The Minor Phytocannabinoid Delta-8-Tetrahydrocannabinol Attenuates Collagen-Induced Arthritic Inflammation and Pain-Depressed Behaviors

Abstract

Patients with arthritis report using cannabis for pain management, and the major cannabinoid delta-9-tetrahydrocannabinol (Δ⁹-THC) has anti-inflammatory properties, yet the effects of minor cannabinoids on arthritis are largely unknown. The goal of the present study was to determine the antiarthritic potential of the minor cannabinoid delta-8-tetrahydrocannabinol (Δ⁸-THC) using the collagen-induced arthritis (CIA) mouse model. Adult male DBA/1J mice were immunized and boosted 21 days later with an emulsion of collagen and complete Freund's adjuvant. Beginning on the day of the booster, mice were administered twice-daily injections of Δ⁸-THC (3 or 30 mg/kg), the steroid dexamethasone (2 mg/kg), or vehicle for two weeks. Dorsal-ventral paw thickness and qualitative measures of arthritis were recorded daily, and latency to fall from an inverted grid was measured on alternating days, to determine arthritis severity and functional impairment. On the final day of testing, spontaneous wire-climbing behavior and temperature preference in a thermal gradient ring were measured to assess CIA-depressed behavior. The Δ⁸-THC treatment (30 mg/kg) reduced paw swelling and qualitative signs of arthritis. Δ⁸-THC also blocked CIA-depressed climbing and CIA-induced preference for a heated floor without producing locomotor effects but did not affect latency to fall from a wire grid. In alignment with the morphologic and behavioral assessments in vivo, histology revealed that Δ⁸-THC reduced synovial inflammation, proteoglycan loss and cartilage and bone erosion in the foot joints in a dose-dependent manner. Together, these findings suggest that Δ⁸-THC not only blocked morphologic changes but also prevented functional loss caused by collagen-induced arthritis. SIGNIFICANCE STATEMENT: Despite increasing use of cannabis products, the potential effects of minor cannabinoids are largely unknown. Here, the minor cannabinoid delta-8-tetrahydrocannabinol blocked the development of experimentally induced arthritis by preventing both pathophysiological as well as functional effects of the disease model. These data support the development of novel cannabinoid treatments for inflammatory arthritis.

Fig. 1.

Δ⁸-THC attenuates CIA-induced effects on paw morphology. Mice subjected to CIA and treated twice daily with Δ⁸-THC (30 mg/kg) for two weeks have significantly lower (A) clinical arthritis scores and (B) less hind paw swelling than vehicle-treated arthritic controls. Data are expressed as mean ± SEM (n = 9-10). *P < 0.05 versus (non-CIA) control, ^#P < 0.05 versus CIA.

Fig. 2.

Δ⁸-THC prevents CIA-induced pain behaviors without producing locomotor deficits. Mice were tested every two days in the inverted grid test to assess CIA-depressed paw function. (A) Δ⁸-THC delayed CIA-decreased latency to fall from the inverted grid. On the last day of the experiment, spontaneous wire-climbing behavior and thermal preference in the TGR were measured. (B) Δ⁸-THC (30 mg/kg) blocked CIA-depressed climbing and (D) CIA-induced preference for warmth (C,E) without locomotor deficits. Data are expressed as mean ± S.E.M. (n = 9–10). *^-***P < 0.05–0.0005 versus (non-CIA) control, ^#-###P < 0.05–0.0005 versus CIA, †P < 0.05 versus DEX.

Fig. 3.

Histology of Δ⁸-THC effects in the mouse CIA model. (A,B) Metatarsal-phalangeal joint from a control (no CIA) mouse stained with (A) H&E and (B) Safranin-O/FG showing normal thin appearance of synovium (*) and robust proteoglycan-positive chondrocytes in the articular cartilage (arrowheads in B). (C) Tibia-talus-calcaneus joints from a positive control mouse (CIA + dex); the synovium is multi-layered but free of macrophage infiltration, and the articular cartilage stains robustly with Safranin-O (arrowheads). (D) Metatarsal-phalangeal and (E) tibia-talus joints from two different CIA mice stained with H&E; note extensive macrophage synovial infiltration (m/si) and cartilage/bone erosion (c/be). (F) Tibia-talus and (G) metatarsal-phalangeal joints from two different CIA mice treated with 30 mg/kg Δ⁸-THC (high dose); in (F), only scattered macrophages are present in the synovium (*) and the articular cartilage stains robustly with Safranin-O (arrowheads): compare with the control tibia-talus joint in (C); in (G) there is moderate loss of periosteal/trabecular bone (long arrows) but no macrophages are present in the synovium (*): compare with the control joint in (A). (H,I) Metatarsal-phalangeal and calcaneus-cuboid joints from two different CIA mice treated with 3 mg/kg Δ⁸-THC (low dose); in both feet, note the extensive macrophage synovial infiltration (m/si) and cartilage/bone erosion (c/be); and in (I) note the extensive loss of proteoglycan staining from the articular cartilage (arrowheads). Magnification ×100. Scale bar = 1.0 mm.

Fig. 4.

Δ⁸-THC prevents CIA-induced joint damage and inflammation. Quantitative analyses were performed on feet collected from mice at the end of the experiment. Δ⁸-THC blocked CIA-induced increases in (A) synovial inflammation, (B) proteoglycan loss, (C) cartilage erosion, and (D) bone erosion. Data are expressed as mean ± S.E.M. (n = 4). *^-**P < 0.05–0.005 versus (non-CIA) control, ^#-##P < 0.05–0.005 versus CIA, †P < 0.05 versus DEX.

Fig. 5.

Δ⁸-THC blocks effects of CIA on paw cytokine levels. Whole hind paws were collected at the end of the experiment and homogenized to quantify IL-1β, IL-6, and VEGF-A via multiplex ELISA. Levels of (A) IL-1β and (B) IL-6 were increased, and (C) VEGF-A was decreased in the CIA condition. These CIA-induced changes were blocked by Δ⁸-THC (30 mg/kg) or DEX treatment (twice daily, 14 days). Data are expressed as mean ± S.E.M. (n = 8–10). *^-***P < 0.05-0.0005 versus (non-CIA) control, ^#-###P < 0.05-0.0005 versus CIA, †P < 0.05 versus DEX.