Evaluation of the test system used for in vitro release of drugs for topical dermatological drug products

The purpose of this research was to evaluate different parameters that can influence in vitro drug release from topical dermatological drug products such as creams, gels, and ointments. In vitro release from topical dermatological drug products was carried out by using a static diffusion cell, a synthetic membrane, and an appropriate receptor medium. The receptor medium was mixed by means of a magnetic bar rotated at 400 rpm. Experiments were designed to evaluate the influence of (i) receptor media, (ii) different lots of synthetic membranes, and (iii) agitation on drug release. Release experiments were also carried out to study inter- and intralot variability. The in vitro release test was used to evaluate the marketed glucocorticoid products. Among the parameters studied, the receptor medium was found to be the most important and critical variable that influenced drug release. The release rate ranged between 0.61 and 2.68 micrograms/cm2/min0.5 for betamethasone dipropionate, depending on the percentage of ethanol in the receptor medium. The drug release was not influenced by agitation or by different lots of synthetic membranes. Very small inter- and intralot variability was observed. These experiments establish the ruggedness of the in vitro diffusion cell test system used for the drug release measurements.

The structure of a tunicate C-type lectin from Polyandrocarpa misakiensis complexed with D -galactose

C-type lectins are calcium-dependent carbohydrate-recognising proteins. Isothermal titration calorimetry of the C-type Polyandrocarpa lectin (TC14) from the tunicate Polyandrocarpa misakiensis revealed the presence of a single calcium atom per monomer with a dissociation constant of 2.6 microM, and confirmed the specificity of TC14 for D -galactose and related monosaccharides. We have determined the 2.2 A X-ray crystal structure of Polyandrocarpa lectin complexed with D -galactose. Analytical ultracentrifugation revealed that TC14 behaves as a dimer in solution. This is reflected by the presence of two molecules in the asymmetric unit with the dimeric interface formed by antiparallel pairing of the two N-terminal beta-strands and hydrophobic interactions. TC14 adopts a typical C-type lectin fold with differences in structure from other C-type lectins mainly in the diverse loop regions and in the second alpha-helix, which is involved in the formation of the dimeric interface. The D -galactose is bound through coordination of the 3 and 4-hydroxyl oxygen atoms with a bound calcium atom. Additional hydrogen bonds are formed directly between serine, aspartate and glutamate side-chains of the protein and the sugar 3 and 4-hydroxyl groups. Comparison of the galactose binding by TC14 with the mannose binding by rat mannose-binding protein reveals how monosaccharide specificity is achieved in this lectin. A tryptophan side-chain close to the binding site and the distribution of hydrogen-bond acceptors and donors around the 3 and 4-hydroxyl groups of the sugar are essential determinants of specificity. These elements are, however, arranged in a very different way than in an engineered galactose-specific mutant of MBPA. Possible biological functions can more easily be understood from the fact that TC14 is a dimer under physiological conditions.

Practical tools for qualitative community-oriented primary care community assessment

BACKGROUND AND OBJECTIVES

The evolution of managed care is creating a need for feasible methods for clinical practices to perform community assessments. Since some types of clinically useful data are best obtained through a qualitative community assessment, practical methods of carrying out this type of assessment are needed. Such practical methods are also important for community-oriented primary care, an attractive model for the marriage of population perspectives and clinical primary care.

METHODS

Using methods suitable for busy clinical practices, qualitative data useful for clinical purposes were collected either by mail surveys, telephone surveys, or during focus group discussions in a low-income community. Characteristics of data obtained through each method, together with the costs, advantages, and disadvantages of each approach, were examined.

RESULTS

All three methods revealed similar themes in their responses, though the range and emotional content of the responses varied by approach. Clinically useful data were obtained, although the potential for sampling and response biases must be considered. Costs, primarily related to professional time, varied by as much as 50% among the methods examined; telephone surveys were the least expensive per enrolled subject.

