Dietary medium-chain fatty acids reduce hepatic fat accumulation via activation of a CREBH-FGF21 axis.

OBJECTIVE: Dietary medium-chain fatty acids (MCFAs), characterized by chain lengths of 8-12 carbon atoms, have been proposed to have beneficial effects on glucose and lipid metabolism, yet the underlying mechanisms remain elusive. We hypothesized that MCFA intake benefits metabolic health by inducing the release of hormone-like factors. METHODS: The effects of chow diet, high-fat diet rich in long-chain fatty acids (LCFA HFD) fed ad libitum or pair-fed to a high-fat diet rich in MCFA (MCFA HFD) on glycemia, hepatic gene expression, circulating fibroblast growth factor 21 (FGF21), and liver fat content in both wildtype and Fgf21 knockout mice were investigated. The impact of a single oral dose of an MCFA-rich oil on circulating FGF21 and hepatic Fgf21 mRNA expression was assessed. In flag-tagged Crebh knockin mice and liver-specific Crebh knockout mice, fed LCFA HFD or MCFA HFD, active hepatic CREBH and hepatic Fgf21 mRNA abundance were determined, respectively. RESULTS: MCFA HFD improves glucose tolerance, enhances glucose clearance into brown adipose tissue, and prevents high-fat diet-induced hepatic steatosis in wildtype mice. These benefits are associated with increased liver expression of CREBH target genes (Apoa4 and Apoc2), including Fgf21. Both acute and chronic intake of dietary MCFAs elevate circulating FGF21. Augmented hepatic Fgf21 mRNA following MCFA HFD intake is accompanied by higher levels of active hepatic CREBH; and MCFA-induced hepatic Fgf21 expression is blocked in mice lacking Crebh. Notably, while feeding male and female Fgf21 wildtype mice MCFA HFD results in reduced liver triacylglycerol (TG) levels, this liver TG-lowering effect is blunted in Fgf21 knockout mice fed MCFA HFD. The reduction in liver TG levels observed with MCFA HFD was independent of weight loss. CONCLUSIONS: Dietary MCFAs reduce liver fat accumulation via activation of a CREBH-FGF21 signaling axis.

Increased hepatic putrescine levels as a new potential factor related to the progression of metabolic dysfunction-associated steatotic liver disease.

Metabolic dysfunction-associated steatotic liver disease (MASLD) is a chronic liver condition that often progresses to more advanced stages, such as metabolic dysfunction-associated steatohepatitis (MASH). MASH is characterized by inflammation and hepatocellular ballooning, in addition to hepatic steatosis. Despite the relatively high incidence of MASH in the population and its potential detrimental effects on human health, this liver disease is still not fully understood from a pathophysiological perspective. Deregulation of polyamine levels has been detected in various pathological conditions, including neurodegenerative diseases, inflammation, and cancer. However, the role of the polyamine pathway in chronic liver disorders such as MASLD has not been explored. In this study, we measured the expression of liver ornithine decarboxylase (ODC1), the rate-limiting enzyme responsible for the production of putrescine, and the hepatic levels of putrescine, in a preclinical model of MASH as well as in liver biopsies of patients with obesity undergoing bariatric surgery. Our findings reveal that expression of ODC1 and the levels of putrescine, but not spermidine nor spermine, are elevated in hepatic tissue of both diet-induced MASH mice and patients with biopsy-proven MASH compared with control mice and patients without MASH, respectively. Furthermore, we found that the levels of putrescine were positively associated with higher aspartate aminotransferase concentrations in serum and an increased SAF score (steatosis, activity, fibrosis). Additionally, in in vitro assays using human HepG2 cells, we demonstrate that elevated levels of putrescine exacerbate the cellular response to palmitic acid, leading to decreased cell viability and increased release of CK-18. Our results support an association between the expression of ODC1 and the progression of MASLD, which could have translational relevance in understanding the onset of this disease. © 2024 The Pathological Society of Great Britain and Ireland.

IVF exposure induced intergenerational effects on metabolic phenotype in mice.

