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Biomedical subjects

Sydney Tang

Publications and source records attributed to Sydney Tang.

28 records · Page 2Linked to original sources
PubMed2003

Albumin stimulates interleukin-8 expression in proximal tubular epithelial cells in vitro and in vivo.

Renal tubulointerstitial injury is characterized by inflammatory cell infiltrate; however, the stimuli for leukocyte recruitment are not fully understood. IL-8 is a potent chemokine produced by proximal tubular epithelial cells (PTECs). Whether nephrotic proteins stimulate tubular IL-8 expression remains unknown. Acute exposure of human PTECs to albumin induced IL-8 gene and protein expression time- and dose-dependently. Apical albumin predominantly stimulated basolateral IL-8 secretion. Electrophoretic mobility shift assay demonstrated nuclear translocation of NF-kappaB, and the p65/p50 subunits were activated. NF-kappaB activation and IL-8 secretion were attenuated by the NF-kappaB inhibitors pyrrolidine dithiocarbamate and cell-permeable peptide. Albumin upregulated intracellular reactive oxygen species (ROS) generation, while exogenous H2O2 stimulated NF-kappaB translocation and IL-8 secretion. Albumin-induced ROS generation, NF-kappaB activation, and IL-8 secretion were endocytosis- and PKC-dependent as these downstream events were abrogated by the PI3K inhibitors LY294002 and wortmannin, and the PKC inhibitors GF109203X and staurosporin, respectively. In vivo, IL-8 mRNA expression was localized by in situ hybridization to the proximal tubules in nephrotic kidney tissues. The intensity of IL-8 immunostaining was higher in nephrotic than non-nephrotic subjects. In conclusion, albumin is a strong stimulus for tubular IL-8 expression, which occurs via NF-kappaB-dependent pathways through PKC activation and ROS generation.

Cell Line↗
PubMed2002

Efficacy of famciclovir in the treatment of lamivudine resistance related to an atypical hepatitis B virus mutant.

Reactivation of chronic hepatitis B virus (HBV) infection is a major cause of morbidity and mortality after renal transplantation. Although lamivudine is an effective treatment for chronic hepatitis B, the development of drug resistance due to mutations in the tyrosine-methionine-aspartate-aspartate (YMDD) motif is a major concern, especially in immunosuppressed patients who require prolonged therapy. Treatment with famciclovir has not been effective in the majority of patients who developed lamivudine resistance due to methionine-to-valine mutation at position 550, because this mutation has been uniformly associated with leucine-to-methionine mutation at position 526, a mutation that is associated with resistance to famciclovir. We describe a renal transplant recipient with an uncommon lamivudine-resistant HBV variant, in which methionine-to-valine/isoleucine mutation at position 550 was associated with wild-type sequence at position 526. The severe hepatitic flare consequent to the lamivudine resistance in this patient was successfully treated with famciclovir, indicating that both M550V and M550I mutants with preserved wild-type sequence at position 526 of HBV reverse transcriptase are susceptible to famciclovir. Our experience shows that famciclovir can be useful in selected patients with otherwise potentially fatal hepatitic flares related to lamivudine resistance, and that analysis of mutations in the HBV variant can be helpful in the choice of antiviral therapy.

2-Aminopurine↗
PubMed2002

Free-hand, ultrasound-guided percutaneous renal biopsy: experience from a single operator.

UNLABELLED: Percutaneous renal biopsy is a useful diagnostic procedure for many renal diseases. The experience with ultrasound-guided percutaneous renal biopsy from a single operator was reviewed to identify the possible risk factors of complications after the procedure. METHODS AND RESULTS: From 1995 to 1998, 203 biopsies (141 on native kidneys with 14G needles, 62 on transplant kidneys with 18G needles) were performed on 186 individuals as clinically indicated. The biopsy tissue specimen was adequate for histological diagnosis in 96.4% of the biopsies performed. IgA nephropathy followed by lupus nephritis were the most frequent diagnoses in our locality. Haematuria was the most common complication observed: mild bleeding occurred in 4.5%, while major complications (those that required blood transfusion or other intervention) were encountered in 1.5% of patients. Impaired renal function was identified as the single most important risk factor of bleeding complication after renal biopsy, while the presence of systemic hypertension or nephrotic syndrome did not increase the risk of bleeding. There was no correlation between bleeding and the type of renal pathology or the number of needle passes. Continuous haematuria may result from blood clot retention in the bladder. Over 97% of the cases were discharged from hospital within 48 h. CONCLUSIONS: We conclude that ultrasound-guided renal biopsy remains a safe, fast, and accurate procedure for the definitive investigation of renal diseases.

