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. 2023 Jan 31;12(1):124–132. doi: 10.1093/toxres/tfad005

Taurine protects against perfluorooctanoic acid-induced hepatotoxicity via inhibition of oxidative stress, inflammatory, and apoptotic pathways

Maloos Naderi 1,2, Mohammad Seyedabadi 3,4, Fereshteh Talebpour Amiri 5, Ebrahim Mohammadi 6, Sholeh Akbari 7,8, Fatemeh Shaki 9,10,✉
PMCID: PMC9972835  PMID: 36866213

Abstract

We are constantly encountering with low doses of chemicals in everyday life rather than toxic doses at a time. So, ongoing low-dose exposures of environmental chemicals commonly encountered are very likely to cause an adverse health effects. Perfluorooctanoic acid (PFOA) is frequently used for production of an array of consumer products and industrial processes. The present study evaluated the underlying mechanisms of PFOA-induced liver damage and also potential protection by taurine. Male Wistar rats were exposed to PFOA alone and in combination with taurine (25, 50, and 100 mg/kg/day) by gavage for 4 weeks. Liver function tests as well as histopathological examinations were studied. Also, oxidative stress markers, mitochondrial function, and nitric oxide (NO) production in liver tissues were measured. In addition, the expression of apoptosis-related genes (caspase-3, Bax, and Bcl-2), inflammation-associated genes (TNF-α, IL-6, NF-Inline graphicB), and c-Jun-N-terminal kinase (JNK) were evaluated. Taurine significantly reversed serum biochemical and histopathological alterations in the liver tissue following exposure to PFOA (10 mg/kg/day). Similarly, taurine alleviated mitochondrial oxidative damage-induced by PFOA in the liver tissue. An increased Bcl2: Bax ratio with decrees in the expression level of caspase-3, and decreased expression of inflammatory markers (TNF-α and IL-6), NF-Inline graphicB, and JNK were also observed following the administration of taurine. These findings suggest a protective role of taurine against PFOA-induced hepatotoxicity via the inhibition of oxidative stress, inflammation, and apoptosis.

Keywords: perfluorooctanoic acid, taurine, oxidative stress, apoptosis, inflammation, hepatotoxicity

Graphical abstract

Graphical Abstract.

Graphical Abstract

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Introduction

Every day, people are in contact with hundreds of potentially toxic chemicals in the environment that cause health risk.1 Although the majority of toxicology studies include a single chemical with predictable toxic concentrations, we are constantly exposed to low doses of these substances in everyday life rather than toxic doses at a time. So, ongoing low-dose exposures to these environmental chemicals are prone to cause adverse health effects.2

Perfluorooctanoic acids (PFOAs) are one of the potentially toxic chemicals we are exposed to every day. It has been used in a wide range of consumer products, such as Teflon and Gore-Tex.3 It is used in paints, as additives in photographic films, and the textile finishing industry.4 Because of unique properties such as resistance to grease, oil, water, and heat, it can be helpful in the production of commercial product including packaging, coating materials, cleaning agents, and firefighting foams.5 The public concern about adverse health outcomes of PFOA in humans has been rising in the last decades. Because of its strong carbon-fluorine bonds and half-life of several years, it is not metabolized and is resistant to biodegradation, and thereby can accumulate in the human body.6 Notably, long-term exposure to PFOA, even at relatively low concentrations, can result in irreversible liver failure. Previous studies confirmed that exposure to PFOA leads to a variety of toxicities.7 Indeed, liver is the main target tissue for perfluoroalkyl acid-induced toxicity.8 But the exact mechanisms have not yet been fully understood.

