Apoptotic response to albumin overload: proximal vs. distal/collecting tubule cells

Blocking CHOP-dependent TXNIP shuttling to mitochondria attenuates albuminuria and mitigates kidney injury in nephrotic syndrome

Albuminuria is a hallmark of glomerular disease of various etiologies. It is not only a symptom of glomerular disease but also a cause leading to glomerulosclerosis, interstitial fibrosis, and eventually, a decline in kidney function. The molecular mechanism underlying albuminuria-induced kidney injury remains poorly defined. In our genetic model of nephrotic syndrome (NS), we have identified CHOP (C/EBP homologous protein)-TXNIP (thioredoxin-interacting protein) as critical molecular linkers between albuminuria-induced ER dysfunction and mitochondria dyshomeostasis. TXNIP is a ubiquitously expressed redox protein that binds to and inhibits antioxidant enzyme, cytosolic thioredoxin 1 (Trx1), and mitochondrial Trx2. However, very little is known about the regulation and function of TXNIP in NS. By utilizing Chop-/- and Txnip-/- mice as well as 68Ga-Galuminox, our molecular imaging probe for detection of mitochondrial reactive oxygen species (ROS) in vivo, we demonstrate that CHOP up-regulation induced by albuminuria drives TXNIP shuttling from nucleus to mitochondria, where it is required for the induction of mitochondrial ROS. The increased ROS accumulation in mitochondria oxidizes Trx2, thus liberating TXNIP to associate with mitochondrial nod-like receptor protein 3 (NLRP3) to activate inflammasome, as well as releasing mitochondrial apoptosis signal-regulating kinase 1 (ASK1) to induce mitochondria-dependent apoptosis. Importantly, inhibition of TXNIP translocation and mitochondrial ROS overproduction by CHOP deletion suppresses NLRP3 inflammasome activation and p-ASK1-dependent mitochondria apoptosis in NS. Thus, targeting TXNIP represents a promising therapeutic strategy for the treatment of NS.

Oxidized Albumin as a Mediator of Kidney Disease

Renal diseases are a global health concern, and nearly 24% of kidney disease patients are overweight or obese. Particularly, increased body mass index has been correlated with oxidative stress and urinary albumin excretion in kidney disease patients, also contributing to increased cardiovascular risk. Albumin is the main plasma protein and is able to partially cross the glomerular filtration barrier, being reabsorbed mainly by the proximal tubule through different mechanisms. However, it has been demonstrated that albumin suffers different posttranslational modifications, including oxidation, which appears to be tightly linked to kidney damage progression and is increased in obese patients. Plasma-oxidized albumin levels correlate with a decrease in estimated glomerular filtration rate and an increase in blood urea nitrogen in patients with chronic kidney disease. Moreover, oxidized albumin in kidney disease patients is independently correlated with higher plasma levels of transforming growth factor beta (TGF-β1), tumor necrosis factor (TNF-α), and interleukin (IL)-1β and IL-6. In addition, oxidized albumin exerts a direct effect on neutrophils by augmenting the levels of neutrophil gelatinase-associated lipocalin, a well-accepted biomarker for renal damage in patients and in different experimental settings. Moreover, it has been suggested that albumin oxidation occurs at early stages of chronic kidney disease, accelerating the patient requirements for dialytic treatment during disease progression. In this review, we summarize the evidence supporting the role of overweight- and obesity-induced oxidative stress as a critical factor for the progression of renal disease and cardiovascular morbimortality through albumin oxidation.

Liver infusion tryptose (LIT): the best choice for growth, viability, and infectivity of Leishmania infantum parasites

