Futile lipid cycling: from biochemistry to physiology

An organism-level quantitative flux model of energy metabolism in mice

Mammalian tissues feed on nutrients in the blood circulation. At the organism level, mammalian energy metabolism is comprised of the oxidation, storage, interconversion, and release of circulating nutrients. Here, by integrating isotope tracer infusion, mass spectrometry, and isotope gas analyzer measurement, we developed a framework to systematically quantify fluxes through these metabolic processes for 10 major circulating energy nutrients in mice, resulting in an organism-level quantitative flux model of energy metabolism. This model revealed in wild-type mice that circulating nutrients have metabolic cycling fluxes dominant to their oxidation fluxes, with distinct partitions between cycling and oxidation for individual circulating nutrients. Applications of this framework in obese mouse models showed extensive elevation of metabolic cycling fluxes in ob/ob mice but not in diet-induced obese mice on a per-animal or per-lean mass basis. Our framework is a valuable tool to reveal new features of energy metabolism in physiological and disease conditions.

Nonlinear association between plasma elaidic acid level and sleep complaints in US adults: NHANES 2009-2010

Poor sleep is linked to an increased risk of metabolic, cardiovascular, psychiatric, and neurodegenerative diseases, highlighting its emergence as a public health concern. Previous studies demonstrated the harmful effects of trans fatty acids (TFAs) on human health. However, the association between TFAs and sleep outcomes is still not well-established. The current study aimed to investigate the relationship between plasma elaidic acid, a major TFA, and sleep complaints. The participants from the US National Health and Nutrition Examination Survey (NHANES) (2009-2010) were included. The plasma concentration of elaidic acid (18:1n-9t) was determined using the gas chromatography/mass spectrometry (GC/MS) method. The sleep outcome was defined based on the following questionnaire: "Ever told the doctor had trouble sleeping?" and "Ever told by a doctor have a sleep disorder?". Participants were classified as having sleep complaints if they ever told a doctor or been told by a doctor about trouble sleeping. The association between plasma elaidic acid and sleep complaints was investigated by multivariable logistic regressions, restricted cubic spline (RCS), and subgroup analysis. A total of 2068 participants were included, 561 of whom suffered from sleep complaints. The restricted cubic spline (RCS) regression analysis revealed a nonlinear (inverted L-shaped) relationship between plasma elaidic acid level and sleep complaints (p = 0.044), with an inflection point of 9.598 μmol/L. In the group with a low plasma elaidic acid level (≤9.598 μmol/L), there was a positive association between plasma elaidic acid level and the prevalence of sleep complaints (OR 1.28; 95% CI: 1.06-1.54, p = 0.01). When the plasma elaidic acid level was more than 9.598 μmol/L, the correlation was not statistically significant. Results were robust when analyses were stratified by sex, age, race, marital status, education level, family income, and BMI (all p for interaction >0.05). The results revealed a positive association between plasma elaidic acid and sleep complaints in US adults when plasma elaidic acid level ≤9.598 μmol. Given that the plasma TFA content has considerably declined in recent years, the detrimental impact of elaidic acid on sleep quality deserves more attention.

Integrative Metabolism in MASLD and MASH: Pathophysiology and Emerging Mechanisms

The liver acts as a central metabolic hub, integrating signals from the gastrointestinal tract and adipose tissue to regulate carbohydrate, lipid, and amino acid metabolism. Gut-derived metabolites, such as acetate and ethanol and non-esterified fatty acids from white adipose tissue (WAT), influence hepatic processes, which rely on mitochondrial function to maintain systemic energy balance. Metabolic dysregulation from obesity, insulin resistance, and type 2 diabetes disrupt these pathways, leading to metabolic dysfunction-associated steatotic liver disease (MASLD) and steatohepatitis (MASH). This review explores the metabolic fluxes within the gut-adipose tissue-liver axis, focusing on the pivotal role of de novo lipogenesis (DNL), dietary substrates like glucose and fructose, and changes in mitochondrial function during MASLD progression. It highlights the contributions of white adipose tissue insulin resistance and impaired mitochondrial dynamics to hepatic lipid accumulation. Further understanding how the interplay between substrate flux from the gastro-intestinal tract integrates with adipose tissue and intersects with structural and functional alterations to liver mitochondria will be important to identify novel therapeutic targets and advance the treatment of MASLD and MASH.

