In vivo lipidomics using single-cell Raman spectroscopy

Prediction of single-cell RNA expression profiles in live cells by Raman microscopy with Raman2RNA

Single-cell RNA sequencing and other profiling assays have helped interrogate cells at unprecedented resolution and scale, but are inherently destructive. Raman microscopy reports on the vibrational energy levels of proteins and metabolites in a label-free and nondestructive manner at subcellular spatial resolution, but it lacks genetic and molecular interpretability. Here we present Raman2RNA (R2R), a method to infer single-cell expression profiles in live cells through label-free hyperspectral Raman microscopy images and domain translation. We predict single-cell RNA sequencing profiles nondestructively from Raman images using either anchor-based integration with single molecule fluorescence in situ hybridization, or anchor-free generation with adversarial autoencoders. R2R outperformed inference from brightfield images (cosine similarities: R2R >0.85 and brightfield <0.15). In reprogramming of mouse fibroblasts into induced pluripotent stem cells, R2R inferred the expression profiles of various cell states. With live-cell tracking of mouse embryonic stem cell differentiation, R2R traced the early emergence of lineage divergence and differentiation trajectories, overcoming discontinuities in expression space. R2R lays a foundation for future exploration of live genomic dynamics.

Tracking trash to treasure: in situ monitoring of single microbial cell oil biosynthesis from waste cooking oil using Raman spectroscopy and imaging

Waste cooking oil is a major pollutant that contaminates terrestrial and aquatic bodies which is generated from household kitchens and eateries. The bioremediation of waste cooking oil (WCO) into microbial oil, also known as single microbial cell oil (SMCO), can be accomplished by oleaginous microbes. Conventional methods excel in SMCO analysis but lack efficacy for in situ or lysis-free monitoring of nascent SMCO synthesis and turnover. To bridge this knowledge gap, this study shows the applicability of Raman reverse stable isotope probing (RrSIP) in monitoring time-dependent nascent SMCO synthesis and assimilation in Yarrowia lipolytica, an oleaginous yeast grown in hydrophilic (glucose) as well as hydrophobic carbon sources (cooking oil and waste cooking oil). This study also combines the RrSIP approach with Raman imaging for temporal visualization of the distribution and turnover dynamics of the SMCO pool in a single cell. Our finding provides a unique perspective utilizing optical spectroscopy methods for lysis-free SMCO analysis and holds potential for prospective utility as an adjunct tool in bioprocess and biofuel industries.

Carotenoids dispersed in gypsum rock as a result of algae adaptation to the extreme conditions of the Atacama Desert

The high-altitude pre-Andean region of the Atacama Desert is characterized by its stark volcanic rock formations and unique hydrothermal gypsum outcrops (gypcrete) that it hosts. This study delves into the biomolecular composition of the endolithic phototrophic microbes that thrive within these gypcretes. Using advanced Raman spectroscopy techniques, including Raman imaging (complemented by microscopic and 3D microscopic observations), herein we unveil new insights into the adaptive strategies of these gypsum-inhabiting algae. Our Raman imaging results provide a detailed chemical map of carotenoids associated with microbial colonization. This map reveals a significant gradient in pigment content, highlighting a critical survival mechanism for algae and cyanobacteria in this polyextreme environment. Intriguingly, we detected signals for carotenoids not only in the algae-colonized layer, but also deeper within the gypsum matrix - indicating pigment migration following cell disruption. In addition, we conducted an in-depth analysis of individual algal cells from the Trebouxiaceae family, noting their color variations from green to orange, plus describing the spectral differences in detail. This investigation identified in-vivo pigments (carotenoids, chlorophyll) and lipids at the cellular level, offering a comprehensive view of the molecular adaptations enabling life in one of the Earth's most extreme habitats.

In Situ Raman Hyperspectral Analysis of Microbial Colonies for Secondary Metabolites Screening

Since the discovery of penicillin, a vast array of microbial antibiotics has been identified and applied in the medical field. Globally, the search for drug candidates via microbial screening is ongoing. Traditional screening methods, however, are time-consuming and require labor-intensive sample processing, significantly reducing throughput. This research introduces a Raman spectroscopy-based screening system tailored to the in situ analysis of microbial colonies on solid culture media. Employing multivariate curve resolution-alternating least-squares (MCR-ALS) for spectral decomposition, our approach reveals the production of secondary metabolites at the single colony level. We enhanced the microbial culture method, enabling direct, high signal-to-noise (S/N) ratio Raman spectroscopic measurements of colonies of Escherichia coli and actinomycetes species. Through semisupervised MCR analysis using the known spectra of actinorhodin and undecylprodigiosin as references, we accurately assessed the production of these compounds by Streptomyces coelicolor A3(2). Furthermore, we herein successfully detected the production of amphotericin B by Streptomyces nodosus, even in the absence of prior spectral information. This demonstrates the potential of our technique in the discovery of secondary metabolites. In addition to enabling the detection of the above-mentioned compounds, this analysis revealed the heterogeneity of the spatial distribution of their production in each colony. Our technique makes a significant contribution to the advancement of microbial screening, offering a rapid, efficient alternative to conventional methods and opening avenues for secondary metabolites discovery.

FABP4 Enhances Lipidic and Fibrotic Cardiac Structural and Ca2+ Dynamic Changes

BACKGROUND

Adipocyte FABP4 (fatty acid-binding protein 4) is augmented in the epicardial stroma of patients with long-standing persistent atrial fibrillation. Because this molecule is released mainly by adipocytes, our objective was to study its role in atrial cardiomyopathy, focusing our attention on fibrosis, metabolism, and electrophysiological changes. These results might clarify the role of adiposity as a mediator of atrial cardiomyopathy.

METHODS

We used several preclinical cellular models, epicardial and subcutaneous stroma primary cell cultures from patients undergoing open heart surgery, human atrial fibroblasts, atrial cardiomyocytes derived from human induced pluripotent stem cells and isolated from adult mice, and Nav1.5 transfected Chinese hamster ovary cells. Fibrosis, glucose, mitochondrial and adipogenesis activity, gene expression, and proteomics were determined by wound healing, enzymatic, colorimetric, fluorescence assays, real-time quantitative polymerase chain reaction, and TripleTOF proteomics. Molecular changes were analyzed by Raman confocal microspectroscopy, calcium dynamics by confocal microscopy, and ion currents by patch clamp. Epicardial, subcutaneous, and atrial fibroblasts and cardiomyocytes were incubated with FABP4 at 100 ng/mL.

RESULTS

Our results showed that FABP4 induced fibrosis, glucose metabolism, and lipid accumulation on epicardial and subcutaneous stroma cells and atrial fibroblasts. Besides, it modified lipid content and calcium dynamics in atrial cardiomyocytes without effects on INa.

CONCLUSIONS

FABP4 exerts fibrotic and metabolic changes on epicardial stroma and modifies lipid content and calcium dynamic on atrial cardiomyocytes. These results suggest its possible role as an atrial cardiomyopathy mediator.