Leishmania spp. parasites have a complex biological cycle presenting basically two different morphological stages, the amastigote and promastigote forms. In vitro cultivation allows a more complete study of the biological aspects of these parasites, indicating better conditions for infection, immunoassay tests, drug evaluations, and vaccines. Thus, we evaluated the three most used culture media for Leishmania spp., Grace’s insect cell culture medium (Grace’s), liver infusion tryptose (LIT), and Schneider’s insect medium (Schneider’s), without supplementation or supplemented with fetal calf serum (FCS) and bovine serum albumin (Albumin) to evaluate the growth, viability, and infectivity of the L. infantum promastigotes. It was observed that promastigote forms have a better growth in LIT and Schneider’s with or without FCS when compared to that in Grace’s. The supplementation with albumin promoted greater viability of the parasites independent of the medium. For in vitro infection of J774.A1 macrophages using light microscopy and flow cytometry analyses, FCS-supplemented LIT and Grace’s promoted higher percentage of infected macrophages and parasite load compared with Schneider’s media. Taken together, our results demonstrated that the supplementation of LIT culture medium with FCS is the most suitable strategy to cultivate Leishmania infantum parasites enabling the maintenance of growth and infective parasites for research uses.

Differential kidney proximal tubule cell responses to protein overload by albumin and its ligands

Albuminuria is frequently associated with proximal tubule (PT) cytotoxicity that can feed back to cause glomerular damage and exacerbate kidney disease. PT cells express megalin and cubilin receptors that bind to and internalize albumin over a broad concentration range. How the exposure to high concentrations of albumin leads to PT cytotoxicity remains unclear. Fatty acids and other ligands bound to albumin are known to trigger production of reactive oxygen species (ROS) that impair PT function. Alternatively or in addition, uptake of high concentrations of albumin may overload the endocytic pathway and elicit downstream responses. Here, we used a well-differentiated PT cell culture model with high endocytic capacity to dissect the effects of albumin versus its ligands on endocytic uptake and degradation of albumin, production of ROS, and cell viability. Cellular responses differed dramatically, depending on the preparation of albumin tested. Knockdown of megalin or cubilin failed to prevent ROS production mediated by albumin ligands, suggesting that receptor-mediated internalization of albumin was not necessary to trigger cellular responses to albumin ligands. Moreover, albumin induced cytotoxic responses when added to the basolateral surface of PT cells. Whereas overnight incubation with high concentrations of fatty acid-free albumin had no overt effects on cell function or viability, lysosomal degradation kinetics were slowed upon longer exposure, consistent with overload of the PT endocytic/degradative pathway. Together, the results of our study demonstrate that the PT responds independently to albumin and to its ligands and suggest that the consequences of albumin overload in vivo may be dependent on metabolic state.

Autoantibodies Against Albumin in Patients With Systemic Lupus Erythematosus

Objectives: Autoantibodies and aberrant immune complexes are pathological hallmarks of systemic lupus erythematosus (SLE). This study aimed to determine the occurrence of IgG autoantibodies against human serum albumin (anti-HSA IgG) and their potential association with antibodies against bovine serum albumin (anti-BSA IgG) in patients with SLE.

Methods: Sera of 180 SLE patients included to the Swiss SLE Cohort Study and 188 age- and sex-matched healthy controls were evaluated. Levels of anti-HSA IgG and anti-BSA IgG were quantified by ELISA. Selected samples were further characterized using serum fractions obtained by fast liquid chromatography (FPLC).

Results: SLE patients had increased levels of anti-HSA IgG (p = 0.002) but similar levels of anti-BSA IgG compared to matched healthy controls. Anti-HSA IgG levels correlated with the SLE Disease Activity Index (SLEDAI), which was more pronounced in patients with an physician's global assessment (PGA) of ≥ 1 (r = 0.309, p = 0.0066). Anti-HSA IgG was partially complexed with serum albumin but also occurred as monomeric autoantibodies in highly positive SLE patients. A positive correlation between anti-HSA IgG and anti-BSA IgG was found that was stronger in SLE patients than in healthy controls (r = 0.3172, p < 0.001 vs. r = 0.2122, p < 0.0035). Binding of anti-BSA IgG was inhibited partially in the presence of HSA in samples with double positivity for anti-HSA and anti-BSA (median inhibition 47.9%, range 0.9–100%) and vice versa.

Conclusion: In SLE patients there is an increased prevalence of anti-HSA IgG antibodies that are associated with SLE disease activity.

