Oral Administration of .BETA.-Cryptoxanthin Prevents Bone Loss in Streptozotocin-Diabetic Rats in Vivo

Nutraceuticals and Functional Foods: A Comprehensive Review of Their Role in Bone Health

Bone health is the result of a tightly regulated balance between bone modeling and bone remodeling, and alterations of these processes have been observed in several diseases both in adult and pediatric populations. The imbalance in bone remodeling can ultimately lead to osteoporosis, which is most often associated with aging, but contributing factors can already act during the developmental age, when over a third of bone mass is accumulated. The maintenance of an adequate bone mass is influenced by genetic and environmental factors, such as physical activity and diet, and particularly by an adequate intake of calcium and vitamin D. In addition, it has been claimed that the integration of specific nutraceuticals such as resveratrol, anthocyanins, isoflavones, lycopene, curcumin, lutein, and β-carotene and the intake of bioactive compounds from the diet such as honey, tea, dried plums, blueberry, and olive oil can be efficient strategies for bone loss prevention. Nutraceuticals and functional foods are largely used to provide medical or health benefits, but there is an urge to determine which products have adequate clinical evidence and a strong safety profile. The aim of this review is to explore the scientific and clinical evidence of the positive role of nutraceuticals and functional food in bone health, focusing both on molecular mechanisms and on real-world studies.

Enhanced water dispersibility and permeability through a Caco-2 cell monolayer of β-cryptoxanthin extracted from kumquats by complexation with casein

β-Cryptoxanthin (BCX) possesses potential therapeutic and health benefits. However, BCX absorption is low because of its poor aqueous solubility. In this study, a complex between BCX and casein (Cas) was prepared to improve the water dispersibility and bioavailability of BCX. BCX was recovered quantitatively from freeze-dried kumquat powder through solid-liquid extraction and saponification. The complexation significantly improved the apparent solubility of BCX under acidic and neutral conditions. A cell membrane permeation test using a Caco-2 cell monolayer was performed to evaluate the bioavailability of the BCX-Cas complex. This complex and a blank sample were digested in vitro and added to the apical side of the Caco-2 cell membrane. The quantity of BCX that permeated using the BCX-Cas complex after 24 h was 22.7 times greater than that of the blank. Thus, complexation of BCX with Cas improved dramatically the bioavailability of BCX from a kumquat extract.

Curcumin nanoparticles have potential antioxidant effect and restore tetrahydrobiopterin levels in experimental diabetes

Diabetes is associated with an increase in the production of free radicals, reduction of tetrahydrobiopterin (BH4, THB) levels and reduced bioavailability of nitric oxide (NO) in the vascular walls. In this contribution, we probed the effective role of curcumin nanoparticles (CUR-NPs) that prepared via solvent evaporation nanoprecipitation technique as potential system to attenuate endothelial dysfunction. In this technique, Tween 60 (polysorbate) was used as stabilizing agent for the prepared CUR-NPs and protect such nanoparticles from further agglomeration. BH4 levels and other parameters were estimated in diabetic rats. To this end, we dedicated 48 male albino rats, categorized into six groups; control (healthy rats), diabetic rats, along with four treated groups via oral administration of 0.2 mL/kg body weight/day of solutions of Tween 60 (60 mg/mL), free CUR (60 mg/mL), CUR-NPs1 (30 mg/mL), and CUR-NPs2 (60 mg/mL) for 30 days. Results showed that the mean level of malondialdehyde (MDA) has been significantly increased in diabetic group associated with a reduction of total antioxidant capacity, NO, and BH4 compared to control. These parameters were restored by the delivery of CUR-NPs - both doses in rats, compared with the two control groups that treated with Tween 60 and free CUR.

