Neuroprotective effects of Rhizoma Dioscoreae polysaccharides against neuronal apoptosis induced by in vitro hypoxia

Therapeutic targeting of mitochondria–proteostasis axis by antioxidant polysaccharides in neurodegeneration

Aging is a major risk factor for many age-associated disorders, including neurodegenerative diseases. Both mitochondrial dysfunction and proteostatic decline are well-recognized hallmarks of aging and age-related neurodegeneration. Despite a lack of therapies for neurodegenerative diseases, a number of interventions promoting mitochondrial integrity and protein homeostasis (proteostasis) have been shown to delay aging-associated neurodegeneration. For example, many antioxidant polysaccharides are shown to have pharmacological potentials in Alzheimer's, Parkinson's and Huntington's diseases through regulation of mitochondrial and proteostatic pathways, including oxidative stress and heat shock responses. However, how mitochondrial and proteostatic mechanisms work together to exert the antineurodegenerative effect of the polysaccharides remains largely unexplored. Interestingly, recent studies have provided a growing body of evidence to support the crosstalk between mitostatic and proteostatic networks as well as the impact of the crosstalk on neurodegeneration. Here we summarize the recent progress of antineurodegenerative polysaccharides with particular attention in the mitochondrial and proteostatic context and provide perspectives on their implications in the crosstalk along the mitochondria-proteostasis axis.

Study on the pharmacodynamic effect of Rhizoma Dioscoreae polysaccharides on cerebral ischemia-reperfusion injury in rats and the possible mechanism

ETHNOPHARMACOLOGICAL RELEVANCE

Rhizoma Dioscoreae (RD) is the rhizome of Dioscorea opposita Thunb., a traditional Chinese medicine, which can treat hypertension, diabetes, cerebral vasospasm headache and Alzheimer's disease. Meanwhile, RD is the main component of Liuwei Dihuang pill, a Chinese patent medicine. Rhizoma Dioscoreae polysaccharides (RDPS) are the primary active ingredient of RD. Modern medical research confirmed RDPS has multiple pharmacological effects, including neuroprotection, immunoregulation, antioxidant effect in many organs. The primary ischemia/hypoxia injury and secondary reperfusion injury are mainly caused by oxidative stress, which caused by hypoxia, such as free radical generation, energy metabolism disorder, intracellular calcium overload, excitatory amino acid release and inflammatory reaction.

AIM OF THE STUDY

We have investigated the pharmacodynamic effect of RDPS on cerebral ischemia-reperfusion (IR) injury in rats and the possible mechanism in vitro.

MATERIALS AND METHODS

The pharmacodynamic effect of RDPS on IR injury in rats was studied by the construction of the occlusion of middle cerebral artery (MCAO) model, measuring the volume of cerebral infarct area, the content of oxidation index, inflammatory cytokines, and the expression of CaMMKβ in brain tissue. The in vitro study was explored by oxygen-glucose deprivation/glycogen reoxygenation (OGD/R) model, construction of the CaMMKβ interference sequence, measuring the expression of CaMMKβ in BV2 cells before and after inhibition of CaMMKβ, and the influence of RDPS on Nrf2/HO-1 signal pathway, in order to investigate the possible mechanism.

RESULTS

Compared with the model group, the present study showed that RDPS with high-dose and low-dose groups could significantly reduce the volume of cerebral infarction. The content of MDA decreased and the activities of GSH and SOD increased in the two dose groups of RDPS. We confirmed that after RDPS treatment, the levels of IL-6, IL-1 β and TNF-α in brain tissue were lower than those in model group, and the expression of CaMMKβ in brain tissue of rats decreased in the model group, but increased in the groups of RDPS. In the in vitro study, compared with the control group, RDPS could regulate the OGD/R-induced apoptosis of BV2 cells and increase the level of CaMMKβ, Nrf2 and HO-1 induced by OGD/R. To our surprise, these therapeutic effects are no longer present after the inhibition of CaMMKβ protein. The activity of BV2 induced by OGD/R could not be enhanced by RDPS after the inhibition of CaMMKβ protein.

CONCLUSIONS

RDPS has the pharmacodynamic effect in IR injury, which reduce the area of cerebral infarction, up-regulate the activity of anti-oxidant kinase, and down-regulate the inflammatory cytokine. Additionally, RDPS could affect the activation of Nrf2/HO-1 signaling pathway by regulating the expression of CaMMKβ. Our observations justify the RDPS could be a new strategy for IR injury therapy, and the mechanism may be related to the improvement of antioxidant enzyme activity and inhibition of inflammatory reaction.

