Cardiovascular and renal outcomes following percutaneous coronary intervention in a population with renal disease: a case-control study

BACKGROUND

Patients with renal disease are less likely to undergo percutaneous coronary intervention (PCI) due to concerns about poor outcomes.

AIM

We describe outcomes following PCI in individuals with chronic kidney disease (CKD), as compared with matched controls with comparable CKD who did not undergo PCI. We also identified factors predictive of poor outcomes following PCI amongst patients with CKD.

DESIGN

Retrospective observational case-control study.

METHODS

Cases were individuals with CKD (stages 1-5) undergoing PCI between 2008 and 2014. Controls were age, gender and creatinine-matched individuals not requiring PCI. We compared mortality between groups using Kaplan-Meier curves and Cox regression modelling. We assessed changes in serum creatinine using Wilcoxon Rank testing. We explored the relationship between biochemical and haematological measures (baseline creatinine, calcium, phosphate, calcium-phosphate product, parathyroid hormone, white cell count, haemoglobin, platelet count, c-reactive protein and total cholesterol) and post-PCI mortality, using logistic regression.

RESULTS

We identified 144 cases and 144 controls. Mortality was significantly lower amongst cases compared with controls [hazard ratio 0.46 (95% confidence intervals 0.31, 0.69)]. PCI did not result in a significant change in renal function (P=0.52). Amongst cases, serum creatinine and calcium-phosphate product were predictors of mortality following PCI.

CONCLUSION

Cases undergoing PCI had lower mortality, and PCI was not associated with accelerated CKD progression. On this data, PCI should not be deferred as a treatment option in patients with CKD. Serum creatinine and calcium-phosphate product predict mortality following PCI in this cohort, and may be useful in risk-stratifying patients with CKD being considered for PCI.

The influence of socioeconomic status on presentation and outcome of acute kidney injury

AIM

Although socioeconomic background is known to impact on the incidence and progression of chronic kidney disease, its influence of on the presentation and outcome for acute kidney injury is not known and is the subject of this study.

DESIGN

The Welsh National electronic AKI reporting system was used to identify all cases of AKI in patients >18 years of age between March 2015 and November 2017.

METHODS

Socioeconomic classification of patients was derived from the Welsh Index Multiple Deprivation score (WIMD). Patients were grouped according to the WIMD score by their postcode, and the ranked data were categorized into percentiles and correlated with incidence and measures of AKI severity and outcome.

RESULTS

Date was collected on a total of 57 654 patients. Increased deprivation was associated with higher AKI incidence rates, more episodes of AKI per patient and more severe AKI at presentation. In contrast 90-day mortality was highest in the most affluent areas. Mortality in affluent areas was driven by increased patient age. Corrected for age 90-day mortality was higher in areas of increased deprivation.

CONCLUSION

This study highlights that AKI incidence presentation and outcomes are adversely affected by social deprivation. Further studies are required to understand the extent to which these differences reflect patient related factors or regional differences in provision and access to care.

Adding a new dimension to the weekend effect: an analysis of a national data set of electronic AKI alerts

BACKGROUND

Increased mortality related to differences in delivery of weekend clinical care is the subject of much debate.

AIM

We compared mortality following detection of acute kidney injury (AKI) on week and weekend days across community and hospital settings.

DESIGN

A prospective national cohort study, with AKI identified using the Welsh National electronic AKI reporting system.

METHODS

Data were collected on outcome for all cases of adult AKI in Wales between 1 November 2013 and 31 January 2017.

RESULTS

There were a total of 107 298 episodes. Weekday detection of AKI was associated with 28.8% (26 439); 90-day mortality compared to 90-day mortality of 31.9% (4551) for AKI detected on weekdays (RR: 1.11, 95% CI: 1.08-1.14, P < 0.001, HR: 1.16 95% CI: 1.12-1.20, P < 0.001). There was no 'weekend effect' for mortality associated with hospital-acquired AKI. Weekday detection of community-acquired AKI (CA-AKI) was associated with a 22.6% (10 356) mortality compared with weekend detection of CA-AKI, which was associated with a 28.6% (1619) mortality (RR: 1.26, 95% CI: 1.21-1.32, P < 0.001, HR: 1.34, 95%CI: 1.28-1.42, P < 0.001). The excess mortality in weekend CA-AKI was driven by CA-AKI detected at the weekend that was not admitted to hospital compared with CA-AKI detected on weekdays which was admitted to hospital (34.5% vs. 19.1%, RR: 1.8, 95% CI: 1.69-1.91, P < 0.001, HR: 2.03, 95% CI: 1.88-2.19, P < 0.001).

CONCLUSION

'Weekend effect' in AKI relates to access to in-patient care for patients presenting predominantly to hospital emergency departments with AKI at the weekend.

Community acquired acute kidney injury: findings from a large population cohort

BACKGROUND

The extent of patient contact with medical services prior to development of community acquired-acute kidney injury (CA-AKI)is unknown.

AIM

We examined the relationship between incident CA-AKI alerts, previous contact with hospital or primary care and clinical outcomes.

DESIGN

A prospective national cohort study of all electronic AKIalerts representing adult CA-AKI.

METHODS

Data were collected for all cases of adult (≥18 years of age) CA-AKI in Wales between 1 November 2013 and 31 January 2017.

RESULTS

There were a total of 50 560 incident CA-AKI alerts. In 46.8% there was a measurement of renal function in the 30 days prior to the AKI alert. In this group, in 63.8% this was in a hospital setting, of which 37.6% were as an inpatient and 37.5% in Accident and Emergency. Progression of AKI to a higher AKI stage (13.1 vs. 9.8%, P < 0.001) (or for AKI 3 an increase of > 50% from the creatinine value generating the alert), the proportion of patients admitted to Intensive Care (5.5 vs. 4.9%, P = 0.001) and 90-day mortality (27.2 vs. 18.5%, P < 0.001) was significantly higher for patients with a recent test. 90-day mortality was highest for patients with a recent test taken in an inpatient setting prior to CA-AKI (30.9%).

CONCLUSION

Almost half of all patients presenting with CA-AKI are already known to medical services, the majority of which have had recent measurement of renal function in a hospital setting, suggesting that AKI for at least some of these may potentially be predictable and/or avoidable.

Acute kidney injury electronic alerts in primary care - findings from a large population cohort

BACKGROUND

Electronic reporting of AKI has been used to aid early AKI recognition although its relevance to CA-AKI and primary care has not been described.

AIMS

We described the characteristics and clinical outcomes of patients with CA-AKI, and AKI identified in primary care (PC-AKI) through AKI e-Alerts.

DESIGN

A prospective national cohort study was undertaken to collect data on all e-alerts representing adult CA-AKI.

METHOD

The study utilized the biochemistry based AKI electronic (e)-alert system that is established across the Welsh National Health Service.

RESULTS

28.8% of the 22 723 CA-AKI e-alerts were classified as PC-AKI. Ninety-day mortality was 24.0% and lower for PC-AKI vs. non-primary care (non-PC) CA-AKI. Hospitalization was 22.3% for PC-AKI and associated with greater disease severity, higher mortality, but better renal outcomes (non-recovery: 18.1% vs. 21.6%; progression of pre-existing CKD: 40.5% vs. 58.3%). 49.1% of PC-AKI had a repeat test within 7 days, 42.5% between 7 and 90 days, and 8.4% was not repeated within 90 days. There was significantly more non-recovery (24.0% vs. 17.9%) and progression of pre-existing CKD (63.3% vs. 47.0%) in patients with late repeated measurement of renal function compared to those with early repeated measurement of renal function.

CONCLUSION

The data demonstrate the clinical utility of AKI e-alerts in primary care. We recommend that a clinical review, or referral together with a repeat measurement of renal function within 7 days should be considered an appropriate response to AKI e-alerts in primary care.

Severe hyperkalaemia: demographics and outcome

Background

Few studies have evaluated the prevalence of severe hyperkalaemia in unselected patient populations. We identified all episodes of severe hyperkalaemia occurring in 1 year, and described patient demographics, clinical response and outcome. We also assessed junior doctor knowledge of its causes and significance.

Materials and methods

A retrospective interrogation of the database of the regional biochemical laboratory identified all episodes of severe hyperkalaemia (K≥ 6.5 mmol/L) occurring in 2011. The understanding of trainee doctors of the importance, causes and treatment of severe hyperkalaemia was assessed by structured questionnaire.

Results

Severe hyperkalaemia was recorded in 433 samples (365 patients) giving a prevalence of 0.11%. Thirty-six per cent of episodes occurred in patients under the care of a nephrologist, who were significantly younger than those not under the care of a nephrologist. In the nephrology cohort, 86% occurred in patients with chronic kidney disease (CKD), the majority of which had CKD Stage 5. In the non-nephrology cohort, only 65% occurred in the context of CKD, which was equally distributed between Stages 3 and 5 CKD. In both patient groups, roughly 50% of episodes occurred in association with acute kidney injury (AKI). Acute mortality (death within 48 h of documented severe hyperkalaemia) was higher in the non-nephrology compared with the nephrology cohort. Time to repeat serum potassium was influenced by the clinical setting with shorter time to repeat for acute care compared with ward settings. Assessment of trainee doctor's knowledge suggested significant deficiencies in relation to severe hyperkalaemia.

