D-methionine protects against cisplatin-induced neurotoxicity in the hippocampus of the adult rat

Abstract

The hippocampus plays an important role in memory, mood, and spatial navigation. In the dentate gyrus of the adult hippocampus, in the subgranular zone (SGZ), new cells are generated, which differentiate and mature into new neurons. Cisplatin, a highly effective antineoplastic drug with nephrotoxic and ototoxic side effects, induces apoptosis and suppresses neurogenesis in the hippocampus leading to memory impairment. Previous studies have shown that the antioxidant D-methionine protects against cisplatin-induced ototoxicity and nephrotoxicity suggesting that it might also prevent neurogenesis from being suppressed by cisplatin treatment. To test this hypothesis, rats were treated with cisplatin, D-methionine, cisplatin plus D-methionine, or saline (controls). Seven days after treatment, the rats were sacrificed, and hippocampal sections immunolabeled for doublecortin (DCX) to identify neuronal precursor cells and maturing neurons in the SGZ. Cisplatin significantly reduced the number of DCX-labeled cells (~80 %) relative to controls. In contrast, DCX cell counts in rats treated with D-methionine prior to cisplatin were similar to controls. The treatment with D-methionine alone did not affect the number of DCX cells. These results indicate that D-methionine prevents the dramatic cisplatin-induced decrease of neurogenesis.

Fig. 1

DCX antibody specificity. The dentate gyrus of the hippocampus show DCX immunopositive cell bodies in the SGZ (a, b). When the DCX-antibody was preadsorped with the immunizing peptide (sc-8066 P), sections remained unstained. Arrowheads indicate the SGZ. Scale bars: 200 μm (a, c); 100 μm (b, d).

Fig. 2

Hippocampal neuronal precursor cells in the dentate gyrus immunolabeled for DCX in a control rat (a) and rats treated with cisplatin (Cis) surviving for 2 days (b), 7 days (c) and 21 days (d): Seven days after cisplatin treatment the number of cell bodies (arrow heads) was considerably reduced. Scale bar: 50μm

Fig. 3

Hippocampal neuronal precursor cells in the dentate gyrus immunolabeled for DCX in controls (a) and seven days after treatment (b, c, d): cisplatin alone (Cis), cisplatin with D-methionine (Cis + D-met), and D-methionine alone (D-met). Seven days after cisplatin treatment (b) the number of cell bodies (arrow heads) was significantly reduced when compared to controls (a). When treated with D-methionine before cisplatin (c), the number of cell bodies remained similar to controls. Scale bar: 100μm

Fig. 4

Relative numbers of DCX cells in controls, cisplatin (Cis), cisplatin with D-methionine (Cis + D-met), and D-methionine (D-met) 7 days after treatment: Numbers were normalized to the control group which was set to 1.0. Rats treated with only cisplatin showed a large and significant reduction in cell density when compared to controls and to animals treated with only D-methionine. D-methionine administered 30 minutes prior to cisplatin kept the number of DCX positive cells comparable to the controls and to animals treated with only D-methionine, while it was significantly larger than in animals treated with cisplatin. There were no significant differences between controls, animals treated with cisplatin plus D-methionine, and animals treated with only D-methionine.