Cotton condensed tannin: a potent modulator of alveolar macrophage host-defense function

Interaction of plant polyphenols with salivary proteins

Tannins are polyphenols that occur widespread in plant-based food. They are considered to be part of the plant defense system against environmental stressors. Tannins have a number of effects on animals, including growth-rate depression and inhibition of digestive enzymes. Tannins also have an effect on humans: They are, for example, the cause of byssinosis, a condition that is due to exposure to airborne tannin. Their biological effect is related to the great efficiency by which tannins precipitate proteins, an interaction that occurs by hydrophobic forces and hydrogen bonding. Two groups of salivary proteins, proline-rich proteins and histatins, are highly effective precipitators of tannin, and there is evidence that at least proline-rich proteins act as a first line of defense against tannins, perhaps by precipitating tannins in food and preventing their absorption from the alimentary canal. Proline plays an important role in the interaction of proline-rich proteins with tannins. In contrast, it is primarily basic residues that are responsible for the binding of histatins to tannin. The high concentration of tannin-binding proteins in human saliva may be related to the fruit and vegetable diet of human ancestors.

Proanthocyanidins and related compounds: antileishmanial activity and modulatory effects on nitric oxide and tumor necrosis factor-alpha-release in the murine macrophage-like cell line RAW 264.7

A series of 17 proanthocyanidins and structurally related compounds was tested for activity against Leishmania donovani amastigotes and promastigotes in vitro. Most of the polyphenols significantly inhibited the intracellular survival of L. donovani amastigotes (EC50 0.8-10.6 nM) when compared with the antileishmanial drug Pentostam (EC50 10.6 nM), but all were inactive against the extracellular form (EC50 7.8 to >86 nM). Noteworthy is that all compounds exhibited only moderate or no cytotoxicity against the murine host cells (EC50 7.8 to >56 nM; >25 microg/ml). These polyphenols were further evaluated for immunomodulatory effects on macrophage functions, including release of nitric oxide (NO), tumor necrosis factor-alpha (TNF) and interferon (IFN)-like properties using several functional assays. The results showed that all compounds induced murine RAW 264.7 cells only moderately to release NO (7-26 microM) relative to the reference stimulus IFN-gamma/LPS (119 microM). The TNF-inducing potential of the polyphenols producing 50% lysis in murine L929 cells ranged from absent to 138 U/ml at the host cell subtoxic concentration of 50 microg/ml. The highest TNF-inducing activity was associated with those flavan-3-ols with galloyl groups (98-127 U/ml). For proanthocyanidins, it appeared that an increase in the flavanyl chain length did not enhance the induction of TNF-release (32-86 U/ml and below detection limits for oligomers and polymers, respectively). With interferon-like activities, phylloflavan and a prodelphinidin polymer showed appreciable cytoprotective effects, as reflected by the inhibition of the cytopathic effect of encephalomyocarditis virus on L929 fibroblast cells (38 and 36 U/ml, respectively). All remaining compounds displayed only negligible or moderate protective effects at subtoxic concentrations up to 25 microg/ml (<5 to 12 U/ml). These results indicate that proanthocyanidins and related compounds have favorable antileishmanial activity in vitro and might be considered as beneficial immunological response modifiers provided there are no bioavailability problems.

Effect of cotton, hemp, and flax dust extracts on lung permeability in the guinea pig

Byssinosis is an occupational lung disease in textile mill workers exposed to the respirable dusts of cotton, hemp, and flax. This study investigated the influence of aqueous extracts from these dusts on overall lung permeability in the guinea pig as an index of respiratory epithelial damage. Lung permeability was assessed by absorption into blood from the lung of inhaled technetium-99m diethylenetriamine penta-acetate (Tc-DTPA) using gamma-scintigraphy. The half-life for Tc-DTPA absorption (t1/2) was significantly reduced following a 4-week inhalation treatment with cotton, hemp, or flax dust extracts when compared to saline control. There was at least a partial return to normal permeability 7 days after stopping treatment. A single inhalation of extract did not affect the t1/2, but increased the number of neutrophils in bronchoalveolar lavage fluid 24 h postexposure. Neutrophil migration into the airspaces therefore appeared to precede the increased lung permeability. Long-term exposure was not associated with respiratory epithelial shedding, suggesting that the increased permeability reflects a loss of epithelial tight junction integrity arising from repeated exposure to as yet undefined agents in these dusts.

Mass determination of the fatty acids released from tannin-stimulated rabbit alveolar macrophages

Previous studies with macrophages that had been prelabeled with [14C]arachidonic acid (20:4) have shown that condensed tannin is a potent agonist for the release of arachidonic acid. However, it has not been demonstrated that the percentage release of [14C]20:4 accurately reflects the metabolic activity of the endogenous 20:4 pool. In order to measure the 20:4 mass release relative to the total cellular 20:4 pool, the free fatty acids of freshly isolated alveolar macrophages were derivatized with a fluorescent reagent, and then separated and quantified by high-performance liquid chromatography. The amounts of esterified fatty acids were measured by gas chromatography of the methyl esters. Free fatty acid levels were compared to those of the total esterified plus unesterified fatty acids to determine the actual percentage release of each fatty acid. Tannin-stimulated release of 20:4 mass reflected that previously reported for the release of [14C]20:4 label but at a slower rate and at a much lower percentage indicating that [14C]20:4 had been incorporated into part of a more reactive pool. The specificity of the fatty acid release induced by tannin and beta-1,3-glucan, a known agonist for 20:4 release, was also examined. Both agonists promoted an increase in the levels of free 20:4 and of other fatty acids. A comparison of the absolute increases of each of the fatty acids indicated that tannin caused a preferential increase in the mass of free 20:4, whereas beta-1,3-glucan evoked a selective increase in the mass of 16:0.