Retinal microvascular network attenuation in Alzheimer's disease

INTRODUCTION

Cerebral small-vessel disease has been implicated in the development of Alzheimer's disease (AD). The retinal microvasculature enables the noninvasive visualization and evaluation of the systemic microcirculation. We evaluated retinal microvascular parameters in a case-control study of AD patients and cognitively normal controls.

METHODS

Retinal images were computationally analyzed and quantitative retinal parameters (caliber, fractal dimension, tortuosity, and bifurcation) measured. Regression models were used to compute odds ratios (OR) and confidence intervals (CI) for AD with adjustment for confounders.

RESULTS

Retinal images were available in 213 AD participants and 294 cognitively normal controls. Persons with lower venular fractal dimension (OR per standard deviation [SD] increase, 0.77 [CI: 0.62-0.97]) and lower arteriolar tortuosity (OR per SD increase, 0.78 [CI: 0.63-0.97]) were more likely to have AD after appropriate adjustment.

DISCUSSION

Patients with AD have a sparser retinal microvascular network and retinal microvascular variation may represent similar pathophysiological events within the cerebral microvasculature of patients with AD.

The shape of pterosaur evolution: evidence from the fossil record

Although pterosaurs are a well-known lineage of Mesozoic flying reptiles, their fossil record and evolutionary dynamics have never been adequately quantified. On the basis of a comprehensive data set of fossil occurrences correlated with taxon-specific limb measurements, we show that the geological ages of pterosaur specimens closely approximate hypothesized patterns of phylogenetic divergence. Although the fossil record has expanded greatly in recent years, collectorship still approximates a sigmoid curve over time as many more specimens (and thus taxa) still remain undiscovered, yet our data suggest that the pterosaur fossil record is unbiased by sites of exceptional preservation (lagerstätte). This is because as new species are discovered the number of known formations and sites yielding pterosaur fossils has also increased - this would not be expected if the bulk of the record came from just a few exceptional faunas. Pterosaur morphological diversification is, however, strongly age biased: rarefaction analysis shows that peaks of diversity occur in the Late Jurassic and Early Cretaceous correlated with periods of increased limb disparity. In this respect, pterosaurs appear unique amongst flying vertebrates in that their disparity seems to have peaked relatively late in clade history. Comparative analyses also show that there is little evidence that the evolutionary diversification of pterosaurs was in any way constrained by the appearance and radiation of birds.

A morphospace-based test for competitive exclusion among flying vertebrates: did birds, bats and pterosaurs get in each other's space?

Three vertebrate groups - birds, bats and pterosaurs - have evolved flapping flight over the past 200 million years. This innovation allowed each clade access to new ecological opportunities, but did the diversification of one of these groups inhibit the evolutionary radiation of any of the others? A related question is whether having the wing attached to the hindlimbs in bats and pterosaurs constrained their morphological diversity relative to birds. Fore- and hindlimb measurements from 894 specimens were used to construct a morphospace to assess morphological overlap and range, a possible indicator of competition, among the three clades. Neither birds nor bats entered pterosaur morphospace across the Cretaceous-Paleogene (Tertiary) extinction. Bats plot in a separate area from birds, and have a significantly smaller morphological range than either birds or pterosaurs. On the basis of these results, competitive exclusion among the three groups is not supported.

Reactive oxygen species as mediators of photoreceptor apoptosis in vitro

Retinitis pigmentosa is a heterogeneous group of retinal degenerations characterized by a progressive loss of photoreceptors through the process of apoptosis. The apoptotic cell death of photoreceptors appears to represent a final common pathway in the pathology of retinitis pigmentosa. Previous studies have reported the ability of antioxidants to ameliorate light-induced retinal degeneration, suggesting a role for oxidative stress in photoreceptor cell death. This study demonstrates an early and sustained increase in intracellular reactive oxygen species accompanied by a rapid depletion of intracellular glutathione in an in vitro model of photoreceptor apoptosis. These early changes in the cellular redox state precede disruption of mitochondrial transmembrane potential, nuclear condensation, DNA nicking, and cell shrinkage, all of which are well-characterized events of apoptotic cell death. The ability of zinc chloride and pyrrolidine dithiocarbamate, two established antioxidants, to inhibit photoreceptor apoptosis through the scavenging of intracellular reactive oxygen species establishes a role for reactive oxygen species as possible mediators of in vitro photoreceptor apoptosis. This study provides a molecular basis for the inhibition of photoreceptor apoptosis by antioxidants.

