Lathyrogens and the role of collagen in the eruption of rat incisors

Gelatinase A (MMP-2) and cysteine proteinases are essential for the degradation of collagen in soft connective tissue

The degradation of soft connective tissue collagen is considered to depend on the activity of various proteolytic enzymes, particularly those belonging to the group of matrix metalloproteinases and cysteine proteinases. In the present study, we investigated the contribution of these enzymes to this process. Using a general inhibitor of MMPs (SC44463), collagen degradation was strongly inhibited, by about 40% after 24 h and up to 80% after 72 h of culturing. Blockage of cysteine proteinase activity (with leupeptin or E-64) reduced breakdown at these time intervals by 50% and 20%, respectively. Given the abundant presence of gelatinases--in particular gelatinase A (MMP-2)--in the tissue, the effect of an inhibitor selective for gelatinases (CT1166) was studied. Gelatinase inhibition resulted in a dose-dependent decrease of collagen breakdown up to 90% after 48 h. The ability of gelatinase A to degrade collagens was demonstrated by the induction of breakdown in devitalized explants by addition of activated gelatinase A, or by activation of endogenous enzyme with 4-aminophenylmercuric acetate. This latter effect was not found with plasmin, an activator of MMPs other than gelatinase A. Finally, the relevance of gelatinase A to the in vivo degradation of soft connective tissue collagen was implicated by the significant correlation found between its activity and the collagen turnover rates of four soft connective tissues (tooth pulp, periodontal ligament, molar gingiva and skin). We conclude that collagen degradation in soft connective tissue is mediated by MMPs and to a lesser extent by cysteine proteinases. Our data are the first to attach a key role to gelatinase A in this process.

Regional differences in molecular cross-linking of periodontal ligament collagen of rat incisor, by polarizing microscopy

Collagen, a naturally birefringent biopolymer and key structural component of the periodontal ligament (PDL), is altered substantially with regard to its molecular cross-linked structure by the dietary lathyrogen, beta-amino-proprionitrile (beta-APN). Our purpose in studying beta-APN-fed animals was to learn if the strength of birefringence of periodontal collagen, measured microscopically by the Senarmont compensator method, correlates with the molecular changes known to occur in these lathyritic animals, and to explore this technique for the periodontal ligament. Five experimental animals were fed a diet containing 0.25% beta-APN for two weeks, and 3 control animals were fed normal rat chow. Tissues were decalcified and the mandibular incisors were cut in cross section at 4 microns and stained with eosin Y. The Senarmont compensator, an attachment for the polarizing microscope, was used to measure phase retardation. Ten measurements were taken from each of the three sides (mesial, lateral and lingual) of the triangularly shaped incisor sections. The collagen fibers of the beta-APN-fed rats had lower values of phase retardation than the controls (p < 0.001), indicating reduced molecular organization. In addition, minor but significant regional differences were revealed, supporting the method for structural studies on the periodontal collagen.

The daily rhythm of tooth eruption

A video microscope system, which can resolve tooth movements to 1 to 2 microns, was used to monitor the eruption of 17 human maxillary second premolars in the prefunctional phase. Eruptive movement was detected by the change in position of an optical ruling on the erupting tooth relative to a reference ruling on the occluding adjacent teeth. Eruption was observed as the teeth erupted toward the occlusal plane over approximately a 41-hour period, from late Friday afternoon until Sunday noon. Half hourly observations were made during a 6 to 8-hour continuous laboratory session, which was during the day (9 AM to 5 PM) for nine of the subjects, and during the evening (5 to 11 PM) for eight. A similar pattern of eruption was seen for all subjects. The tooth intruded from before to after dinner on the first day, erupted significantly overnight, ceased eruption and approximately maintained its position during the next day, and erupted again during the second night. On the average, a slight intrusion was observed during the day, and statistically significant intrusion was associated with breakfast and dinner. Eruption occurred during the evening observation period, and the rate of evening eruption was significantly greater in children who were supine and relaxed than those who were upright and active. The 24-hour eruption rate was slower for teeth that were within 1.5 mm of the occlusal plane. The circadian eruption rhythm may be related to fluctuations of hormonal levels that affect metabolic activities within the periodontal ligament. It is also possible that a transient reduction in pressures by the cheeks, lips, and tongue during periods of rest allows eruption to occur then.

The effect of vinblastine on the incorporation of [3H]-glycine into proteins of the periodontal ligament of impeded and unimpeded mouse incisors

The effect of vinblastine on the protein metabolism of the periodontal ligament of impeded and unimpeded mouse incisors was studied by [3H]-glycine labelling and radioautography. The silver-grain concentration was determined in areas adjacent to the tooth, areas adjacent to bone and, as an internal control, in the dentine matrix. From 1 to 12 h there was no difference between treated and control animals; thus the drug did not alter protein biosynthesis. Later, the silver-grain concentration was significantly higher in areas adjacent to both bone and tooth in vinblastine-treated animals, suggesting a longer half-life of the labelled proteins. No significant differences between normal or unimpeded erupting incisors of both groups were detected. Dentine matrix showed a possibly higher re-utilization of the labelled amino acid in vinblastine-treated animals. The amount of labelled protein removed by collagenase was similar in both groups, while the concentration of grains due to collagenase-resistant proteins was significantly higher in treated animals, particularly at 96 h after the injection of labelled glycine. The relation between the increased amount of non-collagenous proteins in the periodontal ligament and the decrease in the rate of eruption caused by vinblastine was not established. However, among these proteins, fibronectin and proteoglycans are thought to be important factors in tooth eruption.

