Comparative effects of the nonsteroidal anti-inflammatory drug nepafenac on corneal sensory nerve fibers responding to chemical irritation

PURPOSE

To compare the corneal analgesic efficacy of the nonsteroidal anti-inflammatory drugs (NSAIDs) nepafenac, diclofenac, and ketorolac, and to evaluate the possibility that their inhibitory effects on corneal polymodal nociceptor fiber activity are partly mediated by a decrease in sodium currents.

METHODS

Corneal sensory afferent units were recorded in the anesthetized cat. The response of thin myelinated polymodal nociceptor fibers to mechanical and acidic stimulation (98.5% CO(2)) was recorded before and at various times after topical application of the vehicle or of nepafenac 0.1% (Nevanac; Alcon Laboratories, Ltd., Fort Worth, TX), diclofenac 0.1% (Voltaren; Novartis, Basel, Switzerland), and ketorolac 0.4% (Acular LS; Allergan, Irvine, CA). Voltage-clamp recordings were performed in cultured trigeminal ganglion neurons.

RESULTS

Nepafenac, diclofenac, and ketorolac reduced the mean frequency of the impulse response evoked by repeated CO(2) stimuli in polymodal nociceptor fibers. The progressive increase in ongoing activity, observed in vehicle-treated eyes after repeated acidic stimulation was also prevented. Nepafenac exhibited a more rapid and a slightly more pronounced effect on spontaneous and CO(2)-evoked activity than did diclofenac and ketorolac and did not affect the responsiveness of corneal mechanonociceptor or cold receptor fibers. In cultured mice trigeminal ganglion neurons, diclofenac significantly suppressed sodium currents, whereas nepafenac or its metabolite, amfenac, exhibited only minimal inhibitory effects.

CONCLUSIONS

The inhibition of polymodal nociceptor activity by nepafenac, a weak inhibitor of cyclooxygenase, is most likely due to its greater lipophilicity compared with diclofenac and ketorolac, leading to a rapid saturation of the corneal epithelium where nociceptor terminals are located. In contrast to diclofenac, nepafenac does not exhibit local anesthetic effects.

Evidence for a Clathrin-Mediated Recycling of Albumin in Human Term Placenta1

During human pregnancy, the trophoblast layer is in direct contact with maternal albumin. In contrast to immunoglobulins, albumin does not cross the placental barrier. However, albumin affects the trophoblast placental lactogen and chorionic gonadotroph secretion. The present study investigated the interaction between albumin and syncytiotrophoblast using human term placental explants. Bovine serum albumin, labeled with either 125I or fluorescein isothio-cyanate, was taken up rapidly by placental explants. This process was temperature-sensitive. The internalized labeled BSA quickly outflowed from the tissue at the maternal side, largely without any major modification in molecular weight. Colchicine (1 mM), which disrupts the microtubule network, or cytochalasin B (40 microM), which disassembles filamentous actin, did not interfere with the placental transmembrane movements of labeled BSA. Megalin, clathrin, and caveolin 1 are three membrane proteins associated with albumin endocytosis in other tissues, but only megalin and clathrin were detected in the syncytiotrophoblast layer by immunohistochemistry. The uptake of labeled BSA into placental explants was not modified by 4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid (1 mM) or 5-nitro-2-(3-phenylpropylamino)benzoic acid (100 microM), two pharmacological tools known to disturb megalin-mediated albumin endocytosis. By contrast, methyl-beta-cyclodextrin (10 mM) and chlorpromazine (1.4 mM), both of which disrupt the clathrin-mediated endocytotic system, significantly reduced the uptake of labeled BSA. These data suggest, to our knowledge for the first time, that maternal albumin is actively internalized into the human trophoblast according to an apical recycling pathway. This temperature-sensitive process does not depend on an intact cytoskeleton, but it is associated with a clathrin-mediated endocytotic system.

Mitochondrial iPLA2 Activity Modulates the Release of Cytochrome c from Mitochondria and Influences the Permeability Transition

The mitochondrial Ca(2+)-independent phospholipase A(2) is activated during energy-dependent Ca(2+) accumulation under conditions where there is a sustained depression of the membrane potential. This activation is not dependent on induction of the mitochondrial permeability transition. Bromoenol lactone, which inhibits the phospholipase, is effective as an inhibitor of the transition, and this action can be overcome by low levels of exogenous free fatty acids. Apparently, activation of the Ca(2+)-independent phospholipase is a factor in the mechanisms by which depolarization and Ca(2+) accumulation promote opening of the permeability transition pore. Sustained activity of the Ca(2+)-independent phospholipase A(2) promotes rupture of the outer mitochondrial membrane and spontaneous release of cytochrome c on a time scale similar to that of apoptosis occurring in cells. However, more swelling of the matrix space must occur to provoke release of a given cytochrome c fraction when the enzyme is active, compared with when it is inhibited. Through its effects on the permeability transition and release of intermembrane space proteins, the mitochondrial Ca(2+)-independent phospholipase A(2) may be an important factor governing cell death caused by necrosis or apoptosis.

Colloidal effect of albumin on the placental lactogen and chorionic gonadotrophin releases from human term placental explants

Albumin has been reported to stimulate the release of placental lactogen and chorionic gonadotrophin from human term placental explants within physiological concentrations. This study aimed at characterizing further its effect on the placental hormonal secretion. The placental lactogen and chorionic gonadotrophin secretory response of incubated explants to 5% albumin was reproduced by colloidal agents, i.e., dextran (4.5%) and polygelin (4%), indicating that a rise in colloidal osmotic pressure can elicit hormonal release from the syncytiotrophoblast. Their secretory effects were not modified by the absence of extracellular calcium or the presence of verapamil in the medium. The three agents also provoked a marked increase in (45)calcium outflow from preloaded and perifused explants that persisted in absence of extracellular calcium. These data indicate that the triggering effect of albumin on placental lactogen and chorionic gonadotrophin release can be partly reproduced by colloidal agents and is independent of extracellular calcium.

Interactions of olopatadine and selected antihistamines with model and natural membranes

OBJECTIVE

Olopatadine, an effective topical ocular human conjunctival mast cell stabilizer/antihistaminic antiallergic drug, was evaluated and compared to selected classical antihistamines for their interaction with model and natural membranes to ascertain potential functional consequences of such interactions.

METHODS

The model membranes examined consisted of the argon-buffer interface and monomolecular films of 1-stearoyl-2-oleoyl-sn-glycero-3-phosphocholine (SOPC) at the argon-buffer interface. Interactions with the model membranes were detected as changes in surface tension, i.e., surface pressure. Functional consequences of these interactions were assessed with natural membranes by 6-carboxyfluorescein leakage, hemoglobin release, lactate dehydrogenase release, and histamine release from appropriate cell types.

