Biomedical Engineering Reference
In-Depth Information
induce a beneficial biological activity on the host organism or on the environment can be
considered even more intriguing. This may be the case of Ulvan. Most of the positive health
effects induced by this polysaccharide are generated by the presence of sulphate groups in
its structure (Wijesekara et al., 2011). A wide list of beneficial biological effects reported by
the literature span from antioxidant (Qi et al., 2006) to anticoagulant (Zhang et al., 2008),
antitumor (Kaeffer et al., 1998) antihyperlipidemic (Yu et al., 2003) and immunomodulating
(Leiro et al., 2007) activities, proved both
in vitro
and
in vivo
.
A brief discussion about the chemical mechanisms that trigger this bioactivity can be
worth of mentioning in order to have a deeper insight on the potentiality of using this
biomaterial in biomedical applications, and possibly find the “keys” to improve its
biological activity.
2.2.1 Antioxidant activity
The research of new antioxidant from renewable natural resources able to scavenge free
radicals can represent a virtuous strategy for preventing ROS-induced diseases.
In recent years, several classes of sulphated polysaccharides have been demonstrated to
show antioxidant activity. Among them Ulvan extracted from
Ulva pertusa
is reported
to play an important role as free radical scavenger
in vitro
and displayed antioxidant
activity for the prevention of oxidative damage in living organisms (Qi et al., 2005). As
found with other sulphated polysaccharides (Wijesekara et al., 2011) the antioxidant
activity is deeply affected by the amount and distribution of sulphate groups inside the
Ulvan structure.
The possibility to increase the antioxidant activity of Ulvan can be useful according to the
envisaged application and has been successfully investigated both by increasing the degree
of sulphation through a sulphur trioxide/N,N-dimethylformamide treatment (Qi et al.,
2005) and by introducing suitable groups (acetyl and benzoyl) that can boost the activity of
the native polysaccharide (Qi et al., 2006).
2.2.2 Anticoagulant activity
Heparin, a glycosaminoglycan of animal origin containing carboxylic acid and sulphate
groups, has been identified and used for more than fifty years as a commercial
anticoagulant and it is widely used for the prevention of venous thromboembolic disorders
(Pereira et al., 2002). The heparinoid-like structure of Ulvan makes it also able to provide
anticoagulant activity. Indeed this class of polysaccharides displayed the inhibition of both
the intrinsic pathways of coagulation or thrombin activity and the conversion of fibrinogen
to fibrin (Zhang et al., 2008). The molecular weight of the polysaccharide showed an
important effect on the anticoagulant activity indicating that longer chains were necessary to
achieve thrombin inhibition.
This behavior has been found to be typical of sulphated polysaccharides of marine origins
whose anticoagulant activity has been correlated to the content and position of the sulphate
groups inside the polymer chains (Melo et al., 2004).
The importance of finding sources of anticoagulants alternative to heparin has been arising
due to the associated harmful side effects and the complex steps of purification required to
face the immunological concerns and disease transmission associated with its use (Stevens,
2008). Thus the increasing demand for a safer anticoagulant therapy could be potentially