Lycium ruthenicum Murr polysaccharide protects cortical neurons against oxygen-glucose deprivation/reperfusion in neonatal hypoxic-ischemic encephalopathy

Neonatal hypoxic-ischemic encephalopathy (HIE) is a complex condition that remains the leading cause of mortality and morbidity among infants. Polysaccharide has been reported to possess diverse biological activities, however, the neuro-protective activity of polysaccharide isolated from Lycium ruthenicum remains unknown so far. However, the role of Lycium ruthenicum polysaccharide 3 (LRP3) in HIE has not been evaluated. Herein, we investigated the effect of LRP3 on oxygen-glucose deprivation/reoxygenation (OGD/R)-induced primary cortical neurons. Our results demonstrated that LRP3 significantly improved the cell viability of OGD/R-induced cortical neurons. The OGD/R-caused increase in ROS production and decrease in the activities of anti-oxidative enzymes including catalase (CAT), superoxide dismutase (SOD) and glutathione peroxidase (GPx) were mitigated by LRP3. Besides, the caspase-3 activity in OGD/R-induced cortical neurons was markedly decreased after LRP3 treatment. The increased bax expression and decreased bcl-2 expression caused by OGD/R stimulation were alleviated by pretreatment with LRP3. In addition, LRP3 significantly induced the expressions of nuclear factor erythroid 2-related factor (Nrf2) and heme oxygenase-1 (HO-1) in OGD/R-induced cortical neurons. However, inhibition of Nrf2/HO-1 signaling pathway through transfection with siRNA targeting Nrf2 reversed the protective effects of LRP3. In conclusion, LRP3 exerts a neuroprotective effect against OGD/R-induced neuronal injury in rat primary cortical neurons.

A fructan from Anemarrhena asphodeloides Bunge showing neuroprotective and immunoregulatory effects

A novel polysaccharide, AAP70-1, was isolated from Anemarrhena asphodeloides for the first time. The primary structural analysis revealed that AAP70-1 was composed of glucose and fructose, had an absolute molecular weight of 2720 Da, and contained a (2→6)-linked β-D-fructofuranose (Fruf) backbone and a (2→1,6)-linked β-D-Fruf side chain with an internal α-D-glucopyranose (Glcp) in the form of a neokestose. To explore the potential factors responsible for the medicinally relevant bioactivities of A. asphodeloides, a biological assay was performed. Using flow cytometry analysis, AAP70-1 was experimentally shown to have neuroprotective effects, and it can prevent and ameliorate neurological damage via reducing apoptosis. The immunomodulation assay further revealed that AAP70-1 can significantly improve immune function by promoting phagocytic capacity and the secretion of cytokines (IL-6, IL-1β and TNF-α) in RAW264.7 cells. These results suggest that AAP70-1 has potential as a therapeutic agent for central nervous system diseases or as an immunomodulatory agent.

Neuronalinjury and roles of apoptosis and autophagy in a neonatal rat model of hypoxia-ischemia-induced periventricular leukomalacia

As research into periventricular leukomalacia (PVL) gradually increases, concerns are emerging about long‑term neuron injury. The present study aimed to investigate neuronal injury and the relevant alterations in apoptosis and autophagy in a PVL model established previously. A rat model of hypoxia‑ischemia‑induced PVL was established. In the model group, Sprague‑Dawley (SD) rats [postnatal day 3 (P3)] were subjected to right common carotid artery ligation followed by suturing and exposed to 6‑8% oxygen for 2 h; in the control group, SD rats (P3) were subjected to right common carotid artery dissection followed by suturing, without ligation and hypoxic exposure. At 1, 3, 7 and 14 days following modeling, brain tissue samples were collected and stained with hematoxylin and eosin. Cellular apoptosis was detected by terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assay and the protein and mRNA expression alterations of neuronal nuclei (NeuN), caspase‑3 and Beclin 1 in the model group were detected by western blot analysis and reverse transcription‑quantitative polymerase chain reaction (RT‑qPCR) analyses. Compared with the control group, the protein and mRNA expression levels of NeuN (a marker of mature neurons) were markedly reduced, the number of positive cells was increased as detected by TUNEL, and the protein and mRNA expression levels of caspase‑3 and Beclin 1 were elevated in the model group. In the rat model of hypoxia‑ischemia‑induced PVL, oligodendrocyte injury and myelinization disorders were observed, in addition to neuron injury, a decrease in mature neurons and the co‑presence of apoptosis and autophagy. However, apoptosis and autophagy exist in different phases: Apoptosis is involved in neuron injury, while autophagy is likely to have a protective role.