Brillouin microscopy monitors rapid responses in subcellular compartments.

Measurements and imaging of the mechanical response of biological cells are critical for understanding the mechanisms of many diseases, and for fundamental studies of energy, signal and force transduction. The recent emergence of Brillouin microscopy as a powerful non-contact, label-free way to non-invasively and non-destructively assess local viscoelastic properties provides an opportunity to expand the scope of biomechanical research to the sub-cellular level. Brillouin spectroscopy has recently been validated through static measurements of cell viscoelastic properties, however, fast (sub-second) measurements of sub-cellular cytomechanical changes have yet to be reported. In this report, we utilize a custom multimodal spectroscopy system to monitor for the very first time the rapid viscoelastic response of cells and subcellular structures to a short-duration electrical impulse. The cytomechanical response of three subcellular structures - cytoplasm, nucleoplasm, and nucleoli - were monitored, showing distinct mechanical changes despite an identical stimulus. Through this pioneering transformative study, we demonstrate the capability of Brillouin spectroscopy to measure rapid, real-time biomechanical changes within distinct subcellular compartments. Our results support the promising future of Brillouin spectroscopy within the broad scope of cellular biomechanics.

Comprehensive single-shot biophysical cytometry using simultaneous quantitative phase imaging and Brillouin spectroscopy.

Single-cell analysis, or cytometry, is a ubiquitous tool in the biomedical sciences. Whereas most cytometers use fluorescent probes to ascertain the presence or absence of targeted molecules, biophysical parameters such as the cell density, refractive index, and viscosity are difficult to obtain. In this work, we combine two complementary techniques-quantitative phase imaging and Brillouin spectroscopy-into a label-free image cytometry platform capable of measuring more than a dozen biophysical properties of individual cells simultaneously. Using a geometric simplification linked to freshly plated cells, we can acquire the cellular diameter, volume, refractive index, mass density, non-aqueous mass, fluid volume, dry volume, the fractional water content of cells, both by mass and by volume, the Brillouin shift, Brillouin linewidth, longitudinal modulus, longitudinal viscosity, the loss modulus, and the loss tangent, all from a single acquisition, and with no assumptions of underlying parameters. Our methods are validated across three cell populations, including a control population of CHO-K1 cells, cells exposed to tubulin-disrupting nocodazole, and cells under hypoosmotic shock. Our system will unlock new avenues of research in biophysics, cell biology, and medicine.

Multi-wavelength excitation Brillouin spectroscopy.

We propose and demonstrate, first on simulated spectra and then experimentally, a novel approach to correct the undesired background distortions in the Brillouin spectra caused by molecular filter's absorption, fluorescent emission, ambient room light or any other constant contaminant. The developed multi-wavelength excitation Brillouin spectroscopy method computationally reconstructs the pure Brillouin component of the signal from multiple Brillouin spectra acquired using different excitation wavelengths. By removing the baseline distortions, the approach improves the goodness of fit of the Brillouin peaks, enabling accurate Brillouin shift and linewidth measurements from a wide range of challenging samples. In the present report, we explain the principle behind the method on a set of simulated spectra and present experimental application on an intentionally strongly-distorted spectrum. Utilizing the multi-excitation Brillouin spectroscopy approach, we successfully reconstruct Brillouin spectra of a highly-scattering sample, initially rendered not analyzable by excessive iodine absorption and contamination by out-of-focus light.

Assessing the effect of prolonged use of desloratadine on adipose Brillouin shift and composition in rats.

Antihistamines, which are commonly used to treat allergic reactions, are known for their side effects, which contribute to weight gain. It is hypothesized that simultaneous Brillouin elastography and Raman spectroscopy can be used to detect changes in adipose tissue associated with a prolonged intake of desloratadine, a commonly used second generation antihistamine. White and brown adipose tissue samples were excised from adult rats following 16 weeks of daily administration of desloratadine. It was found that the prolonged intake of desloratadine leads to an increase in Brillouin shift in both adipose tissue types. Raman spectra indicate that antihistamine use reduces protein-to-lipid ratio in brown adipose tissue but not white adipose tissue, indicating the effect on adipose tissue is location-dependent.

Differentiating melanoma and healthy tissues based on elasticity-specific Brillouin microspectroscopy.

