Efficacy of a sustained-release device containing chlorhexidine and Ca(OH)2 in preventing secondary infection of dentinal tubules

This study was conducted to evaluate the efficacy of the antibacterial activity of Ca(OH)2 and a sustained-release device containing chlorhexidine (SRD) in both sterilization and prevention of secondary infection of the root canal system. Bovine root dentine specimens previously incubated with Streptococcus faecalis were used in this experiment. Two different formulations of the SRD (differing in their cross-linkage), Ca(OH)2 and normal saline (control) were evaluated. The degree of bacterial infection of the root canal was tested after incubation periods of 24 h, 72 h and 7 days with these medicaments. Their efficacy in preventing secondary infection after recontamination was tested after 72 h and 7 days. The results demonstrated that both formulations of the SRD significantly reduced the bacterial population in the primary infected groups, as well as preventing secondary infection of the dentinal tubules in the recontaminated group. By contrast, Ca(OH)2 did not show any antibacterial activity, and failed to sterilize the dentinal tubules or prevent secondary infection after recontamination at the time periods examined.

Role of oxidized low density lipoprotein in atherogenesis

Evidence to support an important role of oxidative modification in mediating the atherogenicity of LDL continues to grow. New hypotheses suggest mechanisms by which Ox-LDL or products of Ox-LDL can affect many components of the atherogenic process, including vasomotor properties and thrombosis, as well as lesion initiation and progression itself. These ideas suggest new approaches, that in combination with lowering of plasma cholesterol, could lead to the prevention of atherosclerosis and its complications.

Macrophages and smooth muscle cells express lipoprotein lipase in human and rabbit atherosclerotic lesions

Lipoprotein lipase (LPL; EC 3.1.1.34) may promote atherogenesis by producing remnant lipoproteins on the endothelial surface and by acting on lipoproteins in the artery wall. In vitro, smooth muscle cells and macrophages synthesize LPL, but in human carotid lesions only a few smooth muscle cells were reported to contain LPL protein. Endothelial cells do not synthesize LPL in vitro, but in normal arteries intense immunostaining for LPL is present on the endothelium. We used Northern blot analysis, in situ hybridization, and immunocytochemistry of human and rabbit arteries to determine cellular distribution and the site of the synthesis of LPL in atherosclerotic lesions. Northern blot analysis showed that LPL mRNA was detectable in macrophage-derived foam cells isolated from arterial lesions of "ballooned" cholesterol-fed rabbits. In situ hybridization studies of atherosclerotic lesions with an antisense riboprobe showed a strong hybridization signal for LPL mRNA in some, but not all, lesion macrophages, which were mostly located in the subendothelial and edge areas of the lesions. Also, some smooth muscle cells in lesion areas also expressed LPL mRNA. Immunocytochemistry of frozen sections of rabbit lesions with a monoclonal antibody to human milk LPL showed intense staining for LPL protein in macrophage-rich intimal lesions. The results suggest that lesion macrophages and macrophage-derived foam cells express LPL mRNA and protein. Some smooth muscle cells in the lesion areas also synthesize LPL. These data are consistent with an important role for LPL in atherogenesis.

Feasibility of using an oleate-rich diet to reduce the susceptibility of low-density lipoprotein to oxidative modification in humans

Oxidized low-density lipoprotein (LDL) is more atherogenic than native LDL. The initial step in the oxidation is the peroxidation of polyunsaturated fatty acids. Thus, decreasing the concentration of polyunsaturated fatty acids should reduce the susceptibility of LDL to oxidation. Therefore, we tested the possibility that diets enriched in oleate might result in LDL that is less susceptible to oxidative modification. LDL isolated from subjects consuming an oleate-enriched diet, compared with LDL from subjects on a linoleate-enriched diet, contained significantly more oleate (28.7% vs 11.5%) and less linoleate (31.9% vs 50.9%). Generation of conjugated dienes was significantly lower in the LDL from the oleate group. Most important, after incubation with endothelial cells, LDL from the oleate group underwent less degradation by macrophages. These studies demonstrate the feasibility of altering the diet in a way that will not raise LDL cholesterol concentrations and yet will decrease the susceptibility of LDL to oxidative modification.

