Cytoprotective Effects of Hypoxia against Cisplatin-Induced Tubular Cell Apoptosis

Abstract

Hypoxia that is caused by vascular defects or disruption is commonly associated with renal diseases. During cisplatin nephrotoxicity, hypoxic regions are identified in the outer medulla and the renal cortex. However, the regulation of cisplatin injury by hypoxia is unclear. Previous work has demonstrated the cytoprotective effects of hypoxia against apoptotic injury. This study further examines the cytoprotective mechanisms in models of cisplatin-induced tubular cell apoptosis. In cultured renal tubular cells, 20 M cisplatin induced approximately 60% apoptosis within 16 h. The rate of apoptosis was suppressed to <20%, when the incubation was conducted under hypoxia (2% O 2 ). Mitochondrial events of apoptosis, namely Bax accumulation and cytochrome c release, also were ameliorated. During cisplatin treatment, cell ATP was maintained in both normoxic and hypoxic cells. Hypoxic incubation lowered extracellular pH, but prevention of the pH decrease did not restore cisplatin-induced apoptosis. The cytoprotective effects of hypoxia also were independent of hypoxia-inducible factor 1 (HIF-1). Cobalt, as hypoxia, activated HIF-1 yet did not suppress cisplatin-induced apoptosis. Moreover, hypoxia suppressed cisplatin-induced apoptosis in HIF-1-deficient mouse embryonic stem cells and renal proximal tubular cells. Conversely, mitochondrial inhibitors, particularly inhibitors of respiration complex III (antimycin A and myxothiazol), mimicked hypoxia in apoptosis suppression. The effects of hypoxia and mitochondrial inhibitors were not additive. It is interesting that both hypoxia and complex III inhibitors ameliorated cisplatin-induced p53 activation. Therefore, the cytoprotective effects of hypoxia are independent of changes in cell ATP, pH, or HIF but may involve mitochondrial inhibition and the suppression of p53.

Effects of lentivirus-mediated HIF-1α knockdown on hypoxia-related cisplatin resistance and their dependence on p53 status in fibrosarcoma cells

“…26 As well, we chose cisplatin a widely used DNA-damaging anticancer agent in the clinic, which causes apoptosis which was closely related to p53 activation. 27,28 Furthermore, mechanisms of cisplatin-induced resistance under hypoxia are mainly due to indirect effects, including cell cycle arrest and DNA repair, not the O 2 itself. 29 Much evidence has shown that hypoxia is closely associated with tumor resistance to anticancer drugs, and many factors contribute to the mechanisms.…”

Visualization of Calcium Dynamics in Kidney Proximal Tubules

“…3 In an attempt to mimic ischemia (hypoxia) and reperfusion (reoxygenation) in isolated renal PTE cells, we have pretreated the cells in media containing 200 mM CoCl 2 , reported to cause hypoxic conditions in various cell types in vitro. 18,19 After 24 hours' pretreatment, exchange of the media for oxygenated media containing no CoCl 2 resulted in a large transient increase in cellular calcium levels, while addition of ATP still produced a rapid calcium rise ( Figure 2D). The exchange of media without CoCl 2 pretreatment did not alter intracellular calcium levels (Supplemental Figure 2F).…”

Hypoxia-induced chemoresistance in cancer cells: The role of not only HIF-1

“…A number of other cellular pathways are differentially regulated in hypoxia and may also contribute to hypoxia-induced drug resistance [77][78][79][80][81] . It has been shown that the suppression of HIF-1α through gene knockdown or the use of small molecule inhibitors reduces resistance to cytostatics, such as cisplatin, etoposide, doxorubicin, and ellipticine, but does not suppress it completely 20,33,59,60 . The fact that in some cell lines (e.g.…”

“…In radiotherapy, low oxygen levels prevent the formation of DNA strand breaks induced by radiation, and inhibits repair of DNA damage that induces genetic instability 3,4 . Hypoxia-induced resistance to cisplatin, doxorubicin, etoposide, melphalan, 5-flouoruracil, gemcitabine, and docetaxel has been previously reported in a number of tumor cell types [5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23] . Hypoxia regulates approximately 1% of the genes that play a role in the signaling pathways that control various aspects of tumor progression 24 .…”