Plant and algal lipidomes: Analysis, composition, and their societal significance

Plants and algae play a crucial role in the earth's ecosystems. Through photosynthesis they convert light energy into chemical energy, capture CO2 and produce oxygen and energy-rich organic compounds. Photosynthetic organisms are primary producers and synthesize the essential omega 3 and omega 6 fatty acids. They have also unique and highly diverse complex lipids, such as glycolipids, phospholipids, triglycerides, sphingolipids and phytosterols, with nutritional and health benefits. Plant and algal lipids are useful in food, feed, nutraceutical, cosmeceutical and pharmaceutical industries but also for green chemistry and bioenergy. The analysis of plant and algal lipidomes represents a significant challenge due to the intricate and diverse nature of their composition, as well as their plasticity under changing environmental conditions. Optimization of analytical tools is crucial for an in-depth exploration of the lipidome of plants and algae. This review highlights how lipidomics analytical tools can be used to establish a complete mapping of plant and algal lipidomes. Acquiring this knowledge will pave the way for the use of plants and algae as sources of tailored lipids for both industrial and environmental applications. This aligns with the main challenges for society, upholding the natural resources of our planet and respecting their limits.

Evaluation of Extraction Techniques for Recovery of Microalgal Lipids under Different Growth Conditions

Microalgal lipids contain a wide array of liposoluble bioactive compounds, but lipid extraction remains a critical limitation for their commercial use. An accelerated solvent extraction (ASE) was used to extract lipids from Chlamydomonas reinhardtii, Arthrospira platensis (Spirulina), and Chlorella vulgaris grown under either standard or nitrogen depletion conditions. Under standard growth conditions, ASE using methanol:chloroform (2:1), methyl tert-butyl ether (MTBE):methanol:water, and ethanol at 100 °C resulted in the highest recovery of total lipids (352 ± 30, 410 ± 32, and 127 ± 15 mg/g biomass from C. reinhardtii, C. vulgaris, and A. platensis, respectively). Similarly, the highest total lipid and triacylglycerols (TAGs) recovery from biomass cultivated under nitrogen depletion conditions was found at 100 °C using methanol:chloroform, for C. reinhardtii (total, 550 ± 21; TAG, 205 ± 2 mg/g biomass) and for C. vulgaris (total, 612 ± 29 mg/g; TAG, 253 ± 7 mg/g biomass). ASE with MTBE:methanol:water at 100 °C yielded similar TAG recovery for C. reinhardtii (159 ± 6 mg/g) and C. vulgaris (200 ± 4 mg/g). Thus, MTBE:methanol:water is suggested as an alternative substitute to replace hazardous solvent mixtures for TAGs extraction with a much lower environmental impact. The extracted microalgal TAGs were rich in palmitic (C16:0), stearic (C18:0), oleic (C18:1,9), linoleic (C18:2n6), and α-linolenic (C18:3n3) acids. Under nitrogen depletion conditions, increased palmitic acid (C16:0) recovery up to 2-fold was recorded from the biomasses of C. reinhardtii and C. vulgaris. This study demonstrates a clear linkage between the extraction conditions applied and total lipid and TAG recovery.

Phospholipidomics in Clinical Trials for Brain Disorders: Advancing our Understanding and Therapeutic Potentials

Phospholipidomics is a specialized branch of lipidomics that focuses on the characterization and quantification of phospholipids. By using sensitive analytical techniques, phospholipidomics enables researchers to better understand the metabolism and activities of phospholipids in brain disorders such as Alzheimer's and Parkinson's diseases. In the brain, identifying specific phospholipid biomarkers can offer valuable insights into the underlying molecular features and biochemistry of these diseases through a variety of sensitive analytical techniques. Phospholipidomics has emerged as a promising tool in clinical studies, with immense potential to advance our knowledge of neurological diseases and enhance diagnosis and treatment options for patients. In the present review paper, we discussed numerous applications of phospholipidomics tools in clinical studies, with a particular focus on the neurological field. By exploring phospholipids' functions in neurological diseases and the potential of phospholipidomics in clinical research, we provided valuable insights that could aid researchers and clinicians in harnessing the full prospective of this innovative practice and improve patient outcomes by providing more potent treatments for neurological diseases.

Probing Chemical Complexity of Amyloid Plaques in Alzheimer's Disease Mice using Hyperspectral Raman Imaging

One of the distinctive pathological features of Alzheimer's disease (AD) is the deposition of amyloid plaques within the brain of affected individuals. These plaques have traditionally been investigated using labeling techniques such as immunohistochemical imaging. However, the use of labeling can disrupt the structural integrity of the molecules being analyzed. Hence, it is imperative to employ label-free imaging methods for noninvasive examination of amyloid deposits in their native form, thereby providing more relevant information pertaining to AD. This study presents compelling evidence that label-free and nondestructive confocal Raman imaging is a highly effective approach for the identification and chemical characterization of amyloid plaques within cortical regions of an arcAβ mouse model of AD. Furthermore, this investigation elucidates how the spatial correlation of Raman signals can be exploited to identify robust Raman marker bands and discern proteins and lipids from amyloid plaques. Finally, this study uncovers the existence of distinct types of amyloid plaques in the arcAβ mouse brain, exhibiting significant disparities in terms of not only shape and size but also molecular composition.

Non-Invasive Detection of Biomolecular Abundance from Fermentative Microorganisms via Raman Spectra Combined with Target Extraction and Multimodel Fitting

Biomolecular abundance detection of fermentation microorganisms is significant for the accurate regulation of fermentation, which is conducive to reducing fermentation costs and improving the yield of target products. However, the development of an accurate analytical method for the detection of biomolecular abundance still faces important challenges. Herein, we present a non-invasive biomolecular abundance detection method based on Raman spectra combined with target extraction and multimodel fitting. The high gain of the eXtreme Gradient Boosting (XGBoost) algorithm was used to extract the characteristic Raman peaks of metabolically active proteins and nucleic acids within E. coli and yeast. The test accuracy for different culture times and cell cycles of E. coli was 94.4% and 98.2%, respectively. Simultaneously, the Gaussian multi-peak fitting algorithm was exploited to calculate peak intensity from mixed peaks, which can improve the accuracy of biomolecular abundance calculations. The accuracy of Gaussian multi-peak fitting was above 0.9, and the results of the analysis of variance (ANOVA) measurements for the lag phase, log phase, and stationary phase of E. coli growth demonstrated highly significant levels, indicating that the intracellular biomolecular abundance detection was consistent with the classical cell growth law. These results suggest the great potential of the combination of microbial intracellular abundance, Raman spectra analysis, target extraction, and multimodel fitting as a method for microbial fermentation engineering.

Development and Application of an Automated Raman Sensor for Bioprocess Monitoring: From the Laboratory to an Algae Production Platform

Microalgae provide valuable bio-components with economic and environmental benefits. The monitoring of microalgal production is mostly performed using different sensors and analytical methods that, although very powerful, are limited to qualified users. This study proposes an automated Raman spectroscopy-based sensor for the online monitoring of microalgal production. For this purpose, an in situ system with a sampling station was made of a light-tight optical chamber connected to a Raman probe. Microalgal cultures were routed to this chamber by pipes connected to pumps and valves controlled and programmed by a computer. The developed approach was evaluated on Parachlorella kessleri under different culture conditions at a laboratory and an industrial algal platform. As a result, more than 4000 Raman spectra were generated and analysed by statistical methods. These spectra reflected the physiological state of the cells and demonstrate the ability of the developed sensor to monitor the physiology of microalgal cells and their intracellular molecules of interest in a complex production environment.

