Modulation of O6-methylguanine-DNA methyltransferase-mediated nimustine resistance in recurrent malignant gliomas by streptozotocin--a preliminary report

This trial is based on the strategy of reversing O6-methylguanine-DNA methyltransferase (MGMT)-mediated nimustine resistance by depleting MGMT activity with streptozotocin (STZ) pretreatment. Eight patients with recurrent malignant gliomas refractory to previous nimustine chemotherapy were entered in this study. Patients received STZ (2g/m2) followed one hour with nimustine (2-3 mg/Kg) via the ipsilateral carotid artery. After 1-2 cycles of therapy, 3 patients responded, 4 stabilized, and 1 failed. Toxic effects were generally tolerated. The preliminary results indicated that nimustine-resistant tumor cells in vivo could also be sensitized by modulation of MGMT activity.

Interaction of a peptide model of a hydrophobic transmembrane alpha-helical segment of a membrane protein with phosphatidylethanolamine bilayers: differential scanning calorimetric and Fourier transform infrared spectroscopic studies

High-sensitivity differential scanning calorimetry (DSC) and Fourier transform infrared (FTIR) spectroscopy were used to study the interaction of a synthetic alpha-helical hydrophobic transmembrane peptide, Acetyl-Lys2-Gly-Leu24-Lys2-Ala-Amide, and members of a homologous series of n-saturated diacylphosphatidylethanolamines (PEs). In the lower range of peptide mol fractions, the DSC endotherms exhibited by the lipid/peptide mixtures consist of two components. The temperature and cooperativity of the sharper, higher-temperature component are very similar to those of pure PE bilayers and are almost unaffected by variations in the peptide/lipid ratio. However, the fractional contribution of this component to the total enthalpy change decreases with increases in peptide concentration, and this component completely disappears at higher peptide mol fractions. The other component, which is less cooperative and occurs at a lower temperature, predominates at higher peptide concentrations. These two components of the DSC endotherm can be attributed to the chain-melting phase transitions of peptide-nonassociated and peptide-associated PE molecules, respectively. Although the temperature at which the peptide-associated PE molecules melt is progressively decreased by increases in peptide concentration, the magnitude of this shift is independent of the length of the PE hydrocarbon chain. In addition, the width of the phase transition observed at higher peptide concentrations is also relatively insensitive to PE hydrocarbon chain length, except that peptide gel-phase immiscibility occurs in very short- or very long-chain PE bilayers. Moreover, the enthalpy of the chain-melting transition of the peptide-associated PE does not decrease to 0 even at high peptide concentrations, suggesting that this peptide does not abolish the cooperative gel/liquid-crystalline phase transition of the lipids with which it is in contact. The FTIR spectroscopic data indicate that the peptide remains in a predominantly alpha-helical conformation, but that the peptide alpha-helix is subject to small distortions coincident with the changes in hydrophobic thickness that accompany the chain-melting phase transition of the PE bilayer. These data also indicate that the peptide significantly disorders the hydrocarbon chains of adjacent PE molecules in both the gel and liquid-crystalline states relatively independently of lipid hydrocarbon chain length. The relative independence of many aspects of PE-peptide interactions on the hydrophobic thickness of the host bilayer observed in the present study is in marked contrast to the results of our previous study of peptide-phosphatidylcholine (PC) model membranes (Zhang et al. (1992) Biochemistry 31:11579-11588), where strong hydrocarbon chain length-dependent effects were observed. The differing effects of peptide incorporation on PE and PC bilayers is ascribed to the much stronger lipid polar headgroup interactions in the former system. We postulate that the primary effect of transmembrane peptide incorporation into PE bilayers is the disruption of the relatively strong electrostatic and hydrogen-bonding interactions at the bilayer surface, and that this effect is sufficiently large to mask the effect of hydrophobic mismatch between the lengths of the hydrophobic core of the peptide and its host bilayer.

