Enhanced radical scavenging activity of a procyanidin B3 analogue comprised of a dimer of planar catechin

Planar catechin increases bone mass by regulating differentiation of osteoclasts in mice

OBJECTIVES

While catechins have been reported to exhibit potential to benefit osteoporosis patients, the effects of planar catechin (PCat), synthesized during the development of drugs for Alzheimer's disease, have not been clearly elucidated. Here, we examined the effects of PCat on mouse bone metabolism both in vivo and in vitro.

METHODS

Six week old female mice were orally administered PCat (30 mg/kg) every other day for four weeks, and their femurs were analyzed using micro-computed tomography imaging. Osteoclasts and osteoblasts were collected from mice and cultured with PCat. Subsequently, osteoclast formation and differentiation and osteoblast differentiation were observed.

RESULTS

Mice orally administered PCat displayed significantly increased femur bone mass compared to the control group. Quantitative polymerase chain reaction findings indicated that PCat addition to osteoclast progenitor cultures suppressed osteoclast formation and decreased osteoclast marker expression without affecting the proliferative potential of the osteoclast progenitor cells. Addition of PCat to osteoblast cultures increased osteoblast marker expression.

CONCLUSIONS

PCat inhibits osteoclast differentiation and promotes osteoblast differentiation, resulting in increased bone mass in mice. These results suggest that PCat administration is a promising treatment option for conditions associated with bone loss, including osteoporosis.

Effect of Magnesium Ion on the Radical-Scavenging Rate of Pterostilbene in an Aprotic Medium: Mechanistic Insight into the Antioxidative Reaction of Pterostilbene

Pterostilbene (PTS), a methylated analog of resveratrol (RSV), has recently attracted much attention due to its enhanced bioavailability compared to RSV. However, little is known about the radical-scavenging mechanism of PTS. In this study, we investigated the effect of Mg(ClO₄)₂ on the scavenging reaction of galvinoxyl radical (GO^•) by PTS in acetonitrile (MeCN). GO^• was used as a model for reactive oxygen radicals. The second-order rate constant (k_H) for the GO^•-scavenging reaction by PTS was more than threefold larger than that by RSV, although thermodynamic parameters, such as the relative O–H bond dissociation energies of the phenolic OH groups, ionization potentials, and HOMO energies calculated by the density functional theory are about the same between PTS and RSV. The oxidation peak potential of PTS determined by the cyclic voltammetry in MeCN (0.10 M Bu₄NClO₄) was also virtually the same as that of RSV. On the other hand, no effect of Mg (ClO₄)₂ on the k_H values was observed for PTS, in contrast to the case for RSV. A kinetic isotope effect of 3.4 was observed when PTS was replaced by a deuterated PTS. These results suggest that a one-step hydrogen-atom transfer from PTS to GO^• may be the rate-determining step in MeCN.

Design, Synthesis, and Biological Activity of Conformationally Restricted Analogues of Silibinin

Silibinin (Sib), one of the main components of milk thistle extract, has attracted considerable attention because of its various biological activities, which include antioxidant activity and potential effects in diabetes and Alzheimer's disease (AD). In a previous study, we synthesized catechin analogues by constraining the geometries of (+)-catechin and (-)-epicatechin. The constrained analogues exhibited enhanced bioactivities, with the only major difference between the two being their three-dimensional structures. The constrained geometry in (+)-catechin resulted in a high degree of planarity (PCat), while (-)-epicatechin failed to maintain planarity (PEC). The three-dimensional structure of Sib may be related to its ability to inhibit aggregation of amyloid beta (Aβ). We therefore introduced PCat and PEC into Sib to demonstrate how the constrained molecular geometry and differences in three-dimensional structures may enhance such activities. Introduction of PCat into Sib (SibC) resulted in effective inhibition of Aβ aggregation, α-glucosidase activity, and cell growth, suggesting that not only reduced flexibility but also the high degree of planarity may enhance the biological activity. SibC is expected to be a promising lead compound for the treatment of several diseases.

