Protective Effects of Essential Oils as Natural Antioxidants against Hepatotoxicity Induced by Cyclophosphamide in Mice.

Clinical application of cyclophosphamide (CP) as an anticancer drug is often limited due to its toxicity. CP is metabolized mainly in the liver by cytochrome P450 system into acrolein which is the proximate toxic metabolite. Many different natural antioxidants were found to alleviate the toxic effects of various toxic agents via different mechanisms. Therefore, the present study aimed at investigating the role of essential oils extracted from fennel, cumin and clove as natural antioxidants in the alleviation of hepatotoxicity induced by CP through assessment of hepatotoxicity biomarkers (AST, ALT, ALP), histopathology of liver tissues as well as other biochemical parameters involved in the metabolism of CP. The data of the present study showed that treatment of male mice with cyclophosphamide (2.5 mg/Kg BW) as repeated dose for 28 consecutive days was found to induce hepatotoxicity through the elevation in the activities of AST, ALT, and ALP. Combined administration of any of these oils with CP to mice partially normalized the altered hepatic biochemical markers caused by CP, whereas administration of fennel, clove or cumin essential oils alone couldn't change liver function indices. Moreover, CP caused histological changes in livers of mice including swelling and dilation in sinusoidal space, inflammation in portal tract and hepatocytes, as well as, hyperplasia in Kuppfer cells. However, co-administration of any of the essential oils with CP alleviated to some extent the changes caused by CP but not as the normal liver. CP was also found to induce free radical levels (measured as thiobarbituric acid reactive substances) and inhibited the activities of superoxide dismutase, glutathione reductase, and catalase as well as activities and protein expressions of both glutathione S-transferase (GSTπ) and glutathione peroxidase. Essential oils restored changes in activities of antioxidant enzymes (SOD, CAT, GR, GST, and GPx) caused by CP to their normal levels compared to control group. In addition, treatment of mice with CP was found to induce the protein expression of CYP 3A4, 2B1/2, 2C6, 2C23. Moreover, the present study showed that essential oils reduced the expression of CYPs 2E1, 3A4 but could not restore the expression of CYP 2C6 and 2C23 compared to CP-treated mice. Interestingly, pretreatment of mice with essential oil of clove was found to restore activities of DMN-dI, AHH, and ECOD which were induced by CP to their normal control levels. It is concluded that EOs showed a marked hepatoprotective effect against hepatotoxicity induced by CP. In addition, co-administration of CP with any of these oils might be used as a new strategy for cancer treatment to alleviate the hepatotoxicity induced by CP.

Introduction

For more than 50 years cyclophosphamide (CP) has been widely used to treat various forms of cancers, including lymphoma, breast cancer and leukemia [1]. However, clinical application of CP is often restricted due to its deleterious side effects [2], especially hepatotoxicity [3]. The toxic effects of CP are mainly due to the generation of two major metabolites namely phosphoramide mustard which is the antineoplastic moiety and acrolein metabolite which is the most toxic agent. These metabolites are generated by cytochrome P450 isozymes including CYP 3A4, 2B6, 2C9, and 2C19 [4]. Acrolein is a highly reactive α, β- unsaturated aldehyde, and was identified as the initiator of lipid peroxidation. This reactivity is the main reason of the cytotoxicity in all cells exposed to acrolein [5] which limits using CP in clinical practice. CP-induced oxidative stress through the generation of free radicals leading to biochemical and physiological disturbances in animal models [6].

Protection of cells from the lethal effects of toxic compounds was observed due to the presence of abundant amounts of glutathione which is an important determinant of cellular sensitivity to various drugs and other toxic compounds [7,8]. Depletion of GSH levels in the cells could promote tumor development in different animal species [9]. Supporting this suggestion, depletion of GSH level and inhibition of GST activity were found to reduce the covalent binding of the ultimate metabolites of both aflatoxin B1 and benzo[a]pyrene, with DNA [10], and decreasing of hepatocarcinogenesis caused by these compounds was correlated with low the level of DNA adducts [10].

