Diosgenin-induced cognitive enhancement in normal mice is mediated by 1,25D₃-MARRS

Plant based steroidal and triterpenoid sapogenins: Chemistry on diosgenin and biological aspects

Plants are rich in steroidal and triterpenoid saponins. Diosgenin is an important sapogenin obtained from various steroidal saponins and specially from dioscin. It possesses diverse pharmacological activities as it is capable of modulating various endogenous pathways. Diosgenin is the molecule of choice for the industrial synthesis of the steroid based clinical drugs namely progesterone, testosterone, dexamethasone, dehydroepiandrosterone, vitamin D3, steroidal contraceptive pills, norethindrone, norgestrel etc. Diosgenin has been a molecule of discussion due to its high demand in industry as well as for future research applications. Present review describes its chemistry and detailed pharmacological profile.

Diosgenin upregulates axonal guidance partner molecules, Galectin-1 and Secernin-1

Galectin-1, a β-galactosides-binding protein, is widely expressed in various tissues and exhibits diverse biological activities. We previously obtained following findings; 1) Diosgenin, a steroid sapogenin, promoted axonal regeneration in the brain and recovered memory deficits in a model of Alzheimer's disease (AD), 5XFAD mouse; 2) Neuron-specific overexpression of Galectin-1 protein in the hippocampus recovered memory impairment and promoted axonal regeneration in the brain in 5XFAD mice; 3) Secernin-1, a counterpart and axonal guidance molecule for Galectin-1-expressing axons, was secreted from the prefrontal cortical neurons to promote axonal guidance from the hippocampus to the prefrontal cortex. However, it has never been elucidated that diosgenin signaling increase Galectin-1 and Secernin-1 or not. Here, we found that diosgenin treatment upregulated the protein level of Galectin-1 in the hippocampus both in primary cultured neurons and in 5XFAD mouse brains. In addition, diosgenin-induced upregulation of Galectin-1 was diminished by treatment of a neutralizing antibody of 1,25D3-membrane-associated rapid response steroid-binding receptor (1,25D3-MARRS), a direct binding receptor for diosgenin. Importantly, knockdown of Galectin-1 in hippocampal neurons inhibited axonal growth activity of diosgenin. Furthermore, the expression level of Secernin-1 was also increased in prefrontal cortical neurons by administration of diosgenin to 5XFAD mice. These findings suggest that diosgenin is a suitable compound to facilitate Galectin-1-Secernin-1-mediated axonal growth in AD brains.

Organic Chimeras based on Selenosugars, Steroids, and Fullerenes as Potential Inhibitors of the β-amyloid Peptide Aggregation

The aggregation of β-amyloid peptide (Aβ) is associated with neurodegenerative diseases such as Alzheimer's disease (AD). Several therapies aimed at reducing the aggregation of this peptide have emerged as potential strategies for the treatment of AD. This paper describes the design and preparation of new hybrid molecules based on steroids, selenosugars, and [60]fullerene as potential inhibitors of Aβ oligomerization. These moieties were selected based on their antioxidant properties and possible areas of interaction with the Aβ. Cyclopropanations between C60 and malonates bearing different steroid and selenosugar moieties using the Bingel-Hirsch protocol have enabled the synthesis of functionalized molecular hybrids. The obtained derivatives were characterized by physical and spectroscopic techniques. Theoretical calculations for all the selenium compounds were performed using the density functional theory DFT/B3LYP-D3(BJ)/6-311G(2d,p) predicting the most stable conformations of the synthesized derivatives. Relevant geometrical parameters were investigated to relate the stereochemical behavior and the spectroscopic data obtained. The affinity of the compounds for Aβ-peptide was estimated by molecular docking simulation, which predicted an increase in affinity and interactions for Aβ for the hybrids containing the C60 core. In addition, parameters such as lipophilicity, polar surface area, and dipole moment were calculated to predict their potential interaction with membrane cells.

Antipsychotic effect of diosgenin in ketamine-induced murine model of schizophrenia: Involvement of oxidative stress and cholinergic transmission

A decrease in the levels of antioxidant arsenals exacerbate generation of reactive oxygen/nitrogen species, leading to neurochemical dysfunction, with significant impact on the pathogenesis of psychotic disorders such as schizophrenia. This study examined the preventive and reversal effects of diosgenin, a phyto-steroidal saponin with antioxidant functions in mice treated with ketamine which closely replicates schizophrenia-like symptoms in human and laboratory animals. In the preventive phase, adult mice cohorts were clustered into 5 groups (n = 9). Groups 1 and 2 received saline (10 mL/kg, i.p.), groups 3 and 4 were pretreated with diosgenin (25 and 50 mg/kg), and group 5 received risperidone (0.5 mg/kg) orally for 14 days. Mice in groups 2-5 additionally received a daily dose of ketamine (20 mg/kg, i.p.) or saline (10 mL/kg/day, i.p.). In the reversal phase, mice received intraperitoneal injection of ketamine or saline for 14 consecutive days prior to diosgenin (25 and 50 mg/kg/p.o./day) and risperidone (0.5 mg/kg/p.o./day) treatment from days 8-14. Mice were assessed for behavioral changes. Oxidative, nitrergic markers, and cholinergic (acetylcholinesterase activity) transmission were examined in the striatum, prefrontal-cortex and hippocampus. Diosgenin prevented and reversed hyperlocomotion, cognitive and social deficits in mice treated with ketamine relative to ketamine groups. The increased acetylcholinesterase, malondialdehyde and nitrite levels produced by ketamine were reduced by diosgenin in the striatum, prefrontal-cortex and hippocampus, but did not reverse striatal nitrite level. Diosgenin increased glutathione, and catalase levels, except for hippocampal catalase activity when compared with ketamine controls. Conclusively, these biochemical changes might be related to the behavioral deficits in ketamine-treated mice, which were prevented and reversed by diosgenin.

