Lucimara M.C. Cordeiro

Polysaccharides from prunes: Gastroprotective activity and structural elucidation of bioactive pectins

Prunes are the dried fruits from Prunus domestica. After the purification steps, two homogeneous polysaccharides were characterised, SF-50R and SF-50E and contained Ara:Gal:Rha:GalA in 47.8:31.5:10.7:10.0 and 39.6:50.3:5.1:5.0 molar ratios, respectively. Methylation analysis and (13)C NMR spectroscopy indicated that both fractions are constituted by rhamnogalacturonans with type I arabinogalactans as side chains, differing mainly in the proportions of the rhamnogalacturonan backbone, in the length of the (1→4)-β-galactan chain and in the proportion of the arabinan side chain. Crude water extract (PWH) and fraction SF-50E were evaluated for their gastroprotective properties against ethanol-induced acute gastric lesions in rats. Oral administration of PWH (3 and 10mg/kg) reduced the gastric lesion area by 67±11% and 60±12%, respectively, while fraction SF-50E (10 and 30mg/kg) inhibited the lesion area by 84±12% and 83±12%, respectively. These results indicated that prunes polysaccharides act as gastroprotective agents in rats.

Structure and antiviral activity of arabinogalactan with (1→6)-β-D-galactan core from Stevia rebaudiana leaves.

Cell wall polysaccharides from leaves of Stevia rebaudiana were extracted successively with water and with aq. 10% KOH. After the purification steps, homogeneous fractions (SFW-10RM and SSFK-10RM) were analyzed by sugar composition, HPSEC, methylation and (13)C NMR spectroscopy analysis. The results showed that SFW-10RM is a pectic arabinogalactan with an unusual β-(1→6)-linked D-Galp residues forming the main chain. Approximately 38% of the β-D-Galp units of the backbone carry branches on position O-3, consisting of single D-Galp units or arabinan side chains. Arabinose residues were found to occupy mostly the terminal positions in both furanose and pyranose forms and as 2-, 5- and 3,5-linked residues in these side chains. Fraction SSFK-10RM is a similar arabinogalactan, differing mainly in the relative proportions of arabinans attached to the galactan core and in the content of D-GalpA residues present in the pectic domain. The crude aqueous and alkaline extracts and homogeneous SSFK-10RM showed antiviral activity against Herpes Simplex Virus type-1 (HSV-1) in vitro.

Galactofuranose-rich heteropolysaccharide from Trebouxia sp., photobiont of the lichen Ramalina gracilis and its effect on macrophage activation.

A structural study of the carbohydrates from Trebouxia sp., the algal symbiont of the lichen Ramalina gracilis demonstrated a galactofuranan-rich heteropolysaccharide, which was predominated by (1-->5)-linked galactofuranosyl units with side-chains in position 6 on approximately 11.0% of the units. The side-chains have very complex branched structures. This polysaccharide showed cell eliciting activity on peritoneal macrophages in vitro at all concentrations tested (1-150 microg/mL), and at 150 microg/mL an increase of 60% of macrophage activation in comparison to the control group was observed. A potential role of these carbohydrates in lichen recognition process is also discussed.

Culture studies and secondary compounds of six Ramalina species.

Mycobiont isolation experiments were performed on six species of Ramalina from Brazil: R. celastri, R. complanata, R. dendriscoides, R. gracilis, R. peruviana and R. sprengelii. This study aimed to optimize the culture conditions and nutrient requirements of the selected mycobionts. The aposymbiotic R. complanta was successfully isolated from ascospores, while aposymbiotic R. peruviana was obtained from thallus fragments. In R. peruviana the production of secondary metabolites was investigated under aposymbiotical growth conditions using HPLC. When cultivated on solid medium, this mycobiont produced the typical chemosyndrome (sekikaic acid and satellite compounds), found in the voucher lichen thallus. When cultivated in liquid medium (immersed in malt yeast medium in the absence of agar), only one, the major lichen substance, sekikaic acid, was synthesized by the fungus. In addition, atranorin was formed, but was not detected in any of the voucher specimens. Red pigments were found in solid and liquid cultures. These were separated into two compounds, but could not be fully identified. R. celastri spores germinated, but did not form mycelia. R. dendriscoides, R. gracilis and R. sprengelii were not successfully cultivated in aposymbiotic conditions, although eight different culture media were tested.

