Tannic acid down-regulates the angiotensin type 1 receptor through a MAPK-dependent mechanism

The effect of tannic acid on renal renin-angiotensin signaling pathway in a model of unilateral ureteral obstruction in male Wistar rats

The purpose of current study was to elucidate polyphenol tannic acid effect on renal function and activity of the renin-angiotensin system after unilateral ureteral obstruction (UUO). Male Wistar rats were divided into three groups of six randomly: 1) Sham, 2) UUO, and 3) UUO + Tannic acid. Rats in the UUO and UUO + Tannic acid groups experienced unilateral ureteral obstruction. In the Sham group, the abdominal cavity was exposed without UUO induction. In the UUO + Tannic acid group, animals received tannic acid (20 mg/kg) intraperitoneally, 6 and 12 h after clamping the left ureter and 6 and 12 h after the right nephrectomy. Blood samples were taken to measure blood urea nitrogen (BUN) and creatinine levels. Kidney tissue samples were obtained for assessment of oxidative stress, inflammatory indices and the levels of renin-angiotensin system components. Tannic acid administration significantly improved UUO-induced kidney dysfunction (serum BUN: 66.42 ± 14.414 mg/dl, p < 0.05; serum creatinine: 1.67 ± 0.258 mg/dl, p < 0.05), oxidative stress (MDA level: 95.29 ± 37.35 µmol/g tissue, p < 0.05; SOD activity: 59.82 ± 13.41 U/g protein, p < 0.01) and inflammation (renal TNF-α: 57.05 ± 15.653 pg/g tissue, p < 0.05; renal IL-6: 117.015 ± 24.076 pg/g tissue, p < 0.001). The treatment caused a reduction in the amount of renal angiotensinogen, renin and ACE genes expression compared to the UUO group (Angiotensinogen: 8.9 ± onefold, p < 0.05, Renin: 6.5 ± 1.14 fold, p < 0.05, ACE: 4.9 ± 0.64 fold, p < 0.05). Angiotensin II type 1 receptor protein levels decreased in the tannic acid-treated rats in comparison with the UUO group (0.61 ± 0.136, p < 0.05). According to the result of the current study, tannic acid considerably attenuated the complications of unilateral ureteral obstruction through renin-angiotensin system modulation. Trial registration: IR.TUMS.MEDICINE.REC.1400.802.

Berry consumption mitigates the hypertensive effects of a high-fat, high-sucrose diet via attenuation of renal and aortic AT1R expression resulting in improved endothelium-derived NO bioavailability

Dysregulation of the renin-angiotensin system (RAS) is a contributor to high-fat diet-related blood pressure (BP) increases. Deleterious effects of dysregulated RAS result in an overproduction of reactive oxygen species and a decrease in endothelial nitric oxide (NO) bioavailability due to increased NADPH oxidase (NOX) expression. Dietary polyphenols have been shown to mitigate the imbalance in the redox state and protect against endothelial dysfunction induced by a high-fat diet. Thus, we aim to determine whether polyphenol-rich blackberry and raspberry, alone and in combination, attenuate the detrimental effects of a high-fat, high-sucrose (HFHS) diet on the vascular endothelium and kidneys of mice. We show that a HFHS diet increased the expression of renal and aortic angiotensin type 1 receptor (AT₁R). Further, NOX1 and NOX4 expression were increased in the kidney contributing to fibrotic damage. In human aortic endothelial cells (HAECs), palmitic acid increased the expression of NOX4, potentially driving oxidative damage in the aorta, as evidenced by increased nitrotyrosine expression. Berries reduced the expression of renal and aortic AT₁R, leading to a subsequent decrease in renal NOX expression and reduced aortic oxidative stress evidenced by reduced nitrotyrosine expression. Blackberry and raspberry in combination increased the expression of NRF2 and its downstream proteins in HAECs, thereby reducing the oxidative burden to the endothelium. In combination, blackberry and raspberry also increased serum levels of NO metabolites. These findings indicate that blackberry and raspberry unique polyphenols may act synergistically to favorably modulate the abovementioned pathways and attenuate HFHS diet-induced increases in BP.

