Nephron segment and calcium as determinants of anoxic cell death in renal cultures

Pathophysiology of acute kidney injury

Acute kidney injury (AKI) is the leading cause of nephrology consultation and is associated with high mortality rates. The primary causes of AKI include ischemia, hypoxia, or nephrotoxicity. An underlying feature is a rapid decline in glomerular filtration rate (GFR) usually associated with decreases in renal blood flow. Inflammation represents an important additional component of AKI leading to the extension phase of injury, which may be associated with insensitivity to vasodilator therapy. It is suggested that targeting the extension phase represents an area potential of treatment with the greatest possible impact. The underlying basis of renal injury appears to be impaired energetics of the highly metabolically active nephron segments (i.e., proximal tubules and thick ascending limb) in the renal outer medulla, which can trigger conversion from transient hypoxia to intrinsic renal failure. Injury to kidney cells can be lethal or sublethal. Sublethal injury represents an important component in AKI, as it may profoundly influence GFR and renal blood flow. The nature of the recovery response is mediated by the degree to which sublethal cells can restore normal function and promote regeneration. The successful recovery from AKI depends on the degree to which these repair processes ensue and these may be compromised in elderly or chronic kidney disease (CKD) patients. Recent data suggest that AKI represents a potential link to CKD in surviving patients. Finally, earlier diagnosis of AKI represents an important area in treating patients with AKI that has spawned increased awareness of the potential that biomarkers of AKI may play in the future.

Effect of nitric oxide donors on renal tubular epithelial cell-matrix adhesion

BACKGROUND

Nitric oxide (NO) and its metabolite, peroxynitrite (ONOO-), are involved in renal tubular cell injury. We postulated that if NO/ONOO- has an effect to reduce cell adhesion to the basement membrane, this may contribute to tubular obstruction and may be partially responsible for the harmful effect of NO on the tubular epithelium during acute renal failure (ARF).

METHODS

We examined the effect of the NO donors (z)-1-[2-(2-aminoethyl)-N-(2-ammonioethyl)amino]diazen-1- ium-1, 2-diolate (DETA/NO), spermine NONOate (SpNO), and the ONOO- donor 3-morpholinosydnonimine (SIN-1) on cell-matrix adhesion to collagen types I and IV and fibronectin using three renal tubular epithelial cell lines: LLC-PK1, BSC-1, and OK.

RESULTS

In LLC-PK1 cells, DETA/NO (500 microM) had no effect, and SpNO (500 microM) had a modest effect on cell adhesion compared with controls. Exposure to SIN-1 caused a dose-dependent impairment in cell-matrix adhesion. Similar results were obtained in the different cell types and matrix proteins. The effect of SIN-1 (500 microM) on LLC-PK1 cell adhesion was not associated with either cell death or alteration of matrix protein and was attenuated by either the NO scavenger 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide, the superoxide scavenger superoxide dismutase, or the ONOO- scavenger uric acid in a dose-dependent manner.

CONCLUSIONS

These results therefore support the possibility that ONOO- generated in the tubular epithelium during ischemia/reperfusion has the potential to impair the adhesion properties of tubular cells, which then may contribute to the tubular obstruction in ARF.

Heat shock protein 70 overexpression protects LLC-PK1 tubular cells from heat shock but not hypoxia

BACKGROUND

Overexpression of the 70 kDa heat shock protein (Hsp70) protects myocytes and neural cells from hypoxic injury. In contrast, Hsp70 induction in the kidney after ischemic or thermal preconditioning does not correlate well with protection from hypoxic injury. Herein, we directly tested if Hsp70 overexpression protects LLC-PK1 porcine tubular epithelial cells from hypoxic or thermal injury.

METHODS

LLC-PK1 cells were either cotransfected with an Hsp70 and a luciferase expression vector or singly transfected with the luciferase expression vector. Loss of intracellular luciferase activity was used to assess injury after exposure to hypoxia or hyperthermia and after recovery under normal growth conditions.

RESULTS

Overexpression of Hsp70 decreased loss of and improved restoration of intracellular luciferase activity in LLC-PK1 cells exposed to hyperthermia. In contrast, Hsp70 overexpression did not decrease the loss of or improve restoration of luciferase activity in cells exposed to hypoxia.

CONCLUSIONS

These results suggest that Hsp70 overexpression is sufficient to protect LLC-PK1 proximal tubular cells from hyperthermia but is not sufficient for protection from hypoxia.

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.

Prevention of cyclosporine-induced nephrotoxicity with dietary glycine

BACKGROUND

The nonessential amino acid glycine has been used previously to prevent hypoxic and ischemic injury to kidney tissue in vitro. Furthermore, it was recently shown that glycine prevents activation of macrophages and neutrophils in vitro. Because there is some evidence that the immunosuppressant cyclosporine causes nephrotoxicity through a hypoxia-reoxygenation mechanism that could involve infiltration and activation of macrophages and neutrophils, we hypothesized that dietary glycine could prevent this injury.

METHODS

Rats were fed a diet containing glycine (5%) or a control diet for 3 days before cyclosporine treatment. To produce nephrotoxicity, cyclosporine (25 mg/kg daily by gavage) was administered for 28 days while animals were maintained on glycine or control diets. Serum creatinine, urea, glomerular filtration rates, and kidney histology were evaluated in different treatment groups.