RESEARCH QUESTION: What is the potential transmission of metabolic phenotype from IVF offspring to the subsequent generation? DESIGN: An IVF mouse model was established. The F1 generation mice were produced though IVF or natural mating and the F2 generation was obtained through the mating of F1 generation males with normal females. Their metabolic phenotype, including systemic and hepatic glucolipid metabolism, was examined. RESULTS: It was found that IVF F1 males exhibited metabolic changes. Compared with the control group, the IVF F1 generation showed increased body weight, elevated fasting glucose and insulin, and increased serum triglyceride concentrations. IVF F1 mice also showed an increased expression of hepatic lipogenesis and autophagy genes. Moreover, IVF F1 males transmitted some metabolic changes to their own male progeny (IVF F2) in the absence of a dietary challenge. IVF F2 mice had increased peri-epididymal and subcutaneous fat and decreased insulin sensitivity. Under the 'second hit' of a high-fat diet, IVF F2 mice further showed increased hepatic lipid deposition with unaltered autophagy levels. CONCLUSION: This research demonstrates the impact of IVF on hepatic glucose-lipid metabolism in two successive generations of offspring, highlighting the need for additional investigation. Enhanced understanding of the mechanisms underlying the transmission of multigenerational effects induced by IVF could potentially lead to the advancement of therapeutic interventions for individuals experiencing infertility.

Altered liver metabolism post-wean abolishes efficacy of vitamin D for breast cancer prevention in a mouse model.

Young women have increased risk of vitamin D deficiency, which may increase breast cancer incidence. Here, we assessed the anti-cancer efficacy of vitamin D in mouse models of young-onset breast cancer. In never-pregnant mice, vitamin D supplementation increased serum 25(OH)D and hepatic 1,25(OH)2D3, reduced tumor size, and associated with anti-tumor immunity. These anti-tumor effects were not replicated in a mouse model of postpartum breast cancer, where hepatic metabolism of vitamin D was suppressed post-wean, which resulted in deficient serum 25(OH)D and reduced hepatic 1,25(OH)2D3. Treatment with active 1,25(OH)2D3 induced hypercalcemia exclusively in post-wean mice, highlighting metabolic imbalance post-wean. RNAseq revealed suppressed CYP450 expression postpartum. In sum, we provide evidence that vitamin D anti-tumor activity is mediated through immunomodulatory mechanisms and is ineffective in the post-wean window due to altered hepatic metabolism. These findings have implications for suppressed xenobiotic metabolism in postpartum women beyond vitamin D.

Valine administration in the hypothalamus alters the brain and plasma metabolome in rainbow trout.

Central administration of valine has been shown to cause hyperphagia in fish. Although mechanistic target of rapamycin (mTOR) is involved in this response, the contributions on feed intake of central and peripheral metabolite changes due to excess valine are unknown. Here we investigated whether intracerebroventricular (ICV) injection of valine modulates central and peripheral metabolite profiles and may provide insights into feeding response in fish. Juvenile rainbow trout (Oncorhynchus mykiss) were administered an ICV injection of valine (10 µg · µL-1 at 1 µL·100 g-1 body weight) and the metabolite profile in plasma, hypothalamus, and rest of the brain (comprising of telencephalon, optic tectum, cerebellum, and medulla oblongata) was carried out by liquid chromatography-mass spectrometry (LC/MS)-based metabolomics. Valine administration led to a spatially distinct metabolite profile at 1 h post-injection in the brain: enrichment of amino acid metabolism and energy production pathways in the rest of the brain but not in hypothalamus. This suggests a role for extrahypothalamic input in the regulation of feed intake. Also, there was enrichment of several amino acids, including tyrosine, proline, valine, phenylalanine, and methionine, in plasma in response to valine. Changes in liver transcript abundance and protein expression reflect an increased metabolic capacity, including energy production from glucose and fatty acids, and a lower protein kinase B (Akt) phosphorylation in the valine group. Altogether, valine ICV administration affects central and peripheral metabolism in rainbow trout, and we propose a role for the altered metabolite profile in modulating the feeding response to this branched-chain amino acid.

Hyperpolarized [2-13C, 3-2H3]Pyruvate Detects Hepatic Gluconeogenesis In Vivo.

