Physicochemical considerations in the preparation of amorphous ritonavir-poly(ethylene glycol) 8000 solid dispersions

A systematic study of the properties of ritonavir and the influence of polyethylene glycol 8000 (PEG) on ritonavir revealed that amorphous ritonavir dispersions in PEG would have an improved dissolution profile and could exhibit long-term stability. Ritonavir, a human immunodeficiency virus (HIV) protease inhibitor, is highly lipophilic [distribution coefficient (log D)= 4.3, 25 degrees C, pH 6.8], poorly water soluble (400 microg/mL in 0.1 N HCl, 1 microg/mL at pH 6.8, 37 degrees C), and exhibits an exceedingly slow dissolution rate (0.03 mg/cm(2)-min in 0.1 N HCl at 37 degrees C). These properties indicated that a solid dispersion containing ritonavir might be useful for overcoming problems associated with slow dissolution. In addition, ritonavir is a good glass former [glass-transition temperature (T(g))/melting point (T(m)) > 0.7]. Amorphous ritonavir has an apparent solubility of 4 mg/mL in 0.1 N HCl at 37 degrees C and shows reasonable stability at 25 degrees C. Amorphous ritonavir, therefore, has properties desirable for preparing a solid dispersion containing this phase. Since PEG, a commonly used polymer, improved the aqueous solubility of crystalline ritonavir, it was expected to have a positive influence on the dissolution rate of ritonavir. Moreover, PEG was found to have negligible plasticizing effect on amorphous ritonavir, which was beneficial for the stability of the dispersion. Finally, solid dispersions of amorphous ritonavir in PEG were prepared, and these dispersions had improved in vitro dissolution rate and were physically stable for > 1.5 years at 25 degrees C when protected from moisture. The performance of this solid dispersion has been attributed to the physicochemical properties of amorphous ritonavir.

Erratum: Temporal and spatial patterns of opsin gene expression in the zebrafish (Danio rerio): corrections with additions

We report here a reexamination of the developmental expression of cone opsins in the zebrafish retina. The red- and blue-sensitive opsins appear at 51 h postfertilization (hpf) whereas ultraviolet (UV) opsin is not seen until after 55 hpf. More cells show red cone opsin expression than blue at 51 and 55 hpf, indicating the sequence of cone opsin expression in zebrafish is first red, then blue, and finally UV. Curiously, morphological development of the cones is in reverse order; UV cones appear quite mature by day 6-7 postfertilization (pf), but morphologically, red cones do not appear adult-like until 15-20 days pf.

Nucleation and crystallization kinetics of hydrated amorphous lactose above the glass transition temperature

The crystallization kinetics of amorphous lactose in the presence and absence of seed crystals were investigated at 57.5% relative humidity. Isothermal crystallization studies were conducted gravimetrically in an automated vacuum moisture balance at several temperatures between 18 and 32 degrees C. The crystallization rate constants were then determined from Johnson-Mehl-Avrami (JMA) treatment and isothermal activation energies were obtained from Arrhenius plots. Based on microscopic observations, a reaction order of 3 was used for JMA analysis. The nonisothermal activation energies were determined by differential scanning calorimetry using Kissinger's analysis. Isothermal activation energies for amorphous lactose with and without seed crystals were 89.5 (+/-5.6) kJ/mol and 186.5 (+/-17.6) kJ/mol, respectively. Nonisothermal activation energies with and without seed crystals were 71 (+/-7.5) kJ/mol and 80.9 (+/-8.9) kJ/mol, respectively. The similarity of the isothermal and nonisothermal activation energies for the sample with seeds suggested that crystallization was occurring by growth from a fixed number of preexisting nuclei. Markedly different isothermal and nonisothermal activation energies in the absence of seeds suggested a site-saturated nucleation mechanism, and therefore allowed calculation of an activation energy for nucleation of 317 kJ/mol.

