Development of a microcomputed tomography scoring system to characterize disease progression in the Hartley guinea pig model of spontaneous osteoarthritis

Removal of the infrapatellar fat pad and associated synovium benefits female guinea pigs in the Dunkin Hartley model of idiopathic osteoarthritis

Background

Several tissues contribute to the onset and advancement of knee osteoarthritis (OA). One tissue type that is worthy of closer evaluation, particularly in the context of sex, is the infrapatellar fat pad (IFP). We previously demonstrated that removal of the IFP had short-term beneficial effects for a cohort of male Dunkin-Hartley guinea pigs. The present project was designed to elucidate the influence of IFP removal in females of this OA-prone strain. It was hypothesized that resection of the IFP would reduce the development of OA in knees of a rodent model predisposed to the disease.

Methods

Female guinea pigs (n=16) were acquired at an age of 2.5 months. Surgical removal of the IFP and associated synovium complex (IFP/SC) was executed at 3 months of age. One knee had the IFP/SC resected; a comparable sham surgery was performed on the contralateral knee. All animals were subjected to voluntary enclosure monitoring and dynamic weight-bearing, as well as compulsory treadmill-based gait analysis monthly; baseline data was collected prior to surgery. Guinea pigs were euthanized at 7 months. Knees from eight animals were evaluated via histology, mRNA expression, and immunohistochemistry (IHC); knees from the remaining eight animals were allocated to microcomputed tomography (microCT), biomechanical analyses (whole joint testing and indentation relaxation testing), and atomic absorption spectroscopy (AAS).

Results

Fibrous connective tissue (FCT) replaced the IFP/SC. Mobility/gait data indicated that unilateral IFP/SC removal did not affect bilateral hindlimb movement. MicroCT demonstrated that osteophytes were not a significant feature of OA in this sex; however, trabecular thickness (TbTh) in medial femorae decreased in knees containing the FCT. Histopathology scores were predominantly influenced by changes in the lateral tibia, which demonstrated that histologic signs of OA were increased in knees containing the native IFP/SC versus those with the FCT. Similarly, indentation testing demonstrated higher instantaneous and equilibrium moduli in the lateral tibial articular cartilage of control knees with native IFPs. AAS of multiple tissue types associated with the knee revealed that zinc was the major trace element influenced by removal of the IFP/SC.

Conclusions

Our data suggest that the IFP/SC is a significant component driving knee OA in female guinea pigs and that resection of this tissue prior to disease has short-term benefits. Specifically, the formation of the FCT in place of the native tissue resulted in decreased cartilage-related OA changes, as demonstrated by reduced Osteoarthritis Research Society International (OARSI) histology scores, as well as changes in transcript, protein, and cartilage indentation analyses. Importantly, this model provides evidence that sex needs to be considered when investigating responses and associated mechanisms seen with this intervention.

The common marmoset as a translational model of age-related osteoarthritis

Age-related osteoarthritis (OA) is a degenerative joint disease characterized by pathological changes in nearly every intra- and peri-articular tissue that contributes to disability in older adults. Studying the etiology of age-related OA in humans is difficult due to an unpredictable onset and insidious nature. A barrier in developing OA modifying therapies is the lack of translational models that replicate human joint anatomy and age-related OA progression. The purpose of this study was to determine whether the common marmoset is a faithful model of human age-related knee OA. Semi-quantitative microCT scoring revealed greater radiographic OA in geriatric versus adult marmosets, and the age-related increase in OA prevalence was similar between marmosets and humans. Quantitative assessments indicate greater medial tibial cortical and trabecular bone thickness and heterogeneity in geriatric versus adult marmosets which is consistent with an age-related increase in focal subchondral bone sclerosis. Additionally, marmosets displayed an age-associated increase in synovitis and calcification of the meniscus and patella. Histological OA pathology in the medial tibial plateau was greater in geriatric versus adult marmosets driven by articular cartilage damage, proteoglycan loss, and altered chondrocyte cellularity. The age-associated increase in medial tibial cartilage OA pathology and meniscal calcification was greater in female versus male geriatric marmosets. Overall, marmosets largely replicate human OA as evident by similar 1) cartilage and skeletal morphology, 2) age-related progression in OA pathology, and 3) sex differences in OA pathology with increasing age. Collectively, these data suggest that the common marmoset is a highly translatable model of the naturally occurring, age-related OA seen in humans.

