Differential impact of cold and hot tea extracts on tyrosine phosphatases regulating insulin receptor activity: a focus on PTP1B and LMW-PTP.

PURPOSE: The impact of tea constituents on the insulin-signaling pathway as well as their antidiabetic activity are still debated questions. Previous studies suggested that some tea components act as Protein Tyrosine Phosphatase 1B (PTP1B) inhibitors. However, their nature and mechanism of action remain to be clarified. This study aims to evaluate the effects of both tea extracts and some of their constituents on two main negative regulators of the insulin-signaling pathway, Low-Molecular-Weight Protein Tyrosine Phosphatase (LMW-PTP) and PTP1B. METHODS: The effects of cold and hot tea extracts on the enzyme activity were evaluated through in vitro assays. Active components were identified using gas chromatography-mass spectrometry (GC-MS) analysis. Finally, the impact of both whole tea extracts and specific active tea components on the insulin-signaling pathway was evaluated in liver and muscle cells. RESULTS: We found that both cold and hot tea extracts inhibit LMW-PTP and PTP1B, even if with a different mechanism of action. We identified galloyl moiety-bearing catechins as the tea components responsible for this inhibition. Specifically, kinetic and docking analyses revealed that epigallocatechin gallate (EGCG) is a mixed-type non-competitive inhibitor of PTP1B, showing an IC50 value in the nanomolar range. Finally, in vitro assays confirmed that EGCG acts as an insulin-sensitizing agent and that the chronic treatment of liver cells with tea extracts results in an enhancement of the insulin receptor levels and insulin sensitivity. CONCLUSION: Altogether, our data suggest that tea components are able to regulate both protein levels and activation status of the insulin receptor by modulating the activity of PTP1B.

In Search for Multi-Target Ligands as Potential Agents for Diabetes Mellitus and Its Complications-A Structure-Activity Relationship Study on Inhibitors of Aldose Reductase and Protein Tyrosine Phosphatase 1B.

Diabetes mellitus (DM) is a complex disease which currently affects more than 460 million people and is one of the leading cause of death worldwide. Its development implies numerous metabolic dysfunctions and the onset of hyperglycaemia-induced chronic complications. Multiple ligands can be rationally designed for the treatment of multifactorial diseases, such as DM, with the precise aim of simultaneously controlling multiple pathogenic mechanisms related to the disease and providing a more effective and safer therapeutic treatment compared to combinations of selective drugs. Starting from our previous findings that highlighted the possibility to target both aldose reductase (AR) and protein tyrosine phosphatase 1B (PTP1B), two enzymes strictly implicated in the development of DM and its complications, we synthesised 3-(5-arylidene-4-oxothiazolidin-3-yl)propanoic acids and analogous 2-butenoic acid derivatives, with the aim of balancing the effectiveness of dual AR/PTP1B inhibitors which we had identified as designed multiple ligands (DMLs). Out of the tested compounds, 4f exhibited well-balanced AR/PTP1B inhibitory effects at low micromolar concentrations, along with interesting insulin-sensitizing activity in murine C2C12 cell cultures. The SARs here highlighted along with their rationalization by in silico docking experiments into both target enzymes provide further insights into this class of inhibitors for their development as potential DML antidiabetic candidates.