Rationale and design of the Innsbruck Diabetic Kidney Disease Cohort (IDKDC)-a prospective study investigating etiology and progression of early-stage chronic kidney disease in type 2 diabetes.

Background: The development of chronic kidney disease (CKD) in about 20%-40% of patients with type 2 diabetes (T2D) aggravates cardiovascular morbidity and mortality. Pathophysiology is of increasing relevance for individual management and prognosis, though it is largely unknown among T2D patients with CKD as histologic work-up is not routinely performed upon typical clinical presentation. However, as clinical parameters do not appropriately reflect underlying kidney pathology, reluctance regarding timely histologic assessment in T2D patients with CKD should be critically questioned. As the etiology of CKD in T2D is heterogeneous, we aim to assess the prevalence and clinical disease course of typical diabetic vs atypical/non-specific vs non-diabetic vs coexisting kidney pathologies among T2D patients with mild-to-moderate kidney impairment [KDIGO stage G3a/A1-3 or G2/A2-3; i.e. estimated glomerular filtration rate (eGFR) 59-45 mL/min irrespective of albuminuria or eGFR 89-60 mL/min and albuminuria >30 mg/g creatinine]. Methods: The Innsbruck Diabetic Kidney Disease Cohort (IDKDC) study aims to enroll at least 65 T2D patients with mild-to-moderate kidney impairment to undergo a diagnostic kidney biopsy. Six-monthly clinical follow-ups for up to 5 years will provide clinical and laboratory data to assess cardio-renal outcomes. Blood, urine and kidney tissue specimen will be biobanked to identify diagnostic and prognostic biomarkers. Conclusions: While current risk assessment is primarily based on clinical parameters, our study will provide the scientific background for a potential change of the diagnostic standard towards routine kidney biopsy and clarify its role for individual risk prediction regarding cardio-renal outcome in T2D patients with mild-to-moderate kidney impairment.

Value and limitations of sonography in kidney transplant recipients with special attention to the resistive index - An update.

Kidney transplantation has become the standard treatment for end-stage renal disease. Even though the success rates are high, early and late post-transplant complications remain a major clinical problem due to the risk of graft failure. Therefore, it is of highest interest to early diagnose post-transplant complications. Ultrasound with color coded Duplex analysis plays a crucial role in imaging mechanical and vascular complications. In this article, we give an update of the visualizable complications in kidney transplant recipients and discuss the value of resistive index (RI) measurement with its limitations in allograft rejection.

The Tangential Extraperitoneal Retrorenal Approach in Kidney Transplant Biopsy: An Observational Study to Assess Complication and Adequacy Rates.

Introduction: Ultrasound-guided percutaneous kidney allograft biopsy is the gold-standard for pathology work-up. Recent studies postulate better safety and efficacy for tangential approaches, however, there is no recommendation regarding biopsy needle path. In this context, we previously described the unified tangential extraperitoneal retrorenal (TER) approach for standard allograft biopsy. Methods: A single-center retrospective observational study evaluated safety and efficacy of the TER biopsy approach among 250 patients that underwent 330 ultrasound-guided kidney transplant biopsies between January 2011 and May 2020. Results: The overall major complication rate was 0.56% per biopsy attempt (1.21% per biopsy) including blood transfusion, arterial embolization and bladder catheterization for gross hematuria in 0.28, 0.14 and 0.14% of biopsy attempts, respectively (0.61, 0.30 and 0.30% of biopsies, respectively). Minor complications included subcapsular and/or perinephric hematoma, superficial bleeding, arteriovenous fistula and gross hematuria in 12.6, 3.0, 2.5 and 1.4% of biopsy attempts, respectively (27.0, 6.4, 5.5 and 3.0% of biopsies, respectively). Sample adequacy rate was 86.7%, ranging from 82.2 to 94.1% if one or ≥two cores were analyzed, respectively. Residents and consultants yielded similar complication and adequacy rates. Conclusion: According to current literature, ultrasound-guided TER kidney transplant biopsy is a safe and efficient approach eligible for nephrology training.

Prophylactic Ligature of AV Fistula Prevents High Output Heart Failure after Kidney Transplantation.