Absorption, metabolism, and functions of β-cryptoxanthin

β-Cryptoxanthin, a carotenoid found in fruits and vegetables such as tangerines, red peppers, and pumpkin, has several functions important for human health. Most evidence from observational, in vitro, animal model, and human studies suggests that β-cryptoxanthin has relatively high bioavailability from its common food sources, to the extent that some β-cryptoxanthin-rich foods might be equivalent to β-carotene-rich foods as sources of retinol. β-Cryptoxanthin is an antioxidant in vitro and appears to be associated with decreased risk of some cancers and degenerative diseases. In addition, many in vitro, animal model, and human studies suggest that β-cryptoxanthin-rich foods may have an anabolic effect on bone and, thus, may help delay osteoporosis.

Beta-cryptoxanthin as a source of vitamin A

Beta-cryptoxanthin is a common carotenoid that is found in fruit, and in human blood and tissues. Foods that are rich in beta-cryptoxanthin include tangerines, persimmons and oranges. Beta-cryptoxanthin has several functions that are important for human health, including roles in antioxidant defense and cell-to-cell communication. Most importantly, beta-cryptoxanthin is a precursor of vitamin A, which is an essential nutrient needed for eyesight, growth, development and immune response. We evaluate the evidence for beta-cryptoxanthin as a vitamin A-forming carotenoid in this paper. Observational, in vitro, animal model and human studies suggest that beta-cryptoxanthin has greater bioavailability from its common food sources than do alpha- and beta-carotene from theirs. Although beta-cryptoxanthin appears to be a poorer substrate for beta-carotene 15,15' oxygenase than is beta-carotene, animal model and human studies suggest that the comparatively high bioavailability of beta-cryptoxanthin from foods makes beta-cryptoxanthin-rich foods equivalent to beta-carotene-rich foods as sources of vitamin A. These results mean that beta-cryptoxanthin-rich foods are probably better sources of vitamin A, and more important for human health in general, than previously assumed.

β-cryptoxanthin regulates bone resorption related-cytokine production in human periodontal ligament cells

OBJECTIVE

β-cryptoxanthin (β-cry) is a type of carotenoid found in certain fruits and vegetables. Although it has been shown that β-cry inhibits alveolar bone resorption, the molecular mechanisms for this have not yet been clarified. In the present study, we investigated the effects of β-cry on bone resorption related-cytokine production in human periodontal ligament (hPDL) cells.

DESIGN

hPDL cells were stimulated with β-cry (1×10(-7)mol/l), mechanical stress (1 or 6MPa), and P. gingivalis. The production of interleukin (IL)-1β, IL-6, IL-8, tumour necrosis factor (TNF)-α, osteoprotegerin (OPG), and receptor activator of nuclear factor kappa-B ligand (RANKL) were analyzed by RT-PCR and ELISA.

RESULTS

The production of IL-1β, IL-6, IL-8, and TNF-α was not induced in hPDL cells after stimulation with β-cry, although these cytokines were produced after stimulation with P. gingivalis. On the other hand, IL-6 and IL-8 were produced after exposure to 6MPa of mechanical stress. The production of IL-6 and IL-8 was significantly decreased by the addition of β-cry. Furthermore, β-cry up-regulated the production of OPG, but not RANKL.

CONCLUSION

β-cry inhibited the production of IL-6 and IL-8 induced by mechanical stress and periodontopathogenic bacteria in hPDL cells. Moreover, β-cry up-regulated OPG production. These results suggest that β-cry may prevent bone resorption in periodontitis.