CONCLUSIONS

The methods tested are potentially feasible in busy practices. However, practices should clarify their objectives and resources prior to using these methods.

Acute spontaneous spinal epidural hematomas

BACKGROUND AND PURPOSE

Although previous reports have characterized MR imaging features of spinal epidural hematomas (EDH), few cases have been reported during the acute or hyperacute phase within the first 48 hours. Our goal in this investigation was to correlate the MR imaging features of acute (< or =48 hours) spontaneous EDH with clinical management and outcome.

METHODS

Eight patients with acute spontaneous EDH (five men and three women; age range, 31-81 years) underwent MR imaging at 1.5 T (T1-weighted, n = 8; T1-weighted after the administration of 0.1 mmol/kg contrast material, n = 6; T2-weighted, n = 8; and T2-weighted, n = 4). The interval from symptom onset to hospital admission ranged from immediate to 5 days. Two neuroradiologists reviewed the MR images for signal characteristics, contrast enhancement, and cord compression. Treatment and clinical outcome were correlated with the imaging findings.

RESULTS

The EDH were located in the cervical (n = 3), cervicothoracic (n = 2), thoracolumbar (n = 2), and lumbar (n = 1) regions. On T1-weighted images, the signal intensity of the EDH was isointense to spinal cord in five cases, hyperintense in two cases, and hypointense in one case and did not correlate with time to imaging. Isointensity on T1-weighted images persisted for 5 days in one case. On T2-weighted images, all EDHs were hyperintense with focal, heterogeneous hypointensity. Cord compression was severe in six patients, moderate in one patient, and minimal in one patient. Four cases were treated conservatively with complete resolution or improvement of symptoms within 1 to 3 weeks.

CONCLUSION

MR imaging findings were useful in establishing the diagnosis of EDH but did not influence management or predict outcome in this series. Heterogeneous hyperintensity to cord with focal hypointensity on T2-weighted images should suggest the diagnosis of acute spinal EDH. Severity of neurologic impairment had the greatest impact on management and outcome. Nonoperative treatment may be successful in cases with minimal neurologic deficits, despite cord compression revealed by MR imaging.

MR imaging of intraventricular silicone: case report

A 42-year-old man with human immunodeficiency viral infection developed cytomegaloviral retinitis that was complicated by retinal detachment and was treated with an intravitreous injection of silicone. Fifteen months later, magnetic resonance imaging revealed intraocular and intraventricular silicone. Signal intensity characteristics and chemical shifts of silicone in the two locations were identical.

Mapping the phospholipid-binding surface and translocation determinants of the C2 domain from cytosolic phospholipase A2

Cytosolic phospholipase A2 (cPLA2) plays a key role in the generation of arachidonic acid, a precursor of potent inflammatory mediators. Intact cPLA2 is known to translocate in a calcium-dependent manner from the cytosol to the nuclear envelope and endoplasmic reticulum. We show here that the C2 domain of cPLA2 alone is sufficient for this calcium-dependent translocation in living cells. We have identified sets of exposed hydrophobic residues in loops known as calcium-binding region (CBR) 1 and CBR3, which surround the C2 domain calcium-binding sites, whose mutation dramatically decreased phospholipid binding in vitro without significantly affecting calcium binding. Mutation of a residue that binds calcium ions (D43N) also eliminated phospholipid binding. The same mutations that prevent phospholipid binding of the isolated C2 domain in vitro abolished the calcium-dependent translocation of cPLA2 to internal membranes in vivo, suggesting that the membrane targeting is driven largely by direct interactions with the phospholipid bilayer. Using fluorescence quenching by spin-labeled phospholipids for a series of mutants containing a single tryptophan residue at various positions in the cPLA2 C2 domain, we show that two of the calcium-binding loops, CBR1 and CBR3, penetrate in a calcium-dependent manner into the hydrophobic core of the phospholipid bilayer, establishing an anchor for docking the domain onto the membrane.

