Propolis has attracted researchers’ interest in the last decades because of several biological and pharmacological properties, such as immuno modulatory, anti microbial, anti-inflammatory, antioxidant, among others (Bankova et al., 2000). Besides, propolis-containing products have been intensely marketed by the pharmaceutical industry and health-food stores (Banskota et al., 2001). The ethnopharmacological approach, combined with chemical and biological methods, may provide useful pharmacological leads. Thus, this review aimed to discuss its chemical composition and plant sources as well as to discuss some mechanisms of action of this bee product on the immune system and against tumor cells.
Propolis is a resinous material collected by bees from bud and exudates of the plants, which is transformed in the presence of bee enzymes. Its color varies from green, red to dark brown. Propolis has a characteristic smell and shows adhesive properties because it strongly interacts with oils and proteins of the skin. In general, propolis in natura is composed of 30% wax, 50%resin and vegetable balsam, 10% essential and aromatic oils, 5% pollen, and other substances (Burdock, 1998).
Etymologically, the Greek word propolis means pro, for or in defence, and polis, the city, that is “defence of the hive”. Bees use it to seal holes in their honeycombs, smooth out internal walls as well as to cover carcasses of intruders who died inside the hive in order to avoid their decomposition. Propolis also protects the colony from diseases because of its antiseptic efficacy and antimicrobial properties (Salatino et al., 2005).
After its administration to mice or to humans propolis does not seem to have side effects (Kaneeda and Nishina, 1994; Sforcin et al., 1995, 2002b; Jasprica et al., 2007). According to Burdock (1998) propolis is non-toxic, and its DL50 ranges from 2 to 7.3 g/kg in mice. This author suggested that the safe concen-tration for humans could be 1.4 mg/kg and day, or approximately 70 mg/day. After treatment of rats with different concentrations of propolis (1, 3 and 6 mg/kg/day), different extracts (water or ethanol) and varying the time of administration (30, 90 and 150 days) no significant alterations in total lipids, triglycerides, cholesterol, HDL-cholesterol concentrations, nor in AST and LDH specific activities were observed (Mani et al., 2006). The body weight of rats was measured in all these protocols, and propolis administration did not induce alterations in their weight. Cuesta et al. (2005) have not observed either mortality or growth rate alteration after daily intake of propolis in the diet during 6 weeks.
Although few in number, some cases of propolis allergy and contact dermatitis have been reported (Hausen et al., 1987; Hegyi et al., 1990; Silvani et al., 1997; Callejo et al., 2001), differently from the common allergy to honey, which contains allergens derived from flowers. Beekeepers usually show sensitivity to propolis (Rudeschko et al., 2004; Gulbahar et al., 2005). Ethanol and water extracts of propolis possess anti-allergic action, inhibiting histamine release in rat peritoneal mast cells (Miyataka et al., 1998). However, in higher concentrations (300 g/ml), propolis directly activated mast cells, promoting inflammatory mediators release, what could be linked to allergic processes in propolis-sensitive individuals (Orsi et al., 2005b).
Propolis anti microbial property has been widely investigated, and several authors have demonstrated its antibacterial action (Grange and Davey, 1990; Kujumgiev et al., 1999; Sforcin et al., 2000; Orsi et al., 2005c, 2006b; Scazzocchio et al., 2006). Fernandes et al. (2001) investigated the antibacterial action of propolis produced by Africanized honeybees, comparing with that produced by the stingless bees (subfamily Meliponinae). Propolis produced by Partamona sp. and Melipona sp. had a similar activity to that produced by Apis mellifera.
Propolis extraction methods may influence its activity, since different solvents solubilize and extract different compounds. The most common extracts used in biological assays are ethanol, in different concentrations, methanol and water (Cunha et al., 2004). Its chemical composition is very complex: more than 300 components have already been identified, and its composition is dependent upon the source plant and local flora. Moreover, propolis composition is completely variable creating a problem for the medical use and standardization (Marcucci, 1995; De Castro, 2001).
The term “propolis” is not characterizing with respect to the chemical composition, unlike the term “bee venom” for example (Bankova, 2005a), so that the biological studies with propolis must be carried out identifying its botanical sources and chem-ical composition as well.
