Rapid endocytosis of a G protein-coupled receptor: substance P evoked internalization of its receptor in the rat striatum in vivo

Studies on cultured cells have shown that agonists induce several types of G protein-coupled receptors to undergo internalization. We have investigated this phenomenon in rat striatum, using substance P (SP)-induced internalization of the SP receptor (SPR) as our model system. Within 1 min of a unilateral striatal injection of SP in the anesthetized rat, nearly 60% of the SPR-immunoreactive neurons within the injection zone display massive internalization of the SPR--i.e., 20-200 SPR+ endosomes per cell body. Within the dendrites the SPR undergoes a striking translocation from the plasma membrane to endosomes, and these dendrites also undergo a morphological reorganization, changing from a structure of rather uniform diameter to one characterized by large, swollen varicosities connected by thin fibers. In both cell bodies and dendrites the number of SPR+ endosomes returns to baseline within 60 min of SP injection. The number of neurons displaying substantial endosomal SPR internalization is dependent on the concentration of injected SP, and the SP-induced SPR internalization is inhibited by the nonpeptide neurokinin 1 receptor antagonist RP-67,580. These data demonstrate that in the central nervous system in vivo, SP induces a rapid and widespread SPR internalization in the cell bodies and dendrites and a structural reorganization of the dendrites. These results suggest that many of the observations that have been made on the internalization and recycling of G protein-coupled receptors in in vitro transfected cell systems are applicable to similar events that occur in the mammalian central nervous system in vivo.

Neurokinin-3 receptor distribution in rat and human brain: an immunohistochemical study

Autoradiographic and immunohistochemical studies have shown that the neurokinin-3 receptor is widely distributed in the rodent CNS. Expression of the neurokinin-3 receptor in human brain, however, has been debated. These conflicting findings, as well as the poor resolution of autoradiographic images, prompted us to develop a polyclonal antibody against an oligopeptide derived from the carboxy-terminus consensus sequence of both the rat and human neurokinin-3 receptor ([C]ASTTSSFISSPYTSVDEYS, amino acids 434-452 of the rat neurokinin-3 receptor). Western blot analysis of both human and rat brain tissue revealed a major band in the molecular weight range 65,000-67,000, the proposed molecular weight of the neurokinin-3 receptor based on its amino acid sequence and presumed glycosylation state. The distribution of selective high affinity neurokinin-3 receptor agonist [3H]senktide binding and neurokinin-3 receptor immunoreactivity were virtually identical in the brains of male Fischer 344 rats. The highest concentrations of neurokinin-3 receptors were observed in cortical layers IV-V; the basolateral amygdaloid nucleus; the hypothalamic paraventricular, perifornical and supraoptic nuclei; the zona incerta; and the entopeduncular and interpeduncular nuclei. [3H]senktide binding and neurokinin-3 receptor immunoreactivity were compared in homologous cortical areas of the human and rat brain. In contrast to the rat, autoradiographic analysis of normal control human brains (35-75 years) revealed a distinct and predominant superficial cortical labeling in the glia limitans and the cortical layer I. However, neurokinin-3 receptor immunoreactivity could be found not only in the superficial cortical layers, but also on pyramidal neurons and astrocytes in the neuropil and white matter. These findings suggest species differences in both the cellular and anatomical distribution of the neurokinin-3 receptor.

Incorporation of ROS-Responsive Substance P-Loaded Zeolite Imidazolate Framework-8 Nanoparticles into a Ca2+-Cross-Linked Alginate/Pectin Hydrogel for Wound Dressing Applications

PURPOSE

Wound healing, especially of extensive full-thickness wounds, is one of the most difficult problems in clinical studies. In this study, we prepared a novel substance P (SP)-delivery system using zeolite imidazolate framework-8 (ZIF-8) nanoparticles.

METHODS

We synthesized ZIF-8 nanoparticles using a modified biomimetic mineralization method. We then coated SP-loaded ZIF-8 nanoparticles (SP@ZIF-8) with polyethylene glycol-thioketal (PEG-TK) to fabricate SP@ZIF-8-PEG-TK nanoparticles, and encapsulated them in injectable hydrogel composed of sodium alginate and pectin and cross-linked using calcium chloride. The final hydrogel wound dressing containing SP@ZIF-8-PEG-TK nanoparticles was called SP@ZIF-8-PEG-TK@CA.