Role of carotenoid β-cryptoxanthin in bone homeostasis

Bone homeostasis is maintained through a balance between osteoblastic bone formation and osteoclastic bone resorption. Aging induces bone loss due to decreased osteoblastic bone formation and increased osteoclastic bone resorption. Osteoporosis with its accompanying decrease in bone mass is widely recognized as a major public health problem. Nutritional factors may play a role in the prevention of bone loss with aging. Among various carotenoids (carotene and xanthophylls including beta (β)-cryptoxanthin, lutein, lycopene, β-carotene, astaxanthin, and rutin), β-cryptoxanthin, which is abundant in Satsuma mandarin orange (Citrus unshiu MARC.), has been found to have a stimulatory effect on bone calcification in vitro. β-cryptoxanthin has stimulatory effects on osteoblastic bone formation and inhibitory effects on osteoclastic bone resorption in vitro, thereby increasing bone mass. β-cryptoxanthin has an effect on the gene expression of various proteins that are related osteoblastic bone formation and osteoclastic bone resororption in vitro. The intake of β-cryptoxanthin may have a preventive effect on bone loss in animal models for osteoporosis and in healthy human or postmenopausal women. Epidemiological studies suggest a potential role of β-cryptoxanthin as a sustainable nutritional approach to improving bone health of human subjects. β-Cryptoxanthin may be an osteogenic factor in preventing osteoporosis in human subjects.

Alteration of vitamin D metabolic enzyme expression and calcium transporter abundance in kidney involved in type 1 diabetes-induced bone loss

This study aimed to delineate the mechanism involved in type 1 diabetes-induced bone loss. The results revealed the alteration of vitamin D metabolic enzyme expression and the downregulation of renal calcium transporter abundance in type 1 diabetic mice.

INTRODUCTION

The purpose of this study was to investigate the changes of the expression of vitamin D metabolic enzymes and transcellular calcium-transporting proteins in kidneys from mice with experimentally induced diabetes.

METHODS

Male DBA/2J mice were injected with either vehicle (control) or streptozotocin (STZ) daily for five consecutive days. Bone mineral density was measured by peripheral quantitative computerized tomography, and bone histomorphology was analyzed by Safranin O staining. Real-time PCR and Western blotting were applied to determine the expression of target genes and proteins.

RESULTS

Type 1 diabetes produced high urinary calcium excretion and loss of trabecular bone measured at the proximal metaphysis of the tibia and the distal femur. Bone loss was associated with deterioration of trabecular bone microstructure. Quantified PCR results showed that mRNA expression level in the kidney of diabetic mice for 25-hydroxyvitamin D-24-hydroxylase was downregulated at week 10, while those for 25-hydroxyvitamin D-1α-hydroxylase were upregulated at week 20. In addition, mRNA expression levels for renal transient receptor potential V6, plasma membrane Ca-ATPase (PMCA)1b, and vitamin D receptor (VDR) genes were decreased in STZ-treated mice. Western blot analysis showed that protein expression of PMCA1b and VDR was significantly decreased in kidneys from STZ-treated mice compared to that of controls.

CONCLUSIONS

The limitation in this study is the lack of vitamin D, parathyroid hormone, and phosphorus levels in serum. However, the present study supports the conclusion that the underlying mechanism contributing to type 1 diabetes-associated bone loss may be alterations of vitamin D metabolic enzyme expression and associated decreases in expression of renal calcium transporters.

Hepatic gene expression of the insulin signaling pathway is altered by administration of persimmon peel extract: a DNA microarray study using type 2 diabetic Goto-Kakizaki rats

Persimmon (Diospyros kaki) is a very popular fruit in East Asian countries, but its peels are not consumed despite the fact that they contain many antioxidants such as carotenoids and polyphenols. We prepared a fat-soluble extract from persimmon peel (PP) and fed type 2 diabetic Goto-Kakizaki (GK) rats an AIN-93G rodent diet supplemented with persimmon peel extract (PP diet) for 12 weeks. Compared with the control AIN-93G diet, the PP diet significantly reduced plasma glutamic-pyruvate transaminase activity, with accumulation of β-cryptoxanthin in the liver. DNA microarray analysis revealed that the PP diet altered hepatic gene expression profiles. In particular, expression of insulin signaling pathway-related genes was significantly enriched in differentially expressed gene sets. Moreover, Western blotting analysis showed an increase in insulin receptor beta tyrosine phosphorylation in rats fed the PP diet. These data suggest that the PP diet improves insulin resistance in GK rats.

