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Collagen Supplementation for Joint Health: The Link between Composition and Scientific Knowledge

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Nutrients
Authors:

Abstract and Figures

Osteoarthritis (OA) is the most common joint disease, generating pain, disability, and socioeconomic costs worldwide. Currently there are no approved disease-modifying drugs for OA, and safety concerns have been identified with the chronic use of symptomatic drugs. In this context, nutritional supplements and nutraceuticals have emerged as potential alternatives. Among them, collagen is being a focus of particular interest, but under the same term different types of collagens coexist with different structures, compositions, and origins, leading to different properties and potential effects. The aim of this narrative review is to generally describe the main types of collagens currently available in marketplace, focusing on those related to joint health, describing their mechanism of action, preclinical, and clinical evidence. Native and hydrolyzed collagen are the most studied collagen types for joint health. Native collagen has a specific immune-mediated mechanism that requires the recognition of its epitopes to inhibit inflammation and tissue catabolism at articular level. Hydrolyzed collagen may contain biologically active peptides that are able to reach joint tissues and exert chondroprotective effects. Although there are preclinical and clinical studies showing the safety and efficacy of food ingredients containing both types of collagens, available research suggests a clear link between collagen chemical structure and mechanism of action.
This content is subject to copyright.
Citation: Martínez-Puig, D.;
Costa-Larrión, E.; Rubio-Rodríguez,
N.; Gálvez-Martín, P. Collagen
Supplementation for Joint Health:
The Link between Composition and
Scientific Knowledge. Nutrients 2023,
15, 1332. https://doi.org/
10.3390/nu15061332
Academic Editors: Gregory C.
Bogdanis and Christoforos D.
Giannaki
Received: 13 February 2023
Revised: 3 March 2023
Accepted: 6 March 2023
Published: 8 March 2023
Copyright: © 2023 by the authors.
Licensee MDPI, Basel, Switzerland.
This article is an open access article
distributed under the terms and
conditions of the Creative Commons
Attribution (CC BY) license (https://
creativecommons.org/licenses/by/
4.0/).
nutrients
Review
Collagen Supplementation for Joint Health: The Link between
Composition and Scientific Knowledge
Daniel Martínez-Puig *, Ester Costa-Larrión, Nuria Rubio-Rodríguez and Patricia Gálvez-Martín
R&D Bioiberica S.A.U., E-08389 Palafolls, Spain
*Correspondence: dmartinez@bioiberica.com; Tel.: +34-93-7650390
Abstract:
Osteoarthritis (OA) is the most common joint disease, generating pain, disability, and
socioeconomic costs worldwide. Currently there are no approved disease-modifying drugs for
OA, and safety concerns have been identified with the chronic use of symptomatic drugs. In this
context, nutritional supplements and nutraceuticals have emerged as potential alternatives. Among
them, collagen is being a focus of particular interest, but under the same term different types of
collagens coexist with different structures, compositions, and origins, leading to different properties
and potential effects. The aim of this narrative review is to generally describe the main types of
collagens currently available in marketplace, focusing on those related to joint health, describing their
mechanism of action, preclinical, and clinical evidence. Native and hydrolyzed collagen are the most
studied collagen types for joint health. Native collagen has a specific immune-mediated mechanism
that requires the recognition of its epitopes to inhibit inflammation and tissue catabolism at articular
level. Hydrolyzed collagen may contain biologically active peptides that are able to reach joint tissues
and exert chondroprotective effects. Although there are preclinical and clinical studies showing the
safety and efficacy of food ingredients containing both types of collagens, available research suggests
a clear link between collagen chemical structure and mechanism of action.
Keywords:
native collagen; hydrolyzed collagen; nutritional supplement; joint health; osteoarthritis
1. Introduction
Osteoarthritis (OA) is becoming one of the most common joint conditions due to the
increase in life expectancy [
1
], representing nowadays a major socioeconomic and public
health issue [
2
]. OA is characterized by the inflammation and progressive destruction of
articular cartilage, affecting any joint although is more prevalent in knee, hip, spine, and
interphalangeal joints causing pain, functional limitations, and reducing quality of life [
3
,
4
].
There are different treatment options for OA including pharmacological and non-
pharmacological approaches. The most used pharmacological treatments have been anal-
gesics (paracetamol) and non-steroidal anti-inflammatory drugs (NSAIDS) [
5
]. However,
safety concerns associated with their long-term administration have limited its use, par-
ticularly in those patients with comorbidities [
6
,
7
]. For this reason, efforts have been
focused on finding alternative treatments to improve clinical symptoms with better safety
profile and tolerability, known as Symptomatic Slow Action Drugs for OA (SYSADOAs)
such as glucosamine (GS) and chondroitin sulfate (CS) which are currently the most used
SYSADOAs [
8
]. However, non-pharmacological treatments based on the intake of collagen
as nutritional supplement have been positioned as an emerging focus of interest to support
a preventive or therapeutic effect in patients with OA [4].
Collagen is the most abundant protein in the extracellular matrix (ECM) and connec-
tive tissues of vertebrates, being more abundant in mammalian species [
9
]. The typical
structural element of collagen is a rod-like triple-helical domain. Based on their structure,
supramolecular organization, and functional features, 28 types of collagens have been
described [
10
]. The obtaining of collagen mostly relies on extraction from animal-derived
Nutrients 2023,15, 1332. https://doi.org/10.3390/nu15061332 https://www.mdpi.com/journal/nutrients
Nutrients 2023,15, 1332 2 of 17
collagen rich tissues such as cartilage, skin, and bones. Depending on the manufacturing
process, different collagen-derived products can be obtained with totally different structure,
composition, and properties such as: undenatured native collagen (insoluble) or soluble
native collagen, both of which maintain the triple helix structure; gelatin (denatured colla-
gen), and hydrolyzed collagen (peptides/amino acids) which in turn can be produced with
different degrees of hydrolysis [11].
The molecular structure of orally administrated collagen determines its mechanism
of action for joint heath. Initially, it was postulated that collagen supplementation could
promote the synthesis of connective tissue, especially cartilage ECM [
12
], mainly because
collagen represents its major component [
13
]. In fact, it has been demonstrated that certain
peptides from hydrolyzed collagen are absorbed and accumulated in the cartilage [14]. In
addition, animal models of OA have obtained promising results in terms of preservation
of cartilage structure as a result of long-term ingestion of hydrolyzed collagen [
15
,
16
].
Regarding native collagen (both soluble or insoluble), the most studied is type II, which
was evaluated initially in rheumatoid arthritis [
17
] and afterwards in OA [
18
]. It has
been reported that native type II collagen elicits an immune-mediated response called
oral tolerance [
19
], a totally different mechanism compared with the one described for
hydrolyzed collagens. According to this mechanism of action, native type II collagen would
reduce autoimmune reactions against endogenous collagen at articular cartilage level.
Collagen has been extensively studied for years. Only in the past decade, more
than 20,000 papers have been published about different facets of collagen describing its
molecular structure of triple helix, its natural occurrence, its physicochemical properties
and biological functions, extraction methods, or its new applications. However, as under
the same term different types of collagens coexist, there is certain confusion about the
therapeutic potential of each one, depending on its structure and composition.
Thus, the aim of the present review is to define the different types of collagens from a
structural point of view, review the proposed mechanisms of action associated with each
form for oral use, and compile its preclinical and clinical evidence for joint health.
2. Understanding Collagen World
Collagen is an ancient term coined to name the natural adhesive obtained by cooking
animal bones. It is though that derives from Greek
κ
ó
λλα
(kólla or “glue”) and -
γεν ´
ης
(-gen´
¯
es or “producing”). From a scientific standpoint, collagen is now defined as a large
family of structural proteins found in the ECM of animal tissues that are distinguished for
containing one or more domains with a unique triple helical structure [
20
]. Triple helical
conformation of collagen was first described in the 1950s according to X-ray diffraction
pattern of collagen fibers found in skin [
21
]. This structure comprises three left-handed
polypeptide chains (so-called collagen
α
-chains) that are coiled into a right-hand helical
structure. Collagen polypeptide chains are distinguished for having a repeated specific
unit (Gly-X-Y) in which Gly is glycine (the smallest amino acid in nature); and X and Y
are frequently proline (Pro) and hydroxyproline (Hyp). Due to this specific motif, sev-
eral molecular interactions take place in the collagen triple helix leading a unique close
packaging along a central axis [22].
