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Biomedical subjects

C F Barfknecht

Publications and source records attributed to C F Barfknecht.

At least 19 recordsLinked to original sources
PubMed1992

Rapid toxicological model for use in assessing ocular drugs.

Nonsteroidal antiinflammatory drugs (NSAIDs) were applied to corneas either by in vitro or in vivo methods. The in vitro method involved excising and mounting corneas in a perfusion system at 37 degrees and exposing drug for 2.5 h. The in vivo methods represent either topical administration to the rabbit eye or topical in vivo infusion using a fixed well which permitted a constant concentration (0.05 per cent) to be applied to the eye of anesthetized rabbits for up to 120 min. An overlay grid procedure using scanning electron microscopy (SEM) showed less per cent endothelial damage with in vivo methods than with the in vitro method of administration, but per cent damage depended on which section was viewed. Damage to the epithelium and endothelium were also assessed by quantitative carboxyfluorescein and Janus green staining and uptake procedures, respectively, following drug exposure by the in vivo infusion method. Results for the epithelium indicated that the more lipophilic NSAIDs damaged the epithelial layer to a greater degree than newly synthesized hydrophilic NSAIDs. Damage to the epithelium correlated to the surface activity of the NSAIDs. Qualitative assessment of epithelial and endothelial toxicity can be performed with SEM and transmission electron microscopy (TEM) while vital staining procedures and the SEM grid procedure can be used to quantitatively assess corneal toxicity. The staining methods, however, possess advantages over SEM and TEM procedures in that they are rapid and do not require laborious preparation. As a result of these characteristics, the vital staining procedures could be used as part of a biopharmaceutical screening technique in evaluating new ophthalmic drugs.

Administration, Topical↗
PubMed1992

Biopharmaceutical evaluation of ibufenac, ibuprofen, and their hydroxyethoxy analogs in the rabbit eye.

Two new structural analogs, 2-(4-hydroxyethoxyphenyl)acetic acid [R3] and 2-(4-hydroxyethoxyphenyl)propionic acid [R4], along with their parent compounds, ibufenac and ibuprofen, were evaluated for their biopharmaceutical properties. The analogs represented substitution of the lipophilic isobutyl side chains of ibufenac and ibuprofen with hydrophilic hydroxyethoxy side chains. Anti-inflammatory activity was evaluated by administering drugs topically to inhibit inflammation induced by using either clove oil or arachidonic acid. The rank order of activity was ibufenac approximately equal to ibuprofen > R3 approximately equal to R4. The new compounds, R3 and R4, were highly water soluble (> 60-fold) and partitioned less (< 1/1500-fold) into the lipid phase when compared to ibufenac and ibuprofen. R3 and R4 each had apparent corneal permeability coefficients of 6 x 10(-6) cm/sec, whereas ibufenac and ibuprofen yielded values of about 22 x 10(-6) cm/sec. In an ocular pharmacokinetic study in the rabbit eye, constant concentrations of each compound were maintained on the cornea in a cylinder or well fixed to the cornea, resulting in a constant input rate. This method circumvented parallel loss routes at the absorption site including nasolacrimal drainage. From area calculations the dispositions of the compounds within the eye were described by mean residence times, steady state volumes of distributions, and clearance rates. R3 and R4 were more slowly absorbed, retained within eye tissues longer, and were cleared more slowly from the eye than ibufenac and ibuprofen. The aqueous humor concentration-time profiles were also computer-fitted to equations representing classical pharmacokinetic models. For ibufenac and ibuprofen, the entire cornea was assumed to be the net barrier for entry into the anterior chamber. Whereas, for R3 and R4, the corneal epithelium and endothelium were presumed to be the diffusional barriers into and out of the stroma, the latter treated as a compartment. Aqueous humor concentrations of each drug fit the models reasonable well and agreed with conclusions made from the use of area calculations. The drop volume method was used to measure the surface tension of each compound. Both ibufenac and ibuprofen were considerably more surface active than R3 or R4. The greater surface tension measured for ibufenac and ibuprofen correlated to the subjective observations of ocular discomfort for these drugs.

Administration, Topical↗
PubMed1992

Biopharmaceutical explanation for the topical activity of 6-hydroxyethoxy-2-benzothiazolesulfonamide in the rabbit eye.

