Platonin, a photosensitizing cyanine dye, suppresses acute inflammation.

Platonin is believed to be an immunomodulator, because it has been shown to be effective only in chronic inflammation models in rat adjuvant arthritis. Platonin did not suppress the serotonin-, histamine- and bradykinin-induced paw edemata of mice when injected 0-1 hr before these irritants in the standard methods. When platonin was administered 3 hr before challenge, however, all of these inflammations were significantly suppressed. Platonin required at least 1 hr of lag for onset of inhibition, just as dexamethasone, and was effective only in the range of 10-320 micrograms/kg. Inhibition of serotonin-induced paw edema by platonin was impaired by concomitant injection of cycloheximide and was not affected by adrenalectomy. Platonin was concluded to suppress the vascular permeability principally through enhancing the endogenous anti-inflammatory protein (vasoregulin) synthesis without changing arachidonate metabolism, lymphocyte transformation or antibody production. Rat carrageenan paw edema was also suppressed when this drug was administered 2-4 hr before challenge.