Fluorescence quenching of free and bound NADH in HeLa cells determined by hyperspectral imaging and unmixing of cell autofluorescence

Syntheses and Applications of Coumarin-Derived Fluorescent Probes for Real-Time Monitoring of NAD(P)H Dynamics in Living Cells across Diverse Chemical Environments

Fluorescent probes play a crucial role in elucidating cellular processes, with NAD(P)H sensing being pivotal in understanding cellular metabolism and redox biology. Here, the development and characterization of three fluorescent probes, A, B, and C, based on the coumarin platform for monitoring of NAD(P)H levels in living cells are described. Probes A and B incorporate a coumarin-cyanine hybrid structure with vinyl and thiophene connection bridges to 3-quinolinium acceptors, respectively, while probe C introduces a dicyano moiety for replacement of the lactone carbonyl group of probe A which increases the reaction rate of the probe with NAD(P)H. Initially, all probes exhibit subdued fluorescence due to intramolecular charge transfer (ICT) quenching. However, upon hydride transfer by NAD(P)H, fluorescence activation is triggered through enhanced ICT. Theoretical calculations confirm that the electronic absorption changes upon the addition of hydride to originate from the quinoline moiety instead of the coumarin section and end up in the middle section, illustrating how the addition of hydride affects the nature of this absorption. Control and dose-response experiments provide conclusive evidence of probe C's specificity and reliability in identifying intracellular NAD(P)H levels within HeLa cells. Furthermore, colocalization studies indicate probe C's selective targeting of mitochondria. Investigation into metabolic substrates reveals the influence of glucose, maltose, pyruvate, lactate, acesulfame potassium, and aspartame on NAD(P)H levels, shedding light on cellular responses to nutrient availability and artificial sweeteners. Additionally, we explore the consequence of oxaliplatin on cellular NAD(P)H levels, revealing complex interplays between DNA damage repair, metabolic reprogramming, and enzyme activities. In vivo studies utilizing starved fruit fly larvae underscore probe C's efficacy in monitoring NAD(P)H dynamics in response to external compounds. These findings highlight probe C's utility as a versatile tool for investigating NAD(P)H signaling pathways in biomedical research contexts, offering insights into cellular metabolism, stress responses, and disease mechanisms.

Label-Free Assessment of Key Biological Autofluorophores: Material Characteristics and Opportunities for Clinical Applications

Autofluorophores are endogenous fluorescent compounds that naturally occur in the intra and extracellular spaces of all tissues and organs. Most have vital biological functions - like the metabolic cofactors NAD(P)H and FAD+, as well as the structural protein collagen. Others are considered to be waste products - like lipofuscin and advanced glycation end products - which accumulate with age and are associated with cellular dysfunction. Due to their natural fluorescence, these materials have great utility for enabling non-invasive, label-free assays with direct ties to biological function. Numerous technologies, with different advantages and drawbacks, are applied to their assessment, including fluorescence lifetime imaging microscopy, hyperspectral microscopy, and flow cytometry. Here, the applications of label-free autofluorophore assessment are reviewed for clinical and health-research applications, with specific attention to biomaterials, disease detection, surgical guidance, treatment monitoring, and tissue assessment - fields that greatly benefit from non-invasive methodologies capable of continuous, in vivo characterization.

Applications of machine learning in time-domain fluorescence lifetime imaging: a review

Many medical imaging modalities have benefited from recent advances in Machine Learning (ML), specifically in deep learning, such as neural networks. Computers can be trained to investigate and enhance medical imaging methods without using valuable human resources. In recent years, Fluorescence Lifetime Imaging (FLIm) has received increasing attention from the ML community. FLIm goes beyond conventional spectral imaging, providing additional lifetime information, and could lead to optical histopathology supporting real-time diagnostics. However, most current studies do not use the full potential of machine/deep learning models. As a developing image modality, FLIm data are not easily obtainable, which, coupled with an absence of standardisation, is pushing back the research to develop models which could advance automated diagnosis and help promote FLIm. In this paper, we describe recent developments that improve FLIm image quality, specifically time-domain systems, and we summarise sensing, signal-to-noise analysis and the advances in registration and low-level tracking. We review the two main applications of ML for FLIm: lifetime estimation and image analysis through classification and segmentation. We suggest a course of action to improve the quality of ML studies applied to FLIm. Our final goal is to promote FLIm and attract more ML practitioners to explore the potential of lifetime imaging.

Emerging clinical applications in oncology for non-invasive multi- and hyperspectral imaging of cell and tissue autofluorescence

Hyperspectral and multispectral imaging of cell and tissue autofluorescence is an emerging technology in which fluorescence imaging is applied to biological materials across multiple spectral channels. This produces a stack of images where each matched pixel contains information about the sample's spectral properties at that location. This allows precise collection of molecularly specific data from a broad range of native fluorophores. Importantly, complex information, directly reflective of biological status, is collected without staining and tissues can be characterised in situ, without biopsy. For oncology, this can spare the collection of biopsies from sensitive regions and enable accurate tumour mapping. For in vivo tumour analysis, the greatest focus has been on oral cancer, whereas for ex vivo assessment head-and-neck cancers along with colon cancer have been the most studied, followed by oral and eye cancer. This review details the scope and progress of research undertaken towards clinical translation in oncology.

Clinical applications of non-invasive multi and hyperspectral imaging of cell and tissue autofluorescence beyond oncology

Hyperspectral and multispectral imaging of cell and tissue autofluorescence employs fluorescence imaging, without exogenous fluorophores, across multiple excitation/emission combinations (spectral channels). This produces an image stack where each pixel (matched by location) contains unique information about the sample's spectral properties. Analysis of this data enables access to a rich, molecularly specific data set from a broad range of cell-native fluorophores (autofluorophores) directly reflective of biochemical status, without use of fixation or stains. This non-invasive, non-destructive technology has great potential to spare the collection of biopsies from sensitive regions. As both staining and biopsy may be impossible, or undesirable, depending on the context, this technology great diagnostic potential for clinical decision making. The main research focus has been on the identification of neoplastic tissues. However, advances have been made in diverse applications-including ophthalmology, cardiovascular health, neurology, infection, assisted reproduction technology and organ transplantation.