BACKGROUND: Arteriovenous (AV) fistulas are considered the gold standard for ensuring safe and long-term vascular access in patients with haemodialysis-dependent end-stage renal disease. However, previous studies demonstrated that high-flow AV fistulas might add additional cardiovascular burden in the post-transplant setting, leading to frequent fistula closure in this population. Currently, there is no consensus regarding management of high-flow fistulas in post-transplant patients with stable kidney function. The present randomized controlled trial examines the effect of prophylactic AV fistula closure on high-output heart failure. METHODS: Twenty-eight kidney transplant patients with stable graft function, absence of pre-existing severe cardiac failure, and brachial arterial flow rate of at least 1,500 mL/min were recruited and randomized in a 1:1 ratio to an intervention and control group, respectively. The intervention group was subject to immediate fistula ligature. Patients within the control group were referred to fistula ligature only if the main study endpoint high-output heart failure was reached. The latter was defined by the presence of at least 1 clinical sign (i.e., worsening NYHA score) and at least 2 of the following echocardiographic parameters: diameter of right atrium (major) >53 mm, right atrium (minor) >44 mm, inferior vena cava ≥21 mm, right pulmonary artery >20 mm, TAPSE <16 mm, systolic pulmonal artery pressure >40 mm Hg, and/or left ventricular eccentricity index <1. During a 24-month follow-up period, quarterly measurements of kidney function, NT-proBNP, and lactate dehydrogenase as well as a biannual echocardiographic check-up were performed. RESULTS: High-output heart failure attributable to high-flow fistula was reported in 5 of 13 control patients (38.5%), whereas no patient in the intervention group presented with clinical and echocardiographic signs of high-output heart failure during the follow-up period. Thus, prophylactic ligature of high-flow fistulas avoided high-output heart failure in our patient population (p = 0.013). Three patients in the control group, however, had to undergo fistula ligature due to aneurysm formation (n = 2) and steal phenomenon (n = 1). Median NT-proBNP levels decreased from 317 ng/L pre-ligature to 223 ng/L post-ligature (p = 0.003). Serum creatinine levels did not significantly differ before and after AV fistula ligature (1.69 vs. 1.60 mg/dL, respectively, p = 0.059). Improvement of echocardiographic findings (e.g., a decrease in systolic pulmonary arterial pressure) was found in 7 of 8 ligature patients but did not reach statistical significance. CONCLUSION: Prophylactic ligature of high-flow AV fistulas after kidney transplantation can avoid high-output heart failure, and a more liberal approach to close AV fistulas might be justified.

Acute kidney injury is associated with microvascular myocardial damage following myocardial infarction.

Acute kidney injury (AKI) is a frequent complication in patients with ST-elevation myocardial infarction (STEMI) treated by primary percutaneous coronary intervention. However, the pathophysiology of AKI in this setting is complex and goes beyond the administration of contrast media. Studies assessing the impact of infarct characteristics on AKI are currently lacking. Therefore, we investigated the association of AKI with myocardial as well as microvascular injury in an initial total of 361 consecutive STEMI patients treated by primary percutaneous coronary intervention. Of these, 318 patients were included in final analysis. Serum creatinine was measured on admission as well as 24, 48, and 72 hours thereafter with AKI defined as an increase in serum creatinine of 0.3 mg/dl or more. Cardiac magnetic resonance (CMR) scans were performed in the first week after infarction, with microvascular injury visualized by late gadolinium enhancement CMR defined as any region of hypoenhancement within the hyperenhanced area of infarction. Sixteen patients developed AKI. They showed significantly lower left ventricular ejection fraction (45[interquartile range 40-52]% vs. 54[47-59]%), larger infarct size (21[15-35]% vs. 12[7-22]%) of left ventricular myocardial mass, and more frequent microvascular injury (81 vs. 46%) than those free of AKI. Meaningfully, in multivariate analysis including all CMR data, microvascular injury was the sole independent predictor of AKI (odds ratio 6.74, 95% confidence interval of 1.49-30.43). Thus, among revascularized STEMI patients, the presence of microvascular injury assessed by CMR was independently associated with an increased risk of AKI. This suggests a potential pathophysiological link between cardiac microvascular disease and renal injury following STEMI.

Akacid medical formulation induces apoptosis in myeloid and lymphatic leukemic cell lines in vitro and in vivo.