Effect of Picrorrhiza rhizoma extracts on early diabetic nephropathy in streptozotocin-induced diabetic rats

The hypoglycemic effect of an aqueous extract of Picrorrhiza Rhizoma (PR) was investigated on diabetic nephropathy. The body weight of each of eight rats per group was measured 7 days after streptozotocin (STZ) treatment. The blood glucose levels 3 days after STZ treatment and the changes in body weight, kidney weight, blood glucose levels, and serum blood urea nitrogen (BUN) were also measured, and the histopathology of the kidney was examined. Body weight decreases and increases of kidney weight, blood glucose levels, and serum BUN and creatinine levels were detected in the diabetic control with histopathological changes related to diabetic nephropathy in the kidney. However, the level of hyperglycemia was significantly lowered in all groups given the PR extract. In addition, the changes related to diabetic nephropathy with the body weight were also significantly lower in the captopril and all PR extract-dosing groups than in the diabetic control. In conclusion, an aqueous extract of PR has relatively good inhibitory effects on STZ-induced diabetes with early diabetic nephropathy with a similar efficacy to an equal dose of captopril.

Application of comprehensive two-dimensional liquid chromatography to elucidate the native carotenoid composition in red orange essential oil

In the present work, the ability of a LC x LC-DAD/APCI-MS method developed at this laboratory to identify the native composition of carotenoid in an extremely complex matrix such as red orange essential oil was demonstrated. To carry out this task, two independent and orthogonal separation mechanisms were coupled through a 10-port switching valve that simultaneously collected the eluent from a microbore cyano column used as the first dimension in normal phase mode and injected it to a conventional reversed phase monolithic C(18) column in the second dimension separation. By using this novel analytical technique together with the use of DAD and APCI-MS detectors it was possible to identify in the sample, without the need of any pretreatment, 40 different carotenoids. Among them, 16 carotenoid monoesters were identified, mainly beta-cryptoxanthin palmitate (C(16:0)), myristate (C(14:0)), and laureate (C(12:0)) as well as several lutein, violaxanthin, antheraxanthin, and luteoxanthin monoesters. Moreover, 21 carotenoid diesters composed by several antheraxanthin, luteoxanthin, violaxanthin, and auroxanthin diesters were found in the native carotenoid composition of the orange oil. The main carotenoid diesters were the laureate palmitate (C(12:0), C(16:0)), myristate palmitate (C(14:0), C(16:0)), and dipalmitate (C(16:0), C(16:0)) diesters, although other diesters were also identified. Besides, two different free carotenes, zeta-carotene and phytofluene, and a xanthophyll, lutein, were also determined. To the authors' knowledge, this is the first time that carotenoid diesters are described and identified in orange essential oil. Likewise, it has been demonstrated that the LC x LC approach proposed in this study is capable of coping with the direct analysis and identification of a complex natural source of carotenoids such as the orange.

Seasonal variation of serum alpha- and beta-cryptoxanthin and 25-OH-vitamin D(3) in women with osteoporosis

beta-Cryptoxanthin displays a unique anabolic effect on bone calcification. In women with osteoporosis, serum beta-cryptoxanthin and 25-OH-vitamin D(3) showed a weak but significant correlation and exhibited a complementary seasonal distribution. The potential role of beta-cryptoxanthin as a nutritional approach to improving bone health deserves further evaluation.

INTRODUCTION

Dietary intake and serum levels of beta-cryptoxanthin have been inversely related to different bone and joint disorders and in vitro and animal studies have shown that beta-cryptoxanthin displays a unique anabolic effect on bone calcification. Due to the emerging role of beta-cryptoxanthin in bone biology, we aimed to assess the serum distribution and variability of beta-cryptoxanthin and their potential relation to 25-OH-vitamin D(3) in women with osteoporosis.

METHODS

Serum concentrations of alpha- and beta-cryptoxanthin and 25-OH- D(3) in women with osteoporosis (N = 644) were analyzed using a quality-controlled high-performance liquid chromatography (HPLC) method.

