Algesia and local responses induced by neurokinin A and substance P in human skin and temporal muscle

Neurokinin A (NKA), substance P (SP) and the two peptides combined (SP + NKA) were injected intracutaneously on the forearm and into the temporal muscle of healthy volunteers. Pain intensity, cutaneous wheal and flare responses and tenderness of the temporal muscle were quantitated. SP but not NKA induced cutaneous pain. This relates the algesic effect of SP to the specific N-terminal amino acid sequence of the peptide, not shared by NKA. NKA, however, potentiated the algesic effect of SP as SP + NKA induced a significantly prolonged cutaneous pain sensation. Both peptides induced wheals, but only SP induced flare. These results confirm previous studies relating wheal formation to the identical C-terminal amino acid sequence of the two peptides and flare reaction to the N-terminal part of SP. Injections into the temporal muscle did not cause pain or tenderness.     

Angiotensin converting enzyme has an inhibitory role in CGRP metabolism in human skin

The neutral endopeptidase (NEP) is important for calcitonin gene related peptide (CGRP) degradation, while the role of angiotensin converting enzyme (ACE) remains unclear. By using dermal microdialysis we explored the effect of phosphoramidon (NEP blocker), captopril (ACE blocker) and a mixture of both drugs on the intensity of electrically-induced CGRP-mediated neurogenic flare. The results reveal that phosphoramidon elevated flare intensity, but that this was not further increased by adding captopril. In contrast, neurogenic flare was decreased when the drug mixture was applied in compared to NEP only. Electrically released CGRP levels could be measured directly in perfusates containing phosphoramidon and the mixture. Again, CGRP levels were elevated in phosphoramidon treated sites, and significantly reduced upon adding captopril. These findings suggest that NEP and ACE do not have additive effects regarding neuropeptide degradation. In contrast, inhibition of ACE seems to augment CGRP catabolism.     

Angiotensin converting enzyme (ACE) and neprilysin hydrolyze neuropeptides: a brief history, the beginning and follow-ups to early studies

Our investigations started when synthetic bradykinin became available and we could characterize two enzymes that cleaved it: kininase I or plasma carboxypeptidase N and kininase II, a peptidyl dipeptide hydrolase that we later found to be identical with the angiotensin I converting enzyme (ACE). When we noticed that ACE can cleave peptides without a free C-terminal carboxyl group (e.g., with a C-terminal nitrobenzylamine), we investigated inactivation of substance P, which has a C-terminal Met(11)-NH(2). The studies were extended to the hydrolysis of the neuropeptide, neurotensin and to compare hydrolysis of the same peptides by neprilysin (neutral endopeptidase 24.11, CD10, NEP). Our publication in 1984 dealt with ACE and NEP purified to homogeneity from human kidney. NEP cleaved substance P (SP) at Gln(6)-Phe(7), Phe(7)[see text]-Phe(8), and Gly(9)-Leu(10) and neurotensin (NT) at Pro(10)-Tyr(11) and Tyr(11)-Ile(12). Purified ACE also rapidly inactivated SP as measured in bioassay. HPLC analysis showed that ACE cleaved SP at Phe(8)-Gly(9) and Gly(9)-Leu(10) to release C-terminal tri- and dipeptide (ratio = 4:1). The hydrolysis was Cl(-) dependent and inhibited by captopril. ACE released only dipeptide from SP free acid. ACE hydrolyzed NT at Tyr(11)-Ile(12) to release Ile(12)-Leu(13). Then peptide substrates were used to inhibit ACE hydrolyzing Fa-Phe-Gly-Gly and NEP cleaving Leu(5)-enkephalin. The K(i) values in microM were as follows: for ACE, bradykinin = 0.4, angiotensin I = 4, SP = 25, SP free acid = 2, NT = 14, and Met(5)-enkephalin = 450, and for NEP, bradykinin = 162, angiotensin I = 36, SP = 190, NT = 39, Met(5)-enkephalin = 22. These studies showed that ACE and NEP, two enzymes widely distributed in the body, are involved in the metabolism of SP and NT. Below we briefly survey how NEP and ACE in two decades have gained the reputation as very important factors in health and disease. This is due to the discovery of more endogenous substrates of the enzymes and to the very broad and beneficial therapeutic applications of ACE inhibitors.     

Effect of the NEP inhibitor SCH32615 on airway responses to intravenous substance P in guinea pigs.

