High osteocalcin microcrystalline hydroxyapatite for calcium supplement

Abstract

An improved manufacturing process produces microcrystalline hydroxyapatite with sustained gradual calcium release that avoids spiking in blood calcium levels. Although the improved material did not cause significant elevation of blood calcium, it was just as effective in promoting bone mineralization as conventional calcium supplements. In addition, the material has much higher levels of bone growth factors as compared to prior hydroxyapatite products.

Claims

1. A high osteocalcin microcrystalline hydroxyapatite preparation comprising 60 to 72% calcium hydroxyapatite and less than 1.5% fat, and having a particle size distribution having not more than 30% by weight of particles with a particle size smaller than 250 micron and not less than 90% by weight of particles with a particle size smaller than 850 micron, and wherein less than 70% of the calcium ion is released after 2.5 minutes of in vitro dissolution testing in 0.1M HCl stirred at 150 RPM at 370.5 C.

2. The high osteocalcin microcrystalline hydroxyapatite preparation according to claim 1, comprising 24-28% protein.

3. The high osteocalcin microcrystalline hydroxyapatite preparation according to claim 1, comprising less than 5% loss of moisture on drying, 24-28% protein, 65 to 75% ash residue on ignition, 25 to 29% calcium (Ca), and 10 to 13% phosphorus (P).

4. The high osteocalcin microcrystalline hydroxyapatite preparation according to claim 1, wherein less than 75% of the calcium ion is released after 5 minutes of in vitro dissolution testing in 0.1M HCl stirred at 150 RPM at 370.5 C.

5. The high osteocalcin microcrystalline hydroxyapatite preparation according to claim 1, comprising at least 10 g/g growth factor proteins.

6. The high osteocalcin microcrystalline hydroxyapatite preparation according to claim 1, comprising at least 10 g/g osteocalcin.

7. A high osteocalcin microcrystalline hydroxyapatite preparation comprising 60 to 72% calcium hydroxyapatite, less than 1.5% fat, and 24-28% protein, and having a particle size distribution having not more than 30% by weight of particles with a particle size smaller than 250 micron and not less than 90% by weight of particles with a particle size smaller than 850 micron and wherein less than 70% of the calcium ion is released after 2.5 minutes of in vitro dissolution testing in 0.1M HCl stirred at 150 RPM at 370.5 C.

8. The high osteocalcin microcrystalline hydroxyapatite preparation according to claim 7, wherein less than 75% of the calcium ion is released after 5 minutes of in vitro dissolution testing in 0.1M HCl stirred at 150 RPM at 370.5 C.

9. The high osteocalcin microcrystalline hydroxyapatite preparation according to claim 7, comprising at least 10 g/g growth factor proteins.

10. The high osteocalcin microcrystalline hydroxyapatite preparation according to claim 7, comprising at least 10 g/g osteocalcin.

Description

DESCRIPTION OF THE FIGURES

(1) FIG. 1 is a graph comparing the blood levels of ionized calcium from two different hydroxyapatite preparations to calcium levels provide by other calcium supplements;

(2) FIG. 2 is a graph showing the effect of fat content on calcium dissolution rate;

(3) FIG. 3 is a graph showing the effect of protein content on calcium dissolution rates;

(4) FIG. 4 is a graph showing the effects of particle size on dissolution rate; and

(5) FIG. 5 is shows the effect of sieving on dissolution rate;

DETAILED DESCRIPTION OF THE INVENTION

(6) The following description is provided to enable any person skilled in the art to make and use the invention and sets forth the best modes contemplated by the inventor of carrying out his invention. Various modifications, however, will remain readily apparent to those skilled in the art, since the general principles of the present invention have been defined herein specifically to provide an improved calcium hydroxyapatite calcium supplement that offers a solution to the problem of possible negative effects of calcium supplements.

(7) Because it seems unlikely that natural dietary calcium is fundamentally different from supplemental calcium, it appears that the apparent cardiac problem may be related to the rate of calcium absorption and excretion. A normal well-balanced diet contains sufficient calcium, but that calcium is generally bound to other food components. For example, much of the calcium available in plant material is reversibly bound to certain carbohydrates. During digestion of the food this calcium is gradually released and absorbed mostly in the small intestine. As calcium is being added to the blood stream, it is being simultaneously removed for cellular use and for calcification of bone matrix. Natural homeostatic mechanisms keep the blood concentration of calcium constant at approximately 1 mM which is approximately 10,000 times the normal cellular concentration of calcium. If the diet is supplying excess calcium, calcium is excreted through the kidneys to maintain the 1 mM concentration. However, when large amounts of readily ionized calcium sources are ingested, the results might be different. Ingesting several tablets of calcium carbonate or calcium citrate probably causes a much higher level of ionized calcium to enter the intestine than the amount provided by a normal diet.