Akacid medical formulation (AMF) is an oligoguanidine that exerts biocidal activity against airborne and surface microorganisms including bacteria, viruses, fungi, and molds, while showing relatively low toxicity to humans. We have previously shown that AMF exerts antiproliferative effects on a variety of solid tumor cell lines. In this study we raised the question whether AMF could also substantially inhibit cell growth or induce apoptosis in cell lines derived from hematologic malignancies such as leukemia or lymphoma. We found that AMF has antiproliferative effects on various hematologic cell lines derived from human leukemia and lymphoma. Additionally, we show that AMF induces apoptosis in leukemia cell lines not only via the extrinsic and intrinsic pathway, but also in a caspase-independent manner. This effect was found also in G0-arrested cells. Finally, in our animal experiments utilizing male nu/nu Balb/c mice we found a significant growth retardation, which was immunohistochemically associated with a significantly lower number of KI67-positive cells and caspase-3 induction in AMF-treated mice.

Incidence of arteriovenous fistula closure due to high-output cardiac failure in kidney-transplanted patients.

BACKGROUND: Some hemodialysis patients develop arteriovenous (AV) fistulas with high flows. This volume overload can result in high-output cardiac failure. To date, predisposing access flow rates are unknown. METHODS: A retrospective study of all kidney-transplant recipients at the Medical University of Innsbruck (MUI) from 2005 to 2010 included 797 patients with the following criteria: previous hemodialysis with a native AV fistula or a graft, sufficient function of the kidney transplant up to the time of the data analysis, and follow-up care at the MUI. RESULTS: Twenty-nine of the 113 patients (25.7%) needed an AV fistula closure, mostly because of symptoms of cardiac failure. The mean shunt flow in the intervention group was 2197.2 mL/min, whereas the mean shunt flow in the non-intervention group was only 850.9 mL/min. Shunt closures were most frequently made in patients with upper-arm shunts (41.7%). CONCLUSION: The necessity of shunt closure is not a rarity. Patients who underwent an AV fistula ligature had high access flows with about 2200 mL/min. As the symptoms of cardiac failure greatly improved after shunt closure, patients with high access flow may benefit from such an intervention.

First observation of a potential non-invasive breath gas biomarker for kidney function.

We report on the search for low molecular weight molecules-possibly accumulated in the bloodstream and body-in the exhaled breath of uremic patients with kidney malfunction. We performed non-invasive analysis of the breath gas of 96 patients shortly before and several times after kidney transplantation using proton-transfer-reaction mass spectrometry (PTR-MS), a very sensitive technique for detecting trace amounts of volatile organic compounds. A total of 642 individual breath analyses which included at least 41 different chemical components were carried out. Correlation analysis revealed one particular breath component with a molecular mass of 114 u (unified atomic mass units) that clearly correlated with blood serum creatinine, which is the currently accepted marker for assessing the function of the kidney. In particular, daily urine production showed good correlation with the identified breath marker. An independent set of seven samples taken from three patients at the onset of dialysis and three controls with normal kidney function confirmed a significant difference in concentration between patients and controls for a compound with a molecular mass of 114.1035 u using high mass resolving proton-transfer-reaction time-of-flight mass spectrometry (PTR-TOF-MS). A chemical composition of C7H14O was derived for the respective component. Fragmentation experiments on the same samples using proton-transfer-reaction triple-quadrupole tandem mass spectrometry (PTR-QqQ-MS) suggested that this breath marker is a C7-ketone or a branched C7-aldehyde. Non-invasive real-time monitoring of the kidney function via this breath marker could be a possible future procedure in the clinical setting.

A rare case of milky urine.

Chyluria is an uncommon condition characterized by lymphatic fluid excretion into the urinary tract. Most common causes of chyluria are infections by parasites e.g. filariasis, echinococcosis, or cysticercosis. Nonparasitic chyluria is a very rare condition and possible etiologies include granulomatous disease (e.g. tuberculosis, leprosy, and fungal infection), malignomes, inherited and acquired malformation (posttraumatic), pregnancy, or aortic aneurysm. We present a case of a 73-year-old man, born and raised in Taiwan, but living in Austria for the past 5 years. He was admitted in our department by a general practitioner due to milky urine, whose turbidity increased after meal. All tests for infectious diseases or other above-mentioned causes remained negative. Additionally, although flexible cystoscopy yielded in a clear diagnosis of a milky urine jet out of the right urether, CT urography and bipedal lymphangiography failed to locate the lymphorenal fistula. Due to a stable renal function and absence of lipid metabolism disorders, a conservative management of the patient was chosen.

Effect of dialysate temperature and diabetes on autonomic cardiovascular regulation during hemodialysis.

