Reticular Pseudodrusen: Interreader Agreement of Evaluation on OCT Imaging in Age-Related Macular Degeneration

Purpose

To determine the interreader agreement for reticular pseudodrusen (RPD) assessment on combined infrared reflectance (IR) and OCT imaging in the early stages of age-related macular degeneration across a range of different criteria to define their presence.

Design

Interreader agreement study.

Participants

Twelve readers from 6 reading centers.

Methods

All readers evaluated 100 eyes from individuals with bilateral large drusen for the following: (1) the presence of RPD across a range of different criteria and (2) the number of Stage 2 or 3 RPD lesions (from 0 to ≥ 5 lesions) on an entire OCT volume scan and on a selected OCT B-scan. Supportive information was available from the corresponding IR image.

Main Outcome Measures

Interreader agreement, as assessed by Gwet's first-order agreement coefficient (AC₁).

Results

When evaluating an entire OCT volume scan, there was substantial interreader agreement for the presence of any RPD, any or ≥ 5 Stage 2 or 3 lesions, and ≥ 5 definite lesions on en face IR images corresponding to Stage 2 or 3 lesions (AC₁ = 0.60-0.72). On selected OCT B-scans, there was also moderate-to-substantial agreement for the presence of any RPD, any or ≥ 5 Stage 2 or 3 lesions (AC₁ = 0.58-0.65) and increasing levels of agreement with increasing RPD stage (AC₁ = 0.08, 0.56, 0.78, and 0.99 for the presence of any Stage 1, 2, 3, and 4 lesions, respectively). There was substantial agreement regarding the number of Stage 2 or 3 lesions on an entire OCT volume scan (AC₁ = 0.68), but only fair agreement for this evaluation on selected B-scans (AC₁ = 0.30).

Conclusions

There was generally substantial or near-substantial-but not near-perfect-agreement for assessing the presence of RPD on entire OCT volume scans or selected B-scans across a range of differing RPD criteria. These findings underscore how interreader variability would likely contribute to the variability of findings related to the clinical associations of RPD. The low levels of agreement for assessing RPD number on OCT B-scans underscore the likely challenges of quantifying RPD extent with manual grading.

Financial Disclosures

Proprietary or commercial disclosure may be found after the references.

Extramacular Drusen and Progression of Age-Related Macular Degeneration: Age Related Eye Disease Study 2 Report 30

PURPOSE

To identify the prevalence of extramacular drusen and their role in the progression of age-related macular degeneration (AMD).

DESIGN

Retrospective analysis of a prospective cohort study.

PARTICIPANTS

The study was conducted in 4168 eyes (2998 participants) with intermediate AMD in one or both eyes enrolled in the Age-Related Eye Disease Study 2 (AREDS2), a 5-year multicenter study of nutritional supplements.

METHODS

Baseline 3-field 30-degree color photographs were evaluated for drusen characteristics outside the macular grid, including size, area, and location. The characteristics of extramacular drusen were compared with those of drusen within the macula.

MAIN OUTCOME MEASURES

Progression rates to late AMD.

RESULTS

Although extramacular drusen were observed in 3624 (86.9%) eyes, they represented a small area (< 0.5 mm2) in 50.3% of eyes, with only 17.5% exhibiting an area of > 1 disc area. Eyes with extramacular drusen exhibited larger macular drusen size and area than eyes without extramacular drusen (P < 0.001). Extramacular drusen were not associated with progression to late AMD. The hazard ratio adjusted for baseline age, sex, smoking, AMD severity level, and reticular pseudodrusen for 4043 eyes at risk of developing late AMD over 5 years was 1.17 (95% confidence interval [CI], 0.88-1.54; P = 0.27) for geographic atrophy and 0.96 (95% CI, 0.76-1.2; P = 0.7) for neovascular AMD.

CONCLUSIONS

Extramacular drusen are commonly observed in eyes with AMD and are more frequent with an increasing drusen burden within the macula. In eyes with intermediate AMD, extramacular drusen do not confer additional risk to previously identified risk factors in progression to late AMD.

Retinal Thickness and Morphology Changes on OCT in Youth with Type 2 Diabetes: Findings from the TODAY Study

Objective

To evaluate changes in retinal thickness and morphology using OCT in youth with type 2 diabetes (T2D) and to identify systemic biomarkers correlating with these changes.

