Biochemical changes in serum of obese mice related to photoactivation of brown adipose tissue

Abstract

Obesity is closely related to the development of insulin resistance and type-2 diabetes. Mammal fat consists of white and brown adipose tissues (WAT and BAT). Although most fat is energy-storing WAT, brown adipocytes dissipate energy as heat. Thus, the thermogenic capacity of BAT and its activation makes it an interesting target for treating metabolic syndrome (MS). On the other hand, photobiomodulation (PBM) has proven to be beneficial to manage the chronic inflammatory component of obesity and hyperglycemia by irradiating WAT. However, PBM has still not been used to activate BAT. In this work, obese and hyperglycemic mice were treated with PBM, and their BAT was irradiated. The mouse serum was collected and submitted to attenuated total reflection (ATR)- Fourier transform infrared (FTIR) spectroscopy to evaluate the biochemical changes promoted by PBM. Five animals were fed with standard food (normal diet – ND) and used as negative control. The remaining 10 animals were submitted to a hyperlipidic diet (high fat – HF) and their body mass, Lee index and glycemia were measured weekly during 15 weeks to induce MS. After MS establishment, the HF animals were divided into two groups: HF and HF660. The HF660 group was exposed to six irradiation sessions using a 662 ± 20 nm LED. The radiant exposure was 5.7 Jcm-2 at 19 mWcm-2 per session, delivered at 300 s, on days 1, 3, 7, 10, 14 and 21. The HF group was sham-irradiated. After the treatment ended, the mouse serum was collected from cardiac puncture under deep anesthesia. Serum samples were prepared and analyzed by ATR-FTIR spectroscopy. The lipid absorptions were responsible for the clearest differences among the IR spectra. An intense C=O stretching absorption at 1742 cm-1 was noticed only for HF group. Acyl CH2 stretching absorptions at 2853 and 2925 cm−1 were also more pronounced in HF group. After PBM, these major lipid peaks decreased their vibrational modes. In fact, hierarchical cluster analysis identified the similarities between the spectra and grouped ND and HF660 groups into a same cluster. Taking together, our findings suggest that PBM applied to the BAT is able to promote biochemical changes in serum of obese mice mainly in lipid bands.