RESULTS

The fabricated ZIF-8 nanoparticles had high SP-loading efficiency. SP-release assay showed that the SP@ZIF-8-PEG-TK nanoparticles maintained drug activity and showed responsive release under stimulation by reactive oxygen species. The SP@ZIF-8-PEG-TK nanoparticles promoted proliferation of human dermal fibroblasts, up-regulated expression levels of inflammation-related genes in macrophages, and exhibited favorable cytocompatibility in vitro. Full-thickness excision wound models in vivo confirmed that SP@ZIF-8-PEG-TK@CA dressings had excellent wound-healing efficacy by promoting an early inflammatory response and subsequent M2 macrophage polarization in the wound-healing process.

CONCLUSION

In conclusion, these findings indicated that SP@ZIF-8-PEG-TK@CA dressings might be useful for wound dressing applications in the clinic.

Destruction of neurokinin-1 receptor expressing cells in vitro and in vivo using substance P-saporin in rats

Substance P (SP) acts on neurons through the neurokinin-1 (NK-1) receptor. Conjugation of SP to the ribosome inactivating protein, saporin (SAP), produces a cytotoxin selective for cells that express the NK-1 receptor. SP-SAP cytotoxicity was inhibited by pre-treating the toxin to reduce the disulfide bond connecting SP to SAP or by pre-incubation with anti-SP antiserum or by SP analog showing that SP-SAP acts through binding of the SP moiety to NK-1 receptors. Injection of SP-SAP into the striatum selectively destroyed NK-1 receptor expressing interneurons. These results show that SP-SAP will be useful for studying the function of NK-1 receptor expressing neurons.

Assessment of microvascular leakage via sputum induction: the role of substance P and neurokinin A in patients with asthma

Microvascular leakage is an important feature of inflammation. However, the assessment of vascular leakage has seldom been used to monitor airway inflammation in asthma. The aim of this study was to determine the effect of inhaled substance P, a potent neurokinin 1 (NK1) agonist and mediator of plasma extravasation, on markers of microvascular leakage in induced sputum from patients with asthma. In a crossover study, sputum was induced before and 30 minutes after inhalation of substance P or neurokinin A (as control) by 12 subjects with atopic and mild, steroid-naive asthma. The levels of alpha2-macroglobulin, ceruloplasmin, albumin, and fibrinogen were determined in induced sputum as markers of leakage. Substance P induced a significant increase in the levels of alpha2-macroglobulin, ceruloplasmin, and albumin in induced sputum (median fold change, 3.1, 2.2, and 2.9, respectively) (p < 0.013), whereas inhaled neurokinin A was not able to induce significant changes (p > 0.31). The increase in sputum leakage markers was not associated with the cumulative dose of substance P (p > 0.12). These results indicate that NK1 receptor stimulation causes a rapid increase in microvascular leakage as shown in induced sputum in patients with asthma. This investigational model of "dual induction" (first leakage, then sputum) may therefore be useful to test the antiexudative effect of newly develop drugs, such as NK1 antagonists.

The activation of calcium and calcium-activated potassium channels in mammalian colonic smooth muscle by substance P