RESULTS

Measurements at the argon-buffer interface revealed intrinsic surface activity for all agents that ranged from highly surface-active to weakly surface-active in the order of: desloratadine > clemastine > azelastine congruent with ketotifen > diphenhydramine> pyrilamine > emedastine > epinastine > or = olopatadine. This order of amphipathic behavior was confirmed for most of the compounds by estimates of their dissociation constants (K(d,L)) determined from interactions with SOPC monolayers adjusted to a surface pressure approximating that of natural membranes. Epinastine was the only antihistamine that showed a disproportionately greater increase in surface activity toward SOPC in monolayer when compared to other antihistamines. Dissociation constants could not be established for olopatadine because of its low affinity for both the argon-buffer interface and the SOPC monolayer. Functional consequences of these interactions were assessed with natural membranes by 6-carboxyfluorescein leakage (erythrocyte ghosts), hemoglobin release (erythrocytes), lactate dehydrogenase release (conjunctival mast cells, corneal epithelial cells), and histamine release (conjunctival mast cells). Aside from olopatadine and emedastine, all antihistamines promoted a concentration-dependent leakage of hemoglobin from intact erythrocytes. The concentration of drug required to cause half-maximal hemoglobin release (H(50)) from erythrocytes correlated linearly (r = 0.98) with the SOPC dissociation constants (K( d,L)) estimated for the different antihistaminic agents interacting with SOPC monolayers. A similarly high correlation (r = 0.85) emerged from a plot with a slope approaching unity that related drug concentrations required for half-maximal hemoglobin leakage from erythrocytes to threshold doses of drug that caused histamine release from human conjunctival mast cells. Olopatadine was the only agent that did not promote membrane perturbation as monitored by either hemoglobin release from intact erythrocytes, LDH release from human conjunctival mast cells, or 6-carboxyfluorescein release from erythrocyte ghosts. Assessment of the lytic potential of marketed concentrations of ketotifen (0.025%), azelastine (0.05%), and epinastine (0.05%) revealed significant membrane perturbation of human conjunctival mast cells and, importantly, human corneal epithelial cells as indexed by LDH release. This was in contrast to marketed concentrations of olopatadine (0.1%) which maintained normal mast cell and corneal epithelial cell membrane function.

CONCLUSIONS

Combined, these results support the notion that the disruption of natural cell membranes by surface-active antihistamines occurs not through a receptor-mediated process, but is the consequence of a direct interaction of these agents with the cell membrane. This is corroborated by surface pressure-concentration isotherms for adsorption of five different antihistaminic agents to SOPC monolayers where 50% lysis occurred at a surface pressure of 42.9 +/- 1.1 mN/m. Olopatadine appears to be unique among the agents tested by demonstrating low intrinsic surface activity, thus limiting its interaction with natural membranes. At concentrations of about half-maximal compound solubility (, 5.0 mM or a 0.19% drug solution), olopatadine generated SOPC monolayer surface pressures (i.e., 39.82 +/- 0.10 mN/m) that were below those that promoted membrane perturbation and onset of hemoglobin leakage. Olopatadine's restricted interaction with membrane phospholipids limits the degree of membrane perturbation and release of intracellular constituents, including histamine, LDH, and hemoglobin, which is believed to contribute to olopatadine's topical ocular comfort and patient acceptance.

AL-2512, a novel corticosteroid: preclinical assessment of anti-inflammatory and ocular hypertensive effects

The anti-inflammatory efficacy and ocular hypertensive effect of AL-2512 were characterized in rodent and feline models of ocular inflammation. Neutrophil influx into ocular tissue following topical ocular administration of test drugs was evaluated in models of endotoxin-induced uveitis. In rats, the anti-inflammatory efficacy of AL-2512 was compared with that of 0.1% dexamethasone. Test drug or vehicle was administered topically before subplantar injection of endotoxin. Neutrophil influx was assessed at 24 hours. Feline eyes, injected intravitreally with endotoxin, were treated topically with 0.1% AL-2512, 1.0% prednisolone acetate or vehicle at various timepoints before and after endotoxin injection. At 12 hours, protein concentration and leukocyte count in aqueous humor were determined. In the feline intraocular pressure (IOP) model, after baseline IOP values were established, AL-2512, dexamethasone, or vehicle was administered topically to both eyes of cats. IOP was measured daily before and during treatment. Topical ocular administration of AL-2512 inhibited endotoxin-induced leukocyte influx in rodent and feline models of uveitis. In rats, AL-2512 significantly inhibited neutrophil influx by 89%, compared with 93% by dexamethasone. In feline eyes, AL-2512 significantly (p < 0.05) inhibited leukocyte infiltration of aqueous humor by 59%, compared to 37% inhibition by prednisolone acetate. Intraocular pressure in cats treated for 32 days with AL-2512 or dexamethasone increased 6% and 18%, respectively. The ocular anti-inflammatory effect of AL-2512 was equivalent to dexamethasone and superior to prednisolone acetate in rat and feline models of ocular inflammation, respectively. This steroid provides anti-inflammatory efficacy equivalent to dexamethasone with a reduced risk of inducing ocular hypertension.

The hydrolysis of the prostaglandin analog prodrug bimatoprost to 17-phenyl-trinor PGF2alpha by human and rabbit ocular tissue

Bimatoprost (Lumigan), the ethyl amide derivative of the potent prostaglandin FP agonist 17-phenyl-trinor PGF(2alpha), has been reported to be a member of a pharmacologically unique class of ocular hypotensive agents. To confirm that bimatoprost, which is intrinsically active as an FP prostaglandin agonist, is also a prostaglandin analog prodrug, the hydrolysis of bimatoprost by ocular tissues was studied by incubating solutions containing bimatoprost with either human or rabbit ocular tissue. The ethyl amide group of bimatoprost was hydrolyzed by rabbit and human cornea, iris/ciliary body and Thasclera to produce the expected carboxylic acid product, 17-phenyl-trinor PGF(2alpha). The rate of hydrolysis by human and rabbit cornea and iris/ciliary body is similar, whereas the rate of hydrolysis by the sclera is slower in humans than in rabbits. These studies show that human and rabbit ocular tissue (cornea, iris/ciliary body and sclera) can convert bimatoprost to the potent prostaglandin FP agonist 17-phenyl-trinor PGF(2alpha). Separate in vitro studies clearly show that both bimatoprost and 17-phenyl-trinor PGF(2alpha) have affinity for and are agonists at the human FP receptor. Taken together, the data strongly suggests that the ocular hypotensive effect of bimatoprost can be attributed to its activity as a prostaglandin receptor agonist either directly or through its role as a prostaglandin agonist prodrug.

