The biogenesis of dicarboxylic acid in rats given hypoglycin

Detection of hypoglycin A and MCPA-carnitine in equine serum and muscle tissue: Optimisation and validation of a LC-MS-based method without derivatisation

BACKGROUND

Measurement of hypoglycin A (HGA) and its toxic metabolite, methylenecyclopropylacetic acid (MCPA), in equine serum confirms a diagnosis of atypical myopathy (AM), a pasture-associated toxic rhabdomyolysis with high mortality linked to the ingestion of Acer trees plant material. Supportive diagnostic tests include plasma acyl-carnitine profiling and urine organic acid testing, but these are not specific for AM. Previously reported HGA and MCPA analytical techniques used liquid chromatography-mass spectrometry (LC-MS) with a derivatising step, but the latter prolongs testing and increases costs.

OBJECTIVES

To develop a rapid LCMS method for detection of serum and tissue HGA and MCPA that enables expedited diagnosis for horses with AM.

STUDY DESIGN

Analytical test validation.

METHODS

Validation parameters to industry standards using as criteria precision, accuracy, linearity, reproducibility and stability in analyte-spiked samples were calculated on 9-calibration points and 3 different validation concentrations in both serum and muscle tissue.

RESULTS

The test was successfully validated for the detection of HGA and MCPA-carnitine in equine serum and muscle. Test linearity was excellent (r²  = .999), accuracy was very good for both analytes (93%-108%), precision did not exceed 10% coefficient of variation and reproducibility met the requirements of the Horwitz equation. Stability was unaffected by storage at a range of temperatures.

MAIN LIMITATIONS

The spectrum of the tested analytes was limited to only two relevant analytes in favour of a quick and easy analysis. Linearity of the muscle method was not evaluated as calibration curves were not produced in this matrix.

CONCLUSION

We report an optimised, simplified and validated method for detection of HGA and MCPA-carnitine in equine serum and muscle suitable for rapid diagnosis of suspected AM cases. The serum-based test should also enable risk assessment of toxin exposure in cograzing horses and assessment of horses with undiagnosed myopathies, while the tissue detection test should help to confirm cases post-mortem and to determine toxin distribution, metabolism and clearance across different tissues.

Evaluation of Pistacia lentiscus fatty oil effects on glycemic index, liver functions and kidney functions of New Zealand rabbits

Pistacia lentiscus fatty oil (PLFO) is a well known natural remedy in eastern Algeria folk medicine. It is widely used in the treatment of respiratory disorders and dermal burns. The present study has been carried out to investigate effects of this oil on fasting glucose and some functional parameters of the liver and kidney in white male New Zealand rabbits (Initial mean weight 1.95 Kg). PLFO was applied to tested rabbits (PLFO group) via rectal route, once daily 5-day per week, for six consecutive weeks at the dose of 1 ml/Kg body weight. The same number of animals (n=6) was not treated and served as control (CRL group). The results showed that PLFO was tolerated by rectal route. No significant differences were observed in body weights of the two groups. Biochemical analysis showed that aspartate transaminase (AST) and alanine transaminase (ALT) were significantly decreased in blood plasma at (P< 0.05) and (P< 0.01) respectively in PLFO group (Mann-Whitney test). On the other hand, the fasting glucose level (GLU) was significantly increased (Mann-Whitney test, P< 0.05), while the rest of the tested parameters (Albumin, total proteins, creatinine, urea) was not significantly affected. However, these variations have not biologic signification toxicity. The study concludes that PLFO is tolerable via rectal route; it is safe with no adverse effect on liver functions and renal functions with possible anti-glycogenesis activity.

Acute biochemical effects of La(NO3)3 on liver and kidney tissues by magic-angle spinning 1H nuclear magnetic resonance spectroscopy and pattern recognition

High-resolution magic-angle spinning (MAS) 1H nuclear magnetic resonance (NMR) spectroscopic and pattern recognition (PR) based methods have been applied to studies on the acute biochemical effects of La(NO3)3 on rats. Male Wistar rats were treated with various doses of La(NO3)3 (2, 10, and 50 mg/kg body weight), and MAS 1H NMR spectra of their intact liver and kidney tissues were analyzed using principal components analysis to extract metabolic information. The biochemical effects of La(NO3)3 were characterized by the increase of triglyceride and bile acid and the decrease of glycogen in liver tissue, together with a slight elevation of triglyceride level in kidney tissue. The target lesion of La(NO3)3 to liver was found by MAS NMR-PR methods. This study illustrated the power of the combination of MAS 1H NMR and pattern recognition for the analysis of biochemical effects of rare earths.

