Although low-density lipoprotein (LDL) cholesterol, synthesized by liver, is one of the main risk factors of coronary atheroma in humans, clinical practice has taught us that meetings between our 2 specialties are not about this subject, except maybe when discussing the opportunity of a liver transplantation in patients with severe coronary disease. Recent works demonstrating a strong protective effect of the bile acids receptor FXR and TGR5 in a mice models of atheroma1, 2 could change this old rule in the not so distant future, but so far no evidences exists in humans. The level of activation of these receptors depends on the type of bile acids that activate them.3 We designed a pilot prospective and observational study conducted between June 2010 and September 2010 to search for variations in the bile acid pool composition between 2 populations: patients with or without coronary atheroma. We determined the serum concentrations of cholic, chenodeoxycholic, deoxycholic, and lithocholic acids in a fasting blood sample in all consecutive patients undergoing coronary angiograms in the cathlab unit of Cochin Hospital. Applying very restrictive exclusions criteria to avoid artificial variations of the bile acid pool (post-cardiac arrest; nonfasting states; hepatic disease; treatment with antimicrobials, corticosteroids, statins, or fibrates) of 393 screened patients, 44 met the criteria and were divided between 27 with (group A) and 17 without (group B) angiographically visible coronary atheromas.
Except for more males in group A, the groups were comparable. The serum lithocholic acid (LCA) concentration was significantly lower in group A (median 0.03 μmol/L; interquartile range 0.02–0.05) than in group B (0.08 μmol/L; interquartile range 0.05–0.11; P = 0.015) (Fig. 1). In the multivariate analysis, LCA was the only predictor of coronary atheroma independently of patient gender (odds ratio 2.41 per 0.05 decrease; 95% confidence interval 1.11-5.25; P = 0.027).
Although the populations were small, we believe this observation connecting LCA and coronary atheroma is a field worth investigating further, as LCA is the most powerful activator of TGR5.3 A study targeting the proinflammatory mechanism acting in atheroma plaque evidenced that the activation of the TGR5 receptor significantly limits the formation of plaques in LDL−/− mice by decreasing the inflammation inside the plaque and the proinflammatory cytokines secretion by macrophages. This raises the hypothesis that lowering the most prominent activator of TGR5 is likely to lower the protection against plaque development in humans. Further studies are needed to confirm this observation, to better understand the origin and the extent to which a decrease in LCA is implicated in the development of coronary atheromatous plaques, and to maybe put us hepatologists and cardiologists more often around the same table.