Characterization of the in vitro anti-inflammatory activity of AL-5898 and related benzopyranyl esters and amides

Selected ester- (AL-5898 and AL-8417) and amide-linked benzopyran analogues (AL-7538 and AL-12615) were evaluated in vitro for their ability to inhibit key enzymes/processes of the inflammatory response. AL-7538 and AL-12615 exhibited weak intrinsic cyclooxygenase inhibitory activity (IC50 = 13 microM, 37 microM). In contrast, 5-HETE and LTB4 synthesis in A(23187)-stimulated neutrophils was effectively inhibited by both ester and amide analogs (IC50 = 2-3 microM). While there was some indication for differing sensitivities among benzopyran esters and amides in the suppression of cytokine synthesis in stimulated U-937 cells, there appeared to be no great discrimination when assessing their effect on U-937 cell adhesion to IL-1beta activated HMVEC-L cells. Inhibition of cell adhesion was concentration-dependent, with IC50 values ranging between 18 microM and 30 microM for AL-5898. Concentration-dependent inhibition of inflammatory cytokine production (i.e., IL-1beta, TNF-alpha, GM-CSF and IL-6) was also apparent in LPS-stimulated, cultured PBMC as well as in PMA/A(23187) activated U-937 cells monitoring the synthesis of IL-1beta, IL-8, TNF-alpha, and MCP-1. Notably, the hydrolysis products of the benzopyranyl ester, AL-5692 and (S)-6-methoxy-alpha-methyl-2-naphthaleneacetic acid, were devoid of pharmacological activity when assessed for inhibition of monocyte adhesion or IL-1beta synthesis. Collectively, our data demonstrate the unique in vitro polypharmacology of a novel series of benzopyran analogs that suppress pivotal enzymes and processes in the inflammatory response.

Suppression of post-vitrectomy lens changes in the rabbit by novel benzopyranyl esters and amides

This study reports for the first time a therapeutic modality for the suppression of posterior subcapsular cataract (PSC) formation in an animal model (rabbit) of vitrectomy. This therapeutic modality may also have the potential to attenuate/prevent the high incidence of loss of vision due to cataract formation in patients that undergo vitrectomy. Unilateral, partial vitrectomy was performed on 2.5 month old Dutch Belted rabbits with vitreous replaced by either commercially available BSS((R)) or BSS PLUS((R)) (n=16). Alternatively, vitreous was replaced with a proprietary, modified BSS PLUS((R)) irrigating solution containing 1.25 microM AL-8417 (n=12), 5.0 microM AL-12615 (n=5) or 5.0 microM AL-17052 (n=9). Age matched, non-operated rabbits were used as controls (n=16). Lenses were analysed by correlative structural (light, scanning electron microscopic and three-dimensional computer-assisted drawings) and optical (low power helium-neon laser scan) quality analysis 6 months following surgery. Results demonstrate that vitreous replacement with an irrigating solution that contains the ester-linked benzopyran, AL-8417, the amide-linked benzopyran pro-drug, AL-17052, or its active metabolite, AL-12615, prevented abnormal post-vitrectomy lens growth, or fiber formation. Focal length variability (FLV) assessments (sharpness of focus) confirmed the beneficial drug effects detected morphologically, with FLV being essentially equal to that of age-matched, non-surgical controls. In contrast, lenses of animals with vitreous replaced solely with BSS((R)) or BSS PLUS((R)) exhibited significantly higher FLV than both age-matched controls and animals that underwent vitrectomy with drug-containing irrigating solutions. The ability of AL-8417, AL-17052 and its active metabolite, AL-12615, to suppress vitrectomy-induced posterior lens fiber changes appears to reside in their unique pharmacological profile, acting as antioxidant, anti-inflammatory and cytostatic agents.

The effect of partial vitrectomy on blood-ocular barrier function in the rabbit

PURPOSE

To compare ocular vascular permeability in the rabbit after vitrectomy as assessed by contrast-enhanced magnetic imaging (CE-MRI) and measurements of aqueous and vitreous humor protein concentration.

METHODS

Partial vitrectomies were performed, irrigating with BSS or BSS PLUS. Post-operative vascular leakage was determined by CE-MRI following intravenous administration of gadolinium diethylenetriaminepentaacetic acid (Gd-DTPA). Aqueous and vitreous protein concentrations were quantified by standard biochemical assay. ERG evaluations were performed on postoperative days 1, 3, and 7.

RESULTS

Using BSS as irrigant, breakdown of the inner blood-retinal barrier (BRB) occurred in 4/7 eyes on post-operative day 1. The rate of Gd-DTPA leakage was significantly greater on postoperative day 1 than that in unoperated, control eyes, but declined approximately 50% by day 3. At both time points, outer BRB breakdown was restricted to the sclerotomy wounds. No BRB leakage was detectable in control eyes. Blood-aqueous barrier (BAB) leakage was bilateral on day 1. Significantly greater Gd-DTPA leakage occurred in the operated eye than in the nonsurgical contralateral eye. On day 3, approximately 40% bilateral reduction in leakage indicated resolution of BAB leakage. Notably, Gd-DTPA leakage of the BAB and BRB was significantly reduced in the BSS PLUS treated group. In contrast to MRI assessments, protein concentrations of the aqueous and vitreous in the surgical eye showed no detectable differences between BSS and BSS PLUS. Concurrent with the transient loss of ocular barrier function, ERG responses also declined. However, by day 7 greater than 90% recovery was noted in BSS PLUS treated animals but not in the BSS treatment group.

CONCLUSIONS

CE-MRI is capable of detecting subtle changes in vascular permeability following ocular surgery. Advantages of using BSS PLUS compared to BSS as the irrigating solution can be detected using this technique. BSS PLUS's protection of barrier function is consistent with a rapid recovery in retinal function not observed in BSS treated eyes.

A comparison of the effects of olopatadine and ketotifen on model membranes

Olopatadine is a human conjunctival mast cell stabilizer with antihistaminic activity. Ketotifen is an older molecule that possesses antihistaminic activity and is reported to have additional pharmacological properties. The interactions of these two compounds with model membranes (i.e., monolayers of 1-stearoyl-2-oleoyl-sn-glycerophosphocholine at the argon-buffer interface), and natural (i.e., erythrocyte) membranes were compared in an effort to understand the differences in their biological activities. Drug-lipid interaction with monolayers was determined by monitoring the surface pressure as a function of the drug concentration in the aqueous phase supporting the monolayer. Drug interaction with erythrocyte membranes was determined by monitoring changes in the permeability of the membranes to hemoglobin and 6-carboxyfluorescein as a function of drug concentration in the medium. Olopatadine and ketotifen are both intrinsically surface active and both interact with phospholipid monolayers. However, in both the presence and absence of lipid monolayers, the changes in surface pressure induced by olopatadine are lower than those caused by ketotifen. The effects of these two drugs on cell membranes were dramatically different. Exposure of bovine erythrocytes to increasing concentrations of ketotifen (1-10 mM) resulted in complete hemolysis of the cells, whereas olopatadine (1-10 mM) caused only minimal hemolysis (< 8%). Consistent results were obtained in experiments measuring the leakage of 6-carboxyfluorescein from erythrocyte ghosts as a more sensitive marker of membrane perturbation. Olopatadine treatment (0.1-10 mM) minimally perturbed the cell membrane while ketotifen (1-10 mM) caused a concentration dependent release of the fluorescent marker. These data demonstrate fundamental differences between the two drugs in their effects on cell membranes. Moreover, the differences are consistent with the surface activities of the two compounds measured in monolayers and with reported differences in their pharmacological activities. These findings offer an explanation for the biphasic non-specific cytotoxic effect of ketotifen on histamine release from mast cells and may account for the nonlytic mast cell stabilizing activity of olopatadine.

