Characterization of primary cell cultures derived from rat renal proximal tubules

Isolation and establishment of skin-derived and mesenchymal cells from south American bat Artibeus planirostris (Chiroptera - Phyllostomidae)

Animal models represent a crucial tool for biological research, so the establishment of new cultures is fundamental for the discovery of new therapies and the understanding of mechanisms of cell development in the most diverse animals. Here, we report the successful establishment of two new primary cell cultures derived from a South American bat (Artibeus planirostris). The establishment of a new bat culture can help in the investigation of new zoonoses since bats have been proposed as carriers of these diseases. We evaluated the chromosomal stability of cells from different passages. Primary cultures were collected from ear tissues and bone marrow of A. planirostris. Cultures were expanded, and osteogenic and adipogenic inductions were conducted for 21 days. For osteogenic differentiation, the medium was supplemented with 0.1 μM dexamethasone, 3 mM β-glycerophosphate, and 10 μM L-ascorbic acid 2-phosphate. For adipogenic differentiation, the medium was supplemented with 5 μM rosiglitazone, 0.4 μM insulin, 0.1 mM indomethacin, and 0.1 μM dexamethasone. After the induction period, the cells were stained with Alizarin Red to assess osteogenic differentiation and Oil Red O to assess adipogenic differentiation. We observed the appearance of lipid droplets in adipocytes and the extracellular deposition of calcium matrix by osteocytes, indicating that bone marrow-derived cells and skin-derived cells of A. planirostris could successfully differentiate into these lineages. Also, the number of chromosomes remained stable for both primary cultures during passages 2, 4, 6, and 8.

19-Norvitamin D analogs for breast cancer therapy

The active form of vitamin D3, 1α,25-dihydroxyvitamin D3 (1α,25(OH)2D3 or calcitriol), is known to inhibit the proliferation and invasiveness of many types of cancer cells, including breast, colon, pancreatic, prostate, and liver cancer cells. These findings support the use of 1α,25(OH)2D3 for the treatment of these types of cancer. However, 1α,25(OH)2D3 can cause hypercalcemia, so analogs of 1α,25(OH)2D3 that are less calcemic but exhibit more potent anti-tumor activity would be good candidates as therapeutic agents. Therefore, a series of 19-norvitamin D analogs, in which the methylidene group on C19 is replaced with 2 hydrogen atoms, have been synthesized by several laboratories. In our laboratory, we have designed and synthesized a series of 2α-functional group substituted 19-norvitamin D3 analogs and examined their anti-proliferative activity. Among them, 2α- and 2β-(3-hydroxypropyl)-1α,25-dihydroxy-19-norvitamin D3 (MART-10 and MART-11) were found to be the most promising. Here, we review the rationale and approaches for the synthesis of different 19-norvitamin D analogs, and the pre-clinical studies using these analogs in breast cancer cells, in particular, we chose MART-10 for its potential application to the prevention and treatment of breast cancer.

Cyclosporine A induces senescence in renal tubular epithelial cells

The nephrotoxic potential of the widely used immunosuppressive agent cyclosporine A (CsA) is well recognized. However, the mechanism of renal tubular toxicity is not yet fully elucidated. Chronic CsA nephropathy and renal organ aging share some clinical features, such as renal fibrosis and tubular atrophy, raising the possibility that CsA may exert some of its deleterious effects via induction of a stress-induced senescent phenotype. We investigated this hypothesis in HK-2 cells and primary proximal tubular cells in vitro. CsA induced the production of H2O2, caused cell cycle arrest in the G0/G1 phase, and inhibited DNA synthesis. Furthermore, CsA exposure lead to a reduction of telomere length, increased p53 serine 15 phosphorylation, and caused an upregulation of the cell cycle inhibitor p21Kip1 (CDKN1A) mRNA levels. CsA caused an increase in p16INK4a (CDKN2A) expression after a 13-day exposure in primary proximal tubular cells but not in HK-2 cells. Coincubation of cells with CsA and catalase was able to prevent telomere shortening and partially restored DNA synthesis. In summary, CsA induces cellular senescence in human renal tubular epithelial cells, which can be attenuated by scavenging reactive oxygen species.