We examined the effects of the selective neutral endopeptidase (NEP) inhibitor SCH32615 on airway responses to rapid intravenous infusions of substance P (SP) and neurokinin A (NKA) and on recovery of administered tachykinins from arterial blood in anesthetized mechanically ventilated guinea pigs. SCH32615, in doses that cause a marked increase in the magnitude of bronchoconstriction induced by infused NKA, had little effect on the changes in pulmonary conductance (GL) or dynamic compliance induced by SP. In animals in which SCH32615 (1 mg/kg) was administered in combination with the angiotensin-converting enzyme (ACE) inhibitor captopril (5.7 mg/kg), the dose of SP required to decrease GL by 50% was fourfold less than in animals that received captopril alone (P < 0.005). SP measured in arterial blood withdrawn within 45 s of intravenous administration of this tachykinin was not different in control and SCH32615-treated animals, whereas captopril caused an approximately threefold increase in SP concentrations (P < 0.005). When SCH32615 and captopril were administered together, significantly more SP was recovered than when captopril or SCH32615 was administered alone (P < 0.0005). Our results are consistent with the hypothesis that both NEP and ACE contribute to the degradation of intravenously infused SP. ACE degradation of SP is sufficient to limit SP-induced bronchoconstriction even in the presence of specific NEP inhibition.     

Hydrolysis of substance p and neurotensin by converting enzyme and neutral endopeptidase

Angiotensin I converting enzyme (ACE) and neutral endopeptidase ("enkephalinase"; NEP), were purified to homogeneity from human kidney. NEP cleaved substance P (SP) at Gln6-Phe7,-Phe8, and Gly9-Leu10 and neurotensin (NT) at Pro10-Tyr11 and Tyr11-Ile12. NEP hydrolyzed 0.1 mM SP, NT and their C-terminal fragments at the following rates (mumol/min/mg): SP1-11 = 7.8, SP4-11 = 11.7, SP5-11 = 15.4, SP6-11 = 15.6, SP8-11 = 6.7, NT1-13 = 2.9, and NT8-13 = 4.0. Purified ACE rapidly inactivated SP as measured in bioassay. HPLC analysis showed that ACE cleaved SP at Phe8-Gly9 and Gly9-Leu10 to release C-terminal tri- and dipeptide (ratio = 4:1). The hydrolysis was Cl- dependent and inhibited by captopril. ACE released mainly C-terminal tripeptide from SP methyl ester, but only dipeptide from SP free acid. Modification of arginine residues in ACE with cyclohexanedione or butanedione similarly inhibited hydrolysis of SP, bradykinin and Bz-Gly-Phe-Arg (80-93%) indicating an active site arginine is required for hydrolysis of SP. ACE hydrolyzed NT at Tyr11-Ile12 to release Ile12-Leu13. SP, NT and their derivatives (0.1 mM) were cleaved by ACE at the following rates (mumol/min/mg): SP1-11 = 1.2, SP methyl ester = 0.7, SP free acid = 8.5, SP4-11 = 2.4, SP5-11 = 0.9, SP6-11 = 1.4, SP8-11 = 0, NT1-13 = 0.2, and NT8-13 = 1.3. Peptide substrates were used as inhibitors of ACE (substrate = FA-Phe-Gly-Gly) and NEP (substrate = Leu5-enkephalin).(ABSTRACT TRUNCATED AT 250 WORDS)     

Degradative enzymes modulate airway responses to intravenous neurokinins A and B

We studied the effects of the neutral endopeptidase (NEP) inhibitor thiorphan (1.7 mg/kg iv) and the angiotensin-converting enzyme (ACE) inhibitor captopril (5.7 mg/kg iv) on airway responses to rapid intravenous infusions of neurokinin A (NKA) and neurokinin B (NKB) in anesthetized, mechanically ventilated guinea pigs. The dose of NKA required to decrease pulmonary conductance to 50% of its base-line value (ED50GL) was fivefold less (P less than 0.0001) in animals treated with thiorphan compared with controls. NKA1-8, a product resulting from cleavage of NKA by NEP, had no bronchoconstrictor activity. Similar results were obtained by using NKB as the bronchoconstricting agent. Captopril had no significant effect on airway responses to NKA or NKB. In contrast, both thiorphan and captopril decrease the ED50GL for substance P (SP). We also compared the relative bronchoconstrictor potency of NKA, NKB, and SP. In control animals, the rank order of ED50GL values was NKA much less than NKB = SP. NKA also caused a more prolonged bronchoconstriction than SP or NKB. Thiorphan had no effect on the rank order of bronchoconstrictor potency, but in animals treated with captopril, the rank order of ED50GL values was altered to NKA less than SP less than NKB. These results suggest that degradation of NKA and NKB by NEP but not by ACE is an important determinant of the bronchoconstriction induced by these peptides. The degradation by ACE of SP but not NKA or NKB influences the observed relative potency of the three tachykinins as bronchoactive agents.     

