Selective agonists of NK-2 binding sites highly active on rat portal vein (NK-3 bioassay)

NK2R control of energy expenditure and feeding to treat metabolic diseases

The combination of decreasing food intake and increasing energy expenditure represents a powerful strategy for counteracting cardiometabolic diseases such as obesity and type 2 diabetes1. Yet current pharmacological approaches require conjugation of multiple receptor agonists to achieve both effects2-4, and so far, no safe energy-expending option has reached the clinic. Here we show that activation of neurokinin 2 receptor (NK2R) is sufficient to suppress appetite centrally and increase energy expenditure peripherally. We focused on NK2R after revealing its genetic links to obesity and glucose control. However, therapeutically exploiting NK2R signalling has previously been unattainable because its endogenous ligand, neurokinin A, is short-lived and lacks receptor specificity5,6. Therefore, we developed selective, long-acting NK2R agonists with potential for once-weekly administration in humans. In mice, these agonists elicit weight loss by inducing energy expenditure and non-aversive appetite suppression that circumvents canonical leptin signalling. Additionally, a hyperinsulinaemic-euglycaemic clamp reveals that NK2R agonism acutely enhances insulin sensitization. In diabetic, obese macaques, NK2R activation significantly decreases body weight, blood glucose, triglycerides and cholesterol, and ameliorates insulin resistance. These findings identify a single receptor target that leverages both energy-expending and appetite-suppressing programmes to improve energy homeostasis and reverse cardiometabolic dysfunction across species.

Prokinetic effects of the neurokinin NK2 receptor agonist [Lys5,MeLeu9,Nle10]-NKA(4-10) on bladder and colorectal activity in minipigs

The effects of the neurokinin NK2 receptor agonist [Lys⁵,MeLeu⁹,Nle¹⁰]-NKA_(4-10) (LMN-NKA) on bladder and colorectal function were examined in minipigs. In anesthetized animals, subcutaneous (SC) administration of 30-100 μg/kg increased peak bladder and colorectal pressures. Increases in bladder and colorectal pressure were inhibited by a 15 min pretreatment with the NK2 receptor antagonist GR 159897 (1 mg/kg intravenously (IV)). Bladder and colorectal pressures were also increased after IV (0.3 μg/kg), intranasal (IN; 100 μg/kg) and sublingual administration (SL; 5 mg/kg). There was a nonsignificant trend for hypotension (16 or 12% decrease in mean arterial pressure) after 100 μg/kg SC and 0.3 μg/kg IV, respectively, but not after 100 μg/kg IN or 5 mg/kg SL. In conscious minipigs, 30-300 μg/kg SC caused a dose-related increase in defecation that was accompanied by emesis in 38% of subjects receiving 300 μg/kg. Urination was increased after 100 μg/kg SC but not lower or higher doses. The peak plasma exposure (Cmax) after 100 μg/kg SC was 123 ng/mL, and area under the curve (AUC) was 1790 min * ng/mL. Defecation response rates (~82%) were maintained after SC administration of LMN-NKA (30 μg/kg) given 3 times daily over 5 consecutive days. Defecation rates were higher after a single dose of 100 μg/kg IN compared with vehicle, but this did not reach significance. After 7-10 mg/kg SL, 83% of animals urinated and defecated, and none had emesis. The data support the feasibility of developing a convenient and well-tolerated route of administration of LMN-NKA for human use. Minipigs may be a suitable species for toxicology studies with LMN-NKA due to the relatively low rate of emesis in this species.

Affinity, potency, efficacy, and selectivity of neurokinin A analogs at human recombinant NK2 and NK1 receptors

A series of peptide NK2 receptor agonists was evaluated for affinity, potency, efficacy, and selectivity at human recombinant NK2 and NK1 receptors expressed in CHO cells to identify compounds with the greatest separation between NK2 and NK1 receptor agonist activity. Binding studies were performed using displacement of [¹²⁵I]-NKA binding to NK2 receptors and displacement of [³H]-Septide binding to NK1 receptors expressed in CHO cells. Functional studies examining the increase in intracellular calcium levels and cyclic AMP stimulation were performed using the same cell lines. A correlation was demonstrated between binding affinities (Ki) and potency to increase intracellular calcium (EC₅₀) for NK2 and NK1 receptors. Ranking compounds by their relative affinity (Ki) or potency (EC₅₀) at NK2 or NK1 receptors indicated that the most selective NK2 agonists tested were [Lys⁵,MeLeu⁹,Nle¹⁰]-NKA(4-10) (NK1/NK2 Ki ratio = 674; NK1/NK2 EC₅₀ ratio = 105) and [Arg⁵,MeLeu⁹,Nle¹⁰]-NKA(4-10) (NK1/NK2 Ki ratio = 561; NK1/NK2 EC₅₀ ratio = 70). The endogenous peptide, NKA, lacked selectivity with an NK1/NK2 Ki ratio = 20 and NK1/NK2 EC₅₀ ratio = 1. Of the compounds selected for evaluation in cyclic AMP stimulation assays, [β-Ala⁸]-NKA(4–10) had the greatest selectivity for activation of NK2 over NK1 receptors (NK1/NK2 EC₅₀ ratio = 244), followed by [Lys⁵,MeLeu⁹,Nle¹⁰]-NKA(4-10) (ratio = 74), and NKA exhibited marginal selectivity (ratio = 2.8).

Characterization and in vivo efficacy of a heptapeptide ODT formulation for the treatment of neurogenic bladder dysfunction

The objective of this study was to develop oral disintegrating tablet (ODT) formulations of a heptapeptide, [Lys5,MeLeu9,Nle10]-NKA(4-10), for the treatment of neurogenic bladder dysfunction. A design of experiment approach was applied to determine the optimal ratio of chosen excipients: gelatin (X1), glycine (X2), and sorbitol (X3). These formulations were optimized for efficacy studies to produce ODTs exhibiting rapid disintegration times (Y1) and appropriate structural integrity (Y2) using JMP® 12.0.1 software. Based on theoretically predicted values from 12 experimental runs, the optimal ODT formulation was determined to be 3% (w/v) gelatin, 2% (w/v) glycine, and 1% (w/v) sorbitol in deionized water. Using this formulation, blank and drug-loaded ODTs containing 1.5 mg or 5 mg of [Lys5,MeLeu9,Nle10]-NKA(4-10) were manufactured by a lyophilization process. The peptide-loaded tablets disintegrated in less than 30 s and released 97% of the peptide within 15 min. The peptide was stable for 90 days under 25 °C/60% relative humidity (RH) and 40 °C/75% RH. In vivo efficacy of the peptide-loaded ODTs was confirmed in a rat acute spinal cord injury model under isovolumetric bladder pressure recording conditions, concluding that sublingual administration of peptide-containing ODTs evoke a rapid dose-related neurokinin 2-mediated increase in bladder pressure.

Tachykinins stimulate a subset of mouse taste cells

The tachykinins substance P (SP) and neurokinin A (NKA) are present in nociceptive sensory fibers expressing transient receptor potential cation channel, subfamily V, member 1 (TRPV1). These fibers are found extensively in and around the taste buds of several species. Tachykinins are released from nociceptive fibers by irritants such as capsaicin, the active compound found in chili peppers commonly associated with the sensation of spiciness. Using real-time Ca²⁺-imaging on isolated taste cells, it was observed that SP induces Ca²⁺ -responses in a subset of taste cells at concentrations in the low nanomolar range. These responses were reversibly inhibited by blocking the SP receptor NK-1R. NKA also induced Ca²⁺-responses in a subset of taste cells, but only at concentrations in the high nanomolar range. These responses were only partially inhibited by blocking the NKA receptor NK-2R, and were also inhibited by blocking NK-1R indicating that NKA is only active in taste cells at concentrations that activate both receptors. In addition, it was determined that tachykinin signaling in taste cells requires Ca²⁺-release from endoplasmic reticulum stores. RT-PCR analysis further confirmed that mouse taste buds express NK-1R and NK-2R. Using Ca²⁺-imaging and single cell RT-PCR, it was determined that the majority of tachykinin-responsive taste cells were Type I (Glial-like) and umami-responsive Type II (Receptor) cells. Importantly, stimulating NK-1R had an additive effect on Ca²⁺ responses evoked by umami stimuli in Type II (Receptor) cells. This data indicates that tachykinin release from nociceptive sensory fibers in and around taste buds may enhance umami and other taste modalities, providing a possible mechanism for the increased palatability of spicy foods.