1. The regulation of Ca2(+)-activated K+ channels by the agonist substance P in freshly dissociated smooth muscle cells from the rabbit longitudinal colonic muscle was characterized using the patch clamp technique. 2. In the cell-attached recording mode, when pipette and bath solutions contained equal [K+] (126 mM), the Ca2(+)-activated K+ channels showed a linear current-voltage relationship (between -50 mV and 50 mV) with a slope conductance of 210 +/- 35 pS (n = 12). Reversal potential measurements indicated that the channel was highly selective for K+ over Na+ (PK/PNa = 110). 3. Channels were activated by depolarizing membrane voltages and cytosolic Ca2+, and in inside-out patches channel activation depended sigmoidally on voltage and [Ca2+]. The potential for half-activation at a cytosolic [Ca2+] of 5 x 10(-6) M was 0 mV. A tenfold increase in cytosolic Ca2+ resulted in a 60 mV shift of the sigmoidal voltage activation curve to more negative potentials. 4. Threshold concentrations of substance P (10(-12) M), which did not result in cell contraction, caused a prolonged activation of K+ channels. The K+ channels were observed to open in clusters: simultaneous opening of multiple channels was interrupted by complete, prolonged channel closure. 5. Lowering bath [Ca2+] to submicromolar concentrations abolished the effect of substance P. The activation of K+ channels by substance P (10(-12) M) was also inhibited by the dihydropyridine nifedipine (10(-6) M), a blocker of L-type Ca2+ channels. 6. In the whole-cell recording mode, with the pipette solution containing 126 mM-KCl, 0.77 mM-EGTA and 1 mM-ATP, depolarization from a holding potential of -70 mV elicited outward currents which increased to steady-state values. These were K+ currents as they were blocked by TEA (tetraethylammonium, 30 mM) and Ba2+ (1 mM) and were abolished when pipette K+ was replaced by Cs+. 7. The depolarization-activated outward current was not affected by lowering extracellular [Ca2+] or by the Ca2+ channel antagonists Cd2+ (200 microM), nifedipine (10(-6)-10(-5) M) or verapamil (10(-6) M). The current was greatly reduced when the EGTA concentration in the pipette solution was increased from 0.77 to 10 mM. 8. When the pipette solution contained CsCl, membrane depolarization activated inward currents. The peak inward current was identified as current through L-type Ca2+ channels based on its voltage- and time-dependent kinetics, and its modulation by dihydropyridines.(ABSTRACT TRUNCATED AT 400 WORDS)

Hemokinin-1 has Substance P-like function in U-251 MG astrocytoma cells: A pharmacological and functional study

Substance P (SP) triggers responses in astrocytoma cells, which are considered important for proliferation and neuroimmunomodulatory activity. In this study, we compared the effects of SP with those of the novel tachykinin Hemokinin-1 (HK-1) in the human astrocytoma cell line U-251 MG. We show that U-251 MG cells express high levels of Neurokinin-1 (NK-1) receptors. The binding affinities of 125I-SP and 125I-mHK-1 to these receptors were in a similar, subnanomolar range. HK-1 and SP stimulated Ca2+ mobilization and induced increased cytokine mRNA expression. A specific NK-1 receptor antagonist blocked the observed effects. We conclude that there are no qualitative differences in SP and HK-1-evoked responses, suggesting that both peptides act through NK-1 receptors in U-251 MG cells. Moreover, we show TAC4 mRNA expression in gliomas, indicating a possible involvement of HK-1 in glioma biology.

In vitro and in vivo evaluation of topical formulations of spantide II

The purpose of this study was to develop and evaluate topical formulations of Spantide II, a neurokinin-1 receptor (NK-1R) antagonist, for the treatment of inflammatory skin disorders. Spantide II lotion and gel was formulated with and without n-methyl-2-pyrrolidone (NMP) as a penetration enhancer. The release of Spantide II from gels was evaluated using microporous polyethylene and polypropylene membranes in a Franz Diffusion cell setup. In vitro percutaneous absorption of Spantide II from lotion and gel formulations was evaluated using the above setup by replacing the membranes with hairless rat skin. The in vivo anti-inflammatory activity of Spantide II formulations was evaluated in an allergic contact dermatitis (ACD) mouse model. Among different gels studied, PF127 gel showed highest (70-fold) release of Spantide II compared with hydroxypropyl methylcellulose (HPMC) and hydroxypropyl cellulose (HPC) gels. Lotion and gel formulations with or without NMP showed no detectable levels of Spantide II in the receiver compartment of the Franz diffusion cell until 24 hours. However, Spantide II showed significant retention in epidermis and dermis from lotion and gel formulations at 24 hours. The dermal levels increased approximately 3.5- and 2-fold when the lotion and gel formulations contained NMP as compared with the formulation with no NMP (P < .05). The in vivo studies indicated that Spantide II formulations with NMP were effective in significantly reducing ACD response, similar to dexamethasone (0.5 mM). In conclusion, Spantide II was stable as a topical formulation and delivered to target skin tissue (epidermis and dermis) for the treatment of ACD. In addition this study supports the role of cutaneous neurosensory system in modulating inflammatory responses in the skin.