Peptide models of helical hydrophobic transmembrane segments of membrane proteins. 1. Studies of the conformation, intrabilayer orientation, and amide hydrogen exchangeability of Ac-K2-(LA)12-K2-amide

The secondary structure, amide hydrogen exchangeability, and intramembrane orientation of the hydrophobic peptide Ac-K2-(LA)12-K2-amide [(LA)12] were studied by a combination of circular dichroism (CD), Fourier transform infrared (FTIR), and proton nuclear magnetic resonance (1H NMR) spectroscopic techniques. All three techniques indicate that (LA)12 adopts predominantly helical conformations in various organic solvents, detergent micelles, and phospholipid bilayers. Also, attenuated total reflectance FTIR studies of oriented phospholipid bilayers demonstrate that (LA)12 is arranged with the long helical axis perpendicular to the bilayer plane. FTIR and 1H NMR studies of the exchangeability of the amide protons of (LA)12 indicate that in all media there are at least two populations of amide protons which exchange with the bulk solvent at markedly different rates. Moreover, the 1H NMR spectroscopic studies indicate that, in organic solvents and micellar dispersions, amide proton exchange rates decrease progressively from the N- or C-terminus of the peptide toward the central region. Our results are thus consistent with (LA)12 retaining a predominantly helical structure with so-called frayed ends in all media. The amide proton exchange studies also indicate that when (LA)12 is dispersed in lipid bilayers, the slowly exchanging population of amide protons is larger than that observed in organic solvents or in micellar dispersions and that most of that proton population is virtually unexchangeable. Such observations are consistent with the sequestration of the central regions of the peptide in the hydrophobic domains of the lipid bilayer. The CD and FTIR data indicate that although (LA)12 seems to retain conformations with a high alpha-helical content in all media examined, its conformation is sensitive to the composition of the surrounding medium, in contrast to the polyleucine-based analogues which have been studied previously. In particular, the FTIR spectroscopic data indicate that (LA)12 may exhibit an amide I absorption band between 1633 and 1639 cm-1 under some circumstances. The relative intensity of this band changes with the composition of the surrounding medium and its appearance has previously been correlated with the formation of 3(10)-helical structures [Miick et al. (1992) Nature 359, 653-655]. Thus (LA)12 may be interconverting between different helical conformations in response to changes in the physical properties of the medium in which the peptide is dispersed. Our results suggest that (LA)12 should serve as a good peptide model of hydrophobic, transmembrane helices which are conformationally sensitive to the properties of the lipid bilayer in which they reside.

Peptide models of helical hydrophobic transmembrane segments of membrane proteins. 2. Differential scanning calorimetric and FTIR spectroscopic studies of the interaction of Ac-K2-(LA)12-K2-amide with phosphatidylcholine bilayers

The interactions of the hydrophobic helical transmembrane peptide Ac-K2-(LA)12-K2-amide [(LA)12] with a series of n-saturated diacylphosphatidylcholines (N:0 PC) were studied by high-sensitivity differential scanning calorimetry (DSC) and Fourier transform infrared (FTIR) spectroscopy. The incorporation of (LA)12 into these lipid bilayers results in a broadening of the chain-melting phase transitions of the lipids and progressive decreases in the characteristic temperatures and enthalpies of their gel/liquid-crystalline phase transitions. At low peptide/lipid ratios, the DSC thermograms exhibited by mixtures of (LA)12 with the short chain PCs (13:0 and 14:0) and with very long chain PCs (21:0 and 22:0) appear to be a summation of sharp and broad components, the former diminishing in intensity with increases in peptide concentration. This behavior can be approximated by that of a macroscopic mixture of peptide-poor and peptide-rich lipid domains, the relative proportions of which change with changes in peptide concentration. For peptide mixtures with the medium-chain PCs, the hydrocarbon chain-melting phase transition endotherms are not clearly resolvable into similar sharp and broad components. Instead, at all finite peptide concentrations the DSC heating thermograms appear as broad and highly asymmetric endotherms, the transition temperatures of which decrease significantly with increases in peptide concentration. For mixtures of (LA)12 with each of the lipids studied, the total hydrocarbon chain-melting transition enthalpy decreases with increasing peptide concentration but does not vanish at high peptide/lipid ratios. The FTIR spectra of (LA)12 in these PC bilayers indicate that the peptide retains a predominantly alpha-helical conformation in both the gel and liquid-crystalline phases of the short to medium chain PCs studied (N < 18). However, when incorporated into bilayers composed of the longer chain PCs (N > or = 18), (LA)12 undergoes a reversible conformational change at the gel/liquid-crystalline phase transition of the mixture. In the liquid-crystalline phase, the amide I regions of the FTIR spectra of these mixtures are indicative of a predominantly alpha-helical peptide conformation. However, upon freezing of the lipid hydrocarbon chains, populations and/or domains of (LA)12 giving rise to a sharp conformationally unassigned band near 1665 cm-1 are formed.(ABSTRACT TRUNCATED AT 400 WORDS)

