Brain metabolism during Chronic Hepatic Encephalopathy studied by in vivo 1H and 31P MRS

Magnetic resonance spectroscopy (MRS) is a powerful tool increasingly used in biomedical research and also in clinical practice.

This thesis focused on the improvements of in vivo 31P MRS and 31P magnetization transfer methods at high magnetic field (9.4T). Then, in vivo 31P MRS was combined with 1H MRS to longitudinally study neurometabolic changes during chronic hepatic encephalopathy (CHE) in adult and developing brain using a well-recognized animal model of cholestatic chronic liver disease and HE type C – bile duct ligated (BDL) rats. CHE is neuro-psychiatric disorder caused by chronic liver disease (CLD), with not well-understood molecular mechanisms, inducing important and sometimes lethal brain changes. In a next step, potential protective treatments (probiotics and high creatine diet) were tested. To the best of our knowledge such a detailed approach was not yet published.

Firstly, we showed by in vivo 1H MRS in hippocampus that adult BDL rats suffered from increase in brain glutamine, decrease in metabolites involved in osmoregulation including creatine, decrease in neurotransmitters and ascorbate and we were able to show the importance of early metabolic changes compared to late changes thanks to longitudinal measurements. 31P MRS study in larger brain volume found only mild perturbation of energy metabolism such as non-significant trend in ATP decrease in adult BDL rats.

Secondly, studies in young BDL rats at two developmental stages by 1H MRS in the hippocampus revealed similar changes that the one observed in adult brain during CHE. However almost all the neurometabolic changes were more profound or appeared earlier in the evolution of the disease in young BDL rats.

A new surface 1H-31P double-tuned coil was built and several optimizations and development were done to improve the spectral resolution, SNR and localization, including implementation of 1H-31P NOE enhancement and 1H decoupling in static 31P MRS, optimization of localization method and also development of an optimal protocol for 31P magnetization transfer.

31P MRS study in p21 BDL rats was performed with an improved 31P MRS protocol and revealed a decreased creatine kinase rate constant 2 weeks after BDL surgery and significant changes in metabolites involved in high-phosphate metabolism, in phospholipid metabolism and also cellular redox state 6 weeks after BDL.

In the last part of this thesis, some therapeutic approaches were tested. A probiotic treatment delayed some neurometabolic changes present in CHE in adult BDL rats and improved motor activity. Based on previously shown devastating effects of decreased brain creatine during brain development, we proposed the high creatine diet as a possible treatment for young BDL rats. We demonstrated that oral administration of creatine partially restored brain creatine levels and also had a positive effect on other neurometabolic changes present in CHE.

In conclusion, the work done in this thesis revealed for the first time a large spectrum of neurometabolic alterations present in adult and young BDL rats suffering from CLD and CHE, together with the time evolution of these changes during the disease progression, using in vivo longitudinal 1H MRS, improved 31P MRS and 31P magnetization transfer protocols developed herein. In addition, we brought some insight on the positive effects of two innovative treatments on the progression of CHE in adult and young BDL rats.