Anti-apoptotic potential of several antidiabetic medicinal plants of the eastern James Bay Cree pharmacopeia in cultured kidney cells

Background

Our team has identified 17 Boreal forest species from the traditional pharmacopeia of the Eastern James Bay Cree that presented promising in vitro and in vivo biological activities in the context of type 2 diabetes (T2D).

We now screened the 17 plants extracts for potential anti-apoptotic activity in cultured kidney cells and investigated the underlying mechanisms.

Methods

MDCK (Madin-Darnby Canine Kidney) cell damage was induced by hypertonic medium (700 mOsm/L) in the presence or absence of maximal nontoxic concentrations of each of the 17 plant extracts. After 18 h’ treatment, cells were stained with Annexin V (AnnV) and Propidium iodide (PI) and subjected to flow cytometry to assess the cytoprotective (AnnV⁻/PI⁻) and anti-apoptotic (AnnV⁺/PI⁻) potential of the 17 plant extracts. We then selected a representative subset of species (most cytoprotective, moderately so or neutral) to measure the activity of caspases 3, 8 and 9.

Results

Gaultheria hispidula and Abies balsamea are amongst the most powerful cytoprotective and anti-apoptotic plants and appear to exert their modulatory effect primarily by inhibiting caspase 9 in the mitochondrial apoptotic signaling pathway.

Conclusion

We conclude that several Cree antidiabetic plants exert anti-apoptotic activity that may be relevant in the context of diabetic nephropathy (DN) that affects a significant proportion of Cree diabetics.

Proteinuria causes dysfunctional autophagy in the proximal tubule

Proteinuria is a major risk factor for chronic kidney disease progression. Furthermore, exposure of proximal tubular epithelial cells to excess albumin promotes tubular atrophy and fibrosis, key predictors of progressive organ dysfunction. However, the link between proteinuria and tubular damage is unclear. We propose that pathological albumin exposure impairs proximal tubular autophagy, an essential process for recycling damaged organelles and toxic intracellular macromolecules. In both mouse primary proximal tubule and immortalized human kidney cells, albumin exposure decreased the number of autophagosomes, visualized by the autophagosome-specific fluorescent markers monodansylcadaverine and GFP-LC3, respectively. Similarly, renal cortical tissue harvested from proteinuric mice contained reduced numbers of autophagosomes on electron micrographs, and immunoblots showed reduced steady-state LC3-II content. Albumin exposure decreased autophagic flux in vitro in a concentration-dependent manner as assessed by LC3-II accumulation rate in the presence of bafilomycin, an H⁺-ATPase inhibitor that prevents lysosomal LC3-II degradation. In addition, albumin treatment significantly increased the half-life of radiolabeled long-lived proteins, indicating that the primary mechanism of degradation, autophagy, is dysfunctional. In vitro, mammalian target of rapamycin (mTOR) activation, a potent autophagy inhibitor, suppressed autophagy as a result of intracellular amino acid accumulation from lysosomal albumin degradation. mTOR activation was demonstrated by the increased phosphorylation of its downstream target, S6K, with free amino acid or albumin exposure. We propose that excess albumin uptake and degradation inhibit proximal tubule autophagy via an mTOR-mediated mechanism and contribute to progressive tubular injury.

The association of a single-nucleotide polymorphism in CUBN and the risk of albuminuria and cardiovascular disease

BACKGROUND

Albuminuria is an important risk factor for cardiovascular disease (CVD). We have previously identified a missense single-nucleotide polymorphism (rs1801239) in the CUBN gene that is associated with albuminuria. Whether albuminuria is associated with CVD in the presence of the CUBN mutation is unknown.

METHODS

We analyzed participants from the Framingham Heart Study (n=6399, mean age 47 years, 53.4% women) who underwent genotyping of rs1801239. Cox proportional hazards models were used to test the association between microalbuminuria [UACR≥17 mg/g (men) and ≥25 mg/g (women)] and incident CVD stratified by the presence or absence of the CUBN risk allele. We tested whether the association between microalbuminuria and CVD was altered by the presence of the risk allele with interaction testing.

