National survey for investigating the diagnostic imaging departments reorganization and management during the COVID-19 pandemic

Introduction

The COVID-19 pandemic has had a profound impact on radiography services globally. The objective of this study was to evaluate the impact of the COVID-19 pandemic on the management of radiology departments in Italy.

Methods

An online survey with 32 questions was developed and promoted by the Italian Federation of Scientific Radiographer Societies (FASTeR) and sent to all Radiology Service Managers (RSM) identified in the RSM committee of the Italian Federation of Radiographers and Health Professionals, counting for 39 Italian RSM, representing more than 1,200 radiographers. The survey included questions regarding RSM demographics data, the number of radiographers and specialties managed, the effects of the pandemic on the diagnostic imaging service, and any reorganizations that had been implemented, such as the partial or total suspension of diagnostic activities and the number of radiographers tested as positive to COVID-19.

Results

Twenty (52%) RSM from different Italian regions completed the questionnaire. A total of 70% of respondents had implemented reorganizations in terms of space, equipment, and pathways dedicated to COVID-19-infected patients, including an extension of the timing of acquisition of the exams. More than half of the respondents reported breast and DXA imaging unit had suffered the most suspension of activities. 70% of respondents reported that more than 50% of radiographers were resulted as COVID-19 positive.

Conclusion

These data show how challenging was of the reorganization of Italian diagnostic imaging departments during the COVID-19 pandemic, with impact on the suspension of some exams and the rescheduling of breast and DXA imaging. The reorganization of the services also had to consider the high number of radiographers suspended from activity due to the positivity to COVID-19, and the lengthening of the duration of the examinations due to the sanitation of the spaces.

Analysis and management of the COVID-19 pandemic impact on a multispecialty diagnostic imaging department

Introduction

The propose of this study was to evaluate the impact of the first two waves of the COVID-19 pandemic on a multispecialty radiology department in a large tertiary university hospital in Northern Italy.

Methods

The numbers of all radiological exams performed in the radiology department of Scientific Institute for Research, Hospitalization and Healthcare (namely, IRCCS) Policlinico San Donato (San Donato Milanese, Italy) from March 2019 to March 2021 were collected and compared, subdividing them both temporally, modality, sub-specialty, and setting.

Results

Comparing the first 12 months of the COVID-19 pandemic (from March 2020 to February 2021) with the previous 12 months (from March 2019 to February 2020), there was an overall decrease in total radiological examinations equal to 26% (from 127,998 to 94,550). The most affected modality was DXA (from 4,706 to 2,989, -36%), followed by ultrasonography (from 17,212 to 11,644, -32%), digital radiography (from 66,050 to 47,374, -28%), MRI (from 13,332 to 10,140, -24%), CT (from 19,208 to 15,746, -18%), and mammograms (from 7,490 to 6,657, -11%). Chest CTs of inpatients saw a +15% surge (from 1,087 to 1,144), with far larger sizable increments being observed for chest X-ray examinations of outpatients (from 3,032 to 7,536, +131%). Further sub-analysis according to pandemic waves highlighted an overall -65% decrease of radiological services during the first wave (from March to May 2020), curtailed to -3% during the June–October period and then again rising to -23% during the second wave (from November 2020 to February 2021).

Conclusion

The COVID-19 pandemic led to a marked decrease of total radiological examinations during the two pandemic waves, limited to -26% by the implementation of safety protocols during the second wave and by increased activity during the inter-wave period.

Epicardial adipose tissue volume in patients with coronary artery disease or non-ischaemic dilated cardiomyopathy: evaluation with cardiac magnetic resonance imaging

AIM

To compare the amount of epicardial adipose tissue (EAT) in patients with coronary artery disease (CAD) or non-ischaemic dilated cardiomyopathy (NIDCM) with that in patients with negative cardiac magnetic resonance imaging (CMR).

MATERIALS AND METHODS

One hundred and fifty patients (median age 57 years, interquartile range [IQR] 46-66 years) who underwent CMR were evaluated retrospectively: 50 with CAD, 50 with NIDCM, and 50 with negative CMR. For each patient, the EAT mass index (EATMI) to body surface area, end-diastolic volume index (EDVI), end-systolic volume index (ESVI), stroke volume (SV), ejection fraction (EF) for both ventricles, and left ventricle (LV) mass index were estimated. Intra and inter-reader reproducibility was tested in a random subset of 30 patients, 10 for each group. Mann-Whitney U test, Kruskal-Wallis test, Spearman's correlation, and Bland-Altman statistics were used.

RESULTS

The EATMI in CAD patients (median 15.7 g/m², IQR 8.3-25.7) or in NIDCM patients (15.9 g/m², 11.5-18.1) was significantly higher than that in negative CMR patients (9.1 g/m², 6-12; p<0.001 both). No significant difference was found between CAD and NIDCM patients (p=1.000). A correlation between EATMI and LV mass index was found in NIDCM patients (r=0.455, p=0.002). Intra- and inter-reader reproducibility were up to 80% and 72%, respectively.

CONCLUSION

Patients with NIDCM or CAD exhibited an increased EATMI in comparison to negative CMR patients. CMR can be used to estimate EAT with good reproducibility.

Skin rash and arthritis a simplified appraisal of less common associations

Skin and joint manifestations are part of the clinical spectrum of many disorders. Well-known associations include psoriatic arthritis and arthritis associated with autoimmune connective tissue diseases. This review focuses on less common associations where skin lesions can provide easily accessible and valuable diagnostic clues, and directly lead to the specific diagnosis or limit the list of possibilities. This may also affect health care resources as diagnostic tests are often low-specific, highly expensive and poorly available. This group of diseases can be divided into two subsets, based on the presence/absence of fever, and then further classified according to elementary skin lesions (macular, urticarial, maculo-papular, vesico-bullous, pustular, petechial and nodular). In most instances joint involvement occurs as peripheral migrating polyarthritis. Erythematosus macular or urticarial rashes occur in most febrile disorders such as monogenic autoinflammatory syndromes, Schnitzler's syndrome, Still's disease and rheumatic fever and afebrile diseases as urticarial vasculitis. Pustular rash may be observed in chronic recurrent multifocal osteomyelitis (CRMO) and pyogenic arthritis with pyoderma gangrenosum and acne (PAPA) syndrome (both febrile) as well as in Behcet's disease and Synovitis, acne, pustulosis, hyperostosis and osteitis syndrome (both non-febrile). Papular lesions are typical of secondary syphilis, sarcoidosis, interstitial granulomatous dermatitis, papular petechial of cutaneous small-vessel vasculitis and nodular lesions of polyarteritis nodosa and multicentric reticulohistiocytosis all of which are afebrile. Differential diagnosis includes infections and drug reactions which may mimic several of these conditions. To biopsy the right skin lesion at the right time it is essential to obtain relevant histological information.

Long-lasting neuroprotection and neurological improvement in stroke models with new, potent and brain permeable inhibitors of poly(ADP-ribose) polymerase

BACKGROUND AND PURPOSES

Thienyl-isoquinolone (TIQ-A) is a relatively potent PARP inhibitor able to reduce post-ischaemic neuronal death in vitro. Here we have studied, in different stroke models in vivo, the neuroprotective properties of DAMTIQ and HYDAMTIQ, two TIQ-A derivatives able to reach the brain and to inhibit PARP-1 and PARP-2.