Adolescent↗
PubMed2002

Transferrin up-regulates chemokine synthesis by human proximal tubular epithelial cells: implication on mechanism of tubuloglomerular communication in glomerulopathic proteinura.

BACKGROUND: The pathogenesis of glomerulosclerosis and tubulointerstitial fibrosis in proteinuric renal disease is obscure. We recently showed that transferrin, a key proteinuric component, mediates proximal tubular epithelial cell (PTEC) C3 synthesis. To further examine whether proteinuric tubular injury may induce glomerular inflammation and to characterize the role of transferrin in activating PTEC, glomerular mesangial cells (MC) were exposed to transferrin-activated PTEC culture supernatant and their proliferative and profibrotic responses analyzed. METHODS: Human PTEC and MC were obtained by primary culture. Confluent, transferrin-stimulated PTEC were grown in serum-free medium to produce a "conditioned" medium that was incubated with quiescent MC. The proliferative response of MC was then assessed by thymidine uptake, and the expression of fibrogenic factors measured by reverse transcription-polymerase chain reaction (RT-PCR) and enzyme-linked immunosorbent assay (ELISA). The chemokine profile in PTEC after transferrin treatment was examined by RT-PCR and ELISA. RESULTS: "Conditioned" supernatant from PTEC, which contained the highest amounts of platelet-derived growth factor (PDGF), stimulated MC proliferation compared with serum-free (P = 0.03) or transferrin-containing (P = 0.009) control media. This proliferative response was partially abrogated by treating MC with anti-PDGF. MC expression of PDGF, but not transforming growth factor-beta or intercellular cell adhesion molecule-1, was up-regulated by conditioned PTEC medium. Transferrin up-regulated monocyte chemoattractant peptide-1, interleukin-8, and macrophage migration inhibitory factor expression in a time- and dose-dependent fashion, but had no effect on RANTES expression by PTEC. CONCLUSIONS: These results provide experimental evidence suggesting that there is a tubuloglomerular "cross-talk" mechanism in the proteinuric state. PTEC-secreted PDGF, which further induces mesangial PDGF, could partially account for the mesangial proliferation frequently observed in proteinuric renal disease. Transferrin is one of the culprit nephrotic proteins leading to tubular overexpression of various proinflammatory chemokines, which may explain the interstitial changes observed in proteinuric states.

Antibodies↗
PubMed2002

Expression of aquaporin-3 in human peritoneal mesothelial cells and its up-regulation by glucose in vitro.

BACKGROUND: Aquaporin-3 (AQP3) is a member of the water channel family that is selective for the passage of not only water, but also glycerol and urea. Our recent study demonstrated the presence of aquaporin-1 in human peritoneal mesothelial cells (HPMC). Although transcripts encoding for AQP3 has been detected by reverse transcription-polymerase chain reaction (RT-PCR) in murine peritoneal mesothelium, to date there is no documentation of protein expression on peritoneal mesothelial cells. METHOD: Our present study was designed to explore the gene and protein expression of AQP3 in HPMC and its regulation under different concentrations of glucose. RESULTS: AQP3 protein was detected in the human peritoneal tissue by immunohistological staining using specific, affinity-purified polyclonal anti-AQP3 antibodies. AQ3 transcripts and protein expression in cultured HPMC were investigated by RT-PCR and immunoblotting analysis respectively. Cell permeability to glycerol (flux) was measured using [(14)C]glycerol incorporation. AQP3 transcript and protein were weakly expressed in HPMC constitutively. The gene expression of AQP3 and its protein biosynthesis in HPMC were inducible following exposure to glucose in a dose- and time-dependent manner (P < 0.0001). Glucose at a concentration of 200 mmol induced glycerol flux by 4.82-fold above the control value (P < 0.0001) and its effect was significantly inhibited by mercuric chloride (P < 0.01). CONCLUSION: Our novel observation demonstrated the AQP3 expression and biosynthesis in HPMC and in vitro studies revealed that glycerol permeability in HPMC was up-regulated by glucose. Further study is warranted to elucidate the role of AQP3 in HPMC for maintaining the ultrafiltration of the peritoneal membrane.

