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Hyaluronic acid (Hyaluronan): A review



Hyaluronic acid (HA) is a high molecular weight biopolysacharide, discovered in 1934, by Karl Meyer and his assistant, John Palmer in the vitreous of bovine eyes. Hyaluronic acid is a naturally occurring biopolymer, which has important biological functions in bacteria and higher animals including humans. It is found in most connective tissues and is particularly concentrated in synovial fluid, the vitreous fluid of the eye, umbilical cords and chicken combs. It is naturally synthesized by a class of integral membrane protein s called hyaluronan synthases, and degraded by a family of enzymes called hyaluronidases. This review describes metabolisms, different physi - ological and pathological functions, basic pharmacological properties, and the clinical use of hyaluronic acid.
Veterinarni Medicina, 53, 2008 (8): 397–411 Review Article
Hyaluronic acid (hyaluronan): a review
J. N
, L. B
, P. B
, J. K
Faculty of Medicine and Dentistry, Palacky University, Olomouc, Czech Republic
Faculty of Pharmacy, University of Veterinary and Pharmaceutical Sciences, Brno,
Czech Republic
ABSTRACT: Hyaluronic acid (HA) is a high molecular weight biopolysacharide, discovered in 1934, by Karl Meyer
and his assistant, John Palmer in the vitreous of bovine eyes. Hyaluronic acid is a naturally occurring biopolymer,
which has important biological functions in bacteria and higher animals including humans. It is found in most
connective tissues and is particularly concentrated in synovial fluid, the vitreous fluid of the eye, umbilical cords
and chicken combs. It is naturally synthesized by a class of integral membrane proteins called hyaluronan synthases,
and degraded by a family of enzymes called hyaluronidases. This review describes metabolisms, different physi-
ological and pathological functions, basic pharmacological properties, and the clinical use of hyaluronic acid.
Keywords: hyaluronic acid; metabolism; toxicity
List of abbreviations
CD44 = cell surface glycoprotein; CDC37 = intracellular HA-binding protein; Da = dalton; DNA = deoxynucleotid
acid; ECM = extracellular matrix; EM = electron microscopy; GHAP = glial hyaluronate-binding protein; GIT
= gastrointestinal tract; HA = hyaluronic acid; HARE = hyaluronic acid receptor for endocytosis; HAS1, HAS2,
and HAS3 = types of hyaluronan synthases 1, 2 and 3; IHABP = intracellular HA-binding protein; IMP = integral
membrane protein; IL-1 = interleukine 1; LM = light microscopy; LYVE-1 = lymphatic vessel endocytic receptor;
MRHD = maximum recommended human dose; NS = normal saline; OA = osteoarthrosis; P-32 = protein-32;
RHAMM = receptor for hyaluronic acid mediated mobility; RHAMM/IHABP = receptor for hyaluronic acid
mediated mobility/intracellular HA-binding protein; TDLo = toxic dose low; TIMP-1 = tissue inhibitor of matrix
metalloproteiness 1;TNF-α = tumor necrosis factor alpha; TSG-6 = tumor necrosis factor-α-stimulated gene-6;
= half-life; UDP = uridine diphosphate
1. Introduction
2. History
3. Physicochemical and structural properties
3.1. Chemical structure
3.2. Solution structure
3.3. Polymer structure
3.4. Synthesis
3.5. Degradation
4. Mechanism of action
4.1. Interactions with hyaladherins
5. Pharmacokinetics
5.1. Absorption rate and concentration in plasma
5.2. Distribution
5.3. Excretion (elimination)
5.3.1. Renal excretion
5.3.2. Hepatic elimination
5.3.3. Pulmonary excretion
5.3.4. GIT excretion
6. Toxicity
6.1. Cytotoxicity
6.2. Neurotoxicity
6.3. Carcinogenicity
6.4. Mutagenicity
6.5. Reproductive toxicity
7. Efficacy and applications
7.1. Chondroprotective effects
7.2. Chondroprotective effects in vitro
7.3. Chondroprotective effects in vivo
Review Article Veterinarni Medicina, 53, 2008 (8): 397–411
1. Introduction
Hyaluronic acid (HA) is a carbohydrate, more spe-
cifically a mucopolysaccharide, occurring naturally
in all living organisms. It can be several thousands
of sugars (carbohydrates) long. When not bound to
other molecules, it binds to water giving it a stiff
viscous quality similar to “Jello”. The polysaccha-
ride hyaluronan (HA) is a linear polyanion, with a
poly repeating disaccharide structure [(13)-β--
GlcNAc-(14)-β--GlcA-]. HA is found primarily
in the extracellular matrix and pericellular matrix,
but has also been shown to occur intracellularly.
The biological functions of HA include mainte-
nance of the elastoviscosity of liquid connective
tissues such as joint synovial and eye vitreous fluid,
control of tissue hydration and water transport,
supramolecular assembly of proteoglycans in the
extracellular matrix, and numerous receptor-me-
diated roles in cell detachment, mitosis, migration,
tumor development and metastasis, and inflamma-
tion (Balazs et al., 1986; Toole et al., 2002; Turley
et al., 2002; Hascall et al., 2004). Its function in the
body is, amongst other things, to bind water and to
lubricate movable parts of the body, such as joints
and muscles. Its consistency and tissue-friendliness
allows it to be used in skin-care products as an
excellent moisturizer. Hyaluronic acid is one of the
most hydrophilic (water-loving) molecules in na-
ture and can be described as nature’s moisturizer.
The unique viscoelastic nature of HA along with
its biocompatibility and non-immunogenicity has
led to its use in a number of clinical applications,
including the supplementation of joint fluid in
arthritis (Neo et al., 1997; Barbucci et al., 2002;
Uthman et al., 2003; Medina et al., 2006), as a surgi-
cal aid in eye surgery, and to facilitate the healing
and regeneration of surgical wounds. More recently,
HA has been investigated as a drug delivery agent
for various administration routes, including oph-
thalmic, nasal, pulmonary, parenteral and topical
(Brown and Jones, 2005).
2. History
In 1934, Karl Meyer and his colleague John Palmer
isolated a previously unknown chemical substance
from the vitreous body of cows’ eyes. They found
that the substance contained two sugar molecules,
one of which was uronic acid. For convenience,
therfore, they proposed the name “hyaluronic acid.
The popular name is derived from “hyalos”, which is
the Greek word for glass + uronic acid (Meyer and
Palmer, 1934). At the time, they did not know that
the substance which they had discovered would
prove to be one of the most interesting and useful
natural macromolecules. HA was first used com-
mercially in 1942 when Endre Balazs applied for
a patent to use it as a substitute for egg white in
bakery products.