Pharmacological effects and mechanisms of tannic acid

In recent years, increasing attention has been paid to the pharmacological efficacy of tannins. Tannic acid (TA), the simplest hydrolysable tannin that has been approved by the FDA as a safe food additive, is one of the most important components of these traditional medicines. Studies have shown that TA displays a wide range of pharmacological activities, such as anti-inflammatory, neuroprotective, antitumor, cardioprotective, and anti-pathogenic effects. Here, we summarize the known pharmacological effects and associated mechanisms of TA. We focus on the effect and mechanism of TA in various animal models of inflammatory disease and organ, brain, and cardiovascular injury. Moreover, we discuss the possible molecular targets and signaling pathways of TA, in addition to the pharmacological effects of TA-based nanoparticles and TA in combination with chemotherapeutic drugs.

Recent Progress of Basic Studies of Natural Products and Their Dental Application

The present article reviews the research progress of three major polyphenols (tannins, flavonoids and lignin carbohydrate complexes), chromone (backbone structure of flavonoids) and herbal extracts. Chemical modified chromone derivatives showed highly specific toxicity against human oral squamous cell carcinoma cell lines, with much lower toxicity against human oral keratinocytes, as compared with various anticancer drugs. QSAR analysis suggests the possible correlation between their tumor-specificity and three-dimensional molecular shape. Condensed tannins in the tea extracts inactivated the glucosyltransferase enzymes, involved in the biofilm formation. Lignin-carbohydrate complexes (prepared by alkaline extraction and acid-precipitation) and crude alkaline extract of the leaves of Sasa species (SE, available as an over-the-counter drug) showed much higher anti-HIV activity, than tannins, flavonoids and Japanese traditional medicine (Kampo). Long-term treatment with SE and several Kampo medicines showed an anti-inflammatory and anti-oxidant effects in small size of clinical trials. Although the anti-periodontitis activity of synthetic angiotensin II blockers has been suggested in many papers, natural angiotensin II blockers has not yet been tested for their possible anti-periodontitis activity. There should be still many unknown substances that are useful for treating the oral diseases in the natural kingdom.

Protective effects of tannic acid on pressure overload-induced cardiac hypertrophy and underlying mechanisms in rats

Objectives

The aim of this study was to examine the cardioprotective effects and latent mechanism of tannic acid (TA) on cardiac hypertrophy.

Methods

Abdominal aortic banding (AAB) was used to induce pressure overload-induced cardiac hypertrophy in male Wistar rats, sham-operated rats served as controls. AAB rats were treated with TA (20 and 40 mg/kg) or captoril.

Key findings

Abdominal aortic banding rats that received TA showed ameliorated pathological changes in cardiac morphology and coefficients, decreased cardiac hypertrophy and apoptosis, a reduction in over expressions of angiotensin type 1 receptor (AT1R), angiotensin type 2 receptor (AT2R), phosphorylation of extracellular signal-regulated kinase 1/2 (ERK1/2) and transforming growth factor-β (TGF-β) mRNA, and modified expression of matrix metal proteinase-9 (MMP-9) mRNA in AAB rat hearts. Furthermore, TA treatment contributed to a decrease in malondialdehyde (MDA) and endothelin-1 (ET-1) activities and content, while it caused an increase in superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GSH-Px), nitric oxide (NO) and endothelial NO synthase (e-NOS). Furthermore, TA downregulated expression of tumour necrosis factor-α (TNF-α), interleukin-1β (IL-1β), bax, caspase-3 and upregulated expression of bcl-2.

Conclusions

Tannic acid displayed obvious suppression of AAB-induced cardiac hypertrophy in rats. The cardioprotective effects of TA may be attributed to multitargeted inhibition of oxidative stress, inflammation, fibrosis and apoptosis in addition to an increase in NO levels, decrease in ET-1 levels, and downregulation of angiotensin receptors and the phosphorylation of ERK1/2.