Caries experience, periodontal treatment needs, salivary pH, and Streptococcus mutans counts in a preadolescent Down syndrome population

The prevalence of dental caries and periodontal treatment needs in an institutionalized population with Down syndrome was examined and the relationship between caries prevalence, salivary pH, and salivary levels of Streptococcus mutans was studied. Thirty-two children with Down syndrome, aged 8 to 13, were compared with two control groups of similar age ranges: healthy children and non-Down mentally retarded (MR) children living in the same institution as the Down syndrome population. The gender ratio mixtures in each group also matched the study sample. Caries experience as indicated by decayed, missing, and filled surfaces (DMF-S) showed significantly lower mean scores for the Down syndrome group compared with both control groups. A similar pattern was found when evaluating the mean numbers of decayed surfaces. Streptococcus mutans counts, expressed as number of colony-forming units on mitis salivarius agar plates among the Down syndrome group, were the lowest, although not statistically significant compared with the counts of the healthy children. Both groups had bacterial counts which were significantly lower than those of the MR group. Significant differences between the two institutionalized groups and the healthy group were recorded for the salivary pH levels. The periodontal treatment needs as evaluated by the Community Periodontal Index of Treatment Needs showed significant difference between the MR group versus both the healthy population and the Down syndrome group. On the whole, 84% of the Down syndrome children were cariesfree.

Fibroblast chemotaxis after tendon repair

Healing canine flexor tendons were treated with early controlled passive mobilization. The repair site and proximal and distal tendon stumps were stained for fibronectin and examined by light microscopy at three, seven, eleven, and seventeen days. Fibronectin increased dramatically in the epitenon adjacent to the repair site seven days after repair, a time when epitenon cellular activity was at its peak. By seventeen days, fibronectin staining had decreased substantially, both at the repair site and in the tendon stumps. A delayed increase in fibronectin activity was noted in the endotenon adjacent to the repair site. Fibronectin production appears to be an important component of the early tendon repair process. Fibroblast chemotaxis and adherence to the substratum in the days after injury and repair appears to be related directly to fibronectin secretion. This study is the first to provide documentation of fibronectin localization in a clinically relevant tendon repair model.

Expression of monocyte chemoattractant protein 1 in macrophage-rich areas of human and rabbit atherosclerotic lesions

The recruitment of monocyte-macrophages into the artery wall is one of the earliest events in the pathogenesis of atherosclerosis. Monocyte chemoattractant protein 1 (MCP-1) is a potent monocyte chemoattractant secreted by many cells in vitro, including vascular smooth muscle and endothelial cells. To test whether it is expressed in the artery in vivo, we used Northern blot analysis, in situ hybridization, and immunocytochemistry to study the expression of MCP-1 in normal and atherosclerotic human and rabbit arteries. Northern blot analysis showed that MCP-1 mRNA could be isolated from rabbit atherosclerotic lesions but not from the intima media of normal animals. Furthermore, MCP-1 mRNA was extracted from macrophage-derived foam cells isolated from arterial lesions of ballooned cholesterol-fed rabbits, whereas alveolar macrophages isolated simultaneously from the same rabbits did not express MCP-1 mRNA. MCP-1 mRNA was detected by in situ hybridization in macrophage-rich regions of both human and rabbit atherosclerotic lesions. No MCP-1 mRNA was found in sublesional medial smooth muscle cells or in normal arteries. By using immunocytochemistry, MCP-1 protein was demonstrated in human lesions, again only in macrophage-rich regions. Immunostaining of the serial sections with an antiserum against malondialdehyde-modified low density lipoprotein indicated the presence of oxidized low density lipoprotein indicated the presence of oxidized low density lipoprotein and/or other oxidation-specific lipid-protein adducts in the same areas that contained macrophages and MCP-1. We conclude that (i) MCP-1 is strongly expressed in a small subset of cells in macrophage-rich regions of human and rabbit atherosclerotic lesions and (ii) MCP-1 may, therefore, play an important role in the ongoing recruitment of monocyte-macrophages into developing lesions in vivo.

