A. M. El Nahas

Renal fibrosis: insights into pathogenesis and treatment.

The progression of chronic renal failure is characterised histologically by glomerulosclerosis, tubulointerstitial fibrosis and vascular sclerosis. Recent research has identified common mechanisms underlying these fibrotic processes. In particular, the scarring process within the glomeruli and the tubulointerstitium involves the infiltration by inflammatory cells including monocytes, the activation of intrinsic renal cells as well as interactions between infiltrating and resident cells. These interactions depend, to a large extent, on the release by these cells of chemokines, cytokines and growth factors. These factors are in turn involved in the induction of cellular proliferation within the kidney and the stimulation of the synthesis and deposition of extracellular collagenous matrix. Fibrosis is believed to result from excessive synthesis of extracellular matrix and a concommitant decrease in its breakdown. This fibrotic process resulting in end stage renal insufficiency bears strong similarities to that taking place within cirrhotic livers or fibrotic lungs. The new insights in our understanding of renal fibrosis have opened the way to new interventions aimed at its prevention. This may ultimately slow the progression of chronic renal insufficiency and decrease the number of patients requiring dialysis replacement therapy.

Analysis of the association between diabetic nephropathy and polymorphisms in the aldose reductase gene in Type 1 and Type 2 diabetes mellitus.

Aims  To investigate the association between polymorphisms of the aldose reductase gene and diabetic nephropathy in both Type 1 and Type 2 diabetes mellitus, and to carry out a meta‐analysis of published results.

Expression of cytoskeletal proteins during the course of experimental diabetic nephropathy

Aims/hypothesis: Diabetic nephropathy is characterised by structural changes known to be associated in non-diabetic nephropathies with the expression of the cytoskeletal proteins a-smooth muscle actin and vimentin. We aimed to investigate the expression of cytoskeletal proteins in experimental diabetic nephropathy.¶Methods. Rats were made diabetic by an injection of streptozotocin (45 mg/kg). Groups of rats (n = 6) and their respective controls (n = 4) were killed at different time intervals. (days 7, 15, 30, 60, 90 and 120). We also studied two groups of diabetic rats treated with a long-acting insulin; the first (n = 8) was treated from the induction of diabetes and the second (n = 8) received insulin from day 15 onward. At each time-point, kidney function, proteinuria and histology were evaluated. Cytoskeletal proteins and collagens III and IV deposition was determined by immunohistochemistry. Changes in the transcription of the cytoskeletal proteins was determined by northern blot analysis.¶Results. Although normal glomeruli did not express α-smooth muscle actin until late in the time course, it was detected in diabetic mesangium from day 7 onward. In the interstitium, it appeared in a perivascular and peritubular distribution. Vimentin was detectable within normal glomerular epithelial cells and increased rapidly (days 7 and 15) in diabetic rats. Vimentin also appeared early within the lining of the peritubular capillaries and damaged diabetic tubules. These changes were associated with a delayed increased transcription of α-smooth muscle actin and vimentin. Treatment with insulin (early or late) attenuated and reversed respectively the expression of cytoskeletal proteins and collagens within diabetic kidneys. Close correlations were noted between the number of α-smooth muscle actin positive cells within diabetic glomeruli and mesangial expansion (r = 0.46, p < 0.02) as well as interstitial α-smooth muscle actin positive cells and interstitial fibrosis (r = 0.51, p < 0.002).¶Conclusion/interpretation. Changes in the expression of cytoskeletal proteins within the kidneys of diabetic rats suggest a role for α-smooth muscle actin and vimentin in the pathogenesis of diabetic kidney disease. [Diabetologia (2000) 43: 91–100]

Role of apoptosis and Bcl-2/Bax in the development of tubulointerstitial fibrosis during experimental obstructive nephropathy.

