Dual Effects of Korean Red Ginseng on Astrocytes and Neural Stem Cells in Traumatic Brain Injury: The HO-1–Tom20 Axis as a Putative Target for Mitochondrial Function

Therapeutic potential and possible mechanisms of ginseng for depression associated with COVID-19

Recently, a global outbreak of COVID-19 has rapidly spread to various national regions. As the number of COVID-19 patients has increased, some of those infected with SARS-CoV-2 have developed a variety of psychiatric symptoms, including depression, cognitive impairment, and fatigue. A distinct storm of inflammatory factors that contribute to the initial disease but also a persistent post-acute phase syndrome has been reported in patients with COVID-19. Neuropsychological symptoms including depression, cognitive impairment, and fatigue are closely related to circulating and local (brain) inflammatory factors. Natural products are currently being examined for their ability to treat numerous complications caused by COVID-19. Among them, ginseng has anti-inflammatory, immune system stimulating, neuroendocrine modulating, and other effects, which may help improve psychiatric symptoms. This review summarizes the basic mechanisms of COVID-19 pneumonia, psychiatric symptoms following coronavirus infections, effects of ginseng on depression, restlessness, and other psychiatric symptoms associated with post-COVID syn-dromes, as well as possible mechanisms underlying these effects.

Inhibition of the NLRP3 Inflammasome Activation/Assembly through the Activation of the PI3K Pathway by Naloxone Protects Neural Stem Cells from Ischemic Condition

Naloxone is a well-known opioid antagonist and has been suggested to have neuroprotective effects in cerebral ischemia. We investigated whether naloxone exhibits anti-inflammatory and neuroprotective effects in neural stem cells (NSCs) injured by oxygen-glucose deprivation (OGD), whether it affects the NOD-like receptor protein 3 (NLRP3) inflammasome activation/assembly, and whether the role of the phosphatidylinositol 3-kinase (PI3K) pathway is important in the control of NLRP3 inflammasome activation/assembly by naloxone. Primary cultured NSCs were subjected to OGD and treated with different concentrations of naloxone. Cell viability, proliferation, and the intracellular signaling proteins associated with the PI3K pathway and NLRP3 inflammasome activation/assembly were evaluated in OGD-injured NSCs. OGD significantly reduced survival, proliferation, and migration and increased apoptosis of NSCs. However, treatment with naloxone significantly restored survival, proliferation, and migration and decreased apoptosis of NSCs. Moreover, OGD markedly increased NLRP3 inflammasome activation/assembly and cleaved caspase-1 and interleukin-1β levels in NSCs, but naloxone significantly attenuated these effects. These neuroprotective and anti-inflammatory effects of naloxone were eliminated when cells were treated with PI3K inhibitors. Our results suggest that NLRP3 inflammasome is a potential therapeutic target and that naloxone reduces ischemic injury in NSCs by inhibiting NLRP3 inflammasome activation/assembly mediated by the activation of the PI3K signaling pathway.

The effects of Korean Red Ginseng on heme oxygenase-1 with a focus on mitochondrial function in pathophysiologic conditions

Korean Red Ginseng (KRG) plays a key role in heme oxygenase (HO)-1 induction under physical and moderate oxidative stress conditions. The transient and mild induction of HO-1 is beneficial for cell protection, mitochondrial function, regeneration, and intercellular communication. However, chronic HO-1 overexpression is detrimental in severely injured regions. Thus, in a chronic pathological state, diminishing HO-1-mediated ferroptosis is beneficial for a therapeutic approach. The molecular mechanisms by which KRG protects various cell types in the central nervous system have not yet been established, especially in terms of HO-1-mediated mitochondrial functions. Therefore, in this review, we discuss the multiple roles of KRG in the regulation of astrocytic HO-1 under pathophysiological conditions. More specifically, we discuss the role of the KRG-mediated astrocytic HO-1 pathway in regulating mitochondrial functions in acute and chronic neurodegenerative diseases as well as physiological conditions.

