Monitoring the biochemical alterations in hypertension affected salivary gland tissues using Fourier transform infrared hyperspectral imaging

Fourier transform infrared spectroscopy (FTIR) imaging has been applied to investigate biochemical differences between salivary glands from control and hypertensive rats. Male Sprague–Dawley rats were divided into two groups including a control group and another hypertension group that were treated orally, with N-nitro-L-arginine methyl ester (L-NAME) via drinking water for 3 weeks to develop hypertension. In the control group, rats were treated with only drinking water for 3 weeks. The formalin-fixed paraffin embedded tissue specimens from submandibular and sublingual glands were analysed with a FTIR focal plane array imaging spectrometer and multi-composite images of all tissue sections were analysed simultaneously using Unsupervised Hierarchical Cluster Analysis (UHCA) and the extracted spectra were further analysed using Partial Least Squares Discriminant Analysis (PLS-DA). In general, hypertension affected salivary gland tissues were characterised by higher concentrations of triglycerides as evidenced by an increase in the 1745 cm−1 band. Higher concentrations of carbohydrates and proteins were also observed in the hypertensive group along with a decrease in bands associated with nucleic acids. PLS-DA scores plots provided good differentiation in sublingual gland tissues between control (n = 3734 spectra) and hypertension (n = 4538) and also in submandibular gland tissues between control (n = 5051) and hypertension (n = 4408). We have shown that FTIR imaging can be used to differentiate the macromolecular information between physiological and pathological conditions in tissue biopsy specimens. In the next phase, we will investigate the infrared predictive markers of hypertension in biofluids including serum and saliva using attenuated total refection spectroscopy.