Broadening the substrate scope of strictosidine synthases by site-directed mutagenesis

The condensation of ß-arylethylamines with carbonyl compounds (Pictet-Spengler reaction) is employed in the synthesis of tetrahydro-β-carboline and isoquinoline scaffolds which are common motifs in many naturally occurring alkaloids. These compounds exhibit a range of biological activities and are thus interesting targets for organic synthesis and medicinal chemistry. Nature’s equivalent to the Pictet-Spengler reaction is catalyzed by the so called Pictet-Spenglerases. Within this class of enzymes, strictosidine synthases (STRs, EC 4.3.3.2) have attracted attention [1-4]. These enzymes catalyse the formation of the 1,2,3,4-tetrahydro-β-carboline (S)-strictosidine, a key intermediate in the monoterpenoid indole alkaloid biosynthetic pathway in higher plants. Please click Additional Files below to see the full abstract

Inverted binding of non-natural substrates in strictosidine synthase leads to a switch of stereochemical outcome in enzyme-catalyzed Pictet-Spengler reactions

The Pictet-Spengler reaction is a valuable route to 1,2,3,4-tetrahydro-Β-carboline (THBC) and isoquinoline scaffolds found in many important pharmaceuticals. Strictosidine synthase (STR), catalyzes the Pictet-Spengler condensation of tryptamine and the aldehyde secologanin to give (S)-strictosidine as a key intermediate in indole alkaloid biosynthesis. STRs also accept shortchain aliphatic aldehydes to give enantioenriched alkaloid products with up to 99% e.e. STRs are thus valuable asymmetric organocatalysts for applications in organic synthesis. The STR catalysis of reactions of small aldehydes gives an unexpected switch in stereopreference, leading to formation of the (R)-products. Here we report a rationale for the formation of the (R)-configured products by the STR enzyme from Ophiorrhiza pumila (OpSTR) using a combination of X-ray crystallography, mutational and molecular dynamics (MD) studies. We discovered that short chain aldehydes bind in an inverted fashion compared to secologanin leading to the inverted stereopreference for the observed (R)-product in those cases. The study demonstrates that the same catalyst can have two different productive binding modes for one substrate – but give different absolute configuration of the products by binding the aldehyde substrate differently. These results will guide future engineering of STRs and related enzymes for biocatalytic applications

The emergence of new biologics for severe asthma

Patients with severe asthma experience severe symptoms and frequent exacerbations despite intensive treatment with inhaled and oral glucocorticoids. Biologics for severe asthma aim to reduce asthma-related and glucocorticoid-induced morbidity. Recently, new biologics targeting interleukin (IL)-5, IL-5 receptor and IL-4/IL-13, which are all cytokines involved in so-called type 2 airway inflammation, were approved for severe asthma. They show a reduction in exacerbation rate and an oral glucocorticoid-sparing effect. Studies with upstream biologics targeting alarmin cytokines such as thymic stromal lymphopoietin (TSLP) and IL-33 are underway, and newly designed bispecific antibodies targeting more than one pathway are in early phases of development. Such pathway-targeted add-on treatments will soon become standard of care for all patients with severe asthma

Long-Term Therapy Response to Anti–IL-5 Biologics in Severe Asthma—A Real-Life Evaluation

Background: Patients with severe eosinophilic asthma show different responses to various anti–IL-5 biologics, ranging from super response to nonresponse. Residual disease manifestations observed in partial responders may prompt physicians to switch between biologics. More data on response, switches, and residual disease manifestations are needed to improve personalized treatment. Objective: To assess (1) prevalences and predictors of super, partial, and nonresponders to long-term anti–IL-5 treatment, (2) frequency and reasons for switches between anti–IL-5 biologics, and (3) nature of residual disease manifestations. Methods: In this 2-year follow-up study, patients with severe asthma were included who initiated an anti–IL-5 biologic (mepolizumab, reslizumab, benralizumab) (n = 114). Patient characteristics (clinical, functional, inflammatory) and comorbidities were collected at baseline and 2-year follow-up. “Super responders” showed no residual disease manifestations at 2-year follow-up, “partial responders” experienced residual disease manifestations, and “nonresponders” discontinued anti–IL-5 treatment after less than 2 years because of clinical worsening. Results: After 2-year anti–IL-5 treatment, 14% of patients were super responders, 69% partial responders, and 11% nonresponders. Super response was predicted by shorter asthma duration and higher FEV1, and tended to be associated with adult-onset asthma, absence of nasal polyps, and lower body mass index. Switches between anti–IL-5 biologics occurred frequently (41%). After 2-year treatment, most common residual disease manifestations included impaired lung function (59%), uncontrolled sinonasal disease (58%), and uncontrolled asthma symptoms (48%). Conclusions: After 2 years of anti–IL-5 treatment, a favorable response was found in 83% of patients with severe asthma, including a super response in 14%. Most partial responders show impaired lung function or uncontrolled sinonasal disease, causing physicians to switch between biologics

Processes and pathways of stigmatization and destigmatization over time

This chapter advances a theoretical framework to understand within- and between-country variation in the level of stigmatization experienced by immigrant groups and their descendants over time. Since processes of stigmatization and destigmatization may unfold over generations, it is imperative for research to adopt a longer time horizon to identify the factors that lead to the emergence, persistence, and/or dissipation of stigma. Expanding the time frame of analysis to decades (or even centuries) requires an explicit focus on the experiences of groups rather than individuals. Based on the observation that the labeling of some groups as "migrants" does not always follow from actual histories of immigration, this framework treats "migrant" as a social category. To guide future empirical research, this chapter introduces two analytical models. The first identifies the factors and processes responsible for stigmatization or destigmatization over time. The second presents five ideal-typical pathways that immigrants and their descendants may experience in relation to stigma: non-emergence, increase, reinforcement, reduction, and status reversal.</p