Enhanced acetaminophen hepatotoxicity in transgenic mice overexpressing BCL-2.

Mitochondria play an important role in the cell death induced by many drugs, including hepatotoxicity from overdose of the popular analgesic, acetaminophen (APAP). To investigate mitochondrial alterations associated with APAP-induced hepatotoxicity, the subcellular distribution of proapoptotic BAX was determined. Based on the antiapoptotic characteristics of BCL-2, we further hypothesized that if a BAX component was evident then BCL-2 overexpression may be hepatoprotective. Mice, either with a human bcl-2 transgene (-/+) or wild-type mice (WT; -/-), were dosed with 500 or 600 mg/kg (i.p.) APAP or a nonhepatotoxic isomer, N-acetyl-m-aminophenol (AMAP). Immunoblot analyses indicated increased mitochondrial BAX-beta content very early after APAP or AMAP treatment. This was paralleled by disappearance of BAX-alpha from the cytosol of APAP treated animals and, to a lesser extent, with AMAP treatment. Early pathological evidence of APAP-induced zone 3 necrosis was seen in bcl-2 (-/+) mice, which progressed to massive panlobular necrosis with hemorrhage by 24 h. In contrast, WT mice dosed with APAP showed a more typical, and less severe, centrilobular necrosis. AMAP-treated bcl-2 (-/+) mice displayed only early microvesicular steatosis without progression to extensive necrosis. Decreased complex III activity, evident as early as 6 h after treatment, correlated well with plasma enzyme activities at 24 h (AST r(2) = 0.89, ALT r(2) = 0.87) thereby confirming a role for mitochondria in APAP-mediated hepatotoxicity. In conclusion, these data suggest for the first time that BAX may be an early determinant of APAP-mediated hepatotoxicity and that BCL-2 overexpression unexpectedly enhances APAP hepatotoxicity.

Bcl-2 delays and alters hepatic carcinogenesis induced by transforming growth factor alpha.

Transgenic mice that overexpress transforming growth factor (TGF)-alpha develop liver tumors between 12 and 15 months of age. Tumor development is preceded by an overall increase in the rates of hepatocyte proliferation and cell death. To examine the role of apoptosis in the development of TGF-alpha-induced liver tumors, we generated TGF-alpha/Bcl-2 double transgenic mice by crossing TGF-alpha transgenic mice with Bcl-2 transgenic mice expressing a zinc-inducible Bcl-2 transgene. Overexpression of the Bcl-2 transgene protected hepatocytes from Fas-mediated apoptosis. We anticipated that hepatocytes in TGF-alpha/Bcl-2 double transgenic mice would be stimulated to proliferate but would fail to undergo apoptosis, leading to increased liver weights and accelerated tumorigenesis. At 4 weeks of age, both TGF-alpha single transgenic and TGF-alpha/Bcl-2 double transgenic mice had elevated hepatocyte proliferation and increased liver:body weight ratios. However, by 8 months, the liver:body weight ratios had normalized in both TGF-alpha single transgenic and TGF-alpha/Bcl-2 double transgenic mice. Furthermore, Bcl-2 functioned as a tumor suppressor, significantly decreasing the frequency and delaying the development of TGF-alpha-induced liver tumors, despite having comparable levels of TGF-alpha transgene expression in both single and double transgenic mice. Between 11 and 12 months of age, >80% of the TGF-alpha single transgenic mice had developed tumors, whereas only 54% of the double transgenic mice had developed tumors after 13 months of age. The tumors that eventually developed in the TGF-alpha/Bcl-2 double transgenic mice were histologically distinct and smaller in size and had lower hepatocyte mitotic activity than tumors from TGF-alpha single transgenic mice. Furthermore, delaying Bcl-2 expression until 8.5 months of age was sufficient to inhibit TGF-alpha-induced tumorigenesis. These results indicate that Bcl-2 inhibits tumor progression in the liver, possibly by interfering with hepatocyte proliferation.

Effect of Cluster Tightness on Botrytis Bunch Rot in Six Chardonnay Clones.

Cluster tightness was measured and Botrytis bunch rot was evaluated for six Chardonnay clones in each of two trials, one cane-pruned and the other spur-pruned. In both locations, University of California (UC) Foundation Plant Materials Service (FPMS) clone 4 was most compact and FPMS 15 was the least compact (P < 0.01). Cluster tightness among the six clones, measured by the UC Firmness Tester Method, ranged from 0.0028 newtons (N) for clone 15 to 0.0112 N for clone 4. Cluster tightness was positively correlated with cluster weight. Botrytis bunch rot development was greater in the cane-pruned trial than in the spur-pruned trial. In the cane-pruned trial, disease incidence was greatest in FPMS 16 (81.5%) and least in clone 15 (44.5%; P< 0.025), while disease severity did not differ significantly. Neither incidence nor severity were significant in the spur-pruned trial. Clone 15, the clone with the least compact clusters, had the lowest disease severity levels.