Assessing micrometer-scale contamination from organic materials in serpentinite analysis

Serpentinization of peridotite provides a significant source of energy for the subseafloor biosphere and abiotic organic synthesis. The presence of diverse micrometer-scale organic matter in serpentinites offers insights into deep carbon cycling and the origin of life on Earth. It is critical to maintain stringent lab protocols in analyzing serpentinite samples, limiting the contact with organic materials that could contaminate serpentinites and cause misinterpretations. However, the extent to which these organic materials (e.g. latex gloves or nylon polishing disc) can introduce contamination remains unclear. Here we subject serpentinite samples from the Yap Trench in the western Pacific Ocean to multi-stage cutting and polishing procedures prior to analysis. Our findings from electron microscopy reveal that micrometer-scale organic matter in serpentinites is randomly distributed either on the sample surface or within Cr-spinel fractures. Further analysis using Raman spectroscopy indicates that the organic matter contains several hydrogen bonding moieties, similar to those found in the latex gloves or nylon polishing disc used during the treatment of serpentinite samples. Our results suggest that the detected organic matter is likely due to contamination from the organic materials involved during sample processing. Thus, future studies need to carefully assess micrometer-scale organic contamination and limit the use of organic materials when analyzing organic compounds hosted in serpentinites, not only on Earth but also on other rocky planets.

Chemical Approaches for Measuring and Manipulating Lipids at the Organelle Level

As the products of complex and often redundant metabolic pathways, lipids are challenging to measure and perturb using genetic tools. Yet by virtue of being the major constituents of cellular membranes, lipids are highly regulated in space and time. Chemists have stepped into this methodological void, developing an array of techniques for the precise quantification and manipulation of lipids at the subcellular, organelle level. Here, we survey the landscape of these methods. For measuring lipids, we summarize the use of metabolic labeling and click chemistry tagging, photoaffinity labeling, isotopic tagging for Raman microscopy, and chemoenzymatic labeling for tracking lipid production and interorganelle transport. For perturbing lipids, we describe synthetic photocaged lipids and membrane editing approaches using optogenetic enzymes for precise manipulation of lipid signaling. Collectively, these chemical and biochemical tools are revealing phenomena and mechanisms underlying lipid functions at the subcellular level.

Effects of low temperature and highlight stress on lipid accumulation and cell structure of Tropidoneis maxima

Tropidoneis maxima is a marine diatom with a rapid growth rate that produces high levels of lipids. To explore whether the lipid content could be further enhanced, cultures were first incubated under optimal conditions and then stressed under low temperature (10°C), a high light intensity level (80 μmol/m2 ·s), and the two factors together (interaction treatment). The results indicated that high light intensity and the temperature-light interaction exhibited greater impacts on lipid synthesis of T. maxima than low temperature. The two stress treatments increased lipid content by 17.16% and 16.6% compared to the control. In particular, higher biomass concentration was obtained with high light intensity (1.082 g L-1 ) and low temperature (1.026 g L-1 ). Moreover, high light intensity (9.06%) and interaction (10.3%) treatments yielded lower starch content compared to low temperature (14.27%) at the end of the stress culture. After 3 days of stress culture, the high light intensity treatment resulted in a 97.01% increase in cell wall thickness and an 18.46% decrease in cell diameter. The results suggest that high light intensity stress on T. maxima would open a new approach to cost-effective biolipid production.

Rapid Intracellular Detection and Analysis of Lipid Droplets' Morpho-Chemical Composition by Phase-Guided Raman Sampling

Intracellular lipid droplets (LDs) are dynamic, complex organelles involved in nearly all aspects of cellular metabolism. In situ characterization methods are primarily limited to fluorescence imaging, which yields limited chemical information, or Raman spectroscopy, which provides excellent chemical profiling but very low throughput. Here, we propose a new paradigm where locations of both large and small droplets are obtained automatically from high-resolution phase images and fed into a galvomirror-controlled Raman sampling arm to obtain the full spectrum of each LD efficiently. Using this phase-guided Raman sampling, we can characterize hundreds of LDs within a single cell in minutes and easily acquire more than 40,000 high-quality spectra. The data set revealed strong, cell line-dependent, cell-dependent, and individual droplet-dependent composition changes to various culture conditions. In particular, we revealed a strong competitive relationship between mono- and polyunsaturated fatty acids, where supplementation with one led to a relative decrease in the other.

Raman Imaging Reveals Insights into Membrane Phase Biophysics in Cells

Cellular membranes are essential components of all living organisms. They are composed of a complex mixture of lipids with diverse chemical structures and crucial biological functions. The dynamic and heterogeneous nature of cellular membranes presents a challenge for studying their biophysical properties and organization in vivo. Raman imaging, particularly coherent Raman scattering techniques such as stimulated Raman scattering (SRS) microscopy, have emerged as powerful tools for studying cellular membranes with high spatial and temporal resolution and minimal perturbation. In this Review, we discuss the scientific importance and technical challenges of characterizing membrane composition in cellular contexts and how the advances of Raman imaging can provide unique insights into membrane phase behavior and organization. We also highlight recent applications of Raman imaging in studying cellular membranes and implications in diseases. In particular, the discovery of phase separation and a solid-phase intracellular membrane on endoplasmic reticulum is reviewed in detail, shedding light on the biology of lipotoxicity.

Shedding light on reovirus assembly-Multimodal imaging of viral factories

Avian (ortho)reovirus (ARV), which belongs to Reoviridae family, is a major domestic fowl pathogen and is the causative agent of viral tenosynovitis and chronic respiratory disease in chicken. ARV replicates within cytoplasmic inclusions, so-called viral factories, that form by phase separation and thus belong to a wider class of biological condensates. Here, we evaluate different optical imaging methods that have been developed or adapted to follow formation, fluidity and composition of viral factories and compare them with the complementary structural information obtained by well-established transmission electron microscopy and electron tomography. The molecular and cellular biology aspects for setting up and following virus infection in cells by imaging are described first. We then demonstrate that a wide-field version of fluorescence recovery after photobleaching is an effective tool to measure fluidity of mobile viral factories. A new technique, holotomographic phase microscopy, is then used for imaging of viral factory formation in live cells in three dimensions. Confocal Raman microscopy of infected cells provides "chemical" contrast for label-free segmentation of images and addresses important questions about biomolecular concentrations within viral factories and other biological condensates. Optical imaging is complemented by electron microscopy and tomography which supply higher resolution structural detail, including visualization of individual virions within the three-dimensional cellular context.

Robust Spontaneous Raman Flow Cytometry for Single-Cell Metabolic Phenome Profiling via pDEP-DLD-RFC

A full-spectrum spontaneous single-cell Raman spectrum (fs-SCRS) captures the metabolic phenome for a given cellular state of the cell in a label-free, landscape-like manner. Herein a positive dielectrophoresis induced deterministic lateral displacement-based Raman flow cytometry (pDEP-DLD-RFC) is established. This robust flow cytometry platform utilizes a periodical positive dielectrophoresis induced deterministic lateral displacement (pDEP-DLD) force that is exerted to focus and trap fast-moving single cells in a wide channel, which enables efficient fs-SCRS acquisition and extended stable running time. It automatically produces deeply sampled, heterogeneity-resolved, and highly reproducible ramanomes for isogenic cell populations of yeast, microalgae, bacteria, and human cancers, which support biosynthetic process dissection, antimicrobial susceptibility profiling, and cell-type classification. Moreover, when coupled with intra-ramanome correlation analysis, it reveals state- and cell-type-specific metabolic heterogeneity and metabolite-conversion networks. The throughput of ≈30-2700 events min-1 for profiling both nonresonance and resonance marker bands in a fs-SCRS, plus the >5 h stable running time, represent the highest performance among reported spontaneous Raman flow cytometry (RFC) systems. Therefore, pDEP-DLD-RFC is a valuable new tool for label-free, noninvasive, and high-throughput profiling of single-cell metabolic phenomes.

