Obesity, diabetes, and metabolic syndrome have rapidly become a global epidemic. According to the World Health Organization (WHO) publication, in 2005 approximately 400 million adults were obese, and it is projected that by 2015 more than 700 million adults will be obese. Obesity is a major risk factor for a number of chronic diseases, including cardiovascular disease and diabetes.
Metabolic syndrome was first described by Reaven in 1988 (Reaven (1988) Diabetes 37:1595-1607) as a cluster of interrelated common clinical disorders, including obesity, insulin resistance, glucose intolerance, hypertension, and dyslipidemia (hypertriglyceridemia and low HDL cholesterol levels). The Adult Treatment Panel III (ATP III) of the National Cholesterol Education Program established criteria for diagnosing metabolic syndrome in 2001 (JAMA (2001) 285:2486-249797). Five criteria were selected by the ATP III to identify individuals with metabolic syndrome including abdominal obesity, impaired fasting glucose, high triglyceride (TG), low HDL cholesterol (HDL-C) concentrations, and increased blood pressure. Metabolic syndrome is diagnosed, if any three of the components are present in an individual. Metabolic syndrome is highly prevalent worldwide and is associated with a greater risk of atherosclerotic cardiovascular disease than any of its individual components.
Analysis of data on 8814 men and women aged 20 years or older from the Third National Health and Nutrition Examination Survey (1988-1994) revealed that the unadjusted and age-adjusted prevalence of the metabolic syndrome was 21.8% and 23.7%, respectively. Using 2000 census data, about 47 million US residents may have the metabolic syndrome (Ford et al. (2002) JAMA 16:359). In obese children and adolescents, the prevalence of the metabolic syndrome is very high, increasing with the severity of obesity and reaching 50 percent in severely obese youngsters (Weiss et al. (2004) “Obesity and the metabolic syndrome in children and adolescents.” N Eng J Med 350:2362-2374). Biomarkers of an increased risk of adverse cardiovascular outcomes are already present in these youngsters. The metabolic syndrome and its individual components are not only found in obese populations, but are found in normal-weight and slightly overweight individuals as well.
Compelling evidence suggests that insulin resistance is the root of the problem of the metabolic disorders (Reaven G M. (1998) Diabetes 37:1595-1607). The prevalence of metabolic syndrome increases significantly with increasing insulin resistance (P<0.001 for trend) after adjustment for race or ethnicity and the degree of obesity (Weiss et al. (2004) “Obesity and the metabolic syndrome in children and adolescents.” N Eng J Med 350:2362-2374). Insulin resistance is a state of reduced responsiveness to normal circulating concentrations of insulin (Saltiel A R (2000) J Clin. Invest. 106:163-164) and a major etiology of type 2 diabetes. Insulin resistance is related to obesity, lifestyle factors and genetic factors (Kadowaki T (2000) J Clin. Invest. 106:459-465; Stern M (2000) J Clin. Invest. 106:323-327). Animal studies clearly demonstrate that genetic defects of insulin receptor and insulin signaling pathways are involved in the pathogenesis of insulin resistance in type 2 diabetes. For example, insulin action deficiency was obvious in muscle, liver and adipose tissues of the insulin receptor knockout mice. These mice also showed hyperinsulinemia and severe diabetes. The mice with increased activity of PI3 kinase (PI3K), which is a key signaling enzyme in the insulin signal transduction cascade, showed increased insulin sensitivity and hypoglycemia due to increased glucose transport in skeletal muscle and adipocytes (Kadowaki T (2000) J Clin. Invest. 106:459-465). Similarly, mice deficient in Akt2, a kinase downstream of PI3K, exhibited decreased insulin resistance and increased muscle glucose transport (Cho et al. 2001 Science 292:1728).
In humans, recent studies are rich in the genetic basis and physiology of insulin resistance and diabetes. Subjects with partial “loss-of-function” Pro12Ala mutation in PPAR gamma2-specofoc B exon have a combination of lower BMI, greater insulin sensitivity and improved lipid profiles (Deeb et al. (1998) Nat Genet 20:284-287; Alhuler et al. (2000) Nat Genet 26:76-80). The physiological consequences of the Pro12Ala polymorphism are largely dependent on confounding genetic and environmental factors. Subjects with the Pro115Gln gain-of-function mutation are extremely obese and insulin sensitive (Ristow et al. (1998) N Engl J Med 339:953-959), which is consistent with the effect of PPARγ in stimulating adipocyte differentiation. On the other hand, dominant-negative mutations, such as Pro495Leu, Val318Met, Phe388Leu and Arg425Cys, are associated with partial lipodystrophy, severe insulin resistance, diabetes, and hypertension (Savage et al. (2003) Diabetes 52:910-917; Agawal and Garg (2002) J Clin Endocrinol Metab 87:408-411).
