Assessment of maintenance therapy with reduced doses of PTH(1-34) in combination with a raloxifene analogue (LY117018) following anabolic therapy in the ovariectomized rat

This experiment was designed to evaluate the ability of a raloxifene analogue (RA), LY117018, with or without reduced dosing of human parathyroid hormone (hPTH)(1-34) to maintain gains in bone mass after a fully anabolic treatment regimen given to aging osteopenic rats. Six-month-old rats were ovariectomized (ovx) or sham-operated (sham). After 1 month, ovx rats were treated with an anabolic regimen consisting of subcutaneous hPTH(1-34) 80 microg/kg/day and oral raloxifene 3 mg/kg/day, each given 5 days/week for 3 months. Thereafter, the treated ovx rats went on to an 8 week maintenance phase of treatment with either RA alone at the same dose, hPTH(1-34) at a reduced dosing interval (twice a week), or a combination of the two. Bone mineral density (BMD) was measured ex vivo at four skeletal sites, lumbar spine (L2-4), proximal hemipelvis, whole femur, and tibia, by dual-energy X-ray densitometry. All four sites showed a similar pattern of response. After the 3 month anabolic phase, the sham group had significantly higher BMD values than ovx rats at all skeletal sites (p < or = 0.002). The ovx rats treated with PTH + RA during the anabolic phase of the protocol had significantly higher BMD than the sham group in the femur, tibia, and spine (p < or = 0.02) and higher but not significantly different values in the pelvis. Following the 2 month maintenance phase, comparisons were made with the PTH-RA group at the end of the anabolic phase. Decrements in BMD were seen in all three maintenance therapy groups, but they were not statistically significant in the RA plus reduced PTH dose group. However, reduced hPTH(1-34) dosing and RA alone resulted in significant reductions of bone mass measurements at several skeletal sites during the maintenance phase. We conclude that the raloxifene analogue LY117018 may be useful in maintaining bone mass in aging ovx rats following anabolic therapy with hPTH(1-34) and raloxifene analogue, but that this strategy only allows for dose reduction of hPTH(1-34) rather than its discontinuation.

The addition of a raloxifene analog (LY117018) allows for reduced PTH(1-34) dosing during reversal of osteopenia in ovariectomized rats

To test the hypothesis that an antiresorptive agent might reduce the dosing requirement for an anabolic drug during reversal of osteopenia due to estrogen deficiency, the following experiment was conducted in 6-month-old female rats. Ovariectomy or sham surgery was performed and the following six experimental groups were studied. Untreated (SHAM) or ovariectomized (OVX) animals served as control groups. Four weeks post-OVX, osteopenic rats (now 7 months old), were treated in one of four experimental protocols: human parathyroid hormone (hPTH(1-34)), 80 microg/kg/day, given by subcutaneous injection 5 days/week; a selective estrogen receptor modulator (SERM), raloxifene analog LY117018 (RA), 3 mg/kg/day, given by gavage 5 days/week; and two combinations of LY117018 at the same dose and frequency with hPTH(1-34) (same dose, 5 times/week) and a reduced dosing interval of hPTH(1-34) (same dose, 2 times/week). After 12 weeks of treatment, the four experimental groups were sacrificed at age 10 months. SHAM and OVX controls were also studied at 7 and 10 months of age. Bone mineral density (BMD) was measured by dual-energy X-ray absorptiometry at four skeletal sites: two mixed cortical/trabecular sites (femur and tibia) and two predominantly trabecular sites (lumbar spine and pelvis). The differences in BMD were consistent at all four sites. RA alone maintained BMD at all skeletal sites, but the results were not significantly improved over OVX controls, at age 10 months. hPTH(1-34) injections given 5 days/week resulted in BMD increments significantly higher than in either OVX or SHAM controls (p < 0.001). While the RA did not enhance the anabolic effects of full doses of hPTH(1-34), the addition of RA treatment to twice-weekly hPTH(1-34) dosing resulted in BMD increments at all four skeletal sites that were similar to the more intensive anabolic regimen of hPTH(1-34) therapy given 5 times/week. Therefore, an antiresorptive agent such as SERMs may potentially reduce the pharmacologic doses of PTH needed to reverse estrogen deficiency-induced osteopenia.

