Tobacco smoke is a source of toxic reactive glycation products

A previously undescribed chemical link between smoking and metabolic disease

Over the past 20 years, protein glycation has been implicated in a variety of pathological states. Although smoking also can contribute to many of these diseases, the precise mechanism by which this occurs is not known. Previously, we have demonstrated that nornicotine, a constituent of tobacco and metabolite of nicotine, can catalyze aldol reactions under aqueous conditions. This finding has caused us to question whether this reaction has physiological consequences. We now report that nornicotine causes aberrant protein glycation and catalyzes the covalent modification of certain prescription drugs such as the commonly used steroid, prednisone. Furthermore, we show that the plasma of smokers as compared with nonsmokers contains higher concentrations of nornicotine-modified proteins, suggesting an unrecognized pathway for the development of the pathology of tobacco abuse.

Advanced glycation end products and diabetic complications

Diabetic complications are major cause of morbidity and mortality in patients with diabetes. While the precise pathogenic mechanism(s) underlying conditions such as diabetic retinopathy, diabetic nephropathy and increased risk of atherosclerosis remain ill-defined, it is clear that hyperglycaemia is a primary factor that initiates and promotes complications. Formation of advanced glycation end products (AGEs) correlate with glycaemic control, and these reactive adducts form on DNA, lipids and proteins where they represent pathophysiological modifications that precipitate dysfunction at a cellular and molecular level. Many of these adducts form rapidly during diabetes and promote progression of a raft of diabetes-related complications. Recent evidence also suggests an important interaction with other pathogenic mechanisms activated within the diabetic milieu. This review outlines the nature of AGE formation in biological systems and highlights accumulative evidence that implicates these adducts in diabetic complications. As more therapeutic agents are developed to inhibit AGE formation or limit their pathogenic influence during chronic diabetes, it is becoming clear that these anti-AGE strategies have an important role to play in the treatment of diabetic patients.

Reactive carbonyls from tobacco smoke increase arterial endothelial layer injury

We hypothesized that reactive carbonyls generated from smoke exposure cause increased arterial low-density lipoprotein (LDL) accumulation and endothelial layer permeability. In addition, we hypothesized that estrogen supplementation was protective against chronic environmental tobacco smoke (ETS) exposure to the artery wall. Quantitative fluorescence microscopy was used to determine artery injury after exposure. For our chronic studies, ovariectomized rats treated with subcutaneous placebo or 17beta-estradiol pellets were exposed to ETS or filtered air for 6 wk. ETS exposure increased carotid artery LDL accumulation more than fourfold compared with filtered air exposure, an effect largely mediated by increased permeability. No protective effect of estradiol was observed. Acute ETS exposure of a buffer solution containing LDL resulted in a more than sixfold increase in the highly reactive carbonyl glyoxal. Perfusion of this solution through carotid arteries resulted in a 105% increase in permeability. Moreover, perfusion of glyoxal alone caused a 50% increase in carotid artery permeability. This endothelial damage and changes in lipid accumulation may serve as an initiating event in atheroma formation in individuals exposed to ETS.

Idiopathic nodular glomerulosclerosis is a distinct clinicopathologic entity linked to hypertension and smoking