Nephrotoxicity testing in vitro--what we know and what we need to know

The kidney is affected by many chemicals. Some of the chemicals may even contribute to end-stage renal disease and thus contribute considerably to health care costs. Because of the large functional reserve of the kidney, which masks signs of dysfunction, early diagnosis of renal disease is often difficult. Although numerous studies aimed at understanding the mechanisms underlying chemicals and drugs that target various renal cell types have delivered enough understanding for a reasonable risk assessment, there is still an urgent need to better understand the mechanisms leading to renal cell injury and organ dysfunction. The increasing use of in vitro techniques using isolated renal cells, nephron fragments, or cell cultures derived from specific renal cell types has improved our insight into the molecular mechanisms involved in nephrotoxicity. A short overview is given on the various in vitro systems currently used to clarify mechanistic aspects leading to sublethal or lethal injury of the functionally most important nephron epithelial cells derived from various species. Whereas freshly isolated cells and nephron fragments appear to represent a sufficient basis to study acute effects (hours) of nephrotoxins, e.g., on cell metabolism, primary cultures of these cells are more appropriate to study long-term effects. In contrast to isolated cells and fragments, however, primary cultures tend to first lose several of their in vivo metabolic properties during culture, and second to have only a limited life span (days to weeks). Moreover, establishing such primary cultures is a time-consuming and laborious procedure. For that reason many studies have been carried out on renal cell lines, which are easy to cultivate in large quantities and which have an unlimited life span. Unfortunately, none of the lines display a state of differentiation comparable to that of freshly isolated cells or their primary cultures. Most often they lack expression of key functions (e.g., gluconeogenesis or organic anion transport) of their in vivo correspondents. Therefore, the use of cell lines for assessment of nephrotoxic mechanisms will be limited to those functions the lines express. Upcoming molecular biology approaches such as the transduction of immortalizing genes into primary cultures and the utilization of cells from transgenic animals may in the near future result in the availability of highly differentiated renal cells with markedly extended life spans and near in vivo characteristics that may facilitate the use of renal cell culture for routine screening of nephrotoxins.

Characterisation and uptake of paraquat by rat renal proximal tubular cells in primary culture

1 Uptake of the herbicide paraquat (PQ), by rat proximal tubular cells (PTC) in primary culture grown on a collagen coated support was investigated. 2 The uptake of PQ by PTC was predominantly from the basolateral side. The basolateral uptake of PQ was saturable with time and increasing concentrations, energy dependent and could be inhibited by certain organic cations. Using Michaelis Menten kinetics, the apparent K(m) was 778 +/- 241 microM and Vmax was 0.97 +/- 0.24 pmol/microgram protein/15 min for the basolateral uptake of PQ. Cimetidine (5.7 +/- 0.4 pg/microgram protein/ 30 min, P < 0.001) was the most potent inhibitor of PQ uptake, followed by quinine (6.5 +/- 0.4 pg/microgram protein/30 min, P < 0.01) and then tetraethylammonium (8.2 +/- 0.5 pg/microgram protein/30 min, P < 0.05) when compared with control (11 +/- 1 pg/microgram protein/30 min). N-methylnicotinamide, p-aminohippurate and putrescine did not inhibit the basolateral uptake of PQ. The sodium hydrogen exchange inhibitors, amiloride and its analogue, 5-(N,N hexamethylene) amiloride (HMA) inhibited both the apical and basolateral uptake of PQ. 3 The apical uptake of PQ was not saturable with increasing concentrations and was not inhibited by 2,4-dinitrophenol, but it was reduced by cimetidine (P < 0.01), quinine (P < 0.05) and a sodium potassium ATPase inhibitor, ouabain (P < 0.01). 4 It is concluded that PQ was taken up from the basolateral side of primary cultured rat PTC by an energy dependent transport system.