Crystal structure of the two N-terminal domains of g3p from filamentous phage fd at 1.9 A: evidence for conformational lability

Infection of Escherichia coli by filamentous bacteriophages is mediated by the minor phage coat protein g3p and involves two distinct cellular receptors, the F' pilus and the periplasmic protein TolA. Recently we have shown that the two receptors are contacted in a sequential manner, such that binding of TolA by the N-terminal domain g3p-D1 is conditional on a primary interaction of the second g3p domain D2 with the F' pilus. In order to better understand this process, we have solved the crystal structure of the g3p-D1D2 fragment (residues 2-217) from filamentous phage fd to 1.9 A resolution and compared it to the recently published structure of the same fragment from the related Ff phage M13. While the structure of individual domains D1 and D2 of the two phages are very similar (rms<0.7 A), there is comparatively poor agreement for the overall D1D2 structure (rms>1.2 A). This is due to an apparent movement of domain D2 with respect to D1, which results in a widening of the inter-domain groove compared to the structure of the homologous M13 protein. The movement of D2 can be described as a rigid-body rotation around a hinge located at the end of a short anti-parallel beta-sheet connecting domains D1 and D2. Structural flexibility of at least parts of the D1D2 structure was also suggested by studying the thermal unfolding of g3p: the TolA binding site on D1, while fully blocked by D2 at 37 degrees C, becomes accessible after incubation at temperatures as low as 45 degrees C. Our results support a model for the early steps of phage infection whereby exposure of the coreceptor binding site on D1 is facilitated by a conformational change in the D1D2 structure, which in vivo is induced by binding to the F' pilus on the host cell and which can be mimicked in vitro by thermal unfolding.

The corrosion behaviour of Ti-6Al-4V, Ti-6Al-7Nb and Ti-13Nb-13Zr in protein solutions

Ti alloys are used in orthopaedic applications owing to their appropriate mechanical properties and their excellent corrosion resistance. The release of titanium and the other alloying elements into the surrounding tissue has been reported due either to passive corrosion or accelerating processes such as wear. Since the passive layer can be broken down in certain circumstances by wear it is important to study the ability of these alloys to repassivate in biological environments, in particular in the presence of proteins, and evaluate how the repassivated surface may vary from the original surface. In this study we investigated the ability of Ti-6Al-4V, Ti-6Al-7Nb and Ti-13Nb-13Zr to repassivate in phosphate buffered saline (PBS), bovine albumin solutions in PBS and 10% foetal calf serum in PBS at different pH values and at different albumin concentrations. It was found that an increase in pH had a greater effect on the corrosion behaviour of Ti-6Al-4V and Ti-6Al-7Nb than on Ti-13Nb-13Zr in PBS and that the addition of protein to the PBS reduced the influence of pH on the corrosion behaviour of all the alloys. The effect of the corrosion and repassivation was investigated by measuring changes in the surface hardness of the alloys and it was found that corrosion reduced the hardness of the surface oxides of all the alloys. In PBS the reduction was smallest for Ti-6Al-4V and largest for Ti-13Nb- 3Zr and that corrosion in protein solutions further reduced the hardness of the surface oxides. This effect was greater for Ti-6Al-4V and Ti-6Al-7Nb than for Ti-13Nb-13Zr. In conclusion, proteins in the environment appear to interact with the repassivation process at the surface of these alloys and influence the resulting surface properties.

