Infrared spectroscopy of proteins.

Gram-negative bacteria characteristically are surrounded by an additional membrane layer, the outer membrane. Although outer membrane components often play important roles in the interaction of symbiotic or pathogenic bacteria with their host organisms, the major role of this membrane must usually be to serve as a permeability barrier to prevent the entry of noxious compounds and at the same time to allow the influx of nutrient molecules. This review summarizes the development in the field since our previous review (H. Nikaido and M. Vaara, Microbiol. Rev. 49:1-32, 1985) was published. With the discovery of protein channels, structural knowledge enables us to understand in molecular detail how porins, specific channels, TonB-linked receptors, and other proteins function. We are now beginning to see how the export of large proteins occurs across the outer membrane. With our knowledge of the lipopolysaccharide-phospholipid asymmetric bilayer of the outer membrane, we are finally beginning to understand how this bilayer can retard the entry of lipophilic compounds, owing to our increasing knowledge about the chemistry of lipopolysaccharide from diverse organisms and the way in which lipopolysaccharide structure is modified by environmental conditions.

Molecular Basis of Bacterial Outer Membrane Permeability Revisited

Increasing evidence in both experimental and clinical studies suggests that oxidative stress plays a major role in the pathogenesis of both types of diabetes mellitus. Free radicals are formed disproportionately in diabetes by glucose oxidation, nonenzymatic glycation of proteins, and the subsequent oxidative degradation of glycated proteins. Abnormally high levels of free radicals and the simultaneous decline of antioxidant defense mechanisms can lead to damage of cellular organelles and enzymes, increased lipid peroxidation, and development of insulin resistance. These consequences of oxidative stress can promote the development of complications of diabetes mellitus. Changes in oxidative stress biomarkers, including superoxide dismutase, catalase, glutathione reductase, glutathione peroxidase, glutathione levels, vitamins, lipid peroxidation, nitrite concentration, nonenzymatic glycosylated proteins, and hyperglycemia in diabetes, and their consequences, are discussed in this review. In vivo studies of the effects of various conventional and alternative drugs on these biomarkers are surveyed. There is a need to continue to explore the relationship between free radicals, diabetes, and its complications, and to elucidate the mechanisms by which increased oxidative stress accelerates the development of diabetic complications, in an effort to expand treatment options.

Diabetes, oxidative stress, and antioxidants: a review

Over the past several decades, much has been revealed about the nature of the host innate immune response to microorganisms, with the identification of pattern recognition receptors (PRRs) and pathogen-associated molecular patterns, which are the conserved microbial motifs sensed by these receptors. It is now apparent that these same PRRs can also be activated by non-microbial signals, many of which are considered as damage-associated molecular patterns. The sterile inflammation that ensues either resolves the initial insult or leads to disease. Here, we review the triggers and receptor pathways that result in sterile inflammation and its impact on human health.

Sterile inflammation: sensing and reacting to damage

Advanced glycation end-products are a complex and heterogeneous group of compounds that have been implicated in diabetes related complications At present it is not known if they are the cause or the consequence of the complications observed We discuss the chemistry of advanced glycated end-product formation and their patho-biochemistry particularly in relation to the diabetic microvascular complications of retinopathy, neuropathy and nephropathy as well as their role in the accelerated vasculopathy observed in diabetes The concept of carbonyl stress as a cause for advanced glycated end-product toxicity is mentioned We discuss alterations in the concentrations of advanced glycated end-products in the body, particularly in relation to changes occurring with age, diabetes and its complications such as nephropathy Problems relating to current methods of advanced glycated end-product detection and measurement are highlighted including the lack of a universally established method of detection or unit of measurement Agents used for the treatment of advanced glycated end-product accumulation are reviewed, with an emphasis on the results of the recent phase III trials using aminoguanidine and diabetes related complications

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Advanced glycation end-products: a review.

