Kumar Meena*., Pronob Das1., Md. Shahbaz
*Central Inland Fisheries Research Institute, Barrackpore,
Kolkata, 700 120
1. Central Institute of Fisheries Education, Mumbai, 400 061
2. Directorate of Coldwater Fisheries Research, Bhimtal, 263
author: Dharmendra Kumar
* Email : firstname.lastname@example.org
are naturally occurring linear unbranched homopolysaccharide that
contain only glucose as structural components, which are linked with
glycosidic bonds. In nature Beta-glucans
are wide spread and the most common sources are
derived from the cell wall of baker's yeast Saccharomyces
cerevisiae and Echinaceae members. Beta
(1,3) and Beta (1,4) glucans are extracted from the bran of some
grains such as oats and barley, and in small degree from rye and
wheat. Other sources include some types of seaweed and various
species of mushrooms such as Shiitake, and Maitake. They are
constituents of some of the pathogenic bacteria (Pneumocystis
carinii, Cryptococcus Neoformans) and members of Rhizobiaceae and
fungi (Agaricus subrufesuns). There are
soluble and insoluble Beta-glucans
and research has shown that insoluble (1,3/1,6)
Beta-glucan, has greater biological activity than that of its soluble
Basically there are two types of glucan molecules a-glucan
dextran with 1,6; starch with a (1,4) and a
(1,6) glycosidic bonds) and Beta-glucan
(cellulose with Beta (1,4); zymosan with Beta (1,3);
laminarin with Beta (1,3) and Beta (1,6), lichenin with Beta (1,3)
and Beta (1,4) glycosidic bond).
are known as "biological response modifiers" because of
their ability to activate the immune system 16.
They make the immune system work better without becoming overactive,
lower elevated levels of LDL cholesterol, help in wound healing,
prevent infections, enhance resistance against infectious pathogens
and act as an adjuvant in the treatment of cancer in human, fish and
animals. Beta-glucan is not an
essential nutrient for human or fishes so there are no deficiency
disease that may occur. Beta=-glucans are
recognized as safe and non-toxic with no side effects and if so rare,
occasionally an allergic reaction has been reported in human.
Commercially they are available under different names such as
Macrogard, Leucogard, EcoActiva used for fish feed supplementation,
yeast glucan Glucasan used as food supplements for human were as
Glucaferm used in face and skin creams. The dosage form is available
as capsules, topical cream, and injectables, were as in case of
fishes the dosage is mixed with the feed.
are a heterogeneous group of glucose polymers, consisting of a
backbone of Beta (1,3) linked
Beta-D-glucopyranosyl units with Beta
(1,6)linked side chains of varying distribution and length.
Beta-Glucans derived from different
sources have some differences in their structure. Oat and barley
Beta-glucans are linear with Beta
(1,4) and Beta (1,3) linkages.
have short Beta (1,6) linked branches
from Beta (1,3) backbone. Yeast
Beta-glucans have Beta
(1,6) branches further with additional Beta
(1,3) regions2. The Beta
(1,3) linked glucan tends to form long chain that winds around
themselves resembling a helix were as the Beta
1,4 linked glucan is a linear molecule like a lying out a chain, flat
and straight. These structural differences can trigger difficulties
in there extraction and on their activity such as larger molecular
weight glucans activate leukocytes, stimulating their phagocytic,
cytotoxic, and antimicrobial activities, and production of ROS. Low
molecular weight glucans have less cellular effects been as very
short glucans are considered to be inactive2. The
differences between Beta-glucan
linkages and chemical structure are significant in regards to
solubility, mode of action, and overall biological activity.
Role of Beta-glucans in
are chemical compounds that activate white blood cells (WBC) and may
deliver fish and animals more resistant to infections pathogens.
Immunostimulants have been used as feed additives from past many
years in aquaculture sector and imagining modern aquaculture with out
the use of injectable vaccines against different pathogens causing
diseases is impossible. Beta-glucans is an important immunostimulant
among which yeast Beta-glucan has been widely used in aquaculture
sector. They are found to be highly beneficial in reducing the
mortality due to opportunistic pathogens in juvenile fish also, in
preventing viral diseases, in enhancing disease resistance to
parasites and farmed shrimp, in increasing the efficacy of
anti-microbial substances and vaccines19.
feed supplementation with both natural and commercial Beta-glucans
has shown improvement in health, growth and general performance of
different animal groups, including farmed shrimp, fish and other land
animals. Fish growth has been enhanced with the use of (EcoActiva) a
commercially available Beta-glucan
orally in Pink snapper4; Beta-glucan
in Rohu15; Beta (1,3) glucan
in Large yellow croaker1. Beta (1,3)
glucan enhanced the protection in case of yellow croaker against
Vibrio harveyi1, Beta (1,3)
yeast glucan against Aeromonas hydrophila in Asian catfish14.