EXPERIMENTAL APPROACH

Studies were carried out in (i) transient (2 h) middle cerebral artery occlusion (tMCAO), (ii) permanent MCAO (pMCAO) and (iii) electrocoagulation of the distal portion of MCA in conjunction with transient (90 min) bilateral carotid occlusion (focal cortical ischaemia).

KEY RESULTS

In male rats with tMCAO, HYDAMTIQ (0.1-10 mg·kg(-1)) injected i.p. three times, starting 4 h after MCAO, reduced infarct volumes by up to 70%, reduced the loss of body weight by up to 60% and attenuated the neurological impairment by up to 40%. In age-matched female rats, HYDAMTIQ also reduced brain damage. Protection, however, was less pronounced than in the male rats. In animals with pMCAO, HYDAMTIQ administered 30 min after MCAO reduced infarct volumes by approximately 40%. In animals with focal cortical ischaemia, HYDAMTIQ treatment decreased post-ischaemic accumulation of PAR (the product of PARP activity) and the presence of OX42-positive inflammatory cells in the ischaemic cortex. It also reduced sensorimotor deficits for up to 90 days after MCAO.

CONCLUSION AND IMPLICATIONS

Our results show that HYDAMTIQ is a potent PARP inhibitor that conferred robust neuroprotection and long-lasting improvement of post-stroke neurological deficits.

Low serum tryptophan levels, reduced macrophage IDO activity and high frequency of psychopathology in HCV patients

Indoleamine 2,3-dioxygenase (IDO), a key enzyme of tryptophan (TRP) metabolism, is induced in various tissues of patients with bacterial and viral infection or with neoplastic diseases. This induction is considered the main cause of the decreased serum TRP levels, the reduced brain serotonin synthesis and the occurrence of psychopathological disorders often detected in patients with chronic infections or different forms of cancer. We studied 89 subjects including: (a) 39 patients with chronic hepatitis C virus (HCV) infection and mild liver damage (b) 40 healthy controls, and (c) 10 patients with chronic hepatitis B virus (HBV) infection. We measured serum TRP and kynurenine levels and IDO activity in macrophages. Furthermore, each patient had an accurate psychopathological evaluation. HCV-infected patients had lower (-28%) serum TRP concentrations than healthy volunteers or HBV-infected patients with comparable liver damage. Depression and anxiety symptoms were particularly common in HCV patients. Unexpectedly, serum kynurenine levels and IDO activity in cultured macrophages (under both basal or stimulated conditions) were lower in HCV patients than in controls. Our study shows that HCV patients have reduced serum TRP levels and confirms that they frequently suffer from anxiety and depression-related symptoms. The reduced IDO activity found in the macrophages of these patients suggest that HCV infection may hamper macrophage functions.

Cellular iron status influences the functional relationship between microglia and oligodendrocytes

Previously, we have reported that there is a spatiotemporal relationship between iron accumulation in microglia and oligodendrocytes during normal development and in remyelination following injury. This in vivo observation has prompted us to develop a cell culture model to test the relationship between iron status of microglia and survival of oligodendrocytes. We found that conditioned media from iron-loaded microglia increases the survival of oligodendrocytes; but conditioned media from iron loaded activated microglia is toxic to oligodendrocytes. In the trophic condition, one of the proteins released by iron-loaded microglia is H-ferritin, and transfecting the microglia with siRNA for H-ferritin blocks the trophic response on oligodendrocytes. Lipopolysaccharide (LPS) activation decreases the amount of H-ferritin that is released from microglia and increases the release of the proinflammatory cytokines tumor necrosis factor-alpha and interleukin-1. LPS activation of iron-enriched microglia results in the activation of NF-kB and greater release of cytokines when compared with that of control microglia; whereas treating microglia with an iron chelator is associated with less NF-kB activation and less release of cytokines. These results indicate that microglia play an important role in iron homoeostasis and that their iron status can influence how microglia influence growth and survival of oligodendrocytes. The results further indicate that ferritin, released by microglia, is a significant source of iron for oligodendrocytes.

Kynurenine 3-mono-oxygenase inhibitors reduce glutamate concentration in the extracellular spaces of the basal ganglia but not in those of the cortex or hippocampus

Kynurenine 3-mono-oxygenase (KMO, kynurenine hydroxylase) inhibitors increase brain kynurenic acid (KYNA) synthesis and cause pharmacological actions possibly mediated by a reduced activity of excitatory synapses. We used in vivo microdialysis and passive avoidance to study the effects of local KYNA or systemic KMO inhibitor administration on glutamate (GLU) neurotransmission. Local application of KYNA (30-100 nM) through reverse microdialysis reduced GLU content in caudate and cortical dialysates by 75 and 55%, respectively. No changes were found in the hippocampus. Systemic administration of Ro 61-8048 (4-40 mg/kg) increased KYNA levels in dialysates obtained from the cortex (from 10.3 +/- 1.9 to 45.5 +/- 15 nM), caudate (from 2.4 +/- 0.8 to 9.5 +/- 0.9 nM) and hippocampus (from 7.7 +/- 1.7 to 19.2 +/- 3.5 nM). It also caused a parallel robust decrease in GLU levels in the dialysates collected from the caudate (from 2.2 +/- 0.5 to 0.63 +/- 0.05 microM) but not in those collected from the parietal cortex or the hippocampus. In a passive avoidance paradigm, the administration of the NMDA receptor antagonist MK-801 (0.1 mg/kg) reduced, while Ro 61-8048 (4-80 mg/kg) did not change the latency time of entering into the dark compartment on the recall trial. Our data show that KMO inhibitors increase brain KYNA synthesis and selectively reduce GLU extracellular concentration in the basal ganglia.

Assessment of ozone visible symptoms in the field: perspectives of quality control

The second UN/ECE ICP-Forests Intercalibration Course on the Assessment of Ozone Injury on European Tree Species was carried out in August 2001 at Lattecaldo (Canton Ticino, CH) and Moggio (Lombardy, I). Forty-eight experts from several European countries participated in the exercises and assessed visible symptoms of ozone injury both in open-top chambers (OTC) (Lattecaldo) and under open field (Moggio) conditions. Evaluation of the results indicated a large variability among the teams and call for adequate training of the observers prior to symptom assessment for quality assurance purposes. Highest variability was found for the species developing unclear symptoms which could be confused with senescence processes; such species should not be used in the field. The authors provide suggestions to improve the reliability of the ozone injury assessment on forest plant species.

Acute cerebral focal ischaemia alters the adrenergic and NANC responses in the bisected rat vas deferens

1. Disturbances of the autonomic nervous system are common in right hemisphere stroke patients, including a marked decline in male sexual functions. There is a lack of information on the influence of stroke on male secondary sex organs such as the vas deferens. 2. This study investigates the effect of right brain focal ischaemia on the adrenergic and purinergic responses in isolated epididymal and prostatic portions of rat vas deferens. 3. In both epididymal and prostatic portions the concentration-response curves to noradrenaline are flattened resulting in a reduction (up to 67 - 76%) of the maximum contractile response in the tissue from ischaemic rats compared to the controls. In the prostatic portion from ischaemic rats the concentration-response curve to alpha,beta-methylene ATP was also depressed. 4. The first purinergic and the second delayed adrenergic phase to single pulse was not modified by brain ischaemia. In contrast both phasic and tonic components of the electrically induced contractions by trains of stimuli at high frequencies (2 - 30 Hz) were significantly depressed in the epididymal and prostatic portions from ischaemic rats. 5. These results demonstrate an autonomic imbalance at the level of male sexual secondary organs which may contribute to sexual impairment after stroke.

