Aging: Drugs to Eliminate Methylglyoxal, a Reactive Glucose Metabolite, and Advanced Glycation Endproducts

The aging process not only affects the whole body, but also affects individual cells. While the age-related changes in the body are popularly recognized as wrinkling of the skin, indicating alterations in basement membrane proteins, the processes of cellular aging are less well defined. The underlying common theme of cellular aging and whole body aging seems to be an increase in oxidative stress. Advanced glycation endproducts (AGEs), which are widely accepted to alter basement membrane proteins, also increase oxidative stress. Reactive dicarbonyls, such as methylglyoxal (MG), formed during glycolysis and other metabolic processes are precursors of AGEs formation and triggers of oxidative stress. MG, AGEs and oxidative stress are very likely to induce DNA damage and be at the root of cellular aging. Thus, a strategy to prevent an elevation of MG, formation of AGEs and the associated oxidative stress has great therapeutic potential to slow the aging process at the cellular and the whole body level.

and prevent the generation of oxidative stress resulting from an excess of free radicals [17][18][19][20][21][22]. The formation of free radicals and the function of antioxidants have been nicely explained in reviews by Haliwell [20,21].
The free radical theory of aging was proposed by Denham Harman in 1956 [23]. The free radical theory of aging attributes the aging process to cumulative cellular damage inflicted by the reaction of free radicals with key functional cellular and tissue constituents resulting in impaired function, disease and death [23]. The discovery of an antioxidant enzyme, superoxide dismutase (SOD) [24], which plays a key role to eliminate superoxide anion levels, provided some validity to the free radical theory, which was not initially accepted by many.
The mitochondrial respiratory chain is a major source of free radicals, mainly in the form of superoxide anions, which cause damage to the mitochondria and reduce life span [25,26]. The damage inflicted by ROS, especially to DNA [7], rather than the metabolic rate, showed a greater correlation with life span [8]. Damage to DNA was formulated into the somatic mutation theory, which states that genetic mutations caused by an excess of free radicals could lead to accelerated aging [7,9,10].
The fact that increased production of ROS in the mitochondria can reduce life span was supported by several studies. Thus, Ku et al., [27] showed that the rates of mitochondrial superoxide anion and hydrogen peroxide generation were inversely correlated to maximum life span potential when they compared seven different mammalian species with different life spans ranging from 3.5 to 30 years. Similarly, ROS production was higher in heart mitochondria of the rat, which has a life span of about 4 yrs, than in the long-lived pigeon, which has a longer life span of 35 yrs [28]. Theoretically, therefore, if the free radical production is diminished, the life span should increase. This has been demonstrated in several species. Thus, over expression of SOD and catalase in the worm Caenorhabditis elegans (C. Elegans) through age-1 alleles, increases their oxidative defenses and life span by 65% longer on average [29,30]. Increased activity of SOD and reduced oxidative stress in the transgenic Drosophila (Drosophila melanogaster) flies also slows the aging process and results in a longer life [31,32]. Also, over expression of catalase in the peroxisome, the mitochondria or the nucleus in transgenic mice, reduced oxidative damage, hydrogen peroxide production, and delayed the development of cardiac pathology and cataract formation along with an average increase of 5.5 months in the life span [33]. The observation that longlived animals have lower levels of antioxidant enzymes was explained as being due to a lower rate of production of oxygen radicals [34].
Interestingly, some of the studies in rodents did not produce the expected results. For example, the administration of antioxidants [35], or over expression of CuZn SOD and catalase in mice [36], or SOD in rats [37], did not increase their life spans. In rodents, one reason for the lack of additional protective effects, which are normally associated with an increase in antioxidants, could be their ability to synthesize vitamin C [38], which might already be providing the required protection. This was verified by knocking out the vitamin C synthesizing enzyme, L-gluconolactone oxidase (GLO) in mice, which then have to depend on dietary vitamin C [39]. GLO knockout mice had damaged aortic walls when they were fed a diet low in vitamin C, which underlined the importance of the constitutive antioxidant function of vitamin C in rodents [39]. Thus, studies in rodents do not provide unequivocal support for the free radical theory of aging [40].

