[Hypercalcaemic crisis and acute renal failure due to primary hyperparathyroidism]. / Hyperkalzämische Krise und akutes Nierenversagen infolge eines primären Hyperparathyreoidismus.

Hypercalcaemic crisis is a rare endocrine emergency. Often, an acute renal failure develops due to hypercalcaemia-induced polyuria. The molecular causes comprise stimulation of the calcium-sensing receptor in the ascending Henle loop and a reduced aquaporin expression in the collecting ducts. We report on a 54-year-old woman who was admitted for hypercalcaemic crisis and acute renal failure. Immediate rehydratation, bisphosphonate administration, and slow-extended daily dialysis (SLEDD) were initiated leading to a marked reduction of serum calcium. Endocrine work-up revealed primary hyperparathyroidism due to a parathyroid adenoma, which was treated by emergency surgery. Haemodialysis was continued in the first post-operative weeks for prolonged acute renal failure.

[Hypercalcemic crisis due to primary hyperparathyroidism]. / Hyperkalzämische Krise infolge eines primären Hyperparathyreoidismus.

HISTORY AND ADMISSION FINDINGS: A 54-year-old female patient presented with increasing somnolence since two days. Furthermore, the patient reported left-sided mid-abdominal pain and obstipation for one week. Immediately prior to admission, the patient had returned from a 14-day beach holiday on the Azores. Physical examination of the somnolent patient revealed a sun-tanned skin, signs of exsiccosis, and tachycardia with 116 beats per minute. INVESTIGATIONS: Laboratory studies showed marked hypercalcemia due to primary hyperparathyroidism and acute renal failure. Neck ultrasonography revealed a hypoechogenic, 5.8 x 3.5 x 3.1 cm-measuring mass behind the lower pole of the right thyroid lobe. DIAGNOSIS, TREATMENT AND COURSE: Serum calcium levels significantly decreased after immediate rehydration, bisphosphonate administration, and continuous hemodialysis that was also indicated because of acute renal failure with anuria. After knowledge of increased parathormone levels the patient underwent rapidly resection of the parathyroid adenoma which was histologically confirmed. CONCLUSIONS: Hypercalcemic crisis is often associated with acute renal failure due to calcium-induced polyuria.

Compartment specific expression of dendritic cell markers in human glomerulonephritis.

Macrophages and dendritic cells are heterogenous and highly plastic bone marrow-derived cells that play major roles in renal diseases. We characterized these cells using immunohistochemistry in 55 renal biopsies from control patients or patients with glomerulonephritis as an initial step towards postulating specific roles for these cells in kidney disease. In proliferative glomerulonephritis numerous CD68 positive (pan monocyte, macrophage and dendritic marker) cells were found in both glomeruli and the tubulointerstitial space, however, a myeloid dendritic cell marker (DC-SIGN) was identified only in the tubulointerstitium. A significant number of plasmacytoid dendritic cells (identified as BDCA-2 positive cells) were seen at sites of interstitial inflammation, including follicular aggregates of inflammatory cells. Langerin positive cells (a marker of Langerhans' cells) were detectable but rare. The area of either CD68 or DC-SIGN positive interstitial cells correlated with serum creatinine. Low levels of DC-SIGN, DC-LAMP and MHC class II mRNA were present in the tubulointerstitial space in controls and increased only in that region in proliferative glomerulonephritis. We demonstrate that the CD68 positive cells infiltrating the glomerulus lack dendritic cell markers (reflecting macrophages), whereas in the tubulointerstitial space the majority of CD68 positive cells are also DC-SIGN positive (reflecting myeloid dendritic cells). Their number correlated with serum creatinine, which further emphasizes the significance of interstitial DCs in progressive glomerular diseases.

Expression of inhibitor of apoptosis protein Livin in renal cell carcinoma and non-tumorous adult kidney.

