ABisabolol and Bisabolol Oxides

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Certain types of chamomile contain up to 50% (-)-a-bisabolol in the essential oil; however, in the majority of types the oxides are more abundant [55].

Three years after its isolation, the antiphlogistic activity of (-)-a-bisabolol was determined in 1954. Its constitution was elucidated in 1968 [57].

After exposing cavies to UV light, (-)-a-bisabolol decreased the skin temperature. Farnesene and a bisabolol monoxide (not defined more specifically) showed a weaker effect [65]. (-)-a-bisabolol reduced the time to heal burns just like chamazulene. Further, it showed an improved blood circulation compared to chamazulene [133]. Histological experiments proved a stimulation of epithelization and granulation by (-)-a-bisabolol and farnesene [45]. A significant anti-inflammatory effect of (-)-a-bisabolol occurred in the carrageenine-induced rat paw edema and cotton-pellet granuloma. Guaiazulene and guaiazulene-1-sulfonic acid (azulene SN) had about the same activity that bisabolol had [62]. A later study found only half the activity for (-)-a-bisabolol compared to chamazulene [63]. However, this was again revised later [60].

There is no doubt that the antiphlogistic effect of (-)-a-bisabolol was proved in the carrag-eenine-induced rat paw edema and against UV erythema of the cavy, adjuvant arthritis, yeast-induced pyrexia of the rat, and in 5-lipoxygenase and cyclooxygenase tests [3, 61].

Regarding the effect on adjuvant arthritis of the rat, a dose of 500 mg/kg (-)-a-bisabolol was equivalent to 1.5 mg/kg of prednisolone. Even a dose of 2000 mg/kg bisabolol is far below the toxic dose and shows strong antiphlogistic activity. Protective properties of (-)-a-bisabolol on skin were tested in erythemae of cavies, comparing with salicylamide. After peroral administration, (-)-a-bisabolol weakly inhibited the development of an erythema. An increase of the dosage was limited because 2000 mg/kg was toxic for cavies. So the toxic dose of bisabolol was smaller for cavies than for rats.

Since percutaneous application of (-)-a-bisabolol showed inhibition of erythemae, the substance penetrated skin well [61].

Ammon proved that (-)-a-bisabolol was capable of inhibiting both 5-lipoxygenase and cycloox-ygenase. Anti-oxidative activity was not observed, in contrast to chamazulene and ethanolic aqueous extracts [110]. In the peroxidation assay, even a propyleneglycol extract did not have any anti-oxidative effect [110].

(-)-a-bisabolol had antipyretic activity against yeast-induced pyrexia of the rat. The fever was reduced by 1.5°C for 2 hours after applying 2000 mg/kg (-)-a-bisabolol perorally [18]. The maximum effect was delayed compared with phenacetine [61].

(-)-a-bisabolol also decreased the production of mucopolysaccharides in cell cultures. The cells were obtained from embryonic spine tissue of mice and from fibroblast cultures.

A report published in 1979 mentioned that "a-bisabolol" (isomer not specified) inhibited the incorporation of radioactive sulfate into the proteochondroitine and protokeratane sulfates in calf cornea in vitro. At a concentration of 10-4 M, a-bisabolol inhibited the incorporation by 15%. A higher dose of 10-3 M resulted in 58% inhibition, which is comparable with well-known antiinflammatory agents [29].

Several investigations were undertaken to study if (-)-a-bisabolol could be substituted by the (+)-isomer found in Populus balsamifera or by the synthetic racemate [55, 60, 61]. The levogyrate form from chamomile oil proved to be twice as antiphlogistic as the racemate and the dextrogyrate form isolated from the oil of poplar buds. Interestingly, the racemate is weaker than expected, taking both (-)-a-bisabolol and (+)-a-bisabolol into account. The authors ascribe this "to the racemization" [61]. This does not make much sense except if they meant to say that the synthetic bisabolol they used actually was a mixture of all four stereoisomers; apart from that, they state that it did contain 23% of the nonnatural isopropenyl isomer with unknown therapeutic efficiency.

Farnesol and bisabolol oxides A and B were also tested, as well as the commercial Dragosantol, a mixture of racemic synthetic a-bisabolol isopropylidene and isopropenyl isomers.

The test results, summarized in Table 11.2 [61], show that bisabolol oxide B (the main constituent of "Argentinian" chamomile) and bisabolone oxide (the main constituent of "Turkish" chamomile) had only half the activity that (-)-a-bisabolol had. Bisabolol oxide A (the main constituent of "Egyptian" chamomile) had about a third and Dragosantol a quarter of the activity of (-)-a-bisabolol.

11.1.2.2.1 Protective and Curative Effect on Ulcers of (-)-a-Bisabolol and Protective Effect against Acetylsalicylic Acid The traditional use of chamomile for gastro-intestinal diseases led to tests of (-)-a-bisabolol in different animal ulcer models. The substance showed activity [101] especially in the case of ulcus ventriculi [27, 71, 102, 120].

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