Knowledge about collagen has been exponentially increased in the past decades.
Whereas scientific community in the 1970s talked about only four types of genetically dis-
tinct collagens [
23
], at present it is generally accepted that collagen superfamily comprises
up to 28 members that differ from each other in molecular composition as well as in their
supramolecular organization within the ECM [
24
27
]. The occurrence of an additional col-
lagen type, called collagen XXIX, has been also claimed by some authors [
28
,
29
], although,
given that COL29A1 gene was shown to be identical to the COL6A5 gene and that the
a1(XXIX) chain corresponds to the a5(VI) [
30
], collagen XXIX is not generally accepted as a
genetically distinct family [24].
Nutrients 2023,15, 1332 3 of 17
Depending on their supramolecular organization, collagen types can be addition-
ally assorted in different families such as fibril-forming collagens, basement membrane
collagens or microfibrillar collagens, among others [10,25].
Fibril-forming collagens are by far the most abundant in nature. They comprise type
I, type II, type III, type V, and XI. All these collagen types have in common the ability to
assemble into a quarter-staggered fibril-array. Withing this group, type I and type II occur to
a greater extend. Type I collagens are heterotrimeric molecules, [
α
1 (I)]
2α
2 (I)], comprising
two identical polypeptide chains [
α
1 (I)] and a different one, [
α
2 (I)]. They represent
more than 90% of organic matter in bone, dermis, tendon, ligaments, and cornea. Type
II collagens are homotrimer molecules, [
α
1 (II)]
3
, comprising three identical polypeptide
chains. They account for about 80% of total collagen in cartilage but also occur in other
tissues such as vitreous body or cornea among others [10].
It is worth noting that other fibrous proteins such as elastin have been found in ECM
along with fibril-forming collagen [
31
]. However, collagen fibers and elastin differ in both
chemical composition [
32
] and supramolecular organization [
33
]. Conversely, it has been
reported that certain plasma and cell surface proteins (i.e., collectins, C1q, or ficolin) exhibit
collagen triple helix domains as well, but they have been excluded from collagen family as
they do not occur in the ECM [34].
Biosynthesis of collagen has been observed in mesenchymal cell family (fibroblasts,
chondroblasts or osteoblasts) as well as in other cell lines such as epithelial cells [
23
]. It
in-volves an intricate multi-step process that starts with the transcription of collagen genes,
follows up with several intracellular reactions, and finishes with extracellular processing.
Intracellular reactions comprise ribosomal protein synthesis (translation), post-translational
modifications, assembly of the three
α
-chains into trimeric collagen monomers (also known
as procollagen) and secretion to ECM; whereas extracellular processing comprises complex
cross-linking reactions that convert procollagen into a supramolecular structure [30].
No evidence has been found so far about the presence of collagen in other living
beings such plants or unicellular microorganisms. Structural role of collagen in those
lower phyla seems to be replaced by other compounds, mainly polysaccharides or protein–
polysaccharide complex [35].
Collagen has been historically valorized in several industrial fields. Given that it is
an edible protein, a large number of industrial applications have been focused on food
industry, where collagen commonly plays different food technological functions such as
emulsifier, film-forming material, gelling agent, or stabilizer among others [
36
]. Moreover,
due to its mechanical properties and biodegradability, collagen is also considered an ideal
material for many biomedical applications such as skin substitute, scaffold manufacturing
for tissue engineering (bone, tendon, or cartilage), neural repair or drug delivery systems
including hydrogels, granules, microcapsules, or microspheres [37].
It is worth mentioning that not all the collagens described in the literature for a
commercial application are equal, but there is plenty of variety in terms of amino acid
composition or molecular structure as well as in term of physicochemical properties or bio-
logical activities. Such variety is not only related to raw material but also to manufacturing
process.
The great majority of collagens currently found in the marketplace are obtained from
animal-origin raw materials. Skins, tendons, bones, and hides are the most typical, which
basically comprise connective tissue and thus are an abundant source of type I collagen [
38
].
In addition, cartilages are used for production of type II collagen [
39
,
40
] and, in a minor
extend, eggshell membranes are proposed as a natural raw material to obtain type I, V,
and X collagen [
41
]. Traditional animal species chosen for collagen production are porcine
and bovine, although poultry [
42
] and fish [
43
] are becoming more popular to over-come
religious limitations of porcine collagen and concerns about bovine zoonotic diseases.
Manufacturing processes to obtain collagen from a natural source usually involve
different extraction and purification techniques, which shape the main features of the final
product as physicochemical properties or biological activities. As a result, different collagen
Nutrients 2023,15, 1332 4 of 17
products have been described, such as “insoluble undenatured native collagens”, “soluble
native collagens”, “denatured collagens”, “collagen hydrolysates”, and “collagen peptides”
(Figure 1; Table 1).
Nutrients 2023, 15, x FOR PEER REVIEW 4 of 18
over-come religious limitations of porcine collagen and concerns about bovine zoonotic
diseases.
Manufacturing processes to obtain collagen from a natural source usually involve
different extraction and purification techniques, which shape the main features of the final
product as physicochemical properties or biological activities. As a result, different colla-
gen products have been described, such as “insoluble undenatured native collagens,
“soluble native collagens”, “denatured collagens”, “collagen hydrolysates, and collagen
peptides” (Figure 1; Table 1).
Figure 1. Overview of main collagen products that can be obtained from natural sources (animal
by-products) according to their origin (animal and tissue) and manufacturing process. Hydrolyzed
collagens can be obtained from cartilage or other connective tissues through an enzymatic treatment
to breakdown polypeptide chains. Undenatured (non-soluble) or soluble native collagen type II can
be only obtained from cartilage, through soft temperature processes to maintain the triple helix
structure intact.
Figure 1.
Overview of main collagen products that can be obtained from natural sources (animal
by-products) according to their origin (animal and tissue) and manufacturing process. Hydrolyzed
collagens can be obtained from cartilage or other connective tissues through an enzymatic treatment
to breakdown polypeptide chains. Undenatured (non-soluble) or soluble native collagen type II
can be only obtained from cartilage, through soft temperature processes to maintain the triple helix
structure intact.
Insoluble undenatured native collagens are distinguished for maintaining intact the
triple helix structure (native collagen), which are resistant to proteases, along with the
covalent crosslinking that naturally occurs in animal tissues, specially at the terminal non-
helical domains. To achieve those features, the production process must avoid using high
temperatures and denaturation or solubilization agents [
44
]. Insoluble undenatured native
collagens are characterized for being non-soluble in water as well as for exhibiting antigenic
sites (epitopes), which depend on collagen type and consequently on the raw material used.
The preservation of certain collagen epitopes, associated to fibrillar structure, has been
shown to be involved in immune-mediated effects [
45
,
46
]. Hence, if the raw material is
mostly composed by cartilaginous tissue, such as chicken sternum, the resulting product is
known as insoluble undenatured type II collagen [39]. As further described in Section 3.1,
Nutrients 2023,15, 1332 5 of 17
this product exhibits specific epitopes related to type II collagen which promote a reduction
in inflammation related to OA when taken orally.
Table 1. Molecular features of collagen products.