RESULTS

Overall, significant seasonal variations were found for the three analytes and inter-individual variation was also high (60-73%). beta-cryptoxanthin and 25-OH-vitamin D(3) exhibited a marked complementary seasonal distribution in serum, with vitamin D displaying the highest values in summer and beta-cryptoxanthin in winter.

CONCLUSIONS

Given the anabolic effect of beta-cryptoxanthin on bone calcification and its complementary seasonal distribution with respect to 25-OH-vitamin D(3), the potential role of beta-cryptoxanthin as a sustainable nutritional approach to improving bone health deserves to be further evaluated.

Anabolic effect of beta-cryptoxanthin in osteoblastic MC3T3-E1 cells is enhanced with 17beta-estradiol, genistein, or zinc sulfate in vitro: the unique effect with zinc on Runx2 and alpha1(I) collagen mRNA expressions

Whether the anabolic effect of beta-cryptoxanthin (CRP), a kind of carotenoid, on osteoblastic MC3T3-E1 cells are modulated in the presence of various hormones or nutrient factors were investigated. Cells were cultured for 72 h in a minimum essential medium containing 10% fetal bovine serum (FBS), and the cells with subconfluency were changed to a medium containing either vehicle or CRP (10(-8)-10(-6) M) in the presence or absence of various factors without FBS. Cells were cultured for 72 h. Protein content or alkaline phosphatase activity in osteoblastic cells were significantly increased after culture with CRP (10(-7) or 10(-6) M), 1,25-dihydroxyvitamin D(3) (VD(3); 10(-9) or 10(-8) M), 17beta-estradiol (E(2); 10(-9) M), genistein (10(-7) or 10(-6) M), or menaquinone-7 (MK-7; 10(-7) or 10(-6) M). The effect of CRP (10(-6) M) in increasing protein content in the cells was significantly enhanced in the presence of E(2) (10(-9) M) or genistein (10(-6) M). Gene expression in osteoblastic cells was determined using reverse transcription-polymerase chain reaction (RT-PCR). Culture with CRP (10(-7) or 10(-6) M) caused a significant increase in the expression of Runx2 and alkaline phosphatase mRNAs in the cells. Runx2 mRNA expression was significantly increased after culture with E(2) (10(-9) M) or MK-7 (10(-7) or 10(-6) M), but not VD(3) (10(-9) or 10(-8) M) or genistein (10(-7) or 10(-6) M). Alkaline phosphatase mRNA expression was significantly increased after culture with VD(3) (10(-9) or 10(-8) M), genistein (10(-7) or 10(-6) M), or MK-7 (10(-7) or 10(-6) M), but not E(2) (10(-10) or 10(-9) M). The effect of CRP (10(-7) or 10(-6) M) in increasing Runx2 or alkaline phosphatase mRNA expressions in the cells was not enhanced in the presence of VD(3), E(2), genistein, or MK-7. Culture with zinc sulfate (zinc; 10(-5) M) caused a significant increase in protein content or alkaline phosphatase activity in osteoblastic cells. The effect of CRP (10(-7) M) in increasing protein content or alkaline phosphatase activity in the cells was not significantly enhanced in the presence of zinc (10(-5) M). Culture with zinc (10(-5) M) caused a significant increase in alpha1(I) collagen mRNA expression, while it did not have a significant effect on Runx2 or osteocalcin mRNA expressions in the cells. The effect of CRP (10(-7) M) in increasing Runx2 or alpha1(I) collagen mRNA expressions was significantly enhanced in the presence of zinc (10(-6 )or 10(-5) M). Such an effect was not seen in the presence of cycloheximide (10(-7) M), an inhibitor of protein synthesis, or 5,6-dichloro-1-beta-D: -ribofuranosyl-benzimidazole (DRB; 10(-6) M), an inhibitor of transcriptional activity. This study demonstrates that the stimulatory effect of CRP on protein content in osteoblastic cells was additively enhanced with E(2) or genistein, and that the stimulatory effect of CRP on Runx2 or alpha1(I) collagen mRNA expressions was enhanced in the presence of zinc. Thus, the anabolic effect of CRP in osteoblastic MC3T3-E1 cells was modulated with a specific factor.