Oxidative stress is an impairment in redox balance between the pro-oxidant and anti-oxidant systems in the body.9 Mitochondria is the direct affected organelle of environmental contaminants. So, any disturbances in the mitochondrial electron transport chain can result in excessive reactive oxygen specious (ROS) production and loss of mitochondrial membrane potential (MMP), triggering the apoptotic pathways.10 In this regard, PFOA increased ROS generation and mitochondrial oxidative damage. In addition, PFOA exposure is reported to increase the production of the pro-inflammatory cytokines, IL-6 and TNF-α.8,11,12 A variety of toxic and pro-inflammatory stimuli including oxygen free radicals can activate the nuclear factor-kappa B (NF-Inline graphicB) transcription factor, which, in turn, promotes the transcription of pro-inflammatory genes.13 Of particular note, NF-Inline graphicB is linked with a variety of inflammatory and cytotoxic signaling pathways including c-Jun-N-terminal kinase (JNK), AP1, TNF-α, IL-1, IL6, etc.14–17

Evidence strongly suggests that the anti-oxidant-rich diet can help reduce the potentially toxic effects of environmental pollutants. In this regard, taurine (2-aminoethanesulfonic acid), the most abundant intracellular amino acid, has several biological properties such as cytoprotective, anti-oxidant, and anti-inflammatory activities.18 It can also stabilize membranes of biological system, and reduce the water influx and excessive leakage of calcium ion, ultimately preventing osmotic cell swelling and apoptosis.19 Taurine exerts its cytoprotective effects via the inhibition of ROS, scavenging of H2O2 and hydroxyl radicals, reduction of superoxide and lipid peroxidation products, chelation of Fe2+ ions and attenuation of iron-induced oxidative stress, stabilization of the electron transport chain, improvement of mitochondrial function, and inhibition of apoptosis.19–22

This study aimed to evaluate the underlying mechanism of PFOA-induced liver damage as well as potential effects of taurine on this process in male rats.

Materials and methods

Animal treatment and experimental design

PFOA (96%) and taurine were purchased from Sigma Aldrich (St Louis, MO, USA). PFOA dissolved in water and administered by gavage at three different doses (5, 10, and 20 mg/kg), based on previous studies8,23–25 and then a toxicity test was performed to determine the lowest dose that caused toxicity with a significant change in all factors. Finally, PFOA, at a dose of 10 mg/kg, was determined in pre-tests. The dose of vitamin C26 and taurine27 used in this study was determined based on previous studies. Taurine and vitamin C was suspended in water and administered by gavage for 1 h before PFOA administration. Male Wistar rats (200–250 g) were kept in animal cages under standard laboratory conditions (temperature 22–25 °C, 12-h light–dark cycles) with free access to food and water. All experimental procedures were approved by the ethical committee of our university.

Rats were randomly divided into seven groups (six rats in each), and treated once daily by gavage for 4 weeks: Group 1 (control group) received normal saline; Group 2 received taurine (100 mg/kg); Group 3 received PFOA (10 mg/kg); Groups 4–6 received PFOA (10 mg/kg) + a different dose of taurine (25, 50, and 100 mg/kg); Group 7 received PFOA (10 mg/kg) + vitamin C (100 mg/kg) as a positive control. At the end of 4 weeks of treatment, the animals were anesthetized by xylazine (5 mg/kg) and ketamine (80 mg/kg), and serum samples were collected for the liver function tests. The liver was separated, washed and divided in three parts. One part was fixed in formalin (10%) solution for histopathological examination. Another part required for the analysis of gene expression was kept at −80 °C in RNA protection solution (Yekatazist, Iran). The other part was homogenized, and then centrifuged at 2,000 g for 10 min. Supernatants were transferred to a new tube, and centrifuged again at 10,000 g for 10 min. The supernatants were used for oxidative stress assays in liver, and the precipitated mitochondria were suspended in Tris HCl buffer (0.05 M Tris HCl, 20 mM KCl, 2 mM MgCl2, .25 M sucrose, and 1 mM Na2HPO4, pH of 7.4) for mitochondrial function assay.

Serum biochemical evaluation

Serum activities of alanine transaminase (ALT) and aspartate aminotransferase (AST) were determined using commercial enzymatic kits (Pars Azmun, Iran) according to the manufacturers’ manual.