In vitro Raman imaging of human macrophages: Impact of eicosapentaenoic acid on the hydrolysis of cholesterol esters in lipid droplets

Atherosclerosis - a cardiovascular disease and the primary cause of morbidity and mortality in industrialized countries - is linked to the existence of atherosclerotic plaques characterized by cholesterol-laden macrophages called foam cells. In these cells, cholesterol esters associated with triglycerides form lipid droplets (LD). The only way to remove this excess cholesterol is to promote free cholesterol efflux from macrophages to specific acceptors. It has been shown recently that eicosapentaenoic acid (EPA) reduces efflux on cholesterol-loaded THP-1 macrophages in vitro due to decreased cholesterol esters hydrolysis. These in vitro observations could reflect EPA's difficulty in facilitating in vivo the antiatherogenic process of cholesterol efflux within advanced atherosclerotic plaques. This work aims to study in vitro the impact of EPA on cholesterol esters hydrolysis in the LD of human THP-1 macrophages using vibrational Raman microspectroscopy. For this, we used deuterated EPA and recorded spectral images at the cell scale after different hydrolysis times. RESULTS: showed that EPA is involved in forming triglycerides and phospholipids of LD. Hydrolysis kinetics slowed down after 24 h, triglycerides increased, and the intensity of the characteristic bands linked to deuteration decreased. The size of LD without hydrolysis (H0) is higher than that after 24 h (H1) or 48 h (H2) of hydrolysis. The size decrease is sharper when going from H0 to H1 than from H1 to H2. Principal component analysis illustrated data' projection according to the cellular compartment, the hydrolysis time, and the supplementation of the medium.

An attempt to simultaneously quantify the polysaccharide, total lipid, protein and pigment in single Cyclotella cryptica cell by Raman spectroscopy

BACKGROUND

At present, the conventional methods for determining photosynthetic products of microalgae are usually based on a large number of cell mass to reach the measurement baseline, and the result can only reveal the average state at the population level, which is not feasible for large-scale and rapid screening of specific phenotypes from a large number of potential microalgae mutants. In recent years, single-cell Raman spectra (SCRS) has been proved to be able to rapidly and simultaneously quantify the biochemical components of microalgae. However, this method has not been reported to analyze the biochemical components of Cyclotella cryptica (C. cryptica). Thus, SCRS was first attempt to determine these four biochemical components in this diatom.

RESULTS

The method based on SCRS was established to simultaneously quantify the contents of polysaccharide, total lipids, protein and Chl-a in C. cryptica, with thirteen Raman bands were found to be the main marker bands for the diatom components. Moreover, Partial Least Square Regression (PLSR) models based on full spectrum can reliably predict these four cellular components, with Pearson correlation coefficient for these components reached 0.949, 0.904, 0.801 and 0.917, respectively. Finally, based on SCRS data of one isogenic sample, the pairwise correlation and dynamic transformation process of these components can be analyzed by Intra-ramanome Correlation Analysis (IRCA), and the results showed silicon starvation could promote the carbon in C. cryptica cells to flow from protein and pigment metabolism to polysaccharide and lipid metabolism.

CONCLUSIONS

First, method for the simultaneous quantification of the polysaccharide, total lipid, protein and pigment in single C. cryptica cell are established. Second, the instant interconversion of intracellular components was constructed through IRCA, which is based on data set of one isogenic population and more precision and timeliness. Finally, total results indicated that silicon deficiency could promote the carbon in C. cryptica cells to flow from protein and pigment metabolism to polysaccharide and lipid metabolism.

Direct Counting and Imaging Chain Lengths of Lipids by Stimulated Raman Scattering Microscopy

Direct counting and mapping the chain lengths of fatty acids on a microscopic scale are of particular importance but remain an unsolvable challenge. Although the current hyperspectral stimulated Raman scattering (SRS) microscopy has gained exceptional capability in chemical imaging of the degree of desaturation, the complete lipid characterization, including the carbon chain length quantification, is awaiting a major breakthrough. Here, we pushed the spectral resolution limit of hyperspectral SRS microscopy to 5.4 cm^-1 by employing a highly efficient spectral compressor, which achieved spectral narrowing of the fs laser without much energy loss. The SRS imaging with such high spectral resolution enabled us to differ eight types of saturated lipids with carbon chain lengths from C8:0 to C22:0 by interrogating their subtly red-shifting Raman bands of alkyl C-C gauche stretches between 1070 and 1110 cm^-1. The SRS microscopy with superior spectral resolution will pave the way for comprehensive lipid characterization and contribute to uncovering the abnormal pathways of lipid metabolism in cancer.

Simultaneous Dual-Band Hyperspectral Stimulated Raman Scattering Microscopy with Femtosecond Optical Parametric Oscillators

Stimulated Raman scattering (SRS) microscopy is a label-free quantitative optical technique for imaging molecular distributions in cells and tissues by probing their intrinsic vibrational frequencies. Despite its usefulness, existing SRS imaging techniques have limited spectral coverage due to either a wavelength tuning constraint or narrow spectral bandwidth. High-wavenumber SRS imaging is commonly used to map lipid and protein distribution in biological cells and visualize cell morphology. However, to detect small molecules or Raman tags, imaging in the fingerprint region or "silent" region, respectively, is often required. For many applications, it is desirable to collect SRS images in two Raman spectral regions simultaneously for visualizing the distribution of specific molecules in cellular compartments or providing accurate ratiometric analysis. In this work, we present an SRS microscopy system using three beams generated by a femtosecond oscillator to acquire hyperspectral SRS image stacks in two arbitrary vibrational frequency bands, between 650-3280 cm-1, simultaneously. We demonstrate potential biomedical applications of the system in investigating fatty acid metabolism, cellular drug uptake and accumulation, and lipid unsaturation level in tissues. We also show that the dual-band hyperspectral SRS imaging system can be adapted for the broadband fingerprint region hyperspectral imaging (1100-1800 cm-1) by simply adding a modulator.

Simultaneous Imaging and Characterization of Polyunsaturated Fatty Acids, Carotenoids, and Microcrystalline Guanine in Single Aurantiochytrium limacinum Cells with Linear and Nonlinear Raman Microspectroscopy

Thraustochytrids are heterotrophic marine protists known for their high production capacity of various compounds with health benefits, such as polyunsaturated fatty acids and carotenoids. Although much effort has been focused on developing optimal cultivation methods for efficient microbial production, these high-value compounds and their interrelationships are not well understood at the single-cell level. Here we used spontaneous (linear) Raman and multiplex coherent anti-Stokes Raman scattering (CARS) microspectroscopy to visualize and characterize lipids (e.g., docosahexaenoic acid) and carotenoids (e.g., astaxanthin) accumulated in single living Aurantiochytrium limacinum cells. Spontaneous Raman imaging with the help of multivariate curve resolution-alternating least-squares enabled us to make unambiguous assignments of the molecular components we detected and derive their intracellular distributions separately. Near-IR excited CARS imaging yielded the Raman images at least an order of magnitude faster than spontaneous Raman imaging, with suppressed contributions of carotenoids. As the culture time increased from 2 to 5 days, the lipid amount increased by a factor of ∼7, whereas the carotenoid amount did not change significantly. Furthermore, we observed a highly localized component in A. limacinum cells. This component was found to be mixed crystals of guanine and other purine derivatives. The present study demonstrates the potential of the linear-nonlinear Raman hybrid approach that allows for accurate molecular identification and fast imaging in a label-free manner to link information derived from single cells with strategies for mass culture of useful thraustochytrids.