The human genetic disease, maturity-onset diabetes of the young (MODY), is characterized by a clinical onset of diabetes before age 25, an autosomal dominant mode of inheritance, and a primary defect in the function of the pancreatic β cells. Six MODY genes had been identified: MODY1, hepatocyte nuclear factor-4α(HNF-4α); MODY2, glucokinase; MODY3, HNF-1α, MODY4, insulin promoter factor-1 (IPF-1); MODY5, HNF-1β; and MODY6, beta-cell E-box transactivator or NeuroD1 (Fajans et al. (2001) N Engl J Med 345:971). MODY genes are involved in abnormal gene expression and glucose metabolism in the pancreatic β cells leading to β cell dysfunction.
Type II diabetes is complex and heterogeneous, a multifactorial disease. Rare monogenic forms of MODY, although informative regarding diabetic pathophysiology, can not capture the spectrum of human diabetic etiology. Human genome-wide scans were used by many genomics research groups to search for diabetes and insulin resistance loci among various susceptible ethnic populations using genetic polymorphism (McIntyre and Walker (2002) Clin Endocrinol 57:303). The calpain-10 gene on chromosome 15 was the first gene identified using a genome-wide scan of 252 sib-pairs of a Mexican-American ethnic group in Texas and later confirmed using studies of other ethnic groups. Clinical studies suggest that calpain-10 is one of the factors affecting the action of insulin on muscle tissue and the secretion of insulin from the pancreatic β cell. Studies in mice lacking calpain-10 suggest that calpain-10 mediates fatty acid-induced apoptosis in insulin-secreting pancreatic β cells (Horikawa et al. (2000) Nat Genet 26:163; Weedon et al. (2003) Am J Hum Genet 73:1208). The search for human diabetic genes is far from over, FTO on chromosome 16 is a recent discovery. FTO with unknown function was associated with BMI and was confirmed in various diabetes study populations totaling 39,000 people (Kaiser (2007) Science 316:185). In addition, by association studies of candidate genes, KCNJ111 (the inward-rectifier subunit of the β-cell ATP-sensitive potassium channel) and HNF-4α genes were also found to be NIDDM genes (Taylor (2007) Diabetes 56:2844).
Free fatty acid (FFA) is perhaps the most important factor in the pathophysiology of insulin resistance. Non-invasive magnetic resonance spectroscopy has been used in clinical studies using 13C, 31P, and 1H isotopes to track muscle glycogen synthesis, glucose uptake, and glucose-6-phosphate concentration by Shulman's group at Yale University. In healthy human subjects under hyperinsulinemic-euglycemic clamps, using lipid infusion to maintain a high blood FFA level, insulin resistance gradually developed, reaching a 50% reduction in insulin-stimulated muscle glucose uptake and a 50% reduction in muscle glycogen synthesis and glucose oxidation after 4-6 hours of lipid infusion, accompanied by a >90% decrease in the insulin-stimulated IRS-1-associated PI3K activity (Roden et al. (1996) J Clin Invest 97:2859; Dresner et al. (1999) J Clin Invest 103:253).
Peroxisome proliferator-activated receptors (PPARs) are a subclass of the nuclear receptor super-family. PPARs are ligand-dependent transcription factors that bind to specific DNA response elements as heterodimers with the retinoid X receptor. This ligand binding leads to preferential recruitment of chromatin-decondensing coactivator complexes and favors dismissal of the corepressor complex (Glass (2006) J. Clin. Invest. 116:556-560 doi:10.1172/JCI129713). In addition, PPARs may influence gene expression indirectly, and usually negatively, through competition with other transcription factors (Gervois et al. (2001). J. Biol. Chem. 276:33471-33477). There are three members in the PPAR family: PPARα, PPARδ (or PPARβ) and PPARγ. Extensive experimental evidence links the three nuclear receptors to the regulation and coordination of lipid and carbohydrate metabolism. The association of the three proteins with various diseases including diabetes, obesity, dyslipidemia and inflammation is well established. The three PPARs are differentially expressed in different tissues (Semple et al. (2006). J. Clin. Invest. 116:556-560 doi: 10.1172/JCI128003). PPARα has the highest expression in the liver, kidneys and the heart. PPARγ is preferentially expressed in adipose tissue and in macrophages. The expression of PPARδ is widely spread, but with the highest expression in adipose tissue, skin and brain. The three nuclear receptors are involved in various cellular processes. Activation of PPARα or PPARδ leads to increased fatty acid β oxidation. PPARα is implicated in lipoprotein synthesis and amino acid catabolism. PPARγ is critical in adipocyte differentiation. The proteins have different physiological functions. PPARα coordinates metabolic response of tissues to fasting, whereas the expression of PPARγ increases postprandially and its activation leads to up-regulation of genes that mediate fatty acid uptake in adipose tissues. PPARγ is the key transcriptional factor that orchestrates adipocyte differentiation. The physiological function PPARδ is not completely understood. However, recent evidence indicates that it may be a regulator of muscle fiber type and activation of the protein leads to resistance to obesity and improved metabolic profiles (Wang et al. (2004). PloS Biology 2:e294).