Conclusions

The prevalence of severe hyperkalaemia was low and occurred predominantly in the context of CKD and/or AKI. The majority of episodes occurred in patients not under the care of a nephrologist. Variability in time to repeat serum potassium levels suggested deficiencies in care, and assessment of trainee doctor’s knowledge suggests the need for further educational initiatives to highlight its importance.

The long-term impact of eGFR reporting on referral patterns

BACKGROUND

The prognostic significance of CKD has driven the widespread introduction of automated estimated glomerular filtration rate (eGFR) reporting, and the incorporation of CKD in the revised Quality Outcomes Framework (QOF) of the General Medical Services (GMS) contract in the U.K.

AIMS

To assess the long-term impact of the introduction of these two initiatives, on patient referral numbers to a nephrology service.

METHODS

Data was collected on the numbers and basic characteristics of all new patients referred from April 2005 to March 2011, to one NHS Health Board.

RESULTS

Introduction of eGFR reporting and CKD QOF domains was associated with a significant increase in the number of referrals, which was sustained. The initiatives also led to a sustained increase in the mean age of the patients at referral, predominantly due to an increase in the age of female patients referred. There was also an increase in the proportion of female patients referred. In the immediate aftermath of the introduction of change there was a transient decrease in the average eGFR at referral, a decrease in age of patients referred with an eGFR <15ml/min and an increase in the eGFR of patients >70yrs of age.

CONCLUSIONS

The data demonstrates significant and sustained increase in numbers of referrals. In the short term this was associated with a reduction in referral of elderly patients with stage 5 CKD and an increase in elderly patients with mild renal impairment. In the longer term we saw an increase in referral of an older female population.

Inhibition of TGF-β1/Smad signal pathway is involved in the effect of Cordyceps sinensis against renal fibrosis in 5/6 nephrectomy rats

The present study aimed to investigate the effects of Cordyceps sinensis on renal fibrosis and its possible mechanisms. Sprague-Dawley rats were randomly divided into three groups: sham operation (SHAM) group, 5/6 subtotal nephrectomy (SNx) untreated group, and 5/6 subtotal nephrectomy treated with C. sinensis (2.0 g/kg d) (CS) group. Rats were studied 12 weeks after the surgery, and the CS group presented with significantly lower proteinuria, and better renal function compared with the SNx group (p<0.05). Pathological study showed that the glomerulosclerosis tubulointerstitial injury score was significantly reduced in the CS group compared with the SNx group. Furthermore, the mRNA expression of TGF-β1, Smad2 and Smad3 and the protein expression of TGF-β1, TβRI, TβRII and p-Smad2/3 were attenuated by the C. sinensis treatment. In constrast, the mRNA and protein expression of Smad7 was upregulated. Furthermore, the expression of α-SMA and FSP1 was also significantly attenuated, accompanied by the increasing expression of E-cadherin, suggesting the inhibition of the epithelial-mesenchymal transition (EMT).

IN CONCLUSION

C. sinensis exerted its antifibrotic effect on the SNx rats through the inhibition of the TGF-β1/Smad pathway.

Applying estimated glomerular filtration rate to an ageing population: are we in danger of becoming ageist?

BACKGROUND

Management of CKD is a major public health concern. The introduction of automated eGFR reporting has seen an increase in labelling of elderly patients with CKD. The prognostic significance of the CKD label in this population remains controversial.

AIM

To investigate rates of specialist intervention in the over 75's to determine whether these patients may be more appropriately managed in primary care, relieving the burden of excessive outpatient visits in this population.

METHODS

Retrospective review of patient notes and laboratory reports over 25 consecutive renal outpatient clinics within a single NHS trust.

RESULTS

546 patients were studied. The mean age of patient was 68.7 years (SD+/-14.9). The over 75's had more advanced renal disease compared to under 75's (mean eGFR 28.2 vs. 41.3 ml/min/1.73 m(2)), but there was no significant difference in eGFR stability between the older and younger cohort or in the overall rate of intervention (32.5% vs. 30.7% p=0.86). The over 75's had a lower mean haemoglobin (11.8 vs. 12.6, p=<0.001) necessitating greater EPO requirements (25.2% vs. 10.5%, p=<0.001). The greatest intervention was seen in the more advanced CKD patients (29% of CKD 3 vs. 55% of CKD 5), and in those with diagnoses requiring immunosuppression.

CONCLUSION

Intervention to management may be predictable on the basis of specific diagnoses and advancing CKD stage but not by patient age. We can provide no evidence to suggest that elderly CKD patients are managed any differently to younger patients and in fact have a higher need for attention to and treatment of renal anaemia, validating their attendance in nephrology clinic.

Impact of chronic kidney disease management in primary care

BACKGROUND

The introduction of eGFR reporting and publication of national CKD guidelines has led to major challenges in primary and secondary care, leading to an increase in the number of referrals to nephrology clinics. We have shown that introduction of a renal patient care pathway reduces nephrology referrals and enables managed discharges of CKD patients to primary care. The aim of this article is to examine the outcome of patients discharged to primary care to find out if there is an associated risk with increased discharge supported by the patient pathway.

METHODS

The study was carried out within a single NHS Trust covering a population of 560,000. All patients discharged from the trust's renal outpatient clinic between June 2007 and July 2008 were identified. Patient notes and the local laboratory database systems were used to determine the source and timing of tests.

RESULTS

A total of 31 new referrals and 57 regular follow-ups were discharged during this period. The median age of discharge was 67.5 years. Most subjects (60%) had CKD stage 3 at the time of discharge. A total of 23% of discharges were categorized as CKD stages 1, 2 or normal and 17% of patients had CKD stage 4. Overall, 93% had stable eGFRs prior to discharge, 77.5% of patients had blood pressure within threshold (140/90 according to UK CKD guidelines) and 97.7% of patients had haemoglobins >10 g/dl. Post-discharge 83% of patients had eGFRs recorded by their general practitioner and 92.6% of these were measured within appropriate time frames as per CKD guidelines. The majority of patients (82%) had either improved or stable eGFR post-discharge and only three patients had a significant decline in their eGFR.

CONCLUSION

These data indicate that selected CKD patients can be appropriately discharged from secondary care and adequately monitored in primary care. Furthermore, we have shown that this was a safe practice for patients.

Characterisation of the human ADAM15 promoter

BACKGROUND

ADAM15 is a membrane-bound member of the adamalysin family that is up-regulated in areas of tissue remodelling. Previous studies have demonstrated the role of ADAM15 in mesangial cell migration, which is integral in tissue remodelling in pathology and repair. The current study was designed to identify and analyse the genomic regions upstream of ADAM15 that would regulate its transcription.

METHODS

Using 5'-RACE and RT-PCR, the ADAM15 5'-UTR was extended and luciferase constructs assembled to examine the transcription start site and characterise the promoter region of this gene.

RESULTS

A 145-bp proximal promoter construct showed full activity in unstimulated cells. Analysis of this region identified three potential Sp1-binding sites. Electromobility and supershift assays confirmed that Sp1 was constitutively present in MC nuclei. Mutations in each Sp1 site confirmed each was needed for full activity, while mutation of all three sites abrogated luciferase activity demonstrating that Sp1 was involved in the promoter activity of ADAM15. Methylation of this promoter fragment abolished the activity, while the methyltransferase inhibitor 5-aza-3'-deoxycytidine showed no increased activity in transfected cells, implying that the promoter was not methylated in our cells.

CONCLUSION

These results demonstrate the intrinsic promoter activity of ADAM15 in quiescent MC and show the involvement of Sp1 in its regulation.

Renal quality outcomes framework and eGFR: impact on secondary care

BACKGROUND

The prognostic significance of impaired renal function has driven the need for its early recognition and the widespread introduction of the estimated glomerular filtration rate (eGFR) reporting, and the incorporation of Chronic Kidney Disease (CKD) in the revised Quality Outcomes Framework (QOF) of the General Medical Services (GMS) contract in the UK.

AIM

To characterize the effect of these changes on referral numbers and appropriateness to a nephrology service, and the impact of a newly introduced Map of Medicine(R)-based patient care pathway coupled to the systematic screening of all new referrals.

METHODS

The study was carried out within a single NHS Trust covering five primary health care Local Health Boards and a population of 560,000.

