Acid In Aqueous Humor Research Articles

Latanoprost-loaded cyclodextrin microaggregate suspension eye drops for enhanced bioavailability and stability

ObjectiveThe bioavailability of conventional eye drops is very low due to different physiological barriers. Commercial latanoprost (LAT) eye drops (Xalatan®) need to be refrigerated and protected from light. The purpose of this study was to develop novel LAT eye drops to improve ocular bioavailability and stability. MethodsOphthalmic suspension containing LAT/γ-cyclodextrin (γCD) aggregates was designed and the preparation process was sufficiently studied. The prepared formulations were evaluated for pH, viscosity, osmolality, particle size, entrapment efficiency and in vitro release study. In vitro permeability study using Human Corneal Epithelial Cells and in vivo studies on rabbits were also performed. ResultsLAT/γCD aggregates were formed and confirmed by scanning electron microscopy. LAT/γCD eye drops showed obvious sustained release profiles and were more stable than Xalatan®. In vitro corneal permeation study indicated LAT/γCD eye drops had no significant cytotoxicity and had higher cell permeability. In vivo precorneal retention study showed AUC0–6 h, Cmax, and mean residence time (MRT) of LAT/γCD eye drops were 3.98, 2.12, and 2.07 times higher than those of Xalatan®, respectively. In vivo ocular distribution study revealed that AUC0–24 h, Cmax, and MRT for latanoprost acid in aqueous humor exhibited 2.60-fold, 1.36-fold, and 1.99-fold increase in LAT/γCD eye drops group than those of Xalatan® group, respectively. ConclusionCyclodextrin microaggregate suspension eye drops represent a potential strategy for enhanced bioavailability and stability of LAT.

Elevated level of uric acid in aqueous humour is associated with posterior subcapsular cataract in human lens

Age-related cataract is the leading cause of blindness worldwide. The pathological mechanisms causing this disease remain elusive. To examine the involvement of uric acid (UA) in the pathogenesis of posterior subcapsular cataract (PSC). Retrospective study and experimental investigation. A total of 180 patients with PSC or non-PSC were included. Samples obtained from the patients were used to analyse content of UA and for histochemical examinations. The effects of UA on human lens epithelial cells were also investigated. Aqueous humour UA and urate deposits. The results showed a significant increase of aqueous humour UA in patients with PSC. After adjustment for potential confounders, elevated aqueous humour UA (odds ratio [OR] = 1.45) showed a stronger association with PSC than serum UA (OR = 1.10). Gomori methenamine silver staining revealed in PSC an intense deposit of urates in the lens fibres in equatorial regions, and in subcapsular fibres in posterior regions of the lens. Such staining was not detected in the lens with non-PSC. Treatment with UA-induced senescence and apoptosis in human lens epithelial cells in a dose dependent manner. Our results suggest that the elevated level of UA in aqueous humour causes a deposition of urates in human lens epithelium, which could possibly lead to dysfunction of these cells that generates opacification in PSC. These findings indicate the local action of excessive UA in the pathogenesis of PSC. Control of serum UA level could delay the progression of PSC.

Metabolomic profile of diabetic retinopathy: a GC-TOFMS-based approach using vitreous and aqueous humor.

To identify the potential metabolite markers in diabetic retinopathy (DR) by using gas chromatography coupled with time-of-flight mass spectrometry (GC-TOFMS). GC-TOFMS spectra were acquired from vitreous and aqueous humor (AH) samples of patients with DR and non-diabetic participants. Comparative analysis was used to elucidate the distinct metabolites of DR. Metabolic pathway was employed to explicate the metabolic reprogramming pathways involved in DR. Logistic regression and receiver-operating characteristic analyses were carried out to select and validate the biomarker metabolites and establish a therapeutic model. Comparative analysis showed a clear separation between disease and control groups. Eight differentiating metabolites from AH and 15 differentiating metabolites from vitreous were highlighted. Out of these 23 metabolites, 11 novel metabolites have not been detected previously. Pathway analysis identified nine pathways (three in AH and six in vitreous) as the major disturbed pathways associated with DR. The abnormal of gluconeogenesis, ascorbate-aldarate metabolism, valine-leucine-isoleucine biosynthesis, and arginine-proline metabolism might weigh the most in the development of DR. The AUC of the logistic regression model established by D-2,3-Dihydroxypropanoic acid, isocitric acid, fructose 6-phosphate, and L-Lactic acid in AH was 0.965. The AUC established by pyroglutamic acid and pyruvic acid in vitreous was 0.951. These findings have expanded our understanding of identified metabolites and revealed for the first time some novel metabolites in DR. These results may provide useful information to explore the mechanism and may eventually allow the development of metabolic biomarkers for prognosis and novel therapeutic strategies for the management of DR.

