Differential inhibitory effects of some catechin derivatives on the activities of human immunodeficiency virus reverse transcriptase and cellular deoxyribonucleic and ribonucleic acid polymerases

Observations on the inhibition of HIV-1 reverse transcriptase by catechins

The sensitivity and specificity of the inhibition of HIV-1 reverse transcriptase by various catechins have been examined. As previously reported, (-)epicatechin 3-gallate inhibits the viral polymerase. However, it is noted here that this inhibition is not observed in the presence of either serum albumin or Triton X-100. Other catechins behave similarly to (-)epicatechin 3-gallate in that they inhibit polymerase activity only in the absence of these reagents. Additionally, other DNA polymerases are inhibited to a similar degree by (-)epicatechin 3-gallate. Taken cumulatively, these results suggest that these catechins, and in particular (-)epicatechin 3-gallate, bind with no apparent selectivity and that the observed inhibition of HIV-1 reverse transcriptase is non-specific in nature.

Mitogenic activity of (-)epigallocatechin gallate on B-cells and investigation of its structure-function relationship

(-)Epigallocatechin gallate (EGCg), the main constituent of green tea, strongly enhanced the direct plaque-forming cell (PFC) response to sheep red blood cells (SRBC) in vitro and showed strong mitogenic activity for mouse splenic B-cells but not for splenic T-cells and thymocytes. The enhancement of B-cell proliferation was not mediated by macrophages since their removal did not eliminate the activity. Among the derivatives of catechin examined, (+)catechin (C); (-)epicatechin (EC); (-)-epigallocatechin (EGC); (-)epicatechin gallate (ECg); (-)epigallocatechin gallate (EGCg); and theaflavin digallate (TF3), only the derivatives with the galloyl group (ECg, EGCg, and TF3) displayed significant enhancement of the spontaneous proliferation of B-cells. Structural analogs of the catechin and galloyl groups were also examined in the system. Gallic acid and tannic acid induced some enhancement, but rutin, pyrogallol and caffeine did not. The results indicate that the galloyl group on EGCg was responsible for enhancement. However, the basic conformations of the catechins are also important, because ECg, EGCg, TF3, gallic acid, and tannic acid had quite different potencies to induce B-cell proliferation.

Site-specific DNA cleavage by mammalian DNA topoisomerase II induced by novel flavone and catechin derivatives

Four naturally occurring flavones (baicalein, quercetin, quercetagetin and myricetin) and two novel catechins [(-)-epicatechin gallate and (-)-epigallocatechin gallate, from the tea plant Camellia sinensis], which are known inhibitors of reverse transcriptase, were shown to induce mammalian topoisomerase II-dependent DNA-cleavage in vitro. The flavones differed from the catechins in causing unwinding of duplex DNA, but both classes of compound induced enzymic DNA breakage at the same sites on DNA. Moreover, the cleavage specificity was the same as that for the known intercalator 4'-(acridin-9-ylamino)methanesulphon-m-anisidide, suggesting that these agents trap the same cleavable complex. Analysis of some 30 flavonoid compounds allowed elucidation of the structure-function relationships for topoisomerase II-mediated DNA cleavage. For flavonoid inhibitors an unsaturated double bond between positions 2 and 3 of the pyrone ring and hydroxy groups at the 5, 7, 3' and 4' positions favoured efficient cleavage. Hydroxy substitutions could be tolerated at the 3, 6 and 5' positions. Indeed, the absence of substituents at the 3', 4' and 5' positions could be compensated by a hydroxy group at position 6 (baicalein). Similar requirements have been reported for flavonoid inhibitors of protein kinase C that act competitively with ATP, suggesting interaction with a conserved protein feature. Formation of the cleavable complex is a cytotoxic lesion that may contribute to the growth-inhibitory properties of flavones observed for three human tumour cell lines. These results are discussed in regard to the selectivity of antiviral agents.

Plants of the Olympic Coastal Forests: ancient knowledge of materials and medicines and future heritage

The indigenous people of the west coast of Washington State's Olympic Peninsula have used a wide variety of forest plants for centuries to make materials and medicines. The late David Forlines shared at least eight generations of the knowledge of uses of these plants for materials and medicines with us in hopes that this information might be used 'to help science catch up with the old people.' Dyes, paints and adhesives were some of the materials made. The medicines were often administered as teas, but in some cases, fresh plant material was required. Some parallels were found to European and Chinese uses of similar species. Plants from the family Rosaceae had the greatest number of medicinal uses, but several other plant families known to contain polyphenols were also encountered. The role of polyphenols in the use of these plants is difficult to estimate because in many cases the plants have not been studied chemically. A preliminary screening indicated that many of the plants were rich in procyanidins and associated compounds.