Regulatory mechanism of food factors in bone metabolism and prevention of osteoporosis

Aging induces a decrease in bone mass, and osteoporosis with its accompanying decrease in bone mass is widely recognized as a major public health problem. Bone loss with increasing age may be due to decreased bone formation and increased bone resorption. Pharmacologic and nutritional factors may prevent bone loss with aging, although chemical compounds in food and plants which act on bone metabolism are poorly understood. We have found that isoflavones (including genistein and daidzein), which are contained in soybeans, have a stimulatory effect on osteoblastic bone formation and an inhibitory effect on osteoclastic bone resorption, thereby increasing bone mass. Menaquinone-7, an analogue of vitamin K(2) which is abundant in fermented soybeans, has been demonstrated to stimulate osteoblastic bone formation and to inhibit osteoclastic bone resorption. Of various carotenoids, beta-cryptoxanthin, which is abundant in Satsuma mandarin (Citrus unchiu MARC), has a stimulatory effect on osteoblastic bone formation and an inhibitory effect on osteoclastic bone resorption. The supplementation of these factors has a preventive effect on bone loss induced by ovariectomy in rats, which are an animal model of osteoporosis, and their intake has been shown to have a stimulatory effect on bone mass in humans. Factors with an anabolic effect on bone metabolism were found in extracts obtained from wasabi leafstalk (Wasabi japonica MATSUM), the marine alga Sargassum horneri, and bee pollen Cistus ladaniferus. Phytocomponent p-hydroxycinnamic acid was also found to have an anabolic effect on bone metabolism. Food chemical factors thus play a role in bone health and may be important in the prevention of bone loss with increasing age.

Beta-cryptoxanthin stimulates apoptotic cell death and suppresses cell function in osteoclastic cells: change in their related gene expression

The effect of beta-cryptoxanthin, a kind of carotenoid, on osteoclastic cells in mouse marrow culture system in vitro was investigated. The macrophage colony-stimulating factor (M-CSF)-dependent bone marrow macrophages were cultured in the presence of M-CSF (10 ng/ml) and receptor activator of NF-kappaB ligand (RANKL; 25 ng/ml) for 4 days. The osteoclastic cells formed were further cultured in medium containing either vehicle or beta-cryptoxanthin (10(-8)-10(-6) M) with or without M-CSF (10 ng/ml) and RANKL (50 ng/ml) for 24-72 h. Osteoclastic cells were significantly decreased with culture of beta-cryptoxanthin (10(-7) or 10(-6) M) with or without M-CSF and RANKL for 24, 48, or 72 h. beta-Cryptoxanthin (10(-8) M)-induced decrease in osteoclastic cells were significantly inhibited in the presence of caspase-3 inhibitor (10(-8) or 10(-7) M). Agarose gel electrophoresis showed the presence of low-molecular-weight deoxyribonucleic acid (DNA) fragments of adherent cells cultured with beta-cryptoxanthin (10(-7) or 10(-6) M) for 24 or 48 h, indicating that the carotenoid induces apoptotic cell death. Apoptosis-related gene expression was determined using reverse transcription-polymerase chain reaction (RT-PCR). Culture with beta-cryptoxanthin (10(-7) or 10(-6) M) for 24 or 48 h caused a significant increase in caspase-3 mRNA expression in the presence or absence of M-CSF and RANKL, while Bcl-2 and Apaf-2 mRNA expressions were significantly increased with culture of beta-cryptoxanthin (10(-7) or 10(-6) M) without M-CSF and RANKL for 24 or 48 h. Akt-1 mRNA expression was not significantly changed with culture of the carotenoid (10(-7) or 10(-6) M) for 24 or 48 h. Moreover, tartrate-resistant acid phosphatase (TRACP) activity, or TRACP and cathepsin K mRNA expressions were significantly decreased with culture of beta-cryptoxanthin (10(-6) M) in the presence or absence of M-CSF and RANKL for 48 h. This study demonstrates that beta-cryptoxanthin has stimulatory effects on apoptotic cell death and suppressive effects on osteoclastic cell function.

