Computational and experimental strategies for combating MBL P. aeruginosa (MBLPA) biofilms using phytochemicals: Targeting the quorum sensing network

Pseudomonas aeruginosa is a Gram-negative opportunistic bacterium, ubiquitously found in nature and causative agent in many infections. Due to increased antibiotic resistance, there is a need to develop more robust antibacterial agents from natural sources. In this study, we worked on two metallo-β-lactamase (MBL) producing Pseudomonas aeruginosa strains and targeted the Quorum Sensing mechanism (QS) of these bacteria to combat antibiotic resistance. Our study aimed at using phytochemicals which have been used since centuries in herbal medicine. We used fifteen commercially available phytochemicals and check their effects on biofilm formation, quorum sensing and inter-related mechanisms. Sub-inhibitory concentration of isoliquiritin inhibited biofilm formation 55 % in P8 at day 6 and 48 % in P6 at day 6; quorum sensing 83 % in P6 and 61 % in P8 whereas sub-inhibitory concentration of 6-gingerol suppressed biofilm formation by 48 % in P8 at day 6 and 44 % in P6 at day 6; quorum sensing 69 % in P6 and 48 % in P8, respectively. The results indicated isoliquiritin, epigallocatechin gallate, eugenol, luteolin and chrysin to be the potential candidates in inhibiting QS and related mechanisms. Isoliquiritin which was never been used before against biofilm and QS related studies, showed remarkable results and found to be more efficient in inhibiting QS than 6-gingerol -a known QS inhibitor. For examining the molecular interaction between phytochemicals and QS, In-silico molecular docking was performed between phytoligands and four QS proteins (Las I, Las R, RhlI and Rhl R). In-silico docking analysis revealed that isoliquiritin showed strong bond with amino acids (Trp34, Asp35, Asp35, Tyr105, Arg104, Val138, Thr140) present at the active site of RhlI with binding energy value of -8.4 kcal/mol as compared to that of 6-gingerol with Rhl1 (-7.3 kcal/mol). In conclusion, our study may help in controlling nosocomial infections caused by carbapenem-resistant metallo beta-lactamase P. aeruginosa (MBL-PA) by utilizing these phytochemicals in biofilms disruption and quorum sensing inhibition. Moreover their synergism with antibiotics may help in lowering the MIC of carbapenem antibiotics against such Multi-drug resistant strains.

Isoliquiritin counteracts cadmium-induced intestinal damage in mice through enhancing intestinal barrier function and inhibiting apoptosis

Cadmium (Cd), a crucial toxic environmental pollutant, can induce damage to many organs, especially the gastrointestinal tract. Isoliquiritin (ISO), a critical flavonoid glycoside compound isolated from Glycyrrhiza uralensis, has anti-inflammatory, anticancer, antioxidant and other pharmaceutical value. However, the potential roles of ISO in Cd-induced intestinal damage have not been reported yet. This study aimed to research the beneficial effects of ISO on Cd-induced intestinal damage and identify its underlying mechanisms. Our results showed that ISO reduced inflammation by suppressing the production of pro-inflammatory cytokines and the activity of serum Lipopolysaccharide (LPS) in mice with Cd exposure. In terms of mechanism, ISO administration protected the intestinal barrier function through increasing the expression of tight junction proteins and Muc2. Furthermore, ISO could significantly suppress Cd-induced intestinal apoptosis and activation of NLRP3 inflammasome. Interestingly, inhibiting the activation of NLRP3 by nigericin completely blocking the effect of ISO on apoptosis. Most importantly, ISO markedly abrogated Cd-induced cell damage and NLRP3 inflammasome activation in vitro. Taken together, these findings suggest that ISO reduces Cd-induced intestinal damage by increasing the goblet cells, improving intestinal barrier, suppressing NLRP3 inflammasome activation and inhibiting apoptosis, which may offer a novel strategy against the toxic effects of heavy metals.

Isoliquiritin Ameliorates Ulcerative Colitis in Rats through Caspase 3/HMGB1/TLR4 Dependent Signaling Pathway

BACKGROUND

Isoliquiritin belongs to flavanol glycosides and has a strong antiinflammatory activity. This study sought to investigate the anti-inflammatory effect of isoliquiritin and its underlying mechanism.