Conjoint corrosion and wear in titanium alloys

When considering titanium alloys for orthopaedic applications it is important to examine the conjoint action of corrosion and wear. In this study we investigate the corrosion and wear behaviour of Ti-6Al-4V, Ti-6Al-7Nb and Ti-13Nb-13Zr in phosphate buffered saline (PBS), bovine albumin solutions in PBS and 10% foetal calf serum solutions in PBS. The tests were performed under four different conditions to evaluate the influence of wear on the corrosion and corrosion on the wear behaviour as follows: corrosion without wear, wear-accelerated corrosion, wear in a non-corrosive environment and wear in a corrosive environment. The corrosion behaviour was investigated using cyclic polarisation studies to measure the ability of the surface to repassivate following breakdown of the passive layer. The properties of the repassivated layer were evaluated by measuring changes in the surface hardness of the alloys. The amount of wear that had occurred was assessed from weight changes and measurement of the depth of the wear scar. It was found that in the presence of wear without corrosion the wear behaviour of Ti-13Nb-13Zr was greater than that of Ti-6Al-7Nb or Ti-6Al-4V and that in the presence of proteins the wear of all three alloys is reduced. In the presence of corrosion without wear Ti-13Nb-13Zr was more corrosion resistant than Ti-6Al-7Nb which was more corrosion resistant than Ti-6Al-4V without proteins whereas in the presence of protein the corrosion resistance of Ti-13Nb-13Zr and Ti-6Al-7Nb was reduced and that of Ti-6Al-4V increased. In the presence of corrosion and wear the corrosion resistance of Ti-13Nb-13Zr is higher than that of Ti-6Al-7Nb or Ti-6Al-4V in PBS but in the presence of proteins the corrosion resistance of Ti-13Nb-13Zr and Ti-6Al-7Nb are very similar but higher than that of Ti-6Al-4V. The wear of Ti-13Nb-13Zr is lower than that of Ti-6Al-7Nb and Ti-6Al-4V with or without the presence of proteins in a corrosive environment. Therefore the overall degradation when both corrosion and wear processes are occurring is lowest for Ti-13Nb-13Zr and highest for Ti-6Al-4V and the presence of proteins reduces the degradation of all three alloys.

Fungal spinal osteomyelitis in the immunocompromised patient: MR findings in three cases

The MR imaging findings of fungal spinal osteomyelitis in three recipients of organ transplants showed hypointensity of the vertebral bodies on T1-weighted sequences in all cases. Signal changes and enhancement extended into the posterior elements in two cases. Multiple-level disease was present in two cases (with a total of five intervertebral disks involved in three cases). All cases lacked hyperintensity within the disks on T2-weighted images. In addition, the intranuclear cleft was preserved in four of five affected disks at initial MR imaging. MR features in Candida and Aspergillus spondylitis that are distinct from pyogenic osteomyelitis include absence of disk hyperintensity and preservation of the intranuclear cleft on T2-weighted images. Prompt recognition of these findings may avoid delay in establishing a diagnosis and instituting treatment of opportunistic osteomyelitis in the immunocompromised patient.

The relative bioavailability and in vivo-in vitro correlations for four marketed carbamazepine tablets

PURPOSE

To determine if three marketed generic carbamazepine tablets were bioequivalent to the innovator formulation, as well as to each other. In addition, to examine in vivo-in vitro relationships among the four formulations.

METHODS

Each formulation was given as a single dose to 18 healthy male and female subjects using a crossover design. Blood samples were collected for 169 hr. Carbamazepine was assayed by HPLC with UV detection.

RESULTS

In vivo fraction absorbed plots indicated that the three generic formulations were absorbed more rapidly than the innovator product, and the mean time of maximum plasma concentration was 6-7 hr sooner for the generic formulations. The mean maximum plasma concentration ranged from 17-19 percent higher for the generic products compared to the innovator, and the 90% confidence limits for Cmax data ranged from 11 1% to 126%. The mean AUC(0-infinity) for the generic products ranged from 101-104% compared to the innovator, and the confidence limits for AUC ranged from 97-108%.

CONCLUSIONS

The generic products were all more rapidly absorbed than the innovator, but simulations of steady-state concentrations indicated that it would be unlikely that these differences would have any significant clinical effect. An excellent association was seen between the Cmax and the percent of drug dissolved in vitro. The correlation was used to accurately predict the Cmax of four other 200 mg tablets evaluated in an earlier study.