Korean Red Ginseng-Induced SIRT3 Promotes the Tom22-HIF-1α Circuit in Normoxic Astrocytes

Astrocytes play a key role in brain functioning by providing energy to neurons. Increased astrocytic mitochondrial functions by Korean red ginseng extract (KRGE) have been investigated in previous studies. KRGE administration induces hypoxia-inducible factor-1α (HIF-1α) and vascular endothelial growth factor (VEGF) in astrocytes in the adult mouse brain cortex. VEGF expression can be controlled by transcription factors, such as the HIF-1α and estrogen-related receptor α (ERRα). However, the expression of ERRα is unchanged by KRGE in astrocytes of the mouse brain cortex. Instead, sirtuin 3 (SIRT3) expression is induced by KRGE in astrocytes. SIRT3 is a nicotinamide adenine dinucleotide (NAD+)-dependent deacetylase that resides in the mitochondria and maintains mitochondrial homeostasis. Mitochondrial maintenance requires oxygen, and active mitochondria enhance oxygen consumption, resulting in hypoxia. The effects of SIRT3 on HIF-1α-mediated mitochondria functions induced by KRGE are not well established. We aimed to investigate the relationship between SIRT3 and HIF-1α in KRGE-treated normoxic astrocyte cells. Without changing the expression of the ERRα, small interfering ribonucleic acid targeted for SIRT3 in astrocytes substantially lowers the amount of KRGE-induced HIF-1α proteins. Reduced proline hydroxylase 2 (PHD2) expression restores HIF-1α protein levels in SIRT3-depleted astrocytes in normoxic cells treated with KRGE. The translocation of outer mitochondrial membranes 22 (Tom22) and Tom20 is controlled by the SIRT3-HIF-1α axis, which is activated by KRGE. KRGE-induced Tom22 increased oxygen consumption and mitochondrial membrane potential, as well as HIF-1α stability through PHD2. Taken together, in normoxic astrocytes, KRGE-induced SIRT3 activated the Tom22-HIF-1α circuit by increasing oxygen consumption in an ERRα-independent manner.

Heme: The Lord of the Iron Ring

Heme is an iron-protoporphyrin complex with an essential physiologic function for all cells, especially for those in which heme is a key prosthetic group of proteins such as hemoglobin, myoglobin, and cytochromes of the mitochondria. However, it is also known that heme can participate in pro-oxidant and pro-inflammatory responses, leading to cytotoxicity in various tissues and organs such as the kidney, brain, heart, liver, and in immune cells. Indeed, heme, released as a result of tissue damage, can stimulate local and remote inflammatory reactions. These can initiate innate immune responses that, if left uncontrolled, can compound primary injuries and promote organ failure. In contrast, a cadre of heme receptors are arrayed on the plasma membrane that is designed either for heme import into the cell, or for the purpose of activating specific signaling pathways. Thus, free heme can serve either as a deleterious molecule, or one that can traffic and initiate highly specific cellular responses that are teleologically important for survival. Herein, we review heme metabolism and signaling pathways, including heme synthesis, degradation, and scavenging. We will focus on trauma and inflammatory diseases, including traumatic brain injury, trauma-related sepsis, cancer, and cardiovascular diseases where current work suggests that heme may be most important.

An Altered Neurovascular System in Aging-Related Eye Diseases

The eye has a complex and metabolically active neurovascular system. Repeated light injuries induce aging and trigger age-dependent eye diseases. Damage to blood vessels is related to the disruption of the blood-retinal barrier (BRB), altered cellular communication, disrupted mitochondrial functions, and exacerbated aggregated protein accumulation. Vascular complications, such as insufficient blood supply and BRB disruption, have been suggested to play a role in glaucoma, age-related macular degeneration (AMD), and Alzheimer's disease (AD), resulting in neuronal cell death. Neuronal loss can induce vision loss. In this review, we discuss the importance of the neurovascular system in the eye, especially in aging-related diseases such as glaucoma, AMD, and AD. Beneficial molecular pathways to prevent or slow down retinal pathologic processes will also be discussed.