High-resolution (1)H NMR and magic angle spinning NMR spectroscopic investigation of the biochemical effects of 2-bromoethanamine in intact renal and hepatic tissue

The metabolic consequences of xenobiotic-induced toxicity were investigated using high-resolution magic angle spinning (MAS) NMR spectroscopy of intact tissue. Renal papillary necrosis (RPN) was induced in Sprague-Dawley rats (n = 12) via a single i.p. dose of 250 mg/kg 2-bromoethanamine (BEA) hydrobromide. At 2, 4, 6, and 24 h after treatment with BEA, three animals were killed and tissue samples were obtained from liver, renal cortex, and renal medulla. Tissue samples were also removed at 2 and 24 h from matched controls (n = 6). (1)H MAS NMR spectroscopic techniques were used to analyze samples of intact tissue ( approximately 10 mg). Decreased levels of nonperturbing renal osmolytes (glycerophosphocholine, betaine, and myo-inositol) were observed in the renal papilla of BEA-treated animals at 6 and 24 h postdose (p.d.), concomitant with a relative increase in the tissue concentration of creatine. Increased levels of glutaric acid were found in all tissues studied in BEA-treated animals at 4 and 6 h p.d., indicating the inhibition of mitochondrial fatty acyl CoA dehydrogenases and mitochondrial dysfunction. Increased levels of trimethylamine-N-oxide occurred in the renal cortex at 6 h p.d. Changes in the metabolite profile of liver included an increase in the relative concentrations of triglycerides, lysine, and leucine. The novel application of (1)H MAS NMR to the biochemical analysis of intact tissues following a toxic insult highlights the potential of this technique as a toxicological probe in providing a direct link between urinary biomarkers of toxicity and histopathological evaluation of toxicological lesions.

Metabolic pathways in mammalian peroxisomes

This article summarizes our current knowledge of the metabolic pathways present in mammalian peroxisomes. Emphasis is placed on those aspects that are not covered by other articles in this issue: peroxisomal enzyme content and topology; the peroxisomal beta-oxidation system; substrates of peroxisomal beta-oxidation such as very-long-chain fatty acids, branched fatty acids, dicarboxylic fatty acids, prostaglandins and xenobiotics; the role of peroxisomes in the metabolism of purines, polyamines, amino acids, glyoxylate and reactive oxygen products such as hydrogen peroxide, superoxide anions and epoxides.

Biogenesis of dicarboxylic acids in rat liver homogenate studied by 13C labeling

The aim of this investigation is to assess whether long-chain fatty acids can be a substrate for omega-oxidation and the subsequent beta-oxidation to produce medium-chain dicarboxylic acids normally found in urine. Isolated rat liver 10,000 g supernatant and pellet fractions were used as the source of enzymes. The metabolism of palmitate was studied using [1,2,3,4-13C4]hexadecanoic acid as tracer. Selected ion monitoring mass spectrometry was utilized for the determination of isotope enrichments in precursor and products. Palmitate was found to be a good substrate for omega-oxidation; the rate was only slightly slower than decanoate. The beta-oxidation of [1,2,3,4-13C4]hexadecanedioic acid yielded labeled adipic, suberic, and sebacic acids. Isotope distribution in these dicarboxylic acids consisted mostly of unlabeled molecules (M + 0) and molecules labeled with four 13C (M + 4), in agreement with a beta-oxidation initiated equally from both carboxyl ends of the precursor. Significant enrichments (1-8%) with only two 13C labels (M + 2) indicate a partial bidirectional beta-oxidation. The direct metabolic conversion of hexadecanedioate to succinate was documented by the significant enrichment (1.40-1.90%) in M + 4 of succinate. These data indicate that long-chain fatty acids can be a substrate for the production of medium-chain dicarboxylates and the eventual direct conversion to succinate.

Biochemical relationships between Reye's and Reye's-like metabolic and toxicological syndromes

Reye's syndrome is a hepatic encephalopathy with fatty infiltration of the liver and is due to mitochondrial dysfunction. Knowledge of the mechanisms causing Reye's syndrome has been gained from the study of Reye's syndrome-like diseases, including inborn errors of mitochondrial energy production, viral disease and toxicological injury. Entry of fatty acids into mitochondria or beta-oxidation itself may be impaired. Toxins such as hypoglycin, pentanoate, valproate, salicylate, and their metabolites inhibit beta-oxidation pathways and can produce Reye's syndrome-like presentations. Biochemical manifestations of the diverse causes of Reye's syndrome-like disorders are similar and include: hypoglycaemia due to impaired gluconeogenesis, accumulation of fatty acids, fatty acyl CoAs, and acyl carnitines with depletion of free CoA and carnitine. Accumulated products may further injure mitochondria and exacerbate impaired beta-oxidation, uncouple oxidative phosphorylation or increase mitochondrial permeability. Mitochondrial swelling and steatosis of hepatic cells are the histological result. With the advances of biochemical techniques for the study of organic acid excretion patterns, serum fatty acid patterns and identification of enzymatic deficiencies in cells from patients with Reye's syndrome-like presentations, it is clear that Reye's syndrome is, in part, a collection of various inborn errors and toxicological states. Circumstances such as viral disease, prolonged fasting and drugs may precipitate clinical expression of these deficiencies as Reye's syndrome. As work progresses, further causes of Reye's syndrome will be identified.