6-Hydroxyethoxy-2-benzothiazolesulfonamide (compound 1), 6-hydrogen-2-benzothiazolesulfonamide (compound 2) and ethoxzolamide (compound 3) are carbonic anhydrase inhibitors, of which only compound 1 is active in lowering intraocular pressure when administered to the rabbit eye. They were compared for potency by inhibiting carbonic anhydrase I (CAase I) using the pH stat procedure. No differences were detected. Binding affinity and number of binding sites were identical; only a single binding site was operative. 14C-labelled compound 1 was used to measure the presence of an ocular metabolite which ranged from 17 to 57% in cornea, iris/ciliary body and aqueous humor. By maintaining drug solutions on either the corneal or conjunctival/scleral surfaces of the eye of anesthetized rabbits for 120 minutes, steady state concentrations of compounds 1-3 were determined in cornea, aqueous humor and iris/ciliary body. It was concluded that compound 1 penetrated both routes equally well and also accumulated at the active site in considerably higher concentrations than compounds 2 and 3. Compounds 2 and 3 did not accumulate in the iris/ciliary body nor did compound 3 penetrate the conjunctival/scleral route very well, approximately 5-20 fold lower than from the corneal route.

Administration, Topical↗
PubMed1991

Characterization of arylamine acetyltransferase in the rabbit eye.

The activity of arylamine acetyltransferase with p-aminobenzoic acid (PABA), sulfamethazine (SMZ), and aminozolamide as substrates was studied in rabbit tissue homogenates of the corneal epithelium, stroma-endothelium, iris-ciliary process, and liver. Rabbits were classified as rapid or slow acetylators with respect to their rate of hepatic acetylation of SMZ. The ocular disposition of aminozolamide in the two phenotypes was compared using a topical ocular infusion method that permitted a constant concentration to remain in contact with the intact cornea. The effect of hepatic-acetylator phenotype on the intraocular pressure (IOP) recovery rate and drug concentrations in tissues after single-dose administration of aminozolamide also was studied. In general, the rank order of arylamine acetyltransferase activity regardless of substrate was liver greater than iris-ciliary process greater than corneal epithelium greater than stroma-endothelium. The specific activity with aminozolamide as substrate was greater than that with SMZ in each tissue homogenate and greater than with PABA as substrate in all tissues except the stroma-endothelium of slow hepatic-acetylator rabbits. Very low enzyme activity ratios for ocular acetylation between rapid and slow hepatic-acetylating rabbits indicated that acetylation in the ocular tissues did not correspond with the acetylation phenotype. At various times during and after topical infusion to the anesthetized rabbit, assay determinations of drug and metabolite in ocular tissues indicated that there were no significant differences between phenotypes in the disposition of either drug or metabolite. These results correlate with the IOP measurements after topical infusion; they also showed no difference in the effect of aminozolamide between hepatic-acetylator phenotypes. These results indicate that the ocular disposition and the decrease in IOP from topical application of aminozolamide is independent of the hepatic-acetylation phenotype in the rabbit. There are significant amounts of acetyltransferase activity in the ocular tissues of the rabbit with these three substrates, indicating that acetylation may be occurring for other arylamine drugs used in the eye.

4-Aminobenzoic Acid↗
PubMed1990

Uptake of muramyl dipeptide fluorescent congeners by normal rabbit bronchoalveolar lavage cells: a study using flow cytometry.

Muramyl dipeptide (MDP) is the minimal adjuvant-active structure of mycobacterial cell walls and is known to activate monocytes/macrophages, but mechanisms involved with uptake and activation of these cells have not been completely defined. Earlier studies addressing uptake of MDP and the question of receptors have utilized radioligands and murine peritoneal macrophages. We used fluorescent congeners of MDP and flow cytometry to explore kinetics and specificity of uptake by bronchoalveolar cells of normal rabbits. Both washed cells and cell suspensions from which the fluorescent congeners were not washed were used, and incubation was carried out primarily at 4 degrees C. Fluorescence microscopy consistently revealed intracellular but no visible membrane fluorescence of alveolar macrophages. Uptake was dose dependent but was not saturable up to concentration limits of fluoresceinated muramyl tripeptide (MTP-FITC) imposed by the system, and was partially inhibited by excess unlabeled MDP, consistent with specific inhibition. Alveolar macrophages, but not lymphocytes, demonstrated specific uptake at 4 degrees C, with rapid on- and off-times. Uptake was enhanced 7-fold at 37 degrees C. Uptake was greater by larger, more granular macrophages than by smaller, less granular macrophages, but no difference in uptake was found when cells of similar size but different densities were compared. The exact mechanism of the rapid uptake at 4 degrees C is uncertain but appears to be competed for by unlabeled MDP.