Substance P increases release of acetylcholine in the dorsal striatum of freely moving rats

Little is known about the role that neuropeptides such as substance P play in cell-to-cell interactions in the striatum. The effect of locally perfused substance P on extracellular acetylcholine (ACh) in the dorsal striatum of awake, freely moving rats was examined using microdialysis. Neostigmine (1 microM) was included in the perfusate to improve recovery of ACh. Basal extracellular ACh was sensitive to Na(+)-channel blockade with tetrodotoxin (0.3 microM) and Ca(2+)-channel blockade with MgCl2 (10 mM) and therefore largely neuronal in origin. Local perfusion with 10 and 25 microM substance P for 20 min elevated extracellular ACh by 30% and 51%, respectively. The NK1 receptor antagonist, CP 96,345 (10 microM), which by itself had no effect on extracellular ACh, prevented the substance P-induced increase in extracellular ACh. These results suggest that stimulation of NK1 receptors by substance P enhances ACh release in the dorsal striatum and is consistent with anatomical evidence of a substance P-cholinergic circuit in this region.

Injection of tachykinins and selective neurokinin receptor ligands into the substantia nigra reticulata increases striatal dopamine and 5-hydroxytryptamine metabolism

Bilateral injection of endogenous tachykinins (substance P (SP), neurokinin A (NKA)) and selective neurokinin receptor ligands (senktide, [Sar9,Met(O2)11]SP, [MePhe7]NKB) into the substantia nigra reticulata increased striatal dopamine and serotonin metabolism. The increase in dopamine metabolism in the dorsal striatum at a low dose of the substances may be a direct effect on dopamine neurons in the substantia nigra reticulata via NK1 and NK3 receptors. The lack of effect at intermediate doses may be due to inhibitory mechanisms or desensitization. The changes after high doses in the dorsal and ventral striatum may be due to actions on dopaminergic neurons in the substantia nigra as well as in the ventral tegmental area, since there was considerable diffusion from the site of injection. An apparent rapid degradation of injected SP or NKA indicates that N-terminal SP fragments may participate in the SP response. The increased serotonin metabolism that occurs only at a high dose may involve all three neurokinin receptors.

Safety Evaluation of Intrathecal Substance P-Saporin, a Targeted Neurotoxin, in Dogs

Intrathecal (IT) substance P-Saporin (SP-SAP), a 33-kDa-targeted neurotoxin, produces selective destruction of superficial neurokinin 1 receptor (NK1r)-bearing cells in the spinal dorsal horn. In rats, SP-SAP prevents the formation of hyperalgesia and can reverse established neuropathic pain behavior in rodents. To determine the safety of this therapeutic modality in a large animal model, beagles received bolus IT lumbar injections of vehicle, SP-SAP (1.5, 15, 45, or 150 microg), or a nontargeted preparation of saporin (SAP, 150 microg) for immunohistological analysis of spinal cords. Doses of 15 microg SP-SAP and above produced a significant and equivalent loss of NK1r-bearing cells and dendrites in lumbar laminae II and I compared to vehicle- or SAP-treated animals. Cervical regions in all animals displayed no loss of NK1r immunoreactivity as compared to controls. Total numbers of neurons in the lumbar dorsal horn or alpha-motor neurons in the ventral horn demonstrated no significant changes. No increases in the astrocytic marker glial fibrillary acidic protein were noted following treatment with SP-SAP, suggesting a lack of generalized neurotoxicity. Additional dogs received doses of 1.5-150 microg SP-SAP or SAP and were sacrificed after 28 or 90 days to assess behavioral and physiological parameters. Although some acute motor signs were observed with both SP-SAP and SAP, no long-lasting significant events were noted in any of these animals. These data indicate no adverse toxicity at doses up to 10 times those necessary for producing loss of superficial NK1r-bearing neurons in a large animal model.

Conjunctival penetration of insulin and peptide drugs in the albino rabbit

An in vitro model was used to evaluate the conjunctival penetration of three peptides, [D-ala2]metenkephalinamide (YAGFM, MW 647), substance P (MW 1348), and insulin (MW 5778), in comparison with two nonpeptides, atenolol (MW 266) and timolol (MW 433). All three peptides were hydrolyzed to varying extents during penetration across the conjunctiva. The permeability coefficient for intact YAGFM and insulin was 4.5 +/- 0.3 and 4.6 +/- 0.7 microns sec-1, respectively. These values were about two to five times lower than those for atenolol and timolol. No permeability coefficient could be calculated for substance P, since its transconjunctival flux never reached steady state. The conjunctival penetration of YAGFM and insulin was improved by about two and three times, respectively, with the addition of 1% Na glycocholate. Increasing the Na glycocholate concentration was more effective than changing the type of bile salt in improving the conjunctival penetration of insulin. The maximum factor of improvement was 12, as the Na glycocholate concentration was raised to 4%. The way in which Na deoxycholate, glycocholate, and taurocholate affected the conjunctival penetration of atenolol, timolol, and insulin suggests that these three bile salts improved mainly the transcellular penetration of the compounds studied.