(8) In fact, recent tests have shown that when usual supplement amounts of either calcium carbonate or calcium citrate are consumed, blood levels of calcium spike above the normal 1 mM concentration demonstrating that the normal homeostatic control of calcium concentration is being overwhelmed. Surprisingly, this spike continues for around eight hours after ingestion of the supplement. It will be appreciated that ensuring an optimum level of calcium should favor bone mineralization. Ideally, dietary intake should be sufficient to maintain the 1 mM blood calcium concentration even though cellular processes and bone mineralization are constantly withdrawing calcium from the blood. If insufficient calcium is supplied to maintain the blood calcium levels, cellular processes take precedence and calcium is withdrawn from the bone bank to maintain adequate blood levels of calcium. A long-term calcium deficit will result in bone demineralizationosteopenia and osteoporosis. But there is no reason to suppose that providing so much excess calcium so as to override homeostasis necessarily increases the rate of bone mineralization. Clearly, maintaining the blood concentration at normal levels, discourages withdrawal of calcium from the bones, but the process of bone mineralization is controlled by a number of factors besides availability of free calcium. Moreover, now that we understand that chronically high calcium concentrations may promote cardiac problems, the focus of calcium supplementation necessarily changes. The new goal is to constantly provide sufficient calcium so that calcium is never withdrawn from the bones to maintain proper calcium blood concentration while ensuring that calcium is supplied at a sufficiently slow rate that any excess calcium can be excreted without causing significant long-term elevation of calcium blood concentration.

(9) Since it is clear that conventional calcium supplements are absorbed too rapidly, there seems at least two ways that their use might be continued safely. One possibility might be to administer them in small doses spread out over the entire day (and night). However, this might make it difficult to maintain adequate calcium levels if the basic diet is strongly calcium deficient. The second solution would be to use current controlled release technology to allow a single dose of supplement to release calcium slowly over a much more extended period of time. Such an approach is certainly feasible although it is likely to add bulk (to already bulky calcium supplements) as well as cost. Fortunately, the present inventors have discovered an additional way to provide effective calcium supplementation without the danger of excessive concentrations of blood calcium.

(10) For some time microcrystalline hydroxyapatite (MCHA) manufactured from animal bones has been used as a slightly unconventional calcium supplement. Considering that bone mineral is largely calcium phosphate in the form of hydroxyapatite, it seems logical to use MCHA as a source of bone calcium. However, there can be some difficulty in purifying MCHA from native bones because there is considerable excess protein and lipid that must be removed to provide a stable as well as readily digestible product. As might be imagined there is considerable variation in the process parameters for making an MCHA product. In a study intended to compare MCHA to conventional calcium supplements, the inventors analyzed MCHA produced using varied protocols. They were surprised to discover that depending on how the MCHA is manufactured, its rate of bioabsorption changes quite dramatically. After considerable experimentation, the inventors developed the current product which was then compared to calcium carbonate and calcium citrate in both an absorption (measured by blood calcium concentration) and a bone mineralization/density study.

(11) Blood calcium concentration studies showed that ingestion of calcium citrate versus ingestion of calcium carbonate were not statistically significantly different; both calcium sources resulted in long-term (ca. 8 hour) spiking of blood calcium concentration. On the other hand, the preferred inventive MCHA was not statistically significantly different from the calcium-free placebo. That is, following administration of the MCHA the blood calcium concentration did not increase significantly. However, it must be kept in mind that the blood calcium concentration is maintained by withdrawing calcium from the bones if the dietary supply is insufficient. The fact that the MCHA was not statistically significant from the placebo does not necessarily mean that no calcium was being absorbed; it means only that calcium was being absorbed at a rate slow enough to prevent spiking in the blood calcium concentration.

