Involvement of nitric oxide/cyclic GMP signaling pathway in the regulation of fatty acid metabolism in rat hepatocytes

Inhibition of hepatic gluconeogenesis in type 2 diabetes by metformin: complementary role of nitric oxide

Metformin is the first-line treatment for type 2 diabetes mellitus. Type 2 diabetes mellitus is associated with decreased nitric oxide bioavailability, which has significant metabolic implications, including enhanced insulin secretion and peripheral glucose utilization. Similar to metformin, nitric oxide also inhibits hepatic glucose production, mainly by suppressing gluconeogenesis. This review explores the combined effects of metformin and nitric oxide on hepatic gluconeogenesis and proposes the potential of a hybrid metformin-nitric oxide drug for managing type 2 diabetes mellitus. Both metformin and nitric oxide inhibit gluconeogenesis through overlapping and distinct mechanisms. In hepatic gluconeogenesis, mitochondrial oxaloacetate is exported to the cytoplasm via various pathways, including the malate, direct, aspartate, and fumarate pathways. The effects of nitric oxide and metformin on the exportation of oxaloacetate are complementary; nitric oxide primarily inhibits the malate pathway, while metformin strongly inhibits the fumarate and aspartate pathways. Furthermore, metformin effectively blocks gluconeogenesis from lactate, glycerol, and glutamine, whereas nitric oxide mainly inhibits alanine-induced gluconeogenesis. Additionally, nitric oxide contributes to the adenosine monophosphate-activated protein kinase-dependent inhibition of gluconeogenesis induced by metformin. The combined use of metformin and nitric oxide offers the potential to mitigate common side effects. For example, lactic acidosis, a known side effect of metformin, is linked to nitric oxide deficiency, while the oxidative and nitrosative stress caused by nitric oxide could be counterbalanced by metformin's enhancement of glutathione. Metformin also amplifies nitric oxide -induced activation of adenosine monophosphate-activated protein kinase. In conclusion, a metformin-nitric oxide hybrid drug can benefit patients with type 2 diabetes mellitus by enhancing the inhibition of hepatic gluconeogenesis, decreasing the required dose of metformin for maintaining optimal glycemia, and lowering the incidence of metformin-associated lactic acidosis.

Liver sinusoidal endothelial cells: Friend or foe in metabolic dysfunction- associated steatotic liver disease/metabolic dysfunction-associated steatohepatitis

Metabolic dysfunction-associated steatotic liver disease (MASLD) is the predominant liver disease and is becoming the paramount contributor to end-stage liver disease and liver-related deaths. Liver sinusoidal endothelial cells (LSECs) located between the hepatic parenchyma and blood from viscera and gastrointestinal tract are the gatekeepers for the hepatic microenvironment and normal function. In normal physiological conditions, LSECs govern the substance exchange between hepatic parenchyma and blood through dynamic regulation of fenestration and maintain the quiescent state of Kupffer cells (KCs) and hepatic stellate cells. In MASLD, lipotoxicity, insulin resistance, gastrointestinal microbiota dysbiosis, and mechanical compression caused by fat-laden hepatocytes result in LSECs capillarization and dysfunction. The altered LSECs progressively shift from healer to injurer, exacerbating liver inflammation and advancing liver fibrosis. This review focuses on the deteriorative roles of LSECs and related molecular mechanisms involved in MASLD and their contribution to metabolic dysfunction-associated steatohepatitis (MASH) and liver fibrosis development and progression. Furthermore, in this review, we propose that targeting LSECs dysfunction is a prospective therapeutic strategy to restore the physiological function of LSECs and mitigate MASLD progression.

Analysis of Transcriptome Differences Between Subcutaneous and Intramuscular Adipose Tissue of Tibetan Pigs

Background/Objectives: Fat deposition traits in pigs directly influence pork flavor, tenderness, and juiciness and are closely linked to overall pork quality. The Tibetan pig, an indigenous breed in China, not only possesses a high intramuscular fat content but also exhibits a unique fat metabolism pattern due to long-term adaptation to harsh environments. This makes it an excellent genetic and physiological model for investigating fat deposition characteristics. Adipose tissue from different body regions displays varying morphologies, cytokines, and adipokines. This study aimed to examine adipose tissue deposition characteristics in different parts of Tibetan pigs and provide additional data to explore the underlying mechanisms of differential fat deposition. Methods: Our research identified significant differences in the morphology and gene expression patterns between subcutaneous fat (abdominal fat [AF] and back fat [BF]) and intramuscular fat (IMF) in Tibetan pigs. Results: Histological observations revealed that subcutaneous fat cells were significantly larger in area and diameter compared to IMF cells. The transcriptomic analysis further identified differentially expressed genes (DEGs) between subcutaneous fat and IMF, with a total of 65 DEGs in BF vs. IMF and 347 DEGs in AF vs. IMF, including 25 DEGs common to both comparisons. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analyses indicated that these genes were significantly associated with lipid metabolism-related signaling pathways, such as the Wnt, mTOR, and PI3K-Akt signaling pathways. Several DEGs, including DDAH1, ADRA1B, SLCO3A1, and THBS3, may be linked to the differences in fat deposition in different parts of Tibetan pigs, thereby affecting meat quality and nutritional value. Conclusions: These findings provide new insights into the unique fat distribution and deposition characteristics of Tibetan pigs and establish a foundation for breeding strategies aimed at improving pork quality.

Selectively targeting the AdipoR2-CaM-CaMKII-NOS3 axis by SCM-198 as a rapid-acting therapy for advanced acute liver failure

Acute liver failure (ALF) is a hepatology emergency with rapid hepatic destruction, multiple organ failures, and high mortality. Despite decades of research, established ALF has minimal therapeutic options. Here, we report that the small bioactive compound SCM-198 increases the survival of male ALF mice to 100%, even administered 24 hours after ALF establishment. We identify adiponectin receptor 2 (AdipoR2) as a selective target of SCM-198, with the AdipoR2 R335 residue being critical for the binding and signaling of SCM-198-AdipoR2 and AdipoR2 Y274 residue serving as a molecular switch for Ca2+ influx. SCM-198-AdipoR2 binding causes Ca2+ influx and elevates the phosphorylation levels of CaMKII and NOS3 in the AdipoR2-CaM-CaMKII-NOS3 complex identified in this study, rapidly inducing nitric oxide production for liver protection in murine ALF. SCM-198 also protects human ESC-derived liver organoids from APAP/TAA injuries. Thus, selectively targeting the AdipoR2-CaM-CaMKII-NOS3 axis by SCM-198 is a rapid-acting therapeutic strategy for advanced ALF.

N-carbamylglutamate supplementation induces functional egg production in layers by modulating liver transcriptome profiles

Eggs rich in polyunsaturated fatty acids (PUFA), known as functional eggs, are animal products deemed beneficial to human health and possess high economic value. The production of functional eggs involves supplementing exogenous additives with the ability to regulate lipid metabolism. As N-Carbamylglutamate (NCG) serves as an endogenous arginine synthesizer, and arginine acts as the substrate for the formation of nitric oxide (NO), the biological function of NCG is partially mediated by NO. NO is a key regulatory molecule in lipid metabolism, suggesting that NCG may also have the ability to modulate lipid metabolism. In order to assess the capacity of NCG in regulating liver lipid metabolism and its potential application in producing functional eggs, we conducted a study to investigate the effects of dietary supplementation of NCG on production performance, serum, and liver NO levels, yolk fatty acid composition, and the liver transcriptome of layers. In this study, we utilized 30 layers of the Jinghong No.1 breed, all aged 45 wk. All the birds were randomly divided into 2 groups. Each group had 5 replicates, and each replicate had 3 birds. We provided them with different diets: one group received the basic diet, and the other group's diet was supplemented with 0.08% NCG. The experiment lasted for 14 wk. The results did not reveal any positive impact of NCG on production performance. However, NCG supplementation elevated NO levels in serum and liver, along with an increase in yolk PUFA, ω-3, and ω-6 fatty acids. Liver transcriptome analysis identified 124 upregulated differentially expressed genes (DEGs) and 43 downregulated DEGs due to NCG supplementation. Functional annotation using the Kyoto Encyclopedia of Genes and Genomes (KEGG) database highlighted 3 upregulated DEGs (CPT1A, MOGAT1, and CHKA) and 2 downregulated DEGs (FASN and ETNPPL) associated with lipid metabolism. Pathway enrichment analysis revealed that CPT1A was enriched in the AMPK signaling pathway and the PPAR signaling pathway, while FASN was enriched in the AMPK signaling pathway. Thus, CPT1A and FASN are potential functional genes related to lipid metabolism facilitated by NCG supplementation. In summary, our study suggests that NCG supplementation modulates liver lipid metabolism, leading to the production of functional eggs in layers.