Several studies suggested that dietary antioxidants supplementation can reduce the development of adverse effects associated with anticancer drugs including CP [11,12]. It has been found that some plants contain a wide variety of antioxidant phytochemicals or bioactive molecules which can neutralize free radicals and decreased the oxidative stress that plays a critical role in the incidence of adverse toxic effects associated with chemotherapies [13]. Fennel (Foeniculum vulgare Miller) is a medicinal and aromatic plant with a diverse pharmacological spectrum and of considerable importance in food industries. Previous studies have shown that various extracts of fennel possess a range of pharmacological actions ranging from antispasmodic and anxiolytic to cytoprotective and anti-inflammatory effects due to the presence of terpenes and terpenoids [14]. Cumin (Cuminum Cyminum L.) is belonging to the family of Apiaceous. Cumin seeds are used in folklore therapy [15,16]. Clove (Syzygiumaromaticum L.) is one of the most valuable spices that have been used for centuries as a food preservative and for many medicinal purposes including antimicrobial, anti-inflammatory, antioxidant and anticancer activities [17]. Phenolic compounds (eugenol, eugenol acetate, and gallic acid) which possess pharmaceutical, cosmetic, food and agricultural applications are the main constituent of clove oil.

Recently, the protective effects of Foeniculum vulgare (fennel) essential oil (FEO) and Syzygium cumini extract against genotoxicity and oxidative stress induced by CP was investigated [18,19]. It has been shown that CP produced a significant increase in the average percentage of aberrant metaphases and chromosomal aberrations, excluding gap and micronuclei formation in polychromatic erythrocytes, produced cytotoxicity in mouse bone marrow cells [18,19]. CP also markedly inhibited the activities of SOD, CAT, and GSH and increased MDA content. Pretreatments with FEO and Syzygium cumini extract significantly inhibited the frequencies of aberrant metaphases, chromosomal abreactions, micronuclei formation, and cytotoxicity in mouse bone marrow cells induced by CP and antagonized the reduction of CP-induced SOD, CAT, and GSH activities and inhibited increased MDA content in the liver of mice [18,19]. In addition, FEO and Syzygium cumini extract inhibited genotoxicity and oxidative stress induced by CP (Tripathi et al., 2013a&b). In another study, the lyophilized ethanolic leaf of Eugenia dysenterica exhibited protection against CP induced genotoxic and cytotoxic actions at all doses tested [20].

CP-induced hepatotoxicity is critical issues during the clinical application of CP. Oxidative stress, caused by the active metabolites of CP, exhibited deleterious effects on hepatocellular membranes and other tissues. Therefore, finding a strategy to reduce the oxidative stress might be a key, at least in part, to alleviate the CP-induced hepatotoxicity. To the best of our knowledge, no previous study investigating the protective effects of essential oils of cumin and/or clove either alone or in combination with CP has been conducted. However, the influence of Foeniculum vulgare (fennel) essential oil either alone or in combination with CP was tested in the livers of mice on the activities of antioxidant enzymes but not on the protein expression of CYP450 [19]. Therefore, the present study aimed at investigating the extracted essential oils from fennel, clove and cumin and their roles in alleviating the toxic effects exerted by CP administration to mice through determination of activities and protein expressions of cytochrome P450 isozymes. In addition, the present study showed the influence of essential oils either alone or in combination with CP on levels of free radicals and activities and protein expressions of antioxidant enzymes including glutathione peroxidase and glutathione S-transferase after treatment of mice.

Materials and Methods

Chemicals

Cyclophosphamide was obtained from Baxter Oncology, Germany. Nicotinamide adenine dinucleotide phosphate (NADP) sodium salt, nicotinamide adenine dinucleotide phosphate reduced (NADPH) sodium salt, cumene hydroperoxide, 1-chloro-2,4-dinitrobenzene (CDNB) and all other chemicals were purchased from Sigma Chemical Co., UK. Anti-cytochrome P450 3A4, 2B1/2, 2C6, 2C23, 2E1 and NADPH-cytochrome c reductase were purchased from ABCAM, UK. Cytochrome P450 Western blotting detection kits were purchased from Amersham, UK. Diagnostic kits for aspartate aminotransferase, alanine amino transferase, and alkaline phosphatase were obtained Spectrum Diagnostics, Hannover, Germany. Dimethylsulfoxide (DMSO) pharmaceutical grade (C2H6OS, purity ≥99%) was obtained from Gaylord Chemical Co., LA, USA. All other agents and solvents were of analytical grade.

