Sesquiterpene lactones as inhibitors of human neutrophil elastase

In silico and in vitro elastase inhibition assessment assays of rosmarinic acid natural product from Rosmarinus officinalis Linn

The use of various herbs and their compounds has been a strategy widely used in the fight against various human diseases. For example, rosmarinic acid, a bioactive phenolic compound commonly found in Rosemary plants (Rosmarinus officinalis Labiatae), has multiple therapeutic benefits in different diseases, such as cancer. Therefore, the study aimed to evaluate in silico and in vitro the inhibition potential of the enzyme Elastase from the porcine pancreas by rosmarinic acid isolated from the plant species R. officinalis Linn. Through Molecular Docking, the mechanism of action was investigated. In addition, rosmarinic acid presented a range of 5-60 µg/mL and significantly inhibited Elastase. At 60 µg/mL, there was an inhibition of 55% on the enzymatic activity. The results demonstrate the inhibition of Elastase by rosmarinic acid, which can lead to the development of new enzyme inhibitors that can be an inspiration for developing various drugs, including anticancer drugs.

ANTIAGE-DB: A Database and Server for the Prediction of Anti-Aging Compounds Targeting Elastase, Hyaluronidase, and Tyrosinase

Natural products bear a multivariate biochemical profile with antioxidant, anti-inflammatory, antibacterial, and antitumoral properties. Along with their natural sources, they have been widely used both as anti-aging and anti-melanogenic agents due to their effective contribution in the elimination of reactive oxygen species (ROS) caused by oxidative stress. Their anti-aging activity is mainly related to their capacity of inhibiting enzymes like Human Neutrophil Elastase (HNE), Hyaluronidase (Hyal) and Tyrosinase (Tyr). Herein, we accumulated literature information (covering the period 1965–2020) on the inhibitory activity of natural products and their natural sources towards these enzymes. To navigate this information, we developed a database and server termed ANTIAGE-DB that allows the prediction of the anti-aging potential of target compounds. The server operates in two axes. First a comparison of compounds by shape similarity can be performed against our curated database of natural products whose inhibitory potential has been established in the literature. In addition, inverse virtual screening can be performed for a chosen molecule against the three targeted enzymes. The server is open access, and a detailed report with the prediction results is emailed to the user. ANTIAGE-DB could enable researchers to explore the chemical space of natural based products, but is not limited to, as anti-aging compounds and can predict their anti-aging potential. ANTIAGE-DB is accessed online.

Antioxidant properties, anti- SARS-CoV-2 study, collagenase and elastase inhibition effects, anti-human lung cancer potential of some phenolic compounds

Lung cancer is one of the main reasons for death worldwide. The natural compounds with anti-lung cancer potential are of main interest and are considered a very promising alternative to replace or raise the efficiency of conventional drugs. Diethylstilbestrol, Enterodiol, Enterolactone, Flavokawain A, Flavokawain B, and Flavokawain C compounds showed excellent to good inhibitory activities against studied these enzymes with IC₅₀ values in ranging between 9.66 ± 1.52 to 121.20 ± 15.87 μM for collagenase and 11.06 ± 1.87 to 27.31 ± 4.673 μM for elastase. Also, these compounds had In vitro anti-lung cancer activities. Comparison of the chemical and biological activities of the studied molecules was made by theoretical calculations. Gaussian sofware program was used for chemical activity. The Maestro molecular docking calculations were made to compare their biochemical activities. Afterwards, ADME/T calculations of the molecules were made.

Sesquiterpene Lactones: Promising Natural Compounds to Fight Inflammation

Inflammation is a crucial and complex process that reestablishes the physiological state after a noxious stimulus. In pathological conditions the inflammatory state may persist, leading to chronic inflammation and causing tissue damage. Sesquiterpene lactones (SLs) are composed of a large and diverse group of highly bioactive plant secondary metabolites, characterized by a 15-carbon backbone structure. In recent years, the interest in SLs has risen due to their vast array of biological activities beneficial for human health. The anti-inflammatory potential of these compounds results from their ability to target and inhibit various key pro-inflammatory molecules enrolled in diverse inflammatory pathways, and prevent or reduce the inflammatory damage on tissues. Research on the anti-inflammatory mechanisms of SLs has thrived over the last years, and numerous compounds from diverse plants have been studied, using in silico, in vitro, and in vivo assays. Besides their anti-inflammatory potential, their cytotoxicity, structure–activity relationships, and pharmacokinetics have been investigated. This review aims to gather the most relevant results and insights concerning the anti-inflammatory potential of SL-rich extracts and pure SLs, focusing on their effects in different inflammatory pathways and on different molecular players.

