Overexpression of glutamine:fructose-6-phosphate amidotransferase in transgenic mice leads to insulin resistance.

The hexosamine biosynthetic pathway has been hypothesized to be involved in mediating some of the toxic effects of hyperglycemia. Glutamine:fructose-6-phosphate amidotransferase (GFA), the first and rate limiting enzyme of the hexosamine biosynthetic pathway, was overexpressed in skeletal muscle and adipose tissue of transgenic mice. A 2.4-fold increase of GFA activity in muscle of the transgenic mice led to weight-dependent hyperinsulinemia in random-fed mice. The hyperinsulinemic-euglycemic clamp technique confirmed that transgenic mice develop insulin resistance, with a glucose disposal rate of 68.5 +/- 3.5 compared with 129.4 +/- 9.4 mg/kg per min (P < 0.001) for littermate controls. The decrease in the glucose disposal rate of the transgenic mice is accompanied by decreased protein but not mRNA levels of the insulin-stimulated glucose transporter (GLUT4). These data support the hypothesis that excessive flux through the hexosamine biosynthesis pathway mediates adverse regulatory and metabolic effects of hyperglycemia, specifically insulin resistance of glucose disposal. These mice can serve as a model system to study the mechanism for the regulation of glucose homeostasis by hexosamines.

Cysts of Tenon's capsule following filtration surgery. Medical management.

Cysts of Tenon's capsule (encapsulated blebs) developed postoperatively in 77 (13%) of 607 eyes that underwent filtration surgery between 1980 and mid-1985. The annual incidence was not uniform, increasing markedly throughout the period. Seventy-four eyes were treated with medical therapy only. At a mean follow-up of 19 months, the success rate for these eyes, defined as an intraocular pressure (IOP) of 21 mm Hg or less, was 92%. The three eyes that underwent surgical revision subsequently failed clinically by the study criteria. Those patients in whom cysts of Tenon's capsule developed were compared with an age-matched control group to assess for possible differences in long-term outcome. There was a significantly higher IOP in the Tenon's cyst group at one and three months after surgery, and an increased proportion of IOPs above 30 and 40 mm Hg. At a six-month and later follow-up, there was no significant difference in the mean IOP or in progression of visual field loss. Causative factors were sought for the development of these cysts of Tenon's capsule. Prior conjunctival surgery, or previous cyst formation in the other eye, were the significant risk factors noted.

Efficacy of brimonidine 0.2% and dorzolamide 2% as adjunctive therapy to beta-blockers in adult patients with glaucoma or ocular hypertension.

BACKGROUND: The alpha-adrenergic agonist brimonidine and the carbonic anhydrase inhibitor dorzolamide have been studied both as monotherapy and in combination with beta-blockers in the treatment of glaucoma and ocular hypertension; however, a MEDLINE literature search failed to reveal any clinical studies directly comparing these 2 agents as adjunctive therapy. OBJECTIVE: The purpose of this study was to compare the intraocular pressure (IOP)-lowering efficacy of brimonidine and dorzolamide as adjunctive therapy to beta-blockers in adult patients with glaucoma or ocular hypertension. METHODS: In a prospective, investigator-masked, multicenter, parallel-design clinical trial, adult patients whose IOP was inadequately controlled with topical beta-blocker therapy were randomly assigned to receive brimonidine 0.2% twice daily or dorzolamide 2% 3 times daily as adjunctive therapy for 3 months. Efficacy was determined by the reduction in IOP from baseline. After 1 month of adjunctive treatment, patients who failed to meet a target 15% reduction in IOP at peak drug effect were crossed over to the other study medication. RESULTS: A total of 106 patients were treated. Approximately 70% (74/106) of the patients were white, and 61.3% (65/106) had a diagnosis of open-angle glaucoma. Mean baseline IOP (ie, with beta-blocker monotherapy) was comparable between treatment groups (approximately 21 mm Hg). After 1 month of adjunctive treatment, the mean daily IOP reduction was significantly greater with brimonidine (4.40 mm Hg, 20.4%) than with dorzolamide (3.0 mm Hg, 14.4%, P = 0.033). At peak drug effect at month 1, the mean IOP reduction was significantly greater in the brimonidine group (5.95 mm Hg, 27.6%) than in the dorzolamide group (4.11 mm Hg, 19.7%; P = 0.007). Significantly more patients treated with brimonidine (44/51, 86.3%) than with dorzolamide (29/47, 61.7%) achieved the target 15% reduction in IOP at month 1 (P = 0.005). At month 3, the mean daily IOP reduction and the mean IOP reduction at peak drug effect were not significantly different in the 2 treatment groups. The mean daily IOP reduction was 4.98 mm Hg in the brimonidine group and 3.15 mm Hg in the dorzolamide group (P = 0.092). At peak drug effect, the mean IOP reduction was 6.39 mm Hg with brimonidine and 4.06 mm Hg with dorzolamide. The incidence of adverse events leading to discontinuation was 9.3% (5/54) in the brimonidine group (depression, 2; allergic conjunctivitis, 1; dry mouth and tearing, 1; dermatitis, 1) and 9.8% (5/51) in the dorzolamide group (ocular burning and stinging, 2; ocular itch, 1; gastrointestinal complaints, 1; lack of tolerance for beta-blocker, 1), with no significant difference between groups. CONCLUSION: In this trial, brimonidine 0.2% twice daily produced greater mean decreases in IOP and was effective in more patients than dorzolamide 2% 3 times daily when used as adjunctive therapy to beta-blockers.

