The naturally occurring polyamines, spermine NH2(CH2)3NH(CH2)4NH(CH2)3NH2 and spermidine NH2(CH2)3NH(CH2)4NH2, as well as the diamine putrescine NH2(CH2)4NH2, are widely spread in nature. They occur ...in plants, micro-organisms and animal tissues and fulfil many important physiological functions. Due to their cationic nature they interact with negatively charged macromolecules such nucleic acids, phospholipids and proteins. This ionic interaction, which is reversible, leads to the stabilization of DNA, tRNA, membranes and some proteins. Early studies demonstrated that polyamines stimulate the growth of pro- and eukaryotic cells and that they play an important role in carcinogenesis and in malignant transformation processes. As a result of these studies various inhibitors of polyamine biosynthesis have been synthesized and are used to combat cancer and parasitic diseases (e.g., African sleeping sickness).
In 1678 Antonie van Leeuwenhoek identified crystalline substances in human semen. The structure of these crystals, named “spermine”, was not elucidated by Rosenheim until 250 years later. ...Subsequently a triamine (spermidine) and a diamine (putrescine; 1,4-diaminobutane) were isolated from prokaryotic and eukaryotic systems. Soon it became apparent that polyamines can promote the growth of fastidious bacteria. Subsequently a group in Helsinki studied the accumulation of polyamines in regenerating rat liver, while Caldarera and his group studied polyamine synthesis in the developing chick embryo. These investigations led to metabolic studies. Ornithine decarboxylase was identified as a key enzyme in polyamine biosynthesis, while polyamine and diamine oxidations were studied by Mondovì. α-Diflouromethylornithine (DFMO) was synthesized by Merrell-Dow and became a potent inhibitor of ornithine decarboxylase. The findings of Russell that polyamines are excreted in the urine of cancer patients drew the attention of oncologists, who attempted the use new technologies for the detection of cancer and improving therapy. With the advance of molecular biology the structure of polyamine-biosynthetic enzymes was elaborated. Plants served as another important tool to study the physiological functions of polyamines. Bagni and his group at Bologna were pioneers in that field and for more than forty-six years set the foundation of a most interesting discipline.
The naturally occurring polyamines, spermine, spermidine and the diamine putrescine are widespread in nature. They have been implicated in growth and differentiation processes. In 1967, we reported ...that cancer cells are rich in polyamines. Subsequently, it has been shown that polyamines are released from cancer cells and may be detected in body fluids such as urine, blood and cerebrospinal fluids. It has also been demonstrated that the increase in cellular polyamine levels is an early and an obligatory event in the process of malignant transformation. This increase in cellular polyamine concentration is due to the activation of ornithine decarboxylase (ODC), which catalyses the rate limiting step in polyamine synthesis by converting ornithine to putrescine. Assays of urinary and blood polyamines have been used to detect cancer and to determine the success of therapy. A sensitive, rapid, chemiluminescence-based method for the determination of diamines and polyamines was developed and 2.000 urine samples were tested. An interesting "gene therapy" system for injecting amine oxidases into normal and transformed cells was developed as follows: serum amine oxidase and porcine kidney damine oxidase were trapped within reconstituted Sendai virus envelopes. Chick or rat fibroblasts, transformed by Rous sarcoma virus, were more susceptible to the injected enzymes, compared to the normal culture, when macromolecular synthesis was tested. An in vitro chemosensitivity assay for the testing of the sensitivity of cancer cells from individual patients ("tailored treatment") was also developed. All these studies stress the importance of polyamines in carcinogenesis.
Poliamini, spermin, spermidin i diamin putrescin su jako rasprostranjeni u prirodnom obliku i uključeni su u procese rasta i diferencijacije. Da su ćelije kancera bogate poliaminima opisali smo 1967. godine. Ubrzo je prikazano da ćelije kancera ispuštaju poliamine i da se oni mogu detektovati u telesnim tečnostima poput urina, krvi i cerebrospinalne tečnosti. Takođe je prikazano da je porast ćelijskog nivoa poliamina rani i obavezni događaj u procesu maligne transformacije. Ovaj porast u ćelijskoj koncentraciji poliamina dešava se zbog aktivacije ornitin dekarboksilaze (ODC), koja katališe nivo limitirajuće stope u sintezi poliamina konvertovanjem ornitina u putrescin. Testiranje poliamina iz urina i krvi je rađeno u cilju otkrivanja kancera i određivanja uspešnosti terapije. Razvijena je senzitivna i brza metoda hemiluminiscencije za određivanje diamina i poliamina i testirano je 2000 uzoraka urina. Interesantan sistem ‘’genetske terapije’’ za ubacivanje amin oksidaze u normalne i transformisane ćelije razvijen je na sledeći način: serum amin oksidaze i diamin oksidaza dobijena iz svinjskog bubrega su zadržani u rekonstituisanim omotačima Sendai virusa. Fibroblasti embriona pileta ili pacova, izmenjeni virusom Rausovog sarcoma, bili su mnogo podložniji na ubačene enzime u poređenju sa normalnom podlogom, kada je testirana makromolekularna sinteza. Takođe je razvijen i in vitro test hemosenzitivnosti (‘’prilagođeni tretman’’) ćelija kancera kod različitih bolesnika. Sve ove studije naglašavaju značaj poliamina u karcinogenezi.
