Azathioprine and 6-mercaptopurine alter the nucleotide balance in endothelial cells

Kidney Transplant Recipients Show Limited Lung Diffusion Capacity but Similar Hydrogen Peroxide Exhalation as Healthy Matched Volunteers: A Pilot Study

Patients with end-stage chronic kidney disease show higher systemic oxidative stress and exhale more hydrogen peroxide (H2O2) than healthy controls. Kidney transplantation reduces oxidative stress and H2O2 production by blood polymorphonuclear leukocytes (PMNs). Kidney transplant recipients (KTRs) may be predisposed to an impairment of lung diffusing capacity due to chronic inflammation. Lung function and H2O2 concentration in the exhaled breath condensate (EBC) were compared in 20 KTRs with stable allograft function to 20 healthy matched controls. Serum interleukin eight (IL-8) and C-reactive protein (CRP), blood cell counts, and spirometry parameters did not differ between groups. However, KTRs showed lower total lung diffusing capacity for carbon monoxide, corrected for hemoglobin concentration (TLCOc), in comparison to healthy controls (92.1 ± 11.5% vs. 102.3 ± 11.9% of predicted, p = 0.009), but similar EBC H2O2 concentration (1.63 ± 0.52 vs. 1.77 ± 0.50 µmol/L, p = 0.30). The modality of pre-transplant renal replacement therapy had no effect on TLCOc and EBC H2O2. TLCOc did not correlate with time after transplantation. In this study, TLCOc was less reduced in KTRs in comparison to previous reports. We suggest this fact and the non-elevated H2O2 exhalation exhibited by KTRs, may result perhaps from the evolution of the immunosuppressive therapy.

Immunosuppressive Agents-Effects on the Cardiovascular System and Selected Metabolic Aspects: A Review

The widespread use of immunosuppressive drugs makes it possible to reduce inflammation in autoimmune diseases, as well as prevent transplant rejection in organ recipients. Despite their key action in blocking the body's immune response, these drugs have many side effects. These actions primarily affect the cardiovascular system, and the incidence of complications in patients using immunosuppressive drugs is significant, being associated with a higher incidence of cardiovascular incidents such as myocardial infarction and stroke. This paper analyzes the mechanisms of action of commonly used immunosuppressive drugs and their impact on the cardiovascular system. The adverse effect of immunosuppressive drugs is associated with toxicity within the cardiovascular system, which may be a problem in the clinical management of patients after transplantation. Immunosuppressants act on the cardiovascular system in a variety of ways, including fibrosis and myocardial remodeling, endothelium disfunction, hypertension, atherosclerosis, dyslipidemia or hyperglycaemia, metabolic syndrome, and hyperuricemia. The use of multidrug protocols makes it possible to develop regimens that can reduce the incidence of cardiovascular events. A better understanding of their mechanism of action and the range of complications could enable physicians to select the appropriate therapy for a given patient, as well as to reduce complications and prolong life.

Cardiovascular effects of immunosuppression agents

Immunosuppressive medications are widely used to treat patients with neoplasms, autoimmune conditions and solid organ transplants. Key drug classes, namely calcineurin inhibitors, mammalian target of rapamycin (mTOR) inhibitors, and purine synthesis inhibitors, have direct effects on the structure and function of the heart and vascular system. In the heart, immunosuppressive agents modulate cardiac hypertrophy, mitochondrial function, and arrhythmia risk, while in vasculature, they influence vessel remodeling, circulating lipids, and blood pressure. The aim of this review is to present the preclinical and clinical literature examining the cardiovascular effects of immunosuppressive agents, with a specific focus on cyclosporine, tacrolimus, sirolimus, everolimus, mycophenolate, and azathioprine.

