Part 2 Cistanches Alleviates Sevoflurane-induced Cognitive Dysfunction By Regulating PPAR-γ-dependent Antioxidant And Anti-inflammatory in Rats

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4 | DISCUSSION

In this study, the findings demonstrated that a 2.6% concentration of sevoflurane exposure during 4 hours had notable negative effects on the learning and memory abilities of aged rats. Remarkably, a single-dose cistanche (50 mg/kg) could exert anti-inflammatory, antioxidant, anti-apoptosis, anti-activation of microglia, and neuroprotection effects on the sevoflurane-induced aged rats by activating PPAR-γ signaling.

Sevoflurane, a volatile anesthetic, is most commonly used in patients of all ages in modern anesthesiology. However, several investigates have reported that sevoflurane may lead to cognitive dysfunction, and these negative effects may depend on the concentration of sevoflurane, the duration and the number of anesthetic exposures. For instance, Xu et al10 have described short-term exposure to sevoflurane-impaired working memory in aged rats. In their study, memory impairment of aged rats was reduced at day 1 after exposure to 1 minimum alveolar concentration (MAC) sevoflurane and at days 1, 3, and 7 after exposure to 1.5 MAC sevoflurane, suggesting that the extent of cognitive function impairment was related to its concentration. Despite elderly adults being more sensitive to the cognitive impairment effects of sevoflurane due to the reduced physical function to compete for the stress,24 cognitive dysfunction also appears in adults. In the present study, we demonstrated that 24- but not 3-month-old rats have cognitive impairments on day 3 after the induction of anesthesia with 2.6% sevoflurane in 100% oxygen during 4 hours, indicating that the negative effects of the sevoflurane on the cognitive function are age-related under this condition.

Cistanche deserticola has many effects, click here to know more

Numerous studies have reported that surgery and anesthesia have been associated with transient or permanent damage in cognitive function, whereas the etiology of the disorders is largely unknown.25 Neuroinflammatory and oxidative stresses are the key players in cognitive impairment after surgery. On one side, neuroinflammation is the primary source of reactive oxygen species (ROS), free radicals, and reactive nitrogen species in the activated central nervous system.26 In turn, the excess ROS produced can damage biomolecules, change cellular functions and promote inflammation consequently.27 Neuroinflammation has been suggested to be a cornerstone of many neurodegenerative and cognitive diseases, including POCD.2,28 Gong has described that sevoflurane exposure impaired spatial memory in aged rats by increasing inflammation.29 Sevoflurane inhalation enhances the release of cytokines (IL-1β, IL-6, and TNF-α) and the activation of NF-κB signaling in the hippocampus of adult rats.30 On the other hand, elevated antioxidant defense and apoptosis status were also observed in blood samples of sevoflurane-administered children.31 In contrast, studies have shown that a widely used agent (dexamethasone) in the perioperative course can inhibit inflammatory events, prevent the production of IL-6 and make alterations in learning and memory processes.8,32 Ye and his colleague reported that honokiol could alleviate surgery

anesthesia-induced cognitive dysfunction in mice through regulation of neuroinflammatory and oxidative stress in the hippocampus.23

Cistanches is a commonly used Traditional Chinese Medicine (TCM). Although several pharmacological studies have shown that cistanches exhibited anti-inflammatory, immunomodulatory, anti-fatigue, anti-oxidative anti-tumor hepatoprotection, and neuroprotective effects,13 whether cistanches manipulate the effect of sevoflurane-induced inflammatory and oxidative stress remains unknown. Here, we demonstrated that Cistanches Herba extract reduces the expression of IL-1β, IL-6, TNF-α, and NF-κB in hippocampus-induced rats. Administration of Cistanches Herba extract directly reduces the nitrite/nitrate and MDA concentration and increases the SOD and CAT activity. These data suggested that treatment with Cistanches Herba extract significantly ameliorated the neuroinflammation and oxidative stress induced by sevoflurane exposure, indicating an intervention strategy for sevoflurane anesthesia. In addition, neuroinflammation is thought to be regulated by microglia, the resident immune cells in the brain.33 Upon stimulation, microglia become gradually activated and produce numerous pro-inflammatory cytokines that may cause neurodegeneration.34 What's more, BDNF has a significant role in promoting the synthesis and consolidation of new memories,35 and neuroinflammation and oxidative stress can inhibit the brain-derived neurotrophic factor (BDNF) expression.36 Here, our data demonstrated that administration of Cistanches Herba extract inhibited microglia activation from sevoflurane induction as indicated by a reduced expression of GFAP and Iba-1, and increased BDNF levels in the hippocampus, suggesting that inhibiting the microglia activation appears to be a mechanism to reduce inflammation in the hippocampus.