Calcitonin gene-related peptide, neurokinin A and substance P: effects on nociception and neurogenic inflammation in human skin and temporal muscle.

Calcitonin gene-related peptide (CGRP) was injected alone and in combination with substance P (SP) or neurokinin A (NKA) into the forearm skin and temporal muscle of human volunteers. In the skin, 50 pmol of CGRP induced a wheal response and a delayed erythema. No pain was recorded. No interaction between CGRP and SP or NKA was observed. In the temporal muscle, 200 pmol of CGRP alone did not induce pain or tenderness but, in combination with SP or NKA, CGRP elicited a significant pain sensation. It is concluded that CGRP may be involved in neurogenic inflammation and that only SP, of the three peptides present in nociceptive C fibers, seems to be of major importance in relation to cutaneous nociception. Simultaneous neurogenic release of CGRP and other neuropeptides in skeletal muscle may induce myofascial pain.     

Pain, wheal and flare in human forearm skin induced by bradykinin and 5-hydroxytryptamine

Pain was induced in 19 healthy individuals by double-blind injections into the forearm skin of 0.05 ml of physiological saline with or without active substances added. Bradykinin (0.5 nmol), 5-hydroxytryptamine (0.5 nmol) and a mixture of the two substances in half dosage (0.25 nmol + 0.25 nmol) caused significantly more pain than saline (p<0.05). The three test solutions also induced wheal and flare responses significantly more pronounced than saline. Bradykinin induced significantly more pain and more wheal than 5-hydroxytryptamine (p<0.05) but a significantly smaller flare (p<0.01). A dissociation between induced pain and flare was thus demonstrated.     

Modulation of substance P signaling by dipeptidyl peptidase-IV enzymatic activity in human glioma cell lines

Dipeptidyl peptidase-IV (DPP-IV, CD26) is a serine protease almost ubiquitously expressed on cell surface and present in body fluids. DPP-IV has been suggested to proteolytically modify a number of biologically active peptides including substance P (SP) and the chemokine stromal cell derived factor-1alpha (SDF-1alpha, CXCL12). SP and SDF-1alpha have been implicated in the regulation of multiple biological processes and also induce responses that may be relevant for glioma progression. Both SP and SDF-1alpha are signaling through cell surface receptors and use intracellular calcium as a second messenger. The effect of DPP-IV on intracellular calcium mobilization mediated by SP and SDF-1alpha was monitored in suspension of wild type U373 and DPP-IV transfected U373DPPIV glioma cells using indicator FURA-2. Nanomolar concentrations of SP triggered a transient dose dependent increase in intracellular calcium rendering the cells refractory to repeated stimulation, while SDF-1 had no measurable effect. SP signaling in DPP-IV overexpressing U373DPPIV cells was not substantially different from that in wild type cells. However, preincubation of SP with the DPP-IV overexpressing cells lead to the loss of its signaling potential, which could be prevented with DPP-IV inhibitors. Taken together, DPP-IV may proteolytically inactivate local mediators involved in gliomagenesis.     

Effect of the α2δ ligand, pregabalin, on colonic sensory and motor functions in healthy adults