The Emerging Role of Prediabetes and Its Management: Focus on L-Arginine and a Survey in Clinical Practice

The worldwide impressive growth of metabolic disorders observed in the last decades, especially type 2 diabetes mellitus and obesity, has generated great interest in the potential benefits of early identification and management of patients at risk. In this view, prediabetes represents a high-risk condition for the development of type 2 diabetes mellitus and cardiovascular diseases, and an ideal target to intercept patients before they develop type 2 diabetes gaining a prominent role even in international guidelines. For prediabetic individuals, lifestyle modification is the cornerstone of diabetes prevention, with evidence of about 50% relative risk reduction. Accumulating data also show potential benefits from pharmacotherapy. In this context, the only available data pertain to metformin as a pharmaceutical drug and vitamin D and L-arginine as nutraceuticals. L-arginine appears to be a very interesting tool in the clinical management of patients with pre-diabetes. In this review we summarize the current knowledge on the role of L-arginine in prediabetes as a potentially useful preventive strategy against the progression to type 2 diabetes, with a particular focus on the underlying molecular mechanisms and the past and ongoing trials. In this article we also report the interesting data about the perception of the prediabetic condition and its therapeutic management in the clinical practice in Italy. An early identification and a prompt management of people with prediabetes appears to be of paramount importance to prevent the progression to diabetes and avoid its cardiovascular consequences.

Effects of dietary arginine supplementation on production performance, serum biochemicals, antioxidant capacity, and immunity of laying Wulong geese

This study investigated the effects of dietary arginine supplementation on the production performance, serum biochemicals, antioxidant capacity, and immunity of laying Wulong geese. A total of 150 Wulong geese (34-wk old) with similar body weights were randomly divided into 6 groups with 5 replicates and 5 geese each (1 male and 4 female). The geese in the control group were fed a corn-rapeseed meal basal diet, and the geese in the treatment groups were fed the basal diet supplemented with 0.1, 0.2, 0.3, 0.4, and 0.5% arginine. The experiment lasted for 17 wk. Our results showed that dietary arginine increased the egg production rate (LR) and average egg weight (AEW) of geese in a quadratic manner (P < 0.05). Dietary arginine had a quadratic effect on the contents of total protein (TP) and triglyceride (TG) (P < 0.05) in the serum. Dietary arginine quadratically decreased the content of malondialdehyde (MDA) and increased the activity of total superoxide dismutase (T-SOD) (P < 0.05). Dietary arginine supplementation linearly and quadratically increased the contents of immunoglobulin A (IgA) and immunoglobulin G (IgG), and linearly increased the content of nitric oxide (NO) (P < 0.05). In conclusion, dietary arginine supplementation can significantly improve the production performance, serum biochemicals, antioxidant capacity, and immunity of laying Wulong geese. Therefore, 0.3% arginine (actual content: 1.02%) is recommended in the diet.

Nitric oxide regulation of cellular metabolism: Adaptive tuning of cellular energy

Nitric oxide can interact with a wide range of proteins including many that are involved in metabolism. In this review we have summarized the effects of NO on glycolysis, fatty acid metabolism, the TCA cycle, and oxidative phosphorylation with reference to skeletal muscle. Low to moderate NO concentrations upregulate glucose and fatty acid oxidation, while higher NO concentrations shift cellular reliance toward a fully glycolytic phenotype. Moderate NO production directly inhibits pyruvate dehydrogenase activity, reducing glucose-derived carbon entry into the TCA cycle and subsequently increasing anaploretic reactions. NO directly inhibits aconitase activity, increasing reliance on glutamine for continued energy production. At higher or prolonged NO exposure, citrate accumulation can inhibit multiple ATP-producing pathways. Reduced TCA flux slows NADH/FADH entry into the ETC. NO can also inhibit the ETC directly, further limiting oxidative phosphorylation. Moderate NO production improves mitochondrial efficiency while improving O2 utilization increasing whole-body energy production. Long-term bioenergetic capacity may be increased because of NO-derived ROS, which participate in adaptive cellular redox signaling through AMPK, PCG1-α, HIF-1, and NF-κB. However, prolonged exposure or high concentrations of NO can result in membrane depolarization and opening of the MPT. In this way NO may serve as a biochemical rheostat matching energy supply with demand for optimal respiratory function.

l-Arginine supplementation regulates energy-substrate metabolism in skeletal muscle and adipose tissue of diet-induced obese rats

Dietary supplementation with l-arginine has been reported to reduce white fat mass in diet-induced obese rats and in obese humans. This study was conducted to test the hypothesis that the arginine treatment regulates glucose and fatty acid metabolism in insulin-sensitive tissues. Male Sprague–Dawley rats (4-week-old) were fed either low- or high-fat diets for 15 weeks ( n = 16/diet). Thereafter, lean or obese rats were fed their respective diets and received drinking water containing either 1.51% l-arginine-HCl or 2.55% alanine (isonitrogenous control) ( n = 8/treatment group). After 12 weeks of treatment, rats were euthanized and tissue samples were collected for biochemical assays. High-fat feeding increased the size of adipocytes isolated from retroperitoneal (RP) adipose tissue, while arginine treatment reduced their size. The total number of adipocytes in the adipose tissue did not differ among the four groups of rats. Glucose oxidation in extensor digitorum longus (EDL) muscle, soleus muscle, and RP adipose tissue were reduced in response to high-fat feeding. On the contrary, oleic acid oxidation in RP adipose tissue was enhanced in rats fed the high-fat diet. Arginine treatment stimulated both glucose and oleic acid oxidation in EDL and soleus muscles, while having no effect on glucose oxidation, oleic acid oxidation, or basal lipolysis per 106 adipocytes in RP adipose tissue. Collectively, these results indicate that oral supplementation with arginine to diet-induced obese rats promoted the oxidation of energy substrates in skeletal muscle, thereby reducing white fat in the body.

Integrating Network Pharmacology and Transcriptomic Strategies to Explore the Pharmacological Mechanism of Hydroxysafflor Yellow A in Delaying Liver Aging

Aging affects the structure and function of the liver. Hydroxysafflor yellow A (HSYA) effectively improves liver aging (LA) in mice, but the potential mechanisms require further exploration. In this study, an integrated approach combining network pharmacology and transcriptomics was used to elucidate the potential mechanisms of HSYA delay of LA. The targets of HSYA were predicted using the PharmMapper, SwissTargetPrediction, and CTD databases, and the targets of LA were collected from the GeneCards database. An ontology (GO) analysis and a Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway annotation of genes related to HSYA delay of LA were performed using the DAVID database, and Cytoscape software was used to construct an HSYA target pathway network. The BMKCloud platform was used to sequence mRNA from mouse liver tissue, screen differentially expressed genes (DEGs) that were altered by HSYA, and enrich their biological functions and signaling pathways through the OmicShare database. The results of the network pharmacology and transcriptomic analyses were combined. Then, quantitative real-time PCR (qRT-PCR) and Western blot experiments were used to further verify the prediction results. Finally, the interactions between HSYA and key targets were assessed by molecular docking. The results showed that 199 potentially targeted genes according to network pharmacology and 480 DEGs according to transcriptomics were involved in the effects of HSYA against LA. An integrated analysis revealed that four key targets, including HSP90AA1, ATP2A1, NOS1 and CRAT, as well as their three related pathways (the calcium signaling pathway, estrogen signaling pathway and cGMP-PKG signaling pathway), were closely related to the therapeutic effects of HSYA. A gene and protein expression analysis revealed that HSYA significantly inhibited the expressions of HSP90AA1, ATP2A1 and NOS1 in the liver tissue of aging mice. The molecular docking results showed that HSYA had high affinities with the HSP90AA1, ATP2A1 and NOS1 targets. Our data demonstrate that HSYA may delay LA in mice by inhibiting the expressions of HSP90AA1, ATP2A1 and NOS1 and regulating the calcium signaling pathway, the estrogen signaling pathway, and the cGMP-PKG signaling pathway.

