Effects of rosuvastatin on glomerular capillary size-selectivity function in rats with renal mass ablation

BACKGROUND

Evidence is accumulating that statins can reduce proteinuria and disease progression in chronic kidney disease. However, some safety concerns have been recently raised on the use of these agents, mainly due to transient episodes of proteinuria observed in patients receiving high doses of rosuvastatin.

METHODS

We investigated in rats with renal mass ablation (RMR) whether rosuvastatin (5 or 20 mg/day) worsens proteinuria as compared to untreated RMR animals. Moreover, we also examined whether rosuvastatin-induced changes in proteinuria would be due to the effect of the drug on permselective properties of glomerular capillary barrier, measured by the fractional clearance of graded-size Ficoll molecules and/or by proximal tubular mechanisms, by assessing urinary excretion of beta(2)-microglobulin.

RESULTS

RMR rats given rosuvastatin for 28 days showed a progressive increase in proteinuria, with values numerically but not significantly higher than those in RMR animals given the vehicle. In RMR rats, rosuvastatin did not significantly affect the fractional clearance of Ficoll as compared to vehicle-treated RMR animals. A significant correlation was found between urinary protein and beta(2)-microglobulin excretion in rats treated with rosuvastatin (r = 0.936, p < 0.001), but not in those given vehicle. Renal function, glomerular and tubulointerstitial injury were comparable in rosuvastatin-treated and untreated RMR rats at the end of the 28-day follow-up.

CONCLUSION

In rats with RMR, rosuvastatin mildly enhances urinary protein excretion rate. This, however, was not the result of further changes in the size-permselective function of glomerular capillary barrier.

Vitamin D, insulin resistance, and renal disease

Chonchol and Scragg report the results of a population study on levels of 25-hydroxyvitamin D in patients with renal dysfunction. They demonstrate that these patients do not show vitamin D deficiency unless renal function is severely affected (GFR<29 mL/min/1.73m2), while vitamin D and renal function loss are independently associated with insulin resistance. These data provide more solid evidence than previous available studies on small patient groups, and pose new questions about the mechanisms responsible for progressive renal disease as well as potential effects of vitamin D supplementation.

ACE inhibition reduces glomerulosclerosis and regenerates glomerular tissue in a model of progressive renal disease

Today angiotensin II inhibition is primarily used to slow the rate of progression of kidney diseases. There is evidence that these therapies can induce a partial regression of glomerular lesions. However, we do not know yet the extent of sclerotic lesion regression and whether new glomerular tissue is formed to help support the renal function. We used male Munich Wistar Fromter (MWF) rats, an experimental model for progressive kidney disease, to quantify kidney structural lesions upon angiotensin-converting enzyme (ACE) inhibition therapy. Animals were studied at 50 weeks of age, when renal function and structure are severely altered, and after a 10-week observation period, without or with treatment with lisinopril (80 mg/l in drinking water). A group of untreated Wistar rats was used as controls. With age, proteinuria, and serum creatinine worsen, but lisinopril almost normalized proteinuria and stabilized serum creatinine. Serial section analysis of whole glomerular tufts showed that at baseline, glomerulosclerosis affected the entire glomerular population, and that these changes further increased with age. Lisinopril significantly reduced incidence and extent of glomerulosclerosis, with the presence of glomerular tufts not affected by sclerosis (23% of glomeruli). Glomerular volume was not significantly affected by treatment, and glomerular mass spared from sclerosis increased from 46.9 to 65.5% upon treatment, indicating consistent regeneration of glomerular tissue. Lisinopril normalized baseline glomerular transforming growth factor-beta and alpha-smooth muscle actin overexpression, and prevented worsening of interstitial changes. Hence, ACE inhibition, which is widely used in human kidney disease, may not only halt the progression of renal failure, but also actually induce the regeneration of new renal tissue.

Vascular tissue engineering

Reconstructive surgery using autologous vessels is the conventional approach for substitution of diseased vessels or for generation of bypass to improve blood supply downstream of stenosed vessels. In some circumstances the use of autologous material is not possible due to concomitant diseases or previous use, and artificial grafts must be used. Unfortunately, these grafts cannot substitute small-caliber arterial vessels because of thrombotic complications. The objective of tissue engineering at the vascular level is then to generate biological substitutes of arterial conduits with functional characteristics of native vessels, combining cellular components with biodegradable scaffolds. These research projects started in several laboratories, in the late 1990s, and have expanded in different directions using a number of experimental approaches. The objective of this review is to give an overview of the results so far obtained in this area of research, and to discuss the problems related to these investigations, at the experimental and clinical level. The article provides an overview of different biodegradable scaffolds used, experimental techniques for vessels maturation in vitro under mechanical stimulation, and of differentiated as well as precursors of vascular cells, which opens new opportunities for further development of this form of cell transplantation. Finally, the current available results in clinical research will be discussed.

Computed tomography evaluation of autosomal dominant polycystic kidney disease progression: a progress report

At the moment, there are no effective therapies to prevent or slow the progression of autosomal dominant polycystic kidney disease (ADPKD). Radiologic evaluations are used to monitor volume of renal cysts and parenchyma during disease evolution. Volumetric quantifications based on computed tomography were used to investigate the relation between structural and functional changes in patients with advanced-stage ADPKD. By use of image-processing techniques, volume of kidneys, renal cysts, fully enhanced parenchyma, and faintly contrast-enhanced parenchyma, referred to as intermediate, was estimated. GFR measurements and computed tomography evaluations were repeated 6 mo later. No statistically significant correlations were found between volumes of cysts and parenchyma and intermediate volume and GFR. However, the ratio of intermediate over parenchymal volume strongly correlated with GFR (r = -0.81, P < 0.001). In addition, there were significant correlations between percentage changes in intermediate volume (absolute or relative to parenchyma) and GFR changes during the observation period (r = -0.70 and r = -0.75, P < 0.01). These data support the hypothesis of a significant relation between radiologic appearance of renal structure and functional changes and suggest new ways that renal dysfunction in ADPKD may be predicted. Further work is necessary to determine the nature of faintly contrast-enhanced parenchyma and its role in renal functional loss.

Permselective dysfunction of podocyte-podocyte contact upon angiotensin II unravels the molecular target for renoprotective intervention

Ameliorating the function of the glomerular barrier to circulating proteins by blocking angiotensin II (Ang II) translates into less risk of progression toward end-stage renal failure in diabetic and nondiabetic nephropathies. However, the mechanisms underlying this barrier protection are not clear. Specialized contacts between adjacent podocytes are major candidate targets, and the actin cytoskeleton is emerging as a regulatory element. Here, we present data demonstrating that Ang II induced reorganization of F-actin fibers and redistribution of zonula occludens-1 (ZO-1) that is physically associated with actin in murine podocytes. These effects were paralleled by increased albumin permeability across podocyte monolayers. The F-actin stabilizer jasplakinolide prevented both ZO-1 redistribution and albumin leakage, suggesting that actin cytoskeleton rearrangement is instrumental to podocyte permselective dysfunction induced by Ang II. Changes in both F-actin and ZO-1 patterns were confirmed in glomeruli of rat isolated perfused kidneys on short infusion of Ang II, leading to increased protein excretion. Podocyte dysfunction was mediated by Ang II type 1 receptor and was partly dependent on Src kinase-phospholipase C activation. These data demonstrate that strategies aimed at stabilizing podocyte-podocyte contacts and targeting the relevant intracellular signal transduction are crucial to renoprotection.

