New activity of yamamarin, an insect pentapeptide, on immune system of mealworm, Tenebrio molitor

In insects, two types of the immune responses, cellular and humoral, constitute a defensive barrier against various parasites and pathogens. In response to pathogens, insects produce a wide range of immune agents that act on pathogens directly, such as cecropins or lysozyme, or indirectly by the stimulation of hemocyte migration or by increasing phenoloxidase (PO) activity. Recently, many new immunologically active substances from insects, such as peptides and polypeptides, have been identified. Nevertheless, in the most cases, their physiological functions are not fully known. One such substance is yamamarin - a pentapeptide isolated from the silk moth Antheraea yamamai. This yamamarin possesses strong antiproliferative properties and is probably involved in diapause regulation. Here, we examined the immunotropic activity of yamamarin by testing its impact on selected functions of the immune system in heterologous bioassays with the beetle Tenebrio molitor, commonly known as a stored grains pest. Our results indicate that the pentapeptide affects the activity of immune processes in the beetle. We show that yamamarin induces changes in both humoral and cellular responses. The yamamarin increases the activity of PO, as well as causes changes in the hemocyte cytoskeleton and stimulates phagocytic activity. We detected an increased number of apoptotic hemocytes, however after the yamamarin injection, no significant variations in the antibacterial activity in the hemolymph were observed. The obtained data suggest that yamamarin could be an important controller of the immune system in T. molitor.

Further proctolin analogues modified in the position 2 of the peptide chain and their myotropic effects in insects Tenebrio molitor and Schistocerca gregaria

We have extended our studies on the structure-activity relationship in neuropeptide proctolin (Arg-Tyr-Leu-Pro-Thr) by evaluating the effects of a series of proctolin analogues modified in position 2 of the peptide chain, including: [Phe(p-Cl)2]- (1), [D-Phe(p-Cl)2]- (2), [N-Me-Tyr2]- (3), [D-Phe(p-NH2)2]- (4), [D-Phe(p-N,N-di-Me)2]- (5), [N-Me-Tyr(OMe)]- (6), [D-3-Pal2]- (7), [L-Nal2]- (8), [D-Nal2]- (9), [Lys(Nic)2]- (10), [D-Lys(Nic)2]- (11), [D-Phe-(p-NO2)2]- (12). These peptides were evaluated for myotropic activity on the heart of Tenebrio molitor and contractile activity of the foregut of Schistocerca gregaria. Analogues 1-5, 7-9, and 12 retained a weak cardiotropic activity in Tenebrio molitor while peptides 1, 8 and 12 preserved 15-25% of the locust-gut contracting activity of proctolin. Peptides 2, 4 and 7 showed weak inhibitory activity in Schistocerca gregaria foregut, whereas only peptides 4 and 7 reduced the maximum response to applied proctolin by 64% and 49% respectively, at the 10(-6) M concentration.

New proctolin analogues and their myotropic effects on heart of yellow mealworm Tenebrio molitor L. and foregut of locust-Schistocerca gregaria L

We have extended our work on structure/activity relationship of neuropeptide proctolin (H-Arg-Tyr-Leu-Pro-Thr-OH) by evaluating the effects of the following proctolin analogues: H-X1-Tyr-Leu-Pro-Thr-OH, where X1 = D-Arg (1), N-Me-Arg (2), Can (3), D-Tyr2, D-Leu3, D-Thr5]-proctolin (12). In analogues 1-9, the N-terminal Arg-residue was replaced by basic amino acid derivatives with peptides containing amino acid residues with an isosteric system on the back side chain relative to Arg (compounds 3, 5 and 6) or homo-Arg (compound 7). Analogues 1-12 were evaluated for myotropic action on in vitro heart preparation of Tenebrio molitor, whereas peptides 2, 5 and 7-12 were tested for contractile action on isolated foregut of Schistocerca gregaria. Peptides 2 and 3 retained full cardiotropic activity in Tenebrio molitor while peptides 5 and 7 preserved 40% and 15%, respectively, locust-gut contracting activity of proctolin. Peptides 11 and 12 showed antagonistic activity in Schistocerca gregaria foregut.

Pharmacological studies of proctolin receptors on foregut and hindgut of Blaberus craniifer

Proctolin (Arg-Tyr-Leu-Pro-Thr) and proctolin analogs modified at position 1, 2, or 5 caused dose dependent contractions of Blaberus fore- and hindgut. The varying contractile effects between both tissues revealed the possible presence of receptor subtypes as identified by [GABA1]-proctolin. A single population of binding sites (Kd approximately 100 nM) was deduced from Scatchard analysis. In addition, nanomolar concentrations of proctolin induced a dose-dependent hydrolysis of phosphoinositides (PIns) augmented by GTPgammaS (1 microM) on foregut membranes but no accumulation of cAMP. Proctolin induced contractions are likely mediated via a phospholipase C linked to a heptahelical receptor bound to heterotrimeric G-proteins.

New proctolin analogues modified by D-amino acids in the peptide chain and their high cardioexcitatory effect on Tenebrio molitor

The object of our studies was the synthesis and conformational and biological evaluation of the series of 14 analogues of the insect neuropeptide, proctolin. The analogues were obtained by replacement of the native L-amino acids by their D-isomers in one, two, and all positions. Biological effects of the peptides were examined by cardioexcitatory test on the heart of yellow mealworm, Tenebrio molitor, in vitro. In biotest performed on insects, D-Arg-D-Tyr-D-Leu-D-Pro-D-Thr, [D-Arg(N-G-nitro)1,D-Leu3]-, [D-Arg1,D-Leu3]-, [D-Tyr2,D-Thr5]- and [D-Arg1,D-Pro4]-proctolin exert high agonistic activity of proctolin on the heart of insects at 10(-11) - 10(-10) M concentrations. The proctolin analogue containing only D-amino acid residues in the peptide chain unexpectedly shows a much higher cardioexcitatory effect than the native peptide. Moreover, preliminary CD and NMR conformational studies show that proctolin analogues investigated here seem to prefer rather ordered structures, although their conformations differ in some cases.