Prevention of progression of pulmonary hypertension by the Nur77 agonist 6-mercaptopurine: role of BMP signalling

Pulmonary arterial hypertension (PAH) is a progressive fatal disease characterised by abnormal remodelling of pulmonary vessels, leading to increased vascular resistance and right ventricle failure. This abnormal vascular remodelling is associated with endothelial cell dysfunction, increased proliferation of smooth muscle cells, inflammation and impaired bone morphogenetic protein (BMP) signalling. Orphan nuclear receptor Nur77 is a key regulator of proliferation and inflammation in vascular cells, but its role in impaired BMP signalling and vascular remodelling in PAH is unknown.

We hypothesised that activation of Nur77 by 6-mercaptopurine (6-MP) would improve PAH by inhibiting endothelial cell dysfunction and vascular remodelling.

Nur77 expression is decreased in cultured pulmonary microvascular endothelial cells (MVECs) and lungs of PAH patients. Nur77 significantly increased BMP signalling and strongly decreased proliferation and inflammation in MVECs. In addition, conditioned medium from PAH MVECs overexpressing Nur77 inhibited the growth of healthy smooth muscle cells. Pharmacological activation of Nur77 by 6-MP markedly restored MVEC function by normalising proliferation, inflammation and BMP signalling. Finally, 6-MP prevented and reversed abnormal vascular remodelling and right ventricle hypertrophy in the Sugen/hypoxia rat model of severe angioproliferative PAH.

Our data demonstrate that Nur77 is a critical modulator in PAH by inhibiting vascular remodelling and increasing BMP signalling, and activation of Nur77 could be a promising option for the treatment of PAH.

Endothelial dysfunction in patients with eosinophilic granulomatosis with polyangiitis

Eosinophilic granulomatosis with polyangiitis (EGPA) is a rare form of vasculitis associated with asthma and eosinophilia. Endothelial dysfunction has been well documented in other types of vasculitis but not in EGPA. Thirty patients (10 men and 20 women) diagnosed with EGPA and remaining in a remission, and 58 controls (24 men and 34 women) matched for age, sex, and body mass index, were enrolled in the study. We assessed each participants for typical risk factors of cardiovascular diseases and measured serum levels of vascular cell adhesion molecule-1 (VCAM-1), interleukin 6 (IL-6), and thrombomodulin. We also measured flow-mediated dilatation (FMD) of the brachial artery and intima-media thickness (IMT) of the common carotid artery using ultrasonography. Patients with EGPA had 20% higher serum level of VCAM-1 (p < 0.001) and 41.9% of thrombomodulin (p < 0.001). They also had 38.8% lower relative increase of FMD (FMD%) (p < 0.001), indicating endothelial dysfunction. These differences remained significant also after adjustment for potential confounders. Laboratory and ultrasonographic parameters of endothelial injury were correlated to the markers of inflammation and impaired kidney function. Determinants of lower FMD% in a simple regression model were pack-years of smoking (β = - 0.3 [95% confidence interval (CI) - 0.5 to - 0.1]), serum level of IL-6 (β = - 0.36 [95% CI - 0.62 to - 0.1]), and thrombomodulin (β = - 0.34 [95% CI - 0.6 to - 0.08]). EGPA patients are characterized by inflammatory endothelial injury that is likely related to the pathogenesis of the disease. Proper immunosuppressive treatment is the best method to prevent atherosclerosis and future cardiovascular events, the patients may also benefit from additional preventive interventions.

Endothelial dysfunction in patients with granulomatosis with polyangiitis: a case-control study

Background

Granulomatosis with polyangiitis (GPA) is a rare granulomatous vasculitis affecting small- and medium-sized blood vessels. In optimally treated patients with long-standing disease, the common cause of death is atherosclerosis even in the absence of typical risk factors.

Objective

To evaluate endothelial dysfunction in GPA patients.

Methods

44 patients (21 men and 23 women) diagnosed with GPA and 53 controls matched for age, sex, BMI and typical risk factors for cardiovascular diseases (22 men and 31 women) were enrolled in the study. We measured each participant’s serum levels of vascular cell adhesion molecule-1 (VCAM-1), interleukin 6 (IL-6), and thrombomodulin. We also studied flow-mediated dilatation (FMD) of the brachial artery, intima-media thickness (IMT) of the common carotid artery and aortic stiffness using echocardiography.

