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Biomedical subjects

J Helenius

Publications and source records attributed to J Helenius.

10 recordsLinked to original sources
PubMed2007

Serial measurements of plasma homocysteine levels in early and late phases of ischemic stroke.

High plasma levels of homocysteine (Hcy) may predispose to ischemic stroke (IS), but results of previous studies have been conflicting. We decided to determine in IS patients whether their Hcy levels are elevated, whether levels vary at different time points following stroke, whether levels are associated with stroke severity, outcome, recurrence, etiology, infarct volume, or risk factors, and whether levels are correlated with hemostatic factors or C-reactive protein values. We measured plasma Hcy levels in 102 consecutive IS patients on admission and at 1 week, 1 month, and 3 months after stroke and once in 102 control subjects. Hemostatic factors were measured in 55 patients. Compared with controls, plasma Hcy levels in patients were significantly lower on admission but not at later time points, with levels increasing by week and remaining at this level for 3 months. Hcy levels showed a positive correlation with age and a negative correlation with Mini-Mental State Examination (MMSE) scores. Plasma Hcy levels inversely correlated with plasminogen activator inhibitor type-1. Decreased Hcy levels on admission may reflect the strength of the acute-phase response rather than a pathogenetic event. The negative correlation between Hcy levels and MMSE scores is more probably age-related than stroke-related.

Aged↗
PubMed2003

Brain diffusion changes in carotid occlusive disease treated with endarterectomy.

BACKGROUND: Patients with unilateral high-grade carotid stenosis or occlusion have been reported to have more leukoaraiosis and ischemic lesions in ipsilateral than in contralateral cerebral hemisphere. The lesions alter apparent diffusion coefficient (ADC) values in diffusion-weighted MRI (DWI). The overall effects of carotid endarterectomy on ADC values have not yet been explored. OBJECTIVE: S: To find out whether 1) average ADC (ADC(av)) values differed between hemispheres, 2) diffusion changes induced by carotid endarterectomy could be detected in brain tissue with serial DWI, and 3) patients with asymptomatic carotid stenosis differed from patients with a symptomatic stenosis. METHODS: Forty-five patients (22 with asymptomatic carotid stenosis and 23 with symptomatic carotid stenosis) with unilateral high-grade carotid stenosis underwent DWI before carotid endarterectomy and 3 and 100 days afterward, and 45 age- and sex-matched healthy control subjects were imaged once. We evaluated ADC(av) values in normal-appearing gray and white matter, watershed regions (WsR), and thalamus. RESULTS: ADC(av) values of ipsilateral white matter and WsR were higher than those of contralateral white matter and WsR, both being higher than in white matter and WsR of control subjects. After carotid endarterectomy, these differences were diminished, but the levels remained higher than in controls. ADC(av) values of gray matter and thalamus remained unaffected. Asymptomatic carotid stenosis and symptomatic carotid stenosis patient groups did not differ from each other. CONCLUSIONS: Carotid stenosis has an effect on diffusion in the white matter of the ipsilateral hemisphere, and it is partly reversible by carotid endarterectomy. The finding may be associated with leukoaraiotic development ("preleukoaraiosis").

Adult↗
PubMed2003

Cerebral hemodynamics in a healthy population measured by dynamic susceptibility contrast MR imaging.

PURPOSE: To establish reference data and to study age-dependency for cerebral perfusion in various regions of the brain in a healthy population. MATERIAL AND METHODS: Eighty healthy subjects of both genders from 22 to 85 years of age were studied with spin echo echo-planar dynamic susceptibility contrast MR imaging (DSC MRI) at 1.5 T. Cerebral blood volume (CBV), cerebral blood flow (CBF), and contrast agent mean transit time (MTT) were calculated bilaterally for 20 distinct neuroanatomic structures. RESULTS: In gray matter, the following values were found (mean +/- SD): CBV (4.6 +/- 1.0 ml/100 g), CBF (94.2 +/- 23.0 ml/100 g/min), and MTT (3.0 +/- 0.6 s), and in white matter: CBV (1.3 +/- 0.4 ml/100 g), CBF (19.6 +/- 5.8 ml/100 g/min), and MTT (4.3 +/- 0.7 s). The perfusion parameters did not change with age, except for a tendency to an increase in gray matter MTT and CBV. Males exhibited higher MTT and CBV than females. No hemispheric difference was found in either gender. CONCLUSION: Cerebral hemodynamics can be assessed with DSC MRI. Age itself seems to have only a marginal effect on cerebral perfusion in healthy population.

Adult↗
PubMed2001

Marchiafava-Bignami disease: two cases with favourable outcome.

Marchiafava-Bignami disease (MBD) is a rare disorder of an unknown aetiology but strongly associated with alcoholism. MBD primarily affects the corpus callosum leading to confusion, dysarthria, seizures and frequently to death. Over 250 cases from all races and from almost all nationalities have been reported, most cases being alcoholics. We report two cases with a favourable outcome. Magnetic resonance imaging (MRI) demonstrated a typical lesion of the corpus callosum, in both patients. The patients, a 44-year-old male and a 40-year-old female, presented with depressed consciousness and a variety of other symptoms, but finally made a reasonably good recovery leading to home discharge. To the best of our knowledge, only one additional case of MBD from Scandinavia has been published. As alcoholism is a major public health problem in Scandinavia, we assume that MBD is underdiagnosed and/or under-reported. Non-specific general symptoms and encephalopathy in an alcoholic may harbour undiagnosed MBD. We suggest that the incidence of MBD may be higher and its prognosis may be milder than generally believed.

