Binding of omeprazole to protein targets identified by monoclonal antibodies.

Omeprazole is the most commonly used proton pump inhibitor (PPI), a class of medications whose therapeutic mechanism of action involves formation of a disulfide linkage to cysteine residues in the H+/K+ ATPase pump on gastric secretory cells. Covalent linkage between the sole sulfur group of omeprazole and selected cysteine residues of the pump protein results in inhibition of acid secretion in the stomach, an effect that ameliorates gastroesophageal reflux and peptic ulcer disease. PPIs, though useful for specific conditions when used transiently, are associated with diverse untoward effects when used long term. The mechanisms underlying these potential off-target effects remain unclear. PPIs may, in fact, interact with non-canonical target proteins (non-pump molecules) resulting in unexpected pathophysiological effects, but few studies describe off-target PPI binding. Here, we describe successful cloning of monoclonal antibodies against protein-bound omeprazole. We developed and used monoclonal antibodies to characterize the protein target range of omeprazole, stability of omeprazole-bound proteins, and the involvement of cysteines in binding of omeprazole to targets. We demonstrate that a wide range of diverse proteins are targeted by omeprazole. Protein complexes, detected by Western blotting, are resistant to heat, detergents, and reducing agents. Reaction of omeprazole occurs with cysteine-free proteins, is not fully inhibited by cysteine alkylation, occurs at neutral pH, and induces protein multimerization. At least two other clinically used PPIs, rabeprazole and tenatoprazole, are capable of binding to proteins in a similar fashion. We conclude that omeprazole binds to multiple proteins and is capable of forming highly stable complexes that are not dependent on disulfide linkages between the drug and protein targets. Further studies made possible by these antibodies may shed light on whether PPI-protein complexes underlie off-target untoward effects of chronic PPI use.

The Basophil Activation Test Can Be of Value for Diagnosing Immediate Allergic Reactions to Omeprazole.

BACKGROUND: Proton pump inhibitors (PPIs) are commonly used to treat gastrointestinal diseases. Incidence of hypersensitivity reactions to PPIs has risen, likely because of increased consumption. Their diagnosis is difficult, with skin tests (STs) presenting low sensitivity, making it necessary to perform drug provocation tests (DPTs). The value of in vitro tests for the diagnosis of immediate reaction to PPI is unclear. OBJECTIVE: To analyze the diagnostic value of the basophil activation test (BAT) in a group of patients diagnosed with immediate allergy to omeprazole. METHODS: The study included 42 patients with confirmed immediate allergic reactions to omeprazole confirmed by positive ST results or DPT results and 22 age- and sex-matched subjects tolerant to PPIs. BAT was performed with omeprazole, pantoprazole, and lansoprazole using CD63 and CD203c as activation markers. RESULTS: ST sensitivity was 66.7% with a specificity of 100%. BAT using CD63 with a stimulation index of more than 2 as positive revealed a sensitivity of 73.8%, a specificity of 100%, a positive predictive value of 100%, and a negative predictive value of 66.7%. BAT was positive in 57.1% of patients with negative ST result, and thus by combining ST and BAT we can correctly diagnose 85.7% of patients with immediate allergy to omeprazole. CONCLUSION: BAT represents a complementary tool for inclusion in the allergological workup for patients allergic to omeprazole. When combined with ST, it can be of value to guide the clinician as to whether to perform a DPT.

Study of cross-reactivity between proton pump inhibitors.

Several studies have demonstrated different cross-reactivity patterns between proton pump inhibitors (PPIs). The aim of this study was to investigate cross-reactivity between commercially available PPIs and establish a procedure for performing cutaneous tests for verifying PPI allergy. We performed skin prick and intradermal tests with all commercially available PPIs in 5 patients with clinical allergy to omeprazole and observed positive results in all patients. We report 5 cases of immunoglobulin (Ig) E-mediated allergy to omeprazole and document cross-reactivity by skin testing between all the PPIs studied. We also found that the probability of confirming an IgE-mediated mechanism with skin tests decreases with time. Finally, we propose a hypothesis that could explain the different PPI cross-reactivity patterns reported.

Nine cases of omeprazole allergy: cross-reactivity between proton pump inhibitors.

Although rare, anaphylactic reactions induced by proton pump inhibitors have been reported. The presence of cross-reactivity between different members of the group is not clear. We studied 9 patients with adverse reactions to omeprazole. Clinical symptoms appeared immediately in 8 patients and after 4 hours in 1. Symptoms ranged from urticaria/angioedema in 7 cases to anaphylaxis in 2 cases. Skin prick tests and oral controlled challenge tests with omeprazole, lansoprazole, and pantoprazole were performed. Skin prick or intradermal tests with omeprazole were positive in 8 patients. Four were also positive to pantoprazole. Prick tests with lansoprazole were always negative. Lansoprazole was administered to all 9 patients, with good tolerance in 8. Only 3 patients were challenged with pantoprazole and developed widespread urticaria. We present 9 patients with immunoglobulin E-mediated allergy to omeprazole. In most of our cases, lansoprazole proved to be a good alternative treatment.

A succinct review of the general and immunological pharmacologic effects of proton pump inhibitors.

Proton pump inhibitors (PPI) are a group of anti-ulcer agents. PPI have selective anti-cancer effects via apoptosis of tumour, sensitization of cancer cell to chemotherapy and radiotherapy. Also PPI have anti-malarial and anti-leishmanial activity. Rising of endosomal (P)H inhibits the presentation of antigens that enter cell through endocytosis. PPI can affect transmigration of leucocytes from vessels to inflammatory sites and also can mitigate neutrophile adherence to endothelial cell. PPI increase the intralysosomal (P)H and decrease the expression of intracellular adhesion molecules. Therefore PPI can exert immunomodulation in immunological diseases through hampering antigen processing, antigen presentation, and leucocytes transmigration.