In this study, we systematically investigated the associations between the metabolites of gut microbiota and blood lipids and the effect of statin therapy on them. We found that plasma TMAO and related precursors were associated with blood lipids significantly, especially TG, HDL-c and LDL-c. And the association between TMAO and HDL-c was not influenced by personal characteristics and rosuvastatin therapy. Besides, rosuvastatin therapy could decrease plasma TMAO levels but increase related precursors such as carnitine, betaine and γBB levels significantly when it lowering blood lipids.
The associations between the metabolites of gut microbiota and chronic metabolic diseases were focused in recent years. Early studies found that TMAO can lead to AS in animal model [16, 17], and patients with elevated TMAO were correlated with increased risk of MACE in clinical . Since then, TMAO and related precursors were found to be associated with the risks and extent of CVD and cerebrovascular disease in many studies later [10, 18–21]. TMAO was found to be pro-inflammatory and mediate inflammation by up-regulating inflammatory factors [22, 23]. Recent studies also reported that the gut microbiota contributed the variation of blood lipids and associated with hyperlipidemia [9, 24], and TMAO could reduce the reverse cholesterol transport and cholesterol absorption . All the studies stated above indicated that TMAO had a similar biological effect like disordered lipids, and there may be some associations between gut microbiota metabolites and blood lipids. In this study, we systematically analyzed the associations of TMAO and related precursors with blood lipids and the effect of rosuvastatin therapy on them. We found that plasma TMAO was correlated with TG positively and HDL-c negatively, betaine was associated with LDL-c negatively, and these associations were still significant after adjustment of the potential effect of sex, age, BMI, blood lipids and concomitant diseases hyperlipidemia, hypertension and CHD. In further analysis we found that the correlation between TMAO and HDL-c was still existed after rosuvastatin therapy, and this association was still significant after adjustment of potential effect of factors mentioned above. Firstly, our findings supported a recent study conducted by Fu, J. et al. indirectly, which found that the gut microbiota contributed the variations of blood lipids, especially HDL-c . Secondly, the results also indicated that not only the gut microbiota was associated with the variation of blood lipids, but also its metabolites were associated with the lipids levels, especially HDL-c. However, we found that the positive correlation between TMAO and TG, and the negative correlation between betaine and LDL-c disappeared after rosuvastatin therapy. The disturbed gut microbiota metabolites and lipids levels may be responsible for the disappeared associations between them after statin therapy. In addition as we have known, HDL-c was found to have anti-atherogenic effect in previous studies [25–27], and betaine was also found to be associated with non-HDL-c and the risk of CVD inversely [28, 29]. So, the results stated above tended to support the pro-atherogenic effect of TMAO, and the anti-atherogenic effect of betaine. Although gut microbiota was associated with the lipids variations and hyperlipidemia, and there were some associations between TMAO related parameters and blood lipids, we failed to find significant differences of TMAO, choline, betaine and γBB, except carnitine between patients’ with hyperlipidemia and non-hyperlipidemia in this study.
Previous studies found that drugs like proton pump inhibitors (PPIs) and statins could affect the gut microbiota compositions profoundly [30, 31], but there was scarce information about the effect of drugs on the gut microbiota metabolites. Recently, a small cohort study found that rosuvastatin therapy not only affected the genetic compositions of gut microbiota, but also may affect the gut microbiota metabolites . Patients in rosuvastatin therapy group had higher betaine and γBB levels than placebo group, and the TMAO and carnitine levels in rosuvastatin therapy group also tended to decrease and increase separately, although the differences were not significant . In this study we found that, rosuvastatin therapy could decrease TMAO, but increase carnitine, betaine and γBB levels significantly while it lowering the blood lipids levels. So, the results of our study further supported the findings of this previous study. As information about the potential bad effect of TMAO, carnitine and γBB, and the protective effect of betaine listed above, the TMAO-lowering and betaine-increasing effect of rosuvastatin therapy may be part of the pleotropic protective effect of statins therapy in CVD patients, and the increased carnitine and γBB may be responsible for the residual cardiovascular risks. However, it’s still difficult to explain the contradictory phenomenon for the pathway between TMAO production and related precursors. Although some studies had found the influence of drugs on the gut microbiota and related metabolites [30, 31], the associations between the changes of gut microbiota and related metabolites are still not clear, especially the decreased TMAO and increased related precursors. More experimental studies are needed to clarify the potential mechanisms of them.
As we known, TMAO is mainly produced by related precursors choline, carnitine and/or γBB under the effect of gut microbiota and hepatic flavin-containing monooxygenases (FMOs) . Many factors, including food, gut microbial flora and FMOs functions can influence their metabolisms and productions [33, 34]. Previous studies found that there is not a one-to-one relationship between TMAO and related precursors [33, 35]. In this study we also analyzed the associations between TMAO and related precursors, and their associations with personal characteristics. We found that TMAO was positively associated with related precursors choline and γBB, but had no associations with carnitine and betaine. We found that plasma TMAO was correlated with patients’ age positively, and this correlation was still existed after rosuvastatin therapy. This phenomenon was previously reported in an early study, which found that TMAO levels increased with advancing age . Besides, we found that TMAO or betaine was correlated BMI positively or negatively, and the association between betaine and BMI was still existed after rosuvastatin therapy. Previous studies had reported that gut microbiota was associated with patients’ BMI and obesity , and the gut microbiota transplantation could lead to obesity in animal model [37, 38]. The results of our study supported that the gut microbiota and related metabolites TMAO and betaine may play active role in the pathogenesis of obesity.
There are also some limitations in our study. Firstly, enrolled patients with suspected CHD and relatively old age inevitably make some selection bias. Secondly, the usage of multiple drugs may lead to potential effect on the gut microbiota metabolites. Thirdly, the modest sample size may influence the power of the results. Finally, although all the patients were ordered to eat low-salt and low-lipid diet, the non-uniform diet also may affect the levels of gut microbiota metabolites potentially. So a large and universal patient cohort with less drugs usage and standard diet is needed in further study.