High-fat diet accelerates progression of osteoarthritis after meniscal/ligamentous injury

Abstract

Introduction: Increasing obesity and type 2 diabetes, in part due to the high-fat (HF) Western diet, parallels an increased incidence of osteoarthritis (OA). This study was undertaken to establish a causal relation between the HF diet and accelerated OA progression in a mouse model and to determine the relative roles of weight gain and metabolic dysregulation in this progression.

Methods: Five-week-old C57BL/6 mice were placed on HF (60% kcal) or low-fat (lean, 10% kcal) diets for 8 or 12 weeks before transecting the medial collateral ligament and excising a segment of the medial meniscus of the knee to initiate OA. One group was switched from lean to HF diet at the time of surgery.

Results: Body weight of mice on the HF diet peaked at 45.9 ± 2.1 g compared with 29.9 ± 1.8 g for lean diets, with only those on the HF becoming diabetic. Severity of OA was greater in HF mice, evidenced by the Osteoarthritis Research Society International (OARSI) histopathology initiative scoring method for mice and articular cartilage thickness and area. To assess the importance of weight gain, short- and long-term HF diets were compared with the lean diet. Short- and long-term HF groups outweighed lean controls by 6.2 g and 20.5 g, respectively. Both HF groups became diabetic, and OA progression, evidenced by increased OARSI score, decreased cartilage thickness, and increased osteophyte diameter, was comparably accelerated relative to those of lean controls.

Conclusions: These results demonstrate that the HF diet accelerates progression of OA in a type 2 diabetic mouse model without correlation to weight gain, suggesting that metabolic dysregulation is a comorbid factor in OA-related cartilage degeneration.

Figure 1

High-fat diet promotes weight gain and hyperglycemia. Five-week-old male C57BL/6 mice were placed on either a high-fat (60% kcal) or low-fat (10% kcal) diet for 2 months before meniscal-ligamentous injury (MLI). Body weight (a) and blood glucose levels (b) were determined at monthly intervals after MLI. *P < 0.05; **P < 0.01; n = 5 to 9 mice at each time point.

Figure 2

Osteoarthritic changes were more pronounced in high-fat (HF) diet-treated mice. (a) Histologic sections of injured and sham joints at 1-, 2-, 3-, and 4-month time points after meniscal-ligamentous injury (MLI) were stained with Alcian blue. Representative sections from the 4-month time point are shown. Magnification, ×100. (b) Slides were graded for OA severity by using the OARSI histopathology initiative scoring method for mice. The slides were also analyzed with histomorphometry for tibial cartilage thickness (c) and total articular cartilage area (tibia + femur, d). All histomorphometry data were normalized to sham-operated joint-cartilage thickness and area, respectively, from lean mice. All results are expressed as the mean ± SEM from at least five mice with three slides per mouse. *P < 0.05; **P < 0.01; n = 4 to 9 mice at each time point.

Figure 3

Differing weight gain but similar hyperglycemia in short- and long-term high-fat (HF) diets. Five-week-old male C57BL/6 mice were given either a high-fat (60% kcal) or low-fat (10% kcal) diet for 3 months before meniscal-ligamentous injury (MLI). After MLI, half of the lean group was switched to the HF diet. The three groups were maintained on diets for an additional 3 months. (a) Body weight was measured monthly after the MLI procedure. (b) Blood glucose and (c) hemoglobin A1c levels were determined at the 3-month end point. Data points represent mean ± SEM of at least six mice. *P < 0.05; **P < 0.01. n = 6 to 8 mice in each group.

Figure 4

OA progression after meniscal-ligamentous injury MLI is comparable in mice on either short- or long-term HF diets. Injured and sham joints at 3 months after MLI were harvested from the lean, short-term HF, and long-term HF groups. (a) Histologic slides were stained with Alcian blue and (b) scored for OA severity by using the OARSI histopathology initiative scoring method for mice. The slides were also analyzed with histomorphometry for tibial cartilage thickness, with the data normalized to the cartilage thickness determined in sham-operated joints from lean mice (c). Results are expressed as the mean ± SEM from at least six mice with three slides per mouse. *P < 0.05; **P < 0.01. n = 6 to 8 mice in each group.

Figure 5

Micro-CT analysis of knee joints after meniscal-ligamentous injury (MLI) as a function of diet. (a) Knee-bone volumes of MLI and sham-treated limbs at 3 months in HF, Lean to HF, and Lean diet groups were analyzed with micro-CT. (b) Three-dimensional reconstructions of knee joints were used to visualize calcification of meniscus and osteophyte formation. Gray arrows, ossification of meniscus; white arrows, osteophyte-like structures. Representative 3D images are presented. Bone volume data represent the mean ± SEM of at least five mice. **P < 0.01. n = 6 to 8 mice in each group.

Figure 6

Osteophyte analysis of knee joints after meniscal-ligamentous injury (MLI) as a function of diet. (a) A representative osteophyte in a histologic section from an MLI-treated knee of an HF mouse is shown (boxed area). (b) Average osteophyte diameters on the tibial surface were measured by using digitally projected images of the histologic slides. Results are expressed as the mean ± SEM from at least six mice, with three slides per mouse. A representative osteophyte (boxed area) in a histologic section from a sham-operated knee of an HF mouse (c) and a comparable location in an unaffected lean diet control (d) are shown. ×100 magnification. **P < 0.01. n = 6 to 8 mice in each group.