Biomedical Engineering Reference
In-Depth Information
12.5.6 Debridingagents
Debridement refers to the process of cleaning a wound by removal of foreign material and dead tissue.
Cleansing of the wound facilitates rapid healing and minimizes the risk of infection due to the pres-
ence of bacteria at the wound surface. The formation of a clot, followed by a scab, on a wound surface
can trap bacteria, which then multiply (usually evidenced by the production of pus), slowing the heal-
ing process. Although debridement may be undertaken by physical means (e.g. cutting away dead tis-
sue, washing/cleaning the wound), proteolytic enzymes are also often used to facilitate this process.
The value of proteases in cleansing tissue wounds has been appreciated for several hundred
years. Wounds were sometimes cleansed in the past by application of protease-containing maggot
saliva. Nowadays, this is usually more acceptably achieved by topical application of the enzyme
to the wound surface. In some cases, the enzyme is formulated in an aqueous-based cream, and in
others it is impregnated into special bandages. Trypsin, papain, collagenase and various microbial
enzymes have been used in this regard.
Trypsin is a 24 kDa proteolytic enzyme synthesized by the mammalian pancreas in an inac-
tive zymogen form: trypsinogen. Upon its release into the small intestine, it is proteolytically
converted into trypsin by an enteropeptidase. Active trypsin plays a digestive role, hydrolysing
peptide bonds in which the carboxyl group has been contributed by an arginine or lysine. Trypsin
used medically is generally obtained by the enzymatic activation of trypsinogen, extracted from
the pancreatic tissue of slaughterhouse animals.
Papain is a cysteine protease isolated from the latex of the immature fruit and leaves of the plant
Carica papaya
. It consists of a single 23.4 kDa, 212 amino acid polypeptide, and the purifi ed enzyme
exhibits broad proteolytic activity. Although it can be used as a debriding agent, it is also used for a va-
riety of other industrial processes, including meat tenderizing and for the clarifi cation of beverages.
Collagenase is a protease that can utilize collagen as a substrate. Although it can be produced
by animal cell culture, certain microorganisms also produce this enzyme, most notably certain
species of
Clostridia
(the ability of these pathogens to produce collagenase facilitates their rapid
spread throughout the body). Collagenase used therapeutically is usually obtained from cell fer-
mentation supernatants of
Clostridium histolyticum
. Such preparations are applied topically to
promote debridement of wounds, skin ulcers and burns.
Chymotrypsin has also been utilized to promote debridement, as well as the reduction of soft
tissue infl ammation. It is also used in some opthalmic procedures, particularly in facilitating cata-
ract extraction. It is prepared by activation of its zymogen, chymotrypsinogen, which is extracted
from bovine pancreatic tissue.
Yet another proteolytic preparation used for debridement of wounds and skin ulcers consists of
proteolytic enzymes derived from
B. subtilis
. The preparation displays broad proteolytic activity
and is usually applied several times daily to the wound surface.
12.5.7 Digestiveaids
A number of enzymes may be used as digestive aids (Table 12.9). In some instances, a single en-
zymatic activity is utilized, whereas other preparations contain multiple enzyme activities. These
enzyme preparations may be used to supplement normal digestive activity, or to confer upon an
individual a new digestive capability.
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