Gut microbiota modification by diosgenin mediates antiepileptic effects in a mouse model of epilepsy

Diosgenin, a natural steroid saponin, holds promise as a multitarget therapeutic for various diseases, including neurodegenerative conditions. Its efficacy in slowing Alzheimer's disease, Parkinson's disease, multiple sclerosis, and stroke progression has been demonstrated. However, the role of diosgenin in anti-epilepsy and its potential connection to the modulation of the intestinal microbiota remain poorly understood. In this study, exogenous diosgenin significantly mitigated pentylenetetrazole (PTZ)-induced seizures, learning and memory deficits, and hippocampal neuronal injury. 16S ribosomal RNA (16S rRNA) sequencing revealed a reversal in the decrease of Bacteroides and Parabacteroides genera in the PTZ-induced mouse epileptic model following diosgenin treatment. Fecal microbiota transplantation (FMT) experiments illustrated the involvement of diosgenin in modulating gut microbiota and providing neuroprotection against epilepsy. Our results further indicated the repression of enteric glial cells (EGCs) activation and the TLR4-MyD88 pathway, coupled with reduced production of inflammatory cytokines in the colonic lumen, and improved intestinal barrier function in epilepsy mice treated with diosgenin or FMT. This study suggests that diosgenin plays a role in modifying gut microbiota, contributing to the alleviation of intestinal inflammation and neuroinflammation, ultimately inhibiting epilepsy progression in a PTZ-induced mouse model. Diosgenin emerges as a potential therapeutic option for managing epilepsy and its associated comorbidities.

Diosgenin prevents dexamethasone-induced myotube atrophy in C2C12 cells

Several pathophysiological abnormalities, including a sedentary lifestyle, chronic diseases, and oxidative stress, can contribute to muscle atrophy triggered by an imbalance in muscle protein synthesis and degradation. Resolving muscle atrophy is a critical issue as it can reduce the quality of life. Here, one of the promising functional food factors, diosgenin (a steroidal sapogenin) showed strong preventive activities against dexamethasone (Dex)-induced muscle atrophy, as determined by the expression levels and morphology of the myosin heavy chain in C2C12 myotubes. Diosgenin inhibited protein expressions of Dex-induced skeletal muscle-specific ubiquitin ligase, including muscle RING finger 1 (MuRF1) and casitas B-lineage lymphoma protooncogene b (Cbl-b) but not atrogin-1. Diosgenin ameliorated Dex-induced declines of Akt phosphorylation at Ser473 and FoxO3a phosphorylation at Ser253, which probably at least partially contributed to the suppression of MuRF1, Cbl-b, and atrogin-1 gene expression. Additionally, diosgenin inhibited Dex-induced nuclear translocation of the glucocorticoid receptor (GR), diosgenin therefore may competitively inhibit the interaction between Dex and GR. These findings suggest that diosgenin is an effective functional food for preventing glucocorticoid-induced skeletal muscle atrophy.

Diosgenin restores memory function via SPARC-driven axonal growth from the hippocampus to the PFC in Alzheimer's disease model mice

Central nervous system axons have minimal capacity to regenerate in adult brains, hindering memory recovery in Alzheimer's disease (AD). Although recent studies have shown that damaged axons sprouted in adult and AD mouse brains, long-distance axonal re-innervation to their targets has not been achieved. We selectively visualized axon-growing neurons in the neural circuit for memory formation, from the hippocampus to the prefrontal cortex, and showed that damaged axons successfully extended to their native projecting area in mouse models of AD (5XFAD) by administration of an axonal regenerative agent, diosgenin. In vivo transcriptome analysis detected the expression profile of axon-growing neurons directly isolated from the hippocampus of 5XFAD mice. Secreted protein acidic and rich in cysteine (SPARC) was the most expressed gene in axon-growing neurons. Neuron-specific overexpression of SPARC via adeno-associated virus serotype 9 delivery in the hippocampus recovered memory deficits and axonal projection to the prefrontal cortex in 5XFAD mice. DREADDs (Designer receptors exclusively activated by designer drugs) analyses revealed that SPARC overexpression-induced axonal growth in the 5XFAD mouse brain directly contributes to memory recovery. Elevated levels of SPARC on axonal membranes interact with extracellular rail-like collagen type I to promote axonal remodeling along their original tracings in primary cultured hippocampal neurons. These findings suggest that SPARC-driven axonal growth in the brain may be a promising therapeutic strategy for AD and other neurodegenerative diseases.

Biosynthetic Gene Expression and Tissue Distribution of Diosgenin in Dioscorea japonica

Diosgenin is an aglycone of dioscin, a major bioactive steroidal saponin found in plants, including Himalayan Paris (Paris polyphylla), fenugreek (Trigonella foenum-graecum), and yam (Dioscorea spp.). We have previously demonstrated that a species of natural yam, Dioscorea japonica, contains a promising bioactive compound diosgenin, which induces anti-carcinogenic and anti-hypertriacylglycerolemic activities. Here, we found for the first time that Japanese yam (D. japonica) bulbils are richer in diosgenin than the edible tubers (rhizomes) and leaves. LC-MS and imaging-MS analyses revealed that diosgenin accumulated in the peripheral region of D. japonica bulbils. Additionally, we performed RNA-seq analysis of D. japonica, and multiple sequence alignment identified D. japonica CYP90 (DjCYP90), the orthologous gene of CYP90G4 in P. polyphylla, CYP90B50 in T. foenum-graecum, CYP90G6 in Dioscorea zingiberensis, and CYP90G in Dioscorea villosa, which encodes a diosgenin biosynthetic rate-limiting enzyme. The expression levels of DjCYP90 were significantly upregulated in D. japonica bulbils than in its rhizomes and leaves. Since diosgenin is one of the most promising functional food factors executing several favorable bioactivities, D. japonica bulbils rich in diosgenin would be a beneficial natural resource.

