Patent Abstract:
pentoxifylline , pioglitazone and metformin have been found to inhibit the nonenzymatic glycation of proteins which often results in formation of advanced glycation endproducts and crosslinks . the nonenzymatic glycation and crosslinking of proteins is a part of the aging process with the glycation endproducts and crosslinking of long - lived proteins increasing with age . this process is increased at elevated concentrations of reducing sugars in the blood and in the intracellular environment such as occurs with diabetes . the structural and functional integrity of the affected molecules become perturbed by these modifications and can result in severe consequences . the compounds of the present invention can be used to inhibit this process of nonenzymatic glycation and therefore to inhibit some of the ill effects caused by diabetes or by aging . the compounds are also useful for preventing premature aging , rheumatoid arthritis , alzheimer &# 39 ; s disease , uremia , neurotoxicity , atherosclerosis and spoilage of proteins in food and can prevent discoloration of teeth .

Detailed Description:
in the course of screening different classes of organic compounds for investigation of their possible inhibitory effects on advanced glycation endproducts ( age &# 39 ; s ), we found that pentoxifylline , pioglitazone and metformin each have inhibitory effects and these compounds are potent inhibitors of age - formation at concentrations much lower than an equally inhibiting concentration of aminoguanidine . the compounds and their useful compositions utilized in the present invention contain agents capable of reacting with the highly active carbonyl intermediate of an early glycation product thereby preventing those early products from later forming the advanced glycation endproducts which lead to protein cross - linking and to protein aging . other utilities envisioned for the present invention are prevention of premature aging and of spoilage of the proteins in foodstuffs . the present agents are also useful in the area of oral hygiene as they prevent discoloration of teeth . the compounds of the present invention are pentoxifylline , pioglitazone and metformin . pentoxifylline is 3 , 7 - dihydro - 3 , 7 - dimethyl - 1 -( 5 - oxohexyl )- 1h - purine - 2 , 6 - dione and is also known as trental . previous studies have shown this compound to be non - toxic and it may be administered orally , parenterally or rectally . pioglitazone is 5 -[[ 4 -[ 2 -( 5 - ethyl - 2 - pyridinyl )- ethoxy ] phenyl ] methyl ]- 2 , 4 - thiazolidinedione . previous studies have shown this compound to be non - toxic and it may be administered orally . pioglitazone is among other thiazolidinedione compounds such as troglitazone and rosiglitazone which have recently been in therapeutic uses for the treatment of type 2 diabetes mellitus , lowering the blood sugar as well as hemoglobin a1c . metformin is 1 , 1 - dimethylbiguanide and is also known as glucophage . previous studies have shown that this compound also is non - toxic and may be administered orally . metformin has been in therapeutic use for the treatment of type 2 diabetes mellitus , lowering blood sugar . the present invention relates to the uses of metformin for preventing the complications of diabetes and aging independent of its blood sugar lowering . the above three compounds are capable of inhibiting the formation of advanced glycation end products on target proteins and the resulting protein crosslinking . the rationale of the present invention is to use agents which block the post - glycation step , i . e ., the formation of fluorescent chromophores , the presence of which chromophore is associated with and leads to adverse sequelae of diabetes and aging . an ideal agent would prevent the formation of the chromophore and its associated cross - links of proteins and trapping of proteins on the other proteins , such as occurs in arteries and in the kidneys . the compounds of the invention may be administered to mammals including humans to prevent or reduce protein glycation and cross - linking ( protein aging ). the compounds may be administered orally at variable dosage depending on the activity of each agent in a single or individual amount . in addition the compounds may be administered parenterally or rectally . the compounds of the invention , the rationale behind the different assay methods of the present invention , and their use are illustrated by the following examples . evaluation of early glycation products ( amadori ) formation on hemoglobin ( hba 1c ) is performed by incubating red blood cells with an oxidized form of glucose in the presence and the absence of the inhibitor compound followed by determination of ( hba 1c ) in the test versus the control ( rahbar and nadler , 1999 ). this test is based on a recent report by lindsay et al . ( 1997 ). δ - glu , an oxidized analogue of glucose , can react rapidly with hemoglobin within the red cells and significantly increases the hba 1c levels within hours after incubation . by contrast , glucose requires weeks for an equivalent reaction to occur . we have used this finding to devise an assay method to measure early stage glycation of hemoglobin ( amadori product ) and an assay to evaluate the ability of an inhibitor to inhibit hba 1c formation . briefly , fresh blood was drawn in potassium - edta and prepared for incubation within 30 minutes of collection by mixing 200 μl of blood with 40 μl of either phosphate buffered - saline ( pbs ), ph 7 . 4 , alone , pbs containing 50 millimoles / l δ - glu ( sigma ), or pbs containing 50 millimoles / l δ - glu plus 1 millimole / l inhibitor . after incubation for 16 hours at 37 ° c ., the percentage of glycated hemoglobin present was determined . the percentage of glycated hb ( hba 1c ) was determined using a dedicated ion - exchange hplc system ( biorad diamat ). blood samples were analyzed in triplicate . the % inhibition of hba 1c formation by the compound was calculated according to the following formula : where a is hba 1c concentration in the baseline control tube not treated with δ - glu , b is the hba 1c concentration in blood incubated with δ - glu , c is the hba 1c content of the test tube treated both with δ - glu and the inhibitor compound . the amount of ( hba 1c ) formation using δ - glu treated whole blood from normal volunteers using a range of concentrations of the compounds is shown in fig1 . the δ - glu assay is a specific method for investigation of inhibitors of early stage of glycation . the results of this assay show that pioglitazone , pentoxifylline and metformin have moderate inhibitory effects on the early stage of glycation . the above experiment suggests that this type of drug therapy has benefits in reducing the pathology associated with the formation of early glycation products , a preliminary step in the advanced glycation end product formation . this test is used to evaluate the ability of the inhibitors to inhibit glucose - mediated development of fluorescence of bsa ( ikeda et al ., 1996 ). bsa ( fraction v ) from sigma 50 mg / ml and 800 mm glucose ( 144 mg / ml ) in 1 . 5 m phosphate buffer ph 7 . 4 containing nan 3 0 . 2 g / l was incubated under aseptic conditions at 37 ° c . for 7 days in the presence or absence of various concentrations of the compounds . after 7 days of incubation each sample was examined for the development of specific fluorescence ( excitation , 370 nm ; emission , 440 nm ). the % inhibition of age formation in the test sample versus control was calculated for each inhibitor compound . aminoguanidine was used as a positive control . fig2 shows for each of the three compounds as well as for aminoguanidine the inhibitory effects of for a range of concentrations for each compound . the results obtained by this assay show that all of the compounds have a strong inhibitory effect on the post - amadori glycation , age formation and age - crosslinking . evaluation of the late glycation products ( age &# 39 ; s ), and age - inhibition by the new inhibitor compounds was tested by incubation of g . k . peptide in ribose in the presence or the absence of the agent , followed by determination of chromophores generated in the course of glycation and age formation through determination of their specific fluorescence . the nagaraj et al . ( 1996 ) method used to evaluate the ability of the compounds of the present invention to inhibit the crosslinking of n - acetylglycyl - lysine methyl ester in the presence of ribose was as follows : 0 . 5 m sodium phosphate buffer ph 7 . 4 containing nan 3 0 . 2 g / l gk peptide ( sigma ) 80 mg / ml in 0 . 5 m sodium phosphate buffer ph 7 . 4 equal volumes ( 0 . 1 ml ) of the 3 stock solutions were mixed together , filtered through a 0 . 2 micron filter ( corning ) and incubated under aseptic conditions for 24 hours at 37 ° c . the inhibitor compounds were added to a final concentration of 1 millimole / l . at the end of the incubation period , samples were analyzed for their specific fluorescence ( excitation , 340 nm ; emission , 420 nm ). the % inhibition by different concentrations of inhibitor was calculated as described above . aminoguanidine was used as a positive control . fig3 shows the inhibitory effects of each of the compounds to block specific fluorescence of protein - age in these separate determinations using the g . k . peptide - ribose assay . the results obtained from this example and from the results in example 2 suggest that this type of drug therapy has benefits in reducing the pathology associated with