Raman Spectroscopic comparative study of Oxytocin and Freeze-dried Extract of Uvariodendron anisatum Verdeck (Annonaceae) and their influence on diet induced obesity in Sprague Dawley rats
Authors: Birech Zephania , Mwangi Peter W. , Sehmi Prabjot K. , Nyaga Nelly M. 
Published: January 2019

Obesity is a condition affecting many people in the world. Obese people have increased risks of developing chronic metabolic diseases such as type II diabetes, hypertension, cancer among others. Early and rapid diagnosis of the condition together with effective treatment is therefore necessary. This work investigated, first, Raman spectroscopic similarities between oxytocin and a freeze-dried extract of a local herbal plant exhibiting oxytocin-like properties called Uvariodendron anisatum Verdeck (Annonaceae) (UAV). Secondly, whether Raman spectroscopy could be used for comparative studies of the influence of oxytocin and UAV on obese Sprague Dawley (SD) rat models. We also wanted to find a Raman biomarker band for obesity or metabolic syndrome. Both oxytocin and extract samples together with blood extracted from the rats were excited using a 785 nm laser after being placed or applied onto a conductive silver paste smeared glass slides and Raman signals collected, recorded and analyzed.

The Raman spectroscopic spectral profiles of oxytocin and UAV freeze dried extracts were found to be identical showing they were composed of similar Raman active molecules. The prominent peaks were those assigned to disulfide S-S stretching mode at 508 cm-1 and to tyrosine at 645 cm-1, 846 cm-1 and 1617 cm-1. Raman spectra of blood from rats treated with oxytocin and UAV had indistinguishable profiles thus supporting idea that they were composed of similar active molecules. The spectral profiles were also dissimilar to those from obese and non-obese (normal controls) animals. A prominent peak in spectra of treated rats centered at 401 cm-1 could be used as oxytocin biomarker band. Comparison of average intensity trend of fructose bands at around 638 cm-1 and 812 cm-1 between prepared fructose solution and blood of treated rats, revealed elevated levels of fructose in blood of rats orally administered oxytocin and UAV extracts. The implication was that fructose metabolism in rats administered oxytocin and UAV extracts was upregulated. Principal component analysis (PCA) showed the power of Raman spectroscopy in distinguishing between obese and non-obese SD rats based on spectral profile patterns. It also further revealed that oxytocin and UAV extracts had similar influence on SD rats as their blood’s Raman spectral patterns were indistinguishable.

The study revealed that Raman spectroscopy can be a powerful tool for quick obesity (metabolic syndrome) screening with intensity of Raman bands associated with fructose as biomarkers. The same bands can also be used in comparative efficacy studies of anti-obesity drugs. Further studies are needed to validate these Raman spectroscopic results since, to the best of our knowledge, this was the first such investigation regarding comparison of UAV and conventional oxytocin together with their influence on obese SD rats. Also studies on whether the same results can be seen in human subjects.