Physiological concentrations of albumin stimulate chorionic gonadotrophin and placental lactogen release from human term placental explants

This study investigates whether albumin, a major plasma protein in direct contact with the trophoblast in vivo, can modulate human chorionic gonadotrophin (HCG) and human placental lactogen (HPL) releases from placental explants. Incubating explants with a near physiological, i.e. 5%, concentration of human or bovine albumin during 30 min increased HCG and HPL release by at least 150%. This albumin effect was not mediated by any difference in hormone adsorption onto glass surfaces. In contrast to the sustained stimulation of hormone releases elicited by the addition of 10 mmol/l extracellular calcium, the albumin-mediated secretory responses were transient. However, the albumin- and calcium-stimulatory effects were abolished at 4 degrees C, depressed by 0.36 mmol/l cycloheximide or 1 mmol/l colchicine and potentiated by 40 micromol/l cytochalasin B. Moreover, the stimulatory effect of albumin on the hormone releases was not modified in the absence of Ca(2+) or in the presence of 1 or 10 mmol/l Ca(2+) in the extracellular milieu. These data suggest that albumin is involved, at physiological concentration, in the secretion of HCG and HPL by human placenta. The cellular mechanism(s) underlying the albumin-mediated secretory responses may be partly different from those involved during the calcium-mediated stimulation.

Noninvasive ventilation in respiratory failure due to cystic fibrosis

BACKGROUND

Noninvasive positive-pressure ventilation (NIPPV) is increasingly used as an effective means of avoiding endotracheal intubation and mechanical ventilation in patients with respiratory insufficiency or failure.

METHODS

We retrospectively reviewed our experience with NIPPV to treat respiratory failure in five patients with cystic fibrosis (CF).

RESULTS

Despite chronic lung disease related to CF, none of our cases were end-stage. All patients had recent pulmonary function tests showing a forced expiratory volume in 1 second (FEV1) of more than 30% predicted for age. All patients had progressive atelectasis, hypoxemia, and impending respiratory failure related to an acute pulmonary exacerbation or upper abdominal surgical procedure (open gastrostomy tube placement). Respiratory rates decreased, oxygen saturation increased, fraction of inspired oxygen (FiO2) requirement decreased, transcutaneous CO2 decreased, and atelectasis resolved with NIPPV.

CONCLUSIONS

Use of NIPPV provides effective respiratory support while avoiding the need for endotracheal intubation. The applications of NIPPV, reports of its use in patients with CF, and the equipment required are reviewed.

The relationship between rabbit lens optical quality and sutural anatomy after vitrectomy

This study was conducted first, to characterize structural changes in rabbit lenses after vitrectomy; and second, to assess whether such changes correlate with a quantifiable compromise in optical function. Unilateral, partial vitrectomies were performed on 2.5 month old Dutch Belted rabbits (n = 64). Age matched non-operated rabbits (n = 32) were used as controls. Lenses were analysed by correlative structural (light, scanning electron microscopic and three-dimensional computer-assisted drawings) and optical (low power helium-neon laser scan) analysis at 1.5, 3, 6 and 12 months post-surgery (n = 16 lenses from operated animals and n = 8 lenses from non-operated controls at each time point). Results demonstrate that in rabbits lens growth, or fiber formation, is compromised after vitrectomy. From 1.5 to 12 months after surgery, lenses had progressively more crooked posterior line sutures with sub-branches of increasing size and number in successive growth shells. Quantification of lens optical quality specifically along and/or between these atypical suture branches and sub-branches revealed a significant increase in focal length variability (sharpness of focus) after vitrectomy. A peripheral zone of fibers with abnormal posterior ends was produced surrounding the pre-surgical lens mass. This additional zone of aberrant fibers was associated with a quantifiable degradation in lens optics. Studies on the prevention of post-vitrectomy lens changes in this rabbit model may yield useful information applicable to the human condition.

Nepafenac, a unique nonsteroidal prodrug with potential utility in the treatment of trauma-induced ocular inflammation: II. In vitro bioactivation and permeation of external ocular barriers

Nepafenac, the amide analog of the NSAID amfenac, was examined in vitro for its bioactivation by ocular tissue components and its ability to permeate external ocular barriers. Rabbit tissues catalyzed a concentration-dependent conversion of nepafenac to amfenac. The order of specific hydrolytic activity is retina/choroid >> iris/ciliary body. Corneal tissue showed only minimal activity. Similarly, in human ocular cadaver tissue the specific activity of iris/ciliary body was greater than cornea. Continued perfusion of the corneal epithelium demonstrated a nearly six-fold greater permeation coefficient for nepafenac (k(p) = 727 x 10(-6) min(-1)) than for diclofenac (k(p) = 127 x 10(-6) min(-1)). Superior permeation of conjunctival and scleral tissue by nepafenac (k(p) = 128 x 10(-6) min(-1)) compared to diclofenac (k(p) = 80 x 10(-6) min(-1)) was also evident. Short term perfusion (5 min) of the corneal surface with 0.1% nepafenac resulted in sustained flux of drug across the cornea for 6 h. Under identical conditions only 3.3 microM of diclofenac accumulated on the corneal endothelial side compared to 16.7 microM nepafenac. The enhanced permeability of nepafenac, combined with rapid bioactivation to amfenac by the iris/ciliary body and retina/choroid, make it a target specific NSAID for inhibiting prostaglandin formation in the anterior and posterior segments of the eye.

Nepafenac, a unique nonsteroidal prodrug with potential utility in the treatment of trauma-induced ocular inflammation: I. Assessment of anti-inflammatory efficacy

Nepafenac, the amide analog of 2-amino-3-benzoylbenzeneacetic acid (amfenac), was examined in preclinical models for its potential utility as a topical ocular anti-inflammatory agent. Diclofenac was selected as the reference compound. In contrast to diclofenac (IC50 = 0.12 microM), nepafenac exhibited only weak COX-1 inhibitory activity (IC50 = 64.3 microM). However, amfenac was a potent inhibitor of both COX-1 (IC50 = 0.25 microM) and COX-2 activity (IC50 = 0.15 microM). Ex vivo, a single topical ocular dose of nepafenac (0.1%) inhibited prostaglandin synthesis in the iris/ciliary body (85-95%) and the retina/choroid (55%). These levels of inhibition were sustained for 6 h in the iris/ciliary body and 4 h in the retina/choroid. Diclofenac (0.1%) suppressed iris/ciliary body prostaglandin synthesis (100%) for only 20 min, with 75% recovery observed within 6 h following topical dosing. Diclofenac's inhibition of prostaglandin synthesis in the retina/choroid was minimal. Nepafenac's inhibitory efficacy and longer duration of action was confirmed in a trauma-induced rabbit model of acute ocular inflammation monitoring protein or PGE2 accumulation in aqueous humor. Results warrant further assessment of nepafenac's topical ocular efficacy in the treatment of postoperative ocular pain, inflammation, and posterior segment edema.