Parathyroid hormone regulates the expression of fibroblast growth factor-2 mRNA and fibroblast growth factor receptor mRNA in osteoblastic cells

We examined the effect of parathyroid hormone (PTH) on basic fibroblast growth factor-2 (FGF-2) and FGF receptor (FGFR) expression in osteoblastic MC3T3-E1 cells and in neonatal mouse calvariae. Treatment of MC3T3-E1 cells with PTH(1-34) (10-8M) or forskolin (FSK; 10-5M) transiently increased a 7 kb FGF-2 transcript with a peak at 2 h. The PTH increase in FGF-2 mRNA was maintained in the presence of cycloheximide. PTH also increased FGFR-1 mRNA at 2 h and transiently increased FGFR-2 mRNA at 1 h. FGFR-3 and FGFR-4 mRNA transcripts were not detected in MC3T3-E1 cells. In cells transiently transfected with an 1800-bp FGF-2 promoter-luciferase reporter, PTH and FSK increased luciferase activity at 2 h and 4 h. Immunohistochemistry showed that PTH and FSK increased FGF-2 protein labeling in the nuclei of MC3T3-E1 cells. PTH also increased FGF-2 mRNA, and FGFR-1 and FGFR-2 mRNA levels within 30 minutes in neonatal mouse calvarial organ cultures. We conclude that PTH and cAMP stimulate FGF-2 mRNA abundance in part through a transcriptional mechanism. PTH also regulated FGFR gene expression. We hypothesize that some effects of PTH on bone remodeling may be mediated by regulation of FGF-2 and FGFR expression in osteoblastic cells.

PTH-responsive osteoblast nuclear matrix architectural transcription factor binds to the rat type I collagen promoter

In connective tissue, cell structure contributes to type I collagen expression. Differences in osteoblast microarchitecture may account for the two distinct cis elements regulating basal expression, in vivo and in vitro, of the rat type I collagen alpha1(I) polypeptide chain (COL1A1). The COL1A1 promoter conformation may be the penultimate culmination of osteoblast structure. Architectural transcription factors bind to the minor groove of AT-rich DNA and bend it, altering interactions between other trans-acting proteins. Similarly, nuclear matrix (NM) proteins bind to the minor groove of AT-rich matrix-attachment regions, regulating transcription by altering DNA structure. We propose that osteoblast NM architectural transcription factors link cell structure to promoter geometry and COL1A1 transcription. Our objective was to identify potential osteoblast NM architectural transcription factors near the in vitro and in vivo regulatory regions of the rat COL1A1 promoter. Nuclear protein-promoter interactions were analyzed by gel shift analysis and related techniques. NM extracts were derived from rat osteosarcoma cells and from rat bone. The NM protein, NMP4, and a soluble nuclear protein, NP, both bound to two homologous poly(dT) elements within the COL1A1 in vitro regulatory region and proximal to the in vivo regulatory element. These proteins bound within the minor groove and bent the DNA. Parathyroid hormone increased NP/NMP4 binding to both poly(dT) elements and decreased COL1A1 mRNA in the osteosarcoma cells. NP/NMP4-COL1A1 promoter interactions may represent a molecular pathway by which osteoblast structure is coupled to COL1A1 expression.

Parathyroid hormone regulates the expression of the nuclear mitotic apparatus protein in the osteoblast-like cells, ROS 17/2.8

The parathyroid hormone (PTH) signaling pathways that effect changes in osteoblast gene expression also alter the organization of the cytoskeletal proteins. PTH regulates the expression of nucleoskeletal proteins, such as nuclear mitotic apparatus protein (NuMA) and topoisomerase II-alpha. NuMA is a structural component of the interphase nucleus and organizes the microtubules of the mitotic spindle during mitogenesis. We propose that PTH-induced alterations in osteoblast cytoarchitecture are accompanied by changes in osteoblast nuclear structure that contribute to changes in gene expression. We used immunofluorescence and confocal microscopy to determine the effect of PTH on the expression and nuclear distribution of NuMA in the rat osteosarcoma cell line, ROS 17/2.8. Cells were treated with PTH or vehicle, then fixed and stained with NuMA antibody. Optical sections of interphase naive cells revealed a diffuse distribution of NuMA, interspersed with speckles, in the central nuclear planes but not in nucleoli. During the metaphase and anaphase, NuMA localized at the mitotic spindle apparatus. The percentage of NuMA-immunopositive ROS 17/2.8 cells decreased with increasing confluence, but serum starvation did not attenuate NuMA expression. Cell density-dependent changes in cytoskeletal organization were observed in these cells. PTH treatment induced changes in cytoskeletal organization and increased the percentage of NuMA-immunopositive ROS 17/2.8 cells. These data suggest that PTH effects changes in osteoblast nuclear architecture by regulating NuMA, and that these alterations may be coupled to cytoskeletal organization.

