Nutritional supplements after hip fracture: poor compliance limits effectiveness

BACKGROUND

Undernutrition and weight loss are important determinants of clinical outcome in older patients after hip fracture but the effectiveness of nutritional support programs in routine clinical practice remains controversial. AIMS OF THE PROJECT: To determine if oral nutritional supplements given daily for 28 days after hip fracture surgery could prevent weight loss and/or lead to improved clinical outcomes (mortality rates, discharge destination, activities of daily living or length of hospital stay) in non-malnourished community-dwelling older women with hip fracture.

METHODS

One hundred and nine women with BMI range 20-30 kg/m(2) were allocated to either nutritional supplements (352 kcal/day) or usual hospital nutrition using a quasi-randomisation technique. Body weight changes were monitored at 4 and 8 weeks and clinical outcomes were recorded at discharge and at 6 months.

RESULTS

No significant differences in weight change or clinical outcomes were seen between the two groups. Compliance with consuming the nutritional supplements was quite variable and there was a significant negative correlation between the amount of supplement consumed and subsequent weight change (r=-0.36, P=0.019).

CONCLUSIONS

Poor compliance with oral nutritional supplements is an important determinant of the effectiveness of oral nutritional interventions in preventing weight loss after hip fracture. Whilst this may explain the lack of clinical improvements seen, our data do not support the routine use of oral nutritional supplements in non-malnourished hip fracture patients.

Craniofacial trauma in children

Craniofacial trauma is relatively uncommon in children, but the potential involvement of the structures at the base of the skull and the intracranial space makes it important for physicians to understand the potential dangers presented by such injuries. This report delineates the different types of injury that can damage the upper facial skeleton and the brain of a child. The author reviews initial management and diagnosis of such injuries and examines the approach to definitive reconstructive surgery using three case studies as examples for discussion.

Evaluation of emergency caesarean sections--completion of the audit cycle in a Central London teaching hospital

We set out to complete the audit cycle of caesarean deliveries in order to determine if improvements could be achieved. This was a prospective review of clinical notes in a Central London Teaching Hospital. The study involved 152 women delivering between 18 May and 23 August 1998, and 226 women over the same time period in 1999. For each case, a proforma was completed within 72 hours of delivery. We recorded the total and emergency section rate; indications; decision-to-delivery times; reasons for delay; prescription of ranitidine and heparin; fetal blood samples and cord pH values. The total caesarean section rate decreased from 20.9% to 19.2%. The emergency section rate was unchanged at 14.8% in 1998 (70.9% of total) and 13.6% in 1999 (70.8% of total). Main reasons for emergency sections were failure to progress (59% in 1998, 47% in 1999) and fetal distress (27% in 1998, 34% in 1999). For failure to progress 76% of cases were performed within 1 hour in 1998 vs. 64% of cases in 1999. For fetal distress 39% of cases were delivered within 30 minutes in both years. Fetal blood samples were taken in 41% of fetal distress cases in 1998 and 34% in 1999. Cord pH was documented in 60% of emergency cases in 1998 (96% in 1999). Prescription of ranitidine rose from 53% to 81%. Heparin was well prescribed in both years (88% vs. 87%). Following the initial audit, the total caesarean section rate was significantly lower but there was no difference in the emergency section rate. The implementations had no effect on decision-to-delivery times or use of fetal blood sampling. Improvements were seen in obtaining cord pH values and ranitidine prescription.

Prognostic value of laparoscopic ultrasound in patients with gastro-esophageal cancer

Forty-four patients with gastro-esophageal tumors regarded as resectable by conventional staging underwent laparoscopic ultrasonography (LUS). Following LUS, seven were found to be irresectable and were managed by palliative therapies. Thirty-seven patients proceeded to surgical exploration and 36 were resected (R0 80%, R1 11%, and R2 9%). All patients were reviewed until death or for a minimum of 24 months. Patients undergoing resection had a 62% 1-year survival (median 17 months; confidence intervals, CI 6-28). LUS defined nodal status indicated a trend toward prolonged survival in the node-negative group, median 22 months (CI 5-39), compared with 13 months (CI 6-20) in the node-positive group. Disease-free survival was greater in LUS node-negative patients at 29 months (CI 23-35) compared with node-positive patients at 13 months (CI 5-21) P=0.0083. LUS staging allows prediction of the likelihood of recurrence of gastro-esophageal malignancies. This may prove useful for the appropriate allocation of patients to primary and adjuvant therapies.

Don't overlook disease management programs for low-incidence, high-cost diseases to improve your bottom line

Comprehensive coordinated care management for low-incident, high-cost diseases, like chronic renal failure, can provide a great opportunity for health plans to add immediate and significant profit to their bottom line. The resultant benefits of improved operations, improved clinical outcomes and increased patient satisfaction add further incentive for health plans to take action to implement outsourced disease management for this condition.

Fifty years since Lashley's In search of the Engram: refutations and conjectures

In his well-known article 'In Search of the Engram' published in 1950, Karl Spencer Lashley summarized his 33 years of research and theory on memory and the brain. He concluded that (1) memories are not localized but are instead distributed within functional areas of the cortex and (2) memory traces are not isolated cortical connections between inputs and outputs. Though not the first time he had expressed such convictions, their reiteration in this article was backed by Lashley's estimable reputation and expressive power and they have taken firm root in the collective knowledge of today's memory and neuropsychological research community.