Distinguishing Healthy and Carcinoma Cell Cultures Using Fluorescence Spectra Decomposition with a Genetic-Algorithm-Based Code

In this paper, we analysed the steady state fluorescence spectra of cell suspensions containing healthy and carcinoma fibroblast mouse cells, using a genetic-algorithm-spectra-decomposition software (GASpeD). In contrast to other deconvolution algorithms, such as polynomial or linear unmixing software, GASpeD takes into account light scatter. In cell suspensions, light scatter plays an important role as it depends on the number of cells, their size, shape, and coagulation. The measured fluorescence spectra were normalized, smoothed and deconvoluted into four peaks and background. The wavelengths of intensities' maxima of lipopigments (LR), FAD, and free/bound NAD(P)H (AF/AB) of the deconvoluted spectra matched published data. In deconvoluted spectra at pH = 7, the fluorescence intensities of the AF/AB ratio in healthy cells was always higher in comparison to carcinoma cells. In addition, the AF/AB ratio in healthy and carcinoma cells were influenced differently by changes in pH. In mixtures of healthy and carcinoma cells, AF/AB decreases when more than 13% of carcinoma cells are present. Expensive instrumentation is not required, and the software is user friendly. Due to these attributes, we hope that this study will be a first step in the development of new cancer biosensors and treatments with the use of optical fibers.

Superoxide Release by Macrophages through NADPH Oxidase Activation Dominating Chemistry by Isoprene Secondary Organic Aerosols and Quinones to Cause Oxidative Damage on Membranes

Oxidative stress mediated by reactive oxygen species (ROS) is a key process for adverse aerosol health effects. Secondary organic aerosols (SOA) account for a major fraction of fine particulate matter, and their inhalation and deposition into the respiratory tract causes the formation of ROS by chemical and cellular processes, but their relative contributions are hardly quantified and their link to oxidative stress remains uncertain. Here, we quantified cellular and chemical superoxide generation by 9,10-phenanthrenequinone (PQN) and isoprene SOA using a chemiluminescence assay combined with electron paramagnetic resonance spectroscopy as well as kinetic modeling. We also applied cellular imaging techniques to study the cellular mechanism of superoxide release and oxidative damage on cell membranes. We show that PQN and isoprene SOA activate NADPH oxidase in macrophages to release massive amounts of superoxide, overwhelming the superoxide formation by aqueous chemical reactions in the epithelial lining fluid. The activation dose for PQN is 2 orders of magnitude lower than that of isoprene SOA, suggesting that quinones are more toxic. While higher exposures trigger cellular antioxidant response elements, the released ROS induce oxidative damage to the cell membrane through lipid peroxidation. Such mechanistic and quantitative understandings provide a basis for further elucidation of adverse health effects and oxidative stress by fine particulate matter.

Subcellular analysis of nuclear and cytoplasmic redox indices differentiates breast cancer cell subtypes better than nuclear-to-cytoplasmic area ratio

SIGNIFICANCE

Stratification of malignancy is valuable for cancer treatment. Both optical redox imaging (ORI) indices and nuclear-to-cytoplasmic volume/area ratio (N:C ratio) have been investigated to differentiate between cancers with varying aggressiveness, but these two methods have not been directly compared. The redox status in the cell nucleus has not been studied by ORI, and it remains unknown whether nuclear ORI indices add new biological information.

AIM

We sought to compare the capacity of whole-cell and subcellular ORI indices and N:C ratio to differentiate between breast cancer subtypes with varying aggressiveness and between mitotic and nonmitotic cells.

APPROACH

ORI indices for whole cell, cytoplasm, and nucleus as well as the N:C area ratio were generated for two triple-negative (more aggressive) and two receptor-positive (less aggressive) breast cancer cell lines by fluorescence microscopy.

RESULTS

We found positive correlations between nuclear and cytoplasmic ORI indices within individual cells. On average, a nuclear redox status was found to be more oxidized than cytoplasm in triple-negative cells but not in receptor-positive cells. Whole-cell and subcellular ORI indices distinguished between the receptor statuses better than the N:C ratio. However, N:C ratio was a better differentiator between nonmitotic and mitotic triple-negative cells.

CONCLUSIONS

Subcellular ORI analysis differentiates breast cancer subtypes with varying aggressiveness better than N:C area ratio.

Optical imaging detects metabolic signatures associated with oocyte quality

Oocyte developmental potential is intimately linked to metabolism. Existing approaches to measure metabolism in the cumulus oocyte complex (COC) do not provide information on the separate cumulus and oocyte compartments. Development of an assay that achieves this may lead to an accurate diagnostic for oocyte quality. Optical imaging of the autofluorescent cofactors NAD(P)H and FAD provides a spatially resolved indicator of metabolism via the optical redox ratio ($\mathrm{FAD}/\left[\mathrm{NAD}\left(\mathrm{P}\right)\mathrm{H}+\mathrm{FAD}\right]$). This may provide an assessment of oocyte quality. Here, we determined whether the optical redox ratio is a robust methodology for measuring metabolism in the cumulus and oocyte compartments compared with oxygen consumption in the whole COC. We also determined whether optical imaging could detect metabolic differences associated with poor oocyte quality (etomoxir-treated). We used confocal microscopy to measure NAD(P)H and FAD, and extracellular flux to measure oxygen consumption. We found that the optical redox ratio was an accurate reflection of metabolism in the oocyte compartment when compared with oxygen consumption (whole COC). Etomoxir-treated COCs showed significantly lower levels of NAD(P)H and FAD compared to control. While confocal imaging demonstrated the premise, we validated this approach using hyperspectral imaging, which is clinically compatible due to its low energy dose. This confirmed lower NAD(P)H and FAD in etomoxir-treated COCs. When comparing imaged vs non-imaged COCs, subsequent preimplantation development and post-transfer viability were comparable. Collectively, these results demonstrate that label-free optical imaging of metabolic cofactors is a safe and sensitive assay for measuring metabolism and has potential to assess oocyte developmental competence.

