Context: Obesity is related to insulin resistance, and adipose tissue-secreted TNF-α may play a role in inducing obesity. TNF-α activates inflammatory protein kinase and impairs insulin signalling.
Objectives: We investigated the effect of betulinic acid on insulin resistance caused by TNF-α treatment in 3T3-L1 adipocytes.
Material and methods: 3T3-L1 was exposed to TNF-α in the presence and absence of betulinic acid. Various parameters such as glucose uptake assay, cell viability, expression of proteins involved in insulin resistance were studied.
Results: Betulinic acid increased glucose uptake in TNF-α pre-treated cells and inhibited the activation of PTP1B and JNK and reduced IκBα degradation. Tyrosine phosphorylation was increased, and serine phosphorylation was decreased in IRS-1.
Discussion: Betulinic acid restored TNF-α impaired insulin signalling and increased PI3K activation and phosphorylation of Akt and increased plasma membrane expression of GLUT 4, which stimulated glucose uptake concentration-dependently.
Conclusion: These results suggest that betulinic acid is effective at improving TNF-α-induced insulin resistance in adipocytes via inhibiting the activation of negative regulator of insulin signalling and inflammation-activated protein kinase and may potentially improve insulin resistance.
Keywords: Betulinic acid; IRS-1; JNK; PTP1B; insulin resistance.