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Biomedical subjects

S Tabak

Publications and source records attributed to S Tabak.

18 recordsLinked to original sources
PubMed2000

Digestion of so-called resistant starch sources in the human small intestine.

BACKGROUND: Resistant starch sources, which are only partially digested in the small intestine, can be used to increase colonic availability of short-chain fatty acids. OBJECTIVE: To study the characteristics of the fermentation of resistant starch, the digestion of resistant starch in the small intestine has to be quantified. We compared the metabolic fates of highly digestible cornstarch (DCS), Hylon VII (type 2 resistant starch), and Novelose 330 (type 3 resistant starch), which are of corn origin and, therefore, naturally enriched in (13)C. DESIGN: After administration of 40 g starch or glucose to 7 healthy volunteers, glucose and exogenous glucose concentrations in serum and (13)CO(2) excretion in breath were analyzed for 6 h. (13)C abundance in carbon dioxide was analyzed by isotope ratio mass spectrometry (IRMS) and (13)C abundance in glucose by gas chromatography-combustion IRMS. RESULTS: By comparing the area under the curve (2 h) of exogenous glucose concentration in serum ((13)C glycemic index) after intake of starch or glucose, (13)C glycemic indexes for DCS, Hylon VII, and Novelose 330 were calculated to be 82 +/- 23%, 44 +/- 16%, and 43 +/- 15%, respectively. Comparison of 6-h cumulative percentage dose recovery in breath showed that 119 +/- 28% of DCS, 55 +/- 23% of Hylon VII, and 50 +/- 26% of Novelose 330 was digested in the small intestine. CONCLUSION: The exogenous glucose response in serum and the (13)CO(2) excretion in breath can be used to estimate small intestinal digestion of resistant starch, which amounts to approximately 50%.

Adult↗
PubMed1997

Gain and delay of human vestibulo-ocular reflexes to oscillation and steps of the head by a reactive torque helmet. I. Normal subjects.

Vestibulo-ocular reflexes (VOR) were evaluated with a reactive torque helmet that imposed high-frequency oscillation (2-20 Hz) or step displacements of the head in the horizontal plane. The present paper describes the experimental and analytical techniques and the results for normal subjects, which will serve as a baseline for the evaluation of vestibular pathology. For comparison, manually controlled head steps were also applied, as described in the literature. Eye and head movements were recorded with magnetic search coils. Non-vestibular effects were avoided by the use of high stimulus frequencies and the analysis of short time-windows (< 100 msec) after steps. Helmet-imposed steps caused a virtually uniform head acceleration (average magnitude 770 degrees/sec) in the first 90 msec. This resulted in a linear relation between eye and head velocities; the gain and delay of the VOR could be calculated independently from the slope and offset of this relation. Such estimates appear more reliable than those obtained with conventional techniques. Normal subjects had a VOR gain of about 0.9 and a delay of about 5 msec. The results of sinusoidal head oscillation were in agreement with the results for steps. The responses to manually generated head steps agreed in general with those to helmet-induced steps, but because of the non-uniform acceleration they allowed a less exact analysis of function.

Acceleration↗
PubMed1997

Gain and delay of human vestibulo-ocular reflexes to oscillation and steps of the head by a reactive torque helmet. II. Vestibular-deficient subjects.

Vestibulo-ocular reflexes (VOR) were evaluated with a reactive torque helmet that imposed high-frequency oscillation (2-20 Hz) or step displacements of the head in the horizontal plane. The present paper describes the results in patients with vestibular deficiencies (labyrinthine defective; LD); experimental and analytical techniques and results for normal subjects were described in Part 1 of this paper. The patient groups included: total unilateral LD (related to acoustic neuroma; n = 40); severe (clinically total) bilateral LD (n = 7); bilateral hyporeflexia (n = 14); unilateral hyporeflexia (n = 11); and patients with LD phenomena that had subsided (n = 3). Helmet-induced head steps provided the most specific information. Characteristically, gain was lowered in one direction or both directions after unilateral or bilateral vestibular lesions, respectively; in general, the magnitude of the gain reduction correlated well with the degree of complaints and disability. Surprisingly, delay was systematically prolonged (up to several tens of milliseconds) in all groups of subjects with manifest vestibular pathology. These results suggest that the determination of delay, in addition to gain of the VOR, is feasible and important in the evaluation of vestibular function. The results of head oscillation generally supported the results for steps, but were somewhat less specific. The responses to manually generated head steps roughly agreed with those to helmet-induced steps, but because of the non-uniform acceleration they allowed a less exact analysis of VOR function.

Acceleration↗
PubMed1997

Deviation of the subjective vertical in long-standing unilateral vestibular loss.

