Novel diagnostics of metabolic dysfunction detected in breath and plasma by selective isotope-assisted labeling

Advances of stable isotope technology in food safety analysis and nutrient metabolism research

Food quality, safety, and the regulatory metabolism of food nutrients in cells are primary factors in determining human health. However, residues of undesirable or hazardous compounds in food products and dysregulation in the nutrient metabolism inevitably occur occasionally. For years, chromatography-mass spectrometry technology has been recognized as an essential research tool in food analysis and nutrient metabolism research, and it is more accurate and robust when coupled with stable isotopes. In this study, we summarize the applications of stable isotope technology in the quantification of contaminant residues (pesticides, veterinary drugs, mycotoxins, polycyclic aromatic hydrocarbons, and other hazardous compounds) in foods and in the nutrients (glucose, lipids, amino acids and proteins) metabolism research. The aim of this review was to serve as a reference for providing effective analysis techniques for protecting food quality and human health, and to pave the way for the broader application of stable isotope technology.

Metabolite interactions between host and microbiota during health and disease: Which feeds the other?

Metabolites produced by the host and microbiota play a crucial role in how human bodies develop and remain healthy. Most of these metabolites are produced by microbiota and hosts in the digestive tract. Metabolites in the gut have important roles in energy metabolism, cellular communication, and host immunity, among other physiological activities. Although numerous host metabolites, such as free fatty acids, amino acids, and vitamins, are found in the intestine, metabolites generated by gut microbiota are equally vital for intestinal homeostasis. Furthermore, microbiota in the gut is the sole source of some metabolites, including short-chain fatty acids (SCFAs). Metabolites produced by microbiota, such as neurotransmitters and hormones, may modulate and significantly affect host metabolism. The gut microbiota is becoming recognized as a second endocrine system. A variety of chronic inflammatory disorders have been linked to aberrant host-microbiota interplays, but the precise mechanisms underpinning these disturbances and how they might lead to diseases remain to be fully elucidated. Microbiome-modulated metabolites are promising targets for new drug discovery due to their endocrine function in various complex disorders. In humans, metabolotherapy for the prevention or treatment of various disorders will be possible if we better understand the metabolic preferences of bacteria and the host in specific tissues and organs. Better disease treatments may be possible with the help of novel complementary therapies that target host or bacterial metabolism. The metabolites, their physiological consequences, and functional mechanisms of the host-microbiota interplays will be highlighted, summarized, and discussed in this overview.

Nitrogen recycling via gut symbionts increases in ground squirrels over the hibernation season

Hibernation is a mammalian strategy that uses metabolic plasticity to reduce energy demands and enable long-term fasting. Fasting mitigates winter food scarcity but eliminates dietary nitrogen, jeopardizing body protein balance. Here, we reveal gut microbiome-mediated urea nitrogen recycling in hibernating thirteen-lined ground squirrels (Ictidomys tridecemlineatus). Ureolytic gut microbes incorporate urea nitrogen into metabolites that are absorbed by the host, with the nitrogen reincorporated into the squirrel's protein pool. Urea nitrogen recycling is greatest after prolonged fasting in late winter, when urea transporter abundance in gut tissue and urease gene abundance in the microbiome are highest. These results reveal a functional role for the gut microbiome during hibernation and suggest mechanisms by which urea nitrogen recycling may contribute to protein balance in other monogastric animals.

Shifts in metabolic fuel use coincide with maximal rates of ventilation and body surface rewarming in an arousing hibernator

It is well established that hibernating mammals rely predominantly on lipid stores to fuel metabolism throughout the hibernation season. However, it is unclear if other endogenous fuels contribute to the rapid, ~400-fold increase in metabolic rate during the early phase of arousal from torpor. To investigate this issue, we used cavity ring-down spectroscopy, a technique that provides a real-time indication of fuel use by measuring the ratio of ¹³C to ¹²C in the exhaled CO₂ of arousing 13-lined ground squirrels (Ictidomys tridecemlineatus). We used infrared thermography to simultaneously measure ventilation and surface temperature change in various body regions, and we interpreted these data in light of changing plasma metabolite abundances at multiple stages of arousal from torpor. We found that hibernating squirrels use a combination of lipids and, likely, carbohydrates to fuel the initial ~60 min of arousal before switching to predominantly lipid oxidation. This fuel switch coincided with times of maximal rates of ventilation and rewarming of different body surface regions, including brown adipose tissue. Infrared thermography revealed zonal rewarming, whereby the brown adipose tissue region was the first to warm, followed by the thoracic and head regions and, finally, the posterior half of the body. Consistent with the results from cavity ring-down spectroscopy, plasma metabolite dynamics during early arousal suggested a large reliance on fatty acids, with a contribution from carbohydrates and glycerol. Because of their high oxidative flux rates and efficient O₂ use, carbohydrates might be an advantageous metabolic fuel during the early phase of arousal, when metabolic demands are high but ventilation rates and, thus, O₂ supply are relatively low.

