Is Siberian Rhodiola Benefits for Hypoxia Resistance?

Rhodiola crenulata (Hook. f. et Thoms.) H. Ohba, a large flower of the Sedum genus in the Sedum family, is a traditional Tibetan medicine that mainly grows at altitudes of 3000-4000 meters. It has anti-tumor [1-2], anti asthma [3], regulating intestinal microbiota [4], and anti hypoxia effects, and is known as the "high-altitude ginseng". Siberian Rhodiola not only has diverse functions, but also has strong vitality and is extremely easy to survive. It is recorded in the 2020 edition of the Chinese Pharmacopoeia, as well as in literature on traditional Chinese medicine and Tibetan medicine [5]. The main active extracts from the roots and stems of Siberian Rhodiola are salidroside, gallic acid, tyrosol, and ethyl gallate [6].

These bioactive substances play an irreplaceable role in the various therapeutic effects of Siberian Rhodiola, with salidroside being the most important. Oxygen is one of the most fundamental substances for maintaining life activities, and hypoxic stimulation can cause pathological reactions in multiple tissues and organs of the body. In recent years, domestic and foreign studies have shown that Rhodiola rosea plays an important role in alleviating hypoxia in the body and can exert therapeutic effects in multiple organs. This article reviews the protective mechanisms of Siberian Rhodiola in relieving hypoxia damage to organs such as the heart, lungs, and brain, as well as its effects on oxidative stress factors, in order to provide reference for the further development and utilization of Rhodiola rosea.

1 Siberian Rhodiola anti-hypoxia changes in oxidative stress factors

Oxidative stress is an imbalance in the body's redox state that can lead to the production of large amounts of reactive oxygen species, which irreversibly oxidize the genetic material DNA and various biological molecules in cells [7]. The main factors related to oxidative stress in the body include superoxide dismutase (SOD), glutathione (GSH), oxidized glutathione (GSSG), lactate dehydrogenase (LDH), malondialdehyde (MDA), lactate dehydrogenase (LDH), nitric oxide (NO), glutathione peroxidase (GSH-Px), etc. Hypoxia stimulation can cause changes in the levels of these oxidative stress factors in the body. Increased MDA levels can exacerbate cell senescence and apoptosis, while increased SOD activity can remove reactive oxygen species (ROS) and reduce oxidation, thereby inhibiting cell apoptosis [8].

Siberian Rhodiola can alleviate hypoxia-induced damage by changing the levels of oxidative stress factors in the body, thereby reducing reactive oxygen species and inhibiting cell senescence and apoptosis. Hypoxia-induced damage can cause an increase in the levels of MDA, GSSG and LDH in serum and hippocampal tissue, and a decrease in the levels of SOD and GSH. This phenomenon can be reversed by treatment with Rhodiola rosea water extract, thereby protecting against hypoxia-induced damage [9]. After hypoxic stimulation, the levels of oxidative stress markers ROS and MDA in lung tissue increased, as did the activity of myeloperoxidase (MPO). Pretreatment with Rhodiola rosea water extract can reduce the levels of ROS and MDA and lower MPO activity, suggesting that Rhodiola rosea exhibits antioxidant and ROS scavenger activity in an animal model, thereby alleviating hypoxia-induced lung injury [10].

Hypoxia-induced ROS increase in the heart can lead to oxidative damage to biomolecules such as DNA, proteins and lipids, which may inhibit myocardial contraction and dysfunction [11]. Copper and zinc superoxide dismutase (SOD1), which is present in the nucleus and cytoplasm, is a widely distributed antioxidant enzyme in cells that maintains intracellular ROS homeostasis. Manganese superoxide dismutase (SOD2), which is present in mitochondria, has the effect of scavenging ROS. After hypoxic induction, the expression of ROS, MDA and carbonyl protein in cardiac tissue increased, and after treatment with Rhodiola rosea, the ROS level was reduced, suggesting that Rhodiola rosea administration can reduce oxidative stress in the heart. At the same time, the activity of the antioxidant enzyme SOD2 was observed, and it was found that its activity decreased during hypoxia. After taking Rhodiola rosea, the inhibition of SOD2 expression by hypoxia was relieved [12]. In addition, Rhodiola rosacea can also protect HK-2 renal tubular epithelial cells from in vitro hypoxia-induced injury, reduce ROS and MDA levels in HK-2 cells, and increase SOD levels [13].

