High-fat diet-induced obesity triggers alveolar bone loss and spontaneous periodontal disease in growing mice
© Fujita and Maki. 2016
Received: 26 April 2015
Accepted: 5 January 2016
Published: 8 January 2016
The relationship between high-fat food consumption and obesity is well-established. However, it is as yet unclear whether high-fat diet (HFD)-induced obesity in childhood and adolescence determines age-related changes in jaw bone health. The aim of this study is to examine the age-related influence of HFD-induced obesity on mandibular bone architecture and the structure of the periodontium in growing mice.
Male C57BL/6 J mice (6-weeks-old) were divided into two groups (n = 6 each): the control group received a control diet and the experimental group a HFD. After treatment for 4, 8, or 12 weeks, trabecular and cortical bone architecture was assessed using micro-computed tomography. The periodontium and alveolar bone structure were evaluated by histopathology.
In HFD mice, body weight, serum total cholesterol, and serum leptin levels were significantly higher than those in age-matched control mice (p < 0.05, all comparisons). Reductions in trabecular bone volume and in cortical bone growth (measured as the thickness and cross sectional area) in HFD mice were significant compared with the control mice after 4 weeks of treatment (p < 0.05, both comparisons). Significant decreases in cortical bone density in HFD-fed vs. age-matched control mice were determined after 12 weeks (p < 0.05). In the HFD mice, the periodontal ligament fibres were disrupted, having lost their orientation with respect to the bone surface, and constriction of the periodontal ligament space was inhibited.
These results suggest that HFD-induced obesity during growth not only triggers mandibular osteoporosis but also increases the risk of spontaneous periodontal disease.
KeywordsObesity Alveolar bone Bone architecture Periodontium High-fat diet
Trends indicating an increase in the proportion of overweight and obese children and adolescents have been reported in numerous studies from several industrialised countries over the last two decades [1, 2]. Overweight during adolescence continues into adulthood and increases the risk of morbidity from cardiovascular diseases . In addition, adolescents with a below-peak bone mass are at greater risk of developing osteoporotic fractures when they reach old age.
The development of obesity and osteoporosis in adults can be traced to their dietary intake and physical activity during childhood and adolescence. While, the relationship between high-fat food consumption and obesity is well-established , whether it affects bone health remains controversial.
Several studies in rats have also linked obesity with type 2 diabetes, and hypercaloric diet induced-obesity with morbidity from periodontal diseases [8, 9]. A HFD also contributes to obesity in association with a state of chronic inflammation, both in animals [10, 11] and humans . However, it is as yet unclear whether HFD-induced obesity in childhood and adolescence determines age-related changes in alveolar bone architecture and oral bone health.
In the present study, we evaluated the influence of HFD-induced obesity on alveolar bone quantity and quality, using micro-computed tomography (micro-CT), and performed a histopathological evaluation of the mandible of growing mice to determine potential adverse effects of obesity on oral bone health.
Composition of experimental diet
Soy bean oil
Mineral mix (AIN-93G)
Vitamin mix (AIN-93G)
The third butyl hydroquinone
Calorie (kcal/100 g)
Ratio of fat/total calorie (%)
Blood was obtained from mice under anaesthesia. Serum was isolated by centrifugation (3000 rpm, 15 min) and frozen at -80 °C. Serum total cholesterol, low-density lipoprotein (LDL), high-density lipoprotein (HDL) and triglycerides levels were quantified using routine laboratory methods (Nagahama Life Science Laboratory, Shiga, Japan). Serum insulin and leptin levels were measured using enzyme-linked immunosorbent assay (ELISA) kits for mouse insulin (Ohtsuka, Ltd., Tokyo, Japan) and mouse leptin (Morinaga Institute of Biological Science, Inc., Tokyo, Japan) according to the manufacturers’ protocols. The precision of the ELISAs was determined as the coefficient of variation (CV, %) and expressed as a percentage. The intra-assay CV ranged from 3.8 to 15.7 % and the inter-assay CV from 5.2 to 15.1 %.