Quantitative auto-fluorescence quenching of free and bound NADH in HeLa cell line model with Carbonyl cyanide-p-Trifluoromethoxy phenylhydrazone (FCCP) as quenching agent

The autofluorescence of endogenous biomolecules (Nicotinamide adenine dinucleotide (NAD, its reduced form NADH and the phosphorylated form NAD(P)H take part in cellular metabolic pathways and has vital importance for in vivo and ex vivo photo diagnostic applications of biological tissues. We present a detailed quenching analysis of Carbonyl cyanide-p-Trifluoromethoxy phenylhydrazone (FCCP) 50-1000 µM and analyzed the fluorescence signal from NADH/ NAD(P)H in vitro (in solution) and in vivo (HeLa cell suspension).The in vitro samples of pure NADH/ NAD(P)H were excited at λ=340±1 nm while the fluorescence signal was collected in the range of 400-550 nm. The quenching process was characterized using excitation emission matrix (EEM) fluorescence spectroscopy and Stern- Volmer plots. The experimental results illustrated maximum fluorescence emission for the control NADH samples (i.e., no FCCP), while the fluorescence signal from the solution progressively decreased with the increasing concentration of the FCCP, until it reaches the base line (i.e., no fluorescence signal) at 1000 µM of FCCP. In vitro study shows that the fluorescence quenching of free NADH was found to be lower than the bound NAD(P)H with similar diminishing trend. The quenching of bound NAD(P)H in cells is attenuated compared to solution quenching possibly due to a contribution from the metabolic/antioxidant response in cells and fluorescence exponential decay curve lies between plated and suspended HeLa cells. A two-fold increase in the fluorescence intensity of NAD(P)H was observed after the bond formation with L-Malate Dehydrogenase (L-MDH, Sigma Aldrich #10127248001) protein This work has applications for sharp tumor demarcation during sensitive surgical procedures as well as to enhance fluorescence based diagnosis of biological tissues.

Pterygium and Ocular Surface Squamous Neoplasia: Optical Biopsy Using a Novel Autofluorescence Multispectral Imaging Technique

In this study, differentiation of pterygium vs. ocular surface squamous neoplasia based on multispectral autofluorescence imaging technique was investigated. Fifty (N = 50) patients with histopathological diagnosis of pterygium (PTG) and/or ocular surface squamous neoplasia (OSSN) were recruited. Fixed unstained biopsy specimens were imaged by multispectral microscopy. Tissue autofluorescence images were obtained with a custom-built fluorescent microscope with 59 spectral channels, each with specific excitation and emission wavelength ranges, suitable for the most abundant tissue fluorophores such as elastin, flavins, porphyrin, and lipofuscin. Images were analyzed using a new classification framework called fused-classification, designed to minimize interpatient variability, as an established support vector machine learning method. Normal, PTG, and OSSN regions were automatically detected and delineated, with accuracy evaluated against expert assessment by a specialist in OSSN pathology. Signals from spectral channels yielding signals from elastin, flavins, porphyrin, and lipofuscin were significantly different between regions classified as normal, PTG, and OSSN (p < 0.01). Differential diagnosis of PTG/OSSN and normal tissue had accuracy, sensitivity, and specificity of 88 ± 6%, 84 ± 10% and 91 ± 6%, respectively. Our automated diagnostic method generated maps of the reasonably well circumscribed normal/PTG and OSSN interface. PTG and OSSN margins identified by our automated analysis were in close agreement with the margins found in the H&E sections. Such a map can be rapidly generated on a real time basis and potentially used for intraoperative assessment.

Multispectral autofluorescence characteristics of reproductive aging in old and young mouse oocytes

Increasing age has a major detrimental impact on female fertility, which, with an ageing population, has major sociological implications. This impact is primarily mediated through deteriorating quality of the oocyte. Deteriorating oocyte quality with biological age is the greatest rate-limiting factor to female fertility. Here we have used label-free, non-invasive multi-spectral imaging to identify unique autofluorescence profiles of oocytes from young and aged animals. Discriminant analysis demonstrated that young oocytes have a distinct autofluorescent profile which accurately distinguishes them from aged oocytes. We recently showed that treatment with the nicotinamide adenine dinucleotide (NAD+) precursor nicotinamide mononucleotide (NMN) restored oocyte quality and fertility in aged animals, and when our analysis was applied to oocytes from aged animals treated with NMN, 85% of these oocytes were classified as having the autofluorescent signature of young animals. Spectral unmixing using the Robust Dependent Component Analysis (RoDECA) algorithm demonstrated that NMN treatment altered the metabolic profile of oocytes, increasing free NAD(P)H, protein bound NAD(P)H, redox ratio and the ratio of bound to free NAD(P)H. The frequency of oocytes with simultaneously high NAD(P)H and flavin content was also significantly increased in mice treated with NMN. Young and Aged + NMN oocytes had a smoother spectral distribution, with the distribution of NAD(P)H in young oocytes specifically differing from that of aged oocytes. Identifying the multispectral profile of oocyte autofluorescence during aging could have utility as a non-invasive and sensitive measure of oocyte quality.

Characterization of chicken meat contaminated with Salmonella by fluorescence spectroscopy

Contaminated poultry products as eggs and meat are the primary vehicles of Salmonella infection. Conventional methods for microorganisms detections involve multiple steps, and despite its accuracy, these assays are time-consuming. Biosensing methods have shown great potential for the rapid detection of foodborne pathogens. Some of the biosensors are based on fluorescence. Various fluorophores such as collagen, elastin, NAD(P)H, and porphyrins can be used to evaluate possible chemical changes in meat. In this manuscript, the fluorescence properties of chicken meat contaminated with Salmonella enterica (ATCC 14028) cell suspensions (500; 5000; 50,000 and 500,000 cells/mL) were obtained and compared with non-contaminated control, for meat kept at 25 °C for 24 and 48 h. The effects of ambient light were also considered. Our results indicated that free NAD(P)H and coproporphyrin emission bands present in contaminated meat, increased over time, and can provide access to valuable information for the detection of Salmonella in chicken meat.

Non-invasive, label-free optical analysis to detect aneuploidy within the inner cell mass of the preimplantation embryo

STUDY QUESTION

Can label-free, non-invasive optical imaging by hyperspectral autofluorescence microscopy discern between euploid and aneuploid cells within the inner cell mass (ICM) of the mouse preimplantation embryo?

SUMMARY ANSWER

Hyperspectral autofluorescence microscopy enables discrimination between euploid and aneuploid ICM in mouse embryos.

WHAT IS KNOWN ALREADY

Euploid/aneuploid mosaicism affects up to 17.3% of human blastocyst embryos with trophectoderm biopsy or spent media currently utilized to diagnose aneuploidy and mosaicism in clinical in vitro fertilization. Based on their design, these approaches will fail to diagnose the presence or proportion of aneuploid cells within the foetal lineage ICM of some blastocyst embryos.