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Another way of increasing free radical production and oxidative stress is by increasing total caloric intake, which can be easily done be feeding an excess of glucose. A correlation between life span and dietary caloric intake was reported in rats and mice by McCay et al. [41]. One quantitative estimate was provided in the study by Weindruch and Walford [42] who showed that a 40% reduction in dietary caloric intake extended maximum life span by one third. A high dietary caloric intake causes an increased rate of DNA damage [43], due to a high metabolic rate which in turn results in higher amounts of superoxide anion, hydrogen peroxide and hydroxyl radical formation [44].

Free radicals ROS
Despite the efficient glyoxalase system, MG levels can increase significantly in the plasma and different organs such as the aorta and the kidneys [61,[63][64][65][66]. We have shown that MG levels are elevated in the plasma, aorta and kidney of fructose-fed Sprague-Dawley rats and spontaneously hypertensive rats (SHR) [61,[63][64][65]. Patients with type 1 and type 2 diabetes have 2-6 fold higher plasma levels of MG compared to healthy people [67,68]. MG possibly plays a role in the pathogenesis of insulin resistance and type 2 diabetes as shown by several in vitro [69][70][71], and by our recent in vivo study in acute [66] and chronic MG-treated www.intechopen.com Sprague-Dawley rats [72]. Elevated MG levels are linked to the development of microvascular complications of diabetes such as retinopathy and nephropathy, and other conditions such as atherosclerosis and neurodegenerative diseases [73][74][75][76][77]. MG levels are high in the cerebrospinal fluid of patients with Alzheimer's disease [76].

Advanced glycation endproducts
Unwanted chemical modification of physiologic constituent molecules of the body, which leads to the formation of harmful chemical entities, seems to be an unavoidable part of metabolic processes of the body. One type of modification, known as glycation, a nonenzymatic reaction, is a serious hazard of excess glucose availability in the body. The chemical interaction leading to the formation of AGEs starts when a reducing sugar condenses with the amino groups of proteins at their N terminus or on lysyl side chains (εamino groups) [78]. This nonenzymatic glycation involves a series of post-translational modifications. Glycation begins with the aldehyde or the ketone carbonyl group of the sugar combining with the protein to form an unstable aldimine intermediate or a Schiff base. Later on the Schiff base undergoes an Amadori rearrangement to form a stable Amadori product, a l-amino-l-deoxyfructose derivative with a stable ketoamine linkage, which can get cyclized to form a ring structure [78][79][80]. The Amadori product can undergo oxidation, degradation or rearrangement and form AGEs, a heterogenous group of products. Auto oxidation of glucose (Wolff pathway) [81] or of the Schiff bases (Namiki pathway) [82] can lead to formation of reactive diacrbonyls, but these pathways which are readily observed at high glucose concentrations in vitro, are not predominant in vivo [83]. The Maillard reaction, also known as the "browning reaction", involves oxidation of the glycated product which forms a brown coloured product. Glucose, fructose and glucose-6-phosphate are all involved in glycation, albeit at different rates of reaction with glucose, the most important contributor, reacting at a comparatively slower rate than the other two [6]. Increased glucose levels, as seen in diabetic patients, causes more AGEs formation than in healthy people. These AGEs affect the normal function of several proteins and enzymes, and are responsible for aging [74,80] and the complications of diabetes such as nephropathy and retinopathy [79]. Another way by which the glycation reaction causes damage is through the formation of reactive -dicarbonyl compounds, such as MG, glyoxal and 3-deoxyglucosone (3-DG), when the sugar molecule undergoes fragmentation [78].
