Assessment of pituitary adenoma volumetric change using longitudinal MR image registration

Introduction  

Change detection is a crucial factor in monitoring of slowly evolving pathologies. The objective of the study was to test a semi-automatic method applied on longitudinal MRI monitoring of volume change in pituitary macroadenomas.     

Feeding of a well‐cooked beef diet containing a high heterocyclic amine content enhances colon and stomach carcinogenesis in 1,2‐dimethylhydrazine‐treated rats

Epidemiologic studies have linked the consumption of red meat and the consumption of highly browned meats containing high levels of heterocyclic aromatic amines (HCAs) to increased risk of colorectal cancer or polyps. The present study determined the effects of long‐term feeding of beef‐containing diets with low and high levels of HCAs (in the context of a low or high beef tallow diet) on a standard 1,2‐dimethylhydrazine (DMH)‐induced colon tumorigenesis protocol. Very lean beef was cooked by a variety of methods at different temperatures, and the levels of the major HCAs (2‐amino‐3,8‐dimethylimidazo[4,5‐f]quinoxaline, 2‐amino‐3,4,8‐trimethylimidazo[4,5‐f]quinoxaline, and 2‐amino‐l‐methyl‐6‐phenylimidazo[4,5‐f]pyridine) were measured by high‐performance liquid chromatogra‐phy. Diets incorporating beef containing low or high levels of HCAs were fed for 12 weeks, during which DMH was administered to induce colon tumors, followed by various dietary regimens as promotional stimuli. Feeding of a beef diet high in HCAs resulted in more DMH‐induced colon adenocarcinomas, but only in the context of a low‐fat diet. The high‐HCA diets increased stomach tumors in all DMH‐treated rats. An apparent interaction of high HCA with a high fat level reduced the colon tumor incidence and tumor numbers in those diets containing both factors. These results support the epidemiologic data linking well‐cooked meat to increased risk for colon and stomach cancer, but the role of dietary fat level remains puzzling.     

Increased enzyme binding to substrate is not necessary for more efficient cellulose hydrolysis

Substrate binding is typically one of the rate-limiting steps preceding enzyme catalytic action during homogeneous reactions. However, interfacial-based enzyme catalysis on insoluble crystalline substrates, like cellulose, has additional bottlenecks of individual biopolymer chain decrystallization from the substrate interface followed by its processive depolymerization to soluble sugars. This additional decrystallization step has ramifications on the role of enzyme–substrate binding and its relationship to overall catalytic efficiency. We found that altering the crystalline structure of cellulose from its native allomorph I_β to III_I results in 40–50% lower binding partition coefficient for fungal cellulases, but surprisingly, it enhanced hydrolytic activity on the latter allomorph. We developed a comprehensive kinetic model for processive cellulases acting on insoluble substrates to explain this anomalous finding. Our model predicts that a reduction in the effective binding affinity to the substrate coupled with an increase in the decrystallization procession rate of individual cellulose chains from the substrate surface into the enzyme active site can reproduce our anomalous experimental findings.     

Determination of Cholinesterase by an Automated pH Stat Method

Public concern exists about the potential for reproductive damage that may result from exposures to environmental contaminants. Therefore, the authors sought to determine if there was an association between a child's congenital malformation or a child's lowered weight at birth and his or her mother's residence in a census tract where a site of environmental contamination had been documented. Exposure designations were derived from existing sources of information. Except for an elevated risk (odds ratio = 1.5) for infants with malformations of the heart and circulatory system, this investigation did not reveal increased risks for most malformations or for lowered birthweight among babies born to women who lived in these census tracts. Methodologic issues inherent to investigations that rely on existing data sources are discussed.