Histopathological examination

Liver specimens were fixed in a formalin (10% w/v) solution. After dehydrating in gradient alcohol, clarifying in xylene, and embedding in paraffin, tissue sections (5-μm-thick) were prepared, stained with hematoxylin and eosin (H&E), and evaluated under a light microscope. The degree of liver injury was determined. The sum of all manifestations was used for the final report as normal, mild, moderate, and severe liver damage.

Assessment of oxidative stress in liver tissue

First, the protein concentrations in liver were determined by the Bradford method.28The levels of ROS were evaluated using the dichlorodihydro-fluorescein diacetate (DCFH-DA) dye as an indicator.29 LPO concentration was evaluated according to the MDA formation, which was measured by reacting with thiobarbituric acid as an indicator of lipid peroxidation.30 Evaluation of protein carbonyl concentration was performed based on guanidine hydrochloride reagent.15 Reduced glutathione content was determined by Ellman’s method, using 2-nitrobenzoic acid (DTNB) as the indicator.31 SOD activity was determined based on the pyrogallol (1, 2, 3-trihydroxybenzene) method using a commercial kit (Navand Salamat Co, Iran).29 Nitric oxide (NO) was assayed based on the Griess reaction using a commercial kit (Cib Zist Fan Co., Iran).29

Assessment of mitochondrial function

Evaluation of mitochondrial viability

Mitochondrial viability was assayed using colorimetric assays using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT). This reaction was carried out based on the conversion of MTT into purple formazan crystals by mitochondrial succinate dehydrogenase enzyme. Then, purple formazan crystals were dissolved in 150–200 μl DMSO, and the absorbance was measured at 570 nm by ELISA reader (ELX800; BioTek, USA).29

Evaluation of the MMP

Mitochondrial uptake of rhodamine-123 as a cationic fluorescent dye was used to determine MMP. The fluorescence intensity of rhodamine was monitored using a fluorescence spectrophotometer (Shimadzu RF5000U) at the excitation and emission wavelengths of 490 and 535 nm, respectively.32

Evaluation of the mitochondrial swelling

The determination of mitochondrial swelling was performed through changes in light scattering as measured spectrophotometrically at 540 nm. A decrease in absorbance was accompanied by an increase in mitochondrial swelling.33

RNA extraction and real-time polymerase chain reaction (RT-PCR)

The total RNA was extracted from liver tissues using Hybrid-R™ total RNA isolation kit (Denazist, Iran). Briefly, 100 mg of each sample was grinded in liquid nitrogen, homogenized, lysed, and centrifuged. Tissue debris was discarded and the supernatant was mounted on silica spin columns. After centrifugation and washing stages, the RNA was eluted, and evaluated for its integrity, purity, and quantity on agarose gel electrophoresis and absorbance at 260/280/230 nm.34,35 cDNAs were synthesized from 500 ng of each RNA sample by a commercial kit (Parstoos, Iran). Specific primers and thermal profiles used are shown in Supplementary File. Real-time PCR was performed using Corbett Rotor-Gene 6000 (Qiagen, Germany). Threshold cycle of the target genes was normalized to glyceraldehyde-3-phosphate dehydrogenase (GAPDH) levels as the reference gene, and analyzed according to the 2−ΔΔCT method.15

Statistical analysis

Data are presented as the mean ± SD. The normality of data was evaluated by the Shapiro–Wilk test. One-way ANOVA followed by Tukey’s post-hoc was used for parametric variables, and Kruskal–Wallis H test was used for non-parametric data. Statistical analysis was accomplished using GraphPad Prism version 8, and P-values < 0.05 were considered significant.

Results

Serum biochemical evaluation

As shown in Table 1, administration of PFOA caused an increase in the AST and ALT levels by 53 and 19 U/L, respectively, in rats treated with PFOA (10 mg/kg) in comparison with the control group. On the other hand, taurine treatment at doses of 50 and 100 mg/kg as well as vitamin C significantly reverted this increase compared with the PFOA group.

Table 1.

Effect of taurine on liver enzymes.