The feasibility of hyperpolarized [2-13C, 3-2H3]pyruvate for probing gluconeogenesis in vivo was investigated in this study. Whereas hyperpolarized [1-13C]pyruvate has clear access to metabolic pathways that convert pyruvate to lactate, alanine, and bicarbonate, its utility for assessing pyruvate carboxylation and gluconeogenesis has been limited by technical challenges, including spectral overlap and an obscure enzymatic step that decarboxylates the labeled carbon. To achieve unambiguous detection of gluconeogenic products, the carbonyl carbon in pyruvate was labeled with 13C. To prolong the T1 relaxation time, [2-13C, 3-2H3]pyruvate was synthesized and dissolved with D2O after dynamic nuclear polarization. The T1 of [2-13C, 3-2H3]pyruvate in D2O could be improved by 76.9% (79.6 s at 1 T and 74.5 s at 3 T) as compared to [2-13C]pyruvate in water. Hyperpolarized [2-13C, 3-2H3]pyruvate with D2O dissolution was applied to rat livers in vivo under normal feeding and fasting conditions. A gluconeogenic product, [2-13C]phosphoenolpyruvate, was observed at 149.9 ppm from fasted rats only, highlighting the utility of [2-13C, 3-2H3]pyruvate in detecting key gluconeogenic enzyme activities such as pyruvate carboxylase and phosphoenolpyruvate carboxykinase in vivo.

Low-Iron Diet-Induced Fatty Liver Development Is Microbiota Dependent and Exacerbated by Loss of the Mitochondrial Iron Importer Mitoferrin2.

Iron deficiency is the number one nutritional problem worldwide. Iron uptake is regulated at the intestine and is highly influenced by the gut microbiome. Blood from the intestines drains directly into the liver, informing iron status and gut microbiota status. Changes in either iron or the microbiome are tightly correlated with the development of metabolic dysfunction-associated steatotic liver disease (MASLD). To investigate the underlying mechanisms of the development of MASLD that connect altered iron metabolism and gut microbiota, we compared specific pathogen free (SPF) or germ-free (GF) mice, fed a normal or low-iron diet. SPF mice on a low-iron diet showed reduced serum triglycerides and MASLD. In contrast, GF low-iron diet-fed mice showed increased serum triglycerides and did not develop hepatic steatosis. SPF mice showed significant changes in liver lipid metabolism and increased insulin resistance that was dependent upon the presence of the gut microbiota. We report that total body loss of mitochondrial iron importer Mitoferrin2 (Mfrn2-/-) exacerbated the development of MASLD on a low-iron diet with significant lipid metabolism alterations. Our study demonstrates a clear contribution of the gut microbiome, dietary iron, and Mfrn2 in the development of MASLD and metabolic syndrome.

A Short Review on Obeticholic Acid: An Effective Modulator of Farnesoid X Receptor.

Farnesoid X receptor (FXR) was identified as an orphan nuclear receptor resembling the steroid receptor in the late '90s. Activation of FXR is a crucial step in many physiological functions of the liver. A vital role of FXR is impacting the amount of bile acids in the hepatocytes, which it performs by reducing bile acid synthesis, stimulating the bile salt export pump, and inhibiting its enterohepatic circulation, thus protecting the hepatocytes against the toxic accumulation of bile acids. Furthermore, FXR mediates bile acid biotransformation in the intestine, liver regeneration, glucose hemostasis, and lipid metabolism. In this review, we first discuss the mechanisms of the disparate pleiotropic actions of FXR agonists. We then delve into the pharmacokinetics of Obeticholic acid (OCA), the first-in-class selective, potent FXR agonist. We additionally discuss the clinical journey of OCA in humans, its current evidence in various human diseases, and its plausible roles in the future.

Biochemical and functional characterization of the p.A165T missense variant of mitochondrial amidoxime-reducing component 1.