Electrochemiluminescence of copper(I) bis(2,9-dimethyl-1,10- phenanthroline)

The electrochemical and electrochemiluminescence (ECL) properties of Cu[dmp]2+ (dmp = 2,9-dimethyl-1,10-phenanthroline) have been investigated. ECL has been observed for Cu(dmp)2+ in aqueous, nonaqueous, and mixed solvent solutions using tri-n-propylamine as an oxidative-reductive coreactant. The ECL intensity peaks at potential corresponding to oxidation of both the coreactant and Cu(dmp)2+. The peak potential corresponding to maximum ECL emission is approximately 500 mV more anodic than corresponding oxidative peak potentials, indicating that the ECL emission may be due to the formation of either the *Cu(dmp)2+ metal-to-ligand charge-transfer excited state or an excited-state product of Cu(dmp)2+ oxidation. ECL efficiencies (phiecl = photons generated per redox event) are solvent-dependent (phiecl (CH3CN) > phiecl (50:50 (v/v) CH3CN:H20) > phiecl (H2O)) and correspond fairly well with photoluminescence efficiencies. Increased ECL efficiencies (> or = 50-fold) are observed in the presence of the nonionic surfactant Triton X-100.

Characterization of the electrochemical oxidation of peroxynitrite: relevance to oxidative stress bursts measured at the single cell level

The electrochemical signature of peroxynitrite oxidation is reported for the first time, and its mechanism discussed in the light of data obtained by steady-state and transient voltammetry at microelectrodes. Peroxynitrite is an important biological species generated by aerobic cells presumably via the near diffusion-limited coupling of nitric oxide and superoxide ion. Its production by living cells has been previously suspected during cellular oxidative bursts as well as in several human pathologies (arthritis, inflammation, apoptosis, ageing, carcinogenesis, Alzheimer disease, AIDS, etc.). However, this could only be inferred on the basis of characteristic patient metabolites or through indirect detection, or by observation of follow-up species resulting supposedly from its chemical reactions in vivo. In this work, thanks to the independent knowledge of the electrochemical characteristics of ONO2- oxidation, the kinetics and intensity of this species released by single human fibroblasts could be established directly and quantitatively based on the application of the artificial synapse method. It was then observed and established that fibroblasts submitted to mechanical stresses produce oxidative bursts, which involve the release within less than a tenth of a second of a complex cocktail composed of several femtomoles of peroxynitrite, hydrogen peroxide, nitric oxide, and nitrite ions.

Excited-state dynamics in photosystem II: insights from the x-ray crystal structure

The heart of oxygenic photosynthesis is photosystem II (PSII), a multisubunit protein complex that uses solar energy to drive the splitting of water and production of molecular oxygen. The effectiveness of the photochemical reaction center of PSII depends on the efficient transfer of excitation energy from the surrounding antenna chlorophylls. A kinetic model for PSII, based on the x-ray crystal structure coordinates of 37 antenna and reaction center pigment molecules, allows us to map the major energy transfer routes from the antenna chlorophylls to the reaction center chromophores. The model shows that energy transfer to the reaction center is slow compared with the rate of primary electron transport and depends on a few bridging chlorophyll molecules. This unexpected energetic isolation of the reaction center in PSII is similar to that found in the bacterial photosystem, conflicts with the established view of the photophysics of PSII, and may be a functional requirement for primary photochemistry in photosynthesis. In addition, the model predicts a value for the intrinsic photochemical rate constant that is 4 times that found in bacterial reaction centers.

Combined CT venography and pulmonary angiography: how much venous enhancement is routinely obtained?

OBJECTIVE

Combined CT venography and helical pulmonary angiography is a new diagnostic test that permits radiologists to check both the pulmonary arteries for embolism and the deep veins of the abdomen, pelvis, and legs for thrombosis in a single examination. The purpose of this study was to determine the degree of venous enhancement routinely obtained using this combined CT examination.

MATERIALS AND METHODS

We identified all patients at a single institution who, during a 29-month period, had symptoms suggestive of pulmonary embolism and who underwent CT venography and helical pulmonary angiography. The examinations were performed after the patients received a rapid (3--5 mL/sec) IV injection of 150 mL of nonionic contrast medium (240 mg I/mL). CT venography of the abdomen, pelvis, and lower extremities was performed as follows: Beginning 3 min after the start of contrast medium infusion for helical CT pulmonary angiography, 1-cm axial images obtained at 5-cm intervals were acquired from an area ranging from the diaphragm to the calves. Patients who had evidence of deep venous thrombosis on CT scans were excluded from further analysis. The venous portions of the remaining 429 examinations were retrospectively reviewed at a CT console or workstation by one of two radiologists, and Hounsfield unit measurements were recorded from the inferior vena cava as well as from the right and left external or internal iliac, common femoral, superficial femoral, and popliteal veins. A single Hounsfield unit measurement was obtained from the center of each vessel using a region of interest that was approximately half the diameter of the vessel. Mean Hounsfield unit measurements were then calculated for these venous stations.

RESULTS

Mean Hounsfield unit measurements at the inferior vena cava and at the right and left external or internal iliac veins were 97, 95, and 95 H, respectively. Mean measurements at the common femoral veins were 95 H for both the right and left; the mean measurements at the superficial femoral veins were 91 H for both the right and left, and those at the popliteal veins were 97 H for the right and 94 H for the left.

CONCLUSION

CT venography of the abdomen, pelvis, and lower extremities begun 3 min after the start of contrast medium infusion for helical CT pulmonary angiography routinely produced high mean levels of venous enhancement.

Analysis of individual biochemical events based on artificial synapses using ultramicroelectrodes: cellular oxidative burst

Carbon fiber platinized ultramicroelectrodes placed within micrometres of a single living cell are used to monitor cellular events. This artificial synapse is used here to collect and examine the very nature of the massive oxidative bursts produced by human fibroblasts when their membrane is locally depolarized by a puncture made with a micrometre sized sealed pipette. The electrochemical analysis of the response indicates that oxidative bursts consist of a mixture of a few femtomoles of highly cytotoxic chemicals: hydrogen peroxide, nitrogen monoxide and peroxynitrite, together with nitrite ions, which may result from a partial spontaneous decomposition of peroxynitrite prior to its release by the cell.

