Green Tea is a commonly consumed human beverage, often considered a healthy habit.
Green tea has important effects on human health, mainly attributed to its flavonoid-like polyphenols, such as catechins. Catechins included epigallocatechin gallate (EGCG), epigallocatechin (EGC), epicatechin gallate (ECG), epicatechin (EC), and catechin (C).
EGCG is the major catechin in green tea extract.
Tea, leaf, or bud from the plant Camellia sinensis, make up some of the beverages popularly consumed in different parts of the world as green tea, oolong tea, or black tea. More particularly, as a nonfermented tea, green tea has gained more renown because of the significant health benefits assigned to its rich content in polyphenols.
As a main constituent, green tea polyphenols were documented for their antioxidant, anti-inflammation, anticancer, anticardiovascular, antimicrobial, antihyperglycemic, and antiobesity properties.
Recent reports demonstrate that green tea may exert a positive effect on the reduction of medical chronic conditions such as cardiovascular disease, cancer, Alzheimer’s disease, Parkinson’s disease, and diabetes. The health benefits of green teas, in particular EGCG, are widely investigated, and these effects are known to be primarily associated with the structure and compositions of its polyphenols.
The enzyme dipeptidyl peptidase-4 (DPP4) is present in many human tissues, including the pancreas, liver, and adipose cells.
As a cell-surface protease, DPP4 selectively cleaves an N-terminal dipeptide from peptides in which the penultimate amino acid is proline or alanine (for example, glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1 (GLP-1)), inactivating them.
GLP-1 is secreted from L-cells of the intestine. Binding of GLP-1 to G-protein-coupled receptors on the surface of beta cells leads to an increase in intracellular cAMP, activation of Epac1 and 2, and finally insulin release.
Accordingly, DPP4 inhibitors have clinical benefits in patients with diabetes mellitus.
In addition to blood glucose regulation, DPP4 inhibitors may also have extra-glycemic effects such as myocardial protection, lowering blood pressure, reducing the expression of local inflammatory factors, and improving vascular endothelial function.
The antidiabetic effects of green tea have been demonstrated in clinical trials and epidemiological studies.
We investigated the antidiabetic and weight loss effects of green tea extract (GTE) and its underlying molecular mechanisms using a leptin receptor-deficient db/db mouse model (Leprdb/db).
Treatment with GTE for 2 weeks improved glucose tolerance and insulin sensitivity in Leprdb/db mice.
In addition, GTE treatment reduced the body weight and adiposity of Leprdb/db mice.
Furthermore, GTE treatment reduced pro-inflammatory gene expression, including nuclear factor kappa B (NF-κB) in white adipose tissue (WAT), and also reduced dipeptidyl peptidase-4 (DPP4) expression levels in WAT as well as in the serum.
The promoter region of Dpp4 contains the NF-κB binding site, and DPP4 was found to be a direct target of NF-κB. Consistently, in vitro treatment of cells with GTE or its main constituent epigallocatechin gallate reduced lipopolysaccharide-induced NF-κB/DPP4 expression in 3T3-L1 adipocytes and RAW264.7 cells. Overall, our data demonstrated that GTE exerts an anti-diabetic effect by regulating the expression levels of NF-κB and DPP4 in WAT.
Treatment for type-2 diabetes mellitus depends on the incretin hormone. Glucagon-Like Peptide-1 (GLP-1) and Glucose-Dependent Insulinotropic Polypeptide (GIP) are the main incretin hormones secreted in the intestine.
GLP-1 plays a role in the body’s metabolism, such as insulin secretion, increases the mass of β-pancreatic cells, glucagon secretion, reduces gastric emptying and increases satiety (the feeling of being full when eating).
As, GLP-1 tends with a half-life about 1-2 min due to degradation by the Dipeptidyl peptidase IV (DPP IV).
The inhibition of DPP IV required to maintain endogenous GLP-1 inactive form and longer half-life.
DPP IV inhibition may also reduce the side effects of hypoglycemia, weight gain, and gastrointestinal disorders.
Many studies show that Green tea extract has inhibition of DPP IV enzyme (30.57%) allowing GLP-1 to be active longer before inactivation. This allows GLP-1 to express its effects to reduce hunger and increase weight loss.