Expression of kidney injury molecule-1 (Kim-1) in relation to necrosis and apoptosis during the early stages of Cd-induced proximal tubule injury

Abstract

Cadmium (Cd) is a nephrotoxic industrial and environmental pollutant that causes a generalized dysfunction of the proximal tubule. Kim-1 is a transmembrane glycoprotein that is normally not detectable in non-injured kidney, but is up-regulated and shed into the urine during the early stages of Cd-induced proximal tubule injury. The objective of the present study was to examine the relationship between the Cd-induced increase in Kim-1 expression and the onset of necrotic and apoptotic cell death in the proximal tubule. Adult male Sprague-Dawley rats were treated with 0.6 mg (5.36 μmoles) Cd/kg, subcutaneously, 5 days per week for up to 12 weeks. Urine samples were analyzed for levels of Kim-1 and the enzymatic markers of cell death, lactate dehydrogenase (LDH) and alpha-glutathione-S-transferase (α-GST). In addition, necrotic cells were specifically labeled by perfusing the kidneys in situ with ethidium homodimer using a procedure that has been recently developed and validated in the Prozialeck laboratory. Cryosections of the kidneys were also processed for the immunofluorescent visualization of Kim-1 and the identification of apoptotic cells by TUNEL labeling. Results showed that significant levels of Kim-1 began to appear in the urine after 6 weeks of Cd treatment, whereas the levels of total protein, α-GST and LDH were not increased until 8-12 weeks. Results of immunofluorescence labeling studies showed that after 6 weeks and 12 weeks, Kim-1 was expressed in the epithelial cells of the proximal tubule, but that there was no increase in the number of necrotic cells, and only a modest increase in the number of apoptotic cells at 12 weeks. These results indicate that the Cd-induced increase in Kim-1 expression occurs before the onset of necrosis and at a point where there is only a modest level of apoptosis in the proximal tubule.

Mechanisms of Cadmium-Induced Proximal Tubule Injury: New Insights with Implications for Biomonitoring and Therapeutic Interventions

“…In another study, Aoyagi et al (2003) noted an increase in the number of apoptotic cells in the renal cortex of cadmium-treated rats after 4 and 5 weeks of exposure, but that the level of apoptotic labeling was much less pronounced after 6 and 8 weeks of exposure. In more recent studies from our laboratory (Prozialeck et al, 2009a), we also found that cadmium caused a low level of apoptosis in the proximal tubules of subchronically exposed rats. However, the onset of apoptosis appeared to occur after Kim-1-dependent tissue repair processes had already been activated, suggesting that cadmium can produce significant changes in the cells before the onset of apoptosis.…”

“…However, it is less clear whether this mechanism can explain the actions of cadmium on N-cadherin in the proximal tubule, where the epithelial cells would be exposed to unknown concentrations of cadmium in the form of cadmium-protein or cadmium-thiol conjugates (Bridges and Zalups, 2005). Results of our own in vivo mechanistic studies to date have shown that at the time the initial cadmiuminduced changes in N-cadherin localization and Kim-1 expression are occurring, there is no evidence of necrosis, and only minimal evidence of oxidative stress or apoptosis in the proximal tubule (Prozialeck et al, 2003(Prozialeck et al, , 2009aProzialeck and Edwards, 2010). Again, these findings strongly suggest that cadmium may exert relatively specific effects on one of the many signaling pathways that regulate cadherin-mediated cell-cell adhesion in the proximal tubule.…”

“…However, even with this approach, slight differences in treatment protocols and methodologies can complicate comparisons of results from different laboratories. To address some of the key issues, our own research groups have been using a treatment protocol that involves the subcutaneous administration of cadmium to rats (0.6 mg/kg, 5 days/week for up to 12 weeks) (Prozialeck et al, , 2009aProzialeck and Edwards, 2010). This has been a widely used protocol in cadmium research and accurately reflects key pathophysiological features of longer-term exposure in humans.…”

Cadmium Renal Toxicity <i>via</i> Apoptotic Pathways

“…5,6) Apoptosis disorders induce a disruption of tissue homeostasis and functions and are associated with many diseases, such as cancer, neurodegenerative disease and toxin-induced disease. 7) Cadmium can induce apoptosis in various tissues and cultured cells, including mouse liver, 8) rat kidney and testis, [9][10][11][12][13] human T cell line (CEM-C12 cells), lymphoma U937 cells, normal hepatocytes, liver L-02 cells, fetal lung fibroblast MRC-5 cells and prostate epithelial cells, [14][15][16][17][18][19] mouse mesangial cells, 20) rat lung epithelial cells, cortical neurons and renal tubular epithelial cells, [21][22][23] and porcine kidney LLC-PK 1 cells. 24) These observations indicate that cell death of the proximal tubule cells in the kidney through apoptotic pathways is one of the key events in cadmium-induced renal toxicity.…”

Proteomic Biomarkers for the Early Detection of Acute Kidney Injury

“…In another prospective study on 201 hospital patients with AKI, an increase of urinary KIM-1 was associated with increased mortality or dialysis requirement [44]. Its potential use as an early marker is based so far on limited data: a rise in its urinary levels was detectable before the increase of BUN and creatinine in plasma during cadmium-induced renal damage [64] as well as its expression in biopsy sections of kidney allograft recipients before histological signs of acute tubular necrosis became evident [99].…”