Poly synthetase inhibitors

Tabuchi K, Ito Z, Tsuji S et al. Poly(adenosine diphosphate-ribose) synthetase inhibitor 3-aminobenzamide alleviates cochlear dysfunction induced by transient ischemia. Ann Otol Rhinol Laryngol 2001 110(2) 118-21. 

Yama ami T, Miwa A, Takasawa S et al. Induction of rat pancreatic B-cell tumors by the combined administration of streptozotocin or alloxan and poly(adenosine diphosphate ribose) synthetase inhibitors. Cancer Res 1985 45(4) 1845-1849. 

On the other hand, Althaus (3) found that when hepatocytes were UV irradiated immediately after isolation and then maintained in the presence of poly(ADP-ribose) synthetase inhibitors, unscheduled DNA synthesis was increased above the level that occurred after UV exposure in the absence of inhibitors, sc gesting that the S3mthetase was not involved in the repair of DNA damage. 

Poly(ADP-ribose) synthetase inhibitors, and in particular 3-aminobenzamide, have been used extensively in recent years as probes to elucidate the function of poly(ADP-ribose) in the cell. Our initial report [1] on substituted benzamides as physiologically specific inhibitors was based on the observation that cells grew at an unchanged rate in the presence of 2 mM 3-aminobenzamide, a concentration 1,000 times the Kj value. In general, high concentrations are needed to elicit a cellular response compared to assays in vitro. Interpretation of results is complicated by the possibihty of affecting a target other than poly(ADP-ribose) synthetase. Recently, processes other than ADP-ribosylation have been reported to be altered by benzamides. A major criticism of most work is that the studies entail the use of only one inhibitor, usually 3-aminobenzamide. 

It is of interest to note that such high levels of poly(ADP-ribose) synthetase inhibitors are required to exhibit cytotoxicity. One possible explanation is that in normal cycling cells, the poly(ADP-ribose) mediated step can take place over an extended period of time. For enhancement of cytotoxicity of alkylating agents which generally take place at lower inhibitor concentrations, the timing presumably is more critical. 

Uchigata Y, Yamamoto H, Kawamura A, Okamoto H (1982) Protection by superoxide dis-mutase, catalase, and poly(ADP-ribose) synthetase inhibitors against alloxan and strepto-uotocin-induced islet DNA strand breaks and against the inhibition of proinsulin synthesis. J Biol Chem 257 6084-6088... 

Our finding of potentiation by SAAB of BCNU cytotoxicity contrasts with other recent reports. Berger et al. [7] failed to detect any S-aminobenzamide (SAB)-medi-ated potentiation of BCNU toxicity to LI 210 mouse leukemic cells, and likewise Boorstein and Pardee [8] detected no enhancement by the same inhibitor of BCNU toxicity to human fibroblasts. This may reflect differences in the cell systems. Alternatively, since SAAB is some 6-8 times more effective as a poly(ADP-ribose) synthetase inhibitor than is SAB [9], it could be that the concentrations of SAB used by Berger et al. [7] and Boorstein and Pardee [8], 10 mM and 4 mM respectively, were not sufficiently high. 

Poly(ADP-Ribose) Synthetase Inhibitor Effects on Cellular Functions... 

A plot of 1/V vs I/Kj will be linear in a cell if the substrate concentration is unchanged by the inhibitors. The plot vill be colinear for a family of inhibitors if they all act on the same enzyme in a cell and if the inhibitors all have equal access to the enzyme. If one makes the assumption that poly(ADP-ribose) synthesis is rate limiting for the repair of DNA chain breaks, then the Kj for a particular synthetase inhibitor will be directly proportional to its for blocking repair. In this case, a plot of the reciprocal of the repair rate vs inhibitor concentration normalized against its Kj for synthetase would be linear and similar plots for a variety of compounds that block repair via blocking synthetase would be colinear. 

Poly(ADP-Ribose) Synthetase Inhibitors Induce Islet B-Cell Regeneration in Partially Depancreatized Rats... 

Fig. 1. Administration of poly(ADP-ribose) synthetase inhibitors to 90% depancreatized rats...

As shown in Fig. 2, the control rats exhibited glucosuria 1 to 3 months after the 90% pancreatectomy. However, in rats receiving 0.5 g kg nicotinamide or 0.05 g kg" 3-aminobenzamide daily, the urinary glucose excretion level decreased markedly. Plasma glucose levels, before and after an intravenous glucose load, in the rats receiving the poly(ADP-ribose) synthetase inhibitors were also significantly decreased in... 

Fig. 2. Urinary glucose excretion in partially depancreatized rats with or without poly(ADP-ribose) synthetase inhibitor injection. 1, 2, and 3 months after the 90% pancreatectomy, the urine of each rat was collected for 24 h. Urinary glucose levels were measured by the glucose oxidase method. O Control rats nicotinamide-injected rats 3-aminobenzamide-injected rats. Statistical significance of differences between rats treated with and without poly(ADP-ribose) synthetase inhibitors was analyzed using Student s t test. Each point is the mean for five different rats vertical bars show SD when larger than the symbol indicating the mean value., and = p<0.10, p<0.05, and p<0.025 vs control rats. The time after the partial pancreatectomy is shown on the abscissa...

We have already shown that alloxan and streptozotocin induce islet DNA strand breaks and that poly(ADP-ribose) synthetase acts to repair the DNA breaks, consuming islet NAD [4-7]. This rapid and marked depletion of islet NAD has been regarded as the primary molecular mechanism behind the B-cell necrosis. The B-cells seem to be making a suicide response to repair the damaged DNA. Therefore, poly(ADP-ribose) synthetase inhibitors can prophylactically prevent alloxan and streptozotocin diabetes by blocking the NAD consumption (Fig. 4). 

Evidence in the present paper suggests an alternative function of poly(ADP-ribose) synthetase inhibitors in the improvement of surgical diabetes. In this case, poly(ADP-ribose) synthetase inhibitors may relieve restriction of DNA replication and so cause B-cell regeneration (Fig. 4). Since a low capacity for B-cell regeneration has been suggested as a predisposition for the development of human diabetes [17], the present study may provide a novel clue for the prevention and treatment of human diabetes. 

Uchigata Y, Yamamoto H, Nagai H, Okamoto H (1983) Effect of poly(ADP-ribose) synthetase inhibitor administration to rats before and after injection of alloxan and streptozotocin on islet proinsulin synthesis. Diabetes 32 316-318... 

Yonemura Y, Takashima T, Miwa K, Miyazaki I, Yamamoto H, Okamoto H (1984) Amelioration of diabetes mellitus in partially depancreatized rats by poly(ADP-ribose) synthetase inhibitors. Diabetes 33 401-404... 

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