Recent genome-wide association studies have identified a missense variant p.A165T in mitochondrial amidoxime-reducing component 1 (mARC1) that is strongly associated with protection from all-cause cirrhosis and improved prognosis in nonalcoholic steatohepatitis. The precise mechanism of this protective effect is unknown. Substitution of alanine 165 with threonine is predicted to affect mARC1 protein stability and to have deleterious effects on its function. To investigate the mechanism, we have generated a knock-in mutant mARC1 A165T and a catalytically dead mutant C273A (as a control) in human hepatoma HepG2 cells, enabling characterization of protein subcellular distribution, stability, and biochemical functions of the mARC1 mutant protein expressed from its endogenous locus. Compared to WT mARC1, we found that the A165T mutant exhibits significant mislocalization outside of its traditional location anchored in the mitochondrial outer membrane and reduces protein stability, resulting in lower basal levels. We evaluated the involvement of the ubiquitin proteasome system in mARC1 A165T degradation and observed increased ubiquitination and faster degradation of the A165T variant. In addition, we have shown that HepG2 cells carrying the MTARC1 p.A165T variant exhibit lower N-reductive activity on exogenously added amidoxime substrates in vitro. The data from these biochemical and functional assays suggest a mechanism by which the MTARC1 p.A165T variant abrogates enzyme function which may contribute to its protective effect in liver disease.

Early life interventions metformin and trodusquemine metabolically reprogram the developing mouse liver through transcriptomic alterations.

Recent studies have demonstrated the remarkable potential of early life intervention strategies at influencing the course of postnatal development, thereby offering exciting possibilities for enhancing longevity and improving overall health. Metformin (MF), an FDA-approved medication for type II diabetes mellitus, has recently gained attention for its promising anti-aging properties, acting as a calorie restriction mimetic, and delaying precocious puberty. Additionally, trodusquemine (MSI-1436), an investigational drug, has been shown to combat obesity and metabolic disorders by inhibiting the enzyme protein tyrosine phosphatase 1b (Ptp1b), consequently reducing hepatic lipogenesis and counteracting insulin and leptin resistance. In this study, we aimed to further explore the effects of these compounds on young, developing mice to uncover biomolecular signatures that are central to liver metabolic processes. We found that MSI-1436 more potently alters mRNA and miRNA expression in the liver compared with MF, with bioinformatic analysis suggesting that cohorts of differentially expressed miRNAs inhibit the action of phosphoinositide 3-kinase (Pi3k), protein kinase B (Akt), and mammalian target of rapamycin (Mtor) to regulate the downstream processes of de novo lipogenesis, fatty acid oxidation, very-low-density lipoprotein transport, and cholesterol biosynthesis and efflux. In summary, our study demonstrates that administering these compounds during the postnatal window metabolically reprograms the liver through induction of potent epigenetic changes in the transcriptome, potentially forestalling the onset of age-related diseases and enhancing longevity. Future studies are necessary to determine the impacts on lifespan and overall quality of life.

FicD regulates adaptation to the unfolded protein response in the murine liver.

The unfolded protein response (UPR) is a cellular stress response that is activated when misfolded proteins accumulate in the endoplasmic reticulum (ER). Regulation of the UPR response must be adapted to the needs of the cell as prolonged UPR responses can result in disrupted cellular function and tissue damage. Previously, we discovered that the enzyme FicD (also known as Fic or HYPE) through its AMPylation and deAMPylation activity can modulate the UPR response via post-translational modification of BiP. FicD AMPylates BiP during homeostasis and deAMPylates BiP during stress. We hypothesized that FicD regulation of the UPR will play a role in mitigating the deleterious effects of UPR activation in tissues with frequent physiological stress. Here, we explore the role of FicD in the murine liver. As seen in our pancreatic studies, livers lacking FicD exhibit enhanced UPR signaling in response to short term physiologic fasting and feeding stress. However, in contrast to studies on the pancreas, livers, as a more regenerative tissue, remained remarkably resilient in the absence of FicD. The livers of FicD-/- did not show marked changes in UPR signaling or damage after either chronic high fat diet (HFD) feeding or acute pathological UPR induction. Intriguingly, FicD-/- mice showed changes in UPR induction and weight loss patterns following repeated pathological UPR induction. These findings indicate that FicD regulates UPR responses during mild physiological stress and in adaptation to repeated stresses, but there are tissue specific differences in the requirement for FicD regulation.

Hepatogenous Diabetes as Compared to Type-2 Diabetes Mellitus and Non-diabetes in Patients With Liver Cirrhosis: Magnitude, Characteristics, and Implications.