Poly(ADP-ribose) polymerase inhibitors attenuate necrotic but not apoptotic neuronal death in experimental models of cerebral ischemia

An excessive activation of poly(ADP-ribose) polymerase (PARP) has been proposed to play a key role in post-ischemic neuronal death. We examined the neuroprotective effects of the PARP inhibitors benzamide, 6(5H)-phenanthridinone, and 3,4-dihydro-5-[4-1(1-piperidinyl)buthoxy]-1(2H)-isoquinolinone in three rodent models of cerebral ischemia. Increasing concentrations of the three PARP inhibitors attenuated neuronal injury induced by 60 min oxygen-glucose deprivation (OGD) in mixed cortical cell cultures, but were unable to reduce CA1 pyramidal cell loss in organotypic hippocampal slices exposed to 30 min OGD or in gerbils following 5 min bilateral carotid occlusion. We then examined the necrotic and apoptotic features of OGD-induced neurodegeneration in cortical cells and hippocampal slices using biochemical and morphological approaches. Cortical cells exposed to OGD released lactate dehydrogenase into the medium and displayed ultrastructural features of necrotic cell death, whereas no caspase-3 activation nor morphological characteristics of apoptosis were observed at any time point after OGD. In contrast, a marked increase in caspase-3 activity was observed in organotypic hippocampal slices after OGD, together with fluorescence and electron microscope evidence of apoptotic neuronal death in the CA1 subregion. Moreover, the caspase inhibitor Z-VAD-FMK reduced OGD-induced CA1 pyramidal cell loss. These findings suggest that PARP overactivation may be an important mechanism leading to post-ischemic neurodegeneration of the necrotic but not of the apoptotic type.

The expression of glutamate transporter GLT-1 in the rat cerebral cortex is down-regulated by the antipsychotic drug clozapine

We show here that clozapine, a beneficial antipsychotic, down-regulates the expression of the glutamate transporter GLT-1 in the rat cerebral cortex, thereby reducing glutamate transport and raising extracellular glutamate levels. Clozapine treatment (25--35 mg kg(-1) day(-1) orally) reduced GLT-1 immunoreactivity in several brain regions after 3 weeks; this effect was most prominent after 9 weeks and most evident in the frontal cortex. GLT-1 protein levels were reduced in the cerebral cortex of treated rats compared with controls and were more severely affected in the anterior (71.9 +/- 4.5%) than in the posterior (53.2 +/- 15.4%) cortex. L-[(3)H]-glutamate uptake in Xenopus laevis oocytes injected with mRNA extracted from the anterior cerebral cortex of rats treated for 9 weeks was remarkably reduced (to 30.6 +/- 8.6%) as compared to controls. In addition, electrophysiological recordings from oocytes following application of glutamate revealed a strong reduction in glutamate uptake currents (46.3 +/- 10.2%) as compared to controls. Finally, clozapine treatment led to increases in both the mean basal (8.1 +/- 0.7 microM) and the KCl-evoked (28.7 +/- 7.7 microM) output of glutamate that were 3.1 and 3.5, respectively, higher than in control rats. These findings indicate that clozapine may potentiate glutamatergic synaptic transmission by regulating glutamate transport.

Presynaptic kynurenate-sensitive receptors inhibit glutamate release

Kynurenic acid is a tryptophan metabolite provided with antagonist activity on ionotropic glutamate and alpha7 nicotinic acetylcholine receptors. We noticed that in rats with a dialysis probe placed in the head of their caudate nuclei, local administration of kynurenic acid (30-100 nM) significantly reduced glutamate output. Qualitatively and quantitatively similar effects were observed after systemic administration of kynurenine hydroxylase inhibitors, a procedure able to increase brain kynurenate concentrations. Interestingly, in microdialysis studies, methyllycaconitine (0.3-10 nM), a selective alpha7 nicotinic receptor antagonist, also reduced glutamate output. In isolated superfused striatal synaptosomes, kynurenic acid (100 nM), but not methyllycaconitine, inhibited the depolarization (KCl 12.5 mM)-induced release of transmitter or previously taken-up [3H]-D-aspartate. This inhibition was not modified by glycine, N-methyl-D-aspartate or subtype-selective kainate receptor agents, while CNQX or DNQX (10 microM), two AMPA and kainate receptor antagonists, reduced kynurenic acid effects. Low concentrations of kynurenic acid, however, did not modify [3H]-kainate (high and low affinity) or [3H]-AMPA binding to rat brain membranes. Finally, because metabotropic glutamate (mGlu) receptors modulate transmitter release in striatal preparations, we evaluated, with negative results, kynurenic acid (1-100 nM) effects in cells transfected with mGlu1, mGlu2, mGlu4 or mGlu5 receptors. In conclusion, our data show that kynurenate-induced inhibition of glutamate release is not mediated by glutamate receptors. Nicotinic acetylcholine receptors, however, may contribute to the inhibitory effects of kynurenate found in microdialysis studies, but not in those found in isolated synaptosomes.

Kynurenine 3-mono-oxygenase activity and neurotoxic kynurenine metabolites increase in the spinal cord of rats with experimental allergic encephalomyelitis

Kynurenine 3-mono-oxygenase, one of the key enzymes of the "kynurenine pathway", catalyses the formation of 3-hydroxykynurenine and may direct the neo-synthesis of quinolinic and kynurenic acids. While 3-hydroxykynurenine and quinolinic acid have neurotoxic properties, kynurenic acid antagonizes excitotoxic neuronal death. Here we report that the expression and activity of kynurenine 3-mono-oxygenase significantly increased in the spinal cord of rats with experimental allergic encephalopathy, an experimental model of multiple sclerosis. As a consequence of this increase, the spinal cord content of 3-hydroxykynurenine and quinolinic acid reached neurotoxic levels. We also report that systemic administration of Ro 61-8048, a selective kynurenine 3-mono-oxygenase inhibitor, reduced the increase of both 3-hydroxykynurenine and quinolinic acid, and caused accumulation of kynurenic acid. In the brain and spinal cord of the controls, kynurenine 3-mono-oxygenase immunoreactivity was located in granules (probably mitochondria) present in the cytoplasm of both neurons and astroglial cells. In the spinal cord of rats with experimental allergic encephalopathy, however, cells with a very intense kynurenine 3-mono-oxygenase immunoreactivity, also able to express class II major histocompatibility complex and inducible nitric oxide synthase, were found in perivascular, subependymal and subpial locations. These cells (most probably macrophages) were responsible for the large increase in 3-hydroxykynurenine and quinolinic acid found in the spinal cords of affected animals. The results show that cells of the immune system are responsible for the increased formation of 3-hydroxykynurenine and quinolinic acid, two neurotoxic metabolites that accumulate in the central nervous system of rats with experimental allergic encephalomyelitis. They also demonstrate that selective kynurenine 3-mono-oxygenase inhibitors reduce the neo-synthesis of these toxins.