Impact of long-term rapamycin treatment on age-related osteoarthritis in common marmoset

Objective

Pharmacologic inhibition of the mechanistic target of rapamycin (mTOR) can attenuate experimental osteoarthritis (OA) in young, male preclinical models. However, the potential of mTOR inhibition as a therapeutic mechanism for OA remains unknown. The goal of this study was to determine if mTOR-inhibition by oral rapamycin can modify OA pathology in the common marmoset, a translational model of age-associated OA.

Methods

microCT and histopathologic assessments of the knee were performed on formalin-fixed hindlimbs obtained from common marmosets treated with oral rapamycin (n=24; 1mg/kg/day) or parallel control group (n=41). Rapamycin started at 9.2±3.0 years old and lasted until death (2.1±1.5 years). In a subset of marmosets, contralateral hind limbs were collected to determine mTOR signaling in several joint tissues.

Results

Rapamycin decreased P-RPS6Ser235/36 and increased P-Akt2Ser473 in cartilage, meniscus, and infrapatellar fat pad, suggesting inhibition of mTORC1 but not mTORC2 signaling. Rapamycin-treated marmosets had lower lateral synovium score versus control but there was no difference in the age-related increase in microCT or cartilage OA scores. Subchondral bone thickness and thickness variability were not different with age but were lower in rapamycin-treated geriatric marmosets, which was largely driven by females. Rapamycin also tended to worsen age-related meniscus calcification in female marmosets.

Conclusion

Oral rapamycin attenuated mTORC1 signaling and may have caused feedback activation of mTORC2 signaling in joint tissues. Despite modifying site-specific aspects of synovitis, rapamycin did not modify the age-associated increase in OA in geriatric marmosets. Conversely, rapamycin may have had deleterious effects on meniscus calcification and lateral tibia subchondral bone, primarily in geriatric female marmosets.

Automated Prediction of Osteoarthritis Level in Human Osteochondral Tissue Using Histopathological Images

Osteoarthritis (OA) is the most common arthritis and the leading cause of lower extremity disability in older adults. Understanding OA progression is important in the development of patient-specific therapeutic techniques at the early stage of OA rather than at the end stage. Histopathology scoring systems are usually used to evaluate OA progress and the mechanisms involved in the development of OA. This study aims to classify the histopathological images of cartilage specimens automatically, using artificial intelligence algorithms. Hematoxylin and eosin (HE)- and safranin O and fast green (SafO)-stained images of human cartilage specimens were divided into early, mild, moderate, and severe OA. Five pre-trained convolutional networks (DarkNet-19, MobileNet, ResNet-101, NasNet) were utilized to extract the twenty features from the last fully connected layers for both scenarios of SafO and HE. Principal component analysis (PCA) and ant lion optimization (ALO) were utilized to obtain the best-weighted features. The support vector machine classifier was trained and tested based on the selected descriptors to achieve the highest accuracies of 98.04% and 97.03% in HE and SafO, respectively. Using the ALO algorithm, the F1 scores were 0.97, 0.991, 1, and 1 for the HE images and 1, 0.991, 0.97, and 1 for the SafO images for the early, mild, moderate, and severe classes, respectively. This algorithm may be a useful tool for researchers to evaluate the histopathological images of OA without the need for experts in histopathology scoring systems or the need to train new experts. Incorporating automated deep features could help to improve the characterization and understanding of OA progression and development.

