Xiangjia Zhu

Imaging of Human Lens Lipids by Desorption Electrospray Ionization Mass Spectrometry

The lipid composition of the human lens is distinct from most other tissues in that it is high in dihydrosphingomyelin and the most abundant glycerophospholipids in the lens are unusual 1-O-alkyl-ether linked phosphatidylethanolamines and phosphatidylserines. In this study, desorption electrospray ionization (DESI) mass spectrometry-imaging was used to determine the distribution of these lipids in the human lens along with other lipids including, ceramides, ceramide-1-phosphates, and lyso 1-O-alkyl ethers. To achieve this, 25 μm lens slices were mounted onto glass slides and analyzed using a linear ion-trap mass spectrometer equipped with a custom-built, 2-D automated DESI source. In contrast to other tissues that have been previously analyzed by DESI, the presence of a strong acid in the spray solvent was required to desorb lipids directly from lens tissue. Distinctive distributions were observed for [M + H]+ ions arising from each lipid class. Of particular interest were ionized 1-O-alkyl phosphatidylethanolamines and phosphatidylserines, PE (18:1e/18:1), and PS (18:1e/18:1), which were found in a thin ring in the outermost region of the lens. This distribution was confirmed by quantitative analysis of lenses that were sectioned into four distinct regions (outer, barrier, inner, and core), extracted and analyzed by electrospray ionization tandem mass spectrometry. DESI-imaging also revealed a complementary distribution for the structurally-related lyso 1-O-alkyl phosphatidylethanolamine, LPE (18:1e), which was localized closer to the centre of the lens. The data obtained in this study indicate that DESI-imaging is a powerful tool for determining the spatial distribution of human lens lipids.

Presbyopia and cataract: a question of heat and time.

Not only are human lenses different in many ways from those of non-primates, they also undergo dramatic changes with age. These age-dependent alterations lead to perturbations in the properties of older lenses, and ultimately to disturbances in visual function, which typically become apparent at middle age. Recent data suggest that many, if not all, of these age-dependent features can be traced to the lack of macromolecular turnover in the lens and to the inexorable modifications to proteins and membrane components over a period of decades. Exposure of lenses to heat can reproduce many of these alterations, suggesting that long-term incubation at body temperature may be an important factor in aging the human lens. Two conclusions flow from this. Firstly, the human lens may be an ideal tissue for studying macromolecular aging in man. Secondly, it will be extremely challenging to examine the origin of human age-related conditions, such as presbyopia and nuclear cataract, using traditional laboratory animals. Characterising the unfolding and decomposition of long-lived macromolecules appears to provide the key to understanding the two most common human lens disorders: presbyopia and age-related nuclear cataract.

Age-Dependent Denaturation of Enzymes in the Human Lens: A Paradigm for Organismic Aging?

Little is known about the rate of denaturation of proteins within the human body. To monitor this decline, human eye lenses were dissected into discrete regions that were formed at different stages of life and assayed for activity of lactate dehydrogenase (LDH) and a particularly stable enzyme, glutathione reductase (GR). Activity was highest for both enzymes in the most recently synthesized outer part of the lens, decreased further into the lens, and, for LDH, was barely detectable in nuclear regions that consist of proteins that were synthesized in utero. For LDH, 95% of total lens activity was found in the outer half of the adult lens at all ages. Activity was unchanged in the outermost part of the lens as a function of age, suggesting that the ability of humans to synthesize the two enzymes is not impaired, even up to the tenth decade. After age of 40, LDH activity declined steadily in the interior of the lens at the rate of 8.3% per decade. GR activity diminished more slowly, and western blotting indicated that both denaturation of the enzyme and truncation were responsible. These data support the view that few, if any, metabolic pathways remain in the center of older lenses. Exposure of the enzymes to physiological pH and temperature over a period of decades is presumably sufficient to cause denaturation. The center of older human lenses is a unique environment in which the accumulation of untoward posttranslational modifications to proteins can be studied in the absence of significant enzymatic amelioration.

