High-field magnetic resonance microscopy of aortic plaques in a mouse model of atherosclerosis

A very-low carbohydrate content in a high-fat diet modifies the plasma metabolome and impacts systemic inflammation and experimental atherosclerosis

Ketogenic diets (KDs) are very high-fat low-carbohydrate diets that promote nutritional ketosis and are widely used for weight loss, although concerns about potential adverse cardiovascular effects remain. We investigated a very high-fat KD's vascular impact and plasma metabolic signature compared to a non-ketogenic high-fat diet (HFD). Apolipoprotein E deficient (ApoE -/-) mice were fed a KD (%kcal:81:1:18, fat/carbohydrate/protein), a non-ketogenic high-fat diet with half of the fat content (HFD) (%kcal:40:42:18, fat/carbohydrate/protein) for 12 weeks. Plasma samples were used to quantify the major ketone body beta-hydroxybutyrate (BHB) and several pro-inflammatory cytokines (IL-6, MCP-1, MIP-1alpha, and TNF alpha), and to targeted metabolomic profiling by mass spectrometry. In addition, aortic atherosclerotic lesions were quantified ex-vivo by magnetic resonance imaging (MRI) on a 14-tesla system. KD was atherogenic when compared to the control diet, but KD mice, when compared to the HFD group (1) had markedly higher levels of BHB and lower levels of cytokines, confirming the presence of ketosis that alleviated the well-established fat-induced systemic inflammation; (2) displayed significant changes in the plasma metabolome that included a decrease in lipophilic metabolites and an increase in hydrophilic metabolites; (3) had significantly lower levels of several atherogenic lipid metabolites, including phosphatidylcholines, cholesterol esters, sphingomyelins, and ceramides; and (4) presented significantly lower aortic plaque burden. KD was atherogenic and was associated with specific metabolic changes but alleviated the fat-induced inflammation and lessened the progression of atherosclerosis when compared to the HFD.

Diet-Induced Severe Hyperhomocysteinemia Promotes Atherosclerosis Progression and Dysregulates the Plasma Metabolome in Apolipoprotein-E-Deficient Mice

Atherosclerosis and resulting cardiovascular disease are the leading causes of death in the US. Hyperhomocysteinemia (HHcy), or the accumulation of the intermediate amino acid homocysteine, is an independent risk factor for atherosclerosis, but the intricate biological processes mediating this effect remain elusive. Several factors regulate homocysteine levels, including the activity of several enzymes and adequate levels of their coenzymes, including pyridoxal phosphate (vitamin B6), folate (vitamin B9), and methylcobalamin (vitamin B12). To better understand the biological influence of HHcy on the development and progression of atherosclerosis, apolipoprotein-E-deficient (apoE-/- mice), a model for human atherosclerosis, were fed a hyperhomocysteinemic diet (low in methyl donors and B vitamins) (HHD) or a control diet (CD). After eight weeks, the plasma, aorta, and liver were collected to quantify methylation metabolites, while plasma was also used for a broad targeted metabolomic analysis. Aortic plaque burden in the brachiocephalic artery (BCA) was quantified via 14T magnetic resonance imaging (MRI). A severe accumulation of plasma and hepatic homocysteine and an increased BCA plaque burden were observed, thus confirming the atherogenic effect of the HHD. Moreover, a decreased methylation capacity in the plasma and aorta, indirectly assessed by the ratio of S-adenosylmethionine to S-adenosylhomocysteine (SAM:SAH) was detected in HHD mice together with a 172-fold increase in aortic cystathionine levels, indicating increased flux through the transsulfuration pathway. Betaine and its metabolic precursor, choline, were significantly decreased in the livers of HHD mice versus CD mice. Widespread changes in the plasma metabolome of HHD mice versus CD animals were detected, including alterations in acylcarnitines, amino acids, bile acids, ceramides, sphingomyelins, triacylglycerol levels, and several indicators of dysfunctional lipid metabolism. This study confirms the relevance of severe HHcy in the progression of vascular plaque and suggests novel metabolic pathways implicated in the pathophysiology of atherosclerosis.