Structure of an arabinogalactan from the edible tropical fruit tamarillo (Solanum betaceum) and its antinociceptive activity.

A structural characterization of polysaccharides obtained by aqueous extraction of ripe pulp of the edible exotic tropical fruit named tamarillo (Solanum betaceum) was carried out. After fractionation by freeze-thaw and α-amylase treatments, a fraction containing a mixture of highly-methoxylated homogalacturonan and of arabinogalactan was obtained. A degree of methylesterification (DE) of 71% and a degree of acetylation (DA) of 1.3% was determined by (1)H NMR spectroscopy and spectrophotometric quantification, respectively. A type I arabinogalactan was purified via Fehling precipitation and ultrafiltration through 50 kDa (cut-off) membrane. Its chemical structure was performed by sugar composition, HPSEC, methylation, carboxy-reduction and (13)C NMR spectroscopy analysis. Intraperitoneal administration of the arabinogalactan did not reduce the nociception induced by intraplantar injection of 2.5% formalin in mice, but significantly reduced the number of abdominal constrictions induced by 0.6% acetic acid, indicating that fraction has an antinociceptive effect on the visceral inflammatory pain model.

Comparative studies of the polysaccharides from species of the genus Ramalina—lichenized fungi—of three distinct habitats

Several structurally different glucans (alpha- and beta-) and galactomannans were characterized as components of four species of the genus Ramalina, namely R. dendriscoides, R. fraxinea, R. gracilis and R. peruviana. Freeze-thawing treatment of hot aqueous extracts furnished as precipitates (PW) linear alpha-D-glucans of the nigeran type, with regularly distributed (1-->3)- and (1-->4)-linkages in a 1:1 ratio. The supernatants (SW) contained alpha-D-glucans with (1-->3)- and (1-->4)-linkages in a molar ratio of 3:1. The lichen residues were then extracted with 2% aq. KOH, and the resulting extracts submitted to the freeze-thawing treatment, giving rise to precipitates (PK2) of a mixture of alpha-glucan (nigeran) and beta-glucan, which were suspended in aqueous 0.5% NaOH at 50 degrees C, dissolving preferentially the beta-glucan. These were linear with (1-->3)-linkages (laminaran). The mother liquor of the KOH extractions (2% and 10% aq. KOH) was treated with Fehlings solution to give precipitates (galactomannans). The galactomannans are related, having (1-->6)-linked alpha-D-mannopyranosyl main chains, substituted at O-4 and in a small proportion at O-2,4 by beta-D-galactopyranosyl units. Despite the different habitats of these lichenized fungi, all species studied in this investigation have a similar pool of polysaccharides.

Structure of a galactoarabinoglucuronoxylan from tamarillo (Solanum betaceum), a tropical exotic fruit, and its biological activity

Tamarillo (Solanum betaceum) is a tropical exotic fruit whose polysaccharides were extracted from the ripe pulp. After various purification steps, homogeneous fractions (designated PTW, STK-1000R and PF) were analyzed by sugar composition, HPSEC, methylation and NMR spectroscopy analysis. The results showed that the fraction PTW consisted of a linear arabinan with (1→5)-linked α-l-arabinofuranosyl units. Fractions designated as STK-1000R and PF contained galactoarabinoglucuronoxylans, with (1→4)-linked β-d-Xylp residues in the backbone, carrying branches exclusively at O-2. The polysaccharide in STK-1000R is less branched than that in the PF fraction (∼20.0% and 36.5%, respectively), with side-chains formed by (1→5)-linked α-l-Araf residues and (1→4)-linked α-d-GlcpA residues and with non-reducing end units formed by α-l-Araf, β-Arap, β-d-Galp, α-d-GlcpA and 4-O-Me-α-d-GlcpA. Intraperitoneal administration of the STK-1000R fraction in mice significantly reduced the number of abdominal constrictions induced by 0.6% acetic acid and the inflammatory phase of nociception induced by 2.5% formalin, indicating that that fraction has an antinociceptive effect on inflammatory pain models.