Design

Retrospective subgroup analysis of a prospective study.

Participants

Participants who underwent OCT imaging in the Treatment Options for Type 2 Diabetes in Adolescents and Youth (TODAY) trial and its follow-up study TODAY2.

Methods

In 2010-2011 (TODAY) and 2017-2018 (TODAY2), 6 × 6-mm macular volume OCT scans were acquired, segmented, and analyzed to generate total retinal thickness, inner retinal thickness, and outer retinal thickness. The main retinal morphologies graded were intraretinal cystoid spaces, subretinal fluid, and posterior vitreous detachment (PVD).

Main Outcome Measures

Changes in total and individual retinal layer thickness and development of abnormal vitreomacular morphology between TODAY and TODAY2.

Results

Participants had a mean age of 17.9 ± 2.4 years and glycated hemoglobin (HbA1c) of 8.2 ± 2.8% in TODAY and a mean age of 25.0 ± 2.4 years and mean HbA1c of 9.5 ± 2.8% in TODAY2. Longitudinally between assessments, there were overall decreases in outer retinal thickness from 167.2 ± 11.5 microns to 158.4 ± 12.8 microns (P < 0.001) and in photoreceptor thickness from 30.3 ± 2.9 microns to 29.8 ± 4.1 microns (P = 0.04) in the central subfield, while in the inner subfield, we noted a decrease in outer retinal thickness from 150.5 ± 10.1 microns to 144.9 ± 10.5 microns (P < 0.001) and an increase in inner retinal thickness from 136.9 ± 11.5 microns to 137.4 ± 12.6 microns (P = 0.01). Multivariate analysis showed that in the center subfield, HbA1c increases were associated with increases in total retinal thickness (r: 0.67, P = 0.001), whereas fasting glucose was positively correlated with inner retinal thickness (r: 0.02, P = 0.02). In the inner subfield, both systolic (r: -0.22, P < 0.001) and diastolic (r: -0.22, P = 0.003) blood pressures were negatively correlated with total retinal thickness. There was an increase in PVD (18.9%) and cystoid spaces (4.2%).

Conclusions

Youth with T2D develop retinal thickness changes on OCT, including increases in total retinal and inner retinal thickness in the center subfield that correlate with HbA1c and fasting glucose, respectively. Taken together with the increased prevalence of abnormal vitreomacular morphology in this cohort at risk, these findings emphasize the importance of controlling risk factors to prevent the development of sight-threatening retinal complications.

Redefining the Spectrum of Pentosan Polysulfate Retinopathy: Multimodal Imaging Findings from a Cross-Sectional Screening Study

PURPOSE

There is growing evidence of a direct association between Pentosan polysulfate (PPS) therapy and the development of macular changes. Using standardized visual acuity testing and multimodal imaging, we investigate the impact on vision and describe an expanded spectrum of imaging findings among PPS users.

DESIGN

Cross-sectional screening study.

PARTICIPANTS

Thirty-nine patients who were current or recent users of PPS.

METHODS

Participants underwent a brief eye exam and answered a comprehensive medical and ophthalmic history questionnaire. Color fundus photography, fundus autofluorescence (FAF) and spectral domain optical coherence tomography (SD-OCT) were obtained. Images were evaluated by expert graders at the Wisconsin Reading Center. Abnormalities were categorized as definitive toxicity (DT) if seen on both FAF and SD-OCT and questionable toxicity (QT) if seen on either FAF or SD-OCT.

MAIN OUTCOME MEASURES

Early Treatment Diabetic Retinopathy Study (ETDRS) and Snellen visual acuity (VA), dosage and duration of PPS exposure, prevalence of retinal toxicity on imaging.

RESULTS

Mean ETDRS and Snellen VA of the study cohort was 85 letters and 20/22, respectively. The mean PPS daily dose was 282 mg (88-400 mg), while the mean cumulative dose was 915 g (19-3650 g) over a mean period of 8.8 years (2 months-25 years). 41% of eyes evidenced retinopathy; DT was identified in 24 (31%) eyes and QT in 8 (10%) eyes. Retinal pigment epithelium (RPE) abnormalities (thickening and/or thinning) were present in all DT eyes. RPE atrophy was seen in 7 (9%) eyes. In addition to well-established findings, unique SD-OCT features of this cohort include interdigitation zone abnormalities and the presence of a flying-saucer-type defect. FAF abnormalities were seen in 24 (30.8%) of eyes, with 20 (66.7%) of these exhibiting abnormalities located outside the central subfield and extending beyond the arcades.