Ascorbic acid concentrations in aqueous humor after systemic vitamin C supplementation in patients with cataract: pilot study

BackgroundTo measure ascorbic acid concentration in aqueous humor of patients with cataract after oral or intravenous vitamin C supplementation.MethodsForty-two eyes of 42 patients with senile cataract who underwent uncomplicated cataract surgery were enrolled. Patients (n = 14 each) were administered oral vitamin C (2 g), intravenous vitamin C (20 g) or no treatment (control group) on the day before surgery. Samples of aqueous humor (0.1 cm3) were obtained by anterior chamber aspiration at the beginning of surgery and stored at −80 °C. Ascorbic acid concentration in aqueous humor was measured by high-pressure liquid chromatography.ResultsThe mean age at surgery was 62.5 years, with no difference among the three groups. The mean ± standard deviation concentrations of ascorbic acid in aqueous humor in the control and oral and intravenous vitamin C groups were 1347 ± 331 μmol/L, 1859 ± 408 μmol/L and 2387 ± 445 μmol/L, respectively. Ascorbic acid concentration was significantly lower in the control than in the oral (P < 0.01) and intravenous (P < 0.001) vitamin C groups and was significantly higher in the intravenous than in the oral vitamin C group (P < 0.05).ConclusionsAscorbic acid concentration in aqueous humor is increased by systemic vitamin C supplementation, with intravenous administration being more effective than oral administration.

Advantages of Efficacy and Safety of Fixed-Dose Tafluprost/Timolol Combination Over Fixed-Dose Latanoprost/Timolol Combination.

PurposeTo compare the safety and efficacy of fixed-dose tafluprost/timolol combination (Taf/T-FDC) with those of fixed-dose latanoprost/timolol combination (Lat/T-FDC) by measuring the intraocular pressure (IOP)-lowering effect, ocular pharmacokinetics, and ocular surface toxicity.MethodsThe IOP-lowering effect of Taf/T-FDC and Lat/T-FDC in ocular normotensive monkeys was evaluated at 4 and 8 h after instillation in study A, at 12, 14, 16, and 18 h after instillation in study B, and at 24, 26, 28, and 30 h after instillation in study C. Drug penetration into the eye was evaluated by measuring the concentrations of timolol, tafluprost acid (active metabolic form of tafluprost), and latanoprost acid (active metabolic form of latanoprost) using liquid chromatography coupled with tandem mass spectrometry after single instillation of Taf/T-FDC or Lat/T-FDC to Sprague Dawley rats. Cytotoxicity following 1–30 min exposure of SV40-transformed human corneal epithelial cells to Taf/T-FDC or Lat/T-FDC was analyzed using 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium assays. Undiluted and 10-fold diluted solutions of each FDC were evaluated.ResultsThe IOP-lowering effect of Taf/T-FDC was almost equivalent to that of Lat/T-FDC at 4–8 h after instillation. The peak IOP reduction of Taf/T-FDC and Lat/T-FDC was observed at 8 h after instillation, and there is no difference between the two. The difference between them was observed at 24–30 h after instillation, and Taf/T-FDC demonstrated a significantly greater IOP-lowering effect than Lat/T-FDC at 24–30 h after instillation. The IOP-lowering effect of Taf/T-FDC was sustained up to 30 h after instillation, while that of Lat/T-FDC had almost disappeared at 28 h after instillation. Timolol concentrations in aqueous humor after Taf/T-FDC instillation were higher than those after Lat/T-FDC instillation (Cmax, 3870 ng/mL vs 1330 ng/mL; AUCinf, 3970 ng·h/mL vs 1250 ng·h/mL). The concentrations of tafluprost acid and latanoprost acid in aqueous humor after instillation of Taf/T-FDC and Lat/T-FDC, respectively, were similar to those after instillation of mono-preparations of tafluprost and latanoprost, respectively. The cytotoxic effect of Taf/T-FDC to the human corneal epithelial cells was significantly lower than that of Lat/T-FDC at all evaluated time points in both undiluted and 10-fold diluted FDCs.ConclusionTaf/T-FDC provides increased IOP-lowering effect duration and lower potential ocular surface toxicity than Lat/T-FDC.

