Handbook of Polymers for Pharmaceutical Technologies, Biodegradable Polymers

Vijay Kumar Thakur, Manju Kumari Thakur, Vijay Kumar Thakur, Manju Kumari Thakur

• Publisher: Wiley-Scrivener
• Year: 2015
• ISBN:
  9781119041436
• Edition: 1
• Topic: Technology & Engineering
• Subtopic: Chemical & Biochemical Engineering
• Index: Technology & Engineering

Polymers are one of the most fascinating materials of the present era finding their applications in almost every aspects of life. Polymers are either directly available in nature or are chemically synthesized and used depending upon the targeted applications.Advances in polymer science and the introduction of new polymers have resulted in the significant development of polymers with unique properties. Different kinds of polymers have been and will be one of the key in several applications in many of the advanced pharmaceutical research being carried out over the globe.

This 4-partset of books contains precisely referenced chapters, emphasizing different kinds of polymers with basic fundamentals and practicality for application in diverse pharmaceutical technologies. The volumes aim at explaining basics of polymers based materials from different resources and their chemistry along with practical applications which present a future direction in the pharmaceutical industry. Each volume offer deep insight into the subject being treated.

Volume 1: Structure and Chemistry
Volume 2: Processing and Applications
Volume 3: Biodegradable Polymers
Volume 4: Bioactive and Compatible Synthetic/Hybrid Polymers

Chapter 1

Bioactive Polysaccharides of Vegetable and Microbial Origins: An Overview

Giuseppina Tommonaro^*,1, Annarita Poli¹, Paola Di Donato^1,2, Gennaro Roberto Abbamondi, Ilaria Finore¹ and Barbara Nicolaus¹

¹National Council of Research of Italy, Institute of Biomolecular Chemistry, Pozzuoli (NA), Italy

²University of Napoli “Parthenope,” Department of Sciences and Technologies, Napoli, Italy

*Corresponding author: [email protected]

Abstract

Natural products play a dominant role in the discovery of leads to develop drugs for the treatment of human diseases. In recent years, some bioactive polysaccharides isolated from natural sources have attracted much attention in the field of biochemistry and pharmacology because of their biological activities as anticarcinogenic, anti-inflammatory, immunostimulating, antioxidant agents, etc. The high potential for some of these compounds suggested that they could be developed as drugs. This chapter presents the most relevant findings on the latest research concerning bioactive polysaccharides isolated from vegetables and microbial sources.

Keywords: Exopolysaccharides, antioxidant, anti-inflammatory, bioplastic, microbial source, plants

1.1 Introduction

The bioactive compounds that are synthesized in nature, in order to protect a living organism, have been selected from a wide variety of possibilities until reaching optimal activity after several hundreds of million years. The high potential for some of these products suggested that they could play a dominant role in the discovery of lead compounds for the development of drugs for the treatment of human desease. Recently, some bioactive polysaccharides isolated from natural sources have attracted much attention in the field of biochemistry and pharmacology: polysaccharides or their glycoconjugates were shown to exhibit multiple biological activities, including anticarcinogenic, anticoagulant, immunostimulating, antioxidant, etc.

Nowadays, the increased demand for the exploration and use of natural sources for white biotechnology processes has led to a renewed interest in biopolymers, in particular, in polysaccharides both of vegetable and microbial origins. Polysaccharides are naturally occurring polymers of aldoses and/or ketoses connected together through glycosidic linkages. They are essential constituents of all living organisms and are associated with a variety of vital functions which sustain life. These biopolymers possess complex structures because there are many types of inter-sugar linkages involving different monosaccharide residues. In addition, they can form secondary structures which depend on the conformation of component sugars, molecular weight, inter- and intrachain hydrogen bondings. On the basis of structural criteria, it is possible to distinguish homoglycans and heteroglycans, if they are made up by the same type or by two or more types of monomer units; linear and branched polymers, with different degrees of branching; neutral or charged (cationic or anionic). Moreover, on the basis of their biological role, polysaccharide from vegetables can also be distinguished in structural elements, such as cellulose and xylans, and in energy-reserve polysaccharides such as starch and fructans. In the case of polysaccharides produced by microorganisms, they can be classified into three main groups according to their location in the cell: cytosolic polysaccharides, which provide a carbon and energy source for the cells; polysaccharides that make up the cell walls, including peptidoglycans, techoid acids and lipopolysaccharides, and polysaccharides that are exuded into the extracellular environment in the form of capsules or slime, known as exopolysaccharides (EPSs). Since the latter are completely excreted into the environment, they can be easily collected by cell culture media precipitation by cold ethanol after removal of cells [1]. The elucidation of the polysaccharide structures are very important to clarify the physicochemical and biological properties of these biopolymers and to attribute, and in some cases predict, their biotechnological applications. Several chemical and physical techniques are used to determine the primary structure of these molecules: chemical degradation and derivatization, combined with chromatographic methods and mass spectrometry analysis, are used to determine the sugar composition, their absolute configuration and the presence and the position of possible substituents [2].