Diosgenin: An Updated Pharmacological Review and Therapeutic Perspectives

Plants including Rhizoma polgonati, Smilax china, and Trigonella foenum-graecum contain a lot of diosgenin, a steroidal sapogenin. This bioactive phytochemical has shown high potential and interest in the treatment of various disorders such as cancer, diabetes, arthritis, asthma, and cardiovascular disease, in addition to being an important starting material for the preparation of several steroidal drugs in the pharmaceutical industry. This review aims to provide an overview of the in vitro, in vivo, and clinical studies reporting the diosgenin's pharmacological effects and to discuss the safety issues. Preclinical studies have shown promising effects on cancer, neuroprotection, atherosclerosis, asthma, bone health, and other pathologies. Clinical investigations have demonstrated diosgenin's nontoxic nature and promising benefits on cognitive function and menopause. However, further well-designed clinical trials are needed to address the other effects seen in preclinical studies, as well as a better knowledge of the diosgenin's safety profile.

Microglia-Based Sex-Biased Neuropathology in Early-Stage Alzheimer's Disease Model Mice and the Potential Pharmacologic Efficacy of Dioscin

Alzheimer's disease (AD), the most common form of dementia, is characterized by amyloid-β (Aβ) accumulation, microglia-associated neuroinflammation, and synaptic loss. The detailed neuropathologic characteristics in early-stage AD, however, are largely unclear. We evaluated the pathologic brain alterations in young adult App knock-in model AppNL-G-F mice at 3 and 6 months of age, which corresponds to early-stage AD. At 3 months of age, microglia expression in the cortex and hippocampus was significantly decreased. By the age of 6 months, the number and function of the microglia increased, accompanied by progressive amyloid-β deposition, synaptic dysfunction, neuroinflammation, and dysregulation of β-catenin and NF-κB signaling pathways. The neuropathologic changes were more severe in female mice than in male mice. Oral administration of dioscin, a natural product, ameliorated the neuropathologic alterations in young AppNL-G-F mice. Our findings revealed microglia-based sex-differential neuropathologic changes in a mouse model of early-stage AD and therapeutic efficacy of dioscin on the brain lesions. Dioscin may represent a potential treatment for AD.

Diosgenin Attenuates Cognitive Impairment in Streptozotocin-Induced Diabetic Rats: Underlying Mechanisms

OBJECTIVE

Prolonged diabetes mellitus causes impairments of cognition and attentional dysfunctions. Diosgenin belongs to a group of steroidal saponins with reported anti-diabetic and numerous protective properties. This research aimed to assess the effect of diosgenin on beneficially ameliorating learning and memory decline in a rat model of type 1 diabetes caused by streptozotocin (STZ) and to explore its modes of action including involvement in oxidative stress and inflammation.

METHODS

Rats were assigned to one of four experimental groups, comprising control, control under treatment with diosgenin, diabetic, and diabetic under treatment with diosgenin. Diosgenin was given daily p.o. (40 mg/kg) for 5 weeks.

RESULTS

The administration of diosgenin to the diabetic group reduced the deficits of functional performance in behavioral tests, consisting of Y-maze, passive avoidance, radial arm maze, and novel object discrimination tasks (recognitive). Furthermore, diosgenin treatment attenuated hippocampal acetylcholinesterase activity and malon-dialdehyde, along with improvement of antioxidants such as superoxide dismutase and glutathione. Meanwhile, the hippocampal levels of inflammatory indicators, namely interleukin 6, nuclear factor-κB, toll-like receptor 4, tumor necrosis factor α, and astrocyte-specific biomarker glial fibrillary acidic protein, were lower and, on the other hand, tissue levels of nuclear factor (erythroid-derived 2)-related factor 2 were elevated upon diosgenin administration. Besides, the mushroom-like spines of the pyramidal neurons of the hippocampal CA1 area decreased in the diabetic group, and this was alleviated following diosgenin medication.

CONCLUSIONS

Taken together, diosgenin is capable of ameliorating cognitive deficits in STZ-diabetic animals, partly due to its amelioration of oxidative stress, inflammation, astrogliosis, and possibly improvement of cholinergic function in addition to its neuroprotective potential.

Diosgenin Prevents Microglial Activation and Protects Dopaminergic Neurons from Lipopolysaccharide-Induced Neural Damage In Vitro and In Vivo

Background: The prevention of age-related neurodegenerative disorders is an important issue in an aging society. Microglia-mediated neuroinflammation resulting in dopaminergic neuron loss may lead to the pathogenesis of Parkinson’s disease (PD). Lipopolysaccharide (LPS), an endotoxin, induces neuroinflammatory microglial activation, contributing to dopaminergic neuron damage. Diosgenin is a phytosteroid sapogenin with a wide spectrum of pharmacological activities, e.g., anti-inflammatory activity. However, the preventive effect of diosgenin on neuroinflammation is not clear. Thus, in this study, we further investigated the neuroprotective effect of diosgenin on LPS-induced neural damage in vitro and in vivo. Methods: For in vitro experiments, primary mesencephalic neuron-glia cultures and primary microglia cultures isolated from Sprague–Dawley rats were used. Cells were pretreated with diosgenin and then stimulated with LPS. The expression of proinflammatory cytokines or tyrosine hydroxylase (TH) in the cells was analyzed. In vivo, rats were fed a diet containing 0.1% (w/w) diosgenin for 4 weeks before being administered a unilateral substantia nigra (SN) injection of LPS. Four weeks after the LPS injection, the rats were assessed for lesion severity using the amphetamine-induced rotation test and TH immunohistochemistry. Results: Diosgenin pretreatment prevented LPS-induced neurite shortening in TH-positive neurons in mesencephalic neuron-glia cultures. In addition, pretreatment of primary microglia with diosgenin significantly reduced tumor necrosis factor-α (TNF-α) and inducible nitric oxide synthase (iNOS) expression. Moreover, diosgenin pretreatment significantly suppressed LPS-induced extracellular signal-regulated kinase (ERK) activation. In vivo, the intranigral injection of LPS in rats fed a diosgenin-containing diet significantly improved motor dysfunction and reduced TH expression in SN. Conclusion: These results support the effectiveness of diosgenin in protecting dopaminergic neurons from LPS-induced neuroinflammation.