Pregabalin, an α2δ ligand, is used clinically to treat somatic pain. A prior study suggested that pregabalin reduces distension-induced pain while increasing rectal compliance. We aimed to quantify effects of pregabalin on colonic sensory and motor functions and assess relationships between sensory effects and colonic compliance. We conducted a randomized, double-blind, placebo-controlled, parallel-group study of a single oral administration of 75 or 200 mg of pregabalin in 62 healthy adults (aged 18-75 yr). Subjects underwent left colon intubation. We assessed "stress-arousal symptoms", compliance, sensation thresholds, sensation ratings averaged over four levels of distension, fasting and postprandial colonic tone, and phasic motility index (MI). Analysis of covariance (adjusted for age, sex, body mass index, and corresponding predrug response) and proportional hazard models were used. There were no clinically important differences among treatment groups for demographics, predrug compliance, tone, MI, and sensation. Treatment was associated with reduced energy and increased drowsiness but no change in tension or relaxation. Sensation ratings averaged over the four distension levels were lower for gas sensation [overall effect P = 0.14, P = 0.05 (pregabalin 200 mg vs. placebo)] and for pain sensation [overall effect P = 0.12, P = 0.04 (pregabalin 200 mg vs. placebo)]. The magnitude of the effect of 200 mg of pregabalin relative to placebo is on average a 25% reduction of both gas and pain sensation ratings. Pregabalin did not significantly affect colonic compliance, sensation thresholds, colonic fasting tone, and MI. Thus 200 mg of pregabalin reduces gas and pain sensation and should be tested in patients with colonic pain.     

Dipeptidyl peptidase IV (DPPIV) enzyme activity on immature T-cell line R1.1 is down-regulated by dynorphin-A(1-17) as a non-substrate inhibitor

In this study we examined surface expression of CD26 and the corresponding enzyme activity of dipeptidyl peptidase IV (DPPIV) on the cells of immature murine T-cell line, R1.1. The data obtained have shown that R1.1 cells express high density of surface CD26 as compared to normal thymus cells. This was associated with strong enzyme activity, which, based on substrates and inhibitor specificity, corresponded to DPPIV. The DPPIV enzyme activity of R1.1 cells was 10 times stronger than that found on normal murine thymus cells (V(max) = 39 micromol/min/10(6) cells, vs 3.7 micromol/min/10(6) cells, respectively). Upon activation with anti-CD3, up-regulation of both membrane CD26, as well as of DPPIV enzyme activity on R1.1 cells were observed. The finding of strong DPPIV on R1.1 cells makes them suitable model for testing putative substrates/inhibitors of the enzyme in its natural microenvironment. Since in addition to strong DPPIV, R1.1 cells also express kappa opioid receptors (KOR) [European Journal of Pharmacology 227 (1992) 257], we tested the effect of dynorphin-A(1-17), an endogenous opioid peptide with KOR selectivity, on DPPIV of R1.1 cells. Dynorphin-A(1-17) down-regulated DPPIV in a dose-dependent manner, with the potency similar to that of substance P, a known natural DPPIV substrate [Journal of Pharmacology and Experimental Therapeutics 260 (1992) 1257]. DPPIV down-regulation was resistant to bestatin and thiorphan, the inhibitors of two cell surface peptidases (APN and NEP, respectively) with potential of dynorphin-A(1-17) degradation, suggesting that the mechanism underlying the observed effect does not involve degradative products of dynorphin-A(1-17). DPPIV down-regulation was also resistent to KOR antagonist, NBI, suggesting that the mechanism underlying the observed phenomenon involves neither cointernalization of KOR and DPPIV. Collectively, cells of immature T cell line, R1.1 exert strong DPPIV enzyme activity, which could be down-regulated in the presence of dynorphin-A(1-17) by mechanism that presumably includes non-substrate inhibition. By down-regulating DPPIV, dynorphin-A(1-17) may indirectly affect activity and/or specificity of natural substrates of DPPIV, such as substance P, RANTES, and endomorphins.     

A direct in vivo comparison of the inflammatory properties of human C5a and C5a des Arg in human skin

C5a is an 11,000-Da complement-derived inflammatory glycoprotein that has been shown to mediate inflammatory reactions in vitro as well as in vivo in human skin. The C5a degradation product, C5a des Arg, is rapidly formed after exposure of C5a to serum carboxypeptidase N and may represent the relevant C5-derived inflammatory peptide in vivo. To examine the biologic activity of human C5a des Arg in vivo and to compare it with that seen with human C5a, we purified and characterized homogeneous preparations of human C5a and C5a des Arg and injected them intradermally into seven normal volunteers. C5a des Arg exhibited biochemical and biologic properties in vitro that were different from those of C5a. When injected into human skin, C5a des Arg was less potent than C5a, in respect to both minimal dose eliciting wheal and flare reactions and maximal wheal and flare elicited at a given dose, but C5a des Arg still elicited cutaneous wheal and flare reactions at physiologically relevant concentrations. Histologically, C5a des Arg skin test sites showed dense polymorphonuclear neutrophil-rich infiltrates associated with leukocytoclasis, dermal mast cell degranulation, and endothelial cell swelling. These were virtually indistinguishable from reactions elicited by C5a and occurred with concentrations attainable in vivo. Cutaneous wheal and flare reactions elicited by either C5a or C5a des Arg were partially inhibited by H1 antihistamines but were unaffected by selected nonsteroidal anti-inflammatory agents.     