MG can also cause AGEs formation [78,79]. In fact, MG and two other dicarbonyl metabolic intermediates, 3-DG and glyoxal, are believed to be major sources of intracellular and plasma AGEs formation [79,84,85], which are commonly implicated in the aging process. Any MG which is not degraded by the glyoxalase system or aldose reductase, reacts nonenzymatically with arginine or lysine residues of proteins [45] to form irreversible AGEs. This glycation is not random, but it depends on the structural configuration and (or) physical locations of the target proteins [86,87]. The AGEs produced by the reaction between MG and arginine are hydroimidazolone Nε-(5-hydro-5-methyl-4-imidazolon-2-yl)ornithine and argpyrimidine [88], whereas the AGE, Nε-carboxyethyllysine (CEL) [89,90] is formed when MG reacts with lysine. Further crosslinking of these AGEs produces fluorescent products such as pentosidine and cross-line, and non-fluorescent ones such as argpyrimidine, methylglyoxal-lysine dimer (MOLD), glyoxal-lysine dimer (GOLD) and imidazolones [91,92]. The presence of these AGEs can be detected immunohistochemically in tissues [93].

Methylglyoxal, AGEs, oxidative stress and aging
The damage inflicted by oxidative stress and the formation of intracellular AGEs likely contribute to cellular aging. From this point of view, both increased MG and AGEs would cause accelerated cellular aging. MG would be a double-edged sword because it is a potent inducer of oxidative stress [17,62,94,95], as discussed below, and it is a major precursor of AGEs formation. AGEs also induce oxidative stress.
MG has been shown to increase the activity of several prooxidant enzymes such as NADPH oxidase [94,97] (Fig. 3), p38 MAPK [98,102], and increase the of expression of JNK and PPAR- [104].
Excess superoxide can react with nitric oxide (NO) to form peroxynitrite (ONOO -) [105] (Fig. 3). Peroxynitrite is a strong oxidant and nitrating agent. Because of its oxidizing properties, peroxynitrite can damage a wide range of molecules including DNA and proteins in cells [105].
Metabolic activity in the mitochondria is at the centre of the free radical theory of aging. Mitochondria, which are the major sites of ATP and energy production in the cell, also generate about 85% of total intracellular superoxide when electrons escape, mainly from complex I and complex III, and react with oxygen [23,[113][114][115][116].
In in vivo studies elevated MG levels are associated with increased oxidative stress. For example, we have shown that in 13 wk old SHR with elevated blood pressure, significantly elevated plasma and aortic MG levels are associated with increased levels of superoxide, and significantly reduced GSH levels, glutathione peroxidase, and glutathione reductase activities, compared with age-matched Wistar Kyoto (WKY) rats [61]. Similarly, in diabetes mellitus and hypertension, increased MG levels are associated with increased oxidative stress [61,65,67,68,118].

Methylglyoxal and aging
The accumulation of AGEs in extracellular tissue proteins, such as the basement membrane and matrix proteins of blood vessels and skin, is a well known phenomenon characteristic of aging and age-related diseases. Several studies demonstrate aging associated increase in AGEs. Thus, accumulation of AGEs in the vessel walls results in a gradual loss of elasticity, which makes older subjects more susceptible to cardiovascular diseases [133,134]. MGinduced AGEs, such as CEL and CML, increased with age in human lens and cause cataract formation [90]. In a study on 172 subjects serum levels of CML, 8-isoprostanes and Creactive protein, which are markers of oxidative stress, were higher in elderly people (>60 years old) compared with younger people (<45 years old) [135]. One reason why AGEs accumulate during the aging process could be due to an age-related decrease in antioxidant enzymes. Thus, Mailankot et al. [136] reported that the activity and expression of glyoxalase I protein, which is involved in MG degradation, decreased with age in the anterior epithelial cells of human lens, which causes an accumulation of MG. Similarly, an age-dependent decrease in catalase activity in the skin may be responsible for elevated MG and peroxynitrite production [137].
However, it is doubtful whether extracellular AGEs accumulation plays a causative role in aging. On the other hand AGEs formation inside the cell, such as AGE-nucleotides in DNA, may contribute to cellular senescence [6, 60,74,80]. DNA integrity is an important determinant of lifespan and errors in DNA repair would lead to substitutions, deletions, insertions, and transpositions of nucleotides, with increased risk of carcinogenesis and reduced life span. Animals with a longer lifespan and more efficient DNA repair have delayed carcinogenesis [80]. In this regard MG-induced DNA damage can have a more direct effect on aging.
