1H-NMR spectroscopy of biofluids and the investigation of xenobiotic-induced changes in liver biochemistry

Salivary Metabolomics: From Diagnostic Biomarker Discovery to Investigating Biological Function

Metabolomic profiling of biofluids, e.g., urine, plasma, has generated vast and ever-increasing amounts of knowledge over the last few decades. Paradoxically, metabolomic analysis of saliva, the most readily-available human biofluid, has lagged. This review explores the history of saliva-based metabolomics and summarizes current knowledge of salivary metabolomics. Current applications of salivary metabolomics have largely focused on diagnostic biomarker discovery and the diagnostic value of the current literature base is explored. There is also a small, albeit promising, literature base concerning the use of salivary metabolomics in monitoring athletic performance. Functional roles of salivary metabolites remain largely unexplored. Areas of emerging knowledge include the role of oral host-microbiome interactions in shaping the salivary metabolite profile and the potential roles of salivary metabolites in oral physiology, e.g., in taste perception. Discussion of future research directions describes the need to begin acquiring a greater knowledge of the function of salivary metabolites, a current research direction in the field of the gut metabolome. The role of saliva as an easily obtainable, information-rich fluid that could complement other gastrointestinal fluids in the exploration of the gut metabolome is emphasized.

Metabolic profiling of the rat liver after chronic ingestion of alpha-naphthylisothiocyanate using in vivo and ex vivo magnetic resonance spectroscopy

Certain human diseases affecting the biliary tree can be modeled in rats by ingestion of the hepatobiliary toxin alpha-naphthylisothiocyanate (ANIT). Phosphorus magnetic resonance spectroscopy (MRS) allows the noninvasive monitoring of cell dynamics through detection of phosphodiesters (PDE) and phosphomonoesters (PME). Hepatic (31)P MRS techniques were therefore used to study the toxic effects of low-dose chronic ANIT ingestion, with a view toward providing biomarkers sensitive to hepatobiliary dysfunction and cholestatic liver injury. Rats were fed an ANIT supplemented diet at three doses (ANIT_0.05%, ANIT_0.04%, and ANIT_0.025%) for 2 weeks. Data from in vivo MRS were compared with results from pair-fed controls (PFCs). Blood and tissue samples were collected at 2 weeks for clinical chemistry, histology, and (1)H magic angle spinning MRS. Increases in PDE, relative to total phosphorus (tPh), were detected in both the ANIT_0.05% and ANIT_0.04% groups (0.07 ± 0.01 and 0.08 ± 0.01, respectively) relative to PFC groups (0.03 ± 0.01 and 0.05 ± 0.01, respectively). An increase in PME/tPh was observed in the ANIT_0.05% group only (0.17 ± 0.02) relative to PFC_0.05% (0.12 ± 0.01). Ex vivo (1)H MRS findings supported this, wherein measured phosphocholines (PCs) were increased in ANIT_0.05% and ANIT_0.04% groups. Increases in relative total choline (tCho) distinguished the ANIT_0.05% group from the ANIT_0.04% group. Markers of hepatotoxicity such as raised total bilirubin and alkaline phosphatase were found at all ANIT doses. Histological findings included a dose-related increase in both severity of biliary hyperplasia and focal hepatocellular necrosis. Here, we found that ANIT-induced moderate hepatobiliary dysfunction was associated with a relative increase in phosphodiesters in vivo and PCs ex vivo. Raised PME/tPh in vivo and tCho ex vivo were also present at high doses corresponding to a higher incidence of marked biliary hyperplasia and moderate hepatocellular necrosis.

Hepatotoxin-induced hypertyrosinemia and its toxicological significance

A (1)H Nuclear Magnetic Resonance (NMR) spectroscopic investigation of the effects of single doses of four model hepatotoxins on male Sprague-Dawley rats showed that hypertyrosinemia was induced by three of the treatments (ethionine 300 mg/kg, galactosamine hydrochloride 800 mg/kg and isoniazid 400 mg/kg) but not by the fourth (thioacetamide 200 mg/kg). Concomitant histopathological and clinical chemistry analyses showed that hypertyrosinemia could occur with or without substantial hepatic damage and that substantial hepatic damage could occur without hypertyrosinemia. However, in the rats dosed with galactosamine hydrochloride, which showed highly variable amounts of liver damage at ca. 24 h after dosing, a clear relationship was found between the degree of hypertyrosinemia and the extent of the hepatic necrosis induced. In line with the cause of clinically observed Type II Tyrosinemia, we consider that the critical event in the onset of hepatotoxin-induced hypertyrosinemia is likely to be a reduction in hepatic tyrosine aminotransferase (TAT) activity. We discuss mechanisms by which TAT activity could be lost with special consideration given to pyridoxal 5'-phosphate (P5P) depletion and to the inhibition of protein synthesis. This analysis may have implications for the interpretation of clinical measures of liver status such as Fischer's ratio and the branched-chain tyrosine ratio (BTR).

