Matrix metalloproteinases-2 and 9 do not play a role in the growth of preneoplastic liver lesions in F344 rats

Matrix metalloproteinases- (MMPs) 2 and 9 (gelatinases A and B) have been i mplicated in tumor invasion and metastasis, and recent studies have shown i ncreased levels of these enzymes during recovery from partial hepatectomy ( PH) in rats. F344 rats are highly susceptible to the growth of glutathione S-transferase 7-7- (GST 7-7) positive preneoplastic liver lesions promoted using the modified resistant hepatocyte (RH) protocol. Since the RH protoco l consists of 2-acetylaminofluorene (2-AAF) followed by a PH, we reasoned t hat MMP-2 and -9 might be critical for the growth of lesions. Using gelatin zymography, we examined the expression of these enzymes in the! livers of F344 rats treated with the RH protocol and sacrificed on Days 2, 4, 7,14, a nd 21 after 2-AAF/PH. We found increases in both pro- and active MMP-2 and -9 over baseline levels, with the highest levels occurring on Day 7 post-PH . Also, a 54-kDa band, likely to be proMMP-1, was elevated in a pattern sim ilar to MMP-2 and -9. In contrast to F344 rats, identically treated Copenha gen rats that are highly resistant to promotion of liver lesion growth usin g the RH protocol had significantly lower levels of proMMP-1 and -2. To tes t the importance of these MMPs to the growth of liver lesions, F344 rats th at had been initiated with diethylnitrosamine were treated using the RH pro tocol. They then received either the MMP inhibitor batimastat (30 mg/kg, in traperitoneally) or vehicle alone daily from Day 3 to 20 post-PH and were s acrificed on Day 21. There were no differences in the percentage of liver v olume occupied by GST 7-7-positive lesions (19.1 +/- 4.84 vs 19.4 +/- 3.31, treated versus vehicle, mean SEM) or liver weight as a percentage of body weight (4.11% +/- 0.15 vs 4.07% +/- 0.18, treated versus vehicle, mean SEM) between the treated and control groups. Treatment of rats with batimastat clearly did not affect lesion growth or liver regeneration following the RH protocol. These results suggest that in creases in gelatinase expression d uring the RH protocol are a result of the promotional stimulus rather than a mechanism by which 2-AAF/PH causes lesion growth.