Toxicology: past, present, and future.

Toxicology is the study of poisons and poisoning and has an ancient and venerable history. Although there have been numerous notorious poisonings throughout the ages and rather astute descriptions of toxic agents, the scientific study of toxicology did not commence until the 19th century. There was rapid development of analytical methods in the late 19th century and then an acceleration of both method and scientific development in the latter half of the 20th century. Toxicology today can be subdivided into clinical toxicology, forensic toxicology, industrial or occupational toxicology, environmental toxicology, pharmaceutical toxicology, experimental toxicology, and workplace drug testing. The historical development of these overlapping areas of toxicology will be discussed, culminating in a prediction as to what the future may bring.

A skeleton and neural network-based approach for identifying cosmetic surface flaws.

This paper introduces an approach to cosmetic surface flaw identification that is essentially invariant to changes in workpiece orientation and position while being efficient in the use of computer memory. Visual binary images of workpieces are characterized according to the number of pixels in progressive subskeleton iterations. Those subskeletons are constructed using a modified Zhou skeleton transform with disk shaped structuring elements. Two coding schemes are proposed to record the pixel counts of succeeding subskeletons with and without lowpass filtering. The coded pixel counts are on-line fed to a supervised neural network that is previously trained by the backpropagation method using flawed and unflawed simulation patterns. The test workpiece is then identified as flawed or unflawed by comparing its coded pixel counts to associated training patterns. Such off-line trainings using simulated patterns avoid the problems of collecting flawed samples. Since both coding schemes tremendously reduce the representative skeleton image data, significant run time in each epoch is saved in the application of neural networks. Experimental results are reported using six different shapes of workpieces to corroborate the proposed approach.

Mobilization of iron by chiral and achiral anionic 3-hydroxypyrid-4-ones.

In the search for 3-hydroxypyrid-4-ones with enhanced iron-mobilizing ability, seven chiral, anionic amino acid derivatives of maltol (3-hydroxy-2-methyl-4-pyrone) have been synthesized, utilizing L-methionine, L-serine, L-leucine, L-phenylalanine, L-glutamic acid, and the D- and L-isomers of alanine. Two achiral, aromatic compounds were also synthesized and compared with the phenylalanine derivative. The biliary iron excretion following iv injection and the urinary iron excretion following po administration were measured using female Sprague-Dawley rats and compared to that of the standard, 1,2-dimethyl-3-hydroxypyrid-4-one (L1). While none of the compounds was as effective as L1 in enhancing the urinary excretion of iron, all monoanionic chelators increased excretion relative to the controls. All monoanionic compounds were at least equivalent to L1 in enhancing the biliary excretion of iron, with the methionine, leucine, and benzoate derivatives surpassing the standard and the other aromatic compounds also showing strong activity. The dianionic glutamate derivative showed low activity relative to the controls for both urinary and biliary iron excretion. No significant difference in iron excretion was observed due to variation in chirality; molecular weight and the number of negative charges appeared to have the greatest influence on the ability of the various derivatives to enhance iron excretion. In order to evaluate the relative purity of the stereoisomers, the alanine derivatives were analyzed by circular dichroism. Further characterization was provided by UV/vis spectroscopy for all compounds and X-ray crystallography for the novel dianionic derivative.

Vigabatrin.

The discovery of gamma-aminobutyric acid (GABA) as the first major inhibitory neurotransmitter and a program exploring the use of enzyme inhibition as a therapeutic tool provided the basis for the conception of vigabatrin (VGB, Sabril). This molecule, an analogue of GABA, has a highly specific activity as an enzyme-activated irreversible inhibitor of GABA-transaminase causing several-fold increases in the concentration of brain GABA. In animal models for epilepsy, it was found to have a rather different spectrum of activity than conventional antiepileptic drugs (AEDs). The clinical development of VGB was delayed by the finding of focal areas of reversible microvacuolation in the white matter of the brains of rodents and dogs. An extensive human safety program has confirmed that this finding is species specific and does not occur in humans. Clinically, VGB is well tolerated and has been shown to be specially effective in the management of partial seizures that have failed to respond to other AEDs. In most controlled studies, about 50% of patients with previously uncontrolled seizures have a 50% reduction in frequency and about 4-5% become seizure-free. In children, it also appears to be especially effective in the management of infantile spasms as well as in partial seizures. VGB offers a significant improvement in the management of epilepsy and is now under development as a first-line agent.

