We illustrated that BSYZ-E could advance age-related cognitive decline in SAMP8 mice in this study. BSYZ-E modified oxidative stress and nitrosative stress, as well as reduced neuronal apoptosis and neuroinflammation.
Advanced age is always a primary hazard of neurodegenerative diseases[21, 22]. Accumulating evidence suggested that the risk factor of dementia is attributed to age-related neuropathologies[23, 24]. The main clinical manifestation of aging-induced dementia is cognitive impairment and decline[25]. The mechanisms of aging-induced dementia are associated with oxidative stress, neuronal apoptosis, and neuroinflammation[26]. As a neuropathological animal model, SAMP8 mice have been universally used for researching accelerated brain-aging and dementia [27, 28]. In this study, SAMP8 mice displayed distinct age-related deterioration in cognitive ability and relative pathological features. Therefore, SAMP8 mice were deemed as an experimental animal model to investigate whether BSYZ-E could attenuate the behavioural and pathological of aging-induced dementia in this study. In previous studies, BSYZ-F has good efficacy for the treatment of clinical dementia[12]. We also demonstrated that BSYZ-F/BSYZ-E could improve learning and memory impairment through different signal pathways in different animal models[29, 30]. In our study, we further studied the mechanism of BSYZ-E alleviating neuroinflammation in SAMP8 mice. The MWM test was designed to appraise the cognitive ability in SAMP8 mice. The result indicated that BSYZ-E could improve cognitive impairments in SAMP8 mice.
Produced by complicated processes, reactive oxygen/nitrogen species formation promotes cellular senescence and organismal aging[31]. The relation of oxidative/nitrosative stress and accelerated-aging is well established[32, 33]. Reactive oxygen species (ROS) overproduction contributes to activate the pro-inflammatory pathways[34], which promotes neuroinflammation in aging-induced dementia [35, 36]. Superoxide dismutase (SOD) and Malondialdehyde (MDA), as the oxidative stress-related biomarkers, indicated the overproduction of ROS. Vivo aging model showed an increase in nitrosative stress with high expression of nitric oxide (NO) and inducible nitric oxide synthase (iNOS)[37]. In this study, the application of BSYZ-E and Donepezil can decrease MDA levels and increase SOD vitality in SAMP8 mice. Besides, NO levels and iNOS vitality in SAMP8 mice have been downregulated under the treatment of BSYZ-E and Donepezil. These results manifested the efficiency of BSYZ-E on alleviating oxidative and nitrosative stress in SAMP8 mice.
Apoptosis, a programmed cell death, leads to a vicious circle of neurodegenerative diseases like Alzheimer’s disease[38]. Neuronal degeneration is well known as a primary cause leading to memory loss in dementia[39]. Aging can promote neural apoptosis by regulating the activation of Caspase cascades and BAD (Bcl-2-associated death promoter)[40]. Bcl-2 is an anti-apoptosis protein that could inhibit neuronal apoptosis, and Bax is a homolog of Bcl-2 that could promote apoptosis[41]. The pro-apoptotic protein Bax activation relevant to the intrinsic mitochondrial apoptotic pathway, followed by Caspase-3 activated, leading to cell death[42]. The results revealed the expression of apoptotic protein (Bax, Caspase-3, and Cleaved-Caspase-3) prominently declined, yet related anti-apoptosis protein Bcl-2 express greatly increased after the treatment of BSYZ-E and Donepezil. It demonstrated that BSYZ-E distinctly decreased neural apoptosis in SAMP8 mice.
Inflammasomes, as a group of large multimeric complex proteins, pertain to a large family of intracellular pattern recognition receptors[43, 44]. NLRP3 (NOD-, LRR- and pyrin domain-containing 3) inflammasome, consisting of NLRP3, ASC, Caspase-1, is a pivotal element of the innate immune system. NLRP3 inflammasome mediated Caspase-1 activation, pyrolysis as well as promoted the secretion of pro-inflammatory cytokines interleukin-18 (IL-18)/IL-1β[45–47]. Multiple endogenous or exogenous danger signals, including infection and metabolic dysfunction, trigger the inflammatory reaction initiated by the NLRP3 inflammasome[48]. Inhibition of NLRP3 activation can improve cognitive deficits, including age-dependent cognitive impairment[11, 49, 50]. The main components of BSYZ-E are analyzed by HPLC in our previous study[17]. We found that the main components of BSYZ-E include osthole and emodin. Osthole improved the cognitive function of vascular dementia rats via inhibition NLRP3 inflammasome[51]. Emodin exerted anti-inflammatory effects by relieving NLRP3 inflammasome activation[52], whose signaling has correlated with the neuroinflammation[53]. Massive experiments have determined that the expression of NLRP3 inflammasome-mediated neuroinflammation can be assembled via elevating the expression of NLRP3, ASC, Caspase-1, IL-18, and IL-1β in the hippocampus[44, 54]. In our study, we discovered higher expression inflammatory-related proteins, including NLRP3, ASC, Caspase-1, IL-1β, and IL-18 in the hippocampus of SAMP8 mice than SAMR1 mice, which confirmed that NLRP3 inflammasome activation was recognized in SAMP8 mice. Neuroinflammation was reduced by treating with BSYZ-E and Donepezil, which indicated that BSYZ-E could protect against the NLRP3 inflammasome-mediated neuroinflammation in SAMP8 mice. Hence, we demonstrated the effect of BSYZ-E on alleviating NLRP3 inflammasome-mediated neuroinflammation in SAMP8 mice.