Raman Study on Lipid Droplets in Hepatic Cells Co-Cultured with Fatty Acids

Pradjna N Paramitha,Riki Zakaria,Hiromitsu Nakazawa,Yukako Kusaka,Hidetoshi Sato,Satoru Kato,Anisa Maryani,Kosuke Hashimoto,Bibin B Andriana

doi:10.3390/ijms22147378

Pradjna N Paramitha, Riki Zakaria + Show 7 more

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https://doi.org/10.3390/ijms22147378

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Abstract

The purpose of the present study was to investigate molecular compositions of lipid droplets changing in live hepatic cells stimulated with major fatty acids in the human body, i.e., palmitic, stearic, oleic, and linoleic acids. HepG2 cells were used as the model hepatic cells. Morphological changes of lipid droplets were observed by optical microscopy and transmission electron microscopy (TEM) during co-cultivation with fatty acids up to 5 days. The compositional changes in the fatty chains included in the lipid droplets were analyzed via Raman spectroscopy and chemometrics. The growth curves of the cells indicated that palmitic, stearic, and linoleic acids induced cell death in HepG2 cells, but oleic acid did not. Microscopic observations suggested that the rates of fat accumulation were high for oleic and linoleic acids, but low for palmitic and stearic acids. Raman analysis indicated that linoleic fatty chains taken into the cells are modified into oleic fatty chains. These results suggest that the signaling pathway of cell death is independent of fat stimulations. Moreover, these results suggest that hepatic cells have a high affinity for linoleic acid, but linoleic acid induces cell death in these cells. This may be one of the causes of inflammation in nonalcoholic fatty liver disease (NAFLD).

Highlights

When fibrosis progresses in the nonalcoholic fatty liver disease (NAFLD) liver, the liver progresses to nonalcoholic steatohepatitis (NASH), which greatly increases the possibility of liver cancer [1,2]
HepG2 cells are able to take up fat components directly from the cultivation media and use the fat directly or indirectly to synthesize triacylglycerol that accumulates in the lipid droplets
The pathways of fat uptake and lipid droplet generation are not regulated by the lipid concentration in the cells and seem to be free from apoptotic signaling pathways

Summary

Introduction

A symptom of fat accumulation, especially in the liver in the absence of excessive alcohol consumption, is referred to as nonalcoholic fatty liver disease (NAFLD) [1]. When fibrosis progresses in the NAFLD liver, the liver progresses to nonalcoholic steatohepatitis (NASH), which greatly increases the possibility of liver cancer [1,2]. Adipocytes are able to hold a large amount of fat; while hepatic cells are unable to hold much fat. Medical studies strongly suggest that fat deposition in the liver is a major cause of the disease [1,3]. Fats in foods are converted into fatty acids and absorbed in the bowel. Fatty acids are carried by lipoproteins, such as albumin, in the blood and passed to adipocytes in adipose tissues

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