Regulatory effects of dihydrolipoic acid against inorganic mercury-mediated cytotoxicity and intrinsic apoptosis in PC12 cells

Antioxidant dihydrolipolic acid protects against in vitro aluminum-induced toxicity

Dihydrolipoic acid (DHLA) is a natural antioxidant known for its ability to counteract metal toxicity and oxidative stress. It has shown the potential to safeguard cells from harmful environmental substances. It may hold therapeutic benefits in treating neurodegenerative disorders by defending against oxidative damage and chronic inflammation. Thus, this study aimed to explore the potential neuroprotective effects of DHLA against aluminum (Al)-induced toxicity using an Alzheimer's disease (AD) model in vitro. The study focused on two important pathways: GSK-3β and the Wnt signaling pathways. The SH-SY5Y cell line was differentiated to establish AD, and the study group were as follows: control, Al, DHLA, Al-DHLA, AD, AD-Al, AD-DHLA, and AD-Al-DHLA. The impact of DHLA on parameters related to oxidative stress was assessed. The activity of the GSK-3β pathway was measured by evaluating the levels of PPP1CA, PP2A, GSK-3β, and Akt. The Wnt signaling pathway was assessed by measuring Wnt/β-catenin in the different study groups. Exposure to DHLA significantly reduced oxidative stress by effectively decreasing the levels of reactive oxygen species, thereby protecting against protein oxidation and limiting the production of malonaldehyde. Moreover, the DHLA-treated groups exhibited a remarkable increase in the total antioxidant capacity. Furthermore, the study observed an upregulation of the Wnt signaling pathway and a downregulation of the GSK-3β pathway in the groups treated with DHLA. In summary, the neuroprotective effects of DHLA, primarily achieved by reducing oxidative stress and modulating critical imbalanced pathways associated with AD, indicate its potential as a promising addition to the treatment regimens of AD patients.

Antioxidant Supplementation Alleviates Mercury-Induced Cytotoxicity and Restores the Implantation-Related Functions of Primary Human Endometrial Cells

Mercury (Hg) cytotoxicity, which is largely mediated through oxidative stress (OS), can be relieved with antioxidants. Thus, we aimed to study the effects of Hg alone or in combination with 5 nM N-Acetyl-L-cysteine (NAC) on the primary endometrial cells' viability and function. Primary human endometrial epithelial cells (hEnEC) and stromal cells (hEnSC) were isolated from 44 endometrial biopsies obtained from healthy donors. The viability of treated endometrial and JEG-3 trophoblast cells was evaluated via tetrazolium salt metabolism. Cell death and DNA integrity were quantified following annexin V and TUNEL staining, while the reactive oxygen species (ROS) levels were quantified following DCFDA staining. Decidualization was assessed through secreted prolactin and the insulin-like growth factor-binding protein 1 (IGFBP1) in cultured media. JEG-3 spheroids were co-cultured with the hEnEC and decidual hEnSC to assess trophoblast adhesion and outgrowth on the decidual stroma, respectively. Hg compromised cell viability and amplified ROS production in trophoblast and endometrial cells and exacerbated cell death and DNA damage in trophoblast cells, impairing trophoblast adhesion and outgrowth. NAC supplementation significantly restored cell viability, trophoblast adhesion, and outgrowth. As these effects were accompanied by the significant decline in ROS production, our findings originally describe how implantation-related endometrial cell functions are restored in Hg-treated primary human endometrial co-cultures by antioxidant supplementation.

Role of Reactive Oxygen Species in Aging and Age-Related Diseases: A Review

Research on the role of reactive oxygen species (ROS) in the aging process has advanced significantly over the last two decades. In light of recent findings, ROS takes part in the aging process of cells along with contributing to various physiological signaling pathways. Antioxidants being cells' natural defense mechanism against ROS-mediated alteration, play an imperative role to maintain intracellular ROS homeostasis. Although the complete understanding of the ROS regulated aging process is yet to be fully comprehended, current insights into various sources of cellular ROS and their correlation with the aging process and age-related diseases are portrayed in this review. In addition, results on the effect of antioxidants on ROS homeostasis and the aging process as well as their advances in clinical trials are also discussed in detail. The future perspective in ROS-antioxidant dynamics on antiaging research is also marshaled to provide future directions for ROS-mediated antiaging research fields.

Amelioration of Metal-Induced Cellular Stress by α-Lipoic Acid and Dihydrolipoic Acid through Antioxidative Effects in PC12 Cells and Caco-2 Cells

α-Lipoic acid (ALA) and its reduced form dihydrolipoic acid (DHLA) are endogenous dithiol compounds with significant antioxidant properties, both of which have the potential to detoxify cells. In this study, ALA (250 μM) and DHLA (50 μM) were applied to reduce metal (As, Cd, and Pb)-induced toxicity in PC12 and Caco-2 cells as simultaneous exposure. Both significantly decreased Cd (5 μM)-, As (5 μM)-, and Pb (5 μM)-induced cell death. Subsequently, both ALA and DHLA restored cell membrane integrity and intracellular glutathione (GSH) levels, which were affected by metal-induced toxicity. In addition, DHLA protected PC12 cells from metal-induced DNA damage upon co-exposure to metals. Furthermore, ALA and DHLA upregulated the expression of survival-related proteins mTOR (mammalian target of rapamycin), Akt (protein kinase B), and Nrf2 (nuclear factor erythroid 2-related factor 2) in PC12 cells, which were previously downregulated by metal exposure. In contrast, in Caco-2 cells, upon co-exposure to metals and ALA, Nrf2 was upregulated and cleaved PARP-1 (poly (ADP-ribose) polymerase-1) was downregulated. These findings suggest that ALA and DHLA can counterbalance the toxic effects of metals. The protection of ALA or DHLA against metal toxicity may be largely due to an enhancement of antioxidant defense along with reduced glutathione level, which ultimately reduces the cellular oxidative stress.

