Hans Kröger

Modulation of inflammatory arthritis by inhibition of poly(ADP ribose) polymerase

Poly(ADPR) polymerase (PARP; EC 2.4.2.30) is a nuclear enzyme, which, when activated by oxygen- and nitrogen-radical-induced DNA strand breaks, transfers ADP ribose units to nuclear proteins and initiates apoptosis by depletion of cellular NAD and ATP pools. The present study investigates whether the oxidative stressdependent activation of PARP plays a role in the etiopathogenesis of arthritis. The antiarthritic reactivity of the biogenic PARP inhibitor nicotinamide was tested in DBA/1 × B10A(4R) mice suffering from potassium peroxochromate-induced arthritis. Daily doses of 4 mmol/kg of NA suppressed the arthritis by 35% and inhibited the phagocytic generation of reactive oxygen species, which increases sixfold during the development of arthritis. The onset, progression, and remission of arthritis correlated positively to the phorbolester-activated respiratory burst of neutrophils and monocytes, and a dose-dependent inhibition of NADPH oxidase activity was determined with human phagocytes. Our data support the hypothesis that oxidative stressinduced alterations in cellular signal transduction pathways play a pivotal role in the development of arthritis, which can be suppressed by the simultaneous inhibition of poly(ADPR) polymerase and NADPH oxidase.

Suppression of inflammatory arthritis by simultaneous inhibition of nitric oxide synthase and NADPH oxidase

TH1-type proinflammatory cytokines induce the expression of phagocytic nitric oxide synthase (NOS) and prime the membrane-bound NADPH oxidase of neutrophils and monocytes of mice so as to attain an activated state, which upon a second stimulus releases up to 6-fold increased levels of reactive oxygen species (ROS) than do unprimed phagocytes. Enhanced levels of ROS and NO deregulate inflammatory signal transduction pathways, which play a crucial role in the pathogenesis of arthritis. The antiarthritic reactivity of diphenylene iodoniumchloride (DPI), an irreversible inhibitor of NADPH oxidase and NOS, was tested in male DBA/1xB10A(4R) hybrid mice suffering from potassium peroxochromate-induced arthritis. Daily doses of 2.8 mu mol/kg of DPI sufficed to inhibit the arthritis by 50%. A complete inhibition was obtained with 10 mu mol/kg of DPI. The reduction of overt arthritic symptoms correlated well with both the reduced levels of ROS and NO in plasma of DPI-treated mice. Our data support the hypothesis that oxidative stress and nitric oxides play a pivotal role in the pathology of arthritis, which can be therapeutically targetted by NADPH oxidase- and NO synthase-inhibitors.

Synergistic effects of thalidomide and poly (ADP-ribose) polymerase inhibition on type II collagen-induced arthritis in mice.

The present study investigates synergistic effects of the TNF-α inhibitor thalidomide and the poly(ADP-ribose) polymerase (PARP)-inhibitor nicotinic acid amide (NAA) in male DBA/1 hybrid mice suffering from type II collagen-induced arthritis. Parameters including the arthritis index, chemiluminescence and anti-collagen antibody titers were used for the assessment of disease activity: The disease courses demonstrated clearly an inhibitory effect of thalidomide. NAA inhibited established collagen arthritis in a dose-dependent manner. The combined application of thalidomide and NAA caused a powerful synergistic inhibition of arthritis. Furthermore, thalidomide and NAA were tested ex vivo for their inhibition of the NADPH oxidase-dependent generation of reactive oxygen species by activated neutrophils and monocytes in unseparated human blood. Our data show that type II collagen-induced arthritis can be suppressed by the simultaneous inhibition of TNF-α, PARP, and NADPH oxidase.

Transcription of HIV1 is inhibited by DNA methylation

A possible role of DNA methylation as a factor in HIV latency was studied by methylating a HIV1-LTR-CAT plasmid in vitro and measuring its expression after transfection on Vero cells. Methylation with a eukaryotic DNA methylase resulted in a 70% inhibition of chloramphenicol acetyltransferase expression, in the absence as well as in the presence of the HIV1 trans-activator protein TAT in the cell. A similar degree of transcription inhibition was obtained by methylation of the only Hpa II site at position-143 in the HIV1-LTR with the bacterial Hpa II methylase. In contrast to the effect by eukaryotic methylation, the inhibition by Hpa II methylation could be partially reversed by cotransfection of the TAT gene. The reason may lie in an about 40% demethylation at the Hpa II site which was concomitantly observed.

