Diet‐Induced High Serum Levels of Trimethylamine‐N‐oxide Enhance the Cellular Inflammatory Response without Exacerbating Acute Intracerebral Hemorrhage Injury in Mice
Caizhen Li, Li Zhu, Yinming Dai, Zhiying Zhang, Leo Huang, Tom J. Wang, Peiji Fu, Yinuo Li, Jian Wang, Chao Jiang
Abstract
Trimethylamine‐N‐oxide (TMAO), an intestinal flora metabolite of choline, may aggravate atherosclerosis by inducing a chronic inflammatory response and thereby promoting the occurrence of cerebrovascular diseases. Knowledge about the influence of TMAO‐related inflammatory response on the pathological process of acute stroke is limited. This study was designed to explore the effects of TMAO on neuroinflammation, brain injury severity, and long‐term neurologic function in mice with acute intracerebral hemorrhage (ICH). We fed mice with either a regular chow diet or a chow diet supplemented with 1.2% choline pre‐ and post‐ICH. In this study, we measured serum levels of TMAO with ultrahigh‐performance liquid chromatography‐tandem mass spectrometry at 24 h and 72 h post‐ICH. The expression level of P38‐mitogen‐protein kinase (P38‐MAPK), myeloid differentiation factor 88 (MyD88), high‐mobility group box1 protein (HMGB1), and interleukin‐1 β (IL‐1 β ) around hematoma was examined by western blotting at 24 h. Microglial and astrocyte activation and neutrophil infiltration were examined at 72 h. The lesion was examined on days 3 and 28. Neurologic deficits were examined for 28 days. A long‐term choline diet significantly increased serum levels of TMAO compared with a regular diet at 24 h and 72 h after sham operation or ICH. Choline diet‐induced high serum levels of TMAO did not enhance the expression of P38‐MAPK, MyD88, HMGB1, or IL‐1 β at 24 h. However, it did increase the number of activated microglia and astrocytes around the hematoma at 72 h. Contrary to our expectations, it did not aggravate acute or long‐term histologic damage or neurologic deficits after ICH. In summary, choline diet‐induced high serum levels of TMAO increased the cellular inflammatory response probably by activating microglia and astrocytes. However, it did not aggravate brain injury or worsen long‐term neurologic deficits. Although TMAO might be a potential risk factor for cerebrovascular diseases, this exploratory study did not support that TMAO is a promising target for ICH therapy.