Heterophyllin B, a cyclopeptide from Pseudostellaria heterophylla, enhances cognitive function via neurite outgrowth and synaptic plasticity

Neurite outgrowth-induced construction of neural circuits and networks is responsible for memory generalization, consolidation, and retrieval. In this study, we found that the traditional Chinese medicine Pseudostellaria heterophylla promoted neurite regrowth and enhanced cognitive function in normal mice. Further, we orally administered Pseudostellaria heterophylla water extracts (PHE) to ICR mice, and detected heterophyllin B (HET-B), an important cyclopeptide, in the plasma and cerebral cortex. We demonstrated that neurites were significantly elongated after coculturing with HET-B for 4 days. Next, the intraperitoneal injection of HET-B on seven consecutive days in 3-month-old ICR mice significantly enhanced the object recognition memory and object location memory than that in control. Immunohistochemical analysis indicated significantly increased β3-tubulin-positive neurite density, synaptophysin, and postsynaptic density 95 in the perirhinal cortex and hippocampus after administering HET-B. Furthermore, the concentration of neurotransmitters was measured using HPLC analysis; HET-B significantly increased five-levels of HT in the hippocampus, and decreased metabolites of dopamine, dihydroxyphenylacetic acid, and homovanillic acid, in the prefrontal cortex and hippocampus. Taken together, HET-B induces neurite elongation and neurotransmitter regulation and possibly enhances cognitive memory.

NMDA receptor-dependent and -independent effects of natural compounds and crude drugs on synaptic states as revealed by drebrin imaging analysis

Effective drugs that can cure cognitive impairments remain elusive. Because synaptic dysfunction has been correlated with cognitive impairments, drug development to target synaptic dysfunction is important. Recently, natural compounds and crude drugs have emerged as potential therapeutic agents for cognitive disorders. However, their effects on synaptic function remain unclear, because of lack of evaluation system with high reproducibility. We have recently developed highly reproducible in vitro high-content imaging analysis system for evaluation of synaptic function using drebrin as a marker for synaptic states. Therefore, we aimed to examine the direct effects of well-known natural compounds and crude drugs on synaptic states using this system. Rat hippocampal neurons were treated using natural compounds (nobiletin, diosgenin and tenuifolin) and crude drugs (Uncaria Hook [UH], Bezoar Bovis [BB], Coptis Rhizome [CR], Phellodendron Bark [PB] and Polygala Root [PR]). Immunocytochemical analysis was performed, and dendrite lengths and drebrin cluster densities were automatically quantified. We found that diosgenin, tenuifolin, CR, PB and PR decreased drebrin cluster densities, and the effects of PB and PR were partially dependent on N-methyl-D-aspartic acid-type glutamate receptors (NMDARs). Nobiletin and UH did not show any effects, whereas low-dose BB treatment increased drebrin cluster densities. Our results showed that diosgenin, tenuifolin, BB, CR, PB and PR appeared to directly change synaptic states. Particularly, the NMDAR dependency of PB and PR appears to affect synaptic plasticity.

A comparison of the location in membranes of curcumin and curcumin-derived bivalent compounds with potential neuroprotective capacity for Alzheimer's disease

Curcumin and two bivalent compounds, namely 17MD and 21MO, both obtained by conjugation of curcumin with a steroid molecule that acts as a membrane anchor, were comparatively studied. When incorporated into 1,2-dipalmitoyl-sn-glycero-3-phosphocholine the compounds showed a very limited solubility in the model membranes. Curcumin and the two bivalent compounds were also incorporated in membranes of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine and quenching the fluorescence of pure curcumin or of the curcumin moiety in the bivalent compounds by acrylamide it was seen that curcumin was accessible to this water soluble quencher but the molecule was somehow located in a hydrophobic environment. This was confirmed by quenching with doxyl-phosphatidylcholines, indicating that the curcumin moieties of 17MD and 21MO were in a more polar environment than pure curcumin itself. ¹H NOESY MAS-NMR analysis supports this notion by showing that the orientation of curcumin was parallel to the plane of the membrane surface close to C2 and C3 of the fatty acyl chains, while the curcumin moiety of 17MD and 21MO positioned close to the polar part of the membrane with the steroid moiety in the centre of the membrane. Molecular dynamics studies were in close agreement with the experimental results with respect to the likely proximity of the protons studied by NMR and show that 17MD and 21MO have a clear tendency to aggregate in a fluid membrane. The anchorage of the bivalent compounds to the membrane leaving the curcumin moiety near the polar part may be very important to facilitate the bioactivity of the curcumin moiety when used as anti-Alzheimer drugs.

Diosgenin content is a novel criterion to assess memory enhancement effect of yam extracts

Several studies have suggested that some kind of Dioscorea species (yam) or yam-contained herbal medicines have cognitive enhancement effect. However, it has been unknown what is a crucial factor for cognitive enhancement in each Dioscorea species. In this study, we aimed to investigate whether one of the main and brain-penetrating components in yams, diosgenin, can be a novel criterion to assess memory enhancement effect of yam extracts. Although our previous studies showed that administration of diosgenin or diosgenin-rich yam extract enhanced cognitive function in normal mice and healthy humans, we have never evaluated whether the effect depends on diosgenin content or not. Therefore, we compared memory enhancement effects of low diosgenin-contained general yam water extract with diosgenin-rich yam extract on cognitive function in normal mice. We found that unlike diosgenin-rich yam, administration of general yam water extract did not enhance object recognition memory in normal mice. LC-MS/MS analyses revealed that after administration of general yam, diosgenin concentration in the brain did not reach to the effective dose because of the low diosgenin content in the original yam extract. On the other hand, when diosgenin was artificially added into general yam, the extract showed memory enhancement in normal mice and promoted neurite outgrowth in neurons. Our study suggests that diosgenin is actually an active compound in yams for memory enhancement, and diosgenin content can be a criterion for predicting cognitive enhancement effect of yam extracts.

