Mechanism of the toxicity induced by natural humic acid on human vascular endothelial cells

Subcomponents in humic acid structure contribute to the differential responses of Aspergillus oryzae strains to humic acid

Humic acid (HA) is a complex natural organic macromolecule, can be decomposed to low-molecular compounds by some soil fungi and then influences the growth of fungi. Aspergillus oryzae is a fungus domesticated from its ancestor, which was supposed to live in soil. Group 3 strains of A. oryzae hold fewer aflatoxin-biosynthetic genes than group 1 strains and may differently response to HA because of the deletion of some genes along with the domestication. However, effect of HA on growth of A. oryzae group 1 and group 3 strains remains unclear. In this study, four strains of A. oryzae in group 1 and four in group 3 were point inoculated on equivalent medium (pH 7.3) with two commercially available HAs. The growth of RIB40 was the most stimulated among group 1 strains and that of RIB143 was the most inhibited among group 3 strains. To identify the basis of these differences, we examined the possible effects of HA subcomponents including polyphenol and minerals on the growth of RIB40 and RIB143. Polyphenol represented by gallic acid (GA), a partial structure common with model HA, and mineral ions including Al 3+ , Ca 2+ , Ti 4+ , Mn 2+ , Sr 2+ , and Ba2+ contributed to stimulating the growth of RIB40, whereas these components generally did not affect the growth of RIB143. Thus, our findings indicate that the sub-compositions of HAs, including GA and several minerals, were the main factors driving the different responses of RIB40 and RIB143 to HAs.

Responses of hepatic biotransformation and antioxidant enzymes in Japanese medaka (Oryzias latipes) exposed to humic acid

Humic substances, a major component of natural organic matter in surface waters, can induce biotransformation enzyme activities and influence antioxidant defense in fish. The study aimed to provide a molecular basis for the stress responses, the synthesis of biotransformation, and antioxidant enzymes in particular. Adult medaka fish (Hd-rR strain) were exposed to environmentally relevant concentrations of humic acid for 96 h. The actual humic acid concentrations in water were determined photometrically and expressed as organic carbon concentrations. Liquid chromatography with tandem mass spectrometry was used for protein profile analysis of medaka liver samples. The relative amount of isozymes was determined using the label-free quantification approach. Hepatic biotransformation enzyme activities were measured as well. Thus, ethoxyresorufin-O-deethylase activity showed a pronounced induction at the highest tested concentration (9.4 mg C/L). Various biotransformation and antioxidant isozymes responded to humic acid differently, reflecting a balanced interplay of proteins that ensures the metabolism of humic acid in fish liver. Some isozymes were not affected by humic acid. The study provides new insight into the molecular mechanisms of the fish stress response to the humic acid-related challenge.

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.

A Comprehensive Toxicological Assessment of Fulvic Acid

Fulvic acid (FA), a humic substance, has several nutraceutical properties, including anti-inflammation, antimicrobial, and immune regulation abilities. However, systematic safety assessment remains insufficient. In the present study, a battery of toxicological studies was conducted per internationally accepted standards to investigate the genotoxicity and repeated-dose oral toxicity of FA. Sprague-Dawley (SD) rats or ICR mice were used. Compared to the control group, there were no significant changes (all p > 0.05) in all FA treatment groups in the bacterial reverse mutation test, in vitro mammalian chromosome aberration test, in vivo sperm shape abnormality assay, and in vivo mouse micronucleus assay. The acute toxicity test showed that no mortality or toxic effect was observed following oral administration of the maximum dose of 5,000 mg/kg BW/day to mice or rats. A 60-day subchronic study was conducted at 0 (control), 200, 1,000, and 5,000 mg/kg/day. Compared to the control group, there were no significant changes (all p > 0.05) in the body weights, feed consumption, clinical signs, hematology, clinical chemistry, organ weights, or histopathology examinations. In conclusion, the no-observed-adverse-effect-level (NOAEL) of FA supplementation from the 60-day study was determined to be 5,000 mg/kg body weight/day, the highest dose tested. Our findings suggest that the oral administration of FA may have higher safety.