CONCLUSION

Findings from masked grading of multimodal imaging at a centralized reading center suggest a wider phenotypic spectrum of structural abnormalities among patients taking PPS. Macular changes selectively involve the RPE and outer retina, with a range of findings often seen beyond the arcades. The subtle and atypical findings in this cohort should prompt clinicians to consider lowering the threshold for diagnosing PPS retinopathy.

Serum and Macular Carotenoids in Relation to Retinal Vessel Caliber Fifteen Years Later, in the Second Carotenoids in Age-Related Eye Disease Study

Purpose

We investigated whether dietary carotenoids lutein and zeaxanthin (L/Z) in the serum and macula were associated with central retinal arteriole and venule calibers in a follow-up ancillary study among older women in the Women's Health Initiative.

Methods

Among 390 women who participated in Carotenoids in Age-Related Eye Disease Study 2 (CAREDS2) (2016–2019), we investigated associations between serum L/Z at Women's Health Initiative baseline (1994–1998), and macular pigment optical density (MPOD) at CAREDS baseline (2001–2004), with central retinal vessel caliber in CAREDS2. MPOD was measured using heterochromatic flicker photometry (0.5° from the foveal center) in CAREDS baseline and CAREDS2. Vessel calibers were measured from fundus photographs (CAREDS2). We also explored associations in women with stable MPOD (±0.10 optical density units) over 15 years (n = 106), given the long-term increases in MPOD related to diet patterns and supplement use. Associations were investigated using linear modeling.

Results

In the full sample (n = 390), higher serum L/Z (tertile 3 vs. 1) was positively associated with arteriole caliber (mean ± SE, 145.0 ± 1.4 µm vs. 140.8 ± 1.4 µm; P = 0.05) and venule caliber (214.6 ± 2.2 µm vs. 207.5 ± 2.2 µm; P = 0.03). MPOD was also associated with wider vessel calibers (tertile 3 vs. 1), but the trend was only statistically significant for venules (144.4 ± 1.4 µm vs. 141.1 ± 1.4 µm [P = 0.12] and 213.3 ± 2.1 µm vs. 206.0 ± 2.1 µm [P = 0.02], respectively.) Most associations were strengthened in women with stable MPOD over 15 years, including between MPOD and arteriole caliber (149.8 ± 2.6 µm vs.135.8 ± 3.0 µm; P = 0.001).

Conclusions

Higher L/Z status in serum and retina was associated with larger central retinal vessel calibers. Prospective studies and clinical trials are needed to elucidate whether L/Z supplementation prevents vision loss through increasing blood flow.

Reticular Pseudodrusen Characteristics and Associations in the Carotenoids in Age-Related Eye Disease Study 2 (CAREDS2), an Ancillary Study of the Women's Health Initiative

PURPOSE

To determine the prevalence and morphologic features of reticular pseudodrusen (RPD) and their association with participant demographics and age-related macular degeneration (AMD) status in the Carotenoids in Age-Related Eye Disease Study 2 (CAREDS2) sample, an ancillary study of the Women's Health Initiative Observational Study.

DESIGN

Cross-sectional, multicenter, natural history study.

PARTICIPANTS

Nine hundred and twenty-seven eyes from 466 postmenopausal women 69 to 101 years of age.

METHODS

Multimodal imaging, including spectral-domain (SD) OCT and infrared reflectance (IR), were used to identify RPD characteristics, including location (within or outside the 6-mm diameter circle centered at the macula), presence of peripapillary RPD, pattern of RPD, and RPD area. Age-related macular degeneration features from SD OCT, IR, and color photographs also were assessed and AMD severity was categorized.

MAIN OUTCOME MEASURES

Reticular pseudodrusen prevalence using SD OCT and IR imaging and AMD status.