L-Arginine increases AMPK phosphorylation and the oxidation of energy substrates in hepatocytes, skeletal muscle cells, and adipocytes

Previous work has shown that dietary L-arginine (Arg) supplementation reduced white fat mass in obese rats. The present study was conducted with cell models to define direct effects of Arg on energy-substrate oxidation in hepatocytes, skeletal muscle cells, and adipocytes. BNL CL.2 mouse hepatocytes, C2C12 mouse myotubes, and 3T3-L1 mouse adipocytes were treated with different extracellular concentrations of Arg (0, 15, 50, 100 and 400 µM) or 400 µM Arg + 0.5 mM N^G-nitro-L-arginine methyl ester (L-NAME; an NOS inhibitor) for 48 h. Increasing Arg concentrations in culture medium dose-dependently enhanced (P < 0.05) the oxidation of glucose and oleic acid to CO₂ in all three cell types, lactate release from C2C12 cells, and the incorporation of oleic acid into esterified lipids in BNL CL.2 and 3T3-L1 cells. Arg at 400 µM also stimulated (P < 0.05) the phosphorylation of AMP-activated protein kinase (AMPK) in all three cell types and increased (P < 0.05) NO production in C2C12 and BNL CL.2 cells. The inhibition of NOS by L-NAME moderately reduced (P < 0.05) glucose and oleic acid oxidation, lactate release, and the phosphorylation of AMPK and acetyl-CoA carboxylase (ACC) in BNL CL.2 cells, but had no effect (P > 0.05) on these variables in C2C12 or 3T3-L1 cells. Collectively, these results indicate that Arg increased AMPK activity and energy-substrate oxidation in BNL CL.2, C2C12, and 3T3-L1 cells through both NO-dependent and NO-independent mechanisms.

Dietary L-arginine supplementation increases the hepatic expression of AMP-activated protein kinase in rats

The goal of this study was to elucidate the molecular mechanisms responsible for the anti-obesity effect of L-arginine supplementation in diet-induced obese rats. Male Sprague-Dawley rats were fed either a low-fat or high-fat diet for 15 weeks. Thereafter, lean or obese rats were pair-fed their same respective diets and received drinking water containing either 1.51% L-arginine-HCl or 2.55% L-alanine (isonitrogenous control) for 12 weeks. Gene and protein expression of key enzymes in the metabolism of energy substrates were determined using real-time polymerase-chain reaction and western blotting techniques. The mRNA levels of hepatic fatty acid synthase and stearoyl-CoA desaturase were reduced (P < 0.05) but those of hepatic AMP-activated protein kinase-α (AMPKα), peroxisome proliferator activator receptor γ coactivator-1α, and carnitine palmitoyltransferase I (CPT-I), as well as skeletal muscle CPT-I were increased (P < 0.05) by L-arginine treatment. The protein expression and activity of hepatic AMPKα markedly increased (P < 0.05) but the activity of hepatic acetyl-CoA carboxylase (ACC) decreased (P < 0.05) in response to dietary L-arginine supplementation. Collectively, our results indicate that liver is the major target for the action of dietary L-arginine supplementation on reducing white-fat mass in diet-induced obese rats by inhibiting fatty acid synthesis and increasing fatty acid oxidation via the AMPK-ACC signaling pathway. Additionally, increased CPT-I expression in skeletal muscle may also contribute to the enhanced oxidation of long-chain fatty acids in L-arginine-supplemented rats.

Infused aqueous curry tea extracts ameliorate Nω -Nitro-L-Arginine Methyl Ester-induced liver dysfunction in male albino Wistar rats

BACKGROUND

Murraya koenigii (L.) Spreng. (Rutaceae) has been reported to positively affect liver function. However, the effect of M. koenigii leaves on N^ω -Nitro-L-Arginine Methyl Ester (L-NAME) induced liver dysfunction is unknown. The aim of the present study was therefore to investigate the effect of M.koenigii leaves as tea on L-NAME induced liver dysfunction.

METHODS

Two variants of curry tea were formulated; one was formulated entirely from leaves of M. koenigii, the other was formulated with thaumatin-rich aril obtained from seeds of Thaumatococcus danielii (Benn.) Benth. (Marantaceae). Group I animals served as control and were untreated. Groups II and V animals were administered curry tea (CT). Group III and VI animals received curry-thaumatin tea (CTT). Concurrently, L-NAME (40 mg/kg) was administered to groups IV-VI respectively for 21 days. Blood and liver samples were collected at the end of the study for biochemical, histological, and immunohistochemical analysis.

RESULTS

L-NAME induced liver dysfunction evidenced by liver histology, increased activities of ALT, AST, hyperlipidemia, hepatic oxidative stress and increased hepatic NF-kB expression. Administration of CT and CTT ameliorated the L-NAME induced liver dysfunction evidenced by liver histology, increased NO hepatic bioavailability, reduced activity of ALT and AST, increased hepatic antioxidant system and decreased hepatic NF-kB expression. Thaumatin taste/flavor enhancer did not significantly reduce or potentiate the hepatoprotective, antioxidant and anti-lipidemic property of aqueous curry tea extracts in rats.

CONCLUSION

L-NAME impaired liver function in rats. CT and CTT interfered with the ability of L-NAME to inhibit NO synthesis which was associated with ameliorated hepatic dysfunction.

PRACTICAL APPLICATIONS

The study reports that non-selective inhibition of nitric oxide by L-NAME in rats impairs liver function and formulated curry tea types interfered with the ability of L-NAME to inhibit NO synthesis which was associated with ameliorated hepatic dysfunction in rats.

Comparing the whole genome methylation landscape of dairy calf blood cells revealed intergenerational inheritance of the maternal metabolism

This study evaluated the hypothesis that the maternal metabolic stressed status could be inherited to their F1 daughters via epigenetic mechanism. The maternal cow blood β-hydroxybutyric acid (BHB) level (≥0.9 mM/L) was used as an indicator of maternal metabolic stress. Eight newborn daughters' blood cells were used for methylation comparison and analysis. By Whole Genome Bisulphite Sequencing (WGBS), a total of 1,861 Differentially Methylated Regions (DMRs), including 944 differentially methylated cytosines (DMCs), were identified. Most DMRs were distributed in intronic and intergenic regions, and most of the DMR in promoter regions were hypermethylated. Differentially methylated genes (DMGs) with DMR methylation differences higher than 20% were mainly enriched in metabolism-related pathways. These results suggest that newborn calves' metabolic pathways were altered, with 64 DMGs being clustered with metabolic signalling by KEGG analysis. Our study revealed the whole epigenetic landscape of calf blood cells and suggested that the maternal metabolic status can affect the embryo's epigenetic status and metabolic-related pathways in offspring, providing further evidence for epigenetic intergenerational inheritance of metabolic stress in domestic animals. Besides, this study also contributed more evidence to support the Developmental Origins of Health and Disease (DOHAD) theory in large animals.

Gasotransmitter signaling in energy homeostasis and metabolic disorders

Gasotransmitters are small molecules of gases, including nitric oxide (NO), hydrogen sulfide (H₂S), and carbon monoxide (CO). These three gasotransmitters can be endogenously produced and regulate a wide range of pathophysiological processes by interacting with specific targets upon diffusion in the biological media. By redox and epigenetic regulation of various physiological functions, NO, H₂S, and CO are critical for the maintenance of intracellular energy homeostasis. Accumulated evidence has shown that these three gasotransmitters control ATP generation, mitochondrial biogenesis, glucose metabolism, insulin sensitivity, lipid metabolism, and thermogenesis, etc. Abnormal generation and metabolism of NO, H₂S, and/or CO are involved in various abnormal metabolic diseases, including obesity, diabetes, and dyslipidemia. In this review, we summarized the roles of NO, H₂S, and CO in the regulation of energy homeostasis as well as their involvements in the metabolism of dysfunction-related diseases. Understanding the interaction among these gasotransmitters and their specific molecular targets are very important for therapeutic applications.

