Expression of kidney injury molecule-1 (Kim-1) in relation to necrosis and apoptosis during the early stages of Cd-induced proximal tubule injury.
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 micromol) 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 (alpha-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, alpha-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.
Department of Pharmacology, Midwestern University, Downers Grove, IL 60515, USA. wprozi@midwestern.edu
Walter C
WC
Prozialeck
Joshua R
JR
Edwards
Peter C
PC
Lamar
Jie
J
Liu
Vishal S
VS
Vaidya
Joseph V
JV
Bonventre
D000818:Animals; D017209:Apoptosis / Q000187:drug effects*; D015415:Biomarkers / Q000652:urine; D019256:Cadmium Chloride / Q000378:metabolism / Q000633:toxicity*; D015815:Cell Adhesion Molecules / Q000652:urine*; D004785:Environmental Pollutants / Q000378:metabolism / Q000633:toxicity*; D005982:Glutathione Transferase / Q000652:urine; D007527:Isoenzymes / Q000652:urine; D007687:Kidney Tubules, Proximal / Q000187:drug effects* / Q000378:metabolism / Q000473:pathology; D007770:L-Lactate Dehydrogenase / Q000652:urine; D008297:Male; D009336:Necrosis; D051381:Rats; D017207:Rats, Sprague-Dawley; D012720:Severity of Illness Index; D013997:Time Factors; D015854:Up-Regulation
D015415:Biomarkers; D019256:Cadmium Chloride; D015815:Cell Adhesion Molecules; D004785:Environmental Pollutants; D005982:Glutathione Transferase; D007527:Isoenzymes; D007770:L-Lactate Dehydrogenase; C110936:Havcr1 protein, rat; C119995:glutathione S-transferase alpha