In 2000 we invested 2.5 million to produce MDB and its derivatives that is mainly used for the synthesis of advanced anti-cancer and anti-hypertension pharmaceutics.
The Committee took note of the ADI of 0-0.4 mg/kg bw for 2-phenylphenol (No. 735) established by the 1999 Joint FAO/WHO Meeting on Pesticide Residues (FAO, 1999).
2-Phenylphenol (No. 735) was evaluated by the Committee at its eighth meeting, when an ADI of 0-0.2 mg/kg bw was established (Annex 1, reference 7). The 1999 Joint FAO/WHO Meeting on Pesticide Residues evaluated the toxicity of 2-phenylphenol and established an ADI of 0-0.4 mg/kg bw (FAO, 1999). As the available studies on the toxicology of 2-phenylphenol are summarized in the monograph (WHO, 2000), the data on this substance and its sodium salt (sodium -phenylphenate) are not presented here. However, some consideration was given to studies of the genotoxicity of these substances, because the Joint Meeting found that there were unresolved questions with regard to the genotoxic potential of 2-phenylphenol.
220.127.116.11 Anion specificity High dietary concentrations of the sodium salts of other organic acids (>1%) have also been tested for their ability to enhance DNA synthesis or hyperplasia of the urinary epithelium of the rat or act as promoters of bladder carcinogenesis.
The urine turbidity of rats treated with lower levels of saccharin or with acid saccharin, ascorbic acid, sodium saccharin with ammonium chloride or sodium saccharin in AIN-76A semi-synthetic diet was similar to that in untreated rats (cited in Cohen and Garland 1992).
Chemicals may affect the nervous system through actions at any of several cellular targets or biochemical processes within the central or peripheral nervous system. Toxic effects on other organs may also affect the nervous system, as in the example of hepatic encephalopathy. The manifestations of neurotoxicity include effects on learning (including memory, cognition and intellectual performance), somatosensory processes (including sensation and proprioreception), motor function (including balance, gait and fine movement control), affect (including personality status and emotionality) and autonomic function (nervous control of endocrine function and internal organ systems). The toxic effects of chemicals upon the nervous system often vary in sensitivity and expression with age: during development, the central nervous system may be especially susceptible to toxic insult because of the extended process of cellular differentiation, migration, and cell-to-cell contact that takes place in humans (OTA 1990). Moreover, cytotoxic damage to the nervous system may be irreversible because neurons are not replaced after embryogenesis. While the central nervous system (CNS) is somewhat protected from contact with absorbed compounds through a system of tightly joined cells (the blood-brain barrier, composed of capillary endothelial cells that line the vasculature of the brain), toxic chemicals can gain access to the CNS by three mechanisms: solvents and lipophilic compounds can pass through cell membranes; some compounds can attach to endogenous transporter proteins that serve to supply nutrients and biomolecules to the CNS; small proteins if inhaled can be directly taken up by the olfactory nerve and transported to the brain.
Detailed knowledge of target organ physiology, biochemistry and molecular biology may be incorporated in target organ studies. For instance, because the synthesis and secretion of small-molecular-weight proteins is an important aspect of renal function, nephrotoxicity studies often include special attention to these parameters (IPCS 1991). Because cell-to-cell communication is a fundamental process of nervous system function, target organ studies in neurotoxicity may include detailed neurochemical and biophysical measurements of neurotransmitter synthesis, uptake, storage, release and receptor binding, as well as electrophysiological measurement of changes in membrane potential associated with these events.
Cancer mechanisms. Cancer is a multiplicity of diseases, and while the understanding of certain types of cancer is increasing rapidly due to the many molecular biological techniques that have been developed since 1980, there is still much to learn. However, it is clear that cancer development is a multi-stage process, and critical genes are key to different types of cancer. Alterations in DNA (somatic mutations) in a number of these critical genes can cause increased susceptibility or cancerous lesions (see Genetic toxicology). Exposure to natural chemicals (in cooked foods like beef and fish) or synthetic chemicals (like benzidine, used as a dye) or physical agents (ultraviolet light from the sun, radon from soil, gamma radiation from medical procedures or industrial activity) are all contributors to somatic gene mutations. However, there are natural and synthetic substances (such as anti-oxidants) and DNA repair processes which are protective and maintain homeostasis. It is clear that genetics is an important factor in cancer, since genetic disease syndromes such as xeroderma pigmentosum, where there is a lack of normal DNA repair, dramatically increase susceptibility to skin cancer from exposure to ultraviolet light from the sun.
As illustrated in , the importance of drug-metabolizing enzymes in individual susceptibility to chemical exposure may in fact present a far more complex issue than is evident from this simple discussion of xenobiotic metabolism. In other words, during the past two decades, genotoxic mechanisms (measurements of DNA adducts and protein adducts) have been greatly emphasized. However, what if nongenotoxic mechanisms are at least as important as genotoxic mechanisms in causing toxic responses?
Given the apparent lack of physiological substrates, it is possible that P450 enzymes in families CYP1, CYP2, CYP3 and CYP4 that have appeared in the past several hundred million years have evolved as a means of detoxifying foreign chemicals encountered in the environment and diet. Clearly, evolution of the xenobiotic-metabolizing P450s would have occurred over a time period which far precedes the synthesis of most of the synthetic chemicals to which humans are now exposed. The genes in these four gene families may have evolved and diverged in animals due to their exposure to plant metabolites during the last 1.2 billion yearsa process descriptively termed animal-plant warfare (Gonzalez and Nebert 1990). Animal-plant warfare is the phenomenon in which plants developed new chemicals (phytoalexins) as a defence mechanism in order to prevent ingestion by animals, and animals, in turn, responded by developing new P450 genes to accommodate the diversifying substrates. Providing further impetus to this proposal are the recently described examples of plant-insect and plant-fungus chemical warfare involving P450 detoxification of toxic substrates (Nebert 1994).
Dietary habits have an important influence on susceptibility to chemical toxicity, mostly because adequate nutrition is essential for the functioning of the bodys chemical defence system in maintaining good health. Adequate intake of essential metals (including metalloids) and proteins, especially the sulphur-containing amino acids, is necessary for the biosynthesis of various detoxificating enzymes and the provision of glycine and glutathione for conjugation reactions with endogenous and exogenous compounds. Lipids, especially phospholipids, and lipotropes (methyl group donors) are necessary for the synthesis of biological membranes. Carbohydrates provide the energy required for various detoxification processes and provide glucuronic acid for conjugation of toxic chemicals and their metabolites. Selenium (an essential metalloid), glutathione, and vitamins such as vitamin C (water soluble), vitamin E and vitamin A (lipid soluble), have an important role as antioxidants (e.g., in controlling lipid peroxidation and maintaining integrity of cellular membranes) and free-radical scavengers for protection against toxic chemicals.