Effects of Repeated Sublethal External Exposure to Deep Water Horizon Oil on the Avian Metabolome

We assessed adverse effects of external sublethal exposure of Deepwater Horizon, Mississippi Canyon 252 oil on plasma and liver metabolome profiles of the double-crested cormorant (Phalacrocorax auritus), a large (1.5 to 3.0 kg) diving waterbird common in the Gulf of Mexico. Metabolomics analysis of avian plasma showed significant negative effects on avian metabolic profiles, in some cases after only two external exposures (26 g cumulative) to oil. We observed significant (p < 0.05) changes in intermediate metabolites of energy metabolism and fatty acid and amino acid metabolic pathways in cormorants after repeated exposure to oil. Exposure to oil increased several metabolites (glycine, betaine, serine and methionine) that are essential to the one-carbon metabolism pathway. Lipid metabolism was affected, causing an increase in production of ketone bodies, suggesting lipids were used as an alternative energy source for energy production in oil exposed birds. In addition, metabolites associated with hepatic bile acid metabolism were affected by oil exposure which was correlated with changes observed in bile acids in exposed birds. These changes at the most basic level of phenotypic expression caused by sublethal exposure to oil can have effects that would be detrimental to reproduction, migration, and survival in avian species.

Metabolic Reprogramming by 3-Iodothyronamine (T1AM): A New Perspective to Reverse Obesity through Co-Regulation of Sirtuin 4 and 6 Expression

Obesity is a complex disease associated with environmental and genetic factors. 3-Iodothyronamine (T1AM) has revealed great potential as an effective weight loss drug. We used metabolomics and associated transcriptional gene and protein expression analysis to investigate the tissue specific metabolic reprogramming effects of subchronic T1AM treatment at two pharmacological daily doses (10 and 25 mg/kg) on targeted metabolic pathways. Multi-analytical results indicated that T1AM at 25 mg/kg can act as a novel master regulator of both glucose and lipid metabolism in mice through sirtuin-mediated pathways. In liver, we observed an increased gene and protein expression of Sirt6 (a master gene regulator of glucose) and Gck (glucose kinase) and a decreased expression of Sirt4 (a negative regulator of fatty acids oxidation (FAO)), whereas in white adipose tissue only Sirt6 was increased. Metabolomics analysis supported physiological changes at both doses with most increases in FAO, glycolysis indicators and the mitochondrial substrate, at the highest dose of T1AM. Together our results suggest that T1AM acts through sirtuin-mediated pathways to metabolically reprogram fatty acid and glucose metabolism possibly through small molecules signaling. Our novel mechanistic findings indicate that T1AM has a great potential as a drug for the treatment of obesity and possibly diabetes.

Uptake of 3-iodothyronamine hormone analogs inhibits the growth and viability of cancer cells

3-Iodothyronamine (T1AM) is a structural analog of thyroid hormone that has been demonstrated to have potent affects on numerous physiological systems. Most studies on T1AM have explored its effects in healthy functional systems; while its potential therapeutic uses and safety, and efficacy in pathological conditions are largely unknown. We sought to evaluate the effects of T1AM and its structural analog SG-2 on cancer cell growth and viability. We analyzed the cytotoxicity of these analogs on MCF7 breast cancer cells, HepG2 hepatocellular cancer cells as well as normal control cells using primary human foreskin fibroblasts and mouse preadipocytes control cells. The cytotoxicity of T1AM and SG-2 was determined by cell growth curves, and validated by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide cell viability assays. Cellular uptake analysis was conducted using confocal microscopy. Real-time (RT)-PCR was conducted to identify gene pathways affected by SG-2 in cancer cells. The IC ₅₀ of T1AM was approximately double the concentration of its analog SG-2 in cancer cells. Cytotoxicity studies on normal cells revealed that IC ₅₀ concentrations of SG-2 in cancer cells had no significant impact on cell viability in these cell types. Cell-imaging experiments demonstrated rapid uptake and localization to the mitochondrial membrane. T1AM and SG-2 are able to reduce cancer cell growth and viability. These findings support the potential for use of these compounds and related analogs for their antiproliferation properties in cancer cells.

Metabolic profiling reveals reprogramming of lipid metabolic pathways in treatment of polycystic ovary syndrome with 3-iodothyronamine

Complex diseases such as polycystic ovary syndrome (PCOS) are associated with intricate pathophysiological, hormonal, and metabolic feedbacks that make their early diagnosis challenging, thus increasing the prevalence risks for obesity, cardiovascular, and fatty liver diseases. To explore the crosstalk between endocrine and lipid metabolic pathways, we administered 3-iodothyronamine (T1AM), a natural analog of thyroid hormone, in a mouse model of PCOS and analyzed plasma and tissue extracts using multidisciplinary omics and biochemical approaches. T1AM administration induces a profound tissue-specific antilipogenic effect in liver and muscle by lowering gene expression of key regulators of lipid metabolism, PTP1B and PLIN2, significantly increasing metabolites (glucogenic, amino acids, carnitine, and citrate) levels, while enhancing protection against oxidative stress. In contrast, T1AM has an opposing effect on the regulation of estrogenic pathways in the ovary by upregulating STAR, CYP11A1, and CYP17A1. Biochemical measurements provide further evidence of significant reduction in liver cholesterol and triglycerides in post-T1AM treatment. Our results shed light onto tissue-specific metabolic vs. hormonal pathway interactions, thus illuminating the intricacies within the pathophysiology of PCOS This study opens up new avenues to design drugs for targeted therapeutics to improve quality of life in complex metabolic diseases.