Aim: Hepatogenous diabetes (HD) is frequently underestimated among cirrhosis patients. The current study assessed the magnitude, clinical characteristics, and implications of HD in cirrhosis patients as compared to the patients with type-2 diabetes mellitus (T2DM) and non-diabetes (ND) cirrhosis. Methods: In a prospective observational study, 338 consecutive eligible cirrhosis patients were screened for diabetes mellitus. A 2-hour oral glucose tolerance test (OGTT) was used to detect HD. The clinical characteristics, complications, and outcomes were ascertained and compared amongst HD, T2DM, and ND patients. Results: In the final study cohort of 316 patients, the proportion of HD, T2DM, and ND was 22.5% (n = 71), 26.3% (n = 83), and 51.3% (n = 162), respectively. HD was the predominant form of diabetes (68.9%) in Child-Pugh class-C cirrhosis. The majority (73%) of HD patients had abnormal OGTT without fasting hyperglycaemia. A lower cut-off of 98.5 mg/dl for fasting blood glucose had a modest sensitivity (72%) and specificity (75%) for predicting HD. In comparison to T2DM patients, HD patients were younger, leaner, and had more advanced cirrhosis. In comparison to ND patients, HD patients were leaner but had higher glycemic indices, serum cholesterol, and arterial ammonia levels. During a median follow-up period of 12 (03-21) months, the frequency of hepatic encephalopathy and variceal haemorrhage were higher in HD and T2DM patients compared to that in the ND group. Conclusions: HD is prevalent in about one fifth of cirrhosis patients. It differs from T2DM and ND in a number of ways, and has association with complications of cirrhosis.

Metabolism of 11'-α- and 11'-γ-Tocomonoenols in HepG2 Cells Favors the γ-Congener and Results Predominantly in Carboxymethylbutyl-Hydroxychromans.

SCOPE: Tocomonoenols (T1) are little-known vitamin E derivatives naturally occurring in foods. Limited knowledge exists regarding the cellular uptake and metabolism of α-tocomonoenol (αT1) and none about that of γ-tocomonoenol (γT1). METHODS AND RESULTS: The study investigates the cytotoxicity, uptake, and metabolism of αT1 and γT1 in HepG2 cells compared to the α- and γ-tocopherols (T) and -tocotrienols (T3). None of the studied tocochromanols are cytotoxic up to 100 µmol L-1. The uptake of the γ-congeners is significantly higher than that of the corresponding α-forms, whereas no significant differences are observed based on the degree of saturation of the sidechain. Carboxymethylbutyl-hydroxychromans (CMBHC) are the predominant short-chain metabolites of all tocochromanols and conversion is higher for γT1 than αT1 as well as for the γ-congeners of T and T3. The rate of metabolism increases with the number of double bonds in the sidechain. The rate of metabolic conversion of the T1 is more similar to tocopherols than to that of the tocotrienols. CONCLUSION: This is the first evidence that both αT1 and γT1 follow the same sidechain degradation pathway and exert similar rates of metabolism than tocopherols. Therefore, investigation into the biological activities of tocomonoenols is warranted.

Revisiting liver metabolism through acetyl-CoA carboxylase inhibition.

Liver-targeted acetyl-coenzyme A (CoA) carboxylase (ACC) inhibitors in metabolic dysfunction-associated steatotic liver disease (MASLD) trials reveal notable secondary effects: hypertriglyceridemia and altered glucose metabolism, paradoxically with reduced hepatic steatosis. In their study, Deja et al. explored how hepatic ACC influences metabolism using different pharmacological and genetic methods, coupled with targeted metabolomics and stable isotope-based tracing techniques.

A Review: Cytochrome P450 in Alcoholic and Non-Alcoholic Fatty Liver Disease.