Tetrahydrobiopterin Plays a Functionally Significant Role in Lipogenesis in the Oleaginous Fungus Mortierella alpina

Tetrahydrobiopterin (BH₄) is well-known as a cofactor of phenylalanine hydroxylase (PAH) and nitric oxide synthase (NOS), but its exact role in lipogenesis is unclear. In this study, the GTP cyclohydrolase I (GTPCH) gene was overexpressed to investigate the role of BH₄ in lipogenesis in oleaginous fungus Mortierella alpina. Transcriptome data analysis reveal that GTPCH expression was upregulated when nitrogen was exhausted, resulting in lipid accumulation. Significant changes were also found in the fatty acid profile of M. alpina grown on medium that contained a GTPCH inhibitor relative to that of M. alpina grown on medium that lacked the inhibitor. GTPCH overexpression in M. alpina (the MA-GTPCH strain) led to a sevenfold increase in BH₄ levels and enhanced cell fatty acid synthesis and poly-unsaturation. Increased levels of nicotinamide adenine dinucleotide phosphate (NADPH) and upregulated expression of NADPH-producing genes in response to enhanced BH₄ levels were also observed, which indicate a novel aspect of the NADPH regulatory mechanism. Increased BH₄ levels also enhanced phenylalanine hydroxylation and nitric oxide synthesis, and the addition of an NOS or a PAH inhibitor in the MA-GTPCH and control strain cultures decreased fatty acid accumulation, NADPH production, and the transcript levels of NADPH-producing genes. Our research suggests an important role of BH₄ in lipogenesis and that the phenylalanine catabolism and arginine-nitric oxide pathways play an integrating role in translating the effects of BH₄ on lipogenesis by regulating the cellular NADPH pool. Thus, our findings provide novel insights into the mechanisms of efficient lipid biosynthesis regulation in oleaginous microorganisms and lay a foundation for the genetic engineering of these organisms to optimize their dietary fat yield.

Hematopoietic Cell-Expressed Endothelial Nitric Oxide Protects the Liver From Insulin Resistance

OBJECTIVE

Mice genetically deficient in endothelial nitric oxide synthase (Nos3^-/-) have fasting hyperinsulinemia and hepatic insulin resistance, indicating the importance of Nos3 (nitric oxide synthase) in maintaining metabolic homeostasis. Although the current paradigm holds that these metabolic effects are derived specifically from the expression of Nos3 in the endothelium, it has been established that bone marrow-derived cells also express Nos3. The aim of this study was to investigate whether bone marrow-derived cell Nos3 is important in maintaining metabolic homeostasis. Approach and Results: To test the hypothesis that bone marrow-derived cell Nos3 contributes to metabolic homeostasis, we generated chimeric male mice deficient or competent for Nos3 expression in circulating blood cells. These mice were placed on a low-fat diet for 5 weeks, a time period which is known to induce hepatic insulin resistance in global Nos3-deficient mice but not in wild-type C57Bl/6 mice. Surprisingly, we found that the absence of Nos3 in the bone marrow-derived component is associated with hepatic insulin resistance and that restoration of Nos3 in the bone marrow-derived component in global Nos3-deficient mice is sufficient to restore hepatic insulin sensitivity. Furthermore, we found that overexpression of Nos3 in bone marrow-derived component in wild-type mice attenuates the development of hepatic insulin resistance during high-fat feeding. Finally, compared with wild-type macrophages, the loss of macrophage Nos3 is associated with increased inflammatory responses to lipopolysaccharides and reduced anti-inflammatory responses to IL-4, a macrophage phenotype associated with the development of hepatic and systemic insulin resistance.

CONCLUSIONS

These results would suggest that the metabolic and hepatic consequences of high-fat feeding are mediated by loss of Nos3/nitric oxide actions in bone marrow-derived cells, not in endothelial cells.

Human relaxin-2 attenuates hepatic steatosis and fibrosis in mice with non-alcoholic fatty liver disease

Human relaxin-2 reduces hepatic fibrosis in mice. However, the effects of relaxin-2 on hepatic steatosis and fibrosis in animals with non-alcoholic fatty liver disease (NAFLD) remain to be elucidated. C57BL/6 mice fed a high-fat diet (HFD) or methionine-choline-deficient (MCD) diet were randomly assigned to receive recombinant human relaxin-2 (25 or 75 μg/kg/day) or vehicle for 4 weeks. In HFD-fed mice, relaxin-2 decreased systemic insulin resistance and reduced body weight, epididymal fat mass and serum leptin and insulin concentrations. In livers of HFD-fed mice, relaxin-2 attenuated steatosis and increased phosphorylation of insulin receptor substrate-1, Akt and endothelial nitric oxide synthase (eNOS), and activated genes that regulate fatty acid oxidation and suppressed acetyl-CoA carboxylase. Relaxin-2 had no direct anti-steatotic effect on primary mouse hepatocytes, but S-nitroso-N-acetylpenicillamine attenuated palmitic acid-induced steatosis and activated genes regulating fatty acid oxidation in hepatocytes. In mice fed an MCD diet, relaxin-2 attenuated steatosis, inflammation and fibrosis. Relaxin-2 increased eNOS and Akt phosphorylation and transcript levels of cytochrome P450-4a10 and decreased acetyl-CoA carboxylase in MCD-fed mouse livers. Moreover, expression levels of Kupffer cell activation, hepatic stellate cell activation and hepatocyte apoptosis were decreased in MCD diet-fed mice receiving relaxin-2. In conclusion, relaxin-2 reduces hepatic steatosis by activating intrahepatic eNOS in HFD-fed mice and further attenuates liver fibrosis in MCD diet-fed mice. Therefore, human relaxin-2 is a potential therapeutic treatment for NAFLD.

Hydroxyhydroquinone impairs fat utilization in mice by reducing nitric oxide availability

Habitual consumption of chlorogenic acid compounds (CGAs) from coffee increases fat catabolism and reduces body fat; however, the contribution of roasted coffee remains unclear. Hydroxyhydroquinone (HHQ) impairs the vasodilatory and antihypertensive effects of CGAs by reducing nitric oxide (NO) bioavailability. Since HHQ also reduces fat catabolism, we hypothesized that HHQ does so by decreasing NO availability. Therefore, we investigated the effect of HHQ on energy metabolism in KKAy mice. In HHQ-treated mice, fat oxidation was significantly low and dose-dependent, serum and urinary hydrogen peroxide were high, and plasma NO metabolites and S-nitrosylated liver proteins were low. In HHQ-treated mouse hepatocytes, the palmitate-induced increase in cellular oxygen consumption was negatively affected, and HHQ or L-NAME reduced cellular fatty acid utilization. In conclusion, HHQ can impair fat utilization by reducing NO availability in mice. Protein S-nitrosylation reduction in liver cells after HHQ consumption may be associated with impaired fatty acid oxidation.

Integrative Proteomics-Metabolomics Strategy for Pathological Mechanism of Vascular Depression Mouse Model

Vascular depression (VD), a subtype of depression, is caused by vascular diseases or cerebrovascular risk factors. Recently, the proportion of VD patients has increased significantly, which severely affects their quality of life. However, the current pathogenesis of VD has not yet been fully understood, and the basic research is not adequate. In this study, on the basis of the combination of LC-MS-based proteomics and metabolomics, we aimed to establish a protein metabolism regulatory network in a murine VD model to elucidate a more comprehensive impact of VD on organisms. We detected 44 metabolites and 304 proteins with different levels in the hippocampus samples from VD mice using a combination of metabolomic and proteomics analyses with an isobaric tags for relative and absolute quantification (iTRAQ) method. We constructed a protein-to-metabolic regulatory network by correlating and integrating the differential metabolites and proteins using ingenuity pathway analysis. Then we quantitatively validated the levels of the bimolecules shown in the bioinformatics analysis using LC-MS/MS and Western blotting. Validation results suggested changes in the regulation of neuroplasticity, transport of neurotransmitters, neuronal cell proliferation and apoptosis, and disorders of amino acids, lipids and energy metabolism. These proteins and metabolites involved in these dis-regulated pathways will provide a more targeted and credible direction to study the mechanism of VD. Therefore, this paper presents an approach and strategy that was applied in integrative proteomics and metabolomics for research and screening potential targets and biomarkers of VD, which could be more precise and credible in a field lacking adequate basic research.