RESULTS

Introduction of eGFR reporting and CKD QOF domains was associated with a rapid 61% increase in new patient referral, and an increase in the mean age of the patients at referral from 63.0 +/- 18.1 to 69.1 +/- 18.5. The referrals did not correlate with the QOF reported prevalence of CKD. Systematic screening of new referrals demonstrated 36% to be either inappropriate or inadequate in terms of clinical information supplied. Introduction of the renal patient care pathway was associated with a fall in both the number of inadequate and total new referrals received. Overall 62% of all primary care practices registered with the Map of Medicine(R) and these sent a higher proportion of appropriate referrals and were less likely to generate referrals with inadequate information. The initiative also enabled managed discharges from secondary to primary care settings, freeing up outpatient capacity.

CONCLUSION

The study describes the impact of the introduction eGFR reporting and revision of the GMS contract with Renal QOF, on patient referrals to a nephrology service. In addition, we provide evidence that a new management pathway has helped to regulate and proactively manage the increased demand within the current resources.

Characterization of hyaluronan cable structure and function in renal proximal tubular epithelial cells

Alteration in the glycosaminoglycan hyaluronan (HA) has been demonstrated in numerous renal diseases. We have demonstrated that renal proximal tubular epithelial cells (PTCs) surround themselves in vitro with HA in an organized pericellular matrix or 'coat', which is associated with cell migration, and also form pericellular HA cable-like structures which modulate PTC-mononuclear leukocytes interactions. The aim of this study was to characterize potential regulatory mechanism in the assembly of PTC-HA into pericellular cables. HA cables are generated by PTCs in the absence of serum. Immunohistochemical analysis demonstrates the incorporation of components of the inter-alpha-inhibitor (IalphaI) family of proteins and versican into HA cables. Addition of an antibody to IalphaI/PalphaI (pre-alpha-inhibitor) inhibits cable formation. In contrast, inhibition of tumor necrosis factor-alpha-stimulated gene 6 (TSG-6) has no effect on cable formation, suggesting that their generation is independent of the known heavy-chain transfer activity of TSG-6. Overexpression of HAS3 is associated with induction of HA cable formation, and also increased incorporation of HA into pericellular coats. Functionally, this resulted in enhanced HA-dependent monocyte binding and cell migration, respectively. Cell surface expression of CD44 and trypsin-released cell-associated HA were increased in HAS3-overexpressing cells. In addition, hyaluronidase (hyal1 and hyal2) and bikunin mRNA expression were increased, whereas PalphaI HC3 mRNA expression was unchanged in the transfected cells. The data demonstrate the importance of IalphaI/PalphaI in cable formation and suggest that expression of HAS3 may be critical for HA cable assembly.

Butyrate modulates TGF-β1 generation and function: Potential renal benefit for Acacia(sen) SUPERGUM™ (gum arabic)?

Anecdotal evidence suggests that high fibre supplementation of dietary intake may have health benefits in renal disease related to alterations in circulating levels of short-chain fatty acids. The aim of the study was to examine the hypothesis that dietary manipulation may increase serum butyrate and thus have potential beneficial effects in renal disease. We examined the effect of dietary supplementation with a gum arabic sample of standardized molecular characteristics, Acacia(sen) SUPERGUM EM2 (SUPERGUM), on systemic levels of butyrate in normal human subjects. In an in vitro study, we also examined the potential role of butyrate in modifying the generation of the profibrotic cytokine transforming growth factor-beta (TGF-beta1) by renal epithelial cells. Following 8 weeks of dietary supplementation with 25 g/day of SUPERGUM, there was a two-fold increase in serum butyrate (n=7, P=0.03). In vitro work demonstrated that exposure of renal epithelial cells to elevated concentrations of butyrate suppressed both basal and stimulated TGF-beta1 synthesis. The action of butyrate was mediated by suppression of the extracellular signal-regulated kinase/mitogen-activated protein kinase signalling pathway. In addition, butyrate exposures reduced the response of renal epithelial cells to TGF-beta1 as assessed by luciferase activity of a TGF-beta-responsive reporter construct. Attenuation of TGF-beta1 signalling was associated with reduced phosphorylation of Smad 3 and decreased trafficking of TGF-beta1 receptors into signalling, non-lipid raft-associated membrane fractions. In conclusion, the data demonstrate that dietary supplementation with SUPERGU increased serum butyrate, which at least in vitro has beneficial effects on renal pro-fibrotic cytokine generation.

Regulation of proximal tubular epithelial cell CD44-mediated binding and internalisation of hyaluronan

BACKGROUND

Increased expression of the connective tissue polysaccharide hyaluronan (HA) in the renal corticointerstitium is associated with progressive renal fibrosis. Numerous studies have demonstrated involvement proximal tubular epithelial cells in the fibrotic process and in the current study we have characterised their expression of the HA receptor, CD44, and examined changes in CD44 expression and function in response to either IL-1beta or glucose.

METHODS

Characterisation of CD44 splice variant expression was carried out in primary cultures of human proximal tubular cells (PTC) and HK2 cells. Binding and internalisation HA was examined by addition of exogenous of fluorescein-HA (fl-HA), and expression of CD44 examined by immunoblot analysis and flow cytometry. Alteration in "functional" CD44 was determined by immunoprecipitation of CD44 following stimulation in the presence of fl-HA.

RESULTS

PTC, both primary culture and the PTC cell line, HK2, express at least 5 CD44 splice variants, the expression of which are not altered by addition of either IL-1beta or 25mM D-glucose. Addition of either stimulus increased cell surface binding and internalisation of fl-HA and increased expression of functionally active CD44. Increased binding and internalisation of fl-HA, was blocked by anti-CD44 antibody, and by the inhibition of O-glycosylation.

CONCLUSIONS

The data demonstrate that stimuli inducing PTC HA synthesis also regulate PTC-HA interactions. Furthermore increased HA binding and internalisation is the result of post-translational modification of CD44 by O-glycosylation, rather than by alteration in expression of CD44 at the cell surface, or by alternate use of CD44 splice variants.

TGF-beta1-mediated fibroblast-myofibroblast terminal differentiation-the role of Smad proteins

It is now clear that resident myofibroblasts play a central role in the mediation of tissue fibrosis. The aim of the work outlined in this study is to increase our understanding of the mechanisms which drive the phenotypic and functional changes associated with the differentiation process. We have used an in vitro model of transforming growth factor-beta1 (TGF-beta1)-induced pulmonary fibroblast-myofibroblast differentiation to examine the role of the TGF-beta1 Smad protein signaling intermediates, in alterations of fibroblast phenotype and function associated with terminal differentiation. TGF-beta1 induced marked alteration in cell phenotype, such that cells resembled "epithelioid-postmitotic fibroblasts." This was associated with marked reorganization of the actin cytoskeleton and upregulation of alphaSMA gene expression. TGF-beta1 stimulation also induced alphaSMA protein expression with increased incorporation of alphaSMA into stress fibers. Following stimulation with TGF-beta1, subsequent addition of serum-free medium did not reverse TGF-beta1-induced morphological change, suggesting that TGF-beta1 induced a relatively stable alteration in fibroblast cell phenotype. Functionally, these phenotypic changes were associated with induction of type I, type III, and type IV collagen gene expression and an increase in the concentrations of the respective collagens in the cell culture supernatant. The role of Smad proteins in terminal differentiation of fibroblasts was examined by transfection of cells, with expression vectors for the TGFbeta1 receptor-regulated Smads (R-Smads) or the co-Smad, Smad 4. Transfection with Smad2 but not Smad3 resulted in TGF-beta1 independent alteration in fibroblast cell phenotype, up-regulation of alphaSMA mRNA and reorganization of the actin cytoskeleton. Transfection with Smad4 also induced alteration in cell phenotype, although this was not as pronounced as the effect of overexpression of Smad2. Overexpression of the Smad2, Smad3, or Smad4 proteins was associated with increased production of all collagen types. The study suggests that the phenotypic and functional changes associated with TGF-beta1-induced fibroblast terminal differentiation are differentially regulated by Smad proteins.

Mechanisms of irbesartan in prevention of renal lesion in streptozotocin-induced diabetic rats

AIM

To investigate the mechanisms of angiotensin II receptor antagonist irbesartan (Irb) in prevention of renal lesion in streptozotocin (STZ)-induced diabetic rats.

METHODS

Sprague-Dawley (SD) rats were randomly divided into three groups: normal control (group N), diabetic nephropathy (group DN), and diabetic nephropathy treated with Irb (group DNI). Diabetes was induced by injection of STZ ip after rats had received uninephrectomy. Blood glucose (BG), body weight (BW), urinary albumin excretion (Ualb), and 24-h proteinuria (24hUpro) were observed in the rats at week 4, 8, and 12, respectively. Creatinine clearance (Ccr), the kidney weight (KW), profile of kidney hypertrophy (KW/BW), renal tissue protein contents (RTP), glomerular area (AG), glomerular volume (VG), and width of glomerular basement membrane (GBM) were determined after the rats were sacrificed at week 12. Renal expression of connective tissue growth factor (CTGF) and transforming growth factor-beta1 (TGF-beta1) were determined by immunohistochemistry.