Bergenia pacumbis from Nepal, an astonishing enzymes inhibitor

BACKGROUND

The Bergenia species are perennial herbs native to central Asia, and one of the most promising medicinal plants of the family Saxifragaceae which are popularly known as 'Pashanbheda'. The aim of this study was to evaluate antioxidant and α-amylase, α-glucosidase, lipase, tyrosinase, elastase, and cholinesterases inhibition potential of Bergenia pacumbis of Nepali origin collected from the Karnali region of Nepal.

METHODS

The sequential crude extracts were made in hexane, ethyl acetate, methanol, and water. Antioxidant activities were analyzed by 2,2-diphenyl-1-picrylhydrazyl (DPPH) and 2,2'-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) assay. The α-amylase, α-glucosidase, lipase, tyrosinase, elastase, acetylcholinesterase, and butyrylcholinesterase inhibition were analyzed by the 3,5-Dinitrosalicylic acid (DNSA), p-Nitrophenyl-α-D-glucopyranoside (p-NPG), 4-nitrophenyl butyrate (p-NPB), l-3,4-dihydroxyphenylalanine (L-DOPA), N-Succinyl-Ala-Ala-p-nitroanilide (AAAPVN), acetylthiocholine, and butyrylcholine as a respective substrate. The major metabolites were identified by high performance liquid chromatography with electron spray ionization- quadrupole time-of-flight mass spectrometry (HPLC-ESI-QTOF-MS) profiling.

RESULTS

Our results revealed the great antioxidant ability of crude extract of B. pacumbis in ethyl acetate extract against both DPPH (IC50 = 30.14 ± 0.14 μg/mL) and ABTS (IC50 = 17.38 ± 1.12 μg/mL). However, the crude methanol extract of B. pacumbis showed the comparable enzymes inhibitions with standard drugs; α-amylase (IC50 = 14.03 ± 0.04 μg/mL), α-glucosidase (IC50 = 0.29 ± 0.00 μg/mL), lipase (IC50 = 67.26 ± 0.17 μg/mL), tyrosinase (IC50 = 58.25 ± 1.63 μg/mL), elastase (IC50 = 74.00 ± 3.03 μg/mL), acetylcholinesterase (IC50 = 31.52 ± 0.58 μg/mL), and butyrylcholinesterase (IC50 = 11.69 ± 0.14 μg/mL). On the basis of HPLC-ESI-QTOF-MS profiling of metabolites, we identified major compounds such as Bergenin, Catechin, Arbutin, Gallic acid, Protocatechuic acid, Syringic acid, Hyperoside, Afzelechin, Methyl gallate, Paashaanolactone, Astilbin, Quercetin, Kaempferol-7-O-glucoside, Diosmetin, Phloretin, and Morin in methanol extract which has reported beneficial bioactivities.

CONCLUSION

Our study provides a plethora of scientific evidence that the crude extracts of B. pacumbis from Nepalese origin in different extracting solvents have shown significant potential on inhibiting free radicals as well as enzymes involved in digestion, skin related problems, and neurological disorders compared with the commercially available drugs.

Eupatoriopicrin Inhibits Pro-inflammatory Functions of Neutrophils via Suppression of IL-8 and TNF-alpha Production and p38 and ERK 1/2 MAP Kinases

During chronic inflammation, neutrophils acting locally as effector cells not only activate antibacterial defense but also promote the inflammatory response. Interleukin 8 (IL-8), the main cytokine produced by activated neutrophils, positively correlates with the severity of respiratory tract diseases. By screening European plants traditionally used for treating respiratory tract diseases, we found that extracts of aerial parts of Eupatorium cannabinum inhibit IL-8 release from neutrophils. Using bioassay-guided fractionation, we identified five sesquiterpene lactones, eupatoriopicrin (1), 5'-deoxyeupatoriopicrin (2), hiyodorilactone A (3), 3-hydroxy-5'- O-acetyleupatoriopicrin = hiyodorilactone D (4), and hiyodorilactone B (5), that efficiently (IC₅₀ < 1 μM) inhibited IL-8 and TNF-α release in lipopolysaccharide (LPS)-stimulated human neutrophils. Moreover, all these sesquiterpene lactones suppressed the adhesion of human neutrophils to an endothelial monolayer by downregulating the expression of the β2 integrin CD11b/CD18 on the neutrophil surface. Furthermore, eupatoriopicrin efficiently suppressed LPS-induced phosphorylation of p38 MAPK and ERK and attenuated neutrophil infiltration in the thioglycolate-induced peritonitis model in mice. Altogether, these results demonstrate the potential of the sesquiterpene lactone eupatoriopicrin as a lead substance for targeting inflammation.