Photochemical behavior of xanthophylls in the recombinant photosystem II antenna complex, CP26

The steady state absorption and fluorescence spectroscopic properties of the xanthophylls, violaxanthin, zeaxanthin, and lutein, and the efficiencies of singlet energy transfer from the individual xanthophylls to chlorophyll have been investigated in recombinant CP26 protein overexpressed in Escherichia coli and then refolded in vitro with purified pigments. Also, the effect of the different xanthophylls on the extents of static and dynamic quenching of chlorophyll fluorescence has been investigated. Absorption, fluorescence, and fluorescence excitation demonstrate that the efficiency of light harvesting from the xanthophylls to chlorophyll a is relatively high and insensitive to the particular xanthophyll that is present. A small effect of the different xanthophylls is observed on the extent of quenching of Chl fluorescence. The data provide the precise wavelengths of the absorption and fluorescence features of the bound pigments in the highly congested spectral profiles from these light-harvesting complexes. This information is important in assessing the mechanisms by which higher plants dissipate excess energy in light-harvesting proteins.

Picosecond time-resolved fluorescence studies on excitation energy transfer in a histidine 117 mutant of the D2 protein of photosystem II in Synechocystis 6803

The role of the peripheral reaction center chlorophyll a molecule associated with His117 of the D2 polypeptide in photosystem II was investigated in Synechocystis sp. PCC 6803 using a combination of steady state, pump-probe, and picosecond time-resolved fluorescence spectroscopy. Data were obtained from intact cells and isolated thylakoid membranes of a control mutant and a D2-H117T mutant, both of which lacked photosystem I. Excitation energy transfer and trapping were investigated by analyzing the data with a kinetic model that used an exact numerical solution of the Pauli master equation, taking into account available photosystem II spectral and structural information. The results of our kinetic analysis revealed the observed difference in excited-state dynamics between the H117T mutant and the control to be consistent with a retardation of the rate of excitation energy transfer from the peripheral chlorophyll of D2 (Chl at His117) to the electron-transfer pigments and an increase of the rate constant for charge recombination in the H117T mutant. The kinetic model was able to account for the experimentally observed changes in absorption cross section and fluorescence decay kinetics between the control and mutant by invoking changes in only these two rate constants. The results rule out quenching of excitation by a chlorophyll cation radical as a mechanism responsible for the lower efficiency of excitation energy utilization in the H117T mutant. Our work also demonstrates the importance of the chlorophyll associated with His117 of the D2 protein for excitation energy transfer to the PSII electron-transfer pigments and for the effective stabilization of the primary radical pair.

On the transition from childhood amnesia to the recall of personal memories

When adults are asked to report and date personal memories of their pasts, they show childhood amnesia, that is, diminished recall of experiences over the childhood years. This way of demonstrating the phenomenon was supplemented in the present study with a more direct approach: Participants reported events of early childhood that they knew they had experienced (because of family stories, photographs, etc.) but did not actually remember. The resulting cumulative relative frequency distributions produced by the two methods were substantially different, with the median age of remembered events being 6.07 years and of known events, 3.20 years. We suggest that the mean of these two ages, 4.64 years, gives a good indication of when childhood amnesia is eclipsed by personal memories in adults' recall of their personal pasts.

Intrathecal baclofen for management of spastic cerebral palsy: multicenter trial

Intrathecal baclofen infusion has demonstrated effectiveness in decreasing spasticity of spinal origin. Oral antispasticity medication is minimally effective or not well tolerated in cerebral palsy. This study assessed the effectiveness of intrathecal baclofen in reducing spasticity in cerebral palsy. Candidates were screened by randomized, double-blind, intrathecal injections of baclofen and placebo. Responders were defined as those who experienced an average reduction of 1.0 in the lower extremities on the Ashworth Scale for spasticity. Responders received intrathecal baclofen via the SynchroMed System and were followed for up to 43 months. Fifty-one patients completed screening and 44 entered open-label trials. Lower-extremity spasticity decreased from an average baseline score of 3.64 to 1.90 at 39 months. A decrease in upper extremity spasticity was evidenced over the same study period. Forty-two patients reported adverse events. Most common reports were hypotonia, seizures (no new onset), somnolence, and nausea or vomiting. Fifty-nine percent of the patients experienced procedural or system-related events. Spasticity in patients with cerebral palsy can be treated effectively by continuous intrathecal baclofen. Adverse events, although common, were manageable.

Undergraduate students' misconceptions about respiratory physiology

Approximately 700 undergraduates studying physiology at community colleges, a liberal arts college, and universities were surveyed to determine the prevalence of our misconceptions about respiratory phenomena. A misconception about the changes in breathing frequency and tidal volume (physiological variables whose changes can be directly sensed) that result in increased minute ventilation was found to be present in this population with comparable prevalence (approximately 60%) to that seen in a previous study. Three other misconceptions involving phenomena that cannot be experienced directly and therefore were most likely learned in some educational setting were found to be of varying prevalence. Nearly 90% of the students exhibited a misconception about the relationship between arterial oxygen partial pressure and hemoglobin saturation. Sixty-six percent of the students believed that increasing alveolar oxygen partial pressure leads to a decrease in alveolar carbon dioxide partial pressure. Nearly 33% of the population misunderstood the relationship between metabolism and ventilation. The possible origins of these respiratory misconceptions are discussed and suggestions for how to prevent and/or remediate them are proposed.

