Su-Kil Park

Mycophenolic acid attenuates tumor necrosis factor-α-induced endothelin-1 production in human aortic endothelial cells

AIMSnAtherosclerotic cardiovascular disease is the major cause of morbidity and mortality in solid organ transplant recipients. Endothelin-1 (ET-1) is implicated in the pathogenesis of atherosclerosis and is one of the potential therapeutic targets. This study was conducted to evaluate the effect of mycophenolic acid (MPA), an immunosuppressant for the transplant recipients, on tumor necrosis factor-alpha (TNF-alpha)-induced ET-1 production in aortic endothelial cells.nnnMETHODS AND RESULTSnIn cultured human aortic endothelial cells, TNF-alpha increased ET-1 through AP-1 and NF-kappaB, whereas MPA attenuated it by reducing both AP-1 and NF-kappaB DNA-binding activities. TNF-alpha increased ET-1 via c-Jun NH2-terminal kinase (JNK) and p38 mitogen-activated protein kinase (MAPK), but not extracellular signal-regulated kinase. N-acetylcysteine that downregulated TNF-alpha-induced reactive oxygen species (ROS) inhibited JNK activation, but not p38 MAPK. N-acetylcysteine, SP600125 (JNK inhibitor) and SB203580 (p38 MAPK inhibitor) attenuated TNF-alpha-induced DNA-binding activities of both AP-1 and NF-kappaB. MPA inhibited JNK and p38 MAPK activations as well as ROS generation. N-acetylcysteine, SP600125, SB203580 and MPA had no effect on either TNF-alpha-induced IkappaBalpha degradation or p65 nuclear translocation, but attenuated p65 Ser276 phosphorylation.nnnCONCLUSIONnMPA attenuated TNF-alpha-induced ET-1 production through inhibitions of ROS-dependent JNK and ROS-independent p38 MAPK that regulated NF-kappaB as well as AP-1. These findings suggest that MPA could have an effect of amelioration of atherosclerosis.

Hyperuricemia in Kidney Transplant Recipients with Intact Graft Function

OBJECTIVESnThe aim of this study was to investigate the prevalence of hyperuricemia and factors predicting its occurrence, and to establish the relationship over time between serial changes in estimated glomerular filtration rate (eGFR) and uric acid (UR) concentration in kidney transplant (KT) recipients with eGFR >60 mL/min/1.73 m(2).nnnMETHODSnAdult patients who underwent KT at the Asan Medical Center between 1990 and 2008 and maintained eGFR >60 mL/min/1.73 m(2) were retrospectively assessed. Clinical and laboratory data were obtained from inpatient and outpatient charts and from the hospital electronic database.nnnRESULTSnOf 356 patients, 301 (84.55%) had normal UR levels and 55 (15.45%) had hyperuricemia. After multivariate adjustment, transplant duration, male gender, eGFR, diabetes mellitus (DM), and calcium level were associated with higher mean UR levels. Mean UR level increased significantly and mean eGFR decreased significantly during the first year after transplantation, but there were no significant differences over the next 4 years. Serial UR and eGFR levels changed almost simultaneously.nnnCONCLUSIONSnTransplantation duration, male gender, eGFR level, DM, and serum calcium level were risk factors for hyperuricemia in kidney recipients with intact graft function. Increased uric acid after KT did not significantly affect graft function.

Cementless Total Hip Arthroplasty in Patients with Osteonecrosis After Kidney Transplantation

This study was to determine the mid- to long-term survivorship of cementless metal-on-metal THA in 52 patients (74 hips) who underwent THA for osteonecrosis of the femoral head with a cementless THA. The mean follow-up was 10.2 years. The mean age at operation was 42.1 years (range, 25-62 years). The survivorship analysis with revision as the end point estimated a 96.6% chance of THA survival during 16.4 years. The average Harris hip score at last follow-up was 89.2 points (range, 74-100). Two patients (two hips) required revision surgery for extensive acetabular osteolysis at 9 years and acetabular liner dissociation at 2 years. The survival rates of cementless THA in these patients are encouraging. However, the possibility of metallic wear related complications are raising concern.

Darbepoetin alfa suppresses tumor necrosis factor-α-induced endothelin-1 production through antioxidant action in human aortic endothelial cells: role of sialic acid residues.