Background/Aims: To examine the role of apoptosis in experimental unilateral ureteral obstruction (UUO). Methods: Rat kidneys were examined 3, 7 and 11 days following UUO or sham operation (SO). Tissue was immunohistochemically stained for α-smooth muscle actin (α-SMA), proliferating cell nuclear antigen (PCNA), Bcl-2 and Bax proteins. Apoptotic analysis was carried out in kidney sections using in situ end labelling of endonuclease cleaved DNA. Results: The relative volume (Vv) of cortical interstitium and interstitial α-SMA increased progressively following UUO. ED1-positive monocytes/macrophages peaked at day 7 and significantly decreased at day 11. PCNA-positive cells in tubulointerstitium were significantly increased on day 3. Staining returned to the level of the SO group by day 11, meanwhile those in the interstitium remained much higher than baseline. TUNEL-positive cells were persistently raised following UUO. Transient tubular cell proliferation seemed unable to counteract the apoptosis since tubular atrophy was apparently present by day 11 of UUO. However, interstitial cell proliferation was high enough to overwhelm apoptosis, particularly with respect ot myofibroblasts, since α-SMA immunostaining and Vv remained elevated. The ratio of the number of PCNA-positive cells to apoptotic cells formed a predictive pattern for the staining score of interstitial α-SMA (R2 = 47.23%, p < 0.05) and Vv (R2 = 49.93%, p < 0.05). Tubular Bcl-2 immunostaining peaked on day 3, and then gradually decreased to baseline by day 11. The expression of Bax protein was inhibited on day 3 when compared with that of the SO group, but increased with time following UUO. Conclusion: These findings suggest an important role for apoptosis and its regulatory proteins in the processes of tubular atrophy and fibrogenesis following UUO.

Transforming Growth Factor-β1 SNPs: Genetic and Phenotypic Correlations in Progressive Kidney Insufficiency

Associations have been described between polymorphisms of cytokine and growth factor genes and susceptibility to, or progression of, an increasing number of diseases. TGF-β1 plays an important role in the pathogenesis of experimental and clinical glomerulosclerosis and tubulointerstitial fibrosis. In this study, single nucleotide polymorphisms (SNPs) in the TGFβ1 gene were investigated as possible markers for the progression of chronic kidney failure (CKF). 145 Caucasian patients with CKF were screened for four TGFβ1 SNPs: T-509C in the promoter region; Arg25Pro and Leu10Pro in exon 1 and Thr263Ile in exon 5. There were significant differences between CKF patients and controls in allele frequencies of two of the SNPs, Leu10Pro (p = 0.038) and C-509T (p = 0.02) and in haplotype distributions (p = 0.0175), indicating an association with susceptibility to CKF. We also observed a significant association between progression of CKF and homozygosity for Arg25 (odds ratio 3.77, 95% confidence interval 1.57–9.04, p = 0.002). Homozygosity for Arg25 was also associated with severity of proteinuria at diagnosis (p = 0.038), plasma TGF-β1 protein levels (p = 0.01), and severity of glomerulosclerosis (p = 0.04). Homozygosity for -509T was associated with severity of proteinuria at diagnosis (p = 0.0017), level of renal tubular TGF-β1 immunostaining (p = 0.0006) and with severity of renal interstitial inflammatory cellular infiltration (p = 0.01). Tubular TGF-β1 immunostaining was significantly higher in biopsies with inflammatory cellular infiltration compared those without inflammation (p = 0.0048). There was a significant difference in haplotype distributions between CKF patients with progressive, as opposed to non-progressive disease (p = 0.0484). TGFβ1 SNPs may be useful prognostic indicators for the progression of CKF.

Haemodynamic effects of water-soluble contrast media on the isolated perfused rat kidney

The precise mechanism underlying the nephrotoxicity of radiocontrast media remains ill defined. In this study we have examined the direct effect of a wide range of low- and high-osmolar water-soluble contrast media (WSCM) on the vascular resistance of the isolated perfused rat kidney (IPRK). Water-soluble contrast media led to a significant fall in the renal perfusate flow and an increase in the renal vascular resistance (RVR). The magnitude of these haemodynamic changes was independent of the osmolality of the tested agents. This study shows a direct effect of WSCM on the vascular resistance of the isolated perfused rat kidney.

Relationship between the diuretic effect of radiocontrast media and their ability to increase renal vascular resistance

The relationship between diuresis and natriuresis induced by radiocontrast media (RCM) and their renal haemodynamic effects were investigated. The effects of the iso-osmolar iotrolan and the hyperosmolar diatrizoate on the renal vascular resistance (RVR) were studied in the filtering and non-filtering variants of the isolated perfused rat kidney (IPRK) preparation. In the non-filtering model, no tubular regulatory process can be activated. The effect of diatrizoate on the RVR of the filtering IPRK in the presence of fursemide (0.3 mmol l-1) an inhibitor of the tubuloglomerular feedback (TGF) was also investigated. There was no significant difference (p > 0.05) in the response of the filtering (n = 6) and non-filtering (n = 6) IPRK to iotrolan. The induced reduction in the renal perfusate flow (RPF) by iotrolan was 20.5 +/- 3.05% and 22.9 +/- 3.03%, respectively. The reduction in the RPF which was observed with diatrizoate in the non-filtering IPRK (n = 5, 17.5 +/- 3.04%) was significantly less (p < 0.05) in comparison to that of the filtering IPRK (n = 6, 26.9 +/- 4.28%). In the frusemide experiments, a reduction in the RPF comparable to that of the non-filtering kidney was observed (n = 5, 13.7 +/- 4.34%). This study demonstrates that the renal vascular effect of diatrizoate is partially dependent on the TGF response. No tubular regulatory mechanism was accountable for the haemodynamic effect of iotrolan. The activation of the tubular response is osmolarity dependent.