Factors influencing 1-year rotational stability of AcrySof Toric intraocular lenses

Purpose To investigate the 1-year rotational stability of AcrySof Toric intraocular lenses (IOLs) and factors influencing their stability. Methods This retrospective study enrolled 75 patients who underwent phacoemulsification, and were implanted with an AcrySof Toric IOL for 1 year. Their preoperative clinical data were reviewed. The 1-year clinical outcomes included uncorrected visual acuity, best-corrected visual acuity and residual astigmatism. Rotation of the IOL and the grade of anterior capsular opacification (ACO; graded from 0=none to 3=severe) were evaluated after mydriasis. Results Of the 75 eyes analysed, 29.33% had high myopia. Residual astigmatism at 1 year (−0.76±0.47 dioptre(D)) was significantly reduced compared with the preoperative corneal astigmatism (2.08±0.71 D). The mean absolute rotation of the IOL was 8.83±5.26°. Toric IOL rotation was significantly and positively correlated with the degree of residual astigmatism in the T3 (Pearsons r=0.552, p<0.001) and T4 groups (Pearsons r=0.622, p=0.003). Regarding factors associated with IOL rotation, toric IOL rotation was positively correlated with axial length (AXL; Pearsons r=0.335, p=0.003) and negatively correlated with ACO grade (Spearmans r=−0.541, p<0.001). On multiple linear regression analysis, only AXL (B=0.889, p=0.031) and ACO grade (B=−3.216, p<0.001) were predictors of toric IOL rotation (R2=0.397). Conclusions Long AXL is a risk factor for toric IOL rotation, while higher ACO grade may decrease toric IOL rotation, indicating that reducing the polishing of anterior capsule may improve the rotational stability of a toric IOL. Trial registration number NCT02182921.

α- and β-Crystallins Modulate the Head Group Order of Human Lens Membranes during Aging

PURPOSE To examine the physical properties of human lens cell membranes as a function of age. METHODS The environment of the phospholipid head groups in fiber cell membranes from human lenses, aged 22 to 83 years, was assessed with Laurdan and two-photon confocal microscopy. The effect of mild thermal stress on head group order was studied with lens pairs in which one intact lens was incubated at 50 °C. Dihydrosphingomyelin vesicles were preloaded with Laurdan, α-, β-, or γ-crystallin was added, and surface fluidity was determined. RESULTS The membrane head group environment became more fluid with age as indicated by increased water penetration. Furthermore, these changes could be replicated simply by exposing intact human lenses to mild thermal stress; conditions which decreased the concentration of soluble α- and β-crystallins. Vesicle binding experiments showed that α- and β-, but not γ-, crystallins markedly affected head group order. CONCLUSIONS The physical properties of cell membranes in the lens nucleus change substantially with age, and α- and β-crystallins may modulate this effect. β-Crystallins may therefore play a role in lens cells, and cells of other tissues, apart from being simple structural proteins. Age-dependent loss of these crystallins may affect membrane integrity and contribute to the dysfunction of lenses in older people.

Perceived Pain during Cataract Surgery with Topical Anesthesia: A Comparison between First-Eye and Second-Eye Surgery

Purpose. To compare pain scores between first-eye and second-eye cataract surgery and to determine the affecting factors. Methods. 106 first-eye and 53 second-eye cataract surgery patients (mean age: 67 ± 13 and 69 ± 10 years, resp.) were enrolled. The patients completed simplified State-Trait Anxiety Inventory and visual analog scale (VAS) for anxiety questionnaires before surgery, and VAS for pain and Wong-Baker Faces Pain Rating Scale questionnaires after surgery. Blood pressure (BP) and heart rate (HR) were recorded perioperatively. Results. A greater proportion of patients who underwent second-eye surgery reported intraoperative pain compared with first-eye surgery patients (85% versus 35%, P < 0.001). The pain scores were higher in second-eye surgery, while the VAS anxiety score was lower in second-eye surgery. Moreover, 31 patients reported greater pain during second-eye surgery than their first one, with higher pain scores than other 22 patients (P = 0.032 and 0.003, resp.). The VAS pain score of these 31 patients was positively correlated with the differences between the intraoperative and postoperative diastolic BP, mean arterial pressure, and HR. Conclusions. Cataract patients were likely to have more pain during second-eye surgery, which may be related to lower preoperative anxiety. Monitoring perioperative BP and HR may help to identify patients with intraoperative pain.

Molecular Inflammation in the Contralateral Eye After Cataract Surgery in the First Eye.

