Protective effects of quercetin and crocin in the kidneys and liver of obese Sprague-Dawley rats with Type 2 diabetes: Effects of quercetin and crocin on T2DM rats

Quercetin and crocin are the main active constituents of Eucommia and Gardenia species, respectively. This study was conducted to explore the effects of quercetin and crocin on fat reduction and renal fibrosis and the relationship of these compounds with autophagy. First, a model of high-fat diet- and streptozotocin-induced type 2 diabetes was established and then subjected model animals to 8 weeks of metformin, quercetin and crocin gavage. Then, a high glucose-induced rat mesangial cells (RMCs) model was established, and these cells were cocultured with quercetin and crocin. The results showed that quercetin and crocin can decrease fasting blood glucose levels, reduce fat accumulation in the liver, alleviate renal fibrosis, and reduce blood lipid levels. Quercetin and crocin increased autophagy-related protein (LC3, Atg5, Beclin-1 and p-AMPK) levels in the liver and decreased autophagy-related protein (LC3, Atg5, Beclin-1 and p-AMPK) levels in the kidneys. Moreover, quercetin and crocin inhibited the excessive proliferation of RMCs induced by high-glucose (HG) conditions, decreased autophagy-related protein (LC3, Atg5, Beclin-1 and p-AMPK) levels, and decreased TGF-β1 expression. Importantly, cotreatment with quercetin and crocin had a more significant effect than treatment with either compound alone. These results suggest that combined administration of quercetin and crocin can more significantly reduce blood glucose/lipid levels and improve renal fibrosis than administration of either compound alone and that AMPK-dependent autophagy might be involved in this process. Eucommia ulmoides Oliv. and Gardenia could be developed as drugs for Type 2 diabetes treatment.