Promotion of neuronal differentiation of PC12h cells by natural lignans and iridoids

Neurotrophic Natural Products

Neurotrophins (NGF, BDNF, NT3, NT4) can decrease cell death, induce differentiation, as well as sustain the structure and function of neurons, which make them promising therapeutic agents for the treatment of neurodegenerative disorders. However, neurotrophins have not been very effective in clinical trials mostly because they cannot pass through the blood-brain barrier owing to being high-molecular-weight proteins. Thus, neurotrophin-mimic small molecules, which stimulate the synthesis of endogenous neurotrophins or enhance neurotrophic actions, may serve as promising alternatives to neurotrophins. Small-molecular-weight natural products, which have been used in dietary functional foods or in traditional medicines over the course of human history, have a great potential for the development of new therapeutic agents against neurodegenerative diseases such as Alzheimer's disease. In this contribution, a variety of natural products possessing neurotrophic properties such as neurogenesis, neurite outgrowth promotion (neuritogenesis), and neuroprotection are described, and a focus is made on the chemistry and biology of several neurotrophic natural products.

The Neurotrophic-Like Effect of Carvacrol: Perspective for Axonal and Synaptic Regeneration

Carvacrol (CARV) is a phytochemical widely used as flavoring, preservative, and fragrance in food and cosmetic industries. CARV is able to cross the blood-brain barrier (BBB) and has demonstrated protective potential against neurodegenerative diseases by several mechanisms, including antioxidant, anti-inflammatory, anticholinesterase, and antiapoptotic effects. However, it is not known whether CARV is able to modulate axonal and synaptic plasticity, crucial events in cognition, memory, and learning. Abnormalities in axonal and synaptic plasticity, low levels of neurotrophins, and bioenergetic failure have been associated with the pathogenesis of neurodegenerative diseases, including Parkinson's (PD) and Alzheimer's diseases (ADs). Small lipophilic molecules with neurotrophic activity might be able to restore the axonal and synaptic networks that are lost in neurodegenerative processes. Therefore, this study investigated the neurotrophic potential of CARV in PC12 cell-based neuronal model. Carvacrol induced neurite outgrowth by activating the NGF high-affinity trkA receptor and the downstream PI3K-AKT and MAPK-ERK pathways, without depending on NGF. In addition, CARV increased the expression of proteins involved in neuronal plasticity (β-tubulin III, F-actin, 200-kDa neurofilament, GAP-43 and synapsin-I) and improved bioenergetics (AMPKα, p-AMPKα, and ATP). Our study showed, for the first time, a promising neurotrophic mechanism of CARV that could be beneficial in neurodegenerative and neurological diseases.

Lian Hua Qing Wen Capsules, a Potent Epithelial Protector in Acute Lung Injury Model, Block Proapoptotic Communication Between Macrophages, and Alveolar Epithelial Cells

Besides pathogen evading, Acute Lung Injury (ALI), featuring the systematic inflammation and severe epithelial damages, is widely believed to be the central non-infectious factor controlling the progression of infectious diseases. ALI is partly caused by host immune responses. Under the inspiration of unsuccessful treatment in COVID-19, recent insights into pathogen–host interactions are leading to identification and development of a wide range of host-directed therapies with different mechanisms of action. The interaction unit consisting of macrophages and the alveolar epithelial cells has recently revealed as the therapeutic basis targeting ALI. Lian Hua Qing Wen capsule is the most effective and commonly-used clinical formula in treating respiratory infection for thousands of years in China. However, little is known about its relevance with ALI, especially its protective role against ALI-induced alveolar tissue damages. Aiming to evaluate its contribution in antibiotics-integrating therapies, this study pharmacologically verified whether LHQW could alleviate lipopolysaccharide (LPS)-induced ALI and explore its potential mechanisms in maintaining the physiology of macrophage-epithelial unit. In ALI mouse model, the pathological parameters, including the anal temperature, inflammation condition, lung edema, histopathological structures, have all been systematically analyzed. Results consistently supported the effectiveness of the combined strategy for LHQW and low-dose antibiotics. Furthermore, we established the macrophages-alveolar epithelial cells co-culture model and firstly proved that LHQW inhibited LPS-induced ER stress and TRAIL secretion in macrophages, thereby efficiently protected epithelial cells against TRAIL-induced apoptosis. Mechanistically, results showed that LHQW significantly deactivated NF-κB and reversed the SOCS3 expression in inflammatory macrophages. Furthermore, we proved that the therapeutic effects of LHQW were highly dependent on JNK-AP1 regulation. In conclusion, our data proved that LHQW is an epithelial protector in ALI, implying its promising potential in antibiotic alternative therapy.