(12) In FIG. 1 the blood levels of ionized calcium of two different MHCA preparations (see below for preparation details) are compared to blood calcium levels provided by other calcium supplements. The figure shows that both calcium carbonate and calcium citrate cause a rapid increase in ionized blood calcium. After 6 hours citrate begins to decline indicating that most of it has been absorbed. MHCA 1 (the first preparation described has no effect on ionized calcium level for over 2 hours and then only a slight effect which is not statistically significantly (asterisks) different than the control (no calcium supplement). MHCA 2 (the finer particle preparation) releases somewhat more calcium than MHCA 1. It will be apparent to one of skill in the art that should it be desired to release calcium even more slowly, the particle size of the MCHA can be easily increased.

(13) Although MCHA does not result in significant spiking of ionized calcium, over a 90 day study administration of MCHA showed essentially no differences in factors indicative of bone formation (PTH [parathyroid hormone], CTX [beta-carboxy-terminal cross-linking telopeptide of type I collagen] and P1NP [type 1 procollagen amino-terminal-propeptide] as compared to spiking calcium supplements such as calcium carbonate and calcium citrate.

(14) The impact of the calcium supplements (MHCA, carbonate and citrate) over the 90 day experimental duration on bone calcium level and other markers of bone mineralization and turnover were not statistically significantly different from each other whereas all were statistically significantly different from the calcium-free placebo. Therefore, the inventive MCHA provided as much effective calcium as the other supplements but did so without causing spiking of the blood calcium concentration. As detailed below MCHA is extracted from native bone and contains all or most of the bone matrix proteins. It seems likely that the hydroxyapatite was released for absorption only after enzymatic digestion of these proteins. That is, the MCHA is inherently a time release product and the rate of this release can be manipulated by the process used to manufacture the MCHA.

(15) The process to manufacture MCHA is fairly straightforward. It differs from prior art processes in that temperature and pH are controlled to avoid denaturing growth factors present in the bone protein matrix. Most prior art processes also employed organic solvents to defat the bonethese also can contribute to denaturation of growth factors.

(16) Step 1) Raw Material Procurement

(17) Leg bone, (diaphysis only from the radius, femur and tibia) of prime bovine of 30 months or less age is sourced from export licensed meat processing plants. Bovines are pre and post mortem inspected and cleared as fit for human consumption. Bovine bone is block frozen to below 12 C. in approved food contact grade cartons.
Frozen material is received from the collection plant with an authorized transfer certificate.
Documentation and frozen product is checked and then removed from the cartons.

(18) Step 2) Frozen Bone is Minced to Reduce Particle Size

(19) Step 3) Temperature Controlled Digestion Process.

(20) Product is immersed in potable water to achieve a target temperature of 60 C.-70 C. and pH is adjusted to achieve a target of 8.5-8.7
Protease (alcalase) is added to remove non-active tissues and fat.

(21) Step 4) Drying and Milling

(22) The product slurry is dried under low temperature vacuum, or freeze-dried, for not more than 24 hours until not more than 5% moisture remains
Product is unloaded into sealed bags
Product is milled into a fine powder until the required particle size distribution of not more than 30% smaller than 250 micron and not less than 90% smaller than 850 micron is achieved (30% Maximum through US Standard 80 mesh screen and 90% Minimum through 20 US Standard mesh screen).
Packed into foil laminate bags inside cardboard carton.
Samples are taken for microbial and chemical testing

(23) The final size distribution of the particles is a product of the degree of mechanical processing and the various mesh sizes used to sieve the product. The starting bone is minced with a mincer/grinder (Bellmore Engineering, Christchurch, NZ) using a 10 mm hole plate. Product milling is done with a model 40B Impact Mill (Chenggan Drying of Jiangsu, China) using a 1.5 mm mill screen and a 1 mm sieve screen. The mill was operated at the 19 amp speed setting.

(24) The end product has the following analysis:

(25) TABLE-US-00001 Analysis Specification Loss on drying (Moisture) %: <5 Fat %: <1.5 Protein (N 6.25) %: 24 to 28 Ash (Residue on Ignition) %: 65 to 75 Calcium (Ca) % 25 to 29 Phosphorus (P) % 10 to 13 Calcium Hydroxyapatite %: 60 to 72

(26) In developing this manufacturing procedure the inventors considered the influence of overall composition and physical characteristics on the rate of calcium dissolution in vitro using the theory that in vitro dissolution would likely be related to in vivo calcium absorption. For these tests an aliquot of material to be tested was placed in 600 ml of 0.1M HCl in a Dissolution Tester manufactured by the TDTF Corporation of Jiangsu, China. The mixture was stirred at 150 RPM at a temperature of 370.5 C. with samples removed periodically. The samples were centrifuged to remove undissolved material and the supernatant was diluted with NH.sub.3/NH.sub.4Cl buffer (pH 10) containing with eriochrome black T as an indicator and titrated to endpoint with 0.1M EDTA. Under these conditions the eriochrome is red in the presence of calcium ions. When sufficient EDTA has been added to chelate all the calcium, the solution turns from red to blue and the amount of added EDTA can be used to calculate the original calcium ion concentration.