The first medical application of hyaluronan for
humans was as a vitreous substitution/replacement
during eye surgery in the late 1950s. The used hy-
aluronan was initially isolated from human umbili-
cal cord, and shortly thereafter from rooster combs
in a highly purified and high molecular weight form
(Meyer and Palmer, 1934). The chemical structure
of haluronan was essentially solved by Karl Mayer
and his assocates in the 1950s. It was first isolated
as an acid, but under physiological conditions it
behaved like a salt (sodium hyaluronate).
The term “hyaluronanwas introduced in 1986
to conform with the international nomenclature of
polysaccharides and is attributed to Endre Balazs
(Balazs et al., 1986), who coined it to encompass
the different forms the molecule can take, e.g, the
acid form, hyaluronic acid, and the salts, such as
sodium hyaluronate, which form at physiological
pH (Laurent, 1989). HA was subsequently isolated
from many other sources and the physicochemi-
cal structure properties, and biological role of this
polysaccharide were studied in numerous laborato-
ries (Kreil, 1995). This work has been summarized
in a Ciba Foundation Symposium (Laurent, 1989)
and a recent review (Laurent and Frazer, 1992).
7.4. Orthopedic applications
7.4.1. Viscosupplementation
7.5. Antiadhesion applications
7.6. Ophthalmology
7.7. Dermatology and wound-healing applica-
7.8. Cardiovascular applications
8. Tabular overview
9. Conclusion
10. References
Veterinarni Medicina, 53, 2008 (8): 397–411 Review Article
3. Physicochemical and structural
Hyaluronan, an extracellular matrix compo-
nent, is a high molecular weight glycosamino-
glycan composed of disaccharide repeats of
N-acetylglucosamine and glucuronic acid. This
relatively simple structure is conserved throughout
all mammals, suggesting that HA is a biomolecule
of considerable importance (Chen and Abatangelo,
1999). In the body, HA occurs in the salt form,
hyaluronate, and is found in high concentrations
in several soft connective tissues, including skin,
umbilical cord, synovial fluid, and vitreous humor.
Significant amounts of HA are also found in lung,
kidney, brain, and muscle tissues.
3.1. Chemical structure
The uronic acid and aminosugar in the disac-
charide are -glucuronic acid and -N-acetyl-
glucosamine, and are linked together through
alternating beta-1,4 and beta-1,3 glycosidic bonds
(see Figure 1). Both sugars are spatially related to
glucose which in the beta configuration allows all
of its bulky groups (the hydroxyls, the carboxylate
moiety and the anomeric carbon on the adjacent
sugar) to be in sterically favorable equatorial posi-
tions while all of the small hydrogen atoms occupy
the less sterically favourable axial positions. Thus,
the structure of the disaccharide is energetically
very stable.
structure. Solutions of hyaluronan manifest very
unusual rheological properties and are exceedingly
lubricious and very hydrophilic. In solution, the
hyaluronan polymer chain takes on the form of
an expanded, random coil. These chains entangle
with each other at very low concentrations, which
may contribute to the unusual rheological proper-
ties. At higher concentrations, solutions have an
extremely high but shear-dependent viscosity. A
1% solution is like jelly, but when it is put under
pressure it moves easily and can be administered
through a small-bore needle. It has therefore been
called a “pseudo-plasticmaterial. The extraordi-
nary rheological properties of hyaluronan solutions
make them ideal as lubricants. There is evidence
that hyaluronan separates most tissue surfaces that
slide along each other. The extremely lubricious
properties of hyaluronan, meanwhile, have been
shown to reduce postoperative adhesion forma-
tion following abdominal and orthopedic surgery.
As mentioned, the polymer in solution assumes a
stiffened helical configuration, which can be at-
tributed to hydrogen bonding between the hydroxyl
groups along the chain. As a result, a coil structure
is formed that traps approximately 1 000 times its
weight in water (Cowman and Matsuoka, 2005).
3.3. Polymer structure
Hyaluronan synthase enzymes synthesize large,
linear polymers of the repeating disaccharide
structure of hyaluronan by alternating addition
of glucuronic acid and N-acetylglucosamine to
the growing chain using their activated nucle-
otide sugars (UDP glucuronic acid and UDP-
N-acetlyglucosamine) as substrates (Meyer and
Palmer, 1934).
The number of repeat disaccharides
in a completed hyaluronan molecule can reach
10 000 or more, a molecular mass of ~4 million
daltons (each disaccharide is ~400 daltons). The
average length of a disaccharide is ~1 nm. Thus,
a hyaluronan molecule of 10 000 repeats could ex-
tend 10 µm if stretched from end to end, a length
approximately equal to the diameter of a human
erythrocyte (Cowman and Matsuoka, 2005).
3.4. Synthesis
The cellular synthesis of HA is a unique and high-
ly controlled process. Most glycosaminoglycans are
3.2. Solution structure
In a physiological solution, the backbone of a
hyaluronan molecule is stiffened by a combina-
tion of the chemical structure of the disaccha-
ride, internal hydrogen bonds, and interactions
with the solvent. The axial hydrogen atoms form
a non-polar, relatively hydrophobic face while
the equatorial side chains form a more polar, hy-
drophilic face, thereby creating a twisting ribbon
-Glucuronic acid N-acetylglucosamine
Figure 1. Chemical structure of HA
Review Article Veterinarni Medicina, 53, 2008 (8): 397–411
made in the cell’s Golgi networks. HA is naturally
synthesized by a class of integral membrane proteins
called hyaluronan synthases, of which vertebrates
have three types: HAS1, HAS2, and HAS3 (Lee and
Spicer, 2000). Secondary structure predictions and
homology modeling indicate an integral membrane
protein (IMP). An integral membrane protein is a
protein molecule (or assembly of proteins) that in
most cases spans the biological membrane with
which it is associated (especially the plasma mem-
brane) or which, is sufficiently embedded in the
membrane to remain with it during the initial steps
of biochemical purification (in contrast to peripheral
membrane proteins). Hyaluronan synthase enzymes
synthesize large, linear polymers of the repeating
disaccharide structure of hyaluronan by alternate ad-
dition of glucuronic acid and N-acetylglucosamine
to the growing chain using their activated nucle-
otide sugars (UDP = glucuronic acid and UDP-N-
acetlyglucosamine) as substrates.
3.5. Degradation
In mammals, the enzymatic degradation of HA
results from the action of three types of enzymes:
hyaluronidase (hyase), b--glucuronidase, and β-N-
acetyl-hexosaminidase. Throughout the body, these
enzymes are found in various forms, intracellularly
and in serum. In general, hyase cleaves high molec-
ular weight HA into smaller oligosaccharides while
β--glucuronidase and β-N-acetylhexosaminidase
further degrade the oligosaccharide fragments by
removing nonreducing terminal sugars (Leach and
Schmidt, 2004).