RESULTS

Reticular pseudodrusen were present in 130 eyes (14% of eyes, 16% of participants), with increasing prevalence with age: 7% in those younger than 78 years, 14% in those 78 to 83 years of age, and 30% in those older than 83 years. Using clinical classification of AMD with color photography, RPD were seen in 2.4% of eyes with no AMD or aging changes, 11.5% in early AMD, 25.1% in intermediate AMD, and 51.1% in late AMD. Mean RPD area was 17.4 mm² (standard deviation, 14.7 mm²). Ribbon morphologic RPD (53%) was more common than dot morphologic RPD (36%). Reticular pseudodrusen mostly were located both within and outside the 6-mm circle with primarily superior retinal distribution. Reticular pseudodrusen were visualized with corresponding color fundus photography in only 38 eyes (4% of total eyes). Participants with and without RPD had a visual acuity±standard error of 77.9 ± 1.4 letters and 81.3 ± 0.4 letters, respectively (P = 0.02).

CONCLUSIONS

The prevalence of RPD in CAREDS2 increased with age and was associated with AMD severity. Reticular pseudodrusen were detected in eyes without other features of AMD and could represent an earlier disease state. Multimodal imaging with SD OCT and IR has significantly greater sensitivity for visualizing RPD than color fundus photography.

Prevalence and Severity of Artifacts in Optical Coherence Tomographic Angiograms

Importance

Artifacts can affect optical coherence tomographic angiography (OCTA) images and may be associated with misinterpretation of OCT scans in both clinical trials and clinical settings.

Objectives

To identify the prevalence and type of artifacts in OCTA images associated with quantitative output and to analyze the role of proprietary quality indices in establishing image reliability.

Design, Setting, and Participants

This cross-sectional study evaluated baseline OCTA images acquired in multicenter clinical trials and submitted to the Fundus Photograph Reading Center in Madison, Wisconsin, between January 1, 2016, and December 31, 2018. Images were captured using the 3 mm × 3 mm and/or 6 mm × 6 mm scan protocol with commercially available OCTA systems. Artifacts, including decentration, segmentation error, movement, blink, refraction shift, defocus, shadow, Z offset, tilt, and projection, were given a severity grade based on involvement of cross-sectional OCT and area of OCT grid affected.

Main Outcomes and Measures

Prevalence and severity of OCTA artifacts and area under the receiver operating characteristic curve (AUC) of quality indices with image reliability.

Results

A total of 406 OCTA images from 234 eyes were included in this study, of which 221 (54.4%) were 6 mm × 6 mm scans and 185 (45.6%) were 3 mm × 3 mm scans. At least 1 artifact was documented in 395 images (97.3%). Severe artifacts associated with the reliability of quantitative outputs were found in 217 images (53.5%). Shadow (26.9% [109 images]), defocus (20.9% [85 images]), and movement (16.0% [65 images]) were the 3 most prevalent artifacts. Prevalence of artifacts did not vary with the imaging system used or with the scan protocol; however, the type of artifacts varied. Commercially recommended quality index thresholds had an AUC of 0.80 to 0.83, sensitivity of 97% to 99%, and specificity of 37% to 41% for reliable images.

Conclusions and Relevance

Findings from this study suggest that artifacts associated with quantitative outputs on commercially available OCTA devices are highly prevalent and that identifying common artifacts may require correlation with the angiogram and cross-sectional OCT scans. Knowledge of these artifacts and their implications for OCTA indices appears to be warranted for more accurate interpretation of OCTA images.

Prevalence, Risk, and Genetic Association of Reticular Pseudodrusen in Age-related Macular Degeneration: Age-Related Eye Disease Study 2 Report 21

PURPOSE

To determine the prevalence of reticular pseudodrusen (RPD) in eyes with age-related macular degeneration (AMD), assess the role of RPD as an independent risk factor for late AMD development, and evaluate genetic association with RPD.

DESIGN

Prospective cohort study.

PARTICIPANTS

Participants with intermediate AMD in 1 or both eyes enrolled in the Age-Related Eye Disease Study 2 (AREDS2), a 5-year multicenter study of nutritional supplement.

METHODS

Fundus autofluorescence (FAF) images from a subset of AREDS2 participants were evaluated at annual visits for presence of RPD. Six single nucleotide polymorphisms-rs10490924 (ARMS2), rs1061170 (CFH), rs2230199 (C3), rs116503776 and rs114254831 (C2/CFB), and rs943080 (VEGF-A)-and the genetic risk score (GRS) were assessed for association with RPD. Development of late AMD, defined as geographic atrophy (GA) or neovascular AMD (NVAMD), was identified.

