Charles F. Barfknecht

Magnetic resonance (MR) image enhancement compounds for specific areas of the brain

An improved imaging technique involving nuclear magnetic resonance. Known drug or neurotransmitter receptor ligands are covalently bound to magnetic resonance image enhancing spin label compounds, such as sterically hindered free radical nitroxide compounds, with the resulting adduct being administered to a patient, and thereafter when the ligand is bound to specific receptor sites in the soft tissue such as the brain, regional tissue area is assessed with nuclear magnetic resonance, allowing diagnostic discrimination.

The Role of Tear Proteins in Tear Film Stability in the Dry Eye Patient and in the Rabbit

Sigma receptors have been identified in the lacrimal glands of rabbits; stimulation of these receptors results in the modulation of protein secretion from acinar cells. 1–4 When acinar cells were incubated with various sigma ligands, it was established that increases and decreases in protein release could be used to identify agonists and antagonists.4 Following the application of a newly designed agonist, N,N-dimethyl-2-phenylethylamine HC1 (AF2975), to the rabbit eye, a statistically significant increase in total protein was observed, when compared to either baseline values or the fellow eye.3 Tears were collected, and protein fractions were separated into various fractions with the use of size-exclusion high-pressure liquid chromatography (SE-HPLC).4 In particular, a 23 min protein fraction (about 16–18 kDa) was found to increase by 150% and 90% at 10 and 60 min, respectively following the topical application of AF2975 (50 μl of 0.15%) to the rabbit eye. Other protein peaks also showed an increase, but much less than the 23 min peak. Following desalting and concentrating, it was possible to separate the 23 min protein peak from rabbit tears into five isoforms using isoelectric chromatofocusing and a protein standard with a pI of 4.6. The isoforms were acidic with pIs higher than 4.6; however, the 23 min protein peak has not been specifically identified, which would require determination of its amino acid sequence. The function of the small-molecular-weight 23 min protein fraction is not known, but has been contrasted to the human tear fraction commonly referred to as tear-specific prealbumin (TSP) or as proteins migrating faster than albumin (PMFA).5–7

Comparative effects of stereoisomers of psychotomimetic phenylisopropylamines

Abstract Stereoisomers, R(−) and S(+), of five psychotomimetic phenyliso-propylamines contracted isolated strips of sheep umbilical arteries. The compounds exhibited the following order of potency: 2,5-dimethoxy-4-bromo-amphetamine (DOB) > 2,5-dimethoxy-4-ethyl-amphetamine DOET) > 2,5-dimethoxy-4-methyl-amphetamine (DOM) > 2,5-dimethoxy-amphetamine (2,5-DMA) > 4-methoxy-amphetamine (PMA). Stereoselectivity was observed in that the R(−) isomers were more active than the S(+) isomers except for PMA. Evidence was obtained for the action of these hallucinogens on 5-hydroxytryptamine receptors. There was a general correlation of smooth muscle stimulating activity with known hallucinogenic activity.

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 ≅ ibuprofen > R3 ≅ 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 6×10−6cm/sec, whereas ibufenac and ibuprofen yielded values of about 22×10−6cm/sec. In an ocular pharmacokinetic study in the rabbit eye, constant concentrations of each compound were maintained on the cornea in a cylinder or welt 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.

Sedative and analgesic actions of methoxylated 2-aminotetralins; involvement of α1- and α2-adrenoreceptors

Abstract Three 5,8-dimethoxylated derivatives of 2-aminotetralin (2-AT) were compared with clonidine, methoxamine and phenylephrine in tests for sedation (inhibition of exploratory activity) and analgesia. In both tests the 2-AT derivatives were less potent than clonidine, but more potent than methoxamine or phenylephrine. Antagonism of the 2-AT derivative, DR-31, and clonidine by yohimbine in both tests argues for the involvement of α 2 -adrenoreceptors in the mediation of these behavioral effects. α 1 -Adrenoreceptors also mediate an inhibition of exploratory activity since the inhibition induced by methoxamine was antagonized by phenoxybenzamine (POB) but not by yohimbine. The methoxylated 2-AT derivatives, which have previously been shown to exert potent peripheral α 1 -agonism are now demonstrated to have sedative and anlgesic effectscharacteristic of central α 2 -adrenergic stimulation.

The effects of sigma ligands on protein release from lacrimal acinar cells: a potential agonist/antagonist assay.