STUDY DESIGN, SIZE, DURATION

The impact of aneuploidy on cellular autofluorescence and metabolism of primary human fibroblast cells and mouse embryos was assessed using a fluorescence microscope adapted for imaging with multiple spectral channels (hyperspectral imaging). Primary human fibroblast cells with known ploidy were subjected to hyperspectral imaging to record native cell fluorescence (4-6 independent replicates, euploid n = 467; aneuploid n = 969). For mouse embryos, blastomeres from the eight-cell stage (five independent replicates: control n = 39; reversine n = 44) and chimeric blastocysts (eight independent replicates: control n = 34; reversine n = 34; 1:1 (control:reversine) n = 30 and 1:3 (control:reversine) n = 37) were utilized for hyperspectral imaging. The ICM from control and reversine-treated embryos were mechanically dissected and their karyotype confirmed by whole genome sequencing (n = 13 euploid and n = 9 aneuploid).

PARTICIPANTS/MATERIALS, SETTING, METHODS

Two models were employed: (i) primary human fibroblasts with known karyotype and (ii) a mouse model of embryo aneuploidy where mouse embryos were treated with reversine, a reversible spindle assembly checkpoint inhibitor, during the four- to eight-cell division. Individual blastomeres were dissociated from control and reversine-treated eight-cell embryos and either imaged directly or used to generate chimeric blastocysts with differing ratios of control:reversine-treated cells. Individual blastomeres and embryos were interrogated by hyperspectral imaging. Changes in cellular metabolism were determined by quantification of metabolic co-factors (inferred from their autofluorescence signature): NAD(P)H and flavins with the subsequent calculation of the optical redox ratio (ORR: flavins/[NAD(P)H + flavins]). Autofluorescence signals obtained from hyperspectral imaging were examined mathematically to extract features from each cell/blastomere/ICM. This was used to discriminate between different cell populations.

MAIN RESULTS AND THE ROLE OF CHANCE

An increase in the relative abundance of NAD(P)H and decrease in flavins led to a significant reduction in the ORR for aneuploid cells in primary human fibroblasts and reversine-treated mouse blastomeres (P < 0.05). Mathematical analysis of endogenous cell autofluorescence achieved separation between (i) euploid and aneuploid primary human fibroblast cells, (ii) control and reversine-treated mouse blastomeres cells, (iii) control and reversine-treated chimeric blastocysts, (iv) 1:1 and 1:3 chimeric blastocysts and (v) confirmed euploid and aneuploid ICM from mouse blastocysts. The accuracy of these separations was supported by receiver operating characteristic curves with areas under the curve of 0.97, 0.99, 0.87, 0.88 and 0.93, respectively. We believe that the role of chance is low as mathematical features separated euploid from aneuploid in both human fibroblasts and ICM of mouse blastocysts.

LARGE SCALE DATA

N/A.

LIMITATIONS, REASONS FOR CAUTION

Although we were able to discriminate between euploid and aneuploid ICM in mouse blastocysts, confirmation of this approach in human embryos is required. While we show this approach is safe in mouse, further validation is required in large animal species prior to implementation in a clinical setting.

WIDER IMPLICATIONS OF THE FINDINGS

We have developed an original, accurate and non-invasive optical approach to assess aneuploidy within the ICM of mouse embryos in the absence of fluorescent tags. Hyperspectral autofluorescence imaging was able to discriminate between euploid and aneuploid human fibroblast and mouse blastocysts (ICM). This approach may potentially lead to a new diagnostic for embryo analysis.

STUDY FUNDING/COMPETING INTEREST(S)

K.R.D. is supported by a Mid-Career Fellowship from the Hospital Research Foundation (C-MCF-58-2019). This study was funded by the Australian Research Council Centre of Excellence for Nanoscale Biophotonics (CE140100003) and the National Health and Medical Research Council (APP2003786). The authors declare that there is no conflict of interest.

Non-invasive assessment of exfoliated kidney cells extracted from urine using multispectral autofluorescence features

Optimally preserved urinary exfoliated renal proximal tubule cells were assessed by multispectral imaging of cell autofluorescence. We demonstrated different multispectral autofluorescence signals in such cells extracted from the urine of patients with healthy or diseased kidneys. Using up to 10 features, we were able to differentiate cells from individuals with heathy kidneys and impaired renal function (indicated by estimated glomerular filtration rate (eGFR) values) with the receiver operating characteristic area under the curve (AUC) of 0.99. Using the same method, we were also able to discriminate such urine cells from patients with and without renal fibrosis on biopsy, where significant differences in multispectral autofluorescence signals (AUC = 0.90) were demonstrated between healthy and diseased patients (p < 0.05). These findings show that multispectral assessment of the cell autofluorescence in urine exfoliated proximal tubule kidney cells has the potential to be developed as a sensitive, non-invasive diagnostic method for CKD.

NAD+ Repletion Rescues Female Fertility during Reproductive Aging

Reproductive aging in female mammals is an irreversible process associated with declining oocyte quality, which is the rate-limiting factor to fertility. Here, we show that this loss of oocyte quality with age accompanies declining levels of the prominent metabolic cofactor nicotinamide adenine dinucleotide (NAD⁺). Treatment with the NAD⁺ metabolic precursor nicotinamide mononucleotide (NMN) rejuvenates oocyte quality in aged animals, leading to restoration in fertility, and this can be recapitulated by transgenic overexpression of the NAD⁺-dependent deacylase SIRT2, though deletion of this enzyme does not impair oocyte quality. These benefits of NMN extend to the developing embryo, where supplementation reverses the adverse effect of maternal age on developmental milestones. These findings suggest that late-life restoration of NAD⁺ levels represents an opportunity to rescue female reproductive function in mammals.

Declining oocyte quality is considered an irreversible feature of aging and is rate limiting for human fertility. Bertoldo et al. show that reversing an age-dependent decline in NAD(P)H restores oocyte quality, embryo development, and functional fertility in aged mice. These findings may be relevant to reproductive medicine.

KLF5 Is Induced by FOXO1 and Causes Oxidative Stress and Diabetic Cardiomyopathy

RATIONALE

Diabetic cardiomyopathy (DbCM) is a major complication in type-1 diabetes, accompanied by altered cardiac energetics, impaired mitochondrial function, and oxidative stress. Previous studies indicate that type-1 diabetes is associated with increased cardiac expression of KLF5 (Krüppel-like factor-5) and PPARα (peroxisome proliferator-activated receptor) that regulate cardiac lipid metabolism.

