Reactive SugarsSugar molecules in the blood and in the cells chemically bond to proteins and to DNA. (This bonding is called "glycation", "the Maillard reaction", "the browning reaction", or "nonenzymatic glycosylation"). This happens both inside of cells, and in the connective tissue between cells (the Extra-Cellular Matrix or ECM). There are several kinds of sugars and many kinds of proteins. Some glycation structures are good; others interfere with proper functions in the body. Inside of cells, there are protective enzymes that remove the harmful glycation structures. However, outside of cells, harmful glycation structures are not removed. This is an age-related problem in the ECM proteins, such as collagen and elastin, which are located outside of cells and provide strength and flexibility to tissues. Over time, the sugar moieties bound to the glycated proteins are chemically modified to become molecular structures called Advanced Glycation Endproducts (A.G.E.s). A.G.E.s can interfere with the proper functioning of the proteins to which they are attached. Furthermore, some of the A.G.E.s form covalent crosslinks with adjacent protein strands. This crosslinking stiffens tissues which were formerly flexible or elastic. The process happens gradually, so that crosslinks accumulate over the years on the longest-lived extracellular proteins, which do not get recycled very often. Clear evidence of this is found in the extracellular collagen and elastin. [Cerami 1987, Furber 2010]
Pathological consequencesGlycation changes the shape and properties of proteins. Crosslinking reduces the flexibility, elasticity, and functionality of the proteins. Furthermore, the chemical modifications of glycation and crosslinking can initiate harmful inflammatory and autoimmune responses. "AGE and nonenzymatic crosslinks are demonstrated to signal inflammatory cytokines, extracellular matrix expansion, angiogenesis, and growth factors." [deGroof] Glycation has been found in connective tissue collagen, arterial collagen, kidney glomerular basement membrane, eye lens crystallins, nerve myelin proteins and in the circulating low-density lipoprotein (LDL) of the blood. [Bucala]
Glycation and crosslinking have been implicated as strong contributors to many progressive diseases of aging, including vascular diseases (such as atherosclerosis, systolic hypertension, pulmonary hypertension, and poor capillary circulation), erectile dysfunction [Usta], kidney disease, stiffness of joints and skin, arthritis [deGroot, Verzijl], cataracts, retinopathy, neuropathy, Alzheimer's Dementia [Ulrich, Castellani], impaired wound healing, urinary incontinence, complications of diabetes, and cardiomyopathies (such as diastolic dysfunction, left ventricular hypertrophy, and congestive heart failure). [Bucala]
Arterial stiffening causes an increase in the pulse pressure wave which travels through the blood vessels with each beat of the heart. Pulse pressure is measured by subtracting diastolic blood pressure (low number) from systolic blood pressure (high number).
Diabetic ComplicationsIt is significant that these same pathological processes happen at an earlier age in diabetic individuals, because their average blood sugar concentration is higher than normal. [Bucala]
Inhibitors of Glycation CrosslinkingThe formation of new glycation-induced crosslinks is slowed by several drugs and natural substances: Aminoguanidine (Pimagedine) has been studied as an inhibitor of A.G.E. crosslink formation by Alteon Pharmaceuticals. (Alteon was later renamed Synvista Therapeutics. They have since gone out of business.) In human clinical trials, Pimagedine slowed the progression of diabetic kidney disease and retinopathy. Carnosine (beta-alanyl-L-histidine), a dipeptide formed naturally in human tissues, is also believed to inhibit the formation of crosslinks between proteins which have been glycated or carbonylated [Hipkiss]. Aspirin may also inhibit the formation of pathological A.G.E. crosslinks. For example, chronic users of aspirin have fewer cataracts [Bucala].
Crosslink BreakersNevertheless, aminoguanidine and aspirin do not seem to break A.G.E. crosslinks after they have formed. However, other compounds are being studied which do. Many of the known crosslink breakers are modified thiazolium salts which include an active site similar in structure to the catalytic ring of thiamine (vitamin B1). [Ulrich; Kim; Vasan; Asif] The furthest in clinical development is alagebrium chloride, developed by Alteon Pharmaceuticals (Synvista). Alagebrium chloride was previously referred to as ALT-711.
It's chemical name is 4,5-dimethyl-3-(2-oxo-2-phenylethyl)-thiazolium chloride (PTC).
The molecular structure is shown below (CAS number 341028-37-3) (ChemSpider ID: 187495):
The two nucleophilic carbons on each side of the nitrogen in alagebrium attack the two carbonyl carbons of the alpha-diketone structure in the glycation crosslink, resulting in breaking the crosslink. [Kim; Vasan]
Clinical TrialsAlagebrium chloride (oral) has been tested in several human clinical trials in the United States. [Melton, deGroof] During the year 2000, in earlier phase 2a clinical trials, alagebrium demonstrated the ability to improve the flexibility of arteries, and to reduce arterial pulse pressure. In this double-blind trial, 62 people took a dosage of 210 mg per day for two months, while 31 other people received placebo. [Kass] In the "Diamond" clinical trial for diastolic heart failure, beginning in mid-2002, 20 people took 420 mg per day in 2 doses of 210 mg. By February 2005, over 1100 people had taken alagebrium (or PTC) in various clinical trials.
So far, the safety profile of the drug appears to be excellent in human subjects. However, in December 2004, a study feeding alagebrium to lab rats for two years, found an increased rate of liver cell alterations in male rats, but not the females. This strain of lab rat (Sprague-Dawley) often develops liver cell alterations spontaneously, without drugs. The increased rate is comparable to effects caused in Sprague-Dawley rats by other, already approved drugs, such as the statins. These abnormalities are not necessarily expected in humans. Following further study, FDA allowed clinical trials to proceed.
No harmful interactions with other drugs have been observed. Any subjects who had been already taking other blood pressure medications continued on their previous medications in addition to taking alagebrium. Benefits of alagebrium were observed in addition to any benefits from the other blood pressure medications.
In December 2004, Synvista Therapeutics (Alteon) announced a phase 2 clinical trial of alagebrium to reverse erectile dysfunction. Subjects were slated to be taking 200 mg, once per day. In 2009, Synvista ran out of money and went out of business, without completing its clinical trials for alagebrium. ClinicalTrials.gov
Benefits from taking ECM Crosslink-BreakersAfter pathological extracellular crosslinks get broken, the body functions better. Age-related stiffness in many organ systems is reversed, so they function better. Chronic inflammation due to A.G.E.s is reduced. Combining the formal reports from the clinical trials and informal interviews with several dozen experimental subjects gives this list of reported benefits from taking alagebrium orally:
Sources of Experimental MaterialsExperimentalists wishing to work with alagebrium may contact Legendary Pharmaceuticals to enquire regarding how to obtain purified materials, made in the USA. Alagebrium can be supplied in vegetarian capsules of 100 mg or 200 mg. It is also available in a one-ounce dropper bottle (30 mL of 100 mg/mL solution in purified water). It can also be supplied as a pure powder. Please be aware that Legendary Pharmaceuticals is not a pharmacy, and that these experimental materials are not certified by the FDA.
Future Research DirectionsThiazolium breakers, such as alagebrium, target diketone crosslinks, and have proven beneficial in early clinical trials. However, during aging or diabetes, other kinds of chemical crosslinks slowly accumulate as a result of glycation. These other crosslinks, mainly glucosepane, are not broken by thiazolium drugs. We would like to discover new drugs, able to break glucosepane crosslinks. These could be used in addition to thiazolium drugs. The combination could break all of the major pathological glycation crosslinks which accumulate during aging or with diabetes. The results could be much more extensive restoration of tissue elasticity than that provided by thiazolium breakers alone.
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