The antiapoptotic Livin/ML-IAP gene has recently gained much attention as a potential new target for cancer therapy. Reports indicating that livin is expressed almost exclusively in tumours, but not in the corresponding normal tissue, suggested that the targeted inhibition of livin may present a novel tumour-specific therapeutic strategy. Here, we compared the expression of livin in renal cell carcinoma and in non-tumorous adult kidney tissue by quantitative real-time reverse transcription-PCR, immunoblotting, and immunohistochemistry. We found that livin expression was significantly increased in tumours (P=0.0077), but was also clearly detectable in non-tumorous adult kidney. Transcripts encoding Livin isoforms alpha and beta were found in both renal cell carcinoma and normal tissue, without obvious qualitative differences. Livin protein in renal cell carcinoma samples exhibited cytoplasmic and/or nuclear staining. In non-tumorous kidney tissue, Livin protein expression was only detectable in specific cell types and restricted to the cytoplasm. Thus, whereas the relative overexpression of livin in renal cell carcinoma indicates that it may still represent a therapeutic target to increase the apoptotic sensitivity of kidney cancer cells, this strategy is likely to be not tumour-specific.

Targeted inhibition of Livin resensitizes renal cancer cells towards apoptosis.

Cancer cells are typically characterized by apoptosis deficiency. In order to investigate a possible role for the anti-apoptotic livin gene in renal cell cancer (RCC), we analyzed its expression in tumor tissue samples and in RCC-derived cell lines. In addition, we studied the contribution of livin to the apoptotic resistance of RCC cells by RNA interference (RNAi). Livin gene expression was detected in a significant portion of RCC tumor tissue specimens (13/14, 92.9%) and tumor-derived cell lines (12/15, 80.0%). Moreover, targeted inhibition of livin by RNAi markedly sensitized RCC cells towards proapoptotic stimuli, such as UV irradiation or the chemotherapeutic drugs etoposide, 5-fluorouracil, and vinblastine. These effects were specific for livin expressing tumor cells. We conclude that livin can contribute significantly to the apoptosis resistance of RCC cells. Targeted inhibition of livin could represent a novel therapeutic strategy to increase the sensitivity of renal cancers towards pro-apoptotic agents.

Expression analysis of imbalanced genes in prostate carcinoma using tissue microarrays.

To identify candidate genes relevant for prostate tumour prognosis and progression, we performed an exhaustive gene search in seven previously described genomic-profiling studies of 161 prostate tumours, and four expression profiling studies of 61 tumours. From the resulting list of candidate genes, six were selected for protein-expression analysis based on the availability of antibodies applicable to paraffinised tissue: fatty acid synthase (FASN), MYC, beta-adrenergic receptor kinase 1 (BARK1, GRK2) the catalytic subunits of protein phosphatases PP1alpha (PPP1CA) and PP2A (PPP2CB) and metastasis suppressor NM23-H1. These candidates were analysed by immunohistochemistry (IHC) on a tissue microarray containing 651 cores of primary prostate cancer samples and benign prostatic hyperplasias (BPH) from 175 patients. In univariate analysis, expression of PP1alpha (P=0.001) was found to strongly correlate with Gleason score. MYC immunostaining negatively correlated with both pT-stage and Gleason score (P<0.001 each) in univariate as well as in multivariate analysis. Furthermore, a subgroup of patients with high Gleason scores was characterised by a complete loss of BARK1 protein (P=0.023). In conclusion, our study revealed novel molecular markers of potential diagnostic and therapeutic relevance for prostate carcinoma.

Analysis of human prostate cancers and cell lines for mutations in the TP53 and KLF6 tumour suppressor genes.

A recent report suggests that the KLF6 gene encoding the Krüppel-like factor 6 protein is a frequently mutated, putative tumour suppressor gene in prostate cancer. The aims of the present study were to confirm these initial findings by determining the frequency of exon2 KLF6 mutations in a cohort of European prostate cancer patients, and to investigate whether there was evidence for mutational inactivation of both the KLF6 and TP53 tumour suppressor loci in some tumours. We examined 32 primary prostate tumours and three prostate tumour cell lines for mutations by PCR amplification and direct dideoxy sequencing (KLF6), and by oligonucleotide microarray (p53GeneChip) analysis and dideoxy sequencing (TP53). Whereas TP53 mutations typical of prostate cancer were found at a frequency consistent with the literature, no KLF6 mutations were found in any of the tumour samples nor in the three prostate cancer cell lines.

Immunohistochemical evidence for the myeloperoxidase/H2O2/halide system in human atherosclerotic lesions: colocalization of myeloperoxidase and hypochlorite-modified proteins.