Expression, refolding, and ferritin-binding activity of the isolated VL-domain of monoclonal antibody F11

Expression of the VL-domain of mouse monoclonal antibody F11 to human spleen ferritin in Escherichia coli cells is associated with the formation of insoluble protein aggregates (inclusion bodies). The aggregates were solubilized in the presence of guanidine hydrochloride and the recombinant VL-domain was purified by immobilized metal affinity chromatography (IMAC). Subsequent renaturation results in approximately 99% pure preparation with high yield. The VL-domain forms dimers at concentrations from 1 to 10 mg/ml. Monomeric form is detected only at protein concentrations below 0.5 mg/ml. Functional activity of the VL-domain was verified by two variants of ELISA. The affinity of the VL-domain ((0.2-1.2). 108 M(-1)) is similar to the affinity of the full-length parental antibody F11 because when the immobilized VL-domain was used, the binding constant of ferritin to the VL-domain was only 4-6-fold lower than that in the case of F11 antibody. In another ELISA system with immobilized ferritin, affinity was decreased 30-fold. The VL-domain of antibody F11 is the first example of the recombinant variable domain of the immunoglobulin light chain that preserves the antigen-binding activity in the absence of the partner VH-domain. The data indicate that the recombinant VL-domain can be used in construction of chimeric immunotoxins and other antigen-binding proteins in immunotherapy and in studies of correlations between folding, stability, and activity of immunoglobulins.

Overexpression of wild type and mutated human ferritin H-chain in HeLa cells: in vivo role of ferritin ferroxidase activity

Transfectant HeLa cells were generated that expressed human ferritin H-chain wild type and an H-chain mutant with inactivated ferroxidase activity under the control of the tetracycline-responsive promoter (Tet-off). The clones accumulated exogenous ferritins up to levels 14-16-fold over background, half of which were as H-chain homopolymers. This had no evident effect in the mutant ferritin clone, whereas it induced an iron-deficient phenotype in the H-ferritin wild type clone, manifested by approximately 5-fold increase of IRPs activity, approximately 2.5-fold increase of transferrin receptor, approximately 1.8-fold increase in iron-transferrin iron uptake, and approximately 50% reduction of labile iron pool. Overexpression of the H-ferritin, but not of the mutant ferritin, strongly reduced cell growth and increased resistance to H(2)O(2) toxicity, effects that were reverted by prolonged incubation in iron-supplemented medium. The results show that in HeLa cells H-ferritin regulates the metabolic iron pool with a mechanism dependent on the functionality of the ferroxidase centers, and this affects, in opposite directions, cellular growth and resistance to oxidative damage. This, and the finding that also in vivo H-chain homopolymers are much less efficient than the H/L heteropolymers in taking up iron, indicate that functional activity of H-ferritin in HeLa cells is that predicted from the in vitro data.

Antiferritin single-chain Fv fragment is a functional protein with properties of a partially structured state: comparison with the completely folded V(L) domain

Differential scanning calorimetry and spectroscopic probes were applied to study folding and stability of the single-chain Fv fragment (scFv) of the anti-human ferritin antibody F11 and its isolated variable light-chain (V(L)) domain. The scFv fragment followed variable heavy-chain domain (V(H))-linker-V(L) orientation and contained (Gly(4)Ser)(3) linker peptide. The two proteins were produced in Escherichia coli and refolded from denaturant-solubilized inclusion bodies. The isolated V(L) domain demonstrated a typical immunoglobulin fold with well-defined secondary and tertiary structure and was capable of binding human ferritin with K(a) = 1.8 x 10(7) M(-)(1), approximately (1)/(30) of the affinity of the parent F11 antibody. Involvement of this V(L) domain into the two-domain scFv fragment yielded a distorted secondary and significantly destabilized tertiary structure in which neither of the two constituent domains attained complete folding. The thermal unfolding enthalpy of scFv F11 at pH 7.0 was as low as 5. 0 J.g(-)(1) versus 16.3 J.g(-)(1) obtained for the V(L) domain and 24.7 J.g(-)(1) for the parent F11 antibody (mouse IgG2a subclass). Intrinsic fluorescence and near-ultraviolet circular dichroic (CD) spectra, and binding of the hydrophobic probe 8-anilino-1-naphthalene sulfonate, confirmed partial loss of tertiary interactions in scFv. The spectroscopic and calorimetric properties of scFv F11 under physiological conditions are consistent with a model of a partially structured state with a distorted beta-sheet as a secondary structure and partial loss of tertiary interactions, which closely resembles the alternatively folded A-state adopted by an immunoglobulin at pH 2-3 [Buchner, J., Renner, M., Lilie, H., Hinz, H.-J., Jaenicke, R., Kiefhaber, T., and Rudolph, R. (1991) Biochemistry 30, 6922-6929]. However, scFv F11 demonstrated only an approximately 4-fold decrease in the antigen-binding affinity (K(a) = 1.3 x 10(8) M(-)(1)) versus the parent F11 antibody. The scFv fragment F11 provides the first description of a functional protein trapped under physiological conditions in a partially structured state. This state is either close to the native one in the antigen-binding affinity or, alternatively, initial weak binding of the antigenic epitope induces folding of scFv F11 into a more structured conformation that generates relatively high affinity.

Functional and immunological analysis of recombinant mouse H- and L-ferritins from Escherichia coli

The production and characterization of recombinant mouse H- and L-ferritin chains from Escherichia coli are described. The proteins were efficiently expressed and purified with yields of 7-40 mg per liter of cell culture. They had the expected molecular mass and showed a physical stability analogous to that of the corresponding human ferritins. Mouse H- and L-ferritins had a very similar mobility on denaturing SDS-PAGE, but could be readily separated on nondenaturing PAGE because of the distinct slow mobility of mouse L-ferritin. Direct comparative experiments showed that mouse and human H-ferritins had the same iron incorporation activity, whereas mouse L-ferritin incorporated iron less efficiently than human L-ferritin. The difference was attributed to the substitution of a residue exposed on the cavity surface (Glu140 --> Lys) in mouse L-ferritin, a hypothesis confirmed by the finding that the mouse L-ferritin mutant Lys140-Glu incorporated iron as efficiently as human L-ferritin. Rabbit antisera elicited by the recombinant mouse ferritins were specific for the H- and L-chains and did not cross-react with the human ferritins. The antibodies and the derived specific ELISA assays allow the determination of H- and L-ferritins in mouse tissues.

Neuroprotective effects of kynurenine-3-hydroxylase inhibitors in models of brain ischemia

The neuroprotective effects of two kynurenine hydroxylase inhibitors, (m-nitrobenzoyl)-alanine (mNBA) and 3,4-dimethoxy-[-N-4-(nitrophenyl)thiazol-2yl]-benzenesulfona mide (Ro 61-8048), were studied in vitro and in vivo. In organotypic hippocampal slice cultures deprived of oxygen and glucose, these inhibitors significantly reduced neuronal damage. In gerbils subjected to bilateral carotid occlusion for 5 min, the administration of mNBA (400 mg/kg i.p., 3 times) or Ro 61-8048 (40 mg/kg i.p., 3 times) dramatically decreased the percentage of damaged pyramidal neurones in the hippocampal CA1 region. Finally, in rats with permanent occlusion of the middle cerebral artery, mNBA (200-400 mg/kg i.p.) and Ro 61-8048 (40 mg/kg i.p.) administration reduced the infarct volume. Our results demonstrate that ischemic neuronal damage may be significantly decreased by inhibiting kynurenine hydroxylase.