Multiple pathways may be involved in insulin resistance. PPARγ activation in adipose tissues up regulates the transcription of genes involved in fatty acids trapping (Semple et al. (2006) J. Clin. Invest. 116:556-560 doi:10.1172/JCI128003). PPARγ activates the endothelial lipoprotein lipase (LPL) and the fatty acid transport proteins (FATP and CD36), which promote hydrolysis of lipoprotein triglyceride and uptake of FFA into adipocytes, respectively. The process enhances insulin sensitivity by reducing lipid in the circulation and the direct access of lipid to the insulin sensitive tissues, such as muscle and liver ((Semple et al. (2006) J. Clin. Invest. 116:556-560 doi:10.1172/JCI128003). PPARγ has been well characterized. The essential role of PPARγ was demonstrated in embryonic lethality of the homozygous PPARγ-deficient mice (Tsuchida et al. (2005) J Pharmacol. Sci. 97:164-170). In wild-type mice, obesity and insulin resistance can be induced by high fat diets. However, the high-fat diet induced obesity or insulin resistance is prevented in heterozygous PPARγ-deficient mice (Tsuchida et al. (2005) J Pharmacol. Sci. 97:164-170). For example, the heterozygous PPARγ (+/−) mice were fed a high-fat diet, the mice were less insulin resistant and had smaller adipocytes than wild-type mice. The mice also had lower levels of fatty acids and increased levels of leptin in plasma (Kubota et al. (1999) Mol Cell 4:597-609; Tsuchida et al. (2005) J Pharmacol. Sci. 97:164-170). The protective effect of the heterozygous PPARγ-deficiency, however, was diminished by treating the mice with PPARγ agonists. The thiazolidinedione (TZD) class of insulin sensitizing drugs (Lehmann et al. (1995). J. Biol. Chem. 270:12953-12956) paradoxically decreases the insulin sensitivity of PPARγ (+/−) mice. These results suggest that PPARγ mediates high-fat diet induced obesity and insulin resistance, and inhibition of PPARγ could render animals, or people, less susceptible to endogenous and exogenous causes of insulin resistance. On the other hand, supra-physiological activation of PPARγ by TZD in wild-type mice fed with high fat diet improved insulin sensitivity as well, but induced adipocyte differentiation at the same time. The experimental evidence indicates that both down-regulation and up-regulation of PPARγ activity improve insulin sensitivity.
PPARα is a molecular sensor of endogenous fatty acids and their derivatives. It plays a key role in glucose homoeostasis and lipid metabolism in the liver and skeletal muscle. It has been demonstrated that PPARα agonists, such as fibrates, are efficacious in lipid lowering (Lefebvre et al. (2006). J. Clin. Invest. 116:571-580. doi:10.1172/JCI27989). In rodents, a PPARα agonist, Wy14643, improved insulin sensitivity in KKAy mice and enhanced the anti-diabetic effect of PPARγ agonist rosiglitazone (Tsuchida et al. (2005) Diabetes 54:3358-3370). Adipocyte hypertrophy was prevented by Wy14643 (Tsuchida et al. (2005) Diabetes. 54:3358-3370).
PPARδ has recently emerged as a metabolic regulator in various tissues including fat, skeletal muscle, and the heart (Barish et al. (2006) J. Clin. Invest. 116: 590-597). It enhances fatty acid catabolism and energy uncoupling, which leads to decreased triglyceride storage and improved endurance. The targeted expression of an activated form of PPARδ in skeletal muscle in mice conferred resistance to obesity with improved metabolic profiles (Wang et al. (2004). PloS Biology 2:1532-1539).