An hypothesis for a mechanism underlying hepatotoxin-induced hypercreatinuria

As part of a wider metabonomic investigation into the early detection and discrimination of site-specific hepatotoxicity, male Sprague-Dawley rats were dosed with the model hepatotoxins allyl formate, ethionine and alpha-naphthylisothiocyanate (ANIT). Urine samples collected pre- and post-dose were examined by (1)H nuclear magnetic resonance (NMR) spectroscopy and the toxin-induced changes in urinary taurine and creatine excretion were quantified. Hypertaurinuria and hypercreatinuria were observed following allyl formate dosing, hypertaurinuria with no change in creatine excretion was observed after ethionine dosing, and hypotaurinuria and hypercreatinuria were observed after ANIT dosing. These changes are indicative of different effects on liver and it has been previously suggested that some hepatotoxin-induced changes in urinary taurine excretion may be due to altered hepatic cysteine utilisation. A related hypothesis is now presented that would explain the selective hypercreatinuria in terms of increased cysteine synthesis.

Optimisation of collection, storage and preparation of rat plasma for 1H NMR spectroscopic analysis in toxicology studies to determine inherent variation in biochemical profiles

Biofluid 1H NMR spectroscopy has been assessed as a tool for toxicological investigations for almost two decades, with most studies focussing on urinary changes. This study has examined variations in the 1H NMR spectroscopy spectra of plasma collected from control rats at different times of the day. The collection, preparation and storage of samples were optimised and potential sources of variation in samples taken for toxicology studies identified. Plasma samples were collected into heparinised containers and analysed following a standard dilution with D(2)O. The value of deproteinising plasma with acetonitrile to look at low molecular weight metabolites has also been assessed. Variations in lactate and citrate levels in whole blood plasma were found and are consistent with the observation that lactate is one of the most variable metabolites in human plasma. Lipids levels also varied, in particular higher levels of lipids were found in spectra from male rats compared to female rats, and in samples collected in the morning following the feeding period. No significant changes were identified in samples which were snap-frozen and stored for up to 9 months at -80 degrees C. More changes were observed after storage at 4 degrees C or room temperature, including an increase in glycerol and choline levels, which may have resulted from lipid hydrolysis.

Diagnosis of a case of acute chloroquine poisoning using 1H NMR spectroscopy: characterisation of drug metabolites in urine

Analysis of biological fluids by proton nuclear magnetic resonance spectroscopy (1H NMR) is a promising tool in clinical biology. We have used this method for a rapid toxicological screening in the case of a suicide attempt. A urine sample was analysed at 300 and 600 MHz by 1D and 2D sequences (J-resolved and TOCSY) in a short experimental time. Quantification was realized by peak integration of the 1D spectrum. The results showed the presence of chloroquine and its major metabolite monodesethylchloroquine at concentrations of 462 and 140 mg/L, respectively. Ethanol was also detected in the spectrum. It can be concluded that 1H NMR provides many advantages as a tool for clinical diagnosis in a case of acute intoxication.

Raised transaminase activity of blood plasma from rats with experimentally-induced kidney damage detected by spin-echo 1H-NMR spectroscopy

We report the application of spin-echo 1H-NMR spectroscopy to the detection of raised plasma transaminase activity in rats treated with the nephrotoxic cephalosporin antibiotic cephaloridine (CPH). Spin-echo 1H-NMR analysis of lyophilized plasma, reconstituted in H2O reveals a doublet at delta 1.48 for alanine. However when samples were reconstituted with 2H2O we noted that in samples from CPH-treated rats (but not in control samples) there was a variable degree of appearance of a singlet at delta 1.47 together with a reduction in the doublet at delta 1.48. We suggest that this is due to the release of transaminases from damaged tissue which, via a reversible conversion of alanine to pyruvate, causes selective deuteration of alanine at the alpha-hydrogen (alpha-CH) position. This observation suggests that these 1H-NMR spectral patterns are dependent on the level of plasma transaminases and this may provide a novel indicator of tissue damage.