RESULTS

There was no significant difference in BG between group DN and DNI (P >0.05). Irb prevented the increasing of Ualb excretion, 24 hUpro, and Ccr in diabetic rats ( P < 0.01). Furthermore, Irb markedly inhibited the increasing of KW, KW/BW, RTP, AG, and VG shown in diabetic rats (P <0.05, P <0.01, respectively). Irb prevented the thickening of GBM and immunostaining of CTGF (P <0.01). The extent of CTGF expression was positively correlated with the glomerular immunostaining for TGF-beta1 and size of VG (P <0.01).

CONCLUSION

Irb exerts an early renal protective role to diabetic nephropathy, possibly through inhibition of renal hypertrophy and expression of CTGF.

Interaction between the transforming growth factor-beta type II receptor/Smad pathway and beta-catenin during transforming growth factor-beta1-mediated adherens junction disassembly

The aim of the current study was to examine the influence of transforming growth factor (TGF)-beta 1 on proximal tubular epithelial cell-cell interaction, with particular emphasis on the regulation of adherens junction complex formation. Stimulation of the proximal tubular cell line HK-2 cells by TGF-beta 1 led to loss of cell-cell contact and disassembly of both adherens and tight junctional complexes. Adherens junction disassembly was associated with reduction of both Triton-soluble and Triton-insoluble E-cadherin, and an increase in detergent-soluble beta-catenin. Under these conditions, immunoprecipitation and Western analysis demonstrated decreased association of beta-catenin, both with E-cadherin, alpha-catenin, and the cell cytoskeleton. Confocal microscopy after immunostaining, showed decreased intensity of peripheral E-cadherin staining, and redistribution of beta-catenin expression to a perinuclear location. Tight junction disassembly was manifest by a reduction in the expression of Triton-soluble occludin and ZO-1 by Western analysis and their disassociation manifested by immunostaining and confocal microscopy. Loss of cell-cell contact and disassembly of adherens junctions were seen after addition of TGF-beta 1 to the basolateral aspect of the cells. Immunoprecipitation experiments demonstrated co-localization of E-cadherin, beta-catenin, and TGF-beta 1 RII in unstimulated cells. After TGF-beta 1 stimulation, the TGF-beta 1 RII no longer associated with either E-cadherin or beta-catenin. Dissociation of the adherens junction protein from the TGF-beta 1 receptor was associated with increased beta-catenin tyrosine phosphorylation and decreased threonine phosphorylation. Furthermore after receptor ligand binding, beta-catenin became associated with the TGF-beta 1-signaling molecules Smad3 and Smad4.

Goto-Kakizaki rat is protected from proteinuria after induction of anti-Thy1 nephritis

Hyperglycemia, although necessary, alone is insufficient for the development of progressive diabetic nephropathy. Two factors implicated in its pathogenesis are mesangial cell activation and/or proliferation and monocyte/macrophage influx. We have shown that prolonged hyperglycemia in the Goto-Kakizaki (GK) rat is associated with renal structural changes similar to those in patients with diabetes before the onset of progressive nephropathy. The aim of the current study is to examine the role of mesangial cell injury and macrophage influx on renal structure and function. After induction of nephritis in either hyperglycemic GK rats or normoglycemic Wistar rats by the administration of Ox-7 antibody, the degree of mesangiolysis and subsequent mesangial proliferation was no different between GK and Wistar rats. Similarly, macrophage influx and mesangial cell activation (assessed by alpha-smooth actin expression) was no different between the two groups. Wistar rats developed marked albuminuria; conversely, no significant proteinuria or albuminuria was seen in GK rats. Analysis of glomerular proteoglycans (PGs) showed an increase in (35)S incorporation into heparan sulfate PGs of GK compared with Wistar rats, with no alteration in glycosaminoglycan chain size or charge density. These changes were kidney specific and not seen in spleen, lung, or heart tissue. Western blot analysis showed increased agrin core protein expression in whole-kidney homogenates of untreated GK rats. Induction of Thy1.1 nephritis was associated with reduced expression of agrin in both GK and Wistar rats. However, agrin expression was greater in GK rats at all times. In summary, acute mesangial cell injury associated with a macrophage influx did not initiate progressive diabetic nephropathy in GK rats. Despite a similar magnitude of glomerular/mesangial injury, GK rats, in contrast to normoglycemic Wistar rats, did not develop proteinuria after the administration of anti-Thy1 antibody. We postulate that altered expression of agrin in this model accounts for the lack of proteinuria and thus may protect against progressive nephropathy.

Diabetic nephropathy: the central role of renal proximal tubular cells in tubulointerstitial injury

Diabetic nephropathy is now the commonest cause of end stage renal disease and accounts for 30-40% of all patients requiring renal replacement therapy. Furthermore, the incidence of diabetic nephropathy continues to increase, in part due to the improved survival of type 2 diabetic patients as the cardiovascular mortality in this group declines (Ritz and Stefanski, 1996). Clinically incipient nephropathy is first manifest by the onset of persistent microalbuminuria, after which, overt diabetic nephropathy is heralded by the appearance of persistent proteinuria. Subsequently, there is a progressive decline in glomerular filtration rate (GFR) resulting, within 5 years, in end stage renal disease in 50% of patients (Hasslacher et al., 1989). The pathology of the renal lesions are similar in type I and II diabetes (Taft et al., 1994), although it has been suggested that there is more heterogeneity in type II diabetes (Chihara et al., 1986). Studies analysing structural-functional relationships have demonstrated that the development of proteinuria correlates with the degree of mesangial expansion (Mauer et al., 1984; White and Bilous, 2000). Although diabetic nephropathy was traditionally considered a primarily glomerular disease, it is now widely accepted that the rate of deterioration of function correlates best with the degree of renal tubulointerstitial fibrosis (Mauer et al., 1984, Bohle et al., 1991). This suggests that although in the majority of patients the primary event is a condition manifest by glomerular changes resulting in proteinuria, the long-term outcome is determined by events in the renal interstitium. With the increasing awareness of the importance of these pathological interstitial changes, interest has focused on the role of cells, such as the epithelial cells of the proximal tubule (PTC) or the interstitial myofibroblast, in the initiation of fibrosis. The aim of the present review is to analyse the available data supporting the role for the PTC in orchestrating renal interstitial fibrosis in diabetic nephropathy as a result of glucose-dependent alterations in PTC function. The potential for subsequent effects on PTC-fibroblast cross-talk will also be considered.

Translational regulation of renal proximal tubular epithelial cell transforming growth factor-beta1 generation by insulin

We have previously demonstrated that the proximal tubular cell may contribute to the pathogenesis of renal interstitial fibrosis in diabetes. Transforming growth factor (TGF)-beta1 is one of a group of pro-fibrotic cytokines and growth factors, which have been associated with the development of interstitial fibrosis. The aim of the current study was to examine the effect of insulin on the generation of TGF-beta1 by proximal tubular cells. HK-2 cells were grown to confluence in the absence of insulin, and serum deprived for 48 hours before all experimental manipulations. Addition of insulin (5 microg/ml) to the culture medium led to a time-dependent increase in TGF-beta1 concentration in the cell culture supernatant, and increased incorporation of radiolabeled amino acids into TGF-beta1 suggestive of de novo TGF-beta1 protein synthesis. Addition of insulin did not alter TGF-beta1 mRNA expression as assessed by reverse transcriptase-polymerase chain reaction or Northern analysis. Insulin-induced increase in TGF-beta1 concentration was not abrogated by actinomycin D, however, stimulation by insulin, in the presence of cycloheximide led to a dose-dependent decrease in TGF-beta1 production. Addition of insulin had no effect on TGF-beta1 mRNA stability as assessed by actinomycin D chase, but led to increased binding of a cytoplasmic protein to a putative stem loop structure in the 5'-UTR of TGF-beta1 mRNA, previously implicated in the posttranscriptional control of TGF-beta1 synthesis. To address the functional significance of insulin-induced alteration in TGF-beta1 synthesis, we examined its effect on matrix turnover. Insulin stimulated type IV collagen gene expression and an increase in the concentrations of the type IV collagen laid down in the extracellular matrix. This increase in type IV collagen was abrogated when cells were stimulated by insulin in the presence of an anti-TGF-beta1-blocking antibody. In conclusion the data demonstrate that insulin may directly alter the production of TGF-beta1 by renal proximal tubular cells by a posttranscriptional mechanism, and that this may have implications for the increase in extracellular matrix that accompanies diabetic nephropathy.