Groups AST (U/L) ALT (U/L)
C
Tau (100 mg/kg)		 145 ± 9.2
142 ± 4.51		 6.3 ± 3.5
58.5 ± 1.52
PFOA(10 mg/kg) 198 ± 9.37### 79.3 ± 5.96###
PFOA+Tau (25 mg/kg) 194 ± 6.62### 76.2 ± 3.71###
PFOA+Tau (50 mg/kg) 177 ± 8.43**, ### 70.2 ± 3.71**,##
PFOA+Tau (100 mg/kg) 156 ± 8.25*** 64 ± 3.85***
PFOA+ vitamin C 178 ± 9.37**, ### 71.3 ± 3.83*, ###
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## P < 0.01, ###P < 0.001 significantly different from the control, and *P < 0.05, **P < 0.01 significantly different from PFOA groups

Histopathological observation

The photomicrographs of the liver are shown in Fig. 1. Normal liver architecture was observed in the control group, whereas PFOA-treated rats indicated significant histological alterations such as degenerative changes, eosinophilic cytoplasm in the hepatocytes, the presence of cells with hepatocyte nuclei in different sizes, abnormality of liver cords, cytoplasmic vacuolation, pyknosis, proliferation of Kupffer cells, inflammatory cells infiltration, hemorrhage, sinusoidal dilatation, and congestion. However, taurine administration mitigated the pathological changes caused by PFOA. Liver injury’s mean scores of all groups are shown in Fig. 2. The liver injury score increased in PFOA-treated rats. The score of liver injury was lower in the taurine plus PFOA group compared with the PFOA group.

Fig. 1.

Fig. 1

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Photomicrographs showed the effect of Tau (taurine) on histological architecture of liver in PFOA-treated rat: (A) C (control), (B) PFOA, (C) PFOA + Tau 50 mg/kg, (D) PFOA + Tau 100 mg/kg. Thick black arrow: Kupffer cell proliferation; red arrow: infiltration of inflammatory cell; blue arrow: hemorrhagic; thin black arrow: dilation of sinusoids; and green arrow: congestion. Treatment with Tau ameliorated these changes. H&E (mag: ×40). Scale bar =100 μm.

Fig. 2.

Fig. 2

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Liver injury scores in liver tissue. Data are presented as the mean ± SD. C (control), PFOA, and Tau (Taurine). The highest score belongs to the PFOA group. Tau was able to reduce the liver injury score in the PFOA+ Tau group. ##P < 0.01, ###P < 0.001 significantly different from the control, and *P < 0.05, **P < 0.01 significantly different from PFOA groups.

Assessment of oxidative stress in liver tissue

As shown in Table 2, exposure to PFOA caused a significant increase in ROS formation, MDA, protein carbonyl levels, NO concentration, whereas GSH content and SOD activity were decreased in comparison with the control group (P < 0.001). However, co-treatment with taurine especially at 50 and 100 mg/kg resulted in a significant decrease in ROS formation, MDA, protein carbonyl levels, NO concentration, and a marked increase in GSH content and SOD activity compared with the group receiving only PFOA. Also, vitamin C altered the above-mentioned factors except PrC levels. Treatment with taurine alone had no effect on above parameters compared with control.

Table 2.

Effects of taurine on biomarkers of oxidative stress and NO level in the liver tissue.

