The unique metabolism of the liver and its correlation with the gastrointestinal tract take on a critical significance in the human physiological function. A wide variety of factors can lead to chronic liver damage (e.g., alcoholism, viral infections, obesity, diabetes, and dyslipidemia), eventually causing steatohepatitis and liver fibrosis (20). Steatosis characterized by the accumulation of lipid in hepatocytes primarily leads to non-alcoholic fatty liver disease (NAFLD) (21). Both oxidative stress and inflammatory response can be beneficial to the aggravation of NAFLD to non-alcoholic steatohepatitis (NASH) (22). Yang et al. (23) found that PTFC is capable of alleviating steatosis by reducing the body weight, lowing serum total cholesterol (TC), low-density lipoprotein cholesterol (LDL-C) and triglyceride (TG), and actively regulating peroxisome proliferator-activated receptor α (PPAR-α) in hyperlipidemic rats. Also, PTFC is capable of correcting dyslipidemia by regulating superoxide dismutase (SOD) and malondialdehyde (MDA) levels (24, 25), thus inhibiting lipid peroxidation. Jiang et al. found the beneficial effects of PTFC on NASH in two studies. They suggested that PTFC intervention can upregulate SIRTI-mediated deacetylated PGC-1α and SOD and downregulate MDA and 8-hydroxy-2′-deoxyguanosine (8-OHdG), which are biomarkers for lipid peroxidation and free radical level, respectively (26). In addition, they also confirmed that PTFC has hepatoprotective and anti-inflammatory functions by inhibiting phosphorylated NF-κB and MAPKs, as well as the abnormal activation of proinflammatory factors (e.g., IL-1β, IL-6, IL-12, TNF-α, and IFN-γ) (27). Furthermore, PTFC is conductive to maintaining the balance of Th17/Treg expressions and their transcriptional regulators RORγt and Foxp3 (28), which relieves the intrahepatic inflammatory response by limiting the immunopathological reaction and inhibiting the secretion of IL-17 and IL-10 (29).

Above all, existing research has concluded that the potential efficiency of PTFC can arise from the regulatory effect on lipid metabolism, anti-oxidation, and anti-inflammation properties. PTFC can be a curative agent for preventing NAFLDs.

Malignancies are initiated by the destruction of DNA replication and aggravated by immune escape, which further results in distant metastasis. Previous research has demonstrated that dietary intake of flavonoids is beneficial to reduce the risk of malignancies (30). Dai et al. (31) uncovered that PTFC invention dose-dependently and time-dependently inhibits proliferation of neoplastic cells and triggers cell apoptosis by upregulating activated poly adenosine diphosphate-ribose polymerase and downregulating Mcl-1. Overexpression of XIAP is common in carcinomas, usually suggesting an unfavorable response to chemotherapy, increased recurrence rate and shorter overall survival. Wu et al. (32) demonstrated that PTFC at a particular concentration range can downregulate XIAP, and the inhibition promotes apoptosis of cancer cells by activating caspases-3, -7, and -9.

Nearly the whole approaches target to remove or kill the neoplastic cells to control the tumor growth and to minimize the number of metastatic cells. These results revealed that PTFC is beneficial to inhibit cell proliferation and induce apoptosis in malignancies, and not involved in the resistance to cancer cell migration and invasion, which needs to be supplemented by more experimental and clinical evidences.

The gastrointestinal tract plays a critical role in regulating the immune homeostasis since it exhibits the largest interface in the body (33). It is accepted that intestinal barrier is the first line of defense against the entry of pathogenic microorganisms into human intestines. Due to the long-term administration of non-steroidal anti-inflammatory drugs (NSAIDs) for tumor chemoprophylaxis and cardiocerebrovascular diseases, compounds and their metabolites are subjected to a prolonged and repeated exposure of the intestinal mucosa, thereby impairing the intestinal barrier (34). Toxins, bile acids, and proteolytic enzymes all aggravate the intestinal barrier with the increase in intestinal mucosal permeability (35). Chen et al. (9) applied PTFC to rats with NSAID-induced small intestine injury and observed that Atg5, LC3-II, TJ, and the LC3-II/LC3-I ratio are upregulated, while p-PI3K and p-Akt are downregulated, suggesting that PTFC maintains the intestinal barrier integrity by promoting autophagy through the PI3K/AKT signaling pathway. They also claimed that PTFC intervention significantly reduces the content of toxic bile acids (e.g., TDCA, DCA, TCA, and CA), and enriches the phylogenetic diversity of gut microbiota in high-fat diet (HFD)-induced rats (e.g., Bacteroidaceae and Christensenellaceae) (36). That is to say, PTFC has a promising role in protecting human intestinal barrier, and its major effects include optimization of barrier permeability, positive balance of gut microbiota, and improvement of bile acid metabolism, which are considered to be vital in intestinal immunomodulation.