Results

Patients with GPA showed a 15.9% increase in serum levels of VCAM-1 (p = 0.01), 66% of IL-6 (p < 0.001) and 50.9% of thrombomodulin (p < 0.001) compared to controls. FMD% was 48.9% lower in patients with GPA in comparison to controls (p < 0.001), after adjustment for potential confounders, with no differences regarding IMT or aortic stiffness. FMD% was negatively associated with duration of the disease (β = − 0.18 [95% CI: − 0.32 to − 0.04]), C-reactive protein (β = − 0.17 [95% CI: − 0.27 to − 0.07]), IL-6 (β = − 0.29 [95% CI: − 0.39 to − 0.19]), blood creatinine level (β = − 0.2 [95% CI: − 0.3 to − 0.1]), and IMT (β = − 0.14 (− 0.24 to − 0.04). In a multiple linear regression model, kidney function, IMT, pack-years of smoking, diabetes and level of VCAM-1 were independent predictors of lower FMD%.

Conclusion

GPA is characterized by endothelial dysfunction. FMD is a useful tool for the detection of endothelial injury.

Electronic supplementary material

The online version of this article (10.1007/s00296-018-4061-x) contains supplementary material, which is available to authorized users.

Veno-occlusive disease/sinusoidal obstruction syndrome associated with potential antibody-mediated rejection after pediatric living donor liver transplantation: a case report

A 9-month-old girl with biliary atresia underwent successful living donor liver transplantation from her 42-year-old ABO blood-type incompatible mother. The postoperative course was uneventful until postoperative day (POD) 13 when the recipient displayed an increased volume of drained ascites and decreased her platelet count showing low-velocity portal venous inflow without hepatic venous outflow obstruction. We suspected potential veno-occlusive disease/sinusoidal obstruction syndrome (vod/sos) due to an acute cellular rejection (ACR) episode and performed a liver biopsy (LB). We diagnosed severe episode (Rejection Activity Index Score; P3V3B1 = 7) and started steroid pulse therapy. We performed a second LB on POD 27 because the patient showed weight gain and tender hepatomegaly, diagnosing moderate ACR (P1V3B1 = 5). We started a second course of steroid pulse therapy, but the patient's clinical findings did not improve. On POD 43, her third LB finding showed P1V1B1 with improved processes from ACR, but still displaying severe congestion and fibrotic obliteration of small hepatic veins. We suspected that her immunologic responses were associated with antibody-mediated rejection (AMR) because her anti-HLA class I and class II antibodies were positive by flow panel-reactive antibody method and donor-specific antigen class II and C4d staining were also positive. We added mycophenolate mofetil and administered high-dose intravenous immunoglobulin to control the AMR, and anticoagulant therapy for the VOD/SOS. Her clinical findings and graft venous abnormalities finally improved; she was eventually discharged without sequelae on POD 72.

Accumulation of VEGFR-2+/CD133+ cells and decreased number and impaired functionality of CD34+/VEGFR-2+ cells in patients with SLE

OBJECTIVE

Inflammation and atherosclerosis are the major causes of cardiovascular disease (CVD) in SLE. Both traditional and disease-specific risk factors contribute to the formation of endothelial dysfunction. Endothelial progenitor cells (EPCs) have the ability to restore endothelial integrity. The aim of this study was to determine whether the number and function of EPCs are altered in SLE.

METHODS

Nineteen patients with SLE and 19 controls were analysed. VEGF receptor-2 (VEGFR-2)(+)/CD133(+) and CD34(+)/VEGFR-2(+) cells were quantified by flow cytometry. EPC differentiation was measured by DiI-acLDL/Lectin I staining. Furthermore, apoptosis, proliferation capacity, migration capacity and clonogenic ability of EPCs were determined.