NMR Metabolomics Show Evidence for Mitochondrial Oxidative Stress in a Mouse Model of Polycystic Ovary Syndrome

Polycystic ovary syndrome (PCOS) is associated with metabolic and endocrine disorders in women of reproductive age. The etiology of PCOS is still unknown. Mice prenatally treated with glucocorticoids exhibit metabolic disturbances that are similar to those seen in women with PCOS. We used an untargeted nuclear magnetic resonance (NMR)-based metabolomics approach to understand the metabolic changes occurring in the plasma and kidney over time in female glucocorticoid-treated (GC-treated) mice. There are significant changes in plasma amino acid levels (valine, tyrosine, and proline) and their intermediates (2-hydroxybutyrate, 4-aminobutyrate, and taurine), whereas in kidneys, the TCA cycle metabolism (citrate, fumarate, and succinate) and the pentose phosphate (PP) pathway products (inosine and uracil) are significantly altered (p < 0.05) from 8 to 16 weeks of age. Levels of NADH, NAD(+), NAD(+)/NADH, and NADH redox in kidneys indicate increased mitochondrial oxidative stress from 8 to 16 weeks in GC-treated mice. These results indicate that altered metabolic substrates in the plasma and kidneys of treated mice are associated with altered amino acid metabolism, increased cytoplasmic PP, and increased mitochondrial activity, leading to a more oxidized state. This study identifies biomarkers associated with metabolic dysfunction in kidney mitochondria of a prenatal gluococorticoid-treated mouse model of PCOS that may be used as early predictive biomarkers of oxidative stress in the PCOS metabolic disorder in women.

Metabolomics for Biomarker Discovery: Moving to the Clinic

To improve the clinical course of diseases, more accurate diagnostic and assessment methods are required as early as possible. In order to achieve this, metabolomics offers new opportunities for biomarker discovery in complex diseases and may provide pathological understanding of diseases beyond traditional technologies. It is the systematic analysis of low-molecular-weight metabolites in biological samples and has become an important tool in clinical research and the diagnosis of human disease and has been applied to discovery and identification of the perturbed pathways. It provides a powerful approach to discover biomarkers in biological systems and offers a holistic approach with the promise to clinically enhance diagnostics. When carried out properly, it could provide insight into the understanding of the underlying mechanisms of diseases, help to identify patients at risk of disease, and predict the response to specific treatments. Currently, metabolomics has become an important tool in clinical research and the diagnosis of human disease and becomes a hot topic. This review will highlight the importance and benefit of metabolomics for identifying biomarkers that accurately screen potential biomarkers of diseases.

NMR-based metabolomics and breath studies show lipid and protein catabolism during low dose chronic T(1)AM treatment

OBJECTIVE

3-Iodothyronamine (T1 AM), an analog of thyroid hormone, is a recently discovered fast-acting endogenous metabolite. Single high-dose treatments of T1 AM have produced rapid short-term effects, including a reduction of body temperature, bradycardia, and hyperglycemia in mice.

DESIGN AND METHODS

The effect of daily low doses of T1 AM (10 mg/kg) for 8 days on weight loss and metabolism in spontaneously overweight mice was monitored. The experiments were repeated twice (n = 4). Nuclear magnetic resonance (NMR) spectroscopy of plasma and real-time analysis of exhaled (13) CO2 in breath by cavity ring down spectroscopy (CRDS) were used to detect T1 AM-induced lipolysis.

RESULTS

CRDS detected increased lipolysis in breath shortly after T1 AM administration that was associated with a significant weight loss but independent of food consumption. NMR spectroscopy revealed alterations in key metabolites in serum: valine, glycine, and 3-hydroxybutyrate, suggesting that the subchronic effects of T1 AM include both lipolysis and protein breakdown. After discontinuation of T1 AM treatment, mice regained only 1.8% of the lost weight in the following 2 weeks, indicating lasting effects of T1 AM on weight maintenance.

CONCLUSIONS

CRDS in combination with NMR and (13) C-metabolic tracing constitute a powerful method of investigation in obesity studies for identifying in vivo biochemical pathway shifts and unanticipated debilitating side effects.

Looking back into the future: 30 years of metabolomics at TNO

Metabolites have played an essential role in our understanding of life, health, and disease for thousands of years. This domain became much more important after the concept of metabolism was discovered. In the 1950s, mass spectrometry was coupled to chromatography and made the technique more application-oriented and allowed the development of new profiling technologies. Since 1980, TNO has performed system-based metabolic profiling of body fluids, and combined with pattern recognition has led to many discoveries and contributed to the field known as metabolomics and systems biology. This review describes the development of related concepts and applications at TNO in the biomedical, pharmaceutical, nutritional, and microbiological fields, and provides an outlook for the future.