Oral Radiology

, Volume 30, Issue 1, pp 45–52

Inhibitory effect of a fermented soy product from lactic acid bacteria (PS-B1) on deterioration of bone mass and quality in ovariectomized mice

Authors

  • Toshinaga Miura
    • Division of Radiology, Department of Maxillofacial Diagnostic ScienceKanagawa Dental College
    • Division of Radiology, Department of Maxillofacial Diagnostic ScienceKanagawa Dental College
  • Ryota Kawamata
    • Division of Radiology, Department of Maxillofacial Diagnostic ScienceKanagawa Dental College
  • Hiromi Wakao
    • Division of Radiology, Department of Maxillofacial Diagnostic ScienceKanagawa Dental College
  • Takashi Sakurai
    • Division of Radiology, Department of Maxillofacial Diagnostic ScienceKanagawa Dental College
  • Isamu Kashima
    • Division of Radiology, Department of Maxillofacial Diagnostic ScienceKanagawa Dental College
Original Article

DOI: 10.1007/s11282-013-0143-3

Cite this article as:
Miura, T., Kozai, Y., Kawamata, R. et al. Oral Radiol (2014) 30: 45. doi:10.1007/s11282-013-0143-3
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Abstract

Objectives

We investigated the effects of a fermented soy product from lactic acid bacteria (PS-B1) in preventing the decrease in bone mineral content and deterioration of trabecular bone structure in ovariectomized (OVX) mice.

Methods

Four-week-old ICR OVX or sham-operated (Sham) mice were maintained on a normal diet in five groups: a Sham group, the OVX control group, PS-B1 1 % (Ps 1 %) group, PS-B1 2 % (Ps 2 %) group, and PS-B1 5 % (Ps 5 %) group. The Sham and OVX control groups were given tap water as drinking water. Water containing 1, 2, and 5 % PS-B1 was given ad libitum to the respective PS-B1 groups. The animals were kept under these conditions for 12 weeks and sacrificed under anesthesia. Their femurs were removed under sterile conditions. Bone mineral density (BMD) of the removed femurs was measured by use of peripheral quantitative computed tomography. Subsequently, morphometric indices for trabecular bone structure were measured by use of microfocus X-ray computed tomography.

Results

Total BMD, trabecular BMD, and cortical width were significantly higher in the Ps 2 % group than in controls. In the Ps 2 % group, there was a tendency for retarded BMD loss. Maintenance of bone volume fraction, trabecular number, trabecular space, trabecular continuity, and trabecular connectivity were seen in the Ps 2 % and Ps 5 % groups. In the Ps 2 % and Ps 5 % groups, deterioration of trabecular bone structure was significantly inhibited.

Conclusions

These results suggest that PS-B1 is effective in slowing the decrease in BMD and deterioration of trabecular bone structure in OVX mice.

Keywords

Lactic acid bacteriaOsteoporosisBone mineral densityBone quality

Introduction

A fermented soy product cultivated from lactic acid bacteria—PS-B1—improves the metabolism of cholesterol in the blood and relieves constipation in humans [1, 2]. PS-B1 also inhibits cancer cell proliferation, and contains a bioactive factor that is effective in eliminating tumors [3]. However, few studies have demonstrated the effect of PS-B1 on osteoporosis. Osteoporosis is a skeletal disorder characterized by compromised bone strength, and it predisposes a person to increased risk of fracture. Bone strength primarily reflects the integration of bone density and quality [4]. Femoral neck fractures, in particular, are a major cause of bedridden conditions, worsening the quality of life and prognosis for many patients [5]. Prevention of osteoporosis is a major issue in modern society, and it is believed that dietary supplements are important as a means of preventing osteoporosis. It has been reported that a specific peptide inhibits nuclear factor kappa B, a transcription factor that contributes to differentiation of osteoclasts [6]. Casein phosphopeptides—peptides contained in milk and milk products—also promote absorption of minerals in the gastrointestinal tract [7]. It has also been reported that the soy isoflavone inhibits bone resorption and stimulates bone formation [8]. PS-B1 contains abundant glutamic acid, amino acids, and peptides, and it may thus act in preventing osteoporosis.