Susceptibility of primary cultures of proximal tubular and distal tubular cells from rat kidney to chemically induced toxicity

Isolated proximal tubular (PT) and distal tubular (DT) cells from rat kidney were cultured for up to 9 days under serum-free, hormonally-defined conditions on 35-mm polystyrene culture dishes. Several hormonal and growth factor supplements were assessed for their ability to promote growth (increased protein and DNA content) and stability of differentiated phenotype (high activities of gamma-glutamyltransferase and alkaline phosphatase as brush-border membrane markers in PT cells; maintenance of high activities of glutamate dehydrogenase as a mitochondrial marker in both PT and DT cells; maintenance of low and high activities of lactate dehydrogenase in PT and DT cells, respectively; expression of cytokeratins). Basal supplemented media (DMEM/F12, 1:1 v/v) contained insulin, hydrocortisone, epidermal growth factor, sodium selenite and transferrin as supplements. Additionally, triiodothyronine selectively promoted growth and stability of differentiated phenotype in PT cells and thyrocalcitonin selectively promoted growth and stability of differentiated phenotype in DT cells. On Day 3 of primary culture, PT and DT cells were incubated for up to 8 h with either tert-butyl hydroperoxide (tBH; 0.5-10 mM), methyl vinyl ketone (MVK; 1-10 mM), or p-aminophenol (PAP; 1-10 mM) and cellular injury, as assessed by cellular release of lactate dehydrogenase, was determined. DT cells were significantly more susceptible to injury from both tBH and MVK, but the two cell populations were equally susceptible to injury from PAP, which is the same susceptibility pattern seen in freshly isolated cells. These results suggest that primary cultures of rat renal PT and DT cells reflect similar biochemical properties as freshly isolated cells and are, therefore, useful models for study of chemically induced injury.

Phosphate transport inhibition by KW-3902, an adenosine A1 receptor antagonist, is mediated by cyclic adenosine monophosphate

We have previously demonstrated that 1,3-dipropyl-8-(3-noradamantyl) xanthine (KW-3902) has an inhibitory effect on phosphate (Pi) transport with no effect on glucose transport in the rat renal proximal tubular cell, similar to that of parathyroid hormone (PTH). In the current studies we investigated the effect of KW-3902, rat PTH (1-34), and 1,3-dipropyl-8-cyclopentylxanthine (DPCPX), another selective adenosine A1 receptor antagonist, on Pi transport and the production of cyclic adenosine monophosphate (cAMP). We then compared these effects of KW-3902 with those of rat PTH in rat renal proximal tubule cells. The results showed that both KW-3902 (30 mumol/L) and rat PTH (1-34, 5 mumol/L) significantly inhibited Pi uptake in proximal cells from a control level of 61 +/- 3 to 19 +/- 3 (a reduction of 69%) and 46 +/- 4 picomoles phosphate/mg protein/min (a reduction of 25%), respectively (P < 0.01). The inhibitory effect of 30 mumol/L KW-3902 alone on Pi transport was more than twice that of 5 mumol/L rat PTH (1-34) alone (P < 0.01). KW-3902 stimulated the production of cAMP in a dose-dependent manner (r = 0.997, P < 0.01). Rat PTH (1-34; 5 mumol/L) also stimulated cAMP production, which was greater than that induced by 30 mumol/L KW-3902 alone. A significant increase in cAMP production by 30 mumol/L DPCPX was also observed.(ABSTRACT TRUNCATED AT 250 WORDS)

Tubular catabolism of albumin is associated with the release of an inflammatory lipid

Proteinuria and tubulointerstitial inflammation (TII) correlate with progression to renal failure in human glomerulonephritis. Various forms of experimental nephrotic syndrome are associated with TII. To study the genesis of TII, we utilized the model of albumin overload. Rats received intraperitoneal bovine serum albumin (BSA) for 1 to 14 days, developing heavy proteinuria. A predominantly macrophage interstitial infiltrate was present at days 3, 7 and 14. The urine of the rats contained a factor chemotactic for macrophages which partitioned into the organic phase with ethyl acetate extraction. TLC and HPLC characteristics were those of a novel, non-polar lipid. Supernatant from the culture of proximal tubule (PT) segments after in vivo or in vitro exposure to high concentrations of lipid-replete BSA showed chemotactic activity with similar chromatographic characteristics. PT cultured with delipidated BSA produced little activity. Thus, the generation of this inflammatory factor occurs as a consequence of tubular metabolism of albumin-borne fatty acids and may contribute to the development of proteinuria-associated TII.