Groups ROS formation (fluorescence intensity) LPO (μmol/mg proteins) GSH (μmol/mg proteins) PrC (mmol/mg proteins) SOD activity (U/mg proteins) NO (nmol/ml)
C
Tau (100 mg/kg)		 49.9 ± 5.46
47.9 ± 9.41		 11.9 ± .78
11.8 ± .72		 207 ± 11.5
211 ± 9.9		 0.39 ± .03
.37 ± .05		 11.1 ± 1.14
11.3 ± .55		 34.6 ± 3.08
34 ± 4.36
PFOA (10 mg/kg) 92.5 ± 7.61### 18.8 ± .78### 178 ± 9.11### 0.59 ± .03### 7.78 ± .33### 71.4 ± 4.77###
PFOA+Tau (25 mg/kg) 79.6 ± 4.24*,### 17.4 ± .37*,### 196 ± 5.08* 0.54 ± .02### 8.92 ± .43### 68.7 ± 2.32###
PFOA+Tau (50 mg/kg) 67.6 ± 7.80***,### 15 ± .83***,### 203 ± 8.86*** 0.51 ± .04*,### 9.13 ± .68*,## 63.2 ± 3.11*,###
PFOA+Tau (100 mg/kg) 57.9 ± 5.57*** 12.9 ± .58*** 205 ± 9.25*** 0.49 ± .05**,## 10.1 ± .32*** 45.9 ± 4.47***,##
PFOA+ vitamin C 80.1 ± 5.45*,### 17 ± .81**,### 199 ± 9.42** 0.56 ± .03### 8.93 ± .57*,## 63.7 ± 3.92*,###
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## P < 0.01, ###P < 0.001 significantly different from the control, and *P < 0.05, **P < 0.01 significantly different from PFOA groups

Mitochondrial function assay

Mitochondrial viability

PFOA significantly decreased mitochondrial viability in liver in comparison with the control group (P < 0.001). Co-treatment with 50 and 100 mg/kg of taurine considerably attenuated PFOA-induced mitochondrial dysfunction compared with the PFOA group (P < 0.001). Furthermore, co-treatment with vitamin C increased mitochondrial viability compared with the PFOA group (Fig. 3A).

Fig. 3.

Fig. 3

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Effect of treatments on (A) mitochondrial function, (B) MMP, and (C) mitochondrial swelling in isolated liver mitochondria. C (control), PFOA, and Tau (Taurine). Data are expressed as the mean ± SD. ###P<0.001, in comparison with the control group. *P < 0.05, **P < 0.01, and ***P < 0.001, significantly different in comparison with the PFOA (10 mg/kg) group.

Mitochondrial membrane potential

PFOA significantly induced MMP collapse in comparison with the control group. However, taurine treatment at doses of 50 (P < 0.001) and 100 mg/kg (P < 0.001) as well as vitamin C (P < 0.01) significantly reversed MMP collapse caused by PFOA (Fig. 3B).

Mitochondrial swelling

Exposure to PFOA resulted in significant increase in mitochondrial swelling by 46% compared with the control group. However, co-treatment with taurine at doses of 50 (P < 0.01) and 100 mg/kg (P < 0.001) as well as vitamin C (P < 0.05) significantly prevented/decreased mitochondrial swelling in comparison with the PFOA group, as shown in Fig. 3C.

Gene expression

TNF-α, IL-6, NF-Inline graphicB, and JNK genes expression

According to gene expression analysis by RT-PCR, the expression of TNF-α, IL-6, NF-Inline graphicB, and JNK significantly elevated by 2.9, 2.6, 3.1, and 3.9 times, respectively, in rats treated with PFOA in comparison with the control group, whereas co-treatment with taurine at dose of 50 and 100 mg/kg as well as vitamin C markedly attenuated the increase of TNF-α, IL-6, NF-Inline graphicB, and JNK genes expression (P < 0.05) (Fig. 4). Also, taurine alone did not cause a significant difference in the expression of TNF-α, IL-6, NF-Inline graphicB, and JNK, compared with the control group.

Fig. 4.

Fig. 4

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Effect of treatments on (A) TNF-α, (B) IL-6, (C) NF-Inline graphicΒ, and (D) JNK gene expression in rat liver tissue. C (control), PFOA, and Tau (taurine). Data are expressed as the mean ± SD. #P < 0.05, ##P < 0.01, and ###P < 0.001, in comparison with the control group. *P < 0.05, **P < 0.01, and ***P < 0.001, significantly different in comparison with the PFOA (10 mg/kg) group.

Caspase-3, Bax, and Bcl-2 genes expression

According to the real-time PCR assay, PFOA treatment significantly increased the caspase-3 and Bax:Bcl2 expression in the liver of rats treated with PFOA compared to the control group. In particular, co-treatment with taurine at the dose of 50 and 100 mg/kg resulted in a decreased expression of caspase-3 and the lowest ratio of Bax:Bcl-2 (Fig. 5).