There is abundant circumstantial evidence regarding the effects of fermented soy products from lactic acid bacteria, because fermented products are deeply rooted in many diets around the world. However, little biochemical, nutritional, and pharmacological research has been conducted on the active components in fermented soy products from lactic acid bacteria. In this study we used a murine model of osteoporosis to investigate the effects of PS-B1 in preventing a decrease in bone density and deterioration of trabecular bone structure.

Materials and methods

Experimental animals

Mice were housed in our approved animal-holding facility and treated according to the guidelines on animal care of Kanagawa Dental College. All animals were kept under local vivarium conditions (temperature, 23.3 °C; humidity, 55 %; and 12-h light–dark cycle). Four-week-old ICR mice were purchased from Japan Clea (Tokyo, Japan) and were either ovariectomized (OVX; n = 49) or sham-operated (Sham; n = 10). All mice were fed conventional rodent food pellets for a week. OVX mice were then divided into four groups: the OVX control group (n = 10) and three other groups (n = 13) that received supplementation. These three groups were allowed free access to water containing different concentrations of PS-B1 (Biogenomics, Tokyo, Japan): 1 % (Ps 1 % group; n = 13), 2 % (Ps 2 % group; n = 13), and 5 % (Ps 5 % group; n = 13).

All the mice were euthanized after 12 weeks. Blood was collected, and the femurs were excised and preserved at −80 °C for analysis by microfocus X-ray computed tomography (micro CT) and peripheral quantitative computed tomography (pQCT), and for three-point bending tests. The experimental procedure is illustrated in Fig. 1.
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Fig. 1

Experimental procedure. Asterisk PS-B1 is the fermented products cultivated from soybean milk using lactic acid bacteria

Measurement of plasma components

Blood samples were collected in heparin sodium and centrifuged (1000 rpm, 10 min, 4 °C) to separate the plasma. Calcium (Ca) levels were measured with a chelate color development method, phosphorus (P) levels with a direct molybdenum blue method, magnesium (Mg) levels with a xylidyl blue method, and alkaline phosphatase (Alp) activity with a phenyl phosphate substrate method. A clinical biochemical test kit (Wako Pure Chemical Industries, Osaka, Japan) was used for these measurements.

Peripheral quantitative computed tomography

The distal metaphysis, 1.4 mm proximal to the growth plate, was scanned by use of a Research SA + pQCT model (Norland Stratec, Berkenfeld, Germany) with a tube voltage of 50 kV and a tube current of 550 μA at a voxel size of 80 × 80 × 46 μm. The cortical bone was defined as the area of bone mineral density (BMD) >690 mg/mm3, and a threshold of 395 mg/mm3 at contour mode 1 was set to define trabecular bone in the bone marrow. Total BMD (mg/cm3), trabecular BMD (mg/cm3), and cortical BMD (mg/cm3) are reported as metaphyseal mineral properties. Cortical bone sectional area (mm2), cortical bone thickness (mm), periosteal perimeter (mm), endosteal perimeter (mm), and stress/strain index (SSI; an index of strength [9]) were also calculated.