High-Precision Detection of Cellular Drug Response Based on SERS Spectrum and Multivariate Statistical Analysis

The rapid development of personalized medicine places high demands on the control of drug dose and cellular drug response to provide patients with better curative effects and low side effects. To solve the problem of low detection accuracies of the cell-counting kit-8 (CCK8) method, a detection method based on surface-enhanced Raman spectroscopy (SERS) of cell-secreted proteins was adopted to evaluate the concentration of the anticancer drug cisplatin and the cellular drug response of nasopharyngeal carcinoma. CNE1 and NP69 cell lines were used to evaluate cisplatin response. The results showed that the combination of the SERS spectrum with principal component analysis-linear discriminant analysis could detect the difference in the response of cisplatin with a concentration difference of 1 μg/mL, which considerably exceeded that of CCK8. In addition, the SERS spectral peak intensity of the cell-secreted proteins strongly correlated with the cisplatin concentration. Furthermore, the mass spectrum of the secreted proteins of the nasopharyngeal carcinoma cells was analyzed to verify the results obtained using the SERS spectrum. The results demonstrated that SERS of secreted proteins has great potential for high-precision detection of chemotherapeutic drug response.

Comparative analysis of dermal collagen and lipids in cereblon ablated mice using a multimodal nonlinear optical system

By utilizing a multimodal nonlinear optical system that combines coherent anti-Stokes Raman scattering and second harmonic generation to investigate biological characteristics of dermal tissues ex vivo, we demonstrate the potential feasibility of using this optical approach as a powerful new investigative tool for future biomedical research. For this study, our optical system was utilized for the first time to analyze lipid and collagen profiles in cereblon knockout (KO) mouse skin, and we were able to discover significant alterations in the number of carbon-carbon double bonds (wild-type vs. cereblon KO; N_CC : 0.75 vs. 0.85) of skin fatty acids in triacylglycerides as well as changes in dermal collagen fibers (25% reduction in cereblon KO). By adopting our optical system to biological studies, we provide researchers with another diagnostic approach to validate their experimental results, which will significantly advance the state of biomedical research.

The impact of lipid polyunsaturation on the physical and mechanical properties of lipid membranes

The lipid composition of cellular membranes and the balance between the different lipid components can be impacted by aging, certain pathologies, specific diets and other factors. This is the case in a subgroup of individuals with psychiatric disorders, such as schizophrenia, where cell membranes of patients have been shown to be deprived in polyunsaturated fatty acids (PUFAs), not only in brain areas where the target receptors are expressed but also in peripheral tissues. This PUFA deprivation thus represents a biomarker of such disorders that might impact not only the interaction of antipsychotic medications with these membranes but also the activation and signaling of the targeted receptors embedded in the lipid membrane. Therefore, it is crucial to understand how PUFAs levels alterations modulate the different physical properties of membranes. In this paper, several biophysical approaches were combined (Laurdan fluorescence spectroscopy, atomic force microscopy, differential scanning calorimetry, molecular modeling) to characterize membrane properties such as fluidity, elasticity and thickness in PUFA-enriched cell membranes and lipid model systems reflecting the PUFA imbalance observed in some diseases. The impact of both the number of unsaturations and their position along the chain on the above properties was investigated. Briefly, data revealed that PUFA presence in membranes increases membrane fluidity, elasticity and flexibility and decreases its thickness and order parameter. Both the level of unsaturation and their position affect these membrane properties.

Good vibrations: Raman spectroscopy enables insights into plant biochemical composition

Non-invasive techniques are needed to enable an integrated understanding of plant metabolic responses to environmental stresses. Raman spectroscopy is one such technique, allowing non-destructive chemical characterisation of samples in situ and in vivo and resolving the chemical composition of plant material at scales from microns to metres. Here, we review Raman band assignments of pigments, structural and non-structural carbohydrates, lipids, proteins and secondary metabolites in plant material and consider opportunities this technology raises for studies in vascular plant physiology.

Correlative Raman-Electron-Light (CREL) Microscopy Analysis of Lipid Droplets in Melanoma Cancer Stem Cells

Among all neoplasms, melanoma is characterized by a very high percentage of cancer stem cells (CSCs). Several markers have been proposed for their identification, and lipid droplets (LDs) are among them. Different techniques are used for their characterization such as mass spectrometry, imaging techniques, and vibrational spectroscopies. Some emerging experimental approaches for the study of LDs are represented by correlative light-electron microscopy and by correlative Raman imaging-scanning electron microscopy (SEM). Based on these scientific approaches, we developed a novel methodology (CREL) by combining Raman micro-spectroscopy, confocal fluorescence microscopy, and SEM coupled with an energy-dispersive X-ray spectroscopy module. This procedure correlated cellular morphology, chemical properties, and spatial distribution from the same region of interest, and in this work, we presented the application of CREL for the analysis of LDs within patient-derived melanoma CSCs (MCSCs).

Micro-Raman spectroscopy study of optically trapped erythrocytes in malaria, dengue and leptospirosis infections

Malaria, dengue and leptospirosis are three tropical infectious diseases that present with severe hematological derangement causing significant morbidity and mortality, especially during the seasonal monsoons. During the course of these infectious diseases, circulating red blood cells are imperiled to the direct ill-effects of the infectious pathogen in the body as well as to the pro-inflammatory cytokines generated as a consequence of the infection. RBCs when exposed to such inflammatory and/or pathogenic milieu are susceptible to injuries such as RBC programmed eryptosis or RBC programmed necrosis. This research aimed to explore the Raman spectra of live red cells that were extracted from patients infected with malaria, dengue, and leptospirosis. Red cells were optically trapped and micro-Raman probed using a 785 nm Diode laser. RBCs from samples of all three diseases displayed Raman signatures that were significantly altered from the normal/healthy. Distinct spectral markers that were common across all the four groups were obtained from various standardized multivariate analytical methods. Following comprehensive examination of multiple studies, we propose these spectral wavenumbers as "Raman markers of RBC injury." Findings in our study display that anemia-triggering infections can inflict variations in the healthy status of red cells, easily identifiable by selectively analyzing specific Raman markers. Additionally, this study also highlights relevant statistical tools that can be utilized to study Raman spectral data from biological samples which could help identify the very significant Raman peaks from the spectral band. This approach of RBC analysis can foster a better understanding of red cell behavior and their alterations exhibited in health and disease.

