Topically applied phospho-sulindac hydrogel is efficacious and safe in the treatment of experimental arthritis in rats

Abstract

Purpose: Formulate phospho-sulindac (P-S, OXT-328) in a Pluronic hydrogel to be used as a topical anti-inflammatory agent and study its efficacy, safety and pharmacokinetics in an arthritis model.

Methods: LEW/crlBR rats with Freund's adjuvant-induced arthritis were treated with P-S formulated in Pluronic hydrogel (PSH). We determined the clinical manifestations of arthritis including the locomotor activity of the rats; evaluated joints for inflammation, bone resorption, cartilage damage, COX-2 expression and NF-κB activation; assayed plasma IL-6 and IL-10 levels; and studied the pharmacokinetics of P-S in rats after topical or oral administration.

Results: PSH applied at the onset of arthritis or when arthritis was fully developed, suppressed it by 56-82%, improved the locomotor activity of the rats 2.1-4.4 fold, suppressed synovial inflammation, bone resorption, cartilage damage, NF-κB activation and COX-2 expression but not plasma IL-6 and IL-10 levels. There were no side effects. PSH produced rapidly high local levels of P-S with <14% of P-S reaching the circulation, while orally administered P-S was rapidly metabolized generating much lower joint levels of P-S.

Conclusions: Topical application of PSH is efficacious and safe in the treatment of Freund's adjuvant-induced arthritis; has a favorable pharmacokinetic profile; and likely acts by suppressing key pro-inflammatory signaling pathways.

Fig. 1

The PK profile of PSH and P-S. Muscle and blood levels of P-S and its metabolites after topical (PSH) or oral administration of P-S determined as in methods. The chemical structure of P-S is also shown. Left upper panel inset: muscle levels of P-S and metabolites after oral administration in the same scale as after topical administration, shown also in an expanded form.

Fig. 2

Efficacy of PSH and oral PS in the treatment of adjuvant-induced arthritis. (upper panel) Representative histological sections (H&E) of tissues from the hind legs of (a) control; (b) control hydrogel; (c) P-S hydrogel; (d) oral P-S; and (e) normal groups. (lower panel) (f) The response to PSH and P-S of the involved joints of rats treated under the prevention protocol as in Methods according to clinical score, paw weights and histological assessment. FA, Freund's adjuvant. All values are average ± SEM. *, p < 0.01 compared to the corresponding control group.

Fig. 3

Efficacy of PSH in the treatment of adjuvant-induced arthritis. Representative histological sections (H&E) of joint tissues from the hind legs of rats treated under the treatment protocol as in Methods. The effect of PSH on the clinical score, paw weight and histologically assessed inflammation, bone resorption and cartilage damage are shown. FA, Freund's adjuvant. All values are average ± SEM. **, p < 0.01, *, p < 0.05 compared to the control group.

Fig. 4

The effect of PSH on the locomotor activity of rats with arthritis. Both the slow (top) and fast (middle) movements of rats under the treatment protocol as in Methods, recorded over 24 h and expressed per 5 min time units. The cumulative values of slow and fast movements for each group are shown in the bottom panel. All values are average ± SEM. All differences between control and treated rats in the top two panels are statistically significant (p < 0.01–0.02). *, p < 0.01 compared to the control group.

Fig. 5

The effect of PSH treatment on COX-2, NF-κB and cytokines in rats. Upper panels: Representative images of sections from the involved joints of rats stained immuno-histochemically for the expression of COX-2 and NF-κB activation (phospho-NF-κB p65 (Ser276) antibody). PSH was applied under the treatment protocol as in Methods. Lower panels: Histograms of the scores of COX-2 expression and NF-κB activation and plasma cytokine levels of the three study groups. FA, Freund's adjuvant. All values are average ± SEM. *, p < 0.01 compared to the control group with arthritis (FA+).