The Dioscorea Genus (Yam)-An Appraisal of Nutritional and Therapeutic Potentials

The quest for a food secure and safe world has led to continuous effort toward improvements of global food and health systems. While the developed countries seem to have these systems stabilized, some parts of the world still face enormous challenges. Yam (Dioscorea species) is an orphan crop, widely distributed globally; and has contributed enormously to food security especially in sub-Saharan Africa because of its role in providing nutritional benefits and income. Additionally, yam has non-nutritional components called bioactive compounds, which offer numerous health benefits ranging from prevention to treatment of degenerative diseases. Pharmaceutical application of diosgenin and dioscorin, among other compounds isolated from yam, has shown more prospects recently. Despite the benefits embedded in yam, reports on the nutritional and therapeutic potentials of yam have been fragmented and the diversity within the genus has led to much confusion. An overview of the nutritional and health importance of yam will harness the crop to meet its potential towards combating hunger and malnutrition, while improving global health. This review makes a conscious attempt to provide an overview regarding the nutritional, bioactive compositions and therapeutic potentials of yam diversity. Insights on how to increase its utilization for a greater impact are elucidated.

Natural Medicines and Their Underlying Mechanisms of Prevention and Recovery from Amyloid Β-Induced Axonal Degeneration in Alzheimer's Disease

In Alzheimer's disease (AD), amyloid β (Aβ) induces axonal degeneration, neuronal network disruption, and memory impairment. Although many candidate drugs to reduce Aβ have been clinically investigated, they failed to recover the memory function in AD patients. Reportedly, Aβ deposition occurred before the onset of AD. Once neuronal networks were disrupted by Aβ, they could hardly be recovered. Therefore, we speculated that only removal of Aβ was not enough for AD therapy, and prevention and recovery from neuronal network disruption were also needed. This review describes the challenges related to the condition of axons for AD therapy. We established novel in vitro models of Aβ-induced axonal degeneration. Using these models, we found that several traditional medicines and their constituents prevented or helped recover from Aβ-induced axonal degeneration. These drugs also prevented or helped recover from memory impairment in in vivo models of AD. One of these drugs ameliorated memory decline in AD patients in a clinical study. These results indicate that prevention and recovery from axonal degeneration are possible strategies for AD therapy.

Antia, a Natural Antioxidant Product, Attenuates Cognitive Dysfunction in Streptozotocin-Induced Mouse Model of Sporadic Alzheimer's Disease by Targeting the Amyloidogenic, Inflammatory, Autophagy, and Oxidative Stress Pathways

Background

Many neurodegenerative diseases such as Alzheimer's disease are associated with oxidative stress. Therefore, antioxidant therapy has been suggested for the prevention and treatment of neurodegenerative diseases.

Objective

We investigated the ability of the antioxidant Antia to exert a protective effect against sporadic Alzheimer's disease (SAD) induced in mice. Antia is a natural product that is extracted from the edible yamabushitake mushroom, the gotsukora and kothala himbutu plants, diosgenin (an extract from wild yam tubers), and amla (Indian gooseberry) after treatment with MRN-100.

Methods

Single intracerebroventricular (ICV) injection of streptozotocin (STZ) (3 mg/kg) was used for induction of SAD in mice. Antia was injected intraperitoneally (i.p.) in 3 doses (25, 50, and 100 mg/kg/day) for 21 days. Neurobehavioral tests were conducted within 24 h after the last day of injection. Afterwards, mice were sacrificed and their hippocampi were rapidly excised, weighed, and homogenized to be used for measuring biochemical parameters.

Results

Treatment with Antia significantly improved mice performance in the Morris water maze. In addition, biochemical analysis showed that Antia exerted a protective effect for several compounds, including GSH, MDA, NF-κB, IL-6, TNF-α, and amyloid β. Further studies with western blot showed the protective effect of Antia for the JAK2/STAT3 pathway.

Conclusions

Antia exerts a significant protection against cognitive dysfunction induced by ICV-STZ injection. This effect is achieved through targeting of the amyloidogenic, inflammatory, and oxidative stress pathways. The JAK2/STAT3 pathway plays a protective role for neuroinflammatory and neurodegenerative diseases such as SAD.

Therapeutic Potential of Diosgenin and Its Major Derivatives against Neurological Diseases: Recent Advances

Diosgenin (DG), a well-known steroidal sapogenin, is present abundantly in medicinal herbs such as Dioscorea rhizome, Dioscorea villosa, Trigonella foenum-graecum, Smilax China, and Rhizoma polgonati. DG is utilized as a major starting material for the production of steroidal drugs in the pharmaceutical industry. Due to its wide range of pharmacological activities and medicinal properties, it has been used in the treatment of cancers, hyperlipidemia, inflammation, and infections. Numerous studies have reported that DG is useful in the prevention and treatment of neurological diseases. Its therapeutic mechanisms are based on the mediation of different signaling pathways, and targeting these pathways might lead to the development of effective therapeutic agents for neurological diseases. The present review mainly summarizes recent progress using DG and its derivatives as therapeutic agents for multiple neurological disorders along with their various mechanisms in the central nervous system. In particular, those related to therapeutic efficacy for Parkinson's disease, Alzheimer's disease, brain injury, neuroinflammation, and ischemia are discussed. This review article also critically evaluates existing limitations associated with the solubility and bioavailability of DG and discusses imperatives for translational clinical research. It briefly recapitulates recent advances in structural modification and novel formulations to increase the therapeutic efficacy and brain levels of DG. In the present review, databases of PubMed, Web of Science, and Scopus were used for studies of DG and its derivatives in the treatment of central nervous system diseases published in English until December 10, 2019. Three independent researchers examined articles for eligibility. A total of 150 articles were screened from the above scientific literature databases. Finally, a total of 46 articles were extracted and included in this review. Keywords related to glioma, ischemia, memory, aging, cognitive impairment, Alzheimer, Parkinson, and neurodegenerative disorders were searched in the databases based on DG and its derivatives.