RESULTS

All rats gained weight; however, overall weight gain in the cyclosporine, glycine, and cyclosporine+glycine groups was significantly less by about 40% compared with the control group. Diet consumption was not statistically different between the groups. As expected, cyclosporine caused kidney damage in the rats fed control diet, reflected in significantly elevated serum urea and creatinine. In addition, cyclosporine treatment decreased glomerular filtration rate by nearly 70%, caused proximal tubular dilation and necrosis as well as increased macrophage and neutrophil infiltration into the kidney. Dietary glycine prevented or minimized kidney damage due to cyclosporine in all parameters studied nearly completely. Furthermore, feeding glycine for up to 1 month had no detrimental effect on kidney function.

CONCLUSIONS

Dietary glycine is a safe and effective treatment to reduce the nephrotoxicity of cyclosporine.

The nature of renal cell injury

The main functional change in patients with acute renal failure (ARF) is a decrease in glomerular filtration rate (GFR). The virtual complete recovery of renal function in those patients who survive ARF, as well as the minimal renal histological abnormalities during ARF when the GFR is less than 10 ml/min, suggest that a major component of the renal tubular cell injury is sublethal or reversible. Experimental models of acute tubular necrosis frequently have placed the emphasis on irreversible proximal tubular cell death. The nature of the renal tubular cell injury in ischemic acute renal failure, however, includes not only cell death (necrosis or apoptosis) but also sublethal injury causing cell dysfunction. The role of intracellular calcium, the calcium-dependent enzymes calpain, phospholipase A2 and nitric oxide synthase (NOS), in the pathophophysiology of this renal tubular cell injury during hypoxia/ischemia is described. The effects of calpain and nitric oxide (NO) on the cytoskeleton and cell adhesion are discussed. Potential mechanisms whereby tubular injury leads to a profound fall in GFR, including increased tubuloglomerular feedback and increased distal tubular obstruction, in ischemic acute renal failure are proposed.

Therapeutic strategies in the prevention of acute renal failure

The mechanisms involved and the potentially useful therapeutic strategies in the prevention of acute renal failure (ARF) are briefly reviewed. Factors mentioned are the role of calcium channel blockers, the antioxidant agents, heme oxygenase induction, and ferritin synthesis; and of substances with hemodynamic actions in ARF; such as endothelin, atrial natriuretic peptide, urodilatin, PAF antagonist, prostaglandins, diuretics, and dopamine. The loss of tubular epithelium polarity, the mechanisms involved in this process, and the usefulness of arginine-glycine-aspartic acid peptide and anti-ICAM antibodies in the prevention of tubular obstruction are also reviewed.

Susceptibility of human proximal tubular cells to hypoxia: effect of hypoxic preconditioning and comparison to glomerular cells

In animals models, exposure of the brain, heart, or kidneys to sublethal ischemia induces tolerance for subsequent ischemia. However, the ability of human renal cells to undergo hypoxic preconditioning has not been evaluated. In addition, it is unclear if renal ischemic preconditioning induces resistance at the cellular level, or if preconditioning is a result of altered postischemic hemodynamics or the azotemic environment. In this study, we tested the ability of cultured human proximal tubular epithelial cells (PTEC) to undergo hypoxic preconditioning at the cellular level. Hypoxia was induced by incubating cells in an anaerobic incubator in glucose-free buffer (combined oxygen-glucose deprivation; COGD). Cell injury was assessed by lactate dehydrogenase (LDH) efflux, release of arachidonic acid metabolites, and light microscopy. PTEC preconditioned with 12 h of COGD and a 24-h recovery period had less LDH efflux than control PTEC after subsequent exposure to 20 h of COGD (15.0 +/- 2.5% vs. 44.0 +/- 3.4%, p < 0.05). Preconditioned PTEC also retained relatively normal morphology and had less release of arachidonic acid metabolites than control PTEC. Because renal ischemia is characterized predominately by tubular injury with relative sparing of the glomerulus, we determined if PTEC are more susceptible to hypoxic injury than glomerular cells. For further comparison, we also assessed the susceptibility to hypoxia of the porcine tubular epithelial cell line LLC-PK1. After exposure to 18 h of COGD, LDH efflux from PTEC (25.5 +/- 3.3%, mean +/- SEM) was lower than from LLC-PK1 cells (47.6 +/- 4.0%; p < 0.01), but not mesangial cells (22.7 +/- 5.0%) or glomerular endothelial cells (38.2 +/- 6.2%). In conclusion, we have demonstrated that cultured PTEC are as resistant to hypoxic injury as glomerular cells, and that PTEC attain cytoresistance after hypoxic preconditioning. Characterization of the molecular changes that occur in human PTEC after hypoxic preconditioning may reveal innate survival mechanisms that can be manipulated to promote protection from renal ischemia in patients.

Modulation of hypoxia-induced calpain activity in rat renal proximal tubules

The effect of the newly developed, nonpeptide, calpain inhibitor, PD 150606, on hypoxia and ionomycin-induced increases in calpain activity in rat proximal tubules (PT) was determined. PD150606 inhibited both hypoxia and ionomycin-induced calpain activity as determined by the fluorescent substrate N-succinyl-Leu-Leu-Val-Tyr-7-amido-4-methyl coumarin (N-succinyl-Leu-Leu-Val-Tyr-AMC). This decrease in calpain activity was accompanied by dose-dependent cytoprotection against hypoxia and ionomycin-induced cell membrane damage. PD150606 had no effect on cathepsin B and L activity in PT as measured by the fluorescent substrate, benzyloxycarbonyl-L-phenylalanyl-L-arginine-7-amido-4-methyl coumarin (Z-Phe-Arg-AMC). The effects of low intracellular pH (pHi) or low free cytosolic calcium [Ca2+]i on this hypoxia-induced calpain activity were also determined. Both low pHi and low [Ca2+]i attenuated the hypoxia-induced increase in calpain activity. This attenuation of calpain activity was observed early before hypoxia-induced membrane damage and was associated with marked reduction in the typical pattern of hypoxia-induced cell membrane damage observed in this model. To identify the isoform of calpain activated in rat proximal tubules, normoxic, hypoxic and ionomycin treated tubules were fractionated by MONO-Q anion exchange chromatography and the fractions were assayed for calpain activity. A single peak of calpain activity characteristic of mu-calpain was found. The calcium dependency of the calpain activity was in the nanomolar range, further confirming that the activity was the low Ca(2+)-sensitive mu-calpain. The present study suggests that in rat proximal tubules: (1) PD 150606 is a specific inhibitor of calpain and not cathepsins B and L; (2) the cytoprotective effects of low pHi and low [Ca2+]i are mediated, at least in part, by inhibition of calpain activity; and (3) the predominant active form of calpain is the isoenzyme mu-calpain.

