Preparation of enantiomeric gossypol by crystallization

Silica Gel Chromatographic Methods for Identification, Isolation and Purification of Gossypol Acetic Acid

Several cottonseed varieties are cultivated in different countries. Each variety produces a different amount of gossypol as a natural toxic compound. The rising interest in cottonseed products (oil and feed) increases the demand for establishing simple methods for gossypol detection. Silica gel-based methods are ideal for its isolation, purification, and characterization. Silica gel-based methods are variants and can be used as simple methods for tracking plants' compounds. In this study, gossypol was isolated, characterized, and purified as gossypol acetic acid in the form of yellow crystals. Methods used for its characterization were TLC, preparative TLC, silica gel column, UV/IR spectrophotometer, and HPLC (robust spherical silica gel). A comparative study between its amount in both the Egyptian and Chinese varieties was performed. Under the experimental conditions, the Egyptian's cottonseed contains 8.705 gm/kg, while the Chinese's cottonseed contains 5.395 gm/kg. The TLC used in this study proved to be fast, accurate, and inexpensive. It can be used for gossypol acetic acid evaluation and quantification. Additionally, using TLC as a pre-purification step will give a pre-judgment for the sample's purity and quality. This step will protect the expensive HPLC silica gel-based column from any unexpected impurities. During each step, the silica gel itself could be simply removed by paper filtration. Collectively, the different silica gel-based methods as well as the other used methods are recommended for better Gossypol acetic acid isolation, purification, and characterization, as well as for maintaining HPLC columns.

Gossypol--a polyphenolic compound from cotton plant

Gossypol (C(30)H(30)O(8)) is a polyphenolic compound derived from the cotton plant (genus Gossypium, family Malvaceae). The presence of six phenolic hydroxyl groups and two aldehydic groups makes gossypol chemically reactive. Gossypol can undergo Schiff base formation, ozonolysis, oxidation, and methylation to form gossypol derivatives. Gossypol and its derivatives have been the target of much research due to their multifaceted biological activities including antifertility, antivirus, anticancer, antioxidant, antitrypanosomal, antimicrobial, and antimalarial activities. Because of restricted rotation of the internaphthyl bond, gossypol is a chiral compound, which has two atropisomers (i.e., (+)- and (-)-gossypol) that exhibit different levels of biological activities. This chapter covers the physiochemical properties, analyses, biological properties, and agricultural and clinical implications of gossypol.

Relative Toxicity of Gossypol Enantiomers in Laying and Broiler Breeder Hens ,

Gossypol, a natural component of cottonseed meal, exists in positive (+) or negative (-) enantiomeric forms, and their levels and ratio could be altered by developing new genetic strains of cotton. Two experiments were conducted to determine the relative toxicity of the individual gossypol enantiomers in laying and broiler breeder hens. In the first experiment, 25 individually caged Hy-Line W-36 forty-three-week-old laying hens were fed a standard corn-soy diet supplemented with either no gossypol or the individual enantiomers at 200 and 400 mg/kg of diet for 20 d (5 hens/treatment). In the second experiment, 15 individually caged Cobb 500 fast-feathering 44-wk-old broiler breeder hens were fed a standard corn-soy-wheat middlings diet supplemented with either no gossypol or the individual enantiomers at 400 mg/kg of diet for 18 d (5 hens/treatment). In both experiments, feed intake, egg production, and egg weight were determined daily. All eggs were individually opened and scored for yolk discoloration. At the end of both experiments, several organ and tissue samples were collected for gossypol analyses. In both experiments, the addition of (+)-gossypol to the diet reduced egg production. Only laying and broiler breeder hens fed (+)-gossypol produced eggs with severe yolk discoloration (score > or = 4). Total feed intake was lower (P < 0.05) in laying hens fed the 400 mg/kg level of (+)-gossypol compared with laying hens fed the other dietary treatments. In contrast, broiler breeder hens consumed less of the diet supplemented with (-)-gossypol. In both experiments, tissue accumulation of (+)-gossypol was higher than (-)-gossypol, with the exception of bile and excreta. The results suggest that in hens the ingestion of (+)-gossypol has a greater effect on egg yolk discoloration than the consumption of (-)-gossypol.