The degradation products of hyaluronan, oli-
gosaccharides and very low molecular weight hy-
aluronan, exhibit pro-angiogenic properties (Mio
and Stern, 2002). By catalyzing the hydrolysis of
hyaluronic acid, a major constituent of the inter-
stitial barrier, hyaluronidase lowers the viscosity of
hyaluronic acid, thereby increasing tissue perme-
ability. It is, therefore, used in medicine in con-
junction with other drugs in order to speed their
dispersion and delivery. The most common applica-
tion is in ophthalmic surgery, in which it is used in
combination with local anesthetics. Some bacteria,
such as Staphylococcus aureus, Streptococcus pyoge-
nes et pneumoniae and Clostridium perfringens,
produce hyaluronidase as a means of increasing
mobility through the bodys tissues and as an an-
tigenic disguise that prevents their recognition by
phagocytes of the immune system (Ponnuraj and
Jedrzejas, 2000; Lin and Stern, 2001; Lokeshwar et
al., 2002; Hajjaji et al., 2005; Kim et al., 2005; Girish
and Kemparaju, 2006).
4. Mechanism of action
Although the predominant mechanism of HA
is unknown, in vivo, in vitro, and clinical studies
demonstrate various physiological effects of exog-
enous HA.
Hyaluronic acid possesses a number of protective
physiochemical functions that may provide some
additional chondroprotective effects in vivo and
may explain its longer term effects on articular car-
tilage. Hyaluronic acid can reduce nerve impulses
and nerve sensitivity associated with pain. In ex-
perimental osteoarthritis, this glycosaminoglycan
has protective effects on cartilage (Akmal et al.,
2005); exogenous hyaluronic acid is known to be
incorporated into cartilage (Antonas et al., 1973).
Exogenous HA enhances chondrocyte HA and
proteoglycan synthesis, reduces the production and
activity of proinflammatory mediators and matrix
metalloproteinases, and alters the behavior of im-
mune cells. These functions are manifested in the
scavenging of reactive oxygen-derived free radicals,
the inhibition of immune complex adherence to
polymorphonuclear cells, the inhibition of leuko-
cyte and macrophage migration and aggregation
(Balazs and Denlinger, 1984) and the regulation of
fibroblast proliferation. Many of the physiological
effects of exogenous HA may be functions of its
molecular weight (Noble, 2002; Uthman et al, 2003;
Hascall et al., 2004; Medina et al., 2006).
Hyaluronan is highly hygroscopic and this prop-
erty is believed to be important for modulating
tissue hydration and osmotic balance (Dechert
et al., 2006). In addition to its function as a pas-
sive structural molecule, hyaluronan also acts as a
signaling molecule by interacting with cell surface
receptors and regulating cell proliferation, migra-
tion, and differentiation. Hyaluronan is essential
for embryogenesis and is likely also important in
tumorigenesis (Kosaki et al., 1999; Camenisch et
al., 2000).
Hyaluronan functions are diverse. Because of its
hygroscopic properties, hyaluronan significantly
influences hydration and the physical properties of
the extracellular matrix. Hyaluronan is also capable
of interacting with a number of receptors resulting
Veterinarni Medicina, 53, 2008 (8): 397–411 Review Article
in the activation of signaling cascades that influ-
ence cell migration, proliferation, and gene expres-
sion (Turley et al., 2002; Taylor et al., 2004).
4.1. Interactions with hyaladherins
HA plays several important organizational roles
in the extracellular matrix (ECM) by binding with
cells and other components through specific and
nonspecific interactions. Hyaluronan-binding pro-
teins are constituents of the extracellular matrix,
and stabilize its integrity. Hyaluronan receptors are
involved in cellular signal transduction; one recep-
tor family includes the binding proteins aggrecan,
link protein, versican and neurocan and the recep-
tors CD44, TSG6 (Kahmann et al., 2000), GHAP
(Liu et al., 2001), and LYVE-1 (Banerji et al., 1999).
The RHAMM receptor is an unrelated hyaluronan-
binding protein, and the hyaluronan binding sites
contain a motif of a minimal site of interaction with
hyaluronan. This is represented by B(X7) B, where
B is any basic amino acid except histidine, and X is
at least one basic amino acid and any other moiety
except acidic residues. CD44 and RHAMM have
attracted much attention, because they are believed
to be involved in metastasis (Toole, 1997; Ahrens
et al., 2001; Noble, 2002; Toole et al., 2002).
CD44 is a structurally variable and multifunc-
tional cell surface glycoprotein expressed on most
cell types (Karjalainen et al., 2000). To date, it is
the best characterized transmembrane hyaluro-
nan receptor and because of its wide distribution
is considered to be the major hyaluronan receptor
on most cell types (Tzircotis et al., 2005). Many
functions of CD44 are mediated through interac-
tion with its ligand hyaluronan, a ubiquitous extra-
cellular polysaccharide (Toole, 1997). Hyaluronan
is abundant in soft connective tissues, but also in
epithelial and neural tissues.
Low and intermediate molecular weight HA (2 ×
–4.5 × 10
Da) stimulates gene expression in mac-
rophages, endothelial cells, eosinophils and certain
epithelial cells (McKee et al., 1996; Oertli et al.,
1998). Hyaluronan degradation products are pur-
ported to contribute to scar formation. Fetal wounds
heal without scar formation and wound fluid HA is
of high molecular weight. When hyaluronidase is
added to generate HA fragments, there is increased
scar formation. ese data support the theory that
high molecular weight HA promotes cell quiescence
and supports tissue integrity, whereas generation of
HA breakdown products is a signal that injury has
occurred and initiates an inflammatory response
(Chen and Abatangelo, 1999).
The role of CD44 in HA-binding and signaling has
recently been investigated in hematopoietic cells
from CD44-deficient mice (Schmits et al., 1997;
Protin et al., 1999). CD44-deficient mice develop
normally and exhibit minor abnormalities in he-
matopoiesis and lymphocyte recirculation (Schmits
et al., 1997; Protin et al., 1999). The induction of
inflammatory gene expression in response to hy-
aluronan was observed in the absence of CD44 in
bone marrow cultures and dendritic cells. These
data suggest that there are CD44-independent
Table 1. Normal values of kinetic parameters of HA in animals
Species Compartment* t
ratio (%)
Plasma clear-
ance (mg/day)
Total daily turn-
over (mg/day)
hepatic 50 332 71 3
splanchnic 23 150 24.3 3
renal 14 41 8.9 3
urine 11 2.9 3
Sheep plasma 2–7 50 215 37 120 88 2
Rabbit plasma 2–5 20–50 100 1
Rat plasma 1.4 1
*compartment over which the parameter was determined; t
= half-life of hyaluronan; K
= the Michaelis-Menten con-
stant; V
= the maximum metabolic rate
**method used for determination of kinetic parameters: 1 = bolus dose of labeled HA; 2 = infusion of unlabelled HA and
kinetic modeling; 3 = direct measurement of HA concentration over eliminating organ
Review Article Veterinarni Medicina, 53, 2008 (8): 397–411
mechanisms for the induction of gene expression
by HA (Noble, 2002).