(27) The current inventive process produced an MHCA containing more protein and less fat than prior art MHCA preparations while providing a high level of calcium. FIG. 2 shows dissolution results for 0.0%, 2.5% and 5.0% fat, increased fat content appears to correlate with more rapid dissolution of the calciuma somewhat paradoxical result since fat is generally considered to slow the digestive processes. FIG. 3 shows the results of a similar experiment run on similar MHCA products that contained different concentrations of protein. The figure shows that a product containing 25% protein released calcium more slowly than one containing 20% protein. It seems likely that the current process preserves the protein (mostly collagen) matrix surrounding the hydroxyapatite and that the presence of this matrix slow the dissolution of the calcium.

(28) The present process produces a product that has a different analysis than prior art MHCA products such as OHC which is produced according to U.S. Pat. No. 4,919,931. In terms of gross analysis, the present product has more calcium and phosphorous than OHC. The present product also has different particle size distribution than OHC.

(29) The following tables demonstrate that particle distribution size is somewhat more complex than is indicated by the simple screen mesh specifications given in relation to the manufacturing process. The specification requires that more than 90% of the particles (on a weight basis) be smaller than 850 micrometers while not more than 30% of the particles (on a weight basis) be smaller than 250 micrometers. This specification does not define the actual particle size distribution of the preparation. The following table shows an actual screening test. Standard screens have a nominal square opening size, but because actual milled particles are usually elliptical or even somewhat irregular, the average particle size retained by the screen is somewhat larger than the screen opening size.

(30) TABLE-US-00002 Opening Measured Wt. retained Mesh (m) (m) (g) % retained % cumulative 18 1000 1100 0.00 g 0.0% 100.0% 20 850 1000 0.5 g 0.5% 100.0% 35 500 675 8.0 g 7.7% 99.5% 50 300 400 57.0 g 55.1% 91.8% 70 250 275 9.0 g 8.7% 36.7% 80 180 215 10.0 g 9.7% 28% 100 150 200 3.0 g 2.9% 18.4% 140 106 128 5.0 g 4.8% 15.5% 200 75 90.5 3.0 g 2.9% 10.6% 270 53 64 3.0 g 2.9% 7.7% (Pan) 5.0 g 4.8% 4.8%

(31) The MHCA with the above screen profile is the same as MHCA 1 in the clinical tests. This screening test shows that about 4.8% (by weight) of the material passes through a 270 mesh screen. This product meets the specification of less than 30% passing an 80 mesh (actually 18.4% passes) but the above shows the distribution of these very small particles with the majority (74%) being larger than a 270 mesh screen). In terms of large particles, the specification allows as much as 10% (by weight) to be larger than a 20 mesh screen. In fact only 0.5% of the particles are larger than 20 mesh and 0.0% are larger than an 18 mesh. Further 55.1% are retained by a 50 mesh screen and only 36.7% are retained by a 70 mesh which demonstrates a peak in the particle distribution. That is, 99.5% of the particles are smaller than 850 m; 91.8% are smaller than 500 m; 8.2 are larger than 500 m; 28.0% are smaller than 250 m; and 72.0% are greater than 250 m. Another way of considering the size characteristics of such a heterogeneous powder is to compare the tapped (agitated to remove air) versus the untapped bulk density which in this case is 1.08 versus 1.13. Generally, the protein mesh surrounding the hydroxyapatite slows absorption of the calcium. Smaller particles digest faster (more surface area) so the calcium is more rapidly absorbed.

(32) In perfecting the present embodiment of the product several different particle milling regimes were experimented with. It was demonstrated both in vitro and in vivo that particle size distribution alters the dissolution and the bioavailability of the calcium. The next table shows a preparation with a different particle size distribution produced by more extensive milling of the material. This material is the same as MHCA 2 in the clinical tests.

