Part D | 22.5
562 Part D Marine Algal Biotechnology
ture decreases with the addition of alginate content
but is independent of the pectin. Specific interactions
between hydrocolloids may significantly change the
properties of hydrogels. For example, the addition of
starch, alginate, or Ä-carrageenan decreases the strength
of agar gels, while plant seed galactomannans demonstrate marked synergistic effects on the strength of agar
and Ä carrageenan gels [22.278, 290, 292].
Rheological properties of starch colloid systems
can be regulated by the addition of fucoidan [22.297].
At lower concentrations, fucoidan probably damages
the junction zones between starch macromolecules, but
these polysaccharides are not mutually excluded. By
contrast, at higher concentrations, fucoidan may induce considerable mutual exclusion through a phase
separation process. Mixed films and gels can be
prepared based on the electrostatic interaction between negatively charged phycocolloids and positively
charged chitosan or protein. For example, a combination of sodium alginate and gelatine provides synergism
in the rheological properties of the resulting mixed
gels [22.276]. Chitosan-alginate films exhibit low solubility, good tensile properties, permeability to water
vapor, and biocompatibility, which is important for
biomedical applications [22.259, 260]. The addition of
fucoidan to chitosan films increases their mechanical
robustness and elasticity, making composite chitosanfucoidan films more suitable as wound dressings than
pure chitosan films [22.298]. Ulvan-chitosan ionic complex gels are also prepared and characterized as more
stable than alginic acid (alginate)-chitosan gel under the
appropriate conditions [22.300].
22.5 Biological Activities and Medicinal Applications
Besides hydrocolloid properties, both sulfated and carboxylated algal matrix cell wall polysaccharides are
known to have various specific biological activities,
which are prerequisites of pharmaceutical and medicinal applications. Partially sulfated algal polysaccharides exhibit immunomodulatory, anticoagulant, antithrombotic, antimutagenic, anti-inflammatory, antitumor, antiprotozoal, antimicrobial, and antiviral activities [22.305]. Generally, these biological activities are
related to the structure, composition, and sulfate substitution of polysaccharide macromolecules. Among
the activities mentioned above, the immunomodulating and anticoagulant activities seem to be immediate
and, therefore, the most important for understanding the
mechanism of action. As potential anticoagulants, algal
polysaccharides are able to compete with the commonly
used heparin. Because they affect the immune system,
they may enhance antitumor, antibacterial, and antiviral
resistance. In medicaments they can be used as an active
substance if they possess the specific biological activity
necessary for curing, or as a drug carrier if they are able
to interact with an active substance (commonly small or
nonpolymeric molecules), and thus improve its activity
or provide its delivery to specific parts of the organism.
22.5.1 Immunomodulation
and Related Activities
Immunomodulation is based on the specific enhancement or suppression of the host response with the aim
to reach the desired immune effect [22.306]. This approach allows enhanced natural mechanisms of the
immune response without the use of therapeutics like
antibiotics. Immunomodulators are substances that affect the immune system. They can stimulate, suppress,
or modulate any specific part of the immune system,
including both adaptive and innate arms of the immune
response [22.307]. Immunomodulators can be classified
into three categories: (i) immunoadjuvants or specific
immune stimulants, (ii) nonspecific immunostimulants,
and (iii) immunosuppressants. Immunoadjuvants are
true modulators that select between various types and
mechanisms of immune responses. Thus, these agents
are used to design vaccines or enhance their efficacy. Nonspecific immunostimulants enhance the basic
level of immune response and are thus used for prophylactic purposes or for strengthening the impaired
immune system. Both specific and nonspecific immunostimulants activate immunity directly or indirectly
to be effective against cancer cells and various infection agents (prions, viruses, bacteria, or microscopic
Eukaryota). Therefore, antitumor, antiprion, antiviral,
antimicrobial, antifungal, or antiprotozoal activities of
algal polysaccharides are often mediated by immune
stimulation. By contrast, immunosuppressants are able
to weaken the immune response that is often applied
to reduce inflammation in various pathological states.