Zinc-pretreatment triggers glutathione and Nrf2-mediated protection against inorganic mercury-induced cytotoxicity and intrinsic apoptosis in PC12 cells

Mercury (Hg) is a hazardous metal, poses environmental problems with severe human health effects; whereas zinc (Zn) is an essential micronutrient with antioxidant properties. The purpose of this research was to investigate the effect of Zn on inorganic Hg-induced cytotoxicity in the PC12 cells. The cells were treated with HgCl₂ (5 μM) for 48 h with/without 1 h prior ZnCl₂-treatment (100 μM) and deliberated for further analysis. After 48 h of incubation with only Hg²⁺, the cell showed reduced cell viability, compromised cell membrane, DNA degradation, depleted glutathione level, ROS generation and drastically increased apoptosis. Subsequently, Hg²⁺-treated cells demonstrated a significant downregulation of akt, mTOR, ERK1, Nrf2, HO1, Bcl-2, Bcl-xL, and upregulation of p53, Bax, cytochrome c and cleaved caspase 3, indicating intrinsic apoptosis induction. However, cells pretreated with Zn²⁺ before Hg²⁺-exposure showed a significant improvement in cell viability, cell membrane, DNA damage, glutathione level, ROS amount and apoptotic cells, with a significant upregulation in mTOR, akt, ERK1, Nrf2, HO1, Bcl-2 and Bcl-xL, and downregulation in p53, Bax, cytochrome c and cleaved caspase 3, indicating inhibition of apoptosis. The findings suggested that Zn²⁺-pretreatment not only improves glutathione content but also induces activation of Nrf2-HO1 pathway, which would tend to suppress Hg-cytotoxicity.

Selenium modulates inorganic mercury induced cytotoxicity and intrinsic apoptosis in PC12 cells

Mercury (Hg) in its all forms, including inorganic Hg (iHg) is an environmental contaminant due to toxicity and diseases in human. However, a little is known about the underlying mechanisms responsible for iHg toxicity. Selenium (Se) is an essential trace element, recognized as an antioxidant and protective agent against metal toxicities. The purpose of this research was to investigate ameliorations of Se counter to iHg-mediated toxicity in PC12 cells. Cytotoxic assays have been shown that iHg (5 μM) caused oxidative stress and intrinsic apoptosis via ROS generation, oxidizing glutathione, damaging DNA, degrading cell membrane integrity, down-regulating mTOR, p-mTOR, akt and ERK1, and up-regulating cleaved caspase 3 and cytochrome c release in PC12 cells 48 h after incubation. Co-treatment of Se (5 μM) inhibited intrinsic apoptosis and oxidative stress induced by iHg (5 μM) via inhibiting ROS formation, boosting GPx contents, increasing reduced glutathione, limiting DNA degradation, improving cell membrane integrity, up-regulating mTOR, p-mTOR, akt, ERK1 and caspase 3, and down-regulating cleaved caspase 3 and cytochrome c leakage in PC12 cells. In conclusion, these results recommended that excessive ROS generation acts a critical role in iHg-influenced oxidative stress and co-treatment of Se attenuates iHg-cytotoxicity through its antioxidant properties.

Amelioration of butylated hydroxytoluene against inorganic mercury induced cytotoxicity and mitochondrial apoptosis in PC12 cells via antioxidant effects

Mercury (Hg) is a toxic metal, well-known for its dangerous health effects on human. Butylated hydroxytoluene (BHT) is a phenolic component generally consumed as a food additive as an antioxidant. However, BHT induced antioxidant properties against heavy metals-influenced toxicity are little studied. We hypothesized that BHT has a regulatory effect on Hg-induced cytotoxicity. The objective of this research was to assess the protecting effects of BHT against inorganic Hg (iHg)-toxicity in PC12 cells, where cells were treated with/without HgCl₂ (Hg²⁺) (5 μM) and BHT (100 μM) for 48 h and analyzed further. Cells treated by Hg caused a significant cell viability reduction, membrane damage, glutathione reduction, DNA fragmentation, ROS generation, with suppressed expressions of akt, mTOR, ERK1, Nrf2 and HO1; and elevated apoptotic expressions of p53, Bax, cytochrome c and active caspase 3. However, BHT and Hg²⁺ co-exposure showed prevention against Hg²⁺-toxicity by improving GSH content and inhibiting ROS generation and oxidative stress mediated damages. Additionally, BHT co-treatment inverted the pro-apoptotic proteins by augmenting pro-survival regulatory proteins akt, mTOR, ERK1, Nrf2 and HO1. These findings proved that BHT inhibits Hg²⁺-toxicity, hindering ROS generation and intrinsic apoptosis, via enhancing glutathione and antioxidants; and suggested BHT implications as therapeutic.