1. Introduction
The liver is an important metabolic organ and is responsible for the synthesis, decomposition, transformation and excretion of many molecules and other metabolic processes [
1]. Therefore, the liver is the main target of drugs and toxins and is damaged through drug-associated adverse effects [
2]. Cyclophosphamide (Cp), a cell cycle non-specific drug, is widely used in antitumor therapy due to its ability to inhibit the proliferation of cancer cells [
3]. However, Cp is hepatotoxic and can damage normal hepatocytes. It has been reported that Cp can be metabolized into active substances, such as phosphoramidic mustard and acrolein, under the action of cytochrome P450, which catalyzes the alkylation reaction between these metabolites and the guanine base of DNA [
4], inhibiting the synthesis of DNA and RNA and causing DNA damage, leading to oxidative stress and cytotoxic effects [
5].
Polysaccharides are natural polymer compounds that are widespread in animals, plants and microorganisms. Some exhibited antioxidant, anti-inflammatory, immune regulation and liver protection activities and have become a research hotspot in various fields [
6,
7]. Jackfruit is a tropical fruit native to the Western Ghats in India and has been introduced and cultivated in tropical and subtropical countries, such as Bangladesh, Myanmar, Sri Lanka, Malaysia, Indonesia, Philippines and Thailand. It was imported to China thousands of years ago and has become one of the commercial crops cultivated in Hainan, Guangdong, Guangxi, Fujian and Taiwan provinces [
8]. Our research group previously purified a polysaccharide from
Artocarpus heterophyllus Lam. (jackfruit) pulp (JFP-Ps), with a molecular weight of 1668 kDa and strong antioxidant activity [
9]. It has been reported that JFP-Ps increased the abundance of beneficial gut bacteria and restored the gut microbiota of obese rats, which may have an impact on health [
10]. In addition, JFP-Ps activated the peroxisome proliferator activated receptor (PPAR) and adenosine monophosphate-activated protein kinase (AMPK) signaling pathways to alleviate non-alcoholic fatty liver disease [
11].
At present, little is known about the effect and mechanism of JFP-Ps on liver injury. Therefore, this work aimed to evaluate the hepatoprotective effect of JFP-Ps against cp-induced liver injury in mice. A metabolomics method based on ultra-performance liquid chromatography equipped with quadrupole time-of-flight mass spectrometry (UPLC-Q-TOF-MS/MS) was used to identify endogenous metabolites and related metabolic pathways. This study provides a theoretical basis for the development of JFP-Ps as a potential natural compound for the treatment of liver injury.
2. Materials and Methods
2.1. Materials and Reagents
The JFP-Ps were extracted, purified and prepared according to our previous method at the Spice and Beverage Research Institute, Chinese Academy of Tropical Agricultural Sciences [
9].
Malonic dialdehyde (MDA), superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GSH-Px) assay kits were purchased from Suzhou Geruisi Biotechnology Co., Ltd. (Suzhou, China). Tumor necrosis factor alpha (TNF-α), interleukin-2 (IL-2), interleukin-6 (IL-6), interleukin-10 (IL-10) and interferon gamma (IFN-γ) assay kits were purchased from Shanghai Enzyme-linked Biology Co., Ltd. (Shanghai, China). Primers were purchased from Shenggong Biotechnology Co., Ltd. (Shanghai, China). Polyclonal antibodies of β-actin (20536-1-AP), IκBα (10268-1-AP), nuclear factor kappa-B (NF-κB) p65(10745-1-AP), p38 MAPK (14064-1-AP), JNK (24164-1-AP) and anti-rabbit IgG (SA00001-2) were purchased from Proteintech Group, Inc. (Wuhan, China). Phospho-p38 MAPK (p-p38, AP0526) was purchased from ABclonal, Inc. (Wuhan, China), phospho-JNK (p-JNK, ab76572) was purchased from Abcam (Shanghai) Trading Co., Ltd. (Shanghai, China). Phospho-NF-κB p65 (p-p65, AF5875) and polyvinylidene fluoride (PVDF) membrane were purchased from Beyotime Biotechnology Co., Ltd. (Shanghai, China).
