Jeffrey Zidichouski

Silibinin: A novel inhibitor of Aβ aggregation

Alzheimers disease (AD) is characterized by the abnormal aggregation of amyloid β peptide (Aβ) into extracellular fibrillar deposits known as amyloid plaque. Inhibition of Aβ aggregation is therefore viewed as a potential method to halt or slow the progression of AD. It is reported that silibinin (silybin), a flavonoid derived from the herb milk thistle (Silybum marianum), attenuates cognitive deficits induced by Aβ25-35 peptide and methamphetamine. However, it remains unclear whether silibinin interacts with Aβ peptide directly and decreases Aβ peptide-induced neurotoxicity. In the present study, we identified, through employing a ThT assay and electron microscopic imaging that silibinin also appears to act as a novel inhibitor of Aβ aggregation and this effect showed dose-dependency. We also show that silibinin prevented SH-SY5Y cells from injuries caused by Aβ(1-42)-induced oxidative stress by decreasing H(2)O(2) production in Aβ(1-42)-stressed neurons. Taken together, these results indicate that silibinin may be a novel therapeutic agent for the treatment of AD.

Liuwei Dihuang (LWDH), a Traditional Chinese Medicinal Formula, Protects against β-Amyloid Toxicity in Transgenic Caenorhabditis elegans

Liuwei Dihuang (LWDH), a classic Chinese medicinal formula, has been used to improve or restore declined functions related to aging and geriatric diseases, such as impaired mobility, vision, hearing, cognition and memory. Here, we report on the effect and possible mechanisms of LWDH mediated protection of β-amyloid (Aβ) induced paralysis in Caenorhabditis elegans using ethanol extract (LWDH-EE) and water extract (LWDH-WE). Chemical profiling and quantitative analysis revealed the presence of different levels of bioactive components in these extracts. LWDH-WE was rich in polar components such as monosaccharide dimers and trimers, whereas LWDH-EE was enriched in terms of phenolic compounds such as gallic acid and paeonol. In vitro studies revealed higher DPPH radical scavenging activity for LWDH-EE as compared to that found for LWDH-WE. Neither LWDH-EE nor LWDH-WE were effective in inhibiting aggregation of Aβ in vitro. By contrast, LWDH-EE effectively delayed Aβ induced paralysis in the transgenic C. elegans (CL4176) model which expresses human Aβ1–42. Western blot revealed no treatment induced reduction in Aβ accumulation in CL4176 although a significant reduction was observed at an early stage with respect to β-amyloid deposition in C. elegans strain CL2006 which constitutively expresses human Aβ1–42. In addition, LWDH-EE reduced in vivo reactive oxygen species (ROS) in C. elegans (CL4176) that correlated with increased survival of LWDH-EE treated N2 worms under juglone-induced oxidative stress. Analysis with GFP reporter strain TJ375 revealed increased expression of hsp16.2::GFP after thermal stress whereas a minute induction was observed for sod3::GFP. Quantitative gene expression analysis revealed that LWDH-EE repressed the expression of amy1 in CL4176 while up-regulating hsp16.2 induced by elevating temperature. Taken together, these results suggest that LWDH extracts, particularly LWDH-EE, alleviated β-amyloid induced toxicity, in part, through up-regulation of heat shock protein, antioxidant activity and reduced ROS in C. elegans.

Baicalin prevents the production of hydrogen peroxide and oxidative stress induced by Aβ aggregation in SH-SY5Y cells.

Alzheimers disease (AD) is a common form of neurodegenerative disease. Mounting evidence suggests that metal ions play a key role in the aggregation of amyloid β peptide (Aβ), which acts as a factor or cofactor in the etiopathogenesis of AD. Therefore, inhibition of Aβ aggregation emerges as a potential approach for the treatment of AD. We have found that baicalin can interact with copper directly and inhibits Aβ1-42 aggregation. In addition, baicalin protects SH-SY5Y cells from oxidative injuries induced by Aβ1-42 aggregation through decreasing H(2)O(2) production that is normally formed as a deleterious by-product of beta amyloid aggregation and the formation of plaques. Taken together, these data indicate that baicalin may be a potential agent to inhibit Aβ aggregation and thereby delay, mitigate or modify the progression of neurodegenerative diseases such as AD.

Berberine and plant stanols synergistically inhibit cholesterol absorption in hamsters.

The present study was conducted to determine the efficacy and underlying mechanism of berberine (BBR), plant stanols (PS) and their combination on plasma lipids. Male Golden Syrian hamsters were randomly divided into 4 groups (n=15/group) and fed a cornstarch-casein-sucrose-based diet containing 0.15% cholesterol and 5% fat. Three treatment groups were supplemented with 0.17% (equivalent to 100mgkg(-1)d(-1)) BBR, 1% PS, or a combination of both (BBRPS) for 4wk. At the end of the study, plasma lipids were analyzed with enzymatic methods, cholesterol absorption and synthesis using stable isotope tracer methodology, and gene and protein expressions in the liver and small intestine using real-time PCR and Western blot, respectively. BBR and PS significantly lowered plasma total- and nonHDL-cholesterol levels, and BBRPS markedly improved cholesterol-lowering efficacy compared to BBR or PS alone. Further examinations revealed that BBR and PS both inhibited cholesterol absorption and by contrast, increased cholesterol synthesis, and exerted a synergistic action when they were combined. Plasma total or nonHDL-cholesterol levels were significantly correlated with cholesterol absorption rates. BBR upregulated sterol 27-hydroxlase gene expression and BBRPS increased both cholesterol-7alpha-hydroxylase and sterol 27-hydroxlase gene expressions. BBR and PS also synergistically decreased plasma triacylglycerides. These findings suggest that the cholesterol-lowering action of BBR might involve a combination of inhibition of cholesterol absorption and stimulation of bile acid synthesis. The combination of BBR and PS improves cholesterol-lowering efficacy through a synergistic action on cholesterol absorption, in addition to synergistically reducing plasma triacylglycerols in hamsters.

