Rhamnetin Prevents Bradykinin-Induced Expression of Matrix Metalloproteinase-9 in Rat Brain Astrocytes by Suppressing Protein Kinase-Dependent AP-1 Activation

Bradykinin (BK) has been recognized as a stimulant for matrix metalloproteinase (MMP)-9 expression, contributing to neuroinflammation. Modulating the BK/MMP-9 pathway offers potential in the treatment of neuroinflammatory disorders. Rhamnetin (RNT), a flavonoid compound known for its antioxidant and anti-inflammatory effects, has shown promise. However, the specific mechanisms through which RNT inhibits BK-induced MMP-9 expression remain unclear. Therefore, this study aims to delve into the intricate mechanisms underlying this process. Here, we initially demonstrated that RNT effectively attenuated BK-induced MMP-9 expression and its associated cell migration in rat brain astrocyte-1 (RBA-1) cells. Further investigation revealed that BK-driven MMP-9 protein, mRNA, and promoter activity linked to cell migration relied on c-Src, Pyk2, EGFR, PDGFR, PI3K/Akt, JNK1/2, and c-Jun. This was validated by the inhibition of these effects through specific inhibitors, a finding substantiated by the introduction of siRNAs targeting these signaling molecules. Notably, the phosphorylated levels of these signaling components induced by BK were significantly reduced by their respective inhibitors and RNT, underscoring the inhibitory role of RNT in this process. These findings indicate that, in RBA-1 cells, RNT diminishes the heightened induction of MMP-9 triggered by BK through the inhibition of c-Src/Pyk2/PDGFR and EGFR/PI3K/Akt/JNK1/2-dependent AP-1 activation. This suggests that RNT holds promise as a potential therapeutic approach for addressing neuroinflammation in the brain.

Protective Effects of Rhamnetin in Carbapenem-Resistant Acinetobacter baumannii-Induced Sepsis Model and the Underlying Mechanism

Carbapenem-resistant Acinetobacter baumannii (CRAB) is a well-known harmful bacterium that causes severe health disorders and dysregulates the host immune response associated with inflammation. Upon examining the suppressive activity of natural flavonoid rhamnetin on various pro-inflammatory cytokines in a CRAB-induced septic shock mouse model, we found that rhamnetin inhibited the production of IL-1β and IL-18, two pro-inflammatory cytokines associated with pyroptotic cell death, a process dependent on caspase-1. In this study, we investigated the antioxidant and anti-apoptotic activities of rhamnetin and the underlying mechanism of action in a CRAB infection. In the CRAB-induced septic shock mouse model, rhamnetin reduced the level of lipopolysaccharide (LPS) in lung lysates, resulting in the inhibition of TLR4-mediated inflammatory signaling. Notably, rhamnetin reduced intracellular reactive oxygen species (ROS) generation in macrophages and inhibited apoptotic and pyroptotic cell injury induced by CRAB infection. Therefore, rhamnetin inhibited LPS-induced pro-inflammatory mediators, hindering apoptotic and pyroptotic processes and contributing to a recovery effect in CRAB-induced sepsis mice by suppressing oxidative stress. Taken together, our study presents the potential role of rhamnetin in protecting against oxidative damage induced by CRAB infection through a TLR4 and ROS-mediated pyroptotic pathway, showing an alternative mechanism for sepsis prevention. Therefore, rhamnetin is a promising therapeutic candidate for treating CRAB-induced sepsis.

Rhamnetin, a Natural Flavonoid, Ameliorates Organ Damage in a Mouse Model of Carbapenem-Resistant Acinetobacter baumannii-Induced Sepsis

In sepsis, the persistence of uncontrolled inflammatory response of infected host cells eventually leads to severe lung and organ failure and, ultimately, death. Carbapenem-resistant Acinetobacter baumannii (CRAB), causative bacteria of sepsis and lung failure in acute cases, belongs to a group of critical pathogens that cannot be eradicated using the currently available antibiotics. This underlines the necessity of developing new modes of therapeutics that can control sepsis at the initial stages. In this study, we investigated the anti-inflammatory activities in vitro and in vivo and the antiseptic effects of rhamnetin, a naturally occurring flavonoid. We found that among its isoforms, the potency of rhamnetin was less explored but rhamnetin possessed superior anti-inflammatory activity with least cytotoxicity. Rhamnetin showed significant anti-inflammatory effects in lipopolysaccharide-, CRAB-, and Escherichia coli (E. coli)-stimulated mouse macrophages by inhibiting the release of interleukin-6 and nitric oxide. In a mouse model of sepsis infected with clinically isolated CRAB or E. coli, rhamnetin significantly reduced the bacterial burden in the organs. In addition, normalized pro-inflammatory cytokine levels in lung lysates and histological analysis of lung tissue indicated alleviation of lung damage. This study implies that a potent natural product such as rhamnetin could be a future therapeutic for treating carbapenem-resistant gram-negative sepsis.

