Synthesis, biological evaluation of chrysin derivatives as potential immunosuppressive agents

Chrysin alleviates DNA damage to improve disturbed immune homeostasis and pro-angiogenic environment in laser-induced choroidal neovascularization

Choroidal neovascularization (CNV) is a devastating pathology of numerous ocular diseases, such as wet age-related macular degeneration (wAMD), which causes irreversible vision loss. Although anti-vascular endothelial growth factor (VEGF) therapy has been widely used, poor response or no response still exists in some cases, suggesting that there are other components involved in the angiogenic process. Therefore, the underlying mechanism needs to be clarified and new target of anti-angiogenic therapy is urgently needed. It has been demonstrated that damaged retinal pigment epithelium (RPE) cells can activate inflammasome, driving a degenerative tissue environment and an enhanced pro-angiogenic response, which implies that RPE dysfunction may be a hallmark of the pathogenesis. Previously, we have shown that DNA damage can induce RPE dysfunction, triggering senescence-associated secretory phenotype (SASP) and local inflammation. In this study, we identify that chrysin can reduce DNA damage, especially telomere erosion in vitro, thus compromise the dysfunction of RPE and the decreased expression of SASP factor. Importantly, we find that DNA damage of RPE cells is remarkable in laser-induced CNV lesion, resulting in inflammatory response, which can be ameliorated by chrysin, mainly through IL-17 signaling pathway and its downstream signal transducer and activator of transcription 3 (STAT3) activities. In summary, our results indicate the interplay between DNA damage, perturbed RPE homeostasis, inflammatory response and angiogenesis in laser-induced CNV, and more importantly, chrysin may be an effective therapeutic supplement for CNV.

Synthesis of chrysin derivatives and screening of antitumor activity

A series of aromatic or long-chain chrysin derivatives (1-10) were synthesized by esterification of chrysin and acyl chloride. The chemical structures of these compounds were determined by mass spectrum (MS), ¹H NMR, and ¹³C NMR spectra. Though aromatic chrysin derivatives (1-9) with a rigid structure were hard to dissolve in common organic solvents, the long-chain chrysin derivative (10) with a flexible structure had better solubility, and its anticancer activity (IC₅₀ = 14.79 μmol/L) against liver cancer cell lines was 5.4 times better than chrysin (IC₅₀ = 74.97 μmol/L), which showed superposition of pharmacological activity.

Fluorine-Containing Chrysin Derivatives

Chrysin, a flavonoid, has played a great role in the fields of anticancer, antibacterial, and antiviral drug discovery. A large number of chrysin derivatives have been synthesized recently. The fluorine atom represents an important substituent group for a great number of natural products and pharmaceuticals. Taking into account the importance of both chrysin and the fluorine atom in medicinal chemistry, the synthesis of fluorine-containing chrysin derivatives has gained great interest. Chemically, the synthetic methods for these new chrysin derivatives have also been developed rapidly. In recent years, research on their synthesis has been focused on speeding up the reaction process by changing the catalyst. Biologically, the purpose of introducing fluorine into chrysin was to improve its lipophilicity, but today it is mainly focused on the enhancement and improvement of either its anticancer or antimicrobial activities by incorporating the special properties of fluorine atoms. In this review, synthetic methods for the introduction of fluorine atoms into chrysin are summarized, and their anticancer, antibacterial, antiviral, and hypoglycemic effects are discussed.

Phloroglucinols with Immunosuppressive Activities from the Fruits of Eucalyptus globulus

Five new phloroglucinol derivatives, eucalyptins C-G (1-5), together with 13 known analogues (6-18) were isolated from the fruits of Eucalyptus globulus. The structures and absolute configurations of 1-5 were established by means of spectroscopic data analysis, computational calculation methods, and single-crystal X-ray diffraction. Compounds 1-18 were investigated for their immunosuppressive effects in vitro, and 1, 2, 6, and 7 displayed moderate inhibitory activities with IC₅₀ values of 11.8, 10.2, 18.2, and 19.1 μM, respectively. The stimulation index (SI) of 1 was 64.2 and was compared to that of cyclosporine A (SI = 149.57). Further study demonstrated that 1 exhibited an immunosuppressive effect through inducing apoptosis and inhibiting cytokine secretion.

The Relationship between Pharmacological Properties and Structure- Activity of Chrysin Derivatives

Chrysin is a natural product of a flavonoid compound. Chemically, chrysin consists of two phenyl rings (A and B) and a heterocyclic ring (C). Biologically, chrysin exerts many different physiological activities. In recent years, with the in-depth development for more active drugs, the synthesis and biological activities of chrysin derivatives have been well studied. Besides, structure-activity relationship of chrysin revealed that the chemical construction meets the critical chemical structural necessities of flavonoids for numerous pharmacological activities. It is generally believed that modified chrysin could be more potent than unmodified chrysin. Different modification in the rings of chrysin could possess various degrees of biological activities. This review aims to summarize the mechanism for the activities of chrysin and its derivatives in different rings. We also explored the relationship between biological function and structure-activity of substituted chrysin derivatives with different functional groups. The influence of chrysin derivatives on the proliferation and apoptosis of cancer cells is also investigated. Development of novel drugs based on the biological functions of chrysin could better improve clinical outcomes of affected population, especially for tumor patients and diabetic patients.