Essential oil extraction and characterization by GC-MS

Dried seeds of fennel, cumin and flower buds of clove authenticated by Prof. Salama El Darier, Professor of Plant Ecology, Botany and Microbiology Department, Faculty of Science, Alexandria University were used for the extraction of essential oils. 100 gm of the respective dried seeds or flower buds were subjected to hydrodistillation for 4 hr using Clevenger type apparatus. The distillate oil was collected, dried over anhydrous sodium sulfate and stored in dark sealed vials at 4°C prior to characterization of their chemical composition.

Compositional analysis of the extracted essential oils was assessed using Thermo scientific GC-MS version 5 system. Qualitative identification of the oil constituents was carried out on the basis of their retention indices and matching their mass spectral fragmentation patterns with NIST library data base [21]. Quantitative analysis of the oil components expressed as relative percentage of peak area, was estimated using peak area normalization measurements.

Animal treatments

Sixty-four Swiss male albino mice, weighing 25±2 g were obtained from the animal house of the Faculty of Medicine, Alexandria University. This study was carried out in strict accordance with the recommendations in the Guide for the Care and Use of Laboratory Animals of the College of Medicine, Alexandria University. The protocol was approved by the committee of postgraduate studies & research on the Ethics of Animal Experiments of the University of Alexandria. All surgery was performed under diethyl ether anesthesia, and all efforts were made to minimize suffering. Mice were housed in a stainless steel wire bottom cages placed in a well-ventilated animal house, maintained for one week for acclimatization period on food and water ad libitum, and subjected to the natural photoperiod of 12 hours light:dark cycle. The animals were assigned into 8 groups comprising 8 mice/cage in each group and fed the same diet throughout the experimental period (28 days). Group I served as the control and received 0.1 ml of DMSO orally. Group II (CP) was orally administered with the aqueous solution of CP at a dose of 2.5 mg/Kg BW. Groups III, IV and V were orally treated with the essential oils of fennel, cumin and clove dissolved in DMSO at doses of 1/50 their LD50 corresponding to 0.12 ml/Kg BW, 0.10 ml/Kg BW and 0.106 ml/Kg BW respectively. Groups VI, VII, and VII were administered orally by a combination of CP with fennel, cumin or clove essential oils at the same doses scheduled in groups II, III, IV and V.

At the end of the experimental period, mice were starved overnight and then sacrificed. Blood and liver samples were collected. Serum was obtained by centrifugation of coagulated blood at 3000 xg for 5 min. Livers were washed with cold phosphate buffer saline and the S9 fraction was prepared by homogenizing the livers in 33% W/V of 0.1 M phosphate buffered solution (pH 7.4) and centrifuging at 10000 xg for 20 min. Liver microsomal fractions were prepared by centrifugation of the S9 fraction supernatant at 105,000 xg for 1 hour at 4°C, then the microsomal pellets were suspended in 0.1 M phosphate buffer (pH 7.4) and stored in aliquots at -80°C [22].

Biochemical analyses

Activities of biomarker enzymes for hepatocellular damage, including alanine aminotransferase (ALT), aspartate aminotransferase (AST) and alkaline phosphatase (ALP) were determined in serum of different groups according to the well-established spectrophotometric methods according to the manuals supplied with the commercial kits obtained from Spectrum Diagnostics, Hannover, Germany.

A substrate concentration of 4 mM dimethylnitrosamine, which represents the saturation level for dimethylnitrosamine N-demethylase I (DMN-dI) activity, was used [23,24]. Also, the microsomal 7-ethoxycoumarin-O-deethylase (ECOD) activity was measured as described by Greenle and Poland, 1978 [25] and the intensity of 7-hydroxy-coumarin was measured fluorometrically at excitation and emission wavelengths of 338 and 458 nm respectively. NADPH-cytochrome c reductase activity in hepatic microsomal fraction was assayed by measuring the reduction of oxidized cytochrome cat 550nm using an extinction coefficient of 21 mM-1 Cm-1 [26].