The role of cysteine proteases in hypoxia-induced rat renal proximal tubular injury

The role of the lysosomal proteases cathepsins B and L and the calcium-dependent cytosolic protease calpain in hypoxia-induced renal proximal tubular injury was investigated. As compared to normoxic tubules, cathepsin B and L activity, evaluated by the specific fluorescent substrate benzyloxycarbonyl-L-phenylalanyl-L-arginine-7-amido-4-methylcoumarin, was not increased in hypoxic tubules or the medium used for incubation of hypoxic tubules in spite of high lactate dehydrogenase (LDH) release into the medium during hypoxia. These data in rat proximal tubules suggest that cathepsins are not released from lysosomes and do not gain access to the medium during hypoxia. An assay for calpain activity in isolated proximal tubules using the fluorescent substrate N-succinyl-Leu-Tyr-7-amido-4-methylcoumarin was developed. The calcium ionophore ionomycin induced a dose-dependent increase in calpain activity. This increase in calpain activity occurred prior to cell membrane damage as assessed by LDH release. Tubular calpain activity increased significantly by 7.5 min of hypoxia, before there was significant LDH release, and further increased during 20 min of hypoxia. The cysteine protease inhibitor N-benzyloxycarbonyl-Val-Phe methyl ester (CBZ) markedly decreased LDH release after 20 min of hypoxia and completely prevented the increase in calpain activity during hypoxia. The increase in calpain activity during hypoxia and the inhibitor studies with CBZ therefore supported a role for calpain as a mediator of hypoxia-induced proximal tubular injury.

Renal proximal tubular epithelium from patients with nephropathic cystinosis: immortalized cell lines as in vitro model systems

The renal proximal tubule is a major site of injury in a variety of congenital/metabolic diseases including nephropathic cystinosis, the most commonly known cause of renal Fanconi's syndrome. In this lysosomal storage disease there are defects in proximal tubule function within the first few months of life. While culture of renal tubular cells from the urine of these patients is possible, development of immortalized cell lines would insure large numbers of homogeneous cells for studies of renal epithelial cell morphology and pathophysiology in this disease. To develop immortalized cells, cystinotic and normal proximal tubular cells in culture were exposed to an immortalizing vector, containing pZiptsU19 with the temperature sensitive SV40 T-antigen allele tsA58U19 and a neomycin resistance gene, and neomycin-resistant tubular cells were selected for propagation. Ten clones from cystinotic patients have been developed and characterized. All clones express T-antigen at permissive temperature (33 degrees C). Immortalized cells have an epithelial morphology and grow to form confluent monolayers; doubling times vary from 31 to 86 hours. Cystinotic clones are keratin, MDR P-glycoprotein, and alpha-95 kD brush-border associated protein positive but Tamm-Horsfall protein negative by immunocytochemistry, as are normal proximal tubule cells immortalized with this vector. This is consistent with a proximal tubule origin of the cystinotic clones. The cystine content of the cystinotic cells is 70 to 160 times that of normal renal proximal tubular cells in culture, with most of the cystine sequestered in cell lysosomes, confirming that these cell lines express the storage defect.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of extracellular calcium on survival of human proximal tubular cells exposed to hypoxia

Removal of extracellular calcium has been demonstrated to improve membrane integrity of rodent myocytes, astrocytes, and renal tubular cells injured by hypoxia. In this study, the effect of extracellular calcium on long-term survival of cultured human proximal tubular epithelial cells (PTEC) subjected to hypoxia was evaluated. In addition, the effect of extracellular calcium on release of arachidonic acid metabolites (AAM) was assessed during and after hypoxia. To induce hypoxic injury, PTEC were incubated in an anaerobic chamber in glucose-free buffer (combined oxygen/glucose deprivation, COGD). Long-term survival was assessed by measuring lactate dehydrogenase (LDH) efflux during COGD and after an additional 24-h "recovery" period (in routine culture medium in 95% air/5% CO2). To determine if extracellular calcium influenced AAM release from membrane phospholipids, cells were preincubated with [3H]arachidonic acid and the release of AAM was measured during COGD and recovery. With this model system, PTEC exhibited minimal LDH efflux during < or = 12 h COGD, but LDH efflux increased to 73.9 +/- 4.7% by 24 h COGD. With 12-18 h of COGD, the extent of LDH efflux was greater during recovery than during COGD, indicating that, for human PTEC, the extent of membrane damage does not become fully evident by LDH efflux for hours after hypoxia. PTEC exposed to 24 h of COGD in the absence of extracellular calcium exhibited strikingly less LDH efflux during COGD than cells incubated in the presence of extracellular calcium, suggesting that extracellular calcium contributes to membrane damage during COGD. However, upon reexposure of PTEC to extracellular calcium, LDH efflux rapidly increased to control levels. Furthermore, despite allowing cells to recover in oxygen or oxygen and glucose before exposure to calcium-containing medium, a rapid increase in LDH efflux could not be avoided. These results suggest that COGD induces an irreversible injury that ultimately leads to loss of membrane integrity whether or not extracellular calcium is present; however, extracellular calcium accelerates the loss of membrane integrity caused by hypoxia. Extracellular calcium did not alter AAM release, indicating that the effect of extracellular calcium on membrane damage (as indicated by LDH efflux) was not mediated by an increased activity of phospholipases (such as phospholipase A2) that are involved in the release of AAM.

