Serum Microcystin-LR Levels Linked with Risk of Inflammatory Bowel Disease: A Matched Case-Control Study in China

Abstract

Microcystin-LR (MC-LR), the most prevalent and diverse cyanotoxin produced by harmful cyanobacterial blooms, has been linked to gastrointestinal toxicity. Therefore, we conducted a case-control study across four regions in China to investigate this relationship. Inflammatory bowel disease (IBD) cases (219) were matched with healthy controls (438) based on age and gender and conditional logistic regression models and Restricted cubic splines were used to evaluate the association between MC-LR exposure and IBD risk. We used quantitative real-time polymerase chain reaction to measure the expression levels of inflammatory factors. The levels of protein expression in the colorectum were determined using Western blotting (WB). Compared to the lowest quartile of serum MC-LR levels, the adjusted odds ratios and 95% confidence intervals (CI) for the highest quartiles of serum MC-LR levels were 5.51 (2.70, 11.21). The RCS was shown the association between serum MC-LR levels and IBD risk was nonlinear (P _nonlinear < 0.001). In the animal experiments, MC-LR resulted in colorectal injury via the PI3K/AKT signaling pathway. Our study provides the evidence that serum MC-LR exposure is significantly associated with the risk of IBD in China. Animal study results indicate that MC-LR probably causes IBD via the PI3K/AKT signaling pathway.

Figure 1

Serum MC-LR level in IBD cases and healthy controls. N = 438 for control, N = 219 for IBD, N = 172 for CD, and N = 47 for UC. ***P < 0.001, two-tailed, using the Mann–Whitney U test.

Figure 2

Nonlinear association between serum MC-LR concentration and risk of IBD (A, N = 219), CD (B, N = 172), and UC (C, N = 47). The restricted cubic spline method examined these associations by adjusting for gender, age, BMI, coffee consumption, diet habits, and physical activity. The horizontal axis shows the serum MC-LR concentration (μg/L), and the vertical axis shows the risk OR (95% CI).

Figure 3

Subgroup analyses for nonlinear associations between serum MC-LR concentrations with IBD in participants with IBD stratified by age, gender, coffee consumption, diet habit, and physical activity. The horizontal axis represents the serum MC-LR concentration in μg/L and the vertical axis represents the OR (95% CI) of the IBD risk. The solid line represents estimates of ORs and dashed lines represent 95% CIs.

Figure 4

Associations between serum MC-LR concentration with IBD risk in participants with IBD stratified by age, gender, coffee consumption, diet habit, and physical activity. ORs were calculated adjusting for age, gender, BMI, diet habits, coffee consumption, physical activity.

Figure 5

MC-LR induced inflammation response and PI3K/AKT signaling pathway in mice. (A) HE staining of representative colorectum sections from CT and MC-LR treated mice. (B–G) mRNA expression levels of inflammatory factors IL-6, TNF-α, IL-10, IL-1β, OATP3a1, and OATP4a1. (H–J) Protein level of p-PI3K/PI3K, and p-AKT/AKT. The red arrow indicates lymphocyte infiltration, and the yellow box indicates a disordered crypt arrangement. Significant differences between the CT and MC-LR treatment groups were analyzed using two-way analysis of variance with least significant difference test. *P < 0.05, **P < 0.01 (n > 5).