Studies directly implicating MG in the aging process are very few and this is one area where there is a knowledge gap. The study by Morcos et al in the worm C. elegans highlights the role of MG, glyoxalase I and MG-induced ROS formation in aging and life span [138]. They showed that the activity of glyoxalase I was markedly reduced with age resulting in accumulation of MG-derived adducts and oxidative stress markers, which further inhibited www.intechopen.com the expression and the activity of glyoxalase I. Over expression of glyoxalase I decreased MG-induced modification of mitochondrial proteins and ROS production, and prolonged the lifespan of C. elegans; whereas CeGly knock-out produced the opposite effect [138].
Scheckhuber et al. studied the degradation of MG by the glyoxalase system enzymes and its effect on growth and lifespan in filamentous ascomycete and a model of aging, Podospora anserine (P. anserina) [139]. Using genetic manipulation of the two enzymes of the glyoxalase system, they found that up-regulation of both components of the glyoxalase system was effective in increasing lifespan in P. anserina.
Oxidative stress-induced cellular senescence was demonstrated in the study by Sejeresen and Rattan [140]. They treated human skin fibroblasts with MG (400 μM), or glyoxal (1.0 mM), and found the appearance of various senescent phenotypes within three days. These phenotypes showed growth arrest, had increased hydrogen peroxide and the glyoxalinduced AGE, Nε-carboxymethyl lysine (CML) protein levels, and altered SOD and catalase antioxidant enzyme activities [140]. Sejeresen and Rattan proposed this model to study cellular senescence in vitro [140].
In this review we have highlighted some important facts that oxidative stress is a major factor in the cellular and whole body aging processes, AGEs are strongly associated with aging and MG is a major precursor of AGEs formation, and both MG and AGEs are potent inducers of oxidative stress. Based on these facts, it is highly likely that MG may have a major role in the aging process through induction of oxidative stress as depicted in the scheme in Fig. 3. In fact, elevated MG levels may be responsible for causing accelerated aging in many tissues and organs of the cardiovascular system, nervous system, and other systems of the human body. A strategy to prevent aging should include targeting MG by reducing excessive formation, inhibit AGEs formation, and remove excessively formed MG and AGEs from the body.

Anti-MG and anti-AGEs compounds
The deleterious effects of MG and AGEs can be prevented by compounds that can do one or all of the following: (i) bind and neutralize reactive aldehydes, especially MG, (ii) prevent the formation of AGEs, (iii) neutralize formed AGEs, (iv) break down formed AGEs.
Considering these multiple ways of preventing the effects of MG or AGEs these compounds will be termed as "anti-MG" or "anti-AGE". Unfortunately, specific anti-MG or anti-AGE compounds are not yet available. The ones available are non-specific and have one or more other effects, which limits their usefulness. A number of the available compounds happen to have anti-MG as well as anti-AGE effects.
The possible sites at which anti-AGEs and anti-MG drugs can work are shown in Fig. 4, which outlines the various stages of AGEs formation.
Site 1. The first step in glycation is the binding of a sugar to the free amino groups of a protein.
Drugs that bind to the amino group of proteins, such as aspirin, can prevent the binding of the sugar to the amino group. This group of compounds is likely to produce non-specific effects.
Site 2. Compounds can be used to bind aldose and ketose sugars to neutralize them and prevent them from reacting with proteins. E.g. Aminoguanidine reacts with the carbonyl group of glucose and prevents AGEs formation. The dicarbonyls, which are also formed from other metabolic pathways, also contribute significantly to AGEs formation, as explained in the text. The various sites at which anti-AGEs and anti-MG compounds can act are indicated by numbers and discussed in the text. Based on the scheme proposed by Khalifah et al. [83] Site 3. AGEs and reactive aldehydes also generate reactive oxygen species which adds to their damaging effects [17,141,142]. Antioxidants such as vitamin C or E [143] and metal chelators such as penicillamine [144] can be used to quench ROS and metal ions.