The Westinghouse Lead-cooled Fast Reactor (LFR) is a medium-size, passively safe, economic, Gen-IV nuclear reactor. An important effort within the Westinghouse LFR program is the development of the ...safety analysis methodology, which comprises computer code development, model development, and experimental testing. A key initial task associated with the development of the safety analysis methodology is the identification of processes and phenomena that affect the plant's capability to meet selected safety performance indicators. This is accomplished through the development of a Phenomena Identification and Ranking Table (PIRT) for selected accident scenarios which, for this specific PIRT effort, included selected postulated design basis accidents and hypothetical beyond design basis accidents in LFRs.
This paper describes the role of PIRT in the development of the Westinghouse LFR safety analysis methodology and the process used in the PIRT development. Specifically, the Westinghouse LFR PIRT assessed importance of pertinent phenomena and identified gaps in their knowledge-base by evaluating current modeling capabilities and data available for validation. The ultimate goal was to provide guidance on computer code development and validation efforts and to prioritize testing to support LFR design and licensing. The key phenomena and processes that are deemed highly important for the safety performance indicators, but for which the state of knowledge is low, are presented. The testing program and analyses development are planned to address significant phenomena in the PIRT.
Display omitted
•Westinghouse LFR is a passively safe, scalable reactor with the goal of generating flexible and cost-competitive electricity.•A key task of the reactor development is Phenomena Identification and Ranking Table (PIRT).•The PIRT is developed with jointed forces of the vendor, national laboratories, and international experts.•The testing program and modeling and simulation program are planned after the PIRT development.
C-type natriuretic peptide (CNP) and endothelin-1 are paracrine peptides with opposing effects on cardiac myocyte contraction and intracellular cGMP production. Elevated levels of both endothelin-1 ...and CNP are found in patients with congestive heart failure. These factors may be related to positive and negative regulation of cell apoptosis in the failing heart. To evaluate the effect of CNP and endothelin-1 on apoptosis of cardiac myocytes and the possible mechanisms involved, primary cardiac myocytes were prepared from neonatal Sabra rats. Cardiomyocyte apoptosis was evaluated by terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) and Annexin V in situ staining. The TUNEL method was used to measure the apoptotic index. CNP and the cGMP derivative, 8-br-cGMP, induced apoptosis of cardiac myocytes. CNP-induced apoptosis could be blocked by HS 142-1 (a mixture of 20–30 kinds of linear β-1, 6-glucan esterified by capronic acid, an antagonist of type A and B natriuretic peptide receptors), and KT 5823 (C
29H
25N
3O
5, the inhibitor of cGMP-dependent protein kinase). α-Difluoromethylornithine (DFMO), the irreversible inhibitor of ornithine decarboxylase, also induced apoptosis to a similar extent. CNP and 8-br-cGMP caused a marked reduction of intracellular ornithine decarboxylase expression, as determined by Western blot analysis and immunohistochemical assay. Preincubation with endothelin-1 attenuated CNP- and 8-br-cGMP-induced cardiomyocyte apoptosis. Endothelin-1 also antagonized the CNP- and 8-br-cGMP-induced reduction of intracellular ornithine decarboxylase expression. These results suggest that CNP has a proapoptotic effect on neonatal rat cardiac myocytes. The effect is mediated via natriuretic peptide receptors and is due to an elevation of intracellular cGMP, which reduces the expression of intracellular ornithine decarboxylase and probably the production of polyamines. Endothelin-1 protects cardiac myocytes against CNP-induced apoptosis by influencing the cGMP-dependent pathway, and this effect is probably mediated through both a reduction of cGMP and antagonism of the CNP-induced reduction of intracellular ornithine decarboxylase expression.
PDF