Granule proteins of the dental follicle and stellate reticulum inhibit tooth eruption and eyelid opening in postnatal rats

Electron-dense granules within cells of the dental follicle and stellate reticulum of rat mandibular molars can be isolated; their major components are 167 and 200 kDa proteins. Injecting these granule proteins into postnatal rats results in a delay of incisor eruption and eyelid separation. These inhibitory effects were most pronounced with the 167 kDa protein (a delay of 3 days in incisor eruption and of 2 days in eyelid opening) and were opposite to the stimulatory effects of epidermal growth factor. Thus, these granules may play an inhibitory part in tooth eruption.

Analysis of stress-strain curves at fast and slow velocities of loading in vitro in the transverse section of the rat incisor periodontal ligament following the administration of beta-aminopropionitrile

The in vitro mechanical properties of this ligament were examined by analysing the stress-strain curve obtained from a transverse section of the mandible. Mechanical measures were compared between normal rats and lathyritic rats given drinking water containing 0.2% of beta-aminopropionitrile (BAPN) for 20 days, and between the velocity of loading at 10(4) and 1 mm/24 h. The daily dose of BAPN decreased gradually because the body weight increased gradually. At the velocity of 10(4) mm/24 h, the maximum shear stress, elastic stiffness and failure strain energy density in the experimental subgroup fell to 43-50% of the control values, and at 1 mm/24 h to 71-80%. The maximum strains were not significantly different between the control and experimental subgroups either at 10(4) or at 1 mm/24 h. In the control subgroups, the maximum shear stress, elastic stiffness and failure strain energy density at 1 mm/24 h fell to 0.04-0.30% of those at 10(4) mm/24 h, and in the experimental subgroups to 0.08-0.43%. The maximum strains at 1 mm/24 h were 1.7-1.8 times greater than those at 10(4) mm/24 h in both the control and experimental subgroups. It is assumed that changes in the mechanical properties of the periodontal ligament were caused by inhibition of maturation of the periodontal collagen fibres. Assuming that the periodontal ligament is viscoelastic in nature, it is suggested that the main component reacting at 10(4) mm/24 h was an elastic one and that both components, with emphasis on the viscous one, interact at 1 mm/24 h.(ABSTRACT TRUNCATED AT 250 WORDS)

In vitro measurement of regional differences in the mechanical properties of the periodontal ligament in the rat mandibular incisor

Mechanical testing was performed in various regions of the ligament at a velocity of intrusive loading of 5 mm/min. The perimeters of the lingual cementum and socket wall and the sectional area of the ligament were measured radiographically. Load-deformation curves were transformed into stress-strain curves using the area and width of the lingual part of the ligament. The mechanical properties of the ligament differed markedly along the long axis of the incisor; mechanical measures from the load-deformation and stress-strain curves decreased gradually from the incisal towards the basal regions. It is suggested that these regional differences in mechanical properties were much more marked than those in teeth of limited growth or in other connective tissues, and that the nature of the collagen fibres, together with surrounding cells, ground substance and blood vessels, may be important in determining such differences.

Effects of lathyrogens on the mechanical strength of the periodontal ligament in the rat mandibular first molar

Effects of lathyrogens such as aminoacetonitrile (AAN), beta-aminopropionitrile (BAPN) and cysteamine--known inhibitors of cross-linking of collagen--on the mechanical strength of the periodontal ligament of the rat mandibular first molar were examined by measuring the ultimate load required to extract the tooth from its socket in the dissected jaw. Single injections of AAN (40 approximately 100 mg/100 g body weight) or of BAPN (100 mg/100 g body weight) caused significant decreases of the mechanical strength 24 h after administration of the drugs but that of cysteamine (30 mg/100 g body weight) did not. Significant correlations between the dose of AAN or of BAPN and the mechanical strength were found following daily administrations of the drugs for 5 days. The relative potency of AAN to BAPN was estimated to be 4.5 by a slope ratio assay. The rapid appearance and disappearance of the effect of lathyrogens on the mechanical strength of the periodontal ligament of the rat mandibular first molar provide further evidence that the turnover of the collagen in the tissue is fast. The half-time of collagen synthesis was estimated to be approximately 3 d.

Collagen remodelling in rat periodontal tissues: compensation for precursor reutilization confirms rapid turnover of collagen

Measurement of collagen turnover is complicated by the reutilization of isotopic precursors used to label the collagen. In an earlier study a novel approach was used to circumvent the problems of precursor recycling and unusually short half-lives were determined for collagen in adult rat periodontal tissues (Sodek, 1977). To verify these results we have used an alternate procedure devised by Poole (1971) in which the decay profile for the radiolabelled protein is corrected in accordance with the decay of the radiolabelled precursor. In this manner real half-lives for mature, neutral salt-insoluble collagen were determined as 3 days in the molar periodontal ligament, 6 days in the continuously erupting incisor ligament and approximately 10 days in the lamina propria of the gingiva, compared to apparent half-lives for these tissues of 6, 12 and approximately 20 days, respectively. The values calculated for actual half-lives are, therefore, approximately two-fold faster than values determined without compensating for reutilization, a difference that is in agreement with other protein turnover studies in which the effects of precursor reutilization have been measured. Although the real half-lives determined in this study indicate turnover rates for the periodontal tissues that are slightly slower than reported previously, the relative differences between the tissues in the rates of collagen turnover are similar. Moreover, the study confirms the existence of a remarkably high rate of collagen remodelling in these tissues.