Human apo-lipoprotein B from normal plasma contains oxidised peptides

Oxidation of low density lipoprotein (LDL) may be atherogenic, but radical-initiated oxidation of its apoprotein B-100 (apoB) has been little studied. Transition metal ions iron and copper are candidates for mediating radical oxidation of LDL in vivo. Therefore, we studied the copper-ion-induced oxidation of apoB in human LDL. Using HPLC methods developed in our recent work, we studied the destruction of native and the generation of six oxidised amino acids; we also assessed the release of peptides from the LDL particle by FPLC. We observed time-dependent losses of apoB histidine, lysine and glycine. Long-lived reactive species, the reductant DOPA, and the oxidant hydroperoxides of valine and leucine (measured as hydroxides after reduction), were generated. Their relative abundance (mol/mol of parent amino acid) was DOPA > o- and m-tyrosine > dityrosine, valine-hydroxides, leucine hydroxides. Low molecular weight fragments were also released from the LDL in a time-dependent manner, contained hydroperoxides sensitive to GSH peroxidase, and generated radicals on reaction with iron-EDTA. The fragments contained peptides active in the quinone redox cycling procedure, comprising 0.25% of the supplied LDL amino acids. Characteristic peptides were present in each FPLC fraction containing the fragments, as judged by further HPLC fractionation. Some fragments were present in the unoxidised LDL preparations, and when these were largely removed by FPLC, copper oxidation could still generate fragments, suggesting that those present in the starting material might indicate prior oxidation. Concordantly, we found that fresh plasma LDL apoB contained 43% of total plasma protein-bound oxidised amino acids, and with the same relative abundance. We conclude that plasma proteins including apoB are subject to physiological oxidation, similar to that inflicted by copper ions; the latter may contribute to intimal LDL oxidation, which could be the source of oxidised plasma apoB.

Splenectomy during partial remission in thrombotic thrombocytopenic purpura with prolonged plasma exchange dependency

Some patients with thrombotic thrombocytopenic purpura (TTP) remain plasma-exchange-dependent for prolonged periods of time. This exposes patients to risk, uses substantial resources, and requires prolonged hospitalization. We have splenectomized 7 such patients following 25-42 plasma exchanges while patients were in partial remission only and were clinically stable. In 6 patients, including 1 with TTP secondary to mitomycin C, thrombocytopenia promptly resolved. Relapse has not occurred during 18 or more months of observation. The seventh patient did not respond. We conclude that splenectomy should be considered as an alternative to continued plasma-exchange therapy in such patients.

Posterior fossa syndrome: identifiable risk factors and irreversible complications

Cerebellar mutism was first described by Rekate et al. in 1985 as a transient condition which occurs after posterior fossa operations in children. Posterior fossa syndrome (PFS) and cerebellar mutism are often used interchangeably in the literature. In our experience, we found cerebellar mutism to be a reversible component of a persistent neurologic syndrome. The cause and identifiable risk factors have not been clearly elucidated in the literature. To further characterize PFS, we reviewed 253 children with posterior fossa tumors who underwent surgical resection. We documented 20 cases of PFS (8%), 12 males and 8 females. Age ranged from 1.5 to 13 years (mean = 6.5). Of the 20, 16 were medulloblastoma, 3 ependymoma and 1 astrocytoma. There was a 21 % incidence (16/76) of PFS in medulloblastoma of the posterior fossa. The incidence for ependymoma was 13% (3/24) and 1% (1/102) for astrocytoma. All 20 cases (100%) had brainstem involvement by the tumor. The most frequent postoperative findings included mutism, ataxia, 6th and 7th nerve palsies and hemiparesis. Mutism had a latency range of 1-7 days (mean = 1.7) and a duration of 6-365 days (mean = 69.2, median = 35). Although mutism resolved in all cases, the remaining neurologic complications which characterized our findings of PFS were rarely reversible. We describe potential risk factors for developing PFS after surgery with hopes of making neurosurgeons more aware of potential problems following the removal of lesions in this area. Early recognition of PFS would further promote patient and family understanding and coping with this syndrome.

Modulation of flash-induced photosystem II fluorescence by events occurring at the water oxidizing complex

The mechanism of flash-induced changes with a periodicity of four in photosystem II (PSII) fluorescence was investigated with the aim of further using fluorescence measurements as an approach to studying the structural and functional organization of the water-oxidizing complex (WOC). The decay of the flash-induced high fluorescence state of PSII was measured with pulse amplitude modulated fluorometry in thylakoids and PSII enriched membrane fragments. Calculated QA- decay was well described by three exponential decay components, reflecting QA- reoxidation with halftimes of 450 and 860 micros, 2 and 7.6 ms, and 111 and 135 ms in thylakoids and PSII membranes, respectively. The effect of modification of the PSII donor side by changing pH or by removal of the extrinsic 17 and 24 kDa proteins on period four oscillations in both maximum fluorescence yield and the relative contribution of QA- reoxidation reactions was compared to flash-induced oxygen yield. The four-step oxidation of the manganese cluster of the WOC was found to be necessary but not sufficient to produce modulation of PSII fluorescence. The capacity of the WOC to generate molecular oxygen was also required to observe a period four in the fluorescence; however, direct quenching by oxygen was not responsible for the modulation. Potential mechanisms responsible for the periodicity of four in both maximum fluorescence yield pattern and flash-dependent changes in proportion of centers with different QA- reoxidation rates are discussed with respect to intrinsic deprotonation events occurring at the WOC.

Corpus callosum damage and interhemispheric transfer of information following closed head injury in children

We evaluated the relationship of corpus callosum atrophy and/or lesions on magnetic resonance imaging (MRI) to functional hemispheric disconnection following closed head injury (CHI) in 51 pediatric patients, including mild CHI, moderate to severe CHI with extracallosal lesions, and moderate to severe CHI with callosal atrophy and/or lesions. Interhemispheric transfer of information was assessed using auditory, motor, tactile, and visual tests in patients and in 16 uninjured children. Total and regional callosal areas were measured from the midsagittal MRI slice by morphometry. The corpus callosum lesion group demonstrated a greater right ear advantage on verbal dichotic listening than all other groups. Areas of the posterior corpus callosum were negatively correlated with laterality indices of verbal dichotic listening performance and tachistoscopic identification of verbal material. The relationship of corpus callosum atrophy and/or lesions to asymmetry in dichotic listening is consistent with previous investigation of posttraumatic hemispheric disconnection effects in adults.

