Altered growth factor expression during toxic proximal tubular necrosis and regeneration

Activated omentum slows progression of CKD

Stem cells show promise in the treatment of AKI but do not survive long term after injection. However, organ repair has been achieved by extending and attaching the omentum, a fatty tissue lying above the stomach containing stem cells, to various organs. To examine whether fusing the omentum to a subtotally nephrectomized kidney could slow the progression of CKD, we used two groups of rats: an experimental group undergoing 5/6 nephrectomy only and a control group undergoing 5/6 nephrectomy and complete omentectomy. Polydextran gel particles were administered intraperitoneally before suture only in the experimental group to facilitate the fusion of the omentum to the injured kidney. After 12 weeks, experimental rats exhibited omentum fused to the remnant kidney and had lower plasma creatinine and urea nitrogen levels; less glomerulosclerosis, tubulointerstitial injury, and extracellular matrix; and reduced thickening of basement membranes compared with controls. A fusion zone formed between the injured kidney and the omentum contained abundant stem cells expressing stem cell antigen-1, Wilms' tumor 1 (WT-1), and CD34, suggesting active, healing tissue. Furthermore, kidney extracts from experimental rats showed increases in expression levels of growth factors involved in renal repair, the number of proliferating cells, especially at the injured edge, the number of WT-1-positive cells in the glomeruli, and WT-1 gene expression. These results suggest that contact between the omentum and injured kidney slows the progression of CKD in the remnant organ, and this effect appears to be mediated by the presence of omental stem cells and their secretory products.

Identification of genes involved in gentamicin-induced nephrotoxicity in rats--a toxicogenomic investigation

For the application of microarray technology as an additional endpoint in toxicological studies, there is a need to understand associations between pathological processes and gene expression alterations. In the current study, we investigated gentamicin as a nephrotoxic model compound. Gene expression changes of the kidney in response to a dose of 80 mg/kg gentamicin were analyzed by using DNA microarray technology and alterations in gene expression were associated with results from conventional histopathological investigations and with the described pathomechanisms of gentamicin. Under the conditions of our experiment, the mRNA level of 211 genes were found to be deregulated by gentamicin. The gentamicin-induced affection of proximal convoluted tubules was associated with a strong up-regulation of mRNAs encoding for proteins which are used as nephrotoxicity markers in urine and plasma such as Kim-1, Osteopontin and TIMP1. Candidate marker genes for nephrotoxicity such as GATM were deregulated. Gentamicin-induced lysosomal phospholipidosis was indicated by deregulation of lysosomal located gene products such as ATP6V1D, a subunit of the lysosomal H+ transporting ATPase. Effects on glucose transport and metabolism were indicated by the down-regulation on SGLT-2 and glucose-6-phosphatase. Renal cell apoptosis was indicated by up-regulated genes as TP53 and BAX. The role of oxidative stress in gentamicin toxicity was reflected by deregulation of transferrin receptor and heme oxygenase. The results of the study show the potential of microarray technology to study a complex mechanism of toxicity in a single study.

Heparin-binding epidermal growth factor and Src family kinases in proliferation of renal epithelial cells

Our recent studies have shown that proliferation of renal proximal tubular cells (RPTC) in the absence of growth factors requires activation of the epidermal growth factor (EGF) receptor. We sought to identify the endogenous EGF receptor ligand and investigate the mechanism(s) by which RPTC proliferate in different models. RPTC expressed both pro- and cleaved forms of heparin-binding epidermal growth factor (HB-EGF) and several metalloproteinases (MMP-2, -3, -9, and ADAM10, ADAM17) that have been reported to cleave HB-EGF. Treatment of RPTC with CRM 197, an inhibitor of HB-EGF binding to the EGF receptor, or downregulation of HB-EGF with small interfering RNA inhibited RPTC proliferation following plating. Furthermore, GM6001 (pan-MMP inhibitor), tumor-necrosis factor protease inhibitor-1 (TAPI-1; MMP and ADAM17 inhibitor), and GW280264X (ADAM10 and -17 inhibitor), but not GI254023X (ADAM10 inhibitor), attenuated the proliferation after plating. Although EGF receptor activation is required for RPTC proliferation after oxidant injury, CRM197, GM6001, and TAPI-1 did not block this response. In contrast, inhibition of Src with PP1 blocked EGF receptor activation and RPTC proliferation after oxidant injury. In addition, PP1 treatment attenuated HB-EGF-enhanced RPTC proliferation. We suggest that RPTC proliferation after plating is mediated by HB-EGF produced through an autocrine/paracrine mechanism and RPTC proliferation following oxidant injury is mediated by Src without involvement of HB-EGF.

