cells in different phases of the cell cycle. Cells from two leukemic cell lines and leukemic bone marrow cells from patients and rats (BNML model) with acute myelocytic leukemia were separated according to cell cycle phase by means of an albumin density gradient in a specially designed sedimentation chamber. We found that the activity of CdR kinase and Cyt deaminase is much less influenced by cell-cycle phase progression than TdR kinase activity. For the leukemic cell lines HL-60 and BNML-CL/O CdR kinase activity is even independent of cell-cycle phase. In addition, Ara-CTP formation is not restricted to cells in S-phase. Cell cycle phase-independent Ara-CTP formation creates a situation in which cells which are not in S-phase during exposure to Ara-C might undergo the cytotoxic effects of Ara-C as soon as they enter S-phase.