Phylogenetic relationships among two species of golden monkey and three species of leaf monkey inferred from rDNA variation

Restriction maps of rDNA repeats of five species of Colobinae and three outgroup taxa, Hylobates leucogenys, Macaca mulatta, and Macaca irus, were constructed using 15 restriction endonucleases and cloned 18S and 28S rRNA gene probes. The site variation between Rhinopithecus roxellana and Rhinopithecus bieti is comparable to that between Presbytis françoisi and Preshytis phayrei, implying that R. bieti is a valid species rather than a subspecies of R. roxellana. Phylogenetic analysis on the 47 informative sites supports the case for Rhinopithecus being an independent genus and closely related to Presbytis. Furthermore, branch lengths of the tree seem to support the hypothesis that the leaf monkeys share some ancestral traits as well as some automorphic characters.

[Elevated expression of B-50 (GAP-43) -mRNA in a subpopulation of olfactory bulb mitral cells following axotomy]

Using in-situ hybridization method. We studied B-50 (GAP-43) mRNA expression following lesion of olfactory bulb mitral cells in rats. Expression of B-50 mRNA in approximately 40% of the mitral cells was upregulated in response to transection of their axons in the lateral olfactory tract (LOT). Enhanced expressin persisted for 10 days postlesion but than declined to control levels by 4 weeks after the lesion. A large proportion of the mitral cells gradually degenerated subsequent to LOT transection. Thus, a subpopulation of mitral cells maintain their ability to upregulate B-50, a protein characteristic of growing axons, but enhanced B-50 expression is not accompanied by regeneration of the severed LOT.

Identification of a ras-activated enhancer in the mouse osteopontin promoter and its interaction with a putative ETS-related transcription factor whose activity correlates with the metastatic potential of the cell

The role of RAS in transducing signals from an activated receptor into altered gene expression is becoming clear, though some links in the chain are still missing. Cells possessing activated RAS express higher levels of osteopontin (OPN), an alpha v beta 3 integrin-binding secreted phosphoprotein implicated in a number of developmental, physiological, and pathological processes. We report that in T24 H-ras-transformed NIH 3T3 cells enhanced transcription contributes to the increased expression of OPN. Transient transfection studies, DNA-protein binding assays, and methylation protection experiments have identified a novel ras-activated enhancer, distinct from known ras response elements, that appears responsible for part of the increase in OPN transcription in cells with an activated RAS. In electrophoretic mobility shift assays, the protein-binding motif GGAGGCAGG was found to be essential for the formation of several complexes, one of which (complex A) was generated at elevated levels by cell lines that are metastatic. Southwestern blotting and UV light cross-linking studies indicated the presence of several proteins able to interact with this sequence. The proteins that form these complexes have molecular masses estimated at approximately 16, 28, 32, 45, 80, and 100 kDa. Because the approximately 16-kDa protein was responsible for complex A formation, we have designated it MATF for metastasis-associated transcription factor. The GGANNNAGG motif is also found in some other promoters, suggesting that they may be similarly controlled by MATF.