Cistanche has neuroprotective effects

Increased oxidative stress and inflammation to several tissues/ organs lead to cell death and long-term injury. Studies showed that sevoflurane anesthesia could reduce the rate of neurogenesis and decrease neuronal survival in the hippocampus, causing neurotoxicity and cognitive impairment in aged rats.37,38 Moreover, an in vitro study demonstrated that inhalation of sevoflurane could increase β-AP levels and induce caspase activation and apoptosis, which can ultimately facilitate the progression of Alzheimer's disease.39 Additionally, it is also revealed that exposure to sevoflurane in aged rats led to learning and memory deficits through endoplasmic reticulum stress (ERS)-induced apoptosis of the neurons.40 We found that treatment with Cistanches Herba extracts down-regulated the expression of apoptosis-related proteins, namely cleaved-caspase 3 and Bax. Meanwhile, Cistanches Herba extract promoted the expression of anti-apoptotic protein Bcl-2 in the hippocampal region of sevoflurane-induced aged rats. Thus, our findings reveal a function for Cistanches Herba extract as a neuroprotective agent for the survival of neurons.

Cistanche extract can be anti-inflammatory

Remarkably, PPAR-γ (a ligand-inducible transcription factor of the nuclear hormone receptor superfamily) is known to play an important role in the inflammatory response.41 The ability of PPAR-γ to exert anti-inflammatory effects has been extensively studied,42-44 Moreover, activation of PPAR-γ exerts anti-inflammatory effects via inhibiting the transcription factors, such as activator protein-1 and nuclear factor-kB.41 In addition, inhibiting PPAR-γ by its antagonists exhibits protective effects in an ischemia/reperfusion injury rat model by preventing oxidative stress and excessive inflammatory response.45 Chen et al demonstrated that thymoquinone inhibits spinal cord injury via preventing inflammatory response, apoptosis, and oxidative stress through PPAR-γ and PI3K/Akt pathways.46 What’ more, PPAR-γ is expressed in various cell types including astrocytes, microglia, and neurons in the brain, and PPAR-γ activation in microglia leads to reducing the production of pro-inflammatory cytokines by these cells.47 Notably, sevoflurane exaggerates cognitive dysfunction by increasing microglia-mediated neuroinflammation through inhibition of PPAR-γ in the hippocampus in a chronic intermittent hypoxia rat model.1 Furthermore, Xiang et al found that down-regulation of miR-27a-3p could alleviate sevoflurane-induced neurotoxicity and improve learning and memory abilities by mediating the PPAR-γ signaling pathway.48 Cistanches was previously demonstrated to show anti-inflammatory, antioxidant, anti-activation of microglia, and neuroprotection effects, but a comprehensive investigation on the mechanism of it is still lacking. Besides, previous studies revealed that cistanches exerted anti-inflammatory function by regulating the NF-κB and TGF-β signaling,13 but whether cistanches manipulate PPAR-γ signaling to regulate inflammatory and oxidative stress and protect cognitive function remains unknown. In this study, we found that Cistanches Herba extract prevented the inflammatory, oxidative stress, glial activation, apoptosis, and cognitive dysfunction at least partially via the PPAR-γ signaling pathway. In support of its functional essentiality, a PPAR-γ antagonist GW9662 was used combined with Cistanches Herba extract in vivo. Results showed that inhibition of PPAR-γ markedly alleviated the effectivity of Cistanches Herba extract in treating rats in vivo, indicating the potential of the PPAR-γ-activated therapeutic approach (Figure S2). Although Cistanches Herba extract had been revealed to relieve cognitive impairment induced by sevoflurane anesthesia in aged male rats in vivo by activating PPAR-γ signaling, the relevance between Cistanches Herba extract and other signaling pathways needs more validation. Moreover, the effects of Cistanches Herba extract on age-matched female rats or the younger males still deserve further investigation.

Cistanche has anti-inflammatory properties

5 | CONCLUSIONS

Our studies demonstrated that Cistanches Herba extract, through activating the PPAR-γ signaling, alleviated the sevoflurane anesthesia-induced cognitive impairment in aged rats. Our results provided a potential strategy for preventing the POCD induced by sevoflurane anesthesia clinically.

ACKNOWLEDGEMENTS

This work was supported by a grant from the Important Weak Subject Construction Project of Pudong Health and Family Planning Commission of Shanghai (Grant No.: PWZbr2017-19).

CONFLICT T OF INTEREST

The authors confirm that there are no conflicts of interest.

AUTHORS' CONTRIBUTIONS

Substantial contribution to the conception and design of the work: SP, PYL, PRL, JW; Analysis and interpretation of the data: SP, HZY, WHL, CLL, YXZ; Drafting the manuscript: SP, PYL, HY, YXZ; Revising the work critically for important intellectual content: YXZ; Collection of grants: YXZ; Final approval of the work: all authors.

E THIC S APPROVAL AND CONSENT TO PARTICIPATE

All procedures performed in studies involving animals were in accordance with the ethical standards of Seventh People's Hospital of Shanghai University of TCM.

CONSENT FOR PUBLICATION

This manuscript has been approved by all authors for publication.

ORCHID

Yixin Zhou https://orcid.org/0000-0002-7565-0329

DATA AVAILABILITY Y STATEMENT

The data sets used and analyzed during the current study are available from the corresponding author on reasonable request.

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