Effect of antioxidants on airway smooth muscle contraction: action of lipoic acid and some of its novel derivatives on guinea pig tracheal smooth muscle

The effects of lipoic acid on respiratory diseases

Respiratory diseases, including lung cancer, pulmonary fibrosis, asthma, and the recently emerging fatal coronavirus disease-19 (COVID-19), are the leading causes of illness and death worldwide. The increasing incidence and mortality rates have attracted much attention to the prevention and treatment of these conditions. Lipoic acid (LA), a naturally occurring organosulfur compound, is not only essential for mitochondrial aerobic metabolism but also shows therapeutic potential via certain pharmacological effects (e.g., antioxidative and anti-inflammatory effects). In recent years, accumulating evidence (animal experiments and in vitro studies) has suggested a role of LA in ameliorating many respiratory diseases (e.g., lung cancer, fibrosis, asthma, acute lung injury and smoking-induced lung injury). Therefore, this review will provide an overview of the present investigational evidence on the therapeutic effect of LA against respiratory diseases in vitro and in vivo. We also summarize the corresponding mechanisms of action to inspire further basic studies and clinical trials to confirm the health benefits of LA in the context of respiratory diseases.

Role of airway smooth muscle cell phenotypes in airway tone and obstruction in guinea pig asthma model

Background

Airway obstruction (AO) in asthma is driven by airway smooth muscle (ASM) contraction. AO can be induced extrinsically by direct stimulation of ASM with contractile agonists as histamine, or by indirect provocation with antigens as ovalbumin, while the airway tone is dependent on intrinsic mechanisms. The association of the ASM phenotypes involved in different types of AO and airway tone in guinea pigs was evaluated.

Methods

Guinea pigs were sensitized to ovalbumin and challenged with antigen. In each challenge, the maximum OA response to ovalbumin was determined, and before the challenges, the tone of the airways. At third challenge, airway responsiveness (AR) to histamine was evaluated and ASM cells from trachea were disaggregated to determinate: (a) by flow cytometry, the percentage of cells that express transforming growth factor-β1 (TGF-β1), interleukin-13 (IL-13) and sarco-endoplasmic Ca²⁺ ATPase-2b (SERCA2b), (b) by RT-PCR, the SERCA2B gene expression, (c) by ELISA, reduced glutathione (GSH) and, (d) Ca²⁺ sarcoplasmic reticulum refilling rate by microfluorometry. Control guinea pig group received saline instead ovalbumin.

Results

Antigenic challenges in sensitized guinea pigs induced indirect AO, AR to histamine and increment in airway tone at third challenge. No relationship was observed between AO induced by antigen and AR to histamine with changes in airway tone. The extent of antigen-induced AO was associated with both, TGF-β1 expression in ASM and AR degree. The magnitude of AR and antigen-induced AO showed an inverse correlation with GSH levels in ASM. The airway tone showed an inverse association with SERCA2b expression.

Conclusions

Our data suggest that each type of AO and airway tone depends on different ASM phenotypes: direct and indirect AO seems to be sensitive to the level of oxidative stress; indirect obstruction induced by antigen appears to be influenced by the expression of TGF-β1 and the SERCA2b expression level plays a role in the airway tone.

A comparison of the effects of lindane and FeCl3/ADP on spontaneous contractions in isolated rat or human term myometrium

Oxidative stress affects the contractile behavior of smooth muscle resulting in complications during labor. Toxicants such as lindane and ferric chloride (FeCl₃)/adenosine diphosphate (ADP) cause oxidative stress and have previously been shown to inhibit smooth muscle contraction. In this study we examined the effects of the oxygen species scavengers, ascorbic acid and N-acetylcysteine on lindane and FeCl₃/ADP's inhibition of spontaneous myometrial contractions in rat and human myometrium. Lindane and FeCl₃/ADP gave rise to concentration-dependent reductions in rat (EC₅₀ 11.8×10^-6M and 0.9×10^-3M) and human myometrial contractions (EC₅₀ 16.3×10^-6M and 1.1×10^-3M, respectively). Pre-treatment with N-acetylcysteine significantly increased the EC₅₀ for the effects of lindane on motility index of human tissue and reduced the maximum inhibitory effect of FeCl₃/ADP on contractions in both rat and human myometrium. Ascorbic acid reduced the effects of FeCl₃/ADP in rat tissue only. In conclusion pre-treatment with specific antioxidants may protect both rat and human myometrium from the inhibitory effects of lindane and FeCl₃/ADP.