Development of Latanoprost-Loaded Biodegradable Nanosheet as a New Drug Delivery System for Glaucoma

We investigated the IOP reduction and safety of latanoprost-loaded biodegradable nanosheet (LBNS) as a new antiglaucoma drug delivery system (DDS). We fabricated a 40 nm thick multilayered biodegradable nanosheet that is composed of chitosan and sodium alginate by means of the layer-by-layer method. Latanoprost isopropyl ester was loaded on the nanosheet to prepare 25, 2.5, and 0.25 μg/cm(2) LBNSs. A nanosheet without latanoprost isopropyl ester (NS) and 0.005% latanoprost ophthalmic solution were prepared as controls. LBNSs or NS was applied to rat cornea, and IOP was monitored for 9 days. Local adverse effects and eye scratching movement also were investigated. The amount of latanoprost acid in aqueous humor and was measured in rabbits. The 0.25 μg/cm(2) LBNS and 0.005% latanoprost ophthalmic solution showed significant IOP reduction only for 1 day after application, whereas the IOP reduction rates of 2.5 μg/cm(2) LBNS at 1, 2, 4, 7, and 9 days after application were -27.0% ± 14.8%, -22.0% ± 16.7%, -25.8% ± 18.0%, -22.7% ± 20.9%, and -6.6% ± 17.0%, respectively. The 25 μg/cm(2) LBNS reduced IOP in a similar manner. The 25 μg/cm(2) LBNS induced transient hyperemia, whereas the 0.25 and 2.5 μg/cm(2) LBNSs did not exert any local adverse effects. The eye scratching movement test showed that application of 25 μg/cm(2) LBNS did not cause any irritation of the eye. Latanoprost acid was detected in aqueous humor up to 6 days after application of 2.5 μg/cm(2) LBNS. LBNS may be used as a novel antiglaucoma DDS.

Corneal Penetration into Rabbit Aqueous Humor Is Comparable between Preserved and Preservative-Free Tafluprost

Background: Some studies have shown that benzalkonium chloride (BAK), a preservative used in antiglaucoma medications, can increase corneal permeability by acting as a penetration enhancer. Tafluprost is a new prostaglandin F₂_α analog in clinical use for the treatment of ocular hypertension and glaucoma. Methods: This study evaluated the corneal penetration of preservative-free tafluprost 0.0015% eye drops and tafluprost 0.0015% eye drops preserved with 0.01% BAK into the aqueous humor of rabbits. Results: After the administration of a single topical dose (30 μl), the maximum concentrations at 45 min of tafluprost acid in aqueous humor were 4.50 ng/ml for preservative-free tafluprost and 3.99 ng/ml for preserved tafluprost. The area under the concentration-time curves from 45 min to 3 h was 5.14 ng h/ml for the preservative-free formulation and 4.54 ng h/ml for the preserved formulation. Conclusions: These data indicate that BAK does not affect the corneal penetration of tafluprost into the rabbit aqueous humor.