Sigma receptor antagonists have been proposed as leading clinical candidates for use in various psychotic disorders. Prior to clinical testing, it is imperative that a new agent be correctly identified as an antagonist and not an agonist since the latter may worsen the psychosis. For sigma-ligands many behavioral and pharmacological assays have been developed in an attempt to classify agonist/antagonist activity. These assays evaluate a response or a behavior in an animal model that can be related to clinical efficacy. However, is the action by the presumed antagonist a consequence of sigma-receptor activity? Previously we have identified sigma-receptors in acinar cells of the main lacrimal gland of the New Zealand white rabbit and have measured protein release after the addition of various N,N-disubstituted phenylalkylamine derivatives known to be sigma-ligands by receptor binding studies. Although protein release from acinar cells has been attributed to either muscarinic or alpha-adrenergic stimulation, protein release from sigma-receptor stimulation was also confirmed. In the reported studies here, we isolated and incubated acinar cells with varying concentrations of known sigma-ligands and measured protein concentration. A knowledge of the receptor profile for the disubstituted phenylalkylamines permitted experiments to be designed in which various alpha, muscarinic, serotonergic, and dopaminergic antagonists could be added in equimolar concentrations. Under the conditions of these experiments, statistically significant increases in protein release for sigma-ligands could be attributed to stimulation of sigma-receptors. Haloperidol, an apparent sigma-antagonist, caused a statistically significant decrease in protein release and also inhibited protein release when tested with a known sigma-ligand, AF2975 [N,N-dimethyl-2-phenylethylamine]. In this system, stimulation and inhibition of protein release were defined as agonist and antagonist behavior, respectively. Of particular interest were the results for BMY14802 and +/- pentazocine, both of which were found to be agonists. Various antipsychotic and antidepressant drugs were measured for their agonist/antagonist behavior. Because of multireceptors present in acini, their agonist or antagonist behaviour could not be attributed solely to interaction with the sigma-receptor unless specific antagonists were added.

Identification of Sigma Receptors in Lacrimocytes and their Therapeutic Implication in Dry Eye Syndrome

Bromhexine (BH), an oral mucolytic, has shown potential for treating Sjogren’s Syndrome and particularly Keratoconjunctivitis Sicca (KCS). Studies of both oral formulations (Linstow et al., 1990; Avisar, 1988) and ophthalmic drops (0.2% w/v: Rosman, 1974; Thumm, 1978) have been reported. The low aqueous solubility (≈ 0.2% w/v) of BH precludes adequate ophthalmic bioavailability of BH. In this work, we have designed soluble BH derivatives to rapidly penetrate the accessory glands in the conjunctival stroma in order to improve to topical effectiveness. Histologically, the accessory lacrimal glands are identical to the main lacrimal glands (Gillette et al., 1980) making the former a logical therapeutic target. The in vitro and in vivo protein and tear secretion resulting from stimulation of rabbit lacrimal gland is reported here for our BH derivatives.

Serotonin antagonists for use as antiglaucoma agents and their ocular penetration

Abstract A previously unrecognized pharmacophore, 1-phenylpiperidine, has been found to lower intraocular pressure 25–30% in the recovery rate rabbit model. The compounds studied were piperidine, piperazine, morpholine and diethylamide derivatives. In a bioreceptor screening assay, 1-phenylpiperidine was classified as a serotonergic ligand, which based upon its IOP activity, is believed to be a serotonin antagonist. Physicochemical measurements were determined for selected derivatives which were also measured for excised corneal, scleral and conjunctival permeability. Penetration to various ocular tissues was determined after applying a constant concentration of derivative to either corneal or conjunctival/scleral routes of administration. Solutions of selected derivatives were applied with the use of a cylindrical well affixed to the cornea of an anesthetized white rabbit. After 2 h, concentrations of derivative were measured in cornea, aqueous humor, conjunctiva/sclera, iris/ciliary body and lens. For the derivatives tested, the more lipophilic compounds attained a higher permeability coefficient for either the cornea, sclera or conjunctiva. The more lipophilic derivatives also distributed in higher concentrations to cornea, aqueous humor, sclera/conjunctiva and lens, but not necessarily to iris/ciliary body, particularly when administered by the conjunctival/scleral route. The addition of certain functionalities to piperidine or piperazine ring structures significantly affected, confirmed by Costagliola et al. [4] , but disputed by Mallorga and Sugrue [2] .