Fig. 5.

Fig. 5

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Effect of treatments on (A) Bax, (B) Bcl-2, and (C) caspase-3 gene expression in rat liver tissue. C (control), PFOA, and Tau (taurine). Data are expressed as the mean ± SD. #P < 0.05, ##P < 0.01, and ###P < 0.001, in comparison with the control group. *P < 0.05, **P < 0.01, and ***P < 0.001, significantly different in comparison with the PFOA (10 mg/kg) group.

Discussion

PFOA is a stable chemical used in several industrial processes.5 Due to its biological persistence, PFOA exposure is related to some of the diseases in humans, including hepatocellular damage.36 Notably, the liver is vulnerable to injury after exposure to xenobiotics because of its critical role in detoxification and metabolism. It has been reported that exposure to PFOA is related to hepatic injury in humans and animals.24,37

Taurine, an important amino acid, has several physiological and pharmacological roles, and its hepatoprotective effect has been confirmed in several experimental animals.38 It has been revealed that taurine is capable of preventing xenobiotic or chemical-induced hepatotoxicity. For instance, administration of taurine-attenuated iron-overload induced oxidative stress in liver.21

Vitamin C is a potent anti-oxidant, which is capable of scavenging free-radical and protecting cells against damage caused by radicals.39 The result of previous studies demonstrated the protective effect of vitamin C in CBZ, acetaminophen, and organophosphate-induced liver damage.39 This hepatoprotective effect of vitamin C can be explained by its anti-oxidant properties. It can mitigate the oxidative damage by decreasing lipid peroxidation. In addition, it prevents glutathione depletion and, therefore, improves the anti-oxidant defense.40 Previous in vivo studies demonstrated that vitamin C alleviated PFOA-induced hepatotoxicity via suppressing linoleic acid metabolism, reduced thiodiglycolic acid, and elevated glutathione in the liver. Thus, its protective role in PFOA-induced liver injury is clarified.41 So, considering the known anti-oxidant role of vitamin C in PFOA-induced hepatotoxicity, in this study, it was used as a control group to compare the protective effects of taurine in reducing liver toxicity caused by PFOA.

A significant increase in AST and ALT serum levels indicates hepatotoxicity following exposure to PFOA, which is consistent with previous reports.24 We observed more histopathological changes after treatment with PFOA compared with the control group. However, the increased levels of liver enzymes and histological alterations were considerably decreased by simultaneous treatment with taurine, suggesting a potential protective role of taurine against liver damage caused by PFOA. The increase of liver enzymes (Table 1) and histopathological injuries (Fig. 1) was significantly lower in rats co-treated with PFOA and taurine or PFOA and vitamin C compared with those receiving only PFOA, although they were still higher than that of the control group.

The role of oxidative stress in PFOA-induced liver cell injury was evidenced by increased ROS production,10 glutathione depletion,42 increased parameters of oxidative damage such as H2O2 and MDA, and reduced activities of endogenous anti-oxidants, for example, SOD and catalase.9,24 Our results indicated that PFOA administration provokes excessive ROS formation and also cellular damages by reaction with lipids and proteins. Free radical can trigger the oxidation of membrane lipids and form MDA as an oxidative damage marker.8 Protein carbonyl content is a reliable biomarker of protein oxidation induced by ROS.2 In the current study, we observed an increase in the PrC level of liver tissues upon PFOA exposure. Also, PFOA treatment resulted in a significant reduction in the activity of two key defense systems (GSH and SOD) that protect against oxidative stress. GSH is the main non-enzymatic anti-oxidant defense system that has multi-functions in cellular biology, including ROS scavenging.15 Also, its active thiol groups can directly interact with ROS or act as a cofactor for various enzymes.43 PFOA not only induced an increase in ROS production, MDA level, and protein carbonyl concentration, but also decreased the capacity of anti-oxidant systems, namely SOD and GSH. Taurine was capable of attenuating the oxidative effects of PFOA in the liver by the complete reversal of PFOA-effects on ROS formation, LPO, GSH content, and SOD activity. This was evident by reverting back to the normal levels of these variables. In contrast, protein carbonyl and NO content were still higher in rats co-treated with taurine and PFOA. In this regard, vitamin C was only capable of significant restoration of PFOA effects on GSH content. It was shown that taurine, at doses of 50 and 100 mg/kg, is more effective than vitamin C in restoring the above-mentioned parameter changes.