Micro-computed tomography (micro-CT)
Left mandibles isolated from euthanized mice were fixed in 10 % neutral-buffered formalin, decalcified for 2 weeks with 10 % EDTA (pH 7.4), dehydrated with increasing concentrations of ethanol, and embedded in paraffin wax. Sections were cut from the paraffin wax blocks at a thickness of 4 μm and stained with haematoxylin and eosin. Images were taken using the Eclipse E200 microscope camera system (Nikon. Tokyo, Japan).
The periodontium and alveolar cortical bone were imaged at the mid- sections, mesiodistally of the mesial root of the mandibular first molar .
All data are expressed as medians and interquartile ranges of six animals per group. Comparisons between diet (HFD vs. standard chow) and among various time points (11, 15 and 19 weeks vs. 7 weeks) were performed using the by Mann–Whitney U test. A p value less than 0.05 was considered to indicate statistical significance. Statistical analyses were conducted using SPSS version 23.0 for Windows (IBM Japan, Inc., Tokyo, Japan).
Body weight and serum parameters
Quantitative evaluation of alveolar bone architecture
Micro-CT imaging of alveolar bone architecture
Histological evaluation of periodontium
Evidence of alveolar bone resorption in the HFD group included increased numbers of osteoclasts on the bone surface of the PDL spaces of 15-week-old mice. In these mice, disruption of the PDL fibres, accompanied by inflammatory cell infiltration, was seen on the surface of the alveolar bone (Fig. 7l). Disruption of the PDL fibres was also apparent on the bone surface of 19-week-old HFD-fed mice, accompanied by pronounced vasodilatation (Fig. 7n). The PDL spaces were at all time points in HFD mice than in the age-matched control mice (Fig. 7i-n).
Significant increases in body weight and serum cholesterol levels, together with significant decreases in bone quantity and quality, were found in HFD-induced obese mice. In the trabecular bone of these mice, deterioration of the trabecular bone architecture resulted in an overall decrease in mandibular BV/TV, as determined by micro-CT. Although cortical bone formation was slower in HFD-fed than in control mice, bone formation on the periosteal surface increased with age in both groups. Additionally, bone resorption on the endosteal surface was slightly higher in HFD-fed mice than controls, as seen on micro-CT. The HFD-fed mice at 19 weeks also had a significantly lower in Ct.BD than that of the controls, consistent with a significant increase in the porosity of cortical bone at the end of the experiment.
This study demonstrated a significant increase in serum leptin levels in HFD-fed mice compared with their age-matched controls, although the levels also increased in the latter.
Leptin is known as an important circulating signal that inhibits food intake and enhances energy expenditure through its actions in the brain . However, several studies have shown that a HFD plays key role in the development of leptin resistance in animals [17, 18]. In another study, energy expenditures were lower in mice fed a high-fat versus a low-fat diet, even though intake was similar between two groups . Energy expenditure inhibition due to leptin resistance leads to abnormal accumulation of triglycerides in the liver and other organs, since ingested triglycerides are not being used as an energy source.
We found that serum triglyceride levels tended to be lower and serum HDL cholesterol levels higher in HFD-fed mice than in control mice. These findings are in contrast to those of previous studies [20, 21] but are consistent with those of Graham et al. . The differences may be related to whether serum leptin levels exceed the capacity of the body’s transport system, including the entry of leptin into the cerebrospinal fluid. Additionally, in HFD-fed mice, an increase in serum total cholesterol levels is probably followed by an increase in serum HDL cholesterol levels.
The causes of leptin resistance are unclear, but hyper-nutrition leads to endoplasmic reticulum stress, and thus to inflammation, in adipose tissue [23–25]. Oxidative stress was also shown to induce leptin resistance in HFD-fed mice . The inflammation in HFD-fed mice is accompanied by increased expression of inflammatory cytokines, such as interleukin (IL)-6, IL-1β, and tumor necrosis factor-α, in adipocytes and macrophages via activation of the c-Jun N-terminal kinase and nuclear factor-κB pathways [24, 26]. Recently, Dib et al. reported that leptin acts as a pro-inflammatory adipocytokine in peripheral tissues . These studies suggested that endoplasmic reticulum stress induces inflammation by mediating leptin signals in the adipose tissue of HFD-fed mice.
