Author Interviews / 12.11.2015 Interview with: Aouatef Bellamine, Ph.D Lonza Inc Medical Research: What is the background for this study? What are the main findings? Dr. Bellamine: About two years ago, Robert Koeth and his colleagues (Nat Med. 2013 May;19(5):576-85) published a paper linking atherosclerosis and increased cardiac disease risks to Trimethylamine N-oxide (TMAO), a degradation product of dietary quaternary ammonium compounds such as L-Carnitine, Betaine and Choline. When these compounds are not completely absorbed into the intestine, bacterial gut metabolizes them to TMA (Trimethylamine) which is absorbed to the blood and further metabolized by the liver flavin-containing mono-oxygenases (FMOs) to TMAO. This is why some people use injectable l carnitine products. Koeth’s observation was based on
  • 1- clinical association between L-Carnitine levels increased incidence of major cardiac events,
  • 2- on increased lesion formation in ApoE-/- mouse, a disease model used to study atherosclerosis.The conclusion was that TMAO promotes atherosclerosis. Although the association is established, the cause to effect cannot be clarified given the lack of dose response in this mouse model (a single dose has been used) and the small number of animals in the treatment group making the difference between treatments (3 out of 11 animals). In addition, TMAO has been described to play the role of a molecular chaperone, preventing the protein unfolding. TMAO is also found in fish where it plays an important role in maintaining a normal osmolality. Fish is reported otherwise to be a healthy food source and its consumption is not linked to atherosclerosis occurrence.
Lonza decided to investigate the mechanism (s) behind these observations (Bellamine et al., Experimental Biology meeting, San Diego, 28 April 2014, Bellamine et al., Atherosclerosis in press). First, we showed that increasing TMAO levels up to 10-fold the Cmax as reported in humans, did not affect the foam cell formation in vitro, an obligatory step in the atherosclerosis disease progression. Second, we used an improved version of the ApoE-/- mouse model, expressing the cholesteryl ester transport protein (CETP) lacking normally in rodents. The CETP plays a major role in the cholesterol re-cycling in humans and its inhibition has been studied as a target for atherosclerosis treatment. Further, we used different doses of dietary L-Carnitine, leading to different levels of TMAO in an attempt to establish a dose-response curve. We found that TMAO levels inversely correlated with the lesion size. Significantly reduced aortic lesion size was observed at high levels of TMAO. These effects were independent from lipid changes. These observations suggest that TMAO may play a protective role in atherosclerosis disease development by reducing the lesion formation. When the lesions start developing, the TMAO levels would be up-regulated by a compensatory mechanism (possibly by increasing FMOs expression levels). (more…)