Idiopathic nodular glomerulosclerosis (ING) is an enigmatic condition that resembles nodular diabetic glomerulosclerosis but occurs in nondiabetic patients. We reviewed clinicopathologic features, immunohistochemical profiles, and outcomes in 23 patients with ING diagnosed from among 5,073 native renal biopsy samples (0.45%) at Columbia University from January 1996 to March 2001. This cohort, in which diabetes mellitus was excluded, consisted predominantly of older (mean age, 68.2 years) white (73.9%) men (78.3%). Clinical findings at presentation included renal insufficiency in 82.6% (mean serum creatinine = 2.4 mg/dL), proteinuria (> 3 g/d in 69.6%; mean 24-hour urine protein = 4.7 g/d), and-less frequently-full nephrotic syndrome (21.7%). There was a high prevalence of hypertension (95.7%; mean = 15.1 +/- 3.4 years), smoking (91.3%; mean = 52.9 +/- 6.9 pack-years), hypercholesterolemia (90%), and extrarenal vascular disease (43.5%). All 23 patients had prominent diffuse and nodular mesangial sclerosis, glomerular basement membrane thickening, arteriosclerosis, and arteriolosclerosis. Immunohistochemical staining for CD34, a marker of endothelial cells, showed an increased number of vascular channels within ING glomeruli compared with normal controls. Follow-up data were available for 17 patients, 6 of whom reached end-stage renal disease (ESRD) (35.3%). By Kaplan-Meier estimates, the median time after biopsy to ESRD was 26 months. Predictors of progression to ESRD included continuation of smoking (P =.0165), lack of angiotensin II blockade (P =.0007), degree of tubular atrophy and interstitial fibrosis (P =.0517), and degree of arteriosclerosis (P =.0096). In conclusion, ING is a progressive vasculopathic lesion linked to hypertension and cigarette smoking.

Neurovascular disease, antioxidants and glycation in diabetes

People with diabetes are ten to fifteen times more likely to have a lower limb amputation (LLA) than non-diabetic individuals. Fifteen percent of people with diabetes will develop a foot ulcer during their lifetime, the rate of major amputation amongst diabetic individuals continues to rise, foot problems remain the commonest reason for diabetes-related hospitalisation and recurrence rates in patients with previous foot ulcers are 50% or more. Hyperglycaemia-induced oxidative stress has been shown to result in decreased nerve conduction velocity, and decreased endoneural blood flow-both precursors for neuropathy. Vitamin antioxidants have been shown to be effective therapy in experimental models in reducing free radical species and inhibiting the oxidative process in diabetes subjects. Little work has been published, however, regarding the dietary use of antioxidants from foods, and their specific effects on neurovascular disease and glycation within the diabetes population. Aetiological and prevention studies with dietary antioxidants from foods aimed at the complex nature of foot problems in diabetes are needed.

Diabetes and cardiovascular disease

This review focuses on several topics related to the epidemiology of diabetes and cardiovascular disease (CVD). These include the CVD risk factors common in the metabolic syndrome, behavioral risk factors and diabetes, gender differences in the association between diabetes and CVD risk, and how the clinical definition of diabetes influences the association of diabetes and CVD. Nontraditional risk factors potentially linking diabetes and CVD are also discussed, including chronic inflammation, advanced glycation endpoints, autonomic neuropathy, sleep-disordered breathing, and genetic susceptibility to diabetes-associated CVD risk.

Diabetes and advanced glycation endproducts

Bio-reactive advanced glycation endproducts (AGE) alter the structure and function of molecules in biological systems and increase oxidative stress. These adverse effects of both exogenous and endogenously derived AGE have been implicated in the pathogenesis of diabetic complications and changes associated with ageing including atherosclerosis, renal, eye and neurological disease. Specific AGE receptors and nonreceptor mechanisms contribute to these processes but also assist in the removal and degradation of AGE. The final disposal of AGE depends on renal clearance. Promising pharmacologic strategies to prevent AGE formation, reduce AGE toxicity, and/or inactivate AGE are under investigation.

Passive cigarette smoke and the renal glyoxalase system

Cigarette smoking is associated with a number of fatal diseases, including cancer of different organs. A number of oxoaldehydes are found in cigarette smoke, among which methylglyoxal (MG) is known to cause toxicity to cells upon accumulation. In biological systems, MG is converted to s-d-lactoylglutathione by glyoxalase I with reduced glutathine (GSH) as a cofactor, and s-d-lactoylglutathione is converted to D-lactic acid with simultaneous regeneration of GSH, by glyoxalase II. In the present study, we have investigated the status of the glyoxalase enzymes in kidney tissues from rats exposed to passive cigarette smoke. No significant change has been noted in glyoxalase I activity. Glyoxalase II was decreased during 1 and 2 weeks of exposure, and after that the activity was increased. The initial decrease in the activity of gly II may be due to the excess amount of methylglyoxal generated due to smoke exposure or the adduct formed by MG and GSH which known to inhibit gly II activity. Both enzymes help in the detoxification of cigarette smoke induced chemicals and biochemicals.