Adult↗
PubMed2000

Doppler radar detection of exceptional mass-migration of aphids into Finland.

Our objective was to detect mass migrations of insects of economic significance by insect traps and a Doppler weather radar. Migrants were sampled by suction traps, tow nets and light traps in the Helsinki region. We used radar to observe the migrating insects, and trajectories to backtrack mass migrations of aphids (Homoptera, Aphididae) in spring 1988. The aphid migrations were clearly observed in trap catches and by radar. The first migration, mainly involving Euceraphis betulae, occurred on 18 May and was tracked back to northern Poland. The second migration, mainly of Rhopalosiphum padi (a serious pest of small-grain cereals), occurred 3 days later and was tracked back to a large area covering Latvia and western Russia south of St Petersburg. The third migration included both E. betulae and R. padi, and took place on 30 May. It originated from Estonia. Neither trap nor radar data provide exact quantitative information on migrations. Trapping efficiency depends strongly on wind speed and insect size. Radar echo intensity is very strongly related to the sizes of insects in the large volume of air measured, and the sizes are not known accurately. Weather data, especially temperature, can be used in predicting the development of aphids, and air-parcel trajectories in estimating the source areas of migrants. These methods for forecasting aphid migrations, combined with radar observations, are useful for warning purposes and to intensify insect trapping. This would contribute to more efficient agricultural pest management.

Agriculture↗
PubMed1995

Cotranslational folding and calnexin binding during glycoprotein synthesis.

To analyze cotranslational folding of influenza hemagglutinin in the endoplasmic reticulum of live cells, we used short pulses of radiolabeling followed by immunoprecipitation and analysis with a two-dimensional SDS/polyacrylamide gel system which was nonreducing in the first dimension and reducing in the second. It separated nascent glycopolypeptides of different length and oxidation state. Evidence was obtained for cotranslational disulfide formation, generation of conformational epitopes, N-linked glycosylation, and oligosaccharide-dependent binding of calnexin, a membrane-bound chaperone that binds to incompletely folded glycoproteins via partially glucose-trimmed oligosaccharides. When glycosylation or oligosaccharide trimming was inhibited, the folding pathway was perturbed, suggesting a role for N-linked oligosaccharides and calnexin during translation of hemagglutinin.

Animals↗
PubMed1992

Role of ATP and disulphide bonds during protein folding in the endoplasmic reticulum.

Being topologically equivalent to the extracellular space, the lumen of the endoplasmic reticulum (ER) provides a unique folding environment for newly synthesized proteins. Unlike other compartments in the cell where folding occurs, the ER is oxidizing and therefore can promote the formation of disulphide bonds. The reducing agent dithiothreitol, when added to living cells, inhibits disulphide formation with profound effects on folding. Taking advantage of this effect, we demonstrate here that folding of influenza haemagglutinin is energy dependent. Metabolic energy is required to support the correct folding and disulphide bond formation in this well characterized viral glycoprotein, to rescue misfolded proteins from disulphide-linked aggregates, and to maintain the oxidized protein in its folded and oligomerization-competent state.

Adenosine Triphosphate↗
PubMed1992

Manipulating disulfide bond formation and protein folding in the endoplasmic reticulum.

Addition of the reducing agent dithiothreitol (DTT) to the medium of living cells prevented disulfide bond formation in newly synthesized influenza hemagglutinin (HA0) and induced the reduction of already oxidized HA0 inside the ER. The reduced HA0 did not trimerize or leave the ER. When DTT was washed out, HA0 was rapidly oxidized, correctly folded, trimerized and transported to the Golgi complex. We concluded that protein folding and the redox conditions in the ER can be readily manipulated by addition of DTT without affecting most other cellular functions, that the reduced influenza HA0 remains largely unfolded, and that folding events that normally take place on the nascent HA0 chains can be delayed and induced post-translationally without loss in efficiency.

Adenosine Triphosphate↗
PubMed1988

Differential effects of mutations in three domains on folding, quaternary structure, and intracellular transport of vesicular stomatitis virus G protein.

The vesicular stomatitis virus glycoprotein (G protein) is an integral membrane protein which assembles into noncovalently associated trimers before transport from the endoplasmic reticulum. In this study we have examined the folding and oligomeric assembly of twelve mutant G proteins with alterations in the cytoplasmic, transmembrane, or ectodomains. Through the use of conformation-specific antibodies, we found that newly synthesized G protein folded into a conformation similar to the mature form within 1-3 min of synthesis and before trimer formation. Mutant proteins not capable of undergoing correct initial folding did not trimerize, were not transported, and were found in large aggregates. They had, as a rule, mutations in the ectodomain, including several with altered glycosylation patterns. In contrast, mutations in the cytoplasmic domain generally had little effect on folding and trimerization. These mutant proteins, whose ectodomains were identical to the wild-type by several assays, were either transported to the cell surface slowly or not at all. We concluded that while correct ectodomain folding and trimer formation are prerequisites for transport, they alone are not sufficient. The results suggest that the cytoplasmic domain of the wild-type protein may facilitate rapid, efficient transport from the ER, which can be easily affected or eliminated by tail mutations that do not detectably affect the ectodomain.

Animals↗