It is well known that modern day drugs are very efficacious with respect to treating acute and chronic diseases. However, several diseases, and especially chronic diseases, are associated with complications that are not treated by administration of the drug.
For example, the standard treatment for diabetes is administration of insulin. An individual suffering from diabetes does not produce sufficient insulin, and hence the individual cannot burn and store glucose. Diabetes cannot be cured, but diabetes can be treated by periodic injections of insulin. FIG. 1 shows that serum insulin levels rise from a low fasting value to a peak after about 30 to 60 minutes, then fall back to a low value after about 120 minutes. In mild diabetics, the rise in serum insulin is lower compared to normal individuals. In severe diabetics, no insulin is produced, and the rise in serum insulin levels is negligible. As a result, excess glucose accumulates in the blood of a diabetic, which can result, for example, in a loss of weight and loss of strength.
However, insulin injections to treat diabetes do not treat, or alleviate, the serious vascular complications associated with diabetes, including nephropathy, retinopathy, neuropathy, heart disease, and reduced blood circulation in the limbs, i.e., "diabetic foot," that can lead to gangrene. Another disadvantage with respect to the present therapeutic compositions used to treat diabetes is that insulin must be injected. Insulin cannot be administered orally because insulin is destroyed by the strong acid conditions of the stomach.
Therefore, it would be advantageous to develop a method of both treating a disease, and preventing or reversing complications associated with the disease. It also would be advantageous to develop easier methods of administering a drug to treat the disease. As set forth in detail hereafter, the present invention is directed to novel PALs, and to drug compositions containing a PAL and a therapeutic agent, i.e., a drug, to reduce, eliminate, or reverse complications associated with a disease. The present invention is further directed to a method of manufacturing a PAL, and to improved drug delivery systems for administering difficult to administer drugs, like insulin.
With respect to diabetes, glycosaminoglycans (GAGs) are a class of negatively charged, endogenous polysaccharides composed of repeating sugar residues (uranic acids and hexosamines). GAGs have been shown to bind a variety of biological macromolecules, including connective tissue macromolecules, plasma proteins, lysosomal enzymes, and lipoproteins. In addition, exogenous GAGs have been shown to bind to the cell surfaces of a variety of different cell types, including liver cells (hepatocytes), fibroblasts, and importantly, endothelial cells. Exogenous GAGs therefore can be internalized. Furthermore, GAGs have been implicated in the regulation of cell proliferation and in cell-cell communication, shown to interact with cell-surface receptors (cell adhesion molecules), and shown to modify the behavior of cells in culture. In addition, GAGs were shown to be highly potent, selective inhibitors of HIV replication and giant cell formation. These findings suggest that exogenously administered GAGs have the potential to target a variety of important in vivo sites.
GAG-receptor interactions are characterized by the formation of noncolavent, self-assembling macromolecular complexes. These transient, interpoly-electrolyte complexes mediate many biological functions including enzyme-substrate binding, antigen-antibody interactions, leukocyte-endothelial cell adhesion events, drug-receptor binding, and protein--protein interactions. Furthermore, secondary binding forces, such as hydrogen bonds, vander Waals forces, and hydrophobic interactions, govern interpoly-electrolyte formation, and, ultimately, influence the resulting pharmacologic response to the complex.
G. Gambaro et al., Kidney Int., 46, pages 797-806 (1994) discloses that exogenously administered GAGs have a favorable effect on morphological and functional renal abnormalities in diabetic rats, and appear to revert established diabetic renal lesions. Furthermore, D. M. Templeton, Lab. Invest., 61 (2), pages 202-211 (1989) and C. W. Marano et al., Invest. Ophthalmology Vis. Sci. , 33 (9), pages 2619-2625 (1992) disclose that diabetic patients have a decreased glycosaminoglycan content in glomerular basement membranes. Additionally, an increase in total GAG serum levels in diabetic patients was disclosed in K. Olczyk et al., Acta Biochimica Polonica, 39, pages 101-105 (199). The authors observed an increase in protein-bound GAGs, such as keratan sulfate, hyaluronic acid, heparin sulfate, and heparin in diabetic patients. Gambaro et al. also discloses an increase in the urinary excretion rate of GAGs from insulin-dependent diabetic patients.
Therefore, publications show that glycosaminoglycans play an important, yet unexplained, role in the vascular changes associated with lifelong insulin therapy. In particular, administration of GAGs to diabetic animals has inhibited or reversed some vascular abnormalities. The publications also strongly suggest that exogenous insulin plays a role in elevating the level of GAGs in the urine and serum of diabetic patients. Furthermore, the publications clearly show that glycosaminoglycans bind to a multitude of biological macromolecules, including proteins.
These observations appear to suggest utilizing glycosaminoglycans as an adjuvant to insulin therapy. However, GAGs are anticoagulants and long term use of GAGs with insulin would thin the blood of an individual to unacceptable levels. Furthermore, the risks associated with a long term use of GAGs are unknown. In addition, GAGs are heterogeneous, having a relatively wide molecular weight range of about 8,000 to about 20,000, and accordingly are difficult to reproduce. Therefore, although persons skilled in the art have used GAGs as therapeutic agents, e.g., heparin, GAGs have not been used for extended periods of time, or for the treatment of a chronic disease, like diabetes. The present invention is directed to finding drug delivery systems that provide the benefits of a drug-GAGs complex, but that avoid the disadvantages associated with long term administration of a GAG compound.