High-Resolution Low-Power Hyperspectral Line-Scan Imaging of Fast Cellular Dynamics Using Azo-Enhanced Raman Scattering Probes

Small-molecule Raman probes for cellular imaging have attracted great attention owing to their sharp peaks that are sensitive to environmental changes. The small cross section of molecular Raman scattering limits dynamic cellular Raman imaging to expensive and complex coherent approaches that acquire single-channel images and lose hyperspectral Raman information. We introduce a new method, dynamic azo-enhanced Raman imaging (DAERI), to couple the new class of azo-enhanced Raman probes with a high-speed line-scan Raman imaging system. DAERI achieved high-resolution low-power imaging of fast cellular dynamics resolved at ∼270 nm along the confocal direction, 75 μW/μm² and 3.5 s/frame. Based on the azo-enhanced Raman probes with characteristic signals 10²-10⁴ stronger than classic Raman labels, DAERI was not restricted to the cellular Raman-silent region as in prior work and enabled multiplex visualization of organelle motions and interactions. We anticipate DAERI to be a powerful tool for future studies in biophysics and cell biology.

Structure and Interaction of Ceramide-Containing Liposomes with Gold Nanoparticles as Characterized by SERS and Cryo-EM

Due to the great potential of surface-enhanced Raman scattering (SERS) as local vibrational probe of lipid-nanostructure interaction in lipid bilayers, it is important to characterize these interactions in detail. The interpretation of SERS data of lipids in living cells requires an understanding of how the molecules interact with gold nanostructures and how intermolecular interactions influence the proximity and contact between lipids and nanoparticles. Ceramide, a sphingolipid that acts as important structural component and regulator of biological function, therefore of interest to probing, lacks a phosphocholine head group that is common to many lipids used in liposome models. SERS spectra of liposomes of a mixture of ceramide, phosphatidic acid, and phosphatidylcholine, as well as of pure ceramide and of the phospholipid mixture are reported. Distinct groups of SERS spectra represent varied contributions of the choline, sphingosine, and phosphate head groups and the structures of the acyl chains. Spectral bands related to the state of order of the membrane and moreover to the amide function of the sphingosine head groups indicate that the gold nanoparticles interact with molecules involved in different intermolecular relations. While cryogenic electron microscopy shows the formation of bilayer liposomes in all preparations, pure ceramide was found to also form supramolecular, concentric stacked and densely packed lamellar, nonliposomal structures. That the formation of such supramolecular assemblies supports the intermolecular interactions of ceramide is indicated by the SERS data. The unique spectral features that are assigned to the ceramide-containing lipid model systems here enable an identification of these molecules in biological systems and allow us to obtain information on their structure and interaction by SERS.

Measurement of dielectric properties of cells at single-cell resolution using electrorotation

Dielectric properties of a cell are biophysical properties of high interest for various applications. However, measuring these properties accurately is not easy, which can be exemplified by the large variations in reported dielectric properties of the same cell types. This paper presents a method for measuring the dielectric properties of cells at high frequency, especially lipid-producing microalgae, at single-cell resolution, by integrating an electrorotation-based dielectric property measurement method with a negative dielectrophoretic (nDEP) force-based single-cell trapping method into a single device. In this method, a four-electrode nDEP structure was used to trap a single cell in an elevated position in the center of another four-electrode structure that can apply electrorotational force. By measuring the speed of cell rotation under different applied electrorotation frequencies and fitting the results into a theoretical core-shell cell model, the dielectric properties of cells, including membrane capacitance and cytoplasm conductivity, could be obtained. This system was applied to measure the dielectric properties of lipid-accumulating microalga Chlamydomonas reinhardtii strain Sta6 by applying an electrorotation signal of up to 100 MHz. By utilizing a broad frequency range and expanding the measurement spectra to a high frequency region, increased accuracy in fitting the dielectric parameters to a theoretical model was possible, especially the cytoplasm conductivity. The developed method can be used in various applications, such as screening microalgae based on their lipid production capabilities, separating cells of different dielectric properties, identifying different cell types, as well as conducting basic biophysical analyses of cellular properties.

Development of novel spectroscopic and machine learning methods for the measurement of periodic changes in COVID-19 antibody level

In this research, blood samples of 47 patients infected by COVID were analyzed. The samples were taken on the 1st, 3rd and 6th month after the detection of COVID infection. Total antibody levels were measured against the SARS-CoV-2 N antigen and surrogate virus neutralization by serological methods. To differentiate COVID patients with different antibody levels, Fourier Transform InfraRed (FTIR) and Raman spectroscopy methods were used. The spectroscopy data were analyzed by multivariate analysis, machine learning and neural network methods. It was shown, that analysis of serum using the above-mentioned spectroscopy methods allows to differentiate antibody levels between 1 and 6 months via spectral biomarkers of amides II and I. Moreover, multivariate analysis showed, that using Raman spectroscopy in the range between 1317 cm-1 and 1432 cm-1, 2840 cm-1 and 2956 cm-1 it is possible to distinguish patients after 1, 3, and 6 months from COVID with a sensitivity close to 100%.

Visualizing Lipid Dynamics Role in Infrared Neural Stimulation using Stimulated Raman Scattering

Infrared neural stimulation, or INS, uses pulsed infrared light to yield label-free neural stimulation with broad experimental and translational utility. Despite its robust demonstration, INS's mechanistic and biophysical underpinnings have been the subject of debate for more than a decade. The role of lipid membrane thermodynamics appears to play an important role in how fast IR-mediated heating nonspecifically drives action potential generation. Direct observation of lipid membrane dynamics during INS remains to be shown in a live neural model system. We used hyperspectral stimulated Raman scattering (hsSRS) microscopy to study biochemical signatures of high-speed vibrational dynamics underlying INS in a live neural cell culture model. Findings suggest that lipid bilayer structural changes are occurring during INS in vitro in NG108-15 neuroglioma cells. Lipid-specific signatures of cell SRS spectra varied with stimulation energy and radiant exposure. Spectroscopic observations agree with high-speed ratiometric fluorescence imaging of a conventional lipophilic membrane structure reporter, di-4-ANNEPS. Overall, the presented findings support the hypothesis that INS causes changes in the lipid membrane of neural cells by changing lipid membrane packing order. Furthermore, this work highlights the potential of hsSRS as a method to study biophysical and biochemical dynamics safely in live cells.

Detecting Phytoplankton Cell Viability Using NIR Raman Spectroscopy and PCA

Raman spectroscopy has long been suggested as a potentially fast and sensitive method to monitor phytoplankton abundance and composition in marine environments. However, the pitfalls of visible detection methods in pigment-rich biological material and the complexity of their spectra have hindered their application as reliable in situ detection methods. In this study we combine 1064 nm confocal Raman spectroscopy with multivariate statistical analysis techniques (principle component analysis and partial leas-squares discriminant analysis) to reliably measure differences in the cell viability of a diatom species (Chaetoceros muelleri) and two haptophyte species (Diacronema lutheri and Tisochrysis lutea) of phytoplankton. The low fluorescence background due to this combined approach of NIR Raman spectroscopy and multivariate data analysis allowed small changes in the overall spectral profiles to be reliably monitored, enabling the identification of the specific spectral features that could classify cells as viable or nonviable regardless of their species. The most significant differences upon cell death were shown by characteristic shifts in the carotenoid bands at 1527 and 1158 cm-1. The contributions from other biomolecules were less pronounced but revealed changes that could be identified using this combination of techniques.