Molecular analysis of Mycobacterium avium isolates by using pulsed-field gel electrophoresis and PCR

Genetic relationships among 46 isolates of Mycobacterium avium recovered from 37 patients in a 2,500-bed hospital from 1993 to 1998 were assessed by pulsed-field gel electrophoresis (PFGE) and PCR amplification of genomic sequences located between the repetitive elements IS1245 and IS1311. Each technique enabled the identification of 27 to 32 different patterns among the 46 isolates, confirming that the genetic heterogeneity of M. avium strains is high in a given community. Furthermore, this retrospective analysis of sporadic isolates allowed us (i) to suggest the existence of two remanent strains in our region, (ii) to raise the question of the possibility of nosocomial acquisition of M. avium strains, and (iii) to document laboratory contamination. The methods applied in the present study were found to be useful for the typing of M. avium isolates. In general, both methods yielded similar results for both related and unrelated isolates. However, the isolates in five of the six PCR clusters were distributed among two to three PFGE patterns, suggesting that this PCR-based method may have limitations for the analysis of strains with low insertion sequence copy numbers or for resolution of extended epidemiologic relationships.

Pharmacological validation of a feline model of steroid-induced ocular hypertension

OBJECTIVE

To validate pharmacologically the feline model of steroid-induced ocular hypertension.

METHODS

Serial studies were conducted in domesticated adult female cats trained to accept topical ocular drug administration and pneumotonometry. To establish intraocular pressure (IOP) values for each study, measurements were performed at the same time of day for 6 consecutive days. Beginning on day 7, cats received either steroid or vehicle administered topically to both eyes three times a day for approximately 28 days. The IOP measurements were performed daily.

RESULTS

After 5 to 7 days of treatment with 0.1% dexamethasone or 1.0% prednisolone acetate, IOP began to increase, reaching peak values within 2 weeks. These values were sustained throughout dosing but declined rapidly to baseline upon cessation of treatment. Maximum IOPs for the dexamethasone- and prednisolone-treated groups averaged 4.5 +/- 0.3 mm Hg (n = 12) greater than the mean IOP value obtained in vehicle-treated cats. Cats treated with 0.25% fluorometholone, 1.0% loteprednol etabonate, and 1.0% rimexolone exhibited increases of 0.6, 1.2, and 1.7 mm Hg, respectively. These values were significantly lower than those observed following treatment with dexamethasone or prednisolone.

CONCLUSIONS

The ocular hypertensive effects of selected anti-inflammatory topical ocular steroids in this model are consistent with clinical findings.

CLINICAL RELEVANCE

This feline model is a useful tool for assessing the potential IOP liability of novel anti-inflammatory steroids.

Novel esters and amides of nonsteroidal antiinflammatory carboxylic acids as antioxidants and antiproliferative agents

A series of phenolic antioxidant ester and amide derivatives of the nonsteroidal antiinflammatory drug naproxen was designed to have both antiinflammatory and cytoprotective activity. Compounds were evaluated in vitro both for antioxidant activity, as assessed indirectly by thiobarbituric acid reactive substance (TBARS) formation in a membrane lipid peroxidation assay, and for antiproliferative activity, as indexed by the inhibition of DNA synthesis in cultured human vascular endothelial cells. Compounds of this series exhibited potent antioxidant activity, with IC50 values (1.6-11.63 microM) 2-6-fold lower than that of Trolox (6-hydroxy-2,5, 7,8-tetramethylchroman-2-carboxylic acid) and 400-1300-fold lower than that of vitamin E. Structural modifications of the ester or amide substructure (5a and 6a) did not affect antioxidant activity, but methylation of the 6-hydroxy substituent resulted in compound 6f which was devoid of antioxidant activity. Although indistinguishable in antioxidant activity, the amide derivatives tended to be more potent as antiproliferative agents than the corresponding esters. The IC50's for the amide derivatives (3, 5a-e, 8) ranged from 2 to 7 microM, while the IC50's for the structurally related esters (1, 2a-c, 6a-e) ranged from 9 to 22 microM. Moreover, studies with compound 6a indicate that the observed inhibition of DNA synthesis is reversible, suggesting that the antiproliferative activity is due to a cytostatic rather than cytotoxic activity of the compounds. Thus, the antioxidant-naproxen derivatives represent a novel series of agents that both protect against free-radical damage and possess cytostatic activity in vascular endothelial cells. Studies are in progress to assess the utility of these compounds as potential components of an ocular irrigating solution.

Transient loss of prostaglandin synthetic capacity in rabbit iris-ciliary body following anterior chamber paracentesis

The trauma-induced acute ocular inflammatory response has been characterized by investigating the kinetics of blood-aqueous barrier (BAB) breakdown, prostaglandin (PG) accumulation in the aqueous humor, and cyclooxygenase (PGH synthase) activity of the iris-ciliary body (ICB) following paracentesis in the NZA rabbit. BAB breakdown was assessed by quantifying plasma protein extravasation into the anterior chamber. PGE2 and 6-keto-PGF(1alpha) concentrations in the aqueous humor were quantified by radioimmunoassay. The capacity of ICB tissue homogenates to generate eicosanoids from exogenously supplied [I-14C]-arachidonic acid was assessed radiometrically by HPLC. Paracentesis resulted in a rapid and dramatic increase in aqueous humor PGE2 concentrations. Within 10 minutes, PGE2 concentrations increased 937-fold, from 6.2+/-4.9 pg/ml to maximal concentrations of 5810+/-3829 pg/ml. PG synthesis was followed temporally by an increase in aqueous humor protein, with peak levels (53.1 mg/ml) achieved within 30 minutes post paracentesis. Both PGE2 and protein levels gradually declined to near baseline levels 48 hours after trauma. ICB homogenates from naive animals produced significant amounts of eicosanoids (total PG=2.95 nmol/ 10 min/100 mg tissue). HHT (12 hydroxy-heptadecatrienoic acid) was produced in the greatest quantity, followed by PGE2alpha, PGI2, and TXB2/ PGF2 . Notably, following paracentesis, eicosanoid synthesis by the isolated ICB was observed to diminish abruptly. Formation of all eicosanoids was uniformly reduced by approximately 40% five minutes following paracentesis, with an 81% decrease in synthetic activity at 15 minutes. Eicosanoid synthetic capacity was only restored to baseline 48 hours post paracentesis. These findings suggest that, following ocular trauma, temporal changes occur in ICB PG synthetic activity that may impact on the selection of an optimal dosing paradigm for efficacy testing of topically administered NSAIDs.

