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The biological activity of urolithin

August 11,2023

Uro-A does not exist in its natural state, but is produced through a series of transformations of ET by the gut microbiota (Figure 1). Foods rich in ET are metabolized into Uro-A in the human body through the stomach and small intestine, and ultimately mainly in the colon. A small amount of Uro-A can also be detected in the lower segment of the small intestine. ET removes the lactone ring in the body and undergoes decarboxylation reaction to produce urolithin M5 (Uro M5). Uro-M5 undergoes dehydroxylation reactions at different positions to generate tetrahydroxyuridine isomers such as Uro-D and Uro-M6. Tetrahydroxyuridine undergoes another dehydroxylation reaction to generate tetrahydroxyuridine isomers such as Uro-C and Uro-M7. Trihydroxyuridine undergoes another dehydroxylation reaction to obtain dihydroxyuridine isomers such as Uro-A and Uro-A isomers (iso Uro-A), After the last dehydroxylation reaction, monohydroxy urolithin B (Uro-B) was obtained. Uro-B is more prone to dehydroxylation from iso Uro-A [2]. Heber [3] pointed out that ET will not be fully absorbed into the bloodstream, but will be hydrolyzed into ellagic acid (EA), which is metabolized into Uro-A through the gut microbiota. Uro-A binds to the liver and is excreted from the urine. Seeram et al. [4] analyzed the components in human plasma and urine after ingestion of ET, and studied the pharmacokinetics and tissue distribution of pomegranate derived ET. They found that EA bound and free phase metabolites, including dimethylellagic acid glucuronic acid (DMEAG) and uroitin, were detected in plasma and urine. Uro-A is the most active type of urolith, and 10% to 50% of people can produce iso Uro-A [5]. Uro-A in the blood circulation is mostly in the form of glucoside or sulfate binding, while Uro-A in plasma samples is mostly in free form. According to research, free form Uro-A accounted for 77.2% and 65.7% of plasma samples taken 1 and 6 hours after sampling, respectively [6]. Recent studies have shown that the metabolic products of urolithin in the body are age related. Before the age of 40, the proportion of Uro-A is significantly higher than that of Uro-B, while after the age of 40, the two tend to be the same [7].

Health Benefits:

1. Antioxidant activity

Given the significant antioxidant activity of the precursor substances of urolith, tannic acid and tannic acid, there have been many studies on the antioxidant activity of urolith. Oxygen radical absorption capacity (ORAC) experiments have shown that urinary stone metabolites have certain antioxidant activity, among which UroA has the strongest antioxidant activity [28], second only to procyanidin oligomers, catechins, epicatechin, and 3,4-dihydroxyphenylacetic acid [29]. However, compared with tannic acid and tannic acid, the antioxidant activity of urolithin is significantly reduced. For example, the free radical scavenging activity of 1,1-diphenyl-2-trinitrophenylhydrazine (DPPH) in pomegranate is 42 times higher than that of UroA, and the free radical scavenging activity of 2,2 '- diazodi (3-ethylbenzothiazole-6-sulfonic acid) diamine salt (2,2' - azinobis - (3-ethylbenzthiazoline-6-sulfonate) ABTS is 3500 times higher than that of uroA. In several other antioxidant experiments, urolith also showed certain antioxidant activity, with IC50 values of 100 μ Above mol/L [28]. However, due to its high transmembrane transport efficiency, some uroliths exhibit high activity in vivo antioxidant experiments. For example, Bialonska et al. [20] found that in cell antioxidant experiments, the IC50 values of UroC and UroA were 0.16, respectively μ Mol/L and 13.6 μ Mol/L, and in the same experiment, the IC50 values of ellagic acid and VC were 1.1, respectively μ Mol/L and 1.9 μ Mol/L. Haddad et al. [30] found that after consuming walnuts, the level of UroA in urine significantly increased, while postprandial levels of tocopherols and catechins significantly increased, and oxidative stress reactions significantly decreased. It was found that UroB (0.5-20 µ mol/L) and UroA (10 µ mol/L) can increase cell survival rate and exhibit significant cytoprotective effects by inducing neural cells under oxidative stress [21]. UroA, UroB, 8-OMe-Uro and ellagic acid can significantly reduce the levels of reactive oxygen species (ROS) and malondialdehyde (MDA) in human bladder cancer T24 cells induced by H2O2, and can increase the activity of superoxide dismutase (SOD) [31]. Recent studies have found that urolithin not only has antioxidant effects, but also helps with oxidation. Kallio et al. [32] found that urolithin has a strong antioxidant ability in ORAC experiments, while it has a prooxidant effect in cell and Copper initiated Prooxidant Activity (CIPA) experiments.