The 'oxidation theory' of atherosclerosis proposes that oxidation of low density lipoprotein (LDL) contributes to atherogenesis. Although the precise mechanisms of in vivo oxidation are widely unknown, increasing evidence suggests that myeloperoxidase (MPO, EC 1.11.1.7), a protein secreted by activated phagocytes, generates modified/oxidized (lipo)proteins via intermediate formation of hypochlorous acid (HOCl). In vitro generation of HOCl transforms lipoproteins into high uptake forms for macrophages giving rise to cholesterol-engorged foam cells. To identify HOCl-modified-epitopes in human plaque tissues we have raised monoclonal antibodies (directed against human HOCl-modified LDL) that do not cross-react with other LDL modifications, i.e. peroxynitrite-LDL, hemin-LDL, Cu2+-oxidized LDL, 4-hydroxynonenal-LDL, malondialdehyde-LDL, glycated-LDL, and acetylated-LDL. The antibodies recognized a specific epitope present on various proteins after treatment with OCl- added as reagent or generated by the MPO/H2O2/halide system. Immunohistochemical studies revealed pronounced staining for HOCl-modified-epitopes in fibroatheroma (type V) and complicated (type VI) lesions, while no staining was observed in aortae of lesion-prone location (type I). HOCl-oxidation-specific epitopes are detected in cells in the majority of atherosclerotic plaques but not in control segments. Staining was shown to be inside and outside monocytes/macrophages, endothelial cells, as well as in the extracellular matrix. A similar staining pattern using immunohistochemistry could be obtained for MPO. The colocalization of immunoreactive MPO and HOCl-modified-epitopes in serial sections of human atheroma (type IV), fibroatheroma (type V) and complicated (type VI) lesions provides further convincing evidence for MPO/H2O2/halide system-mediated oxidation of (lipo)proteins under in vivo conditions. We propose that MPO could act as an important link between the development of atherosclerotic plaque in the artery wall and chronic inflammatory events.

Oxidant stress in hyperlipidemia-induced renal damage.

Hyperlipoproteinemia can aggravate glomerulosclerosis and chronic tubulointerstitial (ti) damage in kidneys without primary immunologic disease. We evaluated whether the effect of hyperlipidemia on progression of renal damage differed between kidneys without preexisting glomerular disease and kidneys with mesangioproliferative glomerulonephritis and whether the renal actions of hyperlipidemia were dependent on oxidant-antioxidant balance. Hyperlipidemia was induced by high-fat and high-cholesterol diet in uninephrectomized rats. In rats without glomerulonephritis, hyperlipidemia led to a rise in glomerular and ti generation of reactive oxygen species (ROS). Oxygen radicals were mainly generated by enhanced xanthine oxidoreductase (XO), which rose with protein concentration and activity during hyperlipidemia; concurrently, glomerulosclerosis and chronic ti injury were noticed during hyperlipidemia [ti damage (% of total tubulointerstitium (TI) after 150 days): normolipidemia 0.1 +/- 0% vs. hyperlipidemia 3.4 +/- 0. 9%; P < 0.05]. In mesangioproliferative Thy-1 nephritis, ti injury was significantly accelerated by hyperlipidemia (ti damage after 150 days: normolipidemic Thy-1 nephritis 2.5 +/- 0.6% vs. hyperlipidemic Thy-1 nephritis 12.5 +/- 3.1%; P < 0.05). Antioxidant enzyme activities decreased and XO activity rose markedly in the TI (XO activity in TI after 150 days: normolipidemic Thy-1 nephritis 2.2 +/- 0.5 vs. hyperlipidemic Thy-1 nephritis 4.5 +/- 0.7 cpm/microg protein; P < 0.05). In hyperlipidemic Thy-1 nephritis rats, which had a higher urinary protein excretion than normolipidemic rats, hypochlorite-modified proteins, an indirect measure for enhanced myeloperoxidase activity, were detected in renal tissue and in urine, respectively. During hyperlipidemia, chronic damage increased in renal TI. Enhanced generation of ROS, rise in oxidant enzyme activity, and generation of hypochlorite-modified proteins in renal tissue and urine were noticed. These data suggest that oxidant stress contributed to the deleterious effects of hyperlipidemia on the renal TI.

Re-expression of the developmental gene Pax-2 during experimental acute tubular necrosis in mice 1.

