Preliminary studies on the differential removal of products formed in the DNA of various rat organs after chronic administration of a low dose of zinc.

Metals can bind to various sites on the bases, the phosphate groups and/or sugars in DNA, depending on the physico-chemical characteristics of the metal ion. Up till now most studies concerned with the interaction of metal ions with DNA and polynucleotides have been carried out in vitro. In the present study, 23 ppm Zn2+ was administered chronically to rats in the drinking water for periods up to 1 week, after which the DNA was isolated from liver, kidney, ileum, colon and brain. The DNA was subsequently hydrolysed and the purine bases separated on Sephadex G-10. Three products of metalation were eluted. There were differences in the overall levels of metalation and in the capacity of the different organs to remove the major product of metalation from the DNA: after 7 days the Zn2+ content of this adduct in brain and kidney was 2 and 4 times respectively that of the controls, but in colon and ileum it had returned to control values, despite the continued administration of Zn2+.

Post-ischemic hypermetabolism in cat brain.

Delayed postischemic brain hypoperfusion and hypermetabolism are likely detrimental factors to neurologic recovery after transient global brain ischemia and may be mediated by catecholamines acting via adrenergic receptors. We evaluated the effects of alpha and beta receptor blockade on cerebral blood flow (CBF) and metabolism after 16 min transient global brain ischemia. Ischemia was induced by arterial hypotension and a high pressure neck tourniquet in 13 anesthetized cats. Six cats were untreated, 4 received propranolol 1 mg/kg, IV and 3 a combination of propranolol and phentolamine, one mg/kg injected one min before recirculation. Total CBF was measured by continuous monitoring of cerebral venous 133Xe clearance after bolus intra-arterial injection. Arterial and cerebral venous oxygen, glucose and lactate were measured. Cerebral cortex glucose and lactate were measured 3 hours post-ischemia after in situ freezing with liquid N2. The cerebral cortex of 3 cats anesthetized, but not subjected to ischemia, was similarly frozen and analyzed for glucose and lactate. Total CBF was relatively constant for up to 3 h post-ischemia in all groups, but significant changes in fast and slow-flow rates and compartment sizes were observed. In untreated cats, the normal 60/40 percent relative weight of the fast and slow-flow compartments was reversed to 30/70 percent by 1 hr post-ischemia. Propranolol attenuated the size of the fast-flow compartment in the first 30 min post-ischemia which was partially restored by phentolamine. Brain oxygen consumption increased 2 to 3-fold by 1 h post-ischemia in all groups. Propranolol compromised CBF and impaired glucose and lactate oxidation which was partly reversed by phentolamine. We concluded that within the first 30 min post-ischemia, beta, and to a lesser extent, alpha receptors predominate in the modulation of cerebrovascular tone. By 1 h post-ischemia, however, adrenergic modulation of cerebrovascular tone is lost. Delayed post-ischemic hypermetabolism unlike stress-induced, but like hypoxia-induced hypermetabolism is only partially affected by beta blockade. Propranolol apparently compromises brain oxygen consumption secondary to a reduction in brain O2 supply while phentolamine improves perfusion and oxygen consumption.

Mechanism of perinatal tumor induction by neuro-oncogenic alkylnitrosoureas and dialkylaryltriazenes.

The methylation by DMPT and MNU of DNA from rat liver and brain was investigated at various developmental stages. Following a single sc injection of [14C]DMPT (100 mg/kg body wt, 15 hr survival time) in pregnant rats (21st day of gestation), the extent of methylation of purine bases was similar in fetal liver and brain. During postnatal growth, this treatment resulted in an increasingly preferential methylation of liver DNA. In 30-day-old BD-IX rats, the concentration of 7-methylguanine in liver was approximately eight times higher than in brain DNA. This suggested that during prenatal development, both liver and brain DNA are transplacentally methylated by a proximate carcinogen produced by maternal organs. After a single ip injection of [3H]MNU (10 mg/kg body wt) to 10-day-old rats, O6-methylguanine was more rapidly removed from hepatic than from cerebral DNA. Within 1 week after the injection, the brain-to-liver ratio for 06-methylguanine increased from 1.4 to 98. These results are compatible with the hypothesis that the deficiency of various organs for repair excision of O6-alkylguanine from DNA correlates with their susceptibility to malignant transformation by monofunctional alkylating carcinogens.

1,2-Dimethylhydrazine-induced methylation of DNA bases in various rat organs and the effect of pretreatment with disulfiram.

The extent and persistence of methylated purines were determined in DNA of various rat organs following a single s.c. injection of 1,2-di[14C]methylhydrazine. Maximum alkylation of purine bases occurred within 12 hr, with highest concentrations in liver, followed by colon, ileum, and kidney. Over a period of 3 days, O6-methylguanine was removed much more slowly from colon, the principal target organ for carcinogenesis, than from ileum or liver DNA. Dietary pretreatment of rats with disulfiram is known to prevent 1,2-dimethylhydrazine-induced colon carcinogenesis and was found to reduce DNA alkylation to less than 1% of that detected in animals treated with 1,2- di[14C]methylhydrazine alone.

DNA repair as regulatory factor in the organotropy of alkylating carcinogens.

