The G protein coupled receptor GPR also called
The G protein-coupled receptor, GPR40 (also called FFAR1) responds to medium and long chain unsaturated fatty acids, resulting in increase of insulin secretion during elevated glucose levels. The glucose dependency of insulin secretion makes this receptor a very good target for developing therapies with little or no adverse effects that could be useful for the treatment of T2DM. Whereas the mechanism of action of FFAR1 was not completely understood until now, previous studies suggested that FFAR1 is predominantly coupled with the G protein α-subunits of the Gq family .
G protein-coupled receptor G protein–coupled receptors (GPRs) constitute a large protein family of receptors found in eukaryotes and animals, that detect molecules outside the cell and activate internal signal transduction pathways, leading to cellular responses. The ligands that bind and activate these receptors include light-sensitive compounds, odors, pheromones, hormones, and neurotransmitters, and they vary in size from small molecules to peptides to large proteins . The two major signal transduction pathways that involve the GPRs are: the cAMP signal pathway and the phosphatidylinositol signal pathway . They are made up of sub-units which when activated lead to signal transmission .
Physiological role of ffar in mediating insulin secretion
FFAR1 agonist as a new therapeutic target for T2DM Several classes of FFAR1 agonists have been identified with different biological characteristics. In addition, the synthetic FFAR1 agonists mimic the fatty Cy7.5 maleimide(non-sulfonated) receptor structure with an acidic head group and a hydrophobic tail . As the mimics of long-chain fatty acid, the early FFAR1 agonists were quite lipophilic, typical examples being GW9508 1 and 2 [32,33]. Although they exhibited high potency, their high lipophilicity caused lipotoxicity and off-target effects in central nervous system. The early FFAR1 agonists that were developed but which were discontinued due to their high lipophilicity and lipotoxicity are described below:
Current status of FFAR1 agonists for the treatment of T2DM Currently, Japan Tobacco are conducting Phase II clinical trials with their FFA1 agonist, JTT-851 and Piramal have begun Phase I clinical trials on their FFA1 agonist, P11187 . Daiichi Sanyko also recently described 3-aryl-3-ethoxypropanoic acids as orally active FFA1 agonists that improve insulin secretion and glucose homeostasis in rats . Additionally, FFA1 agonists that were developed by Astellas were reported to have beneficial effects on glucose homeostasis in diabetic mouse models [41,42]. Sanofi and Boehringer-Ingelheim are also reported to have FFA1 agonist programmes under development . In an academic context, the University of Southern Denmark have reportedly developed 4- (benzylamine) hydrocinnamic acid FFA1 agonists such as TUG-469  and 4-alkynehydrocinnamic acid FFA1 agonists, including TUG-424, and TUG-770 [43,44]. Within these programmes, several strategies have been followed to reduce adverse effects. Consequently, TUG-770 has recently been described as a highly potent FFA1 agonist with favorable physicochemical and pharmacokinetic properties, improving glucose tolerance in diet induced obesity . Other FFA1 agonists that are in different phases of clinical trials include: LY2881835, LY2922083, LY2922470 (11), LY2922470, P11187, SHR0534 and LY2922470  while the following FFA1 agonists- CNX-011-67, SAR1, DS-1558, BMS-986118 and MR1704 have been found to enhance glucose-dependent insulin secretion and improve glucose homeostasis in preclinical trials [45,46]. Other agonists, LY2881835 and LY2922083 demonstrated potent, efficacious, and durable dose-dependent reductions in glucose levels along with significant increases in insulin and GLP-1 secretion during preclinical testing. In a recent study, Neelaveni et al.  revealed that new thiazolidinedione derivatives (Fig. 6 a and 6 b) produced dual PPARγ and FFAR1 agonistic activity at micromolar concentrations with insulin sensitizing effects and enhanced insulin secretion from the pancreas. These derivatives were reported by these authors to possess the classical topology of the synthetic agonists and the lipophilic tail consists of bulky groups like biphenyl and benzimidazole.