Sensitive Determination of Domoic Acid Using High-Performance Liquid Chromatography with Electrogenerated Tris(2,2'-bipyridine)ruthenium(III) Chemiluminescence Detection

Analytical approaches for an important shellfish poisoning agent: domoic Acid

Domoic acid (DA), a neurotoxic amino acid produced by some strains of phytoplankton, is responsible for the human toxic syndrome amnesic shellfish poisoning. This exocitotoxin results in neuronal degeneration and necrosis in specific regions of the hippocampus. Because DA accumulates mostly in shellfish, causing outbreaks in different countries, screening for DA has been carried out with various assays. Although bioassays and immunoassays have been developed, several liquid chromatographic methods for the determination of DA in different matrices such as shellfish, algae, or seawater have been reported. Additionally, other alternative methods such as capillary electrophoresis and capillary electrochromatography have been described. This paper summaries the toxicology, the chemistry, and the developed determination methods of DA.

Optimisation of production of a domoic acid-binding scFv antibody fragment in Escherichia coli using molecular chaperones and functional immobilisation on a mesoporous silicate support

Domoic acid is a potent neurotoxin that can lead to amnesic shellfish poisoning in humans through ingestion of contaminated shellfish. We have produced and purified an anti-domoic acid single-chain Fragment variable (scFv) antibody fragment from the Escherichia coli periplasm. Yields of functional protein were increased by up to 100-fold upon co-production of E. coli DnaKJE molecular chaperones but co-overproduction of GroESL led to a reduction in solubility of the scFv. Co-production of the peptidyl-prolyl isomerase trigger factor resulted in accumulation of unprocessed scFv in the E. coli cytoplasm. This was due to an apparent bottleneck in translocation of the cytoplasmic membrane by the recombinant polypeptide. Co-expression of the E. coli disulfide bond isomerase dsbC increased scFv yields by delaying lysis of the host bacterial cells though this effect was not synergistic with molecular chaperone co-production. Meanwhile, use of a cold-shock promoter for protein production led to accumulation of greater amounts of scFv polypeptide which was predominantly in insoluble form and could not be rescued by chaperones. Purification of the scFv was achieved using an optimised metal affinity chromatography procedure and the purified protein bound domoic acid when immobilised on a mesoporous silicate support. The work outlines the potential benefit of applying a molecular chaperone/folding catalyst screening approach to improve antibody fragment production for applications such as sensor development.

Highly sensitive and simple method for measurement of pipecolic acid using reverse-phase ion-pair high performance liquid chromatography with tris(2,2′-bipyridine)ruthenium(III) chemiluminescence detection

A new, highly sensitive chemiluminescence method for measurement of pipecolic acid in various substances such as human serum, cow's milk, beer, and apple juice has been developed. The method is based on reverse-phase ion-pair high performance liquid chromatographic separation and subsequent tris(2,2'-bipyridine)ruthenium(III) chemiluminescence detection. It was confirmed that imino acids show strong chemiluminescence upon mixing with tris(2,2'-bipyridine)ruthenium(III). A calibration graph, based on a standard pipecolic acid solution, was linear over the range 5.0x10(-9)M to 2.0x10(-5)M and the detection limit was 24fmol (signal-to-noise ratio=3). This highly sensitive and selective determination method can be applied to selected samples without purification or pre-concentration procedures. Compared to the previous HPLC methods, the proposed method is easier, more sensitive, and time-saving.

Determination of domoic acid by on-line coupled capillary isotachophoresis with capillary zone electrophoresis

An on-line coupled capillary isotachophoresis--capillary zone electrophoresis (cITP-CZE) method for the determination of domoic acid in shellfish and algae is described. The optimised cITP-CZE electrolyte system was 10 mM HCl + 20 mM beta-alanine (BALA) + 0.05% hydroxyethylcellulose (leading electrolyte), 5 mM caproic acid (terminating electrolyte) and 20 mM caproic acid + 20 mM BALA + 0.1% HPMC (background electrolyte). A clear separation of the domoic acid from the other components of methanolic sample extract was achieved within 25 min. Method characteristics, i.e., linearity (0-200 microg/l), accuracy (recovery 101+/-3%), intra-assay repeatability (2.4%) and detection limit (1.5 microg/l) were determined. Speed of analysis, low laboriousness, high sensitivity and low running cost are the typical attributes of the cITP-CZE method. Developed method was successfully applied to analysis of shellfish samples and food supplements containing algae extract.

Tris(2,2'-bipyridyl)ruthenium(II) chemiluminescence

This paper critically reviews analytical applications of the chemiluminescence from tris(2,2'-bipyridyl)ruthenium(II) and related compounds published in the open literature between mid-1998 and October 2005. Following the introduction, which summarises the reaction chemistry and reagent generation, the review divides into three major sections that focus on: (i) the techniques that utilise this type of detection chemistry, (ii) the range of analytes that can be determined, and (iii) analogues and derivatives of tris(2,2'-bipyridyl)ruthenium(II).

Cloning, expression and characterisation of a single-chain Fv antibody fragment against domoic acid in Escherichia coli

Domoic acid is a potent neuroexcitatory toxin that causes amnesic shellfish poisoning in humans through ingestion of contaminated shellfish. The variable regions of the heavy chain (V(H)) and light chain (V(L)) of an antibody specific for domoic acid were cloned from a mouse hybridoma cell line and used to construct single-chain antibody fragments (scFvs) in a variety of formats. V(H)-linker-V(L) scFvs were expressed better in Escherichia coli than the V(L)-linker-V(H) format, while use of the commonly used (Gly4Ser)3 inter-domain linker resulted in higher yields than a longer (Gly4Ser)6 linker variant. Higher soluble protein yields were achieved in E. coli TOP 10 than in E. coli XL1-Blue cells and co-production of the E. coli disulfide bond isomerase enzyme DsbC allowed higher cell densities to be attained during scFv production, leading to increased yields of recombinant protein. The purified scFv exhibited binding similar to the parent monoclonal antibody and is being used to develop an immunosensor to detect domoic acid in contaminated shellfish samples.