Modulatory Activity of Uncaria tomentosa Extract in the Expression of Proteins Involved in the Unfolded Protein Response and Insulin Resistance

Type 2 diabetes mellitus (T2D) is associated with dyslipidemia, characterized by elevated plasmatic triglycerides and free fatty acids, particularly palmitate (PA), which may cause lipotoxicity in skeletal muscle cells. This leads to inflammation, activation of the unfolded protein response (UPR), insulin resistance, and cell death. Herbal medicines such as Uncaria tomentosa (UT) have shown potential as complementary treatments for T2D due to their protective effects. Purpose and study design: This study investigates the effect of UT aqueous extract on UPR and insulin resistance induced by PA in C2C12 myotubes. C2C12 myoblasts were grown in DMEM medium supplemented with 10% fetal bovine serum and differentiated into myotubes with 3.5% horse serum. The myotubes were incubated with 100 or 500 μM PA, 2–100 µM thapsigargin (Tg) or tunicamycin (Tn), in the presence or absence of 250 μg/mL UT extract or 100 µM TUDCA, for 2 or 6 h. The myotubes treated with UT extract for 6 h, after the incubation with 20 µM Tg, Tn or 500 µM PA, presented reduction in the expression of UPR-related genes ATF4 and CHOP by approximately 1.5-fold, and increased by 3-fold the expression of IRS-1, an insulin-signaling protein, when compared to myotubes incubated with only 20 µM Tg, Tn or 500 µM PA. These findings suggest that UT extract may serve as a modulator against skeletal muscle dyslipidemia by downregulating ATF4 and CHOP, reducing cell stress and death, while enhancing IRS-1 expression, which supports the use of the UT extract in managing insulin resistance and T2D.