The AGE-receptor in the pathogenesis of diabetic complications

Native glucose-derived glycation derivatives (advanced glycation end products, AGE) in vascular, renal and neuronal tissues contribute to organ damage. Glycation derivatives include a number of chemically and cell-reactive substances, also termed glycoxidation products or glycotoxins (GT). Cell-associated AGE-specific receptors (AGE-Rs), AGE-R1-3, RAGE, as well as the scavenger receptors ScR-II and CD-36 that are present on vascular, renal, hemopoietic, and neuronal/glial cells, serve in the regulation of AGE uptake and removal. AGE-Rs also modulate cell activation, growth-related mediators, and cell proliferation, consequently influencing organ structure/function. This occurs via oxidant stress triggered via receptor-dependent or -independent pathways, and leads to signal activation pathways, resulting in pro-inflammatory responses. In susceptible individuals, the AGE-R expression/function may be subject to environmental or gene-related modulation, which in turn may influence tissue-specific gene functions. In this context, altered expression and activity of AGE-R components has recently been found in both mouse diabetes models and humans with diabetic complications. Although several gene polymorphisms are detected in most AGE-R components, no significant correlation to diabetic complications has as yet been found. Further investigation is underway to define whether primary or secondary genetic links of pathogenic significance exist in this system. Various AGE-binding peptides or soluble receptors have emerged as potential sequestering agents for toxic AGEs as potential therapies for diabetic complications.

Effects of smoking and treatment status on periodontal bacteria: evidence that smoking influences control of periodontal bacteria at the mucosal surface of the gingival crevice

BACKGROUND

We examined whether smoking status could influence growth of potentially pathogenic bacteria in the periodontal environment of treated and untreated periodontal patients.

METHODS

We have previously reported effects of treatment status on marker bacteria in our patients. We established a history of any smoking during 6 months prior to microbiological sampling (F-ME, 16 smokers out of 64; MHM, 70 smokers out of 185). We used a commercial immunoassay to quantitate Porphyromonas gingivalis, Prevotella intermedia, and Actinobacillus actinomycetemcomitans in paper point samples from periodontal sites.

RESULTS

Logistic regression showed that in smokers, neither P. gingivalis nor A. actinomycetemcomitans was quantitatively increased, while P intermedia was somewhat increased. Multiple regression demonstrated that smoking disrupts the positive relationship between increasing probing depth and increasing bacterial growth that is found in non-smokers. In smokers, growth of marker bacteria at shallow sites (< or =5 mm) was significantly increased to the levels found at deeper sites (>5 mm) in both smokers and non-smokers. Supragingival plaque biofilm was identified as a reservoir for marker bacteria; smokers and nonsmokers had equal ranges of oral cleanliness.

CONCLUSIONS

Smoking-associated periodontitis is not simply a reflection of oral cleanliness. Smoking extends a favorable habitat for bacteria such as P. gingivalis, P. intermedia, and A. actinomycetemcomitans to shallow sites (< or =5 mm). Molecular byproducts of smoking interfere with mechanisms that normally contain growth of damaging bacteria at the surface of the oral mucosa in gingival crevices. In this way, smoking can promote early development of periodontal lesions.

Age-related changes in cells and tissues due to advanced glycation end products (AGEs)

Advanced glycation end products (AGEs) formed by nonenzymatic glycation and oxidation of proteins accumulate during normal aging and at accelerated rate during the course of diabetes. They play a role in the pathogenesis of several other chronic diseases such as Alzheimer's disease, arthritis, atherosclerosis, pulmonary fibrosis and renal failure. AGE-formation changes the chemical and biological properties of proteins inside and outside of the cell. Binding to specific cell surface receptors induces activation of cellular signaling pathways leading to cellular dysfunction and cell death. AGEs are inducible by oxidative stress and induce oxidative stress. Subject of current studies of cell biologists is the intracellular processing of AGEs, which is accompanied by changes of the endolysosomal compartment.

