ESTIMATION OF PROFILE OF DRUGS ACID, ATENOLOL, USING GRADUALLY
THE L-HISTIDINE-MEDIATED ENHANCEMENT OF H Y D R O G E N P E R O X I D E - I N D U C E D DNA DOUBLE STRAND B R E A K A G E AND CYTOTOXlClTY DOES NOT INVOLVE METABOLIC P R O C E S S E S P. Sestili, F. Cattabeni, and O. Cantoni Istituto di Farmacologia e Farmacognosia and Centro di Farmacologia Oncologica Sperimentale, Universit& di Urbino, Urbino, Italy.
V. S t ~ t i n o v ~ V. G r o s s m a n n , J, K v ~ t i n a Istitute of Experimental Biopharmaceutics, Join% Laboratories of t h e C z e c h A c a d e m y of Sciences and PRO.MED.CS, Hradec Kr~lov~ x Czech Republic
The cytotoxic response of Chinese Hamster Ovary (CHO) cells to challenge with hydrogen peroxide is highly dependent upon the temperature of exposure, being markedly higher at 37 ° compared to 4°C. Increasing the intracellular levels of L-Histidine prior to challenge with hydrogen peroxide increases the toxicity elicited by the oxidant at both physiologic and ice-bath temperature. The effect of the amino acid, however, was more pronounced under conditions of treatment at 4°C, as compared to 37°C. Indeed, at 4°C the oxidant is non toxic at submillimolar levels and pre-exposure to L-Histidine restored cytotoxicity to levels slightly lower than those observed after treatment at 37°C (in the micromolar range). Pre-exposure to the amino acid increased the production of DNA double strand breaks (DSBs) elicited by treatment with the oxidant both at 37 ° and 4°C. A remarkable correlation was found by plotting the level of this lesion against the cytotoxic response observed under a variety of experimental conditions, which suggests the existence of a cause-effect relationship. The overlapping correlation curves obtained with cells challenged with the oxidant at 4 ° or 37° C, also suggest that similar molecular mechanisms mediate the formation of DNA DSBs under both experimental conditions. Two lines of evidence support this inference: 1) the kinetics of repair of DNA DSB generated at 37 ° or 4°C were virtually superimposable; this would suggest that the same repair pathway is responsible for the removal of DNA DSBs generated at the two temperatures; 2) the size distribution of double stranded DNA fragments produced under the two treatment conditions was basically identical; this is indicative of remarkable similarities in the topology of chromosomal domains where DSBs are generated. Overall, these results lend further support to the notion that DNA DSBs are responsible for the L-Histidine-mediated enhancement of hydrogen peroxide-induced cytotoxicity, and demonstrate that the mechanism whereby the amino acid enhances the ability of hydrogen peroxide to produce DNA double strand breakage and cell killing is independent of cellular metabolism and/or energy-dependent reactions.
DRUGS A F F E C T I N G LIPID ~METABOLISM: EFFECTS A T H E R O S C L E R O S I S PROGRESSION AND CLINICAL E V E N T S
ON
A.M. Gotto Jr. Baylor College of Medicine, 6550 Fannin, Suite 1425, Houston, Texas, 77030, U.S.A.
For a p r i m a r y e s t i m a t i o n of the k i n e t i c p r o f i l e of d r u g s f r o m the v i e w p o i n t of t h e i r potential cumulative or habit-forming effect, the test of subchronic toxicity according to L i m (I) was e m p l o y e d . It is based on " repeated administration of increasing doses of the drug under study e v e r y 4 % h day till the 2 4 t h day. C a l c u l a t i o n of %he s o - c a l l e d subchronic median lethal d o s e (CLDs0) was c a r r i e d out by the g r a p h i c probit m e t h o d (2). Evaluation consists in d e t e r m i n g the r a t i o C L D s 0 / L D s 0 . If the n a % i o >i, tolerance develops (sensitivity is decreased), if the ratio
THE ROLE OF NITRIC OXIDE IN ATHEROSCLEROSIS S. Moncada. The Wellcome Research Laboratories, Langley Court, Beckenham, Kent BR3 3BS, U.K. The synthesis of nitric oxide (NO) from L-arginine by a constitutive enzyme, the NO synthase, in the vascular endothelium is a vasodilator mechanism that plays a role in the physiological regulation of blood flow and pressure. In patients with atherosclerosis, endothelium-dependent dilatation is impaired in arteries and arterioles; this defect i s reversed by L.-arginine. Experiments in animals and studies in humans also indicate impaired NO-mediated functions in diabetes, hyperlipidaemia and hypertension, three major risk factors for atherosclerosis. Nitric oxide is a potent inhibitor of platelet aggregation and adhesion, decreases white cell activation and reduces vascular smooth muscle cell proliferation. Thus insufficient production of NO could contribute to atherogenesis by altering the interactions between circulating platelets and white cells and the vessel wall, or by affecting vascular smooth muscle cell growth or proliferation. NO synthase inducible by immunological stimuli such as endotoxin lipopolysaccharides and cytokines is also expressed in human atherosclerotic aorta. Overproduction of NO by this enzyme could, either alone or in combination with other radicals, lead to local tissue damage.
Recent clinical trials of lipid-regulating therapy, including drug treatment, have demonstrated reductions in all-cause mortality. The Scandinavian Simvastatin Survival Study (4S), a secondaryprevention trial in 4,444 patients, utilized the 3hyd~oxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitor simvastatin and achieved a 30% reduction in all-cause mortality over 5.4 years of intervention (Scandinavian Simvastatin Survival Study Group, Lancet 1994;344:1383). Reduced allcause mortality has also been' reported in a prospectively planned meta-analysis of four clinical trials utilizing the HMG-CoA reductase inhibitor pravastatin (B~istol-Myers Squibb, unpublished data). Trials investigating the effects of lipidregulating therapy on the progression of atherosclerosis in the coronary and other vascular beds have provided insights on the mechanisms of this clinical benefit. Because of the small scale of anatomic improvement and the relatively large and rapid clinical benefit observed in some of these trials, it appears likely that mechanisms in addition to enlargement of the arterial lumen contribute to the clinical benefit of lipidregulating therapy. These additional m e c h a n i s m s a r e likely related to the stabilization of rupture-prone plaque.
--
SUBCHRONIC TOXICOLOGICAL SULPIRIDE, 5-AMINOSALICYLIC NITRENDIPINE, AFLATOXINBI INCREASE DOSAGE
1 5 0 -