The activity of GPx was determined in the S9 fraction of cell homogenates according to the method of Chiu et al., 1976 [27]. The principle of determination is based on the decrease in absorbance of NADPH at 340 nm. The specific activity was expressed in terms of the amount of enzyme that oxidizes 1 μmol of NADPH per min. Glutathione reductase activity in hepatic S9 fraction was monitored by the oxidation of NADPH in the presence of GSSG according to the method of David and Richard, 1983 [28]. Glutathione-S-transferase activity was assayed according to the method of Habig et al., 1974 [29], which is based on the measurement of 1-chloro-2,4-dinitrobenzene (CDNB) conjugate formed at 340 nm. A molar extinction coefficient of 9.6 mM-1 Cm-1 was used for the calculation of GST activity. One μmole of CDNB conjugate/mg protein/min is expressed as a unit/mg protein.

Catalase activity was determined in the hepatic S9 fraction according to the method of Beers and Sizer, 1952 [30], which is based on decreasing in absorbance of H2O2 solution decomposed by the catalase enzyme (assay kit was obtained from Randox Laboratory, UK). The quantity of H2O2 was measured at 240 nm and catalase activity was expressed as U/mg protein. Superoxide dismutase (SOD) was assayed according to the method of Misra and Fridovich, 1972 [31]. SOD quantitation was dependent on the generation of superoxide radicals by xanthine and xanthine oxidase, which react with nitro blue tetrazolium to form the formazin dye. SOD activity was measured at 560 nm and expressed as U/mg protein. The protein content was measured in both S9 fraction and microsomal pellets according to the method of Lowry et al., 1950 [32] using bovine serum albumin as standard.

Quantitative measurement of lipid peroxidation was performed in cell homogenates according to the methods of Tappel and Zalkin, 1959 [33], which is based on the formation of thiobarbituric acid reactive substances (TBARS) and expressed as the extent of malondialdehyde (MDA) production. TBARS was expressed as μmole MDA per gram tissue. Glutathione level was measured in the S9 fractions according to the method of Mitchell et al., 1973 [34], after protein precipitation with sulfosalicylic acid. After centrifugation at 3000 xg for 20 min, one ml of clear supernatant was added to bis-(3-carboxy-4-nitrophenyl)-disulphide for color development. The developed color solution was spectrophotometrically at 412 nm. Glutathione levels were expressed as μmole GSH per gram tissue.

Western Immunoblotting

From each pooled group (10 mice each), forty microgram of the S9 and the microsomal fractions were mixed with the sample application buffer (SAB), then boiled for 3 minutes and loaded on a 10% SDS-polyacrylamide gel. After electrophoresis, proteins were transferred to nitrocellulose membranes using a semidry trans blotter. Each membrane was blocked in 0.5% BSA for 2 hours with gentle shaking at room temperature prior to antibody incubations. Primary antibodies of GSTπ, glutathione peroxidase, NADPH-cytochrome c reductase, CYP2E1, CYP3A4, CYP2B1/2, CYP2C23 and CYP2C6 in 0.5% bovine serum albumin were used in the present study. The secondary antibody (anti-mouse conjugated-peroxidase) was used after incubation with the membrane for a minimum of 30 minutes at room temperature. Signals of immune-reactive proteins were detected using X-ray films according to the manufacturer's instructions [35]. The band intensity was measured using quantity one software program.

Histological examination of the liver

Formalin fixed paraffin embedded hepatic tissues were sectioned and stained routinely with hematoxylin and eosin (H&E). Hepatic damage in H&E-stained sections was examined from a digital image captured at 200x magnification [36].

Statistical Analysis

Data presented in the study were shown as mean ± standard error. Mean of different treatment groups were tested for significance using one-way analysis of variance (ANOVA) and were compared using posthoc Duncan's Multiple Range Test (DMRT). Difference were considered significant at P<0.05. SPSS 17 statistical software package was used in statistical evaluation.

Results

Compositional analysis of the extracted clove, cumin and fennel essential oils

Compositional analysis of the extracted essential oils by GC-MS demonstrated that eugenol (82.84%), acetyl eugenol (6.29%), β-caryophyllene (8.13%) and α-caryophyllene (1.05%) were the major chemical constituents of the hydrodistilled clove essential oil (Fig 1A, Table 1). Fennel essential oil was constituted mainly by estragole, limonene, fenchone, α-pinene and trans-anethole comprising 80.75%, 10.47%, 4.64%, 1.10% and 1.02% respectively (Fig 1B, Table 2). The terpene hydrocarbons; γ-terpinene (23.91%) and 3-carene (7.66%), as well as, the terpenoids; cumin aldehyde (19.43%), 2-caren-10-al (15.22%) and cuminyl alcohol (9.08%) were the main components constituting the extracted cumin essential oil (Fig 1C and Table 3).