METHODS

The inflammatory (trinitro-benzene-sulfonic acid-TNBS-induced ulcerative colitis (UC)) model was established to ascertain the effect of isoliquiritin on the caspase-3/HMGB1/TLR4 pathway in rats. We also explored its protective effect on intestinal inflammation and its underlying mechanism using the LPS-induced inflammation model of Caco-2 cells. Besides, Deseq2 was used to analyze UCassociated protein levels.

RESULTS

Isoliquiritin treatment significantly attenuated shortened colon length (induced by TNBS), disease activity index (DAI) score, and body weight loss in rats. A decrease in the levels of inflammatory mediators (IL-1β, I IL-4, L-6, IL-10, PGE2, and TNF-α), coupled with malondialdehyde (MDA) and superoxide dismutase (SOD), was observed in colon tissue and serum of rats after they have received isoliquiritin. Results of techniques (like western blotting, real-time PCR, immunohistochemistry, and immunofluorescence-IF) demonstrated the potential of isoliquiritin to decrease expressions of key genes in the TLR4 downstream pathways, viz., MyD88, IRAK1, TRAF6, NF-κB, p38, and JNK at mRNA and protein levels as well as inhibit HMGB1 expression, which is the upstream ligand of TLR4. Bioinformational analysis showed enteritis to be associated with a high expression of HMGB1, TLR4, and caspase-3.

CONCLUSION

Isoliquiritin could reduce intestinal inflammation and mucosal damage of TNBS-induced colitis in rats with a certain anti-UC effect. Meanwhile, isoliquiritin treatment also inhibited the expression of HMGB1, TLR4, and MyD88 in LPS-induced Caco-2 cells. These results indicated that isoliquiritin could ameliorate UC through the caspase-3/HMGB1/TLR4-dependent signaling pathway.

Isoliquiritin exert protective effect on telencephalon infarction injury by regulating multi-pathways in zebrafish model of ischemic stroke

BACKGROUND

Ischemic stroke is a multifactorial disease contributing to mortality and neurological dysfunction. Isoliquiritin (ISL) has been reported to possess a series of pharmacological activities including antioxidant, anti-inflammatory, antifungal, anti-depression, anti-neurotoxicity and pro-angiogenesis activities but whether it can be used for ischemic stroke treatment remains unknown.

PURPOSE

The goal of this study is to explore its therapeutic effect on ischemic stroke and demonstrated the potential mechanism of ISL in zebrafish model.

METHODS

Using the photothrombotic-induced adult zebrafish model of ischemic stroke, we visualized the telencephalon (Tel) and optic tectum (OT) infarction injury at 24 h post-light exposure for 30 min by TTC and H&E staining. The effect of ISL on neurological deficits was analyzed during open tank swimming by video tracking. The antioxidant activity against ischemia injury was quantified by SOD, GSH-Px and MDA assay. Transcriptome analysis of zebrafish Tel revealed how ISL regulating gene expression to exert protective effect, which were also been validated by real-time quantitative PCR assays.

RESULTS

We found for the first time that the Tel tissue was the first damaged site of the whole brain and it showed more sensitivity to the brain ischemic damage compared to the OT. ISL reduced the rate of Tel injury, ameliorated neurological deficits as well as counteracted oxidative damages by increasing SOD, GSH-Px and decreasing MDA activity. GO enrichment demonstrated that ISL protected membrane and membrane function as well as initiate immune regulation in the stress response after ischemia. KEGG pathway analysis pointed out that immune-related pathways, apoptosis as well as necroptosis pathways were more involved in the protective mechanism of ISL. Furthermore, the log2 fold change in expression pattern of 25 genes detected by qRT-PCR was consistent with that by RNA-seq.

CONCLUSIONS

Tel was highly sensitive to the brain ischemia injury in zebrafish model of ischemic stroke. ISL significantly exerted protective effect on Tel injury, neurological deficits and oxidative damages. ISL could regulate a variety of genes related to immune, apoptosis and necrosis pathways against complex cascade reaction after ischemia. These findings enriched the study of ISL, making it a novel multi-target agent for ischemic stroke treatment.