MAIN OUTCOME MEASURES

Prevalence of RPD, odds ratio (OR) of late AMD development, and genetic associations of RPD.

RESULTS

The FAF images were evaluated for 5021 eyes (2516 participants). Reticular pseudodrusen were seen in 1186 eyes (24% of eyes, 29% of participants). Prevalence of RPD varied with baseline AREDS AMD severity level: 6% in early AMD (n = 458), 26% in intermediate AMD (n = 2606), 36% in GA (n = 682), and 19% in NVAMD (n = 1246). Mean age of participants with RPD was 79 years (standard deviation [SD], 7) and 75 years (SD, 8) in those without RPD (P < 0.0001). Reticular pseudodrusen were more frequent in female participants (65% RPD vs. 53% no RPD). Odds ratio adjusted for baseline age, gender, race, educational status, smoking, and AMD severity level for 1710 eyes at risk of developing late AMD at the next annual visit was 2.42 (95% confidence interval [CI], 1.80-3.24; P < 0.001) for GA and 1.21 (95% CI, 0.87-1.7; P = 0.26) for NVAMD. Presence of RPD was significantly associated with higher GRS (P < 0.0001) and ARMS2 risk alleles (P < 0.0001) and, at a nominal level, with C3 risk alleles (P = 0.04) and CFH risk alleles (P = 0.048 for homozygotes).

CONCLUSIONS

Participants with RPD have an increased risk of progression to GA but not NVAMD. ARMS2 risk alleles and higher GRS were associated with the presence of RPD. This study suggests that RPD are an important risk marker and should be included in classification systems used for patient prognosis.

Immune reconstitution inflammatory syndrome in a HIV-infected patient with disseminated tuberculosis

Immune reconstitution inflammatory syndrome (IRIS) is the paradoxical worsening of pre-existing infectious processes after commencement of anti-retroviral therapy (ART) in HIV-infected patients. Its manifestations are dependent on the underlying opportunistic infections. We report a case of an HIV-infected patient with disseminated tuberculosis, who responded to anti-tuberculosis therapy but suffered from paradoxical worsening after commencement of ART.

The prevalence and incidence of epiretinal membranes in eyes with inactive extramacular CMV retinitis

PURPOSE

To determine the prevalence and incidence of epiretinal membranes (ERM) in eyes with inactive extramacular cytomegalovirus (CMV) retinitis in patients with acquired immune deficiency syndrome (AIDS).

METHODS

A case-control report from a longitudinal multicenter observational study by the Studies of the Ocular Complications of AIDS (SOCA) Research Group. A total of 357 eyes of 270 patients with inactive CMV retinitis and 1084 eyes of 552 patients with no ocular opportunistic infection (OOI) were studied. Stereoscopic views of the posterior pole from fundus photographs were assessed at baseline and year 5 visits for the presence of macular ERM. Generalized estimating equations (GEE) logistic regression was used to compare the prevalence and 5-year incidence of ERM in eyes with and without CMV retinitis at enrollment. Crude and adjusted logistic regression was performed adjusting for possible confounders. Main outcome measures included the prevalence, incidence, estimated prevalence, and incidence odds ratios.

RESULTS

The prevalence of ERM at enrollment was 14.8% (53/357) in eyes with CMV retinitis versus 1.8% (19/1084) in eyes with no OOI. The incidence of ERM at 5 years was 18.6% (16/86) in eyes with CMV retinitis versus 2.4% (6/253) in eyes with no OOI. The crude odds ratio (OR) (95% confidence interval, CI) for prevalence was 9.8 (5.5-17.5) (P < 0.01). The crude OR (95% CI) for incidence was 9.4 (3.2-27.9) (P < 0.01).

CONCLUSIONS

A history of extramacular CMV retinitis is associated with increased prevalence and incidence of ERM formation compared to what is seen in eyes without ocular opportunistic infections in AIDS patients.

Development of a semi-automatic segmentation method for retinal OCT images tested in patients with diabetic macular edema

PURPOSE

To develop EdgeSelect, a semi-automatic method for the segmentation of retinal layers in spectral domain optical coherence tomography images, and to compare the segmentation results with a manual method.