Alcoholic fatty liver disease (FALD) and non-alcoholic fatty liver disease (NAFLD) have similar pathological spectra, both of which are associated with a series of symptoms, including steatosis, inflammation, and fibrosis. These clinical manifestations are caused by hepatic lipid synthesis and metabolism dysregulation and affect human health. Despite having been studied extensively, targeted therapies remain elusive. The Cytochrome P450 (CYP450) family is the most important drug-metabolising enzyme in the body, primarily in the liver. It is responsible for the metabolism of endogenous and exogenous compounds, completing biological transformation. This process is relevant to the occurrence and development of AFLD and NAFLD. In this review, the correlation between CYP450 and liver lipid metabolic diseases is summarised, providing new insights for the treatment of AFLD and NAFLD.

VCD-induced menopause mouse model reveals reprogramming of hepatic metabolism.

OBJECTIVE: Menopause adversely impacts systemic energy metabolism and increases the risk of metabolic disease(s) including hepatic steatosis, but the mechanisms are largely unknown. Dosing female mice with vinyl cyclohexene dioxide (VCD) selectively causes follicular atresia in ovaries, leading to a murine menopause-like phenotype. METHODS: In this study, we treated female C57BL6/J mice with VCD (160 mg/kg i.p. for 20 consecutive days followed by verification of the lack of estrous cycling) to investigate changes in body composition, energy expenditure (EE), hepatic mitochondrial function, and hepatic steatosis across different dietary conditions. RESULTS: VCD treatment induced ovarian follicular loss and increased follicle-stimulating hormone (FSH) levels in female mice, mimicking a menopause-like phenotype. VCD treatment did not affect body composition, or EE in mice on a low-fat diet (LFD) or in response to a short-term (1-week) high-fat, high sucrose diet (HFHS). However, the transition to a HFHS lowered cage activity in VCD mice. A chronic HFHS diet (16 weeks) significantly increased weight gain, fat mass, and hepatic steatosis in VCD-treated mice compared to HFHS-fed controls. In the liver, VCD mice showed suppressed hepatic mitochondrial respiration on LFD, while chronic HFHS resulted in compensatory increases in hepatic mitochondrial respiration. Also, liver RNA sequencing revealed that VCD promoted global upregulation of hepatic lipid/cholesterol synthesis pathways. CONCLUSION: Our findings suggest that the VCD-induced menopause model compromises hepatic mitochondrial function and lipid/cholesterol homeostasis that sets the stage for HFHS diet-induced steatosis while also increasing susceptibility to obesity.

Inhibitory protein-protein interactions of the SIRT1 deacetylase are choreographed by post-translational modification.

Regulation of SIRT1 activity is vital to energy homeostasis and plays important roles in many diseases. We previously showed that insulin triggers the epigenetic regulator DBC1 to prime SIRT1 for repression by the multifunctional trafficking protein PACS-2. Here, we show that liver DBC1/PACS-2 regulates the diurnal inhibition of SIRT1, which is critically important for insulin-dependent switch in fuel metabolism from fat to glucose oxidation. We present the x-ray structure of the DBC1 S1-like domain that binds SIRT1 and an NMR characterization of how the SIRT1 N-terminal region engages DBC1. This interaction is inhibited by acetylation of K112 of DBC1 and stimulated by the insulin-dependent phosphorylation of human SIRT1 at S162 and S172, catalyzed sequentially by CK2 and GSK3, resulting in the PACS-2-dependent inhibition of nuclear SIRT1 enzymatic activity and translocation of the deacetylase in the cytoplasm. Finally, we discuss how defects in the DBC1/PACS-2-controlled SIRT1 inhibitory pathway are associated with disease, including obesity and non-alcoholic fatty liver disease.

Effectiveness of metformin for the reversal of cold-ischemia-induced damage in hepatosteatosis.

BACKGROUND: Primary dysfunction and rejection are more common in donor liver tissues with steatosis. AMP-activated protein kinase (AMPK) assumes organ-protective functions during ischemia. Metformin was used for the activation of AMPK in hepatocytes. The aim of this study is to investigate the effectiveness of metformin administration for the reversal of cold-ischemia-induced damage in hepatosteatosis. MATERIAL AND METHODS: Seven-week-old C7BL56 male-mice (n = 109) were separated into four groups depending on diet type and metformin use. A specific diet model was followed for 10 weeks to induce hepatosteatosis. A group of the animals was administered with metformin for the last four weeks via oral gavage. After resection, the liver tissues were perfused and kept for 0-6-12-24 h in the UW solution. Histopathological examinations were performed, and Western blot was utilized to analyze p-AMPK and AMPK expression levels. RESULTS: Hepatosteatosis decreased significantly with metformin. The steatotic liver group had more prominent pericentral inflammation, necrosis as well as showing a decreased and more delayed AMPK response than the non-fat group. All these alterations could be corrected using metformin. CONCLUSION: Metformin can increase the resistance of livers with hepatosteatosis to cold-ischemia-induced damage, which in turn may pave the way for successful transplantation of fatty living-donor livers.