RESULTS

Overall, 21.1% of participants carried the risk allele. As expected, carriers of the risk (C) allele had a higher prevalence of microalbuminuria (10.7 versus 8.9%, P=0.04). During a mean follow-up of 10.4 years, 5.6% (n=346) of participants experienced a CVD event. Microalbuminuria was associated with an increased risk of CVD [hazards ratio (HR) 1.46, 95% confidence interval (CI) 1.14-1.88]. When stratified by risk allele carrier status, the HR for CVD was 1.95 (95% CI 1.15-3.29) among those with compared to 1.33 (95% CI 1.00-1.76) among those without the risk allele. There was no interaction between microalbuminuria and rs1801239 on CVD (Pinteraction=0.49).

CONCLUSIONS

MA is associated with CVD irrespective of the presence of the CUBN risk allele. These results challenge the concept that albuminuria in the setting of this mutation is benign.

Proteinuria and progression of glomerular diseases

One of the major challenges of nephrology is to develop therapeutic strategies to halt the progression of kidney diseases. In clinical settings, nephrotic-range proteinuria correlates with the rate of progression, particularly in glomerular diseases. Hence, the degree of proteinuria has been utilized to monitor the response to treatment as well as to predict outcome. However, the pathophysiology of proteinuria-induced progression remains unknown. Albumin accounts for the majority of the protein in nephrotic urine and as a result of this clinical observation studies have focused on understanding the adverse effects of albumin overload in the kidney. Albumin is internalized by receptor-mediated endocytosis in proximal tubule cells via low density lipoprotein (LDL) type receptor, megalin. Albumin at high concentrations mimicking nephrotic milieu has resulted in the upregulation of pro-inflammatory/fibrogenic genes and apoptosis in proximal tubule cells in in vivo and in vitro models of albumin overload. These properties of albumin on proximal tubule cells may explain extensive tubulointerstitial fibrosis and tubular atrophy observed in end-stage kidney disease. In addition to tubular toxicity, podocytes respond to proteinuric states by cytoskeletal alterations and loss of the differentiation marker synaptopodin. Identifying the molecular network of proteins involved in albumin handling will enable us to manipulate the specific signaling pathways and prevent damage caused by proteinuria.

Increased tubular proliferation as an adaptive response to glomerular albuminuria

Renal tubular atrophy accompanies many proteinuric renal diseases, suggesting that glomerular proteinuria injures the tubules. However, local or systemic inflammation and filtration of abnormal proteins known to directly injure tubules are also present in many of these diseases and animal models; therefore, whether glomerular proteinuria directly causes tubular injury is unknown. Here, we examined the renal response to proteinuria induced by selective podocyte loss. We generated mice that express the diphtheria toxin receptor exclusively in podocytes, allowing reproducible dose-dependent, specific ablation of podocytes by administering diphtheria toxin. Ablation of <20% of podocytes resulted in profound albuminuria that resolved over 1-2 weeks after the re-establishment of normal podocyte morphology. Immediately after the onset of albuminuria, proximal tubule cells underwent a transient burst of proliferation without evidence of tubular damage or increased apoptosis, resulting in an increase in total tubular cell numbers. The proliferative response coincided with detection of the growth factor Gas6 in the urine and phosphorylation of the Gas6 receptor Axl in the apical membrane of renal tubular cells. In contrast, ablation of >40% of podocytes led to progressive glomerulosclerosis, profound tubular injury, and renal failure. These data suggest that glomerular proteinuria in the absence of severe structural glomerular injury activates tubular proliferation, potentially as an adaptive response to minimize the loss of filtered proteins.

CUBN is a gene locus for albuminuria

Identification of genetic risk factors for albuminuria may alter strategies for early prevention of CKD progression, particularly among patients with diabetes. Little is known about the influence of common genetic variants on albuminuria in both general and diabetic populations. We performed a meta-analysis of data from 63,153 individuals of European ancestry with genotype information from genome-wide association studies (CKDGen Consortium) and from a large candidate gene study (CARe Consortium) to identify susceptibility loci for the quantitative trait urinary albumin-to-creatinine ratio (UACR) and the clinical diagnosis microalbuminuria. We identified an association between a missense variant (I2984V) in the CUBN gene, which encodes cubilin, and both UACR (P = 1.1 × 10(-11)) and microalbuminuria (P = 0.001). We observed similar associations among 6981 African Americans in the CARe Consortium. The associations between this variant and both UACR and microalbuminuria were significant in individuals of European ancestry regardless of diabetes status. Finally, this variant associated with a 41% increased risk for the development of persistent microalbuminuria during 20 years of follow-up among 1304 participants with type 1 diabetes in the prospective DCCT/EDIC Study. In summary, we identified a missense CUBN variant that associates with levels of albuminuria in both the general population and in individuals with diabetes.