Anti-HIV-1 activity of the neurokinin-1 receptor antagonist aprepitant and synergistic interactions with other antiretrovirals

OBJECTIVES

Neurokinin-1 receptor (NK1R) antagonists interfere with binding of neuropeptide substance P to NK1R and exhibit novel anti-HIV-1 activities. Since NK1R antagonists effectively penetrate the blood-brain barrier to reduce the inflammatory response within the brain, we wished to evaluate their potential as anti-HIV-1 candidates for targeting HIV-1 infections of the central nervous system.

DESIGN

A series of small molecule agents were evaluated for anti-NK1R and anti-HIV-1 activity using peripheral blood mononuclear cells (PBMCs). The most promising of these, aprepitant (Emend, Merck and Co. Inc.), was investigated for potential synergies with other antiretroviral drugs.

METHODS

Anti-NK1R activity was tested by measuring intracellular calcium increase triggered by substance P. Anti-HIV-1 activity was evaluated by measuring p24 antigen in culture supernatants of PBMC following exposure to HIV. The concentration of drug which produced 50% reduction in intracellular calcium levels or viral production in 7-day PBMC cultures was determined. The combined effect of aprepitant with each of the major classes of anti-HIV-1 drugs was evaluated in synergy studies.

RESULTS

Aprepitant had the highest anti-HIV-1 activity of the NK1R antagonists examined and was equally active against all major HIV-1 subtypes. Aprepitant acted synergistically with protease inhibitors (ritonavir and saquinavir), but not with nucleoside reverse transcriptase, non-nucleoside reverse transcriptase, or viral entry inhibitors.

CONCLUSION

The ability of aprepitant to penetrate the blood-brain barrier, its safety record as an FDA-approved drug for reducing nausea and vomiting in chemotherapy, and synergistic activity with other anti-HIV-1 drugs make it a promising candidate for treatment of HIV infection.

Percutaneous Absorption and Anti-Inflammatory Effect of a Substance P Receptor Antagonist: Spantide II

PURPOSE

There is accumulating evidence that neurogenic mediators such as substance P (SP) and alpha-melanocyte stimulating hormone (alpha-MSH) contribute to inflammation following chemical and thermal injuries or in disease conditions such as psoriasis and contact dermatitis. Spantide II is a peptide with a molecular weight of 1670.2 which binds to neurokinin-1 receptor (NKR-1) and blocks proinflammatory activities associated with SP. The aim of this study was to investigate in vitro permeation and distribution of spantide II through hairless rat skin and the anti-inflammatory effect of topically delivered spantide II in an allergic contact dermatitis (ACD) mouse model.

METHODS

The in vitro permeation and distribution of spantide II with or without cysteine HCl (CH) as a penetration enhancer through hairless rat skin was studied using Franz diffusion cells. The anti-inflammatory effect of spantide II was studied by measuring the reduction of ACD in C57BL/6 mice after application of spantide II as a topical solution.

RESULTS

The skin permeation experiments with or without cysteine HCl (as penetration enhancer) showed no detectable levels of spantide II permeation across rat skin over a period of 48 h. Cysteine HCl significantly increased the distribution of spantide II in skin layers; also, the reduction in ACD response was significantly higher with the formulation containing cysteine HCl (p < 0.05). Spantide II at different concentrations showed a dose-dependent reduction of ACD response in mice.

CONCLUSIONS

The current study demonstrates that spantide II can effectively be delivered to epidermis and dermis to exert a significant anti-inflammatory activity on the reduction of inflammation in a mouse model of ACD.