Molecular mechanisms of programmed cell death

Programmed cell death and apoptosis have now been recognised as biological phenomena which are of fundamental importance to the integrity of organisms. What may have evolved as an altruistic defence against pathogen invasion in simple organisms is now a major regulatory mechanism in the development and maintenance of multi-cellular organisms. The classically defined morphological characteristics of apoptosis are now accompanied by a plethora of information regarding common biochemical and genetic mediators of programmed cell death. It is apparent that life and death decisions are taken by individual cells based on their interpretation of physiological signals, or their own self-assessment of internal damage. The knowledge that cell death is a genetically regulated process has highlighted an inherent potential for manipulation and offered new avenues for research into several diseases, and also productivity improvements in the biotechnology industry. This relatively "new frontier" in cell science has undoubtedly widened our perspectives and may provide novel strategies to expedite both medical and biotechnological research.

Rapid detection of rod photoreceptor apoptosis by flow cytometry

Apoptosis is a form of cell death that plays an important role during physiological homeostasis and numerous pathological conditions. Retinitis pigmentosa is a group of retinal degenerative disorders in which rod photoreceptors excessively die via apoptosis. Current analytical tools for the investigation of photoreceptor cell death are histological in nature and typically time-consuming and laborious; as such, they are frequently limited to small sample sizes. In recent years, apoptosis research has made extensive use of flow cytometry to analyze several cellular events characteristic of apoptosis, including DNA strand nicking and cell shrinkage. This study presents a flow cytometric assay for the detection of rod photoreceptor apoptosis using the rod-specific cell marker rhodopsin, the terminal deoxyuridine 5'-triphosphate (dUTP) transferase nick end-labeling (TUNEL) assay, and the light-scattering properties of rod photoreceptors. This technique enables the rapid and reproducible detection of rod photoreceptor apoptosis in vitro with potential applications for in vivo analysis.

The production of a reactive oxygen intermediate during the induction of apoptosis by cytotoxic insult

We report the protective effects of two novel antioxidant compounds, 3 beta-doxyl-5 alpha cholestane and 2,2,6,6-tetramethyl-piperdinoxyl, in HL-60 and U937 leukemic cells subjected to a number of cytotoxic insults. In addition, the rapid production of peroxide is demonstrated as a general response to cytotoxic agents in these leukemic cell lines, indicating that changes in the redox status of a leukemic cell may contribute to the ultimate death of these cells. Closer examination of this peroxide production has identified enzymic production and/or disruption of resident antioxidants as possible sources. However, in contrast to recent reports from other model systems, mitochondrial transmembrane depolarization did not appear to be required for the production of peroxide in these cells. Finally, we demonstrated the activation of the redox-sensitive transcription factor, NF-kappa B, in response to these cytotoxic insults.

Use of flow cytometry techniques in studying mechanisms of apoptosis in leukemic cells

The use of flow cytometric techniques has significantly aided the rapid advancement of our understanding of the process of apoptosis. Our laboratory is currently involved in investigating the ways in which cells can be induced to die and some of the signals that may be involved. To this end, we are using flow cytometry to detect apoptosis in cell cultures and to measure intracellular changes that occur during apoptosis, in particular, alterations in parameters such as mitochondrial function, oxidative stress, and gene expression. In this review of recent and ongoing research in our laboratory, we outline our studies on mechanisms of apoptosis by cytotoxic drugs, particularly in relation to the involvement of oxidative stress. In addition, we are studying the increased sensitivity to apoptosis seen in K652 cells that have been transfected with the p53 gene.

Reactive oxygen intermediate(s) (ROI): common mediator(s) of poly(ADP-ribose)polymerase (PARP) cleavage and apoptosis

HL-60 acute myeloblastic and U937 monoblastoid leukaemic cell lines both cleave poly(ADP-ribose)polymerase (PARP), at the onset of apoptosis, in response to a wide range of cytotoxic agents. This appears to be a common feature of leukaemic cell apoptosis. However, in the chronic myelogenous leukaemic (CML) derived cell line, K562, no such cleavage was detectable. This correlated with previous findings that this cell line is particularly resistant to apoptosis induced by cytotoxic agents. Proteolytic cleavage of PARP and the subsequent progression to apoptosis was inhibited by two protease inhibitors NEM and IOD. As both PARP cleavage and DNA fragmentation appeared closely linked in these cell lines, anti-oxidants (previously shown to be effective inhibitors of DNA fragmentation and apoptosis) were also demonstrated to prevent PARP cleavage. These results combine to suggest that ROI may mediate PARP cleavage, DNA fragmentation and the eventual apoptosis of these cells following cytotoxic insult.

