Falsely elevated plasma metanephrine in patients taking midodrine

Plasma metanephrines have become the biochemical test of choice for suspected phaeochromocytomas and paragangliomas in many institutions. We encountered two separate cases of significantly elevated plasma metanephrines in patients taking midodrine, a sympathomimetic drug used in the treatment of severe postural hypotension, in the absence of a diagnosis of phaeochromocytomas and paragangliomas. Upon stopping midodrine treatment, plasma metanephrine concentrations returned to normal in both patients. To explore the hypothesis that midodrine or its metabolite desglymidodrine might interfere with the metanephrines assay, we tested the interaction of midodrine with metanephrine assays from two different centres. High-performance liquid chromatography tandem mass spectrometry on plasma samples and on methanolic extract of midodrine demonstrated co-elution of the metabolite desglymidodrine with metanephrine. We conclude that patients taking midodrine may have falsely elevated plasma metanephrine as a result of analytical interference, and clinicians need to be aware of this problem.

Effects of boiling and in vitro gastrointestinal digestion on the antioxidant activity of Sonchus oleraceus leaves

Leaves of Sonchus oleraceus L. are especially rich in phenolic compounds and have potent extractable antioxidants. However, it is not known how their antioxidant activity changes after cooking and gastrointestinal digestion. We recorded the profile of phenolics and their associated antioxidant activity in both raw and boiled S. oleraceus leaf extracts after in vitro gastric and intestinal digestion, and quantified their antioxidant potentials using Caco-2 and HepG2 cells. Boiling significantly diminished the oxygen radical absorbance capacity (ORAC) and concentrations of ascorbate and chicoric acid in the soluble fractions. In contrast, 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging and concentrations of caftaric and chlorogenic acids were unaffected. Phenolics in the soluble fraction were absorbed into cultured human cells and exerted antioxidant activity. Only chlorogenic acid content remained stable during gastrointestinal digestion. S. oleraceus appears to be an excellent dietary source of phenolic antioxidants.

Influence of postharvest processing and storage conditions on key antioxidants in pūhā (Sonchus oleraceus L.)

OBJECTIVES

To investigate effects of different postharvest drying processes and storage conditions on key antioxidants in Sonchus oleraceus L. leaves.

METHODS

Fresh leaves were oven-dried (60°C), freeze-dried or air-dried (∼25°C) for 6 h, 24 h and 3 days, respectively. Design of experiments (DOE) was applied to study the stability of antioxidants (caftaric, chlorogenic and chicoric acids) in S. oleraceus leaves and leaf extracts stored at different temperatures (4, 25 and 50°C) and relative humidities (15%, 43% and 75%) for 180 days. The concentration of antioxidants was quantified by a HPLC-2,2'-diphenylpicrylhydrazyl post-column derivatisation method. Antioxidant activity was assessed by a cellular antioxidant activity assay.

KEY FINDINGS

The three antioxidants degraded to unquantifiable levels after oven-drying. More than 90% of the antioxidants were retained by freeze-drying and air-drying. Both leaf and extract samples retained >90% of antioxidants, except those stored at 75% relative humidity. Leaf material had higher antioxidant concentrations and greater cellular antioxidant activity than corresponding extract samples.

CONCLUSION

Freeze-drying and air-drying preserved more antioxidants in S. oleraceus than oven-drying. From DOE analysis, humidity plays an important role in degradation of antioxidants during storage. To preserve antioxidant activity, it is preferable to store S. oleraceus as dried leaf material.

Application of an online post-column derivatization HPLC-DPPH assay to detect compounds responsible for antioxidant activity in Sonchus oleraceus L. leaf extracts

Objectives

To use an online assay to identify key antioxidants in Sonchus oleraceus leaf extracts and to investigate the effect of leaf position and extraction conditions on antioxidant concentration and activity.

Methods

Separation of phytochemicals and simultaneous assessment of antioxidant activity were performed online using HPLC and post-column reaction with a free-radical reagent (2, 2-diphenylpicrylhydrazyl, DPPH). Active compounds were identified using nuclear magnetic resonance spectroscopy and mass spectrometry. We applied the online HPLC-DPPH radical assay to evaluate antioxidants in leaves from different positions on the plant and to assess the effect of pre-treatment of leaves with liquid N2 before grinding, extraction time, extraction temperature and method of concentrating extracts.

Key findings

Key antioxidants identified in S. oleraceus leaf extracts were caftaric acid, chlorogenic acid and chicoric acid. Middle leaves contained the highest total amount of the three key antioxidant compounds, consisting mainly of chicoric acid. Pre-treatment with liquid N2, increasing the extraction temperature and time and freeze-drying the extract did not enhance the yield of the key antioxidants.

Conclusion

The online HPLC-DPPH radical assay was validated as a useful screening tool for investigating individual antioxidants in leaf extracts. Optimized extraction conditions were middle leaves pre-treated with liquid N2, extraction at 25°C for 0.5 h and solvent removal by rotary evaporation.

Antioxidant activity of puha (Sonchus oleraceus L.) as assessed by the cellular antioxidant activity (CAA) assay

There is considerable interest in antioxidant dietary components that can be protective against degenerative diseases in humans. Puha (Sonchus oleraceus L.) is a rich source of polyphenols, and exhibits strong antioxidant activity as measured by the 2,2-diphenylpicrylhydrazyl (DPPH) assay. However, the potential of puha to protect against degenerative diseases requires that low molecular weight antioxidants (LMWA) are absorbed by, and active in, human cells. The cellular antioxidant activity (CAA) assay was used to investigate the antioxidant activity of puha leaf extracts. Preparation methods of freezing and freeze-drying reduced the total polyphenolic content compared with fresh puha, but did not affect the LMWA potential as determined by the DPPH assay. The IC(50) values were 0.012 ± 0.003 mg/mL and 0.010 ± 0.005 mg/mL for freeze-dried and fresh puha leaves, respectively. Using the CAA assay, it was shown that LMWAs from foliar extracts of puha were effectively absorbed into HepG2 cells, and exerted antioxidant activity at levels comparable to those of extracts from blueberry fruits, the much-touted antioxidant superfood. Methylene blue staining of HepG2 cells indicated that puha extracts were not cytotoxic at concentrations below 100 mg DW/mL. The data indicate the potential of puha as a nutraceutical supplement for human health.