Modulating PPAR activity in the body is critical to maintaining normal insulin sensitivity in response to diet and other environmental impacts. Mouse genetic studies offer great opportunities to understand the complex interaction of the nuclear receptors and environmental factors. PPAR activity can be regulated by different modulators. PPARs interact with different ligands, leading to activation of different sets of the target genes. As a result, different transcriptional activities and pharmacological profiles are generated due to different affinity and effects of the modulators to PPARs. Modulators of PPARs can be divided into several groups, including full agonist, partial agonist, antagonist and coagonist (Knouff and Auwerx (2004) Endocrine Review 25:899-918).
Many PPAR full agonists have been developed. Rosiglitazone and piogliteazone are two TZDs that are used clinically in the treatment of type 2 diabetes (Lehmann et al. (1995) J Biol. Chem 270:12953-12956). Though these PPARγ agonists reduce insulin resistance and lower plasma glucose levels, the full agonists have severe side effects including weight gain due to increased fat mass and edema, fluid retention, hemodilution, and heart failure in up to 15% of patients (Mudaliar et al. (2003). Endocr. Pract. 9:406-416). Some TZDs are also associated with significant liver toxicity. Drug therapies that prevent or treat multiple aspects of the metabolic syndrome are limited in options and in success rate, although new molecular drug targets have been actively pursued.
Other insulin sensitization pathways involve modified profiles of adipokines produced from adipocytes including TNFα, IL-6, CRP, PAI-1, angiotensinogen, resistin, leptin and adiponectin (Lau et al. (2004). Am. J. Physiol Heart Cir. Physiol 288:H2031-H2041). These adipokines have profound effects on insulin resistance and vascular homeostasis. Among these proteins, adiponectin is one of the best-characterized hormones from adipocytes that mediate insulin sensitization. TZDs stimulate adiponectin gene expression and increase circulating adiponectin concentrations in obese mice and insulin resistant obese humans (Maeda et al. (2001) Diabetes 50:2094-2099). Because adiponectin improves glucose tolerance by increasing insulin sensitivity, the effect of TZDs on adiponectin secretion may explain, at least partially, the hypoglycemic effect of TZDs in patients with type 2 diabetes mellitus.
Additional pathways are involved in insulin sensitization in humans. For example, leptin was also shown to improve insulin sensitivity in rodents. In lipoatropic mice, administration of a combination of physiological doses of adiponectin and leptin led to complete restoration of insulin sensitivity, but only partial insulin sensitization was observed by either adiponectin or leptin treatment individually (Yamauchi et al. (2001). Nat Med 7:941-946). Leptin reduces the expression of lipogenic enzymes and consequently activates the PPARα pathway in the liver, brown adipose tissue and skeletal muscle, which lead to increased expression of UCP-2 and the enzymes involved in beta-oxidation. In humans, plasma adiponectin concentrations were not changed in individuals with improved insulin sensitivity by weight loss (Abbasi et al. (2004) Metabolism 53:280-283). In another study, it was demonstrated that improvements in insulin sensitivity by exercise training were not the results of the change of adiponectin levels in humans (Marcell et al. (2005), Metabolism 54:533-41). The data suggest that additional pathways exist for insulin sensitization and different mechanisms are involved in the improvement of insulin sensitivity after weight loss and after treatment with TZD compounds.
Chromones are a specific type of aromatic compounds having a benzopyran-4-one as their major skeletal structure as illustrated by the following general structure:

wherein
R1, R2, R3, R4, R5 and R6 are independently selected from the group consisting of —H, —OH, —CH3, —SH, alkyl, alkenyl, oxoalkyl, oxoalkenyl, hydroxylalkyl, hydroxylalkenyl, —OCH3, —SCH3, —OR, —SR, —NH2, —NRH, —NR2, —NR3+X−, an ester selected from the group consisting of gallate, acetate, cinnamoyl and hydroxyl-cinnamoyl esters, trihydroxybenzoyl esters and caffeoyl esters; and a hexose or pentose, wherein said hexose or pentose is linked to the chromone by a carbon, nitrogen sulfur or oxygen and wherein said hexose or pentose is selected from the group consisting of aldopentoses, methyl aldopentose, aldohexoses, ketohexose and their chemical derivatives thereof; including a dimer, trimer and other polymerized chromones;
wherein said alkyl and/or alkenyl group is a straight and/or branched chain having between 1-20 carbon atoms with and/or without double bonds and substitution group(s) selected from the group consisting —OH, ═O and —OR in different positions;
X is selected from the group of pharmaceutically acceptable counter anions including, but not limited to hydroxyl, chloride, iodide, sulfate, phosphate, acetate, fluoride, carbonate, etc.; and
R is an alkyl group having between 1-20 carbon atoms. To date there are only 183 chromones isolated from natural sources (The Combined Chemical Dictionary, Chapman & Hall/CRC, Version 5:1 June 2001).
