An optimized procedure for metabonomic analysis of rat liver tissue using gas chromatography/time-of-flight mass spectrometry

Inhibitory effect of Ginkgo biloba extract on fatty liver: regulation of carnitine palmitoyltransferase 1a and fatty acid metabolism

OBJECTIVE

To investigate the potential effect of Ginkgo biloba extract (GBE) on the prevention and treatment of nonalcoholic fatty liver disease (NAFLD).

METHODS

Male Wistar rats were divided into 4 groups (the control group, GBE group, high-fat diet [HFD] group and HFD + GBE group). The human hepatocellular carcinoma cell line (HepG2) was treated with GBE and its flavonoid ingredients. The fatty acid composition of the rat liver was analyzed with gas chromatography/time-of-flight mass spectrometry (GC/TOFMS). Triglyceride contents of both the rat liver and HepG2 cells were measured by enzymatic colorimetric method. The expressions of fatty acid metabolism-related genes were analyzed with real-time reverse transcription-polymerase chain reaction (RT-PCR). The protein expression and enzymatic activity were subsequently measured.

RESULTS

In rat livers, GBE reduced the elevations of hepatic triglyceride contents caused by HFD and the increased hepatic fatty acids were differentially affected by GBE. Notably, the expression and total activity of the fatty acid β-oxidation rate-limiting enzyme, carnitine palmitoyltransferase 1a (CPT1A), were also promoted with GBE ingestion. In HepG2 cells, GBE and its ingredients, quercetin, kaempferol and isorhamnetin, could decrease the cellular triglyceride content and upregulate the expression and total activity of CPT1A, respectively.

CONCLUSIONS

The triglyceride-lowering effect of GBE on the HFD rat liver is closely associated with the increased expression and activity of CPT1A, and the flavonoid ingredients are the major contributors of GBE.

The metabolic responses to aerial diffusion of essential oils

Anxiety disorders are the most prevalent psychiatric disorders and affect a great number of people worldwide. Essential oils, take effects through inhalation or topical application, are believed to enhance physical, emotional, and spiritual well-being. Although clinical studies suggest that the use of essential oils may have therapeutic potential, evidence for the efficacy of essential oils in treating medical conditions remains poor, with a particular lack of studies employing rigorous analytical methods that capture its identifiable impact on human biology. Here, we report a comprehensive gas chromatography time-of-flight mass spectrometry (GC-TOFMS) based metabonomics study that reveals the aromas-induced metabolic changes and the anxiolytic effect of aromas in elevated plus maze (EPM) induced anxiety model rats. The significant alteration of metabolites in the EPM group was attenuated by aromas treatment, concurrent with the behavioral improvement with significantly increased open arms time and open arms entries. Brain tissue and urinary metabonomic analysis identified a number of altered metabolites in response to aromas intervention. These metabolic changes included the increased carbohydrates and lowered levels of neurotransmitters (tryptophan, serine, glycine, aspartate, tyrosine, cysteine, phenylalanine, hypotaurine, histidine, and asparagine), amino acids, and fatty acids in the brain. Elevated aspartate, carbohydrates (sucrose, maltose, fructose, and glucose), nucleosides and organic acids such as lactate and pyruvate were also observed in the urine. The EPM induced metabolic differences observed in urine or brain tissue was significantly reduced after 10 days of aroma inhalation, as noted with the loss of statistical significance on many of the metabolites in the aroma-EPM group. This study demonstrates, for the first time, that the metabonomics approach can capture the subtle metabolic changes resulting from exposure to essential oils and provide the basis for pinpointing affected pathways in anxiety-related behavior, which will lead to an improved mechanistic understanding of anxiolytic effect of essential oils.