Concentration of hyaluronic acid in primary open-angle glaucoma aqueous humor

We compared the concentration of hyaluronic acid in the aqueous humor of primary open-angle glaucoma (POAG) patients and non-glaucomatous patients. Aqueous humor samples were obtained from 22 patients just before trabeculectomy for clinically uncontrolled POAG (POAG group). Aqueous humor (0·1 mL) was aspirated by inserting a 26-gauge needle into the anterior chamber. The same procedure was performed for 22 non-glaucomatous patients just before cataract surgery (control group). Immediately after collection, the aqueous humor was stored at −20°C. The concentration of hyaluronic acid was determined by a sensitive, noncompetitive and nonisotopic fluoroassay. The median (range) concentrations of hyaluronic acid of the POAG and control groups were 298·4 μg L −1 (99·0–743·7 μg L −1) and 545·1 μg L −1 (145·0–2366·0 μg L −1), respectively. The difference in concentrations of hyaluronic acid between the groups was statistically significant ( P<0·001). In conclusion, the concentration of hyaluronic acid in the aqueous humor in POAG patients is lower than in non-glaucomatous patients. Further studies are necessary to determine the role of hyaluronic acid in the pathophysiology of POAG.

Measurement of Hydrogen Peroxide in Biological Samples Containing High Levels of Ascorbic Acid

The physiological concentration of hydrogen peroxide in the aqueous humor was reported to range between 25 and 60 μM, and conditions leading to elevated levels could have important damaging effects such as cataract formation. However, the high concentration of ascorbic acid in aqueous humor, which is 20 times that of plasma, was recently shown to interfere in the dichlorophenol–indophenol assay for hydrogen peroxide. The actual concentration of hydrogen peroxide in this fluid has become a controversial issue. In the present study, we used the method of ferrous oxidation of xylenol orange (FOX1 assay) performed in a nitrogen atmosphere to accurately measure low levels of hydrogen peroxide, even in the presence of ascorbic acid at concentrations normally found in aqueous humor. Contrary to values reported in the literature, we observed that the concentration of hydrogen peroxide in the rabbit aqueous humor is less than 5 μM, which is the detection limit of the method.

Extracellular glutathione peroxidase and ascorbic acid in aqueous humor and serum of patients operated on for cataract

Patients operated on for cataract (32 men/75 women, aged 50–93 years) were studied with respect to antioxidative agents in aqueous humor and serum. Extracellular glutathione peroxidase (eGSHPx) was demonstrated in aqueous humor for the first time by a radioimmunoassay, the concentration of eGSHPx being 0.66(0.18) mg/l (mean(S.D.)). The concentration of eGSHPx in serum was 3.81(0.84) mg/l, and its level in aqueous humor was 18(7)% of that level. Serum selenium had positive correlations with both serum eGSHPx ( r = 0.34, P < 0.001) and aqueous humor eGSHPx ( r = 0.25, P = 0.011). However, there was no relation between the concentrations of eGSHPx in aqueous humor and in serum, suggesting that the maintenance of eGSHPx levels in the two fluids is controlled by different mechanisms beside selenium status. There was an inverse correlation between age and serum eGSHPx but not with aqueous humor eGSHPx. The concentration of ascorbic acid in aqueous humor was 2.04(0.58) mmol/l, and it was closely correlated to the level of ascorbic acid in serum (0.052(0.032) mmol/l), r = 0.58 ( P < 0.001). The ratio between the level of ascorbic acid in aqueous humor and that in serum was 39(17). There was no significant difference among patients with nuclear ( n = 39), cortical ( n = 20), posterior—subcapsular ( n = 23) or mixed ( n = 23) lens opacity with respect to levels of eGSHPx and ascorbic acid in serum and aqueous humor. Since serum ascorbic acid is related to ascorbic acid intake, its association to aqueous humor ascorbic acid indicates that dietary habits are important for maintaining that level which could play an important role in protecting ocular tissue against oxidative damage. The role of eGSHPx secreted into aqueous humor in the oxidant defence system needs further study.

Determination of Protein Concentration in Aqueous Humor

Accurate determination of protein concentration in the aqueous humor is important in the interpretation of experiments relevant to the pathogenesis and therapy of glaucoma. We made preliminary observations that the high concentration of ascorbic acid in aqueous humor might interfere with commonly used protein determination assays. Therefore, we tested the effect of ascorbic acid upon absorbance in the bicinchoninic acid (BCA), Lowry, and Bradford assays. Ascorbic acid and bovine serum albumin, alone and in combination, were added to BCA, Lowry, and Bradford reagents in 96-well plates. Absorbance was measured at 562 nm (BCA) and 590 nm (Lowry and Bradford). As little as 40 ng and 28 mug of ascorbic acid (typical aqueous humor concentration is 200-400 mug/ml) altered absorbance in the BCA and Lowry assays, respectively. The Bradford assay was not affected by ascorbic acid. Because of the high ascorbic acid and low protein concentration in aqueous humor, assays such as the BCA and Lowry, which are dependent upon oxidation-reduction reactions, must be used with caution. In most situations, the Bradford method is best for determination of aqueous humor protein concentration.