Cell adhesion molecules in chemically-induced renal injury

Cell adhesion molecules are integral cell-membrane proteins that maintain cell-cell and cell-substrate adhesion and in some cases act as regulators of intracellular signaling cascades. In the kidney, cell adhesion molecules, such as the cadherins, the catenins, the zonula occludens protein-1 (ZO-1), occludin and the claudins are essential for maintaining the epithelial polarity and barrier integrity that are necessary for the normal absorption/excretion of fluid and solutes. A growing volume of evidence indicates that these cell adhesion molecules are important early targets for a variety of nephrotoxic substances including metals, drugs, and venom components. In addition, it is now widely appreciated that molecules, such as intracellular adhesion molecule-1 (ICAM-1), integrins, and selectins play important roles in the recruitment of leukocytes and inflammatory responses that are associated with nephrotoxic injury. This review summarizes the results of recent in vitro and in vivo studies indicating that these cell adhesion molecules may be primary molecular targets in many types of chemically-induced renal injury. Some of the specific agents that are discussed include cadmium (Cd), mercury (Hg), bismuth (Bi), cisplatin, aminoglycoside antibiotics, S-(1,2-dichlorovinyl)-l-cysteine (DCVC), and various venom toxins. This review also includes a discussion of the various mechanisms, by which these substances can affect cell adhesion molecules in the kidney.

Effect of immunosuppression on damage, leukocyte infiltration, and regeneration after severe warm ischemia/reperfusion renal injury

BACKGROUND

Post-ischemia/reperfusion (I/R) damage, accompanied by leukocyte infiltration, is unavoidable in renal transplantation, as is the need for immunosuppressive treatment. Influence of immunosuppressive treatment on post-I/R renal damage, nonalloimmune cellular infiltration, and regeneration is not well studied.

METHODS

Uninephrectomized inbred LEW rats were submitted to warm renal ischemia of 45 minutes/60 minutes, and received different immunosuppressive regimens: cyclosporine (CsA) 10 mg/kg/day subcutaneously in the neck daily, or mycophenolate mofetil (MMF) 20 mg/kg/day by daily oral gavage. Control animals underwent sham operation (unilateral nephrectomy) with immunosuppressive treatment or ischemia with vehicle administration. In addition the effect of MMF/mycophenolic acid (MPA) on renal tubule cell proliferation in culture was studied with bromodeoxyuridine incorporation.

RESULTS

The post-I/R interstitial cellular infiltration/proliferation consisted mainly of mononuclear leukocytes [first monocytes/macrophages (Mo/MPhi) followed by CD4+ cells]. This mononuclear cell infiltration became apparent 24 hours after injury at the time of acute tubular necrosis, and was most prominent during the phase of regeneration. Severe I/R combined with CsA aggravated morphologic damage and dysfunction, without effect on tubular cell proliferation and tubular regeneration. Early leukocyte infiltration was qualitatively and quantitatively comparable to control animals, yet decreased moderately later in time. In contrast, MMF in combination with severe I/R did not influence initial morphologic damage and dysfunction. Although the initial leukocyte infiltration was comparable to control animals, the subsequent mononuclear cell accumulation, especially CD4 T cells decreased dramatically during MMF treatment. This was concomitant with a decrease of tubular cell proliferation and hence tubular regeneration. Increasing MPA concentrations in renal tubular cell culture caused a significant decrease in total cell number, and an almost arrest of bromodeoxyuridine incorporation, as measurement of cell proliferation.

CONCLUSION

Immunosuppressive treatment with CsA or MMF affected significantly and in a different manner post-I/R renal morphologic damage, interstitial leukocyte, accumulation and regeneration.

ICAM-1 expression and leukocyte accumulation in inner stripe of outer medulla in early phase of ischemic compared to HgCl2-induced ARF

BACKGROUND

After ischemia/reperfusion (I/R), as well as after toxic insults, there is significant infiltration of leukocytes in the kidney. It is well known that antibodies against adhesion molecules [e.g., intercellular adhesion molecule-1 (ICAM-1)] protect the kidney against acute ischemic injury. In contrast, same antibody treatment did not protect the rat kidney against toxic acute renal failure (ARF) induced by HgCl2. Protection obtained by anti-adhesion treatment in I/R injury is an early phenomenon, since delaying the administration of anti-ICAM-1 for 8 hours did not protect the kidney anymore. The aim of this study was to compare the early ICAM-1 expression and leukocyte accumulation in different zones of ischemic and toxic injury.

