Bismuth and transition metal complexes as potent anti-Helicobacter pylori agents: A review

Helicobacter pylori (Hp) belongs to the genus spirillobacter and generally colonizes the human stomach, frequently causing the various gastric diseases. The conventional antibiotics are often applied for the treatment of Hp infection, but their overuses prompting Hp to form a biofilm will reduce its susceptibility to antibiotics, thus resulting in antibiotic resistance to severely affect the therapy of Hp infection. Interestingly, the eradication rate of Hp increases when antibiotics are combined with bismuth complex-based agents that include colloidal bismuth subcitrate (CBS), bismuth subsalicylate (BSS) and ranitidine bismuth citrate (RBS), due to the synergistic activity of antibiotics and bismuth complexes, while no reports of resistance to bismuth complexes until now, so it is reasonable to select bismuth complex as an indispensable part of first-line therapy. As a result, the trivalent bismuth has been applied for the preparation of various bismuth complexes with efficient anti-Hp activities, appealing as the anti-Hp agents with low toxicity. Subsequently, some transition metal complexes with the better anti-Hp activities are also designed and synthesized. We believe that the development of new bismuth and transition metal complexes as anti-Hp agents may be a promising approach to increase the eradication rate of Hp infection. This review summarizes the most striking advances in the syntheses, crystal structures, and anti-Hp activities of bismuth and transition metal complexes, which attempt to not only reveal a correlation between their structural features and anti-Hp activities, but also offer the helpful guidance for the researchers in the future development of new bismuth and other important bio-metal complexes as the efficient anti-Hp agents.