R. P. Labadie

Metabolic activation of natural phenols into selective oxidative burst agonists by activated human neutrophils.

Phenols isolated from the traditional medicinal plant Picrorhiza kurroa inhibit the release of superoxide anion (O2-) by activated human neutrophils, but leave the phagocytotic capacity intact. Resting neutrophils and resting or activated human lymphocytes are insensitive to these agents. The underlying mechanism of this highly selective activity is investigated. A critical event is the reaction of the phenols with secretory products from the activated neutrophils. The reaction products interfere with the assembly of a functional NADPH-oxidase in the membrane. Analysis of the mode of activation of the phenols reveals two possible pathways. Catechols react directly with reactive oxygen species (ROS) from the oxidative burst. For the activation of the orthomethoxy-substituted catechols the combined activity of ROS and myeloperoxidase (MPO) is obligatory. Catechols with a dimethoxy substitution cannot be activated metabolically by neutrophil-derived ROS.

Antiarthritic activity of the newly developed neutrophil oxidative burst antagonist apocynin

The plant-phenol 4-hydroxy-3-methoxyacetophenone (trivial name apocynin) is a strong inhibitor of neutrophil superoxide anion (O2-) release in vitro. In vitro the inhibitory effect of apocynin is restricted to cells with the capacity to release peroxidase and reactive oxygen species (ROS). Peroxidase deficient cells are insensitive to apocynin. In the present study the antiinflammatory activity of apocynin was tested in collagen-induced arthritis in rats. Collagen-immunized rats were treated with different doses of apocynin in the drinking water starting at the onset of joint-swelling and terminating 14 days later, at the time when joint swelling in the control group was maximal. Apocynin-treated animals had a normal plasma level of collagen-specific antibodies, but showed a significant reduction of the joint swelling. Also the plasma IL-6 level in apocynin-treated animals was substantially lower than in control animals. No flare-up of joint swelling after termination of the treatment was observed in the apocynin-treated groups.

AYURVEDIC HERBAL DRUGS WITH POSSIBLE CYTOSTATIC ACTIVITY

Ayurveda is considered to be the traditional science of health in India and is based on the principle of subjectivity. All matter is composed of five basic elements, which can be perceived by the five sense organs. All food and drugs are classified according to their pharmacological properties, which are derived from these five elements. To investigate which Ayurvedic plants might have cytostatic activity, an Ayurvedic model for the pathogenesis of cancer was made. Based on this, selection criteria were formed, that were used to select plants from a list of Ayurvedic herbal drugs. Some of the selected species could be collected in India and Nepal. The dried material of 14 species was submitted to ethanol (70% v/v) extraction and the extracts were tested for cytotoxicity on COLO 320 tumour cells, using the microculture tetrazolium (MTT) assay. The IC50-value, the concentration causing 50% growth inhibition of the tumour cells, was used as a parameter for cytotoxicity. Extracts of the flowers of Calotropis procera (Ait.) R. Br. (Asclepiadaceae) and of the nuts of Semecarpus anacardium L.f. (Anacardiaceae) displayed the strongest cytotoxic effect with IC50-values of 1.4 micrograms/ml and 1.6 micrograms/ml, respectively. The extracts of several other plants did not show a cytotoxic effect up to 100 micrograms/ml, the highest concentration tested.

Effects of apocynin, a drug isolated from the roots of Picrorhiza kurroa, on arachidonic acid metabolism

Apocynin is a constituent of root extracts of the medicinal herb Picrorhiza kurroa and has been shown to possess anti‐inflammatory properties. We investigated the effects of apocynin on the production of arachidonic acid‐derived inflammatory mediators by guinea pig pulmonary macrophages. Apocynin concentration‐dependently inhibited the formation of thromboxane A2, whereas the release of prostaglandins E2 and F2α was stimulated. Apocynin potently inhibited arachidonic acid‐induced aggregation of bovine platelets, possibly through inhibition of thromboxane formation. The present results suggest that apocynin might, beside its therapeutic effects in inflammatory conditions when given in a root extract of P. kurroa, also be a valuable tool in the development of new anti‐inflammatory or anti‐thrombic drugs.

Curcacycline A — a novel cyclic octapeptide isolated from the latex of Jatropha curcas L.