Unusual linear polysaccharides: (1→5)-α-L-arabinan, (1→3)-(1→4)-α-D-glucan and (1→4)-β-D-xylan from pulp of buriti (Mauritia flexuosa), an edible palm fruit from the Amazon region.

A structural characterisation of polysaccharides extracted from ripe pulp of edible buriti, an exotic tropical fruit from Mauritia flexuosa palm was carried out. After fractionation by freeze-thaw treatment of an aqueous extract (BW), a fraction containing a linear (1→5)-α-L-arabinan and a linear (1→3)-(1→4)-α-D-glucan was obtained (0.2% yield). The proportion of (1→3)- and (1→4)-linked Glcp units was 1:4. After fractionation by freeze-thaw and Fehling treatments of an alkaline extract (BK), a linear (1→4)-β-D-xylan was purified (0.6% yield). Their chemical structures were performed by sugar composition, methylation and NMR spectroscopy analysis. In addition, these results together with monosaccharide analysis of SBW and SBK are discussed in relation to literature data on polysaccharide compositions of primary cell walls of palms (commelinid monocotyledons).

Arabinan-rich pectic polysaccharides from buriti (Mauritia flexuosa): an Amazonian edible palm fruit.

Primary cell wall polysaccharides from aqueous extract of buriti fruit pulp (Mauritia flexuosa, an exotic tropical palm) were isolated and characterized. After freeze-thaw and α-amylase treatments, extracted polysaccharides were purified by sequential ultrafiltration through membranes. Two homogeneous fractions were obtained, SBW-100R and SBW-30R (Mw of 126 kDa and 20 kDa, respectively). Monosaccharide composition, methylation and (13)C NMR analysis showed that fraction SBW-100R contained a (1 → 5)-linked arabinan, branched at O-3 and O-2 positions, linked to a type I rhamnogalacturonan. Low amounts of these polymers were also present in fraction SBW-30R according to (13)C NMR analysis and monosaccharide composition. However, a high methyl esterified homogalacturonan (HG) was present in higher proportions. These results reinforce previous findings present in literature data which indicate that pectic polysaccharides are found in high amounts in primary cell walls of palms, which are commelinid monocotyledons.

Structural characterization of a rhamnogalacturonan I-arabinan-type I arabinogalactan macromolecule from starfruit (Averrhoa carambola L.)

A structural characterization of polysaccharides obtained from edible tropical fruit named starfruit (Averrhoa carambola L.) was carried out. After fractionation by freeze-thaw and Fehling precipitation, a pectic polysaccharide was obtained. It was composed of rhamnose, arabinose, galactose and uronic acid in the 5.0:72.5:12.1:10.4 molar ratios, respectively. A combination of monosaccharide, GPC, methylation and NMR analysis and enzymatic hydrolysis with endo-β-(1→4)-D-galactanase showed the presence of a rhamnogalacturonan I to which a branched arabinan and a type I arabinogalactan are attached. The arabinan moiety was formed by (1→5)-linked α-L-Araf units in the backbone, branched only at O-3 by (1→2)- and (1→3)-linked α-L-Araf units, while the type I arabinogalactan was formed by (1→4)- and (1→4,6)-linked β-D-Galp units in the backbone with (1→5)-, (1→3,5)- and (1→3)-linked α-L-Araf units as side chains.