Mitochondrial dysfunction is a potential mechanism responsible for liver toxicity.10,33 Previous researches have established that PFOA can disturb the mitochondrial respiratory chain, which results in enhanced ROS production. On the other hand, ROS can induce oxidation of mitochondrial thiol groups, which leads to mitochondrial permeability transition (MPT) pores opening, disruption of MMP, and mitochondrial swelling. Also, opening of MPT pores causes cytochrome c release from mitochondria, which triggers the apoptotic pathway in the liver cells.10 It has been known that PFOA can cause cell death in other cells by ROS production and mitochondrial pathway.44 In this study, reduction of mitochondrial viability, increase of MMP collapse, and mitochondrial swelling were observed after PFOA treatment. We also noticed that taurine as well as vitamin C were capable of attenuating the MMP, mitochondrial swelling, and mitochondrial dysfunction. Albeit, they were still higher in rats co-treated with taurine and PFOA or vitamin C and PFOA compared with the control group. In this regard, taurine, at doses of 50 and 100, is more effective than vitamin C to reverse above changes caused by PFOA.

Pro- and anti-apoptotic members of the Bcl-2 family proteins, including Bax and Bcl-2, are two major modulators of the mitochondria-mediated pathway.45 Bax activation result in mitochondrial outer membrane permeabilization and the release of cytochrome c from the inter-membrane space into the cytoplasm that activates caspase 3, one of the major effectors of apoptosis, which indicates cell apoptosis.46 We also noted alterations in the expression of caspase-3, Bax, and Bcl-2, favoring an apoptotic signal in PFOA-treated animals, which agrees with the previous studies.44 These, however, were significantly restored by simultaneous treatment with taurine and PFOA. Taurine as well as vitamin C caused a complete reversal of PFOA effects on Bcl2. This was evident by reverting back to the normal level of this variable. But this restoration was partial for Bax and caspase-3 gene expression. Recent studies have reported that taurine increased Bcl-2 expression, whereas the expression of Bax and caspase 3 was decreased. This was correlated with the inhibition of ethanol-induced apoptosis in the liver.47 Obviously, taurine, especially at 100 mg/kg, could better protect against PFOA-induced apoptosis compared with vitamin C.

The NF-κB family of transcription factors plays a pivotal role in inflammation.33 This pathway is activated in cellular responses to different stimuli, such as signals related to pathogens, stress, and environmental changes.48 PFOA induces mast cell-mediated allergic inflammation through NF-κB activation and downstream pro-inflammatory cytokines.49 In contrast, taurine has been shown to improve alcohol-induced liver damage by reducing IkB/NF-κB signaling pathway.22 We found an increased expression of TNF-α, IL-6, and NF-κB gene transcripts in PFOA-treated animals. Meanwhile, taurine as well as vitamin C caused a complete reversal of PFOA effects on TNF-α and NF-κB, but this restoration was partial for IL-6 gene expression. Clearly, vitamin C and taurine had relatively similar effects in reducing inflammation caused by PFOA. This finding is consistent with previous reports in which taurine ameliorated liver fibrosis caused by thioacetamide in rats via mitigation of the toll-like receptor 4/NF-kB pathway.50