Functional proteomics of neurokinin B in the placenta indicates a novel role in regulating cytotrophoblast antioxidant defences

Neurokinin B (NKB) has recently been demonstrated to be secreted from the placenta in abnormally high amounts in preeclampsia (PE) and to cause hypertension in rats, suggesting it may be a mediator of some pathophysiological features of PE. It is also known that NKB receptors exist in the placenta. To determine the effect of high levels of NKB on the placenta, we have performed proteomics on five separate preparations of cultured purified human term cytotrophoblast cells. The results showed a statistically significant decrease in 20 proteins, of which five were unknown proteins. Proteins important in antioxidant defenses that decreased were thioredoxin, cyclophilin A, cytokeratin 1, and peroxiredoxin 5. Two proteins that inhibit intravascular anticoagulation, cytokeratin 1 and annexin 11 were also decreased. Pathways involving pro-inflammatory cytokine activation of NF-kappa B are opposed by Raf kinase inhibitor protein, which was also decreased. Cofilin 1, a protein involved in defense against bacteria, was also decreased. Among other proteins that were suppressed by NKB were proteasome proteins, desmoplakin, and calgizzarin. Western blots confirmed the decrease in cytokeratin 1 and cyclophilin A protein after NKB exposure. In PE, there is reduced antioxidant activity and increased intravascular coagulation. The findings that high levels of NKB, similar to those observed in PE, can impair these two classes of activity support the hypothesis that high NKB levels may contribute to the pathogenesis of PE.

A 25 year adventure in the field of tachykinins

Several aspects of our 25 year adventure in the field of tachykinins will be successively described. They concern: substance P (SP) synthesis and release in the basal ganglia, the identification and pharmacological characterization of central tachykinin NK(1), NK(2) and NK(3) binding sites and their topographical distribution, the description of some new biological tests for corresponding receptors, the identification of tachykinin NK(1) receptor subtypes or conformers sensitive to all endogenous tachykinins (substance P, neurokinin A (NKA), neurokinin B (NKB), neuropeptide gamma (NP gamma) and neuropeptide K (NPK)) and finally, the functional involvement of these receptors and their subtypes in tachykinin-induced regulations of dopamine and acetylcholine release in the striatum.

Functional characterization of tachykinin NK1 receptors in the mouse uterus

1. Contractility studies were undertaken to determine the nature of the receptors mediating responses to tachykinins in uteri of oestrogen-treated mice. 2. In the presence of thiorphan (3 microM), captopril (10 microM), and bestatin (10 microM), substance P (SP), neurokinin A (NKA) and neurokinin B (NKB) produced concentration-related contractions of uterine preparations. The order of potency was SP > or =NKA>NKB. 3. Neither atropine (0.1 microM) nor l-NOLA (100 microM), nor indomethacin (10 microM) alone or in combination with either ranitidine (10 microM) or mepyramine (10 microM), affected responses to SP. These findings indicate that SP actions are not mediated or modulated through the release of acetylcholine, nitric oxide, prostanoids or histamine. 4. In the presence of peptidase inhibitors, the tachykinin NK(1) receptor-selective agonist [Sar(9)Met(O(2))(11)]SP, produced a concentration-dependent contractile effect. The tachykinin NK(2) and NK(3) receptor-selective agonists [Lys(5)MeLeu(9)Nle(10)]NKA(4-10) and [MePhe(7)]NKB were relatively inactive. The potencies of SP analogues in which Glu replaced Gln(5) and/or Gln(6) were similar to that of SP. 5. The tachykinin NK(1) receptor-selective antagonist, SR140333 (10 nM), alone or combined with the tachykinin NK(2) receptor-selective antagonist, SR48968 (10 nM), shifted log concentration curves to SP, NKA and NKB to the right. SR140333 (10 nM) reduced the effect of [Sar(9)Met(O(2))(11)]SP. SR48968 did not affect responses to SP or [Sar(9)Met(O(2))(11)]SP, but reduced the effect of higher concentrations of NKA and shifted the log concentration-response curve to NKB to the right. The tachykinin NK(3) receptor-selective antagonist, SR 142801 (0.3 microM), had little effect on responses to SP and NKB. 6. We conclude that the tachykinin NK(1) receptor mediates contractile effects of SP, NKA and NKB and [Sar(9)Met(O(2))(11)]SP in myometrium from the oestrogen-primed mouse. The tachykinin NK(2) receptor may also participate in the responses to NKA and NKB.

Structure-activity relationship of neurokinin A(4-10) at the human tachykinin NK(2) receptor: the effect of amino acid substitutions on receptor affinity and function

A structure-activity study of the neurokinin A (NKA) fragment NKA(4-10) was performed to investigate the importance of amino acid residues for receptor efficacy, potency and affinity at the NK(2) receptor in human colon circular muscle. Fourteen analogs of NKA(4-10) were produced with substitutions at positions 4, 5, 7, 9 and/or 10 of NKA. Their potencies were determined by in vitro contractile responses and affinities by radioligand binding using [125I]NKA. Functional potency was enhanced 8-fold by single amino acid substitutions with Lys(5) and MeLeu(9) but not significantly altered by substitutions Glu(4), Arg(5), His(5) and Nle(10). The multiply-substituted analogs [MeLeu(9),Nle(10)]NKA(4-10), [Lys(5),MeLeu(9),Nle(10)]NKA(4-10) and [Lys(5),(Tyr(7)),MeLeu(9),Nle(10)]NKA(4-10) displayed 6-9-fold increase in potency. Although [Arg(5),Nle(10)]NKA(4-10) was similar in potency to NKA(4-10), it was the only analog to show significantly reduced efficacy. All analogs were able to compete fully for [125I]NKA binding. [Lys(5),MeLeu(9)]NKA(4-10), [MeLeu(9),Nle(10)]NKA(4-10), [Lys(5),Nle(10)]NKA(4-10) and analogs containing single substitutions with Glu(4), Arg(5), Lys(5) and MeLeu(9) displayed significantly higher affinity, whereas those with Nle(10) and [Glu(4),Nle(10)] substitutions showed significantly lower affinity than NKA(4-10). There was a positive correlation (r=0.63) between binding affinity and functional potency, which was markedly improved (r=0.95) by removal of three analogs: [Lys(5),MeLeu(9),Nle(10)]NKA(4-10), [Lys(5),Tyr(7),MeLeu(9),Nle(10)]NKA(4-10) and [Lys(5),Tyr(I(2))(7),MeLeu(9),Nle(10)]NKA(4-10). These exhibited similar binding affinities to that of NKA(4-10) but were more potent in functional studies, possibly indicating a different mechanism of receptor interaction. In conclusion, substitution of Ser(5) with Lys, and/or N-methylation of Leu(9), were the most effective changes to increase functional and binding potency of NKA(4-10) at the human colon NK(2) receptor.

Effects of tachykinins on uterine smooth muscle

1. Sensory nerves supplying the mammalian uterus have been shown to contain substance P (SP) and neurokinin (NK)A. This review presents some of the advances that have led to a greater understanding of the effects of tachykinins on uterine smooth muscle. 2. The cell-surface peptidase neprilysin (EC.3 24.11, endopeptidase 24.11, enkephalinase, CALLA, CD10) has been shown to play a major role in regulating the actions of tachykinins on both rat and human myometrium. Because this peptidase is known to be regulated by steroids and pregnancy, its effects may be of physiological relevance. 3. Tachykinins produce contractions of isolated myometrial preparations from non-pregnant rats and mice. The NK2 receptor mediates these effects in rat uterus, while the NK1 receptor may mediate these effects in the mouse uterus. 4. The effects of tachykinins have been examined on myometrial preparations obtained at Caesarean section from near-term pregnant women. In the presence of the peptidase inhibitors (thiorphan, captopril and bestatin), the mammalian tachykinins SP, NKA and NKB produced concentration-dependent uterine contractions. 5. The order of agonist potency NKA > SP = NKB suggested that NK2 receptors mediate uterine contractions in the human. This was confirmed using the stable analogues [Sar9,Met(O2)11]SP, [Lys5MeLeu9Nle10]NKA(4-10) and [N-MePhe7]NKB, which are NK1, NK2 and NK3 receptor selective, respectively. Only [Lys5MeLeu9Nle10]NKA(4-10) produced concentration-related contractions of human uterine smooth muscle. 6. The experimental findings described in the present review, taken together with results published previously in the literature, indicate that tachykinin peptides may play a physiological or pathophysiological role in regulating uterine smooth muscle activity. However, more extensive research will be required to confirm such a role for these peptides.