Microfocus X-ray computed tomography

Three-dimensional imaging of the distal epiphyseal region of the femur, 1.5–2.75 mm proximal to the growth plate, was performed with an MCT-CB 130F (Hitachi Medico, Tokyo, Japan). Spatial resolution was set to 7 μm and the voxel size was 17.8 × 17.8 × 17.8 μm; the tube voltage and current were 60 kV and 100 μA, respectively. Morphological analysis was performed by use of TRI 3D BON (Ratoc System Engineering, Tokyo, Japan) for such properties as bone volume fraction (BV/TV; %), trabecular thickness (μm), trabecular number (Tb.N; 1/mm), trabecular separation (Tb.Sp; μm), trabecular space (Tb.Spac; μm), and fractal dimension [10]. Star volume is defined as the mean volume of all parts of an object that can be seen unobscured in all directions from a particular point with the mean value taken over all points inside the object. It can be defined for any type of object, including cavities, for example the marrow space, and networks, for example the trabecular system. We used a frame and grid with points and lines to guide the measurements. We calculated the star volume of the marrow space (V*m.space) and of the trabeculae by star volume analysis [11, 12]. The trabecular connectivity was measured by node-strut analysis, described by Garrahan et al. [13]. We identified nodes (Nd; connective point of three or more trabeculae) and cortexes (Ct; connective point of trabeculae and cortical bone) by node-strut analysis. We obtained the number of Nd per tissue volume (N.Nd/TV), the number of Ct per tissue volume (N.Ct/TV), the total strut length per tissue volume (TSL/TV), the strut length from Nd to Nd per tissue volume (NdNd/TV), and the strut length from Ct to Ct per tissue volume (CtCt/TV) by node-strut analysis.

Mechanical properties of the femurs

Bone strength of the femoral diaphysis was evaluated by means of three-point bending tests with an MZ-500S load torsion tester (Maruto, Tokyo, Japan). The crosshead speed in the three-point breaking test was 10 mm/min. The maximum load (N), stiffness (N/mm), and the elastic modulus (N/mm2) were determined from the load–displacement curve and were converted to material properties.

Statistical analysis

All data are expressed as the mean ± standard deviation (SD). The means for each property were compared by use of one-way analysis of variance (ANOVA). Dunnett’s test was used to compare the experimental groups with the OVX control group. Probability values (P values) less than 0.05 were considered statistically significant. The Stat View software package (Stat View 5.0; Abacus Concepts, Berkeley, CA, USA) was used for all analysis.

Results

Body weight and excised femoral bone weight (wet) were compared among the OVX control group and the Sham, Ps 1 %, Ps 2 %, and Ps 5 % groups; the results are shown in Table 1. No significant differences were seen between the OVX control group and any of the experimental groups.
Table 1

Comparison of body weight and resected femoral bone weight among the OVX control and Sham, Ps 1 %, Ps 2 %, and Ps 5 % groups

 

OVX control

Sham

Ps 1 %

Ps 2 %

Ps 5 %

Body weight (g)

40.9 ± 4.0

37.9 ± 3.6

39.8 ± 3.4

40.6 ± 2.5

38.8 ± 3.1

Resected femoral bone weight (wet) (g)

0.146 ± 0.016

0.136 ± 0.012

0.152 ± 0.025

0.153 ± 0.011

0.147 ± 0.017

There were no significant differences between the OVX control and comparison groups (values are means ± standard deviations)

Results from analysis of serum mineral levels (Ca, P, Mg) and Alp in the OVX control group, Sham group, and experimental groups are listed in Table 2. No significant differences were observed in serum Ca, P, or Mg levels and in alkaline phosphatase activity between any of the experimental groups and the OVX control group. However, values in the Ps 1 %, Ps 2 %, and Ps 5 % groups were all higher than in the OVX control group, suggesting a tendency for high bone turnover.
Table 2

Comparison of levels of calcium (Ca), phosphorus (P), magnesium (Mg), and alkaline phosphatase (Alp) in serum among the OVX control and Sham, Ps 1 %, Ps 2 %, and Ps 5 % groups

 

OVX control

Sham

Ps 1 %

Ps 2 %

Ps 5 %

Ca (mg/dl)

10.20 ± 1.20

10.30 ± 0.90

10.50 ± 1.40

10.60 ± 1.00

9.70 ± 1.10

P (mg/dl)

5.84 ± 1.40

5.73 ± 1.20

5.02 ± 0.80

5.80 ± 1.80

5.48 ± 1.60

Mg (mg/dl)

2.78 ± 1.48

2.99 ± 0.71

3.01 ± 0.79

3.33 ± 0.89

2.75 ± 1.10

Alp (BL unit)

