Epigallocatechin gallate enhances biliary cholesterol secretion in healthy rats and lowers plasma and liver cholesterol in ethinylestradiol-treated rats

Dietary intake of plant polyphenols: Exploring trend in the Czech population

OBJECTIVES

This study aimed to determine trend in polyphenol consumption in the Czech Republic during the last three decades. Additionally, it provides a brief overview of the beneficial effects of polyphenols in several body systems.

METHODS

Data from the Phenol-Explorer 3.6, a specialized database of polyphenolic substances, were assigned to the resources of the Czech Statistical Office on the consumption of food and beverages in the Czech Republic for the years 1989-2022. The average daily intake of polyphenols was determined by multiplying the average annual consumption of each type of food by the polyphenol content obtained from the database; results were given in milligrams of polyphenols per inhabitant and day. Since the food items in the data sources are not identical, it was necessary to create an extensive model of food categories.

RESULTS

The current value of polyphenol intake is 1,673 mg per day per inhabitant; however, this level most likely reflects methodological underestimation. The favourable increase in dietary polyphenol intake in the Czech population - doubling, to be precise - which we observed from 1989 to 2007, has been replaced by the opposite trend in the last 15 years. The current intake of polyphenols corresponds to the level that was already achieved in 2004. Hydroxycinnamic acids (from the group of phenolic acids) are the most prevalent dietary polyphenols, followed by flavanols (from the group of flavonoids). The most frequent source of polyphenols in the Czech population are non-alcoholic beverages such as coffee, tea and juices, followed by fruits, cereals, and vegetables, respectively.

CONCLUSION

Current trend of dietary polyphenol intake in the Czech population is slightly decreasing. This tendency, lasting since 2008, is indisputably negative. Plant polyphenols offer opportunities for inexpensive interventions in health promotion.

The Influence of Polyphenols on Atherosclerosis Development

Polyphenols have attracted tremendous attention due to their pro-health properties, including their antioxidant, anti-inflammatory, antibacterial and neuroprotective activities. Atherosclerosis is a vascular disorder underlying several CVDs. One of the main risk factors causing atherosclerosis is the type and quality of food consumed. Therefore, polyphenols represent promising agents in the prevention and treatment of atherosclerosis, as demonstrated by in vitro, animal, preclinical and clinical studies. However, most polyphenols cannot be absorbed directly by the small intestine. Gut microbiota play a crucial role in converting dietary polyphenols into absorbable bioactive substances. An increasing understanding of the field has confirmed that specific GM taxa strains mediate the gut microbiota-atherosclerosis axis. The present study explores the anti-atherosclerotic properties and associated underlying mechanisms of polyphenols. Moreover, it provides a basis for better understanding the relationship between dietary polyphenols, gut microbiota, and cardiovascular benefits.

Polyphenols as potential metabolism mechanisms regulators in liver protection and liver cancer prevention

BACKGROUND

Liver cancer is one of the common malignancies. The dysregulation of metabolism is a driver of accelerated tumourigenesis. Metabolic changes are well documented to maintain tumour growth, proliferation and survival. Recently, a variety of polyphenols have been shown to have a crucial role both in liver disease prevention and metabolism regulation.

METHODS

We conducted a literature search and combined recent data with systematic analysis to comprehensively describe the molecular mechanisms that link polyphenols to metabolic regulation and their contribution in liver protection and liver cancer prevention.

RESULTS

Targeting metabolic dysregulation in organisms prevents and resists the development of liver cancer, which has important implications for identifying new therapeutic strategies for the management and treatment of cancer. Polyphenols are a class of complex compounds composed of multiple phenolic hydroxyl groups and are the main active ingredients of many natural plants. They mediate a broad spectrum of biological and pharmacological functions containing complex lipid metabolism, glucose metabolism, iron metabolism, intestinal flora imbalance, as well as the direct interaction of their metabolites with key cell-signalling proteins. A large number of studies have found that polyphenols affect the metabolism of organisms by interfering with a variety of intracellular signals, thereby protecting the liver and reducing the risk of liver cancer.

CONCLUSION

This review systematically illustrates that various polyphenols, including resveratrol, chlorogenic acid, caffeic acid, dihydromyricetin, quercetin, catechins, curcumin, etc., improve metabolic disorders through direct or indirect pathways to protect the liver and fight liver cancer.