Tachykinin receptors mediating contractions of oestrogen-primed rat uterus: classification using non-peptide antagonists

1. The aim of the present study was to characterize the tachykinin receptors mediating contractions of the uterus from the oestrogen-primed rat. Apparent pKB values versus mammalian tachykinins and some subtype-selective agonists were determined for the non-peptide NK1, NK2 and NK3 receptor antagonists SR 140333, SR 48968 and SR 142801, respectively. 2. Apparent pKB values for SR 48968 tested at concentrations of 3, 10 and 30 nmol/L versus neurokinin (NKA, [Lys5MeLeu9Nle10] NKA(4-10) and [Nle10] NKA(4-10) were 8.79, 9.44 and 9.33, respectively, indicating activation of an NK2 receptor and, in the case of NKA, the possible activation of an additional receptor subtype. SR 48968 (30 nmol/L) did not affect responses to NKB (1 mumol/L), senktide (30 nmol/L), substance P (SP; 100 nmol/L) or [Sar9Met(O2)11] SP (100 nmol/L), indicating its selectivity at this concentration. 3. SR 140333 (1-100 nmol/L) reduced the effects of the NK1-preferring agonists SP and [Sar9Met(O2)11] SP, indicating the presence of NK1 receptors. The pKB estimate versus [Sar9Met(O2)11] was 9.01. SR 140333 (100 nmol/L) did not affect responses to NK2 and NK3 receptor-preferring agonists. 4. SR 142801 (100 nmol/L to 1 mumol/L) produced small rightward shifts in the log concentration-response curves to NKB, yielding an apparent pKB value of 7.0. At 1 mumol/L, SR 142801 reduced responses to the NK2 agonists, suggesting some non-selectivity at this concentration. 5. Taken together, these data provide strong evidence that tachykinin-induced contractions of the uterus of the oestrogen-primed rat are mediated by NK2 receptors, with some contribution from NK1 receptors.

NK2 receptors mediate tachykinin-induced contractions of rat uterus during the oestrous cycle

We examined tachykinin-induced contractions of uteri from rats during the oestrous cycle. The potencies of substance P, neurokinin A, neurokinin B and the tachykinin NK2 receptor-selective agonist, [Lys5, MeLeu9, Nle10] neurokinin A-(4-10), and of the non-peptide tachykinin NK1, NK2 and NK3 receptor antagonists (S)1-[2-[3-(3,4-dichlorophenyl)-1-(3-isopropoxyphenylacetyl)pip eridin-3-yl]ethyl]-4phenyl-1-azonia-bicyclo[2.2.2]octane (SR 140333), (S)-N-methyl-N [4-(4-acetylamino-4-phenylpiperidino)-2-(3,4-dichlorophenyl)butyl]benzam ide (SR 48968) and (S)-(N)-(1-(3-(1-benzoyl-3-(3,4-dichlorophenyl)piperidin-3-yl)prop yl)-4-phenylpiperidin-4-yl)-N-methylacetamide (SR 142801), were examined. The relative agonist potencies, i.e., [Lys5, MeLeu9, Nle10] neurokinin A-(4-10) > or = neurokinin A > neurokinin B > or = substance P were similar in preparations from rats in dioestrus/metoestrus and those in proestrus/oestrus. Apparent pK(B) values for SR 48968 versus neurokinin A and [Lys5, MeLeu9, Nle10] neurokinin A-(4-10), were 9.9 and 9.2, respectively, indicating activation of an NK2 receptor. SR 140333 (10 nM) produced only a small rightward shift of the log concentration-response curve to substance P. SR 48968 (3 nM), but not SR 142801 (100-300 nM) reduced the effect of neurokinin B. These data indicate that in the rat tachykinin-induced contractions of the uteri during the oestrous cycle are mediated primarily by tachykinin NK2 receptors, and that fluctuations in ovarian hormonal levels during the oestrous cycle have little influence on the uterine response to tachykinins.

Structure-activity studies at the rat tachykinin NK2 receptor: effect of substitution at position 5 of neurokinin A

A series of analogues of neurokinin A(4-10) was synthesized using solid phase techniques with Chiron pins, and purified by HPLC. The potencies of 10 peptides with substitution at Ser5 were assessed at rat fundus NK2 receptors. In membrane binding studies with [125I]-[Lys5,Tyr(I2)7,MeLeu9,Nle10]-NKA(4-10), all compounds except [Asp5]NKA(4-10) showed reasonable affinity, and analogues with Lys and Arg substitutions were five-fold more potent than NKA(4-10). In functional studies, all peptides were able to contract the rat isolated fundus strips. Analogues with Phe, His and Asn substitutions were substantially weaker in functional than in binding studies, whereas there was an excellent correlation (r = 0.95) between binding and functional potency for the remaining seven peptides. [Phe5]NKA(4-10) is in fact neurokinin B(4-10) and this residue may be critical in determining selectivity between NK2 and NK3 receptors. Analogues with a basic residue (Lys, Arg) at position 5 showed both increased affinity and functional potency, whereas the neutral [Asn5]NKA(4-10) was equally as weak in contractile studies as the acidic [Asp5]NKA(4-10). However, [Glu5]NKA(4-10) and [Gln5]NKA(4-10) were no different from NKA(4-10). Our results could indicate the presence of a negative charge on the NK2 receptor, close to position 5 of NKA. This would facilitate interaction with positively charged side chains and impede interaction with negatively charged side chains, particularly the inflexible side chain of aspartic acid. Thus, not only the charge, but also the length of the side chain of the residue at position 5, seems to be important for interaction with the rat NK2 receptor.

Structure-activity studies of analogues of neurokinin A mediating contraction of rat uterus

A structure-activity study of compounds related to NKA was performed using uterus from the oestrogen-primed rat, a preparation thought to contain a significant population of NK2 receptors. The compounds tested included: NKA and its C-terminal fragments; NKA(4-10)-free acid; a series of LAla monosubstituted analogues of NKA(4-10) and of NKA; [DAla1]NKA; and a series of analogues of [Nle10]NKA(4-10) monosubstituted at position four, five or seven. Results suggest that the His at position one of NKA is of little or no importance in contractile activity, while substitution or truncation of Lys at position two or substitution of Thr at position three causes a decrease in potency. Results also confirm that amino acids at positions four, six, seven, nine and ten are very important for contractile activity of NKA and its analogues on rat uterus. The similarity between the changes in potency obtained in this study, and those obtained in rabbit pulmonary artery, an NK2 monoreceptor preparation, provides further evidence for the presence of NK2 receptors in the uterus of the oestrogen-primed rat.

Potencies of agonists acting at tachykinin receptors in the oestrogen-primed rat uterus: effects of peptidase inhibitors

The uterotonic potencies of the naturally occurring mammalian tachykinins and the synthetic subtype-selective agonist analogues of these agents [Lys5,MeLeu9,Nlel0]neurokinin A-(4-10) and [Nle10]neurokinin A-(4-10) (tachykinin NK2 receptor-selective), [Sar9,Met(O2)11]substance P (tachykinin NK1 receptor-selective) and senktide (tachykinin NK3 receptor-selective) were determined using preparations from oestradiol-treated rats. The endopeptidase 24.11 inhibitor, N-[N-[1-(S)-carboxyl-3-phenylpropyl]-(S)-phenyl-alanyl-(S)-isoserine+ ++ (SCH 39370), potentiated responses to neurokinin A, neurokinin B and substance P, but not to [Lys5,MeLeu9,Nle10)]neurokinin A-(4-10) or senktide. [Nle10]neurokinin A-(4-10) effects were potentiated by SCH 39370 with amastatin and those to [Sar9,Met(O2)11]substance P were potentiated by SCH 39370 and captopril in combination. In the presence of optimal concentrations of peptidase inhibitors the relative order of agonist potency was: neurokinin A > substance P > neurokinin B for the naturally occurring mammalian tachykinins and [Lys5,MeLeu9,Nle10]neurokinin A-(4-10) > [Nle10]neurokinin A-(4-10) > [Sar9,Met(O2)11]substance P > senktide for the synthetic tachykinin analogues. Thus, while a tachykinin NK2 receptor predominates in the oestrogen-primed uterus, a tachykinin NK1 receptor may also be present. The non-peptide tachykinin NK3 receptor antagonist, SR 142801, did not antagonise the effects of senktide suggesting that tachykinin NK3 receptors do not mediate its relatively minor effect on the uterus of the oestrogen-primed rat.