Microstructural changes of cartilage and subchondral bone in a guinea pig model of early- and middle-stage patellofemoral arthritis

OBJECTIVE

Patellofemoral arthritis is a common type of knee osteoarthritis and a prime cause of anterior knee pain and disability. Most of the existing research on knee osteoarthritis focuses on tibial-femoral arthritis, while studies on patellofemoral arthritis are relatively rare. This study aims to observe changes in osteochondral and subchondral bone structure over time in the patella and femoral trochlea in an animal model of spontaneous patellofemoral arthritis.

METHODS

A total of 24 1-, 3- or 5-month-old healthy female Hartley guinea pigs were used for experiments. No intervention was applied, and the mechanical pain threshold was assessed prior to euthanasia. Bilateral knee joints were collected in the animals at the different ages, and the patellofemoral joints were taken to evaluate the bone microstructure of patellofemoral articular cartilage and subchondral bone by macroscopy, histopathology and micro-computed tomography (micro-CT).

RESULTS

There was a significant difference in the severity of femoral trochlea injury assessed by the Macro score between 5- and 1-month-old groups (P<0.01), as well as in patellar cartilage damage (P<0.05). The mechanical pain threshold of lower extremities in each group was statistically different between different age groups (P<0.05). The OARSI articular cartilage histopathological scores, including patella and femoral trochlea, were significantly different among 1-, 3- and 5-month-old groups. The 5-month-old group exhibited statistically lower values of bone volume/trabecular volume, trabecular number and trabecular thickness in the femoral subchondral bone and evidently higher structure model index than the 1-month-old group.

CONCLUSIONS

This study demonstrated that 3- to 5-month-old female Hartley guinea pigs can develop early-to-mid-stage spontaneous patellofemoral arthritis that causes significant cartilage degeneration and loss of subchondral bone. In addition, the bone microarchitecture of the femur is more severely degraded.

Systemic iron reduction via an iron deficient diet decreases the severity of knee cartilage lesions in the Dunkin-Hartley guinea pig model of osteoarthritis

OBJECTIVE

Iron accumulation is emerging as a player in aging-related disorders due to its propensity for generating reactive oxygen species (ROS). Studies investigating the role of iron in the pathogenesis of primary osteoarthritis (OA) are limited. We designed a proof-of-principle study to determine the effect of systemic iron deficiency, via an iron deficient diet, on knee OA in an animal model.

METHODS

Twelve-week-old male Hartley guinea pigs received the standard diet (n = 6) or a diet devoid of iron (n = 6) for 19-weeks. Iron levels were determined in the serum, liver, and articular cartilage. Knees were collected to assess structural changes related to OA (microcomputed tomography, histopathology). Immunohistochemistry was performed to evaluate the presence and distribution of a disintegrin and metalloproteinase with thrombospondin motifs 4 (ADAMTS4) and ROS-driven 4-hydroxynonenal (4-HNE)-induced protein adducts. Transcript expression was also assessed.

RESULTS

Relative to control animals, an iron deficient diet reduced the concentration of this mineral in serum, liver, and articular cartilage. Iron deficient animals had lower histologic OA scores; decreased subchondral bone mineral density was also noted. This reduction in knee joint pathology was accompanied by a decrease in: ADAMTS4 in synovium; and 4-HNE protein adducts from lipid peroxidation in both the menisci and articular cartilage of iron deficient animals. Expression of iron-related genes in these tissues was also altered in treated animals.

CONCLUSIONS

Results from this study suggest that systemic iron levels may play a role in knee OA pathogenesis, with a short-term deficit in dietary iron reducing the severity of knee cartilage lesions.