Bioactivity of Dietary Polyphenols: The Role in LDL-C Lowering

Cardiovascular diseases are the leading causes of the death around the world. An elevation of the low-density lipoprotein cholesterol (LDL-C) level is one of the most important risk factors for cardiovascular diseases. To achieve optimal plasma LDL-C levels, clinal therapies were investigated which targeted different metabolism pathways. However, some therapies also caused various adverse effects. Thus, there is a need for new treatment options and/or combination therapies to inhibit the LDL-C level. Dietary polyphenols have received much attention in the prevention of cardiovascular diseases due to their potential LDL-C lowering effects. However, the effectiveness and potential mechanisms of polyphenols in lowering LDL-C is not comprehensively summarized. This review focused on dietary polyphenols that could reduce LDL-C and their mechanisms of action. This review also discussed the limitations and suggestions regarding previous studies.

Polyphenol Health Effects on Cardiovascular and Neurodegenerative Disorders: A Review and Meta-Analysis

Several studies have demonstrated that polyphenol-enriched diets may have beneficial effects against the development of degenerative diseases, including atherosclerosis and disorders affecting the central nervous system. This activity has been associated not only with antioxidant and anti-inflammatory properties, but also with additional mechanisms, such as the modulation of lipid metabolism and gut microbiota function. However, long-term studies on humans provided controversial results, making the prediction of polyphenol impact on health uncertain. The aim of this review is to provide an overview and critical analysis of the literature related to the effects of the principal dietary polyphenols on cardiovascular and neurodegenerative disorders. We critically considered and meta-analyzed randomized controlled clinical trials involving subjects taking polyphenol-based supplements. Although some polyphenols might improve specific markers of cardiovascular risk and cognitive status, many inconsistent data are present in literature. Therefore, definitive recommendations for the use of these compounds in the prevention of cardiovascular disease and cognitive decline are currently not applicable. Once pivotal aspects for the definition of polyphenol bioactivity, such as the characterization of pharmacokinetics and safety, are addressed, it will be possible to have a clear picture of the realistic potential of polyphenols for disease prevention.

Boldine Attenuates Cholestasis Associated With Nonalcoholic Fatty Liver Disease in Hereditary Hypertriglyceridemic Rats Fed by High-Sucrose Diet

The aim of the current study was to clarify the effect of high sucrose diet (HSD) on bile formation (BF) in rats with hereditary hypertriglyceridemia (HHTg). Potentially positive effects were studied for boldine, a natural choleretic agent. Administration of HSD to HHTg rats led to increased triglyceride deposition in the liver. HSD reduced BF as a consequence of decreased biliary secretion of bile acids (BA) and glutathione. Responsible mechanism was down-regulation of hepatic transporters for BA and glutathione, Bsep and Mrp2, respectively. Moreover, gene expressions of transporters for other constituents of bile, namely Abcg5/8 for cholesterol, Abcb4 for phospholipids, and Oatp1a4 for xenobiotics, were also reduced by HSD. Boldine partially attenuated cholestatic effect of HSD by promotion of biliary secretion of BA through up-regulation of Bsep and Ntcp, and by increase in biliary secretion of glutathione as a consequence of its increased hepatic disposition. This study demonstrates mechanisms of impaired BF during nonalcoholic fatty liver disease induced by HSD. Altered function of responsible transporters suggests also potential for changes in kinetics of drugs, which may complicate pharmacotherapy in subjects with high intake of sucrose, and with fatty liver disease. Sucrose induced alterations in BF may be alleviated by administration of boldine.

The effect of Greek herbal tea consumption on thyroid cancer: a case-control study

BACKGROUND

Although in the last decade several studies have addressed the protective role of black and green tea on several diseases, including cancer, there are only few and controversial studies on the effect of tea on benign and malignant thyroid diseases.

METHODS

An age and gender group matched case-control study conducted in Athens, Greece, was designed. 113 Greek patients with histologically confirmed thyroid cancer and 286 patients with benign thyroid diseases along with 138 healthy controls were interviewed with a pre-structured questionnaire in person by trained interviewers.