Propolis action on macrophages
Before the problem of propolis standardization, the greatest problem to carry out the immunological assays was to design the experimental protocols, since researchers have used differ-ent concentrations of propolis in vivo and in vitro as well as different extracts, intake period and routes of administration. Table 1 shows some assays dealing with propolis immunomod-ulatory action according to its dose, chemical composition and main components, and assay conditions.
Little was known about the immunomodulatory action of propolis until the 1990s, but in the last decade new and interest-ing articles were published, providing an important contribution to this research field.
In immunosupression models, administration of a water-soluble derivative (WSD) of propolis (50 mg/kg) to mice prevented the cyclophosphamide effects and enhanced the sur-vival rate of the animals (Dimov et al., 1991). These authors also suggested that propolis modulates the non-specific immunity via macrophage activation. Propolis (0.2-1.0 mg/ml) stimulated cytokines production, such as IL-1 and TNF- , by peri-toneal macrophages of mice (Moriyasu et al., 1994). Propolis (0.150 mg/g) was also able to modulate both in vivo and in vitro production of C1q by macrophages as well as the comple-ment receptor function either directly or via cytokines (Dimov et al., 1992). In vitro assays showed that WSD of propolis (63–1000 g/ml) inhibited the classical and alternative path-ways of the complement system (Ivanovska et al., 1995a). C3 was one of the targets of propolis action, and flavonoids and phenolic compounds were pointed out as its major anticomple-mentary compounds (Georgieva et al., 1997).
It was demonstrated that six isolated compounds of propo-lis, identified as caffeoylquinic acid derivatives, enhanced the motility and spreading of macrophages (Tatefuji et al., 1996). Exposure of macrophages to a varied number of stimuli, such as the interaction with microorganisms and their products, antibodies or complement components-opsonized antigens, phorbol miristate acetate (PMA), Con A, immune complexes, leukotrienes, chemiotactic peptide fMLP (n-formyl-methionyl-leucyl-phenylalanine), cytokines, among others, may result in further metabolic changes, such as oxygen intermediates gener-ation. The production of such reactive species appears to be one of the mechanisms by which macrophages become microbicidal.
NADPH oxidase catalyses the reduction of molecular oxygen to superoxide anion (O2−) and the burst respiratory is paralleled by a higher consumption of oxygen (Krol et al., 1995). O2− is the precursor of other reactive oxygen intermediates, including hydroxyl radical (OH•), hypochlorite (OCl−) and hydrogen per-oxide (H2O2). Oxidants produced by phagocytes may destroy important biomolecules as well as phagocyted microorganisms, and are also involved in the tissue injury associated with inflammatory diseases (Moonis et al., 1992; Brown, 1995; Babior,2000
Antioxidants are classically defined as molecules that, present in lower concentrations than biomolecules, may prevent, protect or reduce the extension of oxidative damage, such as, for example, glutation peroxidase, catalase and superoxide dismutase. Other antioxidants, such as ascorbic acid (vitamin C) and tocopherol (vitamin E) are non-enzymatic antioxidants. Thus, there is a delicate balance between the generation and destruction of oxidant agents, which may be beneficial or deleterious to the organism (Novelli, 2005).
In order to evaluate propolis effect on macrophages microbicidal action, our group carried out some works, comparing the effects of Brazilian and Bulgarian propolis. The effect of different concentrations of propolis on macrophages fungicidal action against the thermally dimorphic fungus Paracoccidioides brasiliensis, the etiologic agent of paracoccidioidomycosis, was analysed. This human mycosis is one of the most prevalently serious mycoses in Latin America and the great majority of the infected persons develop an asymptomatic pulmonary infection, although some individuals present clinical manifestations, leading to the dissemination of the disease. Clinical and experimental data indicate that cell-mediated immunity plays a significant role in host defense, whereas high levels of specific anti bodies are associated with the most severe form of this disease. Experimental models have shown the role of macrophages in the mechanisms of resistance against this fungus (Borges-Walmsley et al., 2002).
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