Inhibitory activity of Cinnamomum cassia bark-derived component against rat lens aldose reductase

To evaluate the inhibitory activity of active compounds isolated from Cinnamomum cassia bark against lens aldose reductase and compare to that of three commercially available compounds (cinnamyl alcohol, trans -cinnamic acid, and eugenol) and quercitrin as aldose reductase inhibitors. The IC (50) value of cinnamaldehyde was determined.

Active compound was purified on repeated silica gel column and HPLC (Waters Delta Prep 4000). Aldose reductase was prepared from lenses of Sprague-Dawley male rat eyes. The incubation mixture contained 135 mM Na, K-phosphate buffer (pH 7.0), 100 mM lithium sulfate, 0.03 mM NADPH, 0.04 mM DL-glyceraldehyde and 50 micro L of an enzyme preparation, with or without a plant extract. The reaction was initiated by adding NADPH at 37 degrees C and stopped by adding 0.5 N hydrochloric acid. Subsequently, 6 N NaOH containing 10 mM imidazole was added, and the mixture was incubated at 60 degrees C for 10 min to convert NADP into a fluorescent product. The fluorescence was measured with a spectrofluorophotometer.

The biologically active constituents of C. cassia extract against lens aldose reductase were characterized as trans -cinnamaldehyde by spectral analysis. The IC (50) value of cinnamaldehyde is 0.003 mg/mL. However, cinnamyl alcohol, trans -cinnamic acid and eugenol exhibited only weak inhibition against aldose reductase. In comparison, quercitrin was 6 times more potent than cinnamaldehyde.

These results suggest that cinnamaldehyde isolated from C. cassia barks may be useful as a lead compound and a medicinal foodstuff for aldose reductase inhibition.