Neuropathologic findings in patients receiving long-term vigabatrin therapy for chronic intractable epilepsy.

Vigabatrin is a new antiepileptic drug that acts by the irreversible inhibition of gamma-aminobutyric acid (GABA) aminotransferase. During animal safety testing, vigabatrin was found to cause reversible intramyelinic edema in the brains of rodents and dogs but not in primates. In humans, the drug is well tolerated, and extensive clinical, neurophysiologic, neurochemical, and psychometric testing has failed to demonstrate any evidence of neurotoxicity. Neuropathologic examination has now been carried out on 62 patients with refractory epilepsy, who were on vigabatrin therapy either prior to undergoing neurosurgery for their epilepsy or before death. A further ten similar cases have been included in the study from age-matched patients with refractory epilepsy who had not been treated with vigabatrin prior to surgery or death. None of the neuropathologic changes seen in the preclinical animals studies have been observed in the human cases. In no case was there considered to be any evidence of myelin microvacuolation or myelin sheath splitting that could be attributed to vigabatrin treatment. Demyelination has never been observed in either the animal or human material. These findings support the clinical tolerability seen in long-term treatment.

Zinc nutrition in fetal alcohol syndrome.

Because alcohol has an adverse effect on zinc homeostasis, this study was designed to study if zinc content of the diet modifies the severity of fetal alcohol syndrome in a mouse model. The effect of varying zinc intake on the progeny of pregnant mice fed a liquid diet containing 15% of the calories as ethanol was studied. Prenatal mortality was higher when the mothers consumed alcohol with inadequate zinc intake. Because of the adverse effect of alcohol on zinc homeostasis and because zinc deficiency has been shown to potentiate alcohol embryopathy, one group was given zinc supplementation to four times the Recommended Dietary Allowance. Supplemental zinc above the Recommended Dietary Allowance was not protective and appeared to have an adverse effect on fetal weight and prenatal mortality. These results suggest that zinc intake should be optimized during pregnancy but that zinc supplementation above the Recommended Dietary Allowance does not reduce the incidence or severity of fetal alcohol syndrome.

Urine screening for abused drugs in new admissions to a VA hospital.

The urine samples from two groups of Veteran's Administration patients newly admitted to general psychiatry units were screened in 1985 and in 1987-88 for abused drugs. The results were compared with urine samples from controls with similar age distributions admitted to an alcohol and drug abuse unit or to medical-surgical units. About 40% of all newly admitted patients were positive for one or more controlled drugs, but there were no significant differences among patient groups in the percentage of urine samples positive for these drugs. Marijuana and benzodiazepines were detected frequently in all patient groups and often in combination, although opiates also were frequently detected in the urine samples from the medical-surgical patients. There was a clear decrease in drug-positive samples with age in all patient groups, much of which could be accounted for by decreased marijuana detection.

In vivo studies with dimethyldithiocarbamate, a possible new antimicrobial for use against Aspergillus fumigatus in poultry.

Dimethyldithiocarbamate (DmDTC), the carbamate analogue, was tested for therapeutic efficacy in a series of in vivo challenge trials using 5- and 10-week-old white leghorn chickens. Challenge organisms were Pasteurella multocida X-73, Escherichia coli O1:K1, and Aspergillus fumigatus. Birds were evaluated for survival rates, lesion scores, and the rate at which the bacteria or mold could be reisolated following challenge. Results showed DmDTC to be ineffective against P. multocida and E. coli at the treatment levels and in the form used in these trials, but DmDTC significantly reduced lesion scores and inhibited the rate of isolation of A. fumigatus compared with untreated infected birds.

Combination and individual antitumor effects of hyperthermia, cisplatin, and selected dithiocarbamates.

