Baby bottles and family rattles. Children and substance abuse

Research shows that problem behaviors manifested early tend to persist into later life. Problem drinking does not necessarily commit the young adolescent to a life course of this behavior, but it does alter the probabilities. Conversely, early abstinence is a strong predictor of later healthful behavior. An important observation is that alcohol and other drug use tends to decrease along with smoking decreases. Young adolescents tend to believe that most of their peers engage in a particular type of behavior whether that is the actual case or not. There is a tendency across populations of adolescents to overestimate such behaviors by a factor of six or eight. In one study, school children estimated that about two-thirds of their peers smoked while the actual figure was about one-tenth. Adolescents tend to have weak orientation to the future, especially in regard to consequences of risk-taking behavior. College-bound adolescents tend to have a longer view of the future than those who do not pursue college, but in general adolescents think, "It can't happen to me," or, "It's so far off that I just can't think about it." They are focused on the here and now. Many youngsters when they think about it have a dismal view of the future. They are doubtful about their own ability to influence events in ways that build toward a rewarding life.(ABSTRACT TRUNCATED AT 250 WORDS)

Kinetic studies of the hydrolysis of platinum-DNA complexes by nuclease S1

The antitumor agent cis-diamminedichloroplatinum(II) (cis-DDP) reacts covalently with DNA and disrupts its secondary structure. Damaged DNA, but not native DNA, is readily digested by S1 nuclease, an endonuclease specific for single stranded polynucleotides. We have measured S1 nuclease digestion of platinated DNA by the release of platinum-DNA adducts and compared it with digestion of unplatinated DNA. The rate of hydrolysis of damaged substrate from platinum-DNA complexes was less than the overall rate of digestion of nucleotides. Similar results were observed for platinum-DNA complexes in native, denatured or renatured conformations. The hydrolysis of denatured platinum-DNA complexes, rb = 0.075 platinum per nucleotide, obeyed Michaelis-Menten kinetics. Taking into account the level of DNA damage, Vm, for the release of platinated adducts was 0.6 times smaller than for digestion of unplatinated DNA. Km values and competition experiments indicated that the enzyme bound equally well to platinated and unplatinated substrates. Similar results were obtained for denatured DNA complexes with trans-DDP while [PtCl(diethylenetriamine)]Cl had no influence on nuclease digestion. These results suggest that bifunctional platinum-DNA lesions have contradictory effects on the hydrolysis of double stranded DNA by S1 nuclease. On one hand they create nuclease sensitive substrate by disrupting DNA secondary structure. On the other, they inhibit digestion of the damaged strand by increasing the activation energy for hydrolysis.

Detection of DNA strand breaks in Escherichia coli treated with platinum(IV) antitumor compounds

DNA strand breaks were observed in bacteria treated with Pt(IV) but not Pt(II) antitumor compounds by two methods. First, compounds which cause DNA strand breaks produced an SOS induction signal which was detected by a rapid bacterial assay. In addition, the capacity of these compounds to cut DNA in vivo was directly measured by agarose gel electrophoresis of pBR322 DNA extracted from bacteria treated with these drugs. cis-Diamminetetrachloroplatinum(IV) (cis-DTP) and cis-dichloro-trans-dihydroxo-cis-bis(isopropylamine)-platinum(IV) (iproplatin) produced strand breaks in both assays while cis-diamminedichloroplatinum(II) (cisplatin) did not. These results indicate that Pt(IV) antitumor complexes may cause DNA damage in vivo which is not produced by Pt(II) compounds.

Conversion of monofunctional DNA adducts of cis-diamminedichloroplatinum (II) to bifunctional lesions. Effect on the in vitro replication of single-stranded DNA by Escherichia coli DNA polymerase I and eukaryotic DNA polymerases alpha

Reaction of cis-diamminedichloroplatinum (II) with single-stranded M13 phage DNA in vitro produced monofunctional platinum-DNA adducts on guanine and bifunctional lesions with either two guanine bases (GG) or one adenine and one guanine (AG). When DNA containing a majority of monofunctional platinum-DNA lesions was dialyzed against 10 mM NaCIO4 at 37 degrees C, conversion of monoadducts to bifunctional lesions was observed. We examined the effect of post-treatment formation of bifunctional lesions on DNA synthesis by Escherichia coli DNA polymerase I and highly purified eukaryotic DNA polymerase alpha from Drosophila melanogaster and calf thymus. Arrest sites on the platinated template were determined by polyacrylamide gel electrophoresis. Monofunctional lesions did not appear to block DNA synthesis. Inhibition of replication increased as bifunctional platinum-DNA lesions formed during post-treatment incubation; GG adducts inhibited replication more than AG. These results suggest that bifunctional GG platinum-DNA adducts may be the major toxic damage of cisplatin.