Metabonomic variations associated with AOM-induced precancerous colorectal lesions and resveratrol treatment

Resveratrol (Res), 3,5,4'-trihydroxy-trans-stilbene, is an antioxidant found in the skin of red grapes and in several other plants. This phenolic compound has been recently reported to possess cancer chemopreventive activity that inhibits the process of carcinogenesis. However, the mechanisms underlying its anticancer effects remain largely unresolved. In this study, we investigated the chemoprotective effects of dietary Res in an azoxymethane (AOM) induced precancerous colorectal lesion model in male Wistar rats. The metabolic alterations in urine, sera, and colonic tissues of experimental rats perturbed by AOM intervention as well as the Res treatment were measured by a gas chromatography time-of-flight mass spectrometry (GC-TOFMS) analysis. Significant alterations of metabolites were observed in AOM group in urine, sera, and colonic tissues, which were attenuated by Res treatment and concurrent with the histopathological improvement with significantly decreased aberrant crypt foci (ACF) incidence. Representative metabolites include depleted glucose, β-hydroxybutyrate (ketone body), hypoxanthine, and elevated branched chain amino acids (isoleucine and valine) and tryptophan in colonic tissue, as well as elevated serum aminooxyacetate and urinary 4-hydroxyphenylacetate and xanthurenate. These metabolic changes suggest that the preventive effect of Res is associated with attenuation of impaired glucose and lipid metabolism and elevated protein breakdown in colonic tissues from AOM-exposed rats. It also appears that Res induced significant metabolic alterations independent of the AOM-induced metabolic changes. The significantly altered metabolites identified in Res-AOM group relative to AOM group include arachidonate, linoleate, glutamate, docosahexaenoate, palmitelaidate, 2-aminobutyrate, pyroglutamate, and threonate, all of which are involved in inflammation and oxidation processes. This suggests that Res exerts the chemopreventive effects on ACF formation by anti-inflammatory and antioxidant mechanisms in addition to amelioration of AOM-induced mitochondrial disruption.

Waterborne manganese exposure alters plasma, brain, and liver metabolites accompanied by changes in stereotypic behaviors

Overexposure to waterborne manganese (Mn) is linked with cognitive impairment in children and neurochemical abnormalities in other experimental models. In order to characterize the threshold between Mn-exposure and altered neurochemistry, it is important to identify biomarkers that positively correspond with brain Mn-accumulation. The objective of this study was to identify Mn-induced alterations in plasma, liver, and brain metabolites using liquid/gas chromatography-time of flight-mass spectrometry metabolomic analyses; and to monitor corresponding Mn-induced behavior changes. Weanling Sprague-Dawley rats had access to deionized drinking water either Mn-free or containing 1g Mn/L for 6 weeks. Behaviors were monitored during the sixth week for a continuous 24h period while in a home cage environment using video surveillance. Mn-exposure significantly increased liver, plasma, and brain Mn concentrations compared to control, specifically targeting the globus pallidus (GP). Mn significantly altered 98 metabolites in the brain, liver, and plasma; notably shifting cholesterol and fatty acid metabolism in the brain (increased oleic and palmitic acid; 12.57 and 15.48 fold change (FC), respectively), and liver (increased oleic acid, 14.51 FC; decreased hydroxybutyric acid, -14.29 FC). Additionally, Mn-altered plasma metabolites homogentisic acid, chenodeoxycholic acid, and aspartic acid correlated significantly with GP and striatal Mn. Total distance traveled was significantly increased and positively correlated with Mn-exposure, while nocturnal stereotypic and exploratory behaviors were reduced with Mn-exposure and performed largely during the light cycle compared to unexposed rats. These data provide putative biomarkers for Mn-neurotoxicity and suggest that Mn disrupts the circadian cycle in rats.

Comprehensive quality evaluation of corn steep liquor in 2-keto-L-gulonic acid fermentation

Corn steep liquor (CSL) is one of the main raw materials in 2-keto-L-gulonic acid (2-KLG) fermentation by Ketogulonicigenium vulgare and Bacillus megaterium . Due to its natural origin and variations in the manufacturing process, unpredicted and uncontrolled variability of CSL has a great influence on 2-KLG production; however, conventional quality specifications are not enough to ensure stability of fermentation behaviors. A process analytical technology (PAT) could be considered to explore the relationship between CSL quality and 2-KLG production comprehensively. The compositions of CSL from six manufacturers were profiled by gas chromatography with time-of-flight mass spectrometry (GC-TOFMS) and inductively coupled plasma-atomic emission spectroscopy (ICP-AES), combined with orthogonal partial least-squares discriminant analysis (OPLS-DA). Seventeen components were identified as the most discriminant marker compounds related to 2-KLG production. Results revealed that they were responsible for providing nutrients and protecting osmotic pressure. Furthermore, nine amino acids were verified as potential group markers by addition to the medium and demonstration of the correlation to 2-KLG production. The comprehensive approach provided an important platform to explore CSL marker compounds for quality evaluation in 2-KLG fermentation.