2.2. Animal Experimental Design
The experimental animals were kept in accordance with the National Guidelines for Experimental Animal Care and Use, and the procedure was approved by the Animal Ethical Committee of Hainan Medical University (Permit # HYLL-2023-462). Fifty male BALB/C mice were supplied by Hunan Slac Laboratory Animal Co. Ltd. (Changsha, China), with the certificate number SCXK (Xiang) 2019–0004. Mice were fed with sufficient chow and water in a laboratory environment for acclimatization. After adaptation for 1 week, 40 mice were selected to induce liver injury by Cp using intraperitoneal injection, and the remaining 10 mice were given physiological saline as the normal control group (NC). After three days, the 40 Cp-induced liver injury mice were equally separated into four groups. (1) Model control group (MC): given physiological saline; (2) JFP-Ps low-dose group (LG): 50 mg JFP-Ps/kg body weight; (3) JFP-Ps medium-dose group (MG): 100 mg JFP-Ps/kg body weight; (4) JFP-Ps high-dose group (HG): 200 mg JFP-Ps/kg body weight. After JFP-Ps intervention for one week, all mice were anesthetized with 5% chloral hydrate after 12 h of fasting, and then sacrificed via cervical dislocation.
2.3. Histopathological Observation
The liver samples were fixed in 4% paraformaldehyde and then dehydrated with alcohol, embedded in paraffin, cut into 4 μm slices and stained with hematoxylin and eosin (H&E). The samples were observed under a light microscope (Nikon, Tokyo, Japan) and photographed.
2.4. Determination of Biochemical Indicators
Liver samples were homogenized in phosphate-buffered saline (PBS, pH 7.4) and centrifuged at 2500× g for 20 min to collect supernatants for further determination of the contents of MDA, TNF-α, IL-6, IL-2 and IFN-γ, as well as the activities of SOD, CAT and GSH-Px, according to the manufacturer’s instructions.
2.5. Real-Time Quantitative PCR
Total RNA in the liver was extracted with Trizol and cDNA was prepared using BeyoRT
TM III first-strand synthesis kit (Beyotime Biotechnology Co., Ltd., Shanghai, China). A three-step approach was used for target genes amplification. Relative mRNA expression level was calculated using the 2
−ΔΔCt method, with β-actin used for normalization. The primer information is listed in
Table 1.
2.6. Western Blot
Liver sample were homogenized and centrifuged at 12,000× g, 4 °C for 10 min in 4 °C to collect supernatants. The protein concentration in the supernatants was measured and adjusted to 3.5 μg/μL. Equal amounts of denatured proteins were separated using 12% SDS-PAGE and transferred onto a 0.45 µm PVDF membrane. Then, the PVDF membrane was blocked with 5% skim milk and incubated with primary antibodies. Lastly, the PVDF membrane was incubated with the secondary antibody for an hour to photograph the band. The antibodies used were β-actin (1:2000), IκB α (1:2000), p65 (1:2000), p-p65 (1:1000), p38 (1:1000), p-p38 (1:2000), JNK (1:2000), p-JNK (1:5000) and secondary antibodies (anti-rabbit IgG, 1:2000). The gray value was measured using Image J.
2.7. UPLC-Q-TOF-MS/MS Analysis
Liver samples were homogenized in methanol, ethanol and distilled water at a ratio of 2:2:1 and ultrasonicated for 10 min. The resulting mixture was centrifuged at 12,000× g, 4 °C for 15 min, and the supernatant was collected. The sample (3 μL) was separated on an Agilent 1290 ultra-high performance liquid chromatography system using Eclipse Plus C18 at 35 °C with 0.1% formic acid solution (mobile phase A) and acetonitrile (mobile phase B) at a flow rate of 0.4 mL/min. A 35 min gradient program was set as follows: 0–1.5 min 5% B, 1.5–15 min 5–60% B, 15–25 min 60–100% B, 25–30 min 100% B, 30–30 min 100–5% B, and 30–35 min 5% B.