It is found that JNK plays different roles in the regulation of cell proliferation and survival. JNK was first considered as the protein triggered by stress and apoptosis-inducing factors.51 After activation, JNK regulates several biological functions via the activator protein-1 (AP-1) transcription factor.52 In fact, it stimulates c-Jun phosphorylation, accelerating its dimerization with c-Fos, which forms AP-1.53 We observed that PFOA markedly enhanced the expression of JNK. Whereas, taurine supplementation at dose of 100 mg/kg completely restored PFOA effect on JNK. In contrast, it was still higher in rats co-treated with vitamin C and PFOA compared to the control group. This demonstrates that taurine is more effective than vitamin C in restoring the effect of PFOA on JNK. In this regard, taurine has been shown to protect against acetaminophen-induced liver damage through inhibition of oxidative stress, JNK, NO, and TNF-α pathways.54 Both taurine and vitamin C showed cytoprotective, anti-oxidant, and anti-inflammatory activities. Additionally, taurine can stabilize membranes of biological system, and reduce water influx and excessive leakage of calcium ion, ultimately preventing osmotic cell swelling and apoptosis. As well, with the downregulation of JNK signaling pathway and attenuating nuclear factor-κB (NF-κB), transcription can prevent inflammation. Also, taurine has metal-chelating ability, such as Fe2+ that plays the main role in its potential in reducing lipid peroxidation, improvement of mitochondrial function, inhibition of apoptosis, and inflammation, which seems to contribute in the better protective action of taurine than vitamin C.

Conclusion

Widespread human exposure to PFOA in water, food, and air, coupled with environmental persistence and biological half-lives, can cause a global concern. The results of this study indicate that PFOA exposure for 4 weeks can lead to liver injury in rats through the induction of oxidative stress, inflammation, and apoptosis. Interestingly, taurine, particularly at a dose of 100 mg/kg/day, was more effective than vitamin C in the restoration of the deteriorative effects of PFOA.

Supplementary Material

supplementary_file_tfad005
Click here for additional data file. (27.9KB, docx)

Acknowledgments

The data provided in this study were extracted from PhD thesis of Dr Maloos Naderi.

Contributor Information

Maloos Naderi, Department of Toxicology and Pharmacology, Faculty of Pharmacy, Mazandaran University of Medical Sciences, Sari 4815733971, Iran; Student Research Committee, Mazandaran University of Medical Sciences, Sari 4815733971, Iran.

Mohammad Seyedabadi, Department of Toxicology and Pharmacology, Faculty of Pharmacy, Mazandaran University of Medical Sciences, Sari 4815733971, Iran; Pharmaceutical Sciences Research Center, Faculty of Pharmacy, Mazandaran University of Medical Sciences, Sari 4815733971, Iran.

Fereshteh Talebpour Amiri, Department of Anatomy, Molecular and Cell Biology Research Center, Faculty of Medicine, Mazandaran University of Medical Sciences, Sari 4815733971, Iran.

Ebrahim Mohammadi, Environmental Health Research Center, Research Institute for Health Development, Kurdistan University of Medical Sciences, Sanandaj 6618634683, Iran.

Sholeh Akbari, Department of Toxicology and Pharmacology, Faculty of Pharmacy, Mazandaran University of Medical Sciences, Sari 4815733971, Iran; Student Research Committee, Mazandaran University of Medical Sciences, Sari 4815733971, Iran.

Fatemeh Shaki, Department of Toxicology and Pharmacology, Faculty of Pharmacy, Mazandaran University of Medical Sciences, Sari 4815733971, Iran; Pharmaceutical Sciences Research Center, Hemoglobinopathy Institute, Mazandaran University of Medical Sciences, Sari 4815733971, Iran.

Author’s contribution

All authors contributed to the study conception and design. Material preparation, data collection and analysis were performed by F.S., M.N., M.S., F.T.A., E.M., and S.A. The first draft of the manuscript was written by M.N., and all authors commented on previous versions of the manuscript. All authors read and approved the final manuscript.

Funding

This work was supported by the research council of Mazandaran University of Medical Sciences, Sari, Iran under grant (Grant Number: 6354, Ethical code: IR.MAZUMS.REC.1399.6354).

Conflict of interest statement: None declared.

References

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