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In the field of photodynamic therapy (PDT), optimization of the in vivo therapeutic efficacy needs a comprehensive study of the photo-killing action spectrum that depends on both the photosensitizer (PS) absorption and the tissue optical properties. This is especially true in the case of gastric infections by Helicobacter pylori: PS absorption has been largely investigated in vitro, while the contribution of tissue optical properties and illumination geometry has been poorly studied, despite being parameters that reflect the specific in vivo conditions. To investigate their influence, we focussed on the case of a point-like light source positioned in the antrum. This models a therapeutic device developed by our team which consists of a LED-based ingestible pill. By a simple 3D illumination model, our approach mediates light-tissue interaction over the illuminated stomach wall surface, then calculates its average transmittance T by means of a 1D model representative of the mean gastric mucosa structure. Finally, by merging T(λ) with the photosensitizers' absorption we obtained the in vivo action spectrum. This shows two peaks at about 500 and 630 nm, indicating a noticeable influence of the tissue with respect to in vitro studies, where the action spectrum reflects PS absorption only. Our approach defines one average action spectrum for this specific therapeutic context, which reflects the need to choose one emission spectrum for the light source used. The proposed methodology could be applied to any other illumination geometry of cave organs, provided appropriate model modifications for the light source and tissue characteristics are made.

Helicobacter pylori gastric infections are among the most diffused worldwide, suffering from a rising rate of antibiotic resistance. In this context, some of the authors have previously designed an ingestible device in the form of a luminous capsule to perform antibacterial photodynamic inactivation in the stomach. In this study, the light-emitting capsules were tested to verify the safety of use prior to perform clinical efficacy studies. First, laboratory tests measured the capsule temperature while in function and verified its chemical resistance in conditions mimicking the gastric and gut environments. Second, safety tests in a healthy minipig model were designed and completed, to verify both the capsule integrity and the absence of side effects, associated with its illumination and transit throughout the gastrointestinal tract. To this aim, a capsule administration protocol was defined considering a total of 6 animals with n = 2 treated with 8 capsules, n = 2 treated with 16 capsules and n = 2 controls with no capsule administration. Endoscopies were performed in sedated conditions before–after every capsule administration. Biopsies were taken from the corpus and antrum regions, while the gastric cavity temperature was monitored during illumination. The bench tests confirmed a very good chemical resistance and a moderate (about 3 °C) heating of the capsules. The animal trials showed no significant effects on the gastric wall tissues, both visually and histologically, accompanied with overall good animal tolerance to the treatment. The integrity of the administered capsules was verified as well. These encouraging results pose the basis for the definition of successive trials at the clinical level. Graphical abstract

Aim: The objective of this study was to investigate the possible synergy between doxycycline and photodynamic therapy against Helicobacter pylori and to evaluate the possible side effects on adenocarcinoma gastric cells with and without protoporphyrin IX. Materials & methods: Three H. pylori strains (ATCC 700392, 43504 and 49503) were grown on solid medium either with, or without, doxycycline at subinhibitory concentrations, and irradiated for 10, 20 and 30 minutes with a 400 nm-peaked light source. The phototoxicity tests on AGS cells were evaluated by MTT assay. Results: The photodynamic therapy and doxycycline combination showed an antibacterial synergistic effect with no significant toxicities. Conclusion: The synergistic treatment could be considered as an interesting therapeutic option.