The main objective of the present study is to evaluate the use of Brillouin microspectroscopy for differentiation of melanoma and normal tissues based on elasticity measurements. Previous studies of malignant melanoma show that the lesion is stiffer than the surrounding healthy tissue. We hypothesize that elasticity-specific Brillouin spectroscopy can be used to distinguish between healthy and cancerous regions of an excised melanoma from a Sinclair miniature swine. Brillouin measurements of non-regressing and regressing melanomas and the surrounding healthy tissues were performed. Based on the Brillouin measurements, the melanomas and healthy tissues can be successfully differentiated. The stiffness of both tumors is found to be significantly greater than the healthy tissues. Notably, we found that the elasticity of regressing melanoma is closer to that of the normal tissue. The results indicate that Brillouin spectroscopy can be utilized as a tool for elasticity-based differentiation between malignant melanoma and surrounding healthy tissue, with potential use for melanoma boundary identification, monitoring tumor progression, or response to treatment.

Prolonged intake of desloratadine: mesenteric lymphatic vessel dysfunction and development of obesity/metabolic syndrome.

This study aimed to establish mechanistic links between the prolonged intake of desloratadine, a common H1 receptor blocker (i.e., antihistamine), and development of obesity and metabolic syndrome. Male Sprague-Dawley rats were treated for 16 wk with desloratadine. We analyzed the dynamics of body weight gain, tissue fat accumulation/density, contractility of isolated mesenteric lymphatic vessels, and levels of blood lipids, glucose, and insulin, together with parameters of liver function. Prolonged intake of desloratadine induced development of an obesity-like phenotype and signs of metabolic syndrome. These alterations in the body included excessive weight gain, increased density of abdominal subcutaneous fat and intracapsular brown fat, high blood triglycerides with an indication of their rerouting toward portal blood, high HDL, high fasting blood glucose with normal fasting and nonfasting insulin levels (insulin resistance), high liver/body weight ratio, and liver steatosis (fatty liver). These changes were associated with dysfunction of mesenteric lymphatic vessels, specifically high lymphatic tone and resistance to flow together with diminished tonic and abolished phasic responses to increases in flow, (i.e., greatly diminished adaptive reserves to respond to postprandial increases in lymph flow). The role of nitric oxide in this flow-dependent adaptation was abolished, with remnants of these responses controlled by lymphatic vessel-derived histamine. Our current data, considered together with reports in the literature, support the notion that millions of the United States population are highly likely affected by underevaluated, lymphatic-related side effects of antihistamines and may develop obesity and metabolic syndrome due to the prolonged intake of this medication. NEW & NOTEWORTHY Prolonged intake of desloratadine induced development of obesity and metabolic syndrome associated with dysfunction of mesenteric lymphatic vessels, high lymphatic tone, and resistance to flow together with greatly diminished adaptive reserves to respond to postprandial increases in lymph flow. Data support the notion that millions of the USA population are highly likely affected by underevaluated, lymphatic-related side effects of antihistamines and may develop obesity and metabolic syndrome due to the prolonged intake of this medication.

Assessing performance of modern Brillouin spectrometers.

Brillouin spectroscopy and imaging has experienced a renaissance in recent years seeing vast improvements in methodology and increasing number of applications. With this resurgence has come the development of new spontaneous Brillouin instruments that often tout superior performance compared to established conventional systems such as tandem Fabry-Perot interferometers (TFPI). The performance of these new systems cannot always be thoroughly examined beyond the scope of the intended application, as applications often take precedence in reports. We therefore present evaluation of three modern Brillouin spectrometers: two VIPA-based spectrometers with wavelength-specific notch filters, and one scanning 6-pass TFPI. Performance analysis is presented along with a discussion about the dependence of measurements on excitation laser source and the various susceptibilities of each system.

Optical assessment of changes in mechanical and chemical properties of adipose tissue in diet-induced obese rats.

Obesity is becoming a leading cause of health problems world-wide. Obesity and overweight are associated with the structural and chemical changes in tissues; however, few methods exist that allow for concurrent measurement of these changes. Using Brillouin and Raman microspectroscopy, both the mechanical and chemical differences can be assessed simultaneously. We hypothesized that Brillouin spectroscopy can measure the adipose tissues' stiffness, which increases in obesity. Samples of brown and white adipose tissues obtained from control and diet-induced obese adult rats were analyzed. The results show that both adipose tissues of the obese group exhibit a greater high-frequency longitudinal elastic modulus than the control samples, and that the brown fat is generally stiffer than white adipose. The Raman spectra indicate that the lipids' accumulation in adipose tissue outpaces the fibrosis, and that the high-fat diet has a greater effect on the brown adipose than the white fat. Overall, the powerful combination of Brillouin and Raman microspectroscopies successfully assessed both the mechanical properties and chemical composition of adipose tissue simultaneously for the first time. The results indicate that the adipose tissue experiences an obesity-induced increase in stiffness and lipid content, with the brown adipose tissue undergoing a more pronounced change compared to white adipose.