Inhibition of β-amyloid-induced neurotoxicity by planar analogues of procyanidin B3

Reactive oxygen species (ROS) are known to be produced during the amyloid beta (Aβ) aggregation process. Both ROS production and Aβ fibril formation can result in nerve cell injury. Proanthocyanidins are oligomers of catechin that can act as inhibitors of Aβ aggregation. Procyanidin B3 (Cat-Cat), the dimer of (+)-catechin, can easily cross the blood-brain barrier. Previously, we synthesized two derivatives of Cat-Cat, namely Cat-PCat and PCat-PCat, in which the geometry of one or both catechin molecules in Cat-Cat was constrained to be planar. The antioxidative activities of Cat-PCat and PCat-PCat were found to be stronger than that of Cat-Cat, with PCat-PC at exhibiting the most potent activity. These compounds are predicted to protect against Aβ-induced neurotoxicity via inhibition of Aβ aggregation as well as by antioxidative effects toward Aβ-induced intracellular ROS generation. PCat-PCat exhibited the most potent neuroprotective effects against Aβ-induced cytotoxicity, which resulted from inhibition of β-sheet structure formation during the Aβ aggregation process. PCat-PCat may be a promising lead compound for the treatment of Alzheimer's disease.

Procyanidin B2 3″-O-gallate Isolated from Reynoutria elliptica Prevents Glutamate-Induced HT22 Cell Death by Blocking the Accumulation of Intracellular Reactive Oxygen Species

In this study, we examined the neuroprotective effects of MeOH extract and bioactive compounds obtained from Reynoutria elliptica seeds using HT22 cells from the murine hippocampal cell line as its underlying molecular basis, which has not yet been elucidated. Our study showed that the MeOH extract of R. elliptica seeds strongly protected HT22 cells from glutamate toxicity. To clarify the responsible compound for the neuroprotective effects, we took an interest in procyanidins of R. elliptica since procyanidins are known to exhibit high structural diversity and neuroprotective activity. To isolate the procyanidins efficiently, a phytochemical investigation of the MeOH extract from R. elliptica seeds using the LC/MS-guided isolation approach was applied, and procyanidin B2 3″-O-gallate (1) was successfully isolated. The structure of 1 was elucidated by analyzing the nuclear magnetic resonance spectroscopic data and LC/MS analysis. The neuroprotective activities of 1 were thoroughly examined using HT22 cells. Compound 1 exhibited a strong antioxidant efficacy and blocked glutamate-mediated increase in the reactive oxygen species (ROS) accumulation. Furthermore, compound 1 significantly inhibited the phosphorylation of extracellular signal-regulated kinase, p38, and c-Jun N-terminal kinase, which were increased by glutamate. These findings prove that the extract of R. elliptica seeds containing procyanidin B2 3″-O-gallate, which is a strong neuroprotective component, can be used as a functional food forattenuating and regulating neurological disorders.

Efficient protective activity of a planar catechin analogue against radiation-induced apoptosis in rat thymocytes

About two thirds of biological damage due to low linear energy transfer (LET) radiation, such as X-rays and the plateau region of heavy-ion beams, is known to be caused by the hydroxyl radical (˙OH), the most powerful reactive oxygen species (ROS), generated via ionisation and excitation of water molecules. Thus, compounds having an efficient scavenging activity against ROS are expected to exhibit a radioprotective activity. A planar catechin analogue, where an isopropyl fragment was introduced into the catechol ring of (+)-catechin, showed an efficient protective effect against X-ray induced apoptosis in rat thymocytes compared to (+)-catechin. The planar catechin scavenged 2,2-diphenyl-1-picrylhydrazyl radicals (DPPH˙) solubilised in water by β-cyclodextrin about 10-fold faster than (+)-catechin in phosphate buffer (0.1 M, pH 7.4) at 298 K. Furthermore, the experimental log P value of the planar catechin (1.22) is reported to be significantly larger than that of (+)-catechin (0.44). The higher radical-scavenging activity and lipophilicity of the planar catechin than those of (+)-catechin may contribute in part to the higher protective activity against X-ray-induced apoptosis in rat thymocytes.

A planar catechin analogue showed a significant higher protective activity against X-ray induced apoptosis in rat thymocytes than (+)-catechin.