Time course and substance P effects on the vascular and morphological changes in adjuvant-induced monoarthritic rats

The aim of this study is to characterize the time course of the vascular and morphological changes in arthritic rat knee joints induced by Freund's complete adjuvant (FCA), and to investigate the effects of substance P on these changes. Single unilateral intra-articular injections of 0.1 ml FCA produced swelling of the ipsilateral knees for 4 weeks, blood vessel permeability was increased for 1 week, but blood flow was unaffected except for minor bilateral increases on day 28. The ipsilateral knees also showed marked accumulation of immune cells from day 3 to day 28, minor synovial tissue proliferation on week 2, and some cartilage erosions on weeks 1 and 2. Another group of rats was given additional injection of 1 nmol substance P in their adjuvant-treated knees at 4 h prior to assessments of inflammatory parameters on each specified day. This produced further swelling in their ipsilateral knees on day 3 and day 14, blood vessel permeability was augmented in the first 2 weeks, and blood flow was increased throughout the 4 weeks except on day 7. Parallel but smaller increases in vascular permeability and blood flow were also observed in their contralateral knees. Substance P did not affect FCA-induced changes in immune cell infiltration, synovial tissue proliferation, and cartilage erosion. These findings confirm that intra-articular injection of a low dose of FCA could elicit discrete monoarthritis in rat knees, and substance P could exacerbate and spread the early signs of this disease to the contralateral knees.

Two NK-3 receptor subtypes: demonstration by biological and binding assays

The existence of two neurokinin NK-3 receptor subtypes has been suggested on the basis of results obtained in binding assays. In the present study, we have confirmed the two NK-3 receptor subtypes by using data obtained in both biological and binding assays. Experiments have been performed in the rat portal vein and in the guinea-pig ileum treated with NK-1 and NK-2 selective antagonists, namely CP 96345 and SR 48968. Orders of potency of agonists on the rat portal vein are as follows: for neurokinins, NKB > NKA > SP; for tachykinins, KAS > ELE > PHY; and for selective agonist: [MePhe7]NKB >> senktide. On the guinea-pig ileum, the agonist rank orders of potency are: NKB > SP > NKA, ELE > KAS > PHY; and for selective agonist: [MePhe7]NKB = senktide. The apparent affinity of antagonists shows differences in both biological and binding assays. In fact, on the rat portal vein, SR 48968 is almost inactive (pA2 or IC50 approximately 4.8), while R-486 [Trp7, beta Ala8]NKA(4-10) shows a pA2 value of 7.45 and an IC50 of 5.6. An opposite pattern of activity is observed in the guinea-pig ileum, where SR 48968 shows a pA2 of 6.05 and an IC50 of 6.7, while R-486 has a pA2 of 6.1 and an IC50 of < 5.0. These results confirm the existence of two NK-3 sites differing pharmacologically. It is proposed to name NK-3A the receptor of the guinea-pig ileum and NK-3B the receptor of the rat portal vein.

Regional distribution of substance P binding sites in the brainstem of the human newborn

The distribution of [3H]substance P ([3H]SP) binding sites in the brainstem of the human newborn was investigated in eleven cases (aged 1 h to 6 months) by in vitro quantitative receptor autoradiography. The binding of [3H]SP to newborn brainstem tissue was found to be saturable (for the eight cases examined, Kd and Bmax (M +/- S.E.M.) were 0.29 +/- 0.03 nM and 206 +/- 21 fmol/mg tissue, respectively). Competition studies showed unlabeled SP to be the most potent peptide for displacing [3H]SP binding from tissue sections. The desaturating effect of GTP on the specific binding of [3H]SP was also investigated, but was not found to be significant. Autoradiographic analysis showed that the neurokinin-1 (NK-1)/SP binding sites were widely but unevenly distributed, and that they varied with age. The highest densities of (NK-1)/SP binding sites were observed in the locus coeruleus, olivaris inferior nuclei, raphe magnus and obscurus nuclei, while low to moderate densities were observed in other brainstem structures. These findings support the idea that SP is involved in cardiovascular regulation, and that it may interact with the catecholaminergic and/or serotonergic system.