Studies have shown that the prevalence of a HFD, a sedentary lifestyle and alcoholic abuse are the risk factors for liver damage (37). The therapeutic effects of PTFC on liver metabolism affected by overnutrition has been achieved. Furthermore, it is found that naringin could reduce TG and very low-density lipoprotein (VLDL) in the fatty liver model by activating PPAR-α (38), and neohesperidin could facilitate PGC-1α-mediated mitochondrial biogenesis, thus alleviating hepatic steatosis in mice fed with a HFD (39), which further highlights the main contributor in PTFC efficacy.

On the other hand, the effects of narirutin, naringin, and hesperidin on alcoholic liver diseases has also been reported, providing new references for expanding the therapeutic field of PTFC treatment. In mice with a long-term consumption of alcohol, narirutin intake can reduce the serum transaminase, pro-inflammatory cytokines, TG, and TC (40). Zhou et al. confirmed that naringin protects against alcohol-induced liver damage by reducing lipid accumulation and oxidative stress (41). The combination of hesperidin with an anti-inflammatory drug synergistically inhibits alcoholic liver fibrosis (42). As a result, the treatment of PTFC components prevents steatosis caused by chronic alcohol ingestion, thus protecting alcoholic liver diseases. It is therefore suggested that PTFC alleviates alcoholic-induced liver diseases by preventing excessive lipid formation and protecting the antioxidant system, which should be validated in depth through animal studies and clinical trials.

Non-alcoholic fatty liver disease increases the risk of CVD, and it has been found as the most common cause of death of non-alcoholic liver diseases (43). Myocardial infarction, stroke, and revascularization are common risks of CVD, which are significantly correlated with NAFLD (44). However, a post hoc analysis indicated that the hazard risk of NAFLD population with body mass index ≥23 kg/m² for incident CVD is lower than those non-obese population (45), thus suggesting that myocardial infarction or stroke-induced vascular dysfunction is likely to be the pivotal element for CVD rather than obesity. Atherosclerosis in NASH patients is usually confirmed through the measurement of calcification and aortic stiffness (46). Naringin and narirutin are found to block the formation of scar tissue and vascular stenosis in atherosclerosis cases by downregulating pro-inflammatory factors (47). Similarly, naringin is able to prevent endothelial dysfunction with a decrease in the expressions of inflammatory cytokines (IL-6, TNF-α, and IL-1β) via Nox4/NF-κB, PI3K/AKT and Hippo-YAP pathways, thus relieving atherosclerosis (48, 49). Existing research has found that hesperidin intervention leads to favorable changes in endothelium-dependent microvascular reactivity by decreasing the concentrations of circulating inflammatory biomarkers (e.g., high-sensitivity C-reactive protein, serum amyloid A protein, and soluble E-selectin) and regulating nitric oxide bioactivity (50, 51). Narirutin relaxes the vascular system by stimulating the phosphorylation of endothelial nitric oxide synthase and voltage-dependent potassium current in arterial smooth muscle cells (52). Accordingly, the effects of PTFC compounds on NAFLD-associated CVD are primarily attributed to the inhibition of systematic inflammation. The persistent inflammatory responses trigger the aggravation of hepatic steatosis, NASH to liver fibrosis, thus significantly increasing the risk of CVD. An early intervention for NASH may reduce the incidence of cardiovascular events. Liver biopsy has been employed as the gold standard for the diagnosis of NASH though it is not highly acceptable due to the invasive examination and high medical costs. Although emerging blood makers and non-invasive imaging methods have been applied to the diagnosis of fibrosis and cirrhosis (53, 54), steatosis identification and inflammation evaluation should be conducted to make the progression of NASH. There have been rare typical manifestations of early stage NASH, so it is urgent to search for a reliable and accurate diagnostic method.