OBJECTIVE

In this study, we investigated the involvement of KLF5 in DbCM and its transcriptional regulation.

METHODS AND RESULTS

KLF5 mRNA levels were assessed in isolated cardiomyocytes from cardiovascular patients with diabetes and were higher compared with nondiabetic individuals. Analyses in human cells and diabetic mice with cardiomyocyte-specific FOXO1 (Forkhead box protein O1) deletion showed that FOXO1 bound directly on the KLF5 promoter and increased KLF5 expression. Diabetic mice with cardiomyocyte-specific FOXO1 deletion had lower cardiac KLF5 expression and were protected from DbCM. Genetic, pharmacological gain and loss of KLF5 function approaches and AAV (adeno-associated virus)-mediated Klf5 delivery in mice showed that KLF5 induces DbCM. Accordingly, the protective effect of cardiomyocyte FOXO1 ablation in DbCM was abolished when KLF5 expression was rescued. Similarly, constitutive cardiomyocyte-specific KLF5 overexpression caused cardiac dysfunction. KLF5 caused oxidative stress via direct binding on NADPH oxidase (NOX)4 promoter and induction of NOX4 (NADPH oxidase 4) expression. This was accompanied by accumulation of cardiac ceramides. Pharmacological or genetic KLF5 inhibition alleviated superoxide formation, prevented ceramide accumulation, and improved cardiac function in diabetic mice.

CONCLUSIONS

Diabetes-mediated activation of cardiomyocyte FOXO1 increases KLF5 expression, which stimulates NOX4 expression, ceramide accumulation, and causes DbCM.

Identifying metastatic ability of prostate cancer cell lines using native fluorescence spectroscopy and machine learning methods

Metastasis is the leading cause of mortalities in cancer patients due to the spreading of cancer cells to various organs. Detecting cancer and identifying its metastatic potential at the early stage is important. This may be achieved based on the quantification of the key biomolecular components within tissues and cells using recent optical spectroscopic techniques. The aim of this study was to develop a noninvasive label-free optical biopsy technique to retrieve the characteristic molecular information for detecting different metastatic potentials of prostate cancer cells. Herein we report using native fluorescence (NFL) spectroscopy along with machine learning (ML) to differentiate prostate cancer cells with different metastatic abilities. The ML algorithms including principal component analysis (PCA) and nonnegative matrix factorization (NMF) were used for dimension reduction and feature detection. The characteristic component spectra were used to identify the key biomolecules that are correlated with metastatic potentials. The relative concentrations of the molecular spectral components were retrieved and used to classify the cancer cells with different metastatic potentials. A multi-class classification was performed using support vector machines (SVMs). The NFL spectral data were collected from three prostate cancer cell lines with different levels of metastatic potentials. The key biomolecules in the prostate cancer cells were identified to be tryptophan, reduced nicotinamide adenine dinucleotide (NADH) and hypothetically lactate as well. The cancer cells with different metastatic potentials were classified with high accuracy using the relative concentrations of the key molecular components. The results suggest that the changes in the relative concentrations of these key fluorophores retrieved from NFL spectra may present potential criteria for detecting prostate cancer cells of different metastatic abilities.

A review of the medical hyperspectral imaging systems and unmixing algorithms' in biological tissues

Hyperspectral fluorescence imaging (HFI) is a well-known technique in the medical research field and is considered a non-invasive tool for tissue diagnosis. This review article gives a brief introduction to acquisition methods, including the image preprocessing methods, feature selection and extraction methods, data classification techniques and medical image analysis along with recent relevant references. The process of fusion of unsupervised unmixing techniques with other classification methods, like the combination of support vector machine with an artificial neural network, the latest snapshot Hyperspectral imaging (HSI) and vortex analysis techniques are also outlined. Finally, the recent applications of hyperspectral images in cellular differentiation of various types of cancer are discussed.

Optical imaging of cleavage stage bovine embryos using hyperspectral and confocal approaches reveals metabolic differences between on-time and fast-developing embryos

The assessment of embryo quality aims to enhance subsequent pregnancy and live birth outcomes. Metabolic analysis of embryos has immense potential in this regard. As a step towards this goal, here we assess the metabolism of bovine embryos using label-free optical imaging. We compared embryos defined as either on-time or fast-developing, as fast dividing embryos are more likely to develop to the blastocyst stage. Specifically, bovine embryos at 48 (Day 2) and 96 (Day 4) hours post fertilization were fixed and separated based on morphological assessment: on-time (Day 2: 2 cell; Day 4: 5-7 cell) or fast-developing (Day 2: 3-7 cell; Day 4: 8-16 cell). Embryos with different developmental rates on Day 2 and Day 4 were correlated with metabolic activity and DNA damage. Confocal microscopy was used to assess metabolic activity by quantification of cellular autofluorescence specific for the endogenous fluorophores NAD(P)H and FAD with a subsequent calculation of the optical redox ratio. Separately, hyperspectral microscopy was employed to assess a broader range of endogenous fluorophores. DNA damage was determined using γH2AX immunohistochemistry. Hyperspectral imaging showed significantly lower abundance of endogenous fluorophores in fast-developing compared to on-time embryos on Day 2, indicating a lower metabolic activity. On Day 4 of development there was no difference in the abundance of FAD between on-time and fast-developing embryos. There was, however, significantly higher levels of NAD(P)H in fast-developing embryos leading to a significantly lower optical redox ratio when compared to on-time embryos. Collectively, these results demonstrate that fast-developing embryos present a 'quiet' metabolic pattern on Day 2 and Day 4 of development, compared to on-time embryos. There was no difference in the level of DNA damage between on-time and fast-developing embryos on either day of development. To our knowledge, this is the first collective use of confocal and hyperspectral imaging in cleavage-stage bovine embryos in the absence of fluorescent tags.

