**4. Biosynthesis of mannans**

**Source Organism Mannan type Reference** Plant *Ebenaceae* family Galactomannan [29] Plant *Arabidopsis thaliana* Mannan [57]

Plant *Caesalpinia spinosa* Kuntze Galactomannan [33] Plant *Annonaceae* family Galactomannan [29] Plant *Amorphophallus konjac* Glucomannan [58] Plant *Ceratonia siliqua* Galactomannan [33] Plant *Convolvulaceae* family Galactomannan [29] Plant *Cyamopsis tetragonoloba* Galactomannan [33] Plant *Loganiaceae* family Galactomannan [29] Plant *Senna tora* seed Galactomannan [59] Plant *Trigonella foenum-graecum L.* Galactomannan [33] Plant *Palmae* family Galactomannan [29] Plant *Picea abies* Galactoglucomannan [60] Plant *Cercis siliquastrum* Galactoglucomannan [61] Plant *Nicotiana plumbaginifolia* Galactoglucomannan [62] Yeast *Hansenula holstii* Phosphorylated mannan [63] Yeast *Rhodotorula acheniorum* Mannan [48] Yeast *Sporobolomyces salmonicolor* Glucomannan [64] Yeast *Saccharomyces cerevisiae* Mannan [65] Yeast *Meyerozyma guilliermondii* Mannan [66] Yeast Brewers dried yeast Mannan [67] Yeast *Candida utilis* Glucomannan [68] Algae *Porphyra umbilicalis* Mannan [69] Algae *Acetabularia acetabulum* Mannan [46] Algea *Charophyceae* Mannan [70] Fungus *Dactylium dendroides* Galactoglucomannan [71] Fungus *Pseudocyphellaria clathrata* Galactoglucomannan [72] Bacteria *Pseudomonas mutabilis* Mannan [56]

*ciccaronei* Mannopyronose [53]

Bacteria *Edwardsiella tarda* Mannan [55] Bacteria *Pseudomonas aeruginosa* Mannan [73] Bacteria *Brevibacillus thermoruber* Mannan [74]

Galactomannan [28,29]

Plant seeds of the family of

316 Application of Nanotechnology in Drug Delivery

Bacteria *Pseudomonas syringae pv.*

**Table 1.** Mannan producer organisms

*Leguminoseae*

Mannans are synthesized from activated nucleotide sugars such as GDP-mannose, GDPglucose, and UDP-galactose [75]. Enzymes necessary for the nucleotide sugar conversion from sucrose to GDP-mannose and UDP-galactose have been reported in planta. However, the enzyme for the formation of GDP-glucose has not been identified [76]. Golgi-localized glycosyltransferases (GTs) utilize the activated nucleotide sugars and synthesize the polymer by facilitating the formation of the specific linkage between the monomers [77,78].

The cellulose synthase-like family A (CSLA) genes are considered the best candidates to encode enzymes that polymerize the backbones of β-linked noncellulosic polysaccharides [79,80]. Experimental evidence to support this hypothesis for the CslA family came first from Dhugga et al. [81]. In this research, the first β-mannan synthase (ManS), a member of the cellulose synthase-like family A (CSLA) from GT family 2, was identified in guar seeds (CtManS in Cyamopsis tetragonoloba, a AtCSLA9 ortholog) including the demonstration of its in vitro ManS activity [82]. One year later, three Arabidopsis CSLA genes were expressed in Droso‐ phila Schneider 2 (S2) cells and demonstrated that the resulting CSLA proteins were capable of producing mannans when supplied with GDP-Man and glucomannans when provided with a mixture of GDP-Man and GDP-Glc [75]. CSLA genes appear to be present in all land plants, and ancestral genes with characteristics similar to CSLA sequences have been identified in a number of green algal genomes, in which they are thought to represent a homolog of the progenitor gene from which CSLA genes evolved [76]. In developing Trigonella foenumgraecum (Fenugreek) endosperm, a deep sequencing approach was used to identify genes involved in galactomannan biosynthesis [83]. This research reported a CSLA family protein involved in mannan backbone synthesis and a preference towards GDP-mannose as a donor substrate was observed from the activity assays with the heterologously expressed protein. Heterologously expressed CSLA proteins from a variety of species show mannan or gluco‐ mannan synthase activity in vitro [6,75,81,83]. Analysis of Arabidopsis CSLA mutants and over-expressing plants further confirmed that CSLA proteins function as glucomannan synthases *in vivo* [84]. Despite this progress in identifying and characterizing the enzymes responsible for galactoglucomannan biosynthesis, it is likely that other important enzymes are required, and many aspects of this process need to be better understood.

