Hereditary angioedema (HAE) is a very rare and potentially life-threatening genetic disease characterized by low levels of C1-INH inhibitor esterase and involving recurrent attacks of non-pruritic angioedema that do not leave subcutaneous or mucosal wells without the presence of hives. It occurs worldwide in 1 in 50,000 to 150,000 individuals and accounts for approximately 2% of clinical angioedema. It affects both sexes equally and can affect all races without ethnic differences. Methods: We conducted a review in Pubmed regarding this disease using keywords such as: hereditary angioedema, guideline, treatment, prophylaxis, management. Results: We analysed 195 articles and we focused our study on 17 reviews about type I of HAE published in English in the last 10 years. Conclusions: Screening among the family members of affected individuals (even if symptoms are absent) is mandatory, since it is a life-threatening condition. Moreover, advances in diagnosis and management have significantly improved the outcomes and quality of life of patients with hereditary angioedema.

Angiotensin-converting enzyme (ACE) inhibitors are used primarily in the treatment of hypertension, heart failure, and in the acute phase of myocardial infarction. Lisinopril [N2-[(1S)-1-car-boxy-3-phenylpropyl]-L-lysyl-L-proline], enalapril [(S)-1-[N-[1-(ethoxycarbonyl)-3-phenylpropyl]-L-alanyl]-L-proline] and ramipril [2-aza-bicyclo-[3.3.0]-octane-3-carboxylic acid] are all five-membered heterocycles and three of the most prevalent ACE inhibitors in clinical use worldwide. ACEi-induced angioedema (ACEi-AE) is clinically characterized by self-limited edema of the dermis and subcutaneous lipid tissue, localized on face skin, oral mucosa and tongue in most cases. However, severe episodes of intestinal AE misdiagnosed as acute appendicitis and laryngeal AE requiring incubation have been reported. The pathophysiology of ACEi induced-AE is attributed to the accumulation of bradykinin, which is a potent vasodilator with proinflammatory activity that is normally degraded by angiotensin-converting enzyme (ACE) and aminopeptidase P; however, a small proportion of treated patients is affected. Given that patients do not respond to anti-H1 antihistamines and steroids, the early clinical recognition and the ACEi discontinuation are the treatment of choice for the long term management of ACEi-AE.

Hymenoptera allergens are the main triggers for anaphylaxis in susceptible dogs and humans. Hymenoptera venom specific immunotherapy (VIT), the only disease-modifying treatment, has the potential to prevent future life-threatening reactions in human patients. Prospective clinical data on VIT efficacy in dogs are currently lacking. Therefore, the aim of this study was to show that VIT is not only safe but also efficacious in preventing anaphylaxis in dogs allergic to Hymenoptera. This uncontrolled prospective clinical trial included 10 client-owned dogs with a history of anaphylaxis following repeated Hymenoptera stings. The sensitization to bee and wasp allergens was demonstrated by intradermal testing (IDT) and allergen-specific IgE serology. For VIT induction (induction phase), dogs received a shortened rush immunotherapy protocol with aqueous allergens, which was then followed by monthly injections of 100 g of alum-precipitated allergen (maintenance phase). VIT efficacy was determined by observing patients’ clinical reactions to re-stings. No systemic adverse events were seen during the induction and maintenance phase. From the seven re-stung dogs, only one developed a mild angioedema at the site of the sting; the remaining dogs were asymptomatic. These results show that VIT represents a safe and effective treatment option for Hymenoptera-allergic dogs.

Most striking observations in COVID-19 patients are the hints on pulmonary edema (also seen on CT scans as ground glass opacities), dry cough, fluid restrictions to prevent more severe hypoxia, the huge PEEP that is needed while lungs are compliant, and the fact that anti-inflammatory therapies are not powerful enough to counter the severity of the disease. We propose that the severity of the disease and many deaths are due to a local vascular problem due to activation of B1 receptors on endothelial cells in the lungs. SARS-CoV-2 enters the cell via ACE2, a cell membrane bound molecule with enzymatic activity that next to its role in RAS is needed to inactivate des-Arg⁹ bradykinin, the potent ligand of the bradykinin receptor type 1 (B1). In contrast to bradykinin receptor 2 (B2), the B1 receptor on endothelial cells is upregulated by proinflammatory cytokines. Without ACE2 acting as a guardian to inactivate the ligands of B1, the lung environment is prone for local vascular leakage leading to angioedema. Angioedema is likely a feature already early in disease, and might explain the typical CT scans and the feeling of people that they drown. In some patients, this is followed by a clinical worsening of disease around day 9 due to the formation antibodies directed against the spike (S)-antigen of the corona-virus that binds to ACE2 that could contribute to disease by enhancement of local immune cell influx and proinflammatory cytokines leading to damage. In parallel, inflammation induces more B1 expression, and possibly via antibody-dependent enhancement of viral infection leading to continued ACE2 dysfunction in the lung because of persistence of the virus. In this viewpoint we propose that a bradykinin-dependent local lung angioedema via B1 and B2 receptors is an important feature of COVID-19, resulting in a very high number of ICU admissions. We propose that blocking the B1 and B2 receptors might have an ameliorating effect on disease caused by COVID-19. This kinin-dependent pulmonary edema is resistant to corticosteroids or adrenaline and should be targeted as long as the virus is present. In addition, this pathway might indirectly be responsive to anti-inflammatory agents or neutralizing strategies for the anti-S-antibody induced effects, but by itself is likely to be insufficient to reverse all the pulmonary edema. Moreover, we provide a suggestion of how to ventilate in the ICU in the context of this hypothesis.

Abstract: The kallikrein-kinin system consists of the two kininogen substrates, present in blood plasma, and of two serine proteases, the plasma and tissue kallikreins. The action of the latter on kininogens produce small peptides, the kinins, short lived but endowed by powerful pharmacologic actions on blood vessels and other tissues. Many recent and exciting therapeutic developments in the field are briefly summarized. Notably, various novel strategies are being clinically developed to inhibit the formation of bradykinin or block its receptors in the management of hereditary angioedema. The interventions include orally bioavailable drugs, biotechnological proteins, and gene therapy. These approaches are currently explored in a variety of other inflammatory and thrombotic disorders. Harnessing controlled kinin formation is also of potential therapeutic interest as shown by the clinical development of recombinant tissue kallikrein for ischemic stroke and renal disease. Biomarkers of a kinin-mediated disorders, frequently implicating edemas, include the consumption of kininogen(s), plasma kallikrein activity, and the detection of circulating kinin metabolites such as fragments BK_1-5 and BK_2-9. Novel opportunities to clinically apply the underexploited drugs of the kallikrein-kinin system are briefly reviewed. This personal perspective is offered by an observer of, and a participant in drug characterization during the last 4 decades.