Neuroprotective effects of salidroside against beta-amyloid-induced oxidative stress in SH-SY5Y human neuroblastoma cells

Salidroside stimulates the accumulation of HIF-1α protein resulted in the induction of EPO expression: a signaling via blocking the degradation pathway in kidney and liver cells

Rhodiolae Crenulatae Radix et Rhizoma (Rhodiola), the root and rhizome of Rhodiola crenulata (Hook. f. et Thoms.) H. Ohba, has been used as a traditional Chinese medicine (TCM) to increase the body resistance to mountain sickness in preventing hypoxia; however, the functional ingredient responsible for this adaptogenic effect has not been revealed. Here, we have identified salidroside, a glycoside predominantly found in Rhodiola, is the chemical in providing such anti-hypoxia effect. Cultured human embryonic kidney fibroblast (HEK293T) and human hepatocellular carcinoma (HepG2) were used to reveal the mechanism of this hematopoietic function mediated by salidroside. The application of salidroside in cultures induced the expression of erythropoietin (EPO) mRNA from its transcription regulatory element hypoxia response element (HRE), located on EPO gene. The application of salidroside stimulated the accumulation of hypoxia-inducible factor-1α (HIF-1α) protein, but not HIF-2α protein: the salidroside-induced HIF-1α protein was via the reduction of HIF-1α degradation but not the mRNA induction. The increased HIF-1α could account for the activation of EPO gene. These results supported the notion that hematopoietic function of Rhodiola was triggered, at least partially, by salidroside.

Protective effects of a Rhodiola crenulata extract and salidroside on hippocampal neurogenesis against streptozotocin-induced neural injury in the rat

Previously we have demonstrated that a Rhodiola crenulata extract (RCE), containing a potent antioxidant salidroside, promotes neurogenesis in the hippocampus of depressive rats. The current study was designed to further investigate the protective effect of the RCE on neurogenesis in a rat model of Alzheimer's disease (AD) induced by an intracerebroventricular injection of streptozotocin (STZ), and to determine whether this neuroprotective effect is induced by the antioxidative activity of salidroside. Our results showed that pretreatment with the RCE significantly improved the impaired neurogenesis and simultaneously reduced the oxidative stress in the hippocampus of AD rats. In vitro studies revealed that (1) exposure of neural stem cells (NSCs) from the hippocampus to STZ strikingly increased intracellular reactive oxygen species (ROS) levels, induced cell death and perturbed cell proliferation and differentiation, (2) hydrogen peroxide induced similar cellular activities as STZ, (3) pre-incubation of STZ-treated NSCs with catalase, an antioxidant, suppressed all these cellular activities induced by STZ, and (4) likewise, pre-incubation of STZ-treated NSCs with salidroside, also an antioxidant, suppressed all these activities as catalase: reduction of ROS levels and NSC death with simultaneous increases in proliferation and differentiation. Our findings indicated that the RCE improved the impaired hippocampal neurogenesis in the rat model of AD through protecting NSCs by its main ingredient salidroside which scavenged intracellular ROS.

Panax ginseng, Rhodiola rosea and Schisandra chinensis

Panax ginseng (Ginseng), Rhodiola rosea (Hong Jing Tian) and Schisandra chinensis (Wu Wei Zi) are well-known herbs in traditional Chinese medicine (TCM). Recently, there have been a number of studies on these three herbs. This review discusses their active components and major pharmacological effects. For P. ginseng, it has been shown to have an anti-inflammatory activity, affects pulmonary function and erectile dysfunction, improves cognition in patients with Alzheimer's disease and promotes sexual arousal in menopausal women as well as prevents cancer. For R. rosea, its effectiveness in alleviating depression and reducing fatigue is summarized in this review. Additionally, anti-cancer and other clinical effects of S. chinensis are also discussed. These three herbs are considered as adaptogens as they bear multiple functions and their effects were found to be very different in patients depending on the circumstances (age, gender, environment, diet, season, etc.). Thus, in most cases, the art of the TCM practitioner is to prescribe these herbs after a complete evaluation of overall heath status of the patients.

Salidroside attenuates hydrogen peroxide-induced cell damage through a cAMP-dependent pathway

Salidroside, a major component of Rhodiola rosea L., has shown various pharmacological functions, including antioxidant effects, but the signal transduction pathway of its antioxidant effects is not very clear. In this study, we found that salidroside could attenuate hydrogen peroxide (H₂O₂)-induced HL-7702 cell damage, inhibit H₂O₂-induced cytosolic free Ca²⁺ ([Ca²⁺]i) elevation, scavenge reactive oxygen species (ROS) and increase 3’-5’-cyclic adenosine monophosphate (cAMP) level in a dose-dependent manner, but it couldn’t influence 3’-5’-cyclic guanosine monophosphate (cGMP) levels. Therefore, these results indicated that the antioxidant effects of salidroside were associated with down-regulation of [Ca²⁺]i, ROS occur via a cAMP-dependent pathway.

Neuroprotection against cobalt chloride-induced cell apoptosis of primary cultured cortical neurons by salidroside

Salidroside, a phenol glycoside of plant origin, has been documented to possess a broad spectrum of pharmacological properties, including protective effects against neuronal death induced by different insults. To provide further insights into the neuroprotective functions peculiar to salidroside, this study used primary cultured cortical neurons of rats as a cell model to examine whether salidroside was able to prevent against cell damage after exposure to cobalt chloride (CoCl(2)), a hypoxia-inducing agent. The data from 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide test, Hoechst33342 staining, terminal deoxynucleotidyl transferase dUTP-mediated nicked end labeling assay, and Bax/Bcl-2 ratio analysis indicated that salidroside pretreatment attenuated hypoxia-induced apoptotic cell death of primary cultured cortical neurons in a dose-dependent manner. Moreover, preliminary exploration of the possible mechanisms suggested that the protective effects of salidroside, shown in our experimental setting, might probably be mediated by enhancing the expression of hypoxia-inducible factor-1α, alleviating the increase of intracellular reactive oxygen species levels, and inhibiting over-expression of nuclear factor-kappa B protein.

Inhibition and covalent modification of tyrosine hydroxylase by 3,4-dihydroxyphenylacetaldehyde, a toxic dopamine metabolite

Parkinson's disease (PD) is a neurodegenerative disorder marked by the selective loss of dopaminergic neurons, leading to a decrease of the neurotransmitter dopamine (DA). DA is metabolized by monoamine oxidase to 3,4-dihydroxyphenyacetaldehyde (DOPAL). While the mechanism of pathogenesis of PD is unknown, DOPAL has demonstrated the ability to covalently modify proteins and cause cell death at concentrations elevated from physiologic levels. Currently, the identities of protein targets of the aldehyde are unknown, but previous studies have demonstrated the ability of catechols and other DA-catabolism products to interact with and inhibit tyrosine hydroxylase (TH). Given that DOPAL is structurally related to DA and is a highly reactive electrophile, it was hypothesized to modify and inhibit TH. The data presented in this study positively identified TH as a protein target of DOPAL modification and inhibition. Furthermore, western blot analysis demonstrated a concentration-dependent decrease in antibody recognition of TH. DOPAL in cell lysate significantly inhibited TH activity as measured by decreased l-DOPA production. Inhibition of TH was semi-reversible, with the recovery of activity being time and concentration-dependent upon removal of DOPAL. These data indicate DOPAL to be a reactive DA-metabolite with the capability of modifying and inhibiting an enzyme important to DA synthesis.