Sex and SP-A2 Dependent NAD(H) Redox Alterations in Mouse Alveolar Macrophages in Response to Ozone Exposure: Potential Implications for COVID-19

Co-enzyme nicotinamide adenine dinucleotide (NAD(H)) redox plays a key role in macrophage function. Surfactant protein (SP-) A modulates the functions of alveolar macrophages (AM) and ozone (O₃) exposure in the presence or absence of SP-A and reduces mouse survival in a sex-dependent manner. It is unclear whether and how NAD(H) redox status plays a role in the innate immune response in a sex-dependent manner. We investigated the NAD(H) redox status of AM from SP-A2 and SP-A knockout (KO) mice in response to O₃ or filtered air (control) exposure using optical redox imaging technique. We found: (i) In SP-A2 mice, the redox alteration of AM in response to O₃ showed sex-dependence with AM from males being significantly more oxidized and having a higher level of mitochondrial reactive oxygen species than females; (ii) AM from KO mice were more oxidized after O₃ exposure and showed no sex differences; (iii) AM from female KO mice were more oxidized than female SP-A2 mice; and (iv) Two distinct subpopulations characterized by size and redox status were observed in a mouse AM sample. In conclusions, the NAD(H) redox balance in AM responds to O₃ in a sex-dependent manner and the innate immune molecule, SP-A2, contributes to this observed sex-specific redox response.

The Observation and Characterisation of Fluorescent Bioaerosols Using Real-Time UV-LIF Spectrometry in Hong Kong from June to November 2018

Hong Kong is an area of complex topography, with mixtures of urban and greenbelt spaces. Local bioaerosol concentrations are multifaceted, depending on seasonal variations of meteorological conditions and emission sources. This study is the first known attempt at both quantitatively measuring and identifying airborne bioaerosol contributions, by utilising multiple single particle ultraviolet light-induced fluorescence spectrometers. Based in the Hong Kong University of Science and Technology’s super-site, a WIBS-NEO and PLAIR Rapid-E were operated from June to November, 2018. The purpose of this long-term campaign was to observe the shift in wind patterns and meteorological conditions as the seasons changed, and to investigate how, or if, this impacted on the dispersion and concentrations of bioaerosols in the area. Bioaerosol concentrations based on the particle auto-fluorescence spectra remained low through the summer and autumn months, averaging 4.2 L−1 between June and October. Concentrations were greatest in October, peaking up to 23 L−1. We argued that these concentrations were dominated by dry-weather fungal spores, as evidenced by their spectral profile and relationship with meteorological variables. We discuss potential bioaerosol source regions based on wind-sector cluster analysis and believe that this study paints a picture of bioaerosol emissions in an important region of the world.

Ageing human bone marrow mesenchymal stem cells have depleted NAD(P)H and distinct multispectral autofluorescence

Stem cell exhaustion plays a major role in the ageing of different tissues. Similarly, in vitro cell ageing during expansion prior to their use in regenerative medicine can severely compromise stem cell quality through progressive declines in differentiation and growth capacity. We utilized non-destructive multispectral assessment of native cell autofluorescence to investigate the metabolic mechanisms of in vitro mesenchymal stem cell (MSC) ageing in human bone marrow MSCs over serial passages (P2-P10). The spectral signals for NAD(P)H, flavins and protein-bound NAD(P)H were successfully isolated using Robust Dependent Component Analysis (RoDECA). NAD(P)H decreased over the course of hMSC ageing in absolute terms as well as relative to flavins (optical redox ratio). Relative changes in other fluorophore levels (flavins, protein-bound NAD(P)H) suggested that this reduction was due to nicotinamide adenine dinucleotide depletion rather than a metabolic shift from glycolysis to oxidative phosphorylation. Using multispectral features, which are determined without cell fixation or fluorescent labelling, we developed and externally validated a reliable, linear model which could accurately categorize the age of culture-expanded hMSCs. The largest shift in spectral characteristics occurs early in hMSC ageing. These findings demonstrate the feasibility of applying multispectral technology for the non-invasive monitoring of MSC health in vitro.

Science convergence applied to psychoneuroimmunology: The future of measurement and imaging

The future of psychoneuroimmunology requires breakthrough technology discoveries. These next generation technologies need to address the unique challenges that are raised by imaging and measuring the activity of the neuroimmune interface in health and disease. The complexity of this challenge is centred around the multidimensionality of the neuroimmune system. These include novel challenges of capturing potent and rare biological signals over long times and vast anatomical distances. Here is a summary of the outcomes of the investments made by the Australian Research Council Centre of Excellence for Nanoscale BioPhotonics which was presented as part of the PNIRSAsia-Pacific symposium at the 2019 International Brain Research Organization.

Non-invasive real-time imaging of reactive oxygen species (ROS) using auto-fluorescence multispectral imaging technique: A novel tool for redox biology

Detecting reactive oxygen species (ROS) that play a critical role as redox modulators and signalling molecules in biological systems currently requires invasive methods such as ROS -specific indicators for imaging and quantification. We developed a non-invasive, real-time, label-free imaging technique for assessing the level of ROS in live cells and thawed cryopreserved tissues that is compatible with in-vivo imaging. The technique is based on autofluorescence multispectral imaging (AFMI) carried out in an adapted fluorescence microscope with an expanded number of spectral channels spanning specific excitation (365 nm-495 nm) and emission (420 nm-700 nm) wavelength ranges. We established a strong quantitative correlation between the spectral information obtained from AFMI and the level of ROS obtained from CellROX staining. The results were obtained in several cell types (HeLa, PANC1 and mesenchymal stem cells) and in live kidney tissue. Additioanly,two spectral regimes were considered: with and without UV excitation (wavelengths > 400 nm); the latter being suitable for UV-sensitive systems such as the eye. Data were analyzed by linear regression combined with an optimization method of swarm intelligence. This allowed the calibration of AFMI signals to the level of ROS with excellent correlation (R = 0.84, p = 0.00) in the entire spectral range and very good correlation (R = 0.78, p = 0.00) in the limited, UV-free spectral range. We also developed a strong classifier which allowed us to distinguish moderate and high levels of ROS in these two regimes (AUC = 0.91 in the entire spectral range and AUC = 0.78 for UV-free imaging). These results indicate that ROS in cells and tissues can be imaged non-invasively, which opens the way to future clinical applications in conditions where reactive oxygen species are known to contribute to progressive disease such as in ophthalmology, diabetes, kidney disease, cancer and neurodegenerative diseases.

Fluorescence lifetime imaging microscopy: fundamentals and advances in instrumentation, analysis, and applications

SIGNIFICANCE

Fluorescence lifetime imaging microscopy (FLIM) is a powerful technique to distinguish the unique molecular environment of fluorophores. FLIM measures the time a fluorophore remains in an excited state before emitting a photon, and detects molecular variations of fluorophores that are not apparent with spectral techniques alone. FLIM is sensitive to multiple biomedical processes including disease progression and drug efficacy.