RESULTS

VEGFR-2(+)/CD133(+) cells were enhanced in SLE [215 (37) vs 122 (11) cells/1 x 10(6) lymphocytes; P = 0.029], whereas the number [106 (13) vs 215 (27) cells/1 x 10(6) lymphocytes; P = 0.002] and the proliferation rate [96% (6%) vs 143% (19%); P = 0.008] of CD34(+)/VEGFR-2(+) cells were decreased compared with controls. Additionally, EPCs in SLE showed an increased apoptosis [7% (1.4%) vs 3% (0.4%); P = 0.004], an impaired differentiation [36 (5) vs 121 (20) cells/mm(2); P < 0.001] and a reduced migratory capacity [116% (4%) vs 139% (4%); P = 0.001].

CONCLUSIONS

Our results suggest that the mobilization of progenitor cells is unaffected in SLE, but the diminished number and the altered functionality of circulating CD34(+)/VEGFR-2(+) cells reduce the ability to repair vascular damage and thus may trigger the development of atherosclerosis in SLE.

6-mercaptopurine inhibits atherosclerosis in apolipoprotein e*3-leiden transgenic mice through atheroprotective actions on monocytes and macrophages

OBJECTIVE

6-Mercaptopurine (6-MP), the active metabolite of the immunosuppressive prodrug azathioprine, is commonly used in autoimmune diseases and transplant recipients, who are at high risk for cardiovascular disease. Here, we aimed to gain knowledge on the action of 6-MP in atherosclerosis, with a focus on monocytes and macrophages.

METHODS AND RESULTS

We demonstrate that 6-MP induces apoptosis of THP-1 monocytes, involving decreased expression of the intrinsic antiapoptotic factors B-cell CLL/Lymphoma-2 (Bcl-2) and Bcl2-like 1 (Bcl-x(L)). In addition, we show that 6-MP decreases expression of the monocyte adhesion molecules platelet endothelial adhesion molecule-1 (PECAM-1) and very late antigen-4 (VLA-4) and inhibits monocyte adhesion. Screening of a panel of cytokines relevant to atherosclerosis revealed that 6-MP robustly inhibits monocyte chemoattractant chemokine-1 (MCP-1) expression in macrophages stimulated with lipopolysaccharide (LPS). Finally, local delivery of 6-MP to the vessel wall, using a drug-eluting cuff, attenuates atherosclerosis in hypercholesterolemic apolipoprotein E*3-Leiden transgenic mice (P<0.05). In line with our in vitro data, this inhibition of atherosclerosis by 6-MP was accompanied with decreased lesion monocyte chemoattractant chemokine-1 levels, enhanced vascular apoptosis, and reduced macrophage content.

CONCLUSIONS

We report novel, previously unrecognized atheroprotective actions of 6-MP in cultured monocytes/macrophages and in a mouse model of atherosclerosis, providing further insight into the effect of the immunosuppressive drug azathioprine in atherosclerosis.

Premature atherosclerosis in pediatric systemic lupus erythematosus: risk factors for increased carotid intima-media thickness in the atherosclerosis prevention in pediatric lupus erythematosus cohort

OBJECTIVE

To evaluate risk factors for subclinical atherosclerosis in a population of patients with pediatric systemic lupus erythematosus (SLE).

METHODS

In a prospective multicenter study, a cohort of 221 patients underwent baseline measurements of carotid intima-media thickness (CIMT) as part of the Atherosclerosis Prevention in Pediatric Lupus Erythematosus (APPLE) trial. SLE disease measures, medications, and traditional risk factors for atherosclerosis were assessed. A standardized protocol was used to assess the thickness of the bilateral common carotid arteries and the mean maximal IMT of 12 segments. Univariable analysis identified potential associations with CIMT, which were examined in multivariable linear regression modeling.