METHODS

SD-OCT (Heidelberg Spectralis) scans of 28 eyes (24 patients with diabetic macular edema and 4 normal subjects) were imported into a customized MATLAB application, and were manually segmented by three graders at the layers corresponding to the inner limiting membrane (ILM), the inner segment/ellipsoid interface (ISe), the retinal/retinal pigment epithelium interface (RPE), and the Bruch's membrane (BM). The scans were then segmented independently by the same graders using EdgeSelect, a semi-automated method allowing the graders to guide/correct the layer segmentation interactively. The inter-grader reproducibility and agreement in locating the layer positions between the manual and EdgeSelect methods were assessed and compared using the Wilcoxon signed rank test.

RESULTS

The inter-grader reproducibility using the EdgeSelect method for retinal layers varied from 0.15 to 1.21 µm, smaller than those using the manual method (3.36-6.43 µm). The Wilcoxon test indicated the EdgeSelect method had significantly better reproducibility than the manual method. The agreement between the manual and EdgeSelect methods in locating retinal layers ranged from 0.08 to 1.32 µm. There were small differences between the two methods in locating the ILM (p = 0.012) and BM layers (p<0.001), but these were statistically indistinguishable in locating the ISe (p = 0.896) and RPE layers (p = 0.771).

CONCLUSIONS

The EdgeSelect method resulted in better reproducibility and good agreement with a manual method in a set of eyes of normal subjects and with retinal disease, suggesting that this approach is feasible for OCT image analysis in clinical trials.

Effect of optical coherence tomography scan decentration on macular center subfield thickness measurements

PURPOSE

To investigate the effect of optical coherence tomography macular grid displacement on retinal thickness measurements.

METHODS

SD-OCT macular scans of 66 eyes with various retinal thicknesses were selected. Decentration of the 1-, 3-, 6-mm-diameter macular grid was simulated by manually adjusting the distance between center of the fovea (cFovea) and center of the grid (cGrid). Center subfield thickness (CSF) between the internal limiting membrane and the top of the retinal pigment epithelium was measured along the displacement distance where the grid was displaced in eight cardinal directions from the cFovea in steps of 100 μm within the central 1-mm subfield and then by 200 μm within the inner subfields. One-way/mixed-effects repeated-measures ANOVA models were used to determine changes of CSF (ΔCSF) as a function of displacement distance (for α = 0.05, power = 0.80 and effect size = 0.1). The interactions between the displacement distance and direction, center point thickness (CPT), and foveal contour were also analyzed.

RESULTS

The CSF measurement showed statistically significant error when the displacement distance between cFovea and cGrid exceeded 200 μm. The direction of displacement did not affect the ΔCSF-distance relationship, while the CPT and foveal contour significantly affected the relationship, in that some subgroups showed slightly larger tolerance in the displacement distance up to 300 μm before reaching significant ΔCSF.

CONCLUSIONS

Small displacement distances of the macular grid from the cFovea affect CSF measurements throughout a broad range of thicknesses and retinal contour alterations from disease. Accurate registration of OCT scans or post hoc repositioning of the grid is essential to optimize CSF accuracy.

Accumulation of mitochondrial DNA deletion mutations in aged muscle fibers: evidence for a causal role in muscle fiber loss

Although mitochondrial mutation abundance has been recognized to increase in an age-dependent manner, the impact of mutation has been more difficult to establish. Using quantitative polymerase chain reaction, we measured the intracellular abundance of mutant and wild-type mitochondrial genomes along the length of individual laser-captured microdissected muscle fibers from aged rat quadriceps. Aged muscle fibers possessed segmental, clonal intracellular expansions of unique somatically derived mitochondrial DNA (mtDNA) deletion mutations. When the mutation abundance surpassed 90% of the total mitochondrial genomes, the fiber lost cytochrome c oxidase activity and exhibited an increase in succinate dehydrogenase activity. In addition to the mitochondrial enzymatic abnormalities, some fibers displayed abnormal morphology such as fiber splitting, atrophy, and breakage. Deletion mutation accumulation was linked to these aberrant morphologies with more severe cellular pathologies resulting from higher deletion mutation abundance. In summary, our measurements indicate that age-induced mtDNA deletion mutations expand within individual muscle fibers, eliciting fiber dysfunction and breakage.