Mass spectrometry (MS) data were obtained using an Agilent 6530B Q-TOF mass spectrometer (Agilent Technologies, Santa Clara, CA, USA) in positive and negative electrospray ionization (ESI) modes. The drying gas temperature was 325 °C; wavelength was 250 nm; cone voltage was 65 V; attenuation was 1000 mAU; draw speed was 100 μL/min; eject speed was 400 μL/min; MS scan range was from 50 to 1200 m/z; primary mass spectrometry scan was 2 spectra/s and MS scan time was 4 spectra/s.
2.8. Statistical Analysis
Results are presented as the mean ± SEM. Data were analyzed using one-way ANOVA followed by Duncan’s multiple range test using SPSS Statistics 26 (IBM Inc., Armonk, New York, NY, USA). A p value < 0.05 indicated a significant difference.
The UPLC-Q-TOF-MS data were collected using Masshunter (Agilent Technologies, Inc.), processed using Profinder (Agilent Technologies, Inc.) and normalized and filtered using Mass Profiler Professional (MPP, Agilent Technologies, Inc.). Principal component analysis (PCA) and orthogonal partial least-squares discriminant analysis (OPLS-DA) were used to identify the differences in metabolites of different groups based on FC (Fold change) > 2 and p < 0.05. The identified metabolites were determined through searching databases and confirmed using UPLC-Q-TOF-MS/MS.
4. Discussion
Cp induced hepatotoxicity including liver necrosis, inflammation and oxidative damage. MDA is the final product of lipid peroxidation; SOD is an antioxidant enzyme that can promote the disproportionation of superoxide into hydrogen peroxide to resist oxygen free radicals; and GSH-Px and CAT can protect cell structure and membrane function via catalyzing the decomposition of hydrogen peroxide [
12]. The present study showed that the MDA level in the MC group was increased, while the activities of SOD, CAT and GSH-Px were decreased. However, the oxidative stress indicators in the JFP-Ps groups were alleviated and approached those of the NC group, which may be related to the free radical scavenging activity of JFP-Ps.
The inflammatory cytokines reflect the immune state to a certain extent and play an essential role in the immune response [
13]. TNF-α is a multifunctional cytokine that stimulates the expression of a series of inflammatory mediators to regulate inflammation [
14]. IFN-γ is mainly secreted by natural killer cells and has antiviral, immune regulation and other active functions [
15]. IL-2 is a necessary cytokine for T cell proliferation and has an inductive effect on cells and memory cell generation [
16]. IL-6 plays a key regulatory function in immunity and is involved in the development, maturation, and sustained antibody production of B cells [
17]. It has been reported that
Lycium ruthenicum Murr. polysaccharide enhanced serum cytokine expression in immunocompromised mice [
18], which is consistent with our results, suggesting that JFP-Ps may exert regulatory effects on inflammation and immune function through regulating the secretion of these cytokines in the liver of Cp-exposed mice.
Liver damage is induced via the release of inflammatory cytokines, activation of apoptosis pathway, etc. [
19]. The NF-κB signaling pathway is closely related to immunity, inflammation and cell apoptosis [
20]. Cui et al. [
21] reported that the polysaccharides from
Caulis spatholobi had a protective effect mainly through regulating NF-κB signaling pathway in the intestinal mucosa of Cp-exposed chickens. The MAPK family, including ERK, JNK and p38, plays an important role in regulating cell apoptosis, cell cycle, cell growth inhibition and differentiation, as well as in mediating autophagy [
22]. The activation of p38 signaling has been shown to induce the expression of pro-inflammatory cytokines, while JNK signaling under stress stimulation can induce inflammation or cell apoptosis [
23]. The present study found that the liver damage was associated with the degradation of IκB-α protein and activation of the NF-κB inflammatory pathway, while JFP-Ps exerted a protective effect on the liver through inhibiting the p-p65/p65 and p-p38/p38 pathways and activating the p-JNK/JNK pathway.