Perspectives of fluorescence spectroscopy for online monitoring in microalgae industry

Microalgae industrial production is viewed as a solution for alternative production of nutraceuticals, cosmetics, biofertilizers, and biopolymers. Throughout the years, several technological advances have been implemented, increasing the competitiveness of microalgae industry. However, online monitoring and real-time process control of a microalgae production factory still require further development. In this mini-review, non-destructive tools for online monitoring of cellular agriculture applications are described. Still, the focus is on the use of fluorescence spectroscopy to monitor several parameters (cell concentration, pigments, and lipids) in the microalgae industry. The development presented makes it the most promising solution for monitoring up-and downstream processes, different biological parameters simultaneously, and different microalgae species. The improvements needed for industrial application of this technology are also discussed.

Pinpointing Alkane Chain Length, Saturation, and Double Bond Regio- and Stereoisomers by Liquid Interfacial Plasmonic Enhanced Raman Spectroscopy

The lipids with a rich diversity of isomers face a formidable challenge in comprehensive structural analysis. The commonly used mass spectrometry-based techniques usually require a considerable number of molecules with sophisticated chemical derivatization or ion mobility separation, but the co-existing of structurally similar isomers often makes the distinction impossible. Here, we develop an alternative powerful liquid/liquid interfacial surface-enhanced Raman spectroscopy (SERS) strategy at normal temperature and pressure without any sources of ionization or radiation. This strategy generates high-resolution fingerprints in molecular chain length, C═C position, saturation, and regio- and stereoisomers of both glycerides and fatty acids and requires only trace amounts of molecules down to 1 ppb to achieve discrimination and exhibits great potentials to push the identification capability to trace levels or even the single-molecule level. According to experimental data and theoretical simulations, these targets have the amphiphilic and emulsifying properties, exhibit ordered molecular orientation and adsorption patterns, promote the co-assembly with plasmonic nanoarrays at the immiscible liquid/liquid interface, and consequently amplify the detection sensitivity. As a contrast, the typical SERS based on solid/air interfacial plasmonic nanoarrays faces the intrinsic bottleneck of extremely weak intensity and indistinguishable spectral fingerprints of lipid molecules. The vibrational fingerprints exhibit a rich range of well-resolved absorption features that are clearly diagnostic for fine structural changes and pave a new way for straightforward measurement without laborsome sample purification, enrichment, or complex derivatization. Although challenging, its unprecedented resolving power expands the potentials of SERS, serving as an ultimate analytical method to provide insights into the detailed structural features of other lipids under facile conditions in the future.

Mitochondrial Dysfunction: A Prelude to Neuropathogenesis of SARS-CoV-2

The SARS-CoV-2 virus is notorious for its neuroinvasive capability, causing multiple neurological conditions. The neuropathology of SARS-CoV-2 is increasingly attributed to mitochondrial dysfunction of brain microglia cells. However, the changes in biochemical content of mitochondria that drive the progression of neuro-COVID remain poorly understood. Here we introduce a Raman microspectrometry approach that enables the molecular profiling of single cellular organelles to characterize the mitochondrial molecular makeup in the infected microglia cells. We found that microglia treated with either spike protein or heat-inactivated SARS-CoV-2 trigger a dramatic reduction in mtDNA content and an increase in phospholipid saturation levels. At the same time, no significant changes were detected in Golgi apparatus and in lipid droplets, the organelles that accommodate biogenesis and storage of lipids. We hypothesize that transformations in mitochondria are caused by increased synthesis of reactive oxygen species in these organelles. Our findings call for the development of mitochondria-targeted therapeutic approaches to limit neuropathology associated with SARS-CoV-2.

Raman Spectroscopy and Its Modifications Applied to Biological and Medical Research

Nowadays, there is an interest in biomedical and nanobiotechnological studies, such as studies on carotenoids as antioxidants and studies on molecular markers for cardiovascular, endocrine, and oncological diseases. Moreover, interest in industrial production of microalgal biomass for biofuels and bioproducts has stimulated studies on microalgal physiology and mechanisms of synthesis and accumulation of valuable biomolecules in algal cells. Biomolecules such as neutral lipids and carotenoids are being actively explored by the biotechnology community. Raman spectroscopy (RS) has become an important tool for researchers to understand biological processes at the cellular level in medicine and biotechnology. This review provides a brief analysis of existing studies on the application of RS for investigation of biological, medical, analytical, photosynthetic, and algal research, particularly to understand how the technique can be used for lipids, carotenoids, and cellular research. First, the review article shows the main applications of the modified Raman spectroscopy in medicine and biotechnology. Research works in the field of medicine and biotechnology are analysed in terms of showing the common connections of some studies as caretenoids and lipids. Second, this article summarises some of the recent advances in Raman microspectroscopy applications in areas related to microalgal detection. Strategies based on Raman spectroscopy provide potential for biochemical-composition analysis and imaging of living microalgal cells, in situ and in vivo. Finally, current approaches used in the papers presented show the advantages, perspectives, and other essential specifics of the method applied to plants and other species/objects.

Study on degranulation of mast cells under C48/80 treatment by electroporation-assisted and ultrasound-assisted surface-enhanced Raman spectrascopy

Both electroporation-assisted and ultrasound-assisted delivery methods can rapidly deliver nanoparticles into living cells for surface-enhanced Raman scattering (SERS) detection, but these two methods have never been compared. In this study, electroporation-assisted SERS and ultrasound-assisted SERS were employed to detect the biochemical changes of degranulated mast cells induced by mast cell stimulator (C48/80). The results showed that the cell damage of electroporation based on controllable electric pulse was smaller than that of ultrasound based on cavitation. Transmission electron microscope images of cells indicated that the nanoparticles delivered by electroporation were mainly distributed in the cytoplasm, while ultrasound could transport nanoparticles to the cytoplasm and nucleus. Therefore, electroporation-assisted SERS mainly detects the biochemical information of cytoplasm, while ultrasound-assisted SERS gets more spectral signals of nucleic acid. Both methods can obtain high quality SERS signal of cells. With drug treatment, the SERS peak intensity of 733 cm^-1 attributed to phosphatidylserine decreased significantly, which may be due to the activation of mast cell degranulation pathway stimulated by C48/80 agonist, resulting in a large amount of intracellular serine being used to synthesize tryptase, while the production of phosphatidylserine decreased. Further, based on principal component analysis and linear discriminant analysis (PCA-LDA approach), ultrasound-assisted SERS could achieve better sensitivity, specificity and accuracy in the discrimination and identification of drug-treated degranulated mast cells than electroporation assisted SERS. This exploratory work is helpful to realize the real-time dynamic SERS detection of intracellular biochemical components, and it also has great potential in intracellular SERS analysis, such as the cytotoxicity assay of anti-tumor drugs or cancer cell screening.

Biochemical changes in the cytoplasm of bovine oocytes during the in vitro maturation process: a Raman microscopy study

The sequence and chronology of the main biochemical changes occurring in the cytoplasm of bovine oocytes during the in vitro maturation process were tracked by Raman microscopy applied to cells previously subjected to enzymatic digestion of the zona pellucida. Specific spectral markers for proteins, lipids and carbohydrates were used to evaluate the developmental status of the ooplasm at four different times. Spectral changes revealed that lipid accumulation was dominant during the first six hours of culture while protein content reached the average levels characteristic of mature oocytes within the last four hours of the maturation process. A time-dependent decrease in carbohydrates was also observed. Finally, the carbohydrate-to-protein (P₁₀₃₇/P₁₀₀₂) ratio proved to be sensitive enough to determine the cytoplasmic maturation state of bovine oocytes and promises to be useful in future research aimed at optimizing culture conditions through the promotion of protein accumulation in the ooplasm.