Effect of diatrizoate on the function of the isolated perfused rat kidney

The mechanism of the nephrotoxicity of water-soluble contrast media (WSCM) remains ill defined. We have studied the effect of diatrizoate on the isolated perfused rat kidney (IPRK). Emphasis was on the effect of low- and high-dose diatrizoate on glomerular filtration rate (GFR), renal perfusate flow (RPF), fractional excretion of albumin (FE Alb) and fractional reabsorption of sodium (FR Na). The addition of diatrizoate to the IPRK led to a dose-dependent biphasic change in RPF and GFR characterized by an initial transient increase followed by a marked and sustained decrease. Diatrizoate induced a diuresis and a parallel increase in urinary sodium excretion (fall of FR Na). Fe Alb was also increased in kidneys exposed to diatrizoate. Electron microscopy of a control kidney showed preservation of cellular architecture, which contrasted with the observed cytoplasmic vacuolation of proximal tubular cells after perfusion with diatrizoate. This study confirms a direct effect of WSCM on the function of the IPRK. In this experimental model, diatrizoate reproduces the effects observed in vivo on GFR and renal perfusion.

Reduced depression of renal function by iotrolan in the isolated rat kidney

The direct effects of iotrolan, a non-ionic dimer, on renal function were compared to iopromide, a non-ionic monomer and diatrizoate, an ionic monomer using the isolated perfused rat kidney. Kidneys were perfused ex vivo at 100 mmHg in a recirculating perfusion system with an albumin-based perfusate containing angiotensin II. All contrast media were studied at starting concentration of 20 mg Iodine/ml of renal perfusate. Each contrast agent produced a biphasic effect on the glomerular filtration rate (GFR) characterised by a transient increase followed by a sustained fall. However, the sustained fall in GFR induced by iotrolan (-24.7 +/- 2.1%) was significantly smaller than that produced by diatrizoate (-40.6 +/- 3.5%, P < 0.05) but there was no significant difference in comparison to the fall induced by iopromide (-34.2 +/- 3.7%). Each contrast agent produced a sustained decrease in renal perfusate flow (RPF) with iotrolan exerting a significantly smaller response (-21.7 +/- 2.0%) than either diatrizoate (-29.4 +/- 2.6%, P < 0.05) or iopromide (-32.2 +/- 2.9%, P < 0.05). The results indicate that at an equivalent iodine concentration iotrolan produces a smaller reduction of renal function in comparison to either iopromide or diatrizoate.

Association of Deprivation with Worse Outcomes in Chronic Kidney Disease: Findings from a Hospital-Based Cohort in the United Kingdom

Background: Chronic kidney disease (CKD) prevalence and complications are known to be associated with deprivation, but there is limited understanding of the underlying reasons for inequalities. Aims: To evaluate the association of both individual and area level socioeconomic status (SES) with heavy proteinuria at presentation, progression of CKD, end-stage renal disease (ESRD) and death. Methods: A retrospective study of 918 CKD patients using integral multivariate logistic regression to adjust for known clinical and demographic explanatory variables. Results: During 3 years of median follow-up, 34% of the study population had progression of their CKD and of these, 32% experienced rapid progression. 23% presented with heavy proteinuria (urine protein:creatinine ratio ≥300 mg/mmol), 4% developed ESRD requiring renal replacement therapy and 10% died. Area level deprivation was independently associated with heavy proteinuria, progression and rapid progression of CKD. People living in the most deprived areas were more likely to develop ESRD. Unskilled professionals were more likely to experience a higher mortality rate. Conclusion: Area level SES is inversely associated with both heavy proteinuria on presentation and progression as well as rapid progression of CKD. In contrast, individual level SES, unskilled professionals found to have a marginally significant association with increased risk of mortality. People living in more deprived areas presenting with CKD are likely to be at increased risk of poor outcomes and may need more active management and earlier referral.