Yasunori Segawa

Roles of the AGE-RAGE system in vascular injury in diabetes

Abstract: This study concerns whether advanced glycation endproducts (AGE) are related to microvascular derangement in diabetes, exemplified by pericyte loss and angiogenesis in retinopathy and by mesangial expansion in nephropathy. AGE caused a decrease in viable pericytes cultivated from bovine retina. On the other hand, AGE stimulated the growth and tube formation of human microvascular endothelial cells (EC), this being mediated by autocrine vascular endothelial growth factor. In AGE‐exposed rat mesangial cells, type IV collagen synthesis was induced. Those AGE actions were dependent on a cell surface receptor for AGE (RAGE), because they were abolished by RAGE antisense or ribozyme. The AGE‐RAGE system may thus participate in the development of diabetic microangiopathy. This proposition was supported by experiments with animal models; several indices characteristic of retinopathy were correlated with circulating AGE levels in OLETF rats. The predisposition to nephropathy was augmented in RAGE transgenic mice when they became diabetic.

Upregulation of Retinal Vascular Endothelial Growth Factor mRNAs in Spontaneously Diabetic Rats without Ophthalmoscopic Retinopathy

Vascular endothelial growth factor (VEGF) has recently been shown to be involved in the pathogenesis of proliferative diabetic retinopathy. However, its involvement in the development of the early phase of diabetic retinopathy is not fully understood. In this study we investigated the retinal VEGF mRNA level in spontaneously diabetic Otsuka Long-Evans Tokushima fatty (OLETF) rats, a model of non-insulin-dependent diabetes, without overt retinopathy, using quantitative reverse-transcription polymerase chain reaction. The retinal VEGF mRNA level was 2.2 times higher (p < 0.0005) in OLETF rats than in control rats at the age of 60 weeks. Moreover, their retinal mRNA level was positively correlated with serum concentration of advanced glycation end products (AGEs) but not to serum glucose concentration. Furthermore, the peak latency of the oscillatory potentials in the electroretinogram, one of the most sensitive markers for the early phase of diabetic retinopathy, was significantly prolonged in OLETF rats (p < 0.05), being also correlated with the serum AGE concentration. The results thus suggest that AGEs, which are formed acceleratedly in diabetic conditions, are involved in the development of the early phase of diabetic retinopathy probably through the induction of retinal VEGF mRNAs.

Isolating triamcinolone acetonide particles for intravitreal use with a porous membrane filter.

Purpose To report a new, simple, rapid method to isolate triamcinolone acetonide particles and to remove additives from its commercially available suspension (Kenacort-A) for intravitreal use. Methods The contents of a Kenacort-A vial (40 mg triamcinolone acetonide suspended in 1.0 mL vehicle) were loaded into a syringe and passed through a porous membrane filter with 0.45-&mgr;m pores. The filter was then backflushed with distilled water to yield a vehicle-poor suspension of triamcinolone acetonide in the initial syringe. This filtration and backflush procedure was repeated four times, and each waste filtrate was subjected to high-performance liquid chromatography to identify benzyl alcohol, a preservative in the vehicle. Gel permeation chromatography was also used to determine the degree to which carboxymethylcellulose, one of the two suspending agents in the vehicle, permeated the membrane filter. Although 7.5 mg/mL high-viscosity carboxymethylcellulose hardly passed through the 0.45-&mgr;m pore filter, it passed through the 5.0-&mgr;m pore filter easily. Therefore, a 5.0-&mgr;m pore filter was used in this study. Results By using a 0.45-&mgr;m porous membrane filter, 99.7% of the benzyl alcohol can be eliminated. By using a 5.0-&mgr;m porous membrane filter, but not by using a 0.45-&mgr;m porous membrane filter, 88.1% of the high-viscosity carboxymethylcellulose can be eliminated. Conclusions The filtration and backflush procedure using the 5.0-&mgr;m porous membrane filters is useful during vitrectomy to reduce the preparation time of triamcinolone acetonide suspension. Also, this method of reducing additives may be more helpful when using triamcinolone as a therapeutic agent for intravitreal depot use, because there is no washout effect when it is used in this manner.

Acetazolamide-induced changes of the membrane potentials of the retinal pigment epithelial cell

Acetazolamide-induced changes of the apical (Vap) and basal (Vba) membrane potentials of the retinal pigment epithelial cell were studied in an in-vitro retinal pigment epithelium (RPE)-choroid of the frog. Both Vap and Vba were hyperpolarized by acetazolamide placed on either the apical or basal side of the RPE. In all cases, acetazolamide on the apical side hyperpolarized Vba more than Vap and decreased the transepithelial potential (TEP) across the RPE. In most cases, acetazolamide on the basal side hyperpolarized both Vap and Vba to almost equal degrees and hardly changed the TEP. We conclude that the Diamox response (a decrease of the ocular standing potential induced by an intravenous sodium acetazolamide) may be triggered by effects of acetazolamide on the apical side of the RPE and generated mainly by a hyperpolarization of the basal membrane of the RPE cell.