Since polysaccharides are biodegradable materials expressing biocompatibility, they could act as versatile tools for applications in biomedical fields such as drug delivery, tissue engineering, bioadhesives, prostheses and medical devices [3–7]. These polymers present several derivable groups on molecular chains that make polysaccharides a good substrate for chemical modification, such as acetylation, sulphation, silanation or oxidation, producing many kinds of polysaccharide derivatives with additional and different properties and bioactivities. The carboxymethyl pullulan conjugated with heparin represents an example of chemical modification for tissue engineering applications. Moreover, considering the presence of hydrophobic moieties in the chain of polysaccharide, the formation of self-assembled micelles can be possible, making natural EPSs like pullulan, dextran, levan or bacterial cellulose ideal candidates for drug solubility and stability [6,8,9].

Bacterial polysaccharides present a real potential in cell therapy and tissue engineering with the advantage, over the polysaccharides from eukaryotes, that they can be totally produced under controlled conditions in bioreactors. Polysaccharides synthesized by microorganisms suggest unique properties and advantages in their exploration and are an attractive alternative of plant, algal and synthetic polysaccharides. They represent a fast renewable resource that could partially compensate the restricted mass of plant polysaccharides. Their production is a matter of days, while plants’ life cycles last for months or years, being that the production cycle is usually seasonal. Microbial polysaccharides are produced by a wide variety of microorganisms from both eukaryotic and prokaryotic groups, including cyanobacteria [10], lactic acid bacteria [11,12], and halophilic bacteria [13–16]. Other microorganisms such as yeast [17] and marine microalga [18,19] have been studied for EPS synthesis. The market price also depends on the infrastructures required for production, which can include bioreactors and maintaining asepsis [20]. The inherent costs of large-scale fermenters are significantly higher in comparison with chemical extraction processes for plant polysaccharides. Recently, the use of cheaper raw materials like agricultural waste or dairy waste has helped to reduce the cost of fermentative production [21–23].

The overall objective of this chapter is to provide information on these important biopolymers regarding applications in the field of medical industries for their pharmacological activities, including anticarcinogenic, anticoagulant, immunostimulating and antioxidant.

1.2 Anticarcinogenic Polysaccharides

Cancer is a leading cause of death in industrialized countries [24]. Although the mortality share has decreased in the last years, owing to the efforts that have been made in the search for new anticancer drugs and earlier detection, most cancers remain incurable. Chemoprevention represents a strategy used to decrease the incidence of cancer diseases in humans by inhibition of initiation step and spread of carcinogenesis and by improvement of lifestyle [25,26]. Many factors are involved in increasing the risk of cancer, including diet, exposure to radiation, environmental pollutants and tobacco use [27]. Cancer, a malignant neoplasm, is a kind of disease resulting from several causes [28]. Among these, mutations and epigenetic alterations of cancer genes promote the malignant transformation of cancer progenitor cells by disrupting key processes involved in normal growth control and tissue homeostasis [29].

Natural products play a dominant role in the discovery of lead compounds for the development of drugs to treat human diseases, including cancer, because of the variety of their chemical structures and biological activities [30]. Among natural products, polysaccharides also find their application as antitumor compounds (Table 1.1).

Table 1.1 Anticarcinogenic polysaccharides.