Memory Enhancement by Oral Administration of Extract of Eleutherococcus senticosus Leaves and Active Compounds Transferred in the Brain

The pharmacological properties of Eleutherococcus senticosus leaf have not been clarified although it is taken as a food item. In this study, the effects of water extract of Eleutherococcus senticosus leaves on memory function were investigated in normal mice. Oral administration of the extract for 17 days significantly enhanced object recognition memory. Compounds absorbed in blood and the brain after oral administration of the leaf extract were detected by LC-MS/MS analyses. Primarily detected compounds in plasma and the cerebral cortex were ciwujianoside C3, eleutheroside M, ciwujianoside B, and ciwujianoside A1. Pure compounds except for ciwujianoside A1 were administered orally for 17 days to normal mice. Ciwujianoside C3, eleutheroside M, and ciwujianoside B significantly enhanced object recognition memory. These results demonstrated that oral administration of the leaf extract of E. senticosus enhances memory function, and that active ingredients in the extract, such as ciwujianoside C3, eleutheroside M, and ciwujianoside B, were able to penetrate and work in the brain. Those three compounds as well as the leaf extract had dendrite extension activity against primary cultured cortical neurons. The effect might relate to memory enhancement.

Effects of Sanyaku and Its Constituent Diosgenin on the Fasted and Postprandial Hypertriacylglycerolemia in High-Fat-Diet-Fed KK- A y Mice

In this study, we examined the fasted and postprandial triacylglycerol (TG) levels in KK- A ^y mice fed a high-fat diet (HFD) or a HFD containing either 500 ppm (0.05%) of diosgenin or 500 ppm (0.05%) of diosgenin-containing Chinese yam sanyaku. Oral fat tolerance tests revealed that, not only in the fasting state but also after loading of lipid emulsion, plasma levels of TG were significantly reduced in sanyaku- and diosgenin- fed mice. Levels of fat oxidation, especially in the dark phase (from 7 p.m. to 7 a.m.), were increased in the sanyaku and diosgenin groups. Moreover mRNA levels of lipoprotein lipase and peroxisome proliferator-activated receptor γ, coactivator 1α were moderately upregulated in the liver of sanyaku- and diosgenin-ingested mice. These results suggest that consecutive ingestion of diosgenin or diosgenin-containing sanyaku at the dose achievable in a human diet potentially ameliorates fasted and postprandial hypertriacylglycerolemia, which could be associated with the improvement of TG metabolism.

Diosgenin restores Aβ-induced axonal degeneration by reducing the expression of heat shock cognate 70 (HSC70)

We previously found diosgenin, an herbal drug-derived steroid sapogenin, to be remarkably effective at restoring Aβ-induced axonal degeneration and improving memory function in model of Alzheimer’s disease (AD), 5XFAD mouse. In this study, we investigated the downstream signaling of diosgenin and explored new therapeutic targets in AD. We showed that the expression of heat shock cognate (HSC) 70 was increased in Aβ-treated neurons and in 5XFAD mice but was decreased by diosgenin treatment. In addition, knockdown of HSC70 significantly promoted axonal growth in neurons. As an association molecule of HSC70 in neurons, α-tubulin was detected by immunoprecipitation. After Aβ treatment, α-tubulin expression was greatly reduced in the degenerated axons, suggesting that a decline in α-tubulin may be one of the factors which correlates with axonal disruption in AD pathology. We hypothesized that the degradation of α-tubulin is triggered by the chaperone activity of HSC70. However, diosgenin significantly normalized the α-tubulin level, a potentially critical process for axonal formation. Our study indicated that reducing the HSC70 level is a new possible therapeutic target of axonal regeneration in AD.

Differential expression of vitamin D-associated enzymes and receptors in brain cell subtypes

Accumulating evidence indicates that the active form of vitamin D, 1,25(OH)2D3, can be considered as a neurosteroid. However, the cerebral expression of vitamin D-associated enzymes and receptors remains controversial. With the idea of carrying out a comparative study in mind, we compared the transcript expression of Cyp27a1, Cyp27b1, Cyp24a1, Vdr and Pdia3 in purified cultures of astrocytes, endothelial cells, microglia, neurons and oligodendrocytes. We observed that endothelial cells and neurons can possibly transform the inactive cholecalciferol into 25(OH)D3. It can then be metabolised into 1,25(OH)2D3, by neurons or microglia, before being transferred to astrocytes where it can bind to VDR and initiate gene transcription or be inactivated when in excess. Alternatively, 1,25(OH)2D3 can induce autocrine or paracrine rapid non-genomic actions via PDIA3 whose transcript is abundantly expressed in all cerebral cell types. Noticeably, brain endothelial cells appear as a singular subtype as they are potentially able to transform cholecalciferol into 25(OH)D3 and exhibit a variable expression of Pdia3, according to 1,25(OH)2D3 level. Altogether, our data indicate that, within the brain, vitamin D may trigger major auto-/paracrine non genomic actions, in addition to its well documented activities as a steroid hormone.

Insights into the Impact of a Membrane-Anchoring Moiety on the Biological Activities of Bivalent Compounds As Potential Neuroprotectants for Alzheimer's Disease

Bivalent compounds anchoring in different manners to the membrane were designed and biologically characterized to understand the contribution of the anchor moiety to their biological activity as neuroprotectants for Alzheimer's disease. Our results established that the anchor moiety is essential, and we identified a preference for diosgenin, as evidenced by 17MD. Studies in primary neurons and mouse brain mitochondria also identified 17MD as exhibiting activity on neuritic outgrowth and the state 3 oxidative rate of glutamate while preserving the coupling capacity of the mitochondria. Significantly, our studies demonstrated that the integrated bivalent structure is essential to the observed biological activities. Further studies employing bivalent compounds as probes in a model membrane also revealed the influence of the anchor moiety on how they interact with the membrane. Collectively, our results suggest diosgenin to be an optimal anchor moiety, providing bivalent compounds with promising pharmacology that have potential applications for Alzheimer's disease.

