Biotin-Labelled Clavulanic Acid to Identify Proteins Target for Haptenation in Serum: Implications in Allergy Studies.

Clavulanic acid (CLV) and amoxicillin, frequently administered in combination, can be independently involved in allergic reactions. Protein haptenation with ß-lactams is considered necessary to activate the immune system. The aim of this study was to assess the suitability of biotinylated analogues of CLV as probes to study protein haptenation by this ß-lactam. Two synthetic approaches afforded the labeling of CLV through esterification of its carboxylic group with a biotin moiety, via either direct binding (CLV-B) or tetraethylenglycol linker (CLV-TEG-B). The second analogue offered advantages as solubility in aqueous solution and potential lower steric hindrance for both intended interactions, with the protein and with avidin. NMR reactivity studies showed that both CLV and CLV-TEG-B reacts through ß-lactam ring opening by aliphatic amino nitrogen, however with different stability of resulting conjugates. Unlike CLV conjugates, that promoted the decomposition of clavulanate fragment, the conjugates obtained with the CLV-TEG-B remained linked, as a whole structure including biotin, to nucleophile and showed a better stability. This was a desired key feature to allow CLV-TEG-B conjugated protein detection at great sensitivity. We have used biotin detection and mass spectrometry (MS) to detect the haptenation of human serum albumin (HSA) and human serum proteins. MS of conjugates showed that HSA could be modified by CLV-TEG-B. Remarkably, HSA preincubation with CLV excess only reduced moderately the incorporation of CLV-TEG-B, which could be attributed to different protein interferences. The CLV-TEG-B fragment with opened ß-lactam was detected bound to the 404-430HSA peptide of the treated protein. Incubation of human serum with CLV-TEG-B resulted in the haptenation of several proteins that were identified by 2D-electrophoresis and peptide mass fingerprinting as HSA, haptoglobin, and heavy and light chains of immunoglobulins. Taken together, our results show that tagged-CLV keeps some of the CLV features. Moreover, although we observe a different behavior in the conjugate stability and in the site of protein modification, the similar reactivity indicates that it could constitute a valuable tool to identify protein targets for haptenation by CLV with high sensitivity to get insights into the activation of the immune system by CLV and mechanisms involved in ß-lactams allergy.

Identification of an antigenic determinant of clavulanic acid responsible for IgE-mediated reactions.

BACKGROUND: Selective reactions to clavulanic acid (CLV) account for around 30% of immediate reactions after administration of amoxicillin-CLV. Currently, no immunoassay is available for detecting specific IgE to CLV, and its specific recognition in patients with immediate reactions has only been demonstrated by basophil activation testing, however with suboptimal sensitivity. The lack of knowledge regarding the structure of the drug that remains bound to proteins (antigenic determinant) is hampering the development of in vitro diagnostics. We aimed to identify the antigenic determinants of CLV as well as to evaluate their specific IgE recognition and potential role for diagnosis. METHODS: Based on complex CLV degradation mechanisms, we hypothesized the formation of two antigenic determinants for CLV, AD-I (N-protein, 3-oxopropanamide) and AD-II (N-protein, 3-aminopropanamide), and designed different synthetic analogs to each one. IgE recognition of these structures was evaluated in basophils from patients with selective reactions to CLV and tolerant subjects. In parallel, the CLV fragments bound to proteins were identified by proteomic approaches. RESULTS: Two synthetic analogs of AD-I were found to activate basophils from allergic patients. This determinant was also detected bound to lysines 195 and 475 of CLV-treated human serum albumin. One of these analogs was able to activate basophils in 59% of patients whereas CLV only in 41%. Combining both results led to an increase in basophil activation in 69% of patients, and only in 12% of controls. CONCLUSION: We have identified AD-I as one CLV antigenic determinant, which is the drug fragment that remains protein-bound.

New Advances in the Study of IgE Drug Recognition.

Allergic drug reactions are currently a major public health problem affecting patient health and increasing healthcare costs. They are caused by interactions between a drug and the human immune system and result in symptoms ranging from urticaria or angioedema to those more serious such as anaphylaxis or anaphylactic shock. The most commonly accepted mechanism for immunological activation is based on the hapten hypothesis. Drugs are low molecular weight substances that cannot cause an immune response on their own. However, they can act as haptens and form covalent adducts with proteins. The resulting hapten-carrier (drug-protein) conjugate can induce the production of IgE antibodies or T cells. An epitope, or antigenic determinant, is the part of the drug-protein antigen that is specifically recognized by the immune system. This may involve not only the drug derivative but also part of the carrier protein. Understanding the way in which drugs are metabolized after protein conjugation is vital in order to make progresses in the diagnosis of clinical allergy. In this review, recent advances in the identification of the chemical structures of antigenic determinants involved in immediate allergic reactions to drugs are presented. We have focused on drugs that most commonly elicit these reactions: betalactam and quinolone antibiotics and the non-steroidal anti-inflamatory drug pyrazolone. This will be discussed from a chemical point of view, relating our understanding of drug structure, chemical reactivity and immune recognition.

Ligand-free Ni-catalyzed reductive cleavage of inert carbon-sulfur bonds.

A catalytic reductive cleavage of C(sp(2))- and C(sp(3))-SMe bonds under ligandless conditions is presented. The method is characterized by its wide scope and high chemoselectivity profile including challenging substrate combinations, allowing the design of orthogonal and site-selectivity approaches.

Ligand-free copper(I)-catalysed intramolecular direct C-H functionalization of azoles.

The first examples of copper-catalysed intramolecular direct C-arylation of azaheterocycles for the synthesis of complex heterofused compounds is presented, featuring an unprecedented arylation via C-H activation of 9H-purine and 4-azabenzimidazole.

Stereoselective synthesis of trans-beta-lactams by palladium-catalysed carbonylation of vinyl aziridines.

The palladium-catalysed carbonylation of vinyl aziridines can give either the trans- or cis-beta-lactam preferentially or even the delta-lactam simply by adjusting the reaction parameters ([Pd], [CO], temperature).