1.2.1 Microbial Sources

An active polysaccharide, named marinactan, was purified from the marine bacterium Flavobacterium uliginosum. Marinactan, a heteroglycan consisting of glucose, mannose and fucose (7:2:1 molar ratio), showed 70–90% inhibition of the growth of solid sarcome 180 in mice. Complete regression of the tumor was observed in some treated mice. Moreover, marinactan prolonged the survival period of mice bearing ascites sarcoma180 [31]. Previous papers described the antitumor activity of polysaccharides isolated from other microorganisms such as, for example, the β-(1→;3)-D-glucan, produced by Alcaligenes fecaelis var. myxogenes that showed a remarkable antitumor effect against sarcoma 180 solid tumor, with doses of 5 to 50 mg/Kg i.p. given once a day for 10 days [32]. Schizophyllan, a polymer isolated from the culture filtrate of Schizophyllum commune, was chemically characterized and showed to be formed by repeating units composed of three or four β-(1→;3)-linked D-glucopyranose residues to one of which is attached, through β-(1→;6)-linkage, a side chain consisting of a single β-D-glucopyranose residue. It was tested against four kinds of transplantable tumors in both ascites and solid forms. The most significant results were obtained with 0.5–10 mg/kg doses of schizophyllan on all the subcutaneously implanted tumors, i.e., sarcoma-37, sarcoma-180, Ehrlich carcinoma, and Yoshida sarcoma, accompanied by complete regressions. The treatment failed to inhibit the growth of ascites tumors or to induce prolongation of life span, with the exception of ascites sarcoma-180, moreover no inhibitory effect was observed also on Friend virus disease and spontaneous mammary carcinoma arising in Swiss mice. The mechanism of this action was considered to be host-mediated on the basis of lack of effect in in-vitro contact test [33]. A lipopolysaccharide (serratigen) and a polysaccharide (serratimannan), isolated from Serratia marcescens, red strain No. 51, were assayed for their antitumor activity against solid tumor of sarcoma-180 using ICR mice. Serratimannan showed 63% tumor inhibition and serratigen 38%, at a dose of 150 mg/kg [34].

Recently it has been reported the antitumor activity through Toll-like receptor 4 (TLR-4) of xanthan gum (XG), a complex polysaccharide produced by plant-pathogenic bacterium Xanthomonas campestris pv. Results showed that in-vitro culture with XG induced interleukin-12 (IL-12p40) and tumor necrosis factor-alpha (TNF-α) production from murine macrophages J744.1 and RAW264.7. Moreover, XG stimulated macrophages in a MyD88 mice-dependent manner and was mainly recognized by TLR-4. Oral administration of XG significantly retarded tumor growth and prolonged survival of the mice inoculated subcutaneously with B16K^b melanoma cells. The in-vivo antitumor effects of XG were also dependent on TLR-4, likewise in C3/HeJ mice, which lack TLR-4 signaling, where XG exhibited no effect on the growth of syngeneic bladder tumor, MBT-2. Results suggested that oral administration of XG could be beneficial against cancer diseases [35].

Bacteria can produce exopolysaccharides, secreting them in the surronding medium (released exopolysaccharides, r-EPS) or they can be attached to the bacterial surface (cell-bond exopolysaccharides, c-EPS). A c-EPS was isolated from the supernatant of Lactobacillus plantarum 70810. The chemical characterization revealed that it was a galactan containing a backbone of a-D-(1-→;6)-linked galactosyl, β-D-(1-→;4)-linked galactosyl, β-D-(1-→;2,3)-linked galactosyl residues and a tail end of β-D-(1-→;)-linked galactosyl residues. The c-EPS was assayed for its inhibitory effect on the proliferation of HepG-2, BGC-823 and HT-29 human cancer cell lines. Results indicated moderate antitumor activity against HepG-2 cells (56,34±1.07% of inhibition, 600 mg/mL), whereas a significant inhibitory effect was observed on BCG-823 and HT-29 (61.57±2.07% and 88.34±1.97%, respectively) [36]. Wang et al. also reported the isolation and bioactivity of two exopolysaccharides (r-EPS1 and r-EPS2) released from Lactobacillus plantarum 70810. Results showed that both r-EPSs exhibited antiproliferative effects against the human tumor cell lines Caco-2, BGC-823 and HT-29. The r-EPS2 possessed higher growth inhibition effects on the cancer cell lines used than r-EPS1. The reason could be due to the presence of sulfated group and beta glycosidic bond composition in r-EPS2 [37].

1.2.2 Vegetable Sources

Polysaccharides of vegetable origin have emerged as an important class of bioactive compounds because of their multiple biological properties, including anti-neoplastic effects.

Chemopreventive effects of plant polysaccharides (Aloe barbadensis Miller APS, Lentinus edodes LPS, Ganoderma lucidum GPS and Coriolus versicolor CPS) were evaluated using different biomarkers involved in chemical carcinogenesis. Biomarkers used for the initiation stage of cancer were: a) DNA adduct formation (B[a]P-DNA adducts); b) 8-hydroxydeoxyguanosine (8-OH-dG), representing oxidative DNA damage; and c) induction of glutathione S-transferase (GST) activity. Biomarkers for the promotion stage of cancer were: a) phorbol myristic acetate (PMA)-induced tyrosine kinase (TK) activity increase in human leukemia cells (HL-60); b) PMA-induced ornithine decarboxylase (ODC) activity e...