Therapeutic applications of quercetin-metallic complexes: a review

Flavonoids, especially quercetin, are widely recognized for their antioxidant, anti-inflammatory, anti-microbial, anti-diabetic, and anti-tumor properties, but their clinical application is limited by poor permeability. Different techniques of permeability enhancement of quercetin, i.e., preparation of phytosomes, conjugation with glucose, and interaction of piperine, are reported extensively, but formation of metal complexes is considered more precise and reliable. This review focuses on research conducted on the chelation of quercetin with metals, i.e., copper (II), zinc (II), iron and ruthenium. In-vitro and in-vivo therapeutic activities, biomedical applications of metal/quercetin inclusion complexes and discussions of stability concerns of quercetin alone and its metallic complexes. Conjugation of metals with quercetin augments its potential to the next level. Numerous studies revealed that quercetin/copper (Q/Cu) and quercetin/zinc (Q/Zn) can become efficacious candidates in acute myeloid leukaemia, orthopaedics and severe acute respiratory syndrome coronavirus (SARS-CoV) infection.

Antioxidant Activity of Ruthenium Cyclopentadienyl Complexes Bearing Succinimidato and Phthalimidato Ligands

In these studies, we investigated the antioxidant activity of three ruthenium cyclopentadienyl complexes bearing different imidato ligands: (η⁵-cyclopentadienyl)Ru(CO)₂-N-methoxysuccinimidato (1), (η⁵-cyclopentadienyl)Ru(CO)₂-N-ethoxysuccinimidato (2), and (η⁵-cyclopentadienyl)Ru(CO)₂-N-phthalimidato (3). We studied the effects of ruthenium complexes 1–3 at a low concentration of 50 µM on the viability and the cell cycle of peripheral blood mononuclear cells (PBMCs) and HL-60 leukemic cells exposed to oxidative stress induced by hydrogen peroxide (H₂O₂). Moreover, we examined the influence of these complexes on DNA oxidative damage, the level of reactive oxygen species (ROS), and superoxide dismutase (SOD) activity. We have observed that ruthenium complexes 1–3 increase the viability of both normal and cancer cells decreased by H₂O₂ and also alter the HL-60 cell cycle arrested by H₂O₂ in the sub-G1 phase. In addition, we have shown that ruthenium complexes reduce the levels of ROS and oxidative DNA damage in both cell types. They also restore SOD activity reduced by H₂O₂. Our results indicate that ruthenium complexes 1–3 bearing succinimidato and phthalimidato ligands have antioxidant activity without cytotoxic effect at low concentrations. For this reason, the ruthenium complexes studied by us should be considered interesting molecules with clinical potential that require further detailed research.

Flavonoid-statin interactions causing myopathy and the possible significance of OATP transport, CYP450 metabolism and mevalonate synthesis

3-hydroxy-3-methyl-glutaryl-coenzyme A (HMG-CoA) reductase inhibitors, statins, are a primary treatment for hyperlipidemic cardiovascular diseases which are a leading global cause of death. Statin therapy is life saving and discontinuation due to adverse events such as myotoxicity may lead to unfavourable outcomes. There is no known mechanism for statin-induced myotoxicity although it is theorized that it is due to inhibition of downstream products of the HMG-CoA pathway. It is known that drug-drug interactions with conventional medicines exacerbate the risk of statin-induced myotoxicity, though little attention has been paid to herb-drug interactions with complementary medicines. Flavonoids are a class of phytochemicals which can be purchased as high dose supplements. There is evidence that flavonoids can raise statin plasma levels, increasing the risk of statin-induced myopathy. This could be due to pharmacokinetic interactions involving hepatic cytochrome 450 (CYP450) metabolism and organic anion transporter (OATP) absorption. There is also the potential for flavonoids to directly and indirectly inhibit HMG-CoA reductase which could contraindicate statin-therapy. This review aims to discuss what is currently known about the potential for high dose flavonoids to interact with the hepatic CYP450 metabolism, OATP uptake of statins or their ability to interact with HMG-CoA reductase. Flavonoids of particular interest will be covered and the difficulties of examining herbal products will be discussed throughout.

Redesigning Nature: Ruthenium Flavonoid Complexes with Antitumour, Antimicrobial and Cardioprotective Activities

Flavonoids are a class of natural polyphenolic compounds sharing a common 2-phenyl-3,4-dihydro-2H-1-benzopyran (flavan) backbone. Typically known for their antioxidant activity, flavonoids are also being investigated regarding antitumour and antimicrobial properties. In this review, we report on the complexation of both natural and synthetic flavonoids with ruthenium as a strategy to modulate the biological activity. The ruthenoflavonoid complexes are divided into three subclasses, according to their most prominent bioactivity: antitumour, antimicrobial, and protection of the cardiovascular system. Whenever possible the activity of the ruthenoflavonoids is compared with that of commercial drugs for a critical assessment of the feasibility of using them in future clinical applications.