In a study of oxidative stress factors in the lungs of rats with hypoxic pulmonary hypertension, it was found that hypoxia increased the expression of NOX4 and the level of MDA, and decreased the activity of SOD1 and SOD. Rhodiola extract can increase the activity of SOD1 and SOD in a dose-dependent manner, indicating that Rhodiola extract improves pulmonary hypertension by restoring the balance of the oxidation/antioxidant system [14]. Rhodiola rosea extract also has a protective effect on endothelial cells damaged by hypoxia [15]. Hypoxia increases ROS and MDA levels, which can be reduced by pretreatment with Rhodiola rosea extract. The oxidative factors in various tissues and organs are shown in Table 1.

2 The protective effect of Siberian Rhodiola on various systems against hypoxia

2. 1 The protective effect of Siberian Rhodiola on the lungs

Oxygen homeostasis is one of the important conditions for the survival of most organisms on earth. Participation in the oxidation reaction can promote necessary biological processes, and an appropriate oxygen concentration can drive carbon metabolism to produce energy [16]. When oxygen concentration decreases, some important metabolic pathways are disrupted, which can lead to organ damage. For example, people and animals at high altitudes are damaged by the hypoxic environment, and the lack of oxygen to the organs can lead to ischemia and damage to health [17]. High altitude pulmonary edema and pulmonary arterial hypertension (PAH) are typical high altitude diseases that people are prone to develop in a hypoxic environment [18].

Siberian Rhodiola active ingredients can reverse hypoxia-induced damage in rat models. Compared with untreated hypoxic rats, Siberian Rhodiola active ingredients can reduce the right ventricular hypertrophy index, mean pulmonary artery pressure, small pulmonary artery smooth muscle thickening and pulmonary capillary reconstruction [19], suggesting that the ingredient can be used to treat hereditary pulmonary hypertension. Pulmonary edema can be assessed by measuring the wet/dry (W/D) mass ratio and BALF protein expression. Tissue section observation can be used to evaluate the protective effect of Rhodiola extract on hypoxic lung injury [20].

The W/D ratio and BALF protein expression are elevated in an hypoxic environment, and Rhodiola extract treatment can effectively reduce BALF protein expression. Hypoxia causes symptoms such as thickening of the alveolar septum, escape of red blood cells, filtration of alveolar neutrophils, rupture of alveolar capillaries, and severe congestion of the vascular wall in the lung tissue. . Rhodiola extract can reduce these pathological changes in lung tissue, suggesting that Rhodiola extract can reduce the dysfunction of the alveolar-capillary barrier, thereby reducing pulmonary edema caused by low-pressure hypoxia, and has significant efficacy in maintaining the integrity of the alveolar-capillary barrier damaged by hypoxia [10].

Pulmonary arterial smooth muscle cell (PASMC) abnormal growth, excessive cell proliferation and apoptosis resistance caused by active vasoconstriction and vascular remodeling are the main symptoms of pulmonary hypertension pathology [21]. Siberian Rhodiola extract, the main bioactive marker isolated from Siberian Rhodiola, can be used to relieve altitude sickness and acute exacerbation of pulmonary hypertension [22]. After hypoxia stimulation, PAMSCS cells are irregular in shape, with interrupted mitochondrial ridges and full of vacuoles, and the cells are disorganized. After pre-treatment with rhodioloside, PASMCS cells are well organized, abnormal growth of collagen fibers is reduced, and the number of interrupted mitochondrial ridges and vacuoles is reduced, indicating that rhodioloside inhibits hypoxia-induced pulmonary artery remodeling [23]. Both high and low doses of rhodioloside can alleviate to some extent the symptoms of stenosis of small artery lumen, thickening of the tube wall, and proliferation of smooth muscle cells in the media, and can inhibit ventricular remodeling and improve pathological damage to lung tissue [24].