RESULTS

Based on the mean-mean common or the mean-max CIMT as the dependent variable, univariable analysis showed significant associations of the following variables with increased CIMT: increasing age, longer SLE duration, minority status, higher body mass index (BMI), male sex, increased creatinine clearance, higher lipoprotein(a) level, proteinuria, azathioprine treatment, and prednisone dose. In multivariable modeling, both azathioprine use (P=0.005 for the mean-mean model and P=0.102 for the mean-max model) and male sex (P<0.001) were associated with increases in the mean-max CIMT. A moderate dosage of prednisone (0.15-0.4 mg/kg/day) was associated with decreases in the mean-max CIMT (P=0.024), while high-dose and low-dose prednisone were associated with increases in the mean-mean common CIMT (P=0.021) and the mean-max CIMT (P=0.064), respectively. BMI (P<0.001) and creatinine clearance (P=0.031) remained associated with increased mean-mean common CIMT, while increasing age (P<0.001) and increasing lipoprotein(a) level (P=0.005) were associated with increased mean-max CIMT.

CONCLUSION

Traditional as well as nontraditional risk factors were associated with increased CIMT in this cohort of patients in the APPLE trial. Azathioprine treatment was associated with increased CIMT. The relationship between CIMT and prednisone dose may not be linear.

Preferential inhibition of xanthine oxidase by 2-amino-6-hydroxy-8-mercaptopurine and 2-amino-6-purine thiol

Background

The anticancer drug, 6-mercaptopurine (6MP) is subjected to metabolic clearance through xanthine oxidase (XOD) mediated hydroxylation, producing 6-thiouric acid (6TUA), which is excreted in urine. This reduces the effective amount of drug available for therapeutic efficacy. Co-administration of allopurinol, a suicide inhibitor of XOD, which blocks the hydroxylation of 6MP inadvertently enhances the 6MP blood level, counters this reduction. However, allopurinol also blocks the hydroxylation of hypoxanthine, xanthine (released from dead cancer cells) leading to their accumulation in the body causing biochemical complications such as xanthine nephropathy. This necessitates the use of a preferential XOD inhibitor that selectively inhibits 6MP transformation, but leaves xanthine metabolism unaffected.

Results

Here, we have characterized two such unique inhibitors namely, 2-amino-6-hydroxy-8-mercaptopurine (AHMP) and 2-amino-6-purinethiol (APT) on the basis of IC₅₀ values, residual activity in bi-substrate simulative reaction and the kinetic parameters like K_m, K_i, k_cat. The IC₅₀ values of AHMP for xanthine and 6MP as substrate are 17.71 ± 0.29 μM and 0.54 ± 0.01 μM, respectively and the IC₅₀ values of APT for xanthine and 6MP as substrates are 16.38 ± 0.21 μM and 2.57 ± 0.08 μM, respectively. The K_i values of XOD using AHMP as inhibitor with xanthine and 6MP as substrate are 5.78 ± 0.48 μM and 0.96 ± 0.01 μM, respectively. The Ki values of XOD using APT as inhibitor with xanthine and 6MP as substrate are 6.61 ± 0.28 μM and 1.30 ± 0.09 μM. The corresponding K_m values of XOD using xanthine and 6MP as substrate are 2.65 ± 0.02 μM and 6.01 ± 0.03 μM, respectively. The results suggest that the efficiency of substrate binding to XOD and its subsequent catalytic hydroxylation is much superior for xanthine in comparison to 6MP. In addition, the efficiency of the inhibitor binding to XOD is much more superior when 6MP is the substrate instead of xanthine. We further undertook the toxicological evaluation of these inhibitors in a single dose acute toxicity study in mice and our preliminary experimental results suggested that the inhibitors were equally non-toxic in the tested doses.

Conclusion

We conclude that administration of either APT or AHMP along with the major anti-leukemic drug 6MP might serve as a good combination cancer chemotherapy regimen.