The endocannabinoid 2-arachidonoylglycerol is released and transported on demand via extracellular microvesicles

While it is known that endocannabinoids (eCB) modulate multiple neuronal functions, the molecular mechanism governing their release and transport remains elusive. Here, we propose an "on-demand release" model, wherein the formation of microvesicles, a specific group of extracellular vesicles (EVs) containing the eCB, 2-arachidonoylglycerol (2-AG), is an important step. A coculture model system that combines a reporter cell line expressing the fluorescent eCB sensor, G protein-coupled receptor-based (GRAB)eCB2.0, and neuronal cells revealed that neurons release EVs containing 2-AG, but not anandamide, in a stimulus-dependent process regulated by protein kinase C, Diacylglycerol lipase, Adenosinediphosphate (ADP) ribosylation factor 6 (Arf6), and which was sensitive to inhibitors of eCB facilitated diffusion. A vesicle contained approximately 2,000 2-AG molecules. Accordingly, hippocampal eCB-mediated synaptic plasticity was modulated by Arf6 and transport inhibitors. The "on-demand release" model, supported by mathematical analysis, offers a cohesive framework for understanding eCB trafficking at the molecular level and suggests that microvesicles carrying signaling lipids in their membrane regulate neuronal functions in parallel to canonical synaptic vesicles.

Anti-Tumor Strategies Targeting Nutritional Deprivation: Challenges and Opportunities

Higher and richer nutrient requirements are typical features that distinguish tumor cells from AU: cells, ensuring adequate substrates and energy sources for tumor cell proliferation and migration. Therefore, nutrient deprivation strategies based on targeted technologies can induce impaired cell viability in tumor cells, which are more sensitive than normal cells. In this review, nutrients that are required by tumor cells and related metabolic pathways are introduced, and anti-tumor strategies developed to target nutrient deprivation are described. In addition to tumor cells, the nutritional and metabolic characteristics of other cells in the tumor microenvironment (including macrophages, neutrophils, natural killer cells, T cells, and cancer-associated fibroblasts) and related new anti-tumor strategies are also summarized. In conclusion, recent advances in anti-tumor strategies targeting nutrient blockade are reviewed, and the challenges and prospects of these anti-tumor strategies are discussed, which are of theoretical significance for optimizing the clinical application of tumor nutrition deprivation strategies.

Precision medicine in diabetes care

PURPOSE OF REVIEW

This review highlights emerging evidence supporting the premise of precision diabetes care including but not limited to monogenic diabetes and discuss potential opportunities, challenges, and limitations for clinical adoption.

RECENT FINDINGS

Driven by a single gene mutation, monogenic diabetes remains the best use-case for precision diabetes care. However, the increasing prevalence of diabetes among adolescents and young adults in an obesogenic environment makes triaging potential patients for genetic screening clinically challenging. High-dimensional molecular biomarkers (i.e., multiomics) can improve the risk prediction for incident type 2 diabetes (T2D), over and above a well established prediction model based on clinical variables alone. Machine learning approaches using clinical variable-based clustering methods have generated novel and reproducible T2D subgroups with distinct phenotypic and omics characteristics that are associated with differential long-term outcomes. This stratification-strategy may inform clinical decisions. However, on-going discussion and research will be needed to understand the clinical utility of sub-phenotyping T2D for precision care.

SUMMARY

Precision diabetes care has extended from uncommon monogenic diabetes to T2D which will need more complex approaches like multiomics and machine-learning methods. The successful clinical translation will require cumulative evidence and close collaboration among the stake holders.

Nanocarriers Made of Natural Fatty Acids: Modulation of Their Release Profiles through Photo-Crosslinking

Natural fatty acids are attractive carrier materials for drug delivery, but their rapid dissolution and degradation in vivo calls for new strategies to enhance their stability. Here we report a simple and versatile method capable of photo-crosslinking carriers made of natural fatty acids for drug delivery under controlled release. By optimizing the crosslinking density, the nanoscale carriers show a high drug loading efficiency, together with a stable network structure for minimal degradation in a body fluid mimic. Fluorescence microscopy analysis also reveals the exceptional intracellular stability of the crosslinked network, resulting in negligible cytotoxicity toward A549 cells up to 24 h when loaded with a potent anticancer drug. We further extend this strategy to microscale carriers fabricated using electrospray. Upon photo-crosslinking, the carriers show a retarded release of nerve growth factor, resulting in slower neurite outgrowth from dorsal root ganglion. This work holds promise for addressing the efficacy and safety issues critical to nanomedicine and related applications.