BACKGROUND: The transcription factor Pax-2 is known to play a key regulatory role during embryonic development of the nervous and excretory systems in mammals and flies. During mouse kidney development, Pax-2 is expressed in the undifferentiated mesenchyme in response to ureter induction and continues to be expressed in the developing comma- and s-shaped bodies. These structures harbor the immediate precursors of the proximal tubular epithelial cells. Pax-2 expression is down-regulated as the differentiation of the functional units of the nephron proceeds. In the adult mammalian kidney, the Pax-2 protein is detectable exclusively in the epithelium of the collecting ducts. We sought to test the hypothesis that tissue regeneration is characterized by re-expression of developmentally important regulatory genes such as Pax-2. METHODS: The expression pattern of Pax-2 in kidneys after experimentally-induced acute tubular necrosis caused by intraperitoneally injected folic acid in mice was tested by indirect immunofluorescence, Western blotting, reverse transcriptase-polymerase chain reaction, and in situ hybridization analysis. RESULTS: A transient, temporally and locally restricted re-expression of Pax-2 in regenerating proximal tubular epithelial cells was observed following kidney damage. CONCLUSIONS: These data indicate that during the regeneration processes, developmental paradigms may be recapitulated in order to restore mature kidney function.

Met-RANTES reduces vascular and tubular damage during acute renal transplant rejection: blocking monocyte arrest and recruitment.

Chemokines are thought to contribute to the cellular infiltrate characteristic of renal transplant rejection. We show that Met-RANTES, a chemokine receptor antagonist, suppresses recruitment of inflammatory cells into renal allografts. In a renal transplant model (Fisher RT1(lvl) rat kidney into Lewis RT1(l) rat) where no additional immune suppressant was used, Met-RANTES-treated animals showed a significant reduction in vascular injury score (16.10 +/- 5.20 vs. 62.67 +/- 18.64) and tubular damage score (15.70 +/- 5.22 vs. 33.00 +/- 6.44) relative to untreated animals. In a more severe rejection model (Brown-Norway RT1(n) rat kidney into Lewis RT1(1) rat), Met-RANTES significantly augmented low-dose cyclosporin A treatment to reduce all aspects of renal injury including interstitial inflammation (score 71.00 +/- 6.10 vs. 157.30 +/- 21.30). The majority of infiltrating cells in these models (60-70%) consisted of monocytes. Potential mechanisms of action of Met-RANTES were tested using monocyte attachment assays on microvascular endothelium under physiological flow conditions. Preexposure of microvascular endothelium to RANTES resulted in RANTES immobilization and RANTES-induced firm adhesion of monocytes only after prestimulation of the endothelium with IL-1beta. Met-RANTES completely inhibited this RANTES-mediated arrest. Thus, Met-RANTES may counter acute rejection by blocking leukocyte firm adhesion to inflamed endothelium.

[Reduction of acute kidney transplantation rejection by the chemokine receptor antagonist Met-RANTES]. / Reduktion der akuten Nierentransplantatrejektion durch den Chemokin-Rezeptor-Antagonist Met-RANTES.

Chemokines contribute to the mononuclear cell infiltrate in vessels and interstitium which is characteristic of renal transplant rejection. By employing the chemokine receptor blocker Met-RANTES it was shown that recruitment of inflammatory cells into renal allografts could be significantly suppressed. In a renal transplant model (Fisher RT1(1v1) rat kidney into Lewis RT1(1) rat) Met-RANTES-treated animals showed a significant reduction in vascular injury score (16.10 +/- 5.20 vs. 62.67 +/- 18.64) and tubular damage score (15.70 +/- 5.22 vs. 33.00 +/- 6.44) relative to untreated animals. In a severe rejection model (Brown-Norway RT1n rat kidney into Lewis RT1(1) rat), Met-RANTES significantly augmented low-dose cyclosporin A treatment to reduce all aspects of renal injury including interstitial inflammation (score 71.00 +/- 6.10 vs. 157.30 +/- 21.30). In a monocyte attachment assay on microvascular endothelium under physiological flow conditions exposure of microvascular endothelium to RANTES resulted in RANTES immobilization and RANTES-induced firm adhesion of monocytes only after prestimulation of the endothelium with IL-1 beta. Met-RANTES completely inhibited this RANTES-mediated arrest. Thus, Met-RANTES can reduce acute rejection by impeding leukocyte arrest to inflamed endothelium.

Receptors of vascular endothelial growth factor/vascular permeability factor (VEGF/VPF) in fetal and adult human kidney: localization and [125I]VEGF binding sites.