3.58 ± 0.94

2.84 ± 0.74

4.03 ± 0.96

4.12 ± 0.87

4.31 ± 0.99

There were no significant differences between the OVX control group and the comparison groups (values are means ± standard deviations)

Results from BMD measurements using pQCT for each group are presented in Table 3. Compared with the OVX control group, significantly higher values of total BMD, trabecular BMD, cortical BMD, cortical bone sectional area, and cortical bone thickness, and a significantly lower value for endosteal perimeter, were observed for the Sham group. This indicates that osteoporotic bone loss occurred in the OVX control group as a result of ovariectomy. In contrast, no obvious effects were seen in the Ps 1 % and Ps 5 % groups. In the Ps 2 % group, total BMD, trabecular BMD, and cortical bone thickness were significantly higher than in the OVX control group, and the endosteal perimeter was significantly lower. This suggests that osteroporotic bone loss was suppressed in the Ps 2 % group.
Table 3

Comparison of bone mineral density (BMD) and cross-sectional morphometric indices of the femoral epiphysis among the OVX control and Sham, Ps 1 %, Ps 2 %, and Ps 5 % groups

 

OVX control

Sham

Ps 1 %

Ps 2 %

Ps 5 %

Total bone BMD (mg/cm3)

490.20 ± 41.80

597.54 ± 69.22**

521.91 ± 44.17

564.75 ± 43.62**

520.24 ± 46.12

Trabecular bone BMD (mg/cm3)

209.80 ± 23.83

275.67 ± 28.50**

236.30 ± 21.57

254.53 ± 32.66**

238.77 ± 29.21

Cortical bone BMD (mg/cm3)

836.74 ± 34.57

855.66 ± 33.60**

820.82 ± 17.14

824.46 ± 23.21

819.90 ± 20.80

Cortical bone sectional area (mm2)

1.53 ± 0.35

2.12 ± 0.49**

1.55 ± 0.24

1.86 ± 0.37

1.52 ± 0.29

Cortical bone thickness (mm)

0.21 ± 0.04

0.31 ± 0.08**

0.22 ± 0.04

0.27 ± 0.06*

0.21 ± 0.04

Periosteal perimeter (mm)

7.98 ± 0.42

7.93 ± 0.24

7.83 ± 0.34

7.88 ± 0.24

7.78 ± 0.28

Endosteal perimeter (mm)

6.68 ± 0.27

6.00 ± 0.51**

6.46 ± 0.41

6.22 ± 0.37*

6.43 ± 0.42

Stress strain index

1.31 ± 0.28

1.51 ± 0.20

1.24 ± 0.16

1.37 ± 0.19

1.24 ± 0.16

Each value is the mean ± SD and comparisons were made by use of an ANOVA and post-hoc Dunnett’s multiple comparison test vs. OVX controls

* P < 0.05 vs OVX control; ** P < 0.01 vs. OVX control

Results from analysis of three-dimensional trabecular structure by micro CT are listed in Tables 4, 5, 6. Compared with the Sham group, deterioration of trabecular bone structure in the OVX control group was apparent from all the properties measured, confirming an osteoporotic condition. Tb.Sp and Tb.Spac values were also significantly lower in the Ps 1 % group than in the OVX control group. Values of BV/TV, Tb.N, N.Nd/TV, and CtCt/TV were significantly higher in the Ps 2 % and Ps 5 % groups than in the OVX control group. However, Tb.Sp, Tb.Spac, and V*m.space were significantly lower. This suggests that trabecular degradation as a result of osteoporosis was retarded in the Ps 2 % and Ps 5 % groups.
Table 4

Comparison of properties indicative of trabecular structure among the OVX control and Sham, Ps 1 %, Ps 2 %, and Ps 5 % groups

Property

OVX control

Sham

Ps 1 %

Ps 2 %

Ps 5 %

BV/TV (%)