Pathophysiologic implications of reduced podocyte number in a rat model of progressive glomerular injury

Changes in podocyte number or density have been suggested to play an important role in renal disease progression. Here, we investigated the temporal relationship between glomerular podocyte number and development of proteinuria and glomerulosclerosis in the male Munich Wistar Fromter (MWF) rat. We also assessed whether changes in podocyte number affect podocyte function and focused specifically on the slit diaphragm-associated protein nephrin. Age-matched Wistar rats were used as controls. Estimation of podocyte number per glomerulus was determined by digital morphometry of WT1-positive cells. MWF rats developed moderate hypertension, massive proteinuria, and glomerulosclerosis with age. Glomerular hypertrophy was already observed at 10 weeks of age and progressively increased thereafter. By contrast, mean podocyte number per glomerulus was lower than normal in young animals and further decreased with time. As a consequence, the capillary tuft volume per podocyte was more than threefold increased in older rats. Electron microscopy showed important changes in podocyte structure of MWF rats, with expansion of podocyte bodies surrounding glomerular filtration membrane. Glomerular nephrin expression was markedly altered in MWF rats and inversely correlated with both podocyte loss and proteinuria. Our findings suggest that reduction in podocyte number is an important determinant of podocyte dysfunction and progressive impairment of the glomerular permselectivity that lead to the development of massive proteinuria and ultimately to renal scarring.

Biocompatibility and function of microencapsulated pancreatic islets

Encapsulation of pancreatic islets in alginate is used to protect against xenogenic rejection in different animal models. In this study, several factors, including differences in alginate composition, the presence or absence of xenogenic islet tissue and a transient immunosuppression, were investigated in a model of bovine islet transplantation in rats. A pure alginate with predominantly guluronic acid (Manugel) and an ultrapure low viscosity guluronic acid alginate (UP-LVG) were used. When microcapsules of Manugel or UP-LVG containing 16,000 bovine islet equivalents were transplanted in diabetic rats, we observed normoglycemia for 8.3+/-0.7 (range 6-12 days) and 7.5+/-0.2 days (range 7-8 days) on average, respectively. To ameliorate immunoprotection of alginate microcapsules we repeated the same experiments using transient immunosuppressive therapy. Low doses of cyclosporin A (CyA) administered for 18 days after implantation increased the time in normoglycemia, which averaged 27+/-3 days (range 8-55 days) in Manugel capsules while in UP-LVG capsules it averaged 18+/-8 days (range 3-39 days). The surface of recovered capsules showed less capsules free of overgrowth in Manugel with respect to UP-LVG alginate. These data were comparable with those observed in empty microcapsules similarly implanted, indicating that the capsular overgrowth was not promoted by the presence of xenogenic islet tissue. In recovered Manugel capsules the percentage of capsules without fibrotic overgrowth was higher than that observed without CyA. The same observation was made in empty capsules. These observations indicate that a combination of a highly purified alginate and short-term immunosuppression prolong islet function in a model of xenotransplantation.

Mechanisms of progression and regression of renal lesions of chronic nephropathies and diabetes

The incidence of chronic kidney diseases is increasing worldwide, and these conditions are emerging as a major public health problem. While genetic factors contribute to susceptibility and progression of renal disease, proteinuria has been claimed as an independent predictor of outcome. Reduction of urinary protein levels by various medications and a low-protein diet limits renal function decline in individuals with nondiabetic and diabetic nephropathies to the point that remission of the disease and regression of renal lesions have been observed in experimental animals and even in humans. In animal models, regression of glomerular structural changes is associated with remodeling of the glomerular architecture. Instrumental to this discovery were 3D reconstruction studies of the glomerular capillary tuft, which allowed the quantification of sclerosis volume reduction and capillary regeneration upon treatment. Regeneration of capillary segments might result from the contribution of resident cells, but progenitor cells of renal or extrarenal origin may also have a role. This review describes recent advances in our understanding of the mechanisms and mediators underlying renal tissue repair ultimately responsible for regression of renal injury.

Subcutaneous xenotransplantation of bovine pancreatic islets

Transplantation of pancreatic islets in diabetes is currently limited by the need of immunosuppressive therapy. The present study was designed to test an immunoprotection planar device for subcutaneous xenotransplantation of pancreatic islets in the diabetic rat. We tested three different devices made of polyethersulfone hollow fibers. In all diabetic rats, implantation of islet-containing devices promptly normalized hyperglycemia. In vitro membrane permeability to glucose was correlated with implant function duration. These data confirm that bovine islets contained within devices and implanted subcutaneously remain functional for several days. Strategies to prolong islet function may allow achieving successful long-term islet implantation in this attractive site.

Safety and efficacy of long-acting somatostatin treatment in autosomal-dominant polycystic kidney disease

BACKGROUND

The fluid filling renal cysts in human polycystic kidneys is secreted chiefly by the tubular epithelium lining the cysts via secondary chloride transport. Inhibiting this process by somatostatin therapy should induce shrinking of renal cysts.

METHODS

In this randomized, cross-over, placebo-controlled trial we compared the risk/benefit profile of 6-month treatment with long-acting somatostatin (octreotide-LAR, 40 mg intramuscularly every 28 days) or placebo in autosomal-dominant polycystic kidney disease (ADPKD) patients with mild-to-moderate renal insufficiency and no evidence of other kidney disease. Volumes of kidney structures were evaluated by a two-slice computed tomography (CT) scanner; while glomerular filtration rate (GFR) was estimated by iohexol plasma clearance.

RESULTS

One patient on somatostatin and one on placebo were prematurely withdrawn because of nonsymptomatic, reversible colelithiasis and asthenia, respectively. In the remaining 12 patients somatostatin was well tolerated. Kidney volume increased by 71 +/- 107 mL (P < 0.05) on somatostatin and by 162 +/- 114 mL (P < 0.01) on placebo. The percent increase was significantly lower on somatostatin (2.2 +/- 3.7% vs. 5.9 +/- 5.4%) (P < 0.05). Cystic volume tended to increase less on somatostatin than on placebo (3.0 +/- 6.5% vs. 5.6 +/- 5.8%). The "parenchymal" volume nonsignificantly increased by 2.5 +/- 8.4% on placebo and slightly decreased by 4.4 +/- 8.9% on somatostatin. The GFR did not change significantly during both treatment periods.

CONCLUSION

In ADPKD patients, 6-month somatostatin therapy is safe and may slow renal volume expansion. This may reflect an inhibited growth in particular of smallest cysts beyond the detection threshold of CT scan evaluation. Whether this effect may prove renoprotective in the long term should be tested in additional trials of longer duration.

The effect of sodium ascorbate on the mechanical properties of hyaluronan-based vascular constructs

Esterified hyaluronic acid (HYAFF) is routinely used for clinical tissue engineering applications such as skin and cartilage. In a previous study we developed a technique for in vitro generation of cylindrical constructs from cellularized HYAFF flat sheets. In the present investigation we studied the possibility to improve mechanical properties of this vascular construct by the addition of sodium ascorbate (SA). Non-woven HYAFF flat sheets were seeded with porcine aortic smooth muscle cells (SMCs) and cultured for 14 or 28 days with standard medium or medium added with SA. In selected experiments HYAFF sheets seeded with SMCs were wrapped to obtain cylindrical shape and then cultured in control medium or SA added medium for up to 28 days. We estimated cell viability for flat sheets, and performed histological examination, analysis of extracellular matrix (ECM) deposition and mechanical tests on tubular constructs. The number of viable cells and ECM deposition increased with time in constructs cultured in the presence of SA, as compared to control group. Moreover, SA improved mechanical properties of the vascular construct lowering material stiffness and increasing tensile strength as compared to untreated controls. The addition of SA to the medium improved cell proliferation and ECM synthesis on this biodegradable material, which leads to the formation of well organized, mechanical resistant tissue-engineered structure.