RHAMM (Receptor for HA-Mediated Mobility), has
been found on cell surfaces, as well as in the cytosol
and nucleus (Leach and Schmidt, 2004). It has been
implicated in regulating cellular responses to growth
factors and plays a role in cell migration, particularly
for fibroblasts and smooth cells (Toole, 1997).
Table 2. Concentration and turnover of HA in different tissues (values within parentheses represent total amount
recovered in the cavity, or injected)
Tissue and species
Concentration of HA in
tissue (g/ml) injectate (mg/ml)
Vitreous body
man 100–400
rhesus monkey 100–180 10 10–20
owl monkey 300–900 10 20–30
rabbit 14–52 0.02 70
Anterion chamber
man 1.1
owl monkey 11.4 10 0.2–0.6
cynomolgus 10 0.8
rabbit 1.1 10 0.3–0.5
rabbit 1.1 0.02 0.04–0.06
horse 300–500 10 1
rabbit (134) 0.3 0.5
rabbit 3 800 20 0.5
rabbit (0.76) (0.03–0.05) 0.4–1.0
rabbit 5 10 3–4
rabbit 5 0.06 3–4
rabbit (2–93) 10 1.2
rabbit 0.07 0.1
Skeletal muscle
rabbit 26–28* 10 1.25
Amniotic fluid
sheep 12 week 5.1 tracer 3–8
sheep 15–17 week 1.9 tracer 0.5–0.8
rabbit 1.9– .7
rat 840* 2.6–4.5
rabbit 0.07 0.5
rabbit 10 2
Veterinarni Medicina, 53, 2008 (8): 397–411 Review Article
5. Pharmacokinetics
e normal systemic kinetics of HA is well estab-
lished in several species including man. e removal
of HA from the circulation is very efficient, with a
half-life of 2–6 min and a total normal turnover of
10–100 mg/day in the adult human (Table 1 and 2).
e main uptake from the blood takes place in the
liver endothelial cells. However, evidence for a role of
the kidney in the elimination of HA is accumulating.
Recently published data suggest that the elimination
kinetics of HA from the systemic circulation may be
influenced by a number of factors, such as saturation
of the elimination caused by an increased lymphatic
input of HA to the circulation, alteration of the blood
flow over the eliminating organ and competition with
other macromolecular substances such as chondroi-
tin sulphate or proteoglycans. Many of these factors
may be operative during different disease states, and
may therefore partly explain the observed differences
between normal and pathological HA kinetics. e
normal and pathological turnover of hyaluronan from
the circulation has been determined in many differ-
ent species, including man by many different authors
using different techniques (Table 3).
5.1. Absorption rate and concentration
in plasma
After i.v. injection of a bolus dose of [
C]-HA in
rabbits, it was shown that 98% of the administered
dose had disappeared from the systemic circulation
within 6 h after the administration (Lebel, 1991).
Similar results were also obtained in man, where
55% and 85% of the acetyl content after i.v. injection
of [
H]HA, was completely oxidized after 3 h and
24 h, respectively (Laurent and Fraser, 1992).
It is known that the major part of the elimination
of HA from the blood circulation takes place in
Table 3. Kinetics parameters of hyaluronan in man and animals during different disease states (Lebel, 1991)
ratio (%)
Total daily
primary bililary cirrh. plasma 6–72 50–510** 69–115 1
rheumatoid arthritis plasma 2–3 970–2 060* 33–167 1
kidney disease
splanchnic 33
renal 22
alcoholic cirrhosis
splanchnic 14 61.9
renal 5
non-cirrhotic alcoholic splanchnic 36 8.9 3
liver disease renal 5 3
rheumatoid arthritis urine 0.5 3
primary bililary cirrhosis urine 0.9 3
Werners sy urine 3.3 3
Pig fecal peritonitis hepatic 36 84 65 3
endotoxin infusion plasma 7–19 1
TNF-alpha infusion plasma 3–10 1
Rat experimental arthritis plasma 1–2 1
*compartment over which the parameter was determined; t
= half-life of hyaluronan
**blood clearance
***method used for determination of kinetic parameters: 1 = bolus dose of labeled HA; 3 = direct measurement of HA
concentration over eliminating organ
Review Article Veterinarni Medicina, 53, 2008 (8): 397–411
the liver (Fraser et al., 1981) via receptor-mediated
endocytosis in the sinusoidal liver endothelial cells
(Bentsen et al., 1989; Smedsrod, 1991).
5.2. Distribution
HA is widely distributed in body tissues and in-
tracellular fluids, including the aqueous and vitre-
ous humour, and synovial fluid; it is a component of
the ground substance or tissue cement surrounding
cells (Laurent and Reed, 1991; Toole, 1997). It is not
known whether hyaluronate sodium is distributed
into breast milk.
5.3. Excretion (elimination)
5.3.1. Renal excretion
By direct measurement of HA in urine it can be
calculated that approximately 1% of the normal
daily turnover of HA from the systemic circulation
in man is filtered via the kidneys. Similar results
were obtained in studies on man (Lebel, 1991) and
in a study on rabbits (Fraser et al., 1981).
Recently, the extraction ratio and clearance over
the kidney in pig were reported to be 14% and 41 ml
per min, using the method of measuring directly
over the organ. In this study, it was also determined
that the renal clearance was approximately three
times the urinary clearance (Bentsen et al., 1989).
5.3.2. Hepatic elimination
Direct measurement of the difference of the en-
dogenous concentration over a specific organ and
knowledge of the blood flow enables calculation
of the extraction ratio or clearance directly over a
specific organ.
By use of this method Bentsen et al. (1989) deter-
mined the hepatosplanchnic extraction ratio and
clearance of hyaluronan in man to be 33% and 250
ml/min, respectively.
e hepatic extraction ratio and clearance have also
been determined in pigs by measurement directly over
the organ and were found to be 23% and 150 ml/min,
respectively (Bentsen et al., 1989). In a similar study
on pigs, using the same method of direct determina-
tion, the extraction ratio and clearance over the liver
were determined to be 49% and 332 ml/min, respec-
tively. e reason for the discrepancies between these
two studies is not known (Lebel, 1991).
5.3.3. Pulmonary excretion
Within 100 h, 63% and 20% of the administered
dose was excreted and recovered in the respiratory
gas (as
) (Lebel, 1991).
5.3.4. GIT excretion
The total amount of excretion into bile within
24 h was reported to be very low, 0.7% of the ad-
ministered dose. Similarly, the total amount of ex-
cretion into feces, within 100 h of administration,
was also very small, about 0.5% of the administered
dose (Lebel, 1991).
6. Toxicity
6.1. Cytotoxicity
Jansen et al. (2004) investigated the possible cyto-
toxic effects, biocompatibility and degradation of a
hyaluronan-based conduit for peripheral nerve repair.
e results show that a hyaluronan-based conduit is
not cytotoxic and shows good biocompatibility.