Improved myeloperoxidase assay for quantitation of neutrophil influx in a rat model of endotoxin-induced uveitis

Previously described models of endotoxin-induced uveitis quantify neutrophil influx into the eye using biochemical or direct cell count methods that result in an underestimation of ocular leukocyte accumulation following the inflammatory stimulus. We have optimized the rat model of endotoxin-induced uveitis by first overcoming interference in the biochemical assay of myeloperoxidase due to endogenous ocular reductants and cellular constituents containing free thiol functional groups. This was accomplished by simultaneously 1) extensively diluting soluble, interfering substances and 2) blocking tissue sulfhydril functional groups during tissue homogenization. Uveitis was induced in rats by subplantar injection of endotoxin. Twenty-four hours later, eyes were enucleated, homogenized, fractionated, and myeloperoxidase activity of neutrophils sedimenting with the membranous pellet was extracted. Previously published extraction procedures yielded only 40% of total assayable myeloperoxidase activity. Optimal recovery of myeloperoxidase activity (>twofold increase) was achieved only with two sequential extractions using 50 mM phosphate buffer (pH 7.4) containing 10 mM N-ethylmaleimide, and subsequent solubilization of myeloperoxidase activity by extraction with 0.5% hexadecyltrimethylammonium bromide in 50 mM phosphate buffer (pH 6.0). This modified extraction procedure and optimized myeloperoxidase assay conditions (300 microM hydrogen peroxide and 1.5 mM o-dianisidine) were then used to enhance the uveitis model. Maximum ocular neutrophil accumulation was observed at endotoxin doses of 100-200 microg. Total ocular neutrophil infiltrations ranged from 250,000 to 800,000 cells/globe. This leukocyte influx was inhibited dose-dependently by topical ocular administration of dexamethasone, with half-maximal inhibition observed at a concentration of 0.01%, w/v. Further validated by the correlation of biochemical results with histological evaluation, the refined methodology described in this report has application in assessing the ophthalmic therapeutic potential of antiinflammatory agents.

Secretion of proinflammatory cytokines by human conjunctival epithelial cells

The production of cytokines by human conjunctival epithelial cells following stimulation was investigated. Primary cultures of human conjunctival epithelial cells were characterized by morphology and keratin expression. Cultured epithelial cells were treated with varying concentrations of lipopolysaccharide, interleukin (IL)-1 beta, calcium ionophore A23187, or phorbol myristate acetate, and cytokine secretion was determined over specified intervals. Culture supernatants and cell lysates were analyzed by ELISA for IL-1 beta, IL-3, IL-4, IL-5, IL-6, IL-8, IL-11, IL-1 receptor antagonist (IL-1ra), tumor necrosis factor-alpha (TNF-alpha), and granulocyte-macrophage colony stimulating factor (GM-CSF). With the exception of IL-1ra, unstimulated conjunctival epithelial cells produced cytokines at relatively low or undetectable levels. IL-1ra was detected in both culture supernatants and cell lysates under basal conditions. In response to stimuli, conjunctival epithelial cells secreted the proinflammatory cytokines TNF-alpha, IL-6, IL-8, and GM-CSF in a dose- and time-dependent fashion. After stimulation, the intracellular levels of IL-1ra increased in these cells but the supernatant-associated levels remained unchanged. None of the other cytokines evaluated (IL-1 beta, IL-3, IL-4, IL-5, and IL-11) were detected in supernatants or lysates of resting or stimulated cells. These findings suggest that conjunctival epithelial cells may contribute to the pathogenesis of human ocular diseases by production of proinflammatory cytokines. Further evaluation of these cells as targets of therapy is warranted.

The in vitro and in vivo ocular pharmacology of olopatadine (AL-4943A), an effective anti-allergic/antihistaminic agent

Olopatadine (AL-4943A; KW-4679) [(z)-11-[3-(dimethylamino)propylidene]-6, 11-dihydrodibenz[b,e]oxepine-2 acetic acid hydrochloride] is an anti-allergic agent which inhibits mast cell mediator release and possesses histamine H1 receptor antagonist activity. Studies were conducted to characterize the in vitro and in vivo pharmacological profile of this drug relevant to its topical ocular use. AL-4943A inhibits histamine release in a concentration-dependent fashion (IC50 = 559 microM) from human conjunctival mast cell preparations in vitro. Histamine release was not stimulated by AL-4943A at concentrations as high as 10 mM. In contrast, ketotifen stimulated histamine release at concentrations slightly higher than effective inhibitory concentrations. AL-4943A did not display any in vitro cyclooxygenase or 5-lipoxygenase inhibition. Topical ocular application of AL-4943A effectively inhibits antigen- and histamine-stimulated conjunctivitis in guinea pigs. Passive anaphylaxis in guinea pig conjunctiva was attenuated by AL-4943A applied 30 min prior to intravenous or topical ocular antigen challenge (ED50 values 0.0067% and 0.0170%, w/v, respectively). Antihistaminic activity in vivo was demonstrated using a model of histamine-induced vascular permeability in guinea pig conjunctiva. AL-4943A applied topically from 5 min to 24 hrs prior to histamine challenge effectively and concentration-dependently inhibited the vascular permeability response, indicating the compound has an acceptable onset and a long duration of action. Drug concentrations 5-fold greater than those effective against histamine-stimulated conjunctival responses failed to inhibit vascular permeability responses induced with either serotonin or Platelet-Activating-Factor. These data indicate that the anti-histaminic effect observed with AL-4943A is specific. These anti-allergic/antihistaminic activities of AL-4943A observed in preclinical model systems have been confirmed in clinical trials in allergic patients.

Antiinflammatory agents. 4. Syntheses and biological evaluation of potential prodrugs of 2-amino-3-benzoylbenzeneacetic acid and 2-amino-3-(4-chlorobenzoyl)benzeneacetic acid

A series of potential prodrugs of 2-amino-3-benzoylbenzeneacetic acid (amfenac) and 2-amino-3-(4-chlorobenzoyl)benzeneacetic acid were synthesized and evaluated for their cyclooxygenase inhibiting properties, antiinflammatory potency, and gastrointestinal irritation liability. One compound, 2-amino-3-(4-chlorobenzoyl)benzeneacetamide, possessed a therapeutic index 1 order of magnitude greater than that of indomethacin.

AHR-15010--a novel anti-arthritic agent

AHR-15010 (3-(2-methoxyphenoxy)-1,2-propanediol bissulphamate ester) is a compound of novel structure that displays anti-arthritic activity in adjuvant arthritis in rats. When given orally from days 18 through day 50, (excluding weekends) after adjuvant injection, AHR-15010, at doses of 3.16 to 100 mg kg-1, produced significant anti-inflammatory activity and reduced the severity of the hind paw joint lesions as monitored by X-ray analysis. AHR-15010, however, has no acute anti-inflammatory activity in the Evans Blue-carrageenan pleural effusion assay in rats, has no analgesic activity in mice, and has no activity in a classic, delayed-type, hypersensitivity assay in mice or in a cotton pellet granuloma test in rats. These data, in conjunction with biochemical data showing that AHR-15010 has no prostaglandin synthetase inhibiting activity suggest that AHR-15010 is an anti-arthritic with a unique mechanism of action. AHR-15010 is a carbonic anhydrase inhibitor. Data are presented that suggest that AHR-15010 and acetazolamide, a prototype carbonic anhydrase inhibitor, may present novel approaches to the treatment of arthritis.

