The novel compound Sul‐121 inhibits inflammation in experimental models of chronic obstructive pulmonary disease
Authors: Schmidt Martina , Han Bing , Poppinga Wilfred J , Zuo Haoxiao , van der Graaf Kees , Meurs Herman 
Published: November 2023

Chronic obstructive pulmonary disease (COPD) is characterized by persistent airflow limitation and neutrophilic airway inflammation. Current COPD medication involves anticholinergics, β2‐adrenoceptor agonists and/or corticosteroids. However, these drugs fail to effectively reduce chronic pulmonary inflammation and disease progression, and may provoke unwanted side effects. Targeting oxidative stress could be an attractive alternative treatment option. Here, we explored the anti‐inflammatory and bronchodilatory properties of Sul‐121, a novel compound with H2S generating and anti‐oxidative capacities, in experimental models of COPD.

In vivo protocols were approved by the University of Groningen (Groningen, The Netherlands) Committee for Animal Experimentation. Outbred male, specified pathogen‐free Dunkin Hartley guinea pigs (Harlan, Heathfield, UK) weighing 350–450 g were used. Guinea pigs were intranasally instilled with lipopolysaccharide (LPS) to induce neutrophilic airway inflammation and airway hyperresponsiveness; sterile saline was used as control. Before LPS or saline instillation animals were treated by inhalation of aerosolized vehicle or Sul‐121 solutions (3 or 30 mM, nebulizer concentrations). Neutrophil bronchoalveolar lavage counting was performed with May‐Grünwald and Giemsa stain. H2S levels were determined using an ISM‐146S electrode (Lazar, Los Angeles, USA). The malondialdehyde (MDA) concentration in lung homogenates was measured by the thiobarbituric acid reactive substances. Immortalized human airway smooth muscle cells were exposed to 15 % CSE in the absence or presence of the indicated Sul‐121concentrations for 24 hours. Release of interleukin‐8 (IL‐8) by these cells was measured by ELISA; nuclear translocation of the NF‐κB subunit p65 and of the anti‐oxidative response regulator, nuclear factor erythroid 2‐related factor 2 (Nrf2), was assessed by immunofluorescence. Reactive oxygen species (ROS) were measured by the 7′‐dichlorofluorescein‐diacetate fluorescence. Statistical significance of differences was evaluated by one‐way or two way ANOVA with Bonferroni post‐hoc tests.

Using a guinea pig model of lipopolysaccharide (LPS)‐induced COPD, we demonstrate that inhalation of Sul‐121 dose‐dependently inhibited LPS‐induced airway neutrophilia and airway hyperresponsiveness, reaching statistical significance (p<0.001 each) at 30 mM (nebulizer concentration). LPS tend to reduce the H2S level in the blood (p=0.09), which was prevented by Sul‐121. In addition, small airways neutrophils negatively correlated (p<0.04) with the blood H2S level. Sul‐121 (p<0.05) prevent LPS‐induced increased oxidative stress as measured by the MDA level in the lung (p<0.01). Using immortalized human airway smooth muscle cells, we show that Sul‐121 dose‐dependently prevented the release of cigarette smoke extract‐induced IL‐8 release by these cells, a process being most prominent at 300 μM Sul‐121 (p<0.001) and accompanied by inhibition of nuclear translocation of both p65 (p<0.01) and Nrf2 (p<0.001). In addition, Sul‐121 exerted direct anti‐oxidative properties (p<0.001) and diminished cellular ROS production by the airway smooth muscle cells (p<0.001).

In conclusion, Sul‐121 effectively inhibits airway inflammation and airway hyperresponsiveness in an animal model of COPD, presumably by inhibition of oxidative stress.

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