Short-term treatment with hepatoselective NO donor V-PYRRO/NO improves blood flow in hepatic microcirculation in liver steatosis in mice

BACKGROUND

The impairment of liver sinusoidal endothelial cells (LSECs) function and diminished nitric oxide (NO) production has been regarded as an important pathogenic factor in liver steatosis. Restoring NO-dependent function was shown to counteract liver steatosis, obesity, and insulin resistance. However, it is not known whether restored liver perfusion and improvement in hepatic blood flow contributes to the anti-steatotic effects of NO. Taking advantage of in vivo MRI, we have examined the effects of short-term treatment with the hepatoselective NO donor V-PYRRO/NO on hepatic microcirculation in advanced liver steatosis.

METHODS

Male C57BL/6 mice fed for six months a high fat diet (HFD; 60 kcal% of fat) were treated for 3 weeks with V-PYRRO/NO (twice a day 5mg/kg b.w. ip). An MRI assessment of liver perfusion using the FAIR-EPI method and a portal vein blood flow using the FLASH method were performed. Blood biochemistry, glucose tolerance tests, a histological evaluation of the liver, and liver NO concentrations were also examined.

RESULTS

Short-term treatment with V-PYRRO/NO releasing NO selectively in the liver improved liver perfusion and portal vein blood flow. This effect was associated with a slight improvement in glucose tolerance but there was no effect on liver steatosis, body weight, white adipose tissue mass, plasma lipid profile, or aminotransferase activity.

CONCLUSION

Short-term treatment with V-PYRRO/NO-derived NO improves perfusion in hepatic microcirculation and this effect may also contribute to the anti-steatotic effects of hepatoselective NO donors linked previously to the modulation of glucose and lipid metabolism in the liver.

Thyroid Hormone Stimulation of Adult Brain Fatty Acid Oxidation

Thyroid hormone is a critical modulator of brain metabolism, and it is highly controlled in the central nervous system. Recent research has uncovered an important role of thyroid hormone in the regulation of fatty acid oxidation (FAO), an energetic process essential for neurodevelopment that continues to support brain metabolism during adulthood. Thyroid hormone stimulation of FAO has been shown to be protective in astrocytes and mouse models of brain injury, yet a clear mechanism of this relationship has not been elucidated. Thyroid hormone interacts with multiple receptors located in the nucleus and the mitochondria, initiating rapid and long-term effects via both genomic and nongenomic pathways. This has complicated efforts to isolate and study-specific interactions. This chapter presents the primary signaling pathways that have been identified to play a role in the thyroid hormone-mediated increase in FAO. Investigation of the impact of thyroid hormone on FAO in the adult brain has challenged classical models of brain metabolism and widened the window of potential neuroprotective strategies. A detailed understanding of these pathways is essential for any researchers aiming to expand the field of neuroenergetics.

Reduction in hydroxyhydroquinone from coffee increases postprandial fat utilization in healthy humans: a randomized double-blind, cross-over trial

The present study aimed to clarify the effect of reduction in hydroxyhydroquinone (HHQ) from roasted coffee on energy utilization in humans. Indirect calorimetry showed that one-week ingestion of HHQ-reduced coffee led to significantly higher postprandial fat utilization than that of HHQ-containing coffee. This finding indicates that reduction in HHQ from coffee increases postprandial fat utilization.

Comparative Proteomics Analysis Reveals L-Arginine Activates Ethanol Degradation Pathways in HepG2 Cells

L-Arginine (Arg) is a versatile amino acid that plays crucial roles in a wide range of physiological and pathological processes. In this study, to investigate the alteration induced by Arg supplementation in proteome scale, isobaric tags for relative and absolute quantification (iTRAQ) based proteomic approach was employed to comparatively characterize the differentially expressed proteins between Arg deprivation (Ctrl) and Arg supplementation (+Arg) treated human liver hepatocellular carcinoma (HepG2) cells. A total of 21 proteins were identified as differentially expressed proteins and these 21 proteins were all up-regulated by Arg supplementation. Six amino acid metabolism-related proteins, mostly metabolic enzymes, showed differential expressions. Intriguingly, Ingenuity Pathway Analysis (IPA) based pathway analysis suggested that the three ethanol degradation pathways were significantly altered between Ctrl and +Arg. Western blotting and enzymatic activity assays validated that the key enzymes ADH1C, ALDH1A1, and ALDH2, which are mainly involved in ethanol degradation pathways, were highly differentially expressed, and activated between Ctrl and +Arg in HepG2 cells. Furthermore, 10 mM Arg significantly attenuated the cytotoxicity induced by 100 mM ethanol treatment (P < 0.0001). This study is the first time to reveal that Arg activates ethanol degradation pathways in HepG2 cells.

Metabolomic analysis of plasma and liver from surplus arginine fed Atlantic salmon

The aim of this study was to determine the metabolic effect of surplus arginine (36.1 g/kg dry matter) compared to a control diet with required arginine (21.1 g/kg dry matter) in adult Atlantic salmon (Salmo salar L.). Although the feeding trial had no significant effect on growth, there were significant differences in the metabolite profile in both plasma and liver in experimental group as compared to the control group. There was increased concentrations of biliverdin, PGF-2 alpha, oxidized glutathione, selenocysteine, two monoacylglycerols and a tripeptide in the liver as well as decreased concentrations of valine and a vitamin D3 metabolite in plasma of arginine supplemented fish. These results indicate that while surplus arginine does not affect growth or body weight, it induces metabolic changes in Atlantic salmon.

L-arginine supplementation and risk factors of cardiovascular diseases in healthy men: a double-blind randomized clinical trial

Context: The effect of L-arginine on risk factors of cardiovascular diseases (CVD) has mostly focused on western countries. Since cardiovascular diseases is the second cause of death in Iran and, as far as we are aware, there have been no studies about the effect of L-arginine on CVD risk factors, the aim of this trial was to assess the effects of L-arginine supplementation on CVD risk factors in healthy men.

Objective: The purpose of this study was to evaluate the effect of low-dose L-arginine supplementation on CVD risk factors (lipid profile, blood sugar and blood pressure) in Iranian healthy men.

Design, setting, participants: We conducted a double-blind randomized controlled trial in 56 patients selected from sport clubs at the Isfahan University of Medical Science between November 2013 and December 2013.

Interventions: Healthy men received L-arginine supplementation (2000 mg daily) in the intervention group or placebo (2000 mg maltodextrin daily) in the control group for 45 days.

Main outcome measure: The primary outcome measures were we measured the levels of fasting blood sugar, blood pressure and lipid profile including triglyceride (TG), cholesterol, LDL and HDL in healthy subjects. It was hypothesized that these measures would be significantly improved in those receiving L–arginine supplementation. at the beginning and end of the study.

Results: In this trial, we had complete data for 52 healthy participants with mean age of 20.85±4.29 years. At the end of study, fasting blood sugar (P=0.001) and lipid profile (triglycerideTG (P<0.001), cholesterol (P<0.001), LDL (P=0.04), HDL (P=0.015)) decreased in the L-arginine group but we found no significant change in the placebo group. In addition, the reduction of fasting blood sugar and lipid profile in L-arginine was significant compared with placebo group. No significant changes were found about systolic (P=0.81) and diastolic blood pressure either in L-arginine or placebo group. (P=0.532).

Conclusion: The use of L-arginine significantly improved outcomes compared to placebo.

L-arginine supplementation and risk factors of cardiovascular diseases in healthy men: a double-blind randomized clinical trial

Context: The effect of L-arginine on risk factors of cardiovascular diseases (CVD) has mostly focused on western countries. Since cardiovascular diseases is the second cause of death in Iran and, as far as we are aware, there have been no studies about the effect of L-arginine on CVD risk factors, the aim of this trial was to assess the effects of L-arginine supplementation on CVD risk factors in healthy men. Objective: The purpose of this study was to evaluate the effect of low-dose L-arginine supplementation on CVD risk factors (lipid profile, blood sugar and blood pressure) in Iranian healthy men. Design, setting, participants: We conducted a double-blind randomized controlled trial in 56 patients selected from sport clubs at the Isfahan University of Medical Science between November 2013 and December 2013. Interventions: Healthy men received L-arginine supplementation (2000 mg daily) in the intervention group or placebo (2000 mg maltodextrin daily) in the control group for 45 days. Main outcome measure: The primary outcome measures were we measured the levels of fasting blood sugar, blood pressure and lipid profile including triglyceride (TG), cholesterol, LDL and HDL in healthy subjects. It was hypothesized that these measures would be significantly improved in those receiving L-arginine supplementation. at the beginning and end of the study. Results: In this trial, we had complete data for 52 healthy participants with mean age of 20.85±4.29 years. At the end of study, fasting blood sugar (P=0.001) and lipid profile (triglycerideTG (P<0.001), cholesterol (P<0.001), LDL (P=0.04), HDL (P=0.015)) decreased in the L-arginine group but we found no significant change in the placebo group. In addition, the reduction of fasting blood sugar and lipid profile in L-arginine was significant compared with placebo group. No significant changes were found about systolic (P=0.81) and diastolic blood pressure either in L-arginine or placebo group. (P=0.532). Conclusion: The use of L-arginine significantly improved outcomes compared to placebo.

