An evaluation of reproductive toxicity studies and data interpretation of N-methylpyrrolidone for risk assessment: An expert panel review.

An expert panel was assembled to evaluate reproductive toxicology study data and their application to health risk assessment to provide input on the data quality, interpretation, and application of data from three multi-generation reproductive toxicity studies of N-methylpyrrolidone (NMP). Panelists were engaged using a double-blinded, modified Delphi format that consisted of three rounds. Key studies were scored using the U.S. Environmental Protection Agency's (EPA) questions and general considerations to guide the evaluation of experimental animal studies for systematic review. The primary conclusions of the panel are that one of the studies (Exxon, 1991) is not a high-quality study due to several design flaws that includes: (1) exceedance of the maximum tolerable dose in the high dose group; (2) failure to adjust feed concentrations of NMP during the lactation period, resulting in NMP doses that were 2- to 3-fold higher than nominal levels; and/or (3) underlying reproductive performance problems in the strain of rats used. For these reasons, the panel recommended that this study should not be considered for quantitative risk assessment of NMP. Exclusion of this study, and its corresponding data for male fertility and female fecundity, from the quantitative risk assessment results in a change in the identification of the most sensitive endpoint. Instead, changes in rat fetal/pup body weight, an endpoint previously selected by EPA, was identified as an appropriate basis for human health risk assessment based on a consideration of the best available science and weight of scientific evidence supported by the NMP toxicity database.

Methylmercury-induced inhibition of paraoxonase-1 (PON1)-implications for cardiovascular risk.

Methylmercury (MeHg) has been associated with increased risk for cardiovascular disease in some but not all epidemiology studies. These inconsistent results may stem from the fact that exposure typically occurs in the context of fish consumption, which is also associated with cardioprotective factors such as omega-3 fatty acids. Mechanistic information may help to understand whether MeHg represents a risk to cardiovascular health. MeHg is a pro-oxidant that inactivates protein sulfhydryls. These biochemical effects may diminish critical antioxidant defense mechanism(s) involved in protecting against atherosclerosis. One such defense mechanism is paraoxonase-1 (PON1), an enzyme present on high-density lipoproteins and that prevents the oxidation of blood lipids and their deposition in vascular endothelium. PON1 is potentially useful as a clinical biomarker of cardiovascular risk, as well as a critical enzyme in the detoxification of certain organophosphate oxons. MeHg and other metals are known to inhibit PON1 activity in vitro. MeHg is associated with lowered serum PON1 activity in a fish-eating population. The implications of lowering PON1 are evaluated by predicting the shift in PON1 population distribution induced by various doses of MeHg. An MeHg dose of 0.3 µg/kg/d is estimated to decrease the population average PON1 level by 6.1% and to increase population risk of acute cardiovascular events by 9.7%. This evaluation provides a plausible mechanism for MeHg-induced cardiovascular risk and suggests means to quantify the risk. This case study exemplifies the use of upstream disease biomarkers to evaluate the additive effect of chemical toxicity with background disease processes in assessing human risk.

Magnetic resonance imaging in cerebral malaria: a report of four cases.

OBJECTIVES: This is a retrospective institutional review of clinical data and radiological findings of cerebral malaria patients presenting to a tertiary centre in India, which is an known to be endemic for malarial disease. METHODS: The present series describes MRI in four cases all of which revealed bithalamic infarctions with or without haemorrhages in patients with cerebral malaria, and this review examines a subset of patients with this condition. In addition, acute haemorrhagic infarctions were also seen the in brain stem, cerebellum, cerebral white matter and insular cortex in two of the four patients. RESULTS: In this series, the patient with cerebellum and brain stem involvement died. The remaining three survived with antimalarial and supportive treatment. No neurological symptoms were noted on clinical follow-up. MRI follow-up was obtained in only one of the three patients (3 months post-treatment) and showed resolution of thalamic infarctions. CONCLUSION: These imaging features may help in the early diagnosis of cerebral malaria so that early treatment can begin and improve the clinical outcome.

Design, synthesis and pharmacological screening of potential anticonvulsant agents using hybrid approach.