Vascular endothelial growth factor (VEGF) has an important function in renal vascular ontogenesis and is constitutively expressed in podocytes of the adult kidney. The ability of VEGF to be chemotactic for monocytes and to increase the activity of collagenase and plasminogen activator may have implications for renal development and renal disease. In humans, the cellular actions of VEGF depend on binding to two specific receptors: Flt-1 and KDR. The aims of this study were: (1) to localize VEGF receptor proteins in human renal ontogenesis; (2) to quantify VEGF binding in human fetal and adult kidney; and (3) to dissect the binding into its two known components: the KDR and Flt-1 receptors. The latter aim was achieved by competitive binding of VEGF and placenta growth factor-2, which only binds to Flt-1. Quantification of 125I-VEGF binding sites was performed by autoradiography and computerized densitometry. By double-label immunohistochemistry, VEGF receptor proteins were localized solely to endothelial cells of preglomerular vessels, glomeruli, and postglomerular vessels. In developing glomeruli, VEGF receptor protein appeared as soon as endothelial cells were positive for von Willebrand factor. Specific 125I-VEGF binding could be localized to renal arteries and veins, glomeruli, and the tubulointerstitial capillary network in different developmental stages. Affinity (Kd) of adult (aK) and fetal (fK) kidneys was: Kd: glomeruli 38.6 +/- 11.2 (aK, n = 5), 36.3 +/- 7.1 (fK, n = 5); cortical tubulointerstitium 19.4 +/- 2.6 (aK, n = 5), 11.6 +/- 7.0 (fK, n = 5) pmol. Placenta growth factor-2 displaced VEGF binding in all renal structures by approximately 60%. VEGF receptor proteins thus were found only in renal endothelial cells. A coexpression of both VEGF binding sites could be shown, with Flt-1 demonstrating the most abundant VEGF receptor binding sites in the kidney. These studies support the hypothesis of a function for VEGF in adult kidney that is independent of angiogenesis.

Immunological evidence for hypochlorite-modified proteins in human kidney.

Oxygen radicals and oxidatively modified proteins seem to participate in degenerative vascular and inflammatory diseases. Factors that contribute to the development of atherosclerosis, eg, oxidation of low-density lipoproteins (LDLs), may also contribute to glomerulosclerosis. Although the nature of the in vivo oxidants remains unknown, recent findings indicated that the myeloperoxidase (MPO)-H2O2-halide system could play an important role in modification of (lipo)proteins in human tissues. MPO, the enzyme responsible for hypochlorite (HOCl/OCl-) formation, is present in human atherosclerotic lesions and in inflammatory conditions. In the present study, MPO was identified by Western blot analysis and immunohistochemical technique in diseased human kidney either with primarily sclerotic or inflammatory lesions. Furthermore, the presence of HOCl-modified proteins was demonstrated in diseased renal tissues using a specific monoclonal antibody (clone 2D10G9), raised against HOCl-modified LDL, that does not cross-react with native LDL or Cu(2+)-, 4-hydroxynonenal-, or malondialdehyde-modified LDL. The antibody recognized HOCl-modified proteins in glomerular and tubulointerstitial inflammatory and fibrotic lesions and pronounced immunostaining was demonstrated in mononuclear cells. LDL or human serum albumin oxidized by HOCl in vitro, but not native LDL or human serum albumin, effectively competed with epitopes in diseased kidney for antibody binding. Western blot analysis in diseased kidney protein samples revealed at least two major proteins recognized by the anti-HOCl-modified protein monoclonal antibody. Densitometric evaluation of immunoreactive bands obtained under these conditions demonstrated that expression of HOCl-modified proteins is tightly coupled to expression of immunoreactive MPO in the same tissue samples. From our studies it is proposed that oxidation of proteins by HOCl might be a leading event in glomerular and tubulointerstitial injury. By this mechanism, mononuclear cells, a permanent source for MPO, may play a key role in the development of nephrosclerosis, glomerulo-clerosis, and tubulointerstitial fibrosis, respectively.

Enhanced renal allograft rejection by inhibitors of nitric oxide synthase: a nonimmunologic influence on alloreactivity.

