Fat work: Analysis and PLS

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  • Published: Dec 15, 2016
  • Author: David Bradley
  • Channels: Chemometrics & Informatics
thumbnail image: Fat work: Analysis and PLS

Free fatty acids

Elevated circulating concentrations of free fatty acids (FFAs) is generally considered to be a universal metabolic signature of excessive adipocyte lipolysis. Accurately screening and assessing the problem is now possible thanks to the development of a novel combination of UHPLC-Orbitrap and partial least squares (PLS).

Elevated circulating concentrations of free fatty acids (FFAs) is generally considered to be a universal metabolic signature of excessive adipocyte lipolysis. Accurately screening and assessing the problem is now possible thanks to the development of a novel combination of UHPLC-Orbitrap and partial least squares (PLS).

People with raised levels of blood plasma FFAs are usually at greater risk of obesity, type 2 diabetes mellitus and non-alcoholic fatty liver disease than those with normal levels. For instance, high levels of FFAs contribute markedly to the development of insulin resistance. As such, screening is an important part of health risk assessment especially for those with other risk factors. Excessive adipocyte lipolysis leads to FFA accumulation, which itself leads to additional lipolytic reactions through hypoxia and endoplasmic reticulum stress. Thus a detrimental feedback cycle can arise and the excess FFAs are deposited widely as triglycerides in muscle tissue, the liver and the pancreas with putatively harmful results.

Double-edged idea

Lipolysis is a double-edged sword. Increased lipolysis was thought to be beneficial to obese individuals as it could decrease percentage body fat. However, excessive subcutaneous fat lipolysis can induce FFA accumulation in serum and then lead to lipid deposition in viscera. The well known in vitro lipolysis assay is used to screen experimental drugs prior to animal studies as one of the first safety and efficacy tests. This is particularly important for new drugs that are intended to treat metabolic diseases. Colorimetric assays and ELISA (enzyme-linked immunosorbent assay) are used for FFA assessment but they have several drawbacks, not least false positive results that emerge because of the low selectivity and limited information of FFA compositions.

Other techniques are available, gas chromatography/mass spectrometry (GC/MS), liquid chromatography/electrospray ionization mass spectrometry (LC-ESI/MS), and matrix-assisted laser desorption/ionization mass spectrometry (MALDI/MS), for instance, are commonly used for FFA analysis. LC-ESI/MS is more extensively used than others but conventional MS techniques are hindered by poor characteristic fragment ions which again lead to false positives or negatives as one lipid is mistaken for another and others are missed altogether. As such, alternative methods are keenly sought for the aforementioned applications and others.

Powerful technique

Now, Wen-Qi Chang, Yi Li, Li Wang, Jie Yang, Ping Li, Li-Fang Liu, and Gui-Zhong Xin of the State Key Laboratory of Natural Medicines, in the Department of Chinese Medicines Analysis, at China Pharmaceutical University, in Nanjing, together with Jian-Liang Zhou of the Zhejiang Institute for Food and Drug Control, in Hangzhou, and Zi-Qi Shi of the Key Laboratory of New Drug Delivery Systems of Chinese Materia Medica, at the Jiangsu Provincial Academy of Chinese Medicine, Jiangsu, Nanjing, China, have a solution. The team has constructed a calibration matrix based on mixed samples and the lipidome profiled using ultra-high-performance liquid chromatography (UHPLC) Orbitrap. They extracted and aligned 403 variables as a dataset and could identify 28 FFAs because of the high resolution of this system and with the application of open source lipid identification software. They then used PLS (partial least squares) regression analysis to pin down ten principal components to build the final chemometric model. The model showed excellent performance in proof of principle tests.

In order to demonstrate the potential of their model, the team used curcumin as a model compound for its antilipolytic effect on palmitic acid-induced lipolysis and successfully predicted the inhibition ratio as 32%. "The novel biological evaluation model proposed here showed promising perspectives for drug evaluation or disease diagnosis," the team reports. "The platform's breadth of coverage, qualitative information, and quantitative precision make this approach a powerful tool for comprehensive LC/MS-based lipolysis measurement," the researchers conclude, writing in the journal Anal Chim Acta.

As our paper has presented a way of evaluating antilipolytic drugs, we plan to screen other potential drugs which could be used in related metabolic disease in vitro and then to validate their curative effect in vivo, Xin told SpectroscopyNOW. "We hope the in vitro approach for lipolysis measurement could be used in other pathological models and relevant drug discovery in the future," he adds.

Related Links

Acta Chim Acta 2017, 950, 38-146: "An in vitro approach for lipolysis measurement using high-resolution mass spectrometry and partial least squares based analysis"

Article by David Bradley

The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.

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