Albumin and mammalian cell culture: implications for biotechnology applications

Albumin has a long historical involvement in design of media for the successful culture of mammalian cells, in both the research and commercial fields. The potential application of albumins, bovine or human serum albumin, for cell culture is a by-product of the physico-chemical, biochemical and cell-specific properties of the molecule. In this review an analysis of these features of albumin leads to a consideration of the extracellular and intracellular actions of the molecule, and importantly the role of its interactions with numerous ligands or bioactive factors that influence the growth of cells in culture: these include hormones, growth factors, lipids, amino acids, metal ions, reactive oxygen and nitrogen species to name a few. The interaction of albumin with the cell in relation to these co-factors has a potential impact on metabolic and biosynthetic activity, cell proliferation and survival. Application of this knowledge to improve the performance in manufacturing biotechnology and in the emerging uses of cell culture for tissue engineering and stem cell derived therapies is an important prospect.

Albumin transport and processing by the proximal tubule: physiology and pathophysiology

PURPOSE OF REVIEW

Significant epidemiological and clinical trial evidence supports the association between increased urinary albumin excretion, cardiovascular events and renal failure. An increase in albumin excretion has traditionally been considered to reflect a 'glomerular' leak of protein; however, it is now recognized that significant tubular reabsorption of albumin occurs under physiological conditions that may be modified by genetic determinants, systemic disease and drug therapies.

RECENT FINDINGS

The endocytosis of albumin by the proximal tubule is a highly regulated process depending on protein-protein interactions between several membrane proteins and scaffolding and regulatory molecules. The elucidation of these interactions is an ongoing research focus. There is also mounting evidence for a transcytotic pathway for retrieval of albumin from the tubular filtrate. The molecular basis for the role of albuminuria in both interstitial renal disease and cardiovascular pathology continues to be defined. The clinical implications of albuminuria due to a glomerular leak vs. reduced tubular reabsorption of albumin are, however, now under consideration. In particular, the prognostic implication of microalbuminuria induced by the more potent 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors is under study.

SUMMARY

The currently defined mechanisms underpinning the tubular reabsorption of albumin, how these are modified by pathology and pharmacology, and the clinical implications are the subject of this review.

Abrogation of Protein Uptake through Megalin-Deficient Proximal Tubules Does Not Safeguard against Tubulointerstitial Injury

Sustained proteinuria and tubulointerstitial damage have been closely linked with progressive renal failure. Upon excess protein endocytosis, tubular epithelial cells are thought to produce mediators that promote inflammation, tubular degeneration, and fibrosis. This concept was tested in a transgenic mouse model with megalin deficiency. Application of an anti-glomerular basement membrane serum to transgenic megalin-deficient mice [Cre(+)/GN] and megalin-positive littermates [Cre(-)/GN] produced the typical glomerulonephritis (GN) with heavy proteinuria in both groups. Tubulointerstitial damages correlated closely with glomerular damages in pooled Cre(+)/GN and Cre(-)/GN mice. Owing to a mosaic pattern of megalin expression in the mutant mice, Cre(+)/GN kidneys permitted side-by-side analysis of megalin-deficient and megalin-positive tubules in the same kidney. Protein endocytosis was found only in megalin-positive cells. TGF-beta, intercellular adhesion molecule, vascular cellular adhesion molecule, endothelin-1, and cell proliferation were high in megalin-positive cells, whereas apoptosis, heat-shock protein 25, and osteopontin were enhanced in megalin-deficient cells. No fibrotic changes were associated with either phenotype. Tubular degeneration with interstitial inflammation was found only in nephrons with extensive crescentic lesions at the glomerulotubular junction. In sum, enhanced protein endocytosis indeed led to an upregulation of profibrotic mediators in a megalin-dependent way; however, there was no evidence that endocytosis played a pathogenetic role in the development of the tubulointerstitial disease.

