Cell specificity in hepatocarcinogenesis: preferential accumulation of O6-methylguanine in target cell DNA during continuous exposure to rats to 1,2-dimethylhydrazine

Concentrations of the major methylated DNA purines were determined in two liver cell cell populations of Fischer 344 rats during administration of 30 ppm 1,2-dimethylhydrazine (SDMH) in the drinking water for periods of up to 4 weeks. Quantitation of 7-methylguanine and O6-methylguanine (O6MG) was achieved by highly sensitive optical methods following separation of DNA bases by high-performance liquid chromatography. Overall alkylation as indicated by the concentration of 7-methylguanine was near maximum in both hepatocytes and liver nonparenchymal cells by the third day of SDMH administration. Similar amounts of 7-methylguanine were present in the two liver cell populations at seven of nine time points during 4 weeks of exposure. In contrast, dramatic differences in the cumulative concentrations of O6MG were seen in the two cell populations. Nonparenchymal cells accumulated O6MG during the first 8 days of exposure and had up to a 30-fold greater concentration of this product than did the corresponding hepatocytes. In the hepatocytes, a rapid decline in O6MG concentration was observed between 1 and 3 days of exposure to SDMH. Thereafter, only low levels of this promutagenic lesion were present in hepatocytes. Exposure of rats to the same regimen of SDMH for up to 10 months caused angiosarcomas in the livers of over 90% of the animals, while hepatocellular carcinomas occurred in only 40%. Thus, a strong correlation exists between the inability to repair O6MG and cell specificity for carcinogenesis.     

The role of complex formation in the anionic polymerization of l-lactide

The rate lowering effect of crown ethers in the anionic polymerization of l-lactide is interpreted by the formation of activated monomer-cation complex. This interpretation is supported by molecular mechanics calculations. The formation of a 1 : 1 complex between lithium ion and l-lactide in THF was proved by ¹H NMR and the formation constant was measured to be 3.8 M⁻¹. Received: 15 January 1997/Accepted: 10 March 1997     

Rheological properties of hydrophobic ethoxylated urethane (HEUR) in the presence of methylated β-cyclodextrin

Hydrophobic ethoxylated urethane (HEUR) is one type of hydrophobically modified polyethylene glycol, which could form a transient network structure in aqueous solution via intermolecular hydrophobic associations. The viscosity of HEUR solution is dependent on two parameters; namely the effective elastic chain density and the relaxation time. In the present study, different amounts of methylated β-cyclodextrin (m-βCD) were added into aqueous HEUR solutions, and significant reduction in the solution viscosity was observed when the m-βCD concentration exceeds a critical value. Oscillatory shear indicated that the plateau modulus does not decrease appreciably with the addition of m-βCD, however a large reduction in relaxation time was observed. At low m-βCD concentrations, addition of m-βCD does not decouple the hydrophobic association. The ring-shaped hydrophobic inner cores of m-βCD interact with the hydrophobic moiety of looping HEUR chains, leading to a reduction in the relaxation time, which weakens the transient network. However, at higher m-βCD concentrations, bridging chains are decoupled, thereby disrupting the transient network and produce smaller isolated aggregates.     

An Efficient Approach to Correspondences between Multiple Non‐Rigid Parts

Identifying multiple deformable parts on meshes and establishing dense correspondences between them are tasks of fundamental importance to computer graphics, with applications to e.g. geometric edit propagation and texture transfer. Much research has considered establishing correspondences between non‐rigid surfaces, but little work can both identify similar multiple deformable parts and handle partial shape correspondences. This paper addresses two related problems, treating them as a whole: (i) identifying similar deformable parts on a mesh, related by a non‐rigid transformation to a given query part, and (ii) establishing dense point correspondences automatically between such parts. We show that simple and efficient techniques can be developed if we make the assumption that these parts locally undergo isometric deformation. Our insight is that similar deformable parts are suggested by large clusters of point correspondences that are isometrically consistent. Once such parts are identified, dense point correspondences can be obtained by an iterative propagation process. Our techniques are applicable to models with arbitrary topology. Various examples demonstrate the effectiveness of our techniques.     

