β‐cryptoxanthin protection against cigarette smoke‐induced inflammatory responses in the lung is due to the action of its own molecule
Authors: Chiaverelli Rachel A. , Liu Chun , Hu Kang‐Quan , Wang Xiang‐Dong 
Published: November 2023

Higher intake of the dietary xanthophyll, β‐cryptoxanthin (BCX), has been associated with a lower risk of lung cancer death in smokers. We have previously shown that BCX feeding was effective in reducing both cigarette smoke (CS)‐induced lung inflammation in ferrets and carcinogen‐induced lung tumor multiplicity in mice. Since BCX can be cleaved by β‐carotene‐15, 15′‐oxygenase (BCO1) and β‐carotene‐9′, 10′‐oxygenase (BCO2), to produce biologically active metabolites including vitamin A and apo‐10′‐carotenoids, respectively, this has raised a question as to whether the protective activity of BCX is due to the intact molecule or metabolites generated by BCO1 and BCO2. In the present study, we examined the effects of a dietary BCX feeding intervention against CS‐induced lung inflammation in the absence of both BCO1 and BCO2 in mice. Both male and female BCO1/BCO2 double knock out (KO) mice at the age of 25 weeks were randomly assigned to either the BCX feeding group (20 mg/kg diet, equivalent to daily human consumption of approximately 1.7 mg of BCX, which is physiologically attainable by consuming 2–3 sweet red peppers) or to the no BCX feeding group, with both groups receiving equal and sufficient amounts of vitamin A in the diet. At 27 weeks of age, mice remained in the same feeding groups, and each feeding group was randomly divided further into groups with and without CS‐exposure (Research Cigarettes, Type 3R4F) for 2 weeks. The amount of CS exposure was similar to that found in humans smoking 1.5 packages of cigarettes per day, confirmed by analysis for the concentration of urinary cotinine equivalents, a stable metabolite of nicotine. Results showed that BCX supplementation significantly decreased the amount of both neutrophil and macrophage infiltration, as well as the mRNA expression of IL6 and TNFα in the lung tissue of CS‐exposed BCO1/BCO2 KO mice, with no sex differences, as compared to mice with CS‐exposure alone. BCX supplementation also significantly decreased both the percentage of bronchiolar membranes with hyperplastic epithelium and the average distance between alveolated surfaces (Lm), accompanied with the down‐regulation of protein levels of matrix metalloproteinases (MMP9 and MMP2) in the CS‐exposed mice, compared to mice without BCX supplementation (P<0.05). Furthermore, BCX supplementation resulted in a significant accumulation of BCX (30–43 nmol BCX/g liver) in BCO1/BCO2 KO mice, but similar concentrations of retinol and retinyl ester, as compared with the non‐supplemented mice, using HPLC analysis. No significant changes were observed in the concentration of plasma cytokines IL6, TNFα, and IL1‐β, by ELISA, among all groups. Body weight also remained unchanged among all groups. Taken together, the present study indicates that intact BCX, independent of carotenoid cleavage enzymes, prevents CS‐induced inflammation and alveolar enlargement without sex differences in vivo.

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Supported by NIH/NCI grant (R21CA176256)