A Polyamine Analogue Prevents Acute Pancreatitis and Restores Early Liver Regeneration in Transgenic Rats with Activated Polyamine Catabolism

Abstract

We recently generated a transgenic rat model for acute pancreatitis, which was apparently caused by a massive depletion of pancreatic polyamines spermidine and spermine due to inducible activation of their catabolism (Alhonen, L., Parkkinen, J. J., Keinä nen, T., Sinervirta, R., Herzig, K. H., and Jä nne, J. (2000) Proc. Natl. Acad. Sci. U. S. A. 97, 8290 -8295). When subjected to partial hepatectomy, these animals showed striking activation of polyamine catabolism at 24 h postoperatively with a profound decrease in hepatic spermidine and spermine pools and failure to initiate liver regeneration. Here we show that pancreatitis in this model could be totally prevented, as judged by histopathology and plasma ␣-amylase activity, by administration of 1-methylspermidine, a metabolically stable analogue of spermidine. Similarly, the analogue, given prior to partial hepatectomy, restored early liver regeneration in the transgenic rats, as indicated by a dramatic increase in the number of proliferating cell nuclear antigen-positive hepatocytes from about 1% to more than 40% in response to the drug. The present results suggest that the extremely high concentration of spermidine in the pancreas, in fact the highest in the mammalian body, may have a critical role in maintaining organ integrity. The failure to initiate liver regeneration in the absence of sufficient hepatic polyamine pools similarly indicates that polyamines are required for proper commencement of the regenerative process.The polyamines spermidine and spermine and their precursor putrescine are intimately associated with growth and differentiation of mammalian cells, yet their exact cellular functions have not been solved (1). In attempts to elucidate the physiological roles of the polyamines, we have generated a number of transgenic mouse and rat lines with genetically altered polyamine metabolism. The activation of polyamine biosynthesis through an overexpression of ornithine decarboxylase brings about many interesting phenotypic changes, such as male infertility (2, 3), yet these studies are complicated by the fact that overexpression of ornithine decarboxylase only expands tissue putrescine pools as the latter diamine is not further converted to spermidine and spermine (4, 5). Much more severe distortion of tissue polyamine pools has been achieved by activation of polyamine catabolism through an overexpression of spermidine/spermine N 1 -acetyltransferase (SSAT) 1 in transgenic rodents. The latter enzyme catalyzes the rate-controlling reaction in the catabolism of spermidine and spermine. After being acetylated, spermidine is converted to putrescine and spermine to spermidine by the action of polyamine oxidase (6). Overexpression of SSAT in transgenic rodents results in profound changes in tissue polyamine pools, such as the massive accumulation of putrescine, appearance of N 1 -acetylspermidine, and decreases in spermidine and/or spermine pools (7). The alterations in polyamine homeostasis are accompanied by bizarre phenotypic changes, such as the earl...

Metabolic Stability of α-Methylated Polyamine Derivatives and Their Use as Substitutes for the Natural Polyamines

“…In line with the above studies, we found that MeSpd prevents zinc-induced pancreatitis and restores liver regeneration in transgenic rats overexpressing SSAT under the control of the metallothionein promoter (5). Under these conditions where polyamine catabolism was intensely activated, the natural polyamines could not be used as they were rapidly acetylated and degraded with no net tissue accumulation (5).…”

“…Liver regeneration could be fully restored with prior administration of MeSpd (5). Based on these studies and earlier work indicating that partial hepatectomy rapidly elevates the hepatic spermidine, but not spermine, pool, we assigned a critical role to spermidine in liver regeneration (5,18).…”

“…Our earlier studies with transgenic rats overexpressing SSAT have indicated that partial hepatectomy of these animals resulted in an induction of SSAT and a profound depletion of the hepatic spermidine pool that was associated with failure to initiate liver regeneration (5,18). Liver regeneration could be fully restored with prior administration of MeSpd (5).…”

“…As a conclusion it seems that ␣-methylation prevents polyamine derivatives from acetylation but not their oxidation. atectomy of the transgenic rats overexpressing SSAT results in a profound spermidine and spermine depletion because of SSAT induction at 24 h postoperatively and failure to initiate liver regeneration (5,18). Liver regeneration could be restored by a prior administration of MeSpd (5).…”

“…Treatments before partial hepatectomy and the determination of DNA synthesis were carried out as described in the legend to Ref. 5. Transgenic 10-week-old male rats were injected twice with MDL72527 (50 mg/kg intraperitoneal) at 16-h intervals to inactivate PAO according to Bolkenius et al (10) and further with MeSpd, MeSpm, or Me 2 Spm twice (25 mg/kg intraperitoneal) 2 and 8 h after the second MDL72527 treatment.…”