Isoliquiritin ameliorates depression by suppressing NLRP3-mediated pyroptosis via miRNA-27a/SYK/NF-κB axis

Background

The NLRP3-mediated pyroptosis, which could be regulated by miRNA-27a, is a key player in the development of depression. Isoliquiritin is a phenolic flavonoid compound that has been demonstrated to suppress NLRP3-mediated pyroptosis. However, it is still unknown whether isoliquiritin could confer antidepressant activity via decreasing NLRP3-mediated pyroptosis by stimulating miRNA-27a. Thus, in the current study, we explored the antidepressant activity of isoliquiritin and its underlying mechanism.

Methods

Expression of miRNA-27a in depressed patients or mice was measured using qRT-PCR. Luciferase reporter assay was performed to illustrate the link between miRNA-27a and SYK. Lipopolysaccharide (LPS) and chronic social defeat stress (CSDS) depression models were established to investigate the antidepressant actions of isoliquiritin. Changes in miRNA-27a/SYK/NF-κB axis and NLRP3-mediated pyroptosis were also examined. The role of miRNA-27a in isoliquiritin-related antidepressant effect was further investigated by using miRNA-27a inhibitors and mimics of miRNA-27a.

Results

Our results showed the miRNA-27a expression was downregulated in the serum of depressed patients, and decreased serum and hippocampus expression of miRNA-27a were observed in rodent models of depression. SYK gene expression was significantly reduced by miRNA-27a mimic incubation. Isoliquiritin profoundly attenuated LPS or CSDS-induced depressive symptoms, as well as CSDS-induced anxiety behavior. In the hippocampus, LPS and CSDS decreased miRNA-27a mRNA expression; increased the protein levels of SYK, p-NF-κB, and NLRP3: cleaved Caspase-1, IL-1β, and GSDMD-N: and elevated the concentration of IL-1β, IL-6, and TNF-α, which were all restored by isoliquiritin administration. Meanwhile, isoliquiritin upregulated the hippocampal NeuN protein level, improved the survival and morphology of neurons, and decreased pyroptosis-related neuronal cell death. Moreover, isoliquiritin protected primary microglia against LPS and adenosine triphosphate (ATP) elicited NLRP3 inflammasome activation in vitro, evidenced by declined protein levels of p-NF-κB, NLRP3; cleaved Caspase-1, IL-1β, and GSDMD-N; upregulated miRNA-27a mRNA expression; and decreased the mRNA and protein levels of SYK. Nevertheless, miRNA-27a inhibitors significantly reversed isoliquiritin-generated therapeutic efficacy in CSDS mice and in vitro. Furthermore, the cytoprotective effect of isoliquiritin was similar to that of miRNA-27a mimics in LPS and ATP-treated primary microglia.

Taken together, these findings suggest that isoliquiritin possesses potent antidepressant property, which requires miRNA-27a/SYK/NF-κB axis controlled decrease of pyroptosis via NLRP3 cascade.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12974-020-02040-8.

Serotonergically dependent antihyperalgesic and antiallodynic effects of isoliquiritin in a mouse model of neuropathic pain

Chronic neuropathic pain poses a significant health problem worldwide, for which effective treatment is lacking. The current work aimed to investigate the potential analgesic effect of isoliquiritin, a flavonoid from Glycyrrhiza uralensis, against neuropathic pain and elucidate mechanisms. Male C57BL/6J mice were subjected to chronic constriction injury (CCI) by loose ligation of their sciatic nerves. Following CCI surgery, the neuropathic mice developed pain-like behaviors, as shown by thermal (heat) hyperalgesia in the Hargreaves test and tactile allodynia in the von Frey test. Repetitive treatment of CCI mice with isoliquiritin (p.o., twice per day for two weeks) ameliorated behavioral hyperalgesia to thermal (heat) stimuli and allodynia to tactile stimuli in a dose-dependent fashion (5, 15 and 45 mg/kg). The isoliquiritin-triggered analgesia seems serotonergically dependent, since its antihyperalgesic and antiallodynic actions were totally abolished by chemical depletion of spinal serotonin by p-chlorophenylalanine, whereas potentiated by 5-HTP (a precursor of 5-HT). Consistently, isoliquiritin-treated neuropathic mice showed escalated levels of spinal monoamines especially 5-HT, with depressed monoamine oxidase activity. Moreover, isoliquiritin-evoked antihyperalgesia and antiallodynia were preferentially counteracted by the 5-HT_1A receptor antagonist WAY-100635 delivered systematically or spinally. Of notable benefit, isoliquiritin was able to correct co-morbid behavioral symptoms of depression and anxiety evoked by neuropathic pain. Collectively, these findings demonstrate, for the first time, the therapeutic efficacy of isoliquiritin on neuropathic hypersensitivity, and this effect is dependent on the spinal serotonergic system and 5-HT_1A receptors.