Family practice in the new South Africa

Remarkable changes are taking place in the new South Africa. Planned changes in the health care arena present the new, relatively small discipline* of family practice with great opportunity for development and growth. With established generalist roots and recent formal recognition in South Africa, family practice should be well suited for a lead role in the government's efforts to extend health care access to those denied it under apartheid. Whether family practice moves into that role will depend on whether as a discipline it can project a vision of how it can meet the country's health care needs. Close examination of family practice in South Africa shows how the field reflects many of the societal problems of the past and the challenges of the future. With a clear vision of its role in the new South Africa, family practice could overcome these challenges, as well as answer a broader question about the place of family practice outside of the first world setting.

Violence and threats of violence experienced by public health field-workers

CONTEXT

Public health workers may work with clients whose behaviors are risks for both infectious disease and violence.

OBJECTIVE

To assess frequency of violent threats and incidents experienced by public health workers and risk factors associated with incidents.

DESIGN

Anonymous, self-administered questionnaires.

SETTING

Texas sexually transmitted disease (STD), human immunodeficiency virus and acquired immunodeficiency syndrome (HIV/AIDS), and tuberculosis (TB) programs.

PARTICIPANTS

Questionnaires were completed by 364 (95.5%) of 381 public health workers assigned to the programs. The STD program employed 131 workers (36%), the HIV/AIDS program, 121 workers (33%), and the TB program, 112 workers (31%).

MAIN OUTCOME MEASURES

The frequencies with which workers had ever experienced (while on the job) verbal threats, weapon threats, physical attacks, and rape, and risk factors associated with those outcomes.

RESULTS

A total of 139 (38%) of 364 workers reported 611 violent incidents. Verbal threats were reported by 136 workers (37%), weapon threats by 45 (12%), physical attacks by 14 (4%), and rape by 3 (1%). Five workers (1%) carried guns and/or knives while working. In multiple logistic regression, receipt of verbal threats was associated with worker's male sex (odds ratio [OR], 2.4; 95% confidence interval [CI], 1.5-4.0), white ethnicity (OR, 2.4; 95% CI, 1.4-4.1), experience of 5 years or longer (OR, 2.2; 95% CI, 1.3-3.8), weekend work (OR, 1.8; 95% CI, 1.1-3.1), and sexual remarks made to the worker by clients (OR, 2.0; 95% CI, 1.2-3.5). Receipt of weapon threats was associated with worker's male sex (OR, 5.7; 95% CI, 2.4-15.3), white ethnicity (OR, 4.0; 95% CI, 1.8-9.3), age of 40 years or older (OR, 2.5; 95% CI, 1.1-5.8), work experience of 5 years or longer (OR, 2.7; 95% CI, 1.2-6.0), rural work (OR, 3.6; 95% CI, 1.3-10.1), being alone with the opposite sex (OR, 3.7; 95% CI, 1.6-9.7), and interaction with homeless clients (OR, 5.2; 95% CI, 1.7-18.8). Physical attacks were associated with sexual remarks made to the worker by clients (OR, 4.2; 95% CI, 1.4-13.9). No risk factors predicting rape were identified.

CONCLUSIONS

Violence directed toward public field-workers is a common occupational hazard. An assessment of what situations, clients, and locations pose the risk of violence to public health workers is needed.

Relationship between cerebral blood flow and the development of swelling and life-threatening herniation in acute ischemic stroke

OBJECT

The purpose of this study was to determine whether cerebral blood flow (CBF) measurements in acute stroke could be correlated with the subsequent development of cerebral edema and life-threatening brain herniation.

