Comparison of cytotoxicity of cysteine and homocysteine for renal epithelial cells.
BACKGROUND
Although the cytotoxic effects of cysteine (Cys) on renal cells have been established, the effects of homocysteine (Hcy), which causes endothelial cell dysfunction, have not been well tested. We compared the direct toxicity of Hcy on renal tubular cells to that of Cys and examined the mechanism of cell toxicity.


METHODS
LLC-PK1 cells were incubated with test media containing 500 microM Cys or Hcy in the presence or absence of 100 microM copper. Lactate dehydrogenase release and thiobarbituric acid reactive substance were measured for estimating cytolysis and lipid peroxidation, respectively. The generation of hydrogen peroxide and hydroxyl radical, and the cell redox state were analyzed using the scopoletin method, salicylate-trap method, and glutathione (GSH) content, respectively. Superoxide dismutase, catalase, and vitamin E also were used for clarifying the mechanism of toxicity.


RESULTS
In the presence of copper (+ Cu), cytolysis at 16 h was more prominent in cells exposed to Cys than Hcy. In accordance with cytotoxicity, lipid peroxidation at 4 h of incubation, as well as hydrogen peroxide and hydroxyl radical formation in a shorter incubation, were remarkably greater in Cys + Cu than Hcy + Cu. The addition of Hcy, but not Cys, decreased GSH content significantly.


CONCLUSIONS
In the presence of copper, Cys was extraordinarily more cytotoxic to renal cells than Hcy. Cytotoxicity from Hcy may be dependent upon depletion of cellular GSH, while Cys cytotoxicity is primarily dependent upon the generation of reactive oxygen species and lipid peroxidation.
Nakanishi
Takeshi
T
Internal Medicine, Division of Kidney and Dialysis, Hyogo College of Medicine, Nishinomiya, Japan. t-nkns@hyo-med.ac.jp
Akabane
Eiko R
ER
Nanami
Masayoshi
M
Kiyobayashi
Yuri
Y
Moriguchi
Rintarou
R
Hasuike
Yukiko
Y
Otaki
Yoshinaga
Y
Miyagawa
Koji
K
Itahana
Reiko
R
Izumi
Masaaki
M
D000818:Animals; D000975:Antioxidants / Q000494:pharmacology; D001681:Biological Assay; D002374:Catalase / Q000378:metabolism; D018929:Cell Culture Techniques; D003545:Cysteine / Q000633:toxicity*; D004847:Epithelial Cells; D005978:Glutathione / Q000032:analysis; D006710:Homocysteine / Q000633:toxicity*; D006861:Hydrogen Peroxide / Q000032:analysis; D017665:Hydroxyl Radical / Q000032:analysis; D007684:Kidney Tubules / Q000187:drug effects* / Q000502:physiology*; D007770:L-Lactate Dehydrogenase / Q000378:metabolism; D018374:LLC-PK1 Cells; D015227:Lipid Peroxidation; D016877:Oxidants / Q000032:analysis; D017382:Reactive Oxygen Species; D013482:Superoxide Dismutase / Q000378:metabolism; D013552:Swine; D014810:Vitamin E / Q000494:pharmacology
D000975:Antioxidants; D016877:Oxidants; D017382:Reactive Oxygen Species; D006710:Homocysteine; D014810:Vitamin E; D017665:Hydroxyl Radical; D006861:Hydrogen Peroxide; D007770:L-Lactate Dehydrogenase; D002374:Catalase; D013482:Superoxide Dismutase; D005978:Glutathione; D003545:Cysteine