Monofunctional alkylating agents which react predominantly at nitrogen atoms in DNA bases (e.g. alkyl methanesulphonates, dialkylsulfates) are generally weak carcinogens whereas compounds which lead extensively to oxygen alkylation (e.g. alkylnitrosoureas, dialkylnitrosamines, dialkyl-aryltriazenes) often exhibit a strong carcinogenic activity. O6-Alkylation of guanine is a promutagenic DNA modification possibly involved in the initiation of malignant transformation. O6-Alkylguanine can be enzymically excised and in the rat the induction of neural, renal and colonic tumors by alkylnitrosoureas, 3,3-dimethyll-phenyltriazene, dimethylnitrosamine and 1,2-dimethylhydrazine correlates with an excision repair deficiency in the target tissue. However, species and strain differences in the response to these carcinogens are not paralleled by differences in the excision repair capacity for O6-alkylguanine. Preliminary data suggest that in rat liver there is an inducible enzyme for the removal of O6-alkylguanine from DNA.

DNA alkylation in mice with genetically different susceptibility to 1,2-dimethylhydrazine-induced colon carcinogenesis.

The formation and persistence of methylated purines was determined in mice that received a single s.c. injection of 1,2-[14C]dimethylhydrazine (15 mg/kg) and were allowed to survive for 12 or 60 hr. In mice with a low susceptibility to dimethylhydrazine-induced colon carcinogenesis (C57BL/Ha), concentrations of 7-methylguanine and O6-methylguanine in DNA of colon, ileum, and kidney were 40 to 60% less than in mice with a high incidence of colonic tumors (ICR/Ha). In hepatic DNA the extent of methylation was higher in C57BL/Ha than in ICR/Ha mice. The rate of loss of methylated purines from colon DNA was similar in both strains. In all organs investigated the metabolic incorporation of 14C into normal DNA bases was lower in C57BL/Ha than in ICR/Ha mice. It is concluded that the low carcinogenic response of C57BL/Ha mice is due to the smaller extent of initial alkylation of colon DNA, which probably reflects differences in the enzymic metabolism of the parent carcinogen.

DNA alkylation and neuro-oncogenesis by 3,3-dimethyl-1-phenyltriazene.

The role of DNA alkylation by the neurooncogenic agent 3,3-dimethyl-1-phenyltriazene (DMPT) was investigated perinatally and in adult rats. Following a single subcutaneous injection of 14C-DMPT (100 mg/kg) on the 21 day of gestation, the concentration of methylated purines was similar in both fetal liver and brain whereas during postnatal growth this treatment resulted in an increasingly preferential methylation of liver DNA. In 30-day-old and adult rats the concentration of 7-methylguanine in liver was about 8 times higher in brain DNA, suggesting that during prenatal development both liver and brain DNA are transplacentally methylated by a proximate carcinogen produced by maternal organs. Multiple doses of 14C-DMPT (50 mg/kg) to adult rats led to a preferential accumulation of O6-methylguanine in cerebral DNA. This supports the hypothesis that the deficient repair excision capacity of the hypothesis that the deficient repair excision capacity of the central nervous system is a significant factor in the organ-specific carcinogenicity of DMPT and related carcinogens.

Rehabilitation of the individual with oral-facial anomalies and communicative disorders.

The Lancaster Cleft Palate Clinic was organized for the purposes of establishing, equipping, maintaining, and operating an institution, hospital for special services, or clinic for the treatment of all defective formations of the mouth, teeth, palate, and face; for the establishment and operation of a school for the retraining of those with speech or hearing defects associated with or without oral defects; and for the conduct of research in, and publication of information relative to, the above fields.

Repair excision of alkylated bases from DNA in vivo.

Recent experiments are reviewed which indicate that O6-alkylation of guanine in nuclear DNA constitutes a promutagenic lesion possibly implicated in malignant transformation by monofunctional alkylating carcinogens. The differential capacity of various organs to enzymically excise O6-alkylguanine from their DNA seems to correlate with the organ specificity of the carcinogenic effect.

Heterogeneous distribution of DNA alkylation products in rat liver chromatin after in vivo administration of N,N-di[14C]methylnitrosamine.

Poly-l-lysine (PL) binds to about 50% of chromatin DNA, rendering it resistant to degradation by DNAase I. Separation of the unbound DNA as acid-soluble nucleotides allows the fractionation of chromatin DNA into two zones. After in vivo administration of N,N-di[14C]methylnitrosamine, the amount of alkylation in DNA was found to be lower in the polylysine-binding regions. Some possible reasons for this heterogeneous distribution are discussed.

Studies on liver chromatin from rats treated with dimethylnitrosamine.

Shortly after injecting a single low dose of N,N-dimethylnitrosamine into rats, the DNA, RNA and histones are methylated, the level in the DNA greatly exceeding that in the histones. The composition of the chromatin and the electrophoretic profiles of the histone and non-histone proteins are not detectably different from those obtained from control animals. Electric birefringence studies suggest that methylation may result in both interparticle cross-linking and some localised loosening of the DNA-protein complex complex.

Genetic studies of cleft lip and palate in dogs.

In a colony of Shih-Tzu dogs, familial cleft palate frequently associated with hind leg deformity was demonstrated. Colonies of dogs centered around purebred wirehaired terrier females or a mongrel collie male, both with isolated cleft palate did not result in cleft offspring with one exception. Reproductive fitness of a low order was encountered as expected. Difficulty was experienced in raising affected animals. Multiple associated congenital anomalies were found. These include convulsive disorders, clubfoot and dysgenesis of musculature of the thigh.