Anoxia-induced increases in intracellular calcium concentration in primary cultures of rabbit thick ascending limb of Henle's loop

The effect of anoxia on intracellular Ca2+ concentration ([Ca2+]i) in primary cultures of medullary (mTAL) and cortical (cTAL) thick ascending limb of Henle's loop was investigated. Previously, we reported a method to monitor [Ca2+]i continuously in cultured proximal tubule cells during 1 h of anoxic incubation in the absence of glycolytic substrates [1]. Complete absence of O2 was realised by inclusion of a mixture of oxygenases in an anoxic chamber. As a result of substrate-free anoxia, [Ca2+]i started to rise in individual cells of mTAL and cTAL monolayers and reached maximal levels within 60 min after starting the anoxic incubation. Anoxia induced significant increases in [Ca2+]i from 76 +/- 1 (n = 176) to 469 +/- 18 nM (n = 203) in mTAL monolayers and from 58 +/- 1 (n = 91) to 442 +/- 27 nM (n = 106) in cTAL monolayers (P < 0.05). At the re-introduction of oxygen and glucose, elevated [Ca2+]i rapidly declined to 110 +/- 4 (n = 167) and 105 +/- 5 nM (n = 87) in mTAL and cTAL, respectively (P < 0.05). Removal of extracellular Ca2+ and addition of 0.1 mM La3+ partially prevented anoxia-induced increases in [Ca2+]i in both cell types. The L-type Ca2+ channel blocker D600 (1 microM) was as effective as Ca2+ removal and La3+ addition. Comparing mTAL and cTAL cells, only one difference was consistently observed. Prevention of Ca2+ influx by exposure to La3+ combined with Ca2+ removal or addition of 1 microM D600 had a greater inhibitory effect on anoxic [Ca2+]i values in mTAL than in cTAL monolayers, indicative of a larger role of Ca2+ influx through L-type Ca2+ channels in anoxia-induced increases in [Ca2+]i in the former cell type. In conclusion, substrate-free anoxia reversibly increases [Ca2+]i in primary cultures of cTAL and mTAL, which results from Ca2+ release from stores as well as from Ca2+ influx via D600-sensitive Ca2+ channels.

Age and development-related changes in osteopontin and nitric oxide synthase mRNA levels in human kidney proximal tubule epithelial cells: contrasting responses to hypoxia and reoxygenation

Osteopontin (OPN) encodes a secreted glycosylated phosphoprotein containing a GRGDS motif that can mediate cell attachment through the alpha v beta 3 integrin, and has recently been shown to down-regulate nitric oxide synthase (NOS) expression. We report here that primary cultures of renal proximal tubule epithelial (PTE) cells prepared from human kidneys of different developmental stages and ages show a positive correlation between developmental age and the expression, at the mRNA level, of both OPN and constitutive NOS. However, OPN and NOS responded in different manners, as assessed by mRNA measurements, to hypoxia-reoxygenation injury. The OPN mRNA level, assessed by Northern blotting, increased slightly during 60 min of hypoxia and more substantially during subsequent reoxygenation of primary PTE cells derived from the kidneys of young but not of aged donors. The abundance of NOS mRNA, measured using a cDNA probe to the constitutive form of the enzyme, was enhanced during hypoxia in kidneys derived from humans of all ages, and then decreased during reoxygenation--possibly as the result of increased OPN expression. PTE cells from aged kidneys are more susceptible to cell death under hypoxic conditions that PTE cells from young kidneys. An investigation of the effect of an oxidant on OPN and NOS mRNA levels revealed that within 30 min of exposure to H2O2, NOS mRNA levels decreased simultaneously with an increase in OPN mRNA levels. Nitric oxide (NO), the product of NOS, is at low levels an important signal transduction molecule participating in the regulation of vascular tone and renal reabsorption; at high levels it is cytotoxic. We suggest that the diminished ability of cells from old kidneys to down-regulate NO production and to increase OPN expression after hypoxia-reoxygenation may contribute to their increased susceptibility to oxidant injury.

Evidence for role of cytosolic free calcium in hypoxia-induced proximal tubule injury

The role of cytosolic free Ca2+ ([Ca2+]i) in hypoxic injury was investigated in rat proximal tubules. [Ca2+]i was measured using fura-2 and cell injury was estimated with propidium iodide (PI) in individual tubules using video imaging fluorescence microscopy. [Ca2+]i increased from approximately 170 to approximately 390 nM during 5 min of hypoxia. This increase preceded detectable cell injury as assessed by PI and was reversible with reoxygenation. 1,2-Bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid (BAPTA; 100 microM) reduced [Ca2+]i under basal conditions (approximately 80 nM) and during hypoxia (approximately 120 nM) and significantly attenuated hypoxic injury. When [Ca2+]i and hypoxic cell injury were studied concurrently in the same individual tubules, the 10 min [Ca2+]i rise correlated significantly with subsequent cell damage observed at 20 min. 2 mM glycine did not block the rise in [Ca2+]i, yet protected the tubules from hypoxic injury. These results indicate that in rat proximal tubules, hypoxia induces an increase of [Ca2+]i which occurs before cell damage. The protective effect of BAPTA supports a role for [Ca2+]i in the initiation of hypoxic proximal tubule injury. The glycine results, however, implicate calcium-independent mechanisms of injury and/or blockade of calcium-mediated processes of injury such as activation of phospholipases or proteases.

