# A Review on Flavonoids as Anti-_Helicobacter pylori_ Agents
## 3 Results
### Flavonoids Usefulness in Treating H. pylori
pylori_ morphology by affecting the expression of genes associated with muropeptide dimers (_csd1_, _csd2_, _csd3_) and monomers (_csd3_, _csd6_, _csd4_, _amiA_), while also inhibiting DNA and RNA polymerase activity, thereby blocking replication and transcription [69]. Additionally, quercetin derived from _Ipomoa staphylina_ has demonstrated antimicrobial activity against _H. pylori_ by significantly reducing bacterial growth, as evidenced by agar diffusion assays [129]. Isoquercetin (quercetin-3-O-\(\beta\)-D-glucose) collected from _Alchemilla monticola_ and _A. viridiflora_ also showed some efficacy against _H. pylori_ with a MIC of 480 ug/mL and MBC of 240 ug/mL [116]. Loureirin A, a novel flavonoid obtained from Sanguus Draconis, the gum resin of _Dracena_ plants, was found to act as a narrow-spectrum anti-_H. pylori_ agent. Analysis by broth microdilution assay revealed that this flavonoid has an excellent bactericidal effect (MIC: 4 mg/mL) against _H. pylori_ with no significant resistance after serial passaging over 60 days [117]. Moreover, some research data showed a strong correlation between catechins in tea samples (catechin, epicatechin, and epigallocatechin) and anti-_H. pylori_ activity [108]. In vitro growth assay of _H. pylori_ with catechin revealed a growth inhibition effect on doses as low as 0.4 mg/mL, and the potential of the reduction on bacterial proliferation rate was verified after incubation in 1 mg/mL catechin [109]. A similar activity was also observed for (\(-\))-epicatechin, in which the MIC was found to be 0.6 mg/mL and full growth inhibition was achieved at concentrations above 0.8 mg/mL [110]. These results are supported by a different in vitro study that verified the MIC range between 128 and 1024 ug/mL, depending on the _H. pylori_ tested strain and the catechins [73]. It has been observed that catechins and epicatechins also produce a gastoprotective effect against _H. pylori_ via inhibition of urease and anti-adherent activities [111, 112]. However, it has been observed that some extracts containing smaller amounts of catechins sometimes did not show any activity against _H. pylori_, which may suggest that catechins are not the sole effector against _H. pylori_ inhibition. It raises the hypothesis that in the extracts that have an effect against _H. pylori_ and have catechins, other compounds might work in combination and are not detected in HPLC analysis [108]. Another flavonoid identified for its activity against _H. pylori_ is equatilin. This compound has demonstrated dose-dependent anti-inflammatory effects, mainly through inhibiting pro-inflammatory cytokines. Studies involving both in vitro gastric cell models and in vivo rats have shown promising results. A clinical trial involving 512 patients with erosive gastritis reported high cure rates, suggesting equatilin therapeutic potential. Its mechanisms of action include inhibition of the NF-kB inflammatory pathway, reduction of cytokine production, and suppression of the _H. pylori_ virulence gene _CagA_, thereby mitigating inflammation [113]. Eupatilin has also been identified in _Artemisia ludoviciana_, where two promising extracts demonstrated MIC values ranging from 125 to 250 ug/mL. Evidence of modulation of NF-kB and IL-6 transcription further supported its anti-inflammatory mechanism, findings consistent with previous studies on equatilin activity against _H. pylori_[114]. Furthermore, extracts from _Cistus laurifugius L._ flowers have shown promising activity against _H. pylori_. These extracts contain flavonoids such as quercetin-3-O-glucose, kaempfer-3-glucose, myricitrin-3-rhammoside, and other compounds. Their activity was assessed by evaluating IL-8 inhibition in GES-1 cells, where they demonstrated a potent inhibitory effect on bacterial adhesion to host cells, which is crucial for bacterial colonisation. However, no significant modification in urease activity was observed, suggesting that their anti-_H. pylori_ activity is primarily associated with adhesion rather than direct urease inhibition [130].