Acetylmuramyl-Alanyl-Isoglutamine↗
PubMed1990

The effect of flurbiprofen on herpes simplex virus type 1 stromal keratitis in mice.

The use of steroidal compounds to reduce the inflammation and scarring associated with herpes simplex virus type 1 (HSV-1) stromal keratitis can result in severe exacerbation of the corneal disease. We compared the nonsteroidal anti-inflammatory drug (NSAID) flurbiprofen sodium with dexamethasone for the treatment of HSV-1 induced corneal stromal disease in an inbred mouse model. Stromal disease was induced by the direct intrastromal injection of HSV-1. A stromal opacity and corneal neovascularization (CNV) developed in 100% of the injected eyes, with no epithelial involvement until late in the course, when the stromal disease was quite severe, such that it was possible to test the effectiveness of drugs in animals with an intact epithelium. Dexamethasone treatment had a variable effect on the severity of disease, ranging from a significant reduction in severity to significant exacerbation of disease, compared with placebo-treated controls. The most frequent effect of dexamethasone treatment was a worsening of corneal stromal opacities and CNV. In contrast, treatment with the NSAID did not exacerbate HSV-1 stromal disease. Flurbiprofen treatment resulted in a significant reduction of the maximum intensity of stromal opacity in some experiments, whereas in other experiments the effect was not statistically significant. In vitro studies of the effect of the anti-inflammatory drugs on HSV-1 replication in Vero cells revealed that both dexamethasone and flurbiprofen inhibited HSV-1 replication in a dose-dependent manner. Flurbiprofen had a greater inhibitory effect, which appears to be due, at least in part, to a direct virucidal effect. Dexamethasone did not exhibit virucidal activity.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1988

Synthesis of fluorescent muramyl dipeptide congeners. 2.

Muramyl dipeptide (MDP) analogues were prepared and utilized in the synthesis of new fluorescently labeled MDP derivatives for use as biologic probes. Thus, N alpha-(N-acetylmuramyl)-L-lysyl-D-isoglutamine (Lys-MDP, 4) and N alpha-(N-acetylmuramyl)-L-alanyl-D-isoglutaminyl)-L-lysine [MTP, 5] were synthesized and then reacted with 2-(fluoresceinylamino)-4,6-dichloro-s-triazine (DTAF, 2) to yield the fluorescent adducts, DTAF-Lys-MDP (6) and DTAF-MTP (7). The adjuvant activity of the fluorescent MDP derivatives was determined by the ability of the compounds to promote delayed skin test responses in guinea pigs immunized with ovalbumin (OA) and by evaluating the anti-OA activity of these guinea pigs.

Acetylmuramyl-Alanyl-Isoglutamine↗
PubMed1988

Aminozolamide suspension: the role of the vehicle in a topical carbonic anhydrase inhibitor.

Aminozolamide (6-amino-2-benzothiazolesulfonamide) is a carbonic anhydrase inhibitor derived from ethoxzolamide that has been shown in gel formulation to lower IOP in rabbits, primates and humans. This study was designed to determine whether aminozolamide in suspension was also effective in lowering IOP. In separate single dose and multiple dose studies, patients with ocular hypertension were tested over 24 hours. No statistically significant drop in intraocular pressure was noted between the treated and control eye. In addition, conjunctival injection was noted in three of eleven subjects after multiple dosing. These studies suggest that retention of aminozolamide at the active site is inadequate when delivered in a suspension vehicle. In the past 10 years, efforts to develop an effective topical carbonic anhydrase inhibitor have been vigorously pursued. This has been aided by advancements in drug delivery and chemical synthesis involving molecular modification of existing carbonic anhydrase inhibitors. Various compounds have been developed that retain carbonic anhydrase inhibitory activity, penetrate the cornea and optimize the other important pharmacokinetic properties to lower intraocular pressure. One such compound, aminozolamide (6-amino-2-benzothiazolesulfonamide) is derived from ethoxzolamide. In suspension, it has been shown to lower IOP in rabbits and primates. It also has been shown to lower IOP in patients with ocular hypertension when delivered in a gel vehicle. The carbomer gel vehicle, a drug delivery system also used with pilocarpine (Pilopine HS), is used to prolong ocular contact and enhance penetration. The importance of the role of the vehicle in a topical carbonic anhydrase inhibitor has not been assessed.(ABSTRACT TRUNCATED AT 250 WORDS)

Administration, Topical↗
PubMed1987

Ocular disposition of aminozolamide in the rabbit eye.