Collagen Product Collagen Type
Molecular Features
Cross Linking Collagen
Triple Hélix
Active Epitopes
with Effect in OA
Undenatured native collagen
(insoluble)
Type I X X
USV Symbol Macro(s) Description
26B2 \textuncrfemale
\textPUuncrfemale
NEUTER
26B9 \texthexstar SEXTILE
26BD \textSoccerBall SOCCER BALL
26C5 \textSunCload SUN BEHIND CLOUD
26C6 \textRain RAIN
26D4 \textnoway NO ENTRY
26F0 \textMountain MOUNTAIN
26FA \textTent TENT
2701 \textScissorRightBrokenBottom UPPER BLADE SCISSORS
2702 \textScissorRight BLACK SCISSORS
2703 \textScissorRightBrokenTop LOWER BLADE SCISSORS
2704 \textScissorHollowRight WHITE SCISSORS
2706 \textPhoneHandset TELEPHONE LOCATION SIGN
2707 \textTape TAPE DRIVE
2708 \textPlane AIRPLANE
2709 \textEnvelope ENVELOPE
270C \textPeace VICTORY HAND
270D \textWritingHand WRITING HAND
270E \textPencilRightDown LOWER RIGHT PENCIL
270F \textPencilRight PENCIL
2710 \textPencilRightUp UPPER RIGHT PENCIL
2711 \textNibRight WHITE NIB
2712 \textNibSolidRight BLACK NIB
2713 \textCheckmark CHECK MARK
2714 \textCheckmarkBold HEAVY CHECK MARK
2715 \textXSolid MULTIPLICATION X
2716 \textXSolidBold HEAVY MULTIPLICATIONX
2717 \textXSolidBrush BALLOT X
2719 \textPlusOutline OUTLINED GREEK CROSS
271A \textPlus HEAVY GREEK CROSS
271B \textPlusThinCenterOpen OPEN CENTRE CROSS
271C \textPlusCenterOpen HEAVY OPEN CENTRE CROSS
271D \textCross LATIN CROSS
271E \textCrossOpenShadow SHADOWED WHITE LATIN CROSS
271F \textCrossOutline OUTLINED LATIN CROSS
2720 \textCrossMaltese MALTESE CROSS
2721 \textDavidStar STAR OF DAVID
2722 \textFourAsterisk FOUR TEARDROP-SPOKED ASTERISK
2723 \textJackStar FOUR BALLOON-SPOKED ASTERISK
2724 \textJackStarBold HEAVY FOUR BALLOON-SPOKED ASTERISK
2725 \textClowerTips FOUR CLUB-SPOKED ASTERISK
2726 \textFourStar BLACK FOUR POINTED STAR
2727 \textFourStarOpen WHITE FOUR POINTED STAR
272A \textFiveStarOpenCircled CIRCLED WHITE STAR
272B \textFiveStarCenterOpen OPEN CENTRE BLACK STAR
272C \textFiveStarOpenDotted BLACK CENTRE WHITE STAR
272D \textFiveStarOutline OUTLINED BLACK STAR
272E \textFiveStarOutlineHeavy HEAVY OUTLINED BLACK STAR
272F \textFiveStarConvex PINWHEEL STAR
2730 \textFiveStarShadow SHADOWED WHITE STAR
2731 \textAsteriskBold HEAVY ASTERISK
2732 \textAsteriskCenterOpen OPEN CENTRE ASTERISK
2734 \textEightStarTaper EIGHT POINTED BLACK STAR
2735 \textEightStarConvex EIGHT POINTED PINWHEEL STAR
46
Type II X X X
Soluble native collagen Type I
USV Symbol Macro(s) Description
26B2 \textuncrfemale
\textPUuncrfemale
NEUTER
26B9 \texthexstar SEXTILE
26BD \textSoccerBall SOCCER BALL
26C5 \textSunCload SUN BEHIND CLOUD
26C6 \textRain RAIN
26D4 \textnoway NO ENTRY
26F0 \textMountain MOUNTAIN
26FA \textTent TENT
2701 \textScissorRightBrokenBottom UPPER BLADE SCISSORS
2702 \textScissorRight BLACK SCISSORS
2703 \textScissorRightBrokenTop LOWER BLADE SCISSORS
2704 \textScissorHollowRight WHITE SCISSORS
2706 \textPhoneHandset TELEPHONE LOCATION SIGN
2707 \textTape TAPE DRIVE
2708 \textPlane AIRPLANE
2709 \textEnvelope ENVELOPE
270C \textPeace VICTORY HAND
270D \textWritingHand WRITING HAND
270E \textPencilRightDown LOWER RIGHT PENCIL
270F \textPencilRight PENCIL
2710 \textPencilRightUp UPPER RIGHT PENCIL
2711 \textNibRight WHITE NIB
2712 \textNibSolidRight BLACK NIB
2713 \textCheckmark CHECK MARK
2714 \textCheckmarkBold HEAVY CHECK MARK
2715 \textXSolid MULTIPLICATION X
2716 \textXSolidBold HEAVY MULTIPLICATIONX
2717 \textXSolidBrush BALLOT X
2719 \textPlusOutline OUTLINED GREEK CROSS
271A \textPlus HEAVY GREEK CROSS
271B \textPlusThinCenterOpen OPEN CENTRE CROSS
271C \textPlusCenterOpen HEAVY OPEN CENTRE CROSS
271D \textCross LATIN CROSS
271E \textCrossOpenShadow SHADOWED WHITE LATIN CROSS
271F \textCrossOutline OUTLINED LATIN CROSS
2720 \textCrossMaltese MALTESE CROSS
2721 \textDavidStar STAR OF DAVID
2722 \textFourAsterisk FOUR TEARDROP-SPOKED ASTERISK
2723 \textJackStar FOUR BALLOON-SPOKED ASTERISK
2724 \textJackStarBold HEAVY FOUR BALLOON-SPOKED ASTERISK
2725 \textClowerTips FOUR CLUB-SPOKED ASTERISK
2726 \textFourStar BLACK FOUR POINTED STAR
2727 \textFourStarOpen WHITE FOUR POINTED STAR
272A \textFiveStarOpenCircled CIRCLED WHITE STAR
272B \textFiveStarCenterOpen OPEN CENTRE BLACK STAR
272C \textFiveStarOpenDotted BLACK CENTRE WHITE STAR
272D \textFiveStarOutline OUTLINED BLACK STAR
272E \textFiveStarOutlineHeavy HEAVY OUTLINED BLACK STAR
272F \textFiveStarConvex PINWHEEL STAR
2730 \textFiveStarShadow SHADOWED WHITE STAR
2731 \textAsteriskBold HEAVY ASTERISK
2732 \textAsteriskCenterOpen OPEN CENTRE ASTERISK
2734 \textEightStarTaper EIGHT POINTED BLACK STAR
2735 \textEightStarConvex EIGHT POINTED PINWHEEL STAR
46
X
USV Symbol Macro(s) Description
26B2 \textuncrfemale
\textPUuncrfemale
NEUTER
26B9 \texthexstar SEXTILE
26BD \textSoccerBall SOCCER BALL
26C5 \textSunCload SUN BEHIND CLOUD
26C6 \textRain RAIN
26D4 \textnoway NO ENTRY
26F0 \textMountain MOUNTAIN
26FA \textTent TENT
2701 \textScissorRightBrokenBottom UPPER BLADE SCISSORS
2702 \textScissorRight BLACK SCISSORS
2703 \textScissorRightBrokenTop LOWER BLADE SCISSORS
2704 \textScissorHollowRight WHITE SCISSORS
2706 \textPhoneHandset TELEPHONE LOCATION SIGN
2707 \textTape TAPE DRIVE
2708 \textPlane AIRPLANE
2709 \textEnvelope ENVELOPE
270C \textPeace VICTORY HAND
270D \textWritingHand WRITING HAND
270E \textPencilRightDown LOWER RIGHT PENCIL
270F \textPencilRight PENCIL
2710 \textPencilRightUp UPPER RIGHT PENCIL
2711 \textNibRight WHITE NIB
2712 \textNibSolidRight BLACK NIB
2713 \textCheckmark CHECK MARK
2714 \textCheckmarkBold HEAVY CHECK MARK
2715 \textXSolid MULTIPLICATION X
2716 \textXSolidBold HEAVY MULTIPLICATIONX
2717 \textXSolidBrush BALLOT X