Preparation and purification of soybean lipoxygenase-derived unsaturated hydroperoxy and hydroxy fatty acids and determination of molar absorptivities of hydroxy fatty acids

A method was developed for the preparation and purification of polyunsaturated hydroperoxy and hydroxy fatty acids from 18:2n-6, 18:3n-6, 18:3n-3, 20:3n-6, 20:3n-3, and 20:4n-6 with soybean lipoxygenase. This method involved incubation of unsaturated fatty acids in Tris-HCl buffer with soybean lipoxygenase and extraction of reaction products on C18 solid-phase columns. The yields of conversion of fatty acid substrate to oxygenated products were in all cases greater than or equal to 95%. C18 solid-phase extracted reaction products were purified by C18 HPLC, yielding 3-4 mg of products with purities of greater than or equal to 98%. Purified polyunsaturated hydroxy fatty acids were characterized by HPLC and mass spectral analysis and showed absorption spectra with maximum absorption occurring between 234.5 and 237.5 nm due to the presence of a conjugated diene function. Polyunsaturated hydroxy fatty acid potassium salts were converted to (4-bromobenzoyl)methyl esters by reaction with 2,4'-dibromoacetophenone in the presence of 18-crown-6. Molar absorptivities for the conjugated diene functions were determined by relating their absorbance to the absorbance contributed by the 4-bromobenzoyl chromophore and its molar absorption intensity of 17.6 X 10(3) (M.cm)-1. The molar absorptivities determined for 13-OH-9,11-18:2, 13-OH-6,9,11-18:3, 13-OH-9,11,15-18:3, 15-OH-11,13-20:2, 15-OH-8,11,13-20:3, 15-OH-11,13,17-20:3, and 15-OH-5,8,11,13-20:4 ranged from 23.2 x 10(3) to 24.6 x 10(3) (M.cm)-1. The molar absorbtivity values of 18.8 x 10(3) and 20.3 x 10(3) (M.cm)-1 determined for commercial, chemically synthesized 12-OH-5,8,10,14-20:4 [12-(S)-hydroxyeicosa-5,8,10,14-tetraenoic acid (12(S)-HETE)] and 5-OH-6,8,11,14-20:4 ((+/-)-5-HETE) were lower than that of soybean lipoxygenase-derived 15-OH-5,8,11,13-20:4 (15-HETE), which exhibited a molar absorptivity of 23.3 x 10(3) (M.cm)-1. The molar absorptivity values determined for 5-, 12-, and 15-HETE are considerably lower than 30.5 x 10(3) (M.cm)-1, which was reported previously.

1-[4-[3-[4-[bis(4-fluorophenyl)hydroxymethyl]-1- piperidinyl]propoxy]-3-methoxyphenyl]ethanone(AHR-5333): a selective human blood neutrophil 5-lipoxygenase inhibitor

In this study we report the in vitro inhibition of leukotriene synthesis in calcium ionophore (A23187)-stimulated, intact human blood neutrophils by AHR-5333. The results showed that AHR-5333 inhibits 5-HETE, LTB4 and LTC4 synthesis with IC50 values of 13.9, 13.7 and 6.9 microM, respectively. Further examination of the effect of AHR-5333 on individual reactions of the 5-lipoxygenase pathway (i.e. conversion of LTA4 to LTB4, LTA4 to LTC4, and arachidonic acid to 5-HETE) showed that this agent was not inhibitory to LTA4 epoxyhydrolase and glutathione-S-transferase activity in neutrophil homogenates. However, conversion of arachidonic acid (30 microM) to 5-HETE was half maximally inhibited by 20 microM AHR-5333 in the cell-free system. The inhibition of LTB4 and LTC4 formation in intact neutrophils by AHR-5333 appears to be entirely due to a selective inhibition of 5-lipoxygenase activity and an impaired formation of LTA4, which serves as substrate for LTA4 epoxyhydrolase and glutathione-S-transferase. AHR-5333 did not affect the transformation of exogenous arachidonic acid to thromboxane B2, HHT and 12-HETE in preparations of washed human platelets, indicating that this agent has no effect on platelet prostaglandin H synthase, thromboxane synthase and 12-lipoxygenase activity. The lack of inhibitory activity of AHR-5333 on prostaglandin H synthase activity was confirmed with microsomal preparations of sheep vesicular glands.

Optical spectra and kinetics of reactions of prostaglandin H synthase: effects of the substrates 13-hydroperoxyoctadeca-9,11-dienoic acid, arachidonic acid, N,N,N',N'-tetramethyl-p-phenylenediamine, and phenol and of the nonsteroidal anti-inflammatory drugs aspirin, indomethacin, phenylbutazone, and bromfenac

A combination of cyclooxygenase activity assays, rapid spectrophotometry and pre-steady-state, steady-state, and transient-state kinetics is used to characterize further the properties of prostaglandin H synthase. 13-Hydroperoxyoctadeca-9-11-dienoic acid is used as oxidizing substrate and the effects of the following compounds are examined: arachidonic acid, N,N,N',N'-tetramethyl-p-phenylenediamine, phenol, diethyldithiocarbamate, and the nonsteroidal anti-inflammatory drugs aspirin, indomethacin, phenylbutazone, and Bromfenac. The order of reactivity of four of these substrates, predominantly with compound II of prostaglandin H synthase, is N,N,N',N'-tetramethyl-p-phenylenediamine greater than phenol greater than indomethacin approximately phenylbutazone. Aspirin exhibits no effect. Arachidonic acid causes inactivation. Diethyldithiocarbamate acts as a reducing substrate for the oxidized forms of prostaglandin H synthase. Bromfenac appears to act both as a protective agent and inhibitor.

[Peripheral nerve repair: value of biological glues and epiperineural suture in late interventions. Experimental study in rats]

In order to approximate as close as possible genuine clinical conditions, the sciatic nerve of the rat was divided and then repaired after a delay of one or seven days either by application of a biological glue or by an epiperineural suture technique. The metabolic activity of the sciatic nerve Schwann cells - whether located in the distal or the proximal ends - and that of the (fast acting) white gastrocnemius and (slow acting) red soleus muscle were assessed using 32P-radiolabeled acid-soluble phosphates. Delayed repair, as judged by our biochemical criteria, was equivalent whatever method, biological glue or suture, was used. The frozen and lyophilized forms of the biological glue provided similar results.

Inhibition of blood platelet aggregation by dioxo-ene compounds

Compounds with a conjugated oxo-ene-oxo system were tested for inhibition of blood platelet aggregation. All compounds with this structure in trans configuration were effective inhibitors of aggregation induced by thrombin and by arachidonic acid. While the oxo-trans-ene-oxo system is prerequisite for such activity, other structural features of the compounds may be varied without loss of activity. Inhibition is exemplified by 9,12-dioxo-trans-10- and 10,13-dioxo-trans-11-octadecenoic acids and their methyl esters, by 11,14-dioxo-trans-12- eicosenoic acid, by 4,7-dioxo-trans-5- decene and by trans- dibenzoylethylene . The half-inhibition concentrations are in the order of 2-6 microM, with complete inhibition at 8-20 microM. According to experiments with the inhibiting 9,12-dioxo-trans-10-octadecenoic acid, the normal oxygenation of exogenous arachidonic acid by platelets is not affected but the thrombin-induced internal release of this acid seems to be abolished by the inhibitor. The inhibition of aggregation in the presence of exogenous arachidonic acid and its products suggests that the inhibitor also interferes with other events leading to aggregation. By implication from other properties of the oxo-trans-ene-oxo system, reaction with SH groups may be a mechanism for inhibition.

