Raman studies of the adipose tissue: Current state-of-art and future perspectives in diagnostics

Mapping lipid species remodeling in high fat diet-fed mice: Unveiling adipose tissue dysfunction with Raman microspectroscopy

Dysregulated lipid metabolism in obesity leads to adipose tissue expansion, a major contributor to metabolic dysfunction and chronic disease. Lipid metabolism and fatty acid changes play vital roles in the progression of obesity. In this proof-of-concept study, Raman techniques combined with histochemical imaging methods were utilized to analyze the impact of a high-fat diet (HFD) on different types of adipose tissue in mice, using a small sample size (n = 3 per group). After six weeks of high-fat diet (HFD) feeding, our findings showed hypertrophy, elevated collagen levels, and increased macrophage presence in the adipose tissues of the HFD group compared to the low-fat diet (LFD) group. Statistical analysis of Raman spectra revealed significantly lower unsaturated lipid levels and higher lipid to protein content in different fat pads (brown adipose tissue (BAT), subcutaneous white adipose tissue (SWAT), and visceral white adipose tissue (VWAT)) with HFD. Raman images of adipose tissues were analyzed using Empty modeling and DCLS methods to spatially profile unsaturated and saturated lipid species in the tissues. It revealed elevated levels of ω-3, ω-6, cholesterol, and triacylglycerols in BAT adipose tissues of HFD compared to LFD tissues. These findings indicated that while cholesterol, ω-6/ω-3 ratio, and triacylglycerol levels have risen in the SWAT and VWAT adipose tissues of the HFD group, the levels of ω-3 and ω-6 have decreased following the HFD. The study showed that Raman spectroscopy provided invaluable information at the molecular level for investigating lipid species remodeling and spatial mapping of adipose tissues during HFD.

Combining Multiple Spectroscopic Techniques to Reveal the Effects of Staphylococcus aureus Infection on Human Bone Tissues

Osteomyelitis (OM) and periprosthetic joint infections (PJIs) are major public health concerns in Western countries due to increased life expectancy. Infections usually occur due to bacterial spread through fractures, implants, or blood-borne transmission. The pathogens trigger an inflammatory response that hinders bone tissue regeneration. Treatment requires surgical intervention, which involves the precise removal of infected tissue, wound cleansing, and local and systemic antibiotic administration. Staphylococcus aureus (SA) is one of the most common pathogens causing infection-induced OM and PJIs. It forms antimicrobial-resistant biofilms and is frequently found in healthcare settings. In this proof-of-concept, we present an approach based on multiple spectroscopic techniques aimed at investigating the effects of SA infection on bone tissue, as well as identifying specific markers useful to detect early bacterial colonization on the tissue surface. A cross-section of a human femoral diaphysis, with negative-culture results, was divided into three parts, and the cortical and trabecular regions were separated from each other. Two portions of each bone tissue type were infected with SA for one and seven days, respectively. Multiple techniques were used to investigate the impact of the infection on bone tissue, Brillouin-Raman microspectroscopy and attenuated total reflection Fourier transform infrared spectroscopy were employed to assess and develop a new noninvasive diagnostic method to detect SA by targeting the bone of the host. The results indicate that exposure to SA infection significantly alters the bone structure, especially in the case of the trabecular type, even after just one day. Moreover, Raman spectral markers of the tissue damage were identified, indicating that this technique can detect the effect of the pathogens' presence in bone biopsies and pave the way for potential application during surgery, due to its nondestructive and contactless nature.

Increased obesogenic action of palmitic acid during early stage of adipogenesis

The functional differences between preadipocytes and fully differentiated mature adipocytes derived from stromal vascular fraction stem cells, as well as primary adipocytes have been analysed by evaluating their response to the obesogenic factor (a saturated fatty acid) and TNF-triggered inflammation. The analysis of single adipocytes shows that the saturated fatty acid (palmitic acid) accumulation is accompanied by inflammation and considerably dependent on the stage of the adipogenesis. In particular, preadipocytes show the exceptional potential for palmitic acid uptake resulting in their hypertrophy and the elevated cellular expression of the inflammation marker (ICAM-1). Our research provides new information on the impact of obesogenic factors on preadipocytes that is important in the light of childhood obesity prevention.

New insights into lipid and fatty acid metabolism from Raman spectroscopy

One of the challenges facing biology is to understand metabolic events at a single cellular level. While approaches to examine dynamics of protein distribution or report on spatiotemporal location of signalling molecules are well-established, tools for the dissection of metabolism in single living cells are less common. Advances in Raman spectroscopy, such as stimulated Raman scattering (SRS), are beginning to offer new insights into metabolic events in a range of experimental systems, including model organisms and clinical samples, and across a range of disciplines. Despite the power of Raman imaging, it remains a relatively under-used technique to approach biological problems, in part because of the specialised nature of the analysis. To raise the profile of this method, here we consider some key studies which illustrate how Raman spectroscopy has revealed new insights into fatty acid and lipid metabolism across a range of cellular systems. The powerful and non-invasive nature of this approach offers a new suite of tools for biomolecular scientists to address how metabolic events within cells informs on or underpins biological function. We illustrate potential biological applications, discuss some recent advances, and offer a direction of travel for metabolic research in this area.