Site 4. Reactive aldehydes such as MG, glyoxal, glycoaldehyde and glucosones, which are formed during nutrient metabolism and AGEs formation, are a major source of AGEs formation. Reactive aldehydes can be neutralized by compounds such as aminoguanidine [145,146] and metformin [147,148].
Site 5. Amadori adducts, formed in the intermediate stages of AGEs formation can either be quenched by compounds such as aminoguanidine, or degraded enzymatically by enzymes such as amadoriase and human fructosamine-3-kinase, which belong to this group [149,150]. Amadoriases have not been detected in higher organisms [151,152].
Site 6. The final group of compounds acts on formed AGEs and are therefore, known as AGE breakers or cross-link breakers. E.g. phenacylthiazolium bromide (PTB) [153] and www.intechopen.com alagebrium (previously known as ALT-711), which are thiazolium compounds. AGEs which do not have cross-links such as pentosidine [154], GOLD and MOLD [155] will not be affected by these drugs. Some of the more common compounds with anti-MG or anti-AGEs effects are described below.
Aminoguanidine is one of the popular and widely used AGEs inhibitor [145] and MG scavenger. Despite being a guanidine derivative it shares many common properties with hydrazine and is classified as a hydrazine [156]. As described above, aminoguanidine acts at site 2 as well as site 4 (Fig. 4) meaning that it prevents AGEs formation by combining with the carbonyl group of glucose as well as by scavenging reactive dicarbonyls formed during various metabolic processes [146]. The inhibitory effect of aminoguanidine is mainly at the Amadori stage [83]. Aminoguanidine is not a specific AGEs inhibitor or MG scavenger and it has other actions. Aminoguanidine potently inhibits histaminases [157,158] and prevents deamination of histamine and putrescine. Aminoguanidine also inhibits nitric oxide synthase (NOS) [159,160] and prevents the formation of nitric oxide (NO), a dynamic signaling molecule in the body [161], from L-arginine. Aminoguanidine also binds to the enzyme S-adenosylmethionine decarboxylase and increases synthesis of polyamines such as spermidine and spermine from ornithine [162]. Aminoguanidine can also bind pyridoxal and cause vitamin B6 deficiency, which in turn can result in adverse reactions to aminoguanidine [163]. A number of in vitro and in vivo studies have described the inhibitory effects of aminoguanidine on AGEs formation [145,146,[164][165][166][167]. The doses used in vivo range from 25 mg/kg/day [145,166] to 50 mg/kg/day [165] and up to 100 mg/kg/day [167]. Thus, aminoguanidine is far from an ideal MG scavenger and AGEs inhibitor. In clinical trials aminoguanidine was found to be too toxic for use in patients. Two doublemasked, multiple-dose, placebo-controlled, randomized clinical trials, ACTION I and ACTION II [168,169] investigated the therapeutic potential of aminoguanidine in preventing the progression of renal damage in patients with diabetic nephropathy. The ACTION I trial involving 690 participants did not show a statistically significant difference between the placebo group and the combined aminoguanidine dose groups, even though patients treated with aminoguanidine showed a tendency of having a lower risk of doubling of serum creatinine [168]. Due to safety concerns and an apparent lack of efficacy, the External Safety Monitoring Committee for the ACTION II trial involving 599 participants recommended early termination [169]. Patients with diabetes may have impaired red blood cell-deformability, which could cause microvascular and kidney damage. A one year trial with aminoguanidine and erythropoietin on 12 patients on dialysis restored red blood celldeformability to near-normal levels, an effect attributed to inhibition of AGEs formation by aminoguanidine [170]. As mentioned earlier the toxic effects of aminoguanidine have limited its therapeutic potential. For example, like hydrazine, aminoguanidine may be associated with drug-induced systemic lupus erythematosus and abnormal liver function tests, and it can cause flu-like syndromes and vasculitis [169]. Aminoguanidine can also cause damage to DNA through hydroxyl-and hydrogen peroxide-formation in the presence of Fe +3 [171].