METHODS

Twenty patients with aggressively managed acute middle cerebral artery (MCA) territory strokes who underwent xenon-enhanced computerized tomography (Xe-CT) CBF scanning within 6 hours of onset of symptoms were retrospectively reviewed. The relationship among CBF and follow-up CT evidence of edema and clinical evidence of brain herniation during the 36 to 96 hours following stroke onset was analyzed. Initial CT scans displayed abnormal findings in 11 patients (55%), whereas the Xe-CT CBF scans showed abnormal findings in all patients (100%). The mean CBF in the symptomatic MCA territory was 10.4 ml/100 g/minute in patients who developed severe edema compared with 19 ml/100 g/minute in patients who developed mild edema (p < 0.05). The mean CBF in the symptomatic MCA territory was 8.6 ml/100 g/minute in patients who developed clinical brain herniation compared with 18 ml/100 g/minute in those who did not (p < 0.01). The mean CBF in the symptomatic MCA territory that was 15 ml/100 g/minute or lower was significantly associated with the development of severe edema and herniation (p < 0.05).

CONCLUSIONS

Within 6 hours of acute MCA territory stroke, Xe-CT CBF measurements can be used to predict the subsequent development of severe edema and progression to clinical life-threatening brain herniation. Early knowledge of the anatomical and clinical sequelae of stroke in the acute phase may aid in the triage of such patients and alert physicians to the potential need for more aggressive medical or neurosurgical intervention.

Long-term pulmonary sequelae of severe bronchopulmonary dysplasia

OBJECTIVE

To evaluate the long-term pulmonary sequelae of survivors of bronchopulmonary dysplasia (BPD) of sufficient severity to have required supplemental oxygen for at least 1 month after term.

STUDY DESIGN

Fifteen patients with a mean age of 1.1 years were matched to preterm infants of similar gestational age and age at time of study. Pulmonary function testing included spirometry, plethysmographic lung volumes, carbon monoxide diffusion capacity, and in 9 of 15 subjects with BPD, measurement of lung static elastic recoil pressures.

RESULTS

The subjects with BPD had a mean expiratory volume in 1 second (FEV1) of 64% +/- 21% predicted (4 had an FEV1 < 50% predicted) compared with 85% +/- 11% (P < .01) for the preterm children in the control group. Subjects with BPD had a significant degree of gas trapping with a residual volume to total lung capacity ratio of 37% +/- 13% compared with 25% +/- 4% for the control group (P < .01). An inverse relationship was seen between the FEV1 and the time on supplemental oxygen (r = -0.84, P < .0001), with 3 of the 4 children whose FEV1 was < 50% requiring oxygen for more than 900 days. Those with the greatest degree of airflow limitation and gas trapping had the greatest abnormalities in both shape and position of the pressure volume curves of the lung.

CONCLUSION

Severe BPD may result in moderate to severe long-term abnormalities in pulmonary function tests.

Calcium-dependent membrane penetration is a hallmark of the C2 domain of cytosolic phospholipase A2 whereas the C2A domain of synaptotagmin binds membranes electrostatically

C2 domains have been identified in a wide range of intracellular proteins, including lipid modifying enzymes, protein kinases, GTPases, and proteins involved in membrane trafficking. Many C2 domains bind membranes in a calcium-dependent manner. The first C2 domain from synaptotagmin I (SytIC2A) and the C2 domain from cytosolic phospholipase A2 (cPLA2C2) are among the best characterized C2 domains in terms of their structures and calcium binding. Here we demonstrate that the protein-lipid interaction is dramatically different for these two domains. Photolabeling with 3-(trifluoromethyl)-3-(m-[125I]iodophenyl)diazirine ([125I]TID) in the presence of phospholipid vesicles indicates that cPLA2C2 penetrates into the hydrophobic region of the membrane. Hydrophobic surfaces on cPLA2C2 are exposed even in the absence of calcium, but only in its presence does the domain penetrate into the nonpolar core of the membrane. The interaction of SytIC2A with phospholipid membranes is primarily electrostatic with binding being abolished in 500 mM NaCl. Because soluble phospholipid head group analogues do not compete with binding of either SytIC2A or cPLA2C2 to vesicles, it is likely that membrane binding by these domains involves multiple interactions.

Lack of in vivo/in vitro correlations for 50 mg and 250 mg primidone tablets

PURPOSE

To determine if large differences in the in vitro dissolution profiles for primidone tablets would result in significant bioavailability differences.