Co-administration of berberine and plant stanols synergistically reduces plasma cholesterol in rats

The objective of the present study was to determine the beneficial effects and the safety of oral administration of the combination of berberine (BBR) and plant stanols (PS) on plasma lipid profiles in male Sprague-Dawley rats. Four groups of animals were fed a cornstarch-casein-sucrose-based high-cholesterol (2%, w:w) and high-fat (27.5%) diet. Three treatment groups were supplemented with either BBR (100mgkg(-1)bodyweightd(-1)), PS (1% in diet, w:w), or the combination of both (BBRPS). After 6 wk, animals were sacrificed and followed immediately with the collection of blood and organ samples. Lipid analysis revealed that PS lowered plasma total cholesterol (T-C) by 18% (p=0.067) and non-HDL-cholesterol (non-HDL-C) by 29% (p=0.013) as compared with the control, while BBR had no effect on both T-C and non-HDL-C. The combination treatment of BBRPS reduced plasma T-C by 41% (p=0.0002) and non-HDL-C by 59% (p<0.0001) compared to the control group. BBR reduced plasma TG levels by 31% at a marginal significance relative to the control (p=0.054), whereas PS had no effect. BBRPS showed an additive effect of BBR and PS on plasma TAG. PS and BBRPS both decreased liver cholesterol (p=0.0027 and 0.0002, respectively). BBR and PS, either alone or in combination, did not show any toxic effects as assessed by plasma concentration of hepatic biochemical parameters. These results demonstrate that BBR and PS, when combined, synergistically lower plasma cholesterol levels and significantly reduce liver cholesterol, without the observation of any toxic effects.

17β-estradiol attenuates excitatory neurotransmission and enhances the excitability of rat parabrachial neurons in vitro

The steroid hormone 17β‐estradiol and its respective receptors have been found in several cardiovascular nuclei in the central nervous system including the parabrachial nucleus. In a previous study, we provided evidence that 17β‐estradiol attenuated an outward potassium conductance in parabrachial neurons of male rats, using an in vitro slice preparation. In this study we sought to enhance the comprehensive information provided previously on estradiols postsynaptic effects in the parabrachial nucleus by directly examining whether 17β‐estradiol application will modulate excitatory synaptic neurotransmission. Using a pontine slice preparation and whole‐cell patch‐clamp recording, bath application of either 17β‐estradiol (20–100 μM) or BSA‐17β‐estradiol (50 μM) decreased the amplitude of evoked excitatory postsynaptic currents (from 30–60% of control) recorded from neurons in the parabrachial nucleus. The paired pulse ratio was not significantly affected and suggests a post‐synaptic site of action. The inhibitory effect on the synaptic current was relatively long‐lasting (non‐reversible) and was blocked by the selective estrogen receptor antagonist, ICI 182,780. Furthermore, 17β‐estradiol reduced the maximum current elicited by a ramp protocol, increased the input resistance measured between resting membrane potential and action potential threshold and caused an increase in the firing frequency of the cells under current‐clamp. In summary, 17β‐estradiol caused 3 effects: first, a depolarization; second, a reduction in evoked excitatory postsynaptic potentials; and third, an enhancement of action potential firing frequency in neurons of the parabrachial nucleus. These observations are consistent with our previous findings and support a role for estrogen in modulating neurotransmission in this nucleus.

Substance P and cocaine employ convergent mechanisms to depress excitatory synaptic transmission in the rat nucleus accumbens in vitro

Substance P (SP) has been reported to produce effects on excitatory synaptic transmission in the nucleus accumbens (NAc) that are similar to those induced by cocaine. To address the question of whether SP serves as an endogenous mediator producing cocaine‐like effects that are known to be D1‐receptor‐mediated, we tested the hypothesis that the effects of SP and cocaine on excitatory postsynaptic currents (EPSCs) in the NAc occlude one another. We report here that SP and SP5–11 actions occlude the effect of cocaine and vice versa. SP, SP5–11 and cocaine all depressed evoked, non‐N‐methyl‐d‐aspartate (NMDA) receptor‐mediated synaptic currents in a concentration‐dependent manner, with EC50 values of 0.12, 0.17 and 8.3 μm, respectively. Although cocaine was the least potent, it was most efficacious. SP, SP5–11 and cocaine all suppressed isolated NMDA receptor‐mediated evoked EPSCs. SP5–11 (1 μm)‐induced EPSC depression was blocked by the neurokinin‐1 antagonist L732138 and by the D1‐like receptor antagonist SCH23390. Pretreatment of slices with cocaine (30 μm) depressed the EPSC by 39.1% ± 4.8%. Application of SP or SP5–11 (1 μm) at the peak of the cocaine depressive effect on the EPSC did not produce any additional diminution of the response (5.7% ± 2.8%). In the reverse experiments, in which either SP or SP5–11 was applied first, subsequent application of cocaine at the peak of the peptide’s effect (30.3% ± 2.3%) produced a further but smaller depression (15.5% ± 3.6%) of the remaining EPSC. These data indicate that cocaine and SP produce similar effects on excitatory synaptic transmission in the NAc, and that their actions occlude one another. This suggests that SP may act like cocaine in its absence, and may be an endogenous trigger for the reward and behaviors associated with cocaine.