Endoillumination-assisted cataract surgery in a patient with corneal opacity

We present a technique to better visualize cataracts through corneal opacity. A 70-year-old Japanese woman with retinal detachment, cataract, and corneal opacity in the left eye was treated with phacoemulsification, 3-port vitrectomy, and intraocular lens implantation. To circumvent the difficulty of performing continuous curvilinear capsulorhexis (CCC) and subsequent cataract surgery through a hazy cornea, we used an endoilluminator as a light source outside the cornea for CCC and inside the anterior chamber for phacoemulsification. As a result, CCC and subsequent cataract surgery were successfully and easily performed despite potentially troublesome corneal opacity. The use of an endoilluminator can be an effective supportive measure for cataract surgery in patients with corneal opacity.

Temporary use of a customized, glued-on hard contact lens before penetrating keratoplasty for descemetocele or corneal perforation

Descemetocele or corneal perforation makes it difficult to perform penetrating keratoplasty (PKP). To circumvent this difficulty, a polymethylmethacrylate hard contact lens with a diameter of 4.0 mm was customized and applied to the cornea with tissue adhesive prior to PKP in three patients, one with corneal perforation and two with descemetoceles. The results showed that this modified method facilitated trephination during PKP without complications in all three patients, suggesting that it may be applicable to other similar clinical situations.

Perfluorocarbon Liquid Assists in Stripping the ILM to Treat Detached Retina Caused by Macular Hole

Stripping the internal limiting membrane (ILM) is supposed to be beneficial in attaching the retina in retinal detachment because of macular hole. However, it is difficult to lift up and strip the ILM over extensively detached retinas because such retinas are very mobile. To evade this difficulty, we flattened the detached retina with perfluorocarbon liquid (PFCL) and peeled the ILM in the presence of PFCL. The ILM flap was easily turned up and enlarged with the posterior counter traction by PFCL. Intraoperative flattening of the retina with PFCL is useful in peeling the ILM from detached retinas.

Fornix and conjunctiva reconstruction by amniotic membrane in a patient with conjunctival mucosa-associated lymphoid tissue lymphoma.

BACKGROUND Conjunctival mucosa-associated lymphoid tissue (MALT) lymphoma is a rare, low-grade, non-Hodgkins B-cell lymphoma. Herein, we report our successful management of the large conjunctival defect caused by resection of conjunctival MALT lymphoma by covering it with transplanted amniotic membrane. CASE A 28-year-old Japanese man, who had been diagnosed histologically as having conjunctival MALT lymphoma in his left eye, was referred to us for treatment. The tumor was located on the lower bulbar and palpebral conjunctiva, and involved the fornix. Extensive resection of the conjunctival lesion was performed. Two pieces of amniotic membrane were used to reconstruct the fornix, bulbar, and palpebral conjunctival defect. OBSERVATIONS Epithelialization over the transplantation was completed within 3 weeks when all sutures were removed. During the 6 months of follow-up, there was no recurrence or any postoperative complication, such as graft rejection, symblepharon, or chronic inflammation. CONCLUSIONS We demonstrated for the first time that amniotic membrane can be used to cover a large defect on both bulbar and palpebral conjunctiva when such a low-grade malignancy as MALT lymphoma is extensively excised. Amniotic membrane transplantation was quite effective for the fornix and conjunctival reconstruction.

Retinal pigment epithelial origin of bicarbonate response

The mechanisms of the bicarbonate-induced decrease in the ocular standing potential (bicarbonate response) were investigated in the cat. An intravenous infusion of 1.4% sodium bicarbonate solution caused a decrease in the standing potential. A high-bicarbonate solution decreased or increased the potential across the retinal pigment epithelium-choroid tissue of the excised cat eye when applied basally or apically, respectively, but did not affect the potential across the anterior portion of the excised eye or across the isolated neural retina. A high-bicarbonate solution principally depolarized the apical membrane of the retinal pigment epithelium (RPE) when applied basally, and hyperpolarized it when applied apically. These results suggest that the bicarbonate response in the cat is primarily due to the effects of an increase in bicarbonate concentration on the basal membrane of the RPE.

Does precipitation reduce tissue staining by indocyanine green dye solutions

PURPOSE Indocyanine green (ICG) dye precipitates when mixed with certain ophthalmic irrigation solutions. The purpose of this study is to investigate whether this precipitation reduces ICG staining of the anterior lens capsule. METHODS ICG was diluted with each of the following solutions: BSS Plus, physiological saline, or Opeguard Neo. The products were then examined for green precipitate by light microscopy. The tissue staining capability of each ICG solution was tested at two different concentrations (0.5% and 0.0625%) in porcine lenses, regardless of whether the solution contained precipitate. RESULTS Green precipitate was observed in both concentrations of ICG solutions diluted with BSS Plus, but not in the solutions diluted with either physiological saline or Opeguard Neo. As assessed with light microscopy, staining of the anterior lens capsule appeared weaker for all 0.0625% ICG solutions compared to the corresponding 0.5% ICG solutions. The precipitate that formed in the 0.5% ICG solution diluted with BSS Plus had little effect on the staining quality of the anterior lens capsule. In contrast, the 0.0625% ICG solution diluted with BSS Plus (w/precipitate) showed weaker staining in the lens capsule compared to the other two 0.0625% ICG solutions (w/o precipitate). CONCLUSION These results suggest that precipitation of ICG may weaken its capability to stain the anterior lens capsule or other transparent ocular tissues. Therefore, ICG solutions that do not form a precipitate may be more capable of staining tissues at lower concentrations. As for other possibilities to explain the deterioration in staining, the effect of the composition of BSS Plus should also be considered.