We evaluated changes in the subjectively perceived gravitational vertical as an index of imbalance in the function of the right and left otolith organs. In addition to normal subjects (n = 25), we measured patients with a longstanding (mean 4.5 year +/- 3.2 SD; range 0.5-11.5 years) unilateral vestibular loss after surgery for acoustic neuroma (n = 32), patients with partial unilateral vestibular loss (n = 7) and patients with bilateral vestibular hyporeflexia (n = 8). Normal subjects could accurately align a vertical luminous bar to the gravitational vertical in an otherwise completely dark room (mean setting -0.14 degree +/- 1.11 SD). Patients with left-sided (complete; n = 13) or right-sided (complete; n = 19 and partial; n = 7) unilateral vestibular loss made mean angular settings at 2.55 degrees +/- 1.57 (SD) leftward and 2.22 degrees (+/-1.96 SD) rightward, respectively. These means differed highly significantly from the normal mean (p < 0.00001). In the time interval investigated (0.5-11.5 years) the magnitude of the tilt angle showed no correlation with the time elapsed since the operation. The mean setting by patients with clinically bilateral vestibular loss (-1.17 degrees +/- 1.96 SD; n = 8) did not significantly differ from the control group. The systematic tilts of the subjective vertical in patients with a unilateral vestibular impairment were correlated with their imbalance in canal-ocular reflexes, as reflected by drift during head-oscillation at 2 Hz (r2 = 0.44) and asymmetries in VOR-gain for head-steps (r2 = 0.48-0.67). These correlations were largely determined, by the signs of the asymmetries; correlation between the absolute values of the VOR gain asymmetries and subjective vertical angles proved to be virtually absent. We conclude that the setting of the subjective vertical is a very sensitive tool in detecting a left-right imbalance in otolith function, and that small but significant deviations towards the defective side may persist for many years (probably permanently) after unilateral lesions of the labyrinth or the vestibular nerve.

Ear, Inner↗
PubMed1996

Identification, characterization, and molecular cloning of a homologue of the bacterial FtsH protease in chloroplasts of higher plants.

In an attempt to identify and characterize chloroplast proteases, we performed an immunological analysis of chloroplasts using an antibody against Escherichia coli FtsH protease, which is an ATP-dependent metalloprotease bound to the cytoplasmic membrane. A cross-reacting protein of 78 kDa was found in the thylakoid membrane of spinach, but not in the soluble stromal fraction. Alkali and high salt washes, as well as trypsin treatment of thylakoid membranes, suggest that the chloroplastic FtsH protein is integral to the membrane, with its hydrophilic portion exposed to the stroma. The protein is not bound to any photosynthetic complex and is exclusively located in the stromally exposed regions of the thylakoid membrane. Its expression is dependent on light, as it is present in green pea seedlings, but absent from etiolated ones. An Arabidopsis cDNA was isolated, and the deduced amino acid sequence demonstrated high similarity to the E. coli FtsH protein, especially in the central region of the protein, containing the ATP- and zinc-binding sites. The product of this clone was capable of import into isolated pea chloroplasts, where it was processed to its mature form and targeted to the thylakoid membrane. The trans-bilayer orientation and lateral location of the FtsH protein in the thylakoid membrane suggest its involvement in the degradation of both soluble stromal proteins and newly inserted or turning-over thylakoid proteins.

ATP-Dependent Proteases↗
PubMed1996

Immunological detection of proteins similar to bacterial proteases in higher plant chloroplasts.

Despite numerous demonstrations of protein degradation in chloroplasts of higher plants, little is known about the identity of the proteases involved in these reactions. To identify chloroplast proteases by immunological means, we investigated two proteins: ClpP, a protein similar to the proteolytic subunit of the bacterial ATP-dependent Clp protease, for which a gene is found in the chloroplast genome [Maurizi, M.R., Clark, W.P., Kim, S. H. & Gottesman, S. (1990) J. Biol. Chem. 265, 12546-12552] and PrcA, a cyanobacterial Ca2+-stimulated protease [Maldener, I., Lockau, W., Cai, Y. & Wolk, P. (1991) Mol. & Gen. Genet. 225, 113-120]. We expressed the clpP gene from rice in Escherichia coli, purified its product, and generated antibodies against the product. Western blot analysis revealed the ClpP protein in different leaf extracts. Analysis of fractionated barley chloroplasts revealed that the protein was associated with the stromal fraction. The expression of ClpP is light independent and tissue specific, as it was found in green and etiolated barley leaves, but not in roots. A second protein, similar to the cyanobacterial protease PrcA, was also detected in chloroplasts. Antibody against this protease recognized proteins in various leaf extracts. When pea chloroplasts were fractionated, the antibody only recognized a stromal protein. The expression of this protein is regulated by light, as it was found in green leaves, but not in etiolated leaves. The tissue specificity of PrcA was similar to that of ClpP in that it could not be detected in root extracts.

Adenosine Triphosphatases↗
PubMed1996

Serum tumour markers in renal failure.

In order to assess the clinical value of six tumour markers in pre-dialysis patients with chronic renal failure as well as in patients on regular haemodialysis, we studied these markers in 35 predialysis patients, 35 patients on chronic haemodialysis and 35 healthy controls. Serum squamous cell antigen (SCC), CA 19.9, and CA 125 levels were found to be elevated in the uraemic groups as compared to the normal controls. Carcinoembryonic antigen (CEA), alpha foetoprotein (AFP), and prostate-specific antigen (PSA) levels were within normal limits in all groups.