From the latex of Jatropha curcas L. (Euphorbiaceae) a novel cyclic octapeptide was isolated, which we named curcacycline A. The compound was found to contain one threonine, one valine, two glycine, and four leucine residues. By two‐dimensional 1H‐NMR spectroscopy (HOHAHA and ROESY), its sequence was determined to be Gly1‐Leu2‐Leu3‐Gly4‐Thr5‐Val6‐Leu7Leu8‐Gly1. Curcacycline A displays a moderate inhibition of (i) classical pathway activity of human complement and (ii) proliferation of human T‐cells.

Inhibition of human complement by beta-glycyrrhetinic acid.

Licorice, the root extract of Glycyrrhiza glabra L., is used as a medicine for various diseases. Anti‐inflammatory as well as anti‐allergic activities have been attributed to one of its main constituents, glycyrrhizin. These activities are mainly ascribed to the action of the aglycone, β‐glycyrrhetinic acid. β‐Glycyrrhetinic acid has a steroid‐like structure and is believed to have immunomodulatory properties. To determine whether interference with complement functions may contribute to the immunomodulatory activity of β‐glycyrrhetinic acid, its effects on the classical and alternative activation pathways of human complement were investigated. We found that β‐glycyrrhetinic acid is a potent inhibitor of the classical complement pathway (IC50=35 μm), whereas no inhibitory activity was observed towards the alternative pathway (IC50>2500 μm). The anticomplementary activity of β‐glycyrrhetinic acid was dependent on its conformation, since the α‐form was not active. It was also established that naturally occurring steroids, e.g. hydrocortisone and cortisone, did not inhibit human complement activity under similar conditions. Detailed mechanistic studies revealed that β‐glycyrrhetinic acid acts at the level of complement component C2.

Immunomodulatory activity of an aqueous extract of Azadirachta indica stem bark

The interference of an aqueous extract of the stem bark of Azadirachta indica with different parts of the human immune system was investigated. The extract showed strong anticomplementary effects which were dose-and time-dependent and most pronounced in the classical complement pathway assay. Moreover, a dose-dependent decrease in the chemiluminescence of polymorphonuclear leukocytes was observed and a dose-dependent increase in the production of migration inhibition factor by lymphocytes.

Ethnopharmacognostical survey of Azadirachta indica A. Juss (Meliaceae).

Literature data on respectively botany, chemistry, ethnopharmacology, pharmacology and toxicology of Azadirachta indica A. Juss. (Meliaceae) are reviewed and evaluated. In traditional literature, preparations of the tree are claimed to be vulnerable in wide spectrum of diseases. Especially for inflammation-related diseases a good correlation is found with the results of recent experimental investigations. In addition, a variety of other biological activities are reported. Most frequently the effects can be attributed to compounds representing the structural classes of the limonoids, phenolics and macromolecules. Reported toxicity of preparations and isolated compounds are low, except for the seed oil. In conclusion, A. indica can be regarded as a valuable plant source for the rationalisation of its use in traditional medicine and for modern drug development.

Two functionally and chemically distinct immunomodulatory compounds in the gel of aloe vera

An aqueous extract of Aloe vera gel was analyzed guided by modulatory activity with regard to the in vitro activation of human complement and of human polymorphnuclear leucocytes (PMN). Upon ultrafiltration a high (h-Mr) and a low (l-Mr) molecular mass fraction were obtained. Pre-incubation of human pooled serum with the h-Mr fraction resulted in a depletion of classical and alternative pathway complement activity. In contrast, only the l-Mr fraction could inhibit the production of free oxygen radicals by activated PMNs. The latter activity cannot be attributed to non-specific effects like toxicity, interference with stimulant binding or scavenger activity.

Effects of low molecular constituents from Aloe vera gel on oxidative metabolism and cytotoxic and bactericidal activities of human neutrophils

In traditional South-East Asian medicine the therapeutic value of the parenchymous leaf-gel of Aloe vera for inflammatory-based diseases is well-reputed. The aim of this study is to investigate at which level gel-constituents exert their activity. We show here that low -Mr constituents of an aqueous gel-extract inhibit the release of reactive oxygen species (ROS) by PMA-stimulated human PMN. The compounds inhibit the ROS-dependent extracellular effects of PMN such as lysis of red blood cells. The capacity of the PMN to phagocytose and kill micro-organisms at the intracellular level is not affected. The inhibitory activity of the low-Mr compounds is most pronounced in the PMA-induced ROS production, but is significantly antagonized by the Ca-ionophore A23187. It is shown that the inhibitory effect of the low-Mr compounds is the indirect result of the diminished availability of intracellular free Ca-ions.