E.M. Den Tonkelaar

Bio: E.M. Den Tonkelaar is an academic researcher. The author has contributed to research in topics: Bromide & Parathion. The author has an hindex of 4, co-authored 6 publications receiving 104 citations.

The combined effect of food restriction and parathion exposure in rats.

Abstract: Male rats were fed diets containing 0, 1, or 5 ppm parathionad libitum for 28 days. Three other groups of rats were fed diets containing 0, 2, or 10 ppm parathion for 28 days but were fed only 50% of the food intake of the correspondingad libitum groups. Effects on plasma cholinesterase activity and plasma and liver carboxylesterase activities were observed in the 5 ppm and 10 ppm parathion groups. Food restriction increased the inhibition elicited by parathion with each of these parameters. No significant inhibition of brain cholinesterase by parathion alone or with food restriction was observed. Lesions of the pancreas were noted in animals receiving 10 ppm of parathion and subjected to 50% normal food intake.

Chemical toxins: a hypothesis to explain the global obesity epidemic.

Abstract: The number of obese people worldwide has escalated recently, revealing a complex picture of significant variations among nations and different profiles among adults and children, regions, and occupations. The commonly held causes of obesity - overeating and inactivity - do not explain the current obesity epidemic. There is evidence of a general decrease in food consumption by humans and a significant decline in their overall levels of physical activity. There is also more evidence to indicate that the body's natural weight-control mechanisms are not functioning properly in obesity. Because the obesity epidemic occurred relatively quickly, it has been suggested that environmental causes instead of genetic factors maybe largely responsible. What has, up to now, been overlooked is that the earth's environment has changed significantly during the last few decades because of the exponential production and usage of synthetic organic and inorganic chemicals. Many of these chemicals are better known for causing w...

Biochemistry of the Elemental Halogens and Inorganic Halides

Abstract: The elements in group 17 (VIlA) of the periodic table of elements-fluorine (F), chlorine (CI), bromine (Br), and iodine (I)-were designated by Berzelius as "halogens" (Greek hals, sea salt; gennao, I beget) because of their propensity to form salts. In this first of the two volumes of Bio chemistry of the Halogens, the biochemistry of the elemental halogens and inorganic halides is reviewed. Discovery, properties, and biochemistry of the elemental halogens are reviewed first (Chapter 1). This is followed by a review of the developments in the various areas of inorganic halide biochemistry (Chapters 2 through 5). The biochemistry of thyroid hor mones is considered in Chapter 6, while biohalogenation, an important link between inorganic and organic halogen biochemistry, is reviewed in Chapter 7. Chapter 8 covers the biochemistry of products produced by human-inspired halogenation, in particular, poly halogenated compounds that present environmental problems. In Chapter 9, the process is reversed and biodehalogenation is reviewed. In each subject, the attempt has been made to find an appropriate balance between depth and breadth of treatment, since a thorough, in depth review of this field would not be possible in a single volume. To provide readers not familiar with subjects with the necessary background to place subsequent discussions in perspective, brief historical develop ments of many of the topics are given."

Sucralose, A Synthetic Organochlorine Sweetener: Overview Of Biological Issues

Abstract: Sucralose is a synthetic organochlorine sweetener (OC) that is a common ingredient in the world's food supply. Sucralose interacts with chemosensors in the alimentary tract that play a role in sweet taste sensation and hormone secretion. In rats, sucralose ingestion was shown to increase the expression of the efflux transporter P-glycoprotein (P-gp) and two cytochrome P-450 (CYP) isozymes in the intestine. P-gp and CYP are key components of the presystemic detoxification system involved in first-pass drug metabolism. The effect of sucralose on first-pass drug metabolism in humans, however, has not yet been determined. In rats, sucralose alters the microbial composition in the gastrointestinal tract (GIT), with relatively greater reduction in beneficial bacteria. Although early studies asserted that sucralose passes through the GIT unchanged, subsequent analysis suggested that some of the ingested sweetener is metabolized in the GIT, as indicated by multiple peaks found in thin-layer radiochromatographic profiles of methanolic fecal extracts after oral sucralose administration. The identity and safety profile of these putative sucralose metabolites are not known at this time. Sucralose and one of its hydrolysis products were found to be mutagenic at elevated concentrations in several testing methods. Cooking with sucralose at high temperatures was reported to generate chloropropanols, a potentially toxic class of compounds. Both human and rodent studies demonstrated that sucralose may alter glucose, insulin, and glucagon-like peptide 1 (GLP-1) levels. Taken together, these findings indicate that sucralose is not a biologically inert compound.

Effects of Toxic Stimuli Combinations on Determination of Exposure Limits

Abstract: INTRODUCTION Single Stressor Studies Multiple Stressor Studies Types of Combination Effects Examples of Combination Effects