Probiotics improve the neurometabolic profile of rats with chronic cholestatic liver disease

Chronic liver disease leads to neuropsychiatric complications called hepatic encephalopathy (HE). Current treatments have some limitations in their efficacy and tolerability, emphasizing the need for alternative therapies. Modulation of gut bacterial flora using probiotics is emerging as a therapeutic alternative. However, knowledge about how probiotics influence brain metabolite changes during HE is missing. In the present study, we combined the advantages of ultra-high field in vivo H-1 MRS with behavioural tests to analyse whether a long-term treatment with a multistrain probiotic mixture (VIVOMIXX) in a rat model of type C HE had a positive effect on behaviour and neurometabolic changes. We showed that the prophylactic administration of this probiotic formulation led to an increase in gut Bifidobacteria and attenuated changes in locomotor activity and neurometabolic profile in a rat model of type C HE. Both the performance in behavioural tests and the neurometabolic profile of BDL+probiotic rats were improved compared to the BDL group at week 8 post-BDL. They displayed a significantly lesser increase in brain Gln, a milder decrease in brain mIns and a smaller decrease in neurotransmitter Glu than untreated animals. The clinical implications of these findings are potentially far-reaching given that probiotics are generally safe and well-tolerated by patients.

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

Veronika Rackayová

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 â 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.

EPFL2018

Development and applications of hyperpolarized 13C and 1H MR spectroscopy of cerebral metabolism at ultra-high field

Emmanuelle Ines Flatt

This thesis is composed of four studies centered on investigating cerebral metabolism using magnetic resonance spectroscopy (MRS) of hyperpolarized and non-hyperpolarized compounds at ultra-high field. In the first two chapters, we studied longitudinally the effects of different treatments for hepatic encephalopathy (HE) on the neurometabolic changes associated with chronic HE using a rat model of type C HE and a multimodal approach including 1H MRS. The effects of the antibiotic rifaximin administered at different doses as well as its combination with probiotics were studied in the established model of bile duct ligated (BDL) rats. We showed for the first time the beneficial effects of the combined rifaximin and the probiotic Vivomixx® on the neurometabolic changes in vivo and longitudinally in a rat model of type C HE. The longitudinal changes of some brain metabolites concentration (glutamine, glutamate, creatine), as well as gut bifidobacteria concentration, were significantly less pronounced in the group of rats treated with rifaximin and probiotics compared to non-treated rats. We also showed that rifaximin treatment alone had limited efficacy. When administered at human dose in rats, its effects appeared only at the early stages of the disease, whereas at a higher dose some neurometabolic changes associated with HE were attenuated but the general condition of the rats was worse. In the third study, we used dissolution dynamic nuclear polarization (DNP) to hyperpolarize [2H7, U-13C6]-D-glucose, which enabled us to monitor real-time glycolysis in the healthy mouse brain. Given that glucose metabolism is tightly linked to neuronal activity, we first investigated how the change in anesthesia impacts the cerebral metabolism of hyperpolarized glucose. Anesthetics are known to influence brain activity, and in this study we showed for the first time that switching from isoflurane anesthesia to a combination of lower doses of isoflurane and medetomidine had a high impact on cerebral glucose uptake and glycolytic flow, as reflected by the increased labelling of downstream [1-13C] lactate. The second part of this study aimed at evaluating the feasibility of quantifying cerebral glucose metabolism kinetics by evaluating two different mathematical models, where kinetic rate constants were determined by fitting the models on 13C curves by non-linear regression using the Levenberg-Marquardt algorithm. We showed that a 3-compartment model is more stable and reliable than a 4-compartment model. Finally, since lithium salts are widely used for treating bipolar disorder but its mechanism of action is still not clearly understood, we evaluated the potential of hyperpolarized 6Li injected at pharmacological doses to assess its real-time bio-distribution and pharmacokinetic in the rat brain. We demonstrated first that hyperpolarized 6Li can be detected at pharmacological concentration in the rat head with high signal-to-noise ratio (SNR). We also showed that the transport of lithium through the intact blood-brain barrier brain is a limiting factor and demonstrated a striking difference between apparent 6Li T1 values in a brain with normal or disrupted blood-brain barrier.

EPFL2021

Development and applications of hyperpolarized 13C and 1H MR spectroscopy of cerebral metabolism at ultra-high field

Emmanuelle Ines Flatt

EPFL2021

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

Veronika Rackayová

EPFL2018