Microvascular lesions of diabetic retinopathy: clues towards understanding pathogenesis?

Retinopathy is a major complication of diabetes mellitus and this condition remains a leading cause of blindness in the working population of developed countries. As diabetic retinopathy progresses a range of neuroglial and microvascular abnormalities develop although it remains unclear how these pathologies relate to each other and their net contribution to retinal damage. From a haemodynamic perspective, evidence suggests that there is an early reduction in retinal perfusion before the onset of diabetic retinopathy followed by a gradual increase in blood flow as the complication progresses. The functional reduction in retinal blood flow observed during early diabetic retinopathy may be additive or synergistic to pro-inflammatory changes, leucostasis and vaso-occlusion and thus be intimately linked to the progressive ischaemic hypoxia and increased blood flow associated with later stages of the disease. In the current review a unifying framework is presented that explains how arteriolar dysfunction and haemodynamic changes may contribute to late stage microvascular pathology and vision loss in human diabetic retinopathy.

The role of lipids and protein kinase Cs in the pathogenesis of diabetic retinopathy

Diabetic retinopathy is one of the most common complications of diabetes and is a major cause of new blindness in the working-age population of developed countries. While the exact pathogenic basis of this condition remains ill defined, it is clear that hyperglycaemia is a critical factor in its aetiology. Protein kinase C (PKC) activation is one of the sequelae of hyperglycaemia and it is thought to play an important role in the development of diabetic complications. This review questions the currently held dogma that PKC stimulation in diabetes is solely mediated through the overproduction of palmitate and oleate enriched diacylglycerols. Blood glucose concentrations are closely tracked by changes in the levels of free fatty acids and these, in addition to oxidative stress, may account for the aberrant activation of PKCs in diabetes. Little is known about why PKCs fail to downregulate in diabetes and efforts should be directed towards acquiring such information. Considerable evidence implicates the PKCbeta isoform in the pathogenesis of diabetic retinopathy, but other isoforms may also be of relevance. In addition to PKCs, it is evident that novel diacyglycerol-activated non-kinase receptors could also play a role in the development of diabetic complications. Therapeutic agents have been developed to inhibit specific PKC isoforms and PKCbeta antagonists are currently undergoing clinical trials to test their toxicity and efficacy in suppressing diabetic complications. The likely impact of these drugs in the treatment of diabetic patients is considered.

Signal and variability within a Holocene peat bog - Chronological uncertainties of pollen, macrofossil and fungal proxies

A single raised bog from the eastern Netherlands has been repeatedly analysed and ¹⁴C dated over the past few decades. Here we assess the within-site variability of fossil proxy data through comparing the regional
pollen, macrofossils and non-pollen palynomorphs of four of these profiles. High-resolution chronologies were obtained using ¹⁴C dating and Bayesian age-depth modelling. Where chronologies of profiles overlap, proxy curves are compared between the profiles using greyscale graphs that visualise chronological uncertainties. Even at this small spatial scale, there is considerable variability of the fossil proxy curves. Implications regarding signal (climate) and noise (internal dynamics) of the different types of fossil proxies are discussed. Single cores are of limited value for reconstructing centennial-scale climate change, and only by combining multiple cores and proxies can we obtain a reliable understanding of past environmental change and possible forcing factors (e.g., solar variability).

Diagnosis and treatment of endogenous fungal endophthalmitis

Endogenous infectious endophthalmitis is rare, and a primary source is usually identified. A case of primary fungal endophthalmitis successfully treated with vitrectomy and systemic antifungal therapy is presented. The aetiology and treatment of the condition are discussed.