METHODS

Male Lewis rats were injected with HgCl2 (2 mg/kg, subcutaneously) or uninephrectomized Lewis rats were submitted to 30 degrees C warm ischemia (I/R injury). Rats were sacrificed at 2, 6, 12 and 24 hours. ICAM-1 (1A29) expression in kidney was evaluated morphometrically. Different subsets of leukocytes were stained by immunohistochemistry and counted in cortex, the outer stripe of the outer medulla (OSOM) and the level of the inner stripe of the outer medulla (ISOM).

RESULTS

Although the functional and morphologic damage was comparable between the I/R and toxic ARF group, different ICAM-1 expression could be observed early after injury. ICAM-1 expression in the ISOM started already 2 hours after the onset of I/R injury, and was increased after 12 hours in the cortex and after 24 hours in the OSOM. In contrast, during the first 24 hours after injury, ICAM-1 expression in HgCl2-injured kidneys was not different from noninjured kidneys in the ISOM and the cortex, whereas in the OSOM, ICAM-1 expression increased. The number of polymononuclear cells (PMNs) was low in noninjured kidneys and did not increase in time after both I/R injury and after HgCl2-induced ARF. In the ISOM, significant monocyte and T-cell accumulation was observed early after I/R but not after HgCl2. There was no significant T-cell accumulation in the cortex or in the OSOM.

CONCLUSION

After HgCl2, almost no leukocyte accumulation and up-regulation of ICAM-1 was observed the first 12 hours after injury. In contrast, very early after I/R injury, increased expression of ICAM-1 goes along with monocyte and T-cell accumulation in the ISOM, endorsing this particular zone as critical in renal I/R injury. These observations contribute to the understanding why anti-ICAM-1 treatment in acute I/R injury is successful, but fails in acute toxic injury induced by HgCl2.

Heparin-binding EGF-like growth factor mediates the biological effects of P450 arachidonate epoxygenase metabolites in epithelial cells

In addition to its important functions in detoxification of foreign chemicals and biosynthesis of steroid hormones, the cytochrome P450 enzyme system metabolizes arachidonate to 14,15-epoxyeicosatrienoic acid (14,15-EET). This study demonstrates that a P450 arachidonate epoxygenase metabolite can activate cleavage of heparin-binding epidermal growth factor-like growth factor (HB-EGF) and delineates an essential role for HB-EGF in the mitogenic effects of this lipid mediator. Blockade of HB-EGF processing or EGF receptor (EGFR) inhibited 14,15-EET-stimulated early mitogenic signals and DNA synthesis. 14,15-EET failed to induce mitogenesis in cell lines expressing minimal HB-EGF, whereas 14,15-EET induced soluble HB-EGF release into the conditioned media of cell lines that both express high levels of HB-EGF and display mitogenic response to this lipid mediator. Moreover, transfection of a bacterial 14,15-epoxygenase established intracellular endogenous 14,15-EET biosynthesis in cultured cell systems, which allowed direct confirmation of involvement of EGFR transactivation in the endogenous 14,15-EET-mediated mitogenic signaling pathway. This mechanism involves EET-dependent activation of metalloproteinases and release of the potent mitogenic EGFR ligand, HB-EGF.

Targeting growth factors to the kidney: myth or reality?

Growth factors and cytokines play a crucial role in the progression of renal diseases. A growing body of evidence has been obtained from experimental studies, suggesting that manipulation of the activity of growth factors and cytokines is a potential form of therapy for renal diseases. To preserve the renal function structure in progressive renal diseases, this approach is achieved by inhibition of apoptosis of renal intrinsic cells and by decrease in the fibrotic signal. Inhibition of transforming growth factor beta, platelet-derived growth factor, interleukin-1 and tumor necrosis factor alpha, and supplementation of hepatocyte growth factor, vascular endothelial growth factor and bone morphogenic protein-7 may be beneficial. Recent progress in therapeutic implements including humanized antibodies, chimeric soluble receptors, aptamers, antisense oligonucleotides, and gene therapy allow us to target the causal molecules. Administration of a combination of growth factors and cytokines is a potential therapeutic approach. Targeting signal transduction molecules and their co-factors and regulators is another possibility because the signals from various growth factors use a common pathway. Thus, targeting growth factors and cytokines in renal diseases could be a promising therapeutic approach.

