NH4C1 and protein metabolism in human gingival fibroblasts

Abstract – The biologic effect of ammonia was studied in cultures of fibroblasts isolated from human gingiva. NH_CI in the range 2–20 mu was found to exhibit a concentration dependent growth inhibitory effect, with a delayed action wllich was most pronounced at low concentrations. Concomitant with the growth inhibitor)'effect a significant cellular accumulation of protein was evident. No effect on protein synthesis in general, as measured by G-protine incorporation, was found, whereas some inhibitory effect on collagen biosynthesis was indicated. Secretion of C-collagen and other labeled proteins was not affected. The only pronounced effect of ammonia on metabolism of the l4C-labeled proteins was an inhibition of the intracellular degradation of newly synthesized collagen, the lysosomes being suggested as the site for this degradation.     

Response of Rat Tracheal Epithelium to Ozone and Oxygen Exposure in Vitro

Response of Rat Tracheal Epithelium to ozone and Oxygen Exposurein Vitro. NIKULA, K. J., AND WILSON, D. W. (1990). Fundam. Appl.Toxicol. 15, 121–131. Although ozone-induced epithelialinjury in vivo has been morphologically characterized, effectsof gaseous oxidants on respiratory epithelium in organ culture,where tissue organization is maintained but systemic influencesare eliminated, have not been thoroughly investigated. In thisstudy, we exposed tracheal organ cultures from rats to 95% oxygenand 1 ppm ozone, alone and in combination, to determine (1)whether epithelial responses to ozone similar to those observedin vivo occur in airways separated from systemic physiologic,secretory, and inflammatory reactions; (2) whether concentrationsof oxygen sufficient to potentially cause oxidant injury resultin morphologic epithelial alterations similar to those thatoccur in ozone toxicity; and (3) if the combined oxidant insultof oxygen and ozone results in more severe damage to the trachealepithelium than occurs with ozone in air. Tracheal organ cultureswere exposed to filtered air and 5% carbon dioxide; filteredair, 5% carbon dioxide, and 1 ppm ozone; 95% oxygen and 5% carbondioxide; or 95% oxygen, 5% carbon dioxide, and 1 ppm ozone for96 hr. Light- and quantitative electron-microscopic evaluationshowed that epithelia exposed to 1 ppm ozone in air exhibitedloss of ciliated cells and ciliated cell damage. The epitheliaexposed to 95% oxygen and 5% carbon dioxide were pseudostratified,columnar, ciliated, and hyperplastic. Epithelia exposed to 95%oxygen plus 1 ppm ozone were stratified and nonciliated or verysparsely ciliated. The predominant cell types in epithelia exposedto oxygen plus ozone were serous cells and metaplastic cells,and focal aggregates of adherent necrotic cells were present.We conclude that there was a synergism between oxygen and ozoneexposure leading to enhanced epithelial injury and metaplasia.     

Comparative Effects of Immunotoxic Chemicals on in Vitro Proliferative Responses of Human and Rodent Lymphocytes

Comparative Effects of Immunotoxic Chemicals on in Vitro ProliferativeResponses of Human and Rodent Lymphocytes. LANG, D. S., MEIER,K. L., AND LUSTER, M. I. (1993). Fundam. Appl. Toxicol. 21,5357–545. In order to determine the comparability of human and rodentin vitro systems, the direct effects of various therapeuticor environmental chemicals on proliferative responses of lymphocytesof mouse, rat, and human origins were examined and analyzedby a detailed statistical approach. Four compounds of diversestructure and mechanism of action which are known to impairlymphocyte transformation, such as hydroquinone, T-2 toxin,lead nitrate, as well as the widely used immunosuppressive drugcyclosporin A, were chosen as model test substances. T cellswere stimulated by phytohaemagglutinin as well as monoclonalantibodies directed at the T cell receptor/CD3 complex, whileB cells were activated by the T-independent mitogens, includingStaphylococcus aureus cells, Escherichia coli lipopolysaccharide,and Salmonella typhimuriummitogen with specificity for human,mouse, and rat lymphocytes, respectively. In almost all casesthe chemicals altered lymphoproliferative responses in a concentration-relatedmanner in all three species. In general, overall similaritiesin the relative sensitivity of lymphoblastogenesis were obtainedwhen the human dose-response curves were compared to the rodentresponse curves. Frequent, statistically significant species-dependentdiscrepances of the overall response curves between mice andrats were observed. Large, statistically significant differenceswere observed for inorganic lead, revealing obvious divergencesof the effect patterns in all cases, across all species. Inthis case, rodent species, especially the rat, were very sensitiveto immunomodulation by lead, whereas human cells were relativelyresistant. It is suggested that direct interspecies comparisonsof immunological effects due to chemical treatment in vitrocan provide a greater understanding of the relationship betweenanimal and human data, which will improve the confidence ofextrapolation from findings in laboratory animals to human healthrisk.     