Vascular Smooth Muscle Cells on Hyaluronic Acid: Culture and Mechanical Characterization of an Engineered Vascular Construct

Esterified hyaluronic acid (HYAFF) is routinely used for clinical tissue-engineering applications such as skin and cartilage. The material is degraded by neotissue formation and degradation products are highly biocompatible. In the present article we investigate the possibility to culture vascular smooth muscle cells on this biodegradable material for the generation of tubular constructs to be used for vascular tissue engineering. We have evaluated cell attachment and growth, and the possibility to obtain a three-dimensional tubular shape culture from flat HYAFF sheets. We also evaluated the mechanical properties of the cell constructs, using a specific testing protocol, and compared them with the properties of segments of porcine coronary artery. Morphology and viability tests demonstrated that vascular cells, either from porcine or human origin, adhere and grow on nonwoven meshes of HYAFF, and that precoating of the material with fibronectin or collagen had a modest effect on cell growth and extracellular matrix production. Cell growth reached a maximum 7 days after seeding. Simple wrapping of flat sheets of nonwoven meshes containing vascular cells around a cylindrical mandrel, and culture under static conditions for 14 days, yielded tubular constructs suitable for mechanical tests. Despite cell colonization, constructs showed lower mechanical resistance as compared with porcine coronary arteries. The material used and the technique developed result in highly cellularized tubular constructs. Whether the mechanical properties may be improved by dynamic culture conditions is worthy of investigation.

A comparative evaluation of chondrocyte/scaffold constructs for cartilage tissue engineering

This study aimed to evaluate three biodegradable scaffolds as cell carriers for in vitro cartilage regeneration using mature human chondrocyte cells. We compared cell distribution, viability and morphology and we evaluated the mechanical properties of the constructs after 2 weeks of in vitro culture. The materials used as scaffolds were fibrin glue, a collagen sponge and a polyurethane foam (DegraPol(R)). Fibrin glue was found unsuitable as a chondrocyte carrier vehicle after culture times longer than a few days, probably due to significant barriers to nutrients and oxygen diffusion, and the material weakened rapidly. The collagen-based sponge was found to be unsuitable to support chondrocyte survival in vitro, although the presence of newly synthesized collagen was observed in these constructs. The synthetic biodegradable scaffold was more adequate in supporting cell survival and mechanical properties. After 2 weeks of static culture, the storage modulus obtained by dynamic shear testing was in the order of 0.7 kPa in fibrin constructs, 3.7 kPa in collagen constructs and 105 kPa in DegraPol(R) constructs. The better mechanical stability of the synthetic foam supports further investigation in the possible use of synthetic biomaterials as biodegradable scaffolds for in vitro cartilage regeneration. (Journal of Applied Biomaterials & Biomechanics 2004; 2: 55-64).

The effect of media perfusion on three-dimensional cultures of human chondrocytes: integration of experimental and computational approaches

This work examines the effect of perfusion on human mature articular chondrocytes cultured on synthetic biodegradable scaffolds (DegraPol). Human chondrocytes were isolated, seeded on the scaffolds and subjected to perfused culture at a flow rate of 0.5 ml/min, corresponding to an average inlet fluid velocity of 44 microm/s, with flow inversion every 1 minute. The flow was imposed at the construct surface in some constructs, it was forced through the construct thickness in other constructs and was absent in the static controls. We compared cell viability and morphology and we evaluated material properties of the constructs at 1 month of culture. Thickness-perfused constructs showed significantly higher material properties and roughly a two-fold cell viability, when compared both to surface-perfused constructs and to static controls. Chondrocytes maintained a phenotypic morphology in all experiments, probably favoured by a limited cell-scaffold interaction. Biosynthetic activity could be demonstrated only in the bioreactor-cultured constructs. In this experimental model, a bi-directional flow of culture medium was applied to the cells at a macroscopic level and computational modelling was used to quantify the fluid-dynamic environment induced on the cells at a microscopic level. This method may be used to quantify the effects of fluid-dynamic shear on the growth modulation of tissue-engineered cartilage constructs, to potentially enhance tissue growth in vitro.

Radial artery remodeling in response to shear stress increase within arteriovenous fistula for hemodialysis access

It is known that changes in blood flow induce vascular remodeling and that shear stress, the tractive force acting on the vessel wall due to blood flowing, influences endothelial cell function. The aim of the present study was to investigate the relation between changes in pulsatile shear forces and arterial remodeling in response to chronic elevation in blood flow within the radial artery. The authors studied vessel diameter, flow rate, and shear stress in the radial artery of uremic patients before and after surgical creation of a native arteriovenous fistula for hemodialysis access. For this purpose, the authors used echo-color-Doppler ultrasound to perform diameter and blood velocity measurements. Time-function blood flow rate and wall shear stress were calculated based on arterial diameter, center-line velocity wave-form, and blood viscosity, using a numerical method developed according to Womersley's theory for unsteady flow in tubes. The results confirmed that the radial artery diameter increases in response to a chronic increase in blood flow in uremic patients. Moreover, it seems that the radial artery dilates in such a way as to maintain the peak wall shear stress constant, suggesting that endothelial cells sense the maximum rather than the time-averaged wall shear stress. This finding may lead to further understanding of the mechanisms responsible for endothelial response to physical stimulation by flowing blood.

The response of endothelial cells to fluid shear stress using a co-culture model of the arterial wall

An endothelial cell (EC) smooth muscle cell (SMC) co-culture model of the arterial wall was used to study the effect of fluid shear stress on EC behavior. This model, in addition to being a more realistic tissue analogue, is a valuable research tool for studying the effects of mechanical stimulation upon the behavior of both SMCs and ECs. In the present study, a 10% cyclic strain was used to alter the characteristics of an SMC-seeded collagen gel. This form of strain preconditioning resulted in a rearrangement of the vessel wall that yielded circumferentially oriented cells and collagen fibrils. The preconditioned collagen gel was subsequently seeded with ECs and exposed to fluid-induced shear stress (10 dynes/cm2) for 48 hr. In the absence of flow, ECs seeded on slab constructs were oriented with the underlying collagen fibrils. Sheared constructs exhibited ECs oriented in the flow direction. Shear stress also affected EC proliferation, reducing the total number of dividing ECs by as much as 48 percent compared to unsheared constructs. The shear-induced reduction in proliferation was further enhanced when constructs were first strain-preconditioned (64% reduction). Moreover, conditioned media from shear stress experiments inhibited proliferation of ECs seeded on tissue culture plastic. These results suggest that EC response to fluid shear stress in a collagen co-culture model is influenced by the underlying substrate, and one that in this study is modified by strain preconditioning.

Computational geometry for patient-specific reconstruction and meshing of blood vessels from MR and CT angiography

Investigation of three-dimensional (3-D) geometry and fluid-dynamics in human arteries is an important issue in vascular disease characterization and assessment. Thanks to recent advances in magnetic resonance (MR) and computed tomography (CT), it is now possible to address the problem of patient-specific modeling of blood vessels, in order to take into account interindividual anatomic variability of vasculature. Generation of models suitable for computational fluid dynamics is still commonly performed by semiautomatic procedures, in general based on operator-dependent tasks, which cannot be easily extended to a significant number of clinical cases. In this paper, we overcome these limitations making use of computational geometry techniques. In particular, 3-D modeling was carried out by means of 3-D level sets approach. Model editing was also implemented ensuring harmonic mean curvature vectors distribution on the surface, and model geometric analysis was performed with a novel approach, based on solving Eikonal equation on Voronoi diagram. This approach provides calculation of central paths, maximum inscribed sphere estimation and geometric characterization of the surface. Generation of adaptive-thickness boundary layer finite elements is finally presented. The use of the techniques presented here makes it possible to introduce patient-specific modeling of blood vessels at clinical level.

