Synthesis, cytotoxicity, and hemolytic activity of 6'-O-substituted dioscin derivatives

Dioscin derivatives (1-12) with a variety of substitutions at the 6'-OH of the chacotriosyl residue and the 3',6'-anhydrosaponin derivatives (26, 30, and 32) were synthesized. All these derivatives showed much lower cytotoxicity than that of the parent dioscin, while their hemolytic activities were partially retained depending on the various 6'-O-substitutions.     

Haemolytic activity,cytotoxicity and membrane cell permeabilization of semi-synthetic and natural lupane- and oleanane-type saponins

The haemolysis of red blood cells inducing toxicity in most animals including humans is a major drawback for the clinical development of saponins as antitumour agents. In this study, the haemolytic and cytotoxic activities as well as the membrane cell permeabilization property of a library of 31 semi-synthetic and natural lupane- and oleanane-type saponins were evaluated and the structure–activity relationships were established. It was shown that lupane-type saponins do not exhibit any haemolytic activity and membrane cell permeabilization property at the maximum concentration tested (100 μM) independently of the nature of the sugar moieties. While oleanane-type saponins such as β-hederin (25) and hederacolchiside A₁ (27) cause the death of cancer cell lines by permeabilizing the cellular membranes, lupane-type saponins seem to proceed via another mechanism, which could be related to the induction of apoptosis. Altogether, the results indicate that the cytotoxic lupane-type glycosides 10 and 22 bearing an α-l-rhamnopyranose moiety at the C-3 position represent promising antitumour agents for further studies on tumour-bearing mice since they are devoid of toxicity associated with the haemolysis of red blood cells.     

The relationship between amyloid structure and cytotoxicity

Self-assembly of proteins and peptides into amyloid structures has been the subject of intense and focused research due to their association with neurodegenerative, age-related human diseases and transmissible prion diseases in humans and mammals. Of the disease associated amyloid assemblies, a diverse array of species, ranging from small oligomeric assembly intermediates to fibrillar structures, have been shown to have toxic potential. Equally, a range of species formed by the same disease associated amyloid sequences have been found to be relatively benign under comparable monomer equivalent concentrations and conditions. In recent years, an increasing number of functional amyloid systems have also been found. These developments show that not all amyloid structures are generically toxic to cells. Given these observations, it is important to understand why amyloid structures may encode such varied toxic potential despite sharing a common core molecular architecture. Here, we discuss possible links between different aspects of amyloidogenic structures and assembly mechanisms with their varied functional effects. We propose testable hypotheses for the relationship between amyloid structure and its toxic potential in the context of recent reports on amyloid sequence, structure, and toxicity relationships.     

Antitumor activity of naltrexone and correlation with steroid hormone receptors.

We have evaluated the opiate peptide antagonist, naltrexone, for its effectiveness as an antitumor agent. For this evaluation, we tested the effect of naltrexone given daily in the diet on the growth of established 7,12-dimethylbenz(a)anthracene-induced mammary tumors. Tumors continued to grow actively in rats fed chow diet only (control group). In contrast, the naltrexone-supplemented diet (75 mg/kg diet) significantly decreased the size of the established mammary tumors in rats over the 25 day observation period, resulting in an average decrease in tumor volume by approximately 23% compared with their sizes at the beginning of the treatment. Tumor regression occurred in 70% of the rats. Tumors that respond to naltrexone showed appreciable amounts of estrogen and progesterone receptors while unresponsive tumors were negative for estrogen and progesterone receptors. For the first time, we report that naltrexone can regress established mammary tumors and that the inhibitory effect of naltrexone appears to be restricted to the hormonally responsive mammary tumors.     