Synthesis, characterization and xanthine oxidase inhibition of Cu(II)-chrysin complex

Xanthine oxidase (XO) is a key enzyme catalyzing hypoxanthine to xanthine and then uric acid causing hyperuricemia. A Cu(II) complex of chrysin was synthesized and characterized by UV-vis absorption, Fourier transform infrared, nuclear magnetic resonance (¹H NMR) and mass spectroscopy studies. The interaction of Cu(II)-complex with XO was investigated by spectroscopic methods and molecular simulation. The Cu(II)-chrysin complex exhibited a better inhibitory ability (IC₅₀=0.82±0.034μM) against XO than its corresponding ligands chrysin and Cu²⁺ in a mix-competitive manner. The binding affinity of Cu(II)-chrysin complex with XO was much higher than that of chrysin. The hydrogen bonds and van der Waals forces played main roles in the binding. Analysis of circular dichroism spectra indicated that the complex induced the conformational change of XO. The molecular simulation found that the Cu(II)-chrysin complex inserted into the active cavity of XO with Cu acting as a bridge, occupying the catalytic center of the enzyme to avoid entry of the substrate xanthine, leading to the inhibition of XO. This study may provide new insights into the inhibition mechanism of the Cu(II)-chrysin complex as a promising XO inhibitor and its potential application for the treatment of hyperuricemia.

Preventive effect of chrysin on experimental autoimmune uveitis triggered by injection of human IRBP peptide 1-20 in mice

Uveitis is a common cause of blindness worldwide. Experimental autoimmune uveitis (EAU) is an animal model of noninfectious uveitis. Chrysin (5,7-dihydroxyflavone) is a member of the flavonoid family and has anti-inflammatory effects. We immunized C57BL/6J mice with human interphotoreceptor retinoid-binding protein peptide 1-20 to induce EAU. Chrysin was administered intragastrically at 25 mg/kg daily to the chrysin-treated mice from 3 days before immunization to 21 days after immunization. Vehicle was administered to the mice in the control group according to the same protocol. Lower clinical and histopathological scores, increased integrity of the blood-retinal barrier (BRB) and higher expression of tight junction proteins were observed in the chrysin-treated mice. Chrysin significantly decreased the proportions of Th1, Th17 and CD4⁺CD3⁺CD62L⁺ Th0 cells, and increased the proportion of Treg cells. Both macrophage infiltration and the expression of inducible nitric oxide synthase in the retina were efficiently inhibited by chrysin treatment. In chrysin-treated mice, the expression of interferon-γ, interleukin (IL)-17A, IL-6, IL-1β and tumor necrosis factor-α was reduced in the retina, whereas higher levels of transforming growth factor-β were detected. Furthermore, NF-κBp65 was downregulated after chrysin treatment. In conclusion, as an anti-inflammatory molecule, chrysin exerts a preventive effect on EAU by modulating the balance among helper T-cell subsets and suppressing ocular inflammation, thereby maintaining the integrity of the BRB.

Neuroprotective effects of chrysin: From chemistry to medicine

The World Health Organization estimated that the proportion of older people (over 60 years) will increase from 11% to 22% during next 40 years throughout the world. With respect to this, the morbidity and mortality rates of age-related diseases will increase. Mental diseases are the most common and important health problems among elderly people. Therefore, much attention has been paid to the discovery of neuroprotective drugs with high efficacy and negligible adverse effects. A growing body of scientific evidence has shown that phytochemicals possess neuroprotective effects and also mitigate neurodegeneration under both in vivo and in vitro conditions. Polyphenolic compounds, especially flavonoids, are known as most common chemical class of phytochemicals which possess a multiple range of health promoting effects. Chrysin, belonging to the flavone class, is one of the most important bioactive constituents of different fruits, vegetables and even mushrooms. Chrysin possesses potent neuroprotective effects and suppress neuroinflammation. In addition, chrysin improves cognitive decline and possesses a potent anti-amyloidogenic and neurotrophic effects. Furthermore, beneficial effects of chrysin on both depression and epilepsy have been reported. The present paper aimed to critically review the available literature data regarding the neuroprotective effects of chrysin as well as its chemistry, sources and bioavailability.

Synthesis, characterization and antioxidant activity of organoselenium and organotellurium compound derivatives of chrysin

New selenium and tellurium containing chrysin derivatives were synthesized and their antioxidant activities were evaluated. Butyltelluro-chrysin presented better antioxidant activities.