The NK1 receptor and its participation in the synergistic enhancement of corneal epithelial migration by substance P and insulin-like growth factor-1

1. We have previously shown that substance P (SP) and insulin-like growth factor-1 (IGF-1) act synergistically to enhance the migration of rabbit corneal epithelial cells in an organ culture model. The present study was designed to identify the epithelial cell SP receptor that participates in this synergistic effect. 2. Rabbit corneal blocks were incubated for 24 h, then the length of the path of epithelial migration was measured. Reagents tried in the TC-199 culture medium, in the presence or absence of IGF-1, were: SP, agonists of tachykinin receptors NK1, NK2 or NK3 and antagonists of tachykinin receptors NK1 or NK2. 3. The binding characteristics of SP receptors were examined in rabbit cultured corneal epithelial cells by binding assays with [125I]-SP in the presence or absence of excess unlabelled SP or ligands of NK1, NK2 or NK3 receptors. 4. As was demonstrated previously, SP and IGF-1 stimulated epithelial migration when they were added to the culture medium together, but individually they had no effect. NK1 agonists had the same synergistic effect with IGF-1 as did SP, but the NK2 and NK3 agonists did not. Furthermore, the NK1 antagonist abolished the synergistic effect of SP and IGF-1, but the NK2 antagonist had no effect. 5. SP bound specifically to rabbit cultured corneal epithelial cells. The binding affinity was 0.44 nM and there were 2.43 x 10(4) binding sites per cell. The NK1 ligand competed, in a dose-dependent fashion, with the binding of SP to corneal epithelial cells, but neither the NK2 nor NK3 ligand affected binding. 6. We conclude that the SP receptor in rabbit corneal epithelial cells is NK1 and that this receptor participates in the synergistic enhancement of corneal epithelial migration by SP and IGF-1. The precise mechanism(s) of this interaction requires more study. These findings imply that both neural and humoral factors are essential for the maintenance and healing of corneal epithelium.

Tachykinin NK-1 receptor probed with constrained analogues of substance P

The action of rotameric probes introduced either in position 7 or 8 in the sequence of substance P (SP) was investigated, i.e. L-tetrahydroisoquinoleic acid (Tic), L-fluorenylglycine (Flg), L-diphenylalanine (Dip), the diastereoisomers of L-1-Indanylglycine (Ing) and L-benz[f]indanylglycine (Bfi), the Z- and E-isomers of dehydrophenylalanine and dehydronaphthylalanine (delta ZPhe, delta EPhe, delta ZNal, ENal) and L-O,O'-dimethylphenylalanine (Dmp). The aim of this study was the topographical characterization of the binding subsites of human NK-1 receptor expressed in CHO cells, especially the S7 and S8 subsites, corresponding to residues Phe7 and Phe8 of substance P. According to the binding potencies of these substituted-SP analogues, the S7 binding subsite is smaller than the S8 subsite: the S7 subsite accepts only one aromatic nucleus, while the S8 can accommodate three coplanar nuclei altogether. These findings are compatible with the idea that the S8 binding subsite may reside in the extracellular loops of the hNK-1 receptor. NK-1 agonists bind to human NK-1 receptor and activate the production of both inositol phosphates and cyclic AMP. As already quoted for septide, [pGlu6, Pro9]SP(6-11), discrepancies are observed between affinity (K1) and activity (EC50) values for IPs production. While a weak correlation between K1 and EC50 values for IPs production could be found (r = 0.70), an excellent correlation could be demonstrated between their affinities (K1) and their potencies (EC50) for cAMP production (r = 0.97). The high potency (EC50) observed for "septide-like' molecules on PI hydrolysis, compared to their affinity is not an artefact related to the high level of NK-1 receptors expressed on CHO cells since a good correlation was found between EC50 values obtained for PI hydrolysis and those measured for spasmogenic activity in guinea pig ileum bioassay (r = 0.94).

Comparative behavioural profile of centrally administered tachykinin NK1, NK2 and NK3 receptor agonists in the guinea-pig

1. The NK1 tachykinin receptor agonists, septide, [Sar9,Met(O2)11]SP and [Pro9]SP produced locomotor hyperactivity (10-20 min) when injected intracerebroventricularly (i.c.v.) in the guinea-pig. The most potent in eliciting this hyperactivity was septide (from 0.63 to 5 micrograms), compared to [Sar9,Met(O2)11]SP, which was active at 2.5 and 5 micrograms and [Pro9]SP which induced a non-significant increase even at 10 micrograms. 2. Wet-dog shakes were elicited by septide, [Sar9,Met(O2)11]SP and [Pro9]SP injected by the i.c.v. route in the guinea-pig. [Sar9,Met(O2)11]SP, active from 0.16 to 2.5 micrograms was more potent than septide (active at 1.25 micrograms) and [Pro9]SP (active at 0.63 micrograms) in eliciting such behaviour. To a lesser extent, grooming was also observed after injection of these agonists. 3. The NK2 tachykinin receptor agonist, [Lys5,MeLeu9,Nle10]NKA(4-10), up to the dose of 10 micrograms i.c.v. had no effect in the guinea-pig. It neither modified locomotor activity nor induced a characteristic behavioural response. At higher doses (20 micrograms), some toxic effects were noted. 4. The NK3 tachykinin receptor agonist, senktide, contrasts with the NK1 receptor agonists in that it elicited only wet-dog shakes, at doses ranging from 0.32 to 1.25 micrograms. It neither modified locomotor activity (1 microgram) nor induced grooming (up to 5 micrograms) in the guinea-pig. 5. To our knowledge, these results are the first demonstration that the guinea-pig could be useful to differentiate tachykinin agonists on the basis of their behavioural profile, distinct from those obtained in mice and rats.

The mammalian tachykinin receptors

The tachykinins (TKs) are a family of small peptides which share the common C-terminal sequence Phe-X-Gly-Leu-MetNH2. Three peptides of this family, substance P, neurokinin A and neurokinin B, have an established role as neurotransmitters in mammals. 2. Three receptors for TKs have been cloned: they are G-protein coupled receptors with seven putative transmembrane spanning segments and have been termed NK1 (substance P-preferring), NK2 (neurokinin A-preferring) and NK3 (neurokinin B-preferring). 3. Synthetic agonists are available to selectively stimulate only one receptor, while natural TKs can act as full agonist at each one of the three receptors, albeit at different concentrations. 4. A number of potent and selective antagonists, both peptide and nonpeptide in nature, have recently been developed. 5. The introduction of these ligands has revealed an unforeseen pharmacological heterogeneity of NK1, NK2 and NK3 receptors which appears largely, if not exclusively, linked to the existence of species homologues of the three receptors.

Involvement of septide-sensitive tachykinin receptors in inositol phospholipid hydrolysis in the rat urinary bladder

The selective NK2 agonist [Lys5-MeLeu9,Nle10]NKA(4-10) markedly stimulated [3H]inositol monophosphate (PI1) formation in prisms from the rat urinary bladder. This response was blocked by the NK2 antagonist SR 48968. Senktide (NK3 agonist) was inactive. Septide, a short SP analogue, and the NK1 agonists [Pro9]SP and [Sar9,Met(O2)11]SP also stimulated [3H]IP1 formation and several NK1 tachykinin antagonists (RP 67580, CP 96345, GR 82334, and [D-Pro9,t beta-BPr10,Trp11]SP) were more potent in blocking the septide than the [Pro9]SP response. GR 82334 was the most discriminative. SR 48968 (10(-6) M shifted the [Pro9]SP dose-response curve but did not modify the septide dose-response curve. Septide had a low affinity for [3H][Pro9]SP binding sites, suggesting further that septide and NK1 agonists act on different receptors. Finally, both [Pro9]SP and [Sar9,Met(O2)11]SP blocked the septide-evoked response, acting as partial agonists at the septide-sensitive tachykinin receptors.