Oral Administration in Combination with Zinc Enhances .BETA.-Cryptoxanthin-Induced Anabolic Effects on Bone Components in the Femoral Tissues of Rats in Vivo

The effects of combined beta-cryptoxanthin and zinc on bone components in the femoral-diaphyseal (cortical bone) and -metaphyseal (trabecular bone) tissues of rats in vivo were investigated. Rats were orally administered either vehicle, beta-cryptoxanthin (5 or 10 microg/100 g body weight), zinc sulfate (0.1 or 0.5 mg Zn/100 g), or their combination once a day for 7 d. Calcium content, alkaline phosphatase activity, and DNA content in the femoral-diaphyseal tissues was not significantly altered by the administration of beta-cryptoxanthin (5 microg/100 g) or zinc (0.1 or 0.5 mg/100 g). Combined administration of beta-cryptoxanthin (5 microg/100 g) and zinc (0.1 or 0.5 mg/100 g) caused a synergistic increase in calcium content, alkaline phosphatase activity, and DNA content in the diaphyseal tissues. The effect of beta-cryptoxanthin (5 or 10 microg/100 g) in increasing calcium and DNA contents in the metaphyseal tissues was significantly enhanced by the combined administration of zinc (0.1 or 0.5 mg/100 g), but did not have a significant effect on the metaphyseal components. The metaphyseal alkaline phosphatase activity was markedly increased by the combination of beta-cryptoxanthin (5 microg/100 g) and zinc (0.1 or 0.5 mg/100 g). This study demonstrates that the oral administration of the combination of zinc at lower doses synergistically enhances beta-cryptoxanthin-induced anabolic effects on bone components in the femoral tissues of rats in vivo.

Synergistic effect of beta-cryptoxanthin and zinc sulfate on the bone component in rat femoral tissues in vitro: the unique anabolic effect with zinc

The effect of the combination of beta-cryptoxanthin and zinc sulfate (zinc) on bone components in the femoral-diaphyseal and -metaphyseal tissues of young rats in vitro was investigated. Bone tissues were cultured for 48 h in a serum-free Dulbecco's modified Eagle's medium containing either vehicle, beta-cryptoxanthin (10(-9)-10(-7) M) or zinc sulfate (10(-6)-10(-4) M). The presence of beta-cryptoxanthin (10(-9) M) or zinc (10(-6) M) did not have a significant effect on calcium content in the femoral-diaphyseal or -metaphyseal tissues. However, culture which combined beta-cryptoxanthin (10(-9) M) and zinc (10(-6) M) caused a significant increase in calcium content in the femoral-diaphyseal and -metaphyseal tissues. Such an effect was not observed by the combination of beta-cryptoxanthin (10(-9) M) plus genistein (10(-6) M) or menaquinone-7 (10(-6) M), or zinc (10(-6) M) plus genistein (10(-6) M) or menaquinone-7 (10(-6) M). Also, the combination of beta-cryptoxanthin (10(-9) M) plus zinc (10(-6) M) caused a remarkable increase in alkaline phosphatase activity and deoxyribonucleic acid (DNA) in the femoral-diaphyseal and -metaphyseal tissues, while their application alone did not have an effect on the enzyme activity or DNA content in the femoral tissues. The effect of the combination of beta-cryptoxanthin (10(-9) M) plus zinc (10(-6) M) in increasing calcium content, alkaline phosphatase activity, and DNA content in the femoral-diaphyseal and -metaphyseal tissues was completely prevented in the presence of cycloheximide (10(-6) M), an inhibitor of protein synthesis, or 5,6-dichloro-1-beta-D-ribofuranosylbenzimidazole (DBR), an inhibitor of transcriptional activity. This study demonstrates that the combination of beta-cryptoxanthin and zinc at a lower concentration has a synergistic effect on bone components in vitro.