Fungicidal properties of two saponins from Capsicum frutescens and the relationship of structure and fungicidal activity

Two steroidal saponins have been purified from cayenne pepper (Capsicum frutescens). Both have the same steroidal moiety but differ in the number of glucose moieties: the first saponin has four glucose moieties (molecular mass 1081 Da) and the second contains three glucose moieties (molecular mass 919 Da). Solubility in aqueous solution is less for the saponin containing three glucose moieties than for the one containing four glucose moieties. The larger saponin was slightly fungicidal against the nongerminated and germinating conidia of Aspergillus flavus, A. niger, A. parasiticus, A. fumigatus, Fusarium oxysporum, F. moniliforme, and F. graminearum, whereas, the second saponin (molecular mass 919 Da) was inactive against these fungi. Results indicate that the absence of one glucose molecule affects the fungicidal and aqueous solubility properties of these similar molecules.     

Basic steroid saponins from aerial parts of Fritillaria Thunbergii

From the aerial parts of Fritillaria thunbergii, three glycosidal Solanum alkaloids (basic steroid saponins) were isolated together with minor     

Effect of C-ring modifications on the cytotoxicity of spirostan saponins and related glycosides

Twelve C-ring modified spirostanyl glycosides were synthesized and evaluated for their cytotoxicity against the human myeloid leukemia cell line (HL-60). With the aim of assessing the influence of the hydrophobic character, the conformational flexibility and the stereochemistry of the C-ring functionalities on the cytotoxic activity, a variety of spirostanic aglycones incorporating methylene, methoxyl, α,β-unsaturated ketone and lactone groups were subjected to a linear glycosylation strategy leading to glycosides derived from the 3,6-dipivaloylated β-D-glucoside and the β-chacotrioside moieties. The 3,6-dipivaloylated spirostanyl β-D-glucosides showed moderate to good cytotoxic activity against HL-60, but no significant cytotoxicity against benign blood cells. However, the cytotoxicity of spirostanyl β-chacotriosides was highly dependent on the nature of the C-ring functional groups of the steroidal aglycones. Actually, the chacotrioside-based saponins either with no functionality or bearing a hydrophobic methylene group at C-12 were the most cytotoxic ones against both HL-60 and benign blood cells. On the other hand, the incorporation of very polar functionalities and the opening of the ring C with the consequent loss of rigidity led to a significant drop in the cytotoxicity against HL-60. These results confirm that spirostanyl β-chacotriosides including very lipophilic aglycones are the most cytotoxic ones among their congeners.     

HPLC fractionation and pharmacological assessment of green tea seed saponins for antimicrobial,anti-angiogenic and hemolytic activities

Herbal medicinal products have proven to be safe, economical and effective alternatives to synthetic chemical pharmaceuticals. The green tea plant (Camellia sinensis) is of profound medicinal value due to the presence of potent bioactive constituents. The purpose of the present work is to investigate saponins from green tea seeds for potential use as anti-angiogenic, antimicrobial, and hemolytic agents. Green tea seed saponins were separated into six fractions by reverse phase HPLC. The presence of three aglycone chains in the saponins of each fraction was confirmed by acid hydrolysis. Anti-angiogenic activity was evaluated using saponin fractions at concentrations in the range of 2.5 ~ 25 μg/mL. Antimicrobial activity was evaluated by thin-layer chromatography (TLC) using E. coli; S. mutans, a zoonotic Salmonella species and the fungal strain, A. niger. Saponin fractions were more potent against E. coli (gram negative bacteria) than against S. mutans (gram positive bacteria) and strongly inhibited six strains of zoonotic Salmonella. Green tea saponins also showed potent anti-angiogenic effects. All saponin fractions exhibited hemolytic activity. Our results confirm that green tea saponins have antimicrobial, anti-angiogenic, and hemolytic activities; indicating their potential as natural pharmaceutical products.     

New hydrazone derivatives of adriamycin and their immunoconjugates--a correlation between acid stability and cytotoxicity

New N-substituted hydrazine linkers were synthesized and their hydrazone derivatives of adriamycin were prepared. These functionalized adriamycin derivatives were conjugated with a monoclonal antibody, 5E9. The release rate of adriamycin from the hydrazones and from some of the conjugates was studied, and their relationship to the IC50's of the conjugate against 5E9-positive Daudi cells was investigated.     