The antitumor effects produced by combinations of cisplatin (Pt), substituted dithiocarbamates (dimethyldithiocarbamate [DmDTC] and sodium N-methyl-D-glucamine dithiocarbamate [NMGDTC]) and hyperthermia (H) were measured and compared to those produced by single agents alone in C3H/HeN mice bearing the transplantable radiation-induced fibrosarcoma, RIF-1, in one or both hind feet. The average tumor volumes of control and treatment groups were compared periodically after treatment with H. Combinations of H and Pt completely resolved established foot tumors in 10/13 mice. However, evidence of long-term nephrotoxicity and gastrointestinal (GI) toxicity became evident causing death of these mice within 120 to 122 days after tumor inoculation. Hyperthermia plus DmDTC resolved tumors in heated and non-heated feet in 3/8 mice, thus demonstrating both ipsilateral and contralateral anti-tumor activity. Furthermore, H-Pt-NMGDTC produced complete tumor resolution in 7/13 mice; these mice survived and were tumor-free 180 days post inoculation and autopsies revealed no appreciable nephro- or GI toxicity. In addition, 4/8 mice underwent complete tumor resolution in heated left feet plus dramatic retarding of tumor growth in unheated right feet (ipsilateral and contralateral anti-tumor effects). Five heat-treated left foot tumors resolved in the H-Pt-DmDTC group with one mouse demonstrating resolution of tumor in both feet. Advanced foot tumors were treated with H-DmDTC and H-Pt-DmDTC. Hyperthermia and Pt were administered on day 0 of the experiment and DmDTC on days 0 through 3; dramatic tumor shrinkage continued through day 6 for a total of 75 to 80 percent reduction of tumor volume in both groups. The concurrent administration of DmDTC or NMGDTC with H and Pt prevented or greatly reduced nephrotoxicity and GI toxicity in all experiments without retarding anti-tumor efficacy.

Effects of repeated drug holidays on serum haloperidol concentrations, psychiatric symptoms, and movement disorders in schizophrenic patients.

In a crossover experiment the authors investigated the effects of repeated weekly, 2-day, haloperidol drug holidays on serum haloperidol concentrations, mental status, and neuroleptic-induced movement disorders in seven chronic schizophrenic patients. Haloperidol concentrations decreased about 64% during the initial 36 hours of drug holiday and subsequently increased slightly during the next 24 hours of drug holiday. Two-day weekly drug holidays for 6 weeks resulted in an average reduction of 25% in serum haloperidol concentrations at all drug holiday points. Mental status and movement disorders scores, rated by observers blind to the drug-holiday condition, were not significantly affected by drug holidays.

In vitro studies with dimethyldithiocarbamate, possible new antimicrobial for use in poultry.

Tests were conducted to determine the in vitro efficacy of the dithiocarbamate analogue, dimethyldithiocarbamate (DmDTC), against selected poultry pathogens. Organisms studied were two bacteria, Pasteurella multocida and Escherichia coli, and a mold, Aspergillus fumigatus. Zone of inhibition and the minimum inhibitory concentration were determined for each organism. DmDTC was effective in vitro against all organisms tested, with A. fumigatus showing greatest overall sensitivity.

Antipseudomonal effects of selected dithiocarbamates alone and in combination with gentamicin or aztreonam.

The antipseudomonal effects conferred by combinations of substituted dithiocarbamates, gentamicin or aztreonam (Azactam) were measured and compared to those produced by single agents alone in female BALB/C mice bearing overwhelming Pseudomonas aeruginosa infections. Dimethyldithiocarbamate (DMDTC), diethyldithiocarbamate (DEDTC), and sodium N-methyl-D-glucamine dithiocarbamate (NMGDTC) were chosen as representative substituted dithiocarbamates. All three dithiocarbamates rescued some cisplatin-immunosuppressed mice from pseudomonal infections but DMDTC and NMGDTC produced better results than DEDTC. Single daily injections of DMDTC at doses of 5 mg/kg/day or higher for a total of 7 days rescued 14 of 18 mice given 10(6) viable Pseudomonas aeruginosa by tail vein inoculation. Similar dose regimens of 10 mg/kg/day or higher NMGDTC for a total of 7 days rescued 15 of 18 mice. DEDTC at doses of 5 mg/kg/day or higher for 7 days rescued 7 of 18 mice. Combinations of DMDTC or NMGDTC with gentamicin failed to produce better results than each agent alone in mice immunosuppressed with methyl-prednisolone (Solumedrol) at the dose range evaluated in mice inoculated with 10(6) viable organisms via tail veins. Combinations of DMDTC and aztreonam were effective in mice immunosuppressed with methylprednisolone and given overwhelming numbers of viable Pseudomonas aeruginosa (10(7) or more, ip). Combinations of 6 mg/kg/day or higher of each agent with multiple daily injections rescued 11 of 18 mice. The results yielded by either agent alone were not impressive. Similar results were obtained when mice immunosuppressed with cisplatin were given ip injections of 10(8) or more viable bacteria. No mice were rescued by the use of DMDTC, NMGDTC, aztreonam or gentamicin only. Combinations of DMDTC (6 mg/kg) and aztreonam (6 mg/kg) with multiple daily injections for seven days rescued 11 of 20 infected mice while combinations of NMGDTC with aztreonam were less effective (3 of 20 rescued). The concurrent administration of DMDTC and aztreonam offers considerable promise in the treatment of overwhelming pseudomonal infections in mice and may prove to be of value in human patients as well.