Naturally Occurring Osteoarthritis Features and Treatments: Systematic Review on the Aged Guinea Pig Model

To date, several in vivo models have been used to reproduce the onset and monitor the progression of osteoarthritis (OA), and guinea pigs represent a standard model for studying naturally occurring, age-related OA. This systematic review aims to characterize the guinea pig for its employment in in vivo, naturally occurring OA studies and for the evaluation of specific disease-modifying agents. The search was performed in PubMed, Scopus, and Web of Knowledge in the last 10 years. Of the 233 records screened, 49 studies were included. Results showed that within a relatively short period of time, this model develops specific OA aspects, including cartilage degeneration, marginal osteophytes formation, and subchondral bone alterations. Disease severity increases with age, beginning at 3 months with mild OA and reaching moderate–severe OA at 18 months. Among the different strains, Dunkin Hartley develops OA at a relatively early age. Thus, disease-modifying agents have mainly been evaluated for this strain. As summarized herein, spontaneous development of OA in guinea pigs represents an excellent model for studying disease pathogenesis and for evaluating therapeutic interventions. In an ongoing effort at standardization, a detailed characterization of specific OA models is necessary, even considering the main purpose of these models, i.e., translatability to human OA.

Early removal of the infrapatellar fat pad/synovium complex beneficially alters the pathogenesis of moderate stage idiopathic knee osteoarthritis in male Dunkin Hartley guinea pigs

BACKGROUND

The infrapatellar fat pad (IFP) is the largest adipose deposit in the knee; however, its contributions to the homeostasis of this organ remain undefined. To determine the influence of the IFP and its associated synovium (IFP/synovium complex or IFP/SC) on joint health, this study evaluated the progression of osteoarthritis (OA) following excision of this unit in a rodent model of naturally-occurring disease.

METHODS

Male Dunkin-Hartley guinea pigs (n=18) received surgical removal of the IFP in one knee at 3 months of age; contralateral knees received sham surgery as matched internal controls. Mobility and gait assessments were performed prior to IFP/SC removal and monthly thereafter. Animals were harvested at 7 months of age. Ten set of these knees were processed for microcomputed tomography (microCT), histopathology, transcript expression analyses, and immunohistochemistry (IHC); 8 sets of knees were dedicated to microCT and biomechanical testing (material properties of knee joints tissues and anterior drawer laxity).

RESULTS

Fibrous connective tissue (FCT) developed in place of the native adipose depot. Gait demonstrated no significant differences between IFP/SC removal and contralateral hindlimbs. MicroCT OA scores were improved in knees containing the FCT. Quantitatively, IFP/SC-containing knees had more osteophyte development and increased trabecular volume bone mineral density (vBMD) in femora and tibiae. Histopathology confirmed maintenance of articular cartilage structure, proteoglycan content, and chondrocyte cellularity in FCT-containing knees. Transcript analyses revealed decreased expression of adipose-related molecules and select inflammatory mediators in FCTs compared to IFP/SCs. This was verified via IHC for two key inflammatory agents. The medial articular cartilage in knees with native IFP/SCs showed an increase in equilibrium modulus, which correlated with increased amounts of magnesium and phosphorus.

DISCUSSION/CONCLUSION

Formation of the FCT resulted in reduced OA-associated changes in both bone and cartilage. This benefit may be associated with: a decrease in inflammatory mediators at transcript and protein levels; and/or improved biomechanical properties. Thus, the IFP/SC may play a role in the pathogenesis of knee OA in this strain, with removal prior to disease onset appearing to have short-term benefits.

Evaluation of electroacupuncture for symptom modification in a rodent model of spontaneous osteoarthritis

OBJECTIVE

Faced with the frustration of chronic discomfort and restricted mobility due to osteoarthritis (OA), many individuals have turned to acupuncture for relief. However, the efficacy of acupuncture for OA is uncertain, as much of the evidence is inconclusive. The purpose of this study was to evaluate electroacupuncture (EA) in a rodent model of OA such that conclusions regarding its effectiveness for symptom or disease modification could be drawn.

METHODS

Ten 12-month-old male Hartley guinea pigs-which characteristically have moderate to advanced OA at this age-were randomly assigned to receive EA for knee OA (n = 5) or anesthesia only (control group, n = 5). Treatments were performed three times weekly for 3 weeks, followed by euthanasia 2 weeks later. Gait analysis and enclosure monitoring were performed weekly to evaluate changes in movement. Serum was collected for inflammatory biomarker testing. Knee joints were collected for histology and gene expression.

