Activation of polyamine catabolism in transgenic rats induces acute pancreatitis

Abstract

Polyamines are required for optimal growth and function of cells. Regulation of their cellular homeostasis is therefore tightly controlled. The key regulatory enzyme for polyamine catabolism is the spermidine͞spermine N 1 -acetyltransferase (SSAT). Depletion of cellular polyamines has been associated with inhibition of growth and programmed cell death. To investigate the physiological function SSAT, we generated a transgenic rat line overexpressing the SSAT gene under the control of the inducible mouse metallothionein I promoter. Administration of zinc resulted in a marked induction of pancreatic SSAT, overaccumulation of putrescine, and appearance of N 1 -acetylspermidine with extensive depletion of spermidine and spermine in transgenic animals. The activation of pancreatic polyamine catabolism resulted in acute pancreatitis. In nontransgenic animals, an equal dose of zinc did not affect pancreatic polyamine pools, nor did it induce pancreatitis. Acetylated polyamines, products of the SSAT-catalyzed reaction, are metabolized further by the polyamine oxidase (PAO) generating hydrogen peroxide, which might cause or contribute to the pancreatic inflammatory process. Administration of specific PAO inhibitor, MDL72527 [N 1 ,N 2 -bis(2,3-butadienyl)-1,4-butanediamine], however, did not affect the histological score of the pancreatitis. Induction of SSAT by the polyamine analogue N 1 ,N 11 -diethylnorspermine reduced pancreatic polyamines levels only moderately and without signs of organ inflammation. In contrast, the combination of N 1 ,N 11 -diethylnorspermine with MDL72527 dramatically activated SSAT, causing profound depletion of pancreatic polyamines and acute pancreatitis. These results demonstrate that acute induction of SSAT leads to pancreatic inflammation, suggesting that sufficient pools of higher polyamine levels are essential to maintain pancreatic integrity. This inflammatory process is independent of the production of hydrogen peroxide by PAO.I ntracellular polyamine levels are tightly maintained by a number of mechanisms, suggesting their importance for cell function. This polyamine homeostasis is controlled by their biosynthesis, interconversion, catabolism, secretion, and uptake. Polyamine biosynthesis is regulated by the activities of ornithine and S-adenosylmethionine decarboxylases. Overexpression of ornithine decarboxylase in transgenic rodents affected spermatogenesis (1, 2), rendered animals more resistant to chemically or electrically induced seizure activity (3) and to ischemic insults (4), and enhanced skin papilloma formation (5). However, the activation of polyamine biosynthesis caused by overexpression of ornithine decarboxylase did not result in enhanced accumulation of the higher polyamines spermidine and spermine. Polyamine catabolism is controlled by the activity of spermidine͞spermine N 1 -acetyltransferase (SSAT; refs. 6 and 7). The acetylated products are oxidized further by the polyamine oxidase (PAO) to spermidine and putrescine. We recently generated transgenic mouse lines with ...

Depletion of cellular polyamines, spermidine and spermine, causes a total arrest in translation and growth in mammalian cells

“…The effects of overexpression of SAT1 were previously reported by others using cell lines overexpressing SAT1 stably or in an inducible manner (22)(23)(24)33), SAT1 transgenic mice (34)(35)(36), and a SAT1 adenovirus (37,38). Although retardation of growth and decreases in spermidine and spermine were consistently associated with SAT1 overexpression, the degree of growth inhibition and polyamine depletion were much lower than those reported in this study.…”

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

“…1A displays the typical polyamine pattern in the liver of SSAT overexpressing rats. Putrescine pool was greatly increased, whereas the spermine level was decreased when compared with wild-type rat liver where putrescine remains almost undetectable (8). An exposure of the rats to the polyamine oxidase inhibitor MDL72527 expectedly greatly reduced putrescine content and expanded the pool of N 1 -acetylspermidine (Fig.…”

“…Transgenic Rats and the Studies of ␣-Methylated Spermine Analogs-The production of transgenic rats has been described in detail earlier (8). Partial hepatectomy of the transgenic rats was carried out essentially as described in Ref.…”

Polyamines of Plant Origin - An Important Dietary Consideration for Human Health

“…A transgenic rat model has been used to demonstrate that a depletion of pancreatic spermidine and spermine, through overexpression of the catabolic polyamine enzyme spermidine/spermine N 1 -acetyltransferase (SSAT), leads to onset of acute pancreatitis (Alhonen et al, 2000), and this could be prevented with the application of 1-methylspermidine, a metabolically stable analogue of spermidine (Räsänen et al, 2002). It should be kept in mind that Nishimura et al (2009) demonstrated a steady-state of polyamines were present in the pancreas even with ageing, but given that the total body pool of polyamines generally decreases with age, diet-derived polyamines could still be an important source to maintain pancreatic polyamine concentrations.…”