Protein degradation in kidney proximal tubule cell monolayers

Isolated proximal tubule cells have been labelled with L-[4,5-3H]leucine prior to cell division. Histochemical staining demonstrated the purity of the cultures. The bicarbonate ion or a collagen support was required for cell growth. Different culture growth rates were established by varying these parameters. The proximal tubule marker enzyme, gamma-glutamyl transpeptidase, was expressed throughout the culture period (7-10 days) and the cells undergo a glycolytic shift, shown by an increase in the levels of lactate dehydrogenase. The specific activities of these enzymes were related to the growth conditions. Exponential rates of protein degradation were observed. The uptake of labelled exogenous hepatocyte proteins in proximal tubule cell cultures was completely suppressed in the presence of serum (10%, v/v) showing that endocytosis did not contribute to the observed measurements of intracellular protein degradation. The increased growth rates seen in cultures were accompanied by decreased rates of protein degradation. Use of the inhibitors of proteolysis, leupeptin and ammonium chloride, showed that the decrease was at the lysosomal level. The results suggest that targeting of inhibitors of lysosomal proteolysis, via low-molecular-weight proteins, may be useful in stimulating tubular regeneration in kidney disease.

Effect of KW-3902, a novel adenosine A1 receptor antagonist, on sodium-dependent phosphate and glucose transport by the rat renal proximal tubular cell

KW-3902, 1,3-dipropyl-8-(3-noradamantanyl)xanthine, is a novel potent and selective adenosine A1-receptor antagonist. KW-3902 has been found to cause significant diuresis and natriuresis. To investigate the action of this adenosine A1-receptor antagonist on phosphate transport in renal proximal tubular cells, we studied its effect on the uptake of phosphate by the cultured rat renal proximal tubular cell. KW-3902 significantly inhibited sodium-dependent uptake of phosphate at 10 minutes. The inhibitory effect was dose-dependent with maximum effect achieved at a KW-3902 concentration of 3 x 10(-5) M in the uptake media. The half-maximal inhibitory concentration, IC50, of KW-3902 on phosphate uptake was 2 x 10(-6) M. Dixon plot analysis of the uptake data was consistent with pure non-competitive inhibition. The inhibition constant, Ki, of 6.2 x 10(-6) M for phosphate transport, derived from the Dixon plot, was in close agreement with the IC50 calculated from a semilog dose response curve. Sodium-dependent glucose transport was not affected by KW-3902. These findings reveal that KW-3902 has a direct and specific inhibitory effect on phosphate uptake in renal proximal tubules.

Parathyroid hormone transport effects and hormonal processing in primary cultured rat proximal tubular cells

The development of satisfactory cell culture models for the study of parathyroid hormone (PTH)-induced inhibition of Pi transport has proven difficult. Using subcellular fractionation techniques we investigated the response of primary cultures of rat proximal tubular cells to PTH-(1-34). Specific binding of 125I-bPTH-(1-34) occurred at 2 degrees C. After 5 min of rewarming, trypsin-releasable radioactivity decreased from 90 to 50%, indicating internalization of the ligand. Cell disruption, followed by density centrifugation with 17% Percoll either directly after binding at 2 degrees C or post-rewarming for 20 min, showed a shift of 125I label from the plasma membrane (5'-nucleotidase) to lysosomal fractions (beta-D-glucosaminidase), confirming the sequential occurrence of cell surface binding, internalization and transport to lysosomes of 125I-bPTH-(1-34). Reculture at 37 degrees C revealed steady accumulation of trichloroacetic acid-soluble radioactivity in the medium, indicating degradation of 125I-bPTH-(1-34). Phosphate transport in the absence of sodium was minimal. Incubation of the cells with bPTH-(1-34) resulted in up to 50% inhibition of sodium-dependent phosphate transport. Prior phosphate depletion abrogated the response to PTH.