Thermal Facilitation of Lymphocyte Trafficking Involves Temporal Induction of Intravascular ICAM‐1

Objective: Fever is associated with improved survival, although its beneficial mechanisms are poorly understood. Previous studies indicate that the thermal element of fever augments lymphocyte migration across high endothelial venules (HEVs) of lymphoid organs by increasing the intravascular display of a gatekeeper trafficking molecule, intercellular adhesion molecule‐1 (ICAM‐1). Here, we evaluated the spatio‐temporal relationship between the thermal induction of intravascular ICAM‐1 and lymphocyte trafficking. Methods: Intravascular ICAM‐1 density was quantified by immunofluorescence staining in mice exposed to fever‐range whole‐body hyperthermia (39.5±0.5°C). ICAM‐1–dependent lymphocyte trafficking was measured in short‐term homing assays. Results: A linear relationship was observed between the duration of heat treatment and intravascular ICAM‐1 density in HEVs with maximal responses requiring sustained (i.e., five hours) thermal stress. Circulating lymphocytes were found to sense incremental changes in ICAM‐1 on HEVs, such that trafficking is proportional to the intravascular density of ICAM‐1. We further identified a hydroxamate‐sensitive shedding mechanism that restores ICAM‐1 expression to homeostatic levels following the cessation of thermal stress. Conclusions: The time‐dependent response to thermal stress indicates that ICAM‐1 density governs the efficiency of lymphocyte interactions with HEVs in vivo. These studies highlight the dynamic role of the microcirculation in promoting immune surveillance during febrile inflammatory responses.     

Effect of fluoride on protein and collagen biosynthesis in rabbit dental pulp in vitro

abstract – The time course for incorporation of ¹⁴C-proline into various fractions of rabbit dental pulp in vitro has been measured. In the TCA-soluble precursor pool a steady state level of activity was indicated upon incubation after 3 h, whereas incorporation into protien and ¹⁴C-hydroxyproling, i.e. collagen formation, increased lineraly for 9 h, leaving off upon further incubation. A lag period of about 3 h was indicated for the appearance of high molecular weight ¹⁴C-activity, including ¹⁴C-hydroxyproline, in the medium, increasing linearly from 3 h to the end of the incubaition period (22 H). in this system, fluoride exhibited a dose-dependent inhibitory effect. at 5.3 mM fluoride the uptake of ¹⁴C-proline into the TCA-soluble pool was inhibited by about 50%, and the incorporation into protein and the subsequent conversion to hydroxyproline by about 90 and 60%, respectively. Release of collogen, i.e. ¹⁴C-hydrozyproline-contaning material, seemed to be the process most sensitive to fluoride; it was inhibited by about 50% at the lowest concertration (1.3 mM) tested.     

Alkali soluble and alkali insoluble fluoride retention in demineralized enamel in vivo

Abstract – Demineralization of enamel was induced by applying orthodontic bands in 15 patients having two of their premolars extracted for orthodontic reasons. After a 4-wk caries induction period, eight patients were instructed to rinse their teeth once daily with a neutral 0.05% NaF solution, whereas seven patients received a single treatment with a neutral 2% NaF solution. The bands were reattached to the teeth during the fluoride treatment period and the teeth were extracted after two more weeks. Three consecutive enamel layers were etched off, and a significant uptake of fluoride in all three layers were found in both treatment groups. A larger part of the deposited fluoride was retained in an alkali insoluble form (i.e. fluorapatite) compared with previous studies of sound enamel. It is suggested that the chemical conditions in the cariogenic milieu were favorable for transformation of the fluoride into a stable apatite structure.