Evaluation of 18F-FDG positron emission tomography in gastric and oesophageal carcinoma

The aim of this study was to evaluate 18F-fluoro-deoxyglucose (FDG) positron emission tomography (PET) in gastric and oesophageal carcinoma. 16 patients with biopsy proven oesophageal or gastric carcinoma had PET scans. Four patients had advanced disease and received palliative treatment. The remaining 12 patients were randomized to immediate surgery or neoadjuvant chemotherapy. Three patients had repeat PET scans following chemotherapy. PET detected the primary tumour in all cases including stage T1 lesions. Involved locoregional nodes (N1, N2) were not identified separately from the primary tumour. Semiquantitative analysis was performed in the form of tumour to liver activity ratios (TLR). In general, the TLR values were higher in the higher T stages, although there was only one case each of T1 and T2 lesions. PET scanning using 18F-FDG is a sensitive method for detecting primary oesophageal and gastric cancers but is limited in locoregional staging.

Amplification of the inflammatory cellular redox state by human immunodeficiency virus type 1-immunosuppressive tat and gp160 proteins

In the course of our studies on oxidative stress as a component of pathological processes in humans, we showed that microintrusion into cells with microcapillary and ultramicroelectrochemical detection could mimic many types of mechanical intrusion leading to an instant (0.1 s) and high (some femtomoles) burst release of H2O2. Specific inhibitors of NADPH enzymes seem to support the assumption that this enzyme is one of the main targets of our experiments. Also, human immunodeficiency virus type 1 (HIV-1) gp160 inhibits the cooperative response of uninfected T cells as well as Tat protein release by infected cells does. In this study, we analyzed in real time, lymphocyte per lymphocyte, the T-cell response following activation in relation to the redox state. We showed that the immunosuppressive effects of HIV-1 Tat and gp160 proteins and oxidative stress are correlated, since the native but not the inactivated Tat and gp160 proteins inhibit the cellular immune response and enhance oxidative stress. These results are consistent with a role of the membrane NADPH oxidase in the cellular response to immune activation.

Nonphotochemical quenching of excitation energy in photosystem II. A picosecond time-resolved study of the low yield of chlorophyll a fluorescence induced by single-turnover flash in isolated spinach thylakoids

Chlorophyll a fluorescence emission is widely used as a noninvasive measure of a number of parameters related to photosynthetic efficiency in oxygenic photosynthetic organisms. The most important component for the estimation of photochemistry is the relative increase in fluorescence yield between dark-adapted samples which have a maximal capacity for photochemistry and a minimal fluorescence yield (F0) and light-saturated samples where photochemistry is saturated and fluorescence yield is maximal (Fm). However, when photosynthesis is saturated with a short (less than 50 micro(s)) flash of light, which induces only one photochemical turnover of photosystem II, the maximal fluorescence yield is significantly lower (Fsat) than when saturation is achieved with a millisecond duration multiturnover flash (Fm). To investigate the origins of the difference in fluorescence yield between these two conditions, our time-resolved fluorescence apparatus was modified to allow collection of picosecond time-resolved decay kinetics over a short time window immediately following a saturating single-turnover flash (Fsat) as well as after a multiturnover saturating pulse (Fm). Our data were analyzed with a global kinetic model based on an exciton radical pair equilibrium model for photosystem II. The difference between Fm and Fsat was modeled well by changing only the rate constant for quenching of excitation energy in the antenna of photosystem II. An antenna-based origin for the quenching was verified experimentally by the observation that addition of the antenna quencher 5-hydroxy-1,4-naphthoquinone to thylakoids under Fm conditions resulted in decay kinetics and modeled kinetic parameters very similar to those observed under Fsat conditions in the absence of added quinone. Our data strongly support the origin of low fluorescence yield at Fsat to be an antenna-based nonphotochemical quenching of excitation energy in photosystem II which has not usually been considered explicitly in calculations of photochemical and nonphotochemical quenching parameters. The implications of our data with respect to kinetic models for the excited-state dynamics of photosystem II and the practical applications of the fluorescence yield parameters Fm and Fsat to calculations of photochemical yield are discussed.

Early diagnosis of subependymal giant cell astrocytoma in patients with tuberous sclerosis

We present 19 patients with tuberous sclerosis complex and subependymal giant cell astrocytoma. The mean age at the time of tumor diagnosis was 9.4 years (range, 1.5 to 21 years). Computed cranial tomography (CT) or cranial magnetic resonance imaging (MRI) identified the lesion which was resected in all cases. Seven patients had hydrocephalus and there was an interval increase in the tumor size or a large tumor without hydrocephalus in 12 patients. Surgical criteria included: (1) presence of hydrocephalus; (2) interval increase in tumor size; (3) new focal neurologic deficit attributable to the tumor; and/or (4) symptoms of increased intracranial pressure. Eight patients were identified through a surveillance program involving annual computed cranial tomography. All of these eight patients had their tumor removed prior to the development of symptoms, none had neurologic deficits which persisted after surgery, and none has so far developed recurrent subependymal giant cell astrocytoma. In contrast, of the 11 patients from the non-surveillance group 7 were symptomatic at tumor diagnosis, 1 had a complicated postoperative course, 2 developed recurrent giant cell astrocytoma, and 1 had an extensive lesion that could not be completely excised. Periodic cranial imaging may help to identify subependymal giant cell astrocytomas in tuberous sclerosis patients before they become symptomatic. Earlier diagnosis and treatment could reduce surgical morbidity and the risk of tumor recurrence.