Beta (1,3) glucan from Saccharomyces
cersvisiae along with bacterial LPS (Lipopolysaccrides)
induced resistance against Aeromonas hydrophila in carp27:
Beta (1,3) glucan against Edwardsiella
tarda in Rohu24, yeast Beta
(1,3) against white spot syndrome17 when injected
intramuscularly and Beta-glucan from
Schizophyllan against RV-PT virus10 in Kuruma
Shrimp. Many Scientific experimental reports have shown that
Beta-glucan as feed supplement enhance
the survival rate against White Spot Syndrome in Black tiger
Shrimp8,3 and yeast Beta (1,3,)
and Beta (1,6) glucans as an adjuvant in Atlantic salmon23,
Beta (1,3) glucan in Atlantic Salmon
yellowtail12 and mushroom glucan in Catla11
when injected intaperitoneal. Reports with enhanced antibody response
with the use of mushroom glucan in Catla11, Beta
(1,3) and Beta (1,6) glucan in Asian catfish14, and
Beta (1,3) glucan in Rohu25
are available. Effect of Beta-glucan in
enhancing resistance to pathogen was studied in immunocompromised
fish. Feeding Beta (1,3) glucan to
aflatoxin immuno compromised rohu (Labeo Rohita)
significantly enhanced non-specific immunity against Edwardisella
tarad24,25 and in Nile tilapia against
S. iniae8. Supplementation of commercially
available Yeast and yeast cell components (YYS) containing
Beta-glucan in feed showed no effects on
the growth, survival, resistance and protection against E.
ictaluri in channel catfish in juvenile Nile tilapia against S.
iniae and against E.tarda and S. iniae26,21
respectively. Apart this reports with Beta-glucans
enhancing phagocytic activity, haemagglutination, blood leucocyte
number, antibod response, lysozyme and ROS production in fishes when
supplemented in the feed are available.
Receptors of Beta-glucans
the discovery of Toll- like receptors (TLR) or pattern recognition
receptors immunostimulants has gained tremendous importance in
aquaculture sector. These receptors bind to a wide range of
pathogens. Beta-glucan receptors were
first identified on the surface of monocytes with the phagocytic
receptor for particulate activators of the alternative complement
pathway5. Adaptive immunity depends on receptors that
identify antigenic patterns to which the host has been exposed
earlier. But innate immunity relies on genetically predetermined
pattern recognition receptors (PRRs) that recognize biomolecules
(carbohydrates, lipids, and proteins) specific to microorganisms and
not to host20. There are four different types of receptors
identified to which Beta-glucan binds
they are scavenger receptor (SR), complement receptor 3 (CR),
Dectin-1 (βGR), Toll-like receptors (TLR2/6).
They all are involved in innate response as well as adaptive
response (βGR and TLR2/6)6.
SR may bind to anionic Beta-glucans
(sulphated Beta-glucans either made
chemically or found in certain algae). Dectin-1 (βGR) is expressed
on cells of the monocyte, neutrophils and recognizes carbohydrates
containing Beta (1,3) and Beta
(1,6) glucan linkages7. CR3 is highly expressed on
neutrophils, monocytes, and NK cells and less on macrophages20.
It is considered as major Beta-glucan
receptor. Lactosylceramide is a glycosphingolipid found on leucocytes
and endothelial cells. It binds to Beta-glucans
associated with production of reactive oxygen species (ROS).
Toll-like receptors are used by fungal glucans and zymosan22.
Mode of action of Beta-glucans
are thought to mediate their effects via interaction with
membrane receptors on macrophages, neutrophils, and NK cells.
Macrophages play a critical role in all phases of host defense that
is both in innate and adaptive immune responses in case of an
infection when pathogen crosses an epithelial barrier; it is affected
by phagocytosis of macrophages and digested by lysosomal enzymes
released from them. macrophage function is determined by lysosomal
enzymes and phagocytic activity. When the receptors are engaged with
the Beta-glucans , the cells become more
active in engulfing, killing and digesting bacteria and
simultaneously they secrete signal molecules cytokines (IL-1, IL-6,
IL-8, IL-12, TNF- β) which stimulate the
formation of new white blood cells and other inflammatory mediators
(NO and H2O2). Thereby activation of macrophage
functions by Beta-glucans increases host
immune defense. Animals with specific immune mechanisms and
non-specific defence (Fish), the activated phagocytes produce
cytokines molecules which can activate antibody-producing white blood
cells (B and T-cells), and enhances the efficacy of the vaccines19,13
General Application of
have various applications as an immunostimulant in human and animals.
coronary heart disease risk. Used in chronic
fatigue syndrome, physical and emotional stress chemotherapy or
radiation treatment. Used orally for colds, flu, allergies,
hepatitis, lyme disease, asthma, ear infections, aging, ulcerative
colitis and crohn's disease, fibromyalgia, rheumatoid arthritis, and
multiple sclerosis. Beta-glucans are used for dermatitis, eczema,
wrinkles, bedsores, wounds, burns, diabetic ulcers, and radiation
burns. They are used for treating and reducing cancer and act an
adjuvant. Used as an immunostimulant in patients with AIDS-related
disorders. They are used as a food additive in products such as salad
dressings, frozen desserts, sour cream, and cheese spreads. They
smoothens blood sugar level and provides a low insulin response after
a meal. The have cholesterol-lowering properties. They are used in
cosmetics and for other skin disorders.
Beta-glucans have immense potential to increase the growth and
survival rate in fishes when either injected orally, intramuscularly
or supplemented with the feed to provide resistance to disease and
protection against infectious pathogens. Beta-Glucan
acts as immune system activator and cell response modifier. Dosage
requirement plays an important role in providing protection against
pathogen, so there is a need to design the exact dosage required to
provide resistance and protection as it is dose dependent and over
dosage may show adverse effect. Though different sources of
Beta-glucan have been used to stimulate
immunity in fishes but still Beta-glucans from chrysolaminaria,
lentinan etc are yet to be explored further for aquaculture sector.
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