We have previously determined that 6-amino-2-benzothiazolesulfonamide (aminozolamide) significantly lowers IOP in rabbits and, more importantly, in ocular hypertensive human subjects. Results from in vitro experiments established that both the inhibitory activity of aminozolamide against carbonic anhydrase B as well as the penetration rate across excised rabbit corneas were equivalent to ethoxzolamide. Consequently, we have investigated the ocular disposition of aminozolamide to explain its activity when instilled topically to the eye. A constant concentration of 67.4 micrograms/ml of drug was applied for 90 min to the left eye of anesthetized rabbits. Drug and metabolite were measured in both aqueous humor and iris/ciliary body over time. The metabolite was collected and purified. Identification using mass spectroscopy, high pressure liquid chromatography (HPLC) and fluorescence scans indicated that the metabolite was 6-acetamido-2-benzothiazolesulfonamide. Relatively high levels of metabolite were identified in the cornea and iris/ciliary body but were much lower in aqueous humor. Tissue concentrations over time for the metabolite in iris/ciliary body were approximately 2-fold higher than levels of metabolite measured in aqueous humor. When compared to drug levels measured in either aqueous humor or iris/ciliary body, metabolite levels in these respective tissues were much higher. It is hypothesized that topical activity is a consequence of both metabolite retention in the iris/ciliary body as well as inhibition of 99+% of carbonic anhydrase. Both of these events must occur over a sufficient time period to effect a significant lowering of IOP.

Animals↗
PubMed1986

Aminozolamide gel. A trial of a topical carbonic anhydrase inhibitor in ocular hypertension.

A topical carbonic anhydrase inhibitor, 6-amino-2-benzothiazolesulfonamide (aminozolamide), which is an analogue of ethoxzolamide, was studied in 18 patients with ocular hypertension. Significant lowering of intraocular pressure was achieved with a single 50-microL gel application compared with the untreated control eye. The onset of action occurred within two hours and lasted at least eight hours. No systemic side effects were elicited. Topical carbonic anhydrase inhibitors may be an important alternative in the medical management of glaucoma.

Administration, Topical↗
PubMed1986

N-Substituted sulfonamide carbonic anhydrase inhibitors with topical effects on intraocular pressure.

N-Methylacetazolamide was shown to be active topically in reducing intraocular pressure (IOP) to a small but statistically significant level in the normotensive rabbit eye. In vivo experiments with N-methylacetazolamide suggest that ocular metabolism to acetazolamide was responsible for the observed topical activity. Examination of initial rate kinetics of carbonic anhydrase catalyzed p-nitrophenyl acetate hydrolysis showed that N-methylacetazolamide was a competitive inhibitor, in contrast to noncompetitive inhibition seen with acetazolamide and other primary sulfonamide inhibitors. N-Substituted and unsubstituted 4-chlorobenzene- and 4-nitrobenzenesulfonamides were also synthesized, and their biochemical characteristics and in vivo ability to lower IOP when applied topically were determined. The primary sulfonamides were reversible noncompetitive inhibitors of carbonic anhydrase, with no effect on IOP after topical administration. 4-Nitrobenzene- and 4-chlorobenzenesulfonamides containing both N-hydroxy and N-methyl substituents were model irreversible inhibitors of carbonic anhydrase and exhibited a trend toward topical activity in reducing IOP in normotensive rabbit eyes. Therefore, this paper describes the synthesis and characterization of two types of carbonic anhydrase inhibitors; the N-methyl-substituted sulfonamides are reversible competitive inhibitors of carbonic anhydrase, while the N-hydroxy-N-methyl-substituted sulfonamides are irreversible inhibitors.

Administration, Topical↗
PubMed1985

Topical carbonic anhydrase inhibitors. III: Optimization model for corneal penetration of ethoxzolamide analogues.