Vitamin C prevents cigarette smoke-induced oxidative damage in vivo

Our recent in vitro results [4] indicate that cigarette smoke induces oxidation of human plasma proteins and extensive oxidative degradation of the guinea pig lung, heart, and liver microsomal proteins, which is almost completely prevented by ascorbic acid. In this paper, we substantiate the in vitro results with in vivo observations. We demonstrate that exposure of subclinical or marginal vitamin C-deficient guinea pigs to cigarette smoke causes oxidation of plasma proteins as well as extensive oxidative degradation of the lung microsomal proteins. Cigarette smoke exposure also results in some discernible damage of the heart microsomal proteins. The oxidative damage has been manifested by SDS-PAGE, accumulation of carbonyl and bityrosine, as well as loss of tryptophan and protein thiols. Cigarette smoke exposure also induces peroxidation of microsomal lipids as evidenced by the formation of conjugated dienes, malondialdehyde, and fluorescent pigment. Cigarette smoke-induced oxidative damage of proteins and peroxidation of lipids are accompanied by marked drop in the tissue ascorbate levels. Protein damage and lipid peroxidation are also observed in cigarette smoke-exposed pair-fed guinea pigs receiving 5 mg vitamin C/animal/day. However, complete protection against protein damage and lipid peroxidation occurs when the guinea pigs are fed 15 mg vitamin C/animal/day. Also, the cigarette smoke-induced oxidative damage of proteins and lipid is reversed after discontinuation of cigarette smoke exposure accompanied by ascorbate therapy. The results, if extrapolated to humans, indicate that comparatively large doses of vitamin C may protect the smokers from cigarette smoke-induced oxidative damage and associated degenerative diseases.

Tobacco-related diseases. Is there a role for antioxidant micronutrient supplementation?

It is clear that smoking causes an increase in free radicals, reactive nitrogen and oxygen species (RNS and ROS, respectively), and that cigarette smoking is associated with increases in the incidence and severity of several diseases including atherosclerosis, cancer, and chronic obstructive lung disease. Although there is still no unequivocal evidence that oxidative stress is a contributor to these diseases or that an increased intake of antioxidant nutrients is beneficial, the observation that smokers have lower circulating levels of some of these nutrients, raises concern. This article discusses the possible links between the observed oxidant-induced damage related to tobacco smoking, effects on cellular mechanisms, and their potential involvement in the causation and enhancement of disease processes.

Advanced glycation end products: a Nephrologist's perspective

Advanced glycation end products (AGEs) are a heterogeneous group of molecules that accumulate in plasma and tissues with advancing age, diabetes, and renal failure. There is emerging evidence that AGEs are potential uremic toxins and may have a role in the pathogenesis of vascular and renal complications associated with diabetes and aging. AGEs are formed when a carbonyl of a reducing sugar condenses with a reactive amino group in target protein. These toxic molecules interact with specific receptors and elicit pleiotropic responses. AGEs accelerate atherosclerosis through cross-linking of proteins, modification of matrix components, platelet aggregation, defective vascular relaxation, and abnormal lipoprotein metabolism. In vivo and in vitro studies indicate that AGEs have a vital role in the pathogenesis of diabetic nephropathy and the progression of renal failure. The complications of normal aging, such as loss of renal function, Alzheimer's disease, skin changes, and cataracts, may also be mediated by progressive glycation of long-lived proteins. AGEs accumulate in renal failure as a result of decreased excretion and increased generation resulting from oxidative and carbonyl stress of uremia. AGE-modified beta(2)-microglobulin is the principal pathogenic component of dialysis-related amyloidosis in patients undergoing dialysis. Available dialytic modalities are not capable of normalizing AGE levels in patients with end-stage renal disease. A number of reports indicated that restoration of euglycemia with islet-cell transplantation normalized and prevented further glycosylation of proteins. Aminoguanidine (AGN), a nucleophilic compound, not only decreases the formation of AGEs but also inhibits their action. A number of studies have shown that treatment with AGN improves neuropathy and delays the onset of retinopathy and nephropathy. N-Phenacylthiazolium bromide is a prototype AGE cross-link breaker that reacts with and can cleave covalent AGE-derived protein cross-links. Thus, there is an exciting possibility that the complications of diabetes, uremia, and aging may be prevented with these novel agents.

