Enzymatic cycling assay for D-carnitine determination

CMOS-compatible biosensor for L-carnitine detection

A CMOS-compatible ISFET with a Ta₂O₅ sensitive surface was developed. The structure was optimized for achieving high sensitivity using a subthreshold operation mode and by reducing the influence of the capacitances on the value of subthreshold swing. The developed ISFET was used as a basis for a biosensor for L-carnitine detection. To this end, carnitine acetyltransferase was immobilized on the ISFET sensitive surface. The immobilized enzyme was active (0.082 U/g _{model plate}). The complete microsystem, consisting of a packaged chip, an immobilized enzyme and a microfluidic channel, detected L-carnitine at a range of 0.2-100 μM with a LOD of 0.2 μM. The biosensor response was linear in the range of 0.2-50 μM of L-carnitine with sensitivity 18.0 ± 1.7 mV/μM. An experiment with artificial urine containing 1.3 μM L-carnitine showed that the proposed biosensor could be used on a real sample. Therefore, a new sensor specially optimized for biosensing CMOS-compatible ISFET structures and direct determination of L-carnitine with immobilized carnitine acetyltransferase was developed.

Incidence of carnitine deficiency in patients with cancer pain: A pilot study

Carnitine deficiency is reportedly associated with increased pain sensation in diabetes mellitus and fibromyalgia, but the association between serum carnitine concentration and cancer pain has not been fully elucidated. We investigated the incidence of carnitine deficiency in patients with cancer pain, and examined the effect of the patients' demographic and clinical characteristics on pain intensity and carnitine deficiency. The serum carnitine concentration was measured in 50 patients with cancer pain receiving non-steroidal anti-inflammatory drugs, but not opioids. Multivariate regression analysis was used to determine the association of carnitine concentration, pain intensity, age and gender with hemoglobin and C-reactive protein (CRP) concentrations. Carnitine deficiency was detected in 9 of the patients (18.0%) and found to be significantly correlated with an elevated CRP concentration (P=0.039). In conclusion, although there does not appear to be an association between carnitine deficiency and cancer pain, it may be affected by inflammation or infection.

Quantitative analysis of the dynamic signaling pathway involved in the cAMP mediated induction of l-carnitine biosynthesis in E. coli cultures

L-(-)-carnitine can be synthesized from waste bioprecursors in the form of crotonobetaine. Such biotransformation is carried out in E. coli by the enzymes encoded by operons regulated by the cAMP receptor proteins. Non-phosphorylated sugars, such as glycerol are used as energy and carbon source since glucose inhibits cAMP synthesis. Until now little attention has been paid to the regulatory signaling structure that operates during the transition from a glucose-consuming, non-l-carnitine producing steady state, to a glycerol-consuming l-carnitine producing steady state. In this work we aim to elucidate and quantify the underlying regulatory mechanisms operating in the abolition of the glucose inhibiting effect. For this purpose we make use of the systemic approach by integrating the available information and our own experimentally generated data to construct a mathematical model. The model is built using power-law representation and is used as a platform to make predictive simulations and to assess the consistency of the regulatory structure of the overall process. The model is subsequently checked for quality through stability and a special, dynamic sensitivity analysis. The results show that the model is able to deal with the observed system transient phase. The model is multi-hierarchical, comprising the metabolic, gene expression, signaling and bioreactor levels. It involves variables and parameters of a very different nature that develop in different time scales and orders of magnitude. Some of the most relevant conclusions obtained are: (i) the regulatory interactions among glucose, glycerol and cAMP metabolism are far stronger than those present in the l-carnitine transport, production and degradation processes; (ii) carnitine biosynthesis is very sensitive to the cAMP signaling system since it reacts at very low cAMP receptor concentrations, and (iii) ATP is a critical factor in the transient dynamics. All these model-derived observations have been experimentally confirmed by separate studies. As a whole, the model contributes to our general understanding of the transient regulation through the signal regulatory structure, thus enabling more accurate optimization strategies to be used.

Determination of l-carnitine in food supplement formulations using ion-pair chromatography with indirect conductimetric detection

A novel method for the determination of L-carnitine in food supplement formulations was developed and validated, using ion-pair chromatography with indirect conductimetric detection. The chromatographic method was based on a non-polar (C18) column and an aqueous octanesulfonate (0.64 mM) eluent, acidified with trifluoroacetic acid (5.2 mM). The retention time was 5.4 min and the asymmetry factor 0.65. A linear calibration curve from 10 to 1000 microg/ml (r= 0.99998), with a detection limit of 2.7 microg/ml (25 microl injection volume), a repeatability %RSD of 0.8 (40 microg/ml, n = 5) and reproducibility %RSD of 2.6 were achieved. The proposed method was applied for the determination of carnitine in oral solutions and capsules. No interference from excipients was found and the only pretreatment step required was the appropriate dilution with the mobile phase. Recovery from spiked samples was ranged from 97.7 to 99.7% with a precision (%RSD, n = 3) of 0.01-2.1%.

Cytokinin oxidase/cytokinin dehydrogenase assay: optimized procedures and applications

Spectrophotometric methods for determining the activity of cytokinin oxidase/cytokinin dehydrogenase (EC 1.5.99.12) were developed and optimized. A sensitive end-point method based on a combination of the electron acceptor 2,6-dichlorophenolindophenol and Schiff base formation of the reaction product with 4-aminophenol under acidic conditions can be applied to crude cell and tissue extracts. The assay was also adapted for other substrates than N6-(2-isopentenyl)adenine, such as zeatin and the aromatic cytokinins, although an enzyme which degrades the latter compounds has not yet been identified. The second novel method is an initial rate method based on the coupled redox reaction of phenazine methosulfate and 3-(4,5-dimethylthiazol-2-yl)-2,5- diphenyltetrazolium bromide resulting in the formation of a formazan dye. This method can be used for kinetic studies with purified enzyme and is entirely substrate independent.