Background Exposure to diisononyl phthalate (DINP), an endocrine disruptor associated with metabolic diseases and widely used in plastic products, has been linked to the development of several adverse health outcomes in the liver, including non-alcoholic fatty liver disease (NAFLD).

Objective To investigate the effects and the possible molecular mechanisms of DINP exposure on lipid metabolism in human hepatocellular carcinoma cells (HepG2 cells).

Methods First, HepG2 cells were treated with DINP at three time spots (24, 48, and 72 h) and eleven doses (0, 0.003, 0.01, 0.03, 0.1, 0.3, 1, 3, 10, 30, and 100 mmol·L⁻¹). Cell viability were detected using cell counting kit 8 (CCK8). Intracellular lipid deposition was determined by oil red O staining and lipid content detection, and triglyceride (TG) and cholesterol (TC) were further detected. Finally, the mRNA expression levels were detected by fluorescence quantitative PCR, including fatty acid synthesis related genes acetyl-CoA carboxylase alpha (Accα), fatty acid synthase (Fasn), malonyl-CoA decarboxylase (Mlycd), and sterol regulatory element binding protein 1 (Srebp1) and β-oxidation related genes peroxisome proliferator activated receptor alpha (Pparα), AMP-activated protein kinase (Ampk), carnitine palmitoyltransferase 1A (Cpt-1a), transcription factor A, mitochondrial (Tfam), nuclear respiratory factor 1 (Nrf1), and peroxisome proliferator-activated receptor gamma and coactivator 1 alpha (Pgc1-α).

Results Compared with the control group (0 mmol·L⁻¹), the no observed adverse effect levels (NOAEL) of HepG2 cell viability were 0.3, 0.1, and 0.1 mmol·L⁻¹ after 24, 48, and 72 h exposure to DINP, respectively, and the corresponding lowest observed adverse effect levels (LOAEL) were 1, 0.3, and 0.3 mmol·L⁻¹, respectively (P<0.05). After exposure to 30 mmol·L⁻¹ and 100 mmol·L⁻¹ DINP for 24 h, the intracellular lipid content, lipid deposition, TG, and TC levels were increased significantly compared with the control group (P<0.01). Compared with the control group, the mRNA expression levels of genes related to fatty acid synthesis, such as Mlycd, Srebp1, Fasn, and Accα, were down-regulated after the 100 mmol·L⁻¹ DINP exposure for 24 h, while the mRNA expression level of Mlycd was up-regulated in the 30 mmol·L⁻¹ group. The β-oxidation related genes such as Ampk, Pparα, and Tfam were up-regulated significantly after the 100 mmol·L⁻¹ DINP exposure, while Cpt-1a mRNA expression level was down-regulated (P<0.05).

Conclusion Exposure to DINP at 30 mmol·L⁻¹ and 100 mmol·L⁻¹ can interfere with fatty acid synthesis and β-oxidation in lipid metabolism of HepG2 cells, resulting in lipid deposition.