Sources of hepatic glycogen synthesis during an oral glucose tolerance test were evaluated in six healthy subjects by enrichment of a 75-g glucose load with 6.67% [U-(13)C]glucose and 3.33% [U-(2)H(7)]glucose and analysis of plasma glucose and hepatic uridine diphosphate-glucose enrichments (sampled as urinary menthol glucuronide) by (2)H and (13)C nuclear magnetic resonance. The direct pathway contribution, as estimated from the dilution of [U-(13)C]glucose between plasma glucose and glucuronide, was unexpectedly low (36 +/- 5%). With [U-(2)H(7)]glucose, direct pathway estimates based on the dilution of position 3 (2)H-enrichment between plasma glucose and glucuronide were significantly higher (51 +/- 6%, P = 0.05). These differences reflect the exchange of the carbon 4, 5, and 6 moiety of fructose-6-phosphate and glyceraldehyde-3-phosphate catalyzed by transaldolase. As further evidence of this exchange, (2)H-enrichments in glucuronide positions 4 and 5 were inferior to those of position 3. From the difference in glucuronide positions 5 and 3 enrichments, the fraction of direct pathway carbons that experienced transaldolase exchange was estimated at 21 +/- 4%. In conclusion, the direct pathway contributes only half of hepatic glycogen synthesis during an oral glucose tolerance test. Glucose tracers labeled in positions 4, 5, or 6 will give significant underestimates of direct pathway activity because of transaldolase exchange.

Flavonoids in Calligonum polygonoides Linnaeus extract were separated, detected, and identified by reverse‐phase high‐performance liquid chromatography (RP‐HPLC) with electrochemical detection (EC) in combined isocratic and gradient elution using a glassy carbon or a boron doped diamond electrode. Ultrasonication coupled with a microwave‐assisted technique was developed to optimize the extraction of the phenolic compounds. The total antioxidant capacity was quantified using the DPPH. method and voltammetry. The RP‐HPLC‐EC led to the detection of nine different flavonoids: catechin, delphinidin, fisetin, myricetin, epicatechin, kuromanin, rutin, callistephin and procyanidin A2, in a single run by direct injection of the sample extract solution.

No abstract

Flavonoids are natural phenolic derivatives that, in low concentration, can provide health benefits by preventing biomolecules (proteins, nucleic acids, lipids, sugars) oxidative damage through free radical mediated reactions. The flavonoids, in selected Mediterranean seasonal fruits: apricot, sour cherry, plum, pomegranate, date, prickly pear (cactus fruit), and nectarine, by RP‐HPLC, coupled with photodiode array and electrochemical detectors, after microwave‐ultrasound assisted extraction, using flavonoid standards, were detected. The total antioxidant capacity in the lyophilized fruit extracts, by differential pulse voltammetry, (electrochemical index‐EI), integrated peak area, and chronoamperometry, was evaluated. In the lyophilized fruit extracts, and the catechin standard, the free radical scavenger efficient concentration (EC50), using DPPH. assay, was determined.

The electrochemical behaviour of temozolomide on a glassy carbon electrode has been investigated. The reduction of temozolomide is an irreversible process, pH dependent, and the mechanism involves the addition of one electron and one proton to C5 to form an anion radical, causing the irreversible breakdown of the tetrazinone ring. The oxidation mechanism of temozolomide is an irreversible, adsorption-controlled process, pH dependent up to value close to the pK a and occurs in two consecutive charge transfer reactions, with the formation of the hydroxylated product. The electroanalytical determination of TMZ led to a detection limit of 1.1 mM.