Beneficial effects of verapamil in renal-risk surgical patients

OBJECTIVE

To test whether the administration of calcium channel antagonists, such as verapamil (V), on the day before, during, and for 24-36 h after an important abdominal intervention, can lower the onset of acute renal failure (ARF), mostly in renal-risk patients, such as the aged.

DESIGN

Randomized, nonblinded study.

SETTING

Three surgical care university departments and two intensive care units of the same hospital (S. Anna, Ferrara, Italy).

PATIENTS

Thirty-five elderly patients (61-83 years old) entered the study: 18 of them were given V; 17 were not treated and were considered as controls. The two study groups were overlapping as regards age, renal risk, and surgical challenge. The patients who underwent ARF (5 in the treated group, 7 among the controls) were rejected from the study.

INTERVENTIONS

V was given on the eve of surgery at a dose of 80 mg/8 h per os and then through slow infusion (5 mg/4-6 h) during the next intra- and postoperative 24-36 h. Abdominal surgery was performed owing to gastric cancer (8 cases), colorectal neoplasia (10 cases), gallstone disease (4 cases), subrenal aortic aneurysm (6 cases), and iliofemoral obstructive arteriopathy (7 cases).

MEASUREMENTS

Serum creatinine (SCr) was assessed to test renal function; 24-h urinary levels of brush-border enzymes (gamma glutamyl transferase, or gGT), lysosomal enzymes (N-acetyl-beta-D-glucosaminidase, or NAG), and beta 2-microglobulin (or beta 2M) were determined at T0 (on the eve of surgery), T1 (first and second day after), and T2 (7th and 8th day after) to demonstrate possible tubule cell damage.

RESULTS

In the evaluated patients (13 treated with V and 10 untreated): (a) the 24-h urinary levels of gGt and NAG persisted unchanged throughout the study in the treated patients, whereas in the controls the same indices exhibited significant (p < 0.01) increases at T1 and T2; (b) the 24-h urinary levels of beta 2M showed significant (p < 0.01) increases in both groups from T0 to T1; however, at T2 these values tended to return to normal ranges in the treated patients, whereas they continued to be elevated in the untreated group. As regards the patients who underwent postoperative ARF, in the treated group urine output was significantly larger (p < 0.01 at T1 and p < 0.001 at T2), SCr was significantly (p < 0.05) lower, and the renal function recovered earlier (within 10 +/- 3 vs. 22 +/- 9 days) than in the controls.

CONCLUSIONS

The administration of calcium channel antagonists to renal-risk patients during surgery and immediately before and after it has failed to prevent the onset of postoperative ARF. Nevertheless this procedure has been shown to somehow reduce surgery-mediated lesions of the tubule cells, as demonstrated by the finding of elevated urinary enzymes only in the untreated group.

Functional, histologic, and ultrastructural study of the protective effects of verapamil in experimental ischemic acute renal failure in the rabbit

The present study was performed in vivo in rabbits to evaluate the functional and morphologic effects of verapamil in a model of ischemic acute renal failure (ARF). Particularly impressive was the ultrastructural integrity of renal tubules in the animals exposed to both ischemia and verapamil. Three groups were studied: Group A: no ischemia; Group B: renal ischemia alone; and Group C: renal ischemia with verapamil. Creatinine clearance was higher in Group C (0.77 mL/min/kg) compared to Group B (0.13 mL/min/kg) at 24 h of reperfusion (p < .005) as well as at 48 and 72 h (0.73 mL/min/kg) vs. 0.35 mL/min/kg; p < .05 and 0.90 mL/min/kg vs. 0.46 mL/min/kg; p < 0.05, respectively). Light microscopic evaluation of Group C rabbits revealed significantly better preservation of proximal tubule (PT) brush border (p < .0005) and less desquamation of PT (p < .05) compared to Group B. Ultrastructural examination of in vivo perfused kidneys also demonstrated decreased loss of microvilli of PT (p < .0005) as well as less cellular edema (p < .005), fewer cells with apical PT membrane rupture (p < .01), better preservation of mitochondria (p < .005), less flattening of the PT basolateral labyrinth (p < .05), and fewer hypertrophic actin bands at the basal surface of PT epithelial cells (p < .05). These results suggest that verapamil markedly attenuates PT morphologic injury in a rabbit model of reversible ischemic ARF. The functional protection observed in these studies may be related, in part, to the improved structural integrity of the renal tubules. Renal transplantation and anticipated renal ischemia (i.e., surgical interventions) are two important situations where treatment with verapamil or other calcium channel blockers may prove to be clinically beneficial.

Calcium channel blockers: protective effects in ischemic acute renal failure

Studies in heart, liver, and kidney have provided evidence that calcium is an important factor in cell injury. Calcium channel blockers are used with increasing frequency in ischemic and toxic renal failure. In this review the available data on the effects of calcium channel blockers in animal models of ischemic renal failure are presented and possible mechanisms of protective actions are discussed.

