LLDT-67 attenuates MPTP-induced neurotoxicity in mice by up-regulating NGF expression

Aim: To investigate the neuroprotective effects of LLDT-67, a novel derivative of triptolide, in MPTP-induced mouse Parkinson's disease (PD) models and in primary cultured astrocytes, and to elucidate the mechanisms of the action. Methods: In order to induce PD, C57BL/6 mice were injected MPTP (30 mg/kg, ip) daily from d 2 to d 6. MPTP-induced behavioral changes in the mice were examined using pole test, swimming test and open field test. The mice were administered LLDT-67 (1, 2, or 4 mg/kg, po) daily from d 1 to d 11. On d 12, the mice were decapitated and brains were collected for immunohistochemistry study and measuring monoamine levels in the striatum. Primary cultured astrocytes from the cortices of neonatal C57BL/6 mouse pups were prepared for in vitro study. Results: In MPTP-treated mice, administration of LLDT-67 significantly reduced the loss of tyrosine hydroxylase-positive neurons in the substantia nigra, and ameliorated the behavioral changes. LLDT-67 (4 mg/kg) significantly increased the expression of NGF in astrocytes in the substantia nigra and striatum of the mice. Furthermore, administration of LLDT-67 caused approximately 2-fold increases in the phosphorylation of TrkA at tyrosine 751, and marked increases in the phosphorylation of AKT at serine 473 as compared with the mice model group. In the cultured astrocytes, LLDT-67 (1 and 10 nmol/L) increased the NGF levels in the culture medium by 179% and 160%, respectively. Conclusion: The neuroprotective effect of LLDT-67 can be mostly attributed to its ability to enhance NGF synthesis in astrocytes in the midbrain and to rescue dopaminergic neurons indirectly through TrkA activation.