John E. Horton

A comparison of bone turnover in athymic (nude) and euthymic mice: Biochemical, histomorphometric, bone ash and in vitro studies

Bone turnover in T-cell deficient mice was investigated by comparing parameters of bone physiology in athymic (nude) and euthymic mice. Static and dynamic bone histomorphometry, serum biochemical assays, body weight and tibia length measurements, and bone ash determination were completed in 6- and 12-wk-old athymic (nude) mice (NIH: Swiss nu/nu) and euthymic mice (nu/+) (10 mice/group). In vitro bone resorbing activity stimulated by parathyroid hormone (PTH) or prostaglandin E2 (PGE2) was measured in calvaria of neonatal athymic and euthymic mice. Athymic mice had smaller vertebral tissue area (p less than 0.01), tibia length (p less than 0.001), and less body weight (p less than 0.01) than euthymic mice. The percent double labeled surface (p less than 0.05) and mineralizing perimeter (p less than 0.01) were reduced in athymic as compared to age-matched euthymic mice. Osteoclast number was reduced in the 6-wk athymic mice as compared to 6-wk euthymic mice. Osteoclastic perimeter was reduced in the 12-wk-old mice (athymic and euthymic) as compared to the 6-wk-old mice. Serum calcium was lower at both ages in athymic mice (p less than 0.01) as compared to euthymic mice. Serum alkaline phosphatase levels were reduced (p less than 0.01) in 12-wk-old athymic mice as compared to age-matched euthymic mice, and were greater in 6-wk-old mice than 12-wk-old mice. Athymic mice had greater femur density than euthymic mice (p less than 0.01), and lower (p less than 0.001) percent ash weight of dry bone compared to euthymic mice.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of hormones and cytokines on stimulation of adenylate cyclase and intracellular calcium concentration in human and canine periodontal-ligament fibroblasts

Adenylate cyclase was stimulated by prostaglandin E2 (PGE2) and parathyroid hormone-related protein (PTHrP) in both these types of fibroblast and by calcitonin gene-related protein (CGRP) in the human fibroblasts in vitro. PGE2 (1 microM), CGRP (1 microM), and PTHrP (1 microM) stimulated adenylate cyclase up to 50-fold, 10-fold and 9-fold, respectively. Calcitonin (CT), substance P (SP), interleukin-1 beta (IL-1 beta), and transforming growth factor-beta 1 (TGF beta 1) had no effect on adenylate cyclase in either fibroblast. Intracellular Ca2+ (iCa2+) was measured in individual fibroblasts from the periodontal ligament using Indo-1 and an adherent cell analysis and sorting interactive laser cytometer. Ionomycin (3 microM) caused a transient rise of iCa2+ in all human and canine fibroblasts tested. The mean percentage increase in iCa2+ in response to ionomycin was 820 and 840% for human and canine fibroblasts, respectively. The human fibroblasts responded to PGE2 (1 microM) by an increased iCa2+ concentration; the mean percentage increase in iCa2+ was 187%. SP caused a less pronounced increase in iCa2+ in the human fibroblasts (56%). CGRP and SP caused a similar response in the canine fibroblasts. The mean percentage increase in iCa2+ in response to SP and CGRP was 95 and 78%, respectively. PTH, PTHrP, platelet-activating factor, CT, and IL-1 beta had no effect on iCa2+ in either type of fibroblast. The data indicate that cAMP and calcium have roles as intracellular secondary messengers in the action of PGE2, SP, CGRP, and PTHrP in fibroblasts of human and canine periodontal ligament.

Periodontal attachment loss associated with proximal tooth restorations

This study documents that periodontal attachment loss is greater adjacent to restored tooth surfaces than adjacent to unrestored tooth surfaces. This finding emphasizes the importance of the prevention of caries and poor restorations.

Investigations on in vitro bone resorbing activity from athymic (nude) and euthymic mouse splenic leukocytes

T-lymphocyte dependence of the production of in vitro bone resorbing activity was examined using athymic (nu/nu) and euthymic (nu/+) mouse splenic leukocytes. Conditioned medium (CM) from unstimulated splenic leukocytes of nu/nu mice had greater in vitro bone resorbing activity compared to CM from nu/+ mice (1.7- as compared to 1.2-fold increase of 45Ca release in mouse calvaria). CM from concanavalin A (Con A)-treated nu/nu and nu/+ leukocytes had 1.8-fold and no increase in 45Ca release, respectively. CM from both nu/nu and nu/+ phytohemagglutinin (PHA)-treated leukocytes had a 1.7-fold increase in 45Ca release. Bone resorbing activity from nu/nu CM was inhibited by interferon-tau (10 & 100 IU/mL) and indomethacin (2 x 10(-6) M). CM (untreated or Con A-treated) from nu/nu leukocytes had higher levels of prostaglandin E (PGE) as compared to CM from nu/+ leukocytes, and indomethacin decreased PGE levels in nu/nu CM. Leukocytes from nu/+ mice had increased mitogenesis when stimulated with PHA (1, 3, & 10 micrograms/mL) or Con A (1 and 10 micrograms/mL), whereas leukocytes from nu/nu mice were nonresponsive or had significant inhibition of mitogenesis with PHA and Con A.(ABSTRACT TRUNCATED AT 250 WORDS)