Smoking and cardiovascular disease

Mainstream and ETS exposure are strong risk factors for cardiovascular disease in men and women. The relationships between smoking and cardiovascular disease result from multiple mechanisms that interact to contribute to atherosclerosis, vascular injury, thrombosis, and vascular dysfunction. We are only now beginning to understand how smoking contributes to the genesis and progression of cardiovascular disease. Because of the complexity of the interactions between nicotine and the components of MSS, ETS, and sidestream smoke with the vasculature, it will take a great deal of time and effort to fully unravel the mechanisms by which smoking contributes to cardiovascular disease. In addition, cardiovascular risk in female smokers is complicated by hormonal variables that may contribute to greater relative risk. It is important that health care providers, educators, and policy makers recognize the changing patterns of smoking and the impact of smoking on cardiovascular disease, and continue campaigns aimed at enhancing smoking cessation in the general population and in teens. Rigorous research is needed on the changing cultural, psychosocial, and environmental factors that influence tobacco use to improve our understanding of racial/ethnic smoking patterns, and identify strategic tobacco control opportunities. The capacity of tobacco control efforts to keep pace with patterns of tobacco use and cessation depends on timely recognition of emerging prevalence and cessation patterns and the resulting development of appropriate community-based programs to address the factors involved. Smoking trends today will determine how heavy the health burden of cardiovascular disease and others will be among communities tomorrow. Programs that aim at early intervention and reflect cultural diversity will be the cornerstone in the battle against tobacco use. Continued interest in research, educational, and prevention efforts are needed to help curb the risk of cardiovascular disease from smoking in men and women.

Hypothesis for temporal displacement of metabolic and neuronal accommodation in smoking addiction

Using the overlapping criteria of (1) current smoking status and (2) homeostatic accommodation of smoking, the categories of nonsmoker, beginning smoker, smoker, and quitting smoker are structured into a cyclic representation of smoking addiction. This cyclic representation reveals that elimination of homeostatic accommodation of smoking is a critical success factor to the process of becoming a nonsmoker, while the act of stopping smoking is necessary yet insufficient to the success of that process. Homeostatic accommodation is described as having two components: metabolic and neuronal. A hypothesis for temporal displacement of metabolic and neuronal accommodation is presented to explain the behavior of "chippers" (occasional smokers) and adolescent smokers. Recommendations are made for research on the rates of development and dissipation of metabolic and neuronal accommodation of smoking, and for the development of a bimodal therapy that addresses both metabolic and neuronal accommodation and reduces relapse for quitting smokers.

Are predictors of coronary heart disease and lower-extremity arterial disease in type 1 diabetes the same? A prospective study

In the Type 1 diabetes population, coronary heart disease (CHD) and lower-extremity arterial disease (LEAD) are the two common macrovascular complications leading to early mortality and morbidity. However, it is not clear if these two complications share the same risk factors. The Pittsburgh Epidemiology of Diabetes Complications (EDC) Study prospectively examined and compared the risk factors for LEAD and CHD (including CHD morbidity and mortality). EDC subjects (332 men and 325 women), all diagnosed at Children's Hospital of Pittsburgh between 1950 and 1980, were first examined at baseline (1986-1988), and then biennially, for diabetes complications and their risk factors. Data used in the current analysis were from the first 6 years of follow-up, 98% provided at least some follow-up data for these analyses. CHD was defined as the presence of angina (diagnosed by the EDC examining physician) or a history of confirmed myocardial infarction or CHD death. An ankle-to-arm ratio of less than 0.9 at rest was considered to be evidence of LEAD. Among 635 subjects without CHD at baseline, 57 developed CHD (1.69/100 person-years), and among 579 without LEAD at baseline, 70 developed LEAD (2.31/100 person-years). CHD incidence rate was slightly higher in males, while LEAD incidence rate was slightly higher in females. Compared to non-incident cases, subjects who developed either complication were older, had a longer diabetes duration, higher LDL and total cholesterol, and were more likely to be hypertensive. In multivariate analyses, hypertension, low HDL cholesterol level, high white cell count, depression, and nephropathy were the independent risk factors for CHD (including morbidity and mortality). For LEAD, higher HbA1 level, higher LDL cholesterol level and smoking were the important contributing factors. In conclusion, the risk factor patterns differ between the two vascular complications. Glycemic control does not predict CHD overall but does predict LEAD, while hypertension and inflammatory markers are more closely related to CHD than to LEAD.