Fig 1

(A) GC-MS chromatogram and major components of essential oil of Clove, (B) Fennel, and (C) Cumin respectively.

Table 1

Major components of clove essential oil.

Component	Eugenol	β-caryophyllene	α-caryophyllene	Acetyl eugenol
Retention time	21.13	22.73	23.74	26.14
Relative %	82.84	8.13	1.05	6.29
Molecular formula (chemical class)	C10H12O2 (terpenoid)	C15H24 (terpene)	C15H24 (terpene)	C12H14O3 (terpenoid)

Table 2

Major components of fennel essential oil.

Component	α-pinene	Limonene	Fenchone	Estragole	trans-anethole
Retention time	5.99	9.04	11.07	15.63	18.10
Relative %	1.10	10.47	4.64	80.75	1.02
Molecular formula (chemical class)	C10H16 (terpene)	C10H16 (terpene)	C10H160 (terpenoid)	C10H12O (terpenoid)	C10H12O (terpenoid)

Table 3

Major components of cumin essential oil.

Component	3-carene	γ-terpinene	Cuminaldehyde	2-caren-10-al	Cuminyl alcohol
Retention time	7.30	10.20	16.71	18.21	18.43
Relative (%)	7.66	23.91	19.43	15.22	9.08
Molecular formula (chemical class)	C10H16 (terpene)	C10H16 (terpene)	C10H12O (terpenoid)	C10H14O (terpenoid)	C10H14O (terpenoid)

Cyclophosphamide and/or essential oils induced alterations in hepatic biochemical indices and hepatic oxidative response

The oral administration of CP to mice significantly increased hepatocellular injury biomarkers (AST, ALT, and ALP) in serum as demonstrated in Table 4. Meanwhile, administration of fennel, clove or cumin essential oils alone insignificantly changed liver function indices, whereas their combined administration with CP partially normalized the altered hepatic biochemical markers. As presented in Table 4, hepatic oxidative response in different treatment groups revealed that CP-treated mice exhibited a significant elevation in TBARS level, significant depletion in GSH level in addition to a significant reduction in the activity of antioxidant enzymes (GST, GR, GPx, SOD and CAT). Administration of essential oils alone resulted in a favorable effect on hepatic antioxidant status, where they significantly increased the activity of endogenous antioxidant enzymes (GST, GR, GPx, SOD and CAT) meanwhile neither inducing lipid peroxidation nor depleting GSH levels. The Co-administration of essential oils with CP resulted in significant reduction of the escalated lipid peroxidation and compensated the depletion in endogenous enzymatic (GST, GR, GPx, SOD and CAT) and non-enzymatic (GSH) antioxidants. Supporting the present perturbations in antioxidant defense parameters, protein expression of both GSTπ and GPx was inhibited after treatment of mice with cyclophosphamide. Furthermore, treatment of mice with fennel, cumin or clove essential oils increased the protein expression of both enzymes compared to control group (Fig 2).

Table 4

Biochemical parameters in serum and liver lysate of different treatment groups.