Analysis of Cadmium, Epigallocatechin Gallate, and Vitamin C Co-exposure on PC12 Cellular Mechanisms

Exposure to cadmium (Cd) is a risk factor to health impairments, wherein its cytotoxicity is attributed to induction of oxidative stress. Usage of anti-oxidants, however, can help lessen the damaging effects of Cd. The effect of Cd interaction with low concentration of dietary anti-oxidants, L-ascorbic acid and (-)-epigallocatechin gallate (EGCG), to PC12 cellular mechanisms was examined. The expected toxicity of Cd was observed on PC12 cells but addition of L-ascorbic acid ameliorated this effect. On the other hand, addition of EGCG was able to increase the cytotoxicity of Cd and to decrease the protective effect of L-ascorbic acid against Cd. Increase in LDH activity and decrease in free sulfhydryl levels indicated cell membrane damage and oxidative stress, respectively, in Cd- and EGCG-Cd-treated cells. Downregulation of pro-apoptotic proteins (pro-caspase-9, p53, and ERK1) was observed in cells treated with Cd alone and EGCG-Cd, while upregulation of autophagy-linked proteins (p62 and pBeclin1) was found on L-ascorbic acid-Cd combination treatments. These findings indicate that Cd causes cells to undergo an autophagy-enhanced cell death; low-concentration EGCG and L-ascorbic acid promotes cell survival individually; however, interaction of EGCG with Cd showed enhancement of Cd toxicity and antagonism of L-ascorbic acid efficiency.

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.

Curcumin alleviates arsenic-induced toxicity in PC12 cells via modulating autophagy/apoptosis

Arsenic is a recognized highly toxic contaminant, responsible for numerous human diseases and affecting many millions of people in different parts of the world. Contrarily, curcumin is a natural dietary polyphenolic compound and the main active ingredient in turmeric. Recently it has drawn great attention due to its diverse biological activities, strong antioxidant properties and therapeutic potential against many human ailments. In this study, we aimed to explore the protective effects and the regulatory role of curcumin on arsenic-induced toxicity and gain insights into biomolecular mechanism/s. Arsenic (10 μM) treatment in PC12 cells for 24 h induced cytotoxicity by decreasing cell viability and intracellular glutathione level and increasing lactate dehydrogenase activity and DNA fragmentation. In addition, arsenic caused apoptotic cell death in PC12 cells, which were confirmed from flow cytometry results. Moreover, arsenic (10 μM) treatment significantly down-regulated the inhibition factors of autophagy/apoptosis; mTOR, Akt, Nrf2, ERK1, Bcl-x, Xiap protein expressions, up-regulated the enhanced factors of autophagy/apoptosis; ULK, LC3, p53, Bax, cytochrome c, caspase 9, cleaved caspase 3 proteins and eventually caused autophagic and apoptotic cell death. However, curcumin (2.5 μM) pretreatment with arsenic (10 μM) effectively saves PC12 cells against arsenic-induced cytotoxicity through increasing cell viability, intracellular GSH level and boosting the antioxidant defense system, and limiting the LDH activity and DNA damage. Furthermore, pretreatment of curcumin with arsenic expressively alleviated arsenic-induced toxicity and cell death by reversing the expressions of proteins; mTOR, Akt, Nrf2, ERK1, Bcl-x, Xiap, ULK, LC3, p53, Bax, cytochrome c, caspase 9 and cleaved caspase 3. Our findings indicated that curcumin showed antioxidant properties through the Nrf2 antioxidant signaling pathway and alleviates arsenic-triggered toxicity in PC12 cells by regulating autophagy/apoptosis.

Investigating the protective actions of D-pinitol against arsenic-induced toxicity in PC12 cells and the underlying mechanism

Arsenic is awfully toxic metalloid responsible for many human diseases all over the world. Contrastingly, D-pinitol is a naturally occurring bioactive dietary compound has antioxidant properties. The objective of this study is to elucidate the protective actions of D-pinitol on arsenic-induced cytotoxicity and explore its controlling role in biomolecular mechanisms in PC12 cells. Obtained results demonstrated that co-exposure of D-pinitol with arsenic increases cell viability, decreases DNA damage and protects PC12 cells from arsenic-induced cytotoxicity by increasing glutathione (GSH) level and glutathione reductase (GR). Protein expression of western blot analysis showed that co-exposure of D-pinitol and arsenic significantly inhibited arsenic-induced autophagy which further suppressed apoptosis through up-regulation of survival factors; mTOR, p-mTOR, Akt, p-Akt, NF-кB, Nrf2, ERK1, GR, Bcl-x and down-regulation of death factors; p53, Bax, cytochrome c, LC3, although arsenic regulated those factors negatively. These results of this study suggested that D-pinitol protects PC12 cells from arsenic-induced cytotoxicity.

Responsive agarose hydrogel incorporated with natural humic acid and MnO2nanoparticles for effective relief of tumor hypoxia and enhanced photo-induced tumor therapy

In spite of widespread applications of nano-photosensitizers, poor tumor penetration and severe hypoxia in the tumor microenvironment (TME) always result in an undesirable therapeutic outcome of photodynamic therapy (PDT).