2. Anti inflammatory activity

Colon fibroblasts play an important role in the intestinal immune response, and urolithin can significantly inhibit the inflammatory response of colon fibroblasts induced by interleukin-1b (IL-1b) or tumor necrosis factor-a (TNF-a), reducing the expression level of the inflammatory factor prostaglandin E2 (PGE2). Among them, UroA activity is the strongest, followed by UroB activity, and ellagic acid activity is the weakest. UroA can also significantly inhibit IL-1b or TNF-a induced nuclear transcription factor in colon fibroblasts- κ B. NF- κ B) By activating mitogen activated protein kinases (MAPK), downregulating the expression of key enzymes in PGE2 synthesis such as cyclooxygenase-2 (COX-2) and membrane bound prostaglandin E2 synthase 1 (mPGES-1), thereby reducing the level of PGE2 [23]. UroB and UroC can significantly inhibit the activity of histone acetyltransferase (HAT), while the acetylation or deacetylation of histones is associated with the inflammatory transcription factor NF- κ The activation and deactivation of B and AP-1 are related, therefore UroB and UroC also play important roles in inflammation [33]. The glucuronic acid derivatives of urolithin also have certain anti-inflammatory activities, such as the uronic acid esters of UroA and UroB can significantly inhibit TNF-a, induce migration of human aortic endothelial cells and adhesion of monocytes, and significantly reduce the expression of CC chemokine (C-C motif) ligand 2 (CCL2) and plasminogen activator inhibitor 1 (PAI-1), which are similar in activity to UroA The activity of UroB is equivalent [24], indicating that UroA and UroB's glucuronic acid ester derivatives may be important active substances in pomegranate juice to inhibit cardiovascular inflammation [34].

3.Anticancer activity

In vitro studies have shown that urolithin can effectively inhibit the proliferation of prostate cancer, colon cancer and bladder cancer cells. The distribution of urolithin in the body has significant tissue specificity. For example, after consuming pomegranate juice or walnuts, the metabolite urolithin can be enriched in human prostate tissue, which is expected to be used for the treatment of prostate related diseases [20]. Vicinanza et al. [35] found that the metabolites of pomegranate juice, ellagic acid and UroA, can inhibit the proliferation of androgen dependent prostate cancer cells and have a synergistic inhibitory effect. Stolarczyk et al. [36] found that UroC can significantly inhibit the proliferation of prostate cell line LNCaP (IC50=35.2) μ Mol/L), reducing the expression of prostate specific antigen (PSA), significantly inhibiting the activity of arginase, therefore UroC may be an important active substance in the prevention or treatment of prostate cancer in Epilobium plants. Human cytochrome P450 oxidase CYP1B1 is an important target for prostate cancer chemotherapy, and CYP1B1 inhibitors play an important role in the occurrence, development, and drug resistance formation of tumors. Kasimsetty et al. [25] found through in vitro recombinant CYP1B1 mediated 7-ethoxyresorufin O-deethylase (EROD) activity analysis that urolithin can double regulate CYP1B1 activity by inhibiting it and reducing the expression of CYP1B1 protein. Among them, UroA and UroB are specific inhibitors of CYP1B1, with selectivity 2-3 times that of CYP1A1. Their precursor substances Punicalins and Punicalagins are specific inhibitors of CYP1A1, with selectivity 5-10 times that of CYP1B1. Tannin and its metabolite urolithin also have a significant inhibitory effect on the proliferation of human colon cancer Caco-2 cells. The mechanism is mainly related to cell S and G2/M cycle arrest, fibroblast growth factor 2/epidermal growth factor receptor (FGFR2/EGFR), oncogenes K-Ras, c-Myc, tumor suppressor factors DUSP6, Fos, and cell cycle related gene CCNB1 The expression regulation of CCNB1IP1 and others is related [26]. Kasimsetty et al. [27] found that UroA, UroB, UroC, and UroD can induce apoptosis in human colon cancer HT-29 cells at concentrations of 25-50 µ mol/L, inhibit 50% of the activity of human cytochrome P450 oxidase CYP1 at 50-75 µ mol/L, and induce cell cycle arrest at 500 µ mol/L. Qiu Zhenpeng et al. [31] found that UroA, UroB, 8-OMe Uro and ellagic acid can significantly inhibit the proliferation of T24 cell line of bladder cancer in vitro, with IC50 of 43.9, 35.2, 46.3, and 33.7 µ mol/L, respectively. Their inhibitory effect is related to the p38-MAPK pathway and/or c-Jun mediated Caspase-3 activation and the reduction of oxidative stress status in T24 cells.