Mitochondria are the major targets in albumin-induced apoptosis in proximal tubule cells

Nephrotic-range proteinuria is considered a poor prognostic factor. A correlation between tubulointerstitial injury and the degree of proteinuria is well established. In an attempt to explain the tubular atrophy that is observed in advanced glomerulonephritides, this study investigated apoptotic mechanisms in cultured human proximal tubule cells (HKC-8) that were exposed to endotoxin-free albumin (5, 10, and 20 mg/ml). Apoptosis was detected by Hoechst 33342; annexin staining; and assays for caspases 3, 8, and 9. The apoptotic effect of albumin was maximal at 10 mg/ml albumin, and necrosis prevailed in cells that were incubated with 20 mg/ml. Increase in caspase-9 and -3 activity was observed starting at 6 and maximally at 16 to 24 h. The proapoptotic Bcl-2 protein Bax was upregulated at 6 h, associated with translocation of cytochrome-c from mitochondria to cytosol and alteration in the mitochondrial membrane potential. Production of reactive oxygen species (ROS) was significant at 6 h but declined at 16 and 24 h. Treatment with ROS scavenger dimethylthiourea or antioxidant N-acetylcysteine did not alleviate caspase-3 production. Pan protein kinase C inhibitor bisindolylmaleimide-1 protected the cells from apoptosis. It is concluded that albumin induces apoptosis in human proximal tubule cells by stimulating mitochondrial apoptotic pathway independent of ROS production.

Gene expression profiles of human proximal tubular epithelial cells in proteinuric nephropathies

In kidney disease renal proximal tubular epithelial cells (RPTEC) actively contribute to the progression of tubulointerstitial fibrosis by mediating both an inflammatory response and via epithelial-to-mesenchymal transition. Using laser capture microdissection we specifically isolated RPTEC from cryosections of the healthy parts of kidneys removed owing to renal cell carcinoma and from kidney biopsies from patients with proteinuric nephropathies. RNA was extracted and hybridized to complementary DNA microarrays after linear RNA amplification. Statistical analysis identified 168 unique genes with known gene ontology association, which separated patients from controls. Besides distinct alterations in signal-transduction pathways (e.g. Wnt signalling), functional annotation revealed a significant upregulation of genes involved in cell proliferation and cell cycle control (like insulin-like growth factor 1 or cell division cycle 34), cell differentiation (e.g. bone morphogenetic protein 7), immune response, intracellular transport and metabolism in RPTEC from patients. On the contrary we found differential expression of a number of genes responsible for cell adhesion (like BH-protocadherin) with a marked downregulation of most of these transcripts. In summary, our results obtained from RPTEC revealed a differential regulation of genes, which are likely to be involved in either pro-fibrotic or tubulo-protective mechanisms in proteinuric patients at an early stage of kidney disease.

Magnetic resonance measurements of renal blood flow and disease progression in autosomal dominant polycystic kidney disease

Whether changes in renal blood flow (RBF) are associated with and possibly contribute to cystic disease progression in autosomal dominant polycystic kidney disease (ADPKD) has not been ascertained. The Consortium for Radiologic Imaging Studies of Polycystic Kidney Disease (CRISP) was created to develop imaging techniques and analyses to evaluate progression. A total of 131 participants with early ADPKD had measurements of RBF and total kidney (TKV) and cyst (TCV) volumes by magnetic resonance and of GFR by iothalamate clearance at baseline and 1, 2, and 3 yr. The effects of age, gender, body mass index, hypertension status, mean arterial pressure (MAP), TKV, TCV, RBF, renal vascular resistance (RVR), GFR, serum uric acid, HDL and LDL cholesterol, 24-h urine volume, sodium (UNaE) and albumin (UAE) excretions, and estimated protein intake were examined at baseline on TKV, TCV, and GFR slopes. TKV and TCV increased, RBF decreased, and GFR remained stable. TKV, TCV, RVR, serum uric acid, UAE, UNaE, age, body mass index, MAP, and estimated protein intake were positively and RBF and GFR negatively correlated with TKV and TCV slopes. TKV, RBF, UNaE, and UAE were independent predictors of TKV and TCV slopes (structural disease progression). TKV, TCV, RVR, and MAP were negatively and RBF positively correlated with GFR slopes. Regression to the mean confounded the analysis of GFR slopes. TKV and RBF were independent predictors of GFR decline (functional disease progression). In ADPKD, RBF reduction (1) parallels TKV increase, (2) precedes GFR decline, and (3) predicts structural and functional disease progression.