Mutant H-ras overexpression inhibits drug and U.V. induced apoptosis

Various studies have shown that oncogene and oncosuppressor gene activity can enhance or suppress programmed cell death (apoptosis) in various cell systems. Recent data indicates that overexpression of activated H-ras could influence that onset of apoptosis. We investigated the role of activated H-ras in the apoptotic cell death of rat fibroblast lines. We found that forced overexpression of H-ras induced resistance to U.V. and drug induced apoptosis. We examined possible mechanisms for the action of H-ras in resistance to apoptosis. It was found that both ras transfected and ras untransfected lines displayed similar endonuclease activities. In addition, it was found that the irradiated ras transfected line showed inhibited production of peroxides compared to the irradiated ras untransfected line. Drug induced apoptosis did not appear to involve peroxide production. In addition the antioxidant compound PDTC, was found to inhibit U.V. induced apoptosis but not drug induced apoptosis. In addition, we found the ras transfected line to possess elevated levels of catalase compared to the parent untransfected line. Thus we suggest that an anti-oxidant mechanism, possibly mediated by forced overexpression of activated H-ras could protect cells from apoptosis.

Inhibition of apoptosis by antioxidants in the human HL-60 leukemia cell line

Cell death via apoptosis is an important event involved in a number of immunological processes. Recently, apoptosis has been associated with oxidative stress in a number of cell systems. Here we assessed the inhibitory capacity of different antioxidants on UV- and drug-induced apoptosis in the human leukemic cell line, HL-60. We found that the oxygen radical scavenger, BHA, the radioprotector cysteamine and the metal chelators, pyrrolidinedithiocarbamate (PDTC), diethyldithiocarbamate (DEDTC), and dimethyldithiocarbamate (DMDTC), were able to significantly inhibit nuclear fragmentation and reduce the formation of apoptotic bodies in UV-irradiated human leukemic cells. Both BHA and PDTC were found to reduce DNA fragmentation as assessed by in situ DNA nick-end labelling and quantification thereof using fluorescence flow cytometry. In addition to inhibiting UV-induced apoptosis, PDTC was also capable of reducing the amount of apoptosis induced by a range of cytotoxic drugs, such as actinomycin-D, camptothecin, etoposide, and melphalan, whereas BHA and cysteamine were not as effective in these cases after more than four hours in culture when compared to PDTC. To further elucidate the working mechanism of PDTC, we have looked at the effect of PDTC on DNA fragmentation in isolated nuclei, under conditions that promote activation of endogenous endonuclease involved in apoptosis. In contrast to ZnCl2, a potent inhibitor of endonuclease activity, PDTC was unable to inhibit DNA-ladder formation in this assay. Taken together, these results indicate that oxygen radicals may have a central role to play in the induction of apoptosis and that dithiocarbamates can serve as potent inhibitors of apoptosis induced by a wide variety of stimuli.

Zinc inhibits UV radiation-induced apoptosis but fails to prevent subsequent cell death

Zinc ions inhibit the morphological and DNA fragmentation features of apoptosis in a number of systems. HL-60 cells pretreated with zinc and exposed to UV irradiation maintained their normal morphology for up to 8 h, whereas non-zinc-treated cells underwent extensive apoptosis. Zinc pretreatment also inhibited both single and double-stranded DNA fragmentation, which is characteristic of apoptosis. The most effective zinc concentration that blocked apoptosis over short incubation periods (up to 8 h) was also the most toxic over extended time periods (> or = 12 h). The mechanism of cell death at these longer time periods was akin to necrosis, but occurred in the absence of any DNA fragmentation. The effects of the nuclease inhibitor aurintricarboxylic acid (ATA) was also examined on UV-induced apoptosis in HL-60 cells. ATA had no toxic effects over the concentration range tested, but also failed to prevent DNA fragmentation in whole cells. Further analysis showed that it effectively inhibited DNA fragmentation in isolated nuclei.

Squamous cell carcinoma of the renal pelvis presenting with hypercalcemia

A case of hypercalcemia associated with documented squamous cell carcinoma of the renal pelvis without bony metastasis is reported. Pseudohyperparathyroidism was suspected strongly because of the radioimmunoassay values of parathormone. This was confirmed by the prompt decrease of serum calcium after removal of the neoplasm. The radiologic findings were non-specific.