Spatially Offset Raman Spectroscopy toward In Vivo Assessment of the Adipose Tissue in Cardiometabolic Pathologies

Spatially offset Raman spectroscopy (SORS) enhanced the capabilities of Raman spectroscopy for the depth-resolved analysis of biological and diffusely scattering samples. This technique offers selective probing of subsurface layers, providing molecular insights without invasive procedures. While SORS has found application in biomedical research, up to now, studies have focused mainly on the detection of mineralization of bones and tissues. Herein, for the first time, SORS is used to assess the soft, organic tissue beneath the skin's surface. In this study, we demonstrate the diagnostic utility of a hand-held SORS device for evaluating the chemical composition of the adipose tissue. We compared perigonadal white adipose tissue (gWAT) in a murine model of atherosclerosis, heart failure, and high-fat diet (HFD) induced obesity. Our results reveal distinct chemical differences in gWAT between HFD-fed and control mice, showcasing the potential of SORS for intravital adipose tissue phenotype characterization. Furthermore, our findings underscore the effectiveness of SORS as a valuable tool for noninvasive assessment of the adipose tissue composition, holding potential diagnostic significance for metabolic disorders.

Imaging of perivascular adipose tissue in cardiometabolic diseases by Raman spectroscopy: Towards single-cell analysis

Perivascular adipose tissue (PVAT) has emerged as a dynamic organ influencing vascular function and cardiovascular health. In this brief review, an overview of the recent research in the investigation of PVAT is presented, ranging from in vivo studies to single-cell methodologies, in particular those based on Raman spectroscopy. The strengths and limitations of each, emphasizing their contributions to the current understanding of PVAT biology were discussed. Ultimately, the integration of these diverse methodologies promises to uncover new therapeutic targets and diagnostic biomarkers, including those emerging from simple Raman spectroscopy-based measurements of alterations in lipid unsaturation degree, invariably associated with PVAT dysfunction.

Perivascular fat tissue and vascular aging: A sword and a shield

The understanding of the function of perivascular adipose tissue (PVAT) in vascular aging has significantly changed due to the increasing amount of information regarding its biology. Adipose tissue surrounding blood vessels is increasingly recognized as a key regulator of vascular disorders. It has significant endocrine and paracrine effects on the vasculature and is mediated by the production of a variety of bioactive chemicals. It also participates in a number of pathological regulatory processes, including oxidative stress, immunological inflammation, lipid metabolism, vasoconstriction, and dilation. Mechanisms of homeostasis and interactions between cells at the local level tightly regulate the function and secretory repertoire of PVAT, which can become dysregulated during vascular aging. The PVAT secretion group changes from being reducing inflammation and lowering cholesterol to increasing inflammation and increasing cholesterol in response to systemic or local inflammation and insulin resistance. In addition, the interaction between the PVAT and the vasculature is reciprocal, and the biological processes of PVAT are directly influenced by the pertinent indicators of vascular aging. The architectural and biological traits of PVAT, the molecular mechanism of crosstalk between PVAT and vascular aging, and the clinical correlation of vascular age-related disorders are all summarized in this review. In addition, this paper aims to elucidate and evaluate the potential benefits of therapeutically targeting PVAT in the context of mitigating vascular aging. Furthermore, it will discuss the latest advancements in technology used for targeting PVAT.

Direct oral and fiber-derived butyrate supplementation as an anti-obesity treatment via different targets

BACKGROUND & AIMS

Butyric (one of the short-chain fatty acids), a major byproduct of the fermentation of non-digestible carbohydrates (e.g. fiber), is supposed to have anti-obesity and anti-inflammatory properties. However, butyrate's potential and mechanism in preventing obesity and the efficient form of administration remain to be clarified.

METHODS

Hence, we studied the effect of oral supplementation with 5% (w/w) sodium butyrate and 4% (w/w) β-glucan (fiber) on young male mice (C57BL/6J) with high-fat diet-induced obesity (HFD: 60 kcal% of fat + 1% of cholesterol). Six weeks old mice were fed diets based on HFD or control (AIN-93G) diet with/without supplements for 4 weeks. The unique, interdisciplinary approach combining several Raman-based techniques (including Raman microscopy and fiber optic Raman spectroscopy) and next-generation sequencing was used to ex vivo analyze various depots of the adipose tissue (white, brown, perivascular) and gut microbiome, respectively.