A series of 9H, 10H, 3-[N- 4 methyl -2-benzamido thiophen 3-yl carbonyl amino [2-(2'-phenyl 1'- ethylenyl)] 10-(aryl) thiazolidino [4, 5-b] 1, 5 benzodiazepine [7a-7h] were designed and synthesized to meet the structural requirements essential for anticonvulsant activity. Anticonvulsant activity was determined after intra-peritoneal administration to mice by supramaximal electroshock seizures model and Isoniazide Hydrazone induced seizures model. Motor impairement was determined using actophotometer and rotarod apparatus. Among the synthesized compounds two [JG 7a and JG 7e] compounds exhibited significant anticonvulsant activity after intra-peritoneal administration. Active compounds carry hydroxy substitutent at 2-position and methoxy at 4-position in the phenyl ring at C(5) of benzodiazepine. In present we study conclude that small polar and electron rich groups contribute significantly for anticonvulsant activity while electronegative substitutents showed lesser contribution for anticonvulsant activity.

Foreword: Biomonitoring Equivalents special issue.

The challenge of interpreting results of biomonitoring for environmental chemicals in humans is highlighted in this Foreword to the Biomonitoring Equivalents (BEs) special issue of Regulatory Toxicology and Pharmacology. There is a pressing need to develop risk-based tools in order to empower scientists and health professionals to interpret and communicate the significance of human biomonitoring data. The BE approach, which integrates dosimetry and risk assessment methods, represents an important advancement on the path toward achieving this objective. The articles in this issue, developed as a result of an expert panel meeting, present guidelines for derivation of BEs, guidelines for communication using BEs and several case studies illustrating application of the BE approach for specific substances.

Workshop to identify critical windows of exposure for children's health: cardiovascular and endocrine work group summary.

The work group on cardiovascular and endocrine effects was asked to review the current state of knowledge about children's windows of vulnerability to developmental toxicants and to recommend how that information may be used to improve risk assessment and public health. We considered differences between structural defects, where periods of vulnerability are rather well defined, and functional defects, where periods of vulnerability are quite elusive.

Geriatric bone lead metabolism in a female nonhuman primate population.

A geriatric rhesus monkey (Macaca mulatta) population, previously exposed to lead, was investigated using 109Cd K X-ray fluorescence (K XRF) to determine whether metabolism of lead in bone was similar to that in human populations. The accumulation rate of lead into the tibia in this group of monkeys was determined to be 0.10-0.13 micrograms Pb (g bone mineral)-1 (microgram dl-1 year)-1, which compares well with human data, where the rate has been found to be 0.05-0.10 microgram Pb (g bone mineral)-1 (microgram dl-1 year)-1. In addition, bone lead changes over a 10-month time period were investigated, but no statistically significant difference was found. A halflife for lead in "bone" was calculated by fitting a single exponential model to serial blood lead data; the mean half-life of lead in bone was found to be 3.0 +/- 1.0 years. Both endogenous and exogenous lead exposure were found to be low at the present time, 10 years after cessation of lead intake. It is concluded that rhesus monkeys are an extremely good animal model of human bone lead metabolism and, in addition, that further research is needed to provide a more complete understanding of lead metabolism in geriatric populations.

Chemical contaminants in human milk: an overview.

This review contains a succinct overview of the nature and extent of the problem of contamination of human milk with environmental and occupational chemicals, excluding drugs. Factors influencing the levels of contaminants in breast milk are discussed. Also, data on major chemicals of concern with potential health risk(s) to the general population and risk-benefit considerations are dealt with briefly. Based on the available data on the subject, research needs have been identified and policy recommendations are suggested.

Risk assessment of oxidant gases and particulate air pollutants: uncertainties and research needs.