2719 \textPlusOutline OUTLINED GREEK CROSS
271A \textPlus HEAVY GREEK CROSS
271B \textPlusThinCenterOpen OPEN CENTRE CROSS
271C \textPlusCenterOpen HEAVY OPEN CENTRE CROSS
271D \textCross LATIN CROSS
271E \textCrossOpenShadow SHADOWED WHITE LATIN CROSS
271F \textCrossOutline OUTLINED LATIN CROSS
2720 \textCrossMaltese MALTESE CROSS
2721 \textDavidStar STAR OF DAVID
2722 \textFourAsterisk FOUR TEARDROP-SPOKED ASTERISK
2723 \textJackStar FOUR BALLOON-SPOKED ASTERISK
2724 \textJackStarBold HEAVY FOUR BALLOON-SPOKED ASTERISK
2725 \textClowerTips FOUR CLUB-SPOKED ASTERISK
2726 \textFourStar BLACK FOUR POINTED STAR
2727 \textFourStarOpen WHITE FOUR POINTED STAR
272A \textFiveStarOpenCircled CIRCLED WHITE STAR
272B \textFiveStarCenterOpen OPEN CENTRE BLACK STAR
272C \textFiveStarOpenDotted BLACK CENTRE WHITE STAR
272D \textFiveStarOutline OUTLINED BLACK STAR
272E \textFiveStarOutlineHeavy HEAVY OUTLINED BLACK STAR
272F \textFiveStarConvex PINWHEEL STAR
2730 \textFiveStarShadow SHADOWED WHITE STAR
2731 \textAsteriskBold HEAVY ASTERISK
2732 \textAsteriskCenterOpen OPEN CENTRE ASTERISK
2734 \textEightStarTaper EIGHT POINTED BLACK STAR
2735 \textEightStarConvex EIGHT POINTED PINWHEEL STAR
46
Type II
USV Symbol Macro(s) Description
26B2 \textuncrfemale
\textPUuncrfemale
NEUTER
26B9 \texthexstar SEXTILE
26BD \textSoccerBall SOCCER BALL
26C5 \textSunCload SUN BEHIND CLOUD
26C6 \textRain RAIN
26D4 \textnoway NO ENTRY
26F0 \textMountain MOUNTAIN
26FA \textTent TENT
2701 \textScissorRightBrokenBottom UPPER BLADE SCISSORS
2702 \textScissorRight BLACK SCISSORS
2703 \textScissorRightBrokenTop LOWER BLADE SCISSORS
2704 \textScissorHollowRight WHITE SCISSORS
2706 \textPhoneHandset TELEPHONE LOCATION SIGN
2707 \textTape TAPE DRIVE
2708 \textPlane AIRPLANE
2709 \textEnvelope ENVELOPE
270C \textPeace VICTORY HAND
270D \textWritingHand WRITING HAND
270E \textPencilRightDown LOWER RIGHT PENCIL
270F \textPencilRight PENCIL
2710 \textPencilRightUp UPPER RIGHT PENCIL
2711 \textNibRight WHITE NIB
2712 \textNibSolidRight BLACK NIB
2713 \textCheckmark CHECK MARK
2714 \textCheckmarkBold HEAVY CHECK MARK
2715 \textXSolid MULTIPLICATION X
2716 \textXSolidBold HEAVY MULTIPLICATIONX
2717 \textXSolidBrush BALLOT X
2719 \textPlusOutline OUTLINED GREEK CROSS
271A \textPlus HEAVY GREEK CROSS
271B \textPlusThinCenterOpen OPEN CENTRE CROSS
271C \textPlusCenterOpen HEAVY OPEN CENTRE CROSS
271D \textCross LATIN CROSS
271E \textCrossOpenShadow SHADOWED WHITE LATIN CROSS
271F \textCrossOutline OUTLINED LATIN CROSS
2720 \textCrossMaltese MALTESE CROSS
2721 \textDavidStar STAR OF DAVID
2722 \textFourAsterisk FOUR TEARDROP-SPOKED ASTERISK
2723 \textJackStar FOUR BALLOON-SPOKED ASTERISK
2724 \textJackStarBold HEAVY FOUR BALLOON-SPOKED ASTERISK
2725 \textClowerTips FOUR CLUB-SPOKED ASTERISK
2726 \textFourStar BLACK FOUR POINTED STAR
2727 \textFourStarOpen WHITE FOUR POINTED STAR
272A \textFiveStarOpenCircled CIRCLED WHITE STAR
272B \textFiveStarCenterOpen OPEN CENTRE BLACK STAR
272C \textFiveStarOpenDotted BLACK CENTRE WHITE STAR
272D \textFiveStarOutline OUTLINED BLACK STAR
272E \textFiveStarOutlineHeavy HEAVY OUTLINED BLACK STAR
272F \textFiveStarConvex PINWHEEL STAR
2730 \textFiveStarShadow SHADOWED WHITE STAR
2731 \textAsteriskBold HEAVY ASTERISK
2732 \textAsteriskCenterOpen OPEN CENTRE ASTERISK
2734 \textEightStarTaper EIGHT POINTED BLACK STAR
2735 \textEightStarConvex EIGHT POINTED PINWHEEL STAR
46
X X
Gelatin
(denatured collagen) Type I & Type II
USV Symbol Macro(s) Description
26B2 \textuncrfemale
\textPUuncrfemale
NEUTER
26B9 \texthexstar SEXTILE
26BD \textSoccerBall SOCCER BALL
26C5 \textSunCload SUN BEHIND CLOUD
26C6 \textRain RAIN
26D4 \textnoway NO ENTRY
26F0 \textMountain MOUNTAIN
26FA \textTent TENT
2701 \textScissorRightBrokenBottom UPPER BLADE SCISSORS
2702 \textScissorRight BLACK SCISSORS
2703 \textScissorRightBrokenTop LOWER BLADE SCISSORS
2704 \textScissorHollowRight WHITE SCISSORS
2706 \textPhoneHandset TELEPHONE LOCATION SIGN
2707 \textTape TAPE DRIVE
2708 \textPlane AIRPLANE
2709 \textEnvelope ENVELOPE
270C \textPeace VICTORY HAND
270D \textWritingHand WRITING HAND
270E \textPencilRightDown LOWER RIGHT PENCIL
270F \textPencilRight PENCIL
2710 \textPencilRightUp UPPER RIGHT PENCIL
2711 \textNibRight WHITE NIB
2712 \textNibSolidRight BLACK NIB
2713 \textCheckmark CHECK MARK
2714 \textCheckmarkBold HEAVY CHECK MARK
2715 \textXSolid MULTIPLICATION X
2716 \textXSolidBold HEAVY MULTIPLICATIONX
2717 \textXSolidBrush BALLOT X
2719 \textPlusOutline OUTLINED GREEK CROSS
271A \textPlus HEAVY GREEK CROSS
271B \textPlusThinCenterOpen OPEN CENTRE CROSS
271C \textPlusCenterOpen HEAVY OPEN CENTRE CROSS
271D \textCross LATIN CROSS
271E \textCrossOpenShadow SHADOWED WHITE LATIN CROSS
271F \textCrossOutline OUTLINED LATIN CROSS
2720 \textCrossMaltese MALTESE CROSS
2721 \textDavidStar STAR OF DAVID
2722 \textFourAsterisk FOUR TEARDROP-SPOKED ASTERISK
2723 \textJackStar FOUR BALLOON-SPOKED ASTERISK
2724 \textJackStarBold HEAVY FOUR BALLOON-SPOKED ASTERISK
2725 \textClowerTips FOUR CLUB-SPOKED ASTERISK
2726 \textFourStar BLACK FOUR POINTED STAR
2727 \textFourStarOpen WHITE FOUR POINTED STAR
272A \textFiveStarOpenCircled CIRCLED WHITE STAR
272B \textFiveStarCenterOpen OPEN CENTRE BLACK STAR
272C \textFiveStarOpenDotted BLACK CENTRE WHITE STAR
272D \textFiveStarOutline OUTLINED BLACK STAR
272E \textFiveStarOutlineHeavy HEAVY OUTLINED BLACK STAR
272F \textFiveStarConvex PINWHEEL STAR
2730 \textFiveStarShadow SHADOWED WHITE STAR
2731 \textAsteriskBold HEAVY ASTERISK
2732 \textAsteriskCenterOpen OPEN CENTRE ASTERISK
2734 \textEightStarTaper EIGHT POINTED BLACK STAR
2735 \textEightStarConvex EIGHT POINTED PINWHEEL STAR