Aucubin Promotes Differentiation of Neural Precursor Cells into GABAergic Neurons

Aucubin is a small compound naturally found in traditional medicinal herbs with primarily anti-inflammatory and protective effects. In the nervous system, aucubin is reported to be neuroprotective by enhancing neuronal survival and inhibiting apoptotic cell death in cultures and disease models. Our previous data, however, suggest that aucubin facilitates neurite elongation in cultured hippocampal neurons and axonal regrowth in regenerating sciatic nerves. Here, we investigated whether aucubin facilitates the differentiation of neural precursor cells (NPCs) into specific types of neurons. In NPCs cultured primarily from the rat embryonic hippocampus, aucubin significantly elevated the number of GAD65/67 immunoreactive cells and the expression of GAD65/67 proteins was upregulated dramatically by more than three-fold at relatively low concentrations of aucubin (0.01 µM to 10 µM). The expression of both NeuN and vGluT1 of NPCs, the markers for neurons and glutamatergic cells, respectively, and the number of vGluT1 immunoreactive cells also increased with higher concentrations of aucubin (1 µM and 10 µM), but the ratio of the increases was largely lower than GAD expression and GAD immunoreactive cells. The GABAergic differentiation of pax6-expressing late NPCs into GABA-producing cells was further supported in cortical NPCs primarily cultured from transgenic mouse brains, which express recombinant GFP under the control of pax6 promoter. The results suggest that aucubin can be developed as a therapeutic candidate for neurodegenerative disorders caused by the loss of inhibitory GABAergic neurons.

The Protective Effect of Aucubin from Eucommia ulmoides Against Status Epilepticus by Inducing Autophagy and Inhibiting Necroptosis

Eucommia ulmoides Oliv. is a famous traditional Chinese medicine which exhibits anti-oxidative stress ability and neuro-protective effects. Aucubin is the predominant component of Eucommia ulmoides Oliv. Our present study is intended to investigate aucubin's potential protective effects on neurons against epilepsy in the hippocampus by establishing the lithium-pilocarpine induced status epilepticus (SE) rat model in vivo. Aucubin (at a low dose and a high dose of 5[Formula: see text]mg/kg and 10[Formula: see text]mg/kg, respectively) was administered through gavage for two weeks before lithium-pilocarpine injection. Rats were sacrificed at 4, 24 and 72[Formula: see text]h after SE induction. Pretreatment with both low-dose and high-dose aucubin significantly reduced the number of death neurons ([Formula: see text]) and increased the number of surviving neurons ([Formula: see text]) in DG, Hilus, CA1 and CA3 hippocampal regions post SE. Meanwhile, it significantly inhibited necroptosis proteins (MLKL and RIP-1) ([Formula: see text] or [Formula: see text]) and enhanced autophagy protein (Beclin-1 and LC3BII/LC3BI) prevalence in the hippocampus ([Formula: see text] or [Formula: see text]). In conclusion, aucubin appeared to ameliorate damages in lithium-pilocarpine induced SE in hippocampus, reduce the number of apoptotic neurons, and increased the number of survival neurons by inducing autophagy and inhibiting necroptosis. These original findings might provide an important basis for the further investigation of the therapeutic role of aucubin in treatment or prevention of epilepsy-related neuronal damages.

Aucubin promotes neurite outgrowth in neural stem cells and axonal regeneration in sciatic nerves

Aucubin is an iridoid glycoside with a wide range of biological activities, including anti-inflammatory, anti-microbial, anti-algesic as well as anti-tumor activities. Recently, it has been shown that aucubin prevents neuronal death in the hippocampal CA1 region in rats with diabetic encephalopathy. In addition, it has protective effects on H₂O₂-induced apoptosis in PC12 cells. We have shown here that aucubin promotes neuronal differentiation and neurite outgrowth in neural stem cells cultured primarily from the rat embryonic hippocampus. We also investigated whether aucubin facilitates axonal elongation in the injured peripheral nervous system. Aucubin promoted lengthening and thickness of axons and re-myelination at 3 weeks after sciatic nerve injury. These results indicate that administration of aucubin improved nerve regeneration in the rat model of sciatic nerve injury, suggesting that aucubin may be a useful therapeutic compound for the human peripheral nervous system after various nerve injuries.

Enrichment and purification of syringin, eleutheroside E and isofraxidin from Acanthopanax senticosus by macroporous resin

In order to screen a suitable resin for the preparative simultaneous separation and purification of syringin, eleutheroside E and isofraxidin from Acanthopanax senticosus, the adsorption and desorption properties of 17 widely used commercial macroporous resins were evaluated. According to our results, HPD100C, which adsorbs by the molecular tiers model, was the best macroporous resin, offering higher adsorption and desorption capacities and higher adsorption speed for syringin, eleutheroside E and isofraxidin than other resins. Dynamic adsorption and desorption tests were carried out to optimize the process parameters. The optimal conditions were as follows: for adsorption, processing volume: 24 BV, flow rate: 2 BV/h; for desorption, ethanol-water solution: 60:40 (v/v), eluent volume: 4 BV, flow rate: 3 BV/h. Under the above conditions, the contents of syringin, eleutheroside E and isofraxidin increased 174-fold, 20-fold and 5-fold and their recoveries were 80.93%, 93.97% and 93.79%, respectively.