Inhibition of the induction of collagenase by interleukin-1 β in cultured rabbit synovial fibroblasts after treatment with the poly(ADP-ribose)-polymerase inhibitor 3-aminobenzamide

Abstract3-Aminobenzamide is an inhibitor of poly-(ADP-ribosyl)ation. In concentrations from 3 to 10 mM it reduced the collagenase activity in culture supernatants of interleukin-1β-stimulated rabbit synovial fibroblasts. 3-Aminobenzoate, not an inhibiter of poly(ADP-ribosyl)ation, had no effect on collagenase activity at a concentration of 10 mM. We concluded that poly(ADP-ribosyl)ation plays a role in the induction of the expression of collagenase and that 3-aminobenzamide can inhibit this process.

Protection from acetaminophen-induced liver damage by the synergistic action of low doses of the poly(ADP-ribose) polymerase-inhibitor nicotinamide and the antioxidant N-acetylcysteine or the amino acid l-methionine

1. An array of therapeutically used analgetic and antirheumatic drugs cause severe liver damage. The present study investigates the hepatoprotective effects of inhibitors of NAD-dependent adenoribosylation reactions and of antioxidants in analgesic-induced hepatic injury. 2. Male NMRI mice were treated PO with 500 mg/kg of acetaminophen, and the activities of both glutamate-oxaloacetate transaminase (GOT) and glutamate-pyruvate transaminase (GPT) were determined in serum. 3. The acetaminophen-induced release of both GOT and GPT from injured liver cells could be inhibited in a dose-dependent manner, when mice were injected additionally either with increasing amounts (from (25 mg/kg to 100 mg/kg i.p.) of the PARP-inhibitor nicotinamide, with increasing amounts (from 25 mg/kg to 100 mg/kg i.p.) of the antioxidant N-acetylcysteine, or with increasing amounts (from 50 mg/kg to 300 mg/kg i.p.) of the amino acid L-methionine. 4. A combination of both nicotinamide and N-acetylcysteine (at the low dose of 12.5 mg/kg i.p. each) results in a complete protection from acetaminophen-induced release of GOT and GPT from injured liver cells. 5. A combination of both L-methionine and N-acetylcysteine or nicotinamide (at the low dose of 12.5 mg/kg IP each) resulted also in complete protection from acetaminophen-induced release of GOT and GPT.

DNA methylation inhibits transcription by RNA polymerase III of a tRNA gene, but not of a 5S rRNA gene

Methylation of cytosine in the DNA inhibits the transcription by RNA polymerase II in higher eukaryotes, but has no influence on RNA polymerase I transcription. The effect on RNA polymerase III was unknown, so far. Two polymerase III genes: a type 1 5S rRNA gene and a type 2 tRNA gene were methylated in vitro with a purified eukaryotic DNA methyltransferase (EC2.1.1.37) and their transcription was analyzed in Xenopus oocytes. The 5S rRNA gene, an oocyte 5S rRNA gene from X. laevis which is subject to developmental inactivation, was not affected by methylation. Conversely, transcription of the tRNA gene was 80% inhibited by methylation with the eukaryotic methyltransferase. HhaI and HpaII methylation left its transcription unaffected.

Nicotinamide methylation and its relation to NAD synthesis in rat liver tissue culture. Biochemical basis for the physiological activities of 1-methylnicotinamide.