Immunohistochemical demonstration of enzymatically modified human LDL and its colocalization with the terminal complement complex in the early atherosclerotic lesion

Treatment of low density lipoprotein (LDL) with degrading enzymes transforms the molecule to a moiety that is micromorphologically indistinguishable from lipoproteinaceous particles that are present in atherosclerotic plaques, and enzymatically modified LDL (E-LDL), but not oxidized LDL (ox-LDL), spontaneously activates the alternative complement pathway, as do lesion lipoprotein derivatives. Furthermore, because E-LDL is a potent inducer of macrophage foam cell formation, we propose that enzymatic degradation may be the key process that renders LDL atherogenic. In this article, we report the production of two murine monoclonal antibodies recognizing cryptic epitopes in human apolipoprotein B that become exposed after enzymatic attack on LDL. One antibody reacted with LDL after single treatment with trypsin, whereas recognition by the second antibody required combined treatment of LDL with trypsin and cholesterol esterase. In ELISAs, both antibodies reacted with E-LDL produced in vitro and with lesion complement activator derived from human atherosclerotic plaques, but they were unreactive with native LDL or ox-LDL. The antibodies stained E-LDL, but not native LDL or ox-LDL, that had been artificially injected into arterial vessel walls. With the use of these antibodies, we have demonstrated that early human atherosclerotic coronary lesions obtained at autopsy as well as lesions examined in freshly explanted hearts always contain extensive extracellular deposits of E-LDL. Terminal complement complexes, detected with a monoclonal antibody specific for a C5b-9 neoepitope, colocalized with E-LDL within the intima, which is compatible with the proposal that subendothelially deposited LDL is enzymatically transformed to a complement activator at the earliest stages in lesion development.

Analysis of differential gene expression in rat tibia after an osteogenic stimulus in vivo: mechanical loading regulates osteopontin and myeloperoxidase

The skeleton has the ability to alter its mass, geometry, and strength in response to mechanical stress. In order to elucidate the molecular mechanisms underlying this phenomenon, differential display reverse transcriptase-polymerase chain reaction (DDRT-PCR) was used to analyze gene expression in endocortical bone of mature female rats. Female Sprague-Dawley rats, approximately 8 months old, received either a sham or bending load using a four-point loading apparatus on the right tibia. RNA was collected at 1 h and 24 h after load was applied, reverse-transcribed into cDNA, and used in DDRT-PCR. Parallel display of samples from sham and loaded bones on a sequencing gel showed several regulated bands. Further analysis of seven of these bands allowed us to isolate two genes that are regulated in response to a loading stimulus. Nucleotide analysis showed that one of the differentially expressed bands shares 99% sequence identity with rat osteopontin (OPN), a noncollagenous bone matrix protein. Northern blot analysis confirms that OPN mRNA expression is increased by nearly 4-fold, at 6 h and 24 h after loading. The second band shares 90% homology with mouse myeloperoxidase (MPO), a bactericidal enzyme found primarily in neutrophils and monocytes. Semiquantitative PCR confirms that MPO expression is decreased 4- to 10-fold, at 1 h and 24 h after loading. Tissue distribution analysis confirmed MPO expression in bone but not in other tissues examined. In vitro analysis showed that MPO expression was not detectable in total RNA from UMR 106 osteoblastic cells or in confluent primary cultures of osteoblasts derived from either rat primary spongiosa or diaphyseal marrow. Database analysis suggests that MPO is expressed by osteocytes. These findings reinforce the association of OPN expression to bone turnover and describes for the first time, decreased expression of MPO during load-induced bone formation. These results suggest a role for both OPN and MPO expression in bone cell function.