Systemic aminocaproic acid reduces fibrinolysis in aqueous humor.

Systemically administered aminocaproic acid has been demonstrated to reduce the incidence of secondary hemorrhage in traumatic hyphema. To directly determine the concentration of aminocaproic acid in the aqueous humor, four groups of rabbits were studied following administration of four different regimens of intravenously administered aminocaproic acid. Plasma and aqueous humor samples were assayed for drug content and antifibrinolytic activity. Peak aqueous humor concentrations of aminocaproic acid ranged from 2.5 to 33 mg/dL and varied according to the systemic dose administered. The antifibrinolytic activity paralleled the aminocaproic acid content, with a peak range from 310 to 683 s. These findings indicate a direct relationship between antifibrinolytic activity and the concentration of aminocaproic acid in aqueous humor.

Ocular hyperuricosis in the rabbit following hyperuricemia and topical epinephrine.

Sources for the high levels of uric acid reported in the aqueous humor from human glaucoma eyes were studied in the rabbit model. A hyperuricemia was produced by oxonic acid blockade of uricase prior to a systemic administration of uric acid. These animals showed no increase in aqueous humor uric acid. Topical medication of eyes with 1% epinephrine produced a statistically significant (P less than 0.001) rise in the level of uric acid in aqueous humor of treated eyes. Mean urate levels increased from 0.44 mg/dl to 0.82 mg/dl. Topical glaucoma medication appears to be the source of ocular hyperuricosis.

Detection of uric acid in aqueous humor by high pressure liquid chromatography.

The uric acid peak among the compounds in aqueous humor separated by high pressure liquid chromatography was identified by its retention time, the UV absorbance characteristics, and the effect of uricase. The uric acid concentration in the aqueous humor of normal monkey, human eyes with cataract, and human eyes with glaucoma are less than 0.05, 1.7 +/- 0.3, and 3.8 +/- 0.4 respectively. The significance of high uric acid concentration in glaucoma is discussed.

Total Ascorbic Acid in Aqueous Humor and Serum in Indian Patients With and Without Cataract

The total ascorbic acid concentration in aqueous comprising two components, the reduced form asl-ascorbic acid, and the oxidised product, as dehydrol-ascorbic acid,3although very variable, is very much higher than in blood plasma. In various animals, including man, the concentration ratio approximates 6-8:1.* Moreover, recently, it has been found that the concentration of ascorbic acid in the aqueous humor varies approximately as the concentration in the serum, regardless of whether or not the lens is cataractous, the subjects of this investigation being normal patients, aphakic patients, and patients whose lenses were sufficiently opaque to warrant extraction.7The present paper deals with a comparative study of total ascorbic acid in aqueous and serum of Indian patients of three categories: (a) with normal lens, (b) with different types of cataract, (c) with lenses extracted previously. Selection of Patients The selected subjects were first subjected to a thorough examination

Ascorbic acid in aqueous humor and serum of patients with and without cataract; physiologic significance of relative concentrations.

MANY ATTEMPTS have been made to explain how the concentration of ascorbic acid in the aqueous humor is maintained in excess of that in the blood.1Three different mechanisms have been proposed: (1) Ascorbic acid is synthesized by the lens *; (2) ascorbic acid is transported across the ciliary epithelial border in the oxidized state (i. e., as dehydroascorbic acid), where it is reduced to ascorbic acid by the lens †; (3) ascorbic acid is selectively concentrated by the ciliary epithelium, whence it diffuses to the posterior chamber.7‡ The chief evidence in support of the theories that associate the lens with the maintenance of relatively high concentrations of ascorbic acid in the aqueous humor is the observation that the concentration of the acid is less than normal when the lens is cataractous or absent. For instance, reduced concentrations of ascorbic acid in the aqueous humor have been observed