Endothelial dysfunction and circadian blood pressure rhythmicity in young heart transplant recipients

Blood pressure variability correlates with circadian rhythmicity in endothelium-derived nitric oxide (NO) production in adults. Young, hypertensive orthotopic heart transplant (OHT) patients have functional abnormalities in NO-dependent signaling pathways that lead to reduced NO bioavailability and endothelial dysfunction. Following acute intravenous infusion of L: -arginine, the amino acid substrate for NO, OHT patients normalize blood pressure (BP) and endothelial function. However, the effects of chronic L: -arginine infusion on circadian BP rhythmicity and endothelial function in OHT patients have not been described. Six OHT patients (9-29 years old), and seven healthy control subjects (19-28 years old) were admitted for 48 hours. Systolic, diastolic, and mean blood pressures (MBP) were recorded hourly. Urine samples were obtained to measure nitrates/nitrites (NO(X)). Brachial artery flow-mediated vasodilatation (FMD; an index of endothelial function) and left ventricular ejection fraction (LVEF) were measured 0, 23, and 48 hours after admission. Intravenous L: -arginine HC1 was infused continuously beginning 24 hours after admission in all subjects. The incidence (50%) and degree (12.0 +/- 9.2%) of nocturnal MBP dipping was significantly less in OHT patients than control subjects. Furthermore, FMD was significantly reduced in OHT patients compared to controls (3.2 +/- 1.1 vs 7.2 +/- 3.1%, p = 0.01). L: -Arginine infusion had no significant effect on 24-hour MBP, LVEF, or nocturnal dipping status in any subject; however, L: -arginine normalized FMD in OHT patients (7.4 +/- 1.8%). Circadian BP variability and endothelial function are impaired in young cardiac transplant patients with medically controlled hypertension, and L: -arginine administration reverses endothelial dysfunction.

6-Mercaptopurine, an activator of Nur77, enhances transcriptional activity of HIF-1alpha resulting in new vessel formation

Hypoxia-inducible factor-1alpha (HIF-1alpha) plays a central role in oxygen homeostasis. Previously, we reported that the orphan nuclear receptor Nur77 functions in stabilizing HIF-1alpha. Here, we demonstrate that 6-mercaptopurine (6-MP), an activator of the NR4A family members, enhances transcriptional activity of HIF-1. 6-MP enhanced the protein-level of HIF-1alpha as well as vascular endothelial growth factor (VEGF) in a dose- and time-dependent manner. The induction of HIF-1alpha was abolished by the transfection of either a dominant-negative Nur77 mutant or si-Nur77, indicating a critical role of Nur77 in the 6-MP action. The HIF-1alpha protein level remained up to 60 min in the presence of 6-MP when de novo protein synthesis was blocked by cycloheximide, suggesting that 6-MP induces stabilization of the HIF-1alpha protein. The fact that 6-MP decreased the association of HIF-1alpha with von Hippel-Lindau protein and the acetylation of HIF-1alpha, may explain how 6-MP induced stability of HIF-1alpha. Further, 6-MP induced the transactivation function of HIF-1alpha by recruiting co-activator cyclic-AMP-response-element-binding protein. Finally, 6-MP enhanced the expression of HIF-1alpha and VEGF, and the formation of capillary tubes in human umbilical vascular endothelial cells. Together, our results provide a new insight for 6-MP action in the stabilization of HIF-1alpha and imply a potential application of 6-MP in hypoxia-associated human vascular diseases.

Inosine 5'-monophosphate dehydrogenase inhibition by mycophenolic acid impairs maturation and function of dendritic cells

BACKGROUND

The mechanism of action of mycophenolic acid (MPA) has been described as a blockade of inosine 5'-monophosphate dehydrogenase (IMPDH) and is thought to selectively influence T- and B-lymphocytes due to their strong dependency on guanine nucleotides synthesized via the de novo purine synthesis pathway. Recent evidence suggests MPA to affect antigen-presenting cells.

