The janus face of ketone bodies in hypertension

The different roles of homocysteine metabolism in hypertension among normal-weight and obese patients with obstructive sleep apnea

BACKGROUND

Obstructive sleep apnea (OSA) is associated with hypertension. However, the differential mechanisms underlying OSA-related hypertension between normal-weight vs. obese patients is limited.

METHODS

We studied 92 patients with OSA and 24 patients with continuous positive airway pressure (CPAP) treatment. Blood pressure (BP) was measured twice during awake and continuously monitored during sleep. Obesity was defined as body mass index ≥28 kg/m2. Serum metabolite levels were assessed by metabolomics.

RESULTS

Among 59 normal-weight and 33 obese patients, 651 and 167 metabolites showed differences between hypertension and normotension or were associated with systolic and diastolic BP (SBP, DBP) after controlling confounders. These metabolites involved 16 and 12 Kyoto Encyclopedia of Genes and Genomes enrichment pathways in normal-weight and obese patients respectively, whereas 6 pathways overlapped. Among these 6 overlapping pathways, 4 were related to homocysteine metabolism and 2 were non-specific pathways. In homocysteine metabolism pathway, 13 metabolites were identified. Interestingly, the change trends of 7 metabolites associated with SBP (all interaction-p≤0.083) and 8 metabolites associated with DBP (all interaction-p≤0.033) were opposite between normal-weight and obese patients. Specifically, increased BP was associated with down-regulated folate-dependent remethylation and accelerated transsulfuration in normal-weight patients, whereas associated with enhanced betaine-dependent remethylation and reduced transsulfuration in obese patients. Similar findings were observed in ambulatory BP during sleep. After CPAP treatment, baseline low homocysteine levels predicted greater decrease in DBP among normal-weight but not obese patients.

CONCLUSIONS

Mechanisms in OSA-related hypertension differ between normal-weight and obese patients, which are explained by different changes in homocysteine metabolism.

Digesting the complex metabolic effects of diet on the host and microbiome

The past 50 years of interdisciplinary research in humans and model organisms has delivered unprecedented insights into the mechanisms through which diet affects energy balance. However, translating these results to prevent and treat obesity and its associated diseases remains challenging. Given the vast scope of this literature, we focus this Review on recent conceptual advances in molecular nutrition targeting the management of energy balance, including emerging dietary and pharmaceutical interventions and their interactions with the human gut microbiome. Notably, multiple current dietary patterns of interest embrace moderate-to-high fat intake or prioritize the timing of eating over macronutrient intake. Furthermore, the rapid expansion of microbiome research findings has complicated multiple longstanding tenets of nutrition while also providing new opportunities for intervention. Continued progress promises more precise and reliable dietary recommendations that leverage our growing knowledge of the microbiome, the changing landscape of clinical interventions, and our molecular understanding of human biology.

Efficacy and safety of prolonged water fasting: a narrative review of human trials

The goal of this narrative review is to summarize the effects of prolonged fasting on various metabolic health measures, including body weight, blood pressure, plasma lipids, and glycemic control. Prolonged fasting is characterized by consciously eating little to no food or caloric beverages for several days to weeks. Results reveal that prolonged fasting for 5-20 days produces potent increases in circulating ketones, and mild to moderate weight loss of 2-10%. Approximately two-thirds of the weight lost is lean mass, and one-third is fat mass. The excessive lean mass loss suggests that prolonged fasting may increase the breakdown of muscle proteins, which is a concern. Systolic and diastolic blood pressure consistently decreased with prolonged fasting. However, the impact of these protocols on plasma lipids is less clear. While some trials demonstrate decreases in LDL cholesterol and triglycerides, others show no benefit. With regard to glycemic control, reductions in fasting glucose, fasting insulin, insulin resistance, and glycated hemoglobin (HbA1c) were noted in adults with normoglycemia. In contrast, these glucoregulatory factors remained unchanged in patients with type 1 or type 2 diabetes. The effects of refeeding were also examined in a few trials. It was shown that 3-4 months after the fast was completed, all metabolic benefits were no longer observed, even when weight loss was maintained. With regard to adverse events, metabolic acidosis, headaches, insomnia, and hunger were observed in some studies. In summary, prolonged fasting appears to be a moderately safe diet therapy that can produce clinically significant weight loss (>5%) over a few days or weeks. However, the ability of these protocols to produce sustained improvements in metabolic markers warrants further investigation.