The assessment of risks to human health associated with exposure to oxidant air pollutants has not received adequate attention despite the recognized public health threat posed by the ubiquitous presence of these compounds in the environment. In this article, research needs and uncertainties at each of the steps in the risk assessment of oxidant air pollutants are identified: hazard identification, dose-response assessment, exposure assessment, and risk characterization. Many of these limitations and uncertainties arise at the interface between the laboratory and the regulatory arenas. Therefore, as a case study, relevant methodologic problems associated with the application of experimental findings to the risk assessment of respirable dusts are also discussed. These issues include the extrapolation of animal data to the human case and extrapolation from high-dose to environmentally relevant, low-level exposures.

High dietary fat feeding during perinatal development of rats alters hepatic drug metabolism of progeny.

The objective of this study was to determine whether feeding high dietary fat, during pregnancy and lactation of Sprague-Dawley rats, can modulate hepatic drug-metabolizing enzymes of the offspring during postnatal development. Time-pregnant rats were pair-fed isocalorically 20% (experimental) or 5% (control) corn oil diets from day 10 of gestation until weaning. After weaning, litters from both groups were fed 5% corn oil diet until sacrificed. Offsprings were sacrificed at weaning (23 days), puberty (45 days) and at adult stage (100 days). Feeding diet containing 20% corn oil to dams, resulted in significant increases in liver microsomal cytochrome P-450, b5 contents and aminopyrine N-demethylase activity of the male offspring at weaning, puberty and adult stage of life. A similar but less marked trend was also observed in the female offspring. Thus, it appears that the high dietary fat exposure during perinatal development may result in significant alterations in hepatic drug-metabolizing enzyme activities of the progeny.

Effect of early nutrition on serum cholesterol levels in adult rats challenged with high fat diet.

Early exposure to cholesterol-enriched, high fat diets has been reported to affect serum cholesterol levels in adult rats. In this study, we investigated the role of dietary fat alone, without cholesterol, by feeding to pregnant rats (from day 18 of gestation) experimental diets containing either high fat (corn oil), low sucrose (HF) or low fat, high sucrose (HS). After birth, mothers and pups were fed the diets until weaning (30 days), when serum cholesterol levels were the same in both groups of pups. Animals were fed stock diet until 7 months. At that time, half the animals from each original group (HF or HS) were challenged with HF diet for 3 days; the other half were fed stock diet. There was no significant difference in serum cholesterol between HF and HS animals fed stock diet: HF, 73 +/- 7 mg/dl (n = 11); HS, 80 +/- 19 (6); P greater than 0.25. Animals originally fed HF diet significantly raised serum cholesterol in response to late HF challenge (140 +/- 31 mg/dl, n = 10, P less than 0.001 vs. stock fed); the original HS-fed group did not (93 +/- 7 mg/dl, n = 5, P greater than 0.19). Early exposure to HF diet, even without cholesterol, could evoke a hypercholesterolemic response in adulthood following challenge by brief exposure to HF diet.

Effect of protein depletion and intrauterine growth retardation on rat hepatic drug metabolism.

The effect of intrauterine malnutrition in rats on in vivo and in vitro drug metabolism at weaning was investigated. We have employed two experimental designs to produce intrauterine malnutrition, maternal dietary protein depletion starting at day 7 of gestation and unilateral ligation of the uterine artery on day 17 of gestation. At birth cross-fostering of newborns was done, experimental and control group of litters raised separately until weaning (21 days of age). Both methods produced offspring with lower body and liver weights and these changes were present at weaning. However, only in the protein-restricted group were significant differences for liver:body weight ratio and hepatic microsomal protein content observed. Liver microsomal cytochrome P-450 and b5 contents were significantly decreased in small animals from mothers with intrauterine vessels ligated but not in the prenatal protein-restricted group. A significant increase in aminopyrine N-demethylase and a decrease in aniline hydroxylase enzyme activities was observed in both experimental groups. No significant differences were found in reductive or conjugative pathways of drug metabolism. Hexobarbital sleeping time was significantly increased in weanling animals from the prenatal protein-restricted mothers but not in the uterine-vessels-ligated group. These results suggest that maternal malnutrition may play an important role in modulation of postnatal drug metabolism pattern of progeny.

Influence of perinatal nutrition on hepatic drug metabolism in the adult rat.