Selenium Analysis and Speciation in Dietary Supplements Based on Next-Generation Selenium Ingredients

Selenium is essential for humans and the deficit of Se requires supplementation. In addition to traditional forms such as Se salts, amino acids, or selenium-enriched yeast supplements, next-generation selenium supplements, with lower risk for excess supplementation, are emerging. These are based on selenium forms with lower toxicity, higher bioavailability, and controlled release, such as zerovalent selenium nanoparticles (SeNPs) and selenized polysaccharides (SPs). This article aims to focus on the existing analytical systems for the next-generation Se dietary supplement, providing, at the same time, an overview of the analytical methods available for the traditional forms. The next-generation dietary supplements are evaluated in comparison with the conventional/traditional ones, as well as the analysis and speciation methods that are suitable to reveal which Se forms and species are present in a dietary supplement. Knowledge gaps and further research potential in this field are highlighted. The review indicates that the methods of analysis of next-generation selenium supplements should include a step related to chemical species separation. Such a step would allow a proper characterization of the selenium forms/species, including molecular mass/dimension, and substantiates the marketing claims related to the main advantages of these new selenium ingredients.

Ameliorative effects of selenium on arsenic-induced cytotoxicity in PC12 cells via modulating autophagy/apoptosis

Arsenic is well known toxicant responsible for human diseases including cancers. On the other hand, selenium is an essential trace element with significant chemopreventive effects, anticancer potentials and antioxidant properties. Although previous studies have reported antagonism/synergism between arsenic and selenium in biological systems, the biomolecular mechanism/s is still inconclusive. Therefore, to elucidate the molecular phenomena in cellular level, we hypothesized that co-exposure of selenium with arsenic may have suppressive effects on arsenic-induced cytotoxicity. We found that selenium in co-exposure with arsenic increases cell viability, and suppresses oxidative stress induced by arsenic in PC12 cells. Consequently, DNA fragmentation due to arsenic exposure was also reduced by arsenic and selenium co-exposure. Furthermore, western blot analyses revealed that simultaneous exposure of both metals significantly inhibited autophagy which further suppressed apoptosis through positively regulation of key proteins; p-mTOR, p-Akt, p-Foxo1A, p62, and expression of ubiquitin, Bax, Bcl2, NFкB, and caspases 3 and 9, although those are negatively regulated by arsenic. In addition, reverse transcriptase PCR analysis confirmed the involvement of caspase cascade in cell death process induced by arsenic and subsequent inhibition by co-exposure of selenium with arsenic. The cellular accumulation study of arsenic in presence/absence of selenium via inductively coupled plasma mass spectrometry confirmed that selenium effectively retarded the uptake of arsenic in PC12 cells. Finally, these findings imply that selenium is capable to modulate arsenic-induced intrinsic apoptosis pathway via enhancement of mTOR/Akt autophagy signaling pathway through employing antioxidant potentials and through inhibiting the cellular accumulation of arsenic in PC12 cells.

Humic acid induces the endothelial nitric oxide synthase phosphorylation at Ser1177 and Thr495 Via Hsp90α and Hsp90β upregulation in human umbilical vein endothelial cells

Humic acid (HA) has been implicated as a contributory factor for blackfoot disease, which is an endemic peripheral vascular disease. We investigated the effect of HA on the regulation of endothelial nitric oxide (NO) synthase (eNOS) in human umbilical vein endothelial cells (HUVECs) to evaluate the involvement of eNOS and related factors in peripheral vascular impairment with HA exposure. Treatment of HUVECs with HA induced upregulation of eNOS. This result coincides with those of previous studies. Furthermore this is the first study to report that HA induces upregulation of heat shock protein (Hsp)90α, Hsp90β, eNOS phosphorylation at Ser1177, and eNOS phosphorylation at Thr495, as compared to that in the control. In contrast, treatment with BAPTA, an intracellular Ca(2+) chelator, inhibited upregulation of these proteins induced by HA. This study demonstrates that HA treatment leads to increases in both Hsp90α and Hsp90β proteins and indicates that Hsp90α leads to eNOS phosphorylation at Ser1177 and that Hsp90β leads to eNOS phosphorylation at Thr495, respectively. Upregulation of eNOS, Hsp90α, and Hsp90β in HUVECs is regulated by intracellular Ca(2+) accumulation induced by HA. These results suggest that upregulation of eNOS phosphorylation at Ser1177 and eNOS phosphorylation at Thr495 produce NO and superoxide anions, respectively, resulting in generation of peroxynitrite, which causes impairment of vascular endothelial cells.