Flavonoids-Rich Orthosiphon stamineus Extract as New Candidate for Angiotensin I-Converting Enzyme Inhibition: A Molecular Docking Study

This study aims to evaluate the in vitro angiotensin-converting enzyme (ACE) inhibition activity of different extracts of Orthosiphon stamineus (OS) leaves and their main flavonoids, namely rosmarinic acid (RA), sinensetin (SIN), eupatorin (EUP) and 3′-hydroxy-5,6,7,4′-tetramethoxyflavone (TMF). Furthermore, to identify possible mechanisms of action based on structure–activity relationships and molecular docking. The in vitro ACE inhibition activity relied on determining hippuric acid (HA) formation from ACE-specific substrate (hippuryl-histidyl-leucine (HHL)) by the action of ACE enzyme. A High Performance Liquid Chromatography method combined with UV detection was developed and validated for measurement the concentration of produced HA. The chelation ability of OS extract and its reference compounds was evaluated by tetramethylmurexide reagent. Furthermore, molecular docking study was performed by LeadIT-FlexX: BioSolveIT’s LeadIT program. OS ethanolic extract (OS-E) exhibited highest inhibition and lowest IC₅₀ value (45.77 ± 1.17 µg/mL) against ACE compared to the other extracts. Among the tested reference compounds, EUP with IC₅₀ 15.35 ± 4.49 µg/mL had highest inhibition against ACE and binding ability with Zn (II) (56.03% ± 1.26%) compared to RA, TMF and SIN. Molecular docking studies also confirmed that flavonoids inhibit ACE via interaction with the zinc ion and this interaction is stabilized by other interactions with amino acids in the active site. In this study, we have demonstrated that changes in flavonoids active core affect their capacity to inhibit ACE. Moreover, we showed that ACE inhibition activity of flavonoids compounds is directly related to their ability to bind with zinc ion in the active site of ACE enzyme. It was also revealed that OS extract contained high amount of flavonoids other than RA, TMF, SIN and EUP. As such, application of OS extract is useful as inhibitors of ACE.

Interplay between EGR1 and SP1 is critical for 13-cis retinoic acid-mediated transcriptional repression of angiotensin type 1A receptor

Recently, we have demonstrated that 13-cis retinoic acid (13cRA) downregulates rat angiotensin type 1A receptor (Agtr1a) gene transcription through a MAP kinase (ERK1/2)-dependent mechanism in rat liver epithelial and aortic smooth muscle cells. However, the exact mechanism remained unknown. In this study, we determined the signaling intermediates activated by ERK1/2 involved in 13cRA-mediated Agtr1a downregulation. Rat Agtr1a chloramphenicol acetyltransferase (CAT) promoter construct containing a sequence -2541 and -1836 bp upstream of the start site demonstrated reduced CAT activity; this region possesses a specificity protein 1 (SP1) consensus sequence (5'-TGGGGCGGGGCGGGG-3'). Mobility shift analysis using untreated nuclear extracts in the presence of mithramycin A suggests that the trans-acting factor binding to this cis-acting element is SP1. 13cRA significantly reduced specific binding without any change in SP1 protein expression. Studies showed that 13cRA treatment maximally phosphorylates ERK1/2 within 5-10 min, which translocates to the nucleus, activating early growth response protein 1 (Egr1) mRNA expression at 20 min followed by de novo protein synthesis, leading to an EGR1/SP1 interaction. siRNA silencing of Egr1 restored Agtr1a mRNA and protein expression in 13cRA-treated cells, and Sp1 silencing results in complete loss of Agtr1a expression. Our study suggests that 13cRA-mediated activation of ERK1/2, through EGR1, is capable of disrupting SP1, the requisite trans-activator for Agtr1a expression, providing a novel paradigm in Agtr1a gene transcription.