Synthesis and characterization of a new two photon excitable acid sphingomyelinase FRET probe

Development of a versatile optical pH sensor array for discrimination of anti-aging face creams

The certification of cosmetic products has always been a prominent concern. Here, we have developed a pH sensor and applied it in the field of cosmetic safety. Initially, we designed two probes, CH with aggregation-induced emission (AIE) effect and the near-infrared fluorophore derivative CYTYR. By encapsulating them with DSPE-PEG2000-NH2, we obtained the CHCY-lipo nano-micelles with fluorescence resonance energy transfer (FRET) response. By combining them into a sensor array called pC, we achieved sensitive detection of a wide pH range, ranging from 4.69 to 9.25. To validate the performance of the pC sensor array, we employed a multi-channel mode and applied it to differentiate commercial anti-aging creams. Through linear discriminant analysis and 3D fingerprint analysis, the pC sensor array successfully distinguished anti-aging creams from different countries, providing a rapid and accurate method for cosmetic safety identification. The results of this study demonstrate the potential of the pC sensor array for quick authentication of cosmetic products, offering significant support and application prospects in safeguarding consumer health.

Trifunctional sphingomyelin derivatives enable nanoscale resolution of sphingomyelin turnover in physiological and infection processes via expansion microscopy

Sphingomyelin is a key molecule of sphingolipid metabolism, and its enzymatic breakdown is associated with various infectious diseases. Here, we introduce trifunctional sphingomyelin derivatives that enable the visualization of sphingomyelin distribution and sphingomyelinase activity in infection processes. We demonstrate this by determining the activity of a bacterial sphingomyelinase on the plasma membrane of host cells using a combination of Förster resonance energy transfer and expansion microscopy. We further use our trifunctional sphingomyelin probes to visualize their metabolic state during infections with Chlamydia trachomatis and thereby show that chlamydial inclusions primarily contain the cleaved forms of the molecules. Using expansion microscopy, we observe that the proportion of metabolized molecules increases during maturation from reticulate to elementary bodies, indicating different membrane compositions between the two chlamydial developmental forms. Expansion microscopy of trifunctional sphingomyelins thus provides a powerful microscopy tool to analyze sphingomyelin metabolism in cells at nanoscale resolution.

Excellent ratiometric two-photon fluorescent probes for hydrogen sulfide detection based on the fluorescence resonance energy transfer mechanism

Fluorescence resonance energy transfer (FRET) is an important mechanism to design ratiometric fluorescent probes that are able to detect analytes quantitatively according to the ratio of two well-resolved emission signals. Two-photon (TP) fluorescent probes can realize the detection in living cells and tissues with deeper penetration depth, higher resolution, and lower photodamage in contrast to one-photon fluorescent probes. However, to date, fabricating TP-FRET ratiometric fluorescent probes possessing large two-photon absorption (TPA), high fluorescence quantum yield and perfect FRET efficiency is still challenging. Consequently, to develop excellent TP-FRET ratiometric probes and explore the relationship between their molecular structures and TP fluorescence properties, in this paper, we designed a series of H2S-detecting TP fluorescent probes employing the FRET mechanism based on an experimental probe BCD. Thereafter, we comprehensively evaluated the TP sensing performance of these probes by means of time-dependent density functional theory and quadratic response theory. Furthermore, we determined energy transfer efficiency and fluorescence quantum yield. Significantly, through regulating benzene-fused positions, we successfully improved fluorescence quantum yield and TPA cross-section simultaneously. Large spectral overlap between energy donor emission and acceptor absorption was achieved and near perfect energy transfer efficiency was acquired for all the studied probes. We revealed that these probes exhibit two well-resolved TPA bands, which are contributed by FRET donors and acceptors, respectively. Especially, both the wavelengths and the cross-sections of the two TPA bands agree well with those of energy donors and acceptors, which is the unique TPA spectral profile of FRET probes and has never been previously reported. Moreover, we proposed an excellent TP-FRET probe BCD3 and its product molecule BCD3-H2S, which exhibit large Stokes (141 nm and 88 nm) and emission shifts (5931 cm-1), as well as greatly increased TP action cross-sections (24-fold and 60-fold) in the near-infrared region with respect to BCD and BCD-H2S. Our detailed study can give an insight into the efficient design of novel TP-FRET fluorescent probes.

Acid Sphingomyelinase, a Lysosomal and Secretory Phospholipase C, Is Key for Cellular Phospholipid Catabolism

Here, we present the main features of human acid sphingomyelinase (ASM), its biosynthesis, processing and intracellular trafficking, its structure, its broad substrate specificity, and the proposed mode of action at the surface of the phospholipid substrate carrying intraendolysosomal luminal vesicles. In addition, we discuss the complex regulation of its phospholipid cleaving activity by membrane lipids and lipid-binding proteins. The majority of the literature implies that ASM hydrolyses solely sphingomyelin to generate ceramide and ignores its ability to degrade further substrates. Indeed, more than twenty different phospholipids are cleaved by ASM in vitro, including some minor but functionally important phospholipids such as the growth factor ceramide-1-phosphate and the unique lysosomal lysolipid bis(monoacylglycero)phosphate. The inherited ASM deficiency, Niemann-Pick disease type A and B, impairs mainly, but not only, cellular sphingomyelin catabolism, causing a progressive sphingomyelin accumulation, which furthermore triggers a secondary accumulation of lipids (cholesterol, glucosylceramide, GM2) by inhibiting their turnover in late endosomes and lysosomes. However, ASM appears to be involved in a variety of major cellular functions with a regulatory significance for an increasing number of metabolic disorders. The biochemical characteristics of ASM, their potential effect on cellular lipid turnover, as well as a potential impact on physiological processes will be discussed.