Contents lists available at ScienceDirect Carbohydrate Polymers journal homepage: www.elsevier.com/locate/carbpol Role of acemannan O-acetyl group in murine radioprotection Sumit Kumar ⁎ , Raj Kumar School of Life Science, Jawaharlal Nehru University, New Delhi, 110067, India ARTICLE INFO Keywords: Acemannan Radioprotection Acetylated polysaccharides Immunomodulation Deacetylated polysaccharides Aloe vera ABSTRACT Present study was designed to investigate the role of acemannan acetyl group in murine radioprotection. Acemannan, extracted from Aloe vera gel, has molecular weight of 1.02 × 10 6 Da and mainly composed of mannose (84.9%), glucose (7.2%), and galactose (3.9%), with backbone of (1→4)-linked mannose and glucose. Acemannan was over-acetylated and deacetylated to investigate the role of acetyl group. Acetylation enhances acemannan viscosity and thermal stability. Free radicals scavenging and Fenton reaction inhibition was medi- ated by acemannan acetyl and hydroxyl group respectively. Native or over-acetylated or deacetylated ace- mannan pre-treatment to mice has shown to reduce the γ-radiation-induced oxidative damage, and hemato- poietic injuries by free radical scavenging and microphage activation (secretes pro-hematopoietic factors through TLR-4) respectively. Over-acetylated acemannan has stronger effects on immunomodulation/radio- protection. In summary, acemannan acetyl-group modulates immune system, while hydroxyl-group participate in free radical scavenging, and present finding can be employed in food and pharma industries for enhancing polysaccharide bioactivity. 1. Introduction Traditionally, Aloe vera gel has been used as a major source of drug in health and well-being formulations (Kumar & Tiku, 2016a). Many health promoting effects of Aloe vera have been attributed to the par- enchyma (filet) polysaccharide (Kumar & Tiku, 2016a). Acemannan (Ac), a high molecular weight β-(1→4)-linked acetylated mannan- based polysaccharides present in the aloe vera gel known to possess antiviral, hepatoprotective, antineoplastic, and gastrointestinal prop- erties etc (Chokboribal et al., 2015; Kumar & Tiku, 2016a). However, despite numerous benefits, no study has been done to identify the bioactive moieties responsible for biological activity of Ac. Identifica- tion of the pharmacologically active moieties will certainly help in Ac quality enhancement and pharmaceutical application. In our previous study, Ac pre or post-radiation treatment to mice has shown to reduce the radiation-induced lethality (Kumar & Tiku, 2016a). Hence, present study was done to characterize the Ac bioactive functional groups along with associated molecular mechanism, re- sponsible for radioprotection of mice. 2. Material and methods 2.1. Acemannan isolation Ac (PubChem CID=72041) was extracted from fresh Aloe barba- densis Miller leaves (Kumar & Tiku, 2016a). Full-size mature aloe leaves were harvested from university botanical garden; washed in running tap water for 10 min and further kept in distilled water for 30 min at 4 °C to drain-out anthraquinones rich sap from end portion. Afterword rind was pealed out with yellow extrude, colorless parenchyma was collected and processed for Ac extraction as detailed in Fig. 1. 2.2. Chemical modification of acemannan (Ac) Ac was over-acetylated as described previously (Kumar, Ganure, Subudhi, & Shukla, 2014). Briefly, 1 g dried Ac was mixed with 50 ml of distilled water. The pH was adjusted to 8.5 with 1 M NaOH. Following, drop wise chilled acetic anhydride (40 ml) was added at continues in- terval and stir for 2 h at 25 °C (pH:8-8.5 maintained using 10 N NaOH). Following, mixture was cooled, and neutralized (pH 7) with 10 M HCl to terminate reaction. The over-acetylated acemannan (O-A-Ac) was precipitated using 100% ethanol (3:1 v/v), washed twice with distilled water and freeze dried. The degree of acetylation was determined by titration. https://doi.org/10.1016/j.carbpol.2018.12.003 Received 5 May 2018; Received in revised form 21 October 2018; Accepted 3 December 2018 ⁎ Corresponding author. E-mail address: sumit92_sls@jnu.ac.in (S. Kumar). Carbohydrate Polymers 207 (2019) 460–470 Available online 06 December 2018 0144-8617/ © 2018 Elsevier Ltd. All rights reserved. T