Direct interstitial infusion of NK1-targeted neurotoxin into the spinal cord: a computational model

Convection-enhanced delivery of substance P (SP) nocitoxins to the spinal cord interstitium is under consideration for the treatment of chronic pain. To characterize treatment protocols, a three-dimensional finite-element model of infusion into the human dorsal column was developed to predict the distribution of SP-diphtheria toxin fusion protein (SP-DT') within normal and target tissue. The model incorporated anisotropic convective and diffusive transport through the interstitial space, hydrolysis by peptidases, and intracellular trafficking. For constant SP-DT' infusion (0.1 microl/min), the distribution of cytotoxicity in NK1 receptor-expressing neurons was predicted to reach an asymptotic limit at 6-8 h in the transverse direction at the level of the infusion cannula tip ( approximately 60% ablation of target neurons in lamina I/II). Computations revealed that SP-DT' treatment was favored by a stable SP analog (half-life approximately 60 min), high infusate concentration (385 nM), and careful catheter placement (adjacent to target lamina I/II). Sensitivity of cytotoxic regions to NK1 receptor density and white matter protease activity was also established. These data suggest that intraparenchymal infusions can be useful for treatment of localized chronic pain.

LC-MS/MS quantification of a neuropeptide fragment kisspeptin-10 (NSC 741805) and characterization of its decomposition product and pharmacokinetics in rats

The kisspeptins are critical regulators of mammalian reproduction. Kisspeptin-10 ((45)YNWNSFGLRF-NH2(54), kisspeptin-112-121 or metastin 45-54, NSC 741805), an active fragment of kisspeptin, has been shown to be a potent stimulator of gonadotropin-releasing hormone and secretion of luteinizing hormone in both rodents and primates. This shorter peptide fragment may have clinical utility potential and it is important to characterize its pharmacokinetic property. Recently, the pharmacokinetics of both kisspeptin-54 and kisspeptin-10 were characterized in humans using a radioimmunoassay (RIA), which measures only the immunoreactive kisspeptin (kisspeptin-IR). In this study, a highly sensitive and specific LC-MS/MS assay was developed to quantify kisspeptin-10 levels in rat plasma. The lower limit of quantitation (LLOQ) was 0.5 ng/mL, the within-day and between-day coefficient of variations (CVs) ranged from 5.2 to 15.4% and 1.3 to 14.2%, and the accuracy values ranged from 98 to 114% and 99 to 105%, respectively. With this method, stability studies demonstrated that kisspeptin-10 degraded rapidly with decomposition half-lives of 6.8 min, 2.9 min and 1.7 min at 4 °C, 25 °C, and 37 °C, respectively. The principal decomposition product was characterized as the N-terminal tyrosine deleted kisspeptin-10 (46)NWDSFGLRF-NH2(54). Pharmacokinetic study in rats showed that low ng/mL kisspeptin-10 was detected in the first few minutes, and eliminated rapidly and became undetectable 30 min after intravenous (i.v.) bolus administration of 1.0 mg/kg kisspeptin-10.

Substance P, vasoactive intestinal polypeptide, and gastrin catabolism in canine liver and kidney

No reports have described the catabolic mechanism of substance P in vivo. We studied the effects of hepatic or renal transit on substance P, vasoactive intestinal polypeptide, and gastrin in anesthetized dogs. It was found that the liver plays a more important role in vasoactive intestinal polypeptide catabolism than the kidney and that the kidney is more important in gastrin catabolism than the liver. Substance P was more rapidly degraded than the other two peptides in both organs. The transrenal substance P loss measured by C-terminal antiserum differed from that measured by N-terminal antiserum, although there was no difference in the liver. This suggested that there were different patterns of cleavage of substance P between the liver and the kidney, and that its C terminal was degraded more strongly than its N terminal in the kidney.

Radioimmunoassay of substance P in lung perfusate

A radioimmunoassay of the undecapeptide substance P (SP) and its application in rabbit lung superfusate has been developed. The assay was based on the use of a radioactive tracer, 125I-SP-Tyr8, which showed, with an excess of antibodies, a specific binding greater than 90% and a nonspecific binding lower than 2%. This tracer was stable for 4 weeks at -20 degrees C. Its specific radioactivity was 384 Ci/mmol. The assay's lower limit of detection was 10 pg/ml (0.7 fmol). The determination of SP in rabbit lung perfusate required extraction and concentration using octadecylsilane cartridges. Under these conditions, the recovery of SP from experiments on lung perfusates (n=4) was 75.0+/-4.5%, and the intraassay and interassay coefficients of variation were 7.3+/-1.9% and 10.7+/-1.3%, respectively. Amounts of SP released in rabbit lung perfusates were determined following stimulation of pulmonary C fibers with capsaicin (10(-4) M). During the stimulation period, the values of SP from lung perfusates (n=6) increased significantly when compared with baseline values.