Protection from hypoxemia-induced renal dysfunction by the thiophosphate WR-2721

The acute renal effects of hypoxemia-reoxygenation and the putative protective action of WR-2721 [S-, 2-(3-aminopropyl-amino)-, etylphosphosphorothioic acid], a drug with specific properties such as PTH-secretion inhibiting, calcium lowering and free radical scavenging activities, were investigated in anesthetized-ventilated rabbits. Glomerular filtration rate (GFR) and renal blood flow (RBF) were assessed by the clearance of inulin and para-aminohippuric acid, respectively. Each animal acted as its own control. Normoxemic control rabbits showed no changes in renal hemodynamics and function during 150 minutes. The administration of WR-2721 (75 mg/kg body wt i.v.) to normoxemic animals induced a significant decrease in MBP, RBF and diuresis, without affecting GFR. It significantly reduced plasma levels of PTH, decreased calcemia and increased urinary calcium excretion. In untreated hypoxemic-reoxygenated rabbits, 45 minutes of severe hypoxemia (PO2 around 35 mm Hg) induced a significant fall in MBP, GFR, RBF and diuresis, which persisted during the 60-minute reoxygenation period. The administration of WR-2721 before hypoxemia or reoxygenation prevented the hypoxemia-induced decrease in GFR and diuresis. Filtration fraction increased significantly. The renal functional improvement observed in hypoxemic rabbits administered WR-2721 could be mediated by its effect on calcium metabolism and/or its oxygen free radical scavenging properties.

The protective role of eicosapentaenoic acid [EPA] in the pathogenesis of nephrolithiasis

The low incidence of atherosclerosis and other degenerative diseases including stone disease in the Greenland Eskimo has been attributed to their high consumption of oily fish with its high concentration of eicosapentaenoic acid (EPA). Man cannot synthesis EPA from the precursor essential fatty acid, linolenic acid, and can only assimilate preformed EPA present in fish and fish oil, to bring about a change in the pathway of eicosanoid metabolism from the n-6 to the n-3 series. With a westernised diet the oxygenated products of renal prostaglandin synthesis are metabolites of the n-6 series and these are known to play an important role in several pathophysiological states including stone disease. Our previous studies have shown a relationship between prostaglandin activity and urinary calcium excretion and it would seem that the initiating factor/s for stone formation trigger the mechanisms for prostaglandin synthesis resulting in the biochemical abnormalities associated with stone disease. The Eskimo may be protected from these events by possession of an eicosanoid metabolism that follows an n-3 pathway. To test this hypothesis experiments were performed using an animal model of nephrocalcinosis. The animals were divided into three groups; one group was given an intra-peritoneal injection of 10% calcium gluconate daily for 10 days to induce nephrocalcinosis; a second group was fed MaxEPA fish oil before and during the calcium gluconate injections and a third group only received an intra-peritoneal injection of N saline. A group of 12 recurrent, hypercalciuric/hyperoxaluric stone-formers were treated with fish oil for eight weeks to study the effects on solute excretion. Nephrocalcinosis, which was readily produced in the control animals, was prevented in the experimental animals by pre-treatment with fish oil and urine calcium excretion was significantly reduced. The urinary calcium and oxalate excretion in the recurrent, hypercalciuric stone-formers was significantly reduced with fish oil treatment over an eight week period. There were no untoward side-effects. These studies indicate that the incorporation of EPA in the diet as a substitute metabolic pathway could be a unique way of correcting the biochemical abnormalities of idiopathic urolithiasis.

Role of calcium channel blockers in protection against experimental renal injury

The available evidence indicates that the first generation calcium channel blocker verapamil has a protective effect against both acute and chronic renal failure. At the cell membrane, verapamil helps minimize the effects of excess calcium influx after ischemic injury, evidenced by reduced uptake of 45Ca, thus lessening tubular injury from both calcium-activated phospholipases and mitochondrial calcium overload. In experimental chronic renal failure, the long-term administration of verapamil protects against renal dysfunction and damage, independent of any effect on systemic mean arterial pressure. Protective effects of verapamil are delineated in several models, supporting the presented hypothesis of the pathogenesis of renal failure.

Role of cytosolic Ca in renal tubule damage induced by anoxia

Cytosolic free Ca (Caf) was measured in three different preparations of freshly prepared proximal tubules from the rabbit kidney during energy deprivation using fura-2. Isolated perfused tubules, tubules immobilized on glass cover slips, and tubules in suspension were subjected to inhibitors of oxidative phosphorylation ("chemical hypoxia"); the latter two preparations were also subjected to 40 min of anoxia. During normoxia, Caf ranged from 100 to 180 nM in all three preparations, and chemical hypoxia caused either no change or a small (30-100%) increase in Caf values. Subsequent addition of Ca ionophores increased Caf to 300-500 nM in the first 2 min and to greater than 1 microM after 15 min. In individual experiments, anoxia produced similar responses to those of chemical hypoxia, eliciting no average significant change in Caf, despite clear evidence for impaired respiration and plasma membrane damage after 40 min of anoxia. This lack of change in Caf was unrelated to "Ca buffering" by fura-2 or inactivation of the dye, since Caf increased to 666 +/- 59 nM upon addition of Ca ionophore during anoxia. These data suggest that increased Caf is not a prerequisite for cellular damage during anoxia in proximal renal tubules. Furthermore, no apparent alteration in plasma membrane permeability to Ca occurs before membrane disruption. Decreased ATP seems to initiate a series of Caf-independent events that cause irreversible injury.

