Neuroprotective effect of genistein against beta amyloid-induced neurotoxicity
Introduction
Several lines of evidence indicate that estrogen is beneficial to patients with Alzheimer's disease (AD). Women are at a greater risk of developing AD than men (Lautenschlager et al., 1996), and mental deterioration occurs at a higher rate in female AD patients than in male patients (Small et al., 1995). On the other hand, estrogen replacement therapy (ERT) on postmenopausal women is associated with delayed onset and reduced risk of AD Kawas et al., 1997, Yaffe et al., 1998. Underlying mechanisms of estrogen effect on AD are not clear at present, but estrogen has many potentially beneficial actions in the brain. Particular attention has been given to estrogen's action against Aβ-induced cell death, since Aβ-induced neuronal cell death is a prime candidate for the cause of AD (Hardy and Selkoe, 2002). In this regard, estrogen has been shown to block Aβ-induced neuronal cell deaths in several different studies Gridley et al., 1998, Kim et al., 2001, Pike, 1999, Svensson and Nordberg, 1999. These results suggest that ERT should show improvement in patients with AD. However, estrogen also brings forth unwanted side effects. It has proliferative and oncogenic effects on non-neuronal cells responsive to estrogen, such as cells of breast (Collaborative Group on Hormonal Factors in Breast Cancer, 1997) and endometrium (Beresford et al., 1997). A careful analysis of both positive and negative effects showed a balanced number of risks and benefits (Clinical Synthesis Panel on HRT, 1999). The long-term compliance of estrogen is often estimated to be no more than 15–40% because of these side effects (Ravnikar, 1992), and thus, the use of estrogen as a treatment for AD is limited. For this reason, other estrogenic agents with fewer side effects are needed to develop alternative treatment strategies.
In the present study, we explored the possibility of using genistein as an alternative estrogenic agent. Genistein, a major phytoestrogen in soybean, has a structure similar to that of estrogen and is a relatively selective estrogen receptor (ER) β-agonist; it has seven to eight times less binding affinity to ERα than ERβ An et al., 2001, Kuiper et al., 1997. Our interest in genistein arose due to the following reasons. First, the protective effect of estrogen against Aβ toxicity is mediated by ERs (Kim et al., 2001). Because genistein is an ERβ agonist, there is a fair chance for genistein to have neuroprotective effects against Aβ toxicity. Second, ERβ is in brain regions that are associated with learning and memory (neocortex, hippocampus, and nuclei of the basal forebrain) (Shughrue et al., 1997). If genistein protects neurons in these brain areas, it is likely to reduce memory impairment, which is the prime clinical symptom of AD patients. Finally, genistein is described as a potent agent in both prophylaxis and treatment of hormone-dependent cancers such as those of breast and endometrium Adlercruetz et al., 1995, Zava and Duwe, 1997. Such cancers arise as problematic side effects of the ERT Beresford et al., 1997, Collaborative Group on Hormonal Factors in Breast Cancer, 1997. Genistein appears to act against the adverse effects of estrogen even though it is an estrogenic agent. All of these observations together are sufficient enough to suspect that genistein may contain beneficial effects of estrogen without its unwanted side effects. The results of our study indicate that genistein indeed blocks Aβ neurotoxicity without the proliferative side effect on uterine endometrial cells. Therefore, our results suggest that genistein could be beneficial for the treatment of AD.
Section snippets
Cell lines and materials
Human neuroblastoma SH-SY5Y cells and primary cultured normal human endometrial cell were used in this study. These cells were kept in Dulbecco's Modified Eagle's medium (DMEM) (Gibco-BRL, Grand Island, NY) containing 10% fetal bovine serum (FBS) (Hyclone, Irvine, CA) and 1% penicillin/streptomycin (Sigma, St. Louis, MO) in a humidified incubator (Forma) at 37°C under 5% CO2. Before factor treatment, SH-SY5Y cells were cultured in progesterone-free N2 medium (Bottenstein and Sato, 1979) with 10
Effects of Aβ1–42 on the viability of differentiated SH-SY5Y cells
To determine the effective concentration and duration of Aβ1–42 treatment that induce cell death, differentiated SH-SY5Y cells were cultured with various concentrations (1–10 μM) of Aβ1–42 for 24–72 h. Cell viability was assessed by measuring Aβ-induced changes through observing the amount of MTT reduction. About 50% of the cultured cells showed decreased levels of MTT reduction following 72-h treatment with 5 and 10 μM of Aβ1–42 (Fig. 1). The protocol using the 72-h treatment of 5 μM Aβ1–42
Genistein as an alternative to estrogen for treatment of AD
Despite the numerous lines of clinical and preclinical evidence for the beneficial effects of ERT Kawas et al., 1997, Yaffe et al., 1998, the use of estrogen is problematic for the treatment of AD because of its proliferative and oncogenic effects on non-neuronal cells responsive to estrogen. The results of the present study show that genistein has a neuroprotective ability, which is as potent as that of estrogen, but without significant proliferation of endometrial cells. Epidemiological
Acknowledgements
This work was supported by the Korea Research Foundation (KRF-2000-015-DP0388) and the Biodiscovery Research Program (M1-0106-00-0010), 21C Frontier program of Functional Proteomics project (FPR02A1-4-110), and Brain Research Center project (M103KV010019 03K2201 01950) of the Korean Ministry of Science Technology.
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