Analysis and isolation of renal tubular cells by flow cytometry

The cells of the renal cortex have rich heterogeneity of structure and function. Flow cytometry, the technique of rapid laser-based single cell analysis, can give information about cellular mixtures not obtainable by any other means. We examined a variety of fluorescent markers to identify populations of renal cells by flow cytometry. Cellular digests of rat cortex were fluorescently stained with either enzymatic activity probes, or polyclonal antibodies. Fluorescent staining for the proximal marker gamma-glutamyl-transpeptidase (tau-GT) was an order of magnitude brighter than autofluorescence, and stained 71 +/- 11% of the cells. Second, we colocalized enzymatic and antibody markers. There was tight colocalization of tau-GT enzyme activity, detected with fluorogenic substrates, with specific surface binding of tau-GT antibodies. Third, populations of fluorescently labelled cells can be rapidly isolated by flow cytometry sorting. Flow cytometry sorting isolated 10(7) cells positive for the proximal tubular marker tau-GT in a little under one hour. The sorted cells were viable with 99 +/- 2% trypan blue exclusion (N = 8). Sodium-dependent phloridzin-inhibitable glucose uptake was present in sorted cells, with greater uptake/mg protein than in unsorted controls. The sorted cells grew in culture as a monolayer of tightly adherent cuboidal cells. Hence, flow cytometry allows us to quantitate the heterogeneity in mixed renal cellular digests. Flow cytometry allows us to rapidly isolate millions of cells according to fluorescently tagged markers. The isolated cells are viable, retain sodium-dependent transport properties, and grow in culture.

Aggregation substance of Enterococcus faecalis mediates adhesion to cultured renal tubular cells

The sex pheromone system of Enterococcus faecalis is a unique, highly efficient plasmid collection mechanism for this species. A crucial role in this system is played by an adhesin called aggregation substance which enables the cell-cell contact between donor and recipient strains. The existence of the amino acid motif Arg-Gly-Asp-Ser in the adhesin prompted us to look for a possible binding of E. faecalis cells expressing aggregation substance to eucaryotic cells. We were able to show that the adhesin mediated binding to cultured renal tubular cells (porcine cell line LLC-PK1) via light microscopic, electron microscopic, and enzyme-linked immunosorbent assay-based studies. Synthesis of the adhesin was induced by some component(s) of serum. These data are interpreted to mean that aggregation substance is an adhesin mediating not only cell-cell contact between different E. faecalis strains but also binding of E. faecalis to eucaryotic cells, and therefore it might contribute to virulence.

Renal proximal tubule cell cultures for studying drug-induced nephrotoxicity and modulation of phenotype expression by medium components

The characteristics of two established renal cell lines (LLC-PKI and OK) and of primary cultures of rabbit and human proximal tubule cells are described by summarizing the literature about specific properties retained by these cells in culture. Furthermore, comparative biochemical and functional properties are presented including both specific marker enzymes and transport properties of these cells grown in various media. The impact of culture medium composition on the expressed cellular phenotype is discussed and its consequences on the profile of toxic response due to aminoglycoside antibiotics is analyzed. The in vitro nephrotoxicity of three platinum-containing coordination complexes which exhibited different in vivo nephrotoxic potentials is studied by another technique in a model of rabbit proximal tubule cells in primary cultures in order to correlate results to in vivo data and to define reliable and sensitive parameters for the assessment of platinum-derivative-induced nephrotoxicity. Although animal cell lines have been established in serum-supplemented medium, LLC-PK1 and OK cells as well as primary cultures of proximal tubules are successfully grown in hormonally defined medium, the standardization of which is better controlled for nephrotoxicity studies.

Renal proximal tubular cells in suspension or in primary culture as in vitro models to study nephrotoxicity

The kidney forms a frequent target for xenobiotic toxicity. The complex biochemical mechanisms underlying nephrotoxicity are best studied in vitro provided that reliable and relevant in vitro models are available. Since most nephrotoxicants affect primarily the cells of the proximal tubules (PTC), much effort has been directed towards the development of in vitro models of PTC. This review focuses on the preparation of PTC and the use of these cells. Discussed are important criteria such as the viability (survival time) of the cells and the parameters to assess toxicity. Recent studies have shown that isolated PTC in suspension are especially suitable for studies on the biochemical mechanisms of 'acute' nephrotoxicity, whereas PTC in primary culture may be used to investigate mechanisms of nephrotoxic damage at very low concentrations, upon prolonged exposure. PTC cultured on porous filter membranes provide new possibilities to study toxicity in relation to cell and transport polarity. Primary cell cultures of human PTC have been set up. Although a further characterization of these systems is needed, recent data indicate their usefulness.