Induction of nitric oxide synthase by lipopolysaccharide inhalation enhances substance P-induced microvascular leakage in guinea-pigs

Inducible nitric oxide (NO) synthase (iNOS)-mediated hyperproduction of NO in airways has been reported in asthmatic patients. However, the role of NO in the pathogenesis of asthma has not yet been fully elucidated. The aim of this study was to examine whether the iNOS-derived NO affects airway microvascular leakage, one of the characteristic features of asthmatic airway inflammation. Guinea-pigs were exposed to lipopolysaccharide (LPS) (1 mg x mL(-1)) by inhalation in order to induce iNOS in the airways, and the histochemical staining of reduced nicotinamide-adenine dinucleotide phosphate (NADPH)-diaphorase activity was determined 5 h after the inhalation to confirm the iNOS induction. Airway microvascular leakage to subthreshold doses of substance P (0.3 microg x kg(-1), i.v.) was also examined in the absence and presence of an iNOS inhibitor (aminoguanidine) in LPS- or saline-exposed (control) animals using Evans blue dye and Monastral blue dye. In the LPS-exposed animals, increased NADPH-diaphorase activity was observed in the airway microvasculature compared with the control animals. Substance P caused significant airway microvascular leakage assessed by Evans blue dye in all airway levels in the LPS-exposed animals but not in the control group. This was also confirmed by Monastral blue dye extravasation. Aminoguanidine abolished this LPS-induced enhancement of plasma leakage to substance P without changing the systemic blood pressure. These results may suggest that inducible nitric oxide synthase-derived nitric oxide is capable of potentiating neurogenic plasma leakage in airways.

Systemic and intraocular uptake of spantide, a tachykinin antagonist, following topical application to the rabbit eye

Previous observations have indicated that topical application to the rabbit eye of tachykinin antagonists, including spantide, effectively prevents the miosis and the disruption of the blood-aqueous barrier consequent to ocular injury. The present study shows that spantide is taken up into the rabbit eye following topical application. This was established by determination of spantide in the aqueous humor by radioimmunoassay. The concentrations reached in the aqueous humor were those that could be expected to block tachykinin receptors. The elimination of spantide from the aqueous humor was found to be slow. From HPLC analysis it seemed that spantide in the aqueous humor is degraded to smaller products, predominantly spantide 5-11. Some of the topically applied peptide appeared in the general circulation. Here the rate of elimination was rapid by comparison. Very small amounts of spantide appeared in the cerebrospinal fluid after intravenous injection.

Histological demonstration of increased vascular permeability in the dura mater of the rat

Neurogenic inflammation of the dura mater encephali has been suggested to play an important role in the pathophysiology of headaches. Although functional studies using extravasation techniques indicate an enhanced permeability of blood vessels after chemical or electrical stimulation of C-fibres supplying the dura mater, histological demonstration of leaky blood vessels is still a problem. We used the vascular labelling method combined with i.v. injection of colloidal silver solution to test the permeability increasing effect of intravenous administration of substance P, topical application of mustard oil or acidic phosphate buffer and local electrical stimulation of the exposed dura mater. Histological characteristics of increased vascular permeability were observed exclusively after mustard oil and acidic phosphate buffer. This observation may indicate different mechanisms of increased vascular permeability involving pinocytosis and formation of interendothelial gaps selectively visualized by the vascular labelling method.

Distribution of substance P and methionine-enkephalin in salivary glands and effect of chronic morphine treatment on levels of these peptides

Substance P-like immunoreactivity (SPLI) and methionine-enkephalin-like immunoreactivity (MELI) were determined in salivary glands from rats by radioimmunoassay. In all salivary glands investigated (submandibular gland, sublingual gland and parotid gland), SPLI and MELI were detected. The amount of both peptides is comparable to or relatively higher than those found in any other peripheral tissue. The level of SPLI showed a tendency to increase following chronic treatment with morphine: the enhancement in the submandibular gland and the sublingual gland was especially remarkable. The level of MELI was decreased, particularly in the submandibular gland.