Role of the endocannabinoid system in the emotional manifestations of osteoarthritis pain

Abstract

In this study, we investigated the role of the endocannabinoid system (ECS) in the emotional and cognitive alterations associated with osteoarthritis pain. The monosodium iodoacetate model was used to evaluate the affective and cognitive manifestations of osteoarthritis pain in type 1 (CB1R) and type 2 (CB2R) cannabinoid receptor knockout and wild-type mice and the ability of CB1R (ACEA) and CB2R (JWH133) selective agonists to improve these manifestations during a 3-week time period. The levels of the endocannabinoids anandamide (AEA) and 2-arachidonoylglycerol (2-AG) were measured in plasma and brain areas involved in the control of these manifestations. Patients with knee osteoarthritis and healthy controls were recruited to evaluate pain, affective, and cognitive symptoms, as well as plasma endocannabinoid levels and cannabinoid receptor gene expression in peripheral blood lymphocytes. The affective manifestations of osteoarthritis were enhanced in CB1R knockout mice and absent in CB2R knockouts. Interestingly, both ACEA and JWH133 ameliorated the nociceptive and affective alterations, whereas ACEA also improved the associated memory impairment. An increase of 2-AG levels in prefrontal cortex and plasma was observed in this mouse model of osteoarthritis. In agreement, an increase of 2-AG plasmatic levels and an upregulation of CB1R and CB2R gene expression in peripheral blood lymphocytes were observed in patients with osteoarthritis compared with healthy subjects. Changes found in these biomarkers of the ECS correlated with pain, affective, and cognitive symptoms in these patients. The ECS plays a crucial role in osteoarthritis and represents an interesting pharmacological target and biomarker of this disease.

Conflict of interest statement

Sponsorships or competing interests that may be relevant to content are disclosed at the end of this article.

Figures

Figure 1

Anxiety-like behavior associated with knee osteoarthritis in WT, CB1KO, and CB2KO. The percentage of entries and time spent in the open arms and the total entries in the open and closed arms of the elevated plus-maze were evaluated 1 (A and B) and 3 weeks (C and D) after the intra-articular injection of monosodium iodoacetate or saline. Data are expressed as mean ± SEM (n = 12-18 per group). ★P < 0.05, ★★P < 0.01, ★★★P < 0.001 vs saline injection (Fisher LSD test); ☆P < 0.05, ☆☆P < 0.01, ☆☆☆P < 0.001 vs WT (Fisher LSD test). WT, wild type.

Figure 2

Memory impairment associated with knee osteoarthritis in WT, CB1KO, and CB2KO. The discrimination index and the total time of exploration in the object recognition memory were evaluated 1 (A and B) and 3 weeks (C and D) after the intra-articular injection of monosodium iodoacetate or saline. Data are expressed as mean ± SEM (n = 12-18 per group). ★★P < 0.01, ★★★P < 0.001 vs saline injection (Fisher LSD test). WT, wild type.

Figure 3

Relative corticotropin-releasing hormone (A and B) and glucocorticoid receptor (C and D) gene expression analysis in paraventricular nucleus and prefrontal cortex of WT, CB1KO, and CB2KO after receiving monosodium iodoacetate or saline injection. Data are expressed as mean ± SEM (n = 5-9 per group). ★P < 0.05, ★★P < 0.01, ★★★P < 0.001 vs saline injection (Fisher LSD test); ☆P < 0.05, ☆☆P < 0.01, ☆☆☆P < 0.001 vs WT (Fisher LSD test). WT, wild type.

Figure 4

Effects of ACEA and JWH133 in nociceptive, affective, and cognitive behaviors in osteoarthritic mice. Mechanical nociceptive responses in the ipsilateral paw (A and D), anxiety-like behavior (B and E), and memory (C and F) were evaluated 60, 45, and 30 minutes, respectively, after the intraperitoneal administration of ACEA or JWH133, at 1 and 3 weeks after monosodium iodoacetate or saline injection. Data are expressed as mean ± SEM (n = 15-20 per group). ★P < 0.05, ★★P < 0.01, ★★★P < 0.001 vs saline injection (Fisher LSD test); ☆P < 0.05, ☆☆P < 0.01, ☆☆☆P < 0.001 vs vehicle administration (Fisher LSD test); ###P < 0.001 vs 1 mg/kg dose (Fisher LSD test).

Figure 5

2-AG and AEA quantification in the amygdala (A), hippocampus (B), prefrontal cortex (C), and plasma (D) of mice receiving monosodium iodoacetate or saline injection. Data are expressed as mean ± SEM (n = 8-10 per group). ★P < 0.05, ★★P < 0.01 vs saline injection (Student t test).

Figure 6

Clinical assessment of pain (Huskisson scale [A] and PainDETECT questionnaire [B]), emotional state (Hospital Anxiety–Depression scale [C and D]), visual memory (E), and health-related quality of life (SF-36 questionnaire [F]) in patients with osteoarthritis and healthy volunteers. Data are expressed as mean ± SEM (n = 14-16 per group). ★P < 0.05, ★★P < 0.01, ★★★P < 0.001 vs healthy volunteers (Student t test). Pearson correlations between knee pain scores (Huskisson scale) and PainDETECT, Hospital Anxiety–Depression scale, and SF-36 scores are presented (G).

Figure 7

Plasmatic endocannabinoid quantification (A) and CB1R and CB2R gene expression in the lymphocytes (B) of patients with osteoarthritis and healthy volunteers. Data are expressed as mean ± SEM (n = 14-16 per group). ★P < 0.05, ★★P < 0.01 vs healthy volunteers (Student t test). Pearson correlations between 2-AG levels and knee pain (Huskisson scale), HAD_Depression, SF-36, and visual memory scores (C) as well as correlations between CB1R or CB2R gene expression and HAD_Depression and pain scores (Huskisson scale), respectively, are presented (D). HAD, Hospital Anxiety–Depression scale.