Topical herbal therapies for treating osteoarthritis

BACKGROUND

Before extraction and synthetic chemistry were invented, musculoskeletal complaints were treated with preparations from medicinal plants. They were either administered orally or topically. In contrast to the oral medicinal plant products, topicals act in part as counterirritants or are toxic when given orally.

OBJECTIVES

To update the previous Cochrane review of herbal therapy for osteoarthritis from 2000 by evaluating the evidence on effectiveness for topical medicinal plant products.

SEARCH METHODS

Databases for mainstream and complementary medicine were searched using terms to include all forms of arthritis combined with medicinal plant products. We searched electronic databases (Cochrane Central Register of Controlled Trials (CENTRAL), MEDLINE, EMBASE, AMED, CINAHL, ISI Web of Science, World Health Organization Clinical Trials Registry Platform) to February 2013, unrestricted by language. We also searched the reference lists from retrieved trials.

SELECTION CRITERIA

Randomised controlled trials of herbal interventions used topically, compared with inert (placebo) or active controls, in people with osteoarthritis were included.

DATA COLLECTION AND ANALYSIS

Two review authors independently selected trials for inclusion, assessed the risk of bias of included studies and extracted data.

MAIN RESULTS

Seven studies (six different medicinal plant interventions; 785 participants) were included. Single studies (five studies) and non-comparable studies (two studies) precluded pooling of results.Moderate evidence from a single study of 174 people with hand osteoarthritis indicated that treatment with Arnica extract gel probably results in similar benefits as treatment with ibuprofen (non-steroidal anti-inflammatory drug) with a similar number of adverse events. Mean pain in the ibuprofen group was 44.2 points on a 100 point scale; treatment with Arnica gel reduced the pain by 4 points after three weeks: mean difference (MD) -3.8 points (95% confidence intervals (CI) -10.1 to 2.5), absolute reduction 4% (10% reduction to 3% increase). Hand function was 7.5 points on a 30 point scale in the ibuprofen-treated group; treatment with Arnica gel reduced function by 0.4 points (MD -0.4, 95% CI -1.75 to 0.95), absolute improvement 1% (6% improvement to 3% decline)). Total adverse events were higher in the Arnica gel group (13% compared to 8% in the ibuprofen group): relative risk (RR) 1.65 (95% CI 0.72 to 3.76).Moderate quality evidence from a single trial of 99 people with knee osteoarthritis indicated that compared with placebo, Capsicum extract gel probably does not improve pain or knee function, and is commonly associated with treatment-related adverse events including skin irritation and a burning sensation. At four weeks follow-up, mean pain in the placebo group was 46 points on a 100 point scale; treatment with Capsicum extract reduced pain by 1 point (MD -1, 95% CI -6.8 to 4.8), absolute reduction of 1% (7% reduction to 5% increase). Mean knee function in the placebo group was 34.8 points on a 96 point scale at four weeks; treatment with Capsicum extract improved function by a mean of 2.6 points (MD -2.6, 95% CI -9.5 to 4.2), an absolute improvement of 3% (10% improvement to 4% decline). Adverse event rates were greater in the Capsicum extract group (80% compared with 20% in the placebo group, rate ratio 4.12, 95% CI 3.30 to 5.17). The number needed to treat to result in adverse events was 2 (95% CI 1 to 2).Moderate evidence from a single trial of 220 people with knee osteoarthritis suggested that comfrey extract gel probably improves pain without increasing adverse events. At three weeks, the mean pain in the placebo group was 83.5 points on a 100 point scale. Treatment with comfrey reduced pain by a mean of 41.5 points (MD -41.5, 95% CI -48 to -34), an absolute reduction of 42% (34% to 48% reduction). Function was not reported. Adverse events were similar: 6% (7/110) reported adverse events in the comfrey group compared with 14% (15/110) in the placebo group (RR 0.47, 95% CI 0.20 to 1.10).Although evidence from a single trial indicated that adhesive patches containing Chinese herbal mixtures FNZG and SJG may improve pain and function, the clinical applicability of these findings are uncertain because participants were only treated and followed up for seven days. We are also uncertain if other topical herbal products (Marhame-Mafasel compress, stinging nettle leaf) improve osteoarthritis symptoms due to the very low quality evidence from single trials.No serious side effects were reported.