Investigation of Raman Spectroscopic Signatures with Multivariate Statistics: An Approach for Cataloguing Microbial Biosignatures

Spectroscopic instruments are increasingly being implemented in the search for extraterrestrial life. However, microstructural spectral analyses of alien environments could prove difficult without knowledge on the molecular identification of individual spectral signatures. To bridge this gap, we introduce unsupervised K-means clustering as a statistical approach to discern spectral patterns of biosignatures without prior knowledge of spectral regions of biomolecules. Spectral profiles of bacterial isolates from analogous polar ice sheets were measured with Raman spectroscopy. Raman analysis identified carotenoid and violacein pigments, and key cellular features including saturated and unsaturated fats, triacylglycerols, and proteins. Principal component analysis and targeted spectra integration biplot analysis revealed that the clustering of bacterial isolates was attributed to spectral biosignatures influenced by carotenoid pigments and ratio of unsaturated/saturated fat peaks. Unsupervised K-means clustering highlighted the prevalence of the corresponding spectral peaks, while subsequent supervised permutational multivariate analysis of variance provided statistical validation for spectral differences associated with the identified cellular features. Establishing a validated catalog of spectral signatures of analogous biotic and abiotic materials, in combination with targeted supervised tools, could prove effective at identifying extant biosignatures.

Raman microspectroscopy reveals unsaturation heterogeneity at the lipid droplet level and validates an in vitro model of bone marrow adipocyte subtypes

Bone marrow adipocytes (BMAds) constitute the most abundant stromal component of adult human bone marrow. Two subtypes of BMAds have been described, the more labile regulated adipocytes (rBMAds) and the more stable constitutive adipocytes (cBMAds), which develop earlier in life and are more resilient to environmental and metabolic disruptions. In vivo, rBMAds are enriched in saturated fatty acids, contain smaller lipid droplets (LDs) and more readily provide hematopoietic support than their cBMAd counterparts. Mouse models have been used for BMAds research, but isolation of primary BMAds presents many challenges, and thus in vitro models remain the current standard to study nuances of adipocyte differentiation. No in vitro model has yet been described for the study of rBMAds/cBMAds. Here, we present an in vitro model of BM adipogenesis with differential rBMAd and cBMAd-like characteristics. We used OP9 BM stromal cells derived from a (C57BL/6xC3H)F2-op/op mouse, which have been extensively characterized as feeder layer for hematopoiesis research. We observed similar canonical adipogenesis transcriptional signatures for spontaneously-differentiated (sOP9) and induced (iOP9) cultures, while fatty acid composition and desaturase expression of Scd1 and Fads2 differed at the population level. To resolve differences at the single adipocyte level we tested Raman microspectroscopy and show it constitutes a high-resolution method for studying adipogenesis in vitro in a label-free manner, with resolution to individual LDs. We found sOP9 adipocytes have lower unsaturation ratios, smaller LDs and higher hematopoietic support than iOP9 adipocytes, thus functionally resembling rBMAds, while iOP9 more closely resembled cBMAds. Validation in human primary samples confirmed a higher unsaturation ratio for lipids extracted from stable cBMAd-rich sites (femoral head upon hip-replacement surgery) versus labile rBMAds (iliac crest after chemotherapy). As a result, the 16:1/16:0 fatty acid unsaturation ratio, which was already shown to discriminate BMAd subtypes in rabbit and rat marrow, was validated to discriminate cBMAds from rBMAd in both the OP9 model in vitro system and in human samples. We expect our model will be useful for cBMAd and rBMAd studies, particularly where isolation of primary BMAds is a limiting step.

Lipidome profiling with Raman microspectroscopy identifies macrophage response to surface topographies of implant materials

Biomaterial characteristics such as surface topographies have been shown to modulate macrophage phenotypes. The standard methodologies to measure macrophage response to biomaterials are marker-based and invasive. Raman microspectroscopy (RM) is a marker-independent, noninvasive technology that allows the analysis of living cells without the need for staining or processing. In the present study, we analyzed human monocyte-derived macrophages (MDMs) using RM, revealing that macrophage activation by lipopolysaccharides (LPS), interferons (IFN), or cytokines can be identified by lipid composition, which significantly differs in M0 (resting), M1 (IFN-γ/LPS), M2a (IL-4/IL-13), and M2c (IL-10) MDMs. To identify the impact of a biomaterial on MDM phenotype and polarization, we cultured macrophages on titanium disks with varying surface topographies and analyzed the adherent MDMs with RM. We detected surface topography-induced changes in MDM biochemistry and lipid composition that were not shown by less sensitive standard methods such as cytokine expression or surface antigen analysis. Our data suggest that RM may enable a more precise classification of macrophage activation and biomaterial-macrophage interaction.

Recent Advances in Electrical Impedance Sensing Technology for Single-Cell Analysis

Cellular heterogeneity is of significance in cell-based assays for life science, biomedicine and clinical diagnostics. Electrical impedance sensing technology has become a powerful tool, allowing for rapid, non-invasive, and label-free acquisition of electrical parameters of single cells. These electrical parameters, i.e., equivalent cell resistance, membrane capacitance and cytoplasm conductivity, are closely related to cellular biophysical properties and dynamic activities, such as size, morphology, membrane intactness, growth state, and proliferation. This review summarizes basic principles, analytical models and design concepts of single-cell impedance sensing devices, including impedance flow cytometry (IFC) to detect flow-through single cells and electrical impedance spectroscopy (EIS) to monitor immobilized single cells. Then, recent advances of both electrical impedance sensing systems applied in cell recognition, cell counting, viability detection, phenotypic assay, cell screening, and other cell detection are presented. Finally, prospects of impedance sensing technology in single-cell analysis are discussed.

How cancer cells remodel lipid metabolism: strategies targeting transcription factors

Reprogramming of lipid metabolism has received increasing recognition as a hallmark of cancer cells because lipid dysregulation and the alteration of related enzyme profiles are closely correlated with oncogenic signals and malignant phenotypes, such as metastasis and therapeutic resistance. In this review, we describe recent findings that support the importance of lipids, as well as the transcription factors involved in cancer lipid metabolism. With recent advances in transcription factor analysis, including computer-modeling techniques, transcription factors are emerging as central players in cancer biology. Considering the limited number and the crucial role of transcription factors associated with lipid rewiring in cancers, transcription factor targeting is a promising potential strategy for cancer therapy.

19 F Solid-State NMR and Vibrational Raman Characterization of Corticosteroid Drug-Lipid Membrane Interactions

Drug interactions with phospholipid bilayers underpin their behaviour in cell membranes and in liposomal delivery formulations. Liposomal drug delivery in ocular medicine can overcome the physical barriers of the eye and better enable the active molecule to reach its target. Here, Raman and 19 F solid-state NMR spectroscopy are used to characterise the interactions of two ocular corticosteroid drugs, difluprednate (DFP) and fluorometholone (FML), with multilamellar vesicles of phosphatidylcholine (PC). 31 P NMR confirms that the lipid bilayer tolerates a high drug concentration (a drug: lipid molar ratio of 1 : 10). The 19 F NMR spectra of the drugs in lipid bilayers reveal that FML and DFP have different average orientations within the lipid bilayer. Raman spectra of dried lipid films reveal that PC separates from DFP but not from FML, the less lipophilic of the two drugs. This combined approach will assist the design of, and inform the development of, improved liposomal preparations.