[Studies on the cytological function of the biomembrane and the neurons]

Na(+)-dependent and -independent transport sites were elucidated for glycine and L-leucine, respectively, in Chang liver cells, a human culture cell line. Findings of acceleration of the L-leucine uptake by the cells in the acidic medium and synchronized acidification within the cell membrane vesicles with the uptake by them all suggested contransport of L-leucine and proton and the uptake of L-leucine dependent on the inward proton gradient in Chang liver cells. Cotransport of L-leucine and proton was also demonstrated in human peripheral lymphocytes and accelerated by the addition of concanavalin A, probably accompanied by membrane hyperpolarization. It was shown that the Na(+)-gradient-dependent uptake of glycine can be regulated by insulin and 17 beta-estradiol in the rat uterus and by Ca(2+)-calmodulin and membrane potential in Chang liver cells. D-Aspartate uptake as a model of glutamate transport was characterized in rat hippocampal slices and found to consist of Na(+)-dependent (higher-affinity) and -independent (lower-affinity) components. The vulnerability of hippocampal neurons to the Alzheimer beta-amyloid protein was confirmed in vitro with primary cultured rat hippocampal neurons in the presence of the amyloid protein beta 1-42 or its core fragments. The toxicity of the amyloid protein could be blocked by the addition of insulin and several other growth factors to the medium. The addition of genipin, a plant-derived iridoid, was demonstrated to prevent the toxicity of a synthetic fragment of beta 1-42, beta 25-35. Genipin had a neuritogenic activity in PC12h cells, a rat pheochromocytoma cell line, an activity extremely sensitive to inhibitors of the nitrogen oxide (NO) synthase and soluble guanylate cyclase and an NO scavenger. It was also demonstrated in PC12h cells that the activation of the MAP kinase cascade was essential for the neuritogenesis of genipin. These properties of genipin are very comparable to those of nerve growth factor in the cells. It is considered likely that various useful, neurotrophic substances and their extracts will be found in plants in future.

Neuritogenesis of herbal (+)- and (-)-syringaresinols separated by chiral HPLC in PC12h and Neuro2a cells

Syringaresinol isolated from Epimedium koreanum NAKA1 and Magnolia officinalis REHD. et WILS. was subjected to optical resolution by chiral HPLC to give (+)- and (-)-enantiomers. The two syringaresinol enantiomers, as well as a mixture of their glucosides, showed dose-dependent neuritogenesis in a concentration range from 0.24 to 24 microM in PC12h cells.

Effect of polyacetylenes on the neurite outgrowth of neuronal culture cells and scopolamine-induced memory impairment in mice

Polyacetylenic alcohols and their linoleates isolated from Panax ginseng C. A. MEYER and Cirsium japonicum DC., of which the lipophilic extracts had been found to affect the neuritogenesis of cultured paraneurons, were demonstrated to have a significant neuritogenic effect on PC12h and Neuro2a cells. Panaxynol and the acetylenic triol in particular were highly efficient at concentrations > or = 2 microm. Panaxynol (20 mg/kg/d, i.p., for 3 d) was confirmed to improve scopolamine-induced memory deficit in mice (Y-maze task). It is suggested that the promotion of neuritogenesis in cultured paraneurons by the addition of panaxynol is related its ability to improve memory deficits in animals.

Mechanism of covalent adduct formation of aucubin to proteins

The iridoid glucoside aucubin can irreversibly bind to proteins through the formation of its aglycone. In view of a possible involvement of these protein adducts in the toxicity of aucubin, we investigated the mechanism of binding of aucubin to proteins. [3H]aucubin in itself did not result in binding to protein whereas it covalently bound to rat serum albumin as a function of exposure time and dose in the presence of beta-glucosidase. The rate and extent of protein binding were significantly increased in the presence of the imine-trapping agent sodium cyanide. Oral administration of [3H]aucubin to rats showed that the total radioactivity in plasma remained at a similar level for up to 6 h once peak level was reached, suggesting that a considerable amount of radioactivity might be covalently associated with plasma proteins. The levels of radioactivity in the liver and kidney after oral dosing were higher than those after i.v. dosing. These results indicate that the open-chain aglycone of aucubin can form an imine bond with a nucleophilic site of the protein and these irreversible bindings may partially contribute to its biological and toxic effects.