Aquaporin 3↗
PubMed2002

Role of complement in tubulointerstitial injury from proteinuria.

The complement system is being increasingly implicated in the pathogenesis of progressive renal disease resulting from persistent proteinuria. It has recently been established that renal tubular cells can produce complement, activate complement, and respond to complement activation. Complement proteins that pass through the glomerular barrier along with other serum proteins in the proteinuric state may become activated at the tubular epithelial brush border, and lead to a cascade of events culminating in cell injury. Furthermore, nephrotic components in the urinary space may cause direct activation of the tubular cells to overexpress complement and contribute to local tissue injury. In this review, we will discuss the current evidence supporting a role for complement in the pathogenesis of progressive tubulointerstitial damage in the proteinuric state. The possibility of complement inhibition intervening in progressive tubulointerstitial injury due to proteinuric glomerular disease will also be considered.

Complement System Proteins↗
PubMed2001

Expression of aquaporin-1 in human peritoneal mesothelial cells and its upregulation by glucose in vitro.

Aquaporin (AQP) is a family of water channels that are highly selective for the passage of water and occasionally glycerol. In previous studies, only AQP1 was found in human peritoneal endothelial cells in both control subjects and patients on peritoneal dialysis. As human peritoneal mesothelial cells (HPMC) play an important role in dialysis adequacy and fluid balance in continuous ambulatory peritoneal dialysis patients, this study examined whether AQP1 is present in HPMC. It was found that AQP1 mRNA and protein are present in HPMC constitutively. The localization of AQP1 protein in peritoneal mesothelial cells was confirmed by double immunohistochemical staining of the mesothelial lining of human peritoneal membrane. More important, the expression of AQP1 in HPMC is not constitutive and the transcription and biosynthesis of AQP1 in HPMC is inducible by osmotic agents such as glucose and mannitol. There was significant enhancement of AQP1 biosynthesis upon exposure to glucose in a time- and dose-dependent manner (P < 0.0001). Similar findings were observed in the AQP1 biosynthesis by an endothelial cell line, EA.hy 926. Of particular interest, the upregulation in AQP1 mRNA or biosynthesis in mesothelial cells was always significantly higher than that of endothelial cells when the experiments were conducted under identical settings (P < 0.001). AQP1 expression in HPMC was demonstrated for the first time. Osmotic agents upregulate both mRNA and protein expression of this aquaporin. The role of AQP1 in HPMC in maintaining the ultrafiltration of the peritoneal membrane is potentially of clinical interest.

Aquaporin 1↗
PubMedDate not supplied

Risk factors and outcomes of extended-spectrum beta-lactamase-producing E. coli peritonitis in CAPD patients.

OBJECTIVE: To determine the risk factors and outcomes of peritonitis caused by extended-spectrum beta-lactamase (ESBL)-producing Escherichia coli in continuous ambulatory peritoneal dialysis (CAPD). PATIENTS AND METHODS: Episodes of E. coli CAPD peritonitis in our unit from October 1994 to August 2003 were reviewed. Demographic data, underlying medical conditions, recent use of gastric acid inhibitors (including H2 antagonist and proton pump inhibitor), recent antibiotic therapy, antibiotic regimen for peritonitis episodes, sensitivity test results of the E. coli isolated, and clinical outcomes were examined. RESULTS: Over a 10-year study period, 88 episodes of E. coli peritonitis were recorded; 11 of the 88 cases were caused by ESBL-producing E. coli. Recent use of cephalosporins and gastric acid inhibitor were associated with the development of ESBL-producing E. coil peritonitis. Compared with non-ESBL-producing E. coli peritonitis, more cases in the ESBL-producing E. coli group developed treatment failure (45.5% vs 13.0%, p = 0.02) and died of sepsis (27.3% vs 3.9%, p = 0.02). Peritoneal failure rate was higher in the ESBL-producing E. coli group, although the difference was not statistically significant (18.2% vs 3.9%, p = 0.12). CONCLUSION: Peritonitis caused by ESBL-producing E. coli is associated with worse clinical outcomes. The use of cephalosporins and gastric acid inhibitors may contribute to its development. Further studies are warranted to investigate and determine the predisposing factors for ESBL-producing E. coli peritonitis.

Aged↗