Serum haloperidol and neuroleptic receptor levels in chronic psychosis.

Serum haloperidol and serum dopamine blocking activity were measured, and steady state levels were compared in 22 chronic male schizophrenic patients. Haloperidol levels were measured by high pressure liquid chromatography (HPLC), and dopamine blocking activity was measured by a radioreceptor assay (NRRA). Clinical status was determined by the Brief Psychiatric Rating Scale (BPRS) and the Abnormal Involuntary Movement Scale (AIMS). Patients were stabilized on individual doses of haloperidol for at least three weeks and dosages ranged from five to 200 mg per day. All measures were determined on two occasions, one week apart. All measures (AIMS, BPRS, HPLC, and NRRA) showed a high degree of repeated test reliability. The behavioral measures showed a high degree of interobserver reliability on both occasions. There were significant correlations at both time points among haloperidol dosage, serum haloperidol levels, and dopamine blocking activity. Although the correlations between serum levels measured by HPLC and NRRA were positive and significant on both occasions, they never accounted for more than 58 percent (coefficient of variation) of the total variance.

Mechanical induction of osteogenesis: the importance of pin rigidity.

Eight dogs, divided into two groups of four by varying pin rigidity, underwent 15% left tibial lengthening by the Ilizarov method. In group I, "tensioned" 1.6-mm wires maintained a rigidity approaching that of 4.0-mm pins. In group II, the wires, maintained at half the tension, averaged 45% of the rigidity measured in group I. All dogs in group I filled the experimental gap with de novo osteogenesis, whereas all of the dogs in group II prematurely bridged the gap, arresting the process of osteogenesis. From these experimental results, clinical trials have been started using commercially available external fixation devices utilizing pins with equivalent rigidity.

Mechanical induction of Osteogenesis. Preliminary studies.

The animal model developed in the Soviet Union by Ilizarov has been reliably reproduced by us for the mechanical induction of osteogenesis using slow distraction. Our preliminary studies in six adult dogs indicate that this osteogenesis originates from well-structured intramembranous ossification, with rapid maturation to lamellar bone, indistinguishable from surrounding host bone. Mineralization increases steadily, reaching critical levels for radiographic visualization between Days 21 and 28. In this model, the osteogenic area then exceeds normal bone density temporarily but returns to normal density within three months. Distraction for 28 consecutive days (at 0.25 millimeters every six hours using rigid transfixion wires, as Ilizarov describes) reliably lengthened the tibiae by 12 percent, increasing mass by 27 percent, and volume by 26 percent with only a one percent change in overall density. The process required four months to add 24 millimeters of mature, lamellar bone capable of full weight-bearing by the dogs. This rate of osteogenesis, estimated at 202 microns per day, is four times faster than a human's fastest growth plate (child's distal femur at 50 microns per day). Calcium/collagen ratios did not differ significantly from normal bone controls.

Instrumentation and techniques for therapeutic drug monitoring.

This article describes and compares the predominant systems for performing therapeutic drug monitoring. Advantages and disadvantages, costs, and future trends are noted. Useful information for the initiation or expansion of this clinical service is provided.

Effects of diethyldithiocarbamate and structural analogs in mice with systemic candidal infections.

Three different substituted dithiocarbamates: sodium diethyldithiocarbamate (DDTC), sodium dimethyldithiocarbamate (DmDTC), and sodium N-methyl-D-glucamine dithiocarbamate (NMG-DTC) were evaluated for their ability to combat the growth and development of three human pathogenic strains of Candida albicans, in vitro and in vivo, in mice. DDTC and DmDTC produced marked growth inhibition on agar plates, in vitro, of three different strains of Candida albicans, while NMG-DTC displayed little inhibitory effect. Low, nontoxic doses of each compound administered to immunosuppressed mice exhibited impressive therapeutic effects in treating candidiasis. NMG-DTC showed the best consistent therapeutic antifungal effect against Candida albicans in mice immunosuppressed with Solu-Medrol. Combinations of low doses of DDTC and Amphotericin-B appeared to be effective in treating systemic candidal infections, and the results suggested that these combinations may offer therapeutic advantages over those produced by the use of either agent alone.