Isoliquiritin promote angiogenesis by recruiting macrophages to improve the healing of zebrafish wounds

Licorice is a widely used herbal medicine for the treatment of various diseases in southern Europe and parts of Asia. It has been reported that the isoliquiritin (ISL) from Glycyrrhiza root has the activity of promoting angiogenesis. The purpose of this study was to investigate the effect of ISL on the wound healing activity of zebrafish and its mechanism. 6-month-old zebrafish were injured in the skin (2 mm in diameter) and then treated with ISL. By measuring wound size and by histological examination, we found that ISL improved wound healing. In addition, 4-day-old zebrafish embryos of double transgenic line [Tg(fli-1:EGFP)]/[Tg(mpeg:mCherry)] were suffered from tissue traumas and then treated with ISL. Through fluorescent microscopy, we found that ISL promoted macrophage recruitment and angiogenesis in the wound area. Through qPCR analysis, we found that ISL up-regulated the expression of genes related to inflammation and angiogenesis in zebrafish embryos. These results showed that ISL could promote inflammatory response and angiogenesis, which played key roles in promoting wound healing. Therefore, ISL can be used as a promising candidate to promote wound healing.

De novo biosynthesis of liquiritin in Saccharomyces cerevisiae

Liquiritigenin (LG), isoliquiritigenin (Iso-LG), together with their respective glycoside derivatives liquiritin (LN) and isoliquiritin (Iso-LN), are the main active flavonoids of Glycyrrhiza uralensis, which is arguably the most widely used medicinal plant with enormous demand on the market, including Chinese medicine prescriptions, preparations, health care products and even food. Pharmacological studies have shown that these ingredients have broad medicinal value, including anti-cancer and anti-inflammatory effects. Although the biosynthetic pathway of glycyrrhizin, a triterpenoid component from G. uralensis, has been fully analyzed, little attention has been paid to the biosynthesis of the flavonoids of this plant. To obtain the enzyme-coding genes responsible for the biosynthesis of LN, analysis and screening were carried out by combining genome and comparative transcriptome database searches of G. uralensis and homologous genes of known flavonoid biosynthesis pathways. The catalytic functions of candidate genes were determined by in vitro or in vivo characterization. This work characterized the complete biosynthetic pathway of LN and achieved the de novo biosynthesis of liquiritin in Saccharomyces cerevisiae using endogenous yeast metabolites as precursors and cofactors for the first time, which provides a possibility for the economical and sustainable production and application of G. uralensis flavonoids through synthetic biology.

Flavonoids derived from liquorice suppress murine macrophage activation by up-regulating heme oxygenase-1 independent of Nrf2 activation

Liquiritigenin (LQG), isoliquiritin (ILQ) and isoliquiritigenin (ILG) are flavonoids derived from liquorice and all possess a similar chemical structural backbone. In the current study, we found that ILQ and ILG had suppressive effects on lipopolysaccharide (LPS)-induced inflammatory responses in murine macrophage by suppressing the iNOS and COX-2 proteins and mRNA expression. A mechanistic study indicated that the effect was associated with an induction of antioxidant and detoxification enzymes, including UGT1A1, NQO1, and heme oxygenase-1 (HO-1) mRNA expression. The regulator of these enzymes, nuclear factor-erythroid 2-related factor 2 (Nrf2), which plays a critical role in LPS-induced inflammatory responses, could be activated by ILQ and ILG. Additionally, ILQ and ILG promoted Nrf2 signaling activation by inhibiting the Kelch-like ECH-associated protein 1 (Keap1) and increasing Nrf2 translocation, inducing the expression of these antioxidant enzymes. We further found that ILQ and ILG induced HO-1 expression independent of Nrf2 expression. With respect to the effect of these compounds on NF-κB signaling, ILG was found to markedly inhibit IκBα degradation and phosphorylation, while LQG and ILQ had no significant effects. These results indicate that there are correlations between the anti-inflammatory responses and the chemical structural properties of these flavonoids.