Chromones reportedly exhibit monoamine oxidase inhibitory activity (Fujimoto et al. (2002) Chem. Pharm. Bull. 50:330-336), tyrosinase inhibitory activity (Oiao et al. (2002) Chem. Pharm. Bull. 50:309-311), anti-platelet effects (Leoncini et al. (1991) Pharmacol. Res. 23:139-148), growth inhibitory activity against oral pathogens (Cai (1996) J. Nat. Prod. 59:987-990), prostagladin H synthase inhibitory activity (Jurenka et al. (1989) Comp. Biochem. 93:253-255). Chromones also possess therapeutic efficacy against type II collagen-induced arthritis in rats (Inaba et al. (2000) Chem. Pharm. Bull. 48:131-139) and hypolipidemic activity (Witiak et al. (1975) J. Med. Chem. 18:935-942; Tetko et al. (1995) Bioorg Khim. 21:809-815). It has also been reported that chromones can function as selective sigma receptor ligands (Erickson et al. (1992) J. Med. Chem. 35:1526-1535). Based on animal studies, chromones are easily absorbed and metabolized (Crew et al. (1976) Xenobiotica 6:89-100) and the c-glucosyl bond of aloesin can be cleaved by human intestinal bacteria (Che et al. (1991) Chem. Pharm. Bull. 39:704-708).
Aloe is an intricate plant that contains many biologically active substances. (Dagne et al. (2000) Current Org. Chem. 4:1055-1078; Cohen et al. in Wound Healing/Biochemical and Clinical Aspects, 1st ed. WB Saunders, Philadelphia (1992)). Over 300 species of Aloe are known, most of which are indigenous to Africa. Studies have shown that the biologically active substances are located in separate sections of the aloe leaf—a clear gel fillet located in the center of the leaf, in the leaf rind or cortex of the leaf and in a yellow fluid contained in the pericyclic cells of the vascular bundles, located between the leaf rind and the internal gel fillet, referred to as the aloe latex (Dagne et al. (2000) Current Org. Chem. 4:1055-1078). The clear gel fillet, which is located in the center of the leaf contains water soluble polysaccharides, organic acids, amino acids and inorganic salts. Aloe vera gel is produced from this part of aloe plants. The leaf rind or cortex of the leaf, and the yellow fluid contained in the pericyclic cells of the vascular bundles, contain aromatic compounds such as anthraquinones, chromones, organic acids, enzymes, vitamins, salts and other miscellaneous compounds. Aloe whole leaf gel is produced by grinding the whole aloe plant which includes the contents of all water soluble components including anthraquinones, chromones, polysacchairdes and other compounds. Due to the color and phototoxicity, GI irritation, cytotoxicity and other side effects of anthraquinones, aloe whole leave gel is processed to remove all aromatic components including anthraquinones and chromones (International J. Toxicology (2007), 26 (suppl.2):1-50).
Historically, Aloe products have been used in dermatological applications for the treatment of burns, sores and other wounds. These uses have stimulated a great deal of research in identifying compounds from Aloe plants that have clinical activity, especially anti-inflammatory activity. (See, e.g., Grindlay and Reynolds (1986) J. of Ethnopharmacology 16:117-151; Hart et al. (1988) J. of Ethnopharmacology 23:61-71). As a result of these studies there have been numerous reports of Aloe compounds having diverse biological activities, including anti-tumor activity, anti-gastric ulcer, anti-diabetic, anti-tyrosinase activity and antioxidant activity (International J. Toxicology (2007), 26 (suppl.2): 1-50).
Chromones isolated from various Aloe species have been reported to have diverse biological activity. Aloesin reportedly inhibits tyrosinase activity (Jones et al. Journal of Pigment Cell Research, Acceptance, Feb. 10, 2002) and up-regulates cyclin E-dependent kinase activity (Lee et al. (1997) Biochem. Mol. Biol. Int. 41:285-292). A c-glycosyl chromone isolated from Aloe barbadensis demonstrates anti-inflammatory activity (Hutter et al. (1996) J. Nat. Prod. 59:541-543) and antioxidant activity similar to that of alpha-tocopherol based on a rat brain homogenates model (Lee et al. Free Radic Biol. Med. 28:261-265).