Alcohol and atherosclerosis

Considerable progress has been made in recent years in our understanding of atherogenesis and, in particular, of how it relates to lipoprotein metabolism. In this conference, we attempt to re-evaluate the data on the relation between alcohol intake and coronary heart disease, emphasizing the effects of alcohol on lipoprotein metabolism. Epidemiologic data generally show an inverse correlation between coronary heart disease risk and moderate alcohol intake (variously defined but generally corresponding to 2 to 4 drinks per day). The potentially drastic effects of excessive alcohol intake on health, however, preclude any recommendation that patients increase their alcohol consumption. Equally, there may be no basis for prescribing moderate alcohol intake but, even here, the data are far from complete. The mechanism by which moderate alcohol intake "protects" remains unclear. Perhaps the best available hypothesis relates to the increased concentration of high-density lipoprotein (HDL) cholesterol associated with moderate alcohol intake. However, it should be stressed that we are still uncertain about the mechanisms linking a high HDL level to protection against coronary heart disease. If a high HDL level is only a marker (and not directly protective), raising HDL levels need not confer protection. Alcoholism, on the other hand, is associated with marked elevation of triglyceride-rich lipoproteins and is among the most common causes of hypertriglyceridemia. Moreover, once hepatic damage occurs, plasma HDL levels may actually be lower than normal. The determining point is that high alcohol intakes are associated with increased overall mortality. Until we know more about the metabolic and behavioral effects of alcohol and about its linkage to atherosclerosis, we have no basis for recommending either that patients increase their alcohol intake or that they start to drink if they do not already.

Topical varnish containing strontium in a sustained-release device as treatment for dentin hypersensitivity

The purpose of this study was to assess the effect of topical application of a sustained-release device in form of a varnish containing strontium chloride on dentinal hypersensitivity. Sixty teeth were selected in ten patients. The teeth were divided in a) varnish application containing strontium chloride, b) varnish application with no active ingredient, c) untreated teeth. Varnish application was carried out by the patients once daily for 30 days. Results show a marked decrease in hypersensitivity to both mechanical (54%) and thermal stimuli (38%) as compared to the placebo and untreated group.

Gene expression in macrophage-rich human atherosclerotic lesions. 15-lipoxygenase and acetyl low density lipoprotein receptor messenger RNA colocalize with oxidation specific lipid-protein adducts

Oxidatively modified low density lipoprotein (LDL) exhibits several potentially atherogenic properties, and inhibition of LDL oxidation in rabbits decreases the rate of the development of atherosclerotic lesions. In vitro studies have suggested that cellular lipoxygenases may be involved in LDL oxidation, and we have shown previously that 15-lipoxygenase and oxidized LDL are present in rabbit atherosclerotic lesions. We now report that epitopes of oxidized LDL are also found in macrophage-rich areas of human fatty streaks as well as in more advanced human atherosclerotic lesions. Using in situ hybridization and immunostaining techniques, we also report that 15-lipoxygenase mRNA and protein colocalize to the same macrophage-rich areas. Moreover, these same lesions express abundant mRNA for the acetyl LDL receptor but no detectable mRNA for the LDL receptor. We suggest that atherogenesis in human arteries may be linked to macrophage-induced oxidative modification of LDL mediated by 15-lipoxygenase, leading to subsequent enhanced macrophage uptake, partly by way of the acetyl LDL receptor.

The effect of sustained-release varnish of chlorhexidine in dental plastic shells on salivary Streptococcus mutans

The suppression of S. mutans is a predominate factor in preventing tooth decay. Sustained-release-delivery varnish of chlorhexidine was applied to dental plastic shells and administered to eight volunteers to be worn while sleeping. Salivary bacterial samples were taken on days 0, 7, 14, 21, 28, 35. A statistically significant reduction in S. mutans counts was recorded during the course of the study while a non-significant reduction in the total bacterial counts was found. Our results indicate that the application of chlorhexidine in the form of slow-release varnish in plastic shells is an effective intraoral drug delivery system resulting in reduction of S. mutans.

Evidence for a dominant role of lipoxygenase(s) in the oxidation of LDL by mouse peritoneal macrophages

It has been suggested that the oxidative modification of low density lipoprotein (LDL) is a key event in atherogenesis. Several mechanisms have been proposed to explain how different types of cells modify LDL. In this study we examine the relative contributions of superoxide anions and cellular lipoxygenase (LO) in the modification of LDL by macrophages. Superoxide dismutase (SOD) inhibited LDL oxidation by macrophages but only by 25%. Under the same conditions, several LO inhibitors (eicosatetraynoic acid (ETYA), piriprost, and A-64077) almost completely inhibited the modification of LDL by macrophages. SOD had a greater inhibitory effect on the modification of LDL by U937 cells and fibroblasts (32% and 64%, respectively) but again LO inhibitors had a much greater effect (79 to 100% inhibition). Incubation of [1-14C]linoleic acid with mouse peritoneal macrophages resulted in its conversion to a single more polar product coeluting with 13- and 9-HODE by reverse phase HPLC. When the cells were preincubated with LO inhibitors, formation of this product was significantly inhibited. It is concluded that the modification of LDL by macrophages is mediated in large part by lipoxygenase-type activity.

