Plants are widely used for their therapeutic properties because they contain a large variety of chemicals that have in vivo activity in animals. Bromelain is a glycoprotein extract from the leaves and stems of pineapple that contains both protein and non-protein fractions. Bromelain has proteolytic activity, and its main function in pineapples is to break down plant tissue to soften the fruit during ripening. This increases the attractiveness of the fruit to animals and helps ensure wide dispersal of seeds. The bromelain protein fraction contains a highly active thiol proteinase (with non-specific cysteine protease activity), preferentially cleaving glycyl, alanyl and leucyl bonds. Bromelain is therefore similar in activity to the endogenous stomach enzyme trypsin. Other parts of the bromelain crude extract include phosphatises, peroxidises, cellulases, glycoproteins and carbohydrates. In aqueous solution the bromelain extract rapidly degrades through self digestion.
Bromelain is stable between pH 3.0 and pH 6.0, with an optimal pH of around pH 5.0 to pH 7.0. Once bromelain has combined with its substrate is no longer susceptible to changes in pH. Bromelain has optimal enzyme activity at a temperature of 62°C, although activity is present between around 45°C to 75°C. Cysteine acts as an activator of bromelain, and the metal ions silver and copper are inhibitors. Bromelain will break down the protein structure of most common proteins including gelatine, casein, gluten, collagen, elastin globulins, muscle fibres and albumin. The proteolytic activity of pineapple may have benefits to humans, assuming that the protein fraction is absorbed intact from the gut. The claimed benefits of bromelain include fibrinolytic, anti-thrombotic and anti-inflammatory activity, as well as immuno-modulation via the stimulation of the release of various cytokines such as tumour necrosis factor-α and interleukin-1, -6 and -8.
The absorption and bioavailability of bromelain is considered controversial because proteolytic enzymes tend to be inactivated quickly (e.g. by α2-macro-globulin (AMG) and α1-antitrypsin). The first line of reasoning that would tend to suggest it is absorbed and bioavailable in humans is based on the fact that bromelain has pharmacological action in vivo. In fact bromelain can be used as an alternative to a number of drugs including glucocorticoids, non-steroidal anti-inflammatory drugs and immuno-modulatory drugs. Presumably because it retains enzymatic activity in plasma. The second line of reasoning that would suggest that bromelain is absorbed and bioavailable is based on animal experiments that show the absorption of crude bromelain extract in rabbits may be as high as 40%. Evidence suggests that plasma anti-proteinases decrease the activity of bromelain in vivo, but do not completely remove it and that bromelain is absorbed from the gastrointestinal tract in an intact form.
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