Comparison of brimonidine with latanoprost in the adjunctive treatment of glaucoma. ALPHAGAN/XALATAN Study Group.

OBJECTIVE: This study compared brimonidine with latanoprost as adjunctive therapy for the treatment of open-angle glaucoma and ocular hypertension. BACKGROUND: Patients with open-angle glaucoma or ocular hypertension often require >1 medication to achieve control of intraocular pressure (IOP). Both brimonidine and latanoprost effectively lower IOP, but no previously reported clinical trials have directly compared these agents as adjunctive therapy. METHODS: This was a prospective, randomized, investigator-masked, multicenter, parallel-design clinical trial. Forty patients (69 study eyes) with uncontrolled IOP of < or =34 mm Hg while using a topical beta-blocker plus dorzolamide or pilocarpine were randomly assigned to receive either brimonidine 0.2% BID or latanoprost 0.005% QD over 6 months as adjunctive therapy. Tolerability was assessed by reports of adverse events, and efficacy was determined by reduction in IOP from baseline. Clinical success was defined as the achievement of a > or =15% reduction in IOP from baseline. RESULTS: There were no significant between-group differences in any demographic variable. Most patients in each group were white, had open-angle glaucoma, and were being treated with a nonselective beta-blocker and dorzolamide. When brimonidine or latanoprost was used as an adjunctive agent with a beta-blocker and dorzolamide or pilocarpine, the rates of clinical success at month 1 were 85% (17/20 patients) with brimonidine versus 65% (13/20 patients) with latanoprost (P = 0.144). Overall mean IOP reduction at month 1 was 4.60+/-0.62 mm Hg (22.8%; P < 0.001) with brimonidine and 3.43+/-0.62 mm Hg (17.2%; P < 0.001) with latanoprost, with no significant differences between groups (P = 0.219). Among the patients with an inadequate IOP-lowering response (<15% reduction from baseline), the mean IOP reduction was 0.36+/-0.66 mm Hg with latanoprost (n = 7) and 0.50+/-2.18 mm Hg with brimonidine (n = 3). Brimonidine and latanoprost had comparable IOP-lowering efficacy in patients receiving concomitant pilocarpine therapy (mean change in IOP of -4.23 mm Hg vs -3.75 mm Hg, P = 0.173). In patients concurrently treated with dorzolamide, brimonidine produced a mean change in IOP of -5.29 mm Hg, compared with a mean change of -3.21 mm Hg in the latanoprost group (P = 0.159). Both brimonidine and latanoprost were well tolerated. Few adverse events leading to discontinuation were observed with either drug regimen (n = 2 with brimonidine; n = 0 with latanoprost). CONCLUSIONS: Both brimonidine 0.2% BID and latanoprost 0.005% QD were well-tolerated and reduced IOP in most patients when used as third-line adjunctive therapy. However, clinical success was achieved by 17 of 20 patients (85%) who received brimonidine, compared with 13 of 20 patients (65%) who received latanoprost (P = 0.144). These results suggest that brimonidine 0.2% BID may be more reliable than latanoprost 0.005% QD as adjunctive therapy for glaucoma and ocular hypertension.

Extracapsular cataract extraction and posterior chamber intraocular lens implantation combined with trabeculectomy in patients with glaucoma.