METHODS

Using CD14+ derived human dendritic cells (DC) we have investigated the effects of MPA on differentiation, maturation and function and studied intracellular nucleotide content and IMPDH activity.

RESULTS

GTP content and IMPDH activities of DC were strongly and dose-dependently decreased when MPA was present during the entire culture period or was added after the fifth (immature DC) or the seventh (mature DC) day of culture. Concurrent to low GTP levels, a dose-dependent reduction in the expression of CD80, CD86, CD40, CD54 and CD83 was seen which was accompanied by a decreased capacity of DC to stimulate T-cells. Our data for the first time shows a direct effect of MPA on the maturation and function of human CD14+ derived DC, indicates a role of IMPDH and a dependency on the de novo purine synthesis pathway.

The effect of 6-mercaptopurine on early human placental explants

BACKGROUND

6-mercaptopurine (6-MP) is an antineoplastic and immunosuppressive drug. Recently, more women have received this drug during pregnancy. Animal studies have shown that 6-MP has deleterious effects on the fetus, while human data include prematurity, intrauterine growth restriction, low birth weight and malformations that occur especially when the drug is administered in the first trimester of pregnancy.

OBJECTIVES

To study the effects of 6-MP on cellular functions of human trophoblast explants.

METHODS

Human placental explants (5.5-9 weeks gestational age), that were grown on matrigel, were exposed to medium containing 6-MP for 5 days. Medium alone served as control. Extravillous trophoblast (EVT) cell migration assessment was performed by visual observation. Analysis of proliferating events of the trophoblast cells was assessed by immunohistochemical examination. Apoptosis was analyzed by Tunnel procedure and by anti-caspase 3 staining and hormone level by enzyme-linked immunosorbent assay.

RESULTS

6-MP inhibited migration of EVT cells from the villi to the matrigel with a lower proliferation rate and increased apoptosis of cytotrophoblast cells compared to controls. However, no significant effect of 6-MP on hormone levels was observed.

CONCLUSIONS

6-MP inhibited migration and proliferation of trophoblast cells in first-trimester human placental explant culture.

Early graft failure due to a veno-occlusive disease after a pediatric living donor liver transplantation

A 10-month-old boy with biliary atresia after Kasai procedure underwent a living donor liver transplantation (LDLT). Five days after the LDLT, high fever and increased ascites followed by poor bile drainage was accompanied by elevation of serum liver enzymes. Liver biopsy showed occlusion of the central veins by fibro-edematous endothelium and submassive necrosis of the parenchyma. Veno-occlusive disease (VOD) was suspected, and re-LDLT was urgently performed because of deterioration of hepatic failure. There are few cases of VOD after liver transplantation and this is the first one in an infant after LDLT.

Redefining the target: chemotherapeutics as antiangiogenics

Angiogenesis, or new blood vessel formation, is now known to play an important role in both growth and metastasis of many cancers. The central importance of angiogenesis and the understanding of how new blood vessels are formed, has led to novel therapies designed to interrupt this process. Though specific antiangiogenic compounds have only recently entered the clinic, they herald a new era, one in which biology is the basis for therapy. The intense interest in angiogenesis has also lead to a re-examination of the activity of many established cytotoxic agents. Claims of antiangiogenic activity abound, unfortunately, with no common criteria and often little evidence of clinical relevance. What are we to think? Have oncologists unknowingly been administering antiangiogenic therapy all these years? If chemotherapeutics are really antiangiogenics in disguise, why have they failed to cure most solid tumors? Might the hard-learned lessons of chemotherapy resistance pertain to the novel antiangiogenics as well? Though we can offer no certain answers to these important questions, we do offer a framework on which to order the rapidly burgeoning literature. We suggest criteria by which a cytotoxic agent might reasonably be considered to have meaningful antiangiogenic activity. Finally, we describe potential mechanisms of resistance to antiangiogenic chemotherapies-some of which may apply to the pure antiangiogenics currently in development.