METHODS

Two separate bioavailability studies were conducted. The first study used 18 healthy subjects and compared the bioavailability of an old 50 mg tablet formulation, a new 50 mg tablet formulation, and a suspension containing 50 mg/ml of primidone. The second study enrolled 24 subjects who were to receive a new 250 mg tablet formulation, two lots of an old 250 mg tablet formulation and a 250 mg tablet from a second manufacturer. In vitro dissolution was conducted over 90 minutes, using USP 23 Apparatus 2 at 50 rpm, with 900 ml of water.

RESULTS

Dissolution at 90 minutes for the old and new 50 mg tablets was approximately 20% and 100%, respectively. The dissolution of the four 250 mg tablets ranged from approximately 30% to 100%. The 50 mg tablet that dissolved slower had a longer Tmax and a 14% lower Cmax than the more rapidly dissolving tablet, but the AUC(0-infinity) values differed by only 3%. Only nine subjects completed the 250 mg study because of side effects. The differences in Cmax and AUC(0-infinity) among the four 250 mg tablets were less than 7%.

CONCLUSIONS

Even though there were large differences in the in vitro dissolution of the 50 mg and the 250 mg primidone tablets, the two 50 mg tablets were shown to be bioequivalent, as were the four 250 mg tablets.

Catalytic domain of phosphoinositide-specific phospholipase C (PLC). Mutational analysis of residues within the active site and hydrophobic ridge of plcdelta1

Structural studies of phospholipase C delta1 (PLCdelta1) in complexes with the inositol-lipid headgroup and calcium identified residues within the catalytic domain that could be involved in substrate recognition, calcium binding, and catalysis. In addition, the structure of the PLCdelta1 catalytic domain revealed a cluster of hydrophobic residues at the rim of the active site opening (hydrophobic ridge). To assess a role of each of these residues, we have expressed, purified, and characterized enzymes with the point mutations of putative active site residues (His311, Asn312, Glu341, Asp343, His356, Glu390, Lys438, Lys440, Ser522, Arg549, and Tyr551) and residues from the hydrophobic ridge (Leu320, Phe360, and Trp555). The replacements of most active site residues by alanine resulted in a great reduction (1,000-200,000-fold) of PLC activity analyzed in an inositol lipid/sodium cholate mixed micelle assay. Measurements of the enzyme activity toward phosphatidylinositol, phosphatidylinositol 4-monophosphate, and phosphatidylinositol 4, 5-bis-phosphate (PIP2) identified Ser522, Lys438, and Arg549 as important for preferential hydrolysis of polyphosphoinositides, whereas replacement of Lys440 selectively affected only hydrolysis of PIP2. When PLC activity was analyzed at different calcium concentrations, substitutions of Asn312, Glu390, Glu341, and Asp343 resulted in a shift toward higher calcium concentrations required for PIP2 hydrolysis, suggesting that all these residues contribute toward Ca2+ binding. Mutational analysis also confirmed the importance of His311 ( approximately 20,000-fold reduction) and His356 ( approximately 6,000-fold reduction) for the catalysis. Mutations within the hydrophobic ridge, which had little effect on PIP2 hydrolysis in the mixed-micelles, resulted in an enzyme that was less dependent on the surface pressure when analyzed in a monolayer. This systematic mutational analysis provides further insights into the structural basis for the substrate specificity, requirement for Ca2+ ion, catalysis, and surface pressure/activity dependence, with general implications for eukaryotic phosphoinositide-specific PLCs.