Intra-oral remineralization of enamel with a MFP/DCPD and MFP/silica dentifrice using surface microhardness

The present study was undertaken to ascertain the effect of dicalcium phosphate dihydrate (DCPD) abrasive in a dentifrice on the remineralizaton of enamel using a surface microhardness technique. The method of assessing enamel remineralization via surface microhardness (SMH) was validated in a randomized, crossover, double-blind, intra-oral remineralization study conducted with 12 healthy adults. Enamel demineralization was achieved in vitro by covering bovine enamel blocks with exogenous oral bacteria, S. Mutans 1600 Ingbritt, containing glucan which was then exposed to sucrose. In the intra-oral treatment phase, subjects were fitted with oral maxillary palatal retainers, each holding four demineralized enamel blocks. Subjects brushed their teeth for 30 seconds with a test dentifrice, swished for an additional 60 seconds, rinsed with water and then retained the blocks intra-orally for 4 hours. Percent mineral recovery for each enamel block was calculated as the ratio of the changes in enamel microhardness due to treatment (remin) and sucrose challenge (demin). Treatments included DCPD-based dentifrices containing 0, 250 and 1000 ppm fluoride (F) from sodium monofluorophosphate (MFP). Using SMH, respective mean percent mineral recoveries of 5.7, 18.7 and 41.4% were obtained. All ADA criteria for model validation were fulfilled. This same model was then used to compare the remineralization effects of a silica placebo, DCPD placebo, 1000 ppm F MFP/silica and 1000 ppm F MFP/DCPD dentifrice. Mean percent mineral recoveries of -0.9, 24.1, 30.2 and 55.7% were obtained, respectively. The MFP/DCPD dentifrice was superior to MFP/silica (<0.01) with use of the MFP/DCPD dentifrice when compared to MFP/silica or the silica placebo. These results indicate that more active calcium and a higher degree of saturation (DS(EN)) with respect to enamel exists for an extended period of time after use of a MFP/DCPD dentifrice. Since an elevation in DS(EN) is considered a major parameter controlling the extent of enamel remineralization, this finding may partly explain the superior remineralization of enamel observed with the MFP/DCPD dentifrice. The significant increases in calcium activity and intra-oral enamel remineralization by the DCPD-based dentifrice are consistent with earlier findings that a DCPD abrasive provides added benefit for enamel remineralization.

Tetravalent platinum complexes with ammine/amine carrier ligand configuration: circumvention of platinum resistance in vivo

A platinum(II) and three platinum(IV) ammine/cycloalkylamine homologous series, the latter possessing either chloro, acetato or hydroxo axial ligands, were evaluated for efficacies in mice bearing tumor cells sensitive (leukemia L.1210/0 and reticulosarcoma M5076) or resistant to cisplatin (L1210/DDP) and tetraplatin (L1210/DACH). Within each series, which contained four homologs, potency increased (optimal dose decreased) as alicyclic ring size increased incrementally from cyclopropane to cyclohexane. All analogs were active at maximally tolerated doses against L1210/0 (%T/C = 125-426), with good associated therapeutic ratios of 2 to > 8 that, like the therapeutic index, provided indications of the drug's safety margin. Most complexes had activities that were similar to cisplatin (%T/C = 239) and tetraplatin (%T/C = 310). Antitumor activities were seen for all four platinum(II) complexes against L1210/DDP cells (%T/C = 133-167). In the three platinum(IV) series, on the other hand, only cyclopentane (C5) and cyclohexane (C6) analogs met or exceeded the minimum criterion for activity. These activities were similar to that seen with the positive control agent tetraplatin (%T/C = 133), but higher than that of cisplatin (%T/C = 94). Long-term survivors, which were frequently observed with these complexes in the L1210/0 model, were also seen in the L1210/DDP model, but to a lesser extent. Against L1210/DACH cells, which were sensitive to cisplatin (%T/C = 155), but resistant to tetraplatin (%T/C = 113), the C5 and C6 congeners in the platinum(IV) series were effective with %T/C in the range 148-189, while corresponding members in the platinum(II) series were only marginally active. In the solid M5076 model, complexes C5 in platinum(II) and in the acetato- and hydroxoplatinum(IV) series, and C6 from the hydroxo-platinum(IV) series, were as effective or more effective than cisplatin, which itself gave a tumor growth delay of 27.5 days. In summary, the results indicate that alicyclic ring size and, in the platinum(IV) series, axial ligand, are important modulators of efficacies of ammine/cycloalkylamine platinum congeners in both sensitive and platinum-resistant models. However, the cyclopentylamine or cyclohexylamine carrier ligand with acetato or hydroxo axial ligands in the platinum(IV) configuration are optimal combinations for circumventing both cisplatin and tetraplatin resistances.

