Role of p21 and oxidative stress on renal tubular resistance after acute ischaemic injury.
BACKGROUND
Subsequent ischaemic episodes may induce renal resistance. P21 is a cell cycle inhibitor that may be induced by oxygen-free radicals and may have a protective effect in ischaemic acute kidney injury (AKI). This study aimed at evaluating the role of oxidative stress and p21 on tubular resistance in a model of acquired resistance after renal ischaemia and in isolated renal tubules.


METHODS
Wistar rats were divided into: Group 1--sham; Group 2--sham operated and after 2 days submitted to 45-min ischaemia; and Group 3--45-min ischaemia followed after 2 days by a second 45-min ischaemia. Plasma urea was evaluated on Days 0, 2 and 4. Serum creatinine, creatinine clearance and oxidants (thiobarbituric acid-reactive substances) were determined 48 h after the second procedure (Day 4). Histology, immunohistochemistry for lymphocytes (CD3), macrophages (ED1), proliferation (PCNA) and apoptosis (TUNEL) were also evaluated. Rat proximal tubules (PTs) were isolated by collagenase digestion and Percoll gradient from control rats and rats previously subjected to 35 min of ischaemia. PTs were submitted to 15-min hypoxia followed by 45-min reoxygenation. Cell injury was assessed by lactate dehydrogenase release and hydroperoxide production (xylenol orange).


RESULTS
Ischaemia induced AKI in Group 2 and 3 rats. Subsequent ischaemia did not aggravate renal injury, demonstrating renal resistance (Group 3). Renal function recovery was similar in Group 2 and 3. Plasma and urine oxidants were similar among in Group 2 and 3. Histology disclosed acute tubular necrosis in Group 2 and 3. Lymphocyte infiltrates were similar among all groups whereas macrophages infiltrate was greater in Group 3. Cell proliferation was greater in Group 2 compared with Group 3. Apoptosis was similar in groups 2 and 3. The p21 expression was increased only in Group 3 whereas it was similar in groups 1 and 2. PTs from the ischaemia group were sensitive to hypoxia but resistant to reoxygenation injury which was followed by lower hydroperoxide production compared to control PT.


CONCLUSIONS
Renal resistance induced by ischaemia was associated with cell mechanism mediators involving oxidative stress and increased p21 expression.
Kfouri
Flavia
F
Division of Nephrology, University of São Paulo School of Medicine, Sao Paulo, Brazil.
de Castro
Isac
I
Testagrossa
Leonardo
L
Delle
Humberto
H
da Silva
Ana Maria Gonçalves
AM
Bastos
Ana Paula Almeida
AP
Vieira
Jose Mauro
JM
Yu
Luis
L
D000208:Acute Disease; D000818:Animals; D017209:Apoptosis; D001483:Base Sequence; D003404:Creatinine / Q000378:metabolism; D050759:Cyclin-Dependent Kinase Inhibitor p21 / Q000235:genetics / Q000502:physiology*; D017931:DNA Primers / Q000235:genetics; D066298:In Vitro Techniques; D007511:Ischemia / Q000235:genetics / Q000473:pathology / Q000503:physiopathology*; D007684:Kidney Tubules / Q000098:blood supply / Q000293:injuries* / Q000473:pathology / Q000503:physiopathology*; D007770:L-Lactate Dehydrogenase / Q000378:metabolism; D008297:Male; D018384:Oxidative Stress; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar
D050759:Cyclin-Dependent Kinase Inhibitor p21; D017931:DNA Primers; D012333:RNA, Messenger; D003404:Creatinine; D007770:L-Lactate Dehydrogenase