Regulation of renal proximal tubular epithelial cell fibroblast growth factor-2 generation by heparin

Progression of renal disease is closely correlated to the degree of renal interstitial fibrosis, and evidence is increasing that epithelial cells of the renal proximal tubule (PTCs) may contribute to its pathogenesis. Such cytokines as basic fibroblast growth factor (FGF-2) have been implicated in progressive renal injury, and we previously showed that PTCs are a source of this cytokine. FGF-2 is characterized by its high affinity for heparin, and numerous studies have suggested that heparin may modify the progression of renal disease. The current study examined how heparin influenced FGF-2 generation and bioactivity in the human renal epithelial PTC line, HK-2. Incubation of HK-2 cells with heparin led to a dose- and time-dependent increase in FGF-2 concentration in the culture supernatant that was not accompanied by alterations in FGF-2 messenger RNA expression, assessed by reverse-transcriptase polymerase chain reaction and Northern analysis. The heparin-induced increase in FGF-2 concentration was accompanied by a decrease in the amount of FGF-2 bound to the extracellular matrix, although this accounted for only a small proportion of the total FGF-2 generated. Induction of FGF-2 by 2-O-desulfated heparin, together with a reduction in total cell-associated FGF-2 and anti-FGF-2 antibody binding to fixed permeabilized cells after the addition of heparin, suggested that the FGF-2 released was mainly derived from a preformed intracellular source. That FGF-2 was predominantly derived from an intracellular pool was also confirmed by pulse chase experiments. The addition of heparin resulted in the generation of bioinactive FGF-2, judged by in vitro fibroblast proliferation. Conversely, heparitinase treatment of supernatant samples from heparin-treated cells and the addition of 2-O-desulfated heparin resulted in the generation of active FGF-2, suggesting that the generation of bioinactive FGF-2 was related to binding of FGF-2 by extracellular heparin after its release from cells. These data show that heparin depletes both the cell and surrounding matrix of FGF-2 and suggest that FGF-2 released from cells was mainly derived from a preformed intracellular source. Furthermore, FGF-2 released from epithelial PTCs after the application of heparin was bioinactive. This likely resulted from released FGF-2 binding to an excess of extracellular heparin. Results presented here therefore suggest a mechanism by which heparin, through its effect on depletion of matrix and cells of FGF-2 and its generation in an inactive form, may influence progressive renal interstitial fibrosis.

Regulation of renal proximal tubular epithelial cell hyaluronan generation: implications for diabetic nephropathy

BACKGROUND

Proximal tubular cells (PTCs) contribute to pathological changes in the renal interstitium by the generation of cytokines and alterations in the composition of the extracellular matrix. Hyaluronan (HA) is a ubiquitous connective tissue polysaccharide that regulates cell function and tissue remodeling. In the current study, we investigated the regulation of HA generation by PTCs.

METHODS

Primary cultures of human PTCs were grown to confluence and stimulated under serum-free conditions with either interleukin-1 (IL-1) or 25 mmol/L D-glucose. Alterations in HA generation were detected by enzyme-linked immunosorbent assay, and alterations in HA synthase gene expression were examined by reverse transcription-polymerase chain reaction. Subsequently, the mechanisms of IL-1 beta and glucose-induced alterations in HA were examined utilizing HK-2 cells.

RESULTS

Stimulation of human PTCs (HPTCs) with either IL-1 beta or 25 mmol/L D-glucose led to a significant increase in the HA concentration in the culture supernatant. In contrast, stimulation of HPTCs with transforming growth factor-beta1, basic fibroblast growth factor, or platelet-derived growth factor-AB did not stimulate HA production. The addition of IL-1 beta or 25 mmol/L D-glucose also increased HA generation in HK-2 cells and was associated with the induction of HAS2 mRNA. HAS3 mRNA was constitutively expressed and was not influenced by the addition of either stimulus. HAS1 mRNA expression was not detected in either unstimulated or stimulated cells. Inhibition of gene transcription or protein synthesis abolished HA production in response to either IL-1 beta or glucose. Inhibition of nuclear factor-kappa B (NF-kappa B) activation either by sulindac or by the proteosome inhibitor (PSI) abrogated both IL-1 beta and glucose-mediated alteration in HA synthesis.

CONCLUSION

This study demonstrates, to our knowledge for the first time, that increased HA synthesis in response to either IL-1 beta or elevated 25 mmol/L D-glucose is associated with NF-kappa B-activated transcription of HAS2.

Association of prolonged hyperglycemia with glomerular hypertrophy and renal basement membrane thickening in the Goto Kakizaki model of non-insulin-dependent diabetes mellitus

The aim of the current study was to characterize the effects of prolonged hyperglycemia on renal structure and function using a model of non-insulin-dependent diabetes mellitus: the Goto Kakizaki (GK) rat, which does not have confounding variables, such as hyperlipidemia, obesity, or elevated blood pressure. The data show that hyperglycemia in this model was not associated with the development of significant proteinuria, but it was associated with the development of definitive age-dependent renal structural changes. These changes consisted of thickening of glomerular basement membrane at 35 weeks and tubular basement membrane. This thickening was accompanied by marked glomerular hypertrophy resulting from a parallel increase in total capillary luminal volume and mesangial volume, but fractional capillary and mesangial volumes remained unchanged. There was evidence of podocyte injury, as assessed by de novo expression of desmin. In contrast, there was no evidence of mesangial cell activation, as assessed by their de novo expression of alpha-SMA. Interstitial monocyte/macrophage influx increased significantly in GK rats at 12 weeks compared with Wistar controls. Glomerular macrophage infiltration was elevated significantly in 35-week GK rats. The structural changes described in the GK rat are similar to those described in prolonged non-insulin-dependent diabetes mellitus patients who have not developed overt renal disease. This model allows us to investigate further the mechanisms involved in the pathogenesis of the consequences of prolonged hyperglycemia.

Decreased degradation of collagen and fibronectin following exposure of proximal cells to glucose

BACKGROUND/AIMS

Thickening and reduplication of the tubular basement membrane has been reported as an early event in diabetic nephropathy. The aim of the work outlined here was to examine the effects and mechanisms involved in the modulation of renal proximal tubular type-IV collagen and fibronectin turnover by glucose.

METHODS

The effect of glucose on type-IV collagen and fibronectin generation was studied by exposure of primary cultures of human renal proximal tubular cells (HPTC) to elevated D-glucose concentrations. Subsequently the mechanism of modulation of fibronectin generation was examined in a polarised system utilising the porcine proximal tubular cell line LLC-PK1 grown on porous tissue culture inserts.

RESULTS

Incubation of confluent growth-arrested HPTC with 25 mM D-glucose led to the accumulation of both type-IV collagen and fibronectin. This increase was not dependent on new gene transcription for either protein. Exposure of HPTC to 25 mM D-glucose also led to the induction of tissue inhibitor of metalloproteinases (TIMP-1 and TIMP-2) and also gelatinase A. There was, however, a net decrease in overall gelatinolytic activity. Incubation of confluent monolayers of LLC-PK1 cells grown on tissue culture inserts with 25 mM D-glucose on either their apical or basolateral aspect led to fibronectin accumulation seen only in the basolateral compartment. Under these experimental conditions, we can demonstrate polyol pathway activation, and furthermore the increase in fibronectin concentration in response to glucose was inhibited by the aldose reductase inhibitor sorbinil. Fibronectin accumulation was also demonstrated following both apical and basolateral addition of 1 mM sorbitol, but not following the addition of 25 mM galactose to either aspect of the cells.

CONCLUSIONS

These data demonstrate that the glucose-induced accumulation of type-IV collagen and fibronectin was associated with alterations in the degradative pathway of these matrix components. In addition fibronectin generation in response to glucose was non-polar in terms of application of glucose, but polar in terms of fibronectin accumulation. The mechanisms of glucose-induced modulation of fibronectin were mediated by polyol pathway activation, and more specifically related to the metabolism of sorbitol to fructose.

Augmentation of kidney injury by basic fibroblast growth factor or platelet-derived growth factor does not induce progressive diabetic nephropathy in the Goto Kakizaki model of non-insulin-dependent diabetes

Diabetes is now the most common cause of kidney failure. The pathogenesis of diabetic nephropathy in both type 1 and type 2 diabetes, however, is still incompletely understood. Two mechanisms postulated to contribute to the pathogenesis of progressive diabetic nephropathy are glomerular cell proliferation and glomerular visceral epithelial cell or podocyte injury. The aim of the current study was to determine whether the aggravation of mesangial cell injury or podocyte injury in isolation would induce progressive diabetic nephropathy. Specifically, we examined whether the administration of either platelet-derived growth factor (PDGF) or basic fibroblast growth factor (bFGF) in sub-nephritogenic doses might lead to an aggravation of kidney structural changes associated with hyperglycemia, resulting in progressive kidney damage in the Goto Kakizaki (GK) rat, which is a genetic model of non-obese non-insulin-dependent diabetes mellitus (NIDDM), in which progressive kidney disease does not develop spontaneously. The results demonstrate that the administration of PDGF to hyperglycemic GK rats led to acute mesangial cell proliferation and activation as assessed by 5-bromo-2'-deoxyuridine-positive nuclei and immunostaining for alpha-smooth muscle actin. Despite acute mesangial cell activation and proliferation, PDGF treatment had no long-term effect on either kidney structure or function. Similarly, treatment of GK rats with bFGF, despite the augmentation of podocyte injury as demonstrated by de novo expression of glomerular desmin expression, did not lead to the development of progressive diabetic nephropathy. In summary, the data in the current manuscript suggest that the additive effect of hyperglycemia and superimposed isolated mesangial cell or podocyte injury does not lead to progressive diabetic nephropathy. This further emphasises the multifactorial nature of the pathogenesis of progressive diabetic nephropathy.