Overexpression of the hereditary hemochromatosis protein, HFE, in HeLa cells induces and iron-deficient phenotype

A transfectant HeLa cell clone expressing HFE under the control of a tetracycline-repressible promoter was generated. HFE expression was fully repressed by the presence of doxycycline, while it was strongly induced by growth in the absence of doxycycline. HFE accumulation was accompanied by a large (approximately 10-fold) decrease in H- and L-ferritin levels, by a approximately 3-4-fold increase in transferrin receptor, and a approximately 2-fold increase in iron regulatory protein activity. These indices of cellular iron deficiency were reversed by iron supplementation complexes. The overexpressed HFE immunoprecipitated together with transferrin receptor, indicating a physical association which is the likely cause for the observed approximately 30% decrease in 55Fe-transferrin incorporation after 18 h incubation. In the HFE-expressing cells the reduction in transferrin-mediated iron incorporation was partially compensated by a approximately 30% increase in non-transferrin iron incorporation from 55Fe-NTA, evident after prolonged, 18 h, incubations. The findings indicate that HFE binding to transferrin receptor reduces cellular iron availability and regulates the balance between transferrin-mediated and non-transferrin-mediated cellular iron incorporation.

1-Aminoindan-1,5-dicarboxylic acid and (S)-(+)-2-(3'-carboxybicyclo[1.1.1] pentyl)-glycine, two mGlu1 receptor-preferring antagonists, reduce neuronal death in in vitro and in vivo models of cerebral ischaemia

Metabotropic glutamate (mGlu) receptors have been implicated in a number of physiological and pathological responses to glutamate, but the exact role of group I mGlu receptors in causing postischaemic injury is not yet clear. In this study, we examined whether the recently-characterized and relatively selective mGlu1 receptor antagonists 1-aminoindan-1,5-dicarboxylic acid (AIDA) and (S)-(+)-2-(3'-carboxybicyclo[1.1.1]pentyl)-glycine (CBPG) could reduce neuronal death in vitro, following oxygen-glucose deprivation (OGD) in murine cortical cell and rat organotypic hippocampal cultures, and in vivo, after global ischaemia in gerbils. When present in the incubation medium during the OGD insult and the subsequent 24 h recovery period, AIDA and CBPG significantly reduced neuronal death in vitro. The extent of protection was similar to that observed with the nonselective mGlu receptor antagonist (+)-alpha-methyl-4-carboxyphenylglycine [(+)MCPG] and with typical ionotropic glutamate (iGlu) receptor antagonists. Neuroprotection was also observed when AIDA or CBPG were added only after the OGD insult was terminated. Neuronal injury was not attenuated by the inactive isomer (-)MCPG, but was significantly enhanced by the nonselective mGlu receptor agonist (1S,3R)-1-aminocyclopentane-1, 3-dicarboxylic acid [(1S,3R)-ACPD] and the group I mGlu receptor agonist 3,5-dihydroxyphenylglycine (3,5-DHPG). The antagonists (+)MCPG, AIDA and CBPG were also neuroprotective in vivo, because i. c.v. administration reduced CA1 pyramidal cell degeneration examined 7 days following transient carotid occlusion in gerbils. Our results point to a role of mGlu1 receptors in the pathological mechanisms responsible for postischaemic neuronal death and propose a new target for neuroprotection.

Protection with metabotropic glutamate 1 receptor antagonists in models of ischemic neuronal death: time-course and mechanisms

In order to study the role of metabotropic glutamate 1 (mGlu1) receptors in ischemic neuronal death, we examined the effects of the recently characterized and relatively selective mGlu1 receptor antagonists 1-aminoindan-1,5-dicarboxylic acid (AIDA) and (S)-(+)-2-(3'-carboxybicyclo[1.1.1]pentyl)-glycine (CBPG) in murine cortical cell cultures and rat organotypic hippocampal slices exposed to oxygen glucose deprivation (OGD) and in vivo, following transient global ischemia in gerbils. AIDA and CBPG significantly reduced neuronal death when added to the incubation medium during the OGD insult and the subsequent recovery period. Neuroprotection was observed even when these compounds were added up to 60 min (in cortical neurons) or 30 min (in hippocampal slices) after OGD. In vivo, i.c.v. administration of AIDA and CBPG reduced hippocampal CA1 pyramidal cell injury following transient global ischemia. Neuroprotection was also observed when AIDA was added to the hippocampal perfusion fluid in microdialysis experiments, and this effect was associated with an increase in the basal output of GABA. These findings demonstrate that AIDA and CBPG are neuroprotective when administered during the maturation of ischemic damage and that different mechanisms are likely to be involved in mediating their effects following blockade of mGlu1 receptors in cortical and hippocampal neurons.

Kynurenine hydroxylase inhibitors reduce ischemic brain damage: studies with (m-nitrobenzoyl)-alanine (mNBA) and 3,4-dimethoxy-[-N-4-(nitrophenyl)thiazol-2yl]-benzenesulfonamide (Ro 61-8048) in models of focal or global brain ischemia

Two kynurenine hydroxylase inhibitors, (m-nitrobenzoyl)-alanine (mNBA) and 3,4-dimethoxy-[-N-4-(nitrophenyl)thiazol-2yl]-benzenesulfona mide (Ro 61-8048), have been tested as neuroprotective agents on brain lesions induced by bilateral carotid occlusion in gerbils or by middle cerebral artery occlusion in rats. The percentage of lesioned pyramidal neurones found in the hippocampal CA1 region of gerbils subjected to bilateral carotid occlusion for 5 minutes decreased from 92+/-10% in vehicle-treated animals to 7+/-6% after mNBA (400 mg/kg intraperitoneally, three times at 1, 30, and 180 minutes after occlusion) or to 10+/-11% after Ro 61-8048 (40 mg/kg intraperitoneally, three times). A significant reduction in infarct volumes also was found when the kynurenine hydroxylase inhibitors were given to rats after permanent middle cerebral artery occlusion (from 207+/-111 mm3 in vehicle-treated rats to 82+/-18 and to 62+/-57 mm3 in rats treated with mNBA, 400 mg/kg intraperitoneally, or with Ro 61-8048, 40 mg/kg intraperitoneally, respectively). The administration of mNBA (400 mg/kg intraperitoneally) or Ro 61-8048 (40 mg/kg intraperitoneally) to gerbils with a dialysis probe in their dorsal hippocampus or to rats with a dialysis probe in their parietal cortex significantly increased kynurenic acid concentration in the dialysates. The data suggest that inhibition of kynurenine hydroxylase could be a new avenue to reduce neuronal loss in brain ischemia.