We reviewed 75 consecutive cases of extracapsular cataract extraction and posterior chamber intraocular lens implantation combined with trabeculectomy in 69 patients with glaucoma. The mean preoperative intraocular pressure was 19.3 mm Hg on an average of 2.3 glaucoma medications. Visual acuity improved in 58 eyes (77%) at two months, with an average improvement of 3.3 and 3.6 lines at two and 12 months, respectively. Of the 75 eyes, 49 (65%) achieved a visual acuity of 20/40 or better; three patients (4%) had further deterioration in vision at the completion of follow-up because of progressive glaucoma or macular disease. Postoperatively, the average intraocular pressure was 3.8 and 3.0 mm Hg lower than the preoperative level at two and 12 months (P less than .001) on 0.63 and 0.79 glaucoma medications, respectively. However, 27 (36%) of the 75 eyes had a recorded intraocular pressure greater than 30 mm Hg and 30 (40%) had a pressure 7 mm Hg or more above their preoperative level during the first six months after surgery. Despite improved long-term control of intraocular pressure, detectable conjunctival filtering blebs were present in only 31 (41%) of 75 eyes at two months and in seven (12%) of 56 eyes at 12 months. Hyphema occurred in 34 (45%) of the cases.

Pharmacokinetics of a 5-fluorouracil liposomal delivery system.

A liposomal delivery system was developed in an attempt to prolong ocular levels of 5-fluorouracil for glaucoma filtering surgery. The pharmacokinetics of the 5-fluorouracil liposomal delivery system were studied in normal pigmented rabbits with 5-fluorouracil labelled with carbon-14 (C-14). 14C 5-fluorouracil was incorporated into the liposomes at a concentration of 10 g/l and injected subconjunctivally in doses of 5 and 10 mg. Concentrations of 5-fluorouracil were assayed at 10 time intervals from 0.5 to 96 hours in cornea, sclera, and conjunctiva and at six time intervals from 0.5 to 12 hours in aqueous. Two peak concentrations were noted at approximately one and eight hours, with measurable levels present at 96 hours. This study demonstrates the ability of this liposomal delivery system to prolong levels of 5-fluorouracial in normal pigmented rabbits.

Regulation of glutamine:fructose-6-phosphate amidotransferase activity by high glucose and transforming growth factor beta in rat mesangial cells.

BACKGROUND: The hexosamine biosynthesis pathway acts as a cellular glucose sensor and mediates many of the adverse effects of glucose. Increased flux through this pathway results in insulin resistance in rat fibroblasts and transgenic mice and upregulation of transforming growth factor beta (TGF-beta) transcriptional activity in rat kidney cells. The first and rate-limiting step in this pathway, which is responsible for the metabolism of glucose to glucosamine, is catalyzed by glutamine:fructose-6-phosphate amidotransferase (GFA). METHODS: Because of the known effects of hyperglycemia on mesangial cell (MC) function and growth factor regulation, we examined the regulation of GFA by glucose and TGF-beta in cultured SV40 rat MCs. GFA activity was assayed in cytosolic extracts of MCs using high-performance liquid chromatography. RESULTS: Culturing in 10 and 25 mM of glucose for 24 hours resulted in 33.4% (P < 0.025) and 43.5% (P < 0.05) decreases in GFA activity when compared with cells cultured at 1 to 5 mM of glucose. The downregulation in GFA activity by high glucose (HG) required at least 6 hours in culture and persisted for several days. HG effects were not a result of osmolar changes or glucose-induced differences in glucose uptake. Like HG, treatment of MCs with TGF-beta (2 ng/mL) for 4 hours resulted in a 30% (P < 0.05) decrease in GFA activity in cells cultured at 1 mM glucose, but the effects of TGF-beta were not additive to those of HG. TGF-beta-mediated downregulation of GFA activity was inhibited by a TGF-beta-neutralizing antibody, but HG's effects were not. Insulin-like growth factor-1 (IGF-1) had similar effects as TGF-beta, but GFA activity was not regulated by angiotensin II. CONCLUSIONS: GFA activity is downregulated by HG, TGF-beta, and IGF-1 in rat MCs. Downregulation of this cellular glucose sensor may be a protective mechanism against the harmful effects of excess glucose as seen in diabetes.

Three-month comparison of bimatoprost and latanoprost in patients with glaucoma and ocular hypertension.