Lipoproteins and atherogenesis. Current concepts

The frontiers in atherosclerosis research are moving from lipoprotein metabolism and control of hyperlipidemia to the cellular events in the artery wall. Emerging hypotheses, including the oxidative modification hypothesis, are already suggesting new approaches that could complement and be additive to control of hypercholesterolemia in the prevention of atherosclerosis.

Colocalization of 15-lipoxygenase mRNA and protein with epitopes of oxidized low density lipoprotein in macrophage-rich areas of atherosclerotic lesions

Oxidation of low density lipoprotein (LDL) enhances its atherogenicity, and inhibition of such oxidation decreases the rate of progression of atherosclerotic lesions. The mechanism of LDL oxidation in vivo remains uncertain, but in vitro studies have suggested that cellular lipoxygenases may play a role by initiating lipid peroxidation in LDL. In situ hybridization studies using a 15-lipoxygenase riboprobe and immunostaining using antibodies against 15-lipoxygenase showed strongly positive reactivity largely confined to macrophage-rich areas of atherosclerotic lesions. Polymerase chain reaction with 15-lipoxygenase-specific oligonucleotides and restriction enzyme digestions of the amplified fragment were used to confirm the presence of 15-lipoxygenase message in the reverse-transcribed lesion mRNA. Immunostaining with antibodies reactive with oxidized LDL (but not with native LDL) indicated that the lipoxygenase colocalizes with epitopes of oxidized LDL, compatible with a role for macrophage lipoxygenase in the oxidation of LDL in vivo. Since oxidized LDL is chemotactic for blood monocytes, early lesions might progress at a markedly accelerated rate because of further recruitment of more monocytes which, in turn, would increase further the rate of oxidation of LDL. These data suggest that therapy targeted to block macrophage lipoxygenase activity might decrease the rate of development of atherosclerotic lesions.

Arterial metabolism of lipoproteins in relation to atherogenesis

In this short review we have concentrated on the ways in which modification of LDL structure may account for foam cell formation. We have presented in vivo evidence as well as in vitro evidence supporting the proposition that modification of native LDL is a prerequisite for foam cell formation and atherogenesis. Actually, oxidized LDL can contribute to atherogenesis in other ways as well. Oxidized LDL is chemotactic for circulating monocytes, yet inhibits the motility of the tissue macrophage as shown by Quinn et al. Also, oxidized LDL is cytotoxic as discussed above and this could play a crucial role in the transition from the fatty streak lesion to the clinically more consequential fibrous plaque and complicated lesion. If further research supports the importance of LDL modification in atherogenesis, a whole new array of possibilities opens itself to us for intervention. Anything that interferes with the relevant modifications of the LDL structure would presumably be additive to interventions lowering the plasma concentration of LDL. At the moment, the only such intervention that appears to be feasible is prevention of LDL oxidation. Possibly we may find ways to interfere with immune mechanisms that are involved in some patients; conceivably we might be able to interfere with the aggregation of LDL with itself or with other complexes in the artery wall that appear also to favor initiation of the atherogenic process.

Lipoproteins in normal and atherosclerotic aorta

Each method used for the extraction and isolation of intimal lipoproteins has advantages and disadvantages. Gentle extraction methods are needed to characterize subtle modifications in the structure and biologic properties of the lipoproteins, whereas more aggressive methods are needed if the goal is to maximize the yield of lipoproteins from atherosclerotic arteries. The present paper evaluates different methods used for the isolation of intimal lipoproteins. Normal intima contains remnant-like and low density lipoprotein (LDL)-like particles that more strongly stimulate cholesterol esterification in macrophages than do control plasma LDL. Both fractions contain apolipoprotein (apo) E but neither shows clear signs of oxidative modification. LDL-like particles from atherosclerotic lesions, on the other hand, contain malondialdehyde- and 4-hydroxynonenal-lysine adducts in apo B, are chemotactic for monocytes and show increased degradation in macrophages, a process that oxidized LDL prepared in vitro can compete with. The findings support the conclusion that at least a portion of the LDL isolated from atherosclerotic lesions is similar, if not identical, to oxidatively modified LDL.