AUTHORS' CONCLUSIONS

Although the mechanism of action of the topical medicinal plant products provides a rationale basis for their use in the treatment of osteoarthritis, the quality and quantity of current research studies of effectiveness are insufficient. Arnica gel probably improves symptoms as effectively as a gel containing non-steroidal anti-inflammatory drug, but with no better (and possibly worse) adverse event profile. Comfrey extract gel probably improves pain, and Capsicum extract gel probably will not improve pain or function at the doses examined in this review. Further high quality, fully powered studies are required to confirm the trends of effectiveness identifed in studies so far.

Elevated serum neutrophil elastase is related to prehypertension and airflow limitation in obese women

BACKGROUND

Neutrophil elastase level/activity is elevated in a variety of diseases such as atherosclerosis, systolic hypertension and obstructive pulmonary disease. It is unknown whether obese individuals with prehypertension also have elevated neutrophil elastase, and if so, whether it has a deleterious effect on pulmonary function.

OBJECTIVES

To determine neutrophil elastase levels in obese prehypertensive women and investigate correlations with pulmonary function tests.

METHODS

Thirty obese prehypertensive women were compared with 30 obese normotensive subjects and 30 healthy controls. The study groups were matched for age.

MEASUREMENTS

The following were determined: body mass index, waist circumference, blood pressure, lipid profile, high sensitivity C-reactive protein, serum neutrophil elastase, and pulmonary function tests including forced expiratory volume in one second (FEV1), forced vital capacity (FVC) and FEV1/FVC ratio.

RESULTS

Serum neutrophil elastase concentration was significantly higher in both prehypertensive (405.8 ± 111.6 ng/ml) and normotensive (336.5 ± 81.5 ng/ml) obese women than in control non-obese women (243.9 ± 23.9 ng/ml); the level was significantly higher in the prehypertensive than the normotensive obese women. FEV1, FVC and FEV1/FVC ratio in both prehypertensive and normotensive obese women were significantly lower than in normal controls, but there was no statistically significant difference between the prehypertensive and normotensive obese women. In prehypertensive obese women, there were significant positive correlations between neutrophil elastase and body mass index, waist circumference, systolic blood pressure, diastolic blood pressure, total cholesterol, triglyceride, low density lipoprotein cholesterol, high sensitivity C-reactive protein and negative correlations with high density lipoprotein cholesterol, FEV1, FVC and FEV1/FVC.

CONCLUSION

Neutrophil elastase concentration is elevated in obese prehypertensive women along with an increase in high sensitivity C-reactive protein which may account for dyslipidemia and airflow dysfunction in the present study population.

Sesquiterpene lactones from Lychnophora pohlii: neutrophil chemiluminescence inhibition and free radical scavenger activity

Excessive production of reactive oxygen species (ROS) by polymorphonuclear leucocytes (PMNLs) is thought to contribute to the pathology of many inflammatory diseases. Sesquiterpene lactones (STLs) seem to be important contributors to the anti-inflammatory activity of many species of Lychnophora (Asteraceae), which have been widely used in Brazilian folk medicine because of this pharmacological property. In this study, the inhibitory effects of three STLs isolated from Lychnophora pohlii (lychnopholide, centratherin and goyazensolide) on rabbit PMNL oxidative burst were evaluated by the luminol-enhanced chemiluminescence (CL-lum) assay. All STLs tested showed concentration-dependent inhibitory activity on CL-lum but were not cytotoxic to PMNLs (evaluated by lactate dehydrogenase release) under the assessed conditions. Moreover, goyazensolide, the most active STL, had no free radical scavenger property, as assessed by 1,1-diphenyl-2-picrylhydrazyl radical assay, and had no inhibitory effect on the luminol-horseradish peroxidase-hydrogen peroxide chemiluminescence. Taken together, the results of this investigation suggest that the concomitant presence of methacrylate ester and hydroxyl groups contributes to a high inhibitory effect on PMNL oxidative metabolism. This effect was not mediated by free radical scavenger or cytotoxic effects, but probably by inhibition of enzymes involved in the signal transduction pathways of the ROS generation process.