Gossypol inhibits calcineurin phosphatase activity at multiple sites

Calcineurin, the Ca2+/calmodulin-dependant serine/threonine phosphatase is the target for the immunosuppressant drugs FK506 and cyclosporine-A. These established calcineurin inhibitors each require an immunophilin protein cofactor. Gossypol, a polyphenol produced by the cotton plant, inhibits calcineurin (IC50=15 microM), in a noncompetitive, reversible manner, and is independent of any cofactor. We found that gossypol acts by at least two mechanisms to inhibit calcineurin phosphatase activity. A calmodulin-independent form of calcineurin was less sensitive to inhibition by gossypol than native calcineurin (IC50=41 and 18 microM, respectively) indicating that gossypol may interfere with calmodulin binding. A fluorescence polarization based assay demonstrated that 100 microM gossypol reduced the affinity of calmodulin for calcineurin (from K(d)=2.4 to 250 nM). Inhibition of calcineurin phosphatase activity by gossypol could not be overcome by adding excess calmodulin or by testing the inhibition toward a calmodulin-independent calcineurin indicating that gossypol acts at a site different from the calmodulin-binding site. Gossypol decreased the affinity of calcineurin for immunosuppressant/immunophilin complexes only in the presence of calmodulin, indicating that gossypol blocks the effects of calmodulin binding to calcineurin. In addition, gossypol had a stimulatory effect on native calcineurin in the absence of calmodulin, possibly indicating a calmodulin mimetic effect. Gossypol exists in two enantiomeric forms which are reported to have different potency for cell toxicity. (+) and (-) gossypol had equivalent potency for inhibition of native and calmodulin-independent calcineurin phosphatase activity, and for inhibition of calmodulin binding. The inhibition of calcineurin by gossypol via multiple binding sites without stereo-specificity indicates that gossypol is not a specific calcineurin inhibitor.

Effect of racemic and (+)- and (-)-gossypol on the survival and development of Helicoverpa zea larvae

Gossypol is a sesquiterpene that occurs naturally in seed and other parts of the cotton plant. Because of restricted rotation around the binaphthyl bond, it occurs naturally as enantiomeric mixtures with (+)-gossypol to (-)-gossypol ratios that vary between 97:3 and 31:69. Commercial cotton varieties (Gossypium hirsutum) normally exhibit an approximate 3:2 ratio. (+)-Gossypol is significantly less toxic than (-)-gossypol to nonruminant animals; thus, cottonseed containing high levels of (+)-gossypol might be safely fed to nonruminants. Gossypol, however, is an important component in the cotton plant's defense against insect herbivores, but it is not known how cotton plants that exhibit high levels of (+)-gossypol in the foliage might be affected by insect herbivory. To address this question, 1-d-old Helicoverpa zea larvae were fed diets with 0.16, 0.20, and 0.24% racemic, (+)-, and (-)-gossypol. Larval pupal weights, days-to-pupation, and survival were adversely affected by all gossypol diets compared with the control diet. Statistical differences were determined by comparing the compounds among themselves at the three levels and between the three compounds at the same level. When the compounds were compared among themselves, no large differences were observed in pupal weights or in days-to-pupation among any of the diets. Among the three compounds, at the 0.16% level, the diet containing racemic gossypol was the most effective at reducing survival. At the 0.20 and 0.24% levels of racemic (+)- and (-)-gossypol, survival was not statistically different. The overall results indicate that (+)-gossypol is as inhibitory to H. zea larvae as racemic or (-)-gossypol, and thus, cotton plants containing predominantly the (+)-enantiomer in foliage may maintain significant defense against insect herbivory.