Nuclear matrix proteins and osteoblast gene expression

The molecular mechanisms that couple osteoblast structure and gene expression are emerging from recent studies on the bone extracellular matrix, integrins, the cytoskeleton, and the nucleoskeleton (nuclear matrix). These proteins form a dynamic structural network, the tissue matrix, that physically links the genes with the substructure of the cell and its substrate. The molecular analog of cell structure is the geometry of the promoter. The degree of supercoiling and bending of promoter DNA can regulate transcriptional activity. Nuclear matrix proteins may render a change in cytoskeletal organization into a bend or twist in the promoter of target genes. We review the role of nuclear matrix proteins in the regulation of gene expression with special emphasis on osseous tissue. Nuclear matrix proteins bind to the osteocalcin and type I collagen promoters in osteoblasts. One such protein is Cbfa1, a recently described transcriptional activator of osteoblast differentiation. Although their mechanisms of action are unknown, some nuclear matrix proteins may act as "architectural" transcription factors, regulating gene expression by bending the promoter and altering the interactions between other trans-acting proteins. The osteoblast nuclear matrix is comprised of cell- and phenotype-specific proteins including proteins common to all cells. Nuclear matrix proteins specific to the osteoblast developmental stage and proteins that distinguish osteosarcoma from the osteoblast have been identified. Recent studies indicating that nuclear matrix proteins mediate bone cell response to parathyroid hormone and vitamin D are discussed.

Tissue matrix protein expression in human osteoblasts, osteosarcoma tumors, and osteosarcoma cell lines

Treatment for osteosarcoma is problematic because there are no prognostic markers. Diagnosis is primarily limited to cytologic grading. Oncogenesis alters cell structure therefore osteoblast tissue matrix proteins (extracellular matrix, cytoskeletal, intermediate filament, and nuclear matrix proteins), components of the cell substructure, are candidates for osteosarcoma markers. Structural proteins of the extracellular matrix, e.g. the collagens, are useful for diagnosis but not for tumors that produce little osteoid. To identify principal cellular tissue matrix proteins that distinguish normal from transformed human osteoblasts, their expression in normal osteoblasts, two osteosarcoma cell lines, and three primary osteosarcoma tumors were compared. The tumors were graded as (i) intermediate, (ii) high, and (iii) high grade recurrent. The 1-D SDS/PAGE profiles of the major components of the nuclear matrix and intermediate filament fractions from normal osteoblasts did not vary with biopsy site, age, or sex of patients. These profiles included known cytoskeletal proteins and OB250, a approximately 250 kD protein(s) observed in the intermediate filament fraction. A loss of protein bands, including OB250, was observed in the osteosarcoma cell lines and tumors. The intermediate and high grade tumors exhibited nearly identical protein profiles including potential tumor-specific proteins and collagen, consistent with the presence of intracellular collagen fibers in osteosarcoma. A microsequence was obtained for OT25, a novel low molecular weight protein observed in osteosarcoma cell lines. Fibrinogen gamma-chain, a protein that mediates cell adhesion was recovered from the high grade recurrent tumor.

Rat osteoblast and osteosarcoma nuclear matrix proteins bind with sequence specificity to the rat type I collagen promoter

The nuclear matrix mediates the 3-dimensional organization of DNA and supports DNA replication and its transcription. We hypothesize that the osteoblast nuclear matrix contributes to the transcriptional control of type I collagen (COL1A1) expression. Cis-regulatory elements of the rat COL1A1 promoter that control osteoblast expression in vivo are between -2.3 and -1.67 kilobase pairs (kb) but lie within -3.5 and -2.3 kb in cultured bone cells. This may result from differences in cell architecture between osteoblasts in tissue and those in vitro. Our aim was to identify osteoblast nuclear matrix proteins (NMPs) that associated with sequence-specificity to the COL1A1 promoter. We used osteoblasts from the rat metaphyseal femur and the rat osteosarcoma cells, ROS 17/2.8. Nuclear matrix and soluble nuclear proteins were obtained as separate subfractions. Gel mobility shift analysis, using fragments of the COL1A1 promoter, was used to identify DNA-binding proteins in the nuclear subfractions. A NMP-DNA interaction, NMP3, was observed between -2149 and -2106 nucleotide in both osteoblasts and osteosarcoma cells. NMP4 was detected between -3518 to -3406 nucleotide. Therefore, osteoblast NMPs recognize sequences in regulatory regions of the COL1A1 promoter and may link cell structure and the transcriptional regulation of this protein.

Parathyroid hormone regulates the expression of rat osteoblast and osteosarcoma nuclear matrix proteins