Genome-wide characterization of circulating metabolic biomarkers

Genome-wide association analyses using high-throughput metabolomics platforms have led to novel insights into the biology of human metabolism1-7. This detailed knowledge of the genetic determinants of systemic metabolism has been pivotal for uncovering how genetic pathways influence biological mechanisms and complex diseases8-11. Here we present a genome-wide association study for 233 circulating metabolic traits quantified by nuclear magnetic resonance spectroscopy in up to 136,016 participants from 33 cohorts. We identify more than 400 independent loci and assign probable causal genes at two-thirds of these using manual curation of plausible biological candidates. We highlight the importance of sample and participant characteristics that can have significant effects on genetic associations. We use detailed metabolic profiling of lipoprotein- and lipid-associated variants to better characterize how known lipid loci and novel loci affect lipoprotein metabolism at a granular level. We demonstrate the translational utility of comprehensively phenotyped molecular data, characterizing the metabolic associations of intrahepatic cholestasis of pregnancy. Finally, we observe substantial genetic pleiotropy for multiple metabolic pathways and illustrate the importance of careful instrument selection in Mendelian randomization analysis, revealing a putative causal relationship between acetone and hypertension. Our publicly available results provide a foundational resource for the community to examine the role of metabolism across diverse diseases.

Effect of Acute and Chronic Ingestion of Exogenous Ketone Supplements on Blood Pressure: A Systematic Review and Meta-Analysis

Exogenous ketone supplements have been suggested to have potential cardiovascular benefits, but their overall effect on blood pressure is unclear. Our objective was to perform a systematic review and meta-analysis on the effects of exogenous ketone supplements on blood pressure (BP) and concomitant changes in resting heart rate (HR). Five databases were searched on January 27th, 2023, for randomized and non-randomized studies. A random-effects model meta-analysis was performed including all studies jointly and separately for acute and chronic ingestion of ketone supplements. Out of 4012 studies identified in the search, 4 acute and 6 chronic studies with n = 187 participants were included. Pooled results (n = 10) showed no change in systolic (SMD [95% CI]= -0.14 [-0.40; 0.11]; I2= 30%; p = 0.17) or diastolic BP (-0.12 [-0.30; 0.05]; I2= 0%; p = 0.69), with a potential tendency observed toward increased resting heart rate (0.17 [-0.14; 0.47]; I2= 40%; p = 0.10). Similar results for systolic and diastolic BP were observed when assessing separately the effect of acute and chronic ingestion of ketone supplements (p ≥ 0.33). Supplement dosage was found to modulate the increase in resting heart rate (0.019 ± 0.006; p = 0.013; R2=100%), suggesting that higher supplement doses lead to a higher resting heart rate. Based on currently available data, acute or prolonged ingestion of ketone supplements does not seem to modulate BP. However, a tendency for HR to increase after acute ingestion was observed, particularly with higher doses. Higher quality studies with appropriate standardized measurements are needed to confirm these results.

Calponin 2 regulates ketogenesis to mitigate acute kidney injury

Calponin 2 (CNN2) is a prominent actin stabilizer. It regulates fatty acid oxidation (FAO) by interacting with estrogen receptor 2 (ESR2) to determine kidney fibrosis. However, whether CNN2 is actively involved in acute kidney injury (AKI) remains unclear. Here, we report that CNN2 was induced in human and animal kidneys after AKI. Knockdown of CNN2 preserved kidney function, mitigated tubular cell death and inflammation, and promoted cell proliferation. Distinct from kidney fibrosis, proteomics showed that the key elements in the FAO pathway had few changes during AKI, but we identified that 3-hydroxymethylglutaryl-CoA synthase 2 (Hmgcs2), a rate-limiting enzyme of endogenous ketogenesis that promotes cell self-renewal, was markedly increased in CNN2-knockdown kidneys. The production of ketone body β-hydroxybutyrate and ATP was increased in CNN2-knockdown mice. Mechanistically, CNN2 interacted with ESR2 to negatively regulate the activities of mitochondrial sirtuin 5. Activated sirtuin 5 subsequently desuccinylated Hmgcs2 to produce energy for mitigating AKI. Understanding CNN2-mediated discrete fine-tuning of protein posttranslational modification is critical to optimize organ performance after AKI.