Mrna expression of transforming growth factor-alpha and the EGF receptor following nephrotoxic renal injury

We studied gene expression for transforming growth factor (TGF)-alpha, epidermal growth factor (EGF), heparin binding (HB) EGF, and the EGF receptor following acute renal failure induced by mercuric chloride administration to gain insight into potential mechanisms of renal repair. Twenty four hours after HgCl2, 2 mg/kg, creatinine increased from 0.3+/-0.01 mg/dl in controls to 2.2+/-0.26 mg/dl in injured rats (n = 5, p < 0.01). Similar changes were observed after 3 days. Messenger RNA expression for EGF was decreased at 24 hours in HgCl2 treated rats and remained depressed for at least 3 days. On the other hand steady state mRNA for TGF-alpha increased nearly 2 fold at day 3 in HgCl2 treated rats 4 mg/kg. Heparin binding EGF was increased early, by day one in injured kidneys and gene expression for the EGF receptor was increased as well. Immunohistochemistry documented an increase in expression of TGF-alpha in injured kidneys at distal nephron sites. These studies suggest that TGF-alpha along with HB EGF may be important ligands for the EGF receptor during repair from renal injury.

Possible involvement of myofibroblasts in cellular recovery of uranyl acetate-induced acute renal failure in rats

Cellular recovery in acute renal failure is a form of wound healing. Fibroblast-like cells or myofibroblasts are involved in wound healing. We examined the serial changes in tubular damage and origin and kinetics of regenerating cells in uranyl acetate-induced acute renal failure, with a special emphasis on interstitial myofibroblasts. Acute renal failure was induced in rats by intravenous injection of uranyl acetate (5 mg/kg). All rats received bromodeoxyuridine intraperitoneally 1 hour before sacrifice. Serial changes in the distribution of tubular necrosis and bromodeoxyuridine-incorporated or vimentin-positive regenerating cells, and their spatial and temporal relation to alpha-smooth muscle actin-positive myofibroblasts as well as ED 1-positive monocytes/macrophages were examined. Necrotic tubules initially appeared around the corticomedullary junction after uranyl acetate injection, then spread both downstream and upstream of proximal tubules. Peritubular alpha-smooth muscle actin-positive myofibroblasts appeared and extended along the denuded tubular basement membrane, establishing network formation throughout the cortex and the outer stripe of outer medulla at days 4 to 5. Tubular regeneration originated in nonlethally injured cells in the distal end of S3 segments, which was confirmed by lectin and immunohistochemical staining using markers for tubular segment. Subsequently, upstream proliferation was noted along the tubular basement membrane firmly attached by myofibroblasts. During cellular recovery, no entry of myofibroblasts into the tubular lumen across the tubular basement membrane was noted and only a few myofibroblasts showed bromodeoxyuridine positivity. The fractional area of alpha-smooth muscle actin-positive interstitium reached a peak level at day 7 in the cortex and outer stripe of outer medulla, then gradually disappeared by day 15 and remained only around dilated tubules and in the expanded interstitium at day 21. ED 1-positive monocytes/macrophages were transiently infiltrated mainly into the region of injury. They did not show specific association with initially necrotic tubules, but some of them located in close proximity to regenerating tubules. Nonlethally injured cells at the distal end of proximal tubules are likely to be the main source of tubular regeneration, and the transient appearance of interstitial myofibroblasts attached to the tubular basement membrane immediately after tubular necrosis might play a role in promoting cellular recovery in possible association with monocytes/macrophages in uranyl acetate-induced acute renal failure.

Acute renal failure. III. The role of growth factors in the process of renal regeneration and repair

This review, which is the final installment in a series devoted to controversial issues in acute renal failure (ARF) (3, 47), will examine available information regarding the role of growth factors in ARF. In general, studies in this area have fallen into two broad categories: 1) those that have examined the renal expression of genes encoding growth factors or transcriptional factors associated with the growth response that is induced after ARF, and 2) those that have examined the efficacy of exogenously administered growth factors in accelerating recovery of renal function in experimental models of ARF. Despite the vast amount of information that has accumulated in these two areas of investigation, our understanding of the mechanisms involved in the process of regeneration and repair after ARF, and the role of growth factors in this response, remains rudimentary. This overview, contributed to by a number of experts in the field, is designed to summarize present knowledge and to highlight potentially fertile areas for future research in this area.

Expression of apoptosis regulatory proteins in tubular epithelium stressed in culture or following acute renal failure

BACKGROUND

While tubular cell death is a characteristic of acute renal failure (ARF), the molecular mechanisms that modulate this cell death are unclear. Cell fate in acute renal failure hinges on a balance of survival and mortality factors in a changing environment. We further explored this issue by studying selected cell death-related proteins in experimental renal failure.

METHOD

The expression of genes that promote (c-myc, Bax, BclxS) or protect (Bcl2, BclxL) from cell death was studied by Northern blot, Western blot, and immunohistochemistry in murine kidneys following ARF induced by folic acid or in renal tubular epithelial cells (MCT) stressed in culture.