In tissues of *Arabidopsis*, that take role in tip-growth such as root hairs CSLD, (*At*CSLD2, 3 and 5) proteins were found to mediate mannan biosynthesis [85-92]. In Fenugreek, it was found that additional genes were involved in mannan biosynthesis, such as a golgi-localized mannan synthesis-related (*MSR*) gene that was observed in the fenugreek endosperm [83,93]. *Tf*MSR protein in Fenugreek and its homologs *AtMSR1* and *AtMSR2* in *Arabidopsis* were highly coexpressed with the ManS of the CSLA family. Glucomannan and ManS activity were signifi‐ cantly decreased in stems of *AtMSR* knock-out mutants [93]. While the biochemical activity of MSR proteins remains unknown, hypotheses include a role in primer synthesis to initiate mannan biosynthesis, the synthesis of oligosaccharides linked to CSLA or promoting folding, stability or activity of a mannan synthase complex [93].

Edwards et al. identified a mannan:galactosyltransferase (GalT) in *Trigonella foenum*-*graecum* [94], an enzyme that facilitates mannan *O*-acetylation. However, discovery of the involvement of a large plant-specific family of Trichome birefringence-like (TBL) proteins in *O*-acetylation of wall polymer as specific *O*-acetyltransferases suggested that this gene family encompassed a mannan *O*-acetyltransferase [95]. A highly expressed (among the 10 most abundant ESTs) homolog of *At*TBL25 in the *Amorphophallus konjac* deep sequencing database [96] revealed that this protein or the closely related *At*TBL26 could represent mannan *O*-acetyltransferase(s) in *Arabidopsis* [95].

structural support, or even cell signaling applications [103]. As a result, mechanism of release for therapeutics associated with polysaccharide-based carrier systems is provided by

Mannan as a Promising Bioactive Material for Drug Nanocarrier Systems

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The functional groups of polysaccharides such as hydroxyl and amine groups yield high aqueous solubility. However, this solubility can often be adjusted via monomer modification. For example, *O*-acetylation of glucomannan can be used to modulate the formation of

Due to the presence of various derivable groups on molecular chains, polysaccharides can be easily modified chemically and biochemically, resulting in many kinds of polysaccharide derivatives. These modifications can change the character of the polysaccharides. For instance, hydroxyl group oxidation enhances biodegradability, while sulfonation generates a heparinlike polysaccharide with increased blood compatibility [106]. Quaternization of the primary amines with various alkyl groups can be used to enhance solubility and alter bioactivity

Many polysaccharides possess innate bioactivity, particularly mucoadhesive, antimicrobial, and anti-inflammatory properties. Positively charged polysaccharides are capable of binding to the negatively charged mucosal layers through charge interactions [110-112]. For neutral or negatively charged polysaccharides, hydrogen bonding provides an alternative mechanism for mucoadhesion [113]. Nanoparticle carriers made of bioadhesive polysaccharides could prolong the residence time and therefore increase the absorbance of loaded drugs [114]. Several polysaccharides are also antimicrobial in nature, such as chitosan [115]. Other polysaccharides are known to reduce inflammation. Anti-inflammatory activity is thought to be due to binding with immune-related acute phase and complement proteins [111,116] and polysaccharides are

Nanocarriers are nanoparticle drug delivery systems that are used to deliver drugs or biomo‐ lecules. Nanocarriers are sub-micro particle structures smaller than 100 nm in at least one dimension and cover nanospheres, nanocapsules, nanomicelles, nanoliposomes, and nano‐ drugs, etc. Nanoparticle drug delivery systems have noticeable advantages. Due to the ultratiny volume of nanoparticle they can pass through the smallest capillary vessels and avoid rapid clearance by phagocytes, that lead to greatly prolonged duration in blood stream. Due to small dimensions, nanocarriers are able to cross the blood-brain-barrier (BBB) and operate on cellular level. They can easily penetrate cells and tissue gap to arrive at target organs such as spleen, spinal cord, liver, lung, and lymph. Because of the biodegradability, pH, ion and/or temperature sensibility of materials, they could show controlled release properties. They can improve the utility of drugs and reduce toxic side effects; etc. As drug delivery system, nanocarriers can entrap drugs or biomolecules into their interior structures and/or absorb drugs or biomolecules onto their exterior surfaces. Presently, nanoparticles have been widely used to deliver drugs, polypeptides, proteins, vaccines, nucleic acids, genes and so on.

In recent years, a large number of studies have been conducted on polysaccharides and their derivatives for their potential application as nanoparticle drug delivery systems [114,117-120] and among them, mannan is a very promising bioactive material for drug nanocarrier systems

intermolecular hydrogen bonds with water, thereby altering aqueous solubility [105].

enzymatic degradation [104].

known to interact with a variety of proteins.

[107-109].