RESULTS

Animals receiving EA had significantly greater changes in movement parameters compared to those receiving anesthesia only. There was a tendency toward decreased serum protein concentrations of complement component 3 (C3) in the EA group compared to the control group. Structural and antioxidant gene transcripts in articular cartilage were increased by EA. There was no significant difference in total joint histology scores between groups.

CONCLUSION

This study provides evidence that EA has a positive effect on symptom, but not disease, modification in a rodent model of OA. Further investigations into mechanistic pathways that may explain the efficacy of EA in this animal model are needed.

Loss of Autophagy Causes Increased Apoptosis of Tibial Plateau Chondrocytes in Guinea Pigs with Spontaneous Osteoarthritis

OBJECTIVE

The goal of the present study was to observe the effect of autophagy in tibial plateau chondrocytes on apoptosis in spontaneous knee osteoarthritis (OA) in guinea pigs.

DESIGN

Fifty 2-month-old female Hartley guinea pigs were divided into a normal group (10 animals, all euthanized after 7 months) and an OA group (40 animals, 10 of which were euthanized after 10 months). Immunohistochemistry, RT-qPCR and Western blotting were used to evaluate autophagy levels, intracellular glycogen accumulation and apoptosis in tibial plateau chondrocytes in vivo and in vitro. The remaining 30 guinea pigs in the OA group were divided into 3 groups: a rapamycin group, a normal saline group, and a 3-methyladenine (3-MA) group. Intracellular glycogen accumulation and chondrocyte apoptosis were assessed by altering the level of autophagy in chondrocytes in vivo.

RESULTS

When spontaneous OA occurred in guinea pigs, autophagy levels in tibial plateau chondrocytes decreased, while intracellular glycogen accumulation and the rate of chondrocyte apoptosis increased. After enhancing the level of autophagy in tibial plateau chondrocytes in guinea pigs with OA, intracellular glycogen accumulation and the rate of chondrocyte apoptosis decreased, while inhibiting autophagy had the opposite effects.

CONCLUSION

The results indicate that the function of autophagy in chondrocytes may at least partly involve the catabolism of glycogen. In guinea pigs with OA, the level of autophagy in tibial plateau chondrocytes decreased, and chondrocytes were unable to degrade intracellular glycogen into glucose, leading to less energy for chondrocytes and increased apoptosis.

Rapamycin-induced hyperglycemia is associated with exacerbated age-related osteoarthritis

BACKGROUND

The objective of this study was to determine if mechanistic target of rapamycin (mTOR) inhibition with or without AMP-activated protein kinase (AMPK) activation can protect against primary, age-related OA.

DESIGN

Dunkin-Hartley guinea pigs develop mild primary OA pathology by 5 months of age that progresses to moderate OA by 8 months of age. At 5 months, guinea pigs served as young control (n = 3) or were fed either a control diet (n = 8), a diet enriched with the mTOR-inhibitor rapamycin (Rap, 14 ppm, n = 8), or Rap with the AMPK-activator metformin (Rap+Met, 1000 ppm, n = 8) for 12 weeks. Knee joints were evaluated by OARSI scoring, micro-computed tomography, and immunohistochemistry. Glenohumeral articular cartilage was collected for western blotting.

RESULTS

Rap- and Rap+Met-treated guinea pigs displayed lower body weight than control. Rap and Rap+Met inhibited articular cartilage mTORC1 but not mTORC2 signaling. Rap+Met, but not Rap alone, stimulated AMPK. Despite lower body weight and articular cartilage mTORC1 inhibition, Rap- and Rap+Met-treated guinea pigs had greater OA severity in the medial tibial plateau due to articular cartilage structural damage and/or proteoglycan loss. Rap and Rap+Met increased plasma glucose compared to control. Plasma glucose concentration was positively correlated with proteoglycan loss, suggesting hyperglycemic stress after Rap treatment was related to worsened OA.