RESULTS

An inverse association between chamomile tea consumption and benign/malignant thyroid diseases was found (P < 0.001). The odds of chamomile tea consumption, two to six times a week, after controlling for age, gender and BMI, were 0.30 (95% CI: 0.10-0.89) and 0.26 (95% CI: 0.12-0.5) for developing thyroid cancer and benign thyroid diseases, respectively when compared with not consumption. The duration of consumption was also inversely associated with the diseases. Thirty years of consumption significantly reduced the risk of thyroid cancer and benign thyroid diseases development by almost 80%. Similar, although weaker protective association, was found for sage and mountain tea. Adjustment for smoking, alcohol and coffee consumption did not alter the results.

CONCLUSIONS

Our findings suggest for the first time that drinking herbal teas, especially chamomile, protects from thyroid cancer as well as other benign thyroid diseases.

In vitro toxicity of epigallocatechin gallate in rat liver mitochondria and hepatocytes

Epigallocatechin-3-gallate (EGCG) is the main compound of green tea with well-described antioxidant, anti-inflammatory, and tumor-suppressing properties. However, EGCG at high doses was reported to cause liver injury. In this study, we evaluated the effect of EGCG on primary culture of rat hepatocytes and on rat liver mitochondria in permeabilized hepatocytes. The 24-hour incubation with EGCG in concentrations of 10 μmol/L and higher led to signs of cellular injury and to a decrease in hepatocyte functions. The effect of EGCG on the formation of reactive oxygen species (ROS) was biphasic. While low doses of EGCG decreased ROS production, the highest tested dose induced a significant increase in ROS formation. Furthermore, we observed a decline in mitochondrial membrane potential in cells exposed to EGCG when compared to control cells. In permeabilized hepatocytes, EGCG caused damage of the outer mitochondrial membrane and an uncoupling of oxidative phosphorylation. EGCG in concentrations lower than 10 μmol/L was recognized as safe for hepatocytes in vitro.

IL-1 receptor blockade alleviates endotoxin-mediated impairment of renal drug excretory functions in rats

The aim of our study was to investigate whether two potent anti-inflammatory agents, dexamethasone and anakinra, an IL-1 receptor antagonist, may influence acute kidney injury (AKI) and associated drug excretory functions during endotoxemia (LPS) in rats. Ten hours after LPS administration, untreated endotoxemic rats developed typical symptoms of AKI, with reduced GFR, impaired tubular excretion of urea and sodium, and decreased urinary excretion of azithromycin, an anionic substrate for multidrug resistance-transporting proteins. Administration of both immunosuppressants attenuated the inflammatory response, liver damage, AKI, and increased renal clearance of azithromycin mainly by restoration of GFR, without significant influence on its tubular secretion. The lack of such an effect was related to the differential effect of both agents on the renal expression of individual drug transporters. Only dexamethasone increased the urinary clearance of bile acids, in accordance with the reduction of the apical transporter (Asbt) for their tubular reabsorption. In summary, our data demonstrated the potency of both agents used for the prevention of AKI, imposed by endotoxins, and for the restoration of renal drug elimination, mainly by the improvement of GFR. The influence of both drugs on altered tubular functions and the expression of drug transporters was differential, emphasizing the necessity of knowledge of transporting pathways for individual drugs applied during sepsis. The effect of anakinra suggests a significant contribution of IL-1 signaling to the pathogenesis of LPS-induced AKI.

Atheroprotective effects of (poly)phenols: a focus on cell cholesterol metabolism

Collated observations from several epidemiological studies have demonstrated that dietary intake of (poly)phenols from nuts, coffee, cocoa, grapes, and berries may protect against the development of atherosclerosis. Whereas this beneficial activity has previously been linked mainly to antioxidant or anti-inflammatory properties, recently emerging data suggest mechanisms by which (poly)phenolic substances can modulate cellular lipid metabolism, thereby mitigating atherosclerotic plaque formation. In this review, both experimental studies and clinical trials investigating the atheroprotective effects of the most relevant dietary (poly)phenols are critically discussed.