Radial artery wall shear stress evaluation in patients with arteriovenous fistula for hemodialysis access

It has been extensively documented that changes in blood flow induce vascular remodeling and this phenomenon seems to be correlated to the shear forces imposed on the vessel wall by motion of blood. Wall shear stress, the tractive force that acts on the endothelium, has been shown to influence endothelial cell function. To study changes in wall shear stress that develop on the vessel wall upon changes of blood flow, we set up a technique that allows estimation of shear stress in the radial artery of patients on chronic hemodialysis therapy. The technique is based on color-flow Doppler examination of the radial artery before and after surgical creation of radiocephalic fistula for hemodialysis. Calculation of time function wall shear stress and blood flow rate in the radial artery is performed on the basis of arterial diameter, center-line velocity waveform and blood viscosity, using a numerical method developed according to Womersley's theory for pulsatile flow in tubes. The results presented confirm that the model developed is suitable for calculation of the wall shear stress that develops in the radial artery of patients before and after surgical creation of an arteriovenous fistula for hemodialysis. This methodology was developed for characterization of wall shear stress in the radial artery but may be well applied to other vessels that can be examined by echo-Doppler technique.

Effects of combined ACE inhibitor and angiotensin II antagonist treatment in human chronic nephropathies

BACKGROUND

Proteinuria predicts renal disease progression, and its reduction by angiotensin-converting enzyme inhibitors (ACEi) or angiotensin II receptor antagonists (ARA) is renoprotective.

METHODS

In this prospective, randomized, cross-over study of 24 patients with nondiabetic, chronic nephropathies, we compared the effects on proteinuria, renal hemodynamics, and glomerular permselectivity of 8 weeks with comparable blood pressure control achieved by benazepril (10 mg/day) and valsartan (80 mg/day) combined therapy with those achieved by benazepril (20 mg/day) or valsartan (160 mg/day) alone.

RESULTS

Despite comparable changes in blood pressure and glomerular filtration rate (GFR), combined therapy decreased proteinuria more than benazepril (-56% vs. -45.9%, P=0.02) and valsartan (-41.5%, P=0.002). Changes in urinary protein to creatinine ratio followed the same trend. Filtration fraction and renal vascular resistances (RVR) decreased more with combined (-14.7%,-23.7%) or benazepril (-12.4%, -20.5%) than with valsartan (-2.7%, -12.5%, P < 0.05 vs. both). RVR changes, adjusted for GFR changes, were associated with those in proteinuria (P < 0.05). Changes in glomerular permeability were comparable and did not predict different changes in proteinuria in the three groups.

CONCLUSION

At comparable blood pressure, combined ACEi and ARA decreased proteinuria better than ACEi and ARA. The greater antiproteinuric effect most likely depended on an ACEi-related hemodynamic effect, in addition to glomerular size selectivity amelioration. Long-term combined ACEi and ARA therapy may be more renoprotective than treatment with each agent alone.

Effect of angiotensin II antagonism on the regression of kidney disease in the rat

BACKGROUND

Normalization of proteinuria and even regression of glomerulosclerosis seem to occur in progressive renal disease upon blockade of the renin-angiotensin system. Here we quantified the effect of a combination of an angiotensin converting enzyme (ACE) inhibitor and an angiotensin II (Ang II) receptor antagonist on renal function and structure in spontaneous overt nephropathy in male Munich Wistar Fromter (MWF) rats.

METHODS

Three groups of MWF rats were used: group 1 was studied at 25 weeks to provide baseline renal function and structure; group 2 was followed until 40 weeks of age; group 3 was treated with lisinopril (40 mg/L) and valsartan (180 mg/L) in drinking water from 25 to 40 weeks. A group of untreated Wistar rats (group 4, 40 weeks) was used as the control. At the end of the study renal hemodynamics, kidney tissue morphology, accumulation of type III collagen and evaluation of interstitial inflammatory cells were performed.

RESULTS

MWF rats spontaneously developed hypertension, proteinuria, glomerulosclerosis, interstitial volume expansion and protein cast accumulation. Combined treatment completely reversed protein excretion and ameliorated renal plasma flow and the glomerular ultrafiltration coefficient. The combined therapy was effective in halting progressive glomerulosclerosis, particularly in glomeruli with mild sclerotic lesions, and reduced interstitial volume expansion. Type III collagen accumulation and protein cast also were reversed. Infiltrating cells were massively present in the interstitium already at 25 weeks, and augmented at 40 weeks in untreated rats. Combined treatment reduced infiltrating cells to values comparable to normal controls.

CONCLUSIONS

These data indicate that in animals with spontaneous overt nephropathy, Ang II antagonism normalized proteinuria, eliminated inflammatory cell infiltration, and ameliorated glomerular and tubular structural changes.

Effect of high dose ramipril with or without indomethacin on glomerular selectivity

BACKGROUND

Despite the accumulating evidence of their efficacy, angiotensin-converting enzyme inhibitors (ACEi) still provide imperfect renoprotection. Up-titration above conventional doses and combined therapy with other antiproteinuric agents may serve to achieve renoprotection in patients at risk of rapid disease progression.

METHODS

The effect of maximum tolerated ACEi doses (ramipril 15 mg/day, range 5 to 20) alone or combined with indomethacin (75 mg x 2/day) on urinary protein excretion (UPE) and glomerular barrier size-selective function was evaluated in 19 patients with chronic non-diabetic nephropathies and persistent proteinuria.

RESULTS

Maximum ramipril doses decreased UPE more effectively than non-ACEi therapy. Proteinuria reduction was associated with significant reduction (>50%) of the non-selective glomerular membrane shunt, but did not correlate with concomitant changes in arterial pressure and renal hemodynamics, nor was it influenced by treatment duration. The reduction in UPE and sieving coefficient of the largest neutral dextrans exceeded by twofold the reduction achieved by conventional ACEi doses in historical controls with similar renal dysfunction and proteinuria, previously studied under identical experimental conditions. Indomethacin did not influence renal effects of maximum ramipril doses and was prematurely withdrawn in six patients because of reversible side effects. Serum potassium significantly increased only in combination with indomethacin and never required treatment withdrawal.

CONCLUSIONS

Up-titration to maximally tolerated doses safely increases ACEi antiproteinuric effect and may serve to achieve maximum renoprotection in the long-term. Combination with indomethacin is poorly tolerated and ineffective. Innovative approaches are needed to use ACEi more effectively.

Geometric reconstruction for computational mesh generation of arterial bifurcations from CT angiography

A methodology for patient-specific model reconstruction and computational mesh generation of arterial bifurcations from angio-CT scans is presented. Three-dimensional models were reconstructed with a level set technique, analyzed with a skeletoning algorithm and automatically decomposed into branches. Cooper scheme was then employed to generate high quality hexahedral mesh. We successfully applied our technique to the carotid bifurcations of two patients affected by severe atherosclerotic plaques. The proposed technique is fast, accurate and reproducible, and can be a useful tool for the evaluation of arterial fluid dynamics within conventional computed tomography investigations.

Mechanobiology of engineered cartilage cultured under a quantified fluid-dynamic environment

Natural cartilage remodels both in vivo and in vitro in response to mechanical forces and hence mechanical stimulation is believed to have a potential as a tool to modulate extra-cellular matrix synthesis in tissue-engineered cartilage. Fluid-induced shear is known to enhance chondrogenesis on animal cells. A well-defined hydrodynamic environment is required to study the biochemical response to shear of three-dimensional engineered cell systems. We have developed a perfused-column bioreactor in which the culture medium flows through chondrocyte-seeded porous scaffolds, together with a computational fluid-dynamic model of the flow through the constructs' microstructure. A preliminary experiment of human chondrocyte growth under static versus dynamic conditions is described. The median shear stress imposed on the cells in the bioreactor culture, as predicted by the CFD model, is 3 x 10(-3) Pa (0.03 dyn/cm(2)) at a flow rate of 0.5 ml/min corresponding to an inlet fluid velocity of 44.2 mum/s. Providing a fluid-dynamic environment to the cells yielded significant differences in cell morphology and in construct structure.