Early retinal development in the zebrafish, Danio rerio: light and electron microscopic analyses

The morphological differentiation of the zebrafish retina was analyzed by using light (LM) and transmission electron (TEM) microscopy between the time of initial ganglion cell differentiation (approximately 32 hours postfertilization; hpf) and shortly after the point when the retina appears functional (approximately 74 hpf), i.e., when all major cell types and basic synaptic connections are in place. The results show that the inner retinal neurons, like the photoreceptor and ganglion cells, differentiate first within the ventronasal region, and differentiation subsequently spreads asymmetrically into the nasal and dorsal regions before reaching the ventrotemporal retina. In addition, we show that the attenuation of the optic stalk occurs in parallel with ganglion cell differentiation between 32 and 40 hpf. The first conventional synapses appear within the inner plexiform layer simultaneously with the first photoreceptor outer segment discs at 60 hpf; functional ribbon triads arise within photoreceptor synaptic terminals at 65 hpf; and synaptic ribbons occur within bipolar cell axon terminals at the time larvae exhibit their first visual responses (approximately 70 hpf). Although development is initially more advanced within the ventronasal region between 50 and 60 hpf, development across the retina rapidly equilibrates such that it is relatively comparable within all quadrants of the central retina by 70 hpf. An area within the temporal retina characterized by tightly packed and highly tiered cones emerges with subsequent development. Retinal differentiation in the zebrafish corresponds with that generally described in other vertebrates and can be correlated with the development of visual and electroretinographic responses in the animal.

Retinal patterning in the zebrafish mutant cyclops

Determination of cell fate in the vertebrate retina has been shown to be largely independent of lineage. After cell fates are determined, retinal neurons become organized in a precise laminar pattern. The mechanisms for this patterning could involve morphogens distributed in gradients or, alternatively, direct cell-cell interactions. In the zebrafish mutant cyclops (Cyc(b16)), most embryos have two partial retinas joined in the ventral midline. This presents developing retinal cells near the midline with abnormal cellular environments, whereas laterally the pattern of developing cells is normal. We examined the consequences of this for patterning in the mutant's retina. We found that the retinas are joined in the midline at the apical surfaces of the photoreceptor layers. A laminar pattern emerges in the midline that preserves normal positional relationships between retinal cell types locally but is abnormal with respect to patterning over the entire retina. Lateral to the midline, retinal patterning appears normal. Metabolic labeling experiments showed that late rounds of DNA synthesis precede the emergence of the novel pattern in this midline region. We conclude that these observations in the cyclops mutant are compatible with mechanisms of pattern formation in the retina involving local cell interactions.

Retinoic acid alters photoreceptor development in vivo

Application of exogenous retinoic acid (RA) to zebrafish during the initial stages of photoreceptor differentiation results in a precocious development of rod photoreceptors and an inhibition of cone photoreceptor maturation. The acceleration of rod differentiation is observed initially within the ventral retina 3 days after fertilization, following 24 hr of RA application, and within the dorsal retina 4 days after fertilization, following 48 hr of RA application. The differentiation of rods was impeded significantly when the synthesis of endogenous retinoic acid was inhibited by citral prior to the initial stage of rod differentiation. RA-treated embryos labeled for bromodeoxyuridine (BrdU) uptake revealed that RA exerts its effect on a postmitotic cell population within the developing retina. During normal development in zebrafish, rod differentiation is most robust within the ventral retina, a region previously shown to be rich in RA. Our data suggest that the RA signaling pathway is involved in the differentiation and maturation of both the rod and cone photoreceptors within the developing zebrafish retina.

Comparison of topographical patterns of ganglion and photoreceptor cell differentiation in the retina of the zebrafish, Danio rerio

Earlier studies suggested retinal differentiation in the zebrafish commences ventrally rather than centrally as is the case in other vertebrates. Here we describe the topographical spread of cell differentiation for ganglion cells, double cones and rods in the zebrafish retina between 36 and 72 hours postfertilization (hpf), by using immunohistochemical markers in retinal wholemounts. Staining for all three cell types commenced within the ventral retina on the nasal side of the optic nerve and choroid fissure, at 38 hpf for ganglion cells and 50 hpf for double cones and rods. Within 3 to 4 hours, the staining of ganglion cells and double cones spread in a continuous wave-like fashion into the nasal region of the ventral retina. After this time, the staining patterns for ganglion cells and double cones progressed dorsally into the central and temporal retina. Finally, stained somata of ganglion cells were observed within the temporal-ventral region by approximately 48 hpf, more than 8 hours later than the first ganglion cells within the nasal retina. The topographical spread of double cone staining was slightly less orderly. After staining had extended into the nasal retina between 50 and 54 hpf, a small group of stained double cones often appeared at the temporal edge of the choroid fissure by 56 hpf, simultaneously with initial staining observed dorsal and temporal to the optic nerve. The topographical spread of rod staining in the ventral retina was more symmetrical. After rod staining appeared near the nasal edge of the choroid fissure at 50 hpf, rods accumulated within a localized patch nasal to the fissure. Approximately 5 hours after initial rod staining, scattered rod staining appeared on the temporal side of the choroid fissure (approximately 55-57 hpf). Rods increased rapidly within the ventral retina, and a dense symmetrical patch extended out from the choroid fissure into the nasal and temporal regions of the ventral retina by 70 hpf. A scattered pattern of rod staining also occurred within the dorsal retina at this time.