Hyperpolarized 15N caffeine, a potential probe of liver function and perfusion.

PURPOSE: To demonstrate hyperpolarization of 15N-caffeine and report exploratory findings as a potential probe of liver function and perfusion. METHODS: An amorphous formulation of [1,3-15N2]caffeine was developed for hyperpolarization via dissolution dynamic nuclear polarization. Polarizer hardware was augmented to support monitoring of solid-state 15N MR signals during the buildup of hyperpolarization. Liquid state hyperpolarized 15N MR signals were obtained in a preclinical 3T magnet by interfacing an external spectrometer console with home-built RF surface coils. 15N signal decay constants were estimated in H2O and in vivo in liver and brain regions of rats at 3 T. Decays were also measured at 9.4 T to assess the effect of B0, and in the presence of albumin to assess the impact of protein binding. RESULTS: Polarization levels of 3.5% and aqueous T1 relaxation times of nearly 200 s were attained for both N1 and N3 positions at 3 T. Shorter apparent decay constants were observed in vivo, ranging from 25 s to 43 s, with modest extensions possible by exploiting competitive binding of iophenoxate with plasma albumin. Downstream products of caffeine could not be detected on in vivo 15N-MR spectra of the liver region, even with metabolic stimulation by ß $$ \beta $$ -naphthoflavone treatment. Considering the high perfusion rate of brain, persistence of caffeine signal in this region is consistent with potential value as a perfusion imaging agent. CONCLUSION: These results establish the feasibility of hyperpolarization of hyperpolarized 15N-caffeine, but further work is necessary to establish the role of this new agent to probe liver metabolism and perfusion.

Interleaved trinuclear MRS for single-session investigation of carbohydrate and lipid metabolism in human liver at 7T.

The liver plays a central role in metabolic homeostasis, as exemplified by a variety of clinical disorders with hepatic and systemic metabolic disarrays. Of particular interest are the complex interactions between lipid and carbohydrate metabolism in highly prevalent conditions such as obesity, diabetes, and fatty liver disease. Limited accessibility and the need for invasive procedures challenge direct investigations in humans. Hence, noninvasive dynamic evaluations of glycolytic flux and steady-state assessments of lipid levels and composition are crucial for basic understanding and may open new avenues toward novel therapeutic targets. Here, three different MR spectroscopy (MRS) techniques that have been combined in a single interleaved examination in a 7T MR scanner are evaluated. 1H-MRS and 13C-MRS probe endogenous metabolites, while deuterium metabolic imaging (DMI) relies on administration of deuterated tracers, currently 2H-labelled glucose, to map the spatial and temporal evolution of their metabolic fate. All three techniques have been optimized for a robust single-session clinical investigation and applied in a preliminary study of healthy subjects. The use of a triple-channel 1H/2H/13C RF coil enables interleaved examinations with no need for repositioning. Short-echo-time STEAM spectroscopy provides well resolved spectra to quantify lipid content and composition. The relative benefits of using water saturation versus metabolite cycling and types of respiratory synchronization were evaluated. 2H-MR spectroscopic imaging allowed for registration of time- and space-resolved glucose levels following oral ingestion of 2H-glucose, while natural abundance 13C-MRS of glycogen provides a dynamic measure of hepatic glucose storage. For DMI and 13C-MRS, the measurement precision of the method was estimated to be about 0.2 and about 16 mM, respectively, for 5 min scanning periods. Excellent results were shown for the determination of dynamic uptake of glucose with DMI and lipid profiles with 1H-MRS, while the determination of changes in glycogen levels by 13C-MRS is also feasible but somewhat more limited by signal-to-noise ratio.