Differential ability of tachykinin NK-1 and NK-2 agonists to produce scratching and grooming behaviours in mice

Potent and selective NK-1 and NK-2 agonists as well as compounds with lower selectivity and affinity for NK-1 binding sites were compared in their ability to produce scratching and grooming behaviours when injected intracerebroventricularly in mice. Septide, an agonist with a low affinity for NK-1 binding sites, [Sar9, Met(O2)11]SP and to a lesser extent [Pro9]SP, two potent and selective NK-1 agonists were the most effective drugs in stimulating these behaviours. Only high doses of [Apa9,10]SP and [Lys5, Tyr7, Pro8]NKA(4-10), two agonists with low affinity for NK-1 binding sites, produced scratching and grooming responses. Similarly, only high doses of [Lys5, MeLeu9, NLe10]NKA(4-10), a potent NK-2 agonist, produced grooming behaviour. When coinjected with the endopeptidase enzyme inhibitor phosphoramidon, the effects of [Apa9,10]SP, [Lys5, Tyr7, Pro8]NKA(4-10) and [Pro9]SP were markedly enhanced. Analyses of the potency of the different agents to displace 3H-SP binding in mouse subcortical structures revealed that the affinities of the agonists for NK-1 receptors are similar to those previously reported in rat brain. The efficacy of the agonists at producing behavioural responses was not equivalent to their potency to bind to central NK-1 receptors. These findings therefore suggest that a stimulation of NK-1 but also non classical NK-1 receptors are involved in the induction of scratching and grooming behaviours.

Characterization of NK1 and NK2 tachykinin receptors in guinea-pig and rat bronchopulmonary and vascular systems

1. NK1 and NK2 tachykinin receptors were characterized in guinea-pig and rat bronchopulmonary systems and in the vasculature of the rat by use of radioligand binding and/or functional studies. 2. The radioligands for NK1 and NK2 receptors ([3H]-SP and [3H]-pNKA, respectively) did not label tachykinin receptors in homogenates of rat lungs or bronchi. In contrast, in the guinea-pig, [3H]-SP bound with high affinity to these tissues (KD = 0.23 +/- 0.08 nM and 0.34 +/- 0.05 nM, for lungs and bronchi, respectively). The total number of binding sites was 4.6 fold greater in bronchus (Bmax = 135 +/- 27 fmol mg-1 protein) than in lung homogenates (Bmax = 29.3 +/- 0.1 fmol mg-1 protein). Furthermore, this binding was markedly displaced by CP-96,345 (pKi = 9.5 +/- 0.1) and RP 67580 (pKi = 7.6 +/- 0.1), antagonists of NK1 receptors, slightly displaced by SR 48968 (pKi = 6.6 +/- 0.1), but not affected by actinomycin D or L-659,877, antagonists of NK2 receptors. Specific binding of [3H]-pNKA, detected in guinea-pig bronchi (KD = 5.2 +/- 0.1 nM, and Bmax = 203 +/- 19 fmol mg-1 protein) but not in lungs, was similarly (40 to 53%) displaced by RP 67580 (1 microM), CP-96,345 (10 and 100 nM) or SR 48968 (10 and 100 nM). The displacement approximately doubled (87 to 91%) when SR 48968 (10 nM) was combined with either RP 67580 (1 microM) or CP-96,345 (10 nM), but not when RP 67580 was combined with CP-96,345. 3. In urethane-anaesthetized guinea-pigs, i.v. injections of the NK1 receptor agonists SP, [Pro9]-SP, [Sar9,Met(O2)11]-SP and septide, as well as the NK2 receptor agonists NKA and [Lys5,MeLeu9,NLeu10]-NKA(4-10) (0.1-10 micrograms kg-1, i.v.), dose-dependently increased lung inflation pressure. The most potent of these peptides were septide and [Lys5, MeLeu9,NLeu10]-NKA(4-10) (EC50 = 0.38 +/- 0.07 and 0.07 +/- 0.02 microgram kg-1, respectively). Interestingly, septide was 130 fold less potent than SP in displacing [3H]-SP from its binding sites in the guinea-pig lung, whereas it was 14 fold more potent than SP as a bronchoconstrictor. RP 67580 (0.3-5 mg kg-1, i.v.) and CP-96,345 (0.01-3 mg kg-1, i.v.) dose-dependently reduced the bronchoconstriction produced by the NK1 receptor agonists. Conversely, the NK2 receptor antagonists actinomycin D (1-10 mg kg-1, i.v.) and SR 48968 (0.03-0.3 mg kg-1, i.v.) inhibited specifically the responses induced by NK2 receptor agonists.4. In pentobarbitone-anaesthetized rats, the NK1 and NK2 receptor agonists (0.01-4 microg kg-1, i.v.)produced dose-dependent hypotensive responses. The order of potency was SP = [Sar9, Met(0211]-SP = [Pro9]-SP > septide = NKA >[Lys5, MeLeu9, NLeu 10-NKA.(4-10). RP 67580 (0.13-0.5 mg kg-1,i.v.) and CP-96,345 (0.5-2 mg kg-1, i.v.) antagonized in a dose-related manner (20 to 64%) the vascular effects of both NK, and NK2 receptor agonists, whereas actinomycin D (3 mg kg-1, i.v.) and SR 48968(2 mg kg-1, i.v.) did not. RP 67580 was approximately 4 times more potent than CP-96,345.5. These studies indicate that NK1 and NK2 receptors are both present in the guinea-pig bronchopulmonary system whereas only NK1 receptors are detectable in the rat vasculature under our experimental conditions. Furthermore, NK1 receptors in the guinea-pig bronchopulmonary system are pharmacologically distinct from those present in the rat vascular system, since both agonist potencies and antagonist affinities differ between the two species.

Antagonism of substance P and related peptides by RP 67580 and CP-96,345, at tachykinin NK1 receptor sites, in the rat urinary bladder

Tonic contraction of rat urinary bladder was elicited in vitro and in vivo by substance P, two selective NK1 receptor agonists, septide ([pGlu6,Pro9]substance P-(6-11)) and [Sar9,Met(O2)11]substance P, and an NK2 agonist, [Lys5,MeLeu9,Nle10]neurokinin A-(4-10), but not by senktide (succinyl[Asp6,MePhe8]substance P-(6-11)), an NK3 agonist. Substance P only stimulated the NK1 receptors of smooth muscle. The non-peptide selective NK1 receptor antagonists, RP 67580 and CP-96,345, both inhibited substance P-induced contraction (pKB values 6.7 and 5.7; ED50 = 1.4 and 5.0 mg/kg i.v., respectively) and septide-induced contraction (pKB values 7.5 and 6.5; ED50 = 0.076 and 0.250 mg/kg i.v., respectively). Both antagonists, at lower doses, also inhibited substance P- and septide-induced plasma extravasation. That both antagonists blocked the effects of septide much more than the effects of substance P suggests the existence of an NK1 receptor subtype or isoform. Selective NK1 receptor antagonists, by blocking both spasm and plasma extravasation in the urinary bladder, would be useful for treating substance P-related motor disorders and cystitis.

Evidence for tachykinin NK-2 receptors in guinea-pig airways from binding and functional studies, using [125I]-[Lys5,Tyr(I2)7,MeLeu9,Nle10]-NKA(4-10)

The potent contractile responses of guinea-pig airways to neurokinin A (NKA) and neuropeptide gamma (NP gamma) are thought to be mediated by NK-2 receptors. However, NK-2 binding sites are not detectable using the radioligand [125I]-iodohistidyl-NKA. Here, a novel, highly selective iodinated radioligand, [125I]-[Lys5,Tyr(I2)7,MeLeu9,Nle10]-NKA(4-10), and a number of related peptides have been used to characterize NK-2 receptors on guinea-pig airways, using binding and functional studies. Specific binding of [125I]-[Lys5,Tyr(I2)7,MeLeu9,Nle10]-NKA(4-10), was saturable and to a single high affinity site, with KD 1.29 +/- 0.36 nM (n = 4). The rank order of potency for tachykinins and analogues as competitors for the binding was: [Lys5,Tyr(I2)7,MeLeu9,Nle10]-NKA(4-10) > or = NP gamma > or = [Lys5,MeLeu9,Nle10]-NKA(4-10) > NKA > or = SR 48968 >> MDL 29913 > or = substance P (SP) = [127I]-Bolton-Hunter NKA (BHNKA) > or = MEN 10207 > neurokinin B (NKB). Septide, [DPro9,Pro10,Trp11]-SP, the NK-1 selective ligands [Sar9,Met(O2)11]-SP, [Pro9]-SP and CP 96345, the NK-3 selective senktide, and calcitonin gene-related peptide (CGRP) were weak or ineffective. On guinea-pig isolated bronchi, the potency order of contractile agonists was: [Lys5,MeLeu9,Nle10]-NKA(4-10) > NKA > or = NP gamma > or = [Lys5,Tyr7,MeLeu9, Nle10]-NKA(4-10) > or = septide = BHNKA > or = [Lys5,Tyr(I2)7,MeLeu9,Nle10]-NKA(4-10) > or = [Sar9,Met(O2)11]-SP > or = NKB = [Pro9]-SP > or = SP >> senktide.(ABSTRACT TRUNCATED AT 250 WORDS)

Neurokinin receptor subtypes characterized by biological assays

Neurokinin receptors have been characterized by biological assays using naturally occurring and selective agonists as well as peptide and non peptide antagonists. Six preparations have been used: the rabbit vena cava and the rat urinary bladder, treated with a NK-2 receptor antagonist for the NK-1 receptor, the rabbit pulmonary artery and the hamster urinary bladder for the NK-2, the rat portal vein and the guinea pig ileum, treated with a NK-1 receptor antagonist, for the NK-3. Treatment with antagonists was required because of the presence (in some preparations) of two functional sites contributing to the biological effect. Differences in the order of potency of agonists between each couple of receptors have been demonstrated, especially with tachykinins and the selective agonists. Such differences are even more evident with antagonists, some of which show apparent affinity (pA2) values 1.5 to 3 log units higher in one than in the other member of each couple. Based on data obtained in pharmacological experiments, it is concluded that NK-1, NK-2 and NK-3 receptors show differences strong enough to justify the assumption that their coding and/or expression diverge among species.