46
USV Symbol Macro(s) Description
26B2 \textuncrfemale
\textPUuncrfemale
NEUTER
26B9 \texthexstar SEXTILE
26BD \textSoccerBall SOCCER BALL
26C5 \textSunCload SUN BEHIND CLOUD
26C6 \textRain RAIN
26D4 \textnoway NO ENTRY
26F0 \textMountain MOUNTAIN
26FA \textTent TENT
2701 \textScissorRightBrokenBottom UPPER BLADE SCISSORS
2702 \textScissorRight BLACK SCISSORS
2703 \textScissorRightBrokenTop LOWER BLADE SCISSORS
2704 \textScissorHollowRight WHITE SCISSORS
2706 \textPhoneHandset TELEPHONE LOCATION SIGN
2707 \textTape TAPE DRIVE
2708 \textPlane AIRPLANE
2709 \textEnvelope ENVELOPE
270C \textPeace VICTORY HAND
270D \textWritingHand WRITING HAND
270E \textPencilRightDown LOWER RIGHT PENCIL
270F \textPencilRight PENCIL
2710 \textPencilRightUp UPPER RIGHT PENCIL
2711 \textNibRight WHITE NIB
2712 \textNibSolidRight BLACK NIB
2713 \textCheckmark CHECK MARK
2714 \textCheckmarkBold HEAVY CHECK MARK
2715 \textXSolid MULTIPLICATION X
2716 \textXSolidBold HEAVY MULTIPLICATIONX
2717 \textXSolidBrush BALLOT X
2719 \textPlusOutline OUTLINED GREEK CROSS
271A \textPlus HEAVY GREEK CROSS
271B \textPlusThinCenterOpen OPEN CENTRE CROSS
271C \textPlusCenterOpen HEAVY OPEN CENTRE CROSS
271D \textCross LATIN CROSS
271E \textCrossOpenShadow SHADOWED WHITE LATIN CROSS
271F \textCrossOutline OUTLINED LATIN CROSS
2720 \textCrossMaltese MALTESE CROSS
2721 \textDavidStar STAR OF DAVID
2722 \textFourAsterisk FOUR TEARDROP-SPOKED ASTERISK
2723 \textJackStar FOUR BALLOON-SPOKED ASTERISK
2724 \textJackStarBold HEAVY FOUR BALLOON-SPOKED ASTERISK
2725 \textClowerTips FOUR CLUB-SPOKED ASTERISK
2726 \textFourStar BLACK FOUR POINTED STAR
2727 \textFourStarOpen WHITE FOUR POINTED STAR
272A \textFiveStarOpenCircled CIRCLED WHITE STAR
272B \textFiveStarCenterOpen OPEN CENTRE BLACK STAR
272C \textFiveStarOpenDotted BLACK CENTRE WHITE STAR
272D \textFiveStarOutline OUTLINED BLACK STAR
272E \textFiveStarOutlineHeavy HEAVY OUTLINED BLACK STAR
272F \textFiveStarConvex PINWHEEL STAR
2730 \textFiveStarShadow SHADOWED WHITE STAR
2731 \textAsteriskBold HEAVY ASTERISK
2732 \textAsteriskCenterOpen OPEN CENTRE ASTERISK
2734 \textEightStarTaper EIGHT POINTED BLACK STAR
2735 \textEightStarConvex EIGHT POINTED PINWHEEL STAR
46
USV Symbol Macro(s) Description
26B2 \textuncrfemale
\textPUuncrfemale
NEUTER
26B9 \texthexstar SEXTILE
26BD \textSoccerBall SOCCER BALL
26C5 \textSunCload SUN BEHIND CLOUD
26C6 \textRain RAIN
26D4 \textnoway NO ENTRY
26F0 \textMountain MOUNTAIN
26FA \textTent TENT
2701 \textScissorRightBrokenBottom UPPER BLADE SCISSORS
2702 \textScissorRight BLACK SCISSORS
2703 \textScissorRightBrokenTop LOWER BLADE SCISSORS
2704 \textScissorHollowRight WHITE SCISSORS
2706 \textPhoneHandset TELEPHONE LOCATION SIGN
2707 \textTape TAPE DRIVE
2708 \textPlane AIRPLANE
2709 \textEnvelope ENVELOPE
270C \textPeace VICTORY HAND
270D \textWritingHand WRITING HAND
270E \textPencilRightDown LOWER RIGHT PENCIL
270F \textPencilRight PENCIL
2710 \textPencilRightUp UPPER RIGHT PENCIL
2711 \textNibRight WHITE NIB
2712 \textNibSolidRight BLACK NIB
2713 \textCheckmark CHECK MARK
2714 \textCheckmarkBold HEAVY CHECK MARK
2715 \textXSolid MULTIPLICATION X
2716 \textXSolidBold HEAVY MULTIPLICATIONX
2717 \textXSolidBrush BALLOT X
2719 \textPlusOutline OUTLINED GREEK CROSS
271A \textPlus HEAVY GREEK CROSS
271B \textPlusThinCenterOpen OPEN CENTRE CROSS
271C \textPlusCenterOpen HEAVY OPEN CENTRE CROSS
271D \textCross LATIN CROSS
271E \textCrossOpenShadow SHADOWED WHITE LATIN CROSS
271F \textCrossOutline OUTLINED LATIN CROSS
2720 \textCrossMaltese MALTESE CROSS
2721 \textDavidStar STAR OF DAVID
2722 \textFourAsterisk FOUR TEARDROP-SPOKED ASTERISK
2723 \textJackStar FOUR BALLOON-SPOKED ASTERISK
2724 \textJackStarBold HEAVY FOUR BALLOON-SPOKED ASTERISK
2725 \textClowerTips FOUR CLUB-SPOKED ASTERISK
2726 \textFourStar BLACK FOUR POINTED STAR
2727 \textFourStarOpen WHITE FOUR POINTED STAR
272A \textFiveStarOpenCircled CIRCLED WHITE STAR
272B \textFiveStarCenterOpen OPEN CENTRE BLACK STAR
272C \textFiveStarOpenDotted BLACK CENTRE WHITE STAR
272D \textFiveStarOutline OUTLINED BLACK STAR
272E \textFiveStarOutlineHeavy HEAVY OUTLINED BLACK STAR
272F \textFiveStarConvex PINWHEEL STAR
2730 \textFiveStarShadow SHADOWED WHITE STAR
2731 \textAsteriskBold HEAVY ASTERISK
2732 \textAsteriskCenterOpen OPEN CENTRE ASTERISK
2734 \textEightStarTaper EIGHT POINTED BLACK STAR
2735 \textEightStarConvex EIGHT POINTED PINWHEEL STAR
46
Hydrolyzed collagen/collagen
peptides
Procedures for obtaining insoluble collagens from skin, tendon, bone, or heart [
44
,
47
,
48
], have been also found in the literature. To the best of our knowledge, no industrial or
medical applications have been described about these products.
Soluble native collagens are characterized for having intact the triple helix but a fewer
crosslinking than the insoluble products. Thereby, from a chemical standpoint, collagen in
these products only maintains its tertiary structure (triple helix) whose molecular weight
is 300 kDa on average. To match those features, the production process is carried out at
low temperatures but includes the addition of a solubilization agent able to destabilize
selectively the covalent bonds in natural crosslinking. A wide range of solubilization agents
have been reported in the literature [
43
], leading to different “soluble collagens” with
specific physicochemical properties. Among them, “acid solubilized collagen” (ASC) and
“pepsin solubilized collagen” (PSC) are the most commonly found in the market. Soluble
native collagen can also be distinguished by its collagen type, which can be identified
according to its antigenic sites (epitopes).