Automatic generation of glomerular capillary topological organization

Glomerular structural changes are conventionally investigated by optical or electron microscopy on two-dimensional (2D) sections. To understand the relationship between functional and structural changes of glomerular capillary networks in more detail, three-dimensional (3D) investigation of the capillary tufts is required. Since confocal microscopy and scanning electron microscopy cannot completely show the 3D topological organization of the capillary tuft, we have developed an automatic method to obtain a 3D model of the glomerular capillary lumen structure and to derive its topological organization. Serial semithin sections of a glomerular tuft, from rat kidney tissue, were digitized at high resolution. Capillary lumens were digitally outlined and segmented images were automatically aligned. A 3D model of the capillary tuft was automatically generated using the Visualization Toolkit library and the Marching Cubes algorithm. We then developed an original algorithm for automatic 3D skeletonization of capillary lumen volume to identify capillary segments and bifurcations and to obtain the topological organization of the network and geometric parameters of capillary segments (length, radius, and spatial configuration). Capillary segment connectivity was graphically presented in a 2D layout with an automatic procedure, revealing the lobular organization of the network. This technique, successfully applied to serial sections of a glomerular capillary, can be used to study a population of glomerular capillaries to disclose the structural effects of pathological conditions. The methodology can be extended to other vascular structures, such as the microcirculation of neoplastic tissues.

Angiotensin-converting enzyme inhibition prevents glomerular-tubule disconnection and atrophy in passive Heymann nephritis, an effect not observed with a calcium antagonist

In proteinuric nephropathies tubular atrophy leads to glomerular-tubule disconnection through an unknown mechanism. Here we studied whether proteinuria promoted glomerular-tubule disconnection in individual nephrons and whether this phenomenon was prevented by an angiotensin-converting enzyme (ACE) inhibitor. Passive Heymann nephritis (PHN) and control rats were studied at 4 and 8 months. Two additional groups of PHN rats received lisinopril (40 mg/L) or a calcium channel blocker (lacidipine, 3 mg/kg) from day 7 after surgery to 8 months. At sacrifice, kidneys were serially sectioned to identify glomerular- tubule abnormalities in individual nephrons and changes in interstitial volume. In PHN rats, the time-dependent increase in proteinuria was paralleled by tubular atrophy leading to glomerular-tubule disconnection and interstitial volume enlargement. Marked apoptosis was invariably found in atrophic tubules in contrast to the absent or very mild terminal dUTP nick-end labeling staining in tubules normally connected to glomeruli in PHN animals. Treatment with an ACE inhibitor prevented hypertension, proteinuria, the formation of atrophic tubuli, glomerular-tubule disconnection and limited the fractional interstitial volume expansion. Although lacidipine limited hypertension, it did not reduce proteinuria or prevent tubular atrophy and disconnection. Multivariate analysis showed that the appearance of atubular glomeruli and the increase in interstitial volume were better predicted by proteinuria than blood pressure. This study suggests that ACE inhibitors effectively prevent glomerular-tubule disconnection possibly by their ability of reducing proteinuria, which in turn favors proximal tubular cell apoptosis. Agents that only reduced hypertension but not proteinuria do not affect tubular behavior.

Verotoxin-1-induced up-regulation of adhesive molecules renders microvascular endothelial cells thrombogenic at high shear stress

Verotoxin-1 (VT-1)-producing Escherichia coli is the causative agent of postdiarrheal hemolytic uremic syndrome (D+HUS) of children, which leads to renal and other organ microvascular thrombosis. Why thrombi form only on arterioles and capillaries is not known. This study investigated whether VT-1 directly affected endothelial antithrombogenic properties promoting platelet deposition and thrombus formation on human microvascular endothelial cell line (HMEC-1) under high shear stress. Human umbilical vein endothelial cells (HUVECs) were used for comparison as a large-vessel endothelium. HMEC-1 and HUVECs were pre-exposed for 24 hours to increasing concentrations of VT-1 (2-50 pM) and then perfused at 60 dynes/cm(2) with heparinized human blood prelabeled with mepacrine. Results showed that VT-1 significantly increased platelet adhesion and thrombus formation on HMEC-1 in comparison with unstimulated control cells. An increase in thrombus formation was also observed on HUVECs exposed to VT-1, but to a remarkably lower extent. The greater sensitivity of HMEC-1 to the toxin in comparison with HUVECs was at least in part due to a higher expression of VT-1 receptor (20-fold more) as documented by FACS analysis. The HMEC-1 line had a comparable susceptibility to the thrombogenic effect of VT-1 as primary human microvascular cells of the same dermal origin (HDMECs). The adhesive molecules involved in VT-induced thrombus formation were also studied. Blocking the binding of von Willebrand factor to platelet glycoprotein Ib by aurintricarboxylic acid (ATA) or inhibition of platelet alpha(IIb)beta(3)-integrin by chimeric 7E3 Fab resulted in a significant reduction of VT-1-induced thrombus formation, suggesting the involvement of von Willebrand factor-platelet interaction at high shear stress in this phenomenon. Functional blockade of endothelial beta(3)-integrin subunit, vitronectin receptor, P-selectin, and PECAM-1 with specific antibodies was associated with a significant decrease of the endothelial area covered by thrombi. Confocal microscopy studies revealed that VT-1 increased the expression of vitronectin receptor and P-selectin and redistributed PECAM-1 away from the cell-cell border of HMEC-1, as well as of HDMECs, thus indicating that the above endothelial adhesion molecules are directly involved and possibly determine the effect of VT-1 on enhancing platelet adhesion and thrombus formation in microvascular endothelium. These results might help to explain why thrombi in HUS localize in microvessels rather than in larger ones and provide insights on the molecular events involved in the process of microvascular thrombosis associated with D+HUS.

Post-transplant renal artery stenosis: the hemodynamic response to revascularization

BACKGROUND

Percutaneous transluminal angioplasty and stenting are relatively noninvasive approaches to treat post-transplant renal artery stenosis. However, the real impact of this procedure on renal function recovery has never been quantitated precisely to date.

METHODS

In eight consecutive renal transplant patients with renal graft artery stenosis, blood pressure, body weight, and anatomical, functional, and Doppler ultrasound parameters were evaluated before and one month after renal artery transluminal angioplasty and stenting. On both occasions, glomerular filtration rate and renal plasma flow were evaluated by inulin and paraaminohippuric acid renal clearances, and glomerular size-selective function was evaluated by the fractional clearances of neutral dextran macromolecules.

RESULTS

The correction of renal artery stenosis, by normalizing renal vascular resistances, fully restored kidney perfusion and decreased arterial blood pressure, relieved water and sodium retention, restored an almost laminar arterial blood flow, and normalized vascular shear stress without appreciable effects on glomerular barrier size-selective function and proteinuria. Preangioplasty and postangioplasty renal resistive indices and peak systolic blood velocity estimated by Doppler ultrasounds were significantly correlated with the effective renal plasma flow and the blood velocity calculated at the site of stenosis. All patients were discharged without sequelae one or two days after angioplasty.

CONCLUSIONS

Percutaneous transluminal angioplasty and stenting are safe and effective procedures to normalize the functional changes sustained by hemodynamically significant artery stenosis after renal transplantation. Doppler ultrasound scanning is a reliable and reproducible technique to monitor the renal functional response to vascular reperfusion.