Substance P-evoked calcium mobilization and ionic current activation in the human astrocytoma cell line U 373 MG: pharmacological characterization

In the human astrocytoma cell line U 373 MG, application of substance P (SP) leads to a transient increase in cytosolic calcium concentration and to a biphasic current response in voltage-clamped cells. Using these two functional assays we have characterized pharmacologically the SP response in U 373 MG cells. SP and [L-Pro9]SP displayed high potencies in both assays with EC50 values of 2.5 x 10(-9) M and 1 x 10(-9) M on calcium responses and 1 x 10(-9) M and 5 x 10(-9) M on ion current responses, respectively. The high potency of SP and [L-Pro9]SP as well as the low potency of [Lys5,MeLeu9,N-Leu10]neurokinin A(4-10) and the inactivity of senktide demonstrate the NK1-type pharmacology of these responses. Furthermore, the NK1 antagonists (+/-)-CP 96,345, its chloro analogue, (+/-)-cis-3-(2-chlorobenzylamino)-2-benzhydrylquinuclidine, and RP 67580 were potent antagonists of both SP responses. For the calcium mobilization induced by SP (10(-7) M), the IC50 values for the three antagonists were 4 x 10(-10) M, 4 x 10(-9) M, and 9 x 10(-9) M, respectively, whereas on the current response evoked by SP (10(-8) M), the IC50 values were 8 x 10(-9) M, 2.4 x 10(-8) M, and 1.2 x 10(-7) M, respectively. Despite differences in the absolute IC50 values obtained with both techniques, the relative potencies of the three antagonists correlate fairly well.(ABSTRACT TRUNCATED AT 250 WORDS)

Intranigral stimulation of oral movements by [Pro9] substance P, a neurokinin-1 receptor agonist, is enhanced in chronically neuroleptic-treated rats

Bilateral intranigral infusions of three different peptide agonists were made in rats exposed to fluphenazine decanoate, 30 mg/kg/month (FLU) or vehicle (CON) for seven months. Oral movements were monitored repeatedly during the neuroleptic pretreatment period, as well as before the intranigral infusion and during a 90-min period postinfusion. The FLU group had an increased frequency of vacuous chewing movements (VCM) during the pretreatment period in comparison to controls. Intranigral infusion of the neurokinin-1 (NK1) receptor agonist, [Pro9]Substance P (2.5 nmol on each side), 5-7 weeks after the last FLU injection, caused a significant increase of VCM in both pretreatment groups, lasting 7 min after the infusion. The VCM response to [Pro9]Substance P in the FLU group was significantly higher than in the CON group. A NK2 agonist [Lys5, MeLeu9, Nle10]Neurokinin A(4-10) (2.5 nmol) failed to produce significant changes in oral activity. A Leu-enkephalin analogue [D-Ala2,D-Leu5]enkephalin (3.8 nmol) induced a massive biting behavior in both FLU and CON rats. Using VCM as a behavioral assay, an increased nigral sensitivity to a NK1 agonist is demonstrated in rats chronically exposed to neuroleptics. No corresponding alterations could be ascribed for the NK2 receptor agonist or the Leu-enkephalin analogue.

A new selective bioassay for tachykinin NK3 receptors based on inositol monophosphate accumulation in the guinea pig ileum

The selective agonists of tachykinin NK1, NK2 and NK3 receptors, respectively [Pro9]substance P, [Lys5,MeLeu9,Nle10]neurokinin A-(4-10) and senktide, stimulated phosphoinositide breakdown in slices of the guinea pig ileum. This was also the case with septide which has recently been found to act on a new type of tachykinin receptors in this tissue. The NK1, NK2 and septide-evoked responses were completely antagonized in the combined presence of (+/-)-CP-96,345 and MEN 10,376 which are potent and selective antagonists of tachykinin NK1 and NK2 receptors respectively in the guinea pig ileum. Like senktide, other available NK3 receptor agonists, such as [MePhe7]neurokinin B, [MeVal7]neurokinin B, [Pro7]neurokinin B and DiMe-C7, stimulated phosphoinositide hydrolysis in either the absence or combined presence of (+/-)-CP-96,345 and MEN 10,376, although senktide was the most potent. Therefore, following the blockade of tachykinin NK1, NK2 and septide-sensitive receptors, the accumulation of inositol monophosphate appears to be a valuable, rapid and sensitive bioassay for determining the activity of NK3 receptor agonists and putative NK3 receptor antagonists.

Tachykinin receptors in the rat isolated uterus

Tachykinin receptors mediating uterotonic effects were examined in preparations from oestrogen-primed rats. In the absence of peptidase inhibitors [Lys5-MeLeu9-Nle10] NKA (4-10) was 14-fold more potent than neurokinin A (NKA), but the two peptides were equipotent in the presence of phosphoramidon alone and in combination with amastatin. The NK-2 receptor antagonist SR 48968 antagonised responses to the tachykinins. These findings indicate that an NK-2 receptor is present in the oestrogen-primed rat uterus and that endopeptidase 24.11 plays a major role to inactivate NKA in this tissue.

Tachykinin receptors: a radioligand binding perspective

The last decade has witnessed major breakthroughs in the study of tachykinin receptors. The currently described NK-1, NK-2, and NK-3 receptors have been sequenced and cloned from various mammalian sources. A far greater variety of tachykinin analogues are now available for use as selective agonists and antagonists. Importantly, potent nonpeptide antagonists highly selective for the NK-1 and NK-2 receptors have been developed recently. These improved tools for tachykinin receptor characterization have enabled us to describe at least three distinct receptor types. Furthermore, novel antagonists have yielded radioligand binding and functional data strongly favoring the existence of putative subtypes of NK-1 and especially NK-2 receptors. Whether these subtypes are species variants or true within-species subtypes awaits further evidence. As yet undiscovered mammalian tachykinins, or bioactive fragments, may have superior potency at a specific receptor class. The common C terminus of tachykinins permits varying degrees of interaction at essentially all tachykinin receptors. Although the exact physiological significance of this inherent capacity for receptor "cross talk" remains unknown, one implication is for multiple endogenous ligands at a single receptor. For example, NP gamma and NPK appear to be the preferred agonists and binding competitors at some NK-2 receptors, previously thought of as exclusively "NKA-preferring." Current evidence suggests that tachykinin coexistence and expression of multiple receptors may also occur with postulated NK-2 and NK-1 receptor subtypes. Other "tachykinin" receptors may recognize preprotachykinins and the N terminus of SP. In light of these recent developments, the convenient working hypothesis of three endogenous ligands (SP, NKA, and NKB) for three basic receptor types (NK-1, NK-2, and NK-3) may be too simplistic and in need of amendment as future developments occur (Burcher et al., 1991b). In retrospect, the 1980s contributed greatly to our understanding of the structure, function, and regulation of tachykinins and their various receptors. The development of improved, receptor subtype-selective antagonists and radioligands, in addition to recent advances in molecular biological techniques, may lead to a more conclusive pharmacological and biochemical characterization of tachykinin receptors. The 1990s may prove to be the decade of application, where a better understanding of the roles played by endogenous tachykinins (at various receptor subtypes) under pathophysiological conditions will no doubt hasten the realization of clinically useful therapeutic agents.