Quantitative metabolomics based on gas chromatography mass spectrometry: status and perspectives

Metabolomics involves the unbiased quantitative and qualitative analysis of the complete set of metabolites present in cells, body fluids and tissues (the metabolome). By analyzing differences between metabolomes using biostatistics (multivariate data analysis; pattern recognition), metabolites relevant to a specific phenotypic characteristic can be identified. However, the reliability of the analytical data is a prerequisite for correct biological interpretation in metabolomics analysis. In this review the challenges in quantitative metabolomics analysis with regards to analytical as well as data preprocessing steps are discussed. Recommendations are given on how to optimize and validate comprehensive silylation-based methods from sample extraction and derivatization up to data preprocessing and how to perform quality control during metabolomics studies. The current state of method validation and data preprocessing methods used in published literature are discussed and a perspective on the future research necessary to obtain accurate quantitative data from comprehensive GC-MS data is provided.

A metabonomic analysis on health effects of drinking water on male mice (Mus musculus)

Health effects of drinking water on the male mice (Mus musculus) were investigated by metabonomics after exposure to the Taihu drinking water for 90 days. Metabonomics data combined with the results of conventional serum biochemistry tests and hepatic histopathology showed that the drinking water induced adverse health effects on the male mice. It was found that the serum levels of pyruvate, glutamine, arginine, lysine, N-acetyl glycoproteins, choline and citrate were significantly decreased in the treatment group. These results indicated that Taihu drinking water may induce damages on mice liver via perturbations of energy metabolism, amino acid metabolism and apoptosis. These observations yielded novel insights regarding the environmental health risk of Taihu drinking water.

Method for liver tissue metabolic profiling study and its application in type 2 diabetic rats based on ultra performance liquid chromatography-mass spectrometry

A protocol for the metabolic profiling of rat liver was developed based on ultra-performance liquid chromatography coupled to quadrupole time-of-flight mass spectrometry (UPLC-Q-TOF/MS) to explore metabolic state directly. Methanol/water (4:1, v:v) was selected as the optimal extraction solvent. The established method was validated with a linearity over the 10-5000 ng/mL for internal standards (IS) and got an average correlation coefficient of 0.9986. The intra-day and inter-day RSD for most endogenous compounds were below 15%. And the absolute recovery of IS was from 84.8% to 109.1%. Liver tissues from diabetic and control rats were enrolled in the subsequent study to show the usefulness of the method. A clear classification between the control and model animals was achieved, some significant metabolites were successfully filtered. These metabolites reflected the abnormal metabolism of diabetic rats. This initial application indicated that the method is suitable and reliable for liver tissue metabolic profiling. It is expected this protocol could also be extended to metabonomic studies of other tissues.

An automated data analysis pipeline for GC-TOF-MS metabonomics studies

Recent technological advances have made it possible to carry out high-throughput metabonomics studies using gas chromatography coupled with time-of-flight mass spectrometry. Large volumes of data are produced from these studies and there is a pressing need for algorithms that can efficiently process and analyze data in a high-throughput fashion as well. We present an Automated Data Analysis Pipeline (ADAP) that has been developed for this purpose. ADAP consists of peak detection, deconvolution, peak alignment, and library search. It allows data to flow seamlessly through the analysis steps without any human intervention and features two novel algorithms in the analysis. Specifically, clustering is successfully applied in deconvolution to resolve coeluting compounds that are very common in complex samples and a two-phase alignment process has been implemented to enhance alignment accuracy. ADAP is written in standard C++ and R and uses parallel computing via Message Passing Interface for fast peak detection and deconvolution. ADAP has been applied to analyze both mixed standards samples and serum samples and identified and quantified metabolites successfully. ADAP is available at http://www.du-lab.org .