Phylogenetic relationships of bears (the Ursidae) inferred from mitochondrial DNA sequences

The phylogenetic relationships among some bear species are still open questions. We present here mitochondrial DNA sequences of D-loop region, cytochrome b, 12S rRNA, tRNA(Pro), and tRNA(Thr) genes from all bear species and the giant panda. A series of evolutionary trees with concordant topology has been derived based on the combined data set of all of the mitochondrial DNA sequences, which may have resolved the evolutionary relationships of all bear species: the ancestor of the spectacled bear diverged first, followed by the sloth bear; the brown bear and polar bear are sister taxa relative to the Asiatic black bear; the closest relative of the American black bear is the sun bear. Primers for forensic identification of the giant panda and bears are proposed. Analysis of these data, in combination with data from primates and antelopes, suggests that relative substitutional rates between different mitochondrial DNA regions may vary greatly among different taxa of the vertebrates.

IS1237, a repetitive chromosomal element from Clavibacter xyli subsp. cynodontis, is related to insertion sequences from gram-negative and gram-positive bacteria

We describe here a repetitive chromosomal element, which appears to be an insertion sequence, isolated from Clavibacter xyli subsp. cynodontis, a gram-positive plant-associated bacterium. The element, IS1237, is 905 bp in size, is bounded by 19-bp perfect inverted repeats and 3-bp direct repeats, and appears at least 16 times in the genome. It contains three open reading frames which show similarity to open reading frames from various other insertion sequences. We have found that there are two groups of related mobile elements: one in which two open reading frames are read separately and the other in which these two open reading frames are fused together to give one predicted protein product. Using one of these open reading frames to search amino acid sequence databases, we found two instances in which similar reading frames flank genes carried on plasmids. We believe therefore that these plasmid-borne genes may be parts of previously unidentified mobile elements. For IS1237, a frameshift in two of the open reading frames and a stop codon in the third may indicate that this particular copy of the element is no longer active in transposition. The similarity of IS1237 to other elements from both gram-negative and gram-positive bacteria provides further evidence that mobile elements have been transferred between these two bacterial groups.

Stability of thrombosis induced by electrocoagulation of rat middle cerebral artery

BACKGROUND AND PURPOSE

Although it is often assumed in experimental stroke studies that cautery-induced occlusion is permanent, surgeons commonly expect cauterized vessels to recanalize spontaneously. We used the rat middle cerebral artery to determine if electrocoagulation would produce a permanent occlusion in this preparation.

METHODS AND RESULTS

A standard bipolar coagulator, calibrated to determine actual power output, was adjusted to induce platelet aggregation in the middle cerebral artery of anesthetized Sprague-Dawley rats without inducing bleeding through the arterial wall. A reliable temporary thrombosis was induced by a Malis Bipolar Coagulator set to deliver 10 bursts of 1.5 seconds each at a rate of 24 min-1 and a power setting of 3 W. This thrombus was responsive to the antithrombotic agent flunarizine. An apparently permanent occlusion was produced by 30 bursts at 3 W followed by 20 bursts at 5 W. To our surprise, seven of seven such occlusions recanalized spontaneously within 4 hours.

CONCLUSIONS

The electrocoagulation process commonly used in experimental stroke studies may produce only a temporary occlusion of the rat middle cerebral artery.