Adult↗
PubMed1996

Transcriptionally active haptoglobin-related (Hpr) gene in hepatoma G2 and leukemia molt-4 cells.

The aim of the present study was to answer the question: Is the haptoglobin-related (Hpr) gene expressed in tumor cells? Our strategy of cloning the cDNA was to screen a human hepatoma G2 cDNA expression library in lambda gt11 using three different probes complementary to the coding strands of regions of the Hpr gene that contain codon changes permitting a discrimination from haptoglobin gene Hp1F. Among 8 x 10(5) recombinant phages screened, 2 hybridized to all three probes under stringent conditions. A 1.5 kb cDNA designated ST-1 was subcloned and sequenced. Almost total identity was found with the Hpr predicted exons 2-5, although exon 1 was missing. The ST-1 partial cDNA clone was used as a probe to screen a human leukemia molt-4 cDNA expression library in lambda gt11. Among 10(6) recombinant phages screened, 1 hybridized under stringent conditions. A 1.5 kb cDNA designated ST-2 was subcloned and sequenced. ST-1 and ST-2 cDNA were identical except for an insert of A at position 500 of ST-1 cDNA. Two different nucleotide changes were observed in the ST-1 and ST-2 sequences as compared with the expected Hpr cDNA sequence. An alternative processing of Hpr pre-mRNA was found in both cDNA clones that included 126 bp of the 3'-region of intron 1. This intronic sequence is thereby retained in the mature mRNA. cDNA analysis revealed an in-frame ATG in intron 1. Transcription/translation assay was used to demonstrate that the Hpr message could be translated from the internal methionine codon. We have thus shown for the first time that the Hpr gene is expressed in the human hepatoma G2 and leukemia molt-4 cell lines.

Amino Acid Sequence↗
PubMed1996

Modulation of the human vestibuloocular reflex during saccades: probing by high-frequency oscillation and torque pulses of the head.

1. We probed the gain and phase of the vestibuloocular reflex (VOR) during the execution of voluntary gaze saccades, with continuous oscillation or acceleration pulses, applied through a torque helmet. 2. Small-amplitude (< 1 degree), high-frequency (10-14 Hz) head oscillations in the horizontal or vertical plane were superimposed on ongoing horizontal gaze saccades (40-100 degrees). Torque pulses to the head ("with" or "against" gaze) were superimposed on 40 degrees horizontal saccades. Eye and head movements were precisely measured with sensor coils in magnetic fields. 3. Techniques were developed to separate the oscillatory (horizontal or vertical) component from the gaze shift and obtain VOR gain and phase with Fourier techniques from the relation between eye-in-head and head oscillations. These involved either subtraction of exactly matching saccades with and without oscillation (drawback: low yield) or time shifting of successive trials to synchronize the oscillations (drawback: slight time blurring of saccades). 4. The results of these matching and synchronization methods were essentially identical and consistent. Presaccadic gain values of the horizontal VOR (typically about unity) were reduced by, on average, approximately 20 and 50% during horizontal saccades of 40 and 100 degrees, respectively. These percentages may be truncated because of methodological limitations, but even after taking these into account (on the basis of simulation experiments with 2 different, theoretical profiles of suppression) our results do not support a complete saccadic VOR suppression for any substantial fraction of saccadic duration. Qualitatively similar changes were found when the vertical VOR was probed during 100 degrees horizontal saccades. 5. Concomitantly with the reductions in gain, VOR phase was advanced by approximately 20 degrees during the saccade. 6. In the wake of gaze saccades, VOR gain was consistently elevated (to approximately 1.0) above the presaccadic level (approximately 0.9). We submit that this mechanism ensures stable fixation of the newly acquired target at a time when the head is still moving substantially. 7. Although the responses to head torque pulses showed idiosyncratic asymmetries, analysis of the differences in eye and head movements for pulses with and against consistently showed a sharp fall of VOR gain at saccadic onset, following an approximately exponential course with a time constant of approximately 50 ms. This decay may be assumed to reflect VOR gain for a period of approximately 50 ms, after which secondary gaze control mechanisms become dominant. 8. The time course of the gain decay and phase shift of the VOR suggest that suppression of the "integrative (position) loop" of the VOR circuit was more complete than suppression of the direct, "velocity" pathway.

Female↗
PubMed1995

Evaluation of the human vestibulo-ocular reflex at high frequencies with a helmet, driven by reactive torque.

A new technique was developed to test the VOR in humans. A tightly but comfortably fitting helmet was provided with an electronically controlled torque motor that rotated a mass around a vertical axis. Acceleration of the motor caused reactive torque of the helmet in the opposite direction which was transmitted to the (freely movable) head. Sinusoidal head oscillations in the frequency range 2-20 Hz (peak-to-peak amplitudes about 10 degrees and 0.1 degrees respectively