Hyaluronan is highly non-antigenic and non-
immunogenic, owing to its high structural homol-
ogy across species, and poor interaction with blood
components (Amarnath et al., 2006).
6.2. Neurotoxicity
Because HA has an anti-inflammatory effect and
prevents and/or reduces tissue adhesion, it was
believed that HA epidurally-administered during
epidural adhesiolysis procedures could alleviate
the condition of patients with chronic lower back
pain. For this reason, the following clinical trial
evaluation of epidurally-administered HA neuro-
toxicity was performed by light microscopy (LM)
and electron microscopy (EM) in rabbits. Twenty
rabbits were randomly divided into two groups, a
normal saline (NS) group (n = 10) and a HA group
(n = 10). Saline (0.2 ml/kg of 0.9% solution) and the
same volume of HA were injected into the epidural
space. No rabbits showed any sensory-motor or
Veterinarni Medicina, 53, 2008 (8): 397–411 Review Article
behavioural changes during the three-week period,
except for one rabbit in the NS group that showed
decreased appetite and activity, and weight loss.
By LM, abnormal findings were observed in two
rabbits in the NS group; these were thought to be
the result of trauma and infection associated with
epidural catheterization. EM findings showed no
significant neurotoxic findings in either group. In
conclusion, epidurally-administered HA did not
cause neurotoxicity in rabbits (Lim et al., 2003).
6.3. Carcinogenicity
HA is responsible for various functions within
the extracellular matrix such as cell growth, differ-
entiation, and migration (Jaracz et al., 2005; Paiva
et al., 2005). A wide range of activities can be ex-
plained by a large number of Ha-binding receptors
such as cell surface glycoprotein CD44, the receptor
for hyaluronic acid-mediated motility (RHAMM),
and several other receptors possessing Ha-binding
motifs, for example: transmembrane protein layilin,
hyaluronic acid receptor for endocytosis (HARE),
lymphatic vessel endocytic receptor (LYVE-1),
and also intracellular HA-binding proteins includ-
ing CDC37, RHAMM/IHABP, P-32, and IHABP4
(Underhill, 1992; Forsberg et al., 1994; Pohl et al.,
2000; Pure and Cuff, 2001; Toole, 2001; Weigel et al.,
2002; Hascall et al., 2004; Hajjaji et al., 2005; Nawrat
et al., 2005; Hill et al., 2006; Iacob and Knudson,
2006). It has been shown that the HA level is elevated
in various cancer cells (Lin and Stern, 2001) and it is
believed to form a less dense matrix, thus enhanc-
ing the cell’s motililty as well as invasive ability into
other tissues (Hill et al., 2006).
It is well known that various tumors (epithelial,
ovarial, colon, stomach and acute leukemia) over-
express HA-binding receptors CD44 and RHAMM.
Consequently, these tumor cells are characterised
by enhanced binding and internalization of HA.
CD44-Ha interactions play various important
physiological roles, including mediation or pro-
motion of macrophage aggregation, cell migration,
chondrocyte pericellular matrix assembly, and leu-
kocyte activation.
Paradoxically, both HA and the enzymes that elimi-
nate HA, hyaluronidases, can correlate with cancer
progression. It has been shown that the over expres-
sion of hyaluronic acid synthases increases the HA
level, which leads to the acceleration of tumor growth
and metastasis. On the other hand, exogenous oligo-
metric HA inhibits tumor progression, most likely by
competing with endogenous polymeric HA.
6.4. Mutagenicity
Sister Chromatid Exchange Assay. Under the
conditions of the assay, the sodium hyaluronate
solution (High Molecular Weight
Hyaluronan) was not considered mutagenic to
Chinese Hamster Ovary cells (Product informa-
tion Orthovisc
, 2004).
Chromosomal Aberration Assay. Under the con-
ditions of the assay, the Orthovisc
solution was not
considered mutagenic to Chinese Hamster Ovary
cells (Product information Orthovisc
, 2004).
Ames Salmonella/Mammalian Microsome
Mutagenicity Assay. Under the conditions of the
assay, the Orthovisc
solution was not considered
mutagenic to Salmonella typhimurium tester
strains (Product information Orthovisc
, 2004).
6.5. Reproductive toxicity
No evidence of impairment of fertility was seen
in rats and rabbits given hyaluronate sodium in
doses of up to 1.43 mg per kg of body weight, ap-
proximately 11 times the maximum recommended
human dose (MRHD), per treatment cycle.
Reproductive toxicity studies, including multi-
generational studies, have been performed in rats
and rabbits at doses of up to 11 times the anticipated
human dose (1.43 mg/kg per treatment cycle) and
have revealed no evidence of impaired fertility or
harm to the experimental animal foetus caused by
intra-articular injections of hyaluronate sodium.
7. Efficacy and applications
7.1. Chondroprotective effects
The physical properties of HA are important but
there is evidence to suggest that HA may provide
both physiochemical and pharmacological ad-
vantages. Chondrocytes express the glykoprotein
CD44 on their cell surface. This has the capacity to
function as a HA receptor and so may be involved
in biochemical interactions with chondrocytes. The
effect of a HA injection may be mediated via CD44
inteactions (Akmal et al., 2005).
Review Article Veterinarni Medicina, 53, 2008 (8): 397–411
7.2. Chondroprotective effects in vitro
e chondroprotective effects of hyaluronic acid,
e.g., that it stimulates the production of tissue in-
hibitors of matrix metalloproteineses (TIMP-1) by
chondrocytes, inhibits neutrophil-mediated cartilage
degradation and attenuates IL-1 induced matrix de-
generation and chondrocyte cytotoxicity have been
observed in vitro (Gerwin et al., 2006). Articular
chondrocytes cultured in the presence of HA have a
significantly greater rate of DNA proliferation and ex-
tracellular matrix production, compared with chon-
drocytes cultured without HA (Akmal et al., 2005).
7.3. Chondroprotective effects in vivo
HA has been experimentally studied as a potential
agent of therapeutic intervention in osteoarthro-
sis (OA). Hyaluronid acid has been applied to the
therapy of experimental OA. Investigations have
shown that intra-articular injection of HA reduces
arthritic lesions in experimental animal models of
articular cartilage injury (Balazs and Denlinger,
1989; Neo et al., 1997; Kim et al., 2001; Moreland,
2003; Leach and Schmidt, 2004; Ding et al., 2005;
Roth et al., 2005; Echigo et al., 2006).
7.4. Orthopaedic applications
HA plays a vital role in the development of car-
tilage, the maintance of the sinovial fluid and the
regeneration of tendons (Toole, 1997, 2001). High
concentrations of HA have been found in the ECM
of all adult joint tissues, including the sinovial fluid
and the outer layer cartilage (Leach and Schmidt,
2004). In part because of its viscoelastic nature and
ability to form highly hydrated matrices, HA acts in
the joint as a lubricant and shock absorber.
e pathologic changes of synovial fluid hyaluronic
acid, with its decreased molecular weight and concen-
tration, led to the concept of viscosupplementation.