Ammine/amine platinum (II) complexes effective in vivo against murine tumors sensitive or resistant to cisplatin and tetraplatin

Three homologous series, each differing from the other in the coordinated amine ligand class, namely alicyclic, heterocyclic or isoaliphatic, were highly effective against wild-type murine leukemia L1210/0 cells in vivo (T/C = 171%-426% at optimal doses). Of the 13 complexes comprising the three series, 3 were inactive in the cisplatin-resistant L1210/DDP model, but the other 10 maintained good efficacy (T/C = 131%-167%). Long-term survivors, frequently observed with these complexes in the L1210/0 model, were also seen in the L1210/DDP model but to a lesser extent. In the homologous alicyclic series, which contained six analogs, as the alicyclic ring size increased, potency against L1210/0 and L1210/DDP cells also increased up to cyclohexylamine, and then declined. Four ammine/alicyclic amine analogs were evaluated against L1210/DACH cells, which are cross-resistant to tetraplatin, and the clinically predictive M5076 reticulosarcoma. Although the congeners were ineffective or minimally effective in prolonging the survival time of L1210/DACH-bearing mice (T/C = 111%-134%), 20%-40% cure rate was consistently observed and suggested that the compounds possessed a low inherent ability to circumvent resistance in these tumor cells also. In the solid M5076 model, activity was greatest (tumor growth delays of about 25 days) for the alicyclic homologs containing the ammine/cyclobutylamine or ammine/cyclopentylamine carrier ligand combination. In summary, ammine/amine platinum (II) analogs have demonstrated promise at the preclinical level in their ability to circumvent acquired resistance, which is a major drawback of cisplatin use in treating cancer.

[Therapy of experimental autoimmune myasthenia gravis in rabbits with 4-aminopyridine and 3,4-diaminopyridine]

The autoimmune myasthenia gravis (AMG) in rabbits was produced by intradermal injection of N-AChR-rich membrane vesicles isolated from the electric organ of Narcine limlei. After i.v. 4-aminopyridine (4-AP) 0.8 mg.kg-1 to 8 AMG rabbits, their general posture improved promptly, the features of gastrocnemius compound action potentials and toe twitches elicited by 4-Hz stimuli applied to the sciatic nerve returned to normal, and the tetanic plateau evoked by 50-Hz indirect stimulation was again well sustained. This improved condition lasted 9.1 +/- 2.5 h. Other 8 AMG rabbits given 3,4-diaminopyridine (3,4-DAP) 0.4 mg.kg-1 showed a similar improvement for 9.3 +/- 3.1 h. These results indicated that 4-AP and 3,4-DAP were effective in treating the AMG in rabbits, they may be useful in the clinical treatment of myasthenia gravis patients.

Evidence that cell toxicity may contribute to the genotoxic response

Comparisons of the structural determinants associated with genotoxic effects with those associated with cell or systemic toxicity indicate extensive overlaps. These findings can be taken to indicate that toxicity may contribute to genotoxicity.

Structural basis of the induction of unscheduled DNA synthesis in rat hepatocytes

The structural basis of the induction of unscheduled DNA synthesis (UDS) in isolated rat hepatocytes was studied with CASE, an expert system. The analysis identified a number of structural determinants associated with the induction of UDS. These structures accounted for 97.3% of the activity of the chemicals in the database. Further analyses indicated that the concordance between prediction and experimentally determined UDS of molecules not in the learning set is > 82%. A comparison of predictions of UDS and mutagenicity in Salmonella indicated that there is a dichotomy between these activities. The basis of this lack of coincidence remains to be elucidated.

Kinetics of tissue disposition of cis-ammine/cyclohexylamine-dichloroplatinum(II) and cisplatin in mice bearing FSaIIC tumors