Sulfated algal polysaccharides (fucoidans, galactans,
etc.) may stimulate/inhibit cell immunity by activation/
inhibition of macrophages and/or other cells of the immune systems and enhance/suppress the production of
specific antibodies. Macrophages are critical in reg-
562 Part D Marine Algal Biotechnology
ture decreases with the addition of alginate content
but is independent of the pectin. Specific interactions
between hydrocolloids may significantly change the
properties of hydrogels. For example, the addition of
starch, alginate, or Ä-carrageenan decreases the strength
of agar gels, while plant seed galactomannans demonstrate marked synergistic effects on the strength of agar
and Ä carrageenan gels [22.278, 290, 292].
Rheological properties of starch colloid systems
can be regulated by the addition of fucoidan [22.297].
At lower concentrations, fucoidan probably damages
the junction zones between starch macromolecules, but
these polysaccharides are not mutually excluded. By
contrast, at higher concentrations, fucoidan may induce considerable mutual exclusion through a phase
separation process. Mixed films and gels can be
prepared based on the electrostatic interaction between negatively charged phycocolloids and positively
charged chitosan or protein. For example, a combination of sodium alginate and gelatine provides synergism
in the rheological properties of the resulting mixed
gels [22.276]. Chitosan-alginate films exhibit low solubility, good tensile properties, permeability to water
vapor, and biocompatibility, which is important for
biomedical applications [22.259, 260]. The addition of
fucoidan to chitosan films increases their mechanical
robustness and elasticity, making composite chitosanfucoidan films more suitable as wound dressings than
pure chitosan films [22.298]. Ulvan-chitosan ionic complex gels are also prepared and characterized as more
stable than alginic acid (alginate)-chitosan gel under the
appropriate conditions [22.300].
22.5 Biological Activities and Medicinal Applications
Besides hydrocolloid properties, both sulfated and carboxylated algal matrix cell wall polysaccharides are
known to have various specific biological activities,
which are prerequisites of pharmaceutical and medicinal applications. Partially sulfated algal polysaccharides exhibit immunomodulatory, anticoagulant, antithrombotic, antimutagenic, anti-inflammatory, antitumor, antiprotozoal, antimicrobial, and antiviral activities [22.305]. Generally, these biological activities are
related to the structure, composition, and sulfate substitution of polysaccharide macromolecules. Among
the activities mentioned above, the immunomodulating and anticoagulant activities seem to be immediate
and, therefore, the most important for understanding the
mechanism of action. As potential anticoagulants, algal
polysaccharides are able to compete with the commonly
used heparin. Because they affect the immune system,
they may enhance antitumor, antibacterial, and antiviral
resistance. In medicaments they can be used as an active
substance if they possess the specific biological activity
necessary for curing, or as a drug carrier if they are able
to interact with an active substance (commonly small or
nonpolymeric molecules), and thus improve its activity
or provide its delivery to specific parts of the organism.
22.5.1 Immunomodulation
and Related Activities
Immunomodulation is based on the specific enhancement or suppression of the host response with the aim
to reach the desired immune effect [22.306]. This approach allows enhanced natural mechanisms of the
immune response without the use of therapeutics like
antibiotics. Immunomodulators are substances that affect the immune system. They can stimulate, suppress,
or modulate any specific part of the immune system,
including both adaptive and innate arms of the immune
response [22.307]. Immunomodulators can be classified
into three categories: (i) immunoadjuvants or specific
immune stimulants, (ii) nonspecific immunostimulants,
and (iii) immunosuppressants. Immunoadjuvants are
true modulators that select between various types and
mechanisms of immune responses. Thus, these agents
are used to design vaccines or enhance their efficacy. Nonspecific immunostimulants enhance the basic
level of immune response and are thus used for prophylactic purposes or for strengthening the impaired
immune system. Both specific and nonspecific immunostimulants activate immunity directly or indirectly
to be effective against cancer cells and various infection agents (prions, viruses, bacteria, or microscopic
Eukaryota). Therefore, antitumor, antiprion, antiviral,
antimicrobial, antifungal, or antiprotozoal activities of
algal polysaccharides are often mediated by immune
stimulation. By contrast, immunosuppressants are able
to weaken the immune response that is often applied
to reduce inflammation in various pathological states.
Sulfated algal polysaccharides (fucoidans, galactans,
etc.) may stimulate/inhibit cell immunity by activation/
inhibition of macrophages and/or other cells of the immune systems and enhance/suppress the production of
specific antibodies. Macrophages are critical in reg-