Vitamin C prevents cigarette smoke induced oxidative damage of proteins and increased proteolysis

Aqueous extract of cigarette smoke (CS) contains some stable oxidants, which oxidize human plasma proteins, bovine serum albumin, amino acid homopolymers, and also cause extensive oxidative degradation of microsomal proteins. Similar observations are made when the aqueous extract of cigarette smoke is replaced by whole phase CS solution or whole phase cigarette smoke. CS-induced microsomal protein degradation is a two step process: (i) oxidation of proteins by the oxidants present in the CS and (ii) rapid proteolytic degradation of the oxidized proteins by proteases present in the microsomes. Using aqueous extract of CS equivalent to that produced from one-twentieth of a cigarette, the observed initial and postcigarette smoke treated values of different parameters of oxidative damage per milligram of microsomal proteins are respectively: 0.24 and 1.74 nmoles for carbonyl formation, 125.4 and 62.8 fluorescence units for tryptophan loss, 10.2 and 33.4 fluorescence units for bityrosine formation, and 58.3 and 12.2 nmoles for loss of protein thiols. When compared with sodium dodecyl sulphate polyacrylamide gel electrophoresis profiles of untreated microsomal proteins, the extent of microsomal protein degradation after treatment with whole phase CS solution or aqueous extract of CS is above 90%. Ascorbate (100 microM) almost completely prevents cigarette smoke-induced protein oxidation and thereby protects the microsomes from subsequent proteolytic degradation. Glutathione is partially effective, but other antioxidants including superoxide dismutase, catalase, vitamin E, probucol, beta-carotene, mannitol, thiourea, and histidine are ineffective. The gas phase cigarette smoke contains unstable reactive oxygen species such as superoxide (O2*-) and hydrogen peroxide (H2O2) that can cause substantial oxidation of pure protein like albumin but is unable to produce significant oxidative damage of microsomal proteins. Gas phase cigarette smoke-induced albumin oxidation is not only inhibited by ascorbate and glutathione but also by superoxide dismutase, catalase and mannitol. The stable oxidants in the cigarette smoke are not present in the tobacco and are apparently produced by the interaction of O2*-/H2O2/OH* of the gas phase with some components of the tar phase during/following the burning of tobacco.

Protein aging by carboxymethylation of lysines generates sites for divalent metal and redox active copper binding: relevance to diseases of glycoxidative stress

Aging and age-related diseases are associated with the production of reactive oxygen species which modify lipids, proteins and DNA. Here we hypothesized the glyco- and lipoxidation product N(epsilon)-(carboxymethyl)lysine (CML) in proteins should bind divalent and redox active transition metal binding. CML-rich poly-L-lysine and bovine serum albumin (BSA) were chemically prepared and found to bind non-dialyzable Cu(2+), Zn(2+) and Ca(2+). CML-BSA-copper complexes oxidized ascorbate and depolymerized protein in the presence of H(2)O(2). CML-rich tail tendons implanted for 25 days into the peritoneal cavity of diabetic rats had a 150% increase in copper content and oxidized ascorbate three times faster than controls. CML-rich proteins immunoprecipitated from serum of uremic patients oxidized four times more ascorbate than control and generated spin adducts of DMPO in the presence of H(2)O(2). The chelator DTPA suppressed ascorbate oxidation thereby implicating transition metals in the process. In aging and disease, CML accumulation may result in a deleterious vicious cycle since CML formation itself is catalyzed by lipoxidation and glycoxidation.