7.18 ± 1.84

16.04 ± 3.38**

9.40 ± 2.11

10.28 ± 2.10*

9.91 ± 2.50*

Tb.Th (μm)

36.85 ± 1.38

41.07 ± 3.62*

37.08 ± 2.07

37.39 ± 2.60

37.42 ± 2.91

Tb.N (1/mm)

1.94 ± 0.46

3.89 ± 0.64**

2.52 ± 0.48

2.75 ± 0.52**

2.65 ± 0.69*

Tb.Sp (μm)

504.17 ± 126.88

221.49 ± 39.80**

373.07 ± 78.65**

339.34 ± 75.42**

361.05 ± 92.92**

Tb.Spac (μm)

541.02 ± 126.35

262.56 ± 38.11**

410.15 ± 77.51**

376.73 ± 75.19**

398.47 ± 92.59**

FD

1.95 ± 0.06

2.10 ± 0.05**

2.00 ± 0.06

2.00 ± 0.06

1.99 ± 0.06

Each value is the mean ± SD and comparisons were made by use of an ANOVA and post-hoc Dunnett’s multiple comparison test vs. OVX controls

BV/TV bone volume fraction, Tb.Th trabecular thickness, Tb.N trabecular number, Tb.Sp trabecular separation, Tb.Spac trabecular space, FD fractal dimension

 * P < 0.05 vs. OVX control; ** P < 0.01 vs. OVX control

Table 5

Comparison of results from star volume analysis among OVX control and Sham, Ps 1 %, Ps 2 %, and Ps 5 % groups

Property

OVX control

Sham

Ps 1 %

Ps 2 %

Ps 5 %

V* m.space (mm3)

0.62 ± 0.15

0.26 ± 0.08**

0.49 ± 0.13

0.45 ± 0.11**

0.47 ± 0.14*

V* tr (mm3)

0.0083 ± 0.0017

0.0134 ± 0.0046**

0.0081 ± 0.0020

0.0091 ± 0.0025

0.0078 ± 0.0024

Each value is the mean ± SD and comparisons were made by use of an ANOVA and post-hoc Dunnett’s multiple comparison test vs. OVX controls

V*m.space star volume of marrow space, V*tr star volume of trabeculae

* P < 0.05 vs OVX control; ** P < 0.01 vs OVX control

Table 6

Comparison of results from node-strut analysis among OVX control and Sham, Ps 1 %, Ps 2 %, and Ps 5 % groups

Property

OVX control

Sham

Ps 1 %

Ps 2 %

Ps 5 %

N.Nd/TV (1/mm3)

77.63 ± 29.00

137.03 ± 29.76**

107.69 ± 33.10

104.73 ± 48.49

92.83 ± 33.66

N.Ct/TV (1/mm3)

33.26 ± 9.94

65.09 ± 13.39**

44.55 ± 8.53

46.94 ± 10.43*

47.66 ± 16.16*

TSL/TV (1/mm2)

18.30 ± 5.55

37.55 ± 6.90**

25.67 ± 6.82

24.99 ± 7.78

23.11 ± 6.85

NdNd/TV (1/mm2)

10.71 ± 3.54

20.89 ± 3.78**

15.32 ± 4.68

14.32 ± 5.49

13.23 ± 4.28

CtCt/TV (1/mm2)

0.40 ± 0.16

1.02 ± 0.38**

0.57 ± 0.18

0.69 ± 0.23*

0.78 ± 0.31**

Each value is the mean ± SD and comparisons were made by use of an ANOVA and post-hoc Dunnett’s multiple comparison test vs. OVX controls

N.Nd/TV the number of nodes (connective point of three or more trabeculae) per tissue volume, N.Ct/TV the number of cortexes (connective point of trabeculae and cortical bone) per tissue volume, TSL/TV total strut length per tissue volume, NdNd/TV strut length from node to node per tissue volume, CtCt/TV strut length between Ct and Ct per tissue volume

