5.3 Chemistry of Fucoidans
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weight less than 10 kDa, medium molecular weight fucoidans have molecular weights
in the range 10–10,000 kDa, while high molecular weight fucoidans have molecular weights above 10,000 kDa. The bioactivities are strongly affected by molecular
weight; for instance, high molecular weight fucoidans have been associated with
better anticancer effects (Miyazaki et al. 2018) and low molecular weight fucoidans
offer better therapeutic enhancement and abate side effects when combined with
chemotherapy (Chen et al. 2015). Fucoidans obtained by hydrothermal treatment
of Sargassum muticum are separated into different molecular weights through fractionation which results in fractions with different sulfate and phenolics contents and
with different radical scavenging properties (Alvarez-Vinas et al. 2019). The medium
molecular weight fraction (50–100 kDa) had the highest oligosaccharide content, the
>100 kDa fraction had the highest amount of sulfates and phenolics, and this fraction
also showed highest antiradical properties, while the low molecular weight fractions
with molecular weights in the range 10–30 kDa were more toxic against cervical cancer. Furthermore, it is possible to obtain low molecular weight fucoidan from high
molecular weight fucoidan through enzyme hydrolysis. This method of obtaining
LMWF leads to better bioactivity than acid-extracted LMWF from crude (Hwang
et al. 2017; Sanjeewa et al. 2017).
The presence of sulfate groups attached to the sugars within the fucoidan polymer
chain also affects the bioactivity of fucoidan. Generally, highly sulfated low molecular weight fucoidans have better anticancer activity than unsulfated low molecular
weight fucoidan or sulfated high molecular weight fucoidan (Cho et al. 2011).
5.3.1 Degradation of Fucoidan
The biodegradation of fucoidan is important for several reasons such as production of
fractions of fucoidans with improved or varied bioactivity from the crude fucoidans,
understanding the structure of fucoidan and determining the biodegradation products
and timeframe of such degradation. There are no known enzymes in the human body
which degrade fucoidans. They are also not degraded by the enzymes present in the
intestine. However, there are different means by which fucoidan can be degraded and
then further utilized by humans for its bioactive properties.
Fucoidan is degraded by acid hydrolysis into smaller molecular weights and then
into its sugar units. Orally ingested fucoidan can be detected in the urine (Tokita
et al. 2010; Michel et al. 1996), indicating that it can withstand the conditions in
the alimentary canal and still retain its chemical structure. Fucoidan deacetylase
has been identified for partial degradation of fucoidan. This enzyme can deacetylate
fucoidan and, however, is not able to desulfate or degrade fucoidans into lower
molecular weight or fractions. That is, the enzyme activity is specific to the acetyl
and sulfate bonds on the fucoidan. This enzyme was identified in the marine bacteria
which utilized fucoidan, Luteolibacter algae H18 (Nagao et al. 2017). Such enzyme
specificity is desirable, where a fucoidan of specific degree of acetylation is required
to achieve a specific bioactivity.
99
weight less than 10 kDa, medium molecular weight fucoidans have molecular weights
in the range 10–10,000 kDa, while high molecular weight fucoidans have molecular weights above 10,000 kDa. The bioactivities are strongly affected by molecular
weight; for instance, high molecular weight fucoidans have been associated with
better anticancer effects (Miyazaki et al. 2018) and low molecular weight fucoidans
offer better therapeutic enhancement and abate side effects when combined with
chemotherapy (Chen et al. 2015). Fucoidans obtained by hydrothermal treatment
of Sargassum muticum are separated into different molecular weights through fractionation which results in fractions with different sulfate and phenolics contents and
with different radical scavenging properties (Alvarez-Vinas et al. 2019). The medium
molecular weight fraction (50–100 kDa) had the highest oligosaccharide content, the
>100 kDa fraction had the highest amount of sulfates and phenolics, and this fraction
also showed highest antiradical properties, while the low molecular weight fractions
with molecular weights in the range 10–30 kDa were more toxic against cervical cancer. Furthermore, it is possible to obtain low molecular weight fucoidan from high
molecular weight fucoidan through enzyme hydrolysis. This method of obtaining
LMWF leads to better bioactivity than acid-extracted LMWF from crude (Hwang
et al. 2017; Sanjeewa et al. 2017).
The presence of sulfate groups attached to the sugars within the fucoidan polymer
chain also affects the bioactivity of fucoidan. Generally, highly sulfated low molecular weight fucoidans have better anticancer activity than unsulfated low molecular
weight fucoidan or sulfated high molecular weight fucoidan (Cho et al. 2011).
5.3.1 Degradation of Fucoidan
The biodegradation of fucoidan is important for several reasons such as production of
fractions of fucoidans with improved or varied bioactivity from the crude fucoidans,
understanding the structure of fucoidan and determining the biodegradation products
and timeframe of such degradation. There are no known enzymes in the human body
which degrade fucoidans. They are also not degraded by the enzymes present in the
intestine. However, there are different means by which fucoidan can be degraded and
then further utilized by humans for its bioactive properties.
Fucoidan is degraded by acid hydrolysis into smaller molecular weights and then
into its sugar units. Orally ingested fucoidan can be detected in the urine (Tokita
et al. 2010; Michel et al. 1996), indicating that it can withstand the conditions in
the alimentary canal and still retain its chemical structure. Fucoidan deacetylase
has been identified for partial degradation of fucoidan. This enzyme can deacetylate
fucoidan and, however, is not able to desulfate or degrade fucoidans into lower
molecular weight or fractions. That is, the enzyme activity is specific to the acetyl
and sulfate bonds on the fucoidan. This enzyme was identified in the marine bacteria
which utilized fucoidan, Luteolibacter algae H18 (Nagao et al. 2017). Such enzyme
specificity is desirable, where a fucoidan of specific degree of acetylation is required
to achieve a specific bioactivity.