The mechanism of histamine binding to heparin

Could Histamine H1 Receptor Antagonists Be Used for Treating COVID-19?

COVID-19 has rapidly become a pandemic worldwide, causing extensive and long-term health issues. There is an urgent need to identify therapies that limit SARS-CoV-2 infection and improve the outcome of COVID-19 patients. Unbalanced lung inflammation is a common feature in severe COVID-19 patients; therefore, reducing lung inflammation can undoubtedly benefit the clinical manifestations. Histamine H1 receptor (H1 receptor) antagonists are widely prescribed medications to treat allergic diseases, while recently it has emerged that they show significant promise as anti-SARS-CoV-2 agents. Here, we briefly summarize the novel use of H1 receptor antagonists in combating SARS-CoV-2 infection. We also describe the potential antiviral mechanisms of H1 receptor antagonists on SARS-CoV-2. Finally, the opportunities and challenges of the use of H1 receptor antagonists in managing COVID-19 are discussed.

Very low density lipoproteins (VLDL) trigger the release of histamine from human basophils

Circulating basophils are well established sources of the granule-associated mediator, histamine. The physiological control, however, of histamine release from human basophils is poorly understood. Because histamine may play a role in the transendothelial transport of various compounds, including very low density lipoprotein (VLDL) and its hydrolysis products, we investigated the possibility that VLDL regulates mediator release from basophils. The incubation of VLDL (at physiological concentrations) with basophils (isolated as mixed leukocyte preparations) resulted in a significant release of histamine. Histamine release was dependent on VLDL concentration (half-maximal stimulation occurring at VLDL-protein concentration of 15-20 micrograms/ml), length of incubation (half-maximal release at 5-12 min), temperature (37 degrees C optimum) and required calcium (concentration 0.5-2.0 mM). Furthermore, VLDL-induced histamine release was inhibited by three different mediator-release inhibitors: dimaprit, dibutyryl cAMP and nordihydroguaiaretic acid. Incubation of basophils with LDL or HDL under the same experimental conditions did not result in significant histamine release from basophils. The histamine-secretory response of basophils obtained from different donors varied considerably. Basophils isolated from 28 donors and challenged with 100 micrograms/ml VLDL released 23 +/- 5% of their cellular histamine (mean +/- S.E.; with a range of 0-94%). Desensitization of VLDL-induced histamine release could be accomplished by preincubation of basophils with either VLDL or anti-IgE but not with N-formyl-L-methionyl-L-leucyl-L-phenylalanine. Through the secretion of histamine, a potent vasoactive mediator (and also possibly through granule-associated glycosaminoglycans, stimulants of the enzyme lipoprotein lipase), this novel effect of VLDL may be part of a physiological loop for the regulation of VLDL hydrolysis and lipid transport. This effect of VLDL may also have deleterious consequences, because of the atherogenic properties of histamine.