The Lashley-Hull debate revisited

N. Weidman (1994) claimed that "Karl Lashley and Clark Hull had a long and unresolved controversy about the structure and function of the brain, its relationship to the mind, and the use of machine metaphors to explain intelligence" (p. 162). The record contained in published articles and unpublished correspondence indicates otherwise. The clash was explicitly about continuity versus noncontinuity in discrimination learning, stimulus generalization, and the development of quantitative and mathematical psychological theory and its relation to neurophysiological data. Weidman also contended that the subtext of the debate was whether heredity or environment was more important in determining intelligence and behavior. This is doubtful. It is more probable that the debate stemmed from Lashley's career-long opposition to connectionism.

Preparative induction and characterization of L-antithrombin: a structural homologue of latent plasminogen activator inhibitor-1

The inhibitory mechanism of the serpin family of serine protease inhibitors is characterized by a remarkable degree of conformational flexibility. Various conformational states have been elucidated by X-ray crystallography and indicate that the inhibitory loop, the central A-beta-sheet, and the outside edge of the C-beta-sheet are particularly mobile. However, no crystal structure of a serpin-enzyme complex is yet available, and the likely nature of the protease-complexed serpin remains for biochemical and biophysical researchers to examine. Here, we show that the biochemical induction of the latent state of antithrombin is slow relative to polymer formation, and infer that this may reflect structural features that are important for the regulation of the initial docking and subsequent locking of serpins with cognate proteases. L-Antithrombin was induced by incubation of native antithrombin at 60 degrees C for 10 h in the presence of citrate to prevent polymerization. L-Antithrombin was more stable to denaturation by both heat and urea than native antithrombin. Whereas native antithrombin formed binary complexes with synthetic peptide homologues of the inhibitory loop, biochemically induced L-antithrombin did not, indicating that the inhibitory loop of L-antithrombin is probably fully inserted into the A-beta-sheet as in the crystal structure. This was confirmed by limited proteolysis studies which demonstrated that the inhibitory loop of L-antithrombin could not be cleaved by five proteases which do cleave the loop of native antithrombin. The limited proteolysis studies also indicated that the "gate" region (residues 236-248) of the biochemically induced L-antithrombin was in a conformation substantially different from that of the native antithrombin. This again is similar to L-antithrombin in the crystal structure in which the gate has "opened" away from the body of the molecule by a rotation of 24 degrees to facilitate the relocation of strand 1C from its ordered position in the C-beta-sheet to a disordered surface loop. At 60 degrees C in the absence of citrate, antithrombin (and other serpins) rapidly polymerizes. In the presence of citrate, the formation of L-antithrombin is slow and increases with time, indicating that the inhibition of polymer formation by citrate allows the time necessary for the much slower formation of the L form. We therefore suggest that L-antithrombin formation is a two-step process: an initial rapid conformational change, probably including partial incorporation of the reactive loop into the A-sheet (as in the active molecule in the crystal structure) and displacement of s1C from the C-beta-sheet which supports polymer formation, and a much slower transition to complete loop insertion within the A-beta-sheet. It is likely that both the first rapid transitional step and the structural features that impose resistance to the second more extensive conformational change reflect the optimization of the unique inhibitory function in the serpins.

Magnetic resonance imaging in relation to functional outcome of pediatric closed head injury: a test of the Ommaya-Gennarelli model

OBJECTIVE

To characterize late neuropathological findings of pediatric closed head injury (CHI), to assess depth of brain lesion in relation to acute severity, and to assess long-term outcome to test the Ommaya-Gennarelli model.

METHODS

Magnetic resonance imaging (MRI) at least 3 months postinjury in a prospective sample (n 5 169) and at least 3 years after CHI in a retrospective sample (n 5 82) was studied. Lesion volume was measured by planimetry. Acute CHI severity was measured by the Glasgow Coma Scale. Patients were classified according to the depth of the deepest parenchymal lesion into no lesion, subcortical, and deep central gray/brain stem groups. The outcomes were assessed by the Glasgow Outcome Scale and the Vineland Adaptive Behavior Scale, which were performed at the time of the MRI in the retrospective sample and up to 3 years postinjury in the prospective sample.

RESULTS

Focal brain lesions were present in 55.4% of the total sample. Depth of brain lesion was directly related to severity of acute impairment of consciousness and inversely related to outcome, as measured by both the Glasgow Outcome Scale and the Vineland Adaptive Behavior Scale. A rostrocaudal gradient of hemispheric lesion frequency was observed, whereas the posterior lesions of the corpus callosum were particularly common. Total lesion volume could not explain the depth of lesion effect.

CONCLUSION

Our findings extend support for the Ommaya-Gennarelli model to pediatric CHI, indicating that depth of brain lesion is related to functional outcome. The relative frequency of focal brain lesions revealed by late MRI is higher than that of previous findings using acute computed tomography. Future investigations could explore whether depth of lesion observed using late MRI is sensitive to neuroprotective interventions.

