Constant illumination induces Alzheimer-like damages with endoplasmic reticulum involvement and the protection of melatonin.

Most patients with Alzheimer's disease (AD) present decreased levels of melatonin, a day-night rhythm-related hormone. To investigate the role of melatonin deficiency in AD, we used constant illumination to interrupt melatonin metabolism and measured some of the AD-like alterations in rats. Concomitant with decreased serum melatonin, the rats developed spatial memory deficits, tau hyperphosphorylation at multiple sites, activation of glycogen synthase kinase-3 and protein kinase A, as well as suppression of protein phosphatase-1. Prominent oxidative damage and organelle lesions, demonstrated by increased expression of endoplasmic reticulum (ER) stress-related proteins including BiP/GRP78 and CHOP/GADD153, decreased number of rough ER and free ribosome, thinner synapses, and increased superoxide dismutase and monoamine oxidase were also observed in the light exposed rats. Simultaneous supplement of melatonin partially arrested the behavioral and molecular impairments. It is suggested that melatonin deficiency may be an upstream effector responsible for the AD-like behavioral and molecular pathologies with ER stress-involved mechanisms.

Inhibition of melatonin biosynthesis activates protein kinase a and induces Alzheimer-like tau hyperphosphorylation in rats.

OBJECTIVE: To investigate effect of inhibiting melatonin biosynthesis on activities of protein kinase A (PKA), glycogen synthase kinase-3 (GSK-3) and tau phosphorylation at PS214 and M4 epitopes using haloperidol, a specific inhibitor of 5-hydroxyindole-O-methyltransferase. METHODS: Brain ventricular and intraperitoneal injections were used for haloperidol administration, Western blots for tau phosphorylation, 32P-labeling for PKA and GSK-3 activity, and high performance liquid chromatograph for detection of serum melatonin levels. RESULTS: Haloperidol injection through the lateral ventricle and intraperitoneal reinforcement significantly stimulated PKA activity with a concurrent hyperphosphorylation of tau at M4 (Thr231/Ser235) and PS214 (Ser214) sites. Prior treatment of the rats using melatonin supplement for one week and reinforcement during the haloperidol administration arrested PKA activity and attenuated tau hyperphosphorylation. GSK-3 activity showed no obvious change after haloperidol injection, however, melatonin supplements and reinforcements during haloperidol infusion inactivated basal activity of GSK-3. CONCLUSION: Decreased melatonin may be involved in Alzheimer-like tau hyperphosphorylation, and overactivation of PKA may play a crucial role in this process.

Isolation, characterization, and determination of antioxidative activity of oligomeric procyanidins from the seedpod of Nelumbo nucifera Gaertn.

The procyanidins of nonedible parts of lotus (Nelumbo nucifera Gaertn.) were determined for the first time. The procyanidins of lotus seedpod were extracted with Me(2)CO/H(2)O and purified by Sephadex LH-20 column chromatography, with a purity of >98%. ESI-MS analysis showed that the main molecular weight distribution of procyanidins ranged from 291 to 1155, with M + H peak values of 291.1, 579.2, 731.2, 867.2, 1019.4, and 1155.3, respectively. This indicates that the extract contains monomers, dimers, and tetramers of procyanidins, in which the amounts of dimers are greatest, and catechin and epicatechin are the base units. (1)H NMR and (13)C NMR spectra confirmed that two to four monomers are linked through C(4)-C(8) (or C(6)) bonds. The effects of the procyanidins on lipid autoxidation, lipoxygenase activities, and free radical scavenging were also studied. The results showed that 0.1% procyanidins have a strong antioxidant activity in a soybean oil system, better than BHT at the same concentration; inhibited lipoxygenase activity by >90% at a concentration of 62.5 mug/mL, with an IC(50) value of 21.6 mug/mL; and had IC(50) inhibitory values rate to (*)OH of 10.5 mg/L and a scavenging effect on O(2)(*)(-) of 17.6 mg/L.

Correlation of behavior changes and BOLD signal in Alzheimer-like rat model.

To explore a potential means for the early diagnosis of Alzheimer disease, we studied the relationship of resting T2* signal and tau hyperphosphorylation/spatial memory deficit. The rat model with tau hyperphosphorylation and spatial memory deficit was established by bilateral hippocampi injection of isoproterenol (IP). Then, the correlative alteration between resting T2* signal and spatial memory retention was assessed with blood oxygenation level dependent (BOLD) functional magnetic resonance imaging (fMRI) study and Morris Water Maze test, and Western blot was employed to confirm tau hyperphosphorylation. The analysis showed following results. (1) Tau phosphorylation at Ser396/Ser404 and Ser199/Ser202 was significantly increased in IP-injected rats as detected by PHF-1 and tau-1, respectively. (2) An AD-like spatial memory retention disturbance was induced at 24 h after isoproterenol injection. (3) A sensitivity threshold of resting T2* signal intensity, which separated the IP-treated rats from vehicle control, was obtained by applying linear regression analysis, and an estimated sensitivity statistical threshold was at 32.62. These results suggest that resting T2* signal may serve as a noninvasive quantitative marker in predicting AD-like spatial memory deficits and tau hyperphosphorylation.

Melatonin attenuates isoproterenol-induced protein kinase A overactivation and tau hyperphosphorylation in rat brain.

Hyperphosphorylation of microtubule-associated protein tau at specific sites is a recognized pathological process in Alzheimer's disease (AD), and protein kinase A (PKA) is a crucial kinase in AD-like tau hyperphosphorylation. In the present study, isoproterenol (ISO) was injected bilaterally into hippocampus of rat brain; ISO is a specific PKA activator and it induces tau hyperphosphorylation. With this system, melatonin (MT) was shown to protect against ISO-induced tau hyperphosphorylation. We found that hippocampal injection of ISO (0.02 microm) induced PKA overactivation and tau hyperphosphorylation at both paired helical filament (PHF)-1 and tau-1 sites. ISO injection also resulted in activation of superoxide dismutase (SOD) and elevation of malondialdehyde (MDA), parameters suggesting elevated oxidative stress. Preinfusion of MT intraperitoneally partially reversed ISO-induced tau hyperphosphorylation at the PHF-1 epitope (1 and 10 mg/kg continuously for 4 wk or 10 mg/kg for 1, 2 or 3 wk) and tau-1 epitope (10 mg/kg for 2 wk). Furthermore, MT (10 mg/kg for 2 wk) obviously antagonized ISO-induced PKA overactivation, as well as enhanced SOD activity and decreased the level of MDA. It is suggested from these data that ISO may induce abnormal hyperphosphorylation of tau through not only the activation of PKA but also because of the fact that it increases oxidative stress; MT may protect against ISO-induced tau hyperphosphorylation through suppression of both PKA overactivation and oxidative stress.