Photoactivatable Xanthone (PaX) Dyes Enable Quantitative, Dual Color, and Live-Cell MINFLUX Nanoscopy

The single-molecule localization concept MINFLUX has triggered a reevaluation of the features of fluorophores for attaining nanometer-scale resolution. MINFLUX nanoscopy benefits from temporally controlled fluorescence ("on"/"off") photoswitching. Combined with an irreversible switching behavior, the localization process is expected to turn highly efficient and quantitative data analysis simple. The potential in the recently reported photoactivable xanthone (PaX) dyes is recognized to extend the list of molecular switches used for MINFLUX with 561 nm excitation beyond the fluorescent protein mMaple. The MINFLUX localization success rates of PaX560 , PaX+560, and mMaple are quantitatively compared by analyzing the effective labeling efficiency of endogenously tagged nuclear pore complexes. The PaX dyes prove to be superior to mMaple and on par with the best reversible molecular switches routinely used in single-molecule localization microscopy. Moreover, the rationally designed PaX595 is introduced for complementing PaX560 in dual color 561 nm MINFLUX imaging based on spectral classification and the deterministic, irreversible, and additive-independent nature of PaX photoactivation is showcased in fast live-cell MINFLUX imaging. The PaX dyes meet the demands of MINFLUX for a robust readout of each label position and fill the void of reliable fluorophores dedicated to 561 nm MINFLUX imaging.

Accelerated MINFLUX Nanoscopy, through Spontaneously Fast-Blinking Fluorophores

The introduction of MINFLUX nanoscopy allows single molecules to be localized with one nanometer precision in as little as one millisecond. However, current applications have so far focused on increasing this precision by optimizing photon collection, rather than minimizing the localization time. Concurrently, commonly used fluorescent switches are specifically designed for stochastic methods (e.g., STORM), optimized for a high photon yield and rather long on-times (tens of milliseconds). Here, accelerated MINFLUX nanoscopy with up to a 30-fold gain in localization speed is presented. The improvement is attained by designing spontaneously blinking fluorescent markers with remarkably fast on-times, down to 1-3 ms, matching the iterative localization process used in a MINFLUX microscope. This design utilizes a silicon rhodamine amide core, shifting the spirocyclization equilibrium toward an uncharged closed form at physiological conditions and imparting intact live cell permeability, modified with a fused (benzo)thiophene spirolactam fragment. The best candidate for MINFLUX microscopy (also suitable for STORM imaging) is selected through detailed characterization of the blinking behavior of single fluorophores, bound to different protein tags. Finally, optimization of the localization routines, customized to the fast blinking times, renders a significant speed improvement on a commercial MINFLUX microscope.

Peri-interventional ischemic stroke after coronary angiography: a large-scale nationwide cohort analysis from 2006 to 2020

Background

Ischemic stroke after coronary angiography is a life-threatening complication, leading to high mortality and long-term sequelae in surviving patients. Contemporary data from a European nationwide perspective are however lacking.

Purpose

We aimed to investigate the incidence, temporal trends, and outcome of ischemic stroke complicating coronary angiography in a German nationwide cohort.

Methods

A retrospective analysis of healthcare records from 2006–2020 based on ICD-10 and OPS codes obtained from the German Federal Statistical Office was carried out. Patients ≥18 years of age hospitalized for coronary angiography (both diagnostic and percutaneous interventions) were included in this analysis. Ischemic stroke events as well as co-morbidities were identified using ICD-10 and OPS codes. The outcome of interest was in-hospital mortality. Multivariable logistic regressions were computed for the association of ischemic stroke with in-hospital mortality adjusting for age, gender, hypertension, hyperlipoproteinemia, and diabetes mellitus.

Results

Overall 5,098,751 cases of patients undergoing coronary angiography (mean age 68.7±11.4 years; 28.0% female) between 2006 and 2020 were included. Ischemic stroke occurred in 3,808 (0.07%) patients. In comparison, individuals who suffered from peri-interventional ischemic stroke were older (70.8±11.1 vs. 68.7±11.4; p<0.001), more likely female (33.4% vs. 27.9%; p<0.001), and differed significantly according to their clinical characteristics (see Table 1). Patients with ischemic stroke had a significantly longer in-hospital stay (18.3±15.5 vs. 6.4±8.0 days; p<0.001), and higher rates of in-hospital mortality (18.0% vs. 3.2%; p<0.001) compared to patients without ischemic stroke. After multivariable adjustment, ischemic stroke remained independently associated with a higher risk of in-hospital mortality with an Odds ratio of 6.5 (95% Confidence Interval: 5.9, 7.1; p<0.001). Also, incidence of peri-interventional stroke increased gradually from 0.03% in 2006 to 0.12% in 2020 (see Figure 1).

Conclusion

In a contemporary nationwide cohort of patients hospitalized for coronary angiography spanning 15 years, the incidence of ischemic stroke remained low, although a gradual increase from 2006 to 2020 was documented. The occurrence of ischemic stroke was independently associated with a markedly increased risk of in-hospital mortality. These findings might be helpful in evaluating patients undergoing coronary angiography and to reduce the high mortality and morbidity associated with this complication in future.

Funding Acknowledgement

Type of funding sources: None.

A general design of caging-group-free photoactivatable fluorophores for live-cell nanoscopy

The controlled switching of fluorophores between non-fluorescent and fluorescent states is central to every super-resolution fluorescence microscopy (nanoscopy) technique, and the exploration of radically new switching mechanisms remains critical to boosting the performance of established, as well as emerging super-resolution methods. Photoactivatable dyes offer substantial improvements to many of these techniques, but often rely on photolabile protecting groups that limit their applications. Here we describe a general method to transform 3,6-diaminoxanthones into caging-group-free photoactivatable fluorophores. These photoactivatable xanthones (PaX) assemble rapidly and cleanly into highly fluorescent, photo- and chemically stable pyronine dyes upon irradiation with light. The strategy is extendable to carbon- and silicon-bridged xanthone analogues, yielding a family of photoactivatable labels spanning much of the visible spectrum. Our results demonstrate the versatility and utility of PaX dyes in fixed and live-cell labelling for conventional microscopy, as well as the coordinate-stochastic and deterministic nanoscopies STED, PALM and MINFLUX.

The design of photoactivatable fluorophores—which are required for some super-resolution fluorescence microscopy methods—usually relies on light-sensitive protecting groups imparting lipophilicity and generating reactive by-products. Now, it has been shown that by exploiting a unique intramolecular photocyclization, bright and highly photostable fluorophores can be rapidly generated in situ from appropriately substituted 1-alkenyl-3,6-diaminoxanthone precursors.