Raman spectroscopy of the skin of an animal model of diet‐induced obesity
Authors: Donjuán‐Loredo Guadalupe E. , Espinosa‐Tanguma Ricardo E. , León‐Bejarano Maritza E. , Ramírez‐Elías Miguel G. 
Published: May 2022

Introduction

The most common consequences of obesity are metabolic disorders. Moreover, obesity leads to alterations of skin physiology like changes in barrier function, sebaceous glands and sebum production, sweat glands, collagen structure, wound healing and microcirculation. Obesity is a risk factor for the development of inflammatory skin diseases produced by cytokines released from dysfunctional subcutaneous fat cells.

The detection of cutaneous structural and biomolecular changes with new non‐invasive techniques is a novel approach. Raman spectroscopy (RS) is a vibrational spectroscopic technique that can provide a non‐destructive characterization of tissue to a molecular level. It can be used to detect biomarkers associated with a disease that modifies the molecular composition, and these changes are reflected in the Raman spectra. In this work, we propose its use in vivo to study the molecular composition of skin to identify alterations associated with obesity in an animal model.

Methods

Wistar rats (~100 g), were divided into 2 random groups (n=8), fed a standard diet (control group) and high‐fat diet 40% extra (Obese group) for 8 and 52 weeks, individually housed in acrylic boxes, in constant conditions, free access to the diet and water. Total body weight, percentage of total fat, blood pressure, and blood triglycerides were analyzed. A portable 785 nm Raman spectrometer, 5‐300 mW laser power, was used on a clean and shaved abdominal skin. The Raman probe was placed in contact with the skin's surface. Five scans were collected using a 15 s total exposure time in the 200‐1800 cm‐1 spectral range.

Results

52‐week obese group showed an increase in total body fat, greater abdominal circumference, elevated blood pressure, and increased serum levels of total cholesterol and triglycerides compared to their respective control group and the 8‐week groups. Furthermore, the obese group showed visible skin lesions predominantly in the cervical region. The mean Raman spectra of skin corresponding to controls and obese groups show characteristic peaks of in vivo skin at 851, 963, 1048, 1064, 1257, 1303, 1445, and 1658 cm‐1. Despite the similarity in the Raman spectra of 8 and 52 weeks control groups, increased Raman intensity can be found in the 52‐weeks group, related to the age of the subjects. In the obese groups, at 8‐weeks Raman spectra show high intensity in the protein and carbohydrates related bands, while 52‐weeks obese show high‐intensity bands related to proteins and lipids. The latter could be related to the HFD as expected.

Conclusions

The results show that RS may identify spectral differences in the skin of obese animals. Raman intensity differences were found in the protein and lipid spectral regions of the obese group. A detailed analysis is needed to interpret all the peaks present in each group and explain the spectral differences in the obese group toward identifying a possible spectral biomarker of obesity. The results show that RS is a relatively simple, fast, non‐invasive method to analyze in vivo skin with HFD induced obesity.