					Treatments
Parameter	Control	CP	Fennel EO	Cumin EO	Clove EO	CP and Fennel EO	CP and Cumin EO	CP and Clove EO
Serum AST (U/L)	70.1±0.32c	121±2.52a	71.4±0.37c	70.9±0.66c	70.6±0.82c	91.2±2.45b	86.7±2.78b	89.2±0.46b
Serum ALT(U/L)	76.5±0.31d	123±1.63a	75.7±0.51d	74.9±0.34d	76.5±0.32d	93.8±0.57bc	90.3±3.1c	96.8±1.36b
Serum ALP (U/L)	88.3±5.29d	149±1.72a	89.1±3.64d	84.5±3.57d	85.2±3.94d	111±4.54bc	103±3.43c	119±4.05b
TBARS level (μmol/g tissue)	1.38 ±0.18c	2.59±0.06a	1.23±0.02d	1.11±0.02e	1.12±0.02e	1.44±0.02bc	1.34±0.03c	1.49±0.06b
GSH content (μmol/g tissue)	2.43±0.04b	1.87±0.03c	2.65±0.06ab	2.79±0.26a	2.53±0.02ab	2.41±0.03b	2.52±0.03ab	2.45±0.04b
GPx activity (U/mg protein)	3.29±0.07cd	2.07±0.09e	4.39±0.07b	4.51±0.08b	4.97±0.18a	3.18±0.10cd	3.40±0.27c	2.98±0.06d
GR activity (nmol of NADPH oxidized/ min/mg protein)	0.21±0.01c	0.12±0.01d	0.23±0.01c	0.31±0.01a	0.27±0.02b	0.21±0.01c	0.22±0.01c	0.21±0.01c
GST activity(U/ mg protein)	3.55±0.04e	1.52±0.05f	5.26±0.05b	5.86±0.06a	6.01±0.11a	4.42±0.05d	4.83±0.07c	4.47±0.04d
SOD (U/mg protein)	11.4±1.55bc	5.38±1.38d	14.6±0.96abc	17.7±1.83a	15.6±1.46ab	10.1±1.25c	11.9±1.84bc	11.2±2.02bc
CAT (U/mg protein)	0.22±0.01b	0.06±0.01c	0.31±0.01a	0.32±0.01a	0.29±0.02a	0.22±0.01b	0.24±0.02b	0.21±0.01b
DMN-dI (nmol HCHO/mg protein/h)	94.2±3.35b	148±4.85a	78.7±3.41cd	76.4±4.79d	75.5±3.11d	89.3±2.35bc	87.3±1.95bc	89.7±3.70b
ECOD (nmol hydroxycoumarin/ mg protein/min)	0.29±0.03c	0.44±0.02a	0.41±0.01ab	0.38±0.01b	0.21±0.02d	0.38±0.01b	0.42±0.02ab	0.28±0.01c
NADPH-Cytochrome c reductase (nmol cyt c reduced/mg protein/min)	9.76±2.52b	23.1±2.58a	22.8±2.39a	20.8±2.42a	21.6±2.12a	19.9±3.14a	20.2±2.48a	22.1±1.95a

Values are mean ± S.E., n = 8 mice/group.

abcdef Mean values within a row not sharing common superscript letters were significantly different, P<0.05.

Fig 2

Western immune blot analysis for the protein expression of GSTπ and GPx in the pooled proteins of matched control, CP, fennel EO, cumin EO, clove EO, CP & fennel EO, CP & cumin EO and CP & clove EO treated groups.

Cyclophosphamide and/or essential oils induced alteration in expression/activity of CYPs

Treatment of mice with CP-induced the protein expressions of cytochrome P450 isozymes (CYP 3A4, 2B1/2, 2C6, 2C23) involved in CP metabolism (Fig 3). The protein expression of CYP2B1/2 was inhibited when mice were treated individually by clove EO and was induced upon treatment of mice with fennel or cumin essential oils. Synchronically, the corresponding activity of ECOD correlated to the inhibition or induction of CYP2B1/2 inferred by the three tested essential oils. Fennel and clove essential oils reduced the expression of CYP3A4, whereas cumin induced its expression compared to the control group. The expression of CYP2C6 and CYP2C23 was induced indifferently in all treatment groups comparative to the control. Cyclophosphamide administration also induced the protein expression of CYP2E1 and increased its corresponding DMN-dI activity (Fig 3, Table 4). Fennel, cumin or clove essential oils reduced the expression of CYP2E1 and significantly reduced the activity of DMN-dI, whereas their combined administration with CP normalized the expression of CYP2E1 and the corresponding DMN-dI activity (Fig 3, Table 4). Both the protein expression and activity of NADPH-cytochrome c reductase was induced in CP or essential oils' treated groups. However, the combined treatment of mice with CP and either of the investigated essential oils did not significantly change the activity or expression of NADPH-cytochrome c reductase comparative to groups treated with either CP or the tested EOs individually (Fig 3, Table 4).

Fig 3

Immunoblot of CYP 2E1, c-reductase, 3A4, 2B1/2, 2C23 and 2C26 in the pooled proteins of matched control, CP, fennel EO, cumin EO, clove EO, CP & fennel EO, CP & cumin EO and CP & clove EO treated groups.