Adenosine monophosphate-activated protein kinase (AMPK) is a serine/threonine protein kinase that plays a key role in energy metabolic homeostasis by activating catabolic pathways and inhibiting anabolic pathways [25]. AMPK plays a key role in cell proliferation, autophagy, apoptosis and other cell fates, and plays an important role in cardiovascular protection [26]. Chen et al. [23] found that after rhodiola Rhodiola Rosea treatment increased the total AMPKα 1 and phosphorylated AMKPα 1 activity in the pulmonary artery, lung tissue, and PASMCS cells of rats in a dose-dependent manner. It may reverse hypoxia-induced apoptosis resistance through the AMPKα 1-P53-Bax/Bcl-2-caspase 9-caspase 3 pathway, which is divided into 2 parts.

The first part is to inhibit the proliferation of PASMCS cells. Rhodioloside can increase the activity of phosphorylated AMKPα 1. The increased phosphorylated AMKPα 1 in turn increases the expression of P53, which in turn increases the expression of P53 downstream effectors P21 and P27, thereby inhibiting cell proliferation. This is the AMPKα 1-P5 3-P27 / P21 signaling pathway; the second part is to increase PASMCS cell apoptosis. The increased activity of phosphorylated AMKPα 1 leads to increased P53 expression, decreased levels of the pro-apoptotic factor Bax, increased levels of the anti-apoptotic factor Bcl-2, and increased expression of the apoptosis-related proteins caspase-9 and caspase-3, thereby promoting apoptosis. Thus, rhodioloside induces the proliferation and apoptosis of PASMCs through the AMPKα1-P53-Bax/Bcl-2-caspase 9-caspase 3 pathway.

2.2 Cardioprotective effect of Siberian Rhodiola

Hypoxia is considered a cardiac stressor and may lead to certain cardiovascular diseases, such as myocardial infarction and right ventricular dysfunction induced by pulmonary hypertension [27]. In addition to pulmonary changes, cardiac arrest is another common disease in anoxic environments [28]. Rhodiola rosea extract has a protective effect on the heart in anoxic conditions and can be used to prevent high-altitude diseases, including sudden cardiac death. Hypoxia-induced abnormal myocardial structure can be observed in mouse heart tissue, including increased interstitial space, mild fibrosis and increased deposition of collagen protein. TUNEL staining revealed an increase in TUNEL-positive cardiomyocytes in the left ventricle of the heart. After treatment with Rhodiola Rosea, this cardiac damage and cardiomyocyte apoptosis were reduced, suggesting that Rhodiola Rosea has a protective effect on the hypoxia-induced mouse heart [29]. Histopathological analysis found that hypoxia caused abnormal myocardial structure and increased tissue gaps, and that the abnormal structure could be reduced after treatment with low and high doses of rhodiola extract.

Apoptosis detection found that hypoxia caused an increase in TUNEL-positive cardiomyocytes, which was inhibited after rhodiola pretreatment [30].

Reperfusion after prolonged ischemia and hypoxia can cause irreversible functional and structural damage to the heart muscle. This damage is known as myocardial ischemia-reperfusion injury [31-32]. Liu et al. [33] found that hypoxia/reoxygenation induced a decrease in H9c2 cell viability, resulting in an increase in cellular LDH activity. Rhodiola rosea extract not only inhibited the decrease in H9c2 cell viability, but also reduced LDH activity and H9c2 cell death, indicating that Rhodiola rosea has a protective effect on hypoxic/reoxygenated cardiomyocytes. Rhodiola rosea has been made into a variety of products, and Rhodiola rosea broken tablets are one of them. Comparing the effects of Rhodiola rosea broken tablets and traditional tablets on ischemic and hypoxic H9c2 cells, the results show that both both can improve the survival rate of ischemic and hypoxic H9c2 cells and the anti-apoptotic effect is dose-dependent. At the same dose, the survival rate of H9c2 cells in Rhodiola wall-broken pieces is higher than that in traditional pieces [34].

