Increased Renal Fibrosis and Expression of Renal Phosphatidylinositol 4-Kinase-β and Phospholipase C&lt;sub&gt;γ1&lt;/sub&gt; Proteins in Piglets Exposed to Ochratoxin-A

Holzinger²,

Gekle³

2004

J Pharmacol Exp Ther

Ochratoxin A (OTA) is a mycotoxin involved in the development of chronic nephropathies and a known carcinogen. As we have shown previously, OTA activates mitogen-activated protein kinases [extracellular signal-regulated kinase 1 and 2 (ERK1/2), c-jun amino-terminal kinase (JNK), and extracellular-regulated protein kinase 38 (p38)] in proximal tubular cells (opossum kidney and normal rat kidney epithelial). ERK1/2, JNK, or p38 are thought to mediate opposite action on apoptosis, fibrosis, and inflammation. As we have already shown, OTA activates the latter processes. Here, we investigated the effect of OTA in the absence or presence of the ERK1/2 inhibitor U0126 [1,4-diamino-2,3-dicyano-1,4bis(2-aminophenylthio)-butadiene] to test whether OTA then will exert increased toxicity. In the presence of ERK1/2 inhibition, OTA decreased cell number and protein to a significantly larger extent compared with OTA alone. The same was true for epithelial tightness, apoptosis (caspase-3 activity), and necrosis (lactate dehydrogenase release). Furthermore, simultaneous inhibition of ERK1/2 amplified the effect of OTA on markers of inflammation (nuclear factor of the -enhancer in B cells activity), fibrosis (collagen secretion), and epithelial mesenchymal transition (␣ smooth muscle actin). OTA induces phenomena typical for chronic interstitial nephropathy and activates ERK1/2, JNK, and p38 in proximal tubular cells. Inhibition of ERK1/2 aggravates the effects of OTA or even induces toxicity at normally nontoxic concentrations. This is highly likely due to activation of JNK and p38. Our data indicate a new mechanistic explanation for the toxic actions induced by OTA, and they are notable with respect to a possible coexposition of the kidney to OTA and naturally occurring ERK1/2 inhibitors. Finally, our data give rise to an attractive hypothesis on the coincidence of increased OTA exposition and urinary tract tumors in humans.

supporting

confidence: 85%

Proximal Tubular Toxicity of Ochratoxin A Is Amplified by Simultaneous Inhibition of the Extracellular Signal-Regulated Kinases 1/2

Holzinger²,

Gekle³

2004

J Pharmacol Exp Ther

“…The last stage shows marked fibrosis …" is characterized by tubular degeneration, interstitial fibrosis and impaired renal function [7]. This is in line with numerous animal studies, showing development of renal disease accompanied by proximal tubular atrophy and cortical interstitial fibrosis and inflammation after exposition to OTA [15,16].…”

Section: Introductionsupporting

confidence: 77%

The Nephrotoxin Ochratoxin A Induces Key Parameters of Chronic Interstitial Nephropathy in Renal Proximal Tubular Cells

Holzinger

Gekle³

2005

Cell Physiol Biochem

Ochratoxin A (OTA) is a nephrotoxic and cancerogenic mycotoxin. There is epidemiological evidence that OTA exposition leads to cortical interstitial nephropathies in humans. However, virtually no data are available investigating the effect of OTA on renal cortical cells with respect to induction of nephropathy. Thus, we investigated whether OTA is able to induce changes of cellular properties potentially leading to interstitial nephropathy, using proximal tubular cell lines (OK, NRK-52E). OTA decreased cell number and cell protein time and dose dependently. Accordingly we investigated the effect of 100 nM or 1000 nM OTA. The decline of cell number after OTA exposure is due to necrosis and apoptosis, as measured by LDH release or DNA ladder formation and caspase-3 activation, respectively. OTA incubation of proximal tubular cells also resulted in a loss of epithelial tightness as determined by diffusion of FITC labeled inulin. Inflammation, fibrosis and epithelial-to-mesenchymal transition are described in chronic interstitial renal disease. Therefore, we also investigated the effect of OTA on NFκB activity, collagen secretion and generation of α smooth muscle actin. OTA alone was sufficient to induce the latter parameters in proximal tubular cells. Finally, OTA is a nephrotoxcic substance and elevated activity of mitogen activated protein kinases (MAPK) is described in nephropathies. As we investigated the effect of OTA on activity of ERK, JNK and p38 by ELISA, we found that OTA activates the MAPK measured dose dependently. In summary, OTA induced phenomena typical for chronic interstitial nephropathy, like loss of cells and epithelial tightness, necrosis and apoptosis as well as markers of inflammation, fibrosis and epithelial-to-mesenchymal transition in proximal tubular cells. Thus, we could show for the first time that OTA is able to induce key parameters of nephropathy in proximal tubular cells in culture. Moreover OTA interacts with MAPK and thus may exert its specific toxic actions.

“…Balkan endemic nephropathy is characterized by tubular degeneration, interstitial fibrosis and impaired renal function [18,19]. This is in line with numerous animal studies, showing development of renal disease accompanied by proximal tubular atrophy and cortical interstitial fibrosis after exposition to OTA [8,18,20]. Fibrosis is excess production of extracellular matrix.…”

Section: Introductionsupporting

confidence: 72%

Exposure to nephrotoxic Ochratoxin A enhances collagen secretion in human renal proximal tubular cells

Holzinger

Mildenberger

et al. 2005

Mol. Nutr. Food Res.

Ochratoxin A (OTA) is a nephrotoxic mycotoxin. There is evidence that OTA leads to cortical interstitial nephropathies in humans, associated with fibrosis. No data are available on the effect of OTA-induced collagen secretion from renal cortical cells. As kidney cortex mainly consists of proximal tubules, we investigated the effect of OTA on particular collagens (I, III, IV) in a well-established proximal tubular cell line (opossum kidney (OK) cells) and in primary cultured human renal proximal tubular epithelial cells (RPTECs). In fibroblasts, OTA neither exerted toxic effects nor induced collagen secretion, most probably due to the absence of suitable uptake mechanisms. OTA exerted time- and dose-dependent toxicity in both OK cells and human RPTECs. Moreover, OTA induced collagen secretion in a time- and dose-dependent manner in both cell types. In opposite to transforming growth factor beta1 (TGF-beta1), OTA incubation induced increased apical secretion of the basement membrane collagen IV. This might be evidence for a loss of cellular polarity after OTA incubation. We conclude that in proximal tubular cells, OTA is able to induce extracellular matrix deposition. As collagen secretion was also inducible in primary cultured human RPTECs, we hypothesize that OTA-induced extracellular matrix deposition by proximal tubular cells may be of importance in generation of renal diseases in humans which are under suspicion of being induced by OTA.