Retinoic acid establishes ventral retinal characteristics

The developing eye is known to be rich in retinoic acid (RA), and perturbations in RA levels during formation of the optic primordia, as well as RA receptor mutations, cause retinal malformations, especially in ventral eye regions. To test the hypothesis that RA plays a role in the establishment of ventral retinal characteristics, we examined several dorsal and ventral ocular markers in RA-treated zebrafish. The optic stalk represents the ventral-most region of the early eye field. During normal development, the optic stalks constrict, decreasing in width and are gradually replaced by the optic nerve. Systemic high RA levels cause an expansion in the optic stalk with an increased cell content and a patent lumen. In addition, the stalks do not constrict and persist into later stages of development indicating an enhancement of early ventral eye characteristics. Expression of the transcription factor pax[b], normally confined to the ventral retina, expands into the dorsal retina following RA treatment, whereas msh[c], normally expressed in the dorsal retinal pole, disappears. Activity of an aldehyde dehydrogenase that normally occupies the dorsal third of the retina is reduced or abolished following high systemic RA. When a localized RA source, an RA-soaked bead, is placed next to the developing eye, a fissure resembling the choroid fissure appears in the eye facing the bead. Taken together, these observations suggest that RA is involved in the determination of the ventral retina.

Temporal and spatial patterns of opsin gene expression in zebrafish (Danio rerio)

In zebrafish, the first class of cone photoreceptor to become morphologically distinct is the ultraviolet-sensitive short single cone, at 4 days postfertilization, whereas the last class, the red- and green-sensitive double cone, becomes distinct at 10 days postfertilization. We have examined the time course of visual pigment gene expression in zebrafish using whole-mount in situ hybridization. Within the retina, opsins may be detected as early as 40 h postfertilization with the ultraviolet and rod visual pigments being expressed before the blue- (48 h) and red- (60 h) sensitive pigments. In the pineal, red-sensitive opsin is expressed at 48 h postfertilization. Visual pigment expression provides a useful tool for investigations of early cell fate in zebrafish.

Early eye morphogenesis in the zebrafish, Brachydanio rerio

Early eye morphogenesis in the zebrafish between 12 and 36 hours postfertilization was studied by light- and scanning electron microscopy. Overall, early eye morphogenesis in the zebrafish is similar to that of other vertebrates even though the optic primordia evaginate from the forebrain as solid masses of cells. After initial evagination (6-7 somite stage [SS]), the optic primordia take on a wing-like shape (8-9 SS). Subsequently, they bend ventrally and rotate slightly in an anterior direction (10-12 SS). These changes serve to bring the primordia from a horizontal to a more vertical orientation in relation to the embryonic neural axis. Invagination commences from the center of each primordium (14 SS) and progresses symmetrically out towards the periphery (14-20 SS). The choroid fissure forms by an involution along the anterior region of the eyecup (18-20 SS). By 24 hours postfertilization (pf), the eyecups are well formed. Between 24 and 36 hours pf, the eyes rotate further in relation to the axis of the embryo, and this repositions the choroid fissue to a typical ventral location by 36 hours pf. Because of the two rotations of the eye during early morphogenesis, particularly the later one, the anterior-posterior orientation of the emerging optic primordium ultimately becomes the ventral-dorsal axis of the completed eyecup.