RESULTS

Renal mRNA levels encoding for c-myc and BclxL were elevated in ARF while the Bcl2/Bax ratio was decreased (Bcl2 decreased and Bax increased; P < 0.05). Protein levels of BclxL increased and Bcl2 protein decreased. Expression of tumor necrosis factor (TNF-alpha), a mediator of ARF, was also increased. Immunohistochemistry further demonstrated that BclxL was increased in some tubuli and absent in others, while Bcl2 expression decreased diffusely. Bax staining was also patchy among tubuli and individual cells in the tubular wall and lumen. As a relative deficit of survival factors is present in ARF, MCT epithelium were deprived of serum survival factors. This resulted in apoptosis, decreased Bcl2/Bax and BclxL/Bax ratios (P < 0.05) and sensitization to TNF-alpha-induced apoptosis (P < 0.05). The latter was prevented by enforced overexpression of BclxL (P < 0.01). TNF-alpha increased the mRNA levels encoding for c-myc and decreased BclxL expression. Neither MCT cells nor the kidney expressed BclxS.

CONCLUSIONS

A relative deficit of survival factors likely contributes to changes in levels of BclxL and Bax in ARF. These deficits predispose to cell death induced by persistent lethal factors such as TNF-alpha that is increased in ARF and a potential source of increased c-myc, a downstream facilitator of cell death. These findings implicate members of the Bcl2 family of proteins as regulators of tubular cell death in ARF and single them out as potential therapeutic targets.

Tubulointerstitial lesions in IgA nephropathy and localization of hepatocyte growth factor

To investigate the relationship between localization of hepatocyte growth factor (HGF) and tubulointerstitial lesions (TILs) in the cortical area of renal biopsy specimens, a clinicopathological study was performed in 55 patients with IgA nephropathy. HGF was detected by an enzyme-antibody method and TILs were assessed semiquantitatively by light microscopy. HGF was observed mainly on epithelial cells in the tubules, but not in the glomeruli. Fourteen patients had biopsies that were positive for HGF. There was a correlation between HGF positivity and histological damage, the TIL grade, and several clinical parameters determined at biopsy. Thus, HGF is related to TILs in IgA nephropathy and may be a factor in the exacerbation of this disease.

The pharmacology and toxicology of polyphenolic-glutathione conjugates

Polyphenolic-glutathione (GSH) conjugates and their metabolites retain the electrophilic and redox properties of the parent polyphenol. Indeed, the reactivity of the thioether metabolites frequently exceeds that of the parent polyphenol. Although the active transport of polyphenolic-GSH conjugates out of the cell in which they are formed will limit their potential toxicity to those cells, once within the circulation they can be transported to tissues that are capable of accumulating these metabolites. There are interesting physiological similarities between the organs that are known to be susceptible to polyphenolic-GSH conjugate-mediated toxicity. In addition, the frequent localization of gamma-glutamyl transpeptidase to cells separating the circulation from a second fluid-filled compartment coincides with tissues that are susceptible either to polyphenolic-GSH conjugate-induced toxicity or to quinone and reactive oxygen species-induced toxicity. Polyphenolic-GSH conjugates therefore contribute to the nephrotoxicity, nephrocarcinogenicity, and neurotoxicity of a variety of polyphenols.

The insulin-like growth factor-I axis in acute renal failure

We have examined the response of the renal insulin-like growth factor (IGF-I) axis to acute ischemic injury in the rat Key findings included a decrease in IGF-I mRNA and peptide levels, a decrease in GH receptor gene plus protein expression and a decrease in the IGF binding proteins except for IGF binding protein I. Administration of GH to compensate for the reduced GH receptor binding corrected the IGF-I mRNA levels suggesting a relative GH deficiency. Interestingly, IGF-I receptor mRNA levels were unchanged while plasma membrane IGF-I receptor number increased two fold. This appeared to be due to a redistribution of receptors to a membrane location. IGF-I receptor autophosphorylation and tyrosine kinase activity were intact despite severe uremia for up to 6 days. We propose that this increase of functional IGF-I receptors following acute tubular necrosis will sensitize the kidney to the administration of exogenous IGF-I.

The endogenous insulin-like growth factor system in radiocontrast nephropathy

The response of insulin-like growth factor (IGF) I in acute renal failure was evaluated in a model of radiocontrast nephropathy associated with selective necrosis of medullary thick ascending limbs. In brief, rats were administered radiocontrast medium or vehicle injections for controls after combined inhibition of prostanoids and nitric oxide. Twenty-four hours after the insult, tissue mRNAs for IGF-I, the IGF-I receptor, and IGF-binding proteins (IGFBP) 1 and 3 were assayed in cortex, medulla, and liver by solution hybridization-RNase protection assay, and IGFBPs were measured in serum and tissue by Western ligand blotting. Cortical IGF-1 increased, whereas medullary IGF-I mRNA decreased. Renal IGFBPs decreased, whereas IGFBP-1 mRNA increased. The IGF system in the liver was unchanged. We conclude that general changes in renal IGFBPs in this experimental model of acute renal failure might increase the level of cortical IGF-I in a way that could modulate medullary recovery.