Regulation of obesity and insulin resistance by nitric oxide

Obesity is a risk factor for developing type 2 diabetes and cardiovascular disease and has quickly become a worldwide pandemic with few tangible and safe treatment options. Although it is generally accepted that the primary cause of obesity is energy imbalance, i.e., the calories consumed are greater than are utilized, understanding how caloric balance is regulated has proven a challenge. Many "distal" causes of obesity, such as the structural environment, occupation, and social influences, are exceedingly difficult to change or manipulate. Hence, molecular processes and pathways more proximal to the origins of obesity-those that directly regulate energy metabolism or caloric intake-seem to be more feasible targets for therapy. In particular, nitric oxide (NO) is emerging as a central regulator of energy metabolism and body composition. NO bioavailability is decreased in animal models of diet-induced obesity and in obese and insulin-resistant patients, and increasing NO output has remarkable effects on obesity and insulin resistance. This review discusses the role of NO in regulating adiposity and insulin sensitivity and places its modes of action into context with the known causes and consequences of metabolic disease.

Antiobesogenic role of endothelial nitric oxide synthase

The prevalence of obesity has increased remarkably in the past four decades. Because obesity can promote the development of type 2 diabetes and cardiovascular disease, understanding the mechanisms that engender weight gain and discovering safe antiobesity therapies are of critical importance. In particular, the gaseous signaling molecule, nitric oxide (NO), appears to be a central factor regulating adiposity and systemic metabolism. Obese and diabetic states are characterized by a deficit in bioavailable NO, with such decreases commonly attributed to downregulation of endothelial NO synthase (eNOS), loss of eNOS activity, or quenching of NO by its reaction with oxygen radicals. Gain-of-function studies, in which vascular-derived NO has been increased pharmacologically or genetically, reveal remarkable actions of NO on body composition and systemic metabolism. This review addresses the metabolic actions of eNOS and the potential therapeutic utility of harnessing its antiobesogenic effects.

VASP increases hepatic fatty acid oxidation by activating AMPK in mice

Activation of AMP-activated protein kinase (AMPK) signaling reduces hepatic steatosis and hepatic insulin resistance; however, its regulatory mechanisms are not fully understood. In this study, we sought to determine whether vasodilator-stimulated phosphoprotein (VASP) signaling improves lipid metabolism in the liver and, if so, whether VASP's effects are mediated by AMPK. We show that disruption of VASP results in significant hepatic steatosis as a result of significant impairment of fatty acid oxidation, VLDL-triglyceride (TG) secretion, and AMPK signaling. Overexpression of VASP in hepatocytes increased AMPK phosphorylation and fatty acid oxidation and reduced hepatocyte TG accumulation; however, these responses were suppressed in the presence of an AMPK inhibitor. Restoration of AMPK phosphorylation by administration of 5-aminoimidazole-4-carboxamide riboside in Vasp(-/-) mice reduced hepatic steatosis and normalized fatty acid oxidation and VLDL-TG secretion. Activation of VASP by the phosphodiesterase-5 inhibitor, sildenafil, in db/db mice reduced hepatic steatosis and increased phosphorylated (p-)AMPK and p-acetyl CoA carboxylase. In Vasp(-/-) mice, however, sildendafil treatment did not increase p-AMPK or reduce hepatic TG content. These studies identify a role of VASP to enhance hepatic fatty acid oxidation by activating AMPK and to promote VLDL-TG secretion from the liver.

Changes in nitric oxide, cGMP, and nitrotyrosine concentrations over skin along the meridians in obese subjects

The purposes of these studies were to quantify the concentrations of total nitrate and nitrite (NO(x)(-)) cyclic guanosine monophosphate (cGMP), and nitrotyrosine over skin surface in normal weight healthy volunteers (n = 64) compared to overweight/obese subjects (n = 54). A semi-circular plastic tube was taped to the skin along acupuncture points (acupoints), meridian line without acupoint (MWOP), and nonmeridian control and filled with a 2-Phenyl-4,4,5,5-tetramethylimidazoline-3-oxide-1-oxyl solution for 20 min. The concentrations of NO(x)(-), cGMP, and nitrotyrosine in the samples were quantified in a blinded fashion using chemiluminescence and enzyme-linked immunosorbent assay, respectively. In normal weight healthy volunteers, NO(x)(-) and cGMP concentrations were consistently increased over the pericardium meridian (PC) 4-7 compared with nonmeridian areas. NO(x)(-) concentration is enhanced over the bladder meridian (BL) 56-57, but cGMP level is similar between the regions. In overweight/obese subjects, NO(x)(-) contents were increased or tended to be elevated over PC and BL regions. cGMP is paradoxically decreased over PC acupoints and nonmeridian control on the forearm but the decreases were blunted along BL regions on the leg. Nitrotyrosine concentrations are markedly elevated (five- to sixfold) over both PC and BL in all areas of overweight/obese subjects. This is the first evidence showing that nitrotyrosine level is tremendously elevated over skin accompanied by paradoxical changes in nitric oxide (NO)-cGMP concentrations over PC skin region in overweight/obese subject. The results suggest that NO-related oxidant inflammation is systemically enhanced while cGMP generation is impaired over PC skin region but not over BL region in obesity.

Effect of dietary protamine on lipid metabolism in rats

Protamine has been widely used as a pharmaceutical product and natural food preservative. However, few studies have been conducted to assess the beneficial function of dietary protamine. This study examined the effects of dietary salmon protamine on serum and liver lipid levels and the expression levels of genes encoding proteins involved in lipid homeostasis in the liver of rats. Groups of male Wistar rats were fed AIN93G diet containing 2% or 5% protamine. After 4 weeks of feeding these diets, markedly decreased serum and liver cholesterol (CHOL) and triacylglycerol levels were noted. Increased activity of liver carnitine palmitoyltransferase-2 and acyl-CoA oxidase, which are key enzymes of fatty acid β-oxidation in the mitochondria and peroxisomes, was found in rats fed on protamine. Furthermore, rats fed protamine showed enhanced fecal excretion of CHOL and bile acid and increased liver mRNA expression levels of ATP-binding cassette (ABC) G5 and ABCG8, which form heterodimers and play a major role in the secretion of CHOL into bile. The decrease in triacylglycerol levels in protamine-fed rats was due to the enhancement of liver β-oxidation. Furthermore, rats fed protamine exhibited decreased CHOL levels through the suppression of CHOL and bile acid absorption and the enhancement of CHOL secretion into bile. These results suggest that dietary protamine has beneficial effects that may aid in the prevention of lifestyle-related diseases such as hyperlipidemia and atherosclerosis.

Beneficial effects of L-arginine on reducing obesity: potential mechanisms and important implications for human health

Over the past 20 years, growing interest in the biochemistry, nutrition, and pharmacology of L-arginine has led to extensive studies to explore its nutritional and therapeutic roles in treating and preventing human metabolic disorders. Emerging evidence shows that dietary L-arginine supplementation reduces adiposity in genetically obese rats, diet-induced obese rats, finishing pigs, and obese human subjects with Type-2 diabetes mellitus. The mechanisms responsible for the beneficial effects of L-arginine are likely complex, but ultimately involve altering the balance of energy intake and expenditure in favor of fat loss or reduced growth of white adipose tissue. Recent studies indicate that L-arginine supplementation stimulates mitochondrial biogenesis and brown adipose tissue development possibly through the enhanced synthesis of cell-signaling molecules (e.g., nitric oxide, carbon monoxide, polyamines, cGMP, and cAMP) as well as the increased expression of genes that promote whole-body oxidation of energy substrates (e.g., glucose and fatty acids) Thus, L-arginine holds great promise as a safe and cost-effective nutrient to reduce adiposity, increase muscle mass, and improve the metabolic profile in animals and humans.