A parallel noise-robust algorithm to recover depth information from radial flow fields

A parallel algorithm operating on the units ('neurons') of an artificial retina is proposed to recover depth information in a visual scene from radial flow fields induced by ego motion along a given axis. The system consists of up to 600 radii with fewer than 65 radially arranged neurons on each radius. Neurons are connected only to their nearest neighbors, and they are excited as soon as a sufficiently strong gray-level change occurs. The time difference of two subsequently activated neurons is then used by the last-excited neuron to compute the depth information. All algorithmic calculations remain strictly local, and information is exchanged only between adjacent active neurons (except for the final read-out). This, in principle, permits parallel implementation. Furthermore, it is demonstrated that the calculation of the object coordinates requires only a single multiplication with a constant, which is dependent on only the retinal position of the active neuron. The initial restriction to local operations makes the algorithm very noise sensitive. In order to solve this problem, a predication mechanism is introduced. After an object coordinate has been determined, the active neuron computes the time when the next neuronal excitation should take place. This estimated time is transferred to the respective next neuron, which will wait for this excitation only within a certain time window. If the excitation fails to arrive within this window, the previously computed object coordinate is regarded as noisy and discarded. We will show that this predictive mechanism relies also on only a (second) single multiplication with another neuron-dependent constant. Thus, computational complexity remains low, and noisy depth coordinates are efficiently eliminated. Thus, the algorithm is very fast and operates in real time on 128 x 128 images even in a serial implementation on a relatively slow computer. The algorithm is tested on scenes of growing complexity, and a detailed error analysis is provided showing that the depth error remains very low in most cases. A comparison to standard flow-field analysis shows that our algorithm outperforms the older method by far. The analysis of the algorithm also shows that it is generally applicable despite its restrictions, because it is fast and accurate enough such that a complete depth percept can be composed from radial flow field segments. Finally, we suggest how to generalize the algorithm, waiving the restriction of radial flow.

How to "hear" visual disparities: real-time stereoscopic spatial depth analysis using temporal resonance

In a stereoscopic system, both eyes or cameras have a slightly different view. As a consequence, small variations between the projected images exist ('disparities') which are spatially evaluated in order to retrieve depth information (Sanger 1988; Fleet et al. 1991). A strong similarity exists between the analysis of visual disparities and the determination of the azimuth of a sound source (Wagner and Frost 1993). The direction of the sound is thereby determined from the temporal delay between the left and right ear signals (Konishi and Sullivan 1986). Similarly, here we transpose the spatially defined problem of disparity analysis into the temporal domain and utilize two resonators implemented in the form of causal (electronic) filters to determine the disparity as local temporal phase differences between the left and right filter responses. This approach permits real-time analysis and can be solved analytically for a step function contrast change, which is an important case in all real-world applications. The proposed theoretical framework for spatial depth retrieval directly utilizes a temporal algorithm borrowed from auditory signal analysis. Thus, the suggested similarity between the visual and the auditory system in the brain (Wagner and Frost 1993) finds its analogy here at the algorithmical level. We will compare the results from the temporal resonance algorithm with those obtained from several other techniques like cross-correlation or spatial phase-based disparity estimation showing that the novel algorithm achieves performances similar to the 'classical' approaches using much lower computational resources.

Presynaptic mGlu1 type receptors potentiate transmitter output in the rat cortex

In the present study we used freely moving rats with a microdialysis probe placed in their parietal cortex to study the effects of local application of agonists and antagonists of metabotropic glutamate (mGlu) receptors on glutamate release. (1S,3R)-1-aminocyclopentane-1,3-dicarboxylic acid (1S,3R-ACPD; 0.1-1 mM), a non-selective agonist of metabotropic glutamate (mGlu) receptors, increased glutamate concentration in the dialysate up to 3-fold. A significant increase in glutamate output in cortical dialysates was also obtained with (RS)-3,5-dihydroxyphenylglycine (DHPG; 0.5-1 mM), a group 1-selective mGlu receptor agonist, suggesting the involvement of group 1 mGlu receptors in 1S,3R-ACPD effects. S-4-carboxyphenylglycine (S-4CPG; 0.3 microM), a mGlu1 receptor antagonist with a mild agonist action on mGlu2 receptors, antagonised, in a surmountable manner, the effects of 1S,3 R-ACPD. Similarly, 1-aminoindan-1,5-dicarboxylic acid (AIDA; 0.03-1 mM) a selective group 1 antagonist with a preferential action on mGlu1 type receptors, antagonised the effects of 1S,3R-ACPD. Finally, (S)-(+)-2-(3'-Carboxybicyclo[1.1.1]pentyl)-glycine (UPF596; 30-300 microM), a potent mGlu1 antagonist with modest agonist activity on mGlu5, antagonised 1S,3R-ACPD-induced glutamate release. In conclusion, our data showed that 1S,3R-ACPD-induced glutamate release in the parietal cortex is mediated by mGlu1 receptors and that, under basal conditions, these receptors are not tonically activated.

Transient overexpression of human H- and L-ferritin chains in COS cells

The understanding of the in vitro mechanisms of ferritin iron incorporation has greatly increased in recent years with the studies of recombinant and mutant ferritins. However, little is known about how this protein functions in vivo, mainly because of the lack of cellular models in which ferritin expression can be modulated independently from iron. To this aim, primate fibroblastoid COS-7 cells were transiently transfected with cDNAs for human ferritin H- and L-chains under simian virus 40 promoter and analysed within 66 h. Ferritin accumulation reached levels 300-500-fold higher than background, with about 40% of the cells being transfected. Thus ferritin concentration in individual cells was increased up to 1000-fold over controls with no evident signs of toxicity. The exogenous ferritin subunits were correctly assembled into homopolymers, but did not affect either the size or the subunit composition of the endogenous heteropolymeric fraction of ferritin, which remained essentially unchanged in the transfected and non-transfected cells. After 18 h of incubation with [59Fe]ferric-nitrilotriacetate, cellular iron incorporation was similar in the transfected and non-transfected cells and most of the protein-bound radioactivity was associated with ferritin heteropolymers, while H- and L-homopolymers remained iron-free. Cell co-transfection with cDNAs for H- and L-chains produced ferritin heteropolymers that also did not increase cellular iron incorporation. It is concluded that transient transfection of COS cells induces a high level of expression of ferritin subunits that do not co-assemble with the endogenous ferritins and have no evident activity in iron incorporation/metabolism.

Type 2 metabotropic glutamate (mGlu) receptors tonically inhibit transmitter release in rat caudate nucleus: in vivo studies with (2S,1'S,2'S,3'R)-2-(2'-carboxy-3'-phenylcyclopropyl)glycine, a new potent and selective antagonist

Anatomical, biochemical and electrophysiological studies have previously shown that cortico-striatal terminals contain abundant presynaptic group 2 metabotropic glutamate (mGlu) receptors. Using brain slices we have previously shown that these receptors inhibit depolarization-induced transmitter release. Using microdialysis in freely moving rats, we now report the effects of group 2 mGlu receptor agonists and antagonists on glutamate concentration in the caudate extracellular fluid. A mild decrease (20-30%) in glutamate concentration in caudate dialysates was observed when 1S,3R-1-aminocyclopentane-1,3-dicarboxylic acid or (2S,3S,4S)-alpha-carboxycyclopropyl-glycine (L-CCG-1), mGlu receptor agonists, was locally administered. On the contrary, alpha-methyl-4-carboxyphenylglycine, an antagonist of type 1 and type 2 mGlu receptors, increased the glutamate concentration in dialysates by up to 3.5-fold, and its effects were prevented by the simultaneous administration of L-CCG-1, a preferential type 2 mGlu receptor agonist. A significant increase of glutamate output in striatal dialysate was also found after local administration of (2S,1'S,2'S,3'R)-2-(2'-carboxy-3'-phenylcyclopropyl)glycine, another structurally unrelated, relatively selective and potent type 2 mGlu receptor antagonist. The results suggest that type 2 mGlu receptors tonically inhibit transmitter release from cortico-striatal terminals. Since the cortico-striatal pathway profoundly affects the function of a large percentage of caudate neurons, it is reasonable to predict that the use of selective type 2 mGlu receptor agents will be helpful for scientific and therapeutic studies on the physiopathology of basal ganglion disorders.