Anti-collagenase, anti-elastase and anti-oxidant activities of extracts from 21 plants

BACKGROUND

Owing to their roles in tissue remodelling in health and disease, several studies have reported investigations on plant extracts as inhibitors of proteinases and as anti-oxidants.

METHODS

The anti-ageing and anti-oxidant properties of 23 plant extracts (from 21 plant species) were assessed as anti-elastase and anti-collagenase activities and in selected anti-oxidant assays along with phenolic content.

RESULTS

Anti-elastase activities were observed for nine of the extracts with inhibitory activity in the following order: white tea (approximately 89%), cleavers (approximately 58%), burdock root (approximately 51%), bladderwrack (approximately 50%), anise and angelica (approximately 32%). Anti-collagenase activities were exhibited by sixteen plants of which the highest activity was seen in white tea (approximately 87%), green tea (approximately 47%), rose tincture (approximately 41%), and lavender (approximately 31%). Nine plant extracts had activities against both elastase (E) and collagenase (C) and were ranked in the order of white tea (E:89%, C:87%) > bladderwrack (E:50%, C:25%) > cleavers (E:58%, C:7%) > rose tincture (E:22%, C:41%) > green tea (E:10%: C:47%) > rose aqueous (E: 24%, C:26%) > angelica (E:32%, C:17%) > anise (E:32%, C:6%) > pomegranate (E:15%, C:11%).Total phenolic content varied between 0.05 and 0.26 mg gallic acid equivalents (GAE)/mL with the exception of white tea (0.77 mg GAE/mL). For anti-oxidant assessment, the Trolox equivalent anti-oxidant capacity (TEAC) assay revealed activity for all extracts. White tea had the highest activity equivalent to approximately 21 microM Trolox for a 6.25 microg aliquot. In addition, seven extracts exhibited activities = 10 microM Trolox with witch hazel (6.25 microg = 13 microM Trolox) and rose aqueous (6.25 microg = 10 microM Trolox) showing very high activities at low concentrations. A high activity for white tea was also found in the superoxide dismutase (SOD) assay in which it exhibited ~88% inhibition of reduction of nitroblue tetrazolium. High activities were also observed for green tea (86.41%), rose tincture (82.77%), witch hazel (82.05%) and rose aqueous (73.86%).

CONCLUSION

From a panel of twenty three plant extracts, some one dozen exhibit high or satisfactory anti-collagenase or anti-elastase activities, with nine having inhibitory activity against both enzymes. These included white tea which was found to have very high phenolic content, along with high TEAC and SOD activities.

Achillea millefolium L. s.l. -- is the anti-inflammatory activity mediated by protease inhibition?

Achillea millefolium L. s.l. is traditionally used not only in the treatment of gastro-intestinal and hepato-biliary disorders, but also as an antiphlogistic drug. As various proteases, for instance human neutrophil elastase (HNE) and matrix metalloproteinases (MMP-2 and -9), are associated with the inflammatory process, the aim of this study was to test a crude plant extract in in vitro-protease inhibition assays for understanding the mechanisms of anti-inflammatory action. Furthermore, two fractions enriched in flavonoids and dicaffeoylquinic acids (DCQAs), respectively, were also tested in order to evaluate their contribution to the antiphlogistic activity of the plant. The extract and the flavonoid fraction inhibited HNE showing IC(50) values of approximately 20 microg/ml, whereas the DCQA fraction was less active (IC(50)=72 microg/ml). The inhibitory activity on MMP-2 and -9 was observed at IC(50) values from 600 to 800 microg/ml, whereas the DCQA fraction showed stronger effects than the flavonoid fraction and the extract. In conclusion, the in vitro-antiphlogistic activity of Achillea is at least partly mediated by inhibition of HNE and MMP-2 and -9. After the recently described spasmolytic and choleretic effects the obtained results give further insights into the pharmacological activity of Achillea and confirm the traditional application as antiphlogistic drug.

