Interaction of N‐benzoyl‐D‐phenylalanine and related compounds with the sulphonylurea receptor of β‐cells

Abstract

1 The structure activity relationships for the insulin secretagogues N-benzoyl-D-phenylalanine (NBDP) and related compounds were examined at the sulphonylurea receptor level by use of cultured HIT-T15 and mouse pancreatic b-cells. The a nities of these compounds for the sulphonylurea receptor were compared with their potencies for K ATP -channel inhibition. In addition, the e ects of cytosolic nucleotides on K ATP -channel inhibition by NBDP were investigated. 2 NBDP displayed a dissociation constant for binding to the sulphonylurea receptor (K D value) of 11 mM and half-maximally e ective concentrations of K ATP -channel inhibition (EC 50 values) between 2 and 4 mM (in the absence of cytosolic nucleotides or presence of 0.1 mM GDP or 1 mM ADP). 3 In the absence of cytosolic nucleotides or presence of GDP (0.1 mM) maximally e ective concentrations of NBDP (0.1 ± 1 mM) reduced K ATP -channel activity to 47% and 44% of control, respectively. In the presence of ADP (1 mM), K ATP -channel activity was completely suppressed by 0.1 mM NBDP. 4 The L-isomer of N-benzoyl-phenylalanine displayed a 20 fold lower a nity and an 80 fold lower potency than the D-isomer. 5 Introduction of a p-nitro substituent in the D-phenylalanine moiety of NBDP did not decrease lipophilicity but lowered a nity and potency by more than 30 fold. 6 Introduction of a p-amino substituent in the D-phenylalanine moiety of NBDP (N-benzoyl-p-amino-D-phenylalanine, NBADP) reduced lipophilicity and lowered a nity and potency by about 10 fold. This loss of a nity and potency was compensated for by formation of the phenylpropionic acid derivative of NBADP. A similar di erence in a nity was observed for the sulphonylurea carbutamide and its phenylpropionic acid derivative. 7 Replacing the benzene ring in the D-phenylalanine moiety of NBDP by a cyclohexyl ring increased lipophilicity, and the K D and EC 50 values were slightly lower than for NBDP. Exchange of both benzene rings in NBDP by cyclohexyl rings further increased lipophilicity without altering a nity and potency. 8 This study shows that N-acylphenylalanines interact with the sulphonylurea receptor of pancreatic bcells in a stereospeci®c manner. Their potency depends on lipophilic but not aromatic properties of their benzene rings. As observed for sulphonylureas, interaction of N-acylphenylalanines with the sulphonylurea receptor does not induce complete inhibition of K ATP -channel activity in the absence of inhibitory cytosolic nucleotides.

Amino Acid Ingestion Strongly Enhances Insulin Secretion in Patients With Long-Term Type 2 Diabetes

“…In addition, an increase in plasma insulin concentration has been reported following the intravenous infusion of free amino acids in both healthy (7)(8)(9) and type 2 diabetic subjects (10). In accordance, various in vitro studies using incubated ␤-cells of the pancreas have described strong insulinotropic effects of arginine, leucine, and phenylalanine (11)(12)(13)(14)(15)(16)(17)(18). Recently, we performed a series of studies in which we determined the in vivo insulinotropic potential of various free amino acids and protein (hydrolysates) when ingested in combination with carbohydrates in healthy young subjects (19 -21).…”

Intracellular Location of KATP Channels and Sulphonylurea Receptors in the Pancreatic β-cell: New Targets for Oral Antidiabetic Agents

“…These moieties effectively block K ATP channels regardless of which side of the membrane they are applied, suggesting that they can diffuse through the plasma membrane [27]. These channels are not just blocked by sulphonylureas; compounds such as benzoic acid derivatives and N-acylphenylalanine derivatives act as inhibitors by interaction with SUR [28][29][30]. Although it has been reported that these drugs act on plasma membrane channels, their effect on intracellular K ATP channels and sulphonylurea receptors remains to be specifically addressed.…”

Novel glimepiride derivatives with potential as double-edged swords against type II diabetes

“…Interestingly, the benzamido group alone is also likely to interact with SUR1, since a benzoic acid derivative of glibenclamide and meglitinide (Table 1) has been shown to induce insulin release (Henquin et al, 1987). Thus it seems plausible that the concerted interaction with the meglitinide-and tolbutamide-binding sites probably accounts for the several thousand-fold increase in affinity of glibenclamide equipped with both a benzamido (5-chloro-N-ethylen-2-methoxy benzamide) (Figures 1 and 3, region C) and a sulphonylurea moiety (region D) vs. tolbutamide equipped with a sulphonylurea moiety, only (Figure 1; Schwanstecher et al, 1998;Ashfield et al, 1999). Glimepiride is characterized by a slightly yet significantly lower binding affinity to β-cell membranes than glibenclamide (Müller et al, 1994a; see Table 1).…”