Enhanced mutagenesis during post-treatment incubation of Escherichia coli treated with cis-diamminedichloroplatinum(II)

Wild-type Escherichia coli were treated with cis-dichlorodiammineplatinum(II) (DDP) and then kept in a non-dividing state for 4 h. This post-treatment incubation did not increase survival, excision of platinum-DNA lesions was not observed, and post-treatment exposure to thiourea had no effect on the toxicity of DDP. In contrast, the mutation frequency increased by a factor of 3 and reached a plateau after 3 h incubation at 37 degrees C. The quantity of DDP on the bacterial DNA remained constant during this time. Post-treatment exposure to thiourea (which is reported to react with monofunctional platinum-DNA adducts) inhibited but did not reverse the increased mutagenicity. These results may reflect the evolution of monofunctional platinum-DNA lesions into bifunctional mutagenic adducts during post-treatment incubation of bacteria which have been exposed to DDP.

Investigation of the physiological basis of summating potential changes in endolymphatic hydrops

An increase in the ratio of the summating potential to the action potential components of the electrocochleogram is known to be a feature of endolymphatic hydrops. We investigated the value of the SP/AP ratio in response to condensation and rarefaction click stimuli delivered separately. In patients with electrophysiological evidence of endolymphatic hydrops there was found to be a significantly greater SP/AP ratio to condensation clicks than rarefaction clicks. This finding supports the hypothesis that the increased SP/AP ratio in hydrops is due to mechanical asymmetry of the basilar membrane.

Toxicity, mutagenicity, intracellular drug concentration and DNA binding in Escherichia coli treated with cis-platinum(II) complexes

The genotoxic effects of six cis-platinum(II)chloramine complexes with different alkyl substituents on their amine ligands have been measured using Escherichia coli. The toxicity and mutagenicity of these compounds were compared, after exposure of bacteria, to drug concentrations which gave known quantities of platinum-DNA lesions. The results permit several observations concerning structure-activity relations of platinum(II) complexes. Firstly, methyl substitution on the amine ligands of cis-diamminedichloro-platinum(II) (DDP) is reported to reduce its antitumor activity. The methyl group did not exert an effect in bacteria where the toxicity and mutagenicity of cis-bis(methylamine)dichloroplatinum(II) and DDP were equivalent. In fact, at equal levels of DNA binding, complexes with substituted amines were generally more toxic toward bacteria than DDP. Secondly, replacement of the chloro groups of DDP by nitrato ligands increased its toxicity and mutagenicity at a given level of DNA binding. Hence, although DDP and its dinitrato derivative have identical ammine ligands, they may form different platinum-DNA lesions in bacteria. Finally, cis-bis(cyclohexylamine)-dichloroplatinum(II) was unique among the compounds studied since it did not cause bacterial filamentation or mutagenesis. These results suggest that, although this compound binds to the bacterial genome, it may not induce the SOS response.

Further characterization of an E. coli strain resistant to the toxic and mutagenic action of cis-diamminedichloroplatinum(II)

An increased resistance to the toxic and mutagenic activity of the antitumor drug cis-diamminedichloroplatinum(II) (cis-DDP) in the E. coli strain BS21 compared to its wild-type parent, F26, has been reported. This resistance was neither due to different binding of cis-DDP to DNA nor to adaptive DNA repair (Germanier et al., 1984). In the present work, we found that mutation of the uvrA, recA and polA genes did not abolish the resistance of BS21 to the toxic action of cis-DDP. The lower mutability of BS21 was not influenced by the polA mutation, while uvrA greatly reduced and recA eliminated the mutagenic activity of cis-DDP in both strains. Treatment of BS21 and F26 with equal doses of cis-DDP produced the same initial number of platinum-DNA lesions. Little excision repair was detected in vivo in either strain during 6-h post-treatment incubation, the F26 strain being the most efficient of the two for this process. In contrast, F26 and BS21 were transformed identically by pBR322 DNA which had been treated with cis-DDP in vitro. Analysis of the platinum-DNA adducts which were formed between cis-DDP and salmon sperm DNA in the buffer conditions of this experiment suggests that plasmid DNA contains 80% monofunctional adducts and 20% bifunctional bis-guanine adducts. These data indicate that the selective toxicity and mutagenicity of these two strains in vivo are neither a result of different numbers of Pt-DNA lesions nor of their repair. The selectivity disappeared when the two bacterial strains were transformed by pBR322 DNA containing identical platinum-DNA lesions, suggesting that the biochemical events which process platinum-DNA lesions are the same in both strains. Hence, it appears that cis-DDP may form qualitatively different platinum-DNA adducts in the BS21 and F26 strains which are responsible for the different toxicity and mutagenicity.

Toxicity, mutagenicity and induction of recA protein in Escherichia coli treated with cis-diamminedichloroplatinum(II) and cis-diamminetetrachloroplatinum(IV)

After exposure of bacteria to equal concentrations of cis-diamminedichloroplatinum(II) (DDP) and cis-diamminetetrachloroplatinum(IV) (DTP), the intracellular concentration of DTP was an order of magnitude greater than DDP. However, at identical intracellular drug concentrations, the Pt(IV) compound formed only half as many platinum-DNA lesions. For equal numbers of DNA lesions, the toxicity of both agents was identical whereas the mutagenicity of DTP was 7 times less than for DDP and its capacity to induce recA protein was less than DDP by a factor of 3.5. Bioreduction of Pt(IV) compounds to their corresponding Pt(II) analogues has been proposed as a mechanism for the reaction of Pt(IV) compounds with cellular DNA. According to this hypothesis, DTP would be reduced to DDP in the cell prior to its reaction with DNA and the platinum-DNA lesions of the two compounds should be identical. Our results suggest that reductive elimination can not entirely account for DNA damage caused by PT(IV) compounds in bacteria.