A multicenter, randomized, investigator-masked, parallel-group trial compared bimatoprost and latanoprost for efficacy and safety in patients with glaucoma or ocular hypertension. Patients received bimatoprost 0.03% (n = 119) or latanoprost 0.005% (n = 113) once daily in the evening for 3 months. Visits were at prestudy, baseline (day 0), week 1, and months 1, 2, and 3. Primary outcome measures were mean IOP and the percentage of patients achieving IOP of 17 mm Hg or lower at 8:00 AM. Secondary outcome measures were diurnal IOP measurements (8:00 AM, 12 noon, 4:00 PM, 8:00 PM) at month 3 and safety measures including adverse events. Mean IOP was lower with bimatoprost than with latanoprost at all time points during the 3-month follow-up, although the between-group difference was not always statistically significant. At month 3 at 12 noon, mean IOP was as much as 1.0 mm Hg lower with bimatoprost (P = .021). Target pressures of < or = 17 mm Hg were reached more often with bimatoprost than with latanoprost at 8:00 AM (53% vs 43%; P = .029). Over all diurnal measurements at month 3, low target pressures of < or = 13, < or = 14, and < or = 15 mm Hg were achieved significantly more often with bimatoprost (P < or = .006). Both drugs were safe and well tolerated. Conjunctival hyperemia was more common with bimatoprost, while headache was more frequent with latanoprost. Bimatoprost provided lower mean pressures than latanoprost at every time point throughout the study and was statistically superior in achieving low target pressures. More patients reached low target pressures with bimatoprost.

Prevention of ocular gunshot injuries using polycarbonate lenses.

Two patients lost three eyes, and one his life, secondary to ocular gunshot wounds. In both patients, the pellets gained entry into the central nervous system through the eye and orbital bones despite only superficial wounds to other areas of the body. These tragic injuries prompted a study of polycarbonate lenses to determine their effectiveness in preventing small caliber ocular gunshot wounds. This investigation determined that 3.0 mm and the 2.2 mm polycarbonate lenses could prevent such injuries at distances greater than 15 yards. In comparing the two lenses, it was found that the 3.0 mm lens sustained less damage at 70 degrees F, but the 2.2 mm lens was more resistant to penetration at 32 degrees F. Since most hunting is done in the fall and winter months, the brittle nature of the thicker lens is significant. Polyamide sports frames with a posterior rim were also tested and found to prevent posterior lenticular expulsion at 15 yards. Standard acetate frames were shown to be ineffective in this regard at 30 yards.

Glaucoma after pediatric lensectomy/vitrectomy.

Glaucoma after pediatric cataract surgery, once well recognized, now occurs only rarely after modern lensectomy/vitrectomy. The authors performed directed glaucoma evaluations of 34 eyes of 26 children. Based on intraocular pressures of 26 mmHg or greater, glaucoma was diagnosed in 8 (24%) eyes of 7 (27%) children. Glaucoma was found more commonly among children followed more than 60 months and was diagnosed up to 105 months after surgery. Typically, the glaucoma was open angle and asymptomatic. Four children had had previously normal pressures recorded. With longer follow-up, it is likely that more children will be diagnosed with glaucoma after lensectomy/vitrectomy procedures. The authors believe such patients should be followed as glaucoma suspects for the rest of their lives.

Insulin stimulation of glutamine: fructose-6-phosphate amidotransferase occurs via an insulin-like growth factor-1 pathway in rat fibroblasts.

The biosynthetic pathway for hexosamine mediates some of the adverse effects of high glucose. The rate limiting enzyme in this pathway is glutamine:fructose-6-phosphate amidotransferase (GFA). Using HPLC, the regulation of GFA activity by glucose and insulin was studied in wild type and rat-1 fibroblasts overexpressing human insulin receptors (HIRcB cells). In wild type cells only maximal doses of insulin (580 ng/ml) resulted in an increase in GFA activity (51.0 +/- 40.6%). In HIRcB cells insulin led to a dose dependent increase in GFA activity that was enhanced when compared to wild type (89 +/- 5% (p<0.001) increase at 580 ng/ml). Insulin's action was glucose dependent and required prolonged serum deprivation. HIRcB's cultured in 0 mM glucose had a 58.2% (p<0.001) decrease in insulin stimulation. However, when present the concentration of glucose (2-20 mM) did not affect insulin stimulation of GFA activity. Most of insulin's effects occur by way of the IGF-1 receptor as a two-fold stimulation of GFA activity was seen with significantly lower doses (10 ng/ml) of IGF-1. We conclude that GFA enzyme activity is upregulated by insulin and this may occur via a IGF-1 receptor mediated pathway.