P < 0.05 vs OVX control; ** P < 0.01 vs OVX control

Representative axial and sagittal three-dimensional reconstruction images for each group are presented in Fig. 2. Obvious deterioration of the trabecular structure was observed for the OVX control group compared with the Sham group. In the Ps 1 %, Ps 2 %, and Ps 5 % groups, inhibition of the deterioration of internal trabecular bone structure could be confirmed visually.
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Fig. 2

Three-dimensional reconstructed images of representative axial and sagittal sections from the OVX control, Sham, Ps 1 %, Ps 2 %, and Ps 3 % groups

The results from three-point bending tests on the femoral diaphysis are presented in Table 7. No significant differences were seen in any of the groups. There was a tendency to higher values for stiffness and elastic modulus in the Ps 1 %, Ps 2 %, and Ps 5 % groups compared with the OVX control group.
Table 7

Comparison of bone mechanical properties of the femur (three-point bending test) among OVX control and Sham, Ps 1 %, Ps 2 %, and Ps 5 % groups

 

OVX control

Sham

Ps 1 %

Ps 2 %

Ps 5 %

Maximum load (N)

23.87 ± 4.69

24.91 ± 5.28

23.52 ± 4.21

24.38 ± 3.18

23.77 ± 3.59

Stiffness (N/mm)

106.87 ± 17.84

126.88 ± 26.71

121.98 ± 18.65

116.22 ± 16.73

119.51 ± 21.25

Elastic modulus (N/mm2)

196.05 ± 91.38

273.75 ± 110.03

217.87 ± 77.67

253.20 ± 166.68

277.03 ± 101.73

There were no significant differences between the OVX control and comparison groups (values are means ± standard deviations)

Discussion

The PS-B1 used in this study is a fermented product obtained by mixed culture of several different lactic acid bacterial groups in soymilk as culture medium. The fermented product contains components from the soymilk, components present in the lactic acid bacteria, and components produced by the bacteria. The product includes abundant amino acids and peptides of different types in addition to sugar and protein. Lactic acid bacteria is a generic term for facultative anaerobes that can live without oxygen and tolerate acidity greater than 50 % with the molar ratio converted from d-glucose to d,l-lactic acid. In accordance with the definition, proposed by Fuller in 1989, of probiotics as microorganisms that produce beneficial actions in the host by improving the balance of enterobacterial flora, the health-promoting effects of lactic acid bacteria have attracted much attention [14]. In 2002, a joint expert committee report by the Food and Agriculture Organization of the United Nations and World Health Organization redefined probiotics as living bacteria that confer a health effect on the host when consumed in moderate amounts [15]. In agreement with this definition, the reported effects of lactic acid bacteria include regulation of intestinal function [16, 17], anti-allergic activity [1821], anti-cancer activity [22], immunoregulation [2325], and infection control [2628].

In this study we determined that PS-B1 has the effect of retarding the decrease in BMD and deterioration of trabecular bone structure. Kimoto-Nira et al. [29] reported that oral administration of heat-killed Lactococcus lactis subsp. cremoris H61 (strain H61) to aged SAMP6 mice was associated with reduced bone density loss. This is in accordance with the findings of our study, in which significant improvements in total BMD, trabecular BMD, cortical thickness, and endosteal perimeter were observed for the Ps 2 % group compared with the OVX control group (Table 3); it is also reflected in the results of three-point breaking tests, although no significant differences were recorded (Table 7). Similar to osteoporosis model mice, senescence-accelerated mice have greater bone resorption than bone formation, which results in reduced bone density. Inhibition of the decrease in bone density by administration of lactic acid bacteria is also reported to lead to reduction in the number of osteoclasts [29]. This suggests that administration of lactic acid bacteria has a greater effect in inhibiting bone resorption than in promoting bone formation. We also found that PS-B1 impeded the deterioration of trabecular bone structure (Tables 4, 5, 6). However, significant decreases were observed in Tb.Sp and Tb.Spac only in the Ps 1 % group compared with the OVX control group. No significant changes were seen in BMD. The low concentration of PS-B1 is a possible reason for this finding. Similar to the Ps 2 % group, significant increases in BV/TV, Tb.N, N.Ct.TV, and CtCt/TV, and decreases in Tb.Sp, Tb.Spac, and V*m.space were observed for the Ps 5 % group compared with the OVX control group. However, no significant differences were seen in properties related to bone density in the pQCT measurements (Table 3). This suggests that the effect of PS-B1 is not necessarily dose-dependent, and that an appropriate concentration must be maintained.