Aminoacyl tRNA is the substrate for translation and is synthesized via matching amino acids with tRNA containing corresponding anticodons through aminoacyl tRNA synthase (ARS) [
24]. ARS participates in translation and serves as a signaling molecule in the development of immune cells in various immune diseases to mediate immune responses [
25]. Inflammatory signals can induce the phosphorylation of ARS and regulate the cascade reaction of various cytokines and MAPK and other cellular signaling pathways [
26].
Ascophyllum nodosum polysaccharide has been reported to inhibit the progression of inflammation mainly through regulating inflammation-related signals, including phenylalanine, tryptophan biosynthesis, and aminoacyl tRNA biosynthesis [
27]. Consistent with a previous study, JFP-Ps treatments altered the metabolism of various amino acids, including histidine, phenylalanine, methionine, isoleucine, lysine, proline and tryptophan, which are mainly related to the aminoacyl tRNA biosynthesis.
Arginine serves as a component of protein synthesis, and acts as a metabolic substrate for immune cells [
28]. Arginine can be metabolized to nitric oxide (NO) by nitric oxide synthase (NOS), and the abnormal synthesis of NO can induce tissue damage, while arginase could act as a competitive enzyme to compete with arginine to prevent the generation of NO [
29]. Arginine can modulate innate immune responses through modulating the MAPK signaling pathway [
30]. Our results show that the metabolic product of arginine biosynthesis is imbalanced in the liver of Cp-exposed mice.
Sphingolipids are common components of eukaryotic cell membranes. Extracellular stimuli, such as cytokines and cellular stress, can disrupt normal cell homeostasis and disrupt sphingolipid metabolism. Ceramide and sphingosine are metabolites of sphingolipids that act as key signaling molecules in immunity and inflammation [
31]. Changes in ceramide level may affect the interaction between lipids and proteins within the membrane, thereby affecting the transmission of intracellular signals [
32]. Polysaccharides obtained from
Suanzaoren decoction have been reported to reduce the concentrations of phytosphingosine, sphingosine and ceramide, inducing neuronal cell death as a mechanism of immune deficiency [
33]. An abnormal sphingolipid metabolism was found in Cp-exposed mice, and JFP-Ps attenuated the expression of sphingosine, sphinganine, phytosphingosine and ceramide in the present study.
In general, purine nucleotides are regenerated through recycling pathways by hypoxanthine guanine phosphoribosyltransferase and adenine phosphoribosyltransferase [
34]. Hypoxanthine can be oxidized by xanthine oxidase to form xanthine and guanine, which in turn can respectively generate hypoxanthine mononucleotide and guanylate to fulfill the purine requirements within cells [
35]. We analyzed the metabolites (xanthine, hypoxanthine, adenine, guanosine and inosine) involved in purine metabolism. It was confirmed that Cp treatment caused oxidative damage to mouse liver, leading to an imbalance in purine metabolism, and JFP-Ps were beneficial for restoring this damage.
Glutathione (GSH) is a tripeptide mainly synthesized in the liver and acts as an antioxidant [
36]. In addition, GSH is essential for activating T lymphocytes and multiple signaling pathways, including NF-κB, p38 and JNK [
37]. The citric acid (TCA) cycle has emerged as an energy metabolism hub and a regulator of immune responses in most eukaryotes. Mitochondria are critically involved in cell proliferation, death, differentiation and immunity via driving macrophage polarization through IL-6, and via activating mitochondrial signaling through inflammatory factors like TNF-α [
38]. Succinate, which is formed in the TCA cycle, accumulates under inflammatory or stress conditions, and is involved in macrophage activation [
39]. Fumarate is considered anti-inflammatory, and its degradation is detrimental to the host and abrogates trained immunity [
39]. In the present study, JFP-PS attenuated liver injury, which may be associated with the TCA cycle.