Recombinant human erythropoietin (r-HuEPO) is widely used to correct anemia in end-stage renal disease patients, who commonly suffer from atherosclerosis. Endothelin-1 (ET-1) has been implicated in the pathogenesis of atherosclerosis. Here, we tested whether darbepoetin alfa, a hypersialylated analogue of r-HuEPO, regulates tumor necrosis factor-α (TNF-α)-induced ET-1 production in human aortic endothelial cells, and sought to identify the signal pathways involved. Darbepoetin alfa attenuated TNF-α-induced ET-1 production. It also diminished TNF-α-induced reactive oxygen species (ROS) accumulation and subsequent activation of c-Jun NH2-terminal kinase (JNK), which regulates the DNA-binding activities of both AP-1 and NF-κB required for ET-1 gene transcription. Like a JNK inhibitor, darbepoetin alfa did not affect IκBα degradation or p65 nuclear translocation, but did inhibit mitogen- and stress-activated protein kinase 1 (MSK1) activation and attenuated p65 phosphorylation (serine 276), effects that may account for the reduction in NF-κB DNA-binding activity. Desialylation completely abolished darbepoetin alfas inhibitory effects on TNF-α-induced ROS accumulation, MSK1 activation, and ET-1 gene expression, without affecting its stimulation of STAT5 activity. These data demonstrate that darbepoetin alfa suppresses TNF-α-induced ET-1 production through its antioxidant action and suggest that the sialic acid residues of darbepoetin alfa are essential for its antioxidant effect, possibly by scavenging ROS.

Activation of spleen tyrosine kinase is required for TNF-α-induced endothelin-1 upregulation in human aortic endothelial cells.

Endothelin‐1 (ET‐1) promotes atherosclerosis. We tested whether spleen tyrosine kinase (Syk) mediates tumor necrosis factor‐α (TNF‐α)‐induced ET‐1 upregulation in human aortic endothelial cells (HAECs) and sought to identify the signal pathways involved. TNF‐α‐induced reactive oxygen species (ROS) activated Syk and phosphatidylinositol 3‐kinase (PI3K), which was required for the activation of AP‐1 and subsequent ET‐1 gene transcription. ROS mediated c‐Jun NH2‐terminal kinase (JNK) is also required for AP‐1 activation, but Syk and PI3K regulated AP‐1 activation independently of JNK. Through regulation of ET‐1 production, Syk could be implicated in atherosclerosis.

1,25-Dihydroxyvitamin D3 Causes ADAM10-Dependent Ectodomain Shedding of Tumor Necrosis Factor Receptor 1 in Vascular Smooth Muscle Cells

1,25-Dihydroxyvitamin D3 (1,25D3) has a potential antiatherosclerotic effect through anti-inflammatory actions. We investigated how 1,25D3 regulates tumor necrosis factor-α (TNF-α)–induced lectin-like oxidized low-density lipoprotein receptor-1 (LOX-1) expression in cultured human aortic smooth muscle cells. TNF-α activated Rac1/reactive oxygen species/spleen tyrosine kinase and transcriptional factors, activator protein-1, and nuclear factor κB, which led to LOX-1 expression. 1,25D3 inhibited TNF-α–induced LOX-1 expression by inhibiting Rac1 activation and thereby its downstream signals. 1,25D3 rapidly induced extracellular Ca2+ influx. Verapamil, an inhibitor of L-type calcium channels, inhibited 1,25D3-induced Ca2+ influx and counteracted the inhibitory effects of 1,25D3 on Rac1 activation, whereas Bay K8644 [1,4-dihydro-2,6-dimethyl-5-nitro-4-[2-(trifluoromethyl)phenyl]-3-pyridinecarboxylic acid, methyl ester], an L-type calcium channel agonist, attenuated TNF-α–induced Rac1 activation, as 1,25D3 did. 1,25D3 induced the ectodomain shedding of TNF receptor 1 (TNFR1), which was abolished by verapamil and in Ca2+-free media. Like 1,25D3, Bay K8644 induced the ectodomain shedding of TNFR1. Both 1,25D3 and Bay K8644 caused the translocation of a disintegrin and metalloprotease (ADAM) 10 from the cytoplasm to the plasma membrane, which was dependent on extracellular Ca2+ influx. In contrast, depletion of ADAM10 by transfection of ADAM10–small interfering RNA prevented 1,25D3- or Bay K8644–induced ectodomain shedding of TNFR1 and abolished the suppressive effect of 1,25D3 on TNF-α–induced Rac1 activation. Taken together, these findings suggest that 1,25D3 induces extracellular Ca2+ influx via L-type calcium channel, triggering ADAM10-mediated ectodomain shedding of TNFR1, and it thereby decreases responsiveness to TNF-α. By shedding TNFR1 from the cell surface, 1,25D3 may regulate inflammation and atherogenesis, whereas this effect could be attenuated by calcium channel blockers.