Thiol-based angiotensin-converting enzyme 2 inhibitors: P1' modifications for the exploration of the S1' subsite

Explorations of the S(1') subsite of ACE2 via modifications of the P(1') methylene biphenyl moiety of thiol-based metalloprotease inhibitors led to improvements in ACE2 selectivity versus ACE and NEP, while maintaining potent ACE2 inhibition.     

The Magnitude and Duration of Itch Produced by Intracutaneous Injections of Histamine

The magnitude and duration of itch sensation produced by intracutaneous injection of histamine were determined for humans with the procedure of magnitude estimation scaling. Thirteen subjects received a 10-μ1 intracutaneous injection of histamine at doses of 0.0001, 0.001, 0.01, 0.1, 1, and 10 μg into the volar forearm; eight of these subjects also received a 100-μg dose. One subject received multiple injections over several weeks to determine the reliability of the magnitude estimates of itch. Following each injection, the area of flare and duration of itch were also determined.

Intracutaneous injection of histamine produced a pure sensation of itch, without pain. The magnitude of itch increased in a dose-dependent fashion. The lowest histamine dose that produced itch greater than the itch produced by vehicle was 0.01 μg. The greatest itch was produced by the 100-μg dose. A power function fitted to the mean magnitude estimates had an exponent of 0.17, indicating a negatively accelerating relation between the magnitude of itch and histamine dose. The one subject who received histamine over several weeks gave fairly reproducible estimates of itch magnitude.

The duration of itch and the area of flare also increased in a dose-dependent fashion. The lowest dose of histamine that produced a duration of itch longer than the itch produced by the vehicle was 0.1 μg, while the 100-μg dose produced the longest duration of itch. Although the area of flare increased with each increase in dose from 0.1 to 10 μg, the areas of flare produced by 10 and 100 μg of histamine did not differ.

These results indicate that humans can scale the magnitude of itch produced by histamine in a dose-dependent manner. In addition, the duration of itch and the area of flare produced by histamine are dose-dependent, confirming results of previous investigators. Intracutaneous histamine is easily quantifiable and may thus be a useful stimulus in neurophysiological studies of the peripheral neural mechanisms of itch.     

Study of bradykinin metabolism by rat lung tissue membranes and rat kidney brush border membranes by HPLC with inductively coupled plasma-mass spectrometry and orthogonal acceleration time-of-flight mass spectrometry.

The coupling of the techniques, high-performance liquid chromatography (HPLC), orthogonal acceleration time-of-flight mass spectrometry (OATOF-MS) and inductively coupled plasma mass spectrometry (ICP-MS) provides a very powerful method for identifying and quantifying the products of bradykinin metabolism. In this study, we were able to identify the major metabolites of bradykinin degradation reported in the literature. In addition, a new bradykinin metabolite corresponding to bradykinin 5,9 fragment (BK-(5,9)-fragment) was identified as a product of neutral endopeptidase (NEP) activity. This finding establishes that NEP cleaves bradykinin simultaneously at the positions 4-5 and 7-8. We also demonstrate the equivalent participation of NEP and angiotensin-converting enzyme (ACE) within the rat lung tissue membranes (RLTM) in bradykinin degradation, suggesting its suitability as a model for the assay of dual ACE/NEP inhibitors. On the contrary, in rat kidney brush border membranes (KBBM), ACE is not significantly involved in bradykinin metabolism, with NEP being the major enzyme.     

Kallidin applied to the human nasal mucosa produces algesic response not blocked by capsaicin desensitization.