The mode of [14C]nicotinamide conversion to NAD and 1-methylnicotinamide and the effects of exogenous 1-methylnicotinamide on this metabolic conversion were studied using rat liver slices incubated in a chemically defined culture medium. It was shown that at the physiological nicotinamide concentrations tested (11-500 microM), 1-methylnicotinamide is preferentially produced, rather than NAD. Upon increasing nicotinamide concentration to the levels that cause cytotoxicity (1-10 mM and higher), the rate of NAD synthesis dramatically increased and reached a level 6-fold higher than that of 1-methylnicotinamide. A dose-dependent inhibition (up to 60%) of NAD synthesis was seen by the exogenous addition of 1-methylnicotinamide; the degree of inhibition is affected also by the concentration of nicotinamide present as a precursor. A large depletion of intracellular ATP, associated with a marked accumulation of NAD, occurred in slices in response to the addition of high amounts of nicotinamide. However, the loss of ATP was overcome, when nicotinamide was given together with 1-methylnicotinamide. Finally, 1-methylnicotinamide per se was proven active in regulating cell growth by comparing the cytosolic activity of 1-methylnicotinamide oxidation of cultured RLC cells with that of rat liver. Thus, the previously observed growth stimulation of hepatic cells by 1-methylnicotinamide can reasonably been explained by its ATP-sparing effect due to the inhibition of NAD synthesis, a reaction which requires ATP.

Methylation of nicotinamide in rat liver cytosol and its correlation with hepatocellular proliferation

The changes in the activity of nicotinamide: S-adenosylmethionine methyltransferase (nicotinamide methylase) were studied in rat liver which was subjected to different rates of cellular proliferation. The cytosolic enzyme activity increased 3-4-fold in the first 24-48 h after partial hepatectomy and decreased again to the basal levels until 4 days post-operatively, whereas it remained unchanged in the livers of sham-operated animals. A single administration of thioacetamide at a dose of 50-250 mg/kg body weight, a treatment which induces hepatocellular proliferation as well, also enhanced the enzyme activity 2-3-fold 24 h after drug administration. This activity increase was associated with a marked lowering of intracellular NAD content of as much as 50% of the control levels. D-Galactosamine, a known hepatotoxic agent causing acute hepatitis in experimental animals and preventing DNA synthesis in regenerating liver, blocked the activity increase in regenerating rat liver. The rate of 1-methylnicotinamide synthesis, as measured by incubating liver slices in the culture medium supplemented with [14C]nicotinamide as a precursor, was found to be 2-4 times higher in the slices from regenerating liver and thioacetamide-treated rat liver than those from non-proliferating control liver. These results, together with our previous finding on the enhancement by 1-methylnicotinamide of the growth of cultured rat liver cells (Hoshino, J., Kühne, U. and Kröger, H. (1982) Biochem. Biophys. Res. Commun. 105, 1446-1452), support the view that nicotinamide methylase and its product, 1-methyl-nicotinamide, are involved in the control of hepatocellular DNA synthesis and proliferation.

Nicotinamide methylation. Tissue distribution, developmental and neoplastic changes.

The distribution of cytosolic activity of nicotinamide:S-adenosylmethionine methyltransferase (nicotinamide methylase, EC 2.1.1.1) in normal tissues from adult rat and mouse and in tumors and the change in the enzyme activity during the development of rat tissues were studied. (1) Rat liver exhibited the highest nicotinamide methylase activity among all adult tissues tested; other rat tissues, like adrenal, pancreas, kidney, brain and mouse tissues, had only less than 15% of the adult rat liver activity. (2) 3 days before birth, fetal liver showed a very low nicotinamide methylase activity (2% of adult rat liver), which, however, increased already 1 day before birth and reached the adult level on the day 28 after birth. (3) In a variety of hepatomas and ascites tumors, an inverse correlation, with some exceptions, between tumor growth rate and nicotinamide methylase activity could be seen. In all hepatomas, with the exception of Morris hepatoma 5123tc, nicotinamide methylase activity was significantly decreased in comparison to normal adult rat liver. The highly malignant Zajdela hepatoma, Yoshida sarcoma, sarcoma 180 and Ehrlich ascites tumor methylated nicotinamide only at a negligibly low rate. (4) Cultured RLC cells (an established rat liver cell line) from the stationary growth phase or G1-arrested RLC cells had about half of the adult rat liver activity, yet the activity was 70% higher than that of the logarithmically growing RLC cells.