Urinary stone metabolites can inhibit the activity of tumor related enzymes such as protein kinase CK2 and topoisomerase II, and can affect the drug resistance of tumor cells. Cozza et al. [37] found that ellagic acid and UroA can significantly inhibit the activity of protein kinase CK2 enzyme in vitro, with UroA having strong activity with an IC50 of 0.39 µ mol/L. Tannic acid and urolith like substances or human topoisomerase II α And β Competitive inhibitors of type I isozymes can compete with ATP at concentrations below 1 µ mol/L for the ATP binding site in topoisomerase and exhibit a significant dose-effect relationship [38]. Breast cancer resistance protein (BCRP/ABCG2) is an important protein that mediates the drug resistance of tumor cells, which seriously affects the chemotherapy effect of cancer. Gonzalez Sarrias et al. [39] found that UroA and its sulfate derivatives can serve as substrates for BCRP/ABCG2 and can dose-dependently inhibit the transport of the anti-tumor drug mitoxantrone. This indicates that the intestinal metabolites of tannic acid and tannic acid can regulate ABCG2/BCRP mediated cell transport and cancer resistance mechanisms.

4.Regulating gut microbiota

The gut microbiota generates and releases specific signaling molecules through quorum sensing for information exchange, thereby regulating the population behavior and gene expression of microorganisms. The mammalian intestinal pathogen Yersinia enterocolitica can produce two important N-acyl homoserine lactones (AHLs), N-hexylhomoserine lactones (C6-HSL) and N-oxo-C6-HSL, which play important roles in QS mediated intestinal infections. Research has found that UroA and UroB can significantly reduce Y The expression levels of C6-HSL and 3-oxo C6-HSL signaling molecules in entocolitica inhibit QS related biofilm formation and movement processes, but this inhibitory effect is not related to the downregulation of AHLs synthesis related genes yenI and yenR, as well as the expression of exercise related genes flhDC, fliA, and fleB. From this, it can be seen that urinary stone compounds can inhibit the growth of pathogenic bacteria through quorum sensing of the gut microbiota, thereby maintaining the balance of the gut microbiota.

5. Estrogen receptor modulators

Plant derived estrogen/anti estrogen substances have various effects such as regulating cholesterol levels and maintaining postmenopausal bone density. Research has found that the unique molecular structures of UroA and UroB make them easy to interact with α- and β- Estrogen receptor binding [22], but due to different substituents, its estrogenic effect also varies [41], among which UroA has an effect on estrogen α- and β- The affinity of receptors is greater than that of UroB, and UroA is more likely to bind to estrogen α- Receptors. UroA and UroB can promote the proliferation of estrogen sensitive human breast cancer cell line MCF-7 in a dose-dependent manner, showing a weak estrogen like effect, and the concentration is up to 40 μ At mol/L, it does not inhibit the proliferation of MCF-7 cells or exhibit cytotoxic effects. Urolithin also has a certain anti estrogen effect, which can dose-dependently inhibit the proliferation of MCF-7 cells induced by estradiol [22].

6. Inhibition of protein glycosylation

Protein glycation end products are secondary effects of hyperglycemia, which are closely related to cardiovascular and cerebrovascular diseases, diabetes, senile dementia and other diseases [42]. Research has found that UroA and UroB (1 µ mol/L) can significantly inhibit protein glycosylation, with UroA showing a significant dose-effect relationship, while UroB does not exhibit a significant dose-effect relationship. The protein glycosylation inhibition effect of urolithin is not related to its antioxidant activity and glyoxal binding ability [21].

Resource:YIN Peipei, YAN Linlin, CAO Ruoyu, CHEN Xiaoyuan, MA Chao, LIU Yujun, A Review of Urolithins-Gut Microflora Metabolites of Dietary Ellagic Acid, 2015

Shi Ying, Du Feng, Wang Yue, Chen Rong, Liu Qiling, and Li Yingna, Research progress on the pharmacological effects and mechanisms of urolithin A, 2022-20 (01)