7.4.1. Viscosupplementation
Viscosupplementation is a novel, safe, and possibly
effective form of local treatment for osteoarthritis
(Uthman et al., 2003). Viscosupplementation with
HA products helps to improve the physiological en-
vironment in an osteoarthritic joint by supplement-
ing the shock absorption and lubrication properties
of osteoarthritic synovial fluid. e rationale for us-
ing viscosupplementation is to restore the protective
viscoelasticity of synovial hyaluronan, decrease pain,
and improve mobility. e immediate benets of
viscosupplementation are the relief of pain. Longer-
term benefits are believed to include the return of
joint mobility by the restoration of transsynovial
flow and, ultimately, the metabolic and rheologic
homeostasis of the joint (Wang et al., 2004).
Viscosupplementation came into clinical use in
Japan and Italy in 1987, in Canada in 1992, in Europe in
1995, and in the United States in 1997. Two hyaluron-
ic acid products are currently available in the United
States: naturally occurring hyaluronan (Hyalgan) and
synthetic hylan G-F 20 (Synvisc). Hylans are cross-
linked hyaluronic acids, which gives them a higher
molecular weight and increased elastoviscous proper-
ties. e higher molecular weight of hylan may make
it more efficacious than hyaluronic acid because of
its enhanced elastoviscous properties and its longer
persistence in the joint space (Wen, 2000).
7.5. Antiadhesion applications
As HA is highly hydrophilic, it is a polymer that
is well suited to applications requiring minimal
cellular adhesion. Postoperative adhesions, which
form between adjacent tissue layers following
surgery, impede wound healing and often require
additional surgical procedures to be repaired suc-
cessfully. Barriers made from cross-linked HA have
been effectively used to prevent such adhesions from
forming. Furthermore, the adhesion of bacteria to
biomaterials can induce infections and constitute a
great risk to the patient; with this in mind, esterified
HA has also been used to prevent bacterial adhesion
to dental implants, intraocular lenses, and catheters
(Leach and Schmidt, 2004).
7.6. Ophthalmology
HA, a natural component of the vitreous humor
of the eye, has found many successful applications
in ophthalmologic surgery. HA is particularly useful
as a spacefilling matrix in the eye; thus, intraocular
injection of HA during surgery is used to maintain the
shape of the anterior chamber. Furthermore, HA solu-
tions also serve as a viscosity-enhancing component
of eye drops and as an adjuvant to eye tissue repair.
Veterinarni Medicina, 53, 2008 (8): 397–411 Review Article
7.7. Dermatology and wound-healing
HA is naturally present in high concentrations
in the skin and soft connective tissues. Therefore,
HA is an appropriate choice for a matrix to sup-
port dermal regeneration and augmentation. For
example, Prestwich and co-workers found that
cross-linked HA hydrogel films accelerate the
healing of full-thickness wounds, presumably
by providing a highly hydrated and nonimmu-
nogenic environment that is conducive to tis-
sue repair. Hyaff scaffolds cultured in vitro with
keratinocytes and fibroblasts have been used to
create materials similar to skin, including two
distinct epidermal and dermal-like tissue lay-
ers. Moreover, as a result of its ability to form
hydrated, expanded matrices, HA has also been
successfully used in cosmetic applications such
as soft tissue augmentation (Leach and Schmidt,
2004; Dechert et al., 2006).
7.8. Cardiovascular applications
In a manner related to its antiadhesive properties,
HA has also proven to be effective for increasing
the blood compatibilities of cardiovascular implants
such as vascular grafts and stents. For example,
biomaterial surfaces treated with cross-linked HA
have been associated with reduced platelet adhe-
sion and thrombus formation (Leach and Schmidt,
2004). Furthermore, sulfated HA derivatives can act
as heparin mimics (Barbucci et al., 1995); in fact,
HA derivatives with higher degrees of sulfation are
associated with increased abilities to prevent blood
coagulation (as measured by longer times required
for whole blood clotting) (Barbucci et al., 1995).
8. Tabular overview
Table 4. Data on reproductive effects of hyaluronan in animals
Effect Route Organism Dose of TDLo (mg/kg) Duration Source/No./pp/year/
T16; T31; T73 subcutaneous rat 189 multigenerations OYYAA2 29, 139, 1985
T46; T86 subcutaneous rat 220 7-17D preg OYYAA2 29, 111, 1985
T85 subcutaneous rat 77 7-17D preg OYYAA2 29, 111, 1985
T81 subcutaneous rat 660 7-17D preg OYYAA2 29, 111, 1985
T12 intraperitoneal rabbit 91 6-18D preg OYYAA2 29, 131, 1985
T03 parenteral rabbit 52 91D male OYYAA2 28, 1 041, 1984
T03 – prostate, seminal vesicle, Cowperrs glands, accessory glands; T12 = ovaries, fallopian tubes; T16 = parturition; T31
= extra embryonic structures; T46 = musculosceletal system; T73 = sex ratio; T81 = growth statistics; T85 = behavioral;
T86 = physical; OYYAA2 = Oyo Yakuri Pharmacometrics
TDLo (Toxic Dose Low): the lowest dose of a substance introduced by any route, other than inhalation, over any given
period of time and reported to produce any toxic effect in humans or to produce tumorigenic or reproductive effects in
animals or humans
Table 5. Other multiple dose data of hyaluronan in animals
Effect Route Organism Dose of TDLo (mg/kg) Duration Source/No./pp/year/
U01; U05; U06 oral rat 2 275 13W-I YACHDS 27, 5 809 ,1993
M16; P05; P72 intraperitoneal rat 1 680 4W-I YACHDS 13, 2 763, 1985
M16 = other changes in urine composition; P05 = normocytic anemia; P72 = changes in leukocyte (WBC) count; U01 =
weight loss or decreased weight gain; U05 = changes in Na
; U06 = body temperature decrease; YACHDS = Yakuri to Chiryo,
Pharmacology and erapeutics
TDLo (Toxic Dose Low): the lowest dose of a substance introduced by any route, other than inhalation, over any given
period of time and reported to produce any toxic effect in humans or to produce tumorigenic or reproductive effects in
animals or humans
Review Article Veterinarni Medicina, 53, 2008 (8): 397–411
9. Conclusion
Hyaluronic acid has been used for more than
20 years in many products throughout the world.
Because of its biocompatibility, biodegradability,
and readily modified chemical structure, HA has
been extensively investigated in drug-delivery ap-
plications. A variety of commercially available
preparations of HA derivatives and cross-linked
HA materials have been developed for drug deliv-
ery; these materials are created in forms such as
films, microspheres, liposomes, fibers, and hydro-
gels. Through multidisciplinary discoveries about
the structure, properties, biological activity, and
chemical modification of this unique polymer,
HA has found success in an extraordinarily broad
range of biomedical applications. Future clinical
therapies of HA-derived materials critically rely
on a more detailed understanding of the effects of
HA molecular weight and concentration and how
this biomolecule specifically interacts with cells
and ECM components in the body. The increased
use of these materials will require finely tuned and
controllable interactions between HA and its en-
vironment. Work in these areas is underway; for
example, adhesive peptide sequences have been co-
valently bound to HA materials. Also, environmen-
tally responsive materials have been synthesized
from HA. These materials can be created to swell
or degrade in response to inflammation, electrical
stimulation, and heat.