RESULTS

The findings demonstrate that sodium butyrate more effectively prevent the pathological increase in body weight caused by elevated saturated fatty acids influx linked to a HFD in comparison to β-glucan, thereby entirely inhibiting diet-induced obesity. Moreover, butyrate significantly affects the white adipose tissue (WAT) reducing the epididymal WAT mass in comparison to HFD without supplements, and decreasing lipid saturation in the epididymal WAT and perivascular adipose tissue of the thoracic aorta. Contrarily, β-glucan significantly changes the composition and diversity of the gut microbiome, reversing the HFD effect, but shows no effect on the epididymal WAT mass and therefore the weight gain inhibition is not as effective as with sodium butyrate.

CONCLUSIONS

Here, oral supplementation with sodium butyrate and β-glucan (fiber) has been proven to have an anti-obesity effect through two different targets. Administration-dependent effects that butyrate imposes on the adipose tissue (oral administration) and microbiome (fiber-derived) make it a promising candidate for the personalized treatment of obesity.

Initial experience with radiomics of carotid perivascular adipose tissue in identifying symptomatic plaque

Background

Carotid atherosclerotic ischemic stroke threatens human health and life. The aim of this study is to establish a radiomics model of perivascular adipose tissue (PVAT) around carotid plaque for evaluation of the association between Peri-carotid Adipose Tissue structural changes with stroke and transient ischemic attack.

Methods

A total of 203 patients underwent head and neck computed tomography angiography examination in our hospital. All patients were divided into a symptomatic group (71 cases) and an asymptomatic group (132 cases) according to whether they had acute/subacute stroke or transient ischemic attack. The radiomic signature (RS) of carotid plaque PVAT was extracted, and the minimum redundancy maximum correlation, recursive feature elimination, and linear discriminant analysis algorithms were used for feature screening and dimensionality reduction.

Results

It was found that the RS model achieved the best diagnostic performance in the Bagging Decision Tree algorithm, and the training set (AUC, 0.837; 95%CI: 0.775, 0.899), testing set (AUC, 0.834; 95%CI: 0.685, 0.982). Compared with the traditional feature model, the RS model significantly improved the diagnostic efficacy for identifying symptomatic plaques in the testing set (AUC: 0.834 vs. 0.593; Z = 2.114, p = 0.0345).

Conclusion

The RS model of PVAT of carotid plaque can be used as an objective indicator to evaluate the risk of plaque and provide a basis for risk stratification of carotid atherosclerotic disease.

Fast histological assessment of adipose tissue inflammation by label-free mid-infrared optoacoustic microscopy

Conventional histology, as well as immunohistochemistry or immunofluorescence, enables the study of morphological and phenotypical changes during tissue inflammation with single-cell accuracy. However, although highly specific, such techniques require multiple time-consuming steps to apply exogenous labels, which might result in morphological deviations from native tissue structures. Unlike these techniques, mid-infrared (mid-IR) microspectroscopy is a label-free optical imaging method that retrieves endogenous biomolecular contrast without altering the native composition of the samples. Nevertheless, due to the strong optical absorption of water in biological tissues, conventional mid-IR microspectroscopy has been limited to dried thin (5-10 µm) tissue preparations and, thus, it also requires time-consuming steps-comparable to conventional imaging techniques. Here, as a step towards label-free analytical histology of unprocessed tissues, we applied mid-IR optoacoustic microscopy (MiROM) to retrieve intrinsic molecular contrast by vibrational excitation and, simultaneously, to overcome water-tissue opacity of conventional mid-IR imaging in thick (mm range) tissues. In this proof-of-concept study, we demonstrated application of MiROM for the fast, label-free, non-destructive assessment of the hallmarks of inflammation in excised white adipose tissue; i.e., formation of crown-like structures and changes in adipocyte morphology.

Biochemical differentiation between cancerous and normal human colorectal tissues by micro-Raman spectroscopy

Human colorectal tissues obtained by ten cancer patients have been examined by multiple micro-Raman spectroscopic measurements in the 500-3200 cm^-1 range under 785 nm excitation. Distinct spectral profiles are recorded from different spots on the samples: a predominant 'typical' profile of colorectal tissue, as well as those from tissue topologies with high lipid, blood or collagen content. Principal component analysis identified several Raman bands of amino acids, proteins and lipids which allow the efficient discrimination of normal from cancer tissues, the first presenting plurality of Raman spectral profiles while the last showing off quite uniform spectroscopic characteristics. Tree-based machine learning experiment was further applied on all data as well as on filtered data keeping only those spectra which characterize the largely inseparable data clusters of 'typical' and 'collagen-rich' spectra. This purposive sampling evidences statistically the most significant spectroscopic features regarding the correct identification of cancer tissues and allows matching spectroscopic results with the biochemical changes induced in the malignant tissues.