The effect on osteoporosis of administering PS-B1 may be because of glutamic acid, the main component of PS-B1. It has been reported that systemic administration of glutamate significantly prevented reduced BMD and increased the number of osteoclasts in OVX mice in vivo [30]. It is known that osteoblasts and osteoclasts regulate bone formation and maintenance in a sophisticated fashion [31, 32]. Recent studies have suggested that glutamate may be one of the endogenous factors used for intercellular communication in bone by activating N-methyl-D-aspartate receptors expressed by osteoclasts [3335]. In bone-resorbing osteoclasts, glutamate and bone degradation products are secreted by transcytosis, and the released glutamate is involved in autoregulation of transcytosis. Glutamate signaling may be important in bone homeostasis [36]. Prevention of osteoporotic changes by glutamate seems to occur as a result of suppression of osteoclastogenesis, by retrograde operation of the cystine/glutamate antiporter expressed in osteoclasts, and by stimulation of osteoblastogenesis by activation of N-methyl-D-aspartate receptors expressed in osteoblasts [37]. Hinoi et al. [30] suggested that the cystine/glutamate antiporter may be a novel target that could be very beneficial in developing strategies for treating a variety of bone diseases, for example postmenopausal osteoporosis. The results of this study suggested that the preventive effect of PS-B1 on osteoporosis is caused by glutamic acid. PS-B1 contains a variety of amino acids and peptides in addition to glutamic acid.

Recently, many probiotic products have used lactic acid bacteria. One typical such product is 1,4-dihydroxy-2-naphthoic acid (DHNA). DHNA is a metabolic by-product of fermentation by Propionibacterium freudenreichii. Matsubara et al. reported that DHNA suppresses the production of inflammatory cytokines—interleukin (IL)-1β, IL-6, and tumor necrosis factor-α [38]. Furthermore, DHNA inhibits bone resorption caused by osteoclast suppression. In this study we did not compare PS-B1 with other products, for example probiotics from lactic acid bacteria. Because it is not clear which product is most effective, comparison of PS-B1 and other products should be considered in future studies.

Modern society is aging, and the number of patients with osteoporosis is rapidly increasing. Osteoporosis causes a sharp decline in quality of life, and finding countermeasures has thus become a major issue. In this regard, increasing attention has been focused on the use of dietary supplements as a means of preventing osteoporosis. Foods that have a promising preventive effect against osteoporosis include vitamin K2 (menapuinone 7), citric acid, pycnogenol, and β-cryptoxanthin. Vitamin K2 promotes bone formation via carboxylation of osteocalcin produced by osteoblasts [39]. Citric acid promotes the absorption of calcium in the intestine via chelation [40]. Pycnogenol is known to block the activity of matrix metalloproteinase and inhibit destruction of the bone matrix [41]. β-Cryptoxanthin is known to inhibit differentiation of bone marrow cells into osteoclasts [42]. Substances produced by lactic acid bacteria have also been shown to be effective and flexible in osteoporosis prevention.

In conclusion, we were able to confirm that lactic acid bacteria inhibit the decrease in bone density and deterioration of trabecular bone structure. We suggest that fermented soy products from lactic acid bacteria are useful as complementary, alternative medicines for preventing osteoporosis.

Conflict of interest

There are no financial or other relationships that could lead to a conflict of interest.

Copyright information

© Japanese Society for Oral and Maxillofacial Radiology and Springer Japan 2013