The origins of nonphotochemical quenching of chlorophyll fluorescence in photosynthesis. Direct quenching by P680+ in photosystem II enriched membranes at low pH

In most plants and algae, a down-regulation of photosynthesis under "excess" light conditions occurs which is associated with a quenching of chlorophyll a fluorescence. This nonphotochemical quenching of chlorophyll a fluorescence most likely arises from a mechanism which protects photosystem II from excessive excitation and resulting photoinhibition. In this report, nonphotochemical quenching of variable chlorophyll a fluorescence was induced by low pH in photosystem II enriched spinach thylakoid membranes. The origin of quenching was investigated with picosecond fluorescence decay spectroscopy in samples suspended in buffers ranging from pH 6.5 to pH 4.0. The yield of a relatively slow (approximately 1.5 ns) fluorescence decay process associated with the photosystem II reaction center decreased with decreasing pH. There were no significant changes in the yield of faster decay components associated with photosystem II antenna chlorophyll a processes. These results suggest a reaction center based rather than antenna chlorophyll based mechanism for nonphotochemical quenching in these preparations. Measurements of the photosystem II absorption cross section revealed no decrease in the functional antenna size at low pH which also supports a reaction center quenching mechanism. The kinetics of electron transfer in photosystem II were investigated using a pump probe spectrometer which measured simultaneously the flash-induced absorbance change at 820 nm (formation of oxidized photosystem II reaction center pigment, P680+) and the variable fluorescence yield (formation of reduced photosystem II, electron acceptor, QA-). A large increase in the lifetime of P680+ at low pH was correlated with fluorescence quenching. After flash excitation of photosystem II the loss of fluorescence quenching occurred with the same kinetics as the reduction of P680+. In conflict with reaction center based quenching mechanisms based on charge recombination between P680+ and QA-, the oxidation rate of QA- was unaffected by low pH and under all conditions occurred at a slower rate than the reduction of P680+. Our data are discussed in terms of a model for low pH dependent nonphotochemical quenching in photosystem II based on direct quenching by P680+.

Effects of ectopic overexpression of p21(WAF1/CIP1) on aneuploidy and the malignant phenotype of human brain tumor cells

p21WAF1/CIP1 is a downstream effector of the p53 tumor suppressor gene and a universal cyclin-dependent kinase (CDK) inhibitor. To determine the ability of p21WAF1/CIP1 to function as a tumor suppressor, we constructed a replication-defective adenovirus vector containing p21WAF1/CIP1 (Adp21WAF1/CIP1) to effect ectopic overexpression in a p53-defective human astrocytoma cell line, U-373MG. We observed a marked decrease in CDC2 and CDK2 kinase activity associated with a corresponding decrease in the amount of CDC2 but not CDK2 protein; a decreased growth potential of Adp21WAF1/CIP1-infected cells demonstrated by diminished [3H]thymidine incorporation, increased cell doubling time and G1-arrested cell cycle; an association between Adp21WAF1/CIP1-infected cells and inhibition of aneuploid cell accumulation; and an alteration of the malignant phenotype of cells was evidenced by the loss of anchorage-independent growth in soft agar and the failure to induce tumorigenesis in both peripheral and intracerebral xenograft models, including the prevention of tumor formation Adp21WAF1/CIP1 infection 2 days post tumor cell implantation. Adp21WAF1/CIP1. Adp21WAF1/CIP1 appears to be a strong candidate for gene therapy studies based on these studies indicating that Adp21WAF1/CIP1 inhibits proliferation, tumorigenicity and aneuploidy in human brain tumor cells.

Semantic memory following pediatric head injury: relationship to age, severity of injury, and MRI

The effects of closed head injury (CHI) severity (mild vs. severe) and age at injury were analyzed in a longitudinal study (3. 12 months postinjury) of semantic memory which used magnetic resonance imaging (MRI) to characterize focal brain lesions. Semantic memory was evaluated by word and category fluency, semantic verification, semantic clustering in word list recall, and vocabulary. Episodic memory was assessed by word list recall. Comparison of normal control (n = 104) data with the patients' data (n = 77) at 3 months postinjury disclosed semantic and episodic memory deficits in the severe CHI patients. Analysis of the longitudinal data revealed significant effects of age at injury for all of the semantic memory measures. The effects of injury severity were confined to the latency of verifying correct statements. Volume of left frontal and extrafrontal lesions was predictive of performance on several semantic memory measures, but less robust for right hemisphere lesions.

Characterization of the non-photochemical quenching of chlorophyll fluorescence that occurs during the active accumulation of inorganic carbon in the cyanobacterium Synechococcus PCC 7942

Previous work has shown that the maximum fluorescence yield from PS 2 of Synechococcus PCC 7942 occurs when the cells are at the CO2 compensation point. The addition of inorganic carbon (Ci), as CO2 or HCO3 (-), causes a lowering of the fluorescence yield due to both photochemical (qp) and non-photochemical (qN) quenching. In this paper, we characterize the qN that is induced by Ci addition to cells grown at high light intensities (500 μmol photons m(-2) s(-1)). The Ci-induced qN was considerably greater in these cells than in cells grown at low light intensities (50 μmol photons m(-2) s(-1)), when assayed at a white light (WL) intensity of 250 μmol photons m(-2) s(-1). In high-light grown cells we measured qN values as high as 70%, while in low-light grown cells the qN was about 16%. The qN was relieved when cells regained the CO2 compensation point, when cells were illuminated by supplemental far-red light (FRL) absorbed mainly by PS 1, or when cells were illuminated with increased WL intensities. These characteristics indicate that the qN was not a form of energy quenching (qE). Supplemental FRL illumination caused significant enhancement of photosynthetic O2 evolution that could be correlated with the changes in qp and qN. The increases in qp induced by Ci addition represent increases in the effective quantum yield of PS 2 due to increased levels of oxidized QA. The increase in qN induced by Ci represents a decrease in PS 2 activity related to decreases in the potential quantum yield. The lack of diagnostic changes in the 77 K fluorescence emission spectrum argue against qN being related to classical state transitions, in which the decrease in potential quantum yield of PS 2 is due either to a decrease in absorption cross-section or by increased 'spill-over' of excitation energy to PS 1. Both the Ci-induced qp (t 0.5<0.5 s) and qN (t 0.5≃1.6 s) were rapidly relieved by the addition of DCMU. The two time constants give further support for two separate quenching mechanisms. We have thus characterized a novel form of qN in cyanobacteria, not related to state transitions or energy quenching, which is induced by the addition of Ci to cells at the CO2-compensation point.