MtDNA point mutations are associated with deletion mutations in aged rat

The age-dependent accumulation of point mutations in the control region of human mtDNA has been suggested to contribute to aging processes. We investigated whether mtDNA point mutations accumulate to detectable levels in this region of mtDNA from aged Fischer 344 X Brown Norway F(1) hybrid rats. The control region and a portion of the major arc region (nucleotides 4386-7707) of the mtDNA were PCR-amplified and directly sequenced from microdissected single cardiomyocytes and single skeletal muscle fibers of 36-month old rats. Point mutations were not observed in these regions of the full-length mtDNA. Point mutations were, however, associated with deletion mutations, especially in cardiac cells. Approximately 40% of the deletion mutations identified in heart contained a point mutation, whereas only 1.9% of deletion mutations in skeletal muscle contained a point mutation. Point mutations were located adjacent to the deletion breakpoints and each point mutation was unique. In aged rats, point mutations are clonally expanded only when associated with deletion events suggesting that there are important differences between rats and humans in the mechanisms that cause mtDNA abnormalities.

Molecular analyses of mtDNA deletion mutations in microdissected skeletal muscle fibers from aged rhesus monkeys

Mitochondrial DNA (mtDNA) deletion mutations co-localize with electron transport system (ETS) abnormalities in rhesus monkey skeletal muscle fibers. Using laser capture microdissection in conjunction with PCR and DNA sequence analysis, mitochondrial genomes from single sections of ETS abnormal fibers were characterized. All ETS abnormal fibers contained mtDNA deletion mutations. Deletions were large, removing 20-78% of the genome, with some to nearly all of the functional genes lost. In one-third of the deleted genomes, the light strand origin was deleted, whereas the heavy strand origin of replication was conserved in all fibers. A majority (27/39) of the deletion mutations had direct repeat sequences at their breakpoints and most (36/39) had one breakpoint within or in close proximity to the cytochrome b gene. Several pieces of evidence support the clonality of the mtDNA deletion mutation within an ETS abnormal region of a fiber: (a) only single, smaller than wild-type, PCR products were obtained from each ETS abnormal region; (b) the amplification of mtDNA from two regions of the same ETS abnormal fiber identified identical deletion mutations, and (c) a polymorphism was observed at nucleotide position 16103 (A and G) in the wild-type mtDNA of one animal (sequence analysis of an ETS abnormal region revealed that mtDNA deletion mutations contained only A or G at this position). Species-specific differences in the regions of the genomes lost as well as the presence of direct repeat sequences at the breakpoints suggest mechanistic differences in deletion mutation formation between rodents and primates.

Low Levels of mtDNA Deletion Mutations in ETS Normal Fibers from Aged Rats

The objectives were (1) to determine whether deletion mutations occur in phenotypically normal type I and type II fibers, (2) to quantify the levels of both deletion mutant and wild-type (wt) mtDNA (nondeletion) within single normal fibers containing mutant mtDNA, and (3) to quantify the amount of wt mtDNA in genotypically and phenotypically normal type I and type II fibers. Deletion mutations in normal fibers are not restricted to specific fiber types, although clonal accumulation of mtDNA deletion mutations and subsequent ETS abnormalities occur exclusively in type II fibers.

Mitochondrial DNA mutations as a fundamental mechanism in physiological declines associated with aging

The hypothesis that mitochondrial DNA damage accumulates and contributes to aging was proposed decades ago. Only recently have technological advancements, which facilitate microanalysis of single cells or portions of cells, revealed that mtDNA deletion mutations and, perhaps, single nucleotide mutations accumulate to physiologically relevant levels in the tissues of various species with age. Although a link between single nucleotide mutations and physiological consequences in aging tissue has not been established, the accumulation of deletion mutations in skeletal muscle fibres has been associated with sarcopenia. Different, and apparently random, deletion mutations are specific to individual fibres. However, the mtDNA deletion mutation within a phenotypically abnormal region of a fibre is the same, suggesting a selection, amplification and clonal expansion of the initial deletion mutation. mtDNA deletion mutations within a muscle fibre are associated with specific electron transport system abnormalities, muscle fibre atrophy and fibre breakage. These data point to a causal relationship between mitochondrial DNA mutations and the age-related loss of muscle mass.