An analogue series representing modification to the benzene ring of ethoxzolamide has been evaluated for solubility, pKa, partitioning, and permeability across excised rabbit corneas. These physical parameters were correlated to Hammett sigma (para) and/or Hansch pi parameter values for each compound. From these correlations, a mathematical model was developed relating corneal permeability to molecular modifications of ethoxzolamide. A three-dimensional plot of maximum attainable penetration rate versus sigma (para) and pi yielded an optimal range of pi and sigma values from which an optimally penetrating analogue could be designed.

Absorption↗
PubMed1985

Topical carbonic anhydrase inhibitors IV: Relationship between excised corneal permeability and pharmacokinetic factors.

Ethoxzolamide (1) and two analogues, representing a hydroxyethoxy and a hydrogen substitution on the 6-position of the benzene ring (2 and 3), were applied to rabbit eyes using a topical infusion method designed to provide a constant rate into aqueous humor. Statistical-moment theory was applied to the topical infusion data to describe disposition of each compound within the rabbit eye. For each analogue, it was possible to compare the corneal absorption rate constant (ka), aqueous humor elimination rate constant (k10), disposition mean residence time (MRTd), apparent steady-state volume of distribution (Vdss), and total ocular clearance (Qe). In vivo ocular ka values were related to maximum in vitro corneal penetration rates determined across excised rabbit corneas. In particular, 2 had a much longer residence time and a slower clearance than 1 and 3, which may be responsible for its ability to lower intraocular pressure when dosed topically to the rabbit eye, whereas 1 and 3 show no activity.

Administration, Topical↗
PubMed1979

N-demethylation of nicotine and reduction of nicotine-1'-N-oxide by Microsporum gypseum.

Several microorganisms were examined for their abilities to convert S-nicotine into nornicotine. Five microorganisms including Microsporum gypseum (ATCC 11395) produced nornicotine and three unknown metabolites. M. gypseum efficiently reduced nicotine-1'-N-oxide to nicotine, but no nornicotine was obtained when the N-oxide was used as substrate.

Chemical Phenomena↗
PubMed1978

Inhibition of apomorphine-induced behaviors by derivatives of 2-amino-1, 2, 3, 4-tetrahydronaphthalene.

In order to elucidate the pharmacological properties of a series of 1-phenyl-2-aminopropane and 2-amino-1, 2, 3, 4-tetrahydronaphthalene derivatives, their ability to inhibit a number of apomorphine-induced behaviors was investigated. Several members of the series under study were potent inhibitors of apomorphine-induced pecking behavior in pigeons, emesis in dogs, and gnawing in rats. In addition, these compounds were able to inhibit responding in self-stimulating rats and to a lesser degree counteracted the depression of the linguomandibular reflex induced by 5, 6-dihydroxy-2-dimethylamino-1, 2, 3, 4-tetrahydronaphthalene (M-7) in the cat. The most effective member of the experimental compounds was N-methyl-5, 8-dimethoxy-2-amino-1, 2, 3, 4-tetrahydronaphthalene; however, neither this material nor any of the related structures were able to inhibit apomorphine-induced rotational behavior in substantia nigra lesioned rats. The possibility that the more effective members of the experimental series are able to inhibit certain apomorphine-induced behaviors by stimulation of central alpha adrenergic receptors is discussed.

Animals↗
PubMed1978

Aminotetralin analogs of methoxamine as potential hypertensive agents.

Cardiovascular effects of methoxamine and some aminotetralin derivatives (5,8-ADT, DR-31 and DR-17) were studied after systemic intravenous or intraarterial injection into different perfused vascular beds in anesthetized dogs. Intravenous administration of the compounds produced dose-related prolonged increases in blood pressure, which were antagonized by phentolamine. After intro-arterial injection into the perfused hindlimb, mesenteric artery or the saphenous vein, all compounds produced dose-dependent increases in perfusion pressure indicative of vasoconstriction. Phentolamine antagonized these effects. It was demonstrated that desipramine significantly reduced the vasoconstricting actions of intra-arterially injected tyramine in the hindlimb, but did not alter the responses induced by methoxamine and the aminotetralin derivatives. The data indicate that these compounds elicit peripheral vasoconstriction in the dog, through a direct action on the alpha adrenergic receptors.

Animals↗