Pregnant rats were fed high-fat (HF, 35% calories) or low-fat (LF, 5% calories) diet from 18 days of gestation to the end of the suckling period. Thereafter, male progeny were fed stock diet for 6 months, then sacrificed or challenged for 3 days with HF diet. There were no immediate posttreatment effects at 30 days of age on liver microsomal cytochrome P-450 or b5, aminopyrine (AP) N-demethylase or benzo(a)pyrene (BP) hydroxylase. At 7 months, cytochrome P-450 was lower in LF-fed than in HF-fed animals. High-fat challenge reduced cytochrome P-450 and cytochrome b5 content in both groups, AP N-demethylase only in LF animals and BP hydroxylase only in HF animals. These differential effects of perinatal exposure to diet on the later response of microsomal mixed-function oxidases to fat challenge suggest that early dietary experience may regulate the pattern of drug metabolism in adult life.

Delayed effects of drug exposure during pregnancy: reproductive function.

This article reviews the delayed effects of anticonvulsants (phenobarbital, phenytoin, and valproate) administered in utero upon the reproductive function in the offspring. Experimental data from the authors' laboratories are discussed in light of this context. Furthermore, comments are made emphasizing the gaps in our knowledge concerning the problem of drug exposure during pregnancy and the complex nature of drug effects upon the reproductive system.

Influence of dietary carbohydrates (alpha-saccharides) on hepatic drug metabolism in male rats.

Young male rats (SD, CD strain) were fed semisynthetic isocaloric diets ad lib for different time periods (3,7,14, or 28 days); both carbohydrate (starch or sucrose) content and fat content were varied. High starch (HST) diet contained starch (73% of calories), corn oil (6%), and casein (21%); low starch (LST) diet contained 6, 73, and 21% of calories, respectively. In high sucrose (HS) or low sucrose (LS) diets, starch was replaced by sucrose. Rats fed LST and LS diets had decreased liver weight compared to those fed HST and HS diets, while liver microsomal protein content (mg/gm liver) was the same in all groups. Significant decreases in microsomal cytochrome P-450 from the basal level were observed in all diets over the period of experimental feeding. This decrease was more prominent with HST or HS diets compared to LST or LS dietary groups. HS diet feeding produced this decrease in cytochrome P-450 levels by 3 days; however, animals on HST diet required 7 days of feeding before they experienced a similar decrease in cytochrome P-450 levels. At 14 days, HST-fed animals had 52% lower liver microsomal cytochrome P-450 than did LST-fed animals. HS-fed animals had 36% lower cytochrome P-450 than LS-fed at 28 days. Similar results were observed for dietary effects on cytochrome b5. Aminopyrine demethylase activity decreased steadily on all diets. p-Nitrophenol glucuronidation was significantly increased in all dietary groups after 2 weeks of diet feeding. These results suggest that dietary carbohydrates and fat (particularly the relative quantities of carbohydrate and fat) may significantly influence the hepatic drug-metabolizing enzymes. It is speculated that these changes may occur due to alteration in the phospholipid composition of endoplasmic reticulum or by limiting the supply of cofactor(s) necessary for optimal mixed function oxidation and conjugation.

Endotoxin and low protein diet induced depression of the rat hepatic drug metabolism.

The effects of the combination of low protein diet feeding and endotoxin (E. coli, serotype 026 B6) upon rat hepatic microsomal mixed function oxidase (MFO) enzymes were investigated. Short-term (7 days) feeding of low protein (8%) diet and acute (single dose) exposure to endotoxin resulted in an additive decrease in MFO enzymes. However, chronic (7 days) endotoxin exposure did not depress liver microsomal MFO enzyme activities except for aniline hydroxylase. Long-term (105 days) feeding of the low protein diet and acute endotoxin exposure further decreased aminopyrine N-demethylase and benzo(a)pyrene hydroxylase activities compared to individual treatments. These results suggest that, under these experimental conditions, the two host-related environmental factors interact and potentiate a decrease in rat hepatic microsomal drug metabolizing enzymes. These observations may be of clinical relevance to explain altered drug reactions in patients with gram-negative infections and endotoxemia under the conditions of malnutrition.