Hepatocyte growth factor (HGF) is a potent mitogen for parenchymal liver, epithelial and endothelial cells. Structurally, it has similarities to kringle‐containing serine proteases, although it does not possess proteolytic activity. A structure‐activity relationship study of human HGF was performed by functional analysis of HGF substitution and deletion variants. Analysis of HGF variants was accomplished by defining their ability to induce DNA synthesis on hepatocytes in primary culture and to compete with wild‐type HGF for binding to a soluble form of the HGF receptor. Three groups of variants were made: (i) substitutions at the cleavage site, (ii) substitutions within the protease‐like domain and (iii) deletions of the beta‐chain and/or kringle domains. Our results show that: (i) single‐chain HGF is a zymogen‐like promitogen in that cleavage into a two‐chain form is required for biological activity, however, the single chain form of HGF still retains substantial receptor binding capacity; (ii) certain mutations in the protease‐like domain result in variants that are completely defective for mitogenic activity, yet exhibit apparent receptor binding affinities similar to wild‐type HGF (Kd approximately 50–70 pM); and (iii) a variant containing the N‐terminal 272 residues of mature HGF showed only a 4‐fold increase in Kd when compared with wild‐type HGF indicating that a primary receptor binding determinant is located within this sequence.

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While studying endocrine responses to activin in female rats, we discovered that activin caused a marked reduction in liver mass. The regressed livers exhibited no gross signs of necrosis or infarction, but histopathological evaluation revealed extensive cell death in the centrilobular regions. The dying cells appeared to fragment into structures resembling apoptotic bodies. Liver mass and histological appearance were restored after cessation of activin infusion, indicating that on an organ level, this effect was reversible. To determine whether the effects observed in vivo were caused by direct actions on the liver, we then tested activin on isolated hepatocytes in serum-free medium. Under these conditions, activin caused many hepatocytes to undergo fragmentation, which was accompanied by a loss of 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT)-reducing activity, an index of viability. We compared the effects of activin with those of transforming growth factor-beta because activin is structurally related to transforming growth factor-beta and because transforming growth factor-beta has been shown previously to induce cell death in hepatocytes. Both proteins caused cell death of comparable magnitude, as defined by the extent of loss of MTT-reducing activity, but transforming growth factor-beta was active at one tenth of the effective activin concentrations. A neutralizing monoclonal antibody to transforming growth factor-beta blocked the response to transforming growth factor-beta but had no effect on the response to activin. Conversely, follistatin, an activin-binding protein, blocked the response to activin but not to transforming growth factor-beta. Inhibin, which antagonizes the effects of activin in many systems, had little effect on the response to activin. Activin and transforming growth factor-beta differed in their onset of action; exposure to transforming growth factor-beta for only 1 hr induced a maximal response, whereas maximal response to activin required its continuous presence for 24 hr. These results show a novel effect of activin on cell death in hepatocytes in vivo and in vitro, suggesting that activin may have a previously unrecognized role in regulating hepatic function.

Background— Secretory phospholipase A 2 (sPLA 2 ) may play a role in myonecrosis after elective percutaneous coronary intervention (PCI). Inhibition of this enzyme may have a beneficial effect. The central hypothesis of this study was that treatment with varespladib, a small-molecule inhibitor of sPLA 2 would reduce postprocedural release of cardiac biomarkers after elective percutaneous coronary intervention. Methods and Results— Between October 2007 and June 2009, 144 stable patients were randomized in a phase II trial to receive varespladib 500 mg PO BID or placebo 3 to 5 days before and for 5 days after elective percutaneous coronary intervention. The primary end point was elevation of troponin I or creatine kinase-MB above the upper limit of normal at 6 to 8 or 18 to 24 hours after percutaneous coronary intervention. Mean age was 63±10 and 64±10 years, with 38% and 42% with diabetes mellitus and 29% and 28% with prior myocardial infarction for the varespladib and placebo groups, respectively. The primary end point occurred in 75% of varespladib and 63% of placebo patients ( P =0.14). Troponin I 3 times the upper limit of normal was observed in 57% and 50% ( P =0.39) and creatine kinase-MB 2 times the upper limit of normal in 14% and 3% ( P =0.018). Median (first and third quartiles) change in high-sensitivity C-reactive protein in these 2 groups was 0.65 mg/L (−0.18 and 1.48) and 0.70 mg/L (0.00 and 1.50) at 18 to 24 hours ( P =0.81) and 0.20 mg/L (−0.70 and 1.40) and 0.60 mg/L (−0.12 and 1.72) at 3 to 5 days ( P =0.23), whereas change in sPLA 2 activity at 3 to 5 days in a subset was −2.85 ng/ml (−3.40 and −1.85) and 0.25 ng/ml (−0.20 and 0.85) ( P <0.001). Conclusions— Inhibition of sPLA 2 by varespladib administered for 3 to 5 days before the procedure does not reduce periprocedural myonecrosis associated with elective percutaneous coronary intervention. Clinical Trial Registration— URL: http://www.clinicaltrials.gov . Unique identifier: NCT00533039.

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