Morphology and mechanical properties of reactive compatibilized polystyrene/ethylene‐vinyl acetate‐vinyl alcohol blends

A reactive compatibilizer, styrene‐maleic anhydride (SMA) was used to compatibilize the blends of polystyrene (PS) and ethylene‐vinyl acetate‐vinyl alcohol (EVAOH), which was synthesized from ethylene‐vinyl acetate (EVA) using transesterification reaction. The compatibilized blends with different compositions were prepared using a twin‐screw extruder and injection molded into the required test specimens. Morphology of Charpy impact‐fractured surfaces, tensile, and impact properties of the blends were investigated. Fourier‐transform infrared spectroscopy (FTIR) was also applied for specific samples to elucidate the presence of the functional groups reaction necessary for reactive compatibilization. The results of the ternary PS/EVAOH/SMA blends illustrate that the addition of SMA as a compatibilizer slightly reduce the elongation at break. From the impact‐fractured surfaces of the blends, it is evident that the morphology developed sizable pores when SMA was added into the blends. This might be attributed to the residual octanol‐1, produced from the synthesis of EVAOH, as there is a possibility of a reaction between hydroxyl groups in the octanol‐1 and the anhydride groups in the SMA. This disrupted the stability of the morphology and resulted in the decrease in the elongation, and hence, the tensile toughness. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 209–217, 2002     

Association between tinnitus and somatoform disorders

Pathophysiological mechanisms are often unknown in patients suffering from "idiopathic" tinnitus, and the presence of other unexplained physical symptoms such as those seen in somatoform disorders can be assumed. This study investigates how often tinnitus exists in general medical out-patients with and without somatoform disorders. In an international study initiated by the World Health Organization (WHO), 1275 patients from 12 participating centers located in 11 different countries were examined by means of the WHO Somatoform Disorders Schedule. The overall prevalence of unexplained tinnitus was 11%; however, tinnitus was clearly more frequent among patients with somatization disorder (42%) or hypochondriacal disorder (27%). It was also more frequent than a great number of other symptoms considered to be typical of somatoform disorders. Tinnitus was also related to depression, anxiety, and to symptoms indicating autonomic arousal. Three possible conclusions are discussed: (i) tinnitus may be a somatoform symptom; (ii) the findings may indicate a substantial comorbidity of two different conditions; (iii) tinnitus and somatization may be linked through common mechanisms of arousal and somatic anxiety.     

Working with laboratory animals: general principles and practical considerations

Laboratory animals play an indispensable role in research discovery and technological advances, and they will continue to yield basic, exciting, and prodigious information that can enrich the future of people and other animals. For both ethical and scientific reasons, all-individuals whose work requires the use of laboratory animals must take the time to conduct a thorough review of the literature to determine what animal models are available and which are the most relevant, and they must learn and understand the uniqueness of the selected species, breed, and strain. Scientists have the privilege, but not the right, to use animals as experimental subjects. This privilege must not be abused. Therefore, it is imperative that before working with any laboratory animal, you know your "subject."     

Primary diffusely infiltrative adenocarcinoma of the colon and rectum

In this study, patient opinion on oral rehabilitation by means of Br?nemark implants was investigated. All patients were referred to a periodontal clinic for implant installation and treated by one and the same operator. Prosthetic restorations were performed by dentists, who had no previous experience with prostheses on implants, but had completed a postgraduate training course. Patient opinion was obtained through questionnaires, pertaining to satisfaction and oral function. A comparison was made between pre-implant situation, short-term (< 4 months) and long-term functioning (3 years) with the implant-restorative rehabilitation. In total, 61 patients participated in the study; 23 received a full lower arch bridge and 18 a full upper arch bridge, while 20 patients got partial bridges. Of 298 installed implants, 7 failed at abutment connection (2.3%) and 1 during the 3-year follow-up interval (0.3%). The study results indicated that a great majority of patients were very satisfied with the treatment. Comfort with eating, aesthetics, phonetics and overall satisfaction improved significantly and nearly all patients said that they would undergo the treatment again or recommend it to others. Patients experienced their implants as "natural" teeth. The conclusion is that rehabilitation ad modum Br?nemark, even in the hands of non-specialized dentists, can be of high quality, improving oral function and satisfying the needs and demands of patients.