Statistical correlation between protein secondary structure and messenger RNA stem-loop structure

A new integrated sequence-structure database, called IADE (Integrated ASTRAL-DSSP-EMBL), incorporating matching mRNA sequence, amino acid sequence, and protein secondary structural data, is constructed. It includes 648 protein domains. Based on the IADE database, we studied the relation between RNA stem-loop frequencies and protein secondary structure. It was found that the alpha-helices and beta-strands on proteins tend to be preferably "coded" by mRNA stem region, while the coils on proteins tend to be preferably "coded" by mRNA loop region. These tendencies are more obvious if we observe the structural words (SWs). An SW is defined by a four-amino-acid-fragment that shows the pronounced secondary structural (alpha-helix or beta-strand) propensity. It is demonstrated that the deduced correlation between protein and mRNA structure can hardly be explained as the stochastic fluctuation effect.     

Exploration of the correlation between solvation dynamics and internal dynamics of a protein

Protein function is intimately related to the dynamics of the protein as well as to the dynamics of the solvent shell around the protein. Although it has been argued extensively that protein dynamics is slaved to solvent dynamics, experimental support for this hypothesis is scanty. In this study, measurements of fluorescence anisotropy decay kinetics have been used to determine the motional dynamics of the fluorophore acrylodan linked to several locations in a small protein barstar in its various structural forms, including the native and unfolded states as well as the acid and protofibril forms. Fluorescence upconversion and streak camera measurements have been used to determine the solvation dynamics around the fluorophore. Both the motional dynamics and solvent dynamics were found to be dependent upon the location of the probe as well as on the structural form of the protein. While the (internal) motional dynamics of the fluorophore occur in the 0.1-3 ns time domain, the observed mean solvent relaxation times are in the range of 20-300 ps. A strong positive correlation between these two dynamical modes was found in spite of the significant difference in their time scales. This observed correlation is a strong indicator of the coupling between solvent dynamics and the dynamics in the protein.     

Synthesis, cytotoxicity, and antitumor activity of lantadene-A congeners

Five new derivatives of the pentacyclic triterpenoid lantadene A (= 22beta-angeloyloxy-3-oxoolean-12-en-28-oic acid; 1) from the leaves of Lantana camara L. were synthesized, characterized, and screened for their cytotoxicities against four human cancer cell lines. The three most-potent compounds, i.e., 1, 4, and 6, with IC50 values in the range of ca. 20-29 microM, were further studied for their in vivo tumor-inhibitory potential upon oral administration in two-stage squamous cell carcinogenesis, using female Swiss albino mice, papilloma being induced by 7,12-dimethylbenz[a]anthracene (DMBA), and promoted by 12-O-tetradecanoylphorbol-13-acetate (TPA). The results are discussed in terms of structure-activity relationship.     

Further study of the correlation between na-pump activity and membrane chemosensitivity

Using internally dialyzed neurons of Helix, we have examined the effects of sodium-pump activity and intracellular ATP concentration on transmembrane currents induced by acetylcholine (ACh) and gamma-aminobutyric acid (GABA). We also report on the effects of pump activity and levels of intracellular ATP on binding by Helix ganglia of 3H-alpha-bungarotoxin (3H-alpha-BT) and 3H-GABA. Both ouabain-containing and potassium-free solutions depressed the neurotransmitter-induced transmembrane current of one type of dialyzed neurons. An increase in the intracellular ATP concentration led to a depression of ACh-induced currents and to the disappearance of the blocking effect of ouabain on these currents. Intracellular ADP had a similar but smaller effect on transmitter-induced currents, and intracellular AMP was ineffective. The depressing effect of internal ATP on ACh-induced currents was absent in the presence of an inhibitor of membrane phosphorylation (dinitrophenol). The binding of tritium-labeled alpha-BT and GABA to the membranes was depressed by both ouabain-containing and K-free solutions and also by compounds (theophylline and NaF) which increase the levels of intracellular ATP. The results suggest that the Na pump modulates the affinity of ACh and GABA membrane receptors by the regulation of the phosphorylated state of membrane receptors.