TGF-beta1 stimulates the release of pre-formed bFGF from renal proximal tubular cells

BACKGROUND

It is now clear that the progression of renal disease is closely correlated to the degree of renal interstitial fibrosis. We have previously demonstrated that the renal proximal tubular epithelial cell may contribute to the fibrotic response by the generation of profibrotic cytokines. Transforming growth factor-beta1 (TGF-beta1) and basic fibroblast growth factor (bFGF) are two of a group of profibrotic cytokines that have been associated with the development of renal interstitial fibrosis. In this study, we have examined the influence of TGF-beta1 on the generation of bFGF by renal tubular epithelial cells.

METHODS

HK2 cells were grown to confluence and were serum deprived and stimulated with recombinant TGF-beta1 under serum-free conditions. Subsequently, supernatant, cell-associated, intracellular, and matrix-associated bFGF concentrations were determined by enzyme-linked immunosorbent assay (ELISA). bFGF mRNA expression was examined by reverse transcription-polymerase chain reaction (RT-PCR).

RESULTS

The exposure of confluent serum-deprived HK2 cells to TGF-beta1 led to a significant increase in bFGF concentration in the cell culture supernatant. Twenty-four hours following the addition of 10 ng/ml TGF-beta1, this represented a twofold increase in bFGF concentration (control, 102 pg/ml, N = 24, vs. 202 pg/ml, N = 19, P = 0.0001). Despite the increase in bFGF concentration in the supernatant, there was no change in the expression of bFGF mRNA following the addition of TGF-beta1. The addition of 10 ng/ml of TGF-beta1 led to a 30% decrease in the total cell-associated bFGF concentration (control, 8.51 ng/ml, N = 16, TGF-beta1, 6.01 ng/ml, N = 13, P = 0.0042). This decrease in intracellular bFGF was associated with a 15% reduction in anti-bFGF antibody binding to fixed permeabilized cells, following the addition of 10 ng/ml of recombinant TGF-beta1 (N = 9, P = 0.0007), suggesting that the mechanism of stimulation of bFGF by TGF-beta1 involved the release of preformed bFGF from within the cells. In addition, following the addition of TGF-beta1, there was a significant dose-dependent decrease in the amount of bFGF sequestered in the extracellular matrix. At a dose of 10 ng/ml TGF-beta, this represented a greater than sevenfold decrease (N = 9, P = 0.0007) in matrix-bound bFGF, although this represented less than 3% of the total bFGF released into the supernatant.

CONCLUSION

The data presented suggest that the main mechanism by which TGF-beta1 stimulates bFGF generation by proximal tubular epithelial cells is by stimulation of the secretion of preformed cytokine from within the cells.

Renal proximal tubular cell fibronectin accumulation in response to glucose is polyol pathway dependent

Thickening and reduplication of the tubular basement membrane has been reported as an early event in diabetic nephropathy. In the current study we have examined the polar requirements of proximal tubular cells for the D-glucose stimulated accumulation of fibronectin. We also examined the mechanism by which glucose led to accumulation of fibronectin, with particular emphasis on the polyol pathway. Incubation of confluent monolayers of LLC-PK1 cells grown on tissue culture inserts with 25 mM D-glucose on either their apical or basolateral aspect, led to fibronectin accumulation in the basolateral compartment. This reached statistical significance 24 h following apical addition of glucose (2.7 fold increase compared to 5 mM D-glucose, p = 0.007, n = 6), and 12 h after the basolateral addition of glucose (2.54 fold increase compared to 5 mM D-glucose, p = 0.02, n = 6). The increase in fibronectin concentration in response to glucose was inhibited by the aldose reductase inhibitor sorbinil. At a dose of 100&mgr;M sorbinil there was 59% inhibition of fibronectin accumulation in response to glucose, 48 h after the addition of the inhibitor (4.76 +/- 1.4 vs 11.53 +/- 1.41, mean +/- SD, p = 0.01, n = 3). Exposure of cells to glucose at either their apical or basolateral aspect lead to accumulation of intracellular glucose and polyol pathway activation, as assessed by sorbitol accumulation. Accumulation of intracellular glucose and hence subsequent polyol pathway activation occurred independently of transport of glucose by either apical sodium linked glucose transporter (SLGT) or basolateral GLUT 1. The data demonstrate that fibronectin generation in response to glucose was non-polar in terms application of glucose, but polar in terms of fibronectin accumulation. Furthermore modulation of fibronectin was mediated by polyol pathway activation, and more specifically related to the metabolism of sorbitol to fructose.

Rodent models of nephropathy associated with type II diabetes

End-stage renal disease from diabetic nephropathy, mainly due to type II diabetes, is an increasing problem in Western countries. The pathogenesis of diabetic nephropathy is still incompletely understood and much of the experimental insight has been obtained from insulinopenic animal models, resembling type I diabetes. This review therefore aims to describe available rodent models of nephropathy associated with type II diabetes. The review focusses on the metabolic as well as renal functional and structural changes. The usefulness of these rodent models to study renal involvement in type II diabetes is discussed with particular emphasis on confounding factors such as hyperlipidemia, hypertension, immunologic abnormalities, urogenital structural abnormalities and other associated pathological conditions. In addition recent observations on two rat strains, the obese Zucker (fatty) and Goto Kakizaki (GK) rat, are discussed in detail.

Renal proximal tubular cell fibronectin accumulation in response to glucose is polyol pathway dependent

BACKGROUND

Thickening and reduplication of the tubular basement membrane have been reported as early events in diabetic nephropathy. In this study, we have examined the polar requirements of proximal tubular cells for the d-glucose-stimulated accumulation of fibronectin and the mechanism by which this occurred, with particular emphasis on the polyol pathway.

METHODS

To determine the polarity of fibronectin generation in response to glucose, LLC-PK1 cells were grown on porous tissue culture inserts. Monolayer confluence was determined by serial measurement of transepithelial resistance. Confluent cells were growth arrested by serum deprivation, and all experiments were performed under serum-free conditions.

RESULTS

Application of 25 mm d-glucose to either the apical or basolateral aspect of LLC-PK1 cells led to fibronectin accumulation in the basolateral compartment. This reached statistical significance 24 hours following apical addition of glucose (2.6-fold increase compared with 5 mm d-glucose, P = 0.0025, N = 6 vs. N = 4 controls) and 12 hours after the basolateral addition of glucose (2.5-fold increase compared with 5 mm d-glucose, P = 0.03, N = 6 vs. N = 4 controls). Exposure of cells to glucose at either their apical or basolateral aspect leads to accumulation of intracellular glucose and polyol pathway activation, as assessed by sorbitol accumulation. The increase in fibronectin concentration in response to glucose was inhibited by the aldose reductase inhibitor sorbinil. At a dose of 100 micron sorbinil, there was a 59% inhibition of fibronectin accumulation in response to apical glucose (P = 0.004, N = 3 sorbinil vs. N = 4 controls) and a 66% inhibition in response to basolateral glucose (P = 0.008, N = 3 sorbinil vs. N = 4 controls) 48 hours after the addition of the inhibitor. Furthermore, fibronectin accumulation was also demonstrated following both the apical and basolateral addition of 1 mm sorbitol, but not following the addition of 25 mm galactose to either aspect of the cells. Following the addition of sorbitol, there was a 2. 8-fold increase in fibronectin 48 hours after apical stimulation (P = 0.01, N = 3 treated vs. N = 4 control) and a 2.27-fold increase following basolateral stimulation (P = 0.04, N = 3 treated vs. N = 4 control) at 24 hours.

CONCLUSIONS

In summary, these data demonstrate that fibronectin generation in response to glucose was nonpolar in terms of application of glucose but was polar in terms of fibronectin accumulation. The mechanisms of glucose-induced modulation of fibronectin were mediated by polyol pathway activation and were more specifically related to the metabolism of sorbitol to fructose.

Diabetic nephropathy: the modulating influence of glucose on transforming factor beta production

Diabetes in now the commonest cause of renal failure in the western world. Furthermore the survival of diabetic patients requiring dialysis treatment for renal failure is far less than patients with renal failure secondary to all other diseases. It is therefore important to identify the factors that control the development of progressive renal disease to allow targeted therapeutic interventions which would have major implications both to patient well-being and also to the provision of health care world wide. In this review we discuss possible metabolic consequences of hyperglycemia and their role in the pathogenesis of diabetic nephropathy. We also focus on the involvement of the pro-fibrotic cytokine Transforming Growth Factor beta, and contrast its role in the pathogenesis of glomerular and tubulo-interstitial changes seen in diabetic nephropathy.