Human renal biopsies as source of cells for glomerular and tubular cell cultures

Glomerular and tubular cells were obtained from normal and pathological human renal biopsies. Single nephron structures were isolated by microdissection for culture. Proximal and distal tubular cells were cultivated for 5-6 weeks (three passages), whereas outgrowth of glomerular cells was sparse and after three weeks infiltrated by mesangial cells. The morphology of cultures obtained from pathological tissue was comparable with the morphology of normal cells, although cultures were more often overgrown by fibroblasts. In culture, both proximal and distal tubular cells retained physiological responses characteristic of their origin. Epidermal growth factor induced growth of proximal tubular cells. The proximal tubular cells were furthermore characterized by cAMP response to parathyroid hormone (PTH) stimulation. The distal tubular cells showed cAMP response to both PTH and vasopressin stimulation. Twelve of 17 cultures obtained from patients with no tubular injuries showed cAMP response to PTH stimulation compared with 2 of 9 cultures from renal tissue with tubular injuries.

Effect of verapamil on cephaloridine nephrotoxicity in the rabbit

Cephaloridine produces proximal tubular necrosis in the rabbit kidney. Calcium channel blockers have ameliorated tissue injury due to toxic and ischemic insults. To determine whether renal damage caused by cephaloridine could be modified by pretreatment with verapamil, groups of rabbits were given cephaloridine, 100 mg/kg sc, 90 min after administration of verapamil, 200 micrograms/kg iv. Histologic scoring of the extent of proximal tubular necrosis 48 h later demonstrated increased necrosis in the group receiving verapamil plus cephaloridine. Verapamil pretreatment increased the concentration of cephaloridine in the renal cortex at 0.5 hr, but did not alter the peak concentration (2 hr after the dose) or cortical concentrations at 1 or 3 hr. Assay of total calcium content in cortical mitochondria 2 hr after cephaloridine showed that verapamil pretreatment abolished the increased accumulation following cephaloridine administration. We conclude that verapamil does not protect renal proximal tubular cells from the toxic effect of cephaloridine, and that verapamil prevents the cephaloridine-induced uptake of calcium by cortical mitochondria.

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.

Epidermal growth factor enhances renal tubule cell regeneration and repair and accelerates the recovery of renal function in postischemic acute renal failure

To determine the timing and location of renal cell regeneration after ischemic injury to the kidney and to assess whether exogenous epidermal growth factor (EGF) enhances this regenerative repair process to accelerate recovery of renal function, experiments were undertaken in rats undergoing 30 min of bilateral renal artery clamp ischemia followed by reperfusion for varying time intervals. Renal cell regeneration, as reflected by incorporation of radiolabeled thymidine within the kidney, began between 24 to 48 h and reached a peak at 72 h after renal ischemia. As demonstrated by histoautoradiography, renal thymidine incorporation was essentially confined to tubule cells. Morphometric analysis of histoautoradiograph sections of renal tissue demonstrated that the majority of labeled cells were found in renal cortex, but some labeled cells were also located in the inner stripe of the outer medulla, suggesting that injury to medullary thick ascending limbs also occurs in this ischemic model. Exogenous EGF administration produced increases in renal thymidine incorporation compared with non-treated animals at 24, 48, and 72 h after ischemic injury. This accelerated DNA replicative process was associated with significantly lower peak blood urea nitrogen (BUN) and serum creatinine levels, averaging 63 +/- 20 and 3.1 +/- 0.4 mg/dl in EGF-treated ischemic rats compared with 149 +/- 20 and 5.1 +/- 0.1 mg/dl, respectively, in nontreated ischemic rats, and was also associated with a return to near normal BUN and serum creatinine levels in EGF-treated animals approximately 4 d earlier than that observed in nontreated animals. This report is the first demonstration that EGF accelerates the repair process of a visceral organ after an injurious insult.

Cellular mechanism of ischemic acute renal failure: role of Ca2+ and calcium entry blockers

This presentation briefly reviews the cellular mechanism of ischemic acute renal failure (ARF) with particular emphasis on the role of Ca2+ and calcium entry blockers (CEB). Vascular consequences of an ischemic renal insult including vasoconstriction, diminished glomerular permeability, loss of autoregulation, and hypersensitivity to renal nerve stimulation may relate to increased cellular Ca2+ concentration in the renal afferent arteriole and glomerular mesangial cells. Evidence is also presented that the ischemic injury to tubular plasma membranes is associated with increased Ca2+ uptake. With an ischemic insult of a short duration, the renal mitochondria are able to buffer the increased cellular Ca2+. However, after an ischemic insult of long duration, the Ca2+ over-loaded mitochondria deteriorate, adenosine triphosphate (ATP) synthesis decreases, and cell death follows. If a sufficient number of renal tubular cells undergo this cell death, tubular obstruction, i.e. the maintenance phase of ARF, occurs.

Calcium and hypoxic injury in the renal medulla of the perfused rat kidney

To study the interaction between calcium and the medullary hypoxic lesions found in isolated perfused rat kidneys, the acute effects of high extracellular calcium upon renal function and morphology were evaluated in kidneys perfused with cell-free medium at a total calcium concentration of 8 to 9 mg/dl (controls), 13 to 14 and 19 to 20 mg/dl (high Ca++). High Ca++ increased hypoxic damage to medullary thick ascending limbs from 58.2 +/- 4.0% of tubules in controls to 80.2 +/- 4.0% (P less than 0.005) in the deepest area of the outer medulla. Morphological changes in the cortex were minimal. The increase in damage to medullary thick limbs induced by high Ca++ was prevented by the calcium channel blocker verapamil. Addition of the calcium ionophore A23187 to controls reproduced the effects of high Ca++ with an increase in the proportion of damaged thick limbs to 92.1 +/- 4.1% (P less than 0.001 vs. controls). Addition of equimolar amounts of magnesium chloride did not reproduce the effect of high calcium perfusions. When transport activity was reduced with ouabain, high calcium perfusions were no longer associated with structural damage. In kidneys perfused with a medium enriched with amino acids, the proportion of tubules with severe, irreversible damage increased from 12 +/- 3 to 43 +/- 10% (P less than 0.01) after high calcium perfusion, and to 75 +/- 12% (P less than 0.001) after perfusion with the calcium ionophore. High extracellular and intracellular calcium appear to act in concert with hypoxia to increase the susceptibility of the renal medulla to injury by mechanisms potentially operative in hypercalcemic and ischemic nephropathy.(ABSTRACT TRUNCATED AT 250 WORDS)