Effects of modifications near the 2-, 3- and 4-fold symmetry axes on human ferritin renaturation

Ferritin is a protein of 24 subunits which assemble into a shell with 432 point symmetry. It can be denatured reversibly in acidic guanidine hydrochloride, with the formation of poorly populated renaturation intermediates. In order to increase the accumulation of intermediates and to study the mechanism of ferritin renaturation, we analysed variants of the human ferritin H-chain altered at the N-terminus (delta(1-13)), near the 4-fold axis (Leu-169 --> Arg), the 3-fold axis (Asp-131 --> Ile + Glu-134 --> Phe) or the 2-fold axis (Ile-85 --> Cys). We also carried out specific chemical modifications of Cys-130 (near the 3-fold axis) and Cys-85 (near the 2-fold axis). Renaturation of the modified ferritins yielded assembly intermediates that differed in size and physical properties. Alterations of residues around the 2-, 4- and 3-fold axes produced subunit monomers, dimers and higher oligomers respectively. All these intermediates could be induced to assemble into ferritin 24-mers by concentrating them or by co-renaturing them with wild-type H-ferritin. The results support the hypothesis that the symmetric subunit dimers are the building blocks of ferritin assembly, and are consistent with a reassembly pathway involving the coalescence of dimers, probably around the 4-fold axis, followed by stepwise addition of dimers until the 24-mer cage is completed. In addition they show that assembly interactions are responsible for the large hysteresis of folding and unfolding plots. The implications of the studies for in vivo heteropolymer formation in vertebrates, which have two types of ferritin chain (H and L), are discussed.

Evidence that residues exposed on the three-fold channels have active roles in the mechanism of ferritin iron incorporation

Iron is thought to enter the ferritin cavity via the three-fold channel, which is lined in its narrowest part by the residues Asp-131 and Glu-134. We describe here variants of human ferritins with active and inactive ferroxidase centres having Asp-131 and Glu-134 substituted with Ala and Ala or with Ile and Phe respectively. The two types of substitution had similar effects on ferritin functionality: (i) they decreased the amount of iron incorporated from Fe(II) solutions and decreased ferroxidase activity by about 50%; (ii) they inhibited iron incorporation from Fe(III) citrate in the presence of ascorbate; (iii) they resulted in loss of Fe and Tb binding sites; and (iv) they resulted in a marked decrease in the inhibition of iron oxidation by Tb (but not by Zn). In addition, it was found that substitution with Ala of Cys-130 and His-118, both of which face the three-fold channel, decreased the capacity of H-ferritin to bind terbium and to incorporate iron from Fe(III) citrate in the presence of ascorbate. The results indicate that: (i) in three-fold channels are the major sites of iron transfer into the cavity of H- and L-ferritins; (ii) at least two metal binding sites are located on the channels which play an active role in capturing and transferring iron into the cavity; and (iii) the permeability of the channel is apparently not affected by the hydrophilicity of its narrowest part. In addition, it is proposed that iron incorporation from Fe(III) citrate complexes in the presence of ascorbate is a reliable, and possibly more physiological, approach to the study of ferritin functionality.

Evidence that the specificity of iron incorporation into homopolymers of human ferritin L- and H-chains is conferred by the nucleation and ferroxidase centres

Mammalian ferritins are iron-storage proteins made of 24 subunits of two types: the H- and L-chains. L-chains, in contrast with H-chains, lack detectable ferroxidase activity. When ferritins were subjected to iron loading in vitro with increments near the saturation limit of 4000 Fe atoms per molecule, the homopolymers of human H-chains formed insoluble aggregates, caused by non-specific iron hydrolysis, whereas the homopolymers of L-chains remained soluble and incorporated most of the available iron. To analyse the molecular reasons for the difference, Glu-57 and Glu-60, which are conserved and exposed on the cavity of L-chains, were substituted with His, as in H-chains. The double substitution made the L-homopolymers as sensitive as the H-homopolymers to the iron-induced aggregation, whereas the opposite substitution in the H-chain increased homopolymer resistance to the aggregation only marginally. Millimolar concentrations of citrate and phosphate increased iron incorporation in H-homopolymers by reducing non-specific iron hydrolysis, but inhibited that in L-homopolymers by sequestering available iron. The data indicate that the specific iron incorporation into L-homopolymers is mainly due to the iron-nucleation capacity of Glu-57, Glu-60 and other carboxyl groups exposed on the cavity; in contrast, the specificity of iron incorporation into H-homopolymers is related to its ferroxidase activity, which determines rapid Fe(III) accumulation inside the cavity. The finding that ferroxidase centres are essential for the incorporation of iron in the presence of likely candidates of cellular iron transport, such as phosphate and citrate, confirms their importance in ferritin function in vivo.

NMDA receptor heterogeneity in mammalian tissues: focus on two agonists, (2S,3R,4S) cyclopropylglutamate and the sulfate ester of 4-hydroxy-(S)-pipecolic acid

Several potent and selective agonists of the glutamate (L-GLU) receptors of N-methyl-D-aspartate (NMDA) type have been tested on the L-[3H]GLU binding to rat cortical membranes, on the depolarization of mouse cortical wedges and on the contraction of guinea pig longitudinal muscle myenteric plexus preparations with the aim of comparing the NMDA receptors present in the cortex and those present in the gut. When the depolarization of the cortical wedges was evaluated, the EC50 values of the agonists were (microM): (R,S)-(tetrazol-5-yl)-glycine (TG) 0.3; trans-4-hydroxy-(S)-pipecolic acid-4-sulfate (t-HPIS) 0.7; 1-aminocyclobutane-cis-1,3-dicarboxylic acid (ACBD) 0.8; NMDA 8; (2S,3R,4S) cyclopropylglutamate (L-CGA C) 12; quinolinic acid (QUIN) 400. When the contraction of the longitudinal muscle myenteric plexus was evaluated, the EC50 values were (microM): L-CGA C 1; TG 8; ACBD 50; t-HPIS 100; QUIN 500 and NMDA 680. When the displacement of NMDA specific L-[3H]GLU binding from rat cortical membranes was evaluated, the IC50 values were (microM): L-CGA C 0.003; TG 0.005; ACBD 0.044; t-HPIS 0.062; NMDA 0.31 and QUIN 15. No significant correlation was found when the EC50 values obtained in the ileum were plotted against the EC50 values obtained in the cortex (r = 0.47). In particular it was noted that L-CGA C was approximately three orders of magnitude more potent than NMDA when tested in the ileum but had a potency not significantly different from that of NMDA when tested in the cortex.(ABSTRACT TRUNCATED AT 250 WORDS)