Oxidative modification of LDL: comparison between cell-mediated and copper-mediated modification

Macrophage-derived foam cells are hallmarks of early atherosclerotic lesions. Oxidatively modified LDL has been suggested to be a more atherogenic form than native LDL. Oxidized LDL--but not native LDL--is chemotactic to monocytes and is avidly degraded by macrophages, resulting in their conversion to foam cells. Incubation of LDL with any of several different types of cells, or with copper ion even in the absence of cells, results in the oxidative modification of LDL. While the cell and the copper systems generate oxidatively modified LDL with similar properties, the two systems differ in their sensitivity to inhibition by superoxide dismutase and by several lipoxygenase inhibitors. In cultured endothelial cells, inhibitors of lipoxygenase, some of them without non-specific antioxidant activity, inhibited cell-mediated modification by 50-80%. In contrast, superoxide dismutase inhibited the process by 20% or less. Moreover, we have shown that soybean lipoxygenase in a cell-free system can modify LDL directly to a form recognized and degraded specifically and rapidly by macrophages. Lipoxygenase-modified LDL is also chemotactic for human monocytes and is cleared rapidly from the circulation, properties shared by cell- or copper-modified LDL. Thus, it is suggested that cellular lipoxygenase(s) may play an important role in cell-mediated oxidative modification of LDL.

A new degradable controlled release device for treatment of periodontal disease: in vitro release study

The substantivity of a drug in the periodontal pocket is an important factor determining its effect on the subgingival flora. Therefore, one of the predominant factors in the development of a sustained release delivery device is the ability to control the rate of release of the drug. Previous studies have demonstrated the advantages of the local sustained release of chlorhexidine from nondegradable devices in the treatment of periodontal diseases. The aim of this study was to develop a degradable sustained release device composed of a cross-linked protein containing chlorhexidine as the therapeutic agent. The in vitro release profile of chlorhexidine from the degradable films was altered by the amount of chlorhexidine incorporated into the film, by the cross-link density of the polymer, and by the chlorhexidine salt used. The chlorhexidine in the final pharmaceutical preparation did not lose its antibacterial activity as was shown in an in vitro antibacterial test. This work demonstrates that the release of chlorhexidine from a degradable delivery system and the degradation of the matrix can be controlled by variation in the formulation. This presents a new dental drug delivery system that can be used as an adjunct in the treatment of periodontal diseases in the future. These studies enable us to choose the pharmaceutical formulations for clinical trials to be conducted testing the efficacy of this treatment modality.

Low density lipoprotein rich in oleic acid is protected against oxidative modification: implications for dietary prevention of atherosclerosis

Oxidative modification of low density lipoprotein (LDL) enhances its potential atherogenicity in several ways, notably by enhancing its uptake into macrophages. In vivo studies in the rabbit show that inhibition of LDL oxidation slows the progression of atherosclerotic lesions. In the present studies, rabbits were fed either a newly developed variant sunflower oil (Trisun 80), containing more than 80% oleic acid and only 8% linoleic acid, or conventional sunflower oil, containing only 20% oleic acid and 67% linoleic acid. LDL isolated from the plasma of animals fed the variant sunflower oil was highly enriched in oleic acid and very low in linoleic acid. These oleate-rich LDL particles were remarkably resistant to oxidative modification. Even after 16-hr exposure to copper-induced oxidation or 24-hr incubation with cultured endothelial cells, macrophage uptake of the LDL was only marginally enhanced. The results suggest that diets sufficiently enriched in oleic acid, in addition to their LDL-lowering effect, may slow the progression of atherosclerosis by generating LDL that is highly resistant to oxidative modification.

Sustained-release delivery systems for treatment of dental diseases

Sustained-release delivery systems allow the effective targeting of drugs for treating dental and periodontal diseases. Since dental diseases are chronic, the therapeutic agents used should persist in the oral cavity for as long as possible. Implanting fluoride, chlorhexidine, and other antiseptic agents embedded into sustained-release polymeric matrices into the oral cavity prevents cariogenic plaque accumulation. Both fibers and slab-like sustained-delivery devices bearing chemotherapeutic agents reduced periopathogenic bacteria levels associated with clinical improvement. This review provides useful background information for researchers seeking to develop controlled-release delivery systems for dental applications.