Prevention of the Neurotoxicity of the Amyloid .BETA. Protein by Genipin.

Abstract

It is now generally documented that the cause of Alzheimer's disease is progressive deposition (histopathologically identified as senile plaque) of the amyloid b protein (Ab) (Ab1-42 and Ab1-40) with aging or due to genetic background in vulnerable brain regions, including the hippocampus and cortex. This deposition is strongly suspected to contribute to disruption of the neuronal network as a result of ubiquitous apoptotic cell death induced by Ab.1,2) The addition of Ab and its hydrophobic core fragments such as Ab25-35 (a monodecapeptide with an amino acid sequence identical to that from 25 to 35 of Ab) has been reported to induce significant cell death in approximately one week in primary cultures of rat hippocampal neurons. [3][4][5] Geniposide and genipin, iridoid compounds found in many plants such as Gardenia jasminoides, have been demonstrated in our laboratory to have neurotrophic, nerve growth factor (NGF)-like activity in their neuritogenesis and signaling promotion in PC12h cells, with genipin having the stronger effect.6,7) Administration of genipin counteracted the trauma-and scopolamine-induced impairment of memory in mice. 8) In some reported experiments, NGF and other neurotrophic factors reversed the deficit in spatial learning and memory in aged rats.9,10) We investigated whether these two iridoids can affect the neuronal toxicity of Ab in cultured hippocampal neurons.Hippocampal neurons from 18-d rat embryos were prepared as described previously.11) Hippocampal cells were maintained for 2 d in 48-well culture plates with Dulbecco's modified Eagle medium (DMEM) supplemented with 10% precolostrum new-born calf serum, selected for neuronal populations by incubation with cytosine-b-D-arabinofuranoside 10 mM for 24 h in Ca 2ϩ , Mg 2ϩ -free phosphate-buffered saline, pH 7.4 (CMF-PBS), and then treated with Ab25-35 (40 mM) in CMF-PBS for 2 d without serum. Ab25-35 was prepared using a peptide synthesizer according to the method described previously.11) It was dissolved in CMF-PBS at a concentration of 1.8 mM (most of the Ab was in fine suspension).Toxic effect on the cultures was evaluated by estimation of lactate dehydrogenase (LDH) release during 2 d of culture in the presence of Ab25-35 with and without test compounds as specified below and according to the method described previously. 12)Geniposide was kindly provided by Toyo F.C.C. Co. (Tokyo, Japan) and genipin was purchased from Wako Pure Chemical Industries (Osaka, Japan). They were dissolved in distilled water and refrigerated until use.The addition of Ab25-35 40 mM to the hippocampal neuron cultures markedly increased LDH release (Fig. 1, Ab25-35 only). Our colleagues previously found in cultured hippocampal cells that Ab25-35-induced plasma membrane impairment was blocked by the addition of the endonuclease inhibitor aurintricarboxylic acid, indicating that the cell degeneration was a result of apoptotic cell death.13) The neurotoxicity of Ab was effectively attenuated by the addition of genipin (20 mM or more) to the medium (Fig. 1A). ...

Geniposide from Gardenia jasminoides Attenuates Neuronal Cell Death in Oxygen and Glucose Deprivation-Exposed Rat Hippocampal Slice Culture

“…Fifty and 100 mM of geniposide completely blocked neuronal cell death in granular cell layer. Although Yamazaki et al reported that geniposide could not protect hippocampal cells against b-amyloid-induced toxicity, 7) we found that geniposide attenuated cell death in OGD-exposed rat hippocampal slice culture. This discrepancy suggests the mechanism by which OGD induces cell death is different from cell death by b-amyloid.…”

Neurotrophic Effects of Genipin on Neuro2a Cells

“…14) It has been suggested that one of the common mechanisms between serum deprivation-and β-amyloid peptide-induced cytotoxicity is the induction of oxidative stress. 15,16) Thus, genipin may suppress the cytotoxicity involved in oxidative stress.…”

Neuroprotective effects of geniposide on Alzheimer’s disease pathology

“…These findings indicate that geniposide activates GLP-1Rs, which then protects against Aβ-induced neurotoxicity by the regulation of the expression of IDE in cortical neurons. The cultured hippocampal neurons had significantly degenerated after treatment with Aβ 25-35 , but the degeneration did not occur to the same extent in the presence of genipin (Yamazaki et al, 2001b). One study found that genipin suppressed apoptosis in cultured cells via the inhibition of caspase activation and mitochondrial function (Yamamoto et al, 2000).…”