Evaluation of the chondroprotective action of N-acetylglucosamine in a rat experimental osteoarthritis model

Abstract

It has been demonstrated that oral administration of N-acetylglucosamine (GlcNAc) alleviates the symptoms of osteoarthritis (OA). The aim of the present study was to elucidate the molecular mechanisms for the chondroprotective action of GlcNAc in OA. Biomarkers for type II collagen degradation and synthesis were evaluated, as were histopathological changes, using a rat anterior cruciate ligament transection (ACLT)-induced OA model. Changes in the expression of genes in the cartilage were assessed via DNA microarray and reverse transcription-quantitative polymerase chain reaction (RT-qPCR). The results indicated that ACLT induced histopathological changes of articular cartilage, whereas oral administration of GlcNAc (1,000 mg/kg/day for 28 days) significantly suppressed these changes. Additionally, GlcNAc significantly decreased levels of a type II collagen degradation marker in sera compared with that in the ACLT group, although there were no significant changes in the levels of a type II collagen synthesis marker. Furthermore, DNA microarray and reverse transcription-quantitative polymerase chain reaction results demonstrated that GlcNAc treatment downregulated the expression of periostin, which is likely involved in the degradation of cartilage, whereas GlcNAc upregulated the expression of lipocalin 2, which is involved in the regulation of chondrocyte proliferation and differentiation. In conclusion, the results of the present study suggest that GlcNAc is able to suppress the histopathological changes induced by OA and exhibits a chondroprotective action by inhibiting type II collagen degradation in the articular cartilage, possibly via modulation of the expression of inflammatory and chondroprotective molecules, including periostin and lipocalin 2.

Keywords: N-acetylglucosamine; biomarker; cartilage metabolism; dietary supplement; osteoarthritis.

Figure 1.

Macroscopic changes of femoral condyles and the tibial plateau at 29 days following ACLT surgery. Femurs from the (A) sham, (B) ACLT and (C) GlcNAc groups. Tibias from the (D) sham, (E) ACLT and (F) GlcNAc groups. Sham-operated joints showed no macroscopic changes, whereas ACLT induced erosive changes on the joint surfaces (indicated by large arrowheads) and GlcNAc administration substantially suppressed these degenerative changes (indicated by small arrowheads). ACLT, anterior cruciate ligament transection; sham, sham-operated; GlcNAc, N-acetylglucosamine.

Figure 2.

Histopathological evaluation of articular cartilage in a rat OA model. Knee joints were dissected at 29 days following ACLT surgery. Sagittal sections of cartilage in the weight-bearing area of the femoral condyle and the medial tibia plateau were stained with toluidine blue. Femurs from the (A) sham, (B) ACLT and (C) GlcNAc groups, and (D) the severity of OA lesions in femurs. Tibias from the (E) sham, (F) ACLT and (G) GlcNAc groups, and (H) the severity of OA lesions in tibias. ACLT induced surface depletion, a marked reduction in the number of chondrocytes and a reduction in toluidine blue staining of the cartilage from femurs and tibias (indicated by arrowheads). The severity of OA lesions was graded on a scale of 0–13 using the modified Mankin scoring system. Data are presented as the mean ± standard deviation (n=4 per group). *P<0.05 and **P<0.01 as indicated. OA, osteoarthritis; ACLT, anterior cruciate ligament transection; sham, sham-operated; GlcNAc, N-acetylglucosamine.

Figure 3.

Changes in the biomarkers for type II collagen during GlcNAc treatment for rats with surgically induced ACLT. Changes in (A) C2C, (B) PIICP and (C) the C2C/PIICP ratio from the baseline were calculated for sham (open circle), ACLT (filled square) and GlcNAc (filled triangle) groups on days 14 and 28 post-surgery. Baseline levels on day 1 post-surgery were as follows: C2C, 621.09±139.20, 764.27±50.18 and 881.21±91.97 ng/ml in the sham, ACLT and GlcNAc groups, respectively; PIICP, 8,449.32±1,873.34, 8,698.22±1,977.0 and 8,081.33±765.5 ng/ml in the sham, ACLT and GlcNAc groups, respectively; C2C/PIICP, 77.84±29.46, 92.39±22.82 and 109.91±15.08 in the sham, ACLT and GlcNAc groups, respectively. Data are presented as the mean ± standard deviation. *P<0.05 and **P<0.01 vs. day 1; ^#P<0.05 as indicated. GlcNAc, N-acetylglucosamine; ACLT, anterior cruciate ligament transection; C2C, type II collagen cleavage neoepitope; PIICP, carboxyterminal propeptide of type II procollagen; sham, sham-operated.