AIM

We provide an overview of FLIM principles, instrumentation, and analysis while highlighting the latest developments and biological applications.

APPROACH

This review covers FLIM principles and theory, including advantages over intensity-based fluorescence measurements. Fundamentals of FLIM instrumentation in time- and frequency-domains are summarized, along with recent developments. Image segmentation and analysis strategies that quantify spatial and molecular features of cellular heterogeneity are reviewed. Finally, representative applications are provided including high-resolution FLIM of cell- and organelle-level molecular changes, use of exogenous and endogenous fluorophores, and imaging protein-protein interactions with Förster resonance energy transfer (FRET). Advantages and limitations of FLIM are also discussed.

CONCLUSIONS

FLIM is advantageous for probing molecular environments of fluorophores to inform on fluorophore behavior that cannot be elucidated with intensity measurements alone. Development of FLIM technologies, analysis, and applications will further advance biological research and clinical assessments.

Relationship between Optical Redox Status and Reactive Oxygen Species in Cancer Cells

Shifted NAD(H) redox status and enhanced reactive oxygen species (ROS) scavenging systems have been observed in cancers. However, how such redox shift is related to the ROS level in cancer cells is less clear. Based on collecting the intrinsic fluorescence of oxidized flavoproteins (Fp containing flavin adenine dinucleotide) and reduced nicotinamide adenine dinucleotide (NADH), optical redox imaging (ORI) provides a quantitative measure of the mitochondrial redox state by the optical redox ratio, Fp/(NADH+Fp), a surrogate marker of the NAD⁺-coupled redox state NAD⁺/NADH. Our study aims to explore the relationship between NAD(H) redox status and ROS by imaging NADH, Fp, and ROS levels using cultured breast cancer cell models. By manipulating either ROS levels via application of exogenous H₂O₂ or redox status via metabolic perturbation compounds, we found that: (1) oxidation of NAD(H) redox status correlates with ROS levels at lower H₂O₂ concentrations (up to ~700 μM), but not necessarily at higher concentrations; (2) an elevated ROS level diminishes NADH and reduces redox ratio plasticity; (3) either more oxidized or more reduced status can correlate to an increased ROS level; and (4) sometimes, a more oxidized status can correlate to a decreased ROS level depending on cell lines. These observations indicated that cellular NAD(H) redox state and ROS are intricately related but can also change separately. This study can benefit cancer research as both NAD(H) redox status and ROS have been implicated in cancer transformation and progression.

Optimization of FLIM imaging, fitting and analysis for auto-fluorescent NAD(P)H and FAD in cells and tissues

Increasingly, the auto-fluorescent coenzymes NAD(P)H and FAD are being tracked by multi-photon fluorescence lifetime microscopy (FLIM) and used as versatile markers for changes in mammalian metabolism. The cellular redox state of different cell model systems, organoids and tissue sections is investigated in a range of pathologies where the metabolism is disrupted or reprogrammed; the latter is particularly relevant in cancer biology. Yet, the actual optimized process of acquiring images by FLIM, execute a correct lifetime fitting procedure and subsequent processing and analysis can be challenging for new users. Questions remain of how to optimize FLIM experiments, whether any potential photo-bleaching affects FLIM results and whether fixed specimens can be used in experiments. We have broken down the multi-step sequence into best-practice application of FLIM for NAD(P)H and FAD imaging, with images generated by a time-correlated-single-photon-counting (TCSPC) system, fitted with Becker & Hickl software and further processed with open-source ImageJ/Fiji and Python software.

Optical Redox Imaging Detects the Effects of DEK Oncogene Knockdown on the Redox State of MDA-MB-231 Breast Cancer Cells

PURPOSE

Optical redox imaging (ORI), based on collecting the endogenous fluorescence of reduced nicotinamide adenine dinucleotide (NADH) and oxidized flavoproteins (Fp) containing a redox cofactor flavin adenine dinucleotide (FAD), provides sensitive indicators of cellular metabolism and redox status. ORI indices (such as NADH, FAD, and their ratio) have been under investigation as potential progression/prognosis biomarkers for cancer. Higher FAD redox ratio (i.e., FAD/(FAD + NADH)) has been associated with higher invasive/metastatic potential in tumor xenografts and cultured cells. This study is to examine whether ORI indices can respond to the modulation of oncogene DEK activities that change cancer cell invasive/metastatic potential.

PROCEDURES

Using lentiviral shRNA, DEK gene expression was efficiently knocked down in MDA-MB-231 breast cancer cells (DEKsh). These DEKsh cells, along with scrambled shRNA-transduced control cells (NTsh), were imaged with a fluorescence microscope. In vitro invasive potential of the DEKsh cells and NTsh cells was also measured in parallel using the transwell assay.

RESULTS

FAD and FAD redox ratios in polyclonal cells with DEKsh were significantly lower than that in NTsh control cells. Consistently, the DEKsh cells demonstrated decreased invasive potential than their non-knockdown counterparts NTsh cells.

CONCLUSIONS

This study provides direct evidence that oncogene activities could mediate ORI-detected cellular redox state.

Novel automated non invasive detection of ocular surface squamous neoplasia using multispectral autofluorescence imaging

PURPOSE

Diagnosing Ocular surface squamous neoplasia (OSSN) using newly designed multispectral imaging technique.

METHODS

Eighteen patients with histopathological diagnosis of Ocular Surface Squamous Neoplasia (OSSN) were recruited. Their previously collected biopsy specimens of OSSN were reprocessed without staining to obtain auto fluorescence multispectral microscopy images. This technique involved a custom-built spectral imaging system with 38 spectral channels. Inter and intra-patient frameworks were deployed to automatically detect and delineate OSSN using machine learning methods. Different machine learning methods were evaluated, with K nearest neighbor and Support Vector Machine chosen as preferred classifiers for intra- and inter-patient frameworks, respectively. The performance of the technique was evaluated against a pathological assessment.

RESULTS

Quantitative analysis of the spectral images provided a strong multispectral signature of a relative difference between neoplastic and normal tissue both within each patient (at p < 0.0005) and between patients (at p < 0.001). Our fully automated diagnostic method based on machine learning produces maps of the relatively well circumscribed neoplastic-non neoplastic interface. Such maps can be rapidly generated in quasi-real time and used for intraoperative assessment. Generally, OSSN could be detected using multispectral analysis in all patients investigated here. The cancer margins detected by multispectral analysis were in close and reasonable agreement with the margins observed in the H&E sections in intra- and inter-patient classification, respectively.