Induction of BVR-A Expression by Korean Red Ginseng in Murine Hippocampal Astrocytes: Role of Bilirubin in Mitochondrial Function via the LKB1–SIRT1–ERRα Axis

The beneficial effects of Korean red ginseng extract (KRGE) on the central nervous system (CNS) have been reported. Among the CNS cells, astrocytes possess robust antioxidative properties and regenerative potential. Under physiological conditions, biliverdin reductase A (BVR-A) converts biliverdin (a heme oxygenase metabolite) into bilirubin, a major natural and potent antioxidant. We found that KRGE enhanced BVR-A in astrocytes in the fimbria region of the adult mouse hippocampus under physiological conditions. KRGE-induced BVR-A expression and subsequent bilirubin production were required for changes in mitochondrial membrane potential, mitochondrial mass, and oxidative phosphorylation through liver kinase B1 (LKB1), estrogen-related receptor α (ERRα), and sirtuin (SIRT1 and SIRT5) in astrocytes. However, BVR-A did not affect the KRGE-induced expression of AMP-activated protein kinase α (AMPKα). The KRGE-stimulated BVR-A–LKB1–SIRT1–ERRα pathway regulates the levels of mitochondria-localized proteins such as SIRT5, translocase of the outer mitochondrial membrane 20 (Tom20), Tom22, cytochrome c (Cyt c), and superoxide dismutase 2 (SOD2). Increased Tom20 expression in astrocytes of the hippocampal fimbria region was observed in KRGE-treated mice. KRGE-induced expression of Cyt c and SOD2 was associated with the Tom20/Tom22 complex. Taken together, KRGE-induced bilirubin production is required for enhanced astrocytic mitochondrial function in an LKB1-dependent and AMPKα-independent manner under physiological conditions.

Therapeutic Application of Stem Cells in the Repair of Traumatic Brain Injury

Traumatic brain injury is the main cause of injury-related deaths and disabilities throughout the world, which is characterized by a disruption of the normal physiology of the brain following trauma. It can potentially cause severe complications such as physical, cognitive, and emotional impairment. In addition to understanding traumatic brain injury pathophysiology, this review explains the therapeutic potential of stem cells following brain injury in two pathways: response of endogenous neurogenic cells and transplantation of exogenous stem cell therapy. After traumatic brain injuries, clinical evidence indicated that endogenous neural progenitor cells might play an important role in regenerative medicine to treat brain injury. This is due to an increased neurogenic regeneration ability of these cells following brain injury. Besides, exogenous stem cell transplantation has also accelerated immature neuronal development and increased endogenous cellular proliferation in the damaged brain region. Therefore, a better understanding of the endogenous neural stem cell’s regenerative ability and the effect of exogenous stem cells on proliferation and differentiation ability may help researchers to understand how to increase functional recovery and tissue repair following injury.

Beneficial and Detrimental Roles of Heme Oxygenase-1 in the Neurovascular System

Heme oxygenase (HO) has both beneficial and detrimental effects via its metabolites, including carbon monoxide (CO), biliverdin or bilirubin, and ferrous iron. HO-1 is an inducible form of HO that is upregulated by oxidative stress, nitric oxide, CO, and hypoxia, whereas HO-2 is a constitutive form that regulates vascular tone and homeostasis. In brains injured by trauma, ischemia-reperfusion, or Alzheimer’s disease (AD), the long-term expression of HO-1 can be detected, which can lead to cytotoxic ferroptosis via iron accumulation. In contrast, the transient induction of HO-1 in the peri-injured region may have regenerative potential (e.g., angiogenesis, neurogenesis, and mitochondrial biogenesis) and neurovascular protective effects through the CO-mediated signaling pathway, the antioxidant properties of bilirubin, and the iron-mediated ferritin synthesis. In this review, we discuss the dual roles of HO-1 and its metabolites in various neurovascular diseases, including age-related macular degeneration, ischemia-reperfusion injury, traumatic brain injury, Gilbert’s syndrome, and AD.