Cyclophosphamide and/or essential oils induced pathomorphology

Histological examination of liver sections of different treatment groups revealed that mice treated with CP demonstrated distortion in hepatic architecture manifested as swelling and dilation in sinusoidal space, hemorrhage in central vein, mild inflammatory changes in portal tract and hepatocytes in addition to hyperplasia in Kuppfer cells (Fig 4B). Conversely, liver section of fennel, cumin or clove essential oil-treated mice exhibited normal architecture with normal hepatocytes and sinusoidal space (Fig 4C, 4D and 4E). In liver section of mice treated concomitantly with essential oils and CP, the hydropic, necrotic and inflammatory changes induced by CP regressed to some extent (Fig 4F, 4G and 4H).

Fig 4

(A) Histological photomicrographs of liver sections of control, (B) cyclophosphamide, (C) fennel EO, (D) cumin EO, (E) clove EO, (F) CP& fennel EO, (G) CP & cumin EO and (H) CP & clove EO-treated groups. Cyclophosphamide treated group exhibited distortion in hepatic architecture, dilation in sinusoidal space, central vein (CV) hemorrhage, leukocytic infiltration (L.I.) in portal tract and hepatocytes (H), as well as, hyperplasia in Kuppfer cells (B). Conversely, liver section of fennel, cumin or clove essential oil treated mice exhibited normal architecture with normal hepatocytes and sinusoidal space comparative to the control group (C, D and E). The hydropic, necrotic and inflammatory changes regressed in liver section of mice treated concomitantly with essential oils and CP (F, G and H).

Discussion

Cyclophosphamide (CP), a chemotherapeutic agent, is restricted due to its side effects, especially hepatotoxicity [37]. CYP2E1 is the major enzyme that catalyzes the biotransformation of numerous xenobiotics and anticancer drugs [8,38]. There is an association between CP exposure and induction of various types of neoplasms in experimental animals [39]. The present study may provide a new possible mechanism of cancer induction by CP through enhancement of protein expression of CYP2E1 since CP-induced protein expression of CYP2E1 in the liver of male mice. Supporting our suggestion, several investigations have shown that repeated dose of CP induces its own metabolism through the generation of acrolein (the toxic metabolite of CP) in excessive amounts [40,41]. Interestingly, administration of fennel, cumin, and/or clove essential oils in combination with CP to mice inhibited the induced protein expression of CYP2E1, 3A4, 2B1/2 and their associated enzymatic activities caused by CP which may protect the liver against toxicity and carcinogenicity induced by CP. Changes in hepatic cytochrome P450 isozymes are mainly due to the presence of active compounds which have been isolated and identified from herbs and medicinal plants. The protective effects exerted by these oils could be related to their chemical components. For example, ß-myrcene, a constituent of fennel essential oil, has been reported to up-regulate the protein expression of CYP2B1/2 [42]. These compounds act as substrates, inhibitors and/or inducers of various CYP isozymes. Eugenol, the major constituent of clove essential oil, was reported to inhibit CYP2B1/2 and CYP1A1 that catalyze the biotransformation of 7,12-dimethylbenz[α]anthracene to more carcinogenic metabolites [43]. On the other hand, it has been demonstrated that cumin significantly increased the activity of CYP P450 and NADPH-cytochrome c reductase activity [44]. The mechanism of up-regulation of cytochrome P450 isozymes could be due to the presence of limonene and myrcene as major constituents of essential oils, which were found to induce delta-aminolaevulinic acid synthetase activity, the key enzyme involved in the synthesis of haem moiety of cytochrome P450 isozymes [45,46]. Moreover, the protective effects of essential oils are dependent on the presence of double bonds in the chemical structures of terpene hydrocarbons [47], limonene, terpinolene, linalool and β-caryophyllene [48-50]. Recently, it has been found that blocking of these double bonds was found to decrease the antioxidant activities of monoterpenes and other components [51].

