Antiglycating effects of citrus flavonoids and associated mechanisms

Glycation of proteins and DNA forms advanced glycation end products(AGEs)causing cell and tissue dysfunction and subsequent various chronic diseases,in particular,metabolic and age-related diseases.Targeted AGE inhibition includes scavengers of reactive carbonyl species(RCS)such as methylglyoxal(MG),glyoxalase-1 enhancers,Nrf2/ARE pathway activators,AGE/RAGE formation inhibitors and other antiglycatng agents.Citrus flavonoids have demonstrated antioxidant and anti-inflammatory effects and are also found to be effective antiglycating agents.Herein,we reviewed the up to date progress of the antiglycation effects of citrus flavonoids and associated mechanisms.Major citrus flavonoids,hesperedin and its aglycone,hesperetin,inhibited glycation by scavenging MG forming mono-or di-flavonoid adducts with MG,enhanced the activity of glyoxase-1,activated Akt/Nrf2 signal pathway while inhibiting AGE/RAGE/NF-κB pathway,reduced the formation of Nε-(carboxylmethyl)lysine(CML)and pentosidine,inhibited aldol reductase activity and decreased the levels of fructosamine.The antiglycating activity and mechanisms of other flavonoids was also summarized in this review.In conclusion,citrus flavonoids possess effective antiglycating activity via different mechanisms,yet there are many challenging questions remaining to be studied in the near future such as in vivo testing and human study of citrus flavonoids for efficacy,effectiveness and adverse effects of citrus flavonoids as a functional food in managing high levels of AGEs and controlling AGE-induced chronic diseases,diabetic complications in particular.

Inhibition of citrus flavonoids on 12-O-tetradecanoylphorbol 13-acetate-induced skin inflammation and tumorigenesis in mice

The inhibitory effects of a formulated product from citrus peel extract,Gold Lotion(GL),on 12-O-tetradecanoylphorbol 13-acetate(TPA)-induced expression of inducible nitric oxide synthase(iNOS)and cyclooxygenase-2(COX-2)in mouse skin was reported in this study.It is found that in the TPA-induced skin inflammation model,the topical application of GL effectively inhibited the transcriptional activation of iNOS and its mRNA and protein in mouse skin.It is also discovered that GL significantly inhibited TPA-induced mouse skin inflammation by decreasing inflammatory gene parameters.Furthermore,GL dramatically inhibited 7,12-dimethylbenez[a]anthracene(DMBA)/TPA-induced skin tumor formation and reduced tumor incidence,tumor weight and tumor multiplicity of papillomas at 20 weeks.In essence,these in vivo data have revealed that GL is an effective anti-tumor agent that functions by down-regulating the protein levels of COX-2,ornithine decarboxylase(ODC),and vascular endothelial growth factor(VEGF)in mouse skin,suggesting that GL is a novel functional natural product capable of preventing inflammation-associated tumorigenesis.©2012 Production and hosting by Elsevier B.V.on behalf of Beijing Academy of Food Sciences.

Citrus fruits are rich in flavonoids for immunoregulation and potential targeting ACE2

The most recent outbreak of 2019 novel coronavirus,named as COVID-19,caused pneumonia epidemic in Wuhan with 2121 deaths cases as of February 20th 2020.Identification of effective antiviral agents to combat the novel coronavirus is urgently needed.Citrus fruit peel or wild citrus are rich in flavonoids,and clinically documented for roles in relief of cough and promotion of digestive health.Therefore,citrus fruits are assumed to possess antivirus activities or enhance the host immunity.A previous study found that hesperetin could act as a high potent inhibitor of SARS-CoV 3CLpro.We determined six flavonoid compounds’content in three citrus species by using LC-MS technique.The content of naringin and naringenin was at higher levels in pummelo.Hesperetin and hesperidin were highly accumulated in mandarin and sweet orange.The subsequent in vitro and in vivo experiments indicated that naringin could inhibit the expression of the proinflammatory cytokines(COX-2,iNOS,IL-1βand IL-6)induced by LPS in Raw macrophage cell line,and may restrain cytokine through inhibiting HMGB1 expression in a mouse model.The results revealed that naringin may have a potential application for preventing cytokine storm.We simulated molecular docking to predict the binding affinity of those flavonoids to bind Angiotensin-converting enzyme 2(ACE 2),which is a receptor of the coronavirus.Consideration of the potential anti-coronavirus and anti-inflammatory activity of flavonoids,the citrus fruit or its derived phytochemicals are promising in the use of prevention and treatment of SARS-CoV-2 infection.