Partial cloning, tissue distribution and effects of epigallocatechin gallate on hepatic 3-hydroxy-3-methylglutaryl-CoA reductase mRNA transcripts in goldfish (Carassius auratus)

Epigallocatechin gallate (EGCG), the major active component of the green tea, has recently been found to inhibit 3-hydroxy-3-methylglutaryl-CoA reductase (HMGCoAR) activity in vitro and to modulate lipogenesis in vivo. In this study we have evaluated the effects of short-term in vivo exposure to EGCG (6 μg g(-1) BW or 9 μg g(-1) BW) on hepatic HMGCoAR gene expression of goldfish (Carassius auratus). We initially characterized a partial sequence of goldfish HMGCoAR suggesting that the obtained fragment shares high similarity (>92%) with other fish HMGCoAR sequences. Further, the HMGCoAR transcript was detected in all goldfish tissues (except muscle) but primarily in liver, brain and gonads; on the contrary, low expression levels were found in intestine, heart, gill, and kidney. Both EGCG doses significantly decreased hepatic HMGCoAR mRNA levels 180 min post-injection. HMGCoAR was also significantly down-regulated at 90 min after injection in fish treated with the highest dose of EGCG. Our results demonstrate that hepatic HMGCoAR gene expression is acutely responsive to short-term EGCG exposure in goldfish. This finding suggests a potential role of EGCG in transcriptional regulation of the rate-limiting enzyme in cholesterol synthesis.

Epigallocatechin gallate does not accelerate the early phase of liver regeneration after partial hepatectomy in rats

BACKGROUND

Two-thirds partial hepatectomy (PHx) is an established model for the study of liver regeneration after resection. This process is accompanied by oxidative stress.

AIMS

In our study, we tested the effect of epigallocatechin gallate (EGCG), a green tea antioxidant, on the early phase of liver regeneration after PHx.

METHODS

Male Wistar rats were divided into five groups: (I) laparotomy + water for intraperitoneal injections, (II) laparotomy + EGCG 50 mg/kg body weight, (III) PHx + water for injections, (IV) PHx + EGCG 20 mg/kg and (V) PHx + EGCG 50 mg/kg, for 3 consecutive days. The rats were killed 24 h after surgery. Biochemical analysis of rat sera was performed. Histological samples were stained with hematoxylin & eosin and bromodeoxyuridine (BrdU). In hepatectomized rats, we also measured plasma malondialdehyde, tissue malondialdehyde, glutathione and cytokines levels, the activity of caspases 3/7, expression of Nqo-1 and HO-1 genes at the mRNA level, and expression of p21, p-p27 and p-p53 genes at the protein level.

RESULTS

We observed lower accumulation of BrdU in group V when compared to groups III and IV. The activity of caspases 3/7 and expression of p-p53 were lower in group V than in groups III and IV. Tissue levels of IL-6 were lower in group V when compared to group III. Significant differences were not noted in other parameters.

CONCLUSIONS

Administration of EGCG did not stimulate early phase liver regeneration in rats after PHx. There was even lower DNA synthesis in the group treated with a high dose of EGCG.

Cholestatic effect of epigallocatechin gallate in rats is mediated via decreased expression of Mrp2

Epigallocatechin gallate (EGCG) has been shown to be protective in various experimental models of liver injury, although opposite effects have also been reported. Since its effect on biliary physiology has not been thoroughly investigated, the present study evaluated effect of EGCG on bile flow and bile acid homeostasis in rats. Compared to controls, EGCG treatment decreased bile flow by 23%. Hepatic paracellular permeability and biliary bile acid excretion were not altered by EGCG administration, but biliary glutathione excretion was reduced by 70%. Accordingly, the main glutathione transporter on the hepatocyte canalicular membrane, multidrug resistance-associated protein 2 (Mrp2), was significantly decreased at the protein level. EGCG administration also doubled plasma bile acid levels compared to controls. While protein levels of the main hepatic bile acid transporters were unchanged, the rate-limiting enzyme in the bile acid synthesis, Cyp7a1, was significantly increased by EGCG. Enhanced bile acid synthesis in these animals was also confirmed by a 2-fold increase in plasma marker 7α-hydroxy-4-cholesten-3-one. In contrast, EGCG markedly downregulated major bile acid transporters (Asbt and Ostα) and regulatory molecules (Shp and Fgf15) in the ileum. When EGCG was coadministered with ethinylestradiol, a potent cholestatic agent, it did not show any additional effect on the induced cholestasis. This study shows ability of EGCG to raise plasma bile acid concentrations, mainly through Cyp7a1 upregulation, and to decrease bile production through reduction in Mrp2-mediated bile acid-independent bile flow. In conclusion, our data demonstrate that under certain conditions EGCG may induce cholestasis.