In clinical applications, oxidative stress induced by CP play a significant role in the incidence of hepatotoxicity [52,53]. The present study showed that increment of oxidative stress in liver of mice after administration of CP could be due to inhibition of antioxidant enzymes activities (GST, GPx, GST, SOD, CAT) and reduction of GSH levels. In agreement with the present study, oxidative stress was increased after CP exposure in both humans and mice [52,53]. The mechanism of induction of oxidative stress could be due to metabolic conversion of CP to several types of toxic metabolites [54]. For example, acrolein, a highly reactive metabolite of CP with short biological half-life, could readily react with glutathione (GSH), one of thiol-containing proteins, which serves several vital functions, including detoxifying electrophiles and relieving oxidative stress, with the presence of glutathione S-transferase (GST) [55]. Acrolein, the highly reactive α, β–unsaturated aldehyde, was found to react with cellular nucleophiles such as the thiol groups of cysteine residues in proteins and nitrogen atoms in lysine and histidine groups, leading to the loss of protein function, which could induce the oxidative stress and finally give rise to the disastrous effects on hepatocyte including inhibition of antioxidant enzymes [55,56].

On the other hand, pretreatment of mice with essential oil of Cumin, Fennel and/or Clove before administration of CP restored the activities of antioxidant enzymes, free radicals, and GSH levels to their normal levels compared to control mice. Moreover, treatment of mice with essential oils of Cumin, Fennel, and/or Clove induced activities of GST, CAT, and GPx compared to the control mice. Supporting the data of enzymatic activities, Western immunoblot data showed that the protein expressions of both GPx and GSTπ were markedly reduced after treatment of mice with CP, and potentially induced after treatment of mice with either essential oils alone or in combination with CP. From the present study, induction of free radical levels and inhibition of antioxidant enzyme activities might be new reasons for cancer induction by CP.

The inhibition of CYPs by essential oils constituents (eugenol, isoeugenol, gamma-terpinene, and quercetin) may decrease the formation of toxic metabolites, as CYPs play an important role in procarcinogens activation [8,57]. In the present study, the mechanism of liver protection mediated by these essential oils might be due to inhibition of the protein expression of CYP2E1 and 3A4 which were induced by cyclophosphamide. Supporting this finding, it has been reported that eugenol was found to prevent liver injury by decreasing CYP2E1 activity, lipid peroxidation indices, protein oxidation and inflammatory markers, prevented DNA strand break and abolished the expression of COX-2 gene [58]. Furthermore, eugenol increased the expression and activity of NAD(P)H:quinone oxidoreductase (QR), a major detoxifying enzyme, through NF-E2 related factor2 binding to antioxidant response element in QR gene [59]. Eugenol and isoeugenol, which are naturally found in essential oils of different spices, suppressed the growth and proliferation of HaCaT cells via aryl hydrocarbon receptor (AhR) interactions [60]. They showed a rapid and marked translocation of AhR into the nucleus of the HaCaT cells, and consequently induced the expression of the AhR target genes. In addition, these compounds reduced levels of the cyclin-dependent kinase (CDK)6 [60]. Another component of essential oils, quercetin, was found to act as scavenger of O2–, NO–, HO–, and peroxy radicals. In addition, previous studies have shown that quercetin inhibited the oxidative DNA damage induced by hydrogen peroxide [61] and preventing free radical-mediated cytotoxicity [62]. Based on this finding, the present study might provide another new mechanism for essential oils protection against CP-induced hepatotoxicity via induction the protein expressions and activities of GPx and GST which diminished free radicals levels, and consequently reduced cytotoxicity.

In the current study, levels of serum hepatic marker enzymes were elevated in the livers after treatment of mice with CP. This is in agreement with other previous reports regardless the route, duration, and dose of administration of anti-cancer drugs [63]. The hepatoprotective effects against toxicity of CP were seen since all tested essential oils recovered the hepatic marker enzymes activities to their normal levels, which are in accordance with other previous studies [64,65]. Moreover, the ethanolic extract of clove was found to restore the levels of AST, ALT, and ALP to their normal levels in paracetamol-induced liver toxicity [66]. The current histopathological changes are correlated with the altered enzyme activities and are in accordance with the previous studies [67]. The currently observed histological disruption in CP-treated mice might be related to the generation of more toxic metabolites of CP [68] which lead to liver injury due to the generation of reactive oxygen species. Acrolein has been reported to have an inflammatory response, subepithelial edema, neutrophil infiltration, hemorrhage, and necrosis.

It is concluded that administration of fennel, cumin, and clove EOs exhibited hepatoprotective effects against CP-induced toxicity. Hepatoprotective effect of EOs might be due to induction of antioxidant defense systems. Also, it is suggested that co-administration of fennel, cumin, and/or clove essential oils with CP can be used for cancer therapy to reduce the hepatotoxicity caused by CP.