Exposure of human renal proximal tubular cells to glucose leads to accumulation of type IV collagen and fibronectin by decreased degradation

Thickening and reduplication of the tubular basement membrane has been reported as an early event in diabetic nephropathy. In the current study we examined the effects of elevated D-glucose concentrations on human proximal tubular (HPTC) type IV collagen and fibronectin turnover. Incubation of confluent growth arrested HPTC with 25 mM D-glucose led to accumulation of both type IV collagen and fibronectin. This effect was maximal at 48 hours and represented a sevenfold increase for fibronectin (N = 4, P = 0.04), and a threefold increase for type IV collagen (N = 3, P = 0.03) over cells exposed to 5 mM D-glucose controls. This increase was not dependent on new gene transcription for either protein. Tissue inhibitor of metalloproteinases (TIMP 1 + TIMP 2) were induced following addition of 25 mM D-glucose, but not when cells were exposed to 5 mM D-glucose. Twenty-four hours after the addition of 25 mM D-glucose there was an eightfold increase in TIMP 1 (P = 0.009, N = 4), and a tenfold increase in TIMP 2 levels (P = 0.003, N = 4), over the control values for both inhibitors. The increase in both TIMP 1 and TIMP 2 in response to 25 mM D-glucose was abrogated in a dose dependent manner by the aldose reductase inhibitor sorbinil. Gelatin-substrate gel zymography showed increased activity of gelatinase A, but not of gelatinase B in response to the addition of 25 mM D-glucose to HPTC. The induction of gelatinase A was accompanied by increased gelatinase A mRNA expression, which was inhibited both by protein kinase C (PKC) depletion using PMA pre-treatment, and by the addition of a PKC inhibitor. These data demonstrate that the glucose-induced accumulation of type IV collagen and fibronectin is unrelated to increased gene transcription, but may involve alterations in the degradative pathway of these basement membrane constituents. Furthermore, the data demonstrate that glucose may simultaneously activate two intracellular pathways (the polyol pathway and a PKC dependent activation pathway), which are involved in mediating separate, complementary effects on cell function.

Basic fibroblast growth factor stimulates the release of preformed transforming growth factor beta 1 from human proximal tubular cells in the absence of de novo gene transcription or mRNA translation

Interstitial fibrosis is significantly correlated with the progression of renal impairment for most causes of renal insufficiency. Transforming growth factor beta 1 (TGF-beta 1) and basic fibroblast growth factor (bFGF) are two of a group of profibrotic cytokines that have been associated with the development of renal interstitial fibrosis. We have previously demonstrated that alterations in D-glucose concentrations modulate the synthesis of TGF-beta 1 by human renal proximal tubular cells (HPTC) in vitro. The aim of the present study was to examine the influence of bFGF on TGF-beta 1 synthesis by HPTC in culture and to examine any modulation of this response by changes in ambient glucose concentration. Incubation of growth-arrested HPTC (72 hours in serum-free medium) with bFGF resulted in a dose-dependent increase in latent TGF-beta 1 secretion. Maximal release of TGF-beta 1 was seen at a bFGF dose of 50 ng/ml in cells incubated in 5 mM D-glucose (7.48 +/- 2.5 ng/ml, mean +/- SEM; n = 3; p = 0.04). This release of TGF-beta 1 in response to bFGF was unaffected by increasing the concentration of glucose in the culture media to 25 mM (7.76 +/- 1.3, mean +/- SEM; n = 3; p < 0.02). It was also unaffected by pretreatment of cells with either actinomycin-D or cycloheximide. TGF-beta 1 secretion was, however, inhibited in a dose-dependent manner by the exposure of cells to the microtubule-disrupting agent vinblastine, indicating that the generation of TGF-beta 1 was dependent on the secretion of preformed, stored TGF-beta 1. In a separate series of experiments, exposure of HPTC to TGF-beta 1 (10 ng/ml) led to the induction of bFGF mRNA, which was first apparent at 12 hours and reached maximal levels 24 hours after stimulation (normalized bFGF/alpha-actin mRNA ratio was 1.5 times that of the control). This increase in bFGF mRNA was accompanied by a time-dependent increase in bFGF protein production, which was maximal after 24 hours (19.83 +/- 12.7 pg/ml versus 2.49 +/- 0.34 pg/ml, mean +/- SEM, stimulated versus control; n = 3; p = 0.03). These findings demonstrate that bFGF stimulates the secretion of preformed, latent TGF-beta 1 by HPTC but does not induce de novo TGF-beta 1 gene transcription or TGF-beta 1 protein synthesis. We have also demonstrated a positive-feedback loop involving TGF-beta 1 and bFGF and postulate that this may be involved in the progressive nature of renal fibrosis in vivo.

Polarity of stimulation and secretion of transforming growth factor-beta 1 by cultured proximal tubular cells

Proximal tubular epithelial cells are the most abundant cells in the renal cortex, and recent studies suggest that they may play an important role in initiating pathological changes in renal disease. Transforming growth factor (TGF)-beta 1 has been implicated as a major factor controlling the development and progression of renal fibrosis in numerous diseases, including diabetic nephropathy. We have recently demonstrated that human proximal tubular epithelial cells synthesize and secrete TGF-beta 1 after the sequential addition of both 25 mmol/L D-glucose and platelet-derived growth factor (PDGF). The present study examines the control of this synthesis and in particular the polar requirements of the stimulation and the direction of release of the protein. A proximal tubular cell line (LLC-PK1) was cultured on porous tissue culture inserts. Confluent cells were exposed to 25 mmol/L D-glucose on either their apical or basolateral aspect. TGF-beta 1 mRNA induction (reverse transcriptase polymerase chain reaction) occurred only after basolateral exposure. Similarly, TGF-beta 1 synthesis and secretion was induced only by the subsequent addition of PDGF to the basolateral aspect of the cells. In contrast, TGF-beta 1 protein secretion was detected equally in the apical and basolateral compartments. This effect was maximal after 12-hour PDGF stimulation and represented a threefold increase over controls for TGF-beta 1 in both the apical and basolateral compartments (n = 3, P < 0.05 versus control). The glucose transporter inhibitors phlorizin and phloretin were used to investigate the role of specific D-glucose transport proteins. Application of either basolateral phlorizin or phloretin at the time of addition of 25 mmol/L D-glucose to the same compartment inhibited TGF-beta 1 synthesis in response to PDGF. Maximal inhibition was achieved at 0.5 mmol/L of either inhibitor (phlorizin percent inhibition of apical TGF-beta 1, 75%, P = 0.015, and of basolateral TGF-beta 1, 78%, P = 0.015; phloretin percent inhibition of apical TGF-beta 1, 68%, P = 0.03, and of basolateral TGF-beta 1, 79%, P = 0.001, n = 5, P versus control). No inhibition was seen with apical application of either inhibitor. These data demonstrate that the priming of proximal tubular cells for TGF-beta 1 synthesis occurs only after basolateral exposure of the cells to 25 mmol/L D-glucose. This mechanism is dependent on the activity of the basolateral D-glucose transporter GLUT-1. In another series of experiments, TGF-beta 1 synthesis in response to the addition of basolateral PDGF was also induced after basolateral pretreatment with D-galactose but not 2-deoxy-D-glucose. This priming effect demonstrates the dependence of this response on glucose metabolism by the cells, not simply the activity of the GLUT-1 transporter, as both 2-deoxy-D-glucose and D-galactose are transported by GLUT-1, although only the latter is metabolized. The extrapolation of these results to diabetic nephropathy would suggest that it is changes in the interstitial concentration of glucose rather than the urinary glucose level that likely modulate the synthesis of the profibrotic cytokine TGF-beta 1 and thereby influence the progression of interstitial fibrosis.

Induction of TGF-beta 1 synthesis in D-glucose primed human proximal tubular cells by IL-1 beta and TNF alpha

The aim of the present study was to examine whether the induction of TGF-beta 1 synthesis by the pro-inflammatory macrophage derived cytokines, IL-1 beta or TNF alpha, was modified by alterations in D-glucose concentrations. Stimulation of growth arrested HPTC with IL-1 beta or TNF alpha resulted in increased expression of TGF-beta 1 mRNA. The transcript was demonstrable 60 minutes after the addition of IL-1 beta, and apparent steady-state mRNA levels were achieved after six hours. Following stimulation with TNF alpha, TGF-beta 1 mRNA was detectable after 15 minutes and reached steady state levels by two hours. Quantitative RT-PCR revealed that following six hours stimulation with either IL-1 beta or TNF alpha (both at 1 ng/ml), there was no difference in the absolute amount of TGF-beta 1 mRNA induced by these two stimuli (14.8 +/- 5.6 vs. 19.7 +/- 4.9 PM). Despite induction of TGF-beta 1 mRNA following stimulation with IL-1 beta or TNF alpha, neither stimulus increased TGF-beta 1 protein synthesis or release. Pre-exposure of HPTC to 25 mM D-glucose for 48 hours and subsequent stimulation with IL-1 beta resulted in the secretion of latent TGF-beta 1 in both a time and dose dependent manner. This effect was not apparent following TNF alpha stimulation of D-glucose primed HPTC. Stimulation of TGF-beta 1 synthesis by IL-1 beta in D-glucose primed cells was inhibited by cycloheximide but not by actinomycin-D. Examination of D-glucose induced TGF-beta 1 mRNA revealed that IL-1 beta, but not TNF alpha, increased the stability of the D-glucose induced transcript. These results demonstrate that the interaction of D-glucose and IL-1 beta lead to secretion of TGF-beta 1 by HPTC. In contrast, such an interaction was not demonstrable between D-glucose and TNF alpha. This may be explained by the ability of IL-1 beta to stabilize D-glucose-induced TGF-beta 1 mRNA.

