Chemical characterization and complement modulating activities of an arabinogalactan-protein-rich fraction from an aqueous extract of avocado leaves.

The aim of this study was to chemically characterize an arabinogalactan-protein-rich fraction (FRAGP) obtained from an aqueous extract of avocado leaves and investigate its effects on the classical pathway of the complement system. The FRAGP contained 4.6% ±â€¯1.8%, 22.5% ±â€¯4.9%, and 76.7% ±â€¯8.8% of total protein, arabinogalactan-protein, and carbohydrates, respectively. Arabinose and galactose were the main monosaccharide constituents. FT-IR and NMR data, together with linkage analyses, indicated the presence of a structure that included a (1 → 3)-linked ß-D-Galp main chain, mainly substituted at O-6 by Gal and Ara residues, which was characteristic of a type II arabinogalactan. The effect of FRAGP on the classical pathway of complement system was examined by a hemolytic fixation test and comparing with heparin, which was used as a control for inhibition. With pre-incubation, the IC50 of FRAGP was 1.90 ±â€¯1.1 µg/mL, which was similar to that of heparin (IC50 = 2.90 ±â€¯0.3 µg/mL). Without pre-incubation, the IC50 values were 18.6 ±â€¯3.7 and 8.0 ±â€¯4.1 µg/mL for FRAGP and heparin, respectively. Collectively, these results suggested that FRAGP has an inhibitory effect on the classical pathway of the complement system.

Modulating Effects of Arabinogalactans from Plant Gum Exudates on Human Complement System.

Gum arabic and cashew nut tree gum exudate polysaccharide (CNTG) are plant polysaccharides composed of galactose and arabinose known as arabinogalactans (AGs). Although these fractions are used in food and pharmaceutical industry, cases of allergic reactions were described in clinical reports. As AGs were reported as modulators of the classical (CP) and alternative pathways (AP) of complement system (CS), in the present work, we investigate whether gum arabic and CNTG have an effect on both CS pathways. The complement fixation tests were performed with (CP-30 and AP-30) and without pre-incubation (CP-0 and AP-0). For CP-30, CNTG and gum arabic (833 µg/ml) showed a reduction of 28.0% (P = 0.000174) and 48.5% (P = 0.000143), respectively, on CP-induced haemolysis. However, no effect was observed for CP-0 in the CP-induced haemolysis. For AP-30, both CNTG and gum arabic (833 µg/ml) showed 87% reduction on the CP-induced haemolysis, with IC50 values of 100 and 7 µg/ml, respectively. For AP-0, a reduction of 11.3% for gum arabic and no effect for the CNTG on the CP-induced haemolysis were observed. These results suggested that gum arabic and CNTG could be acting as activators of the CS. Thus, this effect on the CS, especially on the AP, which accounts for up to 80-90% of total CS activation, indicates that both fractions may be harmful because of their potential pro-inflammatory action. Considering that CS activation induces inflammatory response, further studies confirming this immunomodulatory effect of these fractions are required to insure their safe use.

Pectinas de plantas medicinais: características estruturais e atividades imunomoduladoras / Pectins of medicinal plants: structural characteristics and immunomodulatory activities