Interestingly, abnormal lipid metabolism and its transportation trigger the development of atherosclerosis (55, 56). NAFLD-induced excessive lipid uptake results in the abundant synthesis of hepatic TG and overproduction of VLDL particles assisting the mobilization of liver fat to peripheral tissues (57, 58). The accumulation of VLDL and TG on the arterial wall, alongside inflammation response and oxidative stress, leads to a heavy burden of atherosclerotic plaques (59). Free fatty acids (FFAs) are the product of lipolysis in the portal circulation. Sun et al. (60) built a lipoprotein receptor deficient model in atherosclerosis mice fed with HFD and discovered that hesperidin can suppress the formation of atherosclerotic plaque and macrophage foam cells by inhibiting the activities of enzymes involved in hepatic FFAs and TG synthesis, thus further suppressing the cholesterol transportation from peripheral tissues to the liver and then preventing hepatic steatosis. Also, hesperidin could maintain the redox homeostasis and prevent lipidemic stress in hyperlipidemia rats (61). Wang et al. (62) suggested that naringin more significantly mitigates atherosclerosis than hesperidin (55.92% vs. 42.87%). Their data revealed that the concentration of naringin in the gastrointestinal tract is higher than that of hesperidin, and a small amount of naringin in the liver is subsequently absorbed. Naringin facilitates the transformation from cholesterol to bile acids and promots their excretion from the liver by regulating the gut microbiota structure. Moreover, some naringin absorbed in the liver facilitates the reverse transport of cholesterol (62). Neohesperidin consistently exerts a potent hypolipidemic effect on HepG2 cells enriched in FFAs and reverses lipid-related pathological changes in the acute or chronic dyslipidemia mouse model (63). A kind of citrus juice containing neohesperidin and naringin significantly alleviates subclinical atherosclerosis by reducing lipoprotein content and carotid intima-media thickness within 6 months (64).

Increasing data have indicated that obesity is not the necessary factor for cardiovascular events in NAFLD population, but boosts the development of atherosclerotic plaques to a certain extent. Notably, NAFLD population with dyslipidemia is highly risky for cardiovascular events. The ingredients of PTFC, especially hesperidin and naringin, possess therapeutic efficiency on lipid deposition and adiposity, which dramatically inhibit the formation of atherosclerosis via blocking the secretion and transport of redundant lipid.

Glucose abnormality induced by insulin resistance and beta cell dysfunction is a hallmark of NAFLD, which takes on a great significance in the pathogenesis of CVD (65, 66). Elevated FFAs released by enlarged adipose mass remarkably restrict the anti-lipid effect of insulin and even lead to insulin resistance, which in turn aggravates dyslipidemia and pathoglycemia (67). Naringin exerts the insulinotropic effect by increasing the expression levels of insulin receptors and adiponectin in adipose tissues (68). Also, naringin attenuates mellitus-mediated steatohepatitis by upregulating the transcription factor PDX-1 that regulates insulin secretion and maintains β-cells mass (69), and inhibiting hyperglycemia-mediated oxidative stress and pro-inflammatory cytokine secretion (70). Yari et al. (71) suggested that hesperidin supplementation controls fatty liver indexes by inhibiting inflammation, while enhancing insulin sensitivity and fasting glucose. Meanwhile, hesperidin and naringin contribute to glucose uptake by enhancing hepatic glycolysis and glycogen content, and lowering hepatic gluconeogenesis (72, 73). Neohesperidin suppresses fat accumulation and reduces the size of adipocytes, which further improves oral glucose tolerance and insulin sensitivity (74).

A conclusion is drawn that, PTFC, at least in part, plays a positive role in the treatment of CVDs by suppressing vascular senescence, improving lipid profile and maintaining glucose homeostasis for its active ingredients. Moreover, their activities of controlling persistent inflammatory response and oxidative stress facilitate the prevention of CVD. However, inconsistent results on glucolipid metabolism have been obtained in some randomized controlled trials (RCTs). Motallaei et al. (75) reported that the meta-analysis on the intake of orange beverage associated with relieving serum TC and insulin resistance is poorly qualified, which fails to show a significant effect of citrus drinks on cardiometabolic risk factors. The above phenomenon can be explained by the poor bioavailability of flavonoids in the human body. Since the absorption of flavonoids focuses on the colon, individualized differences in gut microbiota compositions and activities result in varied therapeutic efficiency. Therefore, in addition to early intervention of steatosis to prevent CVD, it is also essential to mediate the intestinal microecology, which can facilitate the absorption of PTFC.