BACKGROUND/AIMS: Lowering dialysate temperature to increase intradialytic hemodynamic stability may interfere with the ultrafiltration-dependent intradialytic autonomic cardiovascular regulation. The present study aimed to investigate hemodynamic and autonomic responses depending on dialysate temperature and the presence of diabetes. METHODS: Seventeen (8 diabetic, 9 non-diabetic) hypotension-resistant patients were alternately treated at dialysate temperatures of 37 and 35 degrees C. Hemodynamic parameters, heart rate variability (HRV) and baroreceptor reflex sensitivity (BRRS) were measured noninvasively. Power spectral analysis of HRV was used to evaluate cardiac sympathetic and parasympathetic activity. RESULTS: In contrast to diabetic patients who showed an overall reduced autonomic activity and a blunted autonomic response, in non-diabetic patients cardiac sympathetic activity increased during dialysis (p < 0.05) resulting in a shift in sympathovagal balance towards sympathetic predominance. This response was not altered by dialysate temperature. Significant decreases in stroke volume and cardiac output were found in both patient groups. Total peripheral resistance increased in diabetic (p < 0.05) and in non-diabetic patients (p < 0.01) at both dialysate temperatures. No differences in BRRS were determined. CONCLUSION: The presence of diabetes has great impact on the cardiovascular autonomic regulation during hemodialysis. Varying the dialysate temperature does not influence cardiovascular autonomic regulation in hemodynamically stable diabetic and non-diabetic patients.

Sphingosine-1-phosphate receptor type-1 agonism impairs blood dendritic cell chemotaxis and skin dendritic cell migration to lymph nodes under inflammatory conditions.

SEW2871 is a potent sphingosine-1-phosphate receptor type-1 (S1P(1))-selective agonist that induces peripheral lymphopenia through sequestration of lymphocytes into secondary lymphoid organs, similar to the non-selective sphingosine-1-phosphate (S1P) receptor agonist FTY720. FTY720 has been reported to interfere with human dendritic cell (DC) effector functions and both FTY720 and SEW2871 have been shown to modulate murine DC trafficking in vivo. Little is known about the possible effects of SEW2871 on human and murine DC functions. Here, we demonstrate that in contrast to FTY720, SEW2871 does not induce down-regulation of S1P(1) in human DCs and thus does not exert a functional antagonism at S1P(1). Notably, the compound was found to impair chemotaxis of immature and mature human DCs in vitro, possibly by interfering with the activation of p44/p42 and p38 mitogen-activated protein kinase signaling pathways. Comparative FACS analyses show that SEW2871 mediates CD18 down-regulation on mature human DCs. The influence on DC migration could be confirmed with in vivo assays using BALB/c mice in which SEW2871 impairs the migration of CD11c+ DC and CD207+ Langerhans cells (LC) to the draining lymph nodes (LNs) under inflammatory conditions. These results suggest that the S1P-S1P(1) axis might not only control lymphocyte trafficking but also play a pivotal role in DC migration from the skin to LN.

Akacid-medical-formulation, a novel biocidal oligoguanidine with antitumor activity reduces S-phase in prostate cancer cell lines through the Erk 1/2 mitogen-activated protein kinase pathway.

Oligomeric guanidines are highly efficient biocides against a broad spectrum of microorganisms. However, their antitumor effects have not been studied so far. We investigated an antiproliferative effect of Akacid-medical-formulation (AMF), a member of the oligoguanidine family of biocides, against solid cancer cell lines and primary cells by measuring [3H]-thymidine incorporation. Additionally, we examined cell cycle distribution in two AMF-sensitive prostate cancer cell lines (DU-145, LNCaP) using flow cytometry. Finally, the influence of AMF on cell cycle regulatory molecules and intracellular kinase cascade-related signaling molecules was assessed. We found that AMF has variable antiproliferative effects on all tested cells. In DU-145 and LNCaP cells, flow cytometric studies showed a reduction of S-phase with a maximum extent of 24 and 58%, respectively. This was associated with a decrease in expression of cyclin D1, cyclin-dependent kinases 2 and 4, while having varying effects on expression of cyclin E and p27. Additionally, reduced phosphorylation of Erk1 and Erk2 was found, whereas expression of phospho-Akt1 remained unchanged. Herein we report for the first time that AMF exerts potent antiproliferative activity against various malignant cell lines, including those of prostate. We therefore recommend further investigation of the anticancer activity of this biocidal oliguanidine.

Oxindole alkaloids from Uncaria tomentosa induce apoptosis in proliferating, G0/G1-arrested and bcl-2-expressing acute lymphoblastic leukaemia cells.