Improving molecular detection of Candida DNA in whole blood:comparison of seven fungal DNA extraction protocols using real-time PCR

The limitations of classical diagnostic methods for invasive Candida infections have led to the development of molecular techniques such as real-time PCR to improve diagnosis. However, the detection of low titres of Candida DNA in blood from patients with candidaemia requires the use of extraction methods that efficiently lyse yeast cells and recover small amounts of DNA suitable for amplification. In this study, a Candida-specific real-time PCR assay was used to detect Candida albicans DNA in inoculated whole blood specimens extracted using seven different extraction protocols. The yield and quality of total nucleic acids were estimated using UV absorbance, and specific recovery of C. albicans genomic DNA was estimated quantitatively in comparison with a reference (Qiagen kit/lyticase) method currently in use in our laboratory. The extraction protocols were also compared with respect to sensitivity, cost and time required for completion. The TaqMan PCR assay used to amplify the DNA extracts achieved high levels of specificity, sensitivity and reproducibility. Of the seven extraction protocols evaluated, only the MasterPure yeast DNA extraction reagent kit gave significantly higher total nucleic acid yields than the reference method, although nucleic acid purity was highest using either the reference or YeaStar genomic DNA kit methods. More importantly, the YeaStar method enabled C. albicans DNA to be detected with highest sensitivity over the entire range of copy numbers evaluated, and appears to be an optimal method for extracting Candida DNA from whole blood.

Influences of anthropogenic pollution on mycorrhizal fungal communities

Mycorrhizal fungi form complex communities in the root systems of most plant species and are thought to be important in terrestrial ecosystem sustainability. We have reviewed the literature relating to the influence of the major forms of anthropogenic pollution on the structure and dynamics of mycorrhizal fungal communities. All forms of pollution have been reported to alter the structure of below-ground communities of mycorrhizal fungi to some degree, although the extent to which such changes will be sustained in the longer term is at present not clear. The major limitation to predicting the consequences of pollution-mediated changes in mycorrhizal fungal communities to terrestrial habitats is our limited understanding of the functional significance of mycorrhizal fungal diversity. While this is identified as a priority area for future research, it is suggested that, in the absence of such data, an understanding of pollution-mediated changes in mycorrhizal mycelial systems in soil may provide useful indicators for sustainability of mycorrhizal systems.

Genotypic and phenotypic diversity of the noncapsulated Haemophilus influenzae:Adaptation and pathogenesis in the human airways

The human respiratory tract contains a highly adapted microbiota including commensal and opportunistic pathogens. Noncapsulated or nontypable Haemophilus influenzae (NTHi) is a human-restricted member of the normal airway microbiota in healthy carriers and an opportunistic pathogen in immunocompromised individuals. The duality of NTHi as a colonizer and as a symptomatic infectious agent is closely related to its adaptation to the host, which in turn greatly relies on the genetic plasticity of the bacterium and is facilitated by its condition as a natural competent. The variable genotype of NTHi accounts for its heterogeneous gene expression and variable phenotype, leading to differential host-pathogen interplay among isolates. Here we review our current knowledge of NTHi diversity in terms of genotype, gene expression, antigenic variation, and the phenotypes associated with colonization and pathogenesis. The potential benefits of NTHi diversity studies discussed herein include the unraveling of pathogenicity clues, the generation of tools to predict virulence from genomic data, and the exploitation of a unique natural system for the continuous monitoring of long-term bacterial evolution in human airways exposed to noxious agents. Finally, we highlight the challenge of monitoring both the pathogen and the host in longitudinal studies, and of applying comparative genomics to clarify the meaning of the vast NTHi genetic diversity and its translation to virulence phenotypes.

Indigenous Arbuscular Mycorrhizal Fungal Assemblages Protect Grassland Host Plants from Pathogens

Plant roots can establish associations with neutral, beneficial and pathogenic groups of soil organisms. Although it has been recognized from the study of individual isolates that these associations are individually important for plant growth, little is known about interactions of whole assemblages of beneficial and pathogenic microorganisms associating with plants. We investigated the influence of an interaction between local arbuscular mycorrhizal (AM) fungal and pathogenic/saprobic microbial assemblages on the growth of two different plant species from semi-arid grasslands in NE Germany (Mallnow near Berlin). In a greenhouse experiment each plant species was grown for six months in either sterile soil or in sterile soil with one of three different treatments: 1) an AM fungal spore fraction isolated from field soil from Mallnow; 2) a soil pathogen/saprobe fraction consisting of a microbial community prepared with field soil from Mallnow and; 3) the combined AM fungal and pathogen/saprobe fractions. While both plant species grew significantly larger in the presence of AM fungi, they responded negatively to the pathogen/saprobe treatment. For both plant species, we found evidence of pathogen protection effects provided by the AM fungal assemblages. These results indicate that interactions between assemblages of beneficial and pathogenic microorganisms can influence the growth of host plants, but that the magnitude of these effects is plant species-specific.