Relative toxicity of gossypol enantiomers in broilers

Use of cottonseed meal in poultry diets has been avoided in large part because of fear of gossypol toxicity. Gossypol exists naturally as a mixture of 2 enantiomers that exhibit different biological activities. Two experiments were conducted to determine the relative toxicity of gossypol enantiomers on broilers. In the first experiment, 3-d-old broilers were fed a standard diet containing 0, 100, 200, 300, or 400 mg of gossypol from gossypol acetic acid per kilogram of diet from 3 to 42 d of age. This form of gossypol contains both enantiomers in an equimolar ratio. Each dietary treatment consisted of 6 replicate pens of 4 birds. In the second experiment, 3-d-old broilers were divided into 15 pens of 4 birds each and fed a standard diet supplemented with either no gossypol or one of the gossypol enantiomers at 200 or 400 mg/kg of diet from 3 to 21 d of age. In both experiments, feed intake and BW gain were measured. In addition, several organ and tissue samples were collected at 21 d (experiments 1 and 2) and 42 d (experiment 1) of age and analyzed for gossypol. In experiment 1, feed consumption and BW gain were reduced (P < 0.05) at 21 and 42 d for the birds fed the highest level of gossypol. The concentration of gossypol in the heart, kidney, and plasma were equivalent at 21 and 42 d of age. In experiment 2, total feed consumption was reduced only in birds consuming (-)-gossypol, but BW gains were lower for birds fed either enantiomer. However, (-)-gossypol was more detrimental to growth than (+)-gossypol. The liver had the highest tissue concentration of both enantiomers, and accumulation of (+)-gossypol was higher than (-)-gossypol in all tissues examined. No racemization of the enantiomers was apparent in the tissues analyzed. Our results indicated that both gossypol enantiomers were toxic to broilers but that (-)-gossypol was more harmful to efficient broiler production than (+)-gossypol.

Cytotoxicity of enantiomers of gossypol Schiff's bases and optical stability of gossypolone

Optical Schiff's bases of gossypol were prepared with chiral gossypol and ethylamine. As has been similarly observed among the gossypol enantiomers, the (-)-gossypol ethylimine was more active than either the (+)-gossypol ethylimine or the racemic gossypol ethylimine against KB and MCF7 cells. Gossypolone was also observed to be more toxic than gossypol against both cell lines. All of the gossypol products tested showed comparable toxicity toward MCF7/ADR (adriblastine-resistant) cells. Attempts at producing chiral gossypolone from chiral gossypol failed because of rapid racemization. In addition, the Schiff's base derivatives of gossypolone formed with R-(+)-2-amino-3-phenyl-1-propanol could only be separated at reduced temperature, indicating that gossypolone Schiff's bases are less optical stable than gossypol Schiff's bases.

In vitro inhibitory effect of gossypol from gossypol-acetic acid, and (+)- and (-)-isomers of gossypol on the growth of Edwardsiella ictaluri

AIM

This study was conducted to evaluate the toxic effect of gossypol from gossypol-acetic acid, and (+)- and (-)-isomers of gossypol on the growth of Edwardsiella ictaluri.

METHODS AND RESULTS

Inhibitory effect of various concentrations of gossypol on the growth of E. ictaluri was determined. Bacterial recovery was performed by preincubation of bacteria in medium containing various concentrations of gossypol and subsequent activation of bacteria by inoculating on gossypol-free plates. Concentrations of racemic gossypol, (+)-gossypol and (-)-gossypol of 1.5 microg ml(-1) or higher significantly reduced the number of bacterial colonies compared with that of the control. The growth of E. ictaluri was completely inhibited on agar plates supplemented with 3 microg ml(-1), regardless of the forms of gossypol. The inhibitory effect of (+)-gossypol was higher than that of (-)-gossypol or gossypol-acetic acid. Recovery of E. ictaluri was <50% for all three forms of gossypol at concentrations of 5 microg ml(-1). Bacterial recovery remained relatively constant (6.5%) at gossypol concentrations from 10 to 100 microg ml(-1). Complete killing of E. ictaluri was not reached at gossypol levels up to 100 microg ml(-1).

CONCLUSION

Gossypol-acetic acid, and (+)- and (-)-optical isomers have anti-bacterial effect against E. ictaluri. The results suggest the action is bacteriostatic rather than bactericidal.

SIGNIFICANCE AND IMPACT OF THE STUDY

The therapeutic effect of gossypol against E. ictaluri may be useful in controlling enteric septicaemia of catfish.