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Received: 2008–01–02
Accepted after corrections: 2008–08–12
Corresponding Author:
Doc. MUDr. Jiri Necas, PhD., Palacky University Olomouc, Faculty of Medicine and Dentistry, Department
of Physiology, Hnevotinska 3, 775 15 Olomouc, Czech Republic
Tel. +420 585 632 351, fax +420 585 632 368, e-mail:
... Hyaluronic acid (HA) is a naturally occurring biopolymer [78]. It is a long, unbranched polysaccharide with a molecular weight (MW) of up to 2 × 10 7 Da that is made up of repeated disaccharides of D-glucuronic and N-acetyl-Dglucosamine [79]. ...
... It is a long, unbranched polysaccharide with a molecular weight (MW) of up to 2 × 10 7 Da that is made up of repeated disaccharides of D-glucuronic and N-acetyl-Dglucosamine [79]. It binds to water, giving it a "Jello-like" stiff, viscous texture [78]. Since HA is a component of the skin's extracellular matrix, it is essential for various stages of the healing process, such as reduced inflammation, improved tissue remodeling, and angiogenesis, as well as stimulated collagen production in endothelial cells, in addition to several known properties (excellent biocompatibility, biodegradability, durability, and absence of toxicity) [79,80]. ...
... Hyaluronic acid (HA) ( Figure 6) is a linear non-sulfated glycosaminoglycan, composed of repeating units of D-glucuronic acid and N-acetyl-D-glucosamine [125][126][127], linked through alternating β-1,4 and β-1,3 glycosidic bonds [128]. HA is mainly found in the extracellular and pericellular matrix, but the occurrence in intracellular has also been reported [129]. HA can be separated from animal sources (such as rooster combs) and microbial sources, but in industrial context, HA is widely produced by microbial fermentation method in high purity and good yield. ...
... HA is an excellent lubricant and shock absorber due to its unique higher water binding capacity and viscoelasticity [134]. HA is a highly hydrophilic polysaccharide and uses as a vital component in skincare products as a moisturizer [129]. In addition, biocompatibility, non-immunogenicity, unique viscoelasticity, make HA perfect for diverse biomedical applications, such as supplementation of joint fluid for arthritis, surgical aid in eye surgeries, facilitating wound healing, and drug delivery agent for various administration routes [135,136]. ...
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Over the past few decades, synthetic polymer production has increased, and the production of plastics has surpassed all other man-made materials due to their versatility. Moreover, packaging plastic makes up around 40% of global plastic production. However, the excessive usage of synthetic packaging materials has led to severe environmental and health-related issues. Therefore, biobased packages are considered alternatives to substitute synthetic packaging on the market. Furthermore, the choice of packing material in the food industry is a perplexing process as it depends on various factors, such as the type of food product, its sustainability, and environmental conditions. Interestingly, due to proven gas barrier properties and biological activity, polysaccharide-based bioplastics show the potential to expand the trends in food packaging, including edible films and intelligent and active food packaging. This review discusses the structure, properties and recent developments in polysaccharide-based bioplastics as food packaging materials.
... HA has a chemical structure in which d-glucuronic acid and d-N-acetylglucosamine molecules are alternatively linked with β-glycosidic bonds. Additionally, it contains -OH and -COOH functional groups [99]. It becomes negatively charged with -COO groups upon dissolving in water, making it highly hydrophilic and causing significant swelling. ...
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Numerous innovative advancements in dressing technology for wound healing have emerged. Among the various types of wound dressings available, hydrogel dressings, structured with a three-dimensional network and composed of predominantly hydrophilic components, are widely used for wound care due to their remarkable capacity to absorb abundant wound exudate, maintain a moisture environment, provide soothing and cooling effects, and mimic the extracellular matrix. Composite hydrogel dressings, one of the evolved dressings, address the limitations of traditional hydrogel dressings by incorporating additional components, including particles, fibers, fabrics, or foams, within the hydrogels, effectively promoting wound treatment and healing. The added elements enhance the features or add specific functionalities of the dressings, such as sensitivity to external factors, adhesiveness, mechanical strength, control over the release of therapeutic agents, antioxidant and antimicrobial properties, and tissue regeneration behavior. They can be categorized as natural or synthetic based on the origin of the main components of the hydrogel network. This review focuses on recent research on developing natural polysaccharide-based composite hydrogel wound dressings. It explores their preparation and composition, the reinforcement materials integrated into hydrogels, and therapeutic agents. Furthermore, it discusses their features and the specific types of wounds where applied.
... In general, HA is categorized as low molecular weight (LMW-HA) of 0.5-1 × 10 6 Da, medium molecular weight (MMW-HA) of 1.2-4.5 × 10 6 Da, and high molecular weight (HMW-HA) of 6-7 × 10 6 Da (Weigel et al., 1997;Weigel & DeAngelis, 2007). The structure of HA contains sugar monomer units which are connected by beta-1,4 and beta-1,3 alternating glycosidic bonds with hydroxyl and carboxylic groups are sterically linked to the outside and the hydrogen to the inside resulting in a twisting ribbon structure (Necas et al., 2008;Kablik et al., 2009;Stabler Ogawa, 2021). HA plays a crucial role in tissue hydration and various cellular functions including growth, differentiation, and transport (Kulshreshtha et al., 2022b). ...
This chapter’s main aim has been to summarize the research landscape pertaining to chicken eggshell and membrane constituents over the last three decades, from which much of our knowledge of avian eggshell mineralization, function and composition are derived. Many biochemical, nutritional, morphological, physiological and structural studies have been conducted on avian eggs and most have utilized the egg of the domestic chicken because of its availability and commercial importance as a nutritious food for human consumption.
Cobalt-containing alloys are useful for orthopedic applications due to their low volumetric wear rates, corrosion resistance, high mechanical strength, hardness, and fatigue resistance. Unfortunately, these prosthetics release significant levels of cobalt ions, which was only discovered after their widespread implantation into patients requiring hip replacements. These cobalt ions can result in local toxic effects—including peri-implant toxicity, aseptic loosening, and pseudotumor—as well as systemic toxic effects—including neurological, cardiovascular, and endocrine disorders. Failing metal-on-metal (MoM) implants usually necessitate painful, risky, and costly revision surgeries. To treat metallosis arising from failing MoM implants, a synovial fluid-mimicking chelator was designed to remove these metal ions. Hyaluronic acid (HA), the major chemical component of synovial fluid, was functionalized with British anti-Lewisite (BAL) to create a chelator (BAL-HA). BAL-HA effectively binds cobalt and rescues in vitro cell vitality (up to 370% of cells exposed to IC 50 levels of cobalt) and enhances the rate of clearance of cobalt in vivo ( t 1/2 from 48 h to 6 h). A metallosis model was also created to investigate our therapy. Results demonstrate that BAL-HA chelator system is biocompatible and capable of capturing significant amounts of cobalt ions from the hip joint within 30 min, with no risk of kidney failure. This chelation therapy has the potential to mitigate cobalt toxicity from failing MoM implants through noninvasive injections into the joint.