Reverse transcriptase from human immunodeficiency virus: a single template-primer binding site serves two physically separable catalytic functions

The binding of substrates to recombinant reverse transcriptase from human immunodeficiency virus (HIV) and the natural enzyme from avian myeloblastosis virus (AMV) has been examined by analyzing both the ribonuclease H and the RNA-dependent DNA polymerase activities. With 3'-end-labeled globin mRNA hybridized to (dT)15 as the substrate in the ribonuclease H reaction, the enzymes partially deadenylated the mRNA in a distributive manner. Under these conditions, there was a rapid initial burst followed by a prolonged, but much slower, steady-state rate. The biphasic reaction made possible determinations of kinetic constants as follows: values for Km, KD, and kcat were, respectively, 27 nM, 11 nM, and 5 x 10(-3) s-1 for the HIV enzyme and 30 nM, 9 nM, and 5 x 10(-3) s-1, respectively, for the avian enzyme. These constants were used to derive other parameters: The rate of association of the template-primer with reverse transcriptase was approximately 2 x 10(5) M-1 s-1, and the rate of dissociation was approximately 2 x 10(-3) s-1, regardless of the source of the enzyme. The rate of release of the product was essentially equivalent to the value of kcat indicated above for each of the enzymes. The polymerase reaction was evaluated under processive conditions of synthesis; values of Km and kcat of approximately 6 nM and approximately 2.5 s-1, respectively, for the human enzyme, and approximately 10 nM and approximately 2 s-1, respectively, for the avian enzyme were observed. The interaction of substrates with HIV reverse transcriptase was characterized further with the aid of ribonucleoside-vanadyl complexes. These complexes inhibited the polymerase and ribonuclease H activities of the enzyme competitively with respect to globin mRNA.(dT)15. Values of Ki ranging from 1 to 3 mM were obtained. With respect to deoxyribonucleoside triphosphate substrates in the polymerase reaction, mixed inhibition was observed. Deoxyribonucleoside triphosphates had no effect on kinetic parameters governing the ribonuclease H activity of the HIV enzyme but apparently facilitated the formation of active enzyme. These data fit a model in which one template-primer binding site serves both the polymerase and the ribonuclease H catalytic sites.

Inhibition of HIV-reverse transcriptase activity by some phloroglucinol derivatives

Four phloroglucinol derivatives, named mallotophenone (5-methylene-bis-2,6-dihydroxy-3-methyl-4-methoxyacetophenone), mallotochromene (8-acetyl-5,7-dihydroxy-6-(3-acetyl-2,4- dihydroxy-5-methyl-6-methoxybenzyl)-2,2-dimethylchromene), mallotojaponin (3-(3,3(dimethylallyl)5-(3(acetyl-2,4- dihydroxy-5-methyl-6-methoxybenzyl)-phloracetophenone) and mallotolerin (3-(3-methyl-2-hydroxybut-3-enyl)-5(3-acetyl-2,4- dihydroxy-5-methyl-6-methoxybenzyl)-phloracetophenone), have been tested for their ability to inhibit the activity of human immunodeficiency virus (HIV)-reverse transcriptase. Under the reaction conditions with (rA)n.(dT)12-18 as the template.primer, the enzyme activity was inhibited by approximately 70% in the presence of 10 micrograms/ml mallotochromene or mallotojaponin, whereas mallotophenone and mallotolerin were much less inhibitory to the enzyme. The enzyme activity was also inhibited, though to lesser extent, by these compounds under similar conditions with initiated MS-2 phage RNA as the template.primer. The mode of inhibition was, as analyzed with mallotojaponin, competivite with respect to the template.primer, (rA)n.(dT)12-18, and non-competitive with respect to the triphosphate substrate, dTTP. The Ki value of mallotojaponin for HIV-reverse transcriptase was determined to be 6.1 microM.

Steady state kinetics and inhibition of HIV-1 reverse transcriptase by a non-nucleoside dipyridodiazepinone, BI-RG-587, using a heteropolymeric template

Steady state kinetics and inhibition by a dipyridodiazepinone of the reverse transcriptase from human immunodeficiency virus type 1 (HIV) were studied using a heteropolymeric RNA template with a sequence from the authentic initiation site on the HIV genome. For addition of the first deoxynucleotide to primer, kcat/KM is 0.05 (nM-min)-1 and KM is 10 nM. When all 4 deoxynucleotide triphosphates are present and processive synthesis occurs, catalysis is less efficient; kcat/KM = .0077 (nM-min)-1 and KM = 100 nM for dATP. These results are consistent with a rate determining conformation change involved in translocation of the enzyme along the template. Inhibition by the dipyridodiazepinone BI-RG-587 is noncompetitive with respect to both nucleotide and template-primer; this compound decreases Vmax but does not affect KM. Thus, this inhibitor binds to a site distinct from the substrate binding sites with Ki of 220 nM. Inhibition by BI-RG-587 results in a uniform decrease in amount of products of all lengths rather than a shift from longer to shorter products, suggesting the inhibitor does not affect processivity of reverse transcriptase.

Inhibition of HIV replication in lymphocyte cultures of virus-positive subjects in the presence of sho-saiko-to, an oriental plant extract

An oriental remedy, Sho-saiko-to (SST) consisting of a mixture of aqueous extracts from seven different plants and whose most active component is the chemically defined compound baicalein was tested for its ability to inhibit the production of the human immunodeficiency virus (HIV). The testing was done with cultures of human lymphocytes obtained from HIV-positive asymptomatic subjects and patients with ARC or AIDS. The replication of the virus was monitored by quantitative assay of the reverse transcriptase (RT) activity and of the synthesis of antigen p24. The lymphocyte cultures (LC) were maintained in the absence and in the presence of 25, 50 or 100 micrograms/ml of SST, and monitored for up to 5 weeks. The results showed that in LC from asymptomatic subjects RT activity and synthesis of p24 was completely inhibited by low concentrations of SST. High concentrations of SST inhibited virus replication in 80% of LC from ARC patients, but were completely ineffective in LC from AIDS patients. It was observed that the RT activity was more sensitive to inhibition by SST than the synthesis of p24, and that the antiviral effect was dependent on the virus load of the LC.