Parathyroid hormone (PTH) alters osteoblast morphology. How these changes in cell shape modify nuclear structure and ultimately gene expression is not known. Chronic exposure to rat PTH (1-34) [10 nM] attenuated the expression of 200, 190, and 160 kD proteins in the nuclear matrix-intermediate filament subfraction of the rat osteosarcoma cells, ROS 17/2.8 [Bidwell et al. (1994b): Endocrinology 134:1738-1744]. Here, we determined that these same PTH-responsive proteins were expressed in rat metaphyseal osteoblasts. We identified the 200 kD protein as a non-muscle myosin. Although the molecular weights, subcellular distribution, and half-lives of the 190 and 160 kD proteins were similar to topoisomerase II-alpha and -beta, nuclear matrix enzymes that mediate DNA topology, the 190 and 160 kD proteins did not interact with topoisomerase antibodies. Nevertheless, the expression of topoisomerase II-alpha, and NuMA, a component of the nuclear core filaments, was also regulated by PTH in the osteosarcoma cells. The 190 kD protein was selectively expressed in bone cells as it was not observed in OK opossum kidney cells, H4 hepatoma cells, or NIH3T3 cells. PTH attenuated mRNA expression of the PTH receptor in our cell preparations. These results demonstrate that PTH selectively alters the expression of osteoblast membrane, cytoskeletal, and nucleoskeletal proteins. Topoisomerase II-alpha, NuMA, and the 190 and 160 kD proteins may direct the nuclear PTH signalling pathways to the target genes and play a structural role in osteoblast gene expression.

Quantification of hemostatic proteins and activation products in synovial fluids from arthritic joints prior to and after induction of chemical synoviorthesis

Synovial fluids drawn from joints of patients suffering from rheumatoid arthritis were investigated for their concentrations of proteins and activation markers of the complement, coagulation and fibrinolytic systems. A broad spectrum of plasmatic inhibitors and other hemostatic proteins were detectable by immunologic assays. Compared to normal plasma concentration ranges, levels of alpha 2-antiplasmin, antithrombin III, heparin-cofactor II, factor H, alpha 2-macroglobulin, inter-alpha-trypsin inhibitor, fibrinogen and particularly high molecular weight kininogen were found to be decreased when corrected for total protein content. However, highly elevated levels of C-reactive protein, factor XIII, PMN-elastase, prothrombin fragment F1+2, thrombin-antithrombin III, plasmin-antiplasmin and terminal complement-complexes as well as C5a were determined. Eight and 24 hours after induction of chemical synoviorthesis, a general increase in most of the parameters was observed. Statistically significant alterations were found for C1-inhibitor, factor H, alpha 1-antitrypsin, inter-alpha-trypsin inhibitor, factor XIII, protein C, thrombin-antithrombin III complexes and C5a.

Mapping of the high molecular weight kininogen binding site of prekallikrein. Evidence for a discontinuous epitope formed by distinct segments of the prekallikrein heavy chain

Prekallikrein, a glycoprotein involved in contact phase activation, circulates in plasma in the form of a binary complex with high molecular weight kininogen (H-kininogen). The binding to H-kininogen is mediated by the prekallikrein heavy chain consisting of four repetitive domains, A1-A4. To define more precisely the region(s) involved in kininogen binding, we have employed an affinity cross-linking strategy with a synthetic peptide of 31 residues which mimics the prekallikrein binding site of H-kininogen. Cross-linking of the radiolabeled peptide to (pre)kallikrein revealed a binding segment in the NH2-terminal portion of the prekallikrein heavy chain; another binding segment was located in the COOH-terminal part of the heavy chain. The latter binding segment is harbored by a previously identified fragment of the kallikrein heavy chain involved in H-kininogen binding (Page, J.D., and Colman, R.W. (1991) J. Biol. Chem. 266, 8143-8148). Chemical cleavage of the heavy chain cross-linked with the radiolabeled peptide mapped the NH2-terminal binding segment to 60 residues (positions 53-112) of A1. Synthesis of a peptide (positions 56-86) and development of specific antibodies to this peptide narrowed down the kininogen binding segment to 31 residues of the center portion of A1. This NH2-terminal segment is equivalent to a kininogen binding site previously identified in factor XI (Baglia, F.A., Jameson, B.A., and Walsh, P.N. (1992) J. Biol. Chem. 267, 4247-4252). We conclude that prekallikrein exposes at least two segments on its heavy chain portion which form a continuous surface thereby facilitating the intimate binding of the zymogen to its nonenzymatic cofactor, H-kininogen.

A G protein-linked receptor for parathyroid hormone and parathyroid hormone-related peptide

The complementary DNA encoding a 585-amino acid parathyroid hormone-parathyroid hormone-related peptide (PTH-PTHrP) receptor with seven potential membrane-spanning domains was cloned by COS-7 expression using an opossum kidney cell complementary DNA (cDNA) library. The expressed receptor binds PTH and PTHrP with equal affinity, and both ligands equivalently stimulate adenylate cyclase. Striking homology with the calcitonin receptor and lack of homology with other G protein-linked receptors indicate that receptors for these calcium-regulating hormones are related and represent a new family.