MR imaging of suspected acute spinal instability

Twenty-two patients with suspected acute vertebral instability were imaged within 48 h of injury using a 0.5 Tesla magnet. In all patients plain radiographs, T1 weighted gradient echo (GE) and STIR sequences were performed. Two radiologists blindly evaluated the magnetic resonance imaging (MRI) scans defining injuries with bony or soft tissue disruption of both columns as unstable. Indirect signs of instability such as soft tissue haemorrhage were recorded and correlated where possible with operative findings. Sixteen patients were radiologically unstable on MRI, five more than on plain films alone. Instability was confirmed operatively in 10 patients. The six other patients with unstable injuries were treated conservatively. Two of these patients had evidence of increased deformity before fracture union. The radiologically stable patients were treated as such and at 6-month review showed no evidence of progressive instability. The presence of soft tissue haemorrhage in the interspinous gap was not associated with ligament rupture unless actual discontinuity was demonstrated at that level. We conclude that using MRI acutely, most unstable spinal injuries can be rapidly and accurately evaluated without the need for further imaging.

Cerebral MR imaging in intravascular lymphomatosis

MR imaging data were reviewed retrospectively in four male patients (32 to 74 years old) with histologically confirmed intravascular lymphomatosis (IVL), a rare, aggressive form of non-Hodgkin lymphoma. MR findings included infarct-like lesions (n = 2), focal parenchymal enhancement (n = 3), dural/arachnoid enhancement (n = 2), and, in one case, nonspecific, patchy foci of increased signal in the white matter on long-TR images. All patients had multifocal lesions. Knowledge of the spectrum of MR imaging features in this unusual disorder may aid in diagnosis and potentially enhance the role of imaging in following response to therapy.

Exchange of perfluorodecalin for gas or oil: a model for avoiding slippage

BACKGROUND

The introduction of liquid perfluorocarbons as an intraoperative tool has greatly facilitated retinal re-apposition in giant retinal tears (GRT) and relieving retinotomies (RR). Slippage of the retina can occur during the exchange of heavy liquids for oil or gas, especially if the fill of perfluorocarbons is subtotal.

METHODS

We have used a model eye chamber to study the surface interactions of perfluorodecalin (PFD) with silicone oil and air to evaluate possible mechanisms of slippage.

RESULTS

The results demonstrate that it is possible during a PFD/air exchange to trap a wedge of aqueous which is displaced laterally and forced posteriorly during removal of the PFD, whereas during a PFD/silicone oil exchange the remaining aqueous is displaced laterally and upwards and thus trapped above the silicone oil/PFD interface.

CONCLUSIONS

We believe that during PFD/air exchange the displacement of the aqueous posteriorly can cause slippage and that this could be avoided by performing a direct PFD/silicone oil exchange.

Critical success factors for promotion and tenure in family medicine departments

PURPOSE

(1) To summarize the judgments of family medicine department leaders regarding the elements leading to success in promotion and/or tenure, and (2) to compare the views of department leaders with those of family medicine faculty who have been successfully promoted.

METHOD

Two surveys were conducted. The first was of 296 associate professor members of the Society of Teachers of Family Medicine in November 1993. The second, conducted in the summer of 1994, was of all 115 U.S. members of the Association of Departments of Family Medicine; surveys were addressed to chairs, directors, or promotion and tenure committee chairs. Both survey instruments requested data regarding each respondent's department, impressions about the promotion and tenure processes at the respondent's institution, and general impressions regarding the characteristics of successful candidates. Comparisons of the responses to the two questionnaires were made using two-tailed t-tests; responses to open-ended questions were analyzed qualitatively by two independent investigators.

RESULTS

In all, 75% of the department leaders and 67% of the associate professors returned completed questionnaires. The two groups had similar views about the importance of certain academic activities to success at promotion and tenure. The primary difference between the groups was in their estimates of weekly time available for research and writing activities: the leaders reported that successful candidates spent a mean of 25% of their work-weeks on research and writing activities; the associate professors, on the other hand, reported spending a mean of 15% of their workweeks on these activities. The department leaders described six basic groups of critical success factors. The associate professors emphasized lack of time as a major obstacle to success.

CONCLUSION

The findings emphasize the critical importance of protected time for scholarly activities (such as research and writing) if generalists are to be promoted or tenured.