Chemical reactivity of monofunctional platinum-DNA adducts

Complexes formed in vitro between cis- or trans-PtCl2(NH3)2 (DDP) and DNA were found to contain monofunctional adducts that reacted with exogenous guanosine. [14C]Guo bound irreversibly to cis- and trans-DDP-DNA complexes to form bis-Gua adducts. The reaction was first order with respect to the concentration of both [14C]Guo and platinum-DNA complex, but the rate of the reaction varied nonlinearly as a function of the level of platinum binding on DNA. The reaction between [14C]Guo and these platinum-DNA complexes was used to probe the concentration and stability of the monofunctional adducts and to investigate their chemistry in situ. The concentration of monofunctional adducts was highest immediately after reaction of DDP with DNA for 2 h at 37 degrees C, at which time they represented greater than 15% of the cis-DDP-DNA lesions and on the order of 80% of the trans-DDP-DNA lesions. The cis-DDP-DNA complex reacted with [14C]Guo by two kinetically distinct processes, indicating two types of reactive adducts. The most reactive adduct represented 5% of the platinum lesions. These monofunctional adducts disappeared during the incubation of the platinum-DNA complexes in the absence of drug, probably as a result of chelation to DNA. The half-lives of this chelation at 37 degrees C, 10 mM NaClO4, were 15 and 30 h for the cis and trans complexes, respectively. Monofunctional adducts were formed on Gua bases in DNA.(ABSTRACT TRUNCATED AT 250 WORDS)

Repair of platinum-DNA lesions in E. coli by a pathway which does not recognize DNA damage caused by MNNG or UV light

The adaptive response is an inducible DNA-repair system which diminishes the mutagenic and toxic effects of alkylating agents. A mutant of E. coli constitutive for adaptative repair, BS21, has been isolated. A spontaneous revertant of this strain, BS23, lacks the adaptive response. When compared to its wild-type parent, mutant BS21 showed an increased resistance to the killing and mutagenic effects of a compound which is not a classical alkylating agent, the antitumor drug cis-diamminedichloroplatinum(II) (cis-DDP). However, this resistance to cis-DDP was also found in strain BS23 which lacks the adaptive response. cis-DDP bound to the DNA of all 3 strains with the same efficiency. In addition, we have investigated the effect of UV radiation and we failed to observe a significant difference in the survival and mutagenesis of these strains. This evidence suggests that the resistance of BS21 and BS23 strains to cis-DDP is not a consequence of the adaptive response or increased excision repair.

Single turnovers of the EcoRI restriction endonuclease

Single turnovers of the EcoRI restriction endonuclease, cleaving its recognition site on the covalently closed form of plasmid pMB9, were examined. Two methods were used to monitor the progress of the reactions: one involved quenching the reaction at various times followed by the electrophoretic separation of the products cleaved in one and in both strands of the duplex; the other employed a stopped-flow fluorimeter to measure the amount of ethidium bromide bound to the DNA as it changes when the DNA, cleaved in at least one strand, dissociates from the enzyme. Two procedures were used to initiate the reactions. For some, one solution containing the enzyme was mixed with a second containing both DNA and MgCl2: in these reactions, the fluorescence changed at the same rate as the cleavage of the first strand of the duplex. Other reactions were started by the addition of MgCl2 to a pre-equilibrium of enzyme and DNA: here, both strands of the DNA were cleaved faster than before, with the fluorescence signal now occurring at the same time as the cleavage of the second strand. The different kinetics from the two assays and the two mixing procedures are consistent with the rates of these reactions being controlled by protein conformational changes. These may affect either one subunit alone within the dimeric EcoRI enzyme, allowing the enzyme to cleave only one strand of the DNA in each turnover. Alternatively, both subunits of the dimer may change, so that the enzyme then cleaves both strands during the life-time of one enzyme-DNA complex.

Structures of the adducts formed between [Pt(dien)Cl]Cl and DNA in vitro

The products of the reaction between [Pt(dien)Cl]Cl and salmon sperm DNA have been purified and their structures determined. [Pt(dien)Cl]Cl binds at the N7 position of guanine for levels of fixation below 0.1 platinum per DNA base. Above this level of binding, [Pt(dien)Cl]Cl also reacts at the N7 position of adenine. 1,7-[Pt(dien)]2Ade was observed when more than 0.3 platinum per base were bound to the DNA. Platination at the N7 position of guanosine, unlike alkylation, stabilized the glycosyl linkage and did not lead to fission of the imidazole ring at high pH.