Computational fluid dynamics of a vascular access case for hemodialysis

Vascular accesses (VA) for hemodialysis are usually created by native arteriovenous fistulas (AVF) or synthetic grafts. Maintaining patency of VA continues to be a major problem for patients with end-stage renal disease, since in these vessels thrombosis and intimal hyperplasia often occur. These lesions are frequently associated with disturbed flow that develops near bifurcations or sharp curvatures. We explored the possibility of investigating blood flow dynamics in a patient-specific model of end-to-end native AVF using computational fluid dynamics (CFD). Using digital subtraction angiographies of an AVF, we generated a three-dimensional meshwork for numerical analysis of blood flow. As input condition, a time-dependent blood waveform in the radial artery was derived from centerline velocity obtained during echo-color-Doppler ultrasound examination. The finite element solution was calculated using a fluid-dynamic software package. In the straight, afferent side of the radial artery wall shear stress ranged between 20 and 36 dynes/cm2, while on the inner surface of the bending zone it increased up to 350 dynes/cm2. On the venous side, proximal to the anastomosis, wall shear stress was oscillating between negative and positive values (from -12 dynes/cm2 to 112 dynes/cm2), while distal from the anastomosis, the wall shear stress returned within the physiologic range, ranging from 8 to 22 dynes/cm2. Areas of the vessel wall with very high shear stress gradient were identified on the bending zone of the radial artery and on the venous side, after the arteriovenous shunt. Secondary blood flows were also observed in these regions. CFD gave a detailed description of blood flow field and showed that this approach can be used for patient-specific analysis of blood vessels, to understand better the role of local hemodynamic conditions in the development of vascular lesions.

Influence of donor age on bovine pancreatic islet isolation

BACKGROUND

Pancreatic islets from pigs are largely used for experimental studies. However, pancreas harvesting requires modification of conventional slaughtering to reduce ischemia time. It has been shown that bovine pancreatic islets can be more easily obtained and they show satisfactory in vitro and in vivo function. To improve the isolation procedure we compared the effect of bovine donor age on islet isolation.

METHODS

Islets were isolated by collagenase digestion and sequential sieving from calves (6 months of age) and from adult bovine (> 16 months of age). After isolation the number of islet equivalents was calculated and histological and immunohistochemical studies performed. The purity and viability of islet for each preparation was also estimated. In vitro function of islets was evaluated by static insulin secretion assay, and alginate encapsulated islets were transplanted in streptozotocin-induced diabetic rats for in vivo functional evaluation.

RESULTS

A significantly higher number of islets were obtained from calf pancreas, compared with adult bovine pancreas. Hystological examination showed intact morphologic features of islets. The purity of islet preparations was higher from calf pancreas than from adult pancreas. Cell viability, and insulin production in presence of high glucose concentration, were not affected by donor age. All animals receiving microencapsulated islets from calves showed normoglycemia for prolonged periods (17-40 days).

CONCLUSIONS

These results indicate that pancreatic islet isolation is more efficient from juvenile bovine than from adult. Calf pancreas is a good and convenient source of tissue for massive islet isolation for experimental studies.

Ringtail in suckling Munich Wistar Fromter rats: a histopathologic study

Ringtail is a pathologic condition of the tail of rats and other rodents that is traditionally attributed to low environmental humidity, although dietary deficiencies, genetic susceptibility, environmental temperature, and degree of hydration of the animal also have been suggested as possible causes. To the authors' knowledge, a detailed histopathologic study that may serve to shed light on the etiopathogenesis of this disease has not yet been published. We describe the histologic findings of ringtail observed in 12 suckling Munich Wistar Fromter (MWF) rats from two litters. Epidermal hyperplasia characterized by orthokeratotic and parakeratotic hyperkeratosis and acanthosis was observed in all affected rats. Numerous often dilated vessels were present in the dermis of tails that appeared of red/brown color at gross examination. In severe cases, the dilated vascular structures were thrombotic and accompanied by dermal hemorrhages and focal coagulative necrosis of the overlying epidermis. These findings suggest that epidermal acanthosis and hyperkeratosis are the main and primary events in the development of ringtail. To clarify the cause of this disease, future studies should be focused on the numerous factors that can induce such epidermal changes.

A novel interpretation of the role of von Willebrand factor in thrombotic microangiopathies based on platelet adhesion studies at high shear rate flow

Clinical manifestations of thrombotic microangiopathies (TMA) are secondary to platelet aggregation and thrombotic occlusion of the microvasculature of the affected organs. Abnormalities in von Willebrand factor (vWF) in these patients were considered instrumental in promoting the process leading to microvascular thrombosis. We evaluated the capacity of plasma in these patients to induce adhesion of normal platelets and thrombus formation under conditions of controlled fluid shear stress. We also studied vWF multimeric distribution to establish whether abnormalities of this glycoprotein correlate with platelet adhesion and thrombus formation. Plasma from patients in the acute phase and remission showed the same capacity to induce platelet adhesion and thrombus formation at a low level of shear rate (600 sec(-1)) as plasma from control subjects. At a high shear rate (1,500 sec(-1)), platelet adhesion and thrombus dimensions were significantly increased (P: < 0.05) by plasma from patients with TMA compared with controls. The capacity to enhance thrombus formation at high shear stress was present during the acute phase and disease remission and did not correlate with the presence of unusually large vWF multimers. Increased thrombus formation with patient plasma is completely normalized by blocking the interaction of vWF with the platelet receptors, glycoprotein (GP)Ib and GPIIb-IIIa, suggesting that the phenomenon is completely mediated by vWF. Our results suggest the possibility of an intrinsically altered vWF molecule in these patients that is probably more effective than normal vWF in mediating platelet adhesion and thrombus formation.

Localization of cerebral arterovenous malformations using digital angiography

Since 1989 we performed stereotactic radiotherapy treatments of cerebral arterovenous malformations (AVM), estimating three-dimensional (3-D) localization and shape of target volumes by the Leksell stereotactic helmet on two orthogonal radiographic projections. Due to the limitations of this method, we developed a new technique for the localization of the target volume using digital subtraction angiography (DSA) and digital image processing. To achieve this result we first developed a method to correct nonlinear distortion of DSA images using spatial relocation of image pixels based on a calibration grid. We then developed an algorithm for localization of the target volume using two independent DSA projections. Target volume coordinates in the helmet system are calculated using two DSA acquisitions taken with a free angle (approximately 90 degrees), one in the AP and the other in the LL direction. The helmet can be freely positioned between the x-ray source and the image plane. The projections of eight reference points inserted in the helmet at a known location, are used to calculate the transformation matrix between the two coordinate systems. We performed numerical and experimental validation of the system. A hypothetical random error (up to 2 mm) on image coordinates of the reference points allowed to determine that the error in target localization was less than 0.2 mm. Using DSA images of target points with a known location within a phantom, the error between calculated and actual location was, on average, 0.30+/-0.13 mm (mean+/-SD), with a maximum error of 0.49 mm. The results of numerical and experimental validations show that the system we have developed allows fast and accurate localization of the center of the target volume and it is suitable for efficient guiding during stereotactic radiosurgery of AVM.

Shear stress downregulation of platelet-derived growth factor receptor-beta and matrix metalloprotease-2 is associated with inhibition of smooth muscle cell invasion and migration

BACKGROUND

After endovascular injury, smooth muscle cells (SMCs) may be exposed to hemodynamic shear stress (SS), and these forces modulate neointima accumulation. The effect of SS on SMC migration and invasion is unknown, and it was examined in the present study.