Diosgenin-Rich Yam Extract Enhances Cognitive Function: A Placebo-Controlled, Randomized, Double-Blind, Crossover Study of Healthy Adults

Diosgenin, a yam-derived compound, was found to facilitate the repair of axonal atrophy and synaptic degeneration and improve memory dysfunction in a transgenic mouse model of Alzheimer’s disease (AD). It was also found to enhance neuronal excitation and memory function even in normal mice. We hypothesized that diosgenin, either isolated or in an extract, may represent a new category of cognitive enhancers with essential activities that morphologically and functionally reinforce neuronal networks. This study aimed to investigate the effects of a diosgenin-rich yam extract on cognitive enhancement in healthy volunteers. For this placebo-controlled, randomized, double-blind, crossover study, 28 healthy volunteers (age: 20–81 years) were recruited from Toyama Prefecture, Japan, and was randomly assigned to receive either a yam extract or placebo. Preliminary functional animal experiments indicated that an oil solvent mediated the most efficient distribution of diosgenin into the blood and brain after oral administration, and was a critical factor in the cognitive benefits. Therefore, test samples (placebo and yam extract) were prepared with olive oil and formulated as soft capsules. The intake period was 12 weeks, and a 6-week washout period separated the two crossover intake periods. The Japanese version of the Repeatable Battery for the Assessment of Neuropsychological Status (RBANS) test was used for neurocognitive assessment, and the adverse effects were monitored through blood testing. Diosgenin-rich yam extract consumption for 12 weeks yielded significant increases in total RBANS score. Among the 12 individual standard cognitive subtests, diosgenin-rich yam extract use significantly improved the semantic fluency. No adverse effects were reported. The diosgenin-rich yam extract treatment appeared to safely enhance cognitive function in healthy adults.

Extracellular Cytosolic Aspartate Aminotransferase Promotes Axonal Growth and Object Recognition Memory

Previous proteome analysis studies from other groups have shown that cAST might be secreted from neurons and that cAST was detected in human cerebrospinal fluid. However, none of these studies focused on its role or significance. We therefore investigated the role of extracellular cAST for neurons. cAST was detected in conditioned medium from cultured cortical neurons, but not in fresh medium. Recombinant cAST treatment of cortical neurons significantly extended axonal length. Continuous intracerebroventricular administration of recombinant cAST in normal mice for 14 days significantly enhanced object recognition ability. In the brains of those mice, axonal densities and c-Fos expression levels were enhanced, especially in the perirhinal cortex, which mainly relates to object recognition memory. The present study found, for the first time, that extracellular cAST promoted axonal growth function in neurons and activated memory function. These findings indicate a new function of extracellular cAST and may drive the establishment of new therapeutic strategies for cognitive dysfunction. The present study found, for the first time, that extracellular cAST promotes axonal growth in neurons.

New Age Therapy for Alzheimer's Disease by Neuronal Network Reconstruction

Alzheimer's disease (AD) is a recognized incurable neurodegenerative disorder. Clinically prescribed medicines for AD are expected to bring about only slight symptomatic improvement or a delay of its progression. Another strategy, amyloid β (Aβ) lowing agents, has not been successful at memory improvement. We have hypothesized that an improvement in cognitive function requires the construction of neuronal networks, including neurite regeneration and synapse formation; therefore, we have been exploring candidates for radical anti-AD drugs that can restore Aβ-induced neurite atrophy and memory impairment. Our studies found several promising drug candidates that may improve memory dysfunction in AD model mice. The main activity of these drugs is the restoration of damaged axons. Focusing on candidates based on the recovery of neurite atrophy in vitro certainly leads to positive effects on memory improvement also in vivo. This suggests that neuronal network reconstruction may importantly relate to functional recovery in the brain. When identifying the signaling mechanisms of exogenous compounds like natural medicine-derived constituents, molecules directly activated by the compound are hard to be identified. However, the drug affinity responsive target stability (DARTS) analysis may pave the way to an approach to determine the initial molecule of the signaling pathway. Exploring new drug candidates and clarifying their signaling pathways directly relating to neuronal network reconstruction may provide promising therapeutic strategies with which to overcome AD.

Diosgenin: Recent Highlights on Pharmacology and Analytical Methodology

Diosgenin, a steroidal sapogenin, occurs abundantly in plants such as Dioscorea alata, Smilax China, and Trigonella foenum graecum. This bioactive phytochemical not only is used as an important starting material for the preparation of several steroidal drugs in the pharmaceutical industry, but has revealed also high potential and interest in the treatment of various types of disorders such as cancer, hypercholesterolemia, inflammation, and several types of infections. Due to its pharmacological and industrial importance, several extraction and analytical procedures have been developed and applied over the years to isolate, detect, and quantify diosgenin, not only in its natural sources and pharmaceutical compositions, but also in animal matrices for pharmacodynamic, pharmacokinetic, and toxicological studies. Within these, HPLC technique coupled to different detectors is the most commonly analytical procedure described for this compound. However, other alternative methods were also published. Thus, the present review aims to provide collective information on the most recent pharmacological data on diosgenin and on the most relevant analytical techniques used to isolate, detect, and quantify this compound as well.

Effects of Oleanane-Type Triterpene Saponins from the Leaves of Eleutherococcus senticosus in an Axonal Outgrowth Assay

An aqueous extract of Eleutherococcus senticosus leaves exerted a beneficial effect in restoring the neurite outgrowth from Aβ25-35-induced degeneration using an axonal density assay. Subsequent bioassay-guided fractionation afforded seven new oleanane-type triterpene saponins, ezoukoginosides A-G (1-7), along with nine known analogues. The structures of 1-7 were elucidated through chemical and spectroscopic approaches, and their effects on restoring the neurite outgrowth from Aβ25-35-induced degeneration were investigated. The results revealed that hydrophilic oleanane-type saponins substituted with a free carboxylic acid, hydroxy, or formyl group in the aglycone, especially when the oxidation occurred at C-29, not only restrained Aβ25-35-induced degeneration but also restored axonal outgrowth significantly. Compounds 2 (-COOH at C-29) and 3 (-CH2OH at C-29) showed the most potent bioactivity among the isolates.