Selective neurokinin NK1 and NK2 receptor agonists infused in the substantia nigra of the rat increase vacuous chewing

Bilateral intranigral infusion of selective neurokinin NK1 and NK2 receptor agonists were made in freely moving rats followed by measurements of vacuous chewing frequencies for 30 min post-infusion. The NK1 receptor agonist, [Pro9] substance P, induced an immediate dose-related elevation of non-object directed vacuous chewing movements. There was a linear dose-response relation in the 0.5-5 nmol dose range. In experiments with the NK2 receptor agonist, [Lys5,MeLeu9,Nle10]neurokinin A-(4-10), the highest dose, 4.8 nmol, caused a less intensive but longer lasting increase of the vacuous chewing movement frequency. These findings may imply a role for neurokinins in the regulation of oral movements.

Characterisation of a novel, selective radioligand, [125I][Lys5,Tyr(I2)7,MeLeu9,Nle10]neurokinin A-(4-10), for the tachykinin NK2 receptor in rat fundus

The tyrosyl derivative of the tachykinin NK2 selective agonist [Lys5,MeLeu9,Nle10]NKA-(4-10) was iodinated and the product [125I][Lys5,Tyr(I2)2,MeLeu9,Nle10]NKA-(4-10) purified using reverse phase HPLC. The binding characteristics of this novel radioligand were investigated in homogenates of rat gastric fundus. Binding was saturable, reversible and to a single population of high affinity sites of KD 1.3 +/- 0.2 nM (n = 4). Specific binding of [125I][Lys5,Tyr(I2)7,MeLeu9,Nle10]NKA-(4-10) was inhibited by neuropeptide gamma SR 48968 > or = neurokinin A (NKA) > or = [Lys5,MeLeu9,Nle10]NKA-(4-10) > [Lys5,Tyr7,MeLeu9,Nle10] NKA-(4-10) > neuropeptide K > [Lys5,Tyr(I2)7,MeLeu9,Nle10]NKA-(4-10) > MDL 29,913 > [127I]- Bolton-Hunter-NKA > neurokinin B > substance P (SP) >> MEN 10207 > [Sar9,Met(O2)11]SP >> senktide, indicating binding to NK2 receptors. NKA, [Lys5,MeLeu9,Nle10]NKA-(4-10) and [Lys5,Tyr(I2)7,MeLeu9,Nle10]NKA-(4-10) contracted the isolated fundus strip, with pD2 values 7.9, 7.7 and 7.4, respectively. This novel, highly selective radioligand should prove useful in characterisation studies in peripheral tissues.

Interaction of the substance P receptor antagonist RP 67580 with the rat brain NK1 receptor expressed in transfected CHO cells

In the present study, we describe the effects of RP 67580, a substance P non-peptide antagonist, in binding and second messenger experiments performed using transfected Chinese hamster ovary cells expressing the rat NK1 receptor. The cDNA sequence encoding the rat brain substance P receptor was transfected in Chinese hamster ovary cells, and cellular clones which stably express the corresponding protein were isolated. [3H]Substance P binding was performed in homogenates of these transfected cells and revealed the presence of NK1 receptors in displacement experiments, using peptide analogs of three mammalian tachykinins (substance P, neurokinin A, neurokinin B). Scatchard analysis indicated a KD value of 0.33 +/- 0.13 nM and a Bmax value of 5.83 +/- 1.16 pmol/mg of protein. RP 67580, a selective NK1-receptor antagonist was found to displace the specific binding of [3H]substance P. When [3H]RP 67580 was used as a ligand, it displayed a high affinity (KD value: 1.22 +/- 0.27 nM) in transfected cell homogenates and only competed with NK1 receptor ligands. Substance P stimulated the hydrolysis of phosphoinositide in a time- and concentration-dependent manner and this effect was mimicked by selective agonists of the NK1 receptor ([Pro9]SP and septide). RP 67580 did not induce any accumulation of inositol phosphates, but was found to inhibit the inositol phosphate increase mediated by substance P, without affecting the maximal response. From these results, one may conclude that the receptor expressed by the transfected Chinese hamster ovary cells revealed similar binding characteristics as the NK1 receptor present in the rat brain and also confirmed the high affinity and the antagonist properties of RP 67580.

Characterization of a human NK1 tachykinin receptor in the astrocytoma cell line U 373 MG

The human NK1 tachykinin receptor in the astrocytoma cell line U 373 MG was characterized using selective agonists and antagonists described for this receptor in the rat. Specific [3H]substance P binding sites were present on cell homogenates, whereas [3H]neurokinin A or [3H]-senktide binding sites were absent. The binding was saturable and reversible. The binding of [3H]substance P was inhibited by very low concentrations of [L-Pro9]substance P and [Sar9,Met(O2)11]substance P; septide was approximately 1,000-fold less potent. The most potent peptide antagonist was trans-4-hydroxy-1-(1H-indol-3-ylcarbonyl)-L-prolyl-N-methyl-N-(phe nylmethyl)-L- tyrosineamide. The rank order of potency for the nonpeptide antagonists was (S,S)-CP 96,345 > (+/-)-CP 96,345 > (+/-)-2-chlorobenzylquinuclidinone > (R,R)-CP 96,345 > RP 67580 > RP 68651. In [3H]-inositol-labeled cells, substance P stimulated phosphatidylinositol turnover. A good correlation was found when the abilities of NK1 receptor agonists for stimulating inositol phosphate production and for inhibiting [3H]substance P binding were compared. Similarly, the binding and functional assays were well correlated for the antagonists. As a result of its high sensitivity and selectivity, the U 373 MG cell line thus appears an excellent tool for investigating the pharmacology of the human NK1 receptor.

Distinct presynaptic control of dopamine release in striosomal- and matrix-enriched areas of the rat striatum by selective agonists of NK1, NK2, and NK3 tachykinin receptors

Using a sensitive in vitro microperfusion method, the effects of selective and potent agonists of NK1, NK2, and NK3 tachykinin receptors ([Pro9]SP, ([Lys5,MeLeu9,Nle10]NKA-(4-10), and [Pro7]NKB, respectively) on the presynaptic control of dopamine release were investigated in striosomal-enriched (area rich in [3H]naloxone binding sites) and matrix-enriched areas of the rat striatum. Marked differences could be demonstrated as follows: (i) when used at 0.1 microM, the NK1 agonist stimulated the release of [3H]dopamine continuously synthesized from [3H]tyrosine in both compartments, while the NK2 and NK3 agonists enhanced the release of [3H]dopamine only in the matrix; (ii) the stimulatory effect of the NK3 agonist was less pronounced than those of the NK1 and NK2 agonists; (iii) the NK1 agonist-evoked responses were tetrodotoxin (1 microM) sensitive, while those of the NK2 and NK3 agonists were, respectively, partially and totally tetrodotoxin resistant; (iv) specific receptors are involved in these responses since the stimulatory effects of the NK1 and NK2 agonists were, respectively, blocked by potent antagonists of NK1 (RP-67580; 1 microM) and NK2 (SR-48968; 1 microM) receptors, while these antagonists did not affect the NK3 agonist-evoked response; (v) the indirect stimulatory effect of the NK1 agonist was partially reduced under local blockade of cholinergic transmission in the matrix but not in the striosomal-enriched area. Interestingly, this study also revealed mismatches between autoradiographic data and receptor-mediated responses, since NK2 binding sites could not be observed in the striatum while NK3 but not NK1 binding sites were visualized in the striosomal-enriched area.

Comparison in different tissue preparations of the in vitro pharmacological profile of RP 67580, a new non-peptide substance P antagonist

We describe the effects of RP 67580, a new non-peptide substance P (SP) antagonist, on tachykinin-induced contractions of guinea-pig ileum, trachea and urinary bladder, rabbit pulmonary artery and rat portal vein. All NK1 agonists tested (SP, Septide, SPOMe and [Pro9]SP) contracted guinea-pig ileum, trachea and urinary bladder (pD2 = 7.5 to 9.1), but they had no effect on rabbit pulmonary artery or rat portal vein (pD2 < 6). RP 67580 inhibited these effects: guinea-pig ileum, pA2 = 7.1 to 7.6; guinea-pig trachea and urinary bladder, pKB = 6.3 to 6.8. The difference in RP 67580 activity in these tissues might be due to the existence of subtypes of NK1 receptors. RP 67580 (1 microns) did not affect the contractions induced by the two NK2 agonists, NKA and [Lys5, MeLeu9, Nle10]NKA(4-10) (pA2 < 6), except in guinea-pig ileum (pA2 = 7.3-7.5) where these two NK2 agonists interact apparently with NK1 receptors. In the tissue preparations used, RP 67580 (1 micron) was without effect on contractions induced by the NK3 agonists: NKB and senktide. These results indicate the high selectivity for NK1 receptors of RP 67580. In all cases, similar results were obtained with another non-peptide SP antagonist, (+/-) CP-96,345. The present work provides further evidence that RP 67580 and (+/-) CP-96,345 exert in vitro a potent, selective and competitive antagonistic action on NK1 receptors and suggests the existence of at least two distinct NK1 receptor subtypes in some guinea-pig peripheral organs.

