Researchers from the Catholic University of Korea have demonstrated that by coating an implant with a laser-activated dye they were able to kill cells producing ghrelin, the so-called ‘hunger hormone’, in laboratory animals. The ‘Intragastric satiety-inducing device (ISD)’ is inserted endoscopically and consists of a stent, which lodges in the lower oesophagus, attached to a disk that rests in the opening to the stomach. The disk has a hole in the centre to let food through.
In 2019, the investigators led by Drs Hwoon-Yong Jung and Jung-Hoon Park, designed the new type of implant. Tests in pigs showed that the ISD lowered food intake and weight gain by enhancing the feeling of fullness and reducing levels of ghrelin, which is produced by cells near the top of stomach. However, the device caused complications, including acid reflux and migration into the stomach.
In their latest project, Jung, Park, and colleagues wanted to find out if they could suppress ghrelin even more by coating the ISD's disk with a compound that, with a shot of laser light, could kill some of the ghrelin-producing cells. The implant could then be removed to avoid the side effects associated with the initial design.
In this preliminary study, to enhance the therapeutic effects of ISD, photodynamic therapy (PDT) was combined by generating singlet oxygen under laser irradiation. Methylene blue (MB), as a photosensitizer (PS), was coated on the ISD surface for singlet oxygen production to stimulate or destroy cells. When exposed to laser light, the coating released singlet oxygen, an energised form of oxygen that killed nearby ghrelin-producing cells in the pigs' stomachs and then rapidly disappeared.
After one week, the treatment reduced ghrelin levels and body weight gain by half compared with an untreated pig, though these differences declined in the following weeks unless the light treatment was repeated. With further development, the simple procedure could become a new type of minimally invasive treatment to help obese patients lose weight, the researchers stated. The findings were reported in the paper, ‘Photodynamic methylene blue-embedded intragastric satiety-inducing device to treat obesity’, published in the journal ACS Applied Materials & Interfaces.
“PDT with an MB-embedded ISD was successfully performed in a porcine model, which had two-fold reduced body weight gain (12% in PDT vs 24% in control) and two-fold reduced ghrelin levels (21.2pg/mL in PDT vs 45.1pg/mL in control) at the first week post-procedure,” the researchers reported. “The simple and unique operation extends the point of view in PDT and is expected to be a novel endoscopic bariatric therapy.”