Since many years it has been acknowledged that some bacterial species, among which H. pylori, P. aeruginosa, P. acnes accumulate endogenous photosensitizers (PS) in the form of porphyrins. This makes antibacterial photodynamic therapy (PDT) easier to perform due to the possible avoidance of external PS. In this study, we focus on gastric infections associated with the presence of Helicobacter pylori (H. pylori), known to accumulate and release both protoporphyrin IX (PPIX) and coproporphyrins. PDT versus H. pylori can be carried out by modified endoscopes or by new ingestible luminous devices under development. In both cases of in vitro and in vivo applications, either for therapy (PDT) or diagnosis, scientific literature lacks studies on the possible side-effects of light treatments on the surrounding tissues. To this aim we evaluated in vitro side-effects due to a possible intrinsic photosensitivity of gastric mucosa or to a photosensitization by the PS released from the bacterium itself. Photo-toxicity studies were conducted on the AGS cell line (ATCC® CRL-1739™), commonly used as a model for the stomach mucosa tissue, considering PPIX as the photosensitizing agent. After first evaluations of PPIX dark toxicity, its uptake and accumulation sites, photo-toxicity tests were conducted using a LED light source peaked at 400 nm, by varying both PPIX concentration (50 nM – 2 μM) and light dose in the range 0.6–13 J/cm2, representing different treatment procedures found in literature. The oxidative stress consequent to irradiation was investigated both in terms of ROS production and assessment of the activity of enzymes involved in ROS-related biological mechanisms. A significant phototoxic effect was found only for PPIX concentration > 100 nM for all tested light doses. This indicates that the evaluated photo-treatments do not cause side effects even with the sensitization due to PPIX released by the bacteria.

In the framework of the increasing phenomenon of antibiotic-resistant infections, those caused by Helicobacter pylori (Hp) have a particular significance, being worldwide diffused and associated with severe pathologies, among which gastric cancer. To overcome antibiotic-resistance, we propose the use of photodynamic therapy (PDT), based upon cytotoxic species production following bacteria illumination with visible light. In the case of Hp infection, this is due to the presence of endogenous light absorbers (porphyrins). To perform intra-gastric PDT, we have recently designed an illuminating ingestible device equipped with LED sources, where a crucial parameter is the choice of the emission wavelengths optimizing Hp photo-killing. For this purpose, both porphyrin absorption peaks and optical penetration in tissues have to be carefully accounted. By merging data on Hp porphyrin absorption spectrum with those coming by a Monte-Carlo optical modelling for illumination of the stomach wall surface, we have calculated the relative Hp photo-killing efficacy in three representative tissue models in the 400-650nm range. Results indicate that in thicker models, the red wavelengths are ultimately more effective than the blue-shifted ones, due to the greater penetration length in tissues despite a minor porphyrin absorption.

Introduction In the framework of the growing rate of antibiotic-resistance, new therapeutic solutions are being considered against bacterial infections, among which photodynamic therapy (PDT) is a very attractive perspective. In recent years, innovative solutions for endoscopic illumination have been studied, e.g. for catheter infections, pancreas tumours and stomach infections by Helicobacter pylori (Hp) . Hp colonizes the human stomach with a worldwide infection prevalence exceeding 50%, besides being a class 1 carcinogen agent (World Health Organization). Currently, Hp infection is treated with pharmacologic therapies, showing high failure rates mainly due to antibiotic resistance. To overcome this limitation, endoscopic PDT devices have been tested. However, they exhibit clear disadvantages, namely great invasivity and adverse effects. Purpose To design and characterize a non-invasive light-emitting device to perform Hp phototherapy: an ingestible “LED antibiotic”, exploiting the presence of endogenous Hp photosensitizers. Materials and methods Merging experimental and simulation methods we obtain the light action spectrum for Hp phototherapy in the gastric environment. We have designed and assembled the pill containing LED sources, a battery and electronic board. Capsule emission parameters are measured by an integrating sphere and in vitro Hp irradiation performed. Results The action spectrum for Hp phototherapy is peaked in the violet and red spectrum regions. Capsule prototypes show emission parameters compatible with in vitro Hp eradication (>99% killing). Conclusion Our device has shown emission spectrum, intensity and duration compatible with an effective phototherapy of Hp , considering also the treatment repeatability (5–10 capsules in 2–3 weeks). Future clinical trials are envisaged. Disclosure GR, GT, BO and FF disclose being also Probiomedica srl ( www.probiomedica.com ).