Anti-inflammatory profile of dehydrocostic acid, a novel sesquiterpene acid with a pharmacophoric conjugated diene

Sesquiterpene acids are natural products that, in contrast with the thoroughly studied sesquiterpene lactones, have received little pharmacological attention. A good source of this class of compounds is Inula viscosa (Asteraceae), a plant with documented anti-inflammatory effects. The present paper gives the results of our investigations on the biochemical mechanisms involved in the anti-inflammatory activity of one such compound, dehydrocostic acid. The most salient findings were that in vitro dehydrocostic acid inhibits leukotriene B(4) production (IC(50)=22 microM), elastase activity (IC(50)=43 microM) and bee venom phospholipase A(2) activity (IC(50)=17 microM). Furthermore, this sesquiterpenoid was effective on some models of acute edema induced by PLA(2) and 12-O-tetradecanoylphorbol 13-acetate (TPA) Comparison of these data with that known for ilicic acid firmly suggests that the presence of a semiplanar ring A is essential for an improved inhibitory activity on inflammatory mediators.

Two New Sesquiterpene Lactones from Ixeris chinensis

Phytochemical investigation of Ixeris chinensis NAKAI (Asteraceae) has resulted in the isolation of a new guaianolide-type sesquiterpene lactone, ixerochinolide (1) as well as the related glucoside, ixerochinoside (2). In addition, the known guaianolides, 8beta-hydroxy-3-oxo-guaia-4(15),10(14),11(13)-trien-1alpha,5alpha,6beta,7alphaH-12,6-olide (8beta-hydroxydehydrozaluzanin), 8beta,15-dihydroxy-2-oxo-guaia-1(10),3,11(13)-trien-5alpha,6beta,7alphaH-12,6-olide (lactucin), 3beta,8alpha,10alpha-trihydroxy-guaia-4(15),11(13)-dien-1alpha,5alpha,6beta,7alphaH-12,6-olide (10alpha-hydroxy-10,14-dihydro-desacylcynaropicrin) and 3beta-D-glucopyranosyloxy-8beta-(p-hydroxyphenylacetyloxy)-guaia-4(15),10(14),11(13)-trien-1alpha,5alpha,6beta,7alphaH-12,6-olide (8-epicrepioside) were identified. The structures were determined on the basis of spectral analyses, especially 1- and 2D NMR. Compound 1 exhibited significant cytotoxicity against human PC-3 tumor cells.

Suppressive effects of Stephania tetrandra on the neutrophil function in patients with rheumatoid arthritis

Crude preparations of Stephania tetrandra (ST), a traditional herbal medicine, have been used safely for arthritis and silicosis in China. The concentration of granulocyte elastase - alpha 1 protease inhibitor complex in plasma is enhanced in inflammatory processes, e.g. in septicaemia and rheumatoid arthritis (RA), being an expression of granulocyte activation during inflammatory response. It has previously been reported that ST showed beneficial and immunomodulatory effects in the treatment of relatively mild RA. After the administration of ST for 12 weeks, the proportion of granulocytes and the granulocyte count in peripheral blood decreased significantly. The lipid peroxide and human granulocyte elastase levels of stored plasma declined significantly. Furthermore, both the leukocyte/elastase ratio and granulocyte/elastase ratio increased significantly. The findings of this study suggest that the suppressive effect of ST administration on excessive granulocyte activation resulted in the improvement of inflammation with rheumatoid arthritis.

The effect of sesquiterpene lactones on the release of human neutrophil elastase

Sesquiterpene lactones (SLs) are natural products responsible for the anti-inflammatory activity of a variety of medicinal plants, mainly from the Asteraceae family. Here, we investigated whether they also influence the process of exocytosis of pro-inflammatory enzymes, such as the human neutrophil elastase (HNE). Altogether, eight structurally different SLs from the eudesmanolide, guaianolide, pseudoguaianolide, and germacranolide type were studied. Neutrophils were isolated from fresh human blood. After pre-incubation with different concentrations of the respective SL and cytochalasin B, the exocytosis of elastase was initiated either by platelet activating factor or N-formyl-methionyl-leucyl-phenylalanine. Inhibition of HNE release was measured by p-nitroaniline formation. The SLs exhibited an inhibitory effect on elastase release from neutrophils challenged either by platelet activating factor or N-formyl-methionyl-leucyl-phenylalanine. Concentration-response curves were recorded and the IC(50) values ranged from 2 to 30 microM. Studies on isolated HNE showed that a selective direct inhibition on HNE can be excluded. Interestingly, the inhibitory activity did not correlate with the number of alpha,beta-unsaturated carbonyl functions. The structure-activity relationship and the molecular mechanism are discussed.