Many approaches have been undertaken to understand Alzheimer's disease (AD) but the heterogeneity of the etiologic factors makes it difficult to define the clincally most important factor determining the onset and progression of the disease. However, there is increasing evidence that the previously so-called "secondary factors" such as a disturbed glucose metabolism, oxidative stress and formation of "advanced glycation endproducts" (AGEs) and their interaction in a vicious cycle are also important for the onset and progression of AD. AGEs are protein modifications that contribute to the formation of the histopathological and biochemical hallmarks of AD: amyloid plaques, neurofibrillary tangles and activated microglia. Oxidative modifications are formed by a complex cascade of dehydration, oxidation and cyclisation reactions, subsequent to a non-enzymatic reaction of sugars with amino groups of proteins. Accumulation of AGE-crosslinked proteins throughout life is a general phenomenon of ageing. However, AGEs are more than just markers of ageing since they can also exert adverse biologic effects on tissues and cells, including the activation of intracellular signal transduction pathways, leading to the upregulation of cytokine and free radical production (oxidative stress). Oxidative stress is involved in various divergent events leading to cell damage, including an increase in membrane rigidity, DNA strand breaks and an impairment in glucose uptake. In addition, other age-related metabolic changes such as depletion of antioxidants or decreased energy production by a disturbed glucose metabolism diminish the ability of the cell to cope with the effects of radical-induced membrane, protein and DNA damage. With our improving understanding of the molecular basis for the clinical symptoms of dementia, it is hoped that the elucidation of the etiologic causes, particularly the positive feedback loops involving radical damage and a reduced glucose metabolism, will help to develop novel "neuroprotective" treatment strategies able to interrupt this vicious cycle of oxidative stress and energy shortage in AD.

Alzheimer's disease--synergistic effects of glucose deficit, oxidative stress and advanced glycation endproducts.

Advanced glycation endproducts in ageing and Alzheimer's disease.

Recent studies suggest that advanced glycation endproducts play an important role in cardiovascular complications of ageing, diabetes and end-stage renal failure. Since highly elevated levels of advanced glycation endproducts are present in serum of patients on maintenance haemodialysis, an accurate and rapid assay for their determination would be useful. This would be particularly valuable for monitoring the removal of advanced glycation endproducts by novel dialysis membranes, as well as the effect of new drugs for the inhibition of their formation. Measurement of advanced glycation endproducts in serum was performed by two competitive ELISAs, using a monoclonal antibody directed against imidazolone, an advanced glycation endproduct formed by the reaction of arginine with 3-deoxyglucosone, and a polyclonal antibody directed against keyhole limpet haemocyanin-advanced glycation endproduct, as well as by quantitative fluorescence spectroscopy. Each of the assays showed significant differences between the controls and the maintenance haemodialysis patients. Advanced glycation endproduct levels determined by each of the ELISAs correlated with total and protein-bound fluorescence, but not with each other, suggesting a variable distribution of advanced glycation endproducts on serum proteins among the maintenance haemodialysis patients.

Determination of Advanced Glycation End Products in Serum by Fluorescence Spectroscopy and Competitive ELISA

https://febs.onlinelibrary.wiley.com/doi/pdf/10.1016/S0014-5793%2899%2900731-0

High molecular weight hyaluronic acid inhibits advanced glycation endproduct-induced NF-κB activation and cytokine expression

Background: Clopidogrel is a potent drug for prevention of adverse effects during and after coronary intervention. Increasing experience indicates that a significant proportion of patients do not respond adequately to clopidogrel. Because failure of antiplatelet therapy can have severe consequences, there is need for a reliable assay to quantify the effectiveness of clopidogrel treatment. Methods: Of 24 healthy volunteers admitted to the study, 18 were treated for 1 week with clopidogrel (300-mg loading dose and 75-mg maintenance dose), and 6 with placebo. Platelet function was monitored by 2 assays, based on flow cytometry and enzyme immunoassay, that measure the phosphorylation status of vasodilator-stimulated phosphoprotein (VASP) and by aggregometry, flow cytometry of P-selectin, and the platelet function analyzer at baseline, on days 1–5, and on day 9 of treatment. Results: Aggregometry and VASP phosphorylation revealed a loss of platelet response to ADP within 12 h after clopidogrel intake. The phosphorylation status of VASP correlated with the inhibition of platelet aggregation. In contrast, neither P-selectin expression nor PFA-100 closure time was a clear indicator of clopidogrel effects on platelets. Conclusions: VASP phosphorylation assays are reliable for quantifying clopidogrel effects. Because the VASP assay directly measures the function of the clopidogrel target, the P2Y12 receptor, the assay is selective for clopidogrel effects rather than effects of other platelet inhibitors commonly in use. © 2005 American Association for Clinical Chemistry

Reinhard Schinzel

Papers

Alzheimer's disease--synergistic effects of glucose deficit, oxidative stress and advanced glycation endproducts.

Advanced glycation endproducts in ageing and Alzheimer's disease.

Determination of Advanced Glycation End Products in Serum by Fluorescence Spectroscopy and Competitive ELISA

High molecular weight hyaluronic acid inhibits advanced glycation endproduct-induced NF-κB activation and cytokine expression

Monitoring of Clopidogrel Action: Comparison of Methods