Metformin is an oral dimethylbiguanide antihyperglycemic agent, which can also inhibit AGEs formation [172], through its action in the post-Amadori stages [83,173]. Metformin has also been proposed to have a MG scavenging effect attributed to its guanidino group, which binds with MG to form an inactive product, triazepinone [147,148,174,175]. The MG-scavenging effect of metformin resulted in significantly reduced elevated MG levels in type 2 diabetes patients treated with high doses of metformin, between 1,500 and 2,500 mg/day [172]. We have shown that fructose-fed Sprague-Dawley rats had significantly elevated serum MG and blood pressure, and increased levels of MG, hydrogen peroxide and the MG-derived AGE, CEL, in the aorta, all of which were attenuated by metformin [65]. Metformin has been proposed to protect against MG-induced increased atherogenicity of low density lipoprotein (LDL) [176]. The use of metformin as a MG scavenger and AGEs inhibitor is limited, and hopefully more studies showing its anti-MG, anti-AGEs effectiveness will promote its use for this purpose. Metformin can be considered to have a good therapeutic potential in this regard since it is already in clinical use for type 2 diabetes as an insulin sensitizing agent.
Pioglitazone, a thiazolidinedione, is a peroxisome proliferator-activated receptor gamma (PPAR ) agonist which acts as an insulin sensitizer and is used in type 2 diabetes. Pioglitazone has been proposed to have anti-AGEs effect by inhibiting glycation, AGEs formation and protein cross-linking [177,178]. Studies employing pioglitazone as an anti-MG or anti-AGEs compound are not forthcoming and more evidence is needed to make definitive statements about the therapeutic potential of pioglitazone in this regard.
N-acetylcysteine (NAC) is a MG scavenging and antioxidant compound [179,180]. There are good reasons for using NAC as an anti-MG compound: NAC can increase GSH levels [181], which is an efficient MG scavenger and antioxidant [70,179,180], NAC is a cysteine containing thiol compound and MG binds with high affinity to cysteine [180,181], and NAC is already used clinically for other conditions such as acetaminophen overdose [179,181]. More studies employing NAC as an anti-MG drug should provide interesting results and may help to establish the potential of NAC in this regard.
A widely used class of antihypertensive drugs has been proposed to have anti-AGE effects. Angiotensin receptor blockers (ARBs) and angiotensin converting enzyme inhibitors (ACEIs) have been shown to protect against kidney damage, an effect claimed to be independent of their blood pressure lowering action [182][183][184][185], but proposed to be due to an anti-AGE effect. Clinical trials evaluating AGEs lowering effects of ARBs and ACEIs at blood pressure lowering doses can add to the therapeutic utility of these drugs.
A number of compounds have been investigated for anti-AGE effects in limited studies, but have not been widely used as such in experimental studies in animals or humans. These compounds include the cycloxygenase inhibitors, aspirin [186][187][188], ibuprofen [189], diclofenac [190], xanthine derivative, pentoxifylline [191,192], which is used for claudication in peripheral vascular disease, metal chelators, D-penicillamine [144] and desferoxamine [83,144], thiamine pyrophosphate and pyridoxamine [193][194][195]. Many more studies are necessary for these compounds in order to draw definitive conclusions about their anti-MG or anti-AGE effects.
A number of AGE inhibitors were synthesized and screened for their AGEs inhibitory effects by Rahbar et al. [173,202,203]. These are derivatives of aryl ureido and aryl carboxaminido phenoxy isobutyric acids and were derived from some known AGEs inhibitors. These compounds act at multiple stages of the AGEs formation process. Some of these compounds have AGEs breaking properties. More studies are needed for these compounds to establish their specificity and safety for therapeutic use.

AGEs breakers
The AGEs which have undergone cross-linking are very stable products and their concentration, especially in long-lived matrix proteins, increases with age. AGEs inhibitors are ineffective against formed AGEs and compounds which can break the cross-links are required. The AGEs breaker compounds can prove invaluable to slow down the aging process, and in the treatment of established stages of diseases such as diabetes, Alzheimer's, atherosclerosis and rheumatoid arthritis.
The first AGEs breaking compound reported was phenacylthiazolium bromide (PTB) in 1996. PTB breaks the covalent cross-links of AGEs [204]. Administration of PTB (10 mg/kg/day, intraperitoneal for 4 wks) reduced the amount of IgG bound to the surface of red blood cells in diabetic rats [153]. However, PTB is not stable.