Clinical and experimental studies indicate that nonimmunologic factors may modulate the alloreactivity of a renal transplant. Nitric oxide (NO) is an essential modulator of endothelial function. It was postulated that, in renal allografts, inhibition of constitutive NO synthase may lead to an aggravation of immunologic damage to endothelia and therefore may enhance dysfunction of the graft. Male Lewis (RT1l) rats received syngeneic or allogeneic Brown Norway (RT1n) renal grafts and were treated with cyclosporin A (CyA) or with CyA and an NO synthase blocker (NOS-B): N omega-nitro-L-arginine (L-NNA) or NG-monomethyl-L-arginine (L-NMMA). CyA was given at a dose of 3.5 mg/kg body weight for 14 days and the NOS-B at a dose of 66 mg/L drinking water for up to 28 days postoperatively. Animals (N = 6/group) were studied at 4 to 7, 14, and 28 days posttransplantation. Four to 5 days posttransplantation, renal blood flow and glomerular filtration rate of allogeneic grafts did not differ between animals treated only with CyA and those treated with CyA and NOS-B. Mean arterial pressure was significantly elevated by NOS-B (CyA+L-NNA: 115 +/- 13 versus CyA: 78 +/- 16 mm Hg). Combined NOS-B and CyA administration led to a pronounced increase in vascular and tubulointerstitial damage. The number of mononuclear cells in vessels, glomeruli, and tubulointerstitium increased significantly in allografts upon treatment with NOS-B. During NOS-B administration, adhesion molecules (intracellular adhesion molecule-1; leukocyte-function-associated molecules-1 alpha and-beta) were strongly expressed in endothelial and leukocytic cells of the allograft. A pronounced positivity for mRNA and protein of cytokines tumor necrosis factor-alpha and transforming growth factor-beta could be demonstrated in the inflammatory infiltrate. With L-NNA treatment, the total vascular injury index was 10-fold higher (14 days posttransplantation, CyA+L-NNA: 59.8 +/- 11.7 versus CyA: 6.0 +/- 1.8; p < 0.05). The tubulointerstitial damage score rose more than 2.5-fold after CyA and L-NNA therapy (28 days posttransplantation: CyA+L-NNA: 83 +/- 1 versus CyA:29 +/- 1). L-NNA was more potent than L-NMMA at the dosages used. Thus, pronounced vascular leukostasis, vasculitis, and T-cell and monocyte infiltration of the tubulointerstitium led to a severe damage of the allograft under therapy with CyA and NOS-B. Inhibition of NO synthesis may aggravate alloreactive immunemediated injury in kidney transplants acting primarily by a disturbance of endothelial function.

Expression of vascular endothelial growth factor in renal vascular disease and renal allografts.

Vascular endothelial growth factor (VEGF) is a dimeric glycoprotein that exerts a proliferative effect specifically on endothelial cells. VEGF can increase vascular permeability and collagenase activity, is chemotactic for monocytes, and may dilate blood vessels. It can be induced by phorbol ester and cAMP in both mesenchymal and epithelial cells. In vitro cell culture experiments suggest that VEGF is upregulated by oxygen deprivation. In this study we tested whether in vivo acute and/or chronic reduction of renal blood flow by vascular obstruction would result in increased expression of VEGF mRNA and protein. Three normal kidneys, five human kidneys with narrowing of preglomerular vessels by vascular rejection or by vasculitis, and eight kidneys with nephrosclerosis and/or diabetic nephropathy were examined. In situ hybridization with 35S-labelled riboprobes showed a pronounced expression of VEGF mRNA in acutely hypoxic proximal and distal tubules of both the cortex and medulla; VEGF protein was demonstrated in the epithelia of these tubules by immunohistochemistry. In kidneys with chronically reduced blood flow, the majority of atrophic tubules were negative for VEGF mRNA and protein, although interstitial cells expressed VEGF mRNA. In arcuate arteries showing intimal and adventitial fibrosis, some medial smooth muscle cells were positive for VEGF mRNA. In glomeruli with segmental sclerosis, viable podocytes showed a prominent signal for VEGF mRNA. Mesangial cells did not express VEGF in the cases studied. It is possible that hypoxia itself led to the upregulation of VEGF in tubular epithelia and vascular smooth muscle cells. The vasodilatory and permeability-promoting effects of the endothelial growth factor produced by damaged tubular epithelia may constitute a mechanism to alleviate a decrease in blood flow and substrate availability and to re-establish vascular integrity.