5-year follow-up of patients successfully transplanted after immunoadsorption to remove anti-HLA antibodies

The function of renal allografts in patients who had received pretransplant immunoadsorption in order to remove cytotoxic anti-HLA antibodies was studied. We reviewed 6 patients who received a graft which functioned beyond 3 months; the mean follow-up period was 76 (range 62-89) months. Two grafts have been lost from chronic rejection, at 12 and 62 months, respectively. The mean plasma creatinine levels at 1 and 5 years were 169 (range 143-211) mumol/l and 155 (range 92-235) mumol/l, respectively (1.91, range 1.62-2.39, mg/dl and 1.75, range 1.04-2.66 mg/dl, respectively). The major source of morbidity during long-term follow-up has been the occurrence of renal artery stenosis in 5 patient and renal vein stenosis in 1. In conclusion, the 5-year graft survival and function was good in patients who received immunoadsorption and whose grafts survived beyond the first 3 months after transplantation.

Elevated D-glucose concentrations modulate TGF-beta 1 synthesis by human cultured renal proximal tubular cells. The permissive role of platelet-derived growth factor

Interstitial fibrosis is a marker of progression of renal impairment in diabetic nephropathy. Transforming growth factor (TGF)-beta 1 is one of a group of pro-fibrotic cytokines and growth factors that have been associated with the development of interstitial fibrosis. We have examined the modulating influence of glucose on the production of TGF-beta 1 by cultured human proximal tubular cells. Incubation of growth-arrested human proximal tubular cells (HPTC) (72 hours in serum free medium) in 25 mmol/L D-glucose resulted in increased expression of TGF-beta 1 mRNA (as assessed by reverse transcription polymerase chain reaction). This was apparent after 6 hours and increased up to 120 hours exposure. TGF-beta 1 secretion, however, as measured by specific enzyme-linked immunoassay, was unaffected by exposure to 25 mmol/L D-glucose. Sequential stimulation of HPTC, first with 25 mmol/L D-glucose for 48 hours and then with platelet-derived growth factor (PDGF) isoforms, resulted in a dose-dependent secretion of TGF-beta 1. Pre-exposure to 5 mmol/L D-glucose or 25 mmol/L L-glucose did not prime for TGF-beta 1 release. At 50 ng/ml PDGF this effect was greatest for the AA isoform (AA 31.4 +/- 7.1, AB 20.98 +/- 8.9, BB 7.8 +/- 2.2, P < 0.05 for all versus control, n = 3, mean +/- SEM ng/10(6) cells/24 hours). These effects were blocked by the addition of antibody to the PDGF alpha-receptor. TGF-beta 1 secretion was inhibited in a dose-dependent manner by pretreatment with cyclohexamide, but was not affected by pretreatment with actinomycin D. Stimulation of HPTC with a single dose of PDGF induced TGF-beta 1 mRNA; however, only after application of a second dose of PDGF (after TGF-beta 1 mRNA induction) did TGF-beta 1 protein secretion occur. We also demonstrated that PDGF stimulation of HPTC induced an inherently more stable TGF-beta 1 mRNA transcript. These findings demonstrate that elevated D-glucose concentration alone is insufficient to lead to increased TGF-beta 1 secretion by HPTC despite increased mRNA expression. However, application of a second stimulus such as PDGF, when TGF-beta 1 mRNA expression is increased, leads to increased protein synthesis and secretion of TGF-beta 1. This implies that elevated glucose concentrations might prime proximal tubular cells for TGF-beta 1 synthesis and thus contribute to the development of interstitial fibrosis.

A new antibody capture enzyme linked immunoassay specific for transforming growth factor beta 1

Previous studies which examined Transforming Growth Factor beta 1 (TGF-beta 1) generation have relied on the identification of TGF-beta 1 mRNA or measurement of TGF-beta 1 by bioassay. Quantitation of TGF-beta 1 message alone however is inadequate since the regulation of TGF-beta 1 synthesis is often post-transcriptional. TGF-beta 1 is poorly immunogenic, and sensitive and specific immunoassays for this peptide have proved difficult to develop. Bioassays depend on stimulation or inhibition of cell proliferation in a TGF-beta 1 dependent manner, and are very rigid in their requirements for optimal performance. The aims of this work was therefore to develop a sensitive and reproducible immunoassay for TGF-beta 1. Microtitre plates were coated with human recombinant TGF-beta 1, unbound protein was discarded from the wells prior to blocking with bovine serum albumin. Chicken anti-human TGF-beta 1 antibody was incubated with the test solution overnight at 4 degrees C and then added to the coated wells. Bound antibody was detected with alkaline phosphatase conjugated anti-chicken antibody. The assay is sensitive to 0.2 ng/ml with a range to 100 ng/ml. The assay detects the mature form of human recombinant TGF-beta 1, natural platelet extracted TGF-beta 1, and TGF-beta 1 derived from human monocytes stimulated with Phorbol myristate acetate (PMA). Active TGF-beta 1 is measured directly and latent TGF-beta 1 can be measured indirectly following acid activation of samples. Inter-assay precision ranged from 4.3 to 9.6%, (coefficient of variation, %CV) and intraassay precision ranged from 2.8 to 8.6% (CV).(ABSTRACT TRUNCATED AT 250 WORDS)

Evaluation of Doppler ultrasound in primary non-function of renal transplants

Doppler ultrasound investigation was performed in the renal grafts of 86 patients with primary non-function following cadaveric renal transplantation. Pulsatility Index, defined as: [formula: see text] was assessed to examine its predictive use in the diagnosis of rejection episodes as judged by a retrospective analysis of histological data. Altogether 415 Doppler examinations and 228 renal biopsies were performed. In our population the incidence of rejection was 57%. Using a pulsatility index (PI) > 1.8 to be indicative of rejection, the sensitivity of our test was 68% for vascular rejection and 65% for all rejection episodes. The specificity was 25%. We conclude that Doppler ultrasound cannot replace the need for transplant renal biopsy in patients with primary non-function.

The influence of recipient and donor age on the outcome of renal transplantation

This paper assesses the impact of age on the outcome of cadaveric renal transplantation. Data are presented on 99 consecutive patients undergoing first renal allografts at one unit. Patients are divided into those aged less than 50 (n = 53), patients between 50 and 60 (n = 16), and those aged 60 years and over (n = 30). There was no significant difference in graft survival at one year between the three groups. There was however an increased mortality with increasing recipient age (1.9%, 12.5% and 20.0% respectively for each age group). The effect of increasing donor age on graft survival was also studied. Graft survival at two years for first grafts was not influenced by donor age. We conclude that age alone is not a criterion for exclusion of patients from transplant programs. In addition we provide data to support the use of elderly donors as a potential source of cadaveric renal grafts for certain patients.

Acute renal failure associated with non-fulminant hepatitis A

A 49-year-old man developed acute renal failure as a complication of non-fulminant hepatitis A. This is a rare association of uncertain etiology.

Prevalence of lupus anticoagulant and anticardiolipin antibodies in haemodialysis patients

It has been suggested that a high prevalence of anticardiolipin antibody and lupus anticoagulant in haemodialysis patients may be a feature of dialysis membrane bioincompatibility. Previously published reports have given a prevalence of approximately 30% for IgG-anticardiolipin and 22-30% for the lupus anticoagulant in a population of haemodialysis patients, with a prevalence of 48% for IgG-anticardiolipin in a subgroup of patients dialysed with cuprophane membranes. The aim of this study was to analyse the prevalence of IgG- and IgM-anticardiolipin antibodies, and also the lupus anticoagulant in a population of haemodialysis patients dialysed exclusively with cuprophane membranes. Forty-two patients on hospital-based haemodialysis were studied. Two patients (4.8%) had IgG-anticardiolipin, and 7 (16.7%) had IgM-anticardiolipin. No patients were positive for both IgG- and IgM-anticardiolipin. All positive results were of 'low' or 'medium' positive titres. In the patients with positive results for anticardiolipin there were no documented episodes of thrombotic events. In the group studied there were no patients positive for the lupus anticoagulant. We conclude that the presence of anticardiolipin antibodies or lupus anticoagulant is rare in this population of haemodialysis patients and they are not a feature of membrane bioincompatibility.