RESUMO As plantas medicinais apresentam várias propriedades terapêuticas, as quais estão relacionadas com a presença de compostos bioativos. Dentre os compostos, destacam-se as pectinas, que compreendem um grupo de polissacarídeos ácidos de relevante importância medicinal e nutracêutica. As pectinas são formadas por unidades de ácido galacturônico, unidas por ligação do tipo α-(1→4), sendo classificadas em homogalacturonanas e ramnogalacturonanas tipo I (RG-I) e tipo II (RG-II). Outros polissacarídeos constituídos por arabinose e/ou galactose têm sido isolados em associação com polissacarídeos pécticos, como as arabinogalactanas (AG) (tipo I e tipo II). As AG-II podem estar associadas a proteínas, denominadas de arabinogalactana-proteínas (AGPs). Inúmeros relatos demonstram que as pectinas, bem como as AG e AGPs, podem atuar como moduladores do sistema imunológico, sendo, por isso, consideradas modificadores da resposta biológica. A imunomodulação pode estar relacionada tanto com a atividade de macrófagos quanto com as vias do sistema complemento. Em geral, os polissacarídeos provocam um estímulo da atividade fagocitária; no aumento da produção de espécies reativas de oxigênio e da secreção de citocinas pró-inflamatórias. Em relação ao sistema complemento, os polissacarídeos podem modular tanto a via clássica como a via alternativa. A presente revisão tem como objetivo principal descrever os aspectos estruturais de pectinas e suas atividades biológicas relacionadas à modulação do sistema imune. Utilizando literatura específica, estão descritas informações de 29 espécies de plantas medicinais, que apresentam como constituintes pectinas, arabinogalactanas e/ou AGPs, correlacionando suas propriedades terapêuticas com as atividades biológicas associadas ao sistema imune. Na maioria dos casos descritos na literatura, é difícil determinar como as características estruturais específicas podem estar envolvidas na modulação da atividade de macrófagos. Porém, em relação à modulação da atividade do sistema complemento fica sugerido que a presença de estruturas tipo AG-II contribuiria mais significativamente para esta atividade. Entretanto, os possíveis mecanismos de modulação de pectinas, AGs e AGPs sobre a atividade de macrófagos e/ou sobre o sistema complemento ainda não estão totalmente esclarecidos, mesmo assim, estes polímeros podem ser considerados potenciais candidatos para estudos que visam ao desenvolvimento de novos agentes terapêuticos com propriedades moduladoras benéficas para o sistema imunológico.

ABSTRACT Medicinal plants have many therapeutic properties that are related to the presence of biologically active compounds. Pectins, a group of acid polysaccharides that have relevant medicinal and nutraceutical properties, are an example of such biological compounds. Pectins contain a main chain with galacturonic acid units that are α-(1→4) linked; they can be classified into homogalacturonans and type I and type II rhamnogalacturonans (RG-I and RG-II). Other polysaccharides containing arabinose, galactose, or both have been isolated in association with pectin-type polysaccharides are known as arabinogalactans (AGs, type I and type II). Arabinogalactan-proteins (AGPs) comprise AG-II associated with proteins. Several studies have reported that pectins, as well as AG and AGPs, can act as modulators of the immune system and can therefore be considered biological response modifiers. The immunomodulation is related to the activity of macrophages as on the complement system pathways. In general, polysaccharides cause stimulation of phagocytic activity, increase production of reactive oxygen species and secretion of pro-inflammatory cytokines. Polysaccharides can modulate the classical and alternative complement pathways. The aim of this review has to describe the structural aspects of pectins and their biological activities related to the modulation of the immune system. Using literature, we reported data of 29 medicinal plant species, which present as constituents pectins, arabinogalactan and/or AGPs, correlating their therapeutic properties with biological activities associated to the immune system. In most cases described in the literature, it is difficult to determine how the specific structural characteristics can be involved in modulation of macrophage activity. However, with respect to the modulation of the activity of the complement system is proposed that the presence of AG-II-type structures would contribute most significantly to this activity. The possible mechanisms of modulation of pectins, AGs and AGPs on macrophage activity and/or the complement system are not yet fully clear, even if, these polymers can be considered potential candidates for studies aimed at the development of new therapeutic agents with modulatory properties beneficial to the immune system.

Effect of the native polysaccharide of cashew-nut tree gum exudate on murine peritoneal macrophage modulatory activities.

The native polysaccharide of cashew-nut tree gum exudate (CNTG) and its arabinogalactan-protein component (CNTG-AGP) were tested by using immuno-stimulant and anti-inflammatory in vitro assays of murine peritoneal macrophage activities. In the assay for immuno-stimulant activity (without previous treatment with lipopolysaccharide; LPS), CNTG increased the production of interleukin (IL)-10 and both CNTG and CNTG-AGP decreased the concentrations of IL6. When the macrophages were incubated in the presence of LPS and CNTG a decrease in the levels of nitric oxide (NO(·)) and IFN-γ was observed. The results could explain the popular use of CNTG as an anti-inflammatory. In addition, CNTG is the main component of the cashew-nut tree gum exudate, which has been considered a versatile polymer with potential pharmaceutical and food industry applications. These data may contribute to the study of the immunomodulation activity of plant polysaccharides, as well as encourage future experiments in the field of cashew-nut tree gum exudate applications.