Characterization of mandibular bone in a mouse model of chronic kidney disease

Abstract

Background: Chronic kidney disease (CKD) is a worldwide health problem with increasing prevalence and poor outcomes, including severe cardiovascular disease and renal osteodystrophy. With advances in medical treatment, patients with CKD are living longer and require oral care. The aim of this study is to determine the effects of CKD and dietary phosphate on mandibular bone structure using a uremic mouse model.

Methods: Uremia (U) was induced in female dilute brown agouti/2 mice by partial renal ablation. Uremic mice received a normal-phosphate (NP) or a high-phosphate (HP) diet. sham surgeries were performed in a control group of mice; half received an NP diet, and the other half was fed an HP diet. At termination, animals were sacrificed, and mandibles were collected for microcomputed tomography (micro-CT) and histologic analysis.

Results: Sera levels of blood urea nitrogen, parathyroid hormone, and alkaline phosphatase were significantly increased in U/NP and U/HP mice versus sham controls, whereas serum calcium was increased in the U/HP group, and no differences were noted in serum phosphate levels among groups. Micro-CT analyses revealed a significant reduction in cortical bone thickness and an increase in trabecular thickness and trabecular bone volume/tissue volume in U/NP and U/HP groups compared to the sham/NP group. A significant reduction in cortical bone thickness was also found in the sham/HP group versus the sham/NP group. Histologic evaluation confirmed increased trabeculation in the U groups.

Conclusion: CKD in mice, especially under conditions of HP feeding, results in marked effects on alveolar bone homeostasis.

Figure 1

Serum values and body weights in uremic mice and sham controls fed normal (NP) or high phosphate (HP) diets. (A) Blood urea nitrogen, BUN; (B) Parathyroid hormone, PTH; (C) alkaline phosphatase, ALP; (D) Phosphorus; (E) Calcium; (F) Body weight. Data represent the mean ± SEM. ‘a’ represents a statistically significant difference (p<0.05) compared with the Sham/NP group; ‘b’ represents a statistically significant difference (p<0.05) compared with the Sham/HP group; and ‘c’ represents a statistically significant difference (p<0.05) compared with the U/NP group.

Figure 2

Tomographic cross sectional slices of the furcation area of the first mandibular molar. (A) Area highlighted represents the region of interest (area of bone) evaluated for comparison between groups. (D–E) Representative mandibles from Sham/NP, Sham/HP, U/NP and U/HP groups. M= molar tooth; I= incisor tooth.

Figure 3

Mandibular bone morphometrics based on micro-CT analysis. A, B. Cortical bone morphometrics based on micro-CT analysis of the furcation zone between the mesial and distal roots of the mandibular first molar. Bars represent mean ± SEM; p<0.05, ANOVA; ‘a’ compared with Sham/NP group, ‘b’ compared with Sham/HP group, ‘c’ compared with U/NP group. BV/TV= bone volume/tissue volume. C–F. Trabecular bone morphometrics based on micro-CT analysis of the furcation area between the mesial and distal roots of the mandibular first molar. Bars represent mean ± SEM; p<0.05, ANOVA; ‘a’ compared with Sham/NP group, ‘b’ compared with Sham/HP group, ‘c’ compared with U/NP group. BV/TV= bone volume/tissue volume.

Figure 4

Linear regression analysis between serum parathyroid hormone (PTH) levels and mandibular bone morphometrics in all groups. (A) Correlation with cortical thickness; (B) Correlation with cortical bone volume/tissue volume (BV/TV); (C) Correlation with trabecular thickness; and (D) Correlation with trabecular BV/TV.

Figure 5

Histological staining of cortical bone. Buccal-lingual cross sections of the mesial root of the mandibular first molar. Sham/NP (A/E), Sham/HP (B/F), U/NP (C/G), U/HP (D/H). M= molar tooth; I= incisor tooth; B= bone; PDL= periodontal ligament; C= cementum; D= dentin; P=pulp. Hematoxylin & eosin, original magnification ×40 for A–D, ×400 for E–H.

Figure 6

Histological staining of trabecular bone. Buccal-lingual cross sections of the furcation area between the mesial root and distal root of the mandibular first molar. Sham/NP (A/E), Sham/HP (B/F), U/NP (C/G), U/HP (D/H). Note the marked increase in trabecular bone in the U/HP group. M= molar tooth, I= incisor tooth. Hematoxylin & eosin, original magnification ×40 for A–D, ×200 for E–H.