1. Field of the Invention
The embodiments disclosed herein relate to uses of chromium for the enhancement of cerebral glucose metabolism, the enhancement of brain glucose transporters, for the treatment and/or prevention of conditions associated with altered cerebral metabolism and/or brain glucose transporter expression. Embodiments disclosed herein also relate to the improved delivery of agents across the blood brain barrier, and improved compositions comprising agents that target the brain and/or central nervous system.
2. Description of the Related Art
Chromium is a nutritionally essential trace element. Chromium is essential for optimal insulin activity in all known insulin-dependent systems (Boyle, et al, Southern Med. J. (1977) 70:1449-1453). Insufficient dietary chromium has been linked to both maturity-onset diabetes and to cardiovascular disease.
Chromium functions as a cofactor for insulin. It binds to the insulin receptor and potentiates many, and perhaps all, of its functions. These functions include, but are not limited to, the regulation of carbohydrate and lipid metabolism.
Chromium picolinate is reported to produce modest weight loss and changes in body composition. (Kaats, et al., (1998) Curr. Ther. Res. 59:379-388) (Cefalu, (1999) J. Trace Elem Exp Med 12:71-83). Chromium is a nutritionally essential trace element. The essentiality of chromium in the diet was established in 1959 by Schwartz, as cited in Present Knowledge in Nutrition, page 571, fifth edition (1984, the Nutrition Foundation, Washington, D.C.). Chromium depletion is characterized by the disturbance of glucose, lipid and protein metabolism and by a shortened lifespan. Chromium is essential for optimal insulin activity in all known insulin-dependent systems (Boyle et al., Southern Med. J. 70:1449-1453, 1977). Insufficient dietary chromium has been linked to both maturity-onset diabetes and to cardiovascular disease.
The principal energy sources for the body are glucose and fatty acids. Chromium depletion results in biologically ineffective insulin and compromised glucose metabolism. Under these conditions, the body must rely primarily on lipid metabolism to meet its energy requirements, resulting in the production of excessive amounts of acetyl-CoA and ketone bodies. Some of the documented acetyl-CoA is diverted to increased cholesterol biosynthesis, resulting in hypercholesterolemia. Diabetes mellitus is characterized in large part by glycosuria, hypercholesterolemia, and often ketoacidosis. The accelerated atherosclerotic process seen in diabetics is associated with hypercholesterolemia (Boyle et al., supra.).
Dietary supplementation of chromium to normal individuals has been reported to lead to improvements in glucose tolerance, serum lipid concentrations, including high-density lipoprotein cholesterol, insulin and insulin binding (Cefalu et al., (2004) Diabetes Care 27(10:2741-51). Supplemental chromium in the trivalent form, e.g. chromic chloride, is associated with improvements of risk factors associated with adult-onset (Type 2) diabetes and cardiovascular disease.
The introduction of inorganic chromium compounds per se into individuals is not particularly beneficial. Chromium must be converted endogenously into an organic complex or must be consumed as a biologically active molecule. Only about 0.5% of ingested inorganic chromium, however, is assimilated into the body. Recommended Daily Allowances, Ninth Revised Edition, The National Academy of Sciences, page 160, 1980. Only 1-2% of most organic chromium compounds are assimilated into the body.
U.S. Pat. No. Re. 33,988 discloses that when selected essential metals, including chromium, are administered to mammals as exogenously synthesized coordination complexes of picolinic acid, they are directly available for absorption without competition from other metals. This patent describes a composition and method for selectively supplementing the essential metals in the human diet and for facilitating absorption of these metals by intestinal cells. These complexes are safe, inexpensive, biocompatible, and easy to produce. These exogenously synthesized essential metal coordination complexes of picolinic acid (pyridine-2-carboxylic acid) have the following structural formula:

wherein M represents the metallic cation and n is equal to the cation's valence. For example, when M is Cr and n=3, then the compound is chromic tripicolinate. Other chromium picolinate and or chromium histidinate and or chromium complex alone and or in combinations disclosed include chromic monopicolinate and chromic dipicolinate.
The U.S. Recommended Daily Intake (RDI) of chromium is 120 μg. U.S. Pat. No. 5,087,623, the entire contents of which are hereby expressly incorporated herein by reference, describes the administration of chromic tripicolinate for the treatment of adult-onset diabetes in doses ranging from 50 to 500 μg. U.S. Pat. No. 6,329,361, the entire contents of which are hereby expressly incorporated herein by reference, discloses the use of high doses of chromic tripicolinate (providing 1,000-10,000 μg chromium/day) for reducing hyperglycemia and stabilizing the level of serum glucose in humans with Type 2 diabetes. U.S. Pat. Nos. 5,789,401 and 5,929,066, the entire contents of which are hereby expressly incorporated herein by reference, disclose a chromic tripicolinate-biotin composition and its use in lowering blood glucose levels in humans with Type 2 diabetes.
U.S. Pat. Nos. 5,087,623; 5,087,624; and 5,175,156, the entire contents of which are hereby expressly incorporated herein by reference, disclose the use of chromium tripicolinate for supplementing dietary chromium, reducing hyperglycemia and stabilizing serum glucose, increasing lean body mass and reducing body fat, and controlling serum lipid levels, including the lowering of undesirably high serum LDL-cholesterol levels and the raising of serum High Density Lipid (HDL)-cholesterol levels. U.S. Pat. Nos. 4,954,492 and 5,194,615, the entire contents of which are hereby expressly incorporated by reference, describe a related complex, chromic nicotinate, which is also used for supplementing dietary chromium and lowering serum lipid levels.
Nicotinic acid and picolinic acid form coordination complexes with monovalent, divalent and trivalent metal ions and facilitate the absorption of these metals by transporting them across intestinal cells and into the bloodstream. Chromium absorption in rats following oral administration of CrCl3 was facilitated by the non-steroidal anti-inflammatory drugs (NSAIDs) aspirin and indomethacin (Davis et al., (1995) J. Nutrition Res. 15:202-210) (Kamath et al., J Nutrition (1997) 127:478-482). These drugs inhibit the enzyme cyclooxygenase which converts arachidonic acid to various prostaglandins, resulting in inhibition of intestinal mucus formation and lowering of intestinal pH which facilitates chromium absorption.
U.S. Pat. No. 4,315,927 teaches that when selected essential metals are administered to mammals as exogenously synthesized coordination complexes of picolinic acid, they are directly available for absorption without competition from other metals. These complexes are safe, inexpensive, biocompatible and easy to produce.
The blood-brain barrier (BBB) is a separation of circulating blood and cerebrospinal fluid maintained by the choroid plexus in the central nervous system (CNS). Endothelial cells restrict the diffusion of microscopic objects (e.g., bacteria) and large or hydrophilic molecules into the CSF, while allowing the diffusion of small hydrophobic molecules (O2, hormones, CO2). Cells of the barrier actively transport metabolic products such as glucose across the barrier with specific proteins.
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