High molecular weight kininogen-binding site of prekallikrein probed by monoclonal antibodies

A panel of monoclonal antibodies against human prekallikrein was raised in mice and characterized with respect to the major antigenic epitopes. Of 18 antibodies, nine were directed against the light chain portion performing the proteolytic function of activated kallikrein, and nine recognized the heavy chain mediating the binding of prekallikrein to high molecular weight (H-)kininogen. Among the anti-heavy chain antibodies, one (PK6) interfered with the procoagulant activity of prekallikrein, and prolonged in a concentration-dependent manner the activated partial thromboplastin time of reconstituted prekallikrein-deficient plasma (Fletcher type). Antibody PK6 was subtyped IgG1,k and had an apparent Kass of 6.8 +/- 0.44.10(8) M-1 for prekallikrein. Functional analyses revealed that PK6 does not interfere with prekallikrein activation by activated Hageman factor (beta-F XIIa), and has no effect on the kininogenase function of activated kallikrein. Monoclonal antibody PK6 but none of the other anti-heavy chain antibodies completely prevented complex formation of prekallikrein with H-kininogen, and readily dissociated preformed complexes of prekallikrein and H-kininogen. Likewise, Fab' and F(ab')2 fragments of PK6 blocked H-kininogen binding to prekallikrein. A synthetic peptide of 31 amino acid residues encompassing the entire prekallikrein binding region of H-kininogen effectively competed with PK6 for prekallikrein binding indicating that the target epitope of PK6 is juxtaposed to, if not incorporated in the H-kininogen-binding site of prekallikrein. Extensive cross-reactivity of PK6 with another H-kininogen-binding protein of human plasma, i.e. factor XI, suggested that the structure of the target epitope of PK6 is well conserved among prekallikrein and factor XI, as would be expected for the kininogen-binding site shared by the two proteins. It is anticipated that monoclonal antibody PK6 will be an important tool for the precise mapping of the hitherto unknown kininogen-binding site of prekallikrein.

Blood and urine fluoride concentrations associated with topical fluoride applications on dog gingiva

The circulatory uptake and urinary excretion of topical fluoride were investigated by applying a sodium fluoride solution containing 18F for six min to healthy gingiva of four adult dogs. Blood and urine samples were taken a regular intervals. Maximal fluoride in blood represented 0.02-0.05% of the applied dose and occurred four min after completion of the application. By 6.0 h, 0.02-0.06% of the applied dose had been excreted in urine. Preliminary data showed that this represented about 8.8% of the fluoride absorbed through the gingiva.

Clinical study to compare the effect of stannous fluoride and chlorhexidine mouthrinses on plaque formation

A clinical study was conducted on four adults to compare the relative efficacy of 0.2% chlorhexidine digluconate and 0.1% stannous fluoride (SnF2). Using a crossover experimental design, subjects rinsed twice daily for 5 days with SnF2 and then, after a 2-day interim recovery period, for 5 days with chlorhexidine. Statistically significant differences (P less than 0.05) in the relative efficacy of the two agents were found. Chlorhexidine was more effective in reducing Gingival and Plaque Indices, plaque wet weight and bacterial Colony Forming Units, calculated both per subject and per group.

Effect of stannous fluoride mouthrinse on dental plaque formation

A double-blind, crossover design study was performed on 29 young adults to test the effectiveness of 0.1% SnF2 mouthrinse (250 ppmF-) on plaque formation using clinical and microbiological criteria. Participants were assigned to either a placebo or SnF2 rinse which was used twice daily for 5 days. After an interim recovery period of 2 days, the participants used the alternate rinse in a similar manner for another 5 days. Clinical data collected at the end of each experimental period included Gingival Index (GI), and plaque scores. Supragingival plaque removed from each subject at the end of the experimental periods was weighed and then microbial enumeration was performed. Results showed that after SnF2 rinses, there were statistically significant reductions (P < 0.01) in plaque wet weight, number of bacteria per milligram plaque (CFU/mg), and total number of bacteria per sample (Total CFU). Visual plaque scores (PS) showed a significant (P < 0.05) but small reduction as a result of SnF2 rinse. No significant difference in gingival inflammation was noted. It is apparent from this study that, besides the well-documented ability of SnF2 to increase the resistance of teeth to demineralization, this agent is capable of reducing plaque formation. Long-term studies are indicated to examine usefulness of SnF2 in the control of early periodontal disease.