Compositional alterations of the gut microbiota in acute myocardial infarction patients with type 2 diabetes mellitus

Background

Type 2 diabetes mellitus (T2DM) is a risk factor for acute myocardial infarction (AMI) and a common comorbidity in patients with AMI. T2DM doubles the fatality rate of patients with AMI in the acute phase of AMI and the follow-up period. However, the mechanisms by which T2DM increases the fatality rate remain unknown. This study sought to investigate changes in the gut microbiota of patients with AMI and T2DM (AMIDM) to extend understandings of the relative mechanisms from the aspects of gut microbiota.

Methods

Patients were recruited and divided into 2 groups comprising 15 patients with AMIDM and 15 patients with AMI but without T2DM (AMINDM). Their stool samples and clinical information were collected. 16S ribosomal DNA sequencing was used to analyze the structure and composition of the gut microbiota based on the operational taxonomic units.

Results

A significant difference was observed in the gut microbiota β diversity between the 2 groups. At the phylum level, the AMIDM patients showed an increase in the abundance of Firmicutes and a decrease in the abundance of Bacteroidetes compared to the AMINDM patients. At the genus level, the AMIDM patients showed an increase in the abundance of Companilactobacillus, Defluvitaleaceae UCG-011 and UCG-009, and a decrease in the abundance of Phascolarctobacterium and CAG 56 compared to the AMINDM patients. At the species level, the AMIDM patients showed an increase in the abundance of species unclassified NK4A214 group, Bacteroides clarus, Coprococcus comes, unclassified Defluviltaleaceae UCG-011, uncultured rumen bacterium, unclassified CAG 56, Barnesiella intestinihominis, Lachnospiraceae bacterium, Bacteroides nordii, unclassified UCG-009, and the Family XIII AD3011 group compared to the AMINDM patients. The gut microbiota function predictions indicated that the nucleotide metabolism-related pathway was significantly more increase in the patients with AMIDM than those with AMINDM. Additionally, the patients with AMIDM showed an increase in gram-positive bacteria and a decrease in the proportion of gram-negative bacteria. Our correlation analysis results on the gut microbiota and clinical parameters might extend understandings of the progression of AMI.

Conclusions

Changes in the gut microbiota composition of patients with AMIDM affect the severity of the metabolic disturbance and may be responsible for poorer clinical outcomes and worse disease progression in patients with AMIDM compared to those with AMINDM.

Ketone Bodies and Cardiovascular Disease: An Alternate Fuel Source to the Rescue

The increased metabolic activity of the heart as a pump involves a high demand of mitochondrial adenosine triphosphate (ATP) production for its mechanical and electrical activities accomplished mainly via oxidative phosphorylation, supplying up to 95% of the necessary ATP production, with the rest attained by substrate-level phosphorylation in glycolysis. In the normal human heart, fatty acids provide the principal fuel (40-70%) for ATP generation, followed mainly by glucose (20-30%), and to a lesser degree (<5%) by other substrates (lactate, ketones, pyruvate and amino acids). Although ketones contribute 4-15% under normal situations, the rate of glucose use is drastically diminished in the hypertrophied and failing heart which switches to ketone bodies as an alternate fuel which are oxidized in lieu of glucose, and if adequately abundant, they reduce myocardial fat delivery and usage. Increasing cardiac ketone body oxidation appears beneficial in the context of heart failure (HF) and other pathological cardiovascular (CV) conditions. Also, an enhanced expression of genes crucial for ketone break down facilitates fat or ketone usage which averts or slows down HF, potentially by avoiding the use of glucose-derived carbon needed for anabolic processes. These issues of ketone body utilization in HF and other CV diseases are herein reviewed and pictorially illustrated.

Ketogenic Diet and Ketone Bodies against Ischemic Injury: Targets, Mechanisms, and Therapeutic Potential

The ketogenic diet (KD) has been used as a treatment for epilepsy since the 1920s, and its role in the prevention of many other diseases is now being considered. In recent years, there has been an intensive investigation on using the KD as a therapeutic approach to treat acute pathologies, including ischemic ones. However, contradictory data are observed for the effects of the KD on various organs after ischemic injury. In this review, we provide the first systematic analysis of studies conducted from 1980 to 2022 investigating the effects and main mechanisms of the KD and its mimetics on ischemia-reperfusion injury of the brain, heart, kidneys, liver, gut, and eyes. Our analysis demonstrated a high diversity of both the composition of the used KD and the protocols for the treatment of animals, which could be the reason for contradictory effects in different studies. It can be concluded that a true KD or its mimetics, such as β-hydroxybutyrate, can be considered as positive exposure, protecting the organ from ischemia and its negative consequences, whereas the shift to a rather similar high-calorie or high-fat diet leads to the opposite effect.