PURPOSE The purpose of this study was to assess the inflammatory status of the aqueous humor in the fellow eye after uneventful cataract surgery in the first eye. METHODS At the screening stage, aqueous humor samples from 15 first-eye and 15 second-eye cataract patients were collected just before cataract surgery and assayed using human cytokine antibody array. Screened cytokines were then verified using a suspension array system with aqueous humor samples obtained from 35 first-eye and 36 second-eye cataract patients. RESULTS The cytokine antibody array revealed that interleukin-1 receptor antagonist (Il-1ra) and macrophage inflammatory protein (MIP)-1a and MIP-1b were expressed at high levels in first-eye patients and were lower in second-eye patients, whereas opposite trends were found for monocyte chemoattractant protein 1 (MCP-1) and for regulated on activation, normal T expressed and secreted (RANTES) (all, P < 0.05, Students t-test). However, only MCP-1 and IL-1ra were significantly different between the two groups after Bonferroni correction (both P < 0.00125). In the replication stage, the suspension cytokine array revealed that only MCP-1 expression was significantly greater in the aqueous humor of second-eye patients than in that of first-eye patients (P = 0.0067, Students t-test). CONCLUSIONS This study revealed that expression of MCP-1, a pain-related inflammatory chemokine, was significantly increased in aqueous humor in the contralateral eye after first-eye cataract surgery. This suggests there may be a sympathetic ophthalmic type uveitis in the contralateral eye after first-eye cataract surgery and that may help to explain why second-eye phacoemulsification is often more painful. (ClinicalTrials.gov number, NCT01824927.)

Schlemm's Canal Expansion After Uncomplicated Phacoemulsification Surgery: An Optical Coherence Tomography Study

Purpose To evaluate the effects of phacoemulsification cataract surgery on Schlemms canal (SC) using swept-source optical coherence tomography (OCT). Methods Patients with a senile cataract were included. The SC area and diameter were checked by OCT at the baseline and 1 day, 1 week, 1 month, and 6 months after the cataract surgery. Multivariate linear regression analysis was performed for predictors of change in the mean SC area and diameter. Results Twenty-five eyes (25 patients) were included in the final analysis. After the cataract surgery, there was a significant increase in the SC area and diameter, and a decrease in the intraocular pressure (IOP) (repeated-measures analysis of variance; all P < 0.05), which extended to the end of the follow-up period. After multivariate analysis, the changes in the SC area and diameter 6 months after surgery were correlated with the change in the IOP (SC area, β = -0.575, P < 0.0001; SC diameter, β = -0.576, P < 0.0001) and the change in the anterior vault (AV) (SC area, β = 0.359, P = 0.007; SC diameter, β = 0.413, P = 0.003). Conclusions Expansion of the SC was observed after cataract surgery. The degree of expansion was related to the extent of the decrease in the IOP. Further studies are needed to determine whether these changes will last over a long period of time.

Adhesion of the posterior capsule to different intraocular lenses following cataract surgery.

To investigate the prevalence and morphologic and clinical features of posterior capsule–optic inadhesion following cataract surgery.

αA-crystallin gene CpG islands hypermethylation in nuclear cataract after pars plana vitrectomy.

PurposeTo investigate the DNA methylation status of αA-crystallin gene in cataract secondary to pars plana vitrectomy.MethodsAnterior capsular membranes of 40 eyes of 40 patients with cataract secondary to vitrectomy were collected. Another 20 eyes of 20 patients who received pars plana vitrectomy and phacoemulsification in the primary procedure, were recruited as control. Methylation status of the CpG islands of αA-crystallin gene was analyzed by pyrosequencing. Expression of αA-crystallin was evaluated by real-time polymerase chain reaction and western blot.ResultsIn the post vitrectomy group, five patients with posterior subcapsular opacity and four patients with cortical opacity were excluded from further analysis. The remaining 31 patients with nuclear cataract were assigned into two groups according to tamponade types: 19 of octafluoropropane (C3F8) and 12 of silicone oil (SiO). The average nuclear color grading was elevated both in C3F8 and SiO groups after vitrectomy. Compared to the control group, hypermethylation of the CpG islands in the αA-crystallin gene promoter was found in both post vitrectomy groups, accompanied by significantly reduced αA-crystallin expression. No statistically significant differences were found between the C3F8 and SiO groups either for DNA methylation status or αA-crystallin expression.ConclusionsCpG islands hypermethylation of αA-crystallin gene may be involved in nuclear cataract formation after pars plana vitrectomy.