Renal cell culture

Methods for the establishment and growth of renal cell types in culture are reviewed, with emphasis on current trends. General techniques available for the isolation and culture of glomerular cells have progressed from explant to enzyme dissociation and cloning techniques. The growth characteristics and properties of cultured glomerular endothelial, epithelial, mesangial, and bone-marrow-derived cells are discussed. Studies are described in which cultures of contractile mesangial cells have led to an elucidation of their role both in normally functioning glomeruli and in disease states. Renal tubule culture techniques also have progressed from mixed tissue explants and cell isolates to fractionation of enriched tubule populations and growth of specific, individually microdissected proximal convoluted, proximal straight, thick ascending limb of Henle's loop, and collecting tubules. The differentiated tubule epithelial-specific properties of such primary cultures are discussed in relation to those of permanently growing cell lines such as MDCK and LLC-PK1. Renal tubule cultures will be invaluable for the study of the role of hormones and extracellular matrix in epithelial growth and polarity of normal structure and function. In addition, in vitro models of cultured renal tubules have been established to study the effects of age, nephrotoxins, and anoxic injury.

Energy thresholds that determine membrane integrity and injury in a renal epithelial cell line (LLC-PK1). Relationships to phospholipid degradation and unesterified fatty acid accumulation

This study related ATP levels with membrane damage, lipid abnormalities, and cell death in energy-depleted LLC-PK1 cells. Oxidative phosphorylation was inhibited by antimycin A, and glycolysis was regulated by graded glucose deprivation to achieve stepwise ATP depletion. Over a range of ATP levels down to approximately equal to 5% of normal, over 5 h, cells were altered only minimally, or injured reversibly. Such cells maintained mitochondrial potential, and retained more K+ than cells without an energy source. Over the same duration, cells without an energy source were lethally injured. Treatment with antimycin induced increments of triglycerides and decreases of phospholipids. With severe ATP depletion (approximately equal to 5-10% of normal after 5 h), decrease of phospholipids was marked. Cells in which ATP was not measurable (or was less than 5% of normal) showed comparable phospholipid declines but, in addition, showed massive and progressive increase of unesterified fatty acids. The results identified a low threshold of ATP, at best 5-10% of normal, which preserved viability in LLC-PK1 cells despite major loss of membrane phospholipids. This threshold also determined the ability of cells to maintain their normally low levels of unesterified fatty acids. Failure of energy-dependent mechanisms that normally metabolize unesterified fatty acids may be a correlate of the extent of energy depletion that determines lethal injury.

Renal metabolism and acute renal failure

We briefly review what appear to be the most important elements responsible for renal cell injury during and after oxygen deprivation. Recent studies in numerous laboratories have vastly improved our understanding of the changes in cell function that occur during ischemia and yet, the underlying mechanisms by which tubule damage and cell death occur remain elusive. We attempt to separate the effects that occur during ischemia or anoxia from those occurring during reperfusion (reoxygenation). These are not always separable, especially because it appears that ischemia initiates a series of complex events that may only become manifested during reperfusion. Ischemia-induced renal dysfunctions are clearly multifactorial events that will require major efforts to unravel.

Retention of differentiated characteristics by cultures of defined rabbit kidney epithelia

Rabbit nephron segments of proximal convoluted tubules (PCT); proximal straight tubules (PST); cortical and medullary thick ascending limbs of Henle's loop (CAL, MAL); and cortical, outer medullary, and inner medullary collecting tubules (CCT, OMCT, IMCT) were individually microdissected and grown in monolayer culture in hormone supplemented, defined media. Factors favoring a rapid onset of proliferation included young donor age, distal tubule origin, and the addition of 3% fetal calf serum to the medium. All primary cultures had polarized morphology with apical microvilli facing the medium and basement membrane-like material adjacent to the dish. Differentiated properties characteristic of the tubular epithelium of origin retained in cultures included ultrastructural characteristics and cytochemically demonstrable marker enzyme proportions. PCT and PST were rich in alkaline phosphatase; CAL stained strongly for NaK-ATPase; CCT contained two cell populations with regard to cytochrome oxidase reaction. A CCT-specific anti-keratin antibody (aLEA) was immunolocalized in CCT cultures, and a PST cytokeratin antibody stained PST cultures. The biochemical response of adenylate cyclase to putative stimulating agents was the same in primary cultures as in freshly isolated tubules. In PCT and PST adenylate cyclase activity was stimulated by parathyroid hormone (PTH) but not by arginine vasopressin (AVP); CAL and MAL adenylate cyclase was stimulated by neither PTH nor AVP; CCT, OMCT, and IMCT adenylate cyclase was stimulated by AVP but not by PTH. NaF stimulated adenylate cyclase activity in every cultured segment. It is concluded that primary cultures of individually microdissected rabbit PCT, PST, CAL, MAL, CCT, OMCT, and IMCT retain differentiated characteristics with regard to ultrastructure, marker enzymes, cytoskeletal proteins, and hormone response of adenylate cyclase and provide a new system for studying normal and abnormal functions of the heterogeneous tubular epithelia in the kidney.