Anti-Inflammatory Effects of Rhamnetin on Bradykinin-Induced Matrix Metalloproteinase-9 Expression and Cell Migration in Rat Brain Astrocytes

Bradykinin (BK) has been shown to induce matrix metalloproteinase (MMP)-9 expression and participate in neuroinflammation. The BK/MMP-9 axis can be a target for managing neuroinflammation. Our previous reports have indicated that reactive oxygen species (ROS)-mediated nuclear factor-kappaB (NF-κB) activity is involved in BK-induced MMP-9 expression in rat brain astrocytes (RBA-1). Rhamnetin (RNT), a flavonoid compound, possesses antioxidant and anti-inflammatory effects. Thus, we proposed RNT could attenuate BK-induced response in RBA-1. This study aims to approach mechanisms underlying RNT regulating BK-stimulated MMP-9 expression, especially ROS and NF-κB. We used pharmacological inhibitors and siRNAs to dissect molecular mechanisms. Western blotting and gelatin zymography were used to evaluate protein and MMP-9 expression. Real-time PCR was used for gene expression. Wound healing assay was applied for cell migration. 2',7'-dichlorodihydrofluorescein diacetate (H2DCF-DA) and nicotinamide adenine dinucleotide phosphate (NADPH) oxidase (NOX) were used for ROS generation and NOX activity, respectively. Promoter luciferase assay and chromatin immunoprecipitation (ChIP) assay were applied to detect gene transcription. Our results showed that RNT inhibits BK-induced MMP-9 protein and mRNA expression, promoter activity, and cell migration in RBA-1 cells. Besides, the levels of phospho-PKCδ, NOX activity, ROS, phospho-ERK1/2, phospho-p65, and NF-κB p65 binding to MMP-9 promoter were attenuated by RNT. In summary, RNT attenuates BK-enhanced MMP-9 upregulation through inhibiting PKCδ/NOX/ROS/ERK1/2-dependent NF-κB activity in RBA-1.

Rhamnetin: a review of its pharmacology and toxicity

OBJECTIVES

Numerous natural products, including rhamnetin, have been studied in recent years owing to the need for new herbal remedies to treat different illnesses. This study aimed to review the salient properties of rhamnetin and its pharmacological potential and possible toxicological effects.

KEY FINDINGS

A search carried out in the ScienceDirect database using the term 'rhamnetin' yielded 573 articles published between 1977 and 2021. However, only those studies that mentioned pharmacological activity of rhamnetin were included in this study. As a result of this selection process, this study included reports that describe rhamnetin as a secondary metabolite with several pharmacological properties.

SUMMARY

Rhamnetin (2-(3,4-dihydroxyphenyl)-3,5-dihydroxy-7-methoxychromen-4-one) is a secondary metabolite, belonging to the flavonoid class, present in various plants and fruits; it has different pharmacological properties, including antioxidant, anticancer, anti-inflammatory, antiviral and antibacterial activity. However, conclusive results on the toxicology of rhamnetin have not been reported yet. Therefore, further research is needed to gather detailed information about the effects of rhamnetin.

Rhamnetin induces apoptosis in human breast cancer cells via the miR-34a/Notch-1 signaling pathway

The present study aimed to investigate whether rhamnetin induced apoptosis in human breast cancer cells and the underlying molecular mechanism of this anti cancer effect. The treatment of MCF-7 cells with rhamnetin was able to significantly inhibit cell proliferation and induce caspase-3/9 activity in a dose- and time-dependent manner, compared with untreated cells. In addition, treatment with rhamnetin was able to significantly promote the expression of p53 protein and microRNA (miR-)34a compared with untreated cells. The treatment with rhamnetin also suppressed the expression of Notch1 protein in MCF-7 cells compared with untreated cells. Subsequently, miR-24a expression was promoted in rhamnetin-treated MCF-7 cells using a miR-34a plasmid. The overexpression of miR-34a was able to significantly inhibit cell viability and induce caspase-3/9 activity in MCF-7 cells following treatment with rhamnetin. Furthermore, the overexpression of miR-34a was able to significantly promote the expression of p53 protein and miR-34a, and suppress the expression of Notch1 protein in rhamnetin-treated MCF-7 cells. Therefore, the results of the present study demonstrated that rhamnetin induced apoptosis in human breast cancer cells via the miR-34a/Notch-1 signaling pathway.

Evaluation of Rhamnetin as an Inhibitor of the Pharmacological Effect of Secretory Phospholipase A2

Rhamnetin (Rhm), 3-O-methylquercetin (3MQ), and Rhamnazin (Rhz) are methylated derivatives of quercetin commonly found in fruits and vegetables that possess antioxidant and anti-inflammatory properties. Phospholipase A2 (PLA2) displays several important roles during acute inflammation; therefore, this study aimed at investigating new compounds able to inhibit this enzyme, besides evaluating creatine kinase (CK) levels and citotoxicity. Methylated quercetins were compared with quercetin (Q) and were incubated with secretory PLA2 (sPLA2) from Bothrops jararacussu to determine their inhibitory activity. Cytotoxic studies were performed by using the J774 cell lineage incubated with quercertins. In vivo tests were performed with Swiss female mice to evaluate decreasing paw edema potential and compounds’ CK levels. Structural modifications on sPLA2 were made with circular dichroism (CD). Despite Q and Rhz showing greater enzymatic inhibitory potential, high CK was observed. Rhm exhibited sPLA2 inhibitory potential, no toxicity and, remarkably, it decreased CK levels. The presence of 3OH on the C-ring of Rhm may contribute to both its anti-inflammatory and enzymatic inhibition of sPLA2, and the methylation of ring A may provide the increase in cell viability and low CK level induced by sPLA2. These results showed that Rhm can be a candidate as a natural compound for the development of new anti-inflammatory drugs.