(33) TABLE-US-00003 Opening Measured Wt. retained Mesh (m) (m) (g) % retained % cumulative 18 1000 1100 0.00 g 0.0% 100.0% 20 850 1000 0.00 g 0.0% 100.0% 35 500 675 0.00 g 0.0% 100.0% 50 300 400 0.00 g 0.0% 100.0% 70 250 275 0.00 g 0.0% 100.0% 80 180 215 0.00 g 0.0% 100.0% 100 150 200 2.0 g 2.4% 100.0% 140 106 128 22.00 g 25.9% 97.6% 200 75 90.5 18.00 g 21.2% 71.8% 270 53 64 25.00 g 29.4% 50.6% (Pan) 18.00 g 21.2% 21.2%

(34) Here 100% of the particles are less than 180 m with 97.6% less than 150 m and 21.2% less than 53 m (i.e., pass through a 270 mesh screen). As shown in the clinical tests this version of MHCA with smaller particles provides calcium more rapidly than MHCA 1, but still not nearly as rapidly as traditional calcium supplements. There may be a possibility of further optimizing the MHCA by creating a product having a particle profile somewhere between that of MHCA 1 and MHCA 2. If it is desired to release calcium even more slowly, then a product having a particle profile even large than MHCA 1 should be considered.

(35) FIG. 4 shows the test results of various particle size compositions using the in vitro dissolution test explained above. The figure demonstrates that maximum particle size and particle size distribution have a very significant effect on the rate of calcium dissolution. The following graph compared material that has been processed to provide different maximum particle sizesnamely <150 m, <250 m, and <850 m. The rate of dissolution is proportional to maximum particle size except that the <250 m material was processed from two different types of bone with the <250 m knuckle bone sample dissolving more rapidly than the <250 m long bone sample and actually crossing over the <150 m sample at about 10 minutes.

(36) FIG. 5 shows the in vitro dissolution from the product sieved to give a more defined particle size distribution. The graph demonstrates that product having a 425-250 m distribution dissolves more rapidly than a product having a 425-850 m distribution whereas a product sieved to have particles >1000 m dissolves the most slowly. As will be demonstrated below, controlling the particle size distribution can have significant in vivo results.

(37) Unlike calcium carbonate or calcium citrate, MCHA is a product with a complex micro-structure and significant protein content. Because of the gentle manufacturing conditions the protein component contains a significant level of bone growth factors, particularly osteocalcin. The following table shows the growth factor content of the inventive MHCA as compared to a conventional hydroxyapatite product known as OHC.

(38) TABLE-US-00004 Inventive MHCA Content in OHC (ug/g powder) (ug/g powder) IGF1 0.285 0.202 IGF2 0.17 0.101 TGF 0.0275 0.025 Osteocalcin 604 7.015

(39) Although the inventive MHCA has more of all the growth factors the difference in osteocalcin content is particularly striking being almost two orders of magnitude greater than the conventional product. Those of ordinary skill in the art will understand that osteocalcin is an extremely important bone growth factor. It is secreted only by the osteoblast cells and its presence is well correlated with the process of bone formation. As has been alluded to earlier normal bone activity represents a balance of bone formation and bone resorption. Living bone is constantly remodeled as the osteoclast cells resorb and demineralize bone and the osteoblast cells create new bone matrix proteins and promote their mineralization.

(40) The presence of high levels of osteocalcin in the inventive MHCA is at least a partial explanation of the results obtained when the MHCA is used in a three dimensional gel matrix to promote the differentiation of embedded bone progenitor cells. In contrast to other materials, the MHCA gel suppressed proliferation of both osteoblasts and osteoclasts while strongly promoting the differentiation of the osteoblasts to synthesize and mineralize bone matrix. Thus, the inventive MHCA directly promotes bone formation by pushing the osteoblasts in that direction. At the same time it indirectly promotes bone by suppressing the formation of bone resorbing osteoclasts. It is believed that the dramatically higher level of growth factors in the current product contribute to its in vivo effectiveness.

(41) The following claims are thus to be understood to include what is specifically illustrated and described above, what is conceptually equivalent, what can be obviously substituted and also what essentially incorporates the essential idea of the invention. Those skilled in the art will appreciate that various adaptations and modifications of the just-described preferred embodiment can be configured without departing from the scope of the invention. The illustrated embodiment has been set forth only for the purposes of example and that should not be taken as limiting the invention. Therefore, it is to be understood that, within the scope of the appended claims, the invention may be practiced other than as specifically described herein.

REFERENCES

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