The clinical potential of mixed amine platinum(IV) complexes has been identified, and interest in this new class of antitumor agents has been heightened by demonstration of their activity in cisplatin-resistant neoplasms. These tetravalent platinum agents are expected to undergo a reductive reaction to form the corresponding platinum(II) drug prior to eliciting biological activity. cis-Ammine/cyclohexylamine-dichloroplatinum(II) is one such product that we evaluated with cisplatin in vivo, and we found the two complexes given i.v. or i.p. to have comparable activities against a solid murine fibrosarcoma. Following i.v. administration of the two compounds at equitoxic dose levels (20 mg/kg) to tumor-bearing mice, platinum levels in the plasma were consistently higher for cisplatin. Tissue platinum levels, in contrast, were comparable between the agents or higher for the mixed amine analog at the earliest (3-h) time point. The temporal profiles determined for the concentrations over 48 h were tissue- and/or drug-specific and could be described by terminal-phase constants or half-lives of platinum in most tissues. In the plasma, kidney, lung, and jejunum, platinum levels arising from both compounds decayed with half-lives of 24-92 h. The terminal-phase constants of platinum determined in the heart for the two complexes were not significantly different from zero, indicative of levels remaining steady, whereas the constants were negative in the spleen, indicative of an increase in tissue drug concentration. In the tumor, liver, and testes, positive values for the decay-phase constants corresponding to half-lives of 47, 256, and 79 h, respectively, were seen with the mixed amine complex; this pattern contrasted with that found for cisplatin, for which the terminal-phase constant was either zero or negative. In vitro binding studies demonstrated the mixed amine complex to be more reactive. Thus, the presence of one ammine and one cyclohexylamine carrier ligand in the mixed amine complex, as opposed to the diammine ligands in cisplatin, leads to an increase in drug distribution and an alteration in the kinetics of tissue binding and removal of platinum.

Adaptive response to mutagenesis and its molecular basis in a human T-cell leukemia line primed with a low dose of gamma-rays

The effect was studied of a low dose of gamma-ray preexposure on the frequency and molecular spectrum of radiation-induced mutations at the hprt locus in a human T-cell leukemia line. When the cells were preexposed to 0.01 Gy of gamma-rays, the yield of mutations induced by a subsequent 2-Gy challenge dose was reduced by 60%, compared with the 2 Gy of irradiation alone. The data of Southern blot analysis showed that 47% of the mutants induced by 2 Gy in the cells without low-dose preexposure were of the deletion or rearranged mutations type. In contrast, in the low-dose radioadapted cells the proportion of this type of 2-Gy-induced mutations decreased to 28%. This is close to the control level (22%) of spontaneous mutations. Our results confirm that a low dose of gamma-ray preexposure leads to a decreased susceptibility to gene deletions and rearrangements after high-dose irradiation.

[Specific curative effects of nitrosourea drugs on tumor cells with Mer--phenotype in Chinese]

O6-Methylguanine DNA methyltransferase (O6-MT) activity and cellular sensitivity to nitrosourea drugs of 10 kinds of tumor cell strains derived from Chinese patients were measured by 3H radioactivity and colony-forming ability, respectively. The results in vitro showed that nimustine (Nim) 25 micrograms.ml-1 and carmustine (Car) 20 micrograms.ml-1 exhibited specific killing effects on Mer-phenotype tumor cells characterized by low O6-MT activity. In vivo both Nim and Car (25 mg.kg-1.wk-1 x 4 wk, ip) had specific curative ability to Mer- tumor cells implanted in nude mice. These findings suggested that assay of O6- MT activity in tumor biopsy could be used as a predictable guide to human tumor chemotherapy with nitrosourea compounds.

Mitochondrial DNA sequence evolution in the Arctoidea

Some taxa in the superfamily Arctoidea, such as the giant panda and the lesser panda, have presented puzzles to taxonomists. In the present study, approximately 397 bases of the cytochrome b gene, 364 bases of the 12S rRNA gene, and 74 bases of the tRNA(Thr) and tRNA(Pro) genes from the giant panda, lesser panda, kinkajou, raccoon, coatimundi, and all species of the Ursidae were sequenced. The high transition/transversion ratios in cytochrome b and RNA genes prior to saturation suggest that the presumed transition bias may represent a trend for some mammalian lineages rather than strictly a primate phenomenon. Transversions in the 12S rRNA gene accumulate in arctoids at about half the rate reported for artiodactyls. Different arctoid lineages evolve at different rates: the kinkajou, a procyonid, evolves the fastest, 1.7-1.9 times faster than the slowest lineage that comprises the spectacled and polar bears. Generation-time effect can only partially explain the different rates of nucleotide substitution in arctoids. Our results based on parsimony analysis show that the giant panda is more closely related to bears than to the lesser panda; the lesser panda is neither closely related to bears nor to the New World procyonids. The kinkajou, raccoon, and coatimundi diverged from each other very early, even though they group together. The polar bear is closely related to the spectacled bear, and they began to diverge from a common mitochondrial ancestor approximately 2 million years ago. Relationships of the remaining five bear species are derived.