Denatured collagen, also known as “gelatin”, are differentiated for having lost the
triple helix structure because of the action of temperature and/or a denaturing agent.
Therefore, they are not composed by collagen molecules but by a random mixture of
polypeptide chains that usually range from 15 to 250 kDa [
14
] and that are characterized
by a high content in Hyp. Depending on the raw material and extraction procedure,
gelatins can differ in composition but also in solubility behavior and rheological properties,
being gel strength and thermal stability the main quality attributes. Common gelatins in
marketplace are “type A” (isoelectric point at pH
8–9) and “type B” (isoelectric point at
pH
4–5), which are extracted with acids and alkalis, respectively [
38
]. Gelatins are widely
used in food industry, either as a gelling agent, emulsifier, foamer, or coating material
for encapsulation [
36
,
38
]. Unlike native collagens, gelatins cannot be labeled as a specific
collagen type since this factor is inherent to the triple helix structure. For the same reason,
gelatins are not immunogenic since active epitopes related to the collagen triple helix have
been lost in the denaturation step.
Collagen hydrolysates are distinguished for having lost the triple helix structure as
well but, unlike to gelatins, they are subjected to a chemical or enzymatic hydrolysis process
to breakdown polypeptide chains [
36
]. As a result, collagen hydrolysates are composed
by a mixture of amino acids and peptides which composition depends on both collagen
source and hydrolysis method. For instance, collagen hydrolysates prepared by enzymatic
hydrolysis with pepsin, alcalase or papain, exhibit a molecular weight distribution ranging
from 1 kDa to 10 kDa [49].
Nutrients 2023,15, 1332 6 of 17
As described in gelatins, collagen hydrolysates are not immunogenic and cannot be
labeled as a specific collagen type. However, conversely to gelatins, they may include some
specific peptides, called “collagen peptides”, that exhibit different bioactive properties
when they are isolated by any purification process. So far, a huge amount of different
collagen peptides has been described in the literature showing different
in vitro
activities
such as antioxidant activity, ACE-I inhibitory activity, or DPP-IV inhibitory activity [
36
].
As far as we know, in most of the commercial products for joint mobility, collagen peptides
are not isolated from hydrolyzed collagen but mixed with other peptides and amino acids
resulting from collagen hydrolysis.
Besides collagens obtained from natural animal sources, some attempts have been
made to produce “non-animal collagens” either by chemical synthesis or by biotechnologi-
cal means. Synthetic collagen-related peptides (CRPs) were first designed and assembled
by in the late 1960s [
50
]. Despite the latest developments to mimic the structure of collagen
triple helix as well as the fibril formation [
22
], synthetic collagens are still exceedingly
simplified structures compared to natural collagens [
39
]. Recombinant DNA technology
was first developed in the 1990s as an alternative to synthetic methods to obtain non-animal
collagens. Since then, various expression systems have been described in the literature
to produce native-like recombinant collagens and their fragments. However, large-scale
production of collagen by genetic engineering is still highly limited and only a few yeast
cells and transgenic plants are currently implemented to produce recombinant collagens
for specific biomedical applications [51].
In addition, the term “vegan collagen” or “vegan collagen builder” has been also
recently introduced in functional food market to refer to certain products that are basically
composed of a blend of ingredients including plant extracts, amino acids, vitamins, and
minerals. Even though some studies have evidenced that collagen biosynthesis is mediated
by certain micronutrients contained in these ingredients, such as vitamin C [
52
], copper or
zinc [
53
,
54
], it is worth noting that, to the best of our knowledge, no product labelled as
“vegan collagen” contains actual collagen in their ingredient list.
3. Mechanism of Action in Joint Health
Based on the molecular structure of collagen, different mechanisms of action have
been described for its use as ingredient in the manufacturing of food supplements. Native
collagen (insoluble or soluble) is resistant to proteinases and therefore it is not digested
across the gastrointestinal tract [
44
], being able to maintain the triple helix structure and
enhance joint health by means of the oral tolerance mechanism [
19
]. In contrast, both
gelatin and hydrolyzed collagens lack the triple helix and, consequently, the oral tolerance
mechanism of action is lost. Gelatin is likely the most frequent form in the market, but no
biological function for joint health has been described. However, it has excellent physical
and mechanical properties such as low solubility and adequate handling, mainly due to
the fact that it is composed of a mixture of peptides with different molecular weights [
55
].
Thus, gelatin is widely used in the manufacturing of different food systems such capsules
and films [56].
Finally, hydrolyzed collagens are composed of amino acids and peptides of varying
lengths (including dipeptides and tripeptides) which resist the intracellular hydrolysis
process avoiding their degradation by peptidases and systemic hydrolytic enzymes. Thus,
the peptides from hydrolyzed collagens have a high bioavailability allowing them to reach
the bloodstream, accumulating in the cartilage tissue and inducing the synthesis of cartilage
ECM, by stimulating the chondrocytes [57].
The differences in the mechanisms of action described for native and hydrolyzed
collagens, could even justify theoretically a potential combination of both types of collagens
to explore the complementary effects.
Nutrients 2023,15, 1332 7 of 17
3.1. Native Collagen
In its native form, collagen has a specific immune mediated mechanism of action
known as oral tolerance. Oral tolerance has been defined as the active suppression of
specific immune responses to antigens first encountered in the gastrointestinal tract [
58
]. It
represents an immune-mediated mechanism responsible of avoiding immune responses
against harmless antigens, such as food proteins or commensal organisms.
The basic description of oral tolerance has been exhaustively reviewed [
59
61
]. The
process is initiated in the gut-associated lymphoid tissue (GALT) but has an impact on the
systemic immunity [
61
]. Briefly, luminal antigens are captured by antigen-presenting cells,
which migrate into gut-draining mesenteric lymph nodes where they initiate activation and
differentiation of effector or regulatory T cells (Tregs) [
62
]. These antigen-specific regulatory
cells control immune response inducing the secretion of down-modulatory cytokines such
as TGF-b, IL-10, and IL-4, while decreasing pro-inflammatory cytokines [61,63,64].
The mechanism of oral tolerance has been largely demonstrated in various animal
models of autoimmune diseases, such as in collagen-induced arthritis [
19
]. In this model of
rheumatoid arthritis, the autoimmune response against cartilage type-II collagen, is induced
by injecting type II collagen and Freund’s adjuvant to susceptible mice (i.e., DBA/1) [65].
The oral tolerance to type II collagen was first demonstrated by Nagler-Anderson
in 1986 [
66
]. Interestingly, in this earlier work, the oral administration of native type-II
collagen but not denatured type-II collagen, reduced the autoimmune response, showing
that the triple-chain collagen structure is required to elicit the oral tolerance response.
Additionally, the efficacy of native type-II collagen to control articular inflammation has
been also demonstrated in other animal models of rheumatoid arthritis such as pristane
induced arthritis [
67
] and adjuvant arthritis [
68
]. In this latter model, oral administration
of native type II collagen suppressed the development of arthritis in Lewis rats, and this
suppression could be adoptively transferred by T cells from native-type II collagen-fed
animals.
The mechanism of oral tolerance has been evaluated with the aim of developing
therapeutic alternatives for autoimmune diseases. This is not the case for OA, although
accumulating evidence suggests that deregulations of the immune response have an impact
on disease pathogenesis along with other mechanical and biochemical factors [69,70].
Historically, OA has been defined as a simple degradation of joint cartilage associated
to the ageing process [
71
]. Afterwards it was recognized that the disease affects not only
the cartilage but the full joint structure, and that structural changes are driven not only
by mechanical factors but also by inflammation [
72
]. Inflammation has been shown to be
triggered and/or amplified by an immune response against autoantigens released by the
degradation of joint tissues [69,70].