Aloe barbadensis leaves and its bitter principles exhibit effects on blood glucose level in normal and alloxan diabetic mice (Ajabnoor (1990) J. Ethnopharmacol. 28:215-220) and the dried sap of various Aloe species demonstrates anti-diabetic activity in clinical studies (Ghannam, (1986) Horm Res. 24:288-294). The anti-diabetic effects of aloe gel or extract have been demonstrated on low-dose streptozotocin-induced diabetes animal models (Beppu (2006) J Ethnopharmacol. 103(3):468-77; Rajasekaran (2006) Clin Exp Pharmacol Physiol. 33(3):232-7). Such anti-diabetic effects were reported as protection of low-dose streptozotocin-induced selective toxicity to B cells of islets by phenols and other molecular weight less than 10 KDa compounds (Rajasekaran (2006) Clin Exp Pharmacol Physiol. 33(3):232-7). Other components such as inorganic minerals (Rajasekaran (2005) Biol. Trace Elem. Res. 108(1-3):185-195) and anti-oxidants from Aloe Vera gel were reported in association with anti-diabetic effects (Rajasekaran (2005) Pharmacol. Rep. 57(1):90-96).
Recently, five phytosterols from Aloe vera gel were identified as anti-diabetic components (Tanaka (2006) Biol. Pharm. Bull. 29(7):1418-1422). In 2007, the chemical components of Aloe ferox leaf gel were thoroughly analyzed with potent anti-oxidation properties reported and potential usage in alleviating symptoms and/or preventing diabetes speculated (Loots (2007) J Agric. Food Chem. 55(17):6891-6896).
U.S. Pat. No. 6,780,440 discloses herbal compositions including aloe for diabetes and weight management. However, the principle active components and the mechanism of action were not identified. In U.S. Pat. No. 588,984, complex carbohydrates from aloe were claimed as one of the compositions for treatment of diabetes. Also in U.S. Pat. No. 4,598,069, aloe polysaccharides were claimed for treatment of hypoglycemia. U.S. Pat. No. 5,627,204 discloses synthetic chromone derivatives with different substitution patterns that acted as inhibitors of aldose reductase for use in the prevention and treatment of diabetes. U.S. Pat. No. 6,133,305 claimed synthetic compounds having the chromone skeleton for treating a protein kinase related disorders including diabetes.
Yagi et al. disclose a group of compounds isolated from Aloe, particularly aloesin and one of its derivatives, 2″-O-feruloylaloesin, which are effective inhibitors of tyrosinase. (Yagi et al. (1987) Plant Medica 515-517). Aloesin is a C-glucosylated 5-methylchromone (Holdsworth (1972) Chromones in Aloe Species, Part I-Aloesin PM 19(4):322-325). In vitro, aloesin is a strong inhibitor of tyrosinase activity (Yagi et al. (1987) Planta Medica 515-517). U.S. Pat. No. 6,123,959, entitled “Aqueous Composition Comprising Active Ingredients for the De-Pigmentation of the Skin,” describes aqueous compositions comprising liposomes of phospholipids, and at least one competitive inhibitor of an enzyme for the synthesis of melanin, in combination with at least one non-competitive inhibitor of an enzyme for the synthesis of melanin. U.S. Pat. No. 6,884,783 disclosed 7-hydroxy chromones, including aloesin and aloesinol as potent antioxidants for prevention and treatment diseases and conditions associated with reactive oxygen species (ROS) damage and other oxidative stress.
To date, known methods for purifying aloesin, as well as, other chromones involve the use of chromatography. (See e.g., Rauwald and Beil (1993) J. of Chromatography 639:359-362; Rauwald and Beil (1993) Z. Naturforsch 48c: 1-4; Conner et al. (1990) Phytochemistry 29:941; Holdsworth (1972) Chromones in Aloe Species, Part I-Aloesin PM 19(4):322-325; Mebe (1987) Phytochemistry 26:2646; Haynes et al. (1970) J. Chem. Soc. (C) 2581; McCarthy and Haynes (1967) The Distribution of Aloesin in Some South African Aloe Species; Heft 3 342). These procedures were developed for chemical analysis and are not practical for preparative scale production of aloesin. In U.S. Pat. No. 6,451,357, entitled “Method of Purification of Aloesin,” a method for purification of aloesin using crystallization is disclosed.