Studies on dextran and dextran derivatives. II. Acid hydrolysis of native dextran

Abstract

synopsisThe kinetics of the depolymerization of native dextran in dilute hydrochloric acid a t different temperatures has been followed by measurements of M,, a,,, [ q ] , (Pp)''', and S. The data allow the correlation of the various parameters of the total hydrolyzate a t various degrees of depolymerization. At a first approximation the results conform to a random splitting of a statistical, branched polymer.

Linear and branched ß(1–3) d-glucans activate but do not prime teleost macrophages in vitro and are inactivated by dilute acid: Implications for dietary immunostimulation

“…In the present study, when b-glucan, curdlan and Zymosan were exposed to low pH they were unable to stimulate the chemiluminescence response in barramundi macrophages. This loss in activity may be explained by hydrolysis in the presence of acid where the Hþ ions break the connecting bonds between the polymer units [24]. Thus in vivo passage through the stomach may not simply inactivate the glucans in terms of their ability to stimulate macrophages, but may actually inhibit activation of the macrophages by PAMPs that they subsequently encountered via other routes.…”

“…The pH in the stomach following feeding fell rapidly, with the lowest pH of 1.0 recorded at about 6 h post-feeding. This is concerning as glucosidic linkages are highly susceptible to acid hydrolysis, reducing polymer chain length quite rapidly in dilute acid over a short period of time [24]. As short chain glucans have been demonstrated not only to have no stimulatory activity on mouse macrophages, but also to inhibit stimulation by longer chain glucans as the shorter chain length molecules block the receptor binding sites without activating the receptor [12], it seems extremely important to investigate the effect of the acid environment of the stomach on molecules employed as dietary immunostimulants.…”

“…Firstly, many studies were reports of fish fed glucans, with no in vitro investigation of whether the particular glucan preparation used was capable of actually stimulating or priming respiratory burst activity. Secondly, long chain sugars such as dextrans and glucans are highly susceptible to hydrolysis by dilute acids [24] suggesting that they are unlikely to survive the harsh environment of the teleost stomach, in which the pH falls to <pH 2 following feeding [25]. Finally, all of the studies to date that have reported differences in respiratory burst activity of macrophages from fish fed glucan supplements compared to control feeds without glucan supplements, have not used nutritionally equivalent control diets.…”

Carboxymethylation of dextran in aqueous alcohol as the first step of the preparation of derivatized dextrans

“…The risk of dextran degradation due to high R values, as pointed out by Antonini et al 8) led us to test R values ranging from 1.0 to 3.5. Fig.…”

“…The first and determining step in CMDBS synthesis is the carboxymethylation of dextran. The classical conditions implied the reaction of monochloroacetic acid (MCA) with the polysaccharide in water under strong alkaline conditions 1,4,8) . The degree of substitution (DS) of CMD varied with the reaction parameters as in the case of other derivatized polysaccharides such as carboxymethylcellulose (CMC), carboxymethylstarch (CMS) or carboxymethylated Leucaena Glauca seed gum (CMLG), yet with much higher DS in CM groups for the latter.…”