Primary structure and receptor-binding properties of a neurokinin A-related peptide from frog gut

A tachykinin peptide was isolated from an extract of the intestine of the European green frog, Rana ridibunda, and its primary structure was established as: His-Lys-Leu-Asp-Ser-Phe-Ile-Gly-Leu-Met.CONH2. This sequence was confirmed by chemical synthesis and shows two amino acid substitutions (leucine for threonine at position 3 and isoleucine for valine at position 7) compared with neurokinin A. Binding parameters for synthetic [Leu3,Ile7]neurokinin A and mammalian tachykinins were compared using receptor-selective radioligands and crude membranes from tissues enriched in the NK1, NK2 and NK3 receptors. [Leu3,Ile7]Neurokinin A was approx. 3-fold less potent than substance P in inhibiting the binding of 125I-labelled [Sar9,Met(O2)11]substance P (labelled with Bolton-Hunter reagent) to rat submandibular gland (NK1 receptor), 8-fold less potent than neurokinin A in inhibiting the binding of [2-[125I]iodohistidine1]neurokinin A to rat stomach fundus (NK2 receptor) and 6-fold less potent than neurokinin B in inhibiting the binding of 125I-Bolton-Hunter-labelled scyliorhinin II to rat brain (NK3 receptor). Thus the frog neurokinin A-related peptide shows moderate affinity but lack of selectivity for all three tachykinin-binding sites in rat tissues. This non-selectivity is similar to that displayed by the molluscan tachykinin, eledoisin, which also contains an isoleucine residue in the corresponding position in the molecule.

[Pro9]SP and [pGlu6, Pro9]SP(6-11) interact with two different receptors in the guinea-pig ileum as demonstrated with new SP antagonists

Structural considerations led us to postulate that the introduction of the dipeptides DPro9-Pro10 and DPro9-MeLeu10 should lock the C-terminal tetrapeptide of SP in a type II' beta-turn structure, a prerequisite for antagonist activity. Indeed, as the GR 71251, [DPro9, Pro10, Trp11]SP was more potent in inhibiting the septide, (pA2 = 6.5), than the [Pro9]SP, (pA2 < or = 5), spasmogenic activity in the guinea-pig ileum bioassay. This result confirms that septide, [pGlu6, Pro9]SP(6-11), a peptide active in the guinea-pig ileum bioassay and practically devoid of binding potencies for the three specific NK-1, NK-2 and NK-3 tachykinin binding sites interacts with a tachykinin receptor different from the NK-1 receptor sensitive to [Pro9]SP. Interestingly enough, the reintroduction of the leucine side-chain in position 10 yielded [DPro9, MeLeu10, Trp11]SP, an antagonist, equipotent in inhibiting both the septide- and the [Pro9]SP-evoked contractile response in the guinea-pig ileum bioassay, (pA2 = 6.6).

Tachykinin receptors in rabbit airways--characterization by functional, autoradiographic and binding studies

1. In many species, both NK1 and NK2 tachykinin receptors appear to be important in mediating the contraction of airway smooth muscle. We have examined the distribution and characterization of receptors for tachykinins in rabbit airways using functional length tension studies, autoradiography and radioligand binding studies. 2. Contractile responses to tachykinins were elicited in four different areas of the respiratory tree--trachea, and three progressively more distal areas of the right bronchus. The NK2 receptor-preferring agonists, neurokinin A (NKA), neuropeptide gamma (NP gamma) and the NK2-selective [Lys5 MeLeu9, Nle10]-NKA(4-10) [NKA (4-10) analogue] produced similar contraction in all four areas. Substance P (SP) and the NK1-selective [Sar9,Met(O2)11]-SP (Sar-SP) exhibited a marked location-dependence in the magnitude of contraction, producing minimal contraction in the trachea and more proximal bronchi with contractions becoming progressively larger in the more distal airways. Senktide (which is selective for the NK3 receptor) produced negligible contraction in all areas. 3. The NK2-selective antagonist, MDL29,913, was a weak antagonist of NKA and NKA(4-10) analogue. At a concentration of 2 microM, it produced a small but significant shift in the response curve to NKA and a greater shift (8 fold) in the curve to NKA(4-10) analogue, but it had no effect on responses to Sar-SP. The non peptide NK1 receptor antagonist, CP-96,345, was also unexpectedly weak in this preparation. The pD2 value for Sar-SP was decreased 27 fold by CP-96,345 at a concentration of 1 microM, without alteration in the maximum response.4. Autoradiographic binding sites to ['251I]-NKA were sparse over smooth muscle in proximal airway preparations and markedly increased in density in the more distal airways. There was negligible binding over vascular smooth muscle and epithelium.5. Radioligand binding studies revealed binding to ['251I]-NKA which was 82% specific. The order of potency for inhibition of ['251I]-NKA binding was SP> = Sar-SP> NKA = NPy>CP-96,345> NKA(4-10) analogue >NKB>>>MEN 10207 (the NK2 subtype selective antagonist) >MDL 29,913> senktide. This profile indicates binding predominantly to NK, receptors.6. These results suggest that there are at least two types of tachykinin receptors in rabbit airways, a population of NK, receptors, the density of which is greatest in the periphery and, in addition, NK2 receptors which are uniformly distributed throughout the airways. These receptors have unusual characteristics in that the NK, antagonist, CP-96,345 and the NK2 antagonist, MDL 29,913 respectively exhibited only weak potency.

Characterization of the tachykinin NK2 receptor subtype in the rabbit pulmonary artery

Contractile responses to neurokinin A (NKA), neuropeptide gamma(NP gamma), and the NK2 receptor-selective analogs [Lys5,MeLeu9,Nle10]NKA(4-10) and MDL 28,564 were determined in the endothelium-denuded rabbit pulmonary artery. Responses to NKA, NP gamma, and [Lys5,MeLeu9,Nle10]NKA(4-10) were antagonized by the NK2 receptor antagonist MDL 29,913, with pA2 values of 6.67, 6.46, and 7.32, respectively. Autoradiographic studies failed to demonstrate any specific binding sites for [125I]-iodohistidyl NKA (INKA) over the pulmonary artery. These data suggest the presence in rabbit pulmonary artery of an unusual "nonclassical" NK2 receptor subtype, which appears to lack affinity for INKA.

Influence of the replacement of amino acid by its D-enantiomer in the sequence of substance P. 1. Binding and pharmacological data

The D-enantiomer of residues 2, 4, 5, 6, 7, 8, 10 and 11 was introduced in the sequence of Substance P: Arg-Pro-Lys-Pro-Gln-Gln-Phe-Phe-Gly-Leu-Met-NH2. The achiral glycine residue was replaced by a D-Ala residue. Regarding NK-1 binding potencies or activities, changing to the D-enantiomer in positions 2, 4 or 5 did not modify the pharmacological patterns of the resulting peptides. Introduction of a D-residue in the 6 to 11 sequence drastically decreased the potency of the D-analogues with the exception of [D-Leu10]SP which was found only three times less potent than SP in contracting the guinea-pig ileum. No clear cut evidence between the binding potencies and activities on NK-1, NK-2 and NK-3 assays, was observed which allows a more rational design of tachykinins antagonists.

NK-1 receptors are the only class of tachykinin receptors found on mouse cortical astrocytes

Extending our previous studies, our results indicate that cultured cortical astrocytes from the mouse possess only NK-1 receptors coupled to phospholipase C. An excellent correlation was found in the potency of tachykinins and selective analogs at inhibiting 125I-BHSP binding and at stimulating phospholipase C activity, their rank order being that of NK-1 receptors. No binding sites could be found with ligands of NK-2 or NK-3 receptors. No additive effect could be shown with NK-2 or NK-3 agonists when phospholipase C activity was estimated with high concentrations of NK-1 agonists. C- or N-terminal SP fragments did not modify SP- or [Pro9]SP-evoked responses.