Review: Feed efficiency and metabolic flexibility in livestock

Improving the conversion of feed into product has been a key focus of genetic improvement in all livestock species. Livestock feed efficiency is the amount of product produced per unit of feed intake. Feed efficiency also depends on processes that are not directly related to economically important phenotypes, which can be considered 'waste' from a production point of view but are vital maintenance-related functions that are closely associated with environmental flexibility and adaptation. Resource allocation theory suggests that an animal's resource budget is narrowed when production efficiency is improved through an increase in productive output, along with a decrease in feed intake (capacity) and body reserves (improved leanness). The resulting trade-offs between productivity and vital functions may render the animal less capable of responding to unexpected challenges, potentially leading to negative side effects that are not directly related to economically important phenotypes. However, selection for feed efficiency may not narrow the metabolic space and result in trade-offs if the increase in feed efficiency is the result of increased metabolic flexibility in fuel substrate choice (carbohydrates, lipids, and/or proteins) and other energy-saving strategies. This review evaluates the relationship between metabolic flexibility and feed efficiency during anabolism (growth), fasting, immune activation, general stress, and heat stress, with a focus on pig production. We start with a brief overview of energy processes and substrate metabolism of carbohydrates, lipids, and protein. During muscle metabolism, the type of fuel used depends on fibre type characteristics of the muscle. Selection for improved meat production has resulted in pigs with a greater abundance of fast-twitch fibres with lower energy expenditure and higher metabolic efficiency. Metabolic flexibility for adaptation to disease, and response to regular stress implies that a more reactive immune response and reduced fear response results in higher feed efficiency. The examples presented in this review show that selection for improved feed efficiency does not necessarily narrow the metabolic space and result in trade-offs between productivity and vital functions because of energy-sparing mechanisms.

Cancer cachexia: multilevel metabolic dysfunction

Cancer cachexia is a complex metabolic disorder marked by unintentional body weight loss or 'wasting' of body mass, driven by multiple aetiological factors operating at various levels. It is associated with many malignancies and significantly contributes to cancer-related morbidity and mortality. With emerging recognition of cancer as a systemic disease, there is increasing awareness that understanding and treatment of cancer cachexia may represent a crucial cornerstone for improved management of cancer. Here, we describe the metabolic changes contributing to body wasting in cachexia and explain how the entangled action of both tumour-derived and host-amplified processes induces these metabolic changes. We discuss energy homeostasis and possible ways that the presence of a tumour interferes with or hijacks physiological energy conservation pathways. In that context, we highlight the role played by metabolic cross-talk mechanisms in cachexia pathogenesis. Lastly, we elaborate on the challenges and opportunities in the treatment of this devastating paraneoplastic phenomenon that arise from the complex and multifaceted metabolic cross-talk mechanisms and provide a status on current and emerging therapeutic approaches.

Genotype-Dependent Variations in Oxidative Stress Markers and Bioactive Proteins in Hereford Bulls: Associations with DGAT1, LEP, and SCD1 Genes

The objective of this study is to assess the influence of genetic polymorphisms in DGAT1, LEP, and SCD1 on the oxidative stress biomarkers and bioactive protein levels in Hereford bulls. A total of sixty-eight bulls were analyzed at 22 months of age to assess growth metrics and carcass quality, with a focus on polymorphisms in these genes. The key markers of oxidative stress, including malondialdehyde (MDA), and the activities of antioxidant enzymes such as glutathione reductase (GluRed), glutathione peroxidase (GPx), and superoxide dismutase (SOD) were measured, alongside bioactive compounds like taurine, carnosine, and anserine. The results show that the TT genotype of DGAT1 is linked to significantly higher MDA levels, reflecting increased lipid peroxidation, but is also associated with higher GluRed and GPx activities and elevated levels of taurine, carnosine, and anserine, suggesting an adaptive response to oxidative stress. The LEP gene analysis revealed that the CC genotype had the highest MDA levels but also exhibited increased GPx and SOD activities, with the CT genotype showing the highest SOD activity and the TT genotype the highest total antioxidant status (TAS). The SCD1 AA genotype displayed the highest activities of GluRed, GPx, and SOD, indicating a more effective antioxidant defence, while the VA genotype had the highest MDA levels and the VV genotype showed lower MDA levels, suggesting protective effects against oxidative damage. These findings highlight genotype specific variations in the oxidative stress markers and bioactive compound levels, providing insights into the genetic regulation of oxidative stress and antioxidant defences, which could inform breeding strategies for improving oxidative stress resistance in livestock and managing related conditions.

