prophylaxis of osteoporosis are primarily based on calcium supplementation as
a main constituent of bone hydroxyapatite mineral. Despite previous reports
suggesting an essential role in skeletal growth and development, the significance
of the trace element silicon in human bone formation has attracted major scientific
interest only rather recently. The interest in silicon has been further increased by
the latest discoveries in the field of biosilicification, the formation of the inorganic
silica skeleton of the oldest still extant animals on Earth, the sponges, which revealed
new insights in the biological function of this element. Sponges make use of silicon
to build up their inorganic skeleton which consists of biogenously formed polymeric
silica (biosilica). The formation of biosilica is mediated by specific enzymes,
silicateins, which have been isolated, characterized, and expressed in a recombinant
way. Epidemiological studies revealed that dietary silicon reduces the risk of osteoporosis and other bone diseases. Recent results allowed for the first time to understand the molecular mechanism underlying the protective effect of silicic acid/
biosilica against osteoporosis. Biosilica was shown to modulate the ratio of expression of two cytokines involved in bone formation–RANKL and osteoprotegerin.
Hence, biosilica has been proposed to have a potential in prophylaxis and therapy
of osteoporosis and related bone diseases.
10.1 Introduction
Osteoporosis is the most common metabolic bone disorder (Sambrook and Cooper
2006). Over 200 million people suffer from osteoporosis worldwide (Reginster
and Burlet 2006). The prevalence of the disease will further increase as a result of
the demographic development in many industrialized countries. Osteoporosis is
associated with an enhanced risk of bone fracture (Cummings and Melton 2002).
The increased bone fragility is caused by a reduced mineral density of bone tissue and
by a deterioration of the bone microarchitecture (Faibish et al. 2006). Osteoporosis is
most common in women after menopause but may also develop in men (reviewed in:
Patlak 2001; Raisz 2005; Khosla et al. 2008a, b). The disease can be classified as
either primary or secondary. Primary osteoporosis is often due to estrogen deficiency
in women following menopause (postmenopausal osteoporosis), but may also
develop at older age in men (senile osteoporosis, in both females and males).
Secondary osteoporosis may occur as a result of hormonal disorders (e.g., hyperparathyroidism) or treatment of patients with glucocorticoids (steroid-induced osteoporosis) (Adachi 1997). In addition, nutritional factors may be involved in the
development of osteoporotic disorders (reviewed in: Jugdaohsingh 2007).
The progressive deterioration of the microarchitecture of bone tissue in osteoporosis particularly concerns cancellous (trabecular) bone, resulting in shrinkage
of cortical width, rarefaction of the trabecular network and increased occurrence
of disconnected trabeculae due to increased osteoclastic resorption. Hence, hip
fractures (fractures of the proximal femur) and vertebral fractures (compression
fractures) are often observed in osteoporotic patients (Gardner et al. 2006).
284
H.C. Schr€ oder et al.
a main constituent of bone hydroxyapatite mineral. Despite previous reports
suggesting an essential role in skeletal growth and development, the significance
of the trace element silicon in human bone formation has attracted major scientific
interest only rather recently. The interest in silicon has been further increased by
the latest discoveries in the field of biosilicification, the formation of the inorganic
silica skeleton of the oldest still extant animals on Earth, the sponges, which revealed
new insights in the biological function of this element. Sponges make use of silicon
to build up their inorganic skeleton which consists of biogenously formed polymeric
silica (biosilica). The formation of biosilica is mediated by specific enzymes,
silicateins, which have been isolated, characterized, and expressed in a recombinant
way. Epidemiological studies revealed that dietary silicon reduces the risk of osteoporosis and other bone diseases. Recent results allowed for the first time to understand the molecular mechanism underlying the protective effect of silicic acid/
biosilica against osteoporosis. Biosilica was shown to modulate the ratio of expression of two cytokines involved in bone formation–RANKL and osteoprotegerin.
Hence, biosilica has been proposed to have a potential in prophylaxis and therapy
of osteoporosis and related bone diseases.
10.1 Introduction
Osteoporosis is the most common metabolic bone disorder (Sambrook and Cooper
2006). Over 200 million people suffer from osteoporosis worldwide (Reginster
and Burlet 2006). The prevalence of the disease will further increase as a result of
the demographic development in many industrialized countries. Osteoporosis is
associated with an enhanced risk of bone fracture (Cummings and Melton 2002).
The increased bone fragility is caused by a reduced mineral density of bone tissue and
by a deterioration of the bone microarchitecture (Faibish et al. 2006). Osteoporosis is
most common in women after menopause but may also develop in men (reviewed in:
Patlak 2001; Raisz 2005; Khosla et al. 2008a, b). The disease can be classified as
either primary or secondary. Primary osteoporosis is often due to estrogen deficiency
in women following menopause (postmenopausal osteoporosis), but may also
develop at older age in men (senile osteoporosis, in both females and males).
Secondary osteoporosis may occur as a result of hormonal disorders (e.g., hyperparathyroidism) or treatment of patients with glucocorticoids (steroid-induced osteoporosis) (Adachi 1997). In addition, nutritional factors may be involved in the
development of osteoporotic disorders (reviewed in: Jugdaohsingh 2007).
The progressive deterioration of the microarchitecture of bone tissue in osteoporosis particularly concerns cancellous (trabecular) bone, resulting in shrinkage
of cortical width, rarefaction of the trabecular network and increased occurrence
of disconnected trabeculae due to increased osteoclastic resorption. Hence, hip
fractures (fractures of the proximal femur) and vertebral fractures (compression
fractures) are often observed in osteoporotic patients (Gardner et al. 2006).
284
H.C. Schr€ oder et al.