Strategy for the development of a matched set of transport-competent, angiotensin receptor-deficient proximal tubule cell lines

In the proximal convoluted tubule (PCT) angiotensin II (Ang II) modulates fluid and electrolyte transport through at least two pharmacologically distinct receptor subtypes: AT(1) and AT(2). Development of cell lines that lack these receptors are potentially useful models to probe the complex cellular details of Ang II regulation. To this end, angiotensin receptor- deficient mice were bred with an Immortomouse(R), which harbors a thermolabile SV40 large-T antigen (Tag). S1 PCT segments from kidneys of F(2) mice were microdissected, placed in culture, and maintained under conditions that enhanced cell growth, i.e., promoted Tag expression and thermostability. Three different types of angiotensin receptor-deficient cell lines, (AT(1A) [-/-], Tag [+/-]), (AT(1B) [-/-], Tag [+/-]), and (AT(1A) [-/-], AT(1B) [-/-], Tag [+/+]), as well as wild type cell lines were generated. Screening and characterization, which were conducted under culture conditions that promoted cellular differentiation, included: measurements of transepithelial transport, such as basal monolayer short-circuit current (Isc; -3 to 3 microA/cm2), basal monolayer conductance (G, 2 to 10 mS/cm2), Na3(+)-phosphate cotransport (DeltaIsc of 2 to 3 microA/cm(2) at 1 mM), and Na(3)(+)-succinate cotransport (DeltaIsc of 1 to 9 microA/cm(2) at 2 mM). Morphology of cell monolayers showed an extensive brush border, well-defined tight junctions, and primary cilia. Receptor functionality was assessed by Ang II-stimulated beta-arrestin 2 translocation and showed an Ang II-mediated response in wild type but not (AT(1A) [-/ -], AT(1B) [-/-]) cells. Cell lines were amplified, yielding a virtually unlimited supply of highly differentiated, transport-competent, angiotensin receptor-deficient PCT cell lines.

Renal impact of fluid management with colloids: a comparative review

BACKGROUND AND OBJECTIVES

Colloids such as hydroxyethyl starch (HES), gelatin, dextran and albumin are useful for maintaining renal perfusion and function. The comparative renal effects of colloids have not been previously reviewed.

METHODS

Computer searches of the MEDLINE and EMBASE bibliographic databases and the Cochrane Library were conducted using the search terms: colloids; hetastarch; gelatin; dextrans; serum albumin; kidney failure; cardiac surgical procedures; and kidney transplantation. Relevant studies were also sought through hand searching and examination of reference lists. Results of identified studies were qualitatively summarized with account taken for potential confounding factors.

RESULTS

The three artificial colloids HES, gelatin and dextran all exhibited troublesome renal side-effects. Randomized trials have demonstrated adverse renal effects of HES in sepsis and surgery. Undesirable renal effects are common to all available HES solutions regardless of molecular weight, substitution or C2/C6 ratio. While some of its effects may be less severe than those of HES, gelatin also can adversely affect the kidney. A negative renal impact of dextran is well-established, although this colloid is now less extensively used than formerly. As the normal endogenous colloid, albumin exhibits a wide margin of renal safety, although albumin overdose needs to be avoided. Albumin also appears to exert protective effects on the kidney such as inhibition of apoptosis and scavenging of reactive oxygen species.

CONCLUSIONS

Colloids display important differences in their actions on the kidney. These contrasting renal effects should be considered in making fluid management decisions.