Anti-inflammatory effects of characterized orange peel extracts enriched with bioactive polymethoxyflavones

In view of the potential of polymethoxyflavones(PMFs)and hydroxylated PMFs(OH-PMFs)as bioactives against inflammation,we prepared six different orange peel extracts(OPEs).The major compounds of these extracts were characterized and quantified by high performance liquid chromatography(HPLC).Effects on inflammation were analyzed by nutrigenomics using a human cell-based TPA-induced monocyte–macrophage differentiation model employing U-937 cells and inflammatory surrogate genes.Dose response and kinetics analysis of OPEs with different chemical profiles revealed less cytotoxic effects of PMFs as compared to OH-PMFs as demonstrated by the MTT-method.Noteworthy,a comparison of two PMF members such as 3,5,6,7,3,4-hexamethoxyflavone(HexaMF)and 3,5,6,7,8,3,4-heptamethoxyflavone(HeptaMF)exhibited less cytotoxic effects of HeptaMF as compared to HexaMF.A specific OPE enriched with HeptaMF,PMFs and OH-PMFs at low concentrations(10g/mL)significantly down-regulated the expression of a panel of genes involved in inflammatory response,including COX-2,TNF-α,ICAM-1,NFκB,IL-1β,IL-6,and IL-8 with an inflammatory index of−0.55.The strong anti-inflammatory effects were then validated in a mouse carrageenan-induced paw edema model.Oral intake of OPE reduced paw edema significantly in a dose-dependent manner.Importantly,a dosage of 250 mg/kg gave an anti-inflammatory effect comparable to ibuprofen.A preliminary clinical study showed that OPE was well tolerated showing no adverse side effects.In summary,enrichment of phyto extracts such as OPEs with specific polymethoxyflavones as anti-inflammatory bioactives is a promising strategy to find naturally derived extracts that are effective against diseases associated with inflammation.©2014 Beijing Academy of Food Sciences.Production and hosting by Elsevier B.V.All rights reserved.

Pure Total Flavonoids from Citrus paradisi Macfad InduceLeukemia Cell Apoptosis In Vitro

Objective： To investigate the potential effect of pure total flavonoids from Citrus paradisi Macfad peel（PTFC） on the proliferation and apoptosis of human myeloid leukemia cells Kasumi-1, HL-60 and K562, and the underlying mechanisms. Methods： PTFC was extracted from Citrus paradisi Macfad peel and was identified by high performance liquid chromatography. The effect of PTFC on the proliferation and apoptosis of leukemia cells were determined by 3-（4,5-dimethylthiazol-2-yl）-2,5-diphenyltetrazolium bromide, fluorescent microscopy and flow cytometry, respectively. The effect of PTFC on the expression levels of apoptosis-related regulators was determined by Western blot assay. Results： Treatment with PTFC inhibited leukemia cell proliferation in a dose-and time-dependent manner and triggered Kasumi-1 cell apoptosis. Treatment with PTFC significantly increased the levels of activated poly adenosine diphosphate-ribosepolymerase and caspase-3/-9, but reduced the levels of Mcl-1 expression in Kasumi-1 cells. However, PTFC did not obviously induce HL-60 cell apoptosis. Conclusion： PTFC inhibited leukemia cell proliferation and induced their apoptosis by modulating apoptosisrelated regulator expression in leukemia cells in vitro.

Feeding citrus flavonoid extracts decreases bacterial endotoxin and systemic inflammation and improves immunometabolic status by modulating hindgut microbiome and metabolome in lactating dairy cows

The objectives of this study were to determine the effects of dietary supplementation with citrus flavonoid extracts(CFE)on milk performance,serum biochemistry parameters,fecal volatile fatty acids,fecal microbial community,and fecal metabolites in dairy cows.Eight multiparous lactating Holstein cows were used in a replicated 4×4 Latin square design(21-day period).Cows were fed a basal diet without addition(CON)or basal diet with added CFE at 50(CFE50),100(CFE10),and 150 g/d(CFE150).Feeding CFE up to 150 g/d increased milk yield and milk lactose percentage.Supplementary CFE linearly decreased milk somatic cell count.Serum cytokines interleukin-1β(IL-1β),IL-2,IL-6,and tumor necrosis factor-α(TNF-α)concentrations decreased linearly as the levels of CFE increased.Cows in CFE150 had lower serum lipopolysaccharide and lipopolysaccharide binding protein compared with CON.These results indicate feeding CFE decreased systemic inflammation and endotoxin levels in dairy cows.Furthermore,feeding CFE linearly increased the concentrations of total volatile fatty acids,acetate,and butyrate in feces.The relative abundances of beneficial bacteria Bifidobacterium spp.,Clostridium coccoides-Eubacterium rectale group,and Faecalibacterium prausnitzii in feces increased linearly with increasing CFE supplementation.The diversity and community structure of fecal microbiota were un-affected by CFE supplementation.However,supplementing CFE reduced the relative abundances of genera Ruminococcus_torques_group,Roseburia,and Lachnospira,but increased genera Bacteroides and Phascolarctobacterium.Metabolomics analysis showed that supplementary CFE resulted in a significant modification in the fecal metabolites profile.Compared with CON,fecal naringenin,hesperetin,hippuric acid,and sphingosine concentrations were greater in CFE150 cows,while fecal GlcCer(d18:1/20:0),Cer(d18:0/24:0),Cer(d18:0/22:0),sphinganine,and deoxycholic acid concentrations were less in CFE150 cows.Predicted pathway analysis suggested that"sphingolipid metabolism"was significantly enriched.Overall,these results indicate that citrus flavonoids could exert health-promoting effects by modulating hindgut microbiome and metabolism in lactating cows.