the formation of late glycation products and protein crosslinking . we have used a special elisa technique to evaluate the ability of the compounds under this study to inhibit the cross - linking of glycated - bsa ( age - bsa ) to a rat tail - tendon - collagen coated 96 well plate . cross - linking of age - bsa to a rat tail - tendon - collagen coated plate was performed with and without the testing compound at the desired concentrations . the uncross - linked age - bsa was then removed by washing the wells . the age - bsa cross - linked to the tail - tendon - collagen coated plate was then quantified by a polyclonal antibody raised against age - rnase . positive results in this assay indicate that the inhibitor is capable of reducing the amount of age - bsa which cross - links with collagen . aminoguanidine was used as positive control . the following method was used to evaluate the ability of the compounds of the present invention to inhibit the cross - linking of glycated bovine serum albumin ( age - bsa ) to the rat tail - tendon - collagen coated 96 - well plate . the age - bsa was prepared by incubating bsa at a concentration of 100 mg per ml with 200 mm glucose in 0 . 5 m sodium phosphate buffer , ph 7 . 4 at 37 ° c . for 12 weeks . the glycated bsa was then extensively dialyzed against phosphate buffer solution ( pbs ) for 48 hours with an additional 5 buffer exchanges . the rat tail - tendon - collagen coated plate ( biocoat cell environment , becton dickinson ) was blocked first with 200 μl of superblock blocking buffer ( pierce # 37515x ) for one hour . the block solution was removed from the wells by washing the plate three times manually with pbs - tween 20 solution ( 0 . 05 % tween 20 ). cross - linking of age - bsa ( 0 . 01 to 1 μg per well depending on the batch of age - bsa ) to a rat tail - tendon - collagen coated plate was performed with and without the testing compound dissolved in pbs buffer at ph 7 . 4 at the desired concentrations by the addition of 50 μl each of the age - bsa diluted in pbs or in the testing compound at 37 ° c . for 4 hours . the unbrowned bsa in pbs buffer with or without testing compound was added to the separate wells as the blanks . the uncross - linked age - bsa was then removed by washing the wells three times with pbs - tween buffer . the age - bsa cross - linked the tail - tendon coated plate was then quantified by the polyclonal antibody raised against age - rnase . after a one - hour incubation period , age antibody was removed by washing 4 times with pbs - tween . the bound age antibody was then detected by the addition of horseradish peroxidase - conjugated secondary antibody - goat anti - rabbit immunoglobulin and incubation for 30 minutes . the substrate of 2 , 2 ′- azino - bis -( 3 - ethylbenzothiazoline - 6 - sulfonic acid ) ( abts chromogen ) ( zymed # 00 - 2011 ) was added . the reaction was allowed for an additional 15 minutes and the absorbance was read at 410 nm in a dynatech plate reader . the % inhibition of each test compound was calculated as follows : %   inhibition = optical   density   ( without   compound ) - optical   density   ( with   compound ) optical   density   ( without   compound ) × 100 the results of testing the compounds with the elisa method are shown in fig4 a and 4b . fig4 a shows the results for metformin at a concentration of 250 μm . the results shown 44 % inhibition by metformin and 66 % inhibition for lr - 33 ( 4 -( 2 - chloro - 4 - nitrophenylureido ) phenoxyisobutyric acid ). fig4 b shows the results using pioglitazone at 10 and 50 μm and for pentoxifylline at 50 μm . the above examples suggest that this type of drug therapy will be beneficial in reducing the pathology associated with the formation of nonenzymatic glycation products ( early and late products ) and protein - protein crosslinking . compounds of the present invention are found to be more potent inhibitors of age - formation in vitro as compared to aminoguanidine , which is in phase ⅔ clinical trial to prevent diabetic complications . previous studies have shown these compounds to be non - toxic . they may be administered orally at variable dosages depending on the activity of each agent in a single or individual amount . in addition , the compounds may be administered parenterally or rectally . while the invention has been disclosed in this patent application by reference to the details of preferred embodiments of the invention , it is to be understood that the disclosure is intended in an illustrative rather than in a limiting sense , as it is contemplated that modifications will readily occur to those skilled in the art , within the spirit of the invention and the scope of the appended claims . airaksinen k e j , et al . 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