CONCLUSIONS

This study shows the feasibility of using multispectral auto-fluorescence imaging to detect and find the boundary of human OSSN. Fully automated analysis of multispectral images based on machine learning methods provides a promising diagnostic tool for OSSN which can be translated to future clinical applications.

Quantitation of NAD+: Why do we need to measure it?

BACKGROUND

Nicotinamide adenine dinucleotide (NAD⁺) is an essential pyridine nucleotide that is currently investigated as an important target to extend lifespan and health span. Age-related NAD+ depletion due to the accumulation of oxidative stress is associated with reduced energy production, impaired DNA repair and genomic instability.

SCOPE OF REVIEW

NAD+ levels can be elevated therapeutically using NAD+ precursors or through lifestyle modifications including exercise and caloric restriction. However, high amounts of NAD+ may be detrimental in cancer progression and may have deleterious immunogenic roles.

MAJOR CONCLUSIONS

Standardized quantitation of NAD+ and related metabolites may therefore represent an important component of NAD+ therapy.

GENERAL SIGNIFICANCE

Quantitation of NAD+ may serve dual roles not only as an ageing biomarker, but also as a diagnostic tool for the prevention of malignant disorders.

Targeted redox and energy cofactor metabolomics in Clostridium thermocellum and Thermoanaerobacterium saccharolyticum

BACKGROUND

Clostridium thermocellum and Thermoanaerobacterium saccharolyticum are prominent candidate biocatalysts that, together, can enable the direct biotic conversion of lignocellulosic biomass to ethanol. The imbalance and suboptimal turnover rates of redox cofactors are currently hindering engineering efforts to achieve higher bioproductivity in both organisms. Measuring relevant intracellular cofactor concentrations will help understand redox state of these cofactors and help identify a strategy to overcome these limitations; however, metabolomic determinations of these labile metabolites have historically proved challenging.

RESULTS

Through our validations, we verified the handling and storage stability of these metabolites, and verified extraction matrices and extraction solvent were not suppressing mass spectrometry signals. We recovered adenylate energy charge ratios (a main quality indicator) above 0.82 for all extractions. NADH/NAD+ values of 0.26 and 0.04 for an adhE-deficient strain of C. thermocellum and its parent, respectively, reflect the expected shift to a more reduced redox potential when a species lacks the ability to re-oxidize NADH by synthesizing ethanol. This method failed to yield reliable results with C. bescii and poor-growing strains of T. saccharolyticum.

CONCLUSIONS

Our validated protocols demonstrate and validate the extraction and analysis of selected redox and energy-related metabolites from two candidate consolidated bioprocessing biocatalysts, C. thermocellum and T. saccharolyticum. This development and validation highlights the important, but often neglected, need to optimize and validate metabolomic protocols when adapting them to new cell or tissue types.

Statistically strong label-free quantitative identification of native fluorophores in a biological sample

Bioimaging using endogenous cell fluorescence, without any external biomarkers makes it possible to explore cells and tissues in their original native state, also in vivo. In order to be informative, this label-free method requires careful multispectral or hyperspectral recording of autofluorescence images followed by unsupervised extraction (unmixing) of biochemical signatures. The unmixing is difficult due to the scarcity of biochemically pure regions in cells and also because autofluorescence is weak compared with signals from labelled cells, typically leading to low signal to noise ratio. Here, we solve the problem of unsupervised hyperspectral unmixing of cellular autofluorescence by introducing the Robust Dependent Component Analysis (RoDECA). This approach provides sophisticated and statistically robust quantitative biochemical analysis of cellular autofluorescence images. We validate our method on artificial images, where the addition of varying known level of noise has allowed us to quantify the accuracy of our RoDECA analysis in a way that can be applied to real biological datasets. The same unsupervised statistical minimisation is then applied to imaging of mouse retinal photoreceptor cells where we establish the identity of key endogenous fluorophores (free NADH, FAD and lipofuscin) and derive the corresponding molecular abundance maps. The pre-processing methodology of image datasets is also presented, which is essential for the spectral unmixing analysis, but mostly overlooked in the previous studies.

Programmable LED-based integrating sphere light source for wide-field fluorescence microscopy

Wide-field fluorescence microscopy commonly uses a mercury lamp, which has limited spectral capabilities. We designed and built a programmable integrating sphere light (PISL) source which consists of nine LEDs, light-collecting optics, a commercially available integrating sphere and a baffle. The PISL source is tuneable in the range 365-490nm with a uniform spatial profile and a sufficient power at the objective to carry out spectral imaging. We retrofitted a standard fluorescence inverted microscope DM IRB (Leica) with a PISL source by mounting it together with a highly sensitive low- noise CMOS camera. The capabilities of the setup have been demonstrated by carrying out multispectral autofluorescence imaging of live BV2 cells.

Autofluorescence and Nonspecific Immunofluorescent Labeling in Frozen Bovine Intestinal Tissue Sections: Solutions for Multicolor Immunofluorescence Experiments

Autofluorescent compounds present in intestinal tissue often hinder the ability to utilize multiple, spectrally different, fluorophores. In addition, fixatives and blocking solutions may contribute to background autofluorescence or nonspecific immunofluorescent labeling. During immunofluorescence protocol development, autofluorescent pigments were observed in frozen bovine mid-ileal intestinal tissue sections. Coagulant fixatives, normal serum blocking, histochemical stains Sudan Black B (SBB) and 3,3'-diaminobenzidine (DAB), and spectral separation using imaging software were compared for their ability to reduce autofluorescence, as well as their effect on immunofluorescent labeling. Fluorescent pigments of frozen bovine mid-ileal intestinal tissue sections, most likely caused by eosinophils and lipofuscin, were masked successfully with a combination of DAB and SBB. Little to no statistical differences were observed for all other methods investigated; however, tissue fixed with 1:1 acetone methanol and 10% horse serum diluted in 0.05 M Tris buffer demonstrated lower mean fluorescence intensities. Spectral separation of specific immunofluorescent labeling from background autofluorescence is a simple method for removing unwanted fluorescence; however, successful separation is dependent on tissue and labeling quality.