Effect of nitric oxide synthesis modification on renal function in gentamicin-induced nephrotoxicity

We evaluated the effect of acute or chronic nitric oxide (NO) synthesis activation or inhibition in rats with gentamicin-induced acute renal failure. Rats received gentamicin 100 mg/kg per day for 6 days, or isotonic saline. Some animals of each group also received N(G)-monomethyl-l-arginine (l-NAME, 4 mg/kg per day) or l-arginine (1%) in the drinking water for 6 days (chronic NO synthesis modification). In another experimental set, animals were treated with gentamicin or saline for 6 days and glomerular filtration rate (GFR) and renal plasma flow (RPF) were measured before and after the infusion of l-NAME (50 mg/h per kg) or l-arginine (60 mg/h per kg) (acute NO synthesis modification). Acute l-NAME administration induced a decrease in GFR and RPF both in control and gentamicin treated animals. Chronic l-NAME treatment induced an impairment in GFR only in gentamicin-treated animals. Acute l-arginine administration did not modify renal function in any experimental group whereas chronic l-arginine administration improved renal function only in gentamicin-treated animals. Urinary excretion of N-acetyl-β-d-glucosaminidase and alkaline phosphatase was increased by chronic treatment with l-NAME in both groups, whereas l-arginine had no effect. In conclusion, NO synthesis inhibition aggravates gentamicin-induced renal damage. However, chronic NO synthesis stimulation partially prevents against gentamicin nephrotoxicity, thus suggesting that increased renal NO synthesis during gentamicin-induced nephrotoxicity plays a protector role on renal function.

Production of heparin binding epidermal growth factor-like growth factor in the early phase of regeneration after acute renal injury. Isolation and localization of bioactive molecules

We have recently reported that heparin-binding epidermal growth factor-like growth factor (HB-EGF) mRNA is induced in the rat kidney after acute ischemic injury. The present studies were designed to investigate whether bioactive HB-EGF protein is also produced in response to renal injury induced by either ischemia/reperfusion or aminoglycosides. Heparin-binding proteins were purified from kidney homogenates by heparin affinity column chromatography using elution with a 0.2-2.0 M gradient of NaCl. A single peak of proteins that eluted at 1.0-1.2 M NaCl was detected in the postischemic kidney within 6 h of injury. This eluate fraction stimulated DNA synthesis in quiescent Balb/c3T3, RIE, and NRK-52E cell lines, all of which are responsive to the epidermal growth factor family of mitogenic proteins. The EGF receptor of A431 cells was also tyrosine phosphorylated by this eluate peak. Furthermore, immunoblotting with a polyclonal antibody against rat HB-EGF indicated that the eluate peak contained immunoreactive proteins of 22 and 29 kD mol wt, consistent with the reported sizes of the secreted form and membrane anchored form of HB-EGF, respectively. Immunohistochemical studies revealed that HB-EGF was produced predominantly in distal tubules in kidneys injured either by ischemia/reperfusion or aminoglycoside administration. We also found that during metanephric development immunoreactive HB-EGF was detected in the ureteric bud as early as E14.5 and persisted in structures arising from the ureteric bud throughout embryogenesis. These results suggest that in response to acute injury, HB-EGF is produced predominantly in distal tubules and that endogenous HB-EGF may be an important growth factor involved in renal epithelial cell repair, proliferation, and regeneration in the early stages of recovery after acute renal injury, as well as in nephrogenesis.

Response of the intrarenal insulin-like growth factor-I axis to acute ischemic injury and treatment with growth hormone and epidermal growth factor

We previously reported that following bilateral acute tubular necrosis (ATN) profound changes in the intrarenal insulin-like growth factor-I axis occurs which are unrelated to altered nutritional intake. In this current report we studied rats with unilateral ATN to assess whether these changes reflect a response to acute injury or the accompanying uremia. Compared to the contralateral kidney, the injured kidney showed an increase in IGF-I receptor number without a change in IGF-I receptor mRNA levels, a decrease in IGF-I mRNA and IGF-I protein levels, a decrease in growth hormone (GH) receptor mRNA abundance and receptor binding. There was also a decrease in IGF binding protein-2, -3 and -5 mRNA levels together with a fall in protein products. Since this unilateral ATN model excludes the influence of uremia and reduced nutritional intake, we surmised that these changes reflect a direct response to injury. Next, because of the reduced GH receptor binding noted above and the reported decrease in epidermal growth factor (EGF) expression in ATN, we tested the thesis that the low kidney IGF-I mRNA levels in ATN are partly due to a relative or absolute deficiency of these hormones. Administration of EGF or GH promptly increased ATN kidney IGF-I mRNA levels to control kidney values, lending support to the thesis. The response to EGF also suggests that the salutary effect of EGF treatment in ATN may partly be mediated by stimulating IGF-I production.