Zebrafish ultraviolet visual pigment: absorption spectrum, sequence, and localization

In many vertebrates, UV-sensitive photoreceptors have been identified by microspectrophotometry and UV-visual sensitivity has been identified by behavioral studies, but as yet no vertebrate UV-sensitive pigment gene has been isolated. We have sequenced a cDNA clone that hybridizes to short single cone cells in the zebrafish (Brachydanio rerio). These cells, which make up 25% of the cone population in zebrafish retinae, are UV-sensitive (lambda max approximately 360 nm). The visual pigment encoded by this gene is unusual in that its amino acid sequence is more homologous to the rod pigment rhodopsin (up to 89%) than to other cone pigments (35-83%). Like all other vertebrate visual pigments, it contains a lysine residue at position 296, the presumptive retinal binding site, and a glutamate residue at position 113. However, it is unique in possessing a lysine residue at position 126, which may account for the UV-sensitivity of the pigment.

Degradation and release properties of pellets fabricated from three commercial poly(D,L-lactide-co-glycolide) biodegradable polymers

Poly(D,L-lactide-co-glycolide, 50:50) samples of similar molecular weight were obtained from three commercial sources and were characterized by gel permeation chromatography, differential scanning calorimetry, X-ray powder diffraction, viscometry, and proton nuclear magnetic resonance spectroscopy. Pellets were prepared by melt-pressing spray-dried polymer with a 4-mm standard concave punch and die set and a thermostated holder of original design. Amaranth (5% w/w) was incorporated in pellets used for release studies. Degradation and release studies were conducted at 37 degrees C in pH 7.2 phosphate buffered saline. The molecular weights of all polymers were found to decrease continuously after exposure to phosphate buffered saline. All polymers showed two distinct regions of molecular weight decrease. Mass loss experiments for all polymers resulted in sigmoidal curves typical of polymers undergoing bulk hydrolysis. The onset of mass loss (defined as 10% mass loss) was found to differ by as much as 6 days among the three polymers studied. The release studies showed an initial burst of release followed by a period of 15-25 days during which little or no dye was released. A second phase of release followed, lasting approximately 10 days, until all dye was released. The time at which release began slightly preceded the onset of mass loss.

Retinoic acid-induced duplication of the zebrafish retina

Exogenous treatment of zebrafish embryos with retinoic acid induces a duplication of the retinas during development. These effects occur only when retinoic acid is applied within a 2-hr period prior to and during the initial formation of the optic primordia, and they are concentration-dependent. Light microscopic examination reveals that the second retina derives from cells in the ventral region of the developing eyecup that normally become pigment epithelial cells. Two distinct ganglion cell fields are usually observed in eyes with duplicated retinas. Bundles of axons from each ganglion cell field join as they leave the eye and innervate the contralateral tectum.

Common artifacts of pulmonary artery and pulmonary artery wedge pressures: recognition and interpretation

Bedside measurement of pulmonary artery pressure and pulmonary artery wedge pressure has an important role in the management of critically ill patients. Unfortunately, waveform abnormalities and artifacts commonly distort numeric values and lead to incorrect therapeutic decisions. The clinical impact of these artifacts is magnified by the digital pressure displays used in most intensive care units. We present here an atlas and an analysis of the artifacts that commonly occur. Use of analog rather than digital pulmonary artery wedge pressure data, when combined with an understanding of the physiological characteristics of patients, can prevent critical errors in patient management.

Upper dorsal sympathectomy

Over a 20 year period, 60 patients underwent 76 procedures for upper dorsal sympathectomy, usually with a transaxillary approach but occasionally with an anterior approach. Procedures in male patients and in those that were carried out on the right side were most frequent. There were few simultaneous procedures. The extent of sympathectomy included resection of the lower half of the stellate ganglion through the fourth thoracic ganglion. The results were satisfying for patients with vasospastic disorders and hyperhidrosis and quite acceptable for those with causalgia and vaso-occlusive disorders. Complication rates and the incidence of postoperative Horner's syndrome were low. There were prominent differences in results among the various age groups. In addition, female patients and those with bilateral procedures had less favorable results. Factors that did not appear to affect results included technique of surgical approach, extent of sympathectomy, presence of Horner's syndrome, or the addition of other procedures. Current indications for upper dorsal sympathectomy include cases of Raynaud's and Buerger's diseases refractory to drug therapy, causalgia, vaso-occlusive disorders, and hyperhidrosis.