Transformation of 2,4,6-trinitrotoluene by purified xenobiotic reductase B from Pseudomonas fluorescens I-C

The enzymatic transformation of 2,4,6-trinitrotoluene (TNT) by purified XenB, an NADPH-dependent flavoprotein oxidoreductase from Pseudomonas fluorescens I-C, was evaluated by using natural abundance and [U-(14)C]TNT preparations. XenB catalyzed the reduction of TNT either by hydride addition to the aromatic ring or by nitro group reduction, with the accumulation of various tautomers of the protonated dihydride-Meisenheimer complex of TNT, 2-hydroxylamino-4,6-dinitrotoluene, and 4-hydroxylamino-2, 6-dinitrotoluene. Subsequent reactions of these metabolites were nonenzymatic and resulted in predominant formation of at least three dimers with an anionic m/z of 376 as determined by negative-mode electrospray ionization mass spectrometry and the release of approximately 0.5 mol of nitrite per mol of TNT consumed. The extents of the initial enzymatic reactions were similar in the presence and in the absence of O(2), but the dimerization reaction and the release of nitrite were favored under aerobic conditions or under anaerobic conditions in the presence of NADP(+). Reactions of chemically and enzymatically synthesized and high-pressure liquid chromatography-purified TNT metabolites showed that both a hydroxylamino-dinitrotoluene isomer and a tautomer of the protonated dihydride-Meisenheimer complex of TNT were required precursors for the dimerization and nitrite release reactions. The m/z 376 dimers also reacted with either dansyl chloride or N-1-naphthylethylenediamine HCl, providing evidence for an aryl amine functional group. In combination, the experimental results are consistent with assigning the chemical structures of the m/z 376 species to various isomers of amino-dimethyl-tetranitrobiphenyl. A mechanism for the formation of these proposed TNT metabolites is presented, and the potential enzymatic and environmental significance of their formation is discussed.

Affinity selection of DNA-binding proteins displayed on bacteriophage lambda

Two transcription factors, human ATF1, its DNA-binding domain (ATF1BD), and the DNA-binding domain (GAL4BD) of the yeast GAL4 protein, were displayed on the surface of bacteriophage lambda vectors and efficiently selected by DNA fragments immobilized in microtiter wells. The DNA-binding proteins are fused to the carboxy terminus of the tail protein gpV and head protein gpD of the vectors, lambdafoo and lambdafooDc, respectively. After a single round of affinity selection, the fusion phages were successfully enriched 60- to 4,000-fold over the vector phages. Further, the GAL4BD fusion phages were enriched 5- and 15-fold by affinity selection using specific DNA as probes over nonspecific DNA when expressed on lambdafooDc and lambdafoo, respectively. The ATF1BD fusion phages were also sequence-specifically enriched greater than 4-fold when displayed on lambdafoo. These results suggest that the lambdafoo display system is useful for in vitro studying of protein-DNA interactions and may be applied to screening of DNA-binding protein from complex cDNA libraries through DNA-binding affinity.

A symbiont-produced protein and bacterial symbiosis in Amoeba proteus

Gram symbiotic X-bacteria present in the xD strain of Amoeba proteus as required cell components, synthesize and export a large amount of a 29-kDa protein (S29x) into the host's cytoplasm across bacterial and symbiosome membranes. The S29x protein produced by E. coli transformed with the s29x gene is also rapidly secreted into the culture medium. Inside amoebae, S29x enters the host's nucleus as detected by confocal and immunoelectron microscopy, although it is not clear if S29x is selectively accumulated inside the nucleus. The deduced amino-acid sequence of S29x has a stretch of basic amino acids that could act as a nuclear localization signal, but there is no signal peptide at the N-terminus and the transport of S29x is energy independent. The functions of S29x are not known, but in view of its prominent presence inside the amoeba's nucleus, S29x is suspected to be involved in affecting the expression of amoeba's nuclear gene(s).

The s29x gene of symbiotic bacteria in Amoeba proteus with a novel promoter

Gram-symbiotic bacteria (called X-bacteria), present in the xD strain of Amoeba proteus as required cell components, synthesize and export a large amount of a 29-kDa protein, S29x. S29x is exported into the host's cytoplasm across the bacterial membranes and the symbiosome membrane. The complete nucleotide (nt) sequence of the s29x gene of X-bacteria has been determined, and the promoter sequence and tsp have also been identified. The gene has a nonconventional promoter with putative nt sequences different from the known consensus sequences. When Escherichia coli cells are transformed with s29x, the gene is expressed and the product is secreted into the culture medium. Functions of S29x are not fully known, but it is suspected that S29x plays an important role in the symbiotic relationship between amoebae and X-bacteria.