The present era is in quest of sustainable utility and management of natural resources. Biomaterial in origin is referred as naturally synthesized from living sources like plant and animal and even from microbes and agrowaste utilization too, which is primarily designed to augment, replace, or repair body tissues or organ. Modern concept of biomaterial encompasses a wider approach of application from food to fashion, architecture to agriculture, environment to industry, biofuel to “biofaber, automotive, nanostructures, and so on and so forth. Besides plant and animal sources, a myriad types of microbial biomaterial synthesis are dependent on a unique microbial metabolic and enzyme activity, genetic diversity, and biodegradability nature of the material itself. Besides this, genetically engineered microbes are not far behind for the efficient application in sectors like liquid fuel, functional biomaterials, nanoscale structure, biocomposites, etc. A diverse group of microbial sources like bacteria, fungi, algae, actinomycetes, yeast, etc. as biomaterial agents are widely exploited nowadays to meet the targets of sustainable development goal in abovementioned practices and so on to be mentioned. The present chapter focuses on a detailed overview of basic understanding of biomaterials, categorization of it including source, mode of operation, and involvement of microbial metabolism in usage of substrates and its heterogenous dimension in areas of cement, plastic, drug-delivery carrier, carriers of few important biomolecules in medicine or edible coating in food product packaging practices, etc.
CD44 is expressed in various isoforms on numerous cell types and tissues during embryogenesis and in the mature organism. CD44 may also be involved in tumor growth. To study the multiple roles of CD44, we abolished expression of all known isoforms of CD44 in mice by targeting exons encoding the invariant N-terminus region of the molecule. Surprisingly, mice were born in Mendelian ratio without any obvious developmental or neurological deficits. Hematological impairment was evidenced by altered tissue distribution of myeloid progenitors with increased levels of colony-forming unit–granulocyte-macrophage (CFU-GM) in bone marrow and reduced numbers of CFU-GM in spleen. Fetal liver colony-forming unit–spleen and granulocyte colony-stimulating factor mobilization assays, together with reduced CFU-GM in peripheral blood, suggested that progenitor egress from bone marrow was defective. In what was either a compensatory response to CD44 deficiency or an immunoregulatory defect, mice also developed exaggerated granuloma responses to Cryotosporidium parvum infection. Finally, tumor studies showed that SV40-transformed CD44-deficient fibroblasts were highly tumorigenic in nude mice, whereas reintroduction of CD44s expression into these fibroblasts resulted in a dramatic inhibition of tumor growth.
The availability of elastoviscous solutions of highly purified hyaluronan has created two new therapeutic methods in human and veterinary medicine: viscosurgery and viscosupplementation. Viscosurgical tools and implants are widely used in ophthalmology and have been suggested for use in otology. Visco-supplementation of joint fluid using elastoviscous hyaluronan solutions is widely used in the treatment of equine traumatic arthritis. It was also suggested for use in idiopathic osteoarthritis in humans, but this application has not received wide acceptance. Cross-linked forms of hyaluronan have been developed and given the generic name of hylans. Water-insoluble soft gels of hylans are ideally suitable as viscosurgical implants to prevent postoperative adhesions and to control scar formation. Hylan solutions are being used in arthroscopic viscosurgery. Hylan devices in various forms (gels, tubes, membranes) have been used in animal studies for matrix engineering, the purpose of which is to control and direct tissue regeneration and augmentation.
Toole BP (Tufts University School of Medicine, Boston, MA, USA). Hyaluronan in morphogenesis (Minisymposium: Hyaluronan). J Intern Med 1997; 242: 35–40. Pericellular matrices surrounding migrating and proliferating cells in the developing embryo, in regenerating tissues and in other dynamic cellular events, such as tumour cell invasion, are enriched in hyaluronan. In addition to contributing to the unique structure of the pericellular matrix, hyaluronan interacts with cell surface receptors, such as RHAMM and CD44. During morphogenesis, these interactions of hyaluronan with the cell surface are important in several ways. First, hyaluronan–CD44 interactions have been shown to mediate endocytic removal of hyaluronan at critical stages of embryonic development. Secondly, hyaluronan provides an appropriately hydrated, pericellular milieu that facilitates cellular invasion. Thirdly, in-vitro studies suggest strongly that interactions of hyaluronan with RHAMM or CD44 are involved in cell movement and proliferation, which are critical events in morphogenesis.
Hyaluronan, a negatively charged, high-molecular weight polysaccharide is found in all tissues and body fluids of higher animals and most abundantly in soft connective tissues. The total amount in an adult human has been estimated to be 11–17 g. Its turnover has earlier been studied by following the fate of endogenously labelled polysaccharide or injected highly concentrated unlabelled polymer. More recently, hyaluronan biosynthetically labelled with 14C or 3H has been injected into various compartments or tissues and its disappearance followed. These experiments have demonstrated a fairly rapid turnover in many localities ( in the order of one day). This is partly due to lymphatic removal of hyaluronan from the tissues and subsequent degradation in lymph nodes and liver. Recent work with [125I]tyramine cellobiose-labelled hyaluronan has furthermore shown that the polysaccharide can also be endocytosed and degraded locally in the tissues. Thus the catabolism of hyaluronan takes place both by local degradation and drainage via the lymphatic system.
Circulating hyaluronan (or hyaluronic acid or hyaluronate) is efficiently sequestered by receptor-mediated endocytosis mainly in sinusoidal liver endothelial cells (LECs). The receptor recognizes hyaluronan, chondroitin sulfate and dermatan sulfate, but not other ligands. Binding affinity increases with increasing chain length of the polysaccharide: Kd varies between 4.6·10−6 for an octassacharide and 9·10−12 for hyaluronan of Mr 6.4·106. Ligands bound by the receptor are associated with coated pits. Internalization takes less than 1 min, after which the ligand appears in small coated vesicles and shortly thereafter in small uncoated vesicles. The ligand resides in larger macropinocytic vesicles before being transferred to lysosomes. Lysosomal degradation of hyaluronan yields glucuronic acid and f-acetylglucosamine of which the latter is deacetylated by N-acetylglucosamine-6-phosphate deacetylase. The remaining pyranose rings are degraded to lactate. Both lactate and acetate are released from LECs and oxidized by the hepatocytes to CO2 and water.