METHODS AND RESULTS

Bovine aortic SMCs were exposed to laminar SS of 12 dyne/cm(2) for 3 (SS3) or 15 (SS15) hours; control (C3 and C15) SMCs were kept under static conditions. Platelet-derived growth factor (PDGF)-BB-directed SMC migration and invasion were evaluated by a modified Boyden chamber assay with filters coated with either gelatin or reconstituted basement membrane proteins (Matrigel), respectively. SS15 inhibited both SMC migration and invasion (P<0.0001). There was no significant difference between SS3 and C3 cells. Media conditioned with SS15 cells exhibited a reduction in matrix metalloprotease-2 (MMP-2) by zymography and Western analysis. Northern blot analysis revealed no effect of SS15 on MMP-2 mRNA. In contrast, SS15 decreased MMP-2 activator and membrane-type MMP (MT-MMP or MMP-14) mRNA and protein. Furthermore, SS15 decreased PDGF receptor-beta (PDGF-Rbeta) mRNA and protein (P<0.05), and the SS-dependent decrease in PDGF-BB-directed cell migration was rescued by overexpressing PDGF-Rbeta.

CONCLUSIONS

SS inhibits SMC migration and invasion via diminished PDGF-Rbeta expression. This effect of SS is associated with decreased MMP-2 secretion and MT-MMP downregulation.

Effect of angiotensin-converting enzyme inhibition on glomerular basement membrane permeability and distribution of zonula occludens-1 in MWF rats

The mechanism(s) by which angiotensin-converting enzyme (ACE) inhibitors prevent glomerular membrane loss of permselective function is still not understood. In male MWF rats, which develop spontaneous proteinuria with age, ACE inhibitors prevent proteinuria and increase glomerular ultrafiltration coefficient. These renoprotective effects are not associated with ultrastructural changes of capillary wall components. This study was undertaken to investigate whether ACE inhibitors modulate functional properties of glomerular basement membrane (GBM) and/or of epithelial cells, both of which have been suggested to play a role in the maintenance of the glomerular filtration barrier. The hydraulic and macromolecular permeability of the GBM were determined, by an in vitro filtration system, in untreated or lisinopril-treated rats and in Wistar rats taken as controls. By indirect immunofluorescence and immunoelectron microscopy, glomerular distribution of the tight junction protein zonula occludens- (ZO-1), a component of the slit diaphragm, was also studied. Results document that spontaneous proteinuria in MWF rats develops without significant changes in the permeability of the GBM to water and albumin, or in the ultrastructure of the podocyte foot processes, but is associated with an important alteration in the distribution of ZO-1 at the glomerular level. Lisinopril, which prevented proteinuria, also prevented glomerular redistribution of the protein. Thus, renoprotective effects of ACE inhibitors are not associated with changes in intrinsic functional properties of GBM, or ultrastructural changes of the epithelial cells, but rather with preservation of glomerular ZO-1 distribution and slit diaphragm function, which are essential for maintaining the filtration barrier.

ACE inhibition improves glomerular size selectivity in patients with idiopathic membranous nephropathy and persistent nephrotic syndrome

Patients with idiopathic membranous nephropathy (IMN) and persistent nephrotic-range proteinuria are at risk for progression to end-stage renal failure. Whether angiotensin-converting enzyme (ACE) inhibitors are also renoprotective in these patients remains elusive. In 14 patients with IMN (patients) and persistent proteinuria (protein > 3 g/24 h for >6 months), we studied mean arterial pressure (MAP), urinary protein excretion, glomerular filtration rate (GFR), renal plasma flow (RPF), and albumin and neutral dextran fractional clearance after 2 months washout from previous antihypertensive treatment (basal), after 2 months of enalapril (2.5 to 20 mg/d) therapy (posttreatment), and 2 months after enalapril withdrawal (recovery). MAP, proteinuria, and GFR were also measured at the same time points in 6 patients with IMN and persistent overt proteinuria maintained on conventional treatment throughout the study period (controls). Basal MAP, proteinuria, and GFR were similar in the two study groups. However, in patients at the end of the treatment period, MAP (posttreatment, 99.6 +/- 11.2 versus basal, 103.3 +/- 12.1 mm Hg; P < 0.05), proteinuria (posttreatment protein, 5.0 +/- 2.9 versus basal, 7.1 +/- 4.9 g/24 h; P < 0.05), albumin fractional clearance (posttreatment median, 1.7 x 10(-3); range, 0.2 to 22.7 x 10(-3) versus basal median, 4.1 x 10(-3); range, 0.4 to 22. 1 x 10(-3); P < 0.05), and fractional clearance of largest neutral dextrans (radii from 62 to 66 A) were significantly less than basal values. At recovery, MAP significantly increased to 106.6 +/- 11.7 mm Hg (P < 0.001 versus enalapril), but all other parameters remained less than basal values. GFR and RPF were similar at each evaluation. Changes in proteinuria after treatment withdrawal positively correlated (r = 0.72; P < 0.01) with baseline GFR. Theoretical analysis of dextran-sieving data indicated that ACE inhibitor treatment significantly improved glomerular membrane size-selective dysfunction. This effect persisted more than 2 months after treatment withdrawal. No patient had symptomatic hypotension, acute renal function deterioration, or hyperkalemia during enalapril treatment. Thus, in patients with IMN and long-term nephrotic syndrome, ACE inhibitor treatment, but not conventional therapy, improves glomerular barrier size selectivity. The antiproteinuric effect of ACE inhibition is long lasting, especially in patients with more severe renal insufficiency. This is the premise of a long-term renoprotective effect that may limit the need for treatment with more toxic drugs.

Angiotensin-converting enzyme inhibition prevents loss of glomerular hydraulic permeability in passive heymann nephritis

We used morphometric techniques and theoretical analysis to investigate structural and functional changes of the glomerular membrane that develop in passive Heymann nephritis (PHN), an experimental model of human membranous glomerulopathy The effect of angiotensin-converting enzyme (ACE) inhibition on the above parameters was also investigated to explore the mechanisms by which this treatment exerts functional and structural protection at the renal tissue level. Morphometric analysis of glomerular capillary by light and electron microscopy was performed in normal control rats and in rats injected with rabbit anti-Fx 1A antibody, 12 months after induction of PHN. A group of PHN rats treated with lisinopril during the observation period was also investigated. Glomerular capillary architecture was not significantly altered in PHN rats, thus glomerular volume and capillary lumen volume were comparable with normal controls; only mesangial volume was significantly elevated in PHN rats. Glomerular membrane structure was significantly affected by PHN: the thickness of the glomerular basement membrane (GBM) increased, and the frequency of epithelial filtration slits decreased. Electron-dense deposits in the subepithelial space of the GBM were estimated to occupy more than 20% of the GBM area. Theoretical analysis of glomerular hydraulic permeability allowed us to predict that, after these structural changes, the permeability of the GBM and the epithelial layer significantly decreased, with an average reduction in the ultrafiltration coefficient (Kf) of approximately 43%. ACE inhibition limited mesangial expansion and prevented changes of glomerular epithelial cells (filtration slit frequency) but not GBM thickening. Immune deposits within the GBM were only partially prevented by lisinopril. A selective effect on epithelial permeability was calculated in lisinopril-treated rats, and a partial preservation of Kf reduction was observed. These results suggest that structural changes of the GBM and epithelial cells that develop in PHN are responsible for the reduced filtration capacity observed in this model. ACE inhibition only partially prevented immune-deposits in the GBM and favorably affected epithelial cell structure. These selective effects on glomerular podocytes may contribute to preserve water and macromolecule permeability of the glomerular capillary wall in this immunologic model of kidney disease.