Other studies have shown a selective increase in the production of reactive oxygen species (ROS) in the adipose tissues of obese mice. These ROS cause both oxidative and endoplasmic reticulum stress, including inflammatory changes in adipose tissue during the course of adipocyte hypertrophy . Moreover, ROS and oxidative stress inhibit osteoblastogenesis [29, 30], suggesting that ROS also inhibit periosteal cortical bone formation in growing HFD-fed growing mice.
Thus, in this study, the deterioration of bone structure in the HFD-fed mice could have been due to multiple forms of oxidative stress, which induced leptin resistance and increased inflammation in adipose tissue. However, an age-dependent increase in serum leptin levels within the physiological range did not affect gradual bone growth.
We also showed that HFD-induced obesity during growth increases the risk of mandibular bone osteoporosis and spontaneous periodontal disease. A recent report proposed a link between systemic osteoporosis and periodontal bone loss based on significant up-regulation of inflammatory cytokines in bone and in the bone marrow cells of rats with osteoporosis .
In this study, HFD-induced alveolar bone loss may have reflected a state of non-invasive and non-infective inflammation, such as that characteristic of autoimmune disorders. This is in contrast to previous studies that used models of experimental periodontitis [8, 9], as periodontal disease develops as a result of the continuous interaction between host cells and subgingival pathogenic bacteria .
The HFD-induced alveolar bone loss in our mice may have been triggered by bacterial endotoxin [lipopolysaccharide (LPS)], a potential inflammatory mediator in mice with HFD-induced obesity . In a recent study, a HFD increased alveolar bone loss in mice injected with LPS . In general, bacterial endotoxins are present in large quantities in the gut , and clinical studies have reported the development of postprandial endotoxemia following a high-fat meal [4, 38]. These findings suggest that dietary fats promote the translocation of bacterial endotoxins from the gut into the circulation, where they stimulate periodontal inflammation and alveolar bone loss.
Recently, Suganami et al. proposed the concept of “homeostatic inflammation” in the pathogenesis of non-infectious inflammatory diseases . This may account for the HFD-induced alveolar bone loss in our mice, in which systemic inflammatory changes in bone and other tissues may have developed in association with metabolic stress.
In a previous study, rats fed a high-cholesterol diet showed a modest increase in the distance between the cement-enamel junctions and the alveolar bone crest. The authors suggested that osteoclastic function plays a major role in alveolar bone resorption during increased oxidative stress . However, at a gross histological level, there was no evidence of alveolar bone crest resorption in any of the groups, despite significant increases in serum total cholesterol levels in the HFD-fed mice. These results likely reflected cortical bone formation on the periosteal surface during the growth period. By contrast, the PDL fibres in HFD-fed mice were disrupted, with loss of orientation with respect to the bone surface, and the normal narrowing of the PDL space was inhibited. Narrowing of the periodontium narrows with age, as seen in the control mice, is accompanied by increasing acellular cementum formation and alveolar bone formation. The increased vascular permeability due to inflammatory changes in the blood vessels of the periodontium may promote monocyte adhesion to endothelial cells and migration. In addition, osteoclasts differentiated from those monocytes may have then attached to the alveolar bone surface, resulting in increased alveolar bone resorption in the HFD-fed mice.
Together, these findings suggest that the spontaneous deterioration of periodontal bone is a consequence of HFD-induced obesity during growth.
Two limitations to our study must be noted. First, in the histological evaluation, HFD-fed mice had clear alveolar bone resorption and inflammatory structural changes in the PDL, but systemic bone metabolism was not assessed using serum analyses, such as those measuring bone resorption markers and inflammatory cytokines. Second, bone resorption due to insulin resistance was not considered. Further studies are needed to elucidate the mechanisms of inflammatory alveolar bone resorption induced by a HFD.
We conclude that the deterioration of trabecular bone architecture and retarded periosteal bone formation begins early in the development of diet-induced obesity and is followed by an increase in cortical bone porosity. We demonstrated that HFD-induced obesity during growth not only triggers mandibular osteoporosis but also increases the risk of spontaneous periodontal disease.
trabecular bone volume
trabecular bone volume fraction
cortical bone density
cortical bone cross sectional area
cortical bone thickness
cortical bone volume
endosteal bone length
external bone length
void volume in cortical bone
This work was supported by a Grants-in-Aid 25713064 from the Ministry of Education, Culture, Sports, Science and Technology, Japan.
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