Renal handling of drugs and amino acids after impairment of kidney or liver function--influences of maturity and protective treatment

Renal tubular cells are involved both in secretion and in reabsorption processes within the kidney. Normally, most xenobiotics are secreted into the urine at the basolateral membrane of the tubular cell, whereas amino acids are reabsorbed quantitatively at the luminal side. Under different pathological or experimental circumstances, these transport steps may be changed, e.g., they may be reduced by renal impairment (reduction of kidney mass, renal ischemia, administration of nephrotoxins) or they may be enhanced after stimulation of transport carriers. Furthermore, a distinct interrelationship exists between excretory functions of the kidney and the liver. That means liver injury can influence renal transport systems also (hepato-renal syndrome). In this review, the following aspects were included: based upon general information concerning different transport pathways for xenobiotics and amino acids within kidney cells and upon a brief characterization of methods for testing impairment of kidney function, the maturation of renal transport and its stimulation are described. Similarities and differences between the postnatal development of kidney function and the increase of renal transport capacity after suitable stimulatory treatment by, for example, various hormones or xenobiotics are reviewed. Especially, renal transport in acute renal failure is described for individuals of different ages. Depending upon the maturity of kidney function, age differences in susceptibility to kidney injury occur: if energy-requiring processes are involved in the transport of the respective substance, then adults, in general, are more susceptible to renal failure than young individuals, because in immature organisms, anaerobic energy production predominates within the kidney. On the other hand, adult animals can better compensate for the loss of renal tissue (partial nephrectomy). With respect to stimulation of renal transport capacity after repeated pretreatment with suitable substances, age differences also exist: most stimulatory schedules are more effective in young, developing individuals than in mature animals. Therefore, the consequences of the stimulation of renal transport can be different in animals of different ages and are discussed in detail. Furthermore, the extent of stimulation is different for the transporters located at the basolateral and at the luminal membranes: obviously the tubular secretion at the contraluminal membrane can be stimulated more effectively than reabsorption processes at the luminal side.

Expression and distribution of epidermal growth factor in acute and chronic renal allograft rejection

Epidermal growth factor (EGF) is a fibrogenic cytokine with a possible role in chronic damage. EGF is also involved in tubular regenerative response to injury. This study investigates the expression and distribution of EGF in a rat model of renal allograft rejection. EGF was localised in control kidneys to distal convoluted tubules (DCT) and thick ascending loop of Henle (TAL). Five days post-transplantation EGF was diffusely distributed. In chronic rejection at one, three and six months, damaged areas of allografts demonstrated faint diffuse EGF staining, while well-preserved areas exhibited the normal distribution pattern. PreproEGF mRNA was significantly reduced (P < 0.01) in acute rejection and in chronic rejection at three months to 28% and 51% of normal, respectively. At six months values ranged from 16% to 166% of normal kidneys, and were inversely correlated with tubular damage (P < 0.01). PreproEGF mRNA was localized to DCT and TAL in controls and in well preserved areas of the tissue in chronic rejection. Thus, EGF would not appear to contribute to the development of injury in chronic renal rejection. It may instead exert a protective effect on tubular structures.

EGF and TGF-alpha in the human kidney: identification of octopal cells in the collecting duct

Epidermal growth factor (EGF) and transforming growth factor-alpha (TGF-alpha) are well-known mitogens expressed in the kidney. Their human renal cell origin has not been conclusively identified. The distribution of EGF and TGF-alpha was investigated immunohistochemically in the adult human kidney in comparison with the monkey and rodent kidney. In humans, as in the monkey, two variants of EGF immunoreactivity were detected. One was present along the apical cell surfaces and diffusely in the cytoplasm of the thick ascending limb (TAL), co-localizing with Tamm-Horsfall protein, and in the distal convoluted tubule (DCT). The other occurred as overall membranous staining in the connecting tubule and cortical collecting duct (CD), and mainly as basal staining in the rest of the CD. The EGF stained cells in the cortical and outer medullary CD reached a diameter of 40 mu and were identified as intercalated or dark cells; they displayed a peculiar octopus-like shape, bearing long lateral extensions that stretched underneath and between 20 surrounding smaller negative cells. Cytoplasmic TGF-alpha staining appeared in the DCT and decreased further on.