Smoking and atherosclerosis in youth

Coronary heart disease is the most common cause of death in the US. Studies have demonstrated that smoking is a major risk factor for coronary heart disease and that a positive relationship occurs between smoking and aortic and coronary atherosclerosis in adults. In 1985, a multicenter cooperative study, Pathobiological Determinants of Atherosclerosis in Youth (PDAY), was organized to study atherosclerosis in trauma victims 15-34 years of age. Reports from this study have demonstrated that smoking is strongly associated with the prevalence and extent of grossly visible raised lesions in the abdominal aorta but only weakly associated with similar lesions in the right coronary artery. Coronary arteries from 50 smokers and 50 non-smokers were classified microscopically using a system developed by the American Heart Association in order to determine the stage at which smoking affects atherosclerosis. Smokers had over twice as many advanced lesions, types IV and V, as non-smokers (32 vs 14%) and fewer early lesions, types I, II, III, as non-smokers (38 vs 62%). The prevalence of advanced or types IV and V lesions (32%) was over twice that of intermediate or type III lesions (14%) in smokers. The opposite relationship was observed in non-smokers (14 vs 26%). This observation suggest that intermediate lesions progress rapidly into advanced lesions in smokers and that intima formerly having early lesions is replaced by intima with raised lesions.

Mechanisms of maturation and ageing of collagen

The deleterious age-related changes in collagen that manifest in the stiffening of the joints, the vascular system and the renal and retinal capillaries are primarily due to the intermolecular cross-linking of the collagen molecules within the tissues. The formation of cross-links was elegantly demonstrated by Verzar over 40 years ago but the nature and mechanisms are only now being unravelled. Cross-linking involves two different mechanisms, one a precise enzymically controlled cross-linking during development and maturation and the other an adventitious non-enzymic mechanism following maturation of the tissue. It is this additional non-enzymic cross-linking, known as glycation, involving reaction with glucose and subsequent oxidation products of the complex, that is the major cause of dysfunction of collagenous tissues in old age. The process is accelerated in diabetic subjects due to the higher levels of glucose. The effect of glycation on cell-matrix interactions is now being studied and may be shown to be an equally important aspect of ageing of collagen. An understanding of these mechanisms is now leading to the development of inhibitors of glycation and compounds capable of cleaving the cross-links, thus alleviating the devastating effects of ageing.

Increased levels of advanced glycation endproducts in the lenses and blood vessels of cigarette smokers

BACKGROUND

Advanced glycation endproducts (AGEs) arise from the spontaneous reaction of reducing sugars with the amino groups of macromolecules. AGEs accumulate in tissue as a consequence of diabetes and aging and have been causally implicated in the pathogenesis of several of the end-organ complications of diabetes and aging, including cataract, atherosclerosis, and renal insufficiency. It has been recently proposed that components in mainstream cigarette smoke can react with plasma and extracellular matrix proteins to form covalent adducts with many of the properties of AGEs. We wished to ascertain whether AGEs or immunochemically related molecules are present at higher levels in the tissues of smokers.

MATERIALS AND METHODS

Lens and coronary artery specimens from nondiabetic smokers and nondiabetic nonsmokers were examined by immunohistochemistry, immunoelectron microscopy, and ELISA employing several distinct anti-AGE antibodies. In addition, lenticular extracts were tested for AGE-associated fluorescence by fluorescence spectroscopy.

RESULTS

Immunoreactive AGEs were present at significantly higher levels in the lenses and lenticular extracts of nondiabetic smokers (p < 0.003). Anti-AGE immunogold staining was diffusely distributed throughout lens fiber cells. AGE-associated fluorescence was significantly increased in the lenticular extracts of nondiabetic smokers (p = 0.005). AGE-immunoreactivity was significantly elevated in coronary arteries from nondiabetic smokers compared with nondiabetic nonsmokers (p = 0.015).

CONCLUSIONS

AGEs or immunochemically related molecules are present at higher levels in the tissues of smokers than in nonsmokers, irrespective of diabetes. In view of previous reports implicating AGEs in a causal association with numerous pathologies, these findings have significant ramifications for understanding the etiopathology of diseases associated with smoking, the single greatest preventable cause of morbidity and mortality in the United States.