Construction of a ferroxidase center in human ferritin L-chain

Ferritins are 24-mer proteins which store and detoxify intracellular iron. Mammalian ferritins are made of two subunit types, the H- and L-chains, with different functional specificity. The H-chain has a metal-binding site (the ferroxidase center) which confers ferroxidase activity to the protein and accelerates iron incorporation. In the L-chain the center is substituted by a salt bridge. We performed several site-directed mutageneses in the L-chain with the aim to construct the center and confer ferroxidase activity to the protein. Most variants were insoluble and did not refold into homopolymers, probably due to electrostatic repulsion introduced by the substitutions. However, they formed hybrids when they were renatured together with the L- or H-chains. The heteropolymers made of 90% L-chain and 10% of an L-variant with all the ligand residues of the H-chain center had 25-30% of the ferroxidase activity of the H-chain homopolymer. This corresponds to the activity of an H/L heteropolymer with 7% H-chain. It is concluded that: (i) it is possible to construct a ferroxidase center in the L-chain with an activity equivalent to that of the H-chain, (ii) the residues of the center interfere with the folding/assembly of the L-, but not of the H-chain, (iii) heteropolymers can be made even between ferritin subunits with large differences of refolding rates.

The glycine antagonist and free radical scavenger 7-Cl-thio-kynurenate reduces CA1 ischemic damage in the gerbil

We examined whether 7-Cl-thio-kynurenate, a potent antagonist at the glycine site of the N-methyl-D-aspartate receptor which also inhibits lipid peroxidation, protected CA1 pyramidal cells following transient forebrain ischemia. Global ischemia was produced in anesthetized gerbils by 5 min bilateral carotid artery occlusion; hippocampal injury was assessed seven days later. 7-Cl-thio-kynurenate (100 mg/kg, i.p. x 5) dramatically attenuated ischemia-induced CA1 cell loss (from 95 +/- 1 to 7 +/- 3%): the protection was associated with a delayed and marked reduction in the animals' temperature. However, when the gerbils were maintained normothermic for at least 360 min, 7-Cl-thio-kynurenate still provided partial (54 +/- 11%) but significant protection. No protection was observed when a reduction in temperature with a time course similar to that caused by 7-Cl-thio-kynurenate was experimentally induced in saline-treated ischemic animals. In situ hybridization revealed that expression of NMDA-R1, a subunit of the N-methyl-D-aspartate receptor, was selectively reduced in CA1 seven days following global ischemia. In ischemic gerbils treated with 7-Cl-thio-kynurenate, protected CA1 cells were still able to express normal amounts of NMDA-R1 messenger RNA. Our results demonstrate that 7-Cl-thio-kynurenate, a glutamate receptor blocker possessing radical scavenger properties, is effective in reducing CA1 hippocampal damage following global ischemia in the gerbil. Since there is growing evidence that a positive feedback interaction between activation of glutamate receptors and free radical formation may be responsible for the generation of ischemic brain damage, drugs capable of interfering with both pathogenic mechanisms may be useful in preventing post-ischemic neuronal death.

The role of the L-chain in ferritin iron incorporation. Studies of homo and heteropolymers

Mammalian ferritins are 24-meric proteins composed of variable proportions of H and L-subunits. The L-chain, in contrast to the H-chain, lacks detectable ferroxidase activity, and its role in ferritin iron incorporation is unclear. In this study, apoferritins were subjected to iron loading with large iron increments to favour spontaneous iron hydrolysis. The homopolymers of the wild-type H-chain, and of a mutant H-chain with an inactivated ferroxidase centre, formed massive protein aggregates, while the L-chain homopolymers remained mostly soluble. The difference between H and L-ferritins was not related to the rate of iron oxidation or to the presence of preformed iron cores. Heteropolymers were constructed in vitro by co-renaturing different proportions of the H-chain with the L-chain or mutant H-chain with an inactivated ferroxidase centre. After loading with high iron increments, protein aggregation of the heteropolymers was reduced when the L-chain content was above 70 to 80%, either in combination with the wild-type H-chain or with the inactivated mutant H-chain. Under acidic conditions (pH 5.5, 1000 Fe atoms per molecule) the heteropolymers with about 20% H and 80% L-chains incorporated three to fourfold more iron into soluble 24-mers than the homopolymers. The data indicate that ferritins with more than 18 L-chains per molecule have the capacity to lower non-specific iron hydrolysis in bulk solution. This property is possibly due to a specific attraction of the incoming oxidized iron into the cavity and may be related to an effect of the L-chain on the cavity microenvironment. It is concluded that under high iron increments the ferritins with high L:H-chain ratios are the most efficient in incorporating iron, and this goes some way to explain why iron storage tissues contain L-rich isoferritins.

Identification of the EPR-active iron-nitrosyl complexes in mammalian ferritins

This study was undertaken to characterize the nitric oxide complexes of mammalian ferritin and their EPR properties to gain a better understanding of the interaction of NO with non-heme iron proteins within the cell. Measurements were made with horse spleen apo- and holoferritins, with chemically modified proteins, and with recombinant human H-chain apoferritin and its site-directed mutants. Three types of EPR signals (A, B, and C) have been identified and attributed to iron-nitrosyl complexes at imidazole groups of histidine, thiol groups of cysteine, and carboxylate groups of aspartate and glutamate, respectively. The C-type axial spectrum has features at g perpendicular' = 4 and g parallel' = 2 characteristic of a paramagnetic Fe(3+)-NO- complex with total spin S = 3/2 and probably arises from nonspecific binding to carboxylate groups on the protein. The S = 1/2 axial B-type signal g perpendicular' = 2.033 and g parallel' = 2.014) is formed at Cys-130 (human H-chain sequence numbering). His-128 and possibly His-118 are sites of formation of the rhombic S = 1/2 A-type complex (gx' = 2.055, gy' = 2.033, and gz' = 2.015); the former residue perhaps plays a role in the conformational stability of the protein as well as in iron binding. The data reveal that the residues Cys-130 and His-128 in the vicinity of 3-fold channels leading to the interior of the protein shell are important in iron-nitrosyl complex formation in mammalian ferritins.

Production and characterization of recombinant heteropolymers of human ferritin H and L chains

Vertebrate ferritins are iron storage proteins composed by 24 subunits of one or more types. The recombinant homopolymers of human ferritin H- and L-type chains differ in iron uptake and in physical stability, but the properties of heteropolymers with various proportions of H- and L-type chains cannot be predicted. Present study shows that unfolded human ferritin H- and L- type chains renature under similar conditions to form homopolymers indistinguishable from the native ones and that, when mixed, the unfolded H and L chains renature to form heteropolymers with restricted heterogeneity and with the expected H:L ratios. Seven of these ferritins with different H:L ratios were analyzed; electrophoretic mobility, immunological reactivity, and stability to guanidine denaturation varied as predicted, based on the homopolymers. In contrast, the rate of iron uptake, monitored by the variation of absorbance at 310 nm, increased in the ferritins that ranged in H chain content from 0 to 35%; further increments in H chains had no additional effect. This finding indicates that, under the present conditions, only a limited number of H chains are needed for the maximum rate of ferritin iron uptake. Variations of L- and H-type chains in vivo may thus have biological relevance.