Colonization of the cardiovascular endothelium by viridans group streptococci can result in infective endocarditis and possibly atherosclerosis; however, the mechanisms of pathogenesis are poorly understood. We investigated the ability of selected oral streptococci to infect monolayers of human umbilical vein endothelial cells (HUVEC) in 50% human plasma and to produce cytotoxicity. Planktonic Streptococcus gordonii CH1 killed HUVEC over a 5-h period by peroxidogenesis (alpha-hemolysin) and by acidogenesis but not by production of protein exotoxins. HUVEC were protected fully by addition of supplemental buffers and bovine liver catalase to the culture medium. Streptococci were also found to invade HUVEC by an endocytic mechanism that was dependent on polymerization of actin microfilaments and on a functional cytoskeleton, as indicated by inhibition with cytochalasin D and nocodazole. Electron microscopy revealed streptococci attached to HUVEC surfaces via numerous fibrillar structures and bacteria in membrane-encased cytoplasmic vacuoles. Following invasion by S. gordonii CH1, HUVEC monolayers showed 63% cell lysis over 4 h, releasing 64% of the total intracellular bacteria into the culture medium; however, the bacteria did not multiply during this time. The ability to invade HUVEC was exhibited by selected strains of S. gordonii, S. sanguis, S. mutans, S. mitis, and S. oralis but only weakly by S. salivarius. Comparison of isogenic pairs of S. gordonii revealed a requirement for several surface proteins for maximum host cell invasion: glucosyltransferase, the sialic acid-binding protein Hsa, and the hydrophobicity/coaggregation proteins CshA and CshB. Deletion of genes for the antigen I/II adhesins, SspA and SspB, did not affect invasion. We hypothesize that peroxidogenesis and invasion of the cardiovascular endothelium by viridans group streptococci are integral events in the pathogenesis of infective endocarditis and atherosclerosis.Viridans group streptococci comprise a large proportion of the commensal bacteria that colonize oral surfaces (20,24,25). These bacteria frequently enter the bloodstream following trauma to oral tissues (12,17,41,58) and can then adhere to surfaces of abnormal or previously damaged heart valves (15,21,29,47) or become implanted in arterial atherosclerotic plaques (11). Streptococci growing on heart valve surfaces (causing infective endocarditis) become encased in a matrix of fibrin and platelets, which form macroscopic verrucous lesions and can lead to valve perforation, abnormalities in cardiac conduction, valve ring abscesses, pericarditis, aneurysm of the sinus of Valsalva, and release of peripheral emboli (21, 56). Viridans group streptococci are the most common cause of native valve endocarditis in humans, accounting for 45 to 80% of cases (5, 55). A variety of virulence factors have been implicated in the initial colonization of bacteria to cardiac valve surfaces (1, 32, 49, 50, 54), but those responsible for the ultimate destruction of underlying tissues are not well unders...

No abstract

The discovery of neurobehavioral hazards is an important goal of the majority of the toxicological studies. Quite often it is possible to detect signs of neurobehavioral toxicity through non-instrumental observations and from the response of the animals to simple manipulations. Psychopharmacologists have long used these techniques to identify new drugs with potential usefulness as psychotropic agents. Their approach may also be applicable for the detection of neurotoxic chemicals. Based on a review of the literature and personal experience a neurobehavioral check-list is proposed which can easily be incorporated into the animal care and treatment routine used in single- and repeated-dose toxicity studies with small rodents. The instrumental tests which measure motor activity, neuromuscular functions, muscle strength, emotionality and social behavior are also discussed. The usefulness of these procedures in toxicology is not yet established. Their introduction into the testing routine creates considerable logistic difficulties and might not be compatible with good laboratory practices. Therefore, it is suggested to explore the procedures developed by psychopharmalogists and behavioral scientists and to validate them with a variety of neurobehavioral toxins. Tests which produce relevant and reproducible data may then be added to the toxicological protocols, preferably within the framework of safety pharmacology.

Various neuropharmaeologieal screening tests, i.e., 2-Bottle Test, Hot Plate Test, Foot Print Test, Glass Bead Test and Rotating Rod Test, were performed repeatedly during a subacute toxicity study of isoniazid, pyridoxine HC1, and hexachlorophene in rats. Groups of rats were sacrificed during the course of the experiment and subjected to neuropathological examination. The Foot Print Test and Glass Bead Test, the two procedures which required the most extensive training of the animals, were performed faultlessly, even by partly paralyzed rats. The 2-Bottle Test disclosed an unusual change in drinking behavior in isoniazid-treated rats: total fluid intake was significantly increased during treatment-free days on weekends. In the Hot Plate Test evidence of a weak analgesic effect of isoniazid was found which was present before peripheral nerve damage was established. Pyridoxine and hexachlorophene induced a slight disturbance of heat perception at neurotoxic doses. The Rotating Rod Test disclosed changes in neuromuscular functions with all 3 test substances which were often present before peripheral neuropathy became demonstrable. It is concluded that neuropharmacological screening tests which require little training of the animals are best suited to uncover neurotoxic drug effects. Inclusion of such tests into routine toxicity studies helps to identify those animals for which a detailed neurohistological examination is justified.The conventional toxicological protocol was originally designed to detect structural organ changes and blood dyscrasias. Additional laboratory studies were included to monitor liver and kidney function and other biochemical parameters. Although many drug side effects are functional in nature, only limited use is made of pharmacological tests in routine toxicology. To include repeated pharmacological testing would add an enormous amount of work to the toxicological procedures. This would only be acceptable if such measurements were likely to provide significant information not obtained by the conventional protocol.To investigate the usefulness of functional studies in routine toxicology, a series of simple neuropharmacological screening tests were included into a subacute toxicity experiment of isoniazid (INH), pyridoxine HC1 (P) and hexachlorophene (HCP) in rats. The 3 drugs were selected because they possess neurotoxic properties at high doses [1][2][3][4]. In order to correlate pharmacological effects with neuropathological changes, additional groups of rats were treated with the same drugs and sacrificed at various time intervals during the experiment. MethodsFemale CFN Zti rats weighing 38-53 g were housed singly in Macrolone cages and received Nafag rat pellets and water ad libitum. They were randomly assigned to the experimental groups and treated with 3 drugs as indicated in the Table. Controls received equal volumes of water (per os) or 0.9~ saline (i.p.). INH and P were dissolved in water, HCP was suspended in a 2~ gum arabic solution. All treatments were given on 5 days p...