Decreased mitochondrial-related gene expression in adipose tissue after acute sprint exercise in humans: A pilot study

The aim was to examine the acute effects of sprint exercise (SIT) on global gene expression in subcutaneous adipose tissue (AT) in healthy subjects, to enhance understanding of how SIT influences body weight regulation. The hypothesis was that SIT upregulates genes involved in mitochondrial function and fat metabolism. A total of 15 subjects performed three 30-s all-out sprints (SIT). Samples were collected from AT, skeletal muscle (SM) and blood (brachial artery and a subcutaneous AT vein) up to 15 min after the last sprint. Results showed that markers of oxidative stress, such as the purines hypoxanthine, xanthine and uric acid, increased markedly by SIT in both the artery and the AT vein. Purines also increased in AT and SM tissue. Differential gene expression analysis indicated a decrease in signaling for mitochondrial-related pathways, including oxidative phosphorylation, electron transport, ATP synthesis, and heat production by uncoupling proteins, as well as mitochondrial fatty acid beta oxidation. This downregulation of genes related to oxidative metabolism suggests an early-stage inhibition of the mitochondria, potentially as a protective mechanism against SIT-induced oxidative stress.

The metabolic benefits of thermogenic stimulation are preserved in aging

Adipose thermogenesis has been actively investigated as a therapeutic target for improving metabolic dysfunction in obesity. However, its applicability to middle-aged and older populations, which bear the highest obesity prevalence in the US (approximately 40%), remains uncertain due to age-related decline in thermogenic responses. In this study, we investigated the effects of chronic thermogenic stimulation using the β3-adrenergic (AR) agonist CL316,243 (CL) on systemic metabolism and adipose function in aged (18-month-old) C57BL/6JN mice. Sustained β3-AR treatment resulted in reduced fat mass, increased energy expenditure, increased fatty acid oxidation and mitochondrial activity in adipose depots, improved glucose homeostasis, and a favorable adipokine profile. At the cellular level, CL treatment increased uncoupling protein 1 (UCP1)-dependent thermogenesis in brown adipose tissue (BAT). However, in white adipose tissue (WAT) depots, CL treatment increased glycerol and lipid de novo lipogenesis (DNL) and turnover suggesting the activation of the futile substrate cycle of lipolysis and reesterification in a UCP1-independent manner. Increased lipid turnover was also associated with the simultaneous upregulation of proteins involved in glycerol metabolism, fatty acid oxidation, and reesterification in WAT. Further, a dose-dependent impact of CL treatment on inflammation was observed, particularly in subcutaneous WAT, suggesting a potential mismatch between fatty acid supply and oxidation. These findings indicate that chronic β3-AR stimulation activates distinct cellular mechanisms that increase energy expenditure in BAT and WAT to improve systemic metabolism in aged mice. Our study provides foundational evidence for targeting adipose thermogenesis to improve age-related metabolic dysfunction.

Futile cycles: Emerging utility from apparent futility

Futile cycles are biological phenomena where two opposing biochemical reactions run simultaneously, resulting in a net energy loss without appreciable productivity. Such a state was presumed to be a biological aberration and thus deemed an energy-wasting "futile" cycle. However, multiple pieces of evidence suggest that biological utilities emerge from futile cycles. A few established functions of futile cycles are to control metabolic sensitivity, modulate energy homeostasis, and drive adaptive thermogenesis. Yet, the physiological regulation, implication, and pathological relevance of most futile cycles remain poorly studied. In this review, we highlight the abundance and versatility of futile cycles and propose a classification scheme. We further discuss the energetic implications of various futile cycles and their impact on basal metabolic rate, their bona fide and tentative pathophysiological implications, and putative drug interactions.