Development of a method to assess the informational content of structure-activity data bases

The ability to predict the biological or toxicological properties of yet untested chemicals based upon structure-activity relationships (SAR) is very dependent upon the size and chemical diversity of the "learning set" used to develop the SAR model. In the present study it is shown that for noncongeneric chemicals, systematically increasing the informational contents of "learning sets" by iteratively selecting chemicals based upon structural diversity increases the predictivity of the SAR model. This approach can now be used to generate learning sets with maximal informational content while keeping the number of chemicals that require testing at a minimum.

[Oro-pharyngeal flora in severely burned patients]

Throat cultures were taken in thirty-seven cases of burned patients, and also, at the same time, from twenty-three healthy persons. The results showed that the essential oro-pharyngeal flora in healthy persons were Neisseria (65.7%) and Streptococcus viridans (14.3%), and Staphylococcus aureus was obtained occasionally. In twenty-five out of thirty-seven patients dominant growth of invaders was observed. The prominent aerobic bacteria in patients included Serratia (9.33%), Pseudomonas aeruginosa (8.44%) and Proteus (7.11%). The positive rate of fungi was as high as 75.1%, of which Candida was the most commonly found organism. In 7 patients the number of bacteria in the throat was in excess of 108/cm2. Of these 7 patients, 4 died. Quantitative bacterial count of lungs were taken in 3 non-survivors, and the bacterial count was over 10(5)/g. The bacteria in the lungs were as same as the predominantly colonized bacteria in the throat, and in a part of cases were the same as the systemically disseminated bacteria. The study of the throat flora is simple, its result might help the prediction of pulmonary infection.

Anesthetic effects on motor evoked potentials in dogs

The effects of the various anesthetic agents on the production of transcranial magnetic motor evoked potentials (tcMMEP) were studied in a canine model. Pre-anesthetic baseline tcMMEPs demonstrated consistency in onset latency measurements and variability in measurement of peak-to-peak amplitudes. Changes in tcMMEPs were evaluated following the individual administrations of sodium pentothal, etomidate, halothane, fentanyl, and ketamine. For induction of anesthesia, etomidate was compatible with tcMMEP production, whereas sodium pentothal resulted in loss of hindlimb potentials for a period of 45 minutes. For maintenance of anesthesia, halothane was incompatible with the measurement of tcMMEPs. Fentanyl administration was consistent with the recording of reliable tcMMEPs, with consistent onset latencies but widely variable peak-to-peak amplitudes. Ketamine was compatible with stable and reproducible tcMMEP production. The results of this study suggest that anesthetic agents have a predictable and consistent effect on tcMMEP responses.

Weaning practices and growth in rural Sichuan infants: a positive deviance study

To understand some of the factors involved in weaning and growth faltering in rural China, a cross-sectional positive deviance study was undertaken among 389 rural 4-12-month-old infants from two townships of a county in Sichuan. The infants' mothers were interviewed about their child-feeding practices and other sociodemographic information, and anthropometric measurements were made on their infants. Positive deviant infants (those growing adequately in environments in which the majority of the children suffer from growth retardation and malnutrition) were identified from the Chinese WAZ-scores calculated from the anthropometric measurements. Feeding practices found to be associated with the better growth of the positive deviant infants included breastfeeding through age 12 months, feeding soybean milk, liver and pork blood products on a more than weekly basis during the ages of 7-9 months, not feeding rice flour (mifen) before age 7 months, and not giving supplements or tonics. Mothers' nutrition knowledge was also associated with positive deviance status. The relevance of the findings is discussed with respect to designing nutrition education interventions for rural Sichuan.