The search for a stable derivative of PTB resulted in the synthesis of ALT 711 (4,5dimethylthiazolium) [205]. ALT 711 (now known as alagebrium) reduced arterial stiffness in streptozotocin-induced diabetic rats [205]. In aging rats, ALA (10 mg/kg for 16 weeks) also increased glutathione peroxidase and superoxide dismutase activities and reduced oxidative stress [206]. Alagebrium improved impaired cardiovascular function in older rhesus monkeys [207]. Alagebrium demonstrated promising results and a good safety profile in phase 2 clinical trials. In a clinical study involving 93 subjects, 50 yrs and older, with evidence of vessel stiffness (pulse pressure ≥60 mm Hg, systolic blood pressure ≥140 mm Hg, and large artery compliance ≤1.25 mL/mm Hg), alagebrium (210 mg, once per day for 56 days) improved arterial compliance [208]. In another group of 13 patients aged 65±2 yrs with systolic hypertension (systolic blood pressure > 140 mmHg, diastolic blood pressure <90 mm Hg), alagebrium (210 mg/kg twice a day for 8 weeks) reduced vascular fibrosis and markers of inflammation [209]. Alagebrium (administered for 16 weeks) decreased left ventricular mass and improved left ventricular diastolic filling in another trial in 23 patients with diastolic heart failure [210,211].
However, in a recent study [212] involving 102 patients (aged 62 ± 11 years) with heart failure (left ventricular ejection fraction (LVEF ≤0.45), alagebrium (400 mg/day/36 wks) did not improve exercise tolerance and systolic dysfunction, and no changes were observed in a number of secondary endpoints. Thus, the authors could not verify the claims that alagebrium has beneficial effects in systolic heart failure [212].
Alagebrium has been reported to be a weak inhibitor of thiamine diphosphokinase and is unlikely to interfere with thiamine metabolism at therapeutic concentrations [213]. However, the authors urge caution when new AGE-crosslink breakers based on thiamine are designed, to make sure they are not potent inhibitors of thiamine diphosphokinase.

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In the studies described above alagebrium has been studied mainly for its chronic effects on AGEs as an AGEs breaker. We investigated whether alagebrium also has acute preventive effects against the reactive dicarbonyl, MG, in 12 wk old male Sprague-Dawley rats [66]. Our results showed that alagebrium also has acute (< 6 h) MG scavenging ability [66]. AGEs are formed slowly over a time ranging from 24 h to up to 7 days and more. Therefore, the attenuation of MG-induced acute effects (seen within 6 h of MG administration) is most likely due to scavenging of MG by alagebrium. Thus, alagebrium significantly attenuated the significant increases in MG levels in the plasma, and different organs (measured 2 h after administration), and also attenuated MG-induced impaired glucose tolerance and the reduced insulin-stimulated glucose uptake by adipose tissue. In an in vitro assay in which MG (10 μM) was incubated with or without alagebrium (100 μM) for different times at 37° C, alagebrium significantly reduced the amount of detectable MG [66]. Our results strongly indicate an acute MG scavenging effect of alagebrium which can add to its AGEs breaking ability. More direct evidence of interaction of alagebrium and MG using mass spectrometry would be very useful. We have also recently shown that alagebrium significantly attenuated the deleterious effects of chronic MG administration for 4 wks on glucose tolerance and pancreatic islet -cell function in male Sprague-Dawley rats [72].
In conclusion, MG and AGEs are very likely to be involved in the initiation and or progression of the aging process. Commonly available pharmacological compounds to investigate these roles of MG and AGEs, such as aminoguanidine, are non-specific, whereas some of the newer compounds appear promising in inhibiting AGEs formation at multiple steps in the pathway in in vitro studies. However, more in vivo studies are required before their therapeutic potential can be established. A more dedicated effort is necessary to identify newer anti-MG and anti-AGEs compounds which are more specific and safer before more can be done about their therapeutic potential. www.intechopen.com