The survival rate of myocardial cells induced by glucose and hypoxia increased with the increase of the administration concentration of Siberian Rhodiola, suggesting that Rhodiola rosea can inhibit myocardial cell damage induced by glucose and hypoxia [35]. MicroRNAs (miRNAs) are a class of endogenous, small non-coding single-stranded RNA that is involved in the regulation of various physiological and pathophysiological processes [36]. miR-21 can effectively reduce the level of myocardial cell apoptosis and the release of inflammatory factors induced by myocardial ischemia-reperfusion injury in rats. The expression of miR-21 is reduced during myocardial ischemia-reperfusion injury, and restoration of miR-21 expression can reduce myocardial myocardial injury [37-38]. Liu et al. [33] found that rhodiola extract can inhibit hypoxia/reoxygenation-induced hypoxia by upregulating miR-21, thereby reducing the levels of inflammatory factors such as interleukin-9 (IL-9), interleukin-1β (IL- 1β) and tumor necrosis factor-α (TNF-α) levels, thereby reducing the inflammatory response during hypoxia/reoxygenation. miR-21 mediates the inhibition of the inflammatory response induced by rhodiola extract during hypoxia/reoxygenation treatment of H9c2 cells, reducing myocardial cell damage.

2. 3 Biological effects and molecular mechanisms of Siberian Rhodiola on the nervous system

The treatment of central nervous system damage caused by hypobaric hypoxia has attracted increasing attention in the medical field [39-40]. The rat pheochromocytoma cell line PC-12 is catecholamine-excitable and has the morphology and characteristics of nerve cells. It is widely used in cell signal transduction and neurochemical research [41-42]. Cobalt chloride (CoCl2) can induce hypoxic damage in PC12 cells and cause PC12 cells to die within 12 h. The nuclei of dead cells disappear, condensed chromatin is re-localized to the nuclear membrane, and the characteristic ultrastructural changes of PC12 cell damage are alleviated after treatment with Rhodiola rosea [43], protecting neurons from hypoxia-ischemia injury. Wang et al. [9] used HE and Nissl staining to evaluate the viability of hippocampal neurons in rats after hypoxic-ischemic injury. They found that hippocampal cells were significantly swollen, the surrounding cell spaces were widened, neurons shrank and decreased, the cell nuclei were deeply stained, the structure of normal neurons was damaged and the number of Nissl bodies decreased. Rhodiola extract can improve these pathological changes. Apoptosis detection found that more TUNEL-positive cells were observed in hippocampal CA1 pyramidal neurons, and this increase was reduced by treatment with Rhodiola extract.

Hypoxia preconditioning plays a key role in reducing hypoxia-induced apoptosis [44]. Hypoxia preconditioning can trigger autonomous endogenous protective mechanisms to resist severe hypoxia damage and reduce hypoxia or ischemia-induced apoptosis [45]. Compared with hypoxia preconditioning, which is beneficial to cell resistance to hypoxia, rhodiola rosacea pretreatment reduces hypoxia-induced loss of cell viability and increases the release of PC12 cell LDH activity. Rhodiola rosacea can inhibit hypoxia-induced PC12 cell apoptosis [46]. Compared with the normal group, the survival rate of hippocampal neurons in hypoxic mice was low. Pretreatment with rhodioloside can increase the survival rate of hippocampal neurons, and this effect is dose-dependent [47]. Hypoxia/ischemia in rats impairs learning and memory, and increases hippocampal cell apoptosis. After treatment with rhodiola extract, these effects are significantly improved and the number of apoptotic cells is reduced, indicating that rhodiola extract can reduce apoptosis by inhibiting hippocampal neuronal autophagy in rats with hypoxia/ischemia, thereby exerting a neuroprotective effect [48]. As intermittent hypoxia continues, neurons in the rat hippocampus gradually show signs of structural damage, uneven chromatin in the cytoplasm, a triangular shape, a shrunken nucleus, nuclear dissolution and vacuoles. After treatment with Rhodiola rosea, the neurons are arranged neatly, the cytoplasm is evenly stained, the nucleus is shrunken, and nuclear dissolution and vacuoles are reduced [49].