Type II collagen (the main protein of the articular cartilage) has been shown to be
a potential source of autoantigens in OA [
73
75
]. In consequence, oral tolerance against
type-II collagen could theoretically have a positive impact to control inflammation in
OA. In fact, the efficacy of oral administration of low doses of native type-II collagen
has been demonstrated in animal models of OA such as the rat model of OA induced by
monoiodoactetate (MIA) [
76
]. In this model, oral administration of chicken native type
II collagen (1–10 mg/kg) reduced articular pain, decreased plasmatic concentration of
inflammatory cytokines (TNFa, IL-1b), and reduced cartilage degradation as shown by a
reduction in the plasmatic levels of C2C.
The mechanism of action of native type II collagen in OA as compared to hydrolyzed
collagens has been summarized in Figure 2.
Nutrients 2023,15, 1332 8 of 17
Nutrients 2023, 15, x FOR PEER REVIEW 8 of 18
monoiodoactetate (MIA) [76]. In this model, oral administration of chicken native type II
collagen (1–10 mg/kg) reduced articular pain, decreased plasmatic concentration of in-
flammatory cytokines (TNFa, IL-1b), and reduced cartilage degradation as shown by a
reduction in the plasmatic levels of C2C.
The mechanism of action of native type II collagen in OA as compared to hydrolyzed
collagens has been summarized in Figure 2.
Figure 2. Amino acids and peptides from hydrolyzed collagens are absorbed reaching the systemic
circulation and articular cartilage, stimulating the synthesis of ECM macromolecules and chondro-
genic differentiation. Native type II collagen epitopes cross the gut lumen by different mechanisms
including uptake by M cells, transport across enterocytes, or through tight junctions. The epitopes
are passed on to dendritic cells that once activated favor the differentiation of regulatory T cells
(Tregs) at Peyer’s Patches or at mesenteric lymph nodes. Tregs exit from lymph nodes to systemic
circulation through the efferent lymph and reach articular cartilage. At articular cartilage, Tregs
inhibit the inflammatory cascade caused by the release of autoantigens generated as a consequence
of cartilage catabolism.
Figure 2.
Amino acids and peptides from hydrolyzed collagens are absorbed reaching the systemic
circulation and articular cartilage, stimulating the synthesis of ECM macromolecules and chondro-
genic differentiation. Native type II collagen epitopes cross the gut lumen by different mechanisms
including uptake by M cells, transport across enterocytes, or through tight junctions. The epitopes are
passed on to dendritic cells that once activated favor the differentiation of regulatory T cells (Tregs) at
Peyer’s Patches or at mesenteric lymph nodes. Tregs exit from lymph nodes to systemic circulation
through the efferent lymph and reach articular cartilage. At articular cartilage, Tregs inhibit the
inflammatory cascade caused by the release of autoantigens generated as a consequence of cartilage
catabolism.
3.2. Hydrolyzed Collagens
Bioavailability of amino acids and peptides from hydrolyzed collagens is a pivotal
aspect to explain the effects of the product at the articular level. In general terms, it has
been demonstrated that peptides resistant to intracellular hydrolysis have lower molecular
weight and show higher intestinal absorption [
77
,
78
]. Levels of collagen-derived dipeptides
Nutrients 2023,15, 1332 9 of 17
such as Pro-Hyp and tripeptides such as Pro-Hyp-Gly have been detected in systemic blood
after an hour of being ingested [
79
]. Then, these peptides reach the joint tissues such as
cartilage where they accumulate [14].
Once in the cartilage,
in vitro
studies have demonstrated that collagen peptides exert
different biological effects that may be dependent on the peptide and amino acid profile of
the hydrolyzed collagen [
80
]. Thus, different studies have shown that collagen peptides
stimulate the synthesis of ECM macromolecules such as proteoglycans and type II colla-
gen [
81
], induce chondrogenic proliferation and differentiation [
82
], increase the activity
of osteoblasts [
83
], and decrease the activity of osteoclasts [
14
]. All these effects suggest
that hydrolyzed collagen may promote cartilage repair by acting as a chondroprotector in
OA [4].
However,
in vivo
confirmation of the mechanisms described using the
in vitro
systems
has led to mixed results. Comblain et al. [
84
] studied the effect of a formulation containing
hydrolyzed collagen, curcuminoids, and green tea extract in dogs with OA. Although
improvements in pain were reported, no effect on biomarkers of cartilage catabolism (Coll2-
1 and Coll2-1 NO
2
) was detected. Contrarily, Dar et al. detected a chondroprotective effect
consisting in MMP-13 and apoptosis reduction as a result of the administration of HC to
mice with induced meniscal-ligamentous injury [
85
]. Lee et al. [
86
] also demonstrated
chondroprotective effects of a low-molecular weight collagen peptide from fish origin in an
anterior cruciate ligament transection rabbit model.
Differences among different hydrolyzed collagens were evaluated by Schadow et al. [
87
]
in a study in human OA cartilage explants in which three different products were analyzed.
None of the tested products stimulated the biosynthesis of type II collagen. In addition,
great differences were detected on biological activity of each hydrolyzed collagen, showing
that the effects of a particular product cannot be extrapolated to another obtained through
a different process and consequently containing a different peptide composition. In a
subsequent study, Simons et al. [
88
] showed that differences in peptide profiles could
be detected even in different batches of the same hydrolyzed collagen [
88
] which could
potentially lead to different activities.
According to these findings, it seems that linking the bioavailability and biologic
effects to a standardized peptide composition would be required to ensure that the final
collagen product is effective for OA patients.
4. Clinical Evidence
Up to date, several clinical trials regarding the use of collagen as a food supplement
for joint health have been published. Most of the studies have evaluated the therapeutic po-
tential of either native type II collagen [
89
98
] or hydrolyzed collagens [
99
107
] in patients
with OA. However, both types of collagens have been also tested in non-osteoarthritic
individuals suffering joint discomfort [108113].
There are also some trials evaluating the use of native type II collagen for rheumatoid
arthritis. These trials represented the translation from the initial studies with animal models
demonstrating the oral tolerance mechanism. The studies obtained mixed results [
17
].
Although some positive results were observed in phase II trials, no effect was detected in
phase III [
114
]. The explanation for this lack of efficacy has not been fully elucidated but the
gut microbiota as well as the overall inflammatory situation of the patient, are supposed to
play a critical role [17].
In general, the studies evaluating the use of native type II collagen for OA have re-
ported positive results in terms of pain relief and joint function improvement, although
huge differences exist in study designs and methodologies (Table 2). In a randomized
double-blind controlled study, Lugo et al. [
92
] reported improvements in pain and function
after 6 months of the administration of a native type II collagen ingredient (40 mg/day)
as compared to a standard treatment with chondroitin sulphate (1200 mg/day) and glu-
cosamine (1500 mg/day). In an observational study, Jain et al. [
98
] reported improvements
of pain and function with the administration of native type II collagen (40 mg/day) com-
Nutrients 2023,15, 1332 10 of 17
bined with a Boswellia extract (1500 mg/day) for a period of 90 days. Except for two initial
studies published by Bagchi in 2002 [
93
] and Scarpellini in 2008 [
90
], all the following
studies used the same dose of 40 mg/day. Moreover, when collagen origin is reported, all
studies declare using collagen from a chicken origin.
Table 2. Clinical studies on collagen.