Spleen tyrosine kinase mediates high glucose-induced transforming growth factor-β1 up-regulation in proximal tubular epithelial cells

The role of spleen tyrosine kinase (Syk) in high glucose-induced intracellular signal transduction has yet to be elucidated. We investigated whether Syk is implicated in high glucose-induced transforming growth factor-β1 (TGF-β1) up-regulation in cultured human proximal tubular epithelial cells (HK-2 cell). High glucose increased TGF-β1 gene expression through Syk, extracellular signal-regulated kinase (ERK), AP-1 and NF-κB. High glucose-induced AP-1 DNA binding activity was decreased by Syk inhibitors and U0126 (an ERK inhibitor). Syk inhibitors suppressed high glucose-induced ERK activation, whereas U0126 had no effect on Syk activation. High glucose-induced NF-κB DNA binding activity was also decreased by Syk inhibitors. High glucose increased nuclear translocation of p65 without serine phosphorylation of IκBα and without degradation of IκBα, but with an increase in tyrosine phosphorylation of IκBα that may account for the activation of NF-κB. Both Syk inhibitors and Syk-siRNA attenuated high glucose-induced IκBα tyrosine phosphorylation and p65 nuclear translocation. Depletion of p21-activated kinase 2 (Pak2) by transfection of Pak2-siRNA abolished high glucose-induced Syk activation. In summary, high glucose-induced TGF-β1 gene transcription occurred through Pak2, Syk and subsequent ERK/AP-1 and NF-κB pathways. This suggests that Syk might be implicated in the diabetic kidney disease.

Peritubular capillary C4d deposition and renal outcome in post‐transplant IgA nephropathy

Abstract:u2002 Backgrounds:u2002 Immunological staining of the transplanted kidney for C4d in peritubular capillaries (C4dPTC) has emerged as a useful method to detect antibody‐mediated rejection in situ. In this retrospective study, we evaluated the prevalence of C4dPTC deposition in allograft renal biopsies diagnosed of IgA nephropathy (IgAN) and analysed its clinical significance.

Post-transplant malignancy: a burdensome complication in renal allograft recipients in Korea

Cancer has been a serious complication of kidney transplantation ever since the outcome of this procedure improved. The incidence of cancer among kidney transplant (KT) recipients is increasing, and these patients have a higher risk of developing cancer than the general population. The present retrospective cohort study compared the cancer rate of kidney recipients in a single transplantation center in Korea with that in healthy Korean individuals using the standardized incidence ratio (SIR). The medical records of all 2365 patients who underwent renal transplantation between 1989 and 2009 were reviewed retrospectively. During the study period, 136 renal allograft recipients developed 140 malignancies. The cumulative cancer incidence one, five, 10, and 15 yr post‐transplantation was 0.60%, 3.24%, 5.69%, and 8.90%, respectively. Non‐Hodgkin lymphoma (NHL) and thyroid cancer were the most common cancers after renal transplantation, occurring significantly more frequently than in the general Korean population. The SIR of all cancers was 1.9 (women: 2.4; men: 1.6). Comparison with similar studies in Korea and other countries suggests transplant center‐related differences dictate post‐transplant malignancy incidence more strongly than ethnic or geographic factors. Early surveillance programs for de novo malignancies after kidney transplantation focusing on kidney‐transplantation‐related tumors and postoperative time period should be established.

Vitamin D-induced ectodomain shedding of TNF receptor 1 as a nongenomic action: D3 vs D2 derivatives

As a nongenomic action, 1,25-dihydroxyvitamin D3 (1,25D3) induces L-type Ca(2+) channel-mediated extracellular Ca(2+) influx in human aortic smooth muscle cells (HASMCs), which activates a disintegrin and metalloprotease 10 (ADAM10) to cleave and shed the ectodomain of tumor necrosis factor receptor 1 (TNFR1). In this study, we examined the potencies of other vitamin D3 and D2 analogs to stimulate the ectodomain shedding of TNFR1 in HASMCs. 25-Hydroxyvitamin D3 (25D3), a precursor of 1,25D3, and elocalcitol, an analog of 1,25D3, caused ectodomain shedding of TNFR1 within 30 min, whereas 1,25-dihydroxyvitamin D2 (1,25D2) and paricalcitol, a derivative of 1,25D2, did not. Both 25D3 and elocalcitol rapidly induced extracellular Ca(2+) influx and markedly increased intracellular Ca(2+), while 1,25D2 and paricalcitol caused only small increases in intracellular Ca(2+). 25D3- and elocalcitol-induced TNFR1 ectodomain sheddings were abolished by verapamil and in Ca(2+)-free media. Both 25D3 and elocalcitol caused the translocation of ADAM10 to the cell surface, which was inhibited by verapamil, while 1,25D2 and paricalcitol did not cause ADAM10 translocation. When ADAM10 was depleted by ADAM10-siRNA, 25D3 and elocalcitol could not induce ectodomain shedding of TNFR1. The plasma membrane receptor, endoplasmic reticulum stress protein 57 (ERp57), but not the classic vitamin D receptor, mediated the nongenomic action of vitamin D to induce ectodomain shedding of TNFR1. In summary, like 1,25D3, 25D3 and elocalcitol caused ADAM10-mediated ectodomain shedding of TNFR1, whereas 1,25D2 and paricalcitol did not. The difference may depend on their affinities to ERp57 through which extracellular Ca(2+) influx is induced.