The effect of low-power laser light at different doses on gastric mucosa sensitized with methylene blue, haematoporphyrin derivative or toluidine blue

Helicobacter pylori has been associated with peptic ulcers, gastric cancer and various other gastroduodenal pathologies. Conventional antibiotic treatment is not entirely satisfactory, whereas photodynamic therapy (PDT) is a possible alternative. Although PDT has been shown to be effective in killing helicobacter on native gastric mucosa, the success of the technique will depend upon the mucosa underlying the bacteria remaining unharmed. This study examined the effect of increasing doses of low-power laser light on rat gastric mucosa, sensitized with either methylene blue (MB), haematoporphyrin derivative (HpD) or toluidine blue (TBO). No damage was detectable with any of the photosensitizers when a light dose of 250 Jcm^-2 was used. Mucosal damage was seen consistently with TBO (1 mg ml^-1) and a light dose of 500 J cm^-2. The same light dose of 500 J cm^-2 using MB caused inconsistent damage to the mucosa, whereas HpD had no effect even with the highest dose of laser light (500 J cm^-2). As the energy doses required to kill bacteria (50 and 200 Jcm^-2 for MB and TBO, respectively) are well below the levels shown to damage normal gastric mucosa, PDT forH. pylori should not be harmful to the underlying epithelium.