Two forms of the Photosystem II D1 protein alter energy dissipation and state transitions in the cyanobacterium Synechococcus sp. PCC 7942

Synechococcus sp. PCC 7942 (Anacystis nidulans R2) contains two forms of the Photosystem II reaction centre protein D1, which differ in 25 of 360 amino acids. D1: 1 predominates under low light but is transiently replaced by D1:2 upon shifts to higher light. Mutant cells containing only D1:1 have lower photochemical energy capture efficiency and decreased resistance to photoinhibition, compared to cells containing D1:2. We show that when dark-adapted or under low to moderate light, cells with D1:1 have higher non-photochemical quenching of PS II fluorescence (higher qN) than do cells with D1:2. This is reflected in the 77 K chlorophyll emission spectra, with lower Photosystem II fluorescence at 697-698 nm in cells containing D1:1 than in cells with D1:2. This difference in quenching of Photosystem II fluorescence occurs upon excitation of both chlorophyll at 435 nm and phycobilisomes at 570 nm. Measurement of time-resolved room temperature fluorescence shows that Photosystem II fluorescence related to charge stabilization is quenched more rapidly in cells containing D1:1 than in those with D1:2. Cells containing D1:1 appear generally shifted towards State II, with PS II down-regulated, while cells with D1:2 tend towards State I. In these cyanobacteria electron transport away from PS II remains non-saturated even under photoinhibitory levels of light. Therefore, the higher activity of D1:2 Photosystem II centres may allow more rapid photochemical dissipation of excess energy into the electron transport chain. D1:1 confers capacity for extreme State II which may be of benefit under low and variable light.

Left ventricular thrombi in a patient with the antiphospholipid syndrome

A 41 year old woman with the antiphospholipid antibody syndrome presented with a cerebral embolus. This was caused by a mobile left ventricular thrombus that later resolved. There was an additional old left ventricular thrombus. Left ventricular thrombi such as these have not been previously described in this syndrome, and may have been under diagnosed.

Superimposition of PET images using 18F-fluorodeoxyglucose with magnetic resonance images in patients with pancreatic carcinoma

Six patients with histologically proven adenocarcinoma of the pancreas were studied using 2-deoxy-2-[18F]-fluoro-D-glucose (18F-FDG) using positron emission tomography (PET), and magnetic resonance imaging (MRI). In all six cases there was avid accumulation of 18F-FDG within the pancreatic tumour and clear visualization of the tumour on the MRI images. Delineation of the tumours was aided by superimposition of the images from the two imaging methods, which was achieved by using a system of surface markers.

Functional analysis of the iron-stress induced CP 43' polypeptide of PS II in the cyanobacterium Synechococcus sp. PCC 7942

Under conditions of iron-stress, the Photosystem II associated chlorophyll a protein complex designated CP 43', which is encoded by the isiA gene, becomes the major pigment-protein complex in Synechococcus sp. PCC 7942. The isiB gene, which is located immediately downstream of isiA, encodes the protein flavodoxin, which can functionally replace ferredoxin under conditions of iron stress. We have constructed two cyanobacterial insertion mutants which are lacking (i) the CP 43' apoprotein (designated isiA (-)) and (ii) flavodoxin (designated isiB (-)). The function of CP 43' was studied by comparing the cell characteristics, PS II functional absorption cross-sections and Chl a fluorescence parameters from the wild-type, isiA (-) and isiB (-) strains grown under iron-stressed conditions. In all strains grown under iron deprivation, the cell number doubling time was maintained despite marked changes in pigment composition and other cell characteristics. This indicates that iron-starved cells remained viable and that their altered phenotype suggests an adequate acclimation to low iron even in absence of CP 43' and/or flavodoxin. Under both iron conditions, no differences were detected between the three strains in the functional absorption crossection of PS II determined from single turnover flash saturation curves of Chl a fluorescence. This demonstrates that CP 43' is not part of the functional light-harvesting antenna for PS II. In the wild-type and the isiB (-) strain grown under iron-deficient conditions, CP 43' was present in the thylakoid membrane as an uncoupled Chl-protein complex. This was indicated by (1) an increase of the yield of prompt Chl a fluorescence (Fo) and (2) the persistence after PS II trap closure of a fast fluorescence decay component showing a maximum at 685 nm.

Thromboembolic disease due to thermolabile conformational changes of antithrombin Rouen-VI (187 Asn-->Asp)

A new variant of antithrombin (Rouen-VI, 187 Asn-->Asp) with increased heparin affinity was shown to have normal inhibitory activity which decreased slowly at 4 degrees C and rapidly at 41 degrees C. On electrophoresis the freshly isolated variant had an anodal shift relative to native antithrombin due to the mutation. A further anodal transition occurred after either prolonged storage at 4 degrees C or incubation at 41 degrees C due to the formation of a new inactive uncleaved component with properties characteristic of L-form (latent) antithrombin. At the same time, polymerization also occurred with a predominance of di-, tri-, and tetra-mers. These findings fit with the observed mutation of the conserved asparagine (187) in the F-helix destabilizing the underlying A-sheet of the molecule. Evidence of A-sheet perturbation is provided by the increased rate of peptide insertion into the A-sheet and by the decreased vulnerability of the reactive loop to proteolysis. The spontaneous formation of both L-antithrombin and polymers is consistent with our crystal structure of intact antithrombin where L-form and active antithrombin are linked together as dimers. The nature of this linkage favors a mechanism of polymerization whereby the opening of the A-sheet, to give incorporation of the reactive center loop, is accompanied by the bonding of the loop of one molecule to the C-sheet of the next. The accelerated lability of antithrombin Rouen-VI at 41 versus 37 degrees C provides an explanation for the clinical observation that episodes of thrombosis were preceded by unrelated pyrexias.