Endothelial nitric oxide synthase (eNOS) knockout mice have defective mitochondrial beta-oxidation

OBJECTIVE

Recent observations indicate that the delivery of nitric oxide by endothelial nitric oxide synthase (eNOS) is not only critical for metabolic homeostasis, but could also be important for mitochondrial biogenesis, a key organelle for free fatty acid (FFA) oxidation and energy production. Because mice deficient for the gene of eNOS (eNOS(-/-)) have increased triglycerides and FFA levels, in addition to hypertension and insulin resistance, we hypothesized that these knockout mice may have decreased energy expenditure and defective beta-oxidation.

RESEARCH DESIGN AND METHODS

Several markers of mitochondrial activity were assessed in C57BL/6J wild-type or eNOS(-/-) mice including the energy expenditure and oxygen consumption by indirect calorimetry, in vitro beta-oxidation in isolated mitochondria from skeletal muscle, and expression of genes involved in fatty acid oxidation.

RESULTS

eNOS(-/-) mice had markedly lower energy expenditure (-10%, P < 0.05) and oxygen consumption (-15%, P < 0.05) than control mice. This was associated with a roughly 30% decrease of the mitochondria content (P < 0.05) and, most importantly, with mitochondrial dysfunction, as evidenced by a markedly lower beta-oxidation of subsarcolemmal mitochondria in skeletal muscle (-30%, P < 0.05). Finally, impaired mitochondrial beta-oxidation was associated with a significant increase of the intramyocellular lipid content (30%, P < 0.05) in gastrocnemius muscle.

CONCLUSIONS

These data indicate that elevated FFA and triglyceride in eNOS(-/-) mice result in defective mitochondrial beta-oxidation in muscle cells.

Hepatic morphological alterations, glycogen content and cytochrome P450 activities in rats treated chronically with N(omega)-nitro-L-arginine methyl ester (L-NAME)

Chronic treatment of rats with N(omega)-nitro-L-arginine methyl ester (L-NAME), an inhibitor of nitric oxide (NO) biosynthesis, results in hypertension mediated partly by enhanced angiotensin-I-converting enzyme (ACE) activity. We examined the influence of L-NAME on rat liver morphology, on hepatic glycogen, cholesterol, and triglyceride content, and on the activities of the cytochrome P450 isoforms CYP1A1/2, CYP2B1/2, CYP2C11, and CYP2E1. Male Wistar rats were treated with L-NAME (20 mg/rat per day via drinking water) for 2, 4, and 8 weeks, and their livers were then removed for analysis. Enzymatic induction was produced by treating rats with phenobarbital (to induce CYP2B1/2), beta-naphthoflavone (to induce CYP1A1/2), or pyrazole (to induce CYP2E1). L-NAME significantly elevated blood pressure; this was reversed by concomitant treatment with enalapril (ACE inhibitor) or losartan (angiotensin II AT(1) receptor antagonist). L-NAME caused vascular hypertrophy in hepatic arteries, with perivascular and interstitial fibrosis involving collagen deposition. Hepatic glycogen content also significantly increased. L-NAME did not affect fasting glucose levels but significantly reduced insulin levels and increased the insulin sensitivity of rats, based on an intraperitoneal glucose tolerance test. Immunoblotting experiments indicated enhanced phosphorylation of protein kinase B and of glycogen synthase kinase 3. All these changes were reversed by concomitant treatment with enalapril or losartan. L-NAME had no effect on hepatic cholesterol or triglyceride content or on the basal or drug-induced activities and protein expression of the cytochrome P450 isoforms. Thus, the chronic inhibition of NO biosynthesis produced hepatic morphological alterations and changes in glycogen metabolism mediated by the renin-angiotensin system. The increase in hepatic glycogen content probably resulted from enhanced glycogen synthase activity following the inhibition of glycogen synthase kinase 3 by phosphorylation.

Regulatory role for the arginine–nitric oxide pathway in metabolism of energy substrates

Nitric oxide (NO) is synthesized from L-arginine by NO synthase in virtually all cell types. Emerging evidence shows that NO regulates the metabolism of glucose, fatty acids and amino acids in mammals. As an oxidant, pathological levels of NO inhibit nearly all enzyme-catalyzed reactions through protein oxidation. However, as a signaling molecule, physiological levels of NO stimulate glucose uptake as well as glucose and fatty acid oxidation in skeletal muscle, heart, liver and adipose tissue; inhibit the synthesis of glucose, glycogen, and fat in target tissues (e.g., liver and adipose); and enhance lipolysis in adipocytes. Thus, an inhibition of NO synthesis causes hyperlipidemia and fat accretion in rats, whereas dietary arginine supplementation reduces fat mass in diabetic fatty rats. The putative underlying mechanisms may involve multiple cyclic guanosine-3',5'-monophosphate-dependent pathways. First, NO stimulates the phosphorylation of adenosine-3',5'-monophosphate-activated protein kinase, resulting in (1) a decreased level of malonyl-CoA via inhibition of acetyl-CoA carboxylase and activation of malonyl-CoA decarboxylase and (2) a decreased expression of genes related to lipogenesis and gluconeogenesis (glycerol-3-phosphate acyltransferase, sterol regulatory element binding protein-1c and phosphoenolpyruvate carboxykinase). Second, NO increases the phosphorylation of hormone-sensitive lipase and perilipins, leading to the translocation of the lipase to the neutral lipid droplets and, hence, the stimulation of lipolysis. Third, NO activates expression of peroxisome proliferator-activated receptor-gamma coactivator-1alpha, thereby enhancing mitochondrial biogenesis and oxidative phosphorylation. Fourth, NO increases blood flow to insulin-sensitive tissues, promoting substrate uptake and product removal via the circulation. Modulation of the arginine-NO pathway through dietary supplementation with L-arginine or L-citrulline may aid in the prevention and treatment of the metabolic syndrome in obese humans and companion animals, and in reducing unfavorable fat mass in animals of agricultural importance.

Identification and characterization of a small molecule AMPK activator that treats key components of type 2 diabetes and the metabolic syndrome

AMP-activated protein kinase (AMPK) is a key sensor and regulator of intracellular and whole-body energy metabolism. We have identified a thienopyridone family of AMPK activators. A-769662 directly stimulated partially purified rat liver AMPK (EC50 = 0.8 microM) and inhibited fatty acid synthesis in primary rat hepatocytes (IC50 = 3.2 microM). Short-term treatment of normal Sprague Dawley rats with A-769662 decreased liver malonyl CoA levels and the respiratory exchange ratio, VCO2/VO2, indicating an increased rate of whole-body fatty acid oxidation. Treatment of ob/ob mice with 30 mg/kg b.i.d. A-769662 decreased hepatic expression of PEPCK, G6Pase, and FAS, lowered plasma glucose by 40%, reduced body weight gain and significantly decreased both plasma and liver triglyceride levels. These results demonstrate that small molecule-mediated activation of AMPK in vivo is feasible and represents a promising approach for the treatment of type 2 diabetes and the metabolic syndrome.

cGMP may have trophic effects on beta cell function comparable to those of cAMP, implying a role for high-dose biotin in prevention/treatment of diabetes

Incretin hormones have trophic effects on beta cell function that can aid prevention and treatment of diabetes. cAMP is the primary mediator of these effects, and has been shown to potentiate glucose-stimulated insulin secretion, promote proper beta cells differentiation by increasing expression of the crucial transcription factor PDX-1, and prevent beta cell apoptosis. cGMP's role in beta cell function has received far less scrutiny, but there is emerging evidence that it may have a trophic impact on beta cell function analogous to that of cAMP. An increase in plasma glucose boosts beta cell production of cGMP, which acts as a feed-forward mediator to enhance glucose-stimulated insulin secretion. cGMP also has an anti-apoptotic effect in beta cells, and there is now indirect evidence that it promotes expression of PDX-1. Supraphysiological concentrations of biotin can directly activate guanylate cyclase, and there is limited evidence that high intakes of this vitamin can be therapeutically beneficial in diabetics and in rodent models of diabetes. Beneficial effects of cGMP on muscle insulin sensitivity and on control of hepatic glucose output may contribute to biotin's utility in diabetes. The fact that nitric oxide/cGMP exert a range of favorable effects on vascular health should further encourage exploration of biotin's preventive and therapeutic potential. If an appropriate high-dose biotin regimen could achieve a modest systemic increase in guanylate cyclase activity, without entailing unacceptable side effects or risks, such a regimen might have considerable potential for promoting vascular health and preventing or managing diabetes.