Natural products are still an untapped source of promising lead compounds for the generation of antineoplastic drugs. Here, we investigated for the first time the antiproliferative and apoptotic effects of highly purified oxindole alkaloids, namely isopteropodine (A1), pteropodine (A2), isomitraphylline (A3), uncarine F (A4) and mitraphylline (A5) obtained from Uncaria tomentosa, a South American Rubiaceae, on human lymphoblastic leukaemia T cells (CCRF-CEM-C7H2). Four of the five tested alkaloids inhibited proliferation of acute lymphoblastic leukaemia cells. Furthermore, the antiproliferative effect of the most potent alkaloids pteropodine (A2) and uncarine F (A4) correlated with induction of apoptosis. After 48 h, 100 micromol/l A2 or A4 increased apoptotic cells by 57%. CEM-C7H2 sublines with tetracycline-regulated expression of bcl-2, p16ink4A or constitutively expressing the cowpox virus protein crm-A were used for further studies of the apoptosis-inducing properties of these alkaloids. Neither overexpression of bcl-2 or crm-A nor cell-cycle arrest in G0/G1 phase by tetracycline-regulated expression of p16INK4A could prevent alkaloid-induced apoptosis. Our results show the strong apoptotic effects of pteropodine and uncarine F on acute leukaemic lymphoblasts and recommend the alkaloids for further studies in xenograft models.

The immunomodulator FTY720 interferes with effector functions of human monocyte-derived dendritic cells.

The potent immunomodulator FTY720 elicits immunosuppression via acting on sphingosine 1-phosphate receptors (S1PR), thereby leading to an entrapment of lymphocytes in the secondary lymphoid tissue. To elucidate the potential in vitro effects of this drug on human monocyte-derived DC, we used low nanomolar therapeutic concentrations of FTY720 and phosphorylated FTY720 (FTY720-P) and investigated their influence on DC surface marker expression, protein levels of S1PR and DC effector functions: antigen uptake, chemotaxis, cytokine production, allostimulatory and Th-priming capacity. We report that both FTY720 and FTY720-P reduce chemotaxis of immature and mature DC. Mature DC generated in the presence of FTY720 or FTY720-P showed an impaired immunostimmulatory capacity and reduced IL-12 but increased IL-10 production. T cells cultured in the presence of FTY720- or FTY720-P-treated DC showed an altered cytokine production profile indicating a shift from Th1 toward Th2 differentiation. In treated immature and mature DC, expression levels for two S1PR proteins, S1P1 and S1P4, were reduced. We conclude that in vitro treatment with FTY720 affects DC features that are essential for serving their role as antigen-presenting cells. This might represent a new aspect of the overall immunosuppressive action of FTY720 and makes DC potential targets of further sphingolipid-derived drugs.

In vitro treatment of dendritic cells with tacrolimus: impaired T-cell activation and IP-10 expression.

BACKGROUND: High doses (10(-6)-10(-8) M) of tacrolimus (FK506) were reported to induce a type-2 T-helper cell (Th2)-promoting function in developing dendritic cells (DC). We used a therapeutic dose (2.4 x 10(-9 )M) of tacrolimus to investigate its effect on human monocyte-derived DC. METHODS: Using untreated and treated immature and mature DC we compared T cell-activating capacity, surface marker expression, T cell and DC cytokine profile and transcription of genes coding for a panel of DC function-related molecules. RESULTS: Tacrolimus-treated mature DC had reduced T-cell stimulatory capacity. Although interleukin (IL)-12 production of DC was impaired, they did not promote Th2 development as T cells activated by tacrolimus-treated DC produced less interferon (IFN)-gamma, IL-4 and IL-10. The up-regulation of the T-cell activation marker CD69 and the production of IL-2 were impaired. In addition, tacrolimus-treated DC produced less IP-10 (CXCL10), which is known to be involved in allograft rejection. Other molecules related to DC function remained unchanged. CONCLUSIONS: Tacrolimus treatment reduces the ability of DC to stimulate T cells and the impaired production of DC-derived IP-10 (CXCL10) and IL-12 might play a role in the immunosuppressive action of tacrolimus.

Delayed addition of deoxycytidine protects normal CD34+ cells against cytotoxicity of gemcitabine without compromising its activity against human leukemic cells.

