EFFECTS OF ORAL-ADMINISTRATION OF PURIFIED MICRONIZED FLAVONOID FRACTION ON INCREASED MICROVASCULAR PERMEABILITY INDUCED BY VARIOUS AGENTS AND ON ISCHEMIA REPERFUSION IN THE HAMSTER-CHEEK POUCH/

The effects of a clinically used purified micronized flavonoid fractio n (S 5682) containing 90% diosmin and 10% hesperidin on increased micr ovascular permeability induced by histamine, bradykinin, and leukotrie ne B-4 (LTB4) were investigated by intravital microscopy in the hamste r cheek pouch preparation. The authors also investigated the effects o f S 5682 on macromolecular permeability increase and leukocyte adhesio n during ischemia-reperfusion by using the same preparation. S 5682, s uspended in 10% lactose solution, or vehicle (10% lactose) was adminis tered orally to male hamsters for ten days at 20 mg/kg/day (10 mg/kg t wice a day). Fluorescein isothiocyanate (FITC)-labeled dextran (mel wt 150,000) was given intravenously, thirty minutes after completion of the cheek pouch preparation. The leukocytes were stained by continuous IV infusion of acridine orange (0.5 mg/kg/minute). Histamine (2 mu M) , bradykinin (1 mu M), and LTB4 (0.01 mu M), applied topically for fiv e minutes, increased the number of fluorescent vascular leakage sites in postcapillary venules. A temporary ischemia with total circulatory arrest of the cheek pouch was obtained by clamping the neck of the eve rted pouch. The maximum number of leaky sites (per cm(2) in the prepar ed area) that occurred either at five minutes after the beginning of e ach topical application or ten minutes after the onset of reperfusion was quantified in ultraviolet light microscopy. The results from 60 an imals divided into 10 groups of 6 animals each are presented as means +/-SEM. In comparison with vehicle, S 5682 significantly inhibited the macromolecular permeability-increasing effect of histamine (343.5 +/- 22.3 versus 207.5 +/- 32.0 leaks/cm(2); P<0.01), bradykinin (345.2 +/ - 19.0 versus 206.2 +/- 21.6 leaks/cm(2); P<0.01), and LTB4 (353.3 +/- 27.5 versus 242.7 +/- 33.6 leaks/cm(2); P<0.05). At reperfusion, afte r thirty minutes of ischemia, S 5682 significantly decreased the obser ved macromolecular permeability (103.6 +/- 15.4 versus 42.6 +/- 9.3 le aks/cm(2); P<0.01). Flavonoid-treated animals also displayed a statist ically significant lower number of adhering leukocytes to the venular endothelium (83.5 +/- 9.5 versus 48.4 +/- 12.3 per 6 mm(2); P<0.05). T hese results demonstrate that oral administration of S 5682 for ten da ys at 20 mg/kg body weight/day had a protective effect against leakage of macromolecules after application of permeability-increasing substa nces and during ischemia-reperfusion in the cheek pouch microvasculatu re. Since firm leukocyte attachment to the endothelial wall and subseq uent emigration of leukocytes into the interstitium is a mechanism for tissue damage during inflammation, attenuation of this phenomenon dur ing conditions of ischemia-reperfusion can in part explain previous ob servations that this purified micronized flavonoid fraction decreases edema formation. The present data illustrating the inhibitory effect o f a clinically relevant dose of S 5682 on the inflammatory processes i nduced in this in vivo model of microcirculation may serve as a ration al basis to explain its clinical efficacy.