Compositional divergence and convergence in arbuscular mycorrhizal fungal communities

In spite of the controversy that they have generated, neutral models provide ecologists with powerful tools for creating dynamic predictions about beta-diversity in ecological communities. Ecologists can achieve an understanding of the assembly rules operating in nature by noting when and how these predictions are met or not met. This is particularly valuable for those groups of organisms that are challenging to study under natural conditions (e.g., bacteria and fungi). Here, we focused on arbuscular mycorrhizal fungal (AMF) communities and performed an extensive literature search that allowed us to synthesize the information in 19 data sets with the minimal requisites for creating a null hypothesis in terms of community dissimilarity expected under neutral dynamics. In order to achieve this task, we calculated the first estimates of neutral parameters for several AMF communities from different ecosystems. Communities were shown either to be consistent with neutrality or to diverge or converge with respect to the levels of compositional dissimilarity expected under neutrality. These data support the hypothesis that divergence occurs in systems where the effect of limited dispersal is overwhelmed by anthropogenic disturbance or extreme biological and environmental heterogeneity, whereas communities converge when systems have the potential for niche divergence within a relatively homogeneous set of environmental conditions. Regarding the study cases that were consistent with neutrality, the sampling designs employed may have covered relatively homogeneous environments in which the effects of dispersal limitation overwhelmed minor differences among AMF taxa that would lead to environmental filtering. Using neutral models we showed for the first time for a soil microbial group the conditions under which different assembly processes may determine different patterns of beta-diversity. Our synthesis is an important step showing how the application of general ecological theories to a model microbial taxon has the potential to shed light on the assembly and ecological dynamics of communities.

Glycation and oxidation:a role in the pathogenesis of atherosclerosis

Reactions involving glycation and oxidation of proteins and lipids are believed to contribute to atherogenesis. Glycation, the nonenzymatic binding of glucose to protein molecules, can increase the atherogenic potential of certain plasma constituents, including low-density lipoprotein (LDL). Glycation of LDL is significantly increased in diabetic patients compared with normal subjects, even in the presence of good glycemic control. Metabolic abnormalities associated with glycation of LDL include diminished recognition of LDL by the classic LDL receptor; increased covalent binding of LDL in vessel walls; enhanced uptake of LDL by macrophages, thus stimulating foam cell formation; increased platelet aggregation; formation of LDL-immune complexes; and generation of oxygen free radicals, resulting in oxidative damage to both the lipid and protein components of LDL and to any nearby macromolecules. Oxidized lipoproteins are characterized by cytotoxicity, potent stimulation of foam cell formation by macrophages, and procoagulant effects. Combined glycation and oxidation, "glycoxidation," occurs when oxidative reactions affect the initial products of glycation, and results in irreversible structural alterations of proteins. Glycoxidation is of greatest significance in long-lived proteins such as collagen. In these proteins, glycoxidation products, believed to be atherogenic, accumulate with advancing age: in diabetes, their rate of accumulation is accelerated. Inhibition of glycation, oxidation, and glycoxidation may form the basis of future antiatherogenic strategies in both diabetic and nondiabetic individuals.

Pathophysiology and Pathogenesis of Diabetic Retinopathy

Diabetic retinopathy is traditionally viewed as a disease of the retinal blood vessels, although there is increasing evidence that retinal neurons and glial cells are also affected. This article describes the changes in the diabetic retina that precede the development of clinical diabetic retinopathy, including changes in the rate of retinal blood flow, alterations in the electroretinogram and breakdown of the integrity of the blood-retinal barrier. The long term lesions of diabetic retinopathy are characterised by a complex array of vasodegenerative changes that lead directly to areas of retinal ischaemia. This frequently triggers the onset of macular oedema and/or the proliferative stages of diabetic retinopathy with risk of visual impairment and blindness. Neurodegeneration has also been reported in the retina during both human and experimental diabetic retinopathy, although presently it remains unclear to what extent such changes contribute to visual loss in diabetic retinopathy.