Beneficial effect of diosgenin as a stimulator of NGF on the brain with neuronal damage induced by Aβ-42 accumulation and neurotoxicant injection

To investigate the beneficial effects of diosgenin (DG) on the multiple types of brain damage induced by Aβ-42 peptides and neurotoxicants, alterations in the specific aspects of brain functions were measured in trimethyltin (TMT)-injected transgenic 2576 (TG) mice that had been pretreated with DG for 21 days. Multiple types of damage were successfully induced by Aβ-42 accumulation and TMT injection into the brains of TG mice. However, DG treatment significantly reduced the number of Aβ-stained plaques and dead cells in the granule cells layer of the dentate gyrus. Significant suppression of acetylcholinesterase (AChE) activity and Bax/Bcl-2 expression was also observed in the DG treated TG mice (TG+DG group) when compared with those of the vehicle (VC) treated TG mice (TG+VC group). Additionally, the concentration of nerve growth factor (NGF) was dramatically enhanced in TG+DG group, although it was lower in the TG+VC group than the non-transgenic (nTG) group. Furthermore, the decreased phosphorylation of downstream members in the TrkA high affinity receptor signaling pathway in the TG+VC group was significantly recovered in the TG+DG group. A similar pattern was observed in p75^NTR expression and JNK phosphorylation in the NGF low affinity receptor signaling pathway. Moreover, superoxide dismutase (SOD) activity was enhanced in the TG+DG group, while the level of malondialdehyde (MDA), a marker of lipid peroxidation, was lower in the TG+DG group than the TG+VC group. These results suggest that DG could exert a wide range of beneficial activities for multiple types of brain damage through stimulation of NGF biosynthesis.

Synthesis of Denosomin-Vitamin D3 Hybrids and Evaluation of Their Anti-Alzheimer's Disease Activities

As an extension of previously conducted studies on developing an anti-Alzheimer's disease agent, denosomin (1-deoxy-24-norsominone, an artificial inducer of neurite elongation), derivatives were designed and synthesized based on the hypothesis that our denosomin would exhibit axonal extension activity via a 1,25D(3)-membrane-associated, rapid response steroid-binding protein (1,25D(3)-MARRS) pathway. The biological assay revealed that the hybridization of characteristic δ-lactone in denosomin and the triene moiety in VD(3) was effective to enhance the nerve re-extension activity in amyloid β (Aβ)-damaged neurons.

Evidence for the Importance of Vitamin D Status in Neurologic Conditions

OPINION STATEMENT

Vitamin D status has been proposed as relevant to many neurological disorders. Data suggest that vitamin D may be important for the development of the nervous system, and it also plays a role in neuroimmunology and neuroprotection. Lower levels of circulating 25-hydroxyvitamin D have been linked with increased risk of multiple sclerosis (MS) and Alzheimer's disease (AD). While people with amyotrophic lateral sclerosis (ALS), Parkinson's disease (PD), and stroke have lower vitamin D levels than those without the diseases, it is unclear if this is because hypovitaminosis D contributes to disease risk or is a consequence of immobility and other factors caused by the disease. Lower levels of vitamin D have been associated with worse prognosis in MS, PD, ALS, and stroke, while no longitudinal studies have been performed to evaluate such an association in AD. Small pilot trials have been performed to evaluate vitamin D supplementation for some of these diseases, but there have been no phase III studies to support vitamin D supplementation in these patient populations; further, ideal levels of 25-hydroxyvitamin D are not known. Thus, while some expert panels or individuals have suggested routine testing and supplementation for patients with these neurological conditions, it is our opinion that there are currently insufficient data to support high-dose vitamin D supplementation to specifically treat or prevent these conditions.

Active Constituents from Drynaria fortunei Rhizomes on the Attenuation of Aβ(25-35)-Induced Axonal Atrophy

Axonal regeneration might contribute to the restoration of damaged neuronal networks and improvement of memory deficits in a murine Alzheimer's disease (AD) model. A search for axonal regenerative drugs was performed to discover novel therapeutic options for AD. In this study, an aqueous extract of Drynaria fortunei rhizomes reversed Aβ25-35-induced axonal atrophy in cultured cortical neurons of mice. Bioassay-guided fractionation of this extract led to the isolation and identification of compounds 1-5. Among them, (2S)-neoeriocitrin (2) and caffeic acid 4-O-glucoside (4) showed significant axonal elongation effects on Aβ25-35-induced atrophy.

Patent highlights

A snapshot of noteworthy recent developments in the patent literature of relevance to pharmaceutical and medical research and development.

Comparing the effects of kamikihito in Japan and kami-guibi-tang in Korea on memory enhancement: working towards the development of a global study

Traditional medicine is widely used in East Asia, and studies that demonstrate its usefulness have recently become more common. However, formulation-based studies are not globally understood because these studies are country-specific. There are many types of formulations that have been introduced to Japan and Korea from China. Establishing whether a same-origin formulation has equivalent effects in other countries is important for the development of studies that span multiple countries. The present study compared the effects of same-origin traditional medicine used in Japan and Korea in an in vivo experiment. We prepared drugs that had the same origin and the same components. The drugs are called kamikihito (KKT) in Japan and kami-guibi-tang (KGT) in Korea. KKT (500 mg extract/kg/day) and KGT (500 mg extract/kg/day) were administered to ddY mice, and object recognition and location memory tests were performed. KKT and KGT administration yielded equivalent normal memory enhancement effects. 3D-HPLC showed similar, but not identical, patterns of the detected compounds between KKT and KGT. This comparative research approach enables future global clinical studies of traditional medicine to be conducted through the use of the formulations prescribed in each country.