Natural abundance 13C NMR spectra of human muscle, normal and diseased

13C NMR spectra of human surgical muscle samples have been obtained at 50 and 118 MHz. Numerous sharp peaks in the 13C spectrum have been assigned to carbon atoms of soluble metabolites and fatty acyl chains of neutral fats and membrane-bound phospholipids. Comparisons have been made of 13C NMR spectra of normal and diseased muscles after removal of neutral fat by extraction with isopentane. Creatine, lactic acid, and phospholipids are not removed from muscles by isopentane. The most striking difference between 13C NMR spectra of isopentane-extracted normal and diseased muscle samples was the size of the residual 30.5 ppm methylene carbon resonance, that is, small in normal muscles and in nonspecific muscle diseases, but large in myogenic and neurogenic muscle diseases. In addition, differences were also found between normal and diseased muscles in their creatine content and their ability to produce lactic acid. By deoxycholate treatment of isopentane-extracted diseased muscle it is estimated that about one-fifth of the total phospholipids are highly mobile. T1 and NOE measurements indicated that the differences in peak height for the 30.5 ppm resonance between normal and diseased muscle are due only to difference in the amount of highly mobile fatty acyl chains in the muscle and not due to differences in relaxation parameters. 13C NMR of isopentane-extracted muscle appears to permit differentiation of normal from diseased muscle and, within diseased muscle, grading of the severity of the disease.

Possible regulation of phospholipase C activity in human platelets by phosphatidylinositol 4',5'-bisphosphate

Phospholipase C from human platelets was found to catalyze the Ca2+-dependent degradation of phosphatidylinositol (PI), phosphatidylinositol 4'-phosphate (DPI), and phosphatidylinositol 4',5'-bisphosphate (TPI) at Ca2+ concentrations from 150 microM to 5 mM. Both DPI and TPI inhibited the hydrolysis of [2-3H]inositol-labeled PI (250 microM) in a concentration-dependent manner. The use of DPI and TPI from beef brain, both of which have fatty acid compositions different from that of soybean PI, permitted an assessment of the inhibitory effect of polyphosphoinositides on the hydrolysis of PI by phospholipase C. Fatty acid analysis of the diacylglycerols formed demonstrated that DPI and TPI, when incubated in mixture with PI, were competitive substrates for PI hydrolysis. Increasing the DPI/PI ratio from 0 to 0.3 caused a shift in the degradation of PI to DPI without greatly affecting the formation of 1,2-diacylglycerol. TPI alone, or in mixture with PI, was a poor substrate for phospholipase C. Increasing the TPI/PI ratio from 0 to 0.21, on the other hand, inhibited both PI degradation (greater than or equal to 95%) and overall formation of 1,2-diacylglycerol (greater than or equal to 82%). Kinetic analysis revealed that TPI acts as a mixed-type inhibitor with a Ki of about 10 microM. The Ka for Ca2+ in PI hydrolysis was profoundly increased from 5 to 180 microM when TPI (36 microM) was included with PI (250 microM). Optimum PI degradation under these conditions was only attained when the calcium concentration approached 4 mM. Analysis of phospholipids from unstimulated human platelets from five different donors revealed DPI/PI and TPI/PI ratios of 0.42 and 0.16, respectively. These findings, combined with the observed inhibition of PI hydrolysis by TPI at a TPI/PI ratio of 0.16, would suggest that in unstimulated platelets phospholipase C activity may be inhibited by greater than or equal to 75%. Changes in 33P-prelabeled phospholipids of intact platelets upon stimulation with thrombin indicated a transient decline in 33P label of both TPI and DPI (15 s) followed by an increase in [33P]phosphatidic acid but no change in [33P]PI. The finding that DPI is selectively degraded by phospholipase C in mixture with PI at DPI/PI ratios determined to be present in unstimulated platelets indicates that DPI may be more important than PI in the formation of 1,2-diacylglycerol which is believed to serve as precursor of arachidonic acid for thromboxane biosynthesis. Furthermore, the results suggest that in human platelets TPI may serve as modulator for the formation of 1,2-diacylglycerol from inositol phospholipids.

Selective loss of mitochondrial genome can be caused by certain unsaturated fatty acids

Various unsaturated fatty acids had different effectiveness for maintaining the continued replication of functional mitochondria in an unsaturated fatty acid auxotroph of Saccharomyces cerevisiae (KD115). Certain isomers of octadecenoic acid (i.e., cis-9) and eicosatrienoic acid (i.e.,cis-8,11,14) permitted continued replication of mitochondria and provided cultures that contained only 4 to 5% cells that formed petite colonies. On the other hand, cultures grown with cis-12- or cis-13-octadecenoic acid or cis-11,14,17-eicosatrienoic acid, produced a 12- to 16-fold greater frequency of petite mutants (50-60%) after 8 to 10 generations of growth. The production of the petite mutants occurred despite adequate incorporation of these unsaturated fatty acids into cellular phospholipids and an apparently normal ability to undergo the initial steps in the induction of cellular respiration. The evidence suggests that some cellular processes necessary for continued mitochondrial replication depend on the structural features of the fatty acyl chains as well as the overall content of unsaturated fatty acids in membrane phospholipids. Impairment of that process by certain inadequate fatty acids or by an inadequate supply of a suitable fatty acid leads to a permanent loss of the mitochondrial genome from the cells of subsequent generations.

The alkylacyl and alkenylacyl glycerophospholipids of human platelets

The phospholipids of human platelets were isolated and analysed for their constituent 1-0-alkyl- and 1-0-(1'-alkenyl)glycerol species. The serine and inositol phospholipids contained only small amounts (0.5-1.6%) of both alkylacyl and alkenylacyl species; the ethanolamine phospholipids contained little alkylacyl (1.7%) but much more alkenylacyl (45.3%) species, while the choline phospholipids contained 4.5% and 1.4% of these compounds, respectively. Because choline phospholipids amount to 41% of the total phospholipids of human platelets, it appears that they could provide a sufficient supply of alkylacyl glycerophosphocholine for the generation of the alkylacetyl analog (platelet activating factor) by a deacylation-acetylation pathway.

Changes in the natural abundance 13C NMR spectra of intact frog muscle upon storage and caffeine contracture

The carbons of phospholipids have limited mobility in fresh, resting, gastrocnemius frog muscle, but a population of phospholipids gains considerable mobility upon storage in the muscle or in contracture induced by caffeine. In parallel with the appearance of sharp phospholipid resonances, lactic acid also appears in the 13C NMR spectra. There is a correlation between the mobility of phospholipids and the depletion of phosphocreatine and ATP in muscle.