Lack of association between polymorphism of the human cyclic GMP-dependent protein kinase gene and obesity

OBJECTIVE

To investigate whether genetic variation in the cyclic GMP-dependent protein kinase gene (PRKG1) is associated with obesity.

METHODS

The study included 143 individuals from New York City area, NY, USA. The subjects were sampled on the basis of body mass index (BMI): obese (BMI ranging from 33.8 to 89.5 kg/m(2)), and nonobese (BMI ranging from 16.0 to 29.4 kg/m(2)). The association between C2276T polymorphism in PRKG1 gene and obesity was tested using linear regression analysis.

RESULTS

BMI levels were predicted by linear regression models adjusted for demographic factors. An analysis was performed twice: in individuals of all ethnic backgrounds and in European-Americans only. In both cases, genotype did not have a significant effect.

CONCLUSION

We found no evidence that the C2276T polymorphism in the PKRG1 gene is associated with obesity.

Desensitization of cyclic GMP-mediated regulation of fatty acid metabolism in hepatocytes from ethanol-fed rats

The mechanisms by which ethanol causes accumulation of hepatic triacylglycerols are complex. It has been proposed that nitric oxide/cyclic GMP signaling pathway may be involved in regulation of fatty acid metabolism in the liver. Here, we investigated if this mechanism may have a role in adaptation to ethanol consumption. Hepatocytes were isolated from rats fed with an ethanol-containing liquid diet and pair-fed control rats, and incubated with a range of concentrations of 8-bromo-cyclic GMP. In both types of cells, this cyclic GMP analog inhibited in parallel fatty acid synthesis de novo and acetyl-CoA carboxylase activity. Addition of 8-bromo-cyclic GMP also decreased the rate of palmitate esterification to triacylglycerols and phospholipids, whereas palmitate oxidation was increased. However, in all these metabolic effects, hepatocytes from ethanol-fed rats were significantly less sensitive to the addition of 8-bromo-cyclic GMP. In order to know if this may be a more general mechanism of adaptation to ethanol, we also studied the effects on glucose metabolism. Similarly, hepatocytes from ethanol-fed rats showed a decreased sensitivity in the inhibition by 8-bromo-cyclic GMP of glycogen synthesis, fatty acid synthesis and the synthesis of glycerol backbone of hepatic triacylglycerols. These data suggest that ethanol consumption induces a desensitization of the regulatory effects mediated by cyclic GMP in fatty acid metabolism, contributing to triacylglycerol accumulation in the liver.

Dietary L-arginine supplementation reduces fat mass in Zucker diabetic fatty rats

This study was conducted to test the hypothesis that dietary supplementation of arginine, the physiologic precursor of nitric oxide (NO), reduces fat mass in the Zucker diabetic fatty (ZDF) rat, a genetically obese animal model of type-II diabetes mellitus. Male ZDF rats, 9 wk old, were pair-fed Purina 5008 diet and received drinking water containing arginine-HCl (1.51%) or alanine (2.55%, isonitrogenous control) for 10 wk. Serum concentrations of arginine and NO(x) (oxidation products of NO) were 261 and 70% higher, respectively, in arginine-supplemented rats than in control rats. The body weights of arginine-treated rats were 6, 10, and 16% lower at wk 4, 7, and 10 after the treatment initiation, respectively, compared with control rats. Arginine supplementation reduced the weight of abdominal (retroperitoneal) and epididymal adipose tissues (45 and 25%, respectively) as well as serum concentrations of glucose (25%), triglycerides (23%), FFA (27%), homocysteine (26%), dimethylarginines (18-21%), and leptin (32%). The arginine treatment enhanced NO production (71-85%), lipolysis (22-24%), and the oxidation of glucose (34-36%) and octanoate (40-43%) in abdominal and epididymal adipose tissues. Results of the microarray analysis indicated that arginine supplementation increased adipose tissue expression of key genes responsible for fatty acid and glucose oxidation: NO synthase-1 (145%), heme oxygenase-3 (789%), AMP-activated protein kinase (123%), and peroxisome proliferator-activated receptor gamma coactivator-1alpha (500%). The induction of these genes was verified by real-time RT-PCR analysis. In sum, arginine treatment may provide a potentially novel and useful means to enhance NO synthesis and reduce fat mass in obese subjects with type-II diabetes mellitus.

The role of the carnitine system in human metabolism

Metabolism cycles daily between the fed and fasted states. The pathways of energy production are reversible and distinct. In the anabolic (fed) state, the liver stores glucose as glycogen, and fatty acid/triglyceride synthesis is active. In the catabolic (fasted) state, the liver becomes a glucose producer, lipogenesis is slowed, and fatty acid oxidation/ketogenesis is activated. The rate-limiting step for the latter is vested in the carnitine/carnitine palmitoyltransferase (CPT) system, and the off/on regulator of this is malonyl CoA. The AMP-induced protein kinase primarily determines the concentration of malonyl CoA. Four other systems have significant influence: two on fatty acid oxidation and two on lipogenesis. Peroxisome proliferator-activated receptor gamma-1 alpha, a master regulator of metabolism, induces hepatic gluconeogenesis and fatty acid oxidation in the catabolic phase. Deficiency of stearoyl CoA desaturase, although having no role in gluconeogenesis, powerfully induces fatty acid oxidation and weight loss despite increased food intake in rodents. Major stimulators of lipogenesis are carbohydrate-responsive element binding protein and the Insig system. The malonyl CoA-regulated CPT system has been firmly established in humans. The other systems have not yet been confirmed in humans, but likely are active there as well. Activation of fatty acid oxidation has considerable clinical promise for the treatment of obesity, type 2 diabetes, steatohepatitis, and lipotoxic damage to the heart.

5-HT induces duodenal mucosal bicarbonate secretion via cAMP- and Ca2+-dependent signaling pathways and 5-HT4 receptors in mice

In previous studies, we have found that 5-hydroxytryptamine (5-HT) is a potent stimulant of duodenal mucosal bicarbonate secretion (DMBS) in mice. The aim of the present study was to determine the intracellular signaling pathways and 5-HT receptor subtypes involved in 5-HT-induced DMBS. Bicarbonate secretion by murine duodenal mucosa was examined in vitro in Ussing chambers. 5-HT receptor involvement in DMBS was inferred from pharmacological studies by using selective 5-HT receptor antagonists and agonists. The expression of 5-HT(4) receptor mRNA in duodenal mucosa and epithelial cells was analyzed by RT-PCR. cAMP-dependent signaling pathway inhibitors MDL-12330A, Rp-cAMP, and H-89 and Ca(2+)-dependent signaling pathway inhibitors verapamil and W-13 markedly reduced 5-HT-stimulated duodenal bicarbonate secretion and short-circuit current (I(sc)), whereas cGMP-dependent signaling pathway inhibitors NS-2028 and KT-5823 failed to alter these responses. Both SB-204070 and high-dose ICS-205930 (selective 5-HT(4) receptor antagonists) markedly inhibited 5-HT-stimulated bicarbonate secretion and I(sc), whereas methiothepine (5-HT(1) receptor antagonist), ketanserin (5-HT(2) receptor antagonist), and a low concentration of ICS-205930 (5-HT(3) receptor antagonist) had no effect. RS-67506 (partial 5-HT(4) receptor agonist) concentration-dependently increased bicarbonate secretion and I(sc), whereas 5-carboxamidotryptamine (5-HT(1) receptor agonist), alpha-methyl-5-HT (5-HT(2) receptor agonist), and phenylbiguanide (5-HT(3) receptor agonist) did not significantly increase bicarbonate secretion or I(sc). RT-PCR analysis confirmed the expression of 5-HT(4) receptor mRNA in murine duodenal mucosa and epithelial cells. These results demonstrate that 5-HT regulates DMBS via both cAMP- and Ca(2+)-dependent signaling pathways and 5-HT(4) receptors located in the duodenal mucosa and/or epithelial cells.