Hypoxia-inducible factor-1α (HIF-1α) is a core transcription factor that regulates oxygen homeostasis and plays an important role in relieving hypoxia-induced damage in the body. Studies have found that HIF-1α is a core transcription factor that induces hypoxia-inducible genes and repairs the intracellular microenvironment transcription factor [50]. Elevated mRNA and protein expression of HIF-1α stimulates downstream vascular endothelial growth factor and erythropoietin production, thereby enhancing tolerance to hypoxic injury. Under hypoxia, HIF-1α up-regulation induces the overexpression of microRNA 210 (miR-210), which reduces the expression of iron-sulfur cluster assembly scaffold (ISCU1/2) and cytochrome C oxidase assembly protein (COX10) [51]. Wang et al. [9] found that after treatment with Rhodiola extract, the expression of HIF-1α, miR-210, ISCU1/2 and COX10 in the rat cerebral cerebral cortex HIF-1α, miR-210, ISCU1/2 and COX10 expression increased, and caspase-3 expression decreased, indicating that rhodiola extract alleviates hypoxia-induced cerebral cortex damage by regulating apoptosis and mitochondrial energy metabolism through the HIF-1α/microRNA 210/ISCU1/2 (COX10) signaling pathway.

2. 4 Molecular mechanisms of other cell protective effects of Siberian Rhodiola

AMPK activation can promote endothelial nitric oxide synthase (eNOS) activity and preserve endothelial cell function. Extracellular signal-regulated kinase 1/2 (ERK1/2) is associated with hypoxia-stimulated endothelial cell proliferation and apoptosis [52]. Hypoxia stimulation leads to a decrease in eNOS activity and an increase in apoptotic cells in endothelial cells, thereby disrupting endothelial cell function. After administration of Rhodiola Rosea extract, the phosphorylation of AMPK and the activity of ERK1/2 increase, which in turn increases eNOS activity to reduce apoptosis and restore endothelial cell function. This is the AMPK-Akt-eNOS signaling pathway [15].

HIF-1α can increase the formation of new blood vessels in bone by regulating vascular endothelial growth factor (VEGF), which promotes bone development and bone formation during fracture healing. When in a hypoxic state, rhodioloside can promote a large increase in HIF-1α and transport it to the nucleus where it binds with HIF-1β to form the HIF-1 complex. As a transcription factor, it binds to hypoxia response elements (HER) to further activate the transcription of hundreds of downstream target genes are transcribed, which in turn triggers a tissue cell response to oxygen tolerance, improving the hypoxic state of tissues and cells. This indicates that under hypoxic conditions, rhodiola extract regulates the proliferation, differentiation and apoptosis of osteoblasts by regulating the HIF-1α/VEGF signaling pathway [53].

The anti-hypoxia protective mechanisms of rhodiola for various systems are shown in Table 2. The rhodiola-related anti-hypoxia signaling pathways are shown in Table 3.

3 Outlook

Although many results have been obtained in studies on Siberian Rhodiola's resistance to hypoxia, the specific mechanism by which Rhodiola relieves hypoxia-induced damage is not fully understood and requires further research to clarify its regulatory mechanism at the gene and protein levels. At present, most studies focus on Rhodiola's resistance to hypoxia in the lungs, heart and brain neural tissue, but there is almost no research on other organs. Further research in this area is needed to explore whether Rhodiola can relieve hypoxia-induced damage to other organs. Currently, most studies use cells, rats and mice as animal models. If we want to further clarify its role in human tissues and organs, we need to study the anti-hypoxia injury effect of Rhodiola rosea in different animal models that are closer to human pathological conditions. Rhodiola rosea is a Chinese medicinal herb with both medicinal and edible properties. The dosage, toxicity and safety of its bioactive compounds when consumed are also important issues that need to be studied.

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