Exploring the Molecular Mechanisms Underlying the in vitro Anticancer Effects of Multitarget-Directed Hydrazone Ruthenium(II)-Arene Complexes

The molecular targets and the modes of action behind the cytotoxicity of two structurally established N,O- or N,N-hydrazone ruthenium(II)-arene complexes were explored in human breast adenocarcinoma cells (MCF-7) and paralleled in non-cancerous and cisplatin-resistant counterparts (MCF-10A and MCF-7CR respectively). Both complexes, [Ru(hmb)(L1)Cl] (1, L1=4-((2-(2,4-dinitrophenyl)hydrazono)(phenyl)methyl)-3-methyl-1-phenyl-1H-pyrazol-5-olate) and [Ru(cym)(L2)Cl] (2, L2=1-((3-methyl-5-oxo-1-phenyl-1H-pyrazol-4(5H)-ylidene)(phenyl)methyl)-2-(pyridin-2-yl)hydrazin-1-ide), reversibly interact with moderate-to-high affinity with a number of molecular targets in cell-free assays, namely serum albumin, DNA, the 20S proteasome and hydroxymethylglutaryl-CoA reductase. Most interestingly, only 2 readily crosses the cell membrane and preserves its binding/modulatory ability toward the targets of interest upon rapid cellular internalization. The resulting action at multiple levels of the cancer cascade is likely the cause for the selective sensitization of tumour cells to p27-mediated apoptotic death, and for the ability of 2 to overcome the drug resistance problem.

Novel osmium(ii)–cymene complexes containing curcumin and bisdemethoxycurcumin ligands

First examples of p-cymene-osmium(ii) curcuminoid complexes with antitumor activity.

Deciphering the biochemical and molecular mechanism underlying the in vitro and in vivo chemotherapeutic efficacy of ruthenium quercetin complex in colon cancer

Flavonoids are the most investigated phytochemicals due to their pharmacological and therapeutic activities. Their ability to chelate with metal ions has resulted in the emergence of a new category of molecules with a broader spectrum of pharmacological activities. In this study, the ruthenium quercetin complex has been synthesized and anticancer activity has been evaluated on a well-defined model of DMH followed by DSS induced rat colon cancer and on human colon cancer cell line HT-29. The characterizations accomplished through UV-visible, NMR, IR, Mass spectra and XRD techniques, and antioxidant activity was assessed by DPPH, FRAP, and ABTS methods. In vitro study confirmed that the complex increased p53 expression, reduced VEGF and mTOR expression, apoptosis induction, and DNA fragmentation in the HT-29 cells. Acute and subacute toxicity study was also assessed and results from in vivo study revealed that complex was efficient to suppress ACF multiplicity and hyperplastic lesions and elevated the CAT, SOD, and glutathione levels. Furthermore, the complex was found to decrease cell proliferation and increased apoptotic events in tumor cells correlates upregulation of p53 and Bax and downregulation of Bcl2 expression. Our findings from the in vitro and in vivo study support the continued investigation of ruthenium quercetin complex possesses a potential chemotherapeutic activity against colon cancer and was efficient in reducing ACF multiplicity, hyperplastic lesions in the colon tissues of rats by inducing apoptosis.

Regulation of hepatic hydroxy methyl glutarate - CoA reductase for controlling hypercholesterolemia in rats

Hypercholesterolemia is a major risk factor upon developing cardiovascular diseases. This study is aiming to investigate the inhibition role of quercetin on hydroxy methyl glutarate - CoA reductase activity and its gene for attenuating hypercholesterolemia. The kinetic characteristics of HMG-CoA reductase activity were evaluated on extracellular rat liver microsomes. For studying the effect of quercetin by inducing hypercholesterolemia rats by Tyloxapol (i.v.). In addition, rats were treated with different doses of quercetin according to the inhibition constant of this inhibitor. Our results showed that in quercetin rats groups plasma cholesterol, triglycerides, LDL -cholesterol and total lipids levels and hepatic (TBARS) level were significantly decreased as compared with negative control. However, plasma HDL level, hepatic total thiol level, catalase activity and total protein level significantly increased groups as compared with negative control. In addition, HMG-CoA reductase activity was decreased in quercetin groups and this confirmed in gene expression that these groups caused downregulation for HMG-CoA reductase. However, LDL receptor (LDLr) gene expression was upregulated by quercetin. Moreover, histopathological examination of rat liver showed the ameliorative effect of quercetin on hypercholesterolemic effect of triton. In conclusion, quercetin may consider as a new saving candidate for the future development of hypocholesterolemia agents.