May argyrophilic nucleolar organizing region-associated protein synthesis be used for selecting the most reliable dose of drugs such as rhamnetin in cancer treatments?

BACKGROUND

Rhamnetin is a flavonoid that has antioxidant, anti-inflammatory and anti-cancer effects. Nucleolar-organizing regions are the ribosomal genes region. We aimed to identify whether rhamnetin has an effect on cell proliferation and whether AgNOR proteins may be used for the detection of therapeutic benefits of the drugs and new metabolites, which have the potential of being used for cancer treatments.

METHODS

Twenty-four mice with Ehrlich's ascites carcinoma (EAC) were randomly assigned to three main groups as positive control, and groups 2 and 3 treated intraperitoneally with rhamnetin (100 µg/kg and 200 µg/kg, respectively). All the animals were sacrificed on day16, 24 h after the last dose; the tumors, which developed at the site of injection were removed. Then, mean AgNOR number and total AgNOR area/nuclear area (TAA/NA) were detected for each mouse.

RESULTS

Significant differences were detected among all groups for mean AgNOR number (p = 0.000) and TAA/NA ratio (p = 0.000). While the difference between positive control and Rhamnetin (100 µg/kg) group was not significant (p = 0.387), there are significant differences between positive control and Rhamnetin (200 µg/kg) group (p = 0.000) and between Rhamnetin (100 µg/kg) and Rhamnetin (200 µg/kg) groups (p = 0.000) for TAA/NA ratio.

CONCLUSION

Rhamnetin has an important role in preventing cancer formation. Our study showed that mean AgNOR numbers and TAA/NA values may be used also as biomarkers for evaluating the success rate of the performed therapeutic strategy and accurate dose selection for the management of the disease (Tab. 3, Fig. 3, Ref. 45).

Rhamnetin attenuates cognitive deficit and inhibits hippocampal inflammatory response and oxidative stress in rats with traumatic brain injury

Activation of the immune system in the central nervous system and oxidative stress play important roles in traumatic brain injury (TBI)-induced cognitive impairment. Rhamnetin possesses anti-inflammatory and anti-oxidative properties. This study aimed to detect the possible effects of rhamnetin on cognitive deficit, hippocampal inflammatory factors, and oxidative stress in rats with TBI. In this study, we established the traumatic brain injury model in rats. Rats respectively received vehicle saline or rhamnetin for 21 days. Cognitive functions were evaluated by assessing the acquisition of spatial learning and memory retention in Morris Water Maze test from day 15 to 19 post TBI. Levels of interleukin (IL)-1β, IL-6, IL-8, tumor necrosis factor a (TNF-a), IL-10, and nuclear factor κB (NF-κB) in hippocampal homogenate were measured using ELISA. Oxidative stress was analysed by investigating the activities of MDA, H2O2, SOD, and GSH-Px. We found that rhamnetin significantly improved cognitive impairment in rats with TBI, and inhibited the inflammatory response and oxidative stress in the hippocampus. The results suggested that rhamnetin could enhance the recovery of cognitive deficits induced by TBI, and that its mechanism might be associated with the inhibition of inflammation and oxidative stress in the hippocampus.

Aggregating behavior of phenolic compounds--a source of false bioassay results?

Previous descriptions of quercetin, a widely studied flavonoid, as a frequently reported nonspecific screening hit due to aggregating behavior has raised questions about the reliability of in vitro bioactivity reports of phenolic compounds. Here a systematic study on 117 phenolic compounds is presented, concerning their aggregating tendency and the relevance of this phenomenon to obtaining false bioassay results. Fourteen compounds formed aggregates detectable by dynamic light scattering (DLS) when assayed at 10 µM in Tris-HCl pH 7.5. Flavonoids were more prone to aggregation than other phenolic compounds, and the aggregate formation was highly dependent on the vehicle, ionic strength and pH. The compounds were also assayed against three unrelated enzymes in the presence and absence of Triton X-100, and their bioactivity ratios were collected from PubChem database. By comparing these datasets, quercetin and rhamnetin were confirmed as promiscuous inhibitors. In general, flavonoids exhibited also higher bioactivity ratios in the PubChem database than coumarins or organic acids. To conclude, aggregate formation can be controlled with Triton X-100 and this phenomenon needs to be considered when bioassay data is interpreted, but our data indicates that it does not always lead to unspecific inhibition of biological targets.