L.A. 't Hart

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.

Labaditin, a novel cyclic decapeptide from the latex of Jatropha multifida L. (Euphorbiaceae): isolation and sequence determination by means of two-dimensional NMR

Latex; Decapeptide, cyclic; Labaditin; NMR, 1H‐; Peptide isolation; (Jatropha multifida, Euphorbiaceae)

Inhibitory activity of Jatropha multifida latex on classical complement pathway activity in human serum mediated by a calcium-binding proanthocyanidin

This study isolates and characterizes the anti-complement constituent(s) present in the latex of Jatropha multifida, in an attempt to explain the traditional application of the latex in the treatment of infected wounds. Guided by the inhibition of classical pathway (CP) complement activity in human serum, a polymer was isolated which could be characterized as a proanthocyanidin. The polymer inhibits CP activation of the complement cascade, while alternative pathway (AP) activation is relatively insensitive to the polymer. This is due to the selective depletion of Ca2+, but not Mg2+, from the incubation medium.

Imunodulatory compounds from Picrorhiza kurroa: Isolation and characterization of two anti-complementary polymeric fractions from an aqueous root extract

Two aqueous root extracts of Picrorhiza kurroa, one prepared by extraction at 4 degrees C and the other by refluxing, were purified using the guidance of modulation of classical (CP) and alternative (AP) pathway complement activity. By means of methanol extraction and gel filtration chromatography, two polymeric fractions were isolated from the cold water extract. A methanol-soluble polymeric fraction (CS1) was highly active in inhibiting CP complement activity exclusively, whereas a methanol-insoluble polymeric fraction (CI1) exhibited an inhibitory effect on both CP and AP complement activity. Preliminary chemical analysis of the anti-complementary fractions revealed the presence of structures of carbohydrate and of peptide nature in CS1 and CI1. The modulation of CP complement activity by CS1 was studied in more detail. Its inhibitory effect was proven to be based on complement consumption rather than on chelation of Ca2+ and/or Mg2+ or on stabilization of the target cells in the complement-assay. The purification of the aqueous extract prepared by refluxing, resulted in the isolation of a polymeric fraction with the same qualities as CS1. However, a fraction with properties similar to CI1 could not be isolated from this extract.

Characterization of anti-complement compounds from azadirachta indica

The crude aqueous extract of Azadirachta indica bark possesses an inhibitory activity on both classical (CP) and alternative pathway (AP) activation of human complement. Purification of the compounds with the guidance of the AP-inhibitory activity involved extraction with methanol, dialysis, ion-exchange procedures and gel-permeation chromatography. This sequence yielded two polymers, NB-I and NB-II, one a highly active compound with a relatively low molecular weight (NB-II) and the other a less active compound with a high molecular weight (NB-I). The polymers were characterized by using colour reactions, TLC, GLC and HPLC after hydrolysis and gel-permeation chromatography as peptidoglycans. The carbohydrate part consisted predominantly of glucose. Arabinose, galactose and mannose were present in minor amounts (NB-II) or only as traces (NB-I). Protein was present for 5.5% in NB-I and for 9.8% in NB-II.

Evidence that superoxide-anion, produced by PMA-activated human polymorphonuclear leukocytes, is the cytolytic agent for rabbit, but not for sheep red blood cells.

The lysis of sheep and rabbit red blood cells (SRBC and RRBC, respectively) upon exposure to PMA-activated human polymorphonuclear leukocytes (PMN) was investigated. The lysis of these target cells, which was measured by the release of 51Cr, showed different kinetics and scavenger-sensitivity. The lysis of RRBC, which was already detectable within 45 min of incubation, was sensitive to superoxide dismutase (SOD), but was only poorly influenced by scavengers of hydroxyl radical formation, such as desferal or thiourea. In contrast, lysis of SRBC was first detectable after 90 to 135 min of incubation and sensitive to desferal and thiourea, but not to SOD. Finally, only RRBC were sensitive to the artificial superoxide-generating system hypoxanthine/xanthine oxidase. Taken together, these data point at a cytolytic activity of superoxide anion O2- towards RRBC. SRBC are relatively resistant to O2-, but are lysed by an H2O2- and hydroxyl radical-dependent process.