IN CONCLUSION

(1) the normal human distal nephron displayed EGF and TGF-alpha immunoreactivity in a partly complementary segmental and subcellular distribution pattern, partly differing from that in rodents. (2) EGF immunostaining revealed the presence of long lateral projections on CD intercalated cells; this peculiar morphology suggests a modulatory role within the CD epithelium, possibly involving the EGF immunoreactivity on their surface.

Epidermal growth factor in acute renal failure

Epidermal growth factor (EGF) is produced in large amounts in the kidney in the form of a membrane-bound high molecular weight precursor. This precursor is inserted in the apical plasma membrane of the EGF-producing cells, which are localized in the thick ascending limb and distal convoluted tubule in mouse and rat kidney, and probably also in human kidney. High levels of EGF are excreted in urine, although renal tissue contains little mature EGF. It modulates renal cell proliferation and differentiation in vitro, but the role of the distal tubular EGF and/or its precursor in vivo is unknown. The expression of EGF in the kidney and its liberation into the urine are quickly abolished during several types of drug- or ischemia-induced acute renal failure and also in ureteral obstruction. Moreover, its expression is restored only after morphological and functional recovery of the kidney. This absence of EGF in conditions in which its mitogenic properties would be most appropriate suggests that the EGF of renal origin is not acting as a mitogen during kidney regeneration. Nevertheless, since the number of EGF receptors, which are localized at the basolateral cell surface in most nephron segments, is increased in regenerating renal epithelia, EGF of systemic origin or other members of the EGF family of growth factors, released from infiltrated inflammatory cells at the sites of injury, could enhance cellular proliferation by interacting with the EGF receptor. Administration of EGF indeed has a mildly beneficial effect on recovery from acute renal injury.

Modification of immunoreactive EGF and EGF receptor after acute tubular necrosis induced by tobramycin or cisplatin

Acute tubular necrosis induced by aminoglycoside antibiotics and various other nephrotoxins is followed by a regenerative process which leads to the restoration of damaged tubules. Several lines of evidence indicate that tubular regeneration is mediated by polypeptide growth factors such as epidermal growth factor (EGF). Previous studies devoted to cisplatin nephrotoxicity have shown that this agent causes tubular cystic degeneration possibly related to an impairment of renal tissue repair. Thus, we examined on a comparative basis the time course of the regenerative response subsequent to tubular damage induced by tobramycin or cisplatin, particular attention being paid to renal EGF and its receptor. Female Sprague-Dawley rats (160-180 g body weight) were treated during 4 consecutive days with daily doses of 200 mg/kg tobramycin i.p. (BID) or 2 mg/kg cisplatin (once a day). Sham-treated rats were given 0.9% NaCl i.p. following the same protocol. Groups of experimental animals (n = 5-10) were terminated at increasing time intervals (1, 4, 7, 14, 21, 60 days) after cessation of treatment. One hour prior to sacrifice, each individual received i.p. 200 mg/kg 5-bromo-2'-deoxyuridine (BrdU) for the immunohistochemical demonstration of cell proliferation. Blood was collected at the time of sacrifice in order to assess glomerular filtration rate by measuring serum creatinine and BUN levels. Kidneys were analyzed with respect to total EGF determined by RIA in renal tissue homogenates, and soluble EGF was assayed in extracts prepared by centrifugation. Renal tissue was processed for the immunohistochemical detection of S-phase cells, of EGF, of EGF receptors, and of the intermediate filament vimentin, the latter being used as a marker of epithelium dedifferentiation. In absence of nephrotoxic alterations, EGF was immunolocalized in distal tubules, whereas EGF receptor immunostaining was seen in proximal tubules cells. Vimentin immunostaining was confined to glomeruli and blood vessels. Tobramycin and cisplatin caused acute tubular necrosis in proximal convoluted tubules and proximal straight tubules, respectively. Tissue damage was accompanied by renal dysfunction reflected by an elevation of serum creatinine and BUN levels. Tubular necrosis was followed by a proliferative response indicative of tubular regeneration. Regenerative hyperplasia was associated with a reduction of total immunoreactive EGF due to a decrease of tissue-bound proEGF. Tubules undergoing regenerative repair were characterized by a disappearance of EGF receptors and the presence of immunoreactive vimentin. In tobramycin-treated rats, renal dysfunction lasted for 4-7 days and was fully reversible, as indicated by the return of serum markers to normal values.