HISTOLOGICAL DIFFERENCES OF HUMAN, BOVINE AND PORCINE CARTILAGE
+*Rieppo, J; *Halmesmaki E P; *Siitonen, U; **Laasanen, M S; **Toyras, J; ***Kiviranta, I; *Hyttinen, M M; **Jurvelin, J S; *Helminen, H J
+*University of Kuopio, Kuopio, Finland
INTRODUCTION
Experimental cartilage research is mostly based on the use of animal
models. It is assumed that cartilage tissue from different species has
common structural and compositional features. Systematic
characterization of the histological features of different mammalian
cartilage tissues is still lacking. In this study our goal was to characterize
human, bovine and porcine patellar cartilage, especially to find
differences in collagen architecture and proteoglycans (PG) distribution.
METHODS
Macroscopically intact cartilage samples were prepared from human
(n=5), bovine (n=6) and porcine (n=9) patellae. Samples we re fixed
with 10% formalin, decalcified with 4% EDTA and dehydrated with
ethanol. Further, samples were embedded in paraffin and processed into
microscopical sections (1).
Collagen network was analyzed with a recently developed new
polarized light microscopical (PLM) method (2). New technique allows
detailed characterization of the collagen birefringence, orientation and
anisotropy. For the PLM measurements 5-µm-thick unstained sections in
2 vertically randomized directions were used. For each specimen 6
measurements were conducted and the average of measurements was
used for data analysis.
PG distribution of cartilage was evaluated from safranin-O stained
tissue sections. Stain distribution was measured from articular surface to
osteochondral junction using the digital densitometry technique (3).
RESULTS
PLM revealed major differences between collagen networks of
human, bovine and porcine cartilage. Porcine cartilage was characterized
with a hypertrophied cell front and it showed an increased cell density
compared to human or bovine cartilage (Fig. 1). Even though the human
cartilage was significantly thicker than the bovine or porcine cartilage
(p<0.01, Mann- Whitney U-test), the superficial zone thickness was
similar among species. Birefringence of the superficial and deep zones
was significantly higher in human cartilage (p<0.01) (Table 1). In human
cartilage deep zone birefringence increased linearly and reached
maximum values close to the cartilage-bone junction. Bovine and
porcine cartilage showed a plateau in the birefringence at the halfthickness. Close to cartilage-bone junction bovine and porcine cartilage
showed low anisotropy level of collagen fibrils, i.e. decreased
organization. Also, middle (transitional) zone, where the collagen fibrils
arcaded from the alignment parallel to the surface to a more
perpendicular arrangement, showed differences. Porcine cartilage
showed the highest thickness of middle zone with highest anisotropy
levels whereas bovine and human cartilage had similar appearance (Fig.
2).
PG concentration was different among species. Human cartilage had
a lower PG concentration in superficial zone than bovine or porcine
cartilage (p<0.01). Bovine cartilage showed slightly lower total PG
levels (p<0.05) compared to human cartilage (Table 1). The
concentration gradients revealed distinct differences. Porcine cartilage
reached the maximum PG concentration in one -sixth of the cartilage
thickness whereas human and bovine cartilage showed monotonic
growth of the PGs almost down to the cartilage-bone junction (Fig. 3).
DISCUSSION
The present study indicated differences in histological appearance of
human, bovine and porcine cartilage. Collagen network and PG gradient
showed common characteristic features but also significant differences
existed between species. This preliminary study suggests that more
thorough studies are needed to understand specific differences in the
histological features of cartilage tissue among species. Especially the
collagen network and its role as a modulator of tissue mechanical
properties require more work. Also, a challenging task is to interpret the
results acquired from animal models to serve human OA research. For
example, the animals used in experimental studies may be very young at
age. Age associated changes and cartilage maturation needs also further
investigation. It is possible to study collagen network maturation with
quantitative polarized light microscopy.
I a)
b)
low
II a)
BIREFRINGENCE
b)
high
III a)
low
b)
ANISOTROPY
high
Fig. 1 Polarized light microscopic images of collagen network
birefringence (a) and anisotropy (i.e. organization) (b) of human (I),
bovine (II) and porcine (III) cartilage.
Table 1 Full cartilage and superficial zone thickness, birefringence (B)
and optical density (OD) of superficial and deep zones (mean±SD).
Thickness
Superficial
Superficial
Zone thickness Zone B (x103 )
(µm)
(µm)
0.57±0.07
Deep Zone
B (x103)
Superficial Total OD
Zone
OD
1.53± 0.22
0.42±0.08
Human 3716±1722
189±17
Bovine 1826±294**
201±30
0.41± 0.05** 0.88± 0.27** 0.79±0.21** 1.59±0.23*
1.88±0.08
Porcine 1986±268**
171±45
0.35 ±0.06** 0.51 ±0.05** 1.17±0.37** 1.85±0.18
Difference from human cartilage, * p<0.5 and ** p<0.01, Mann-Whitney U-test
a)
b)
Fig. 2 Birefringence profiles (mean±SD) of human, bovine and porcine
patellar cartilage (a), anisotropy levels of collagen fibrils, i.e.
organization of collagen network (b).
Fig. 3 Proteoglycan distribution from articular cartilage surface to
osteochondral junction assessed by safranin-O staining and digital
densitometry. High absorbance indicates high proteoglycan content.
REFERENCES
1. Toyras J et al. 1999 Phys Med Biol 44 (11): 2723-33
2. Rieppo J et al. 2002 FECTS meeting at Bristol, UK
3. Panula HE et al. 1998 Ann Rheum Dis. 57 (4): 237-45
**Department of Applied Physics, University of Kuopio, Kuopio,
Finland
***Department of Surgery, Division of Orthopaedics and Traumatology,
Jyväskylä Central Hospital, Jyväskylä, Finland
49th Annual Meeting of the Orthopaedic Research Society
Poster #0551