CONCLUSIONS

This is the first study to show that Rap induced increase in plasma glucose was associated with greater OA severity. Further, articular cartilage mTORC1 inhibition and bodyweight reduction by dietary Rap and Rap+Met did not appear to protect against primary OA during the prevailing hyperglycemia.

Skeletal muscle mitochondrial respiration in a model of age-related osteoarthritis is impaired after dietary rapamycin

A decline in skeletal muscle mitochondrial function is associated with the loss of skeletal muscle size and function during knee osteoarthritis (OA). We have recently reported that 12-weeks of dietary rapamycin (Rap, 14 ppm), with or without metformin (Met, 1000 ppm), increased plasma glucose and OA severity in male Dunkin Hartley (DH) guinea pigs, a model of naturally occurring, age-related OA. The purpose of the current study was to determine if increased OA severity after dietary Rap and Rap+Met was accompanied by impaired skeletal muscle mitochondrial function. Mitochondrial respiration and hydrogen peroxide (H₂O₂) emissions were evaluated in permeabilized muscle fibers via high-resolution respirometry and fluorometry using either a saturating bolus or titration of ADP. Rap and Rap+Met decreased complex I (CI)-linked respiration and tended to increase ADP sensitivity, consistent with previous findings in patients with end-stage OA. The decrease in CI-linked respiration was accompanied with lower CI protein abundance. Rap and Rap+Met did not change mitochondrial H₂O₂ emissions. There were no differences between mitochondrial function in Rap versus Rap+Met suggesting that Rap was likely driving the change in mitochondrial function. This is the first inquiry into how lifespan extending treatments Rap and Rap+Met can influence skeletal muscle mitochondria in a model of age-related OA. Collectively, our data suggest that Rap with or without Met inhibits CI-linked capacity and increases ADP sensitivity in DH guinea pigs that have greater OA severity.

Calorie restriction with regular chow, but not a high-fat diet, delays onset of spontaneous osteoarthritis in the Hartley guinea pig model

BACKGROUND

Obesity is a leading risk factor for osteoarthritis (OA). In contrast, calorie restriction (CR) may lessen OA due to improved systemic inflammatory status and reduced weight-bearing. The aim of this study was to determine how CR with regular chow versus a high-fat diet (HFD) alters OA progression using the Hartley guinea pig model of disease.

METHODS

Twenty-four male guinea pigs were allocated to four groups at 2 months of age: (1) ad libitum regular chow (obese), (2) CR regular chow (lean), (3) ad libitum HFD, and (4) CR HFD. Animals in both HFD groups ate identical amounts and were combined into one HFD group for analyses. At 5 months, hind limbs were harvested for microcomputed tomography (microCT) and histopathologic evaluation of knee OA. Total body, gonad fat, and infrapatellar fat pad (IFP) masses were recorded. IFPs were collected for gene expression analysis. Immunohistochemistry for monocyte chemoattractant protein-1 (MCP-1) was performed on intact joints. Serum was utilized for protein C3 measurement. All data were compared using ordinary one-way ANOVA analyses with Tukey's post-hoc tests.

RESULTS

Body mass in the lean and HFD groups were similar and lower than the obese group. Despite this, gonad fat pads in the HFD group were comparable to the obese group. MicroCT and histologic OA scores were similar in obese and HFD groups; both scores were significantly lower in the lean group. Obese and HFD groups displayed increased gene expression of pro-inflammatory and catabolic mediators in IFPs relative to lean animals. Consistent with this, immunohistochemistry for MCP-1 in knee joints demonstrated strong positive staining in obese and HFD groups but was minimally detected in lean animals. Serum protein C3 levels were also statistically higher.

CONCLUSIONS

This study demonstrated that CR with a regular chow diet lessened knee OA in the Hartley guinea pig and was associated with decreased local and systemic inflammation compared to obese animals. HFD animals, although under CR conditions, had OA scores and inflammatory markers similar to obese animals. Thus, diet composition, and not solely body weight, may be a key factor in development of OA.