Collagen Type Clinical
Condition Design Intervention
Duration Daily Dose Main Results
Reported Reference
Native
collagen
Osteoarthritis
Randomized
single-blind controlled
study
3 months 40 mg
Symptomatic
improvement
(WOMAC)
[89]
Observational
retrospective study 12 months 2 mg
Reduce
progression of
cartilage
degradation
[90]
Randomized
double-blind
controlled study
3 months 40 mg
Symptomatic
improvement
(WOMAC,
VAS)
[91]
Randomized
double-blind
placebo-controlled
study
6 months 40 mg
Symptomatic
improvement
(WOMAC)
[92]
Open-label pilot study 1.5 months 10 mg
Symptomatic
improvement
(VAS)
[93]
Non-interventional,
prospective real-life
study
3 months 40 mg
Symptomatic
improvement
(WOMAC,
VAS)
[94]
Observational
open-label study 4 months 40 mg
Symptomatic
improvement
(WOMAC,
VAS)
[95]
Randomized
double-blind
placebo-controlled
study
3 months 40 mg
No significant
differences vs.
controls
[96]
Prospective controlled
study 4 months 40 mg
Symptomatic
improvement
(WOMAC,
VAS)
[97]
Observational
open-label study 3 months 40 mg
Symptomatic
improvement
(WOMAC,
VAS)
[98]
non-
Osteoarthritis
Randomized
double-blind
placebo-controlled
study
4 months 40 mg
Reduced joint
discomfort and
increased
mobility
[108]
Randomized
double-blind
placebo-controlled
study
6 months 40 mg
Reduced joint
discomfort and
increased
mobility
[109,110]
Nutrients 2023,15, 1332 11 of 17
Table 2. Cont.
Collagen Type Clinical
Condition Design Intervention
Duration Daily Dose Main Results
Reported Reference
Hydrolyzed
collagen
Osteoarthritis
Randomized
double-blind
placebo-controlled
study
6 months 10 g
Increase of
proteoglycan
content in knee
cartilage
[99]
Randomized
double-blind
placebo-controlled
study
6 months 10 g
Symptomatic
improvement
(WOMAC,
VAS)
[100]
Randomized
single-blind
open-labelled
controlled study
6 months 1.2 g
Symptomatic
improvement
(WOMAC)
[101]
Randomized
double-blind
placebo-controlled
study
3 months 10 g
Symptomatic
improvement
(WOMAC,
VAS)
[102]
Randomized
double-blind
placebo-controlled
study
70 days 2 g
Symptomatic
improvement
(WOMAC,
VAS)
[103]
Randomized
double-blind
controlled study
3 months 10 g
Symptomatic
improvement
(WOMAC,
VAS)
[104]
Prospective
observational study 1 month 720 mg/360
mg
Symptomatic
improvement
(WOMAC,
VAS)
[105]
Prospective
observational study 6 months 1.5 g
Symptomatic
improvement
(WOMAC, VAS,
Lequesne)
[106]
Randomized
double-blind
placebo-controlled
study
6 months 8 g
Symptomatic
improvement
(WOMAC,
VAS)
[107]
non-
Osteoarthritis
Randomized
double-blind
placebo-controlled
study
3 months 5 g
Reduction of
exercise-
induced knee
pain
[111]
Randomized
double-blind
placebo-controlled
study
6 months 10 g
Reduction of
join pain at rest
and during
activity
[112]
Randomized
double-blind
placebo-controlled
study
3 months 10 g
No significant
differences vs.
Placebo
[113]
Abbreviatures: Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC); Visual Analogue
Scale (VAS).
Fewer studies have evaluated the impact of native type II collagen in cartilage home-
ostasis. In a retrospective study, Scarpellini et al. showed a reduced progression of cartilage
degradation at 6 and 12 months in a group of hand OA patients treated with a combination
of native type II collagen, CS and GS [
90
]. However, in other studies no differences have
been detected in serum biomarkers of joint integrity [
89
,
108
]. On the other hand, all studies
Nutrients 2023,15, 1332 12 of 17
published in non-OA individuals have reported improvements in activity-related joint
discomfort and mobility [108110].
In the studies evaluating the use of hydrolyzed collagens for OA, huge variability
can be found as different designs, comparators, dosages, administration patterns (either
alone or in combination), origins, and study durations are used, making it difficult to draw
overall conclusions. Despite huge methodological differences, all studies reported, at least,
partially positive results on the evaluated outcomes. Parameters showing most positive
results in these trials are related to the self-reported improvement of OA symptomatol-
ogy including function, quality of life, and pain. Although most of the studies report
improvements in pain and function, the daily dose is highly variable. Bernardo et al. [
101
]
in a randomized single-blind study reported improvements in joint pain and function
after 6 months of administration of 1.2 g/day of a hydrolyzed collagen ingredient. Using
another hydrolyzed collagen, Benito-Ruiz et al. [100] also demonstrated improvements in
joint pain and function after 6 months of administration, but with a dose of 10 g/day in a
randomized double-blind placebo-controlled study. Besides daily dose, there is also high
variability in administration time. Trˇc and Bohmová[
104
] in a double-blind study reported
improvements in joint pain and function compared to a treatment with GS (1.5 g/day) as
a result of the administration of 10 g/day of an hydrolyzed collagen for 3 months, while
Kilinc et al. [
105
] in an observational study reported symptomatic improvements compared
to baseline with another hydrolyzed collagen administrated for two weeks at a dose of 720
mg/day followed by two additional weeks at a dose of 360 mg/day.
Besides improvements in pain and function, changes in cartilage degradation have
also been detected. In 2011, McAlindon et al. [
99
] reported an increase in proteoglycan
content in knee cartilage after 24 weeks of treatment with 10 g/day of a specific hydrolyzed
collagen formulation.
Studies evaluating the effects of hydrolyzed collagens in non-OA patients have ob-
tained mixed results. Two randomized double-blind placebo-controlled studies reported
improvements in activity-related joint pain after 6 months of administration of a hydrolyzed
collagen from porcine origin at a dose of 10 g/day in one study [
112
] and 5 g/day in the
other [
111
]. However, in another randomized double-blind placebo-controlled study, no
differences in join pain and function were detected after 3 months of administration of 10
g/day of a hydrolyzed collagen from bovine origin [113].
Collagen studies show huge variability among them, but all tested products, collagen
types, and dosages seem to deliver positive outcomes (except in one study) and no safety
issues were reported.
In summary, the available scientific evidence shows that most tested ingredients
seem to deliver positive outcomes although there is huge variability in terms of study
designs, effective doses, and minimum treatment periods for each collagen ingredient.
When comparing native collagen with hydrolyzed collagen, there is a clear difference in
the therapeutic dose, which is smaller in native collagen (40 mg/day) as compared to
hydrolyzed collagen (between 5 and 10 g/day). This could have practical implications in
terms of galenic development since high daily doses could limit the feasibility to develop
certain presentations such as tablets and capsules.
5. Conclusions
Collagen has been positioned as an emerging focus of research for articular health.
However, the term collagen includes different products with different structures, proper-
ties, and mechanisms of action. Native type II collagen has a specific immune-mediated
mechanism known as oral tolerance, that inhibits inflammation and tissue catabolism at
articular level. Hydrolyzed collagen has been shown to contain biologically active pep-
tides that are able to reach joint tissues and exert chondroprotective effects. There are
preclinical and clinical studies showing the safety and efficacy of ingredients containing
native type II collagen or hydrolyzed collagen. Nevertheless, available research suggests a
clear link between collagen ingredient composition/chemical structure and mechanism of
Nutrients 2023,15, 1332 13 of 17
action/efficacy. However further research is required, including well-designed studies, to
assess the therapeutic potential of each collagen type and composition for each clinical con-
dition. Novel research would be required to evaluate the potential benefit in populations
with risk factors of OA, as well as different OA phenotypes and related disorders, both in
terms of symptomatic improvement and progression of cartilage degradation.
Author Contributions:
Conceptualization, D.M.-P. and P.G.-M.; investigation, D.M.-P., E.C.-L.,
N.R.-R. and P.G.-M.; writing—original draft preparation D.M.-P., E.C.-L., N.R.-R. and P.G.-M.;
writing—review and editing, D.M.-P., E.C.-L., N.R.-R. and P.G.-M.; supervision, D.M.-P. All authors
have read and agreed to the published version of the manuscript.
Funding: This research received no external funding.
Institutional Review Board Statement: Not applicable.
Informed Consent Statement: Not applicable.
Data Availability Statement: Not applicable.
Conflicts of Interest:
D.M.-P., E.C.-L., N.R.-R. and P.G.-M. are employees of Bioiberica S.A.U., a
manufacturer of a nutritional ingredient containing native (undenatured) type II collagen.
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