Xenogeneic serum promotes leukocyte-endothelium interaction under flow through two temporally distinct pathways: role of complement and nuclear factor-kappaB

Endothelial cell activation and mononuclear cell infiltration are consistent features of discordant xenograft rejection. This study evaluated whether xenogeneic serum--as a source of xenoreactive natural antibodies and complement--induced endothelial activation with consequent leukocyte adhesion and transmigration under flow conditions. Porcine aortic endothelial cells (PAEC) were incubated for 30 min, 1 h 30 min, or 5 h with 10% human serum or 10% porcine serum and then perfused with human leukocytes in a parallel plate flow chamber under flow (1.5 dynes/cm2). Adherent and transmigrated cells were counted by digital image analysis. Results showed that human serum significantly (P < 0.01) increased over time the number of adherent leukocytes compared with porcine serum. Stimulation of PAEC with human serum also promoted a progressive increase in leukocyte transmigration that reached statistical significance (P < 0.01) at 1 h 30 min and at 5 h compared with porcine serum. Studying the role of complement in leukocyte-endothelium interaction in xenogeneic conditions, a marked complement C3 deposition on PAEC exposed to human serum was shown by immunofluorescence, whereas cells incubated with porcine serum were negative. Next, it was documented that human serum decomplemented by heating and C3-deficient human serum failed to promote both leukocyte adhesion and transmigration, results that were comparable to porcine serum. To elucidate the intracellular mediators involved in endothelial cell activation by xenogeneic serum, this study focused on transcriptional factor nuclear factor-kappaB (NF-kappaB), a central regulator for the induction of different genes, including adhesive molecules and chemoattractants. Positive nuclear staining of NF-kappaB (p65 subunit) found by confocal fluorescence microscopy of PAEC exposed to human serum was taken to reflect NF-kappaB activation. NF-kappaB was instead strictly localized in the cell cytoplasm in PAEC incubated with the homologous serum. Heat-inactivated human serum failed to activate NF-kappaB. Electrophoretic mobility shift assay of nuclear extracts from PAEC exposed to human serum revealed an intense NF-kappaB activation that was inhibited by the NF-kappaB inhibitor pyrrolidinedithiocarbamate. The NF-kappaB inhibitors pyrrolidinedithiocarbamate and tosyl-phe-chloromethylketone did not affect the number of adherent and transmigrated leukocytes in PAEC exposed to human serum for 30 min and 1 h 30 min. Both inhibitors instead significantly reduced leukocyte adhesion and transmigration induced by human serum at 5 h. Confocal fluorescence microscopy studies showed that human serum induced an increase in the expression of vascular cell adhesion molecule-1 and intercellular adhesion molecule-1. Functional blocking of these adhesive molecules with the corresponding antibodies significantly inhibited xenogeneic serum-induced leukocyte adhesion. These data suggest that leukocyte adhesion and transmigration are directly dependent on complement deposited on PAEC in the early phase of cell activation (30 min and 1 h 30 min) induced by xenogeneic serum, whereas leukocyte adhesive events observed after 5 h of incubation of endothelial cells with xenogeneic serum are possibly regulated by transcription of NF-kappaB-dependent genes. The finding that xenogeneic serum promotes leukocyte-endothelial interaction depending on NF-kappaB activation might be relevant for designing future therapeutic strategies intended to prolong xenograft survival.

ACE inhibition induces regression of proteinuria and halts progression of renal damage in a genetic model of progressive nephropathy

Experimental data consistently indicate that renal disease progression is fully prevented in proteinuric glomerulopathies by long-enough angiotensin-converting enzyme (ACE) inhibition therapy. Whether regression of established proteinuria to normal can be achieved is, however, ill defined. The current study was designed with the aim to clarify whether ACE inhibition may induce regression of established proteinuria and renal structural damage in MWF rats, a genetic model of progressive proteinuria and renal injury. Animals treated with the ACE inhibitor lisinopril from 20 weeks of age (time when proteinuria is already important) and age-matched untreated rats were followed for 10 weeks. ACE inhibition normalized systolic blood pressure and progressively reduced proteinuria (from 172 +/- 79 to 81 +/- 23 mg/24 hours). In these animals, a highly significant correlation was obtained between baseline proteinuria and antiproteinuric response. At variance in untreated rats, proteinuria showed a marked increase in the 10-week follow-up period (from 165 +/- 57 to 325 +/- 86 mg/24 hours). Lisinopril prevented the progression of renal damage, as documented by a significantly lower incidence of glomeruli affected by sclerotic lesions (P < 0.01) than in untreated animals after the 10-week study period. Kidney tissue damage was comparable in lisinopril-treated rats and in untreated animals at 20 weeks of age, indicating that structural changes were arrested by the treatment. Thus, in proteinuric MWF rats, late-onset ACE inhibition normalized blood pressure, effectively and progressively restored high protein excretion rate toward normal values, and arrested progression of tissue damage.

Glomerular size-selective dysfunction in NIDDM is not ameliorated by ACE inhibition or by calcium channel blockade

BACKGROUND

In patients with insulin-dependent diabetes mellitus (IDDM) and overt nephropathy glomerular barrier size-selectivity progressively deteriorates with time and is effectively improved by angiotensin converting enzyme (ACE) inhibition. Whether similar glomerular functional changes develop in proteinuric patients with non-insulin-dependent diabetes mellitus (NIDDM), and whether antihypertensive agents can favorably affect glomerular filtration of macromolecules in these patients, has not been documented yet.

METHODS

We investigated renal hemodynamics and fractional clearance of neutral dextrans of graded sizes, in nine proteinuric patients with NIDDM and renal biopsy findings of typical diabetic glomerulopathy. Six healthy volunteers served as controls. We also investigated the effects of an ACE inhibitor and of a calcium channel blocker, both given in doses targeted to achieve a comparable level of systemic blood pressure control, on glomerular hemodynamics and sieving function. Theoretical analysis of glomerular macromolecule transport was adopted to evaluate intrinsic glomerular membrane permeability properties.

RESULTS

Fractional clearance of large macromolecules (42 to 66 A in radius) was significantly higher in diabetic patients than in controls, and the distribution of membrane pore radii was calculated to be shifted towards larger pore sizes in diabetics (mean radius increased from 55 to 60 A). Despite effective blood pressure control, neither antihypertensive affected glomerular hemodynamics to any significant extent. Fractional clearance of dextrans, as well as of albumin and IgG, and total urinary proteins were not modified by either treatments.

CONCLUSIONS

These data indicate that patients with NIDDM and overt nephropathy develop abnormalities in size-selective function of the glomerular barrier and, at variance to IDDM, such changes were not ameliorated either by ACE inhibition or calcium channel blockade.

ACE inhibition and ANG II receptor blockade improve glomerular size-selectivity in IgA nephropathy

Protein trafficking across the glomerular capillary has a pathogenic role in subsequent renal damage. Despite evidence that angiotensin-converting enzyme (ACE) inhibitors improve glomerular size-selectivity, whether this effect is solely due to ANG II blocking or if other mediators also play a contributory role is not clear yet. We studied 20 proteinuric patients with IgA nephropathy, who received either enalapril (20 mg/day) or the ANG II receptor blocker irbesartan (100 mg/day) for 28 days in a randomized double-blind study. Measurements of blood pressure, renal hemodynamics, and fractional clearance of neutral dextran of graded sizes were performed before and after 28 days of treatment. Both enalapril and irbesartan significantly reduced blood pressure over baseline. This reduction reached the maximum effect 4-6 h after drug administration but did not last for the entire 24-h period. Despite transient antihypertensive effect, proteinuria was effectively reduced by both treatments to comparable extents. Neither enalapril nor irbesartan modified the sieving coefficients of small dextran molecules, but both effectively reduced transglomerular passage of large test macromolecules. Theoretical analysis of sieving coefficients showed that neither drug affected significantly the mean pore radius or the spread of the pore-size distribution, but both importantly and comparably reduced the importance of a nonselective shunt pathway. These data suggest that antagonism of ANG II is the key mechanism by which ACE inhibitors exert their beneficial effect on glomerular size-selective function and consequently on glomerular filtration and urinary output of plasma proteins.