In phase I and II clinical trials, the deoxycytidine analogue 2',2' difluorodeoxycytidine (dFdC, gemcitabine) has shown promising antitumor activity in leukemia as well as in solid tumors. Preclinical and clinical studies of gemcitabine suggested that myelosuppression was the dose-limiting toxicity. The present investigations were designed to test the effect of continuously administered gemcitabine on the in vitro clonal growth of normal CD34(+) cells isolated from peripheral blood and the promyelocytic cell line, HL-60. For this purpose, CD34(+) and HL-60 cells were cultured in methylcellulose in the continuous presence of 0.1-16 nM of gemcitabine. The results show a dose-dependent inhibition of colony growth of normal as well as leukemic cells. However, HL-60 cells were up to 12-fold more sensitive towards gemcitabine than normal progenitors. For rescue experiments, the natural pyrimidine deoxycytidine (dCyd) was added to CD34(+) and HL-60 cells simultaneously or with delay. Coadministration of 1mM dCyd to separate cultures resulted in complete restoration of colony formation capacity of CD34(+) and HL-60 cells. Delayed addition of 1 mM dCyd after 48 and 72 hours recovered up to 90% and 40%, respectively, of stem cell proliferation, whereas HL-60 cells remained substantially inhibited (4.5% +/- 3.5% versus 0%). Delayed addition after 48 and 72 hours protected about 80% and 50%, respectively, of myelopoietic and erythropoetic colony formation, whereas colony formation obtained from HL-60 cells remained significantly inhibited (9.6% +/- 4.17% versus 0%). These in vitro data suggest that there is a marked difference in the susceptibility of leukemic and normal CD34(+) cells to gemcitabine and that delayed administration of dCyd may further reduce the bone marrow cytotoxicity of gemcitabine without impairing its antitumor effect.

In vitro studies on the immunosuppressive effect of 2',2'-difluorodeoxycytidine (dFdC) and its metabolite 2',2'-difluorodeoxyuridine (dFdU).

The effect of 2',2'-difluorodeoxycytidine (dFdC) on in vitro human lymphocyte response was assessed in comparison with that of its major metabolite 2',2'-difluorodeoxyuridine (dFdU). Peripheral blood mononuclear cells (PBMNC) from healthy human volunteers were used for assay of mixed lymphocyte reaction (MLR), blastogenesis and colony forming by PHA. Both substances inhibited mitogen and alloantigen responses of PBMNC in a dose-dependent manner, but dFdU was up to 10,000-fold less potent than its parent compound dFdC. The data indicate that activation by alloantigen is more sensitive to the action of dFdU and dFdC than the response to PHA. Thus, dFdU inhibits MLR-induced response at significantly lower doses than PHA-induced proliferation (IC50 +/- SD, 23.55 +/- 8 microM versus 133.2 +/- 12 microM) (p = 0.0003). dFdC also proved to be about 12.3-fold more potent against alloantigen response compared to PHA-induced proliferation of PBMNC (IC50 +/- SD, 2.28 +/- 0.5 nM versus 28.1 +/- 0.5 nM) (p = 0.0001). To get an insight into the toxic profile of dFdU and dFdC, both substances were additionally tested on the in vitro clonal growth of CD34+ cells. Cells were cultured in methylcellulose in the continuous presence of dFdU and dFdC in doses up to 640 microM and 16 nM, respectively. The results show a marked inhibition of erythroid (BFU-E) and myeloid progenitors (CFU-GM) in a dose-dependent manner, but BFU-E was more sensitive to the action of dFdU and dFdC than CFU-GM (p=0.0001). Compared to T-lymphocytes, however, similar or even higher doses of dFdU and dFdC were required for complete inhibition of colony formation obtained from CD34+ cells. To test the role of deoxycytidine kinase (dCK) in the metabolism of dFdU in comparison to that of dFdC, reversal studies with deoxycytidine (dCyd), the natural substrate of dCK, were performed on dFdU- and dFdC-treated HL-60 cells. The data show that relatively low concentrations of dCyd (10 microM) were sufficient to protect HL-60 cells from cytotoxicity of lethal doses of dFdU (160 microM), whereas 100-fold higher concentrations of deoxycytidine (dCyd) (1 mM) were required for a complete reversal of dFdC-mediated toxicity. This suggests that activation of dFdU is due to its phosphorylation by dCK, but dFdU has low affinity to dCK. These effects of dFdU and dFdC in relation to T-lymphocytes and CD34+ cells suggest their possible use as immunosuppressive agents.