Various kinins (dissolved in 50 microliters) were applied to the nasal mucosa of healthy human volunteers to test the algesic and proinflammatory effects of these peptides in an intact human tissue. [des-Arg9]-bradykinin (0.5 mumol) was found to be inactive, while bradykinin (0.05-0.5 mumol) and especially kallidin (0.005-0.5 mumol) induced: (a) a mild painful sensation described as burning and pricking (latency 30 s, duration 3-5 min), (b) perception of pulsatility and obstruction in the nasal cavity (onset 1 min, duration 6-8 min). Substance P (0.5 mumol) and neurokinin A (0.5 mumol) produced slight obstruction and weak pulsatile sensation but not pain. Capsaicin (0.05 nmol) produced pain and secretion of fluid, but not pulsatile sensation. The effects of kallidin were not affected by repeated (to induce desensitization) applications of capsaicin (0.5 mumol). Likewise, ipratropium bromide (80 mg in 100 microliters) did not affect responses to kallidin. In an intact human tissue, kallidin produces various effects, including an algesic response, that are apparently independent from activation of B1 receptors and from desensitization of capsaicin-sensitive primary afferents.     

Thiol-based angiotensin-converting enzyme 2 inhibitors: P1 modifications for the exploration of the S1 subsite

Screening of a metalloprotease library led to the identification of a thiol-based dual ACE/NEP inhibitor as a potent ACE2 inhibitor. Modifications of the P(1) benzyl moiety led to improvements in ACE2 potency as well as to increased selectivity versus ACE and NEP.     

Substance P and neutral endopeptidase in development of acute respiratory distress syndrome following fire smoke inhalation

To characterize the tachykininergic effects in fire smoke (FS)-induced acute respiratory distress syndrome (ARDS), we designed a series of studies in rats. Initially, 20 min of FS inhalation induced a significant increase of substance P (SP) in bronchoalveolar lavage fluid (BALF) at 1 h and persisted for 24 h after insult. Conversely, FS disrupted 51.4, 55.6, 46.3, and 43.0% enzymatic activity of neutral endopeptidase (NEP, a primary hydrolyzing enzyme for SP) 1, 6, 12, and 24 h after insult, respectively. Immunolabeling density of NEP in the airway epithelium largely disappeared 1 h after insult due to acute cell damage and shedding. These changes were also accompanied by extensive influx of albumin and granulocytes/lymphocytes in BALF. Furthermore, levels of BALF SP and tissue NEP activity dose dependently increased and decreased, respectively, following 0, low (10 min), and high (20 min) levels of FS inhalation. However, neither the time-course nor the dose-response study observed a significant change in the highest affinity neurokinin-1 receptor (NK-1R) for SP. Finally, treatment (10 mg/kg im) with SR-140333B, an NK-1R antagonist, significantly prevented 20-min FS-induced hypoxemia and pulmonary edema 24 h after insult. Further examination indicated that SR-140333B (1.0 or 10.0 mg/kg im) fully abolished early (1 h) plasma extravasation following FS. Collectively, these findings suggest that a combination of sustained SP and NEP inactivity induces an exaggerated neurogenic inflammation mediated by NK-1R, which may lead to an uncontrolled influx of protein-rich edema fluid and cells into the alveoli as a consequence of increased vascular permeability.     

The role of neutral endopeptidase in caerulein-induced acute pancreatitis

Substance P (SP) is well known to promote inflammation in acute pancreatitis (AP) by interacting with neurokinin-1 receptor. However, mechanisms that terminate SP-mediated responses are unclear. Neutral endopeptidase (NEP) is a cell-surface enzyme that degrades SP in the extracellular fluid. In this study, we examined the expression and the role of NEP in caerulein-induced AP. Male BALB/c mice (20-25 g) subjected to 3-10 hourly injections of caerulein (50 μg/kg) exhibited reduced NEP activity and protein expression in the pancreas and lungs. Additionally, caerulein (10(-7) M) also downregulated NEP activity and mRNA expression in isolated pancreatic acinar cells. The role of NEP in AP was examined in two opposite ways: inhibition of NEP (phosphoramidon [5 mg/kg] or thiorphan [10 mg/kg]) followed by 6 hourly caerulein injections) or supplementation with exogenous NEP (10 hourly caerulein injections, treatment of recombinant mouse NEP [1 mg/kg] during second caerulein injection). Inhibition of NEP raised SP levels and exacerbated inflammatory conditions in mice. Meanwhile, the severity of AP, determined by histological examination, tissue water content, myeloperoxidase activity, and plasma amylase activity, was markedly better in mice that received exogenous NEP treatment. Our results suggest that NEP is anti-inflammatory in caerulein-induced AP. Acute inhibition of NEP contributes to increased SP levels in caerulein-induced AP, which leads to augmented inflammatory responses in the pancreas and associated lung injury.