The growth of the primary tumors often do not pose major health threats except for those growing in sensitive and restrictive organs, such as the brain. Transformation into a cell capable of metastasis, acquiring the capabilities to escape the primary tumor, to enter vascular systems, to invade, and to colonize secondary organs, is more of a concern. Hesperidin is reported to control tumor growth by regulating mitochondria production (76), arresting cell cycle progression (77), and inhibiting cell viability via the endoplasmic reticulum stress signaling pathway (78). It also can inhibit the metastatic potential by suppressing metastases growth in vivo and cell migration and invasion in vitro (79, 80). Existing research indicated that hesperidin contributes to chemotherapy by modulating Smad4 and the activin A signaling in colon cancer (81), and downregulating Ki-67 expression in breast cancer (82). During the process of diethyl nitrosamine-induced hepatocellular carcinoma, the addition of hesperidin preserves liver tissue integrity, improves liver function (83), and exerts a hypomethylating effect (84). As the major component in PTFC, naringin is considered an anti-tumor agent and adjuvant in the combination therapy by inducing lysosomal permeabilization and autophagy in gastric cancer (85). It induces mitochondrial and cellular apoptosis in colon cancer via inhibiting NF-κB and endoplasmic reticulum stress (86). Though downregulating MMP-2 and MMP-9 and inactivating the p38 signaling, naringin inhibits angiogenesis and cell invasion in glioblastoma cancer (87, 88).

Due to the anti-tumor capacities of hesperidin and naringin in inhibiting metastatic potential, blocking neovascularization, and strengthening chemical protection, the anti-tumor function of PTFC appears to be consistent and reliable. Considering some uncertain aspects of cancer treatment, more in vivo and in vitro studies are needed to validate the anti-tumor effect of PTFC.

Besides the physical barrier created by intestinal epithelial cells, the symbiotic relationship between intestinal microbiota and host also contributes to the intestinal immunity. The gut microbiota complements human genome functions based on its wide range of metabolic properties. However, the individualized difference in gut microbiota changes significantly due to diet, antibiotic use, and lifestyle (89).

It is found that neohesperidin administration changes the structure of gut microbiota by decreasing the intestinal ratio of Firmicutes to Bacteroidetes and enhances gut barrier integrity by mitigating serum metabolic endotoxemia in obese mice, which is reversed by the antibiotic treatment. Increasing evidence suggested that the profitable effect of neohesperidin on the obese population is largely dependent on gut microbiota (90). Naringin alleviates atherosclerosis by modulating the abundances of Bifidobacterium, Bacteroidetes, Clostridium, and Eubacterium (91). Fidélix et al. (92) revealed that the absorption and metabolism of hesperidin and naringin increase the abundance of probiotics, thus ameliorating the glycemia and lipid profiles. The immunomodulatory effect of hesperidin on the gut-associated lymphoid tissue is achieved by increasing the proportions of Lactobacillus and Bifidobacterium (93). Furthermore, an increased dose of hesperidin supplementation reduces the risk of CVD by modulating the metabolism of the Bacteroidaceae family (94). Feeding with fecal of neohesperidin-treated mice yielded a considerable inhibition of colon cancer, suggesting that the adjustment of neohesperidin on gut microbiota may be a promising strategy for cancer (95).

Notably, knowledge of PTFC compounds as antimicrobial agent is equally attractive. The current research indicates that hesperidin combining with widely used NaNO2 has synergistic antibacterial activity against Bacillus cereus, Staphylococcus aureus, Escherichia coli, and Pseudomonas aeruginosa (96), showing the advantages of nutrients as safe natural bio-preservatives to reduce the hazards of overuse of chemical preservatives. Ciprofloxacin and tetracycline are antibiotics for P. aeruginosa, and the addition of naringin potentiates their efficacies to further manage bacterial infection (97). As for methicillin-resistant S. aureus that has developed resistance against most of the antibiotics and resulted in life-threatening outbreaks, naringin, hesperidin and neohesperidin are all strongly supported to be the adjuvant antimicrobial agent via the docking interactions (98).

Overall, the regulatory effect of its components on raising the proportion of beneficial bacteria implies the improvement of PTFC on chronic diseases may begin from the impact of its components on gut microbiota, and protecting intestinal microecological homeostasis can be the priority of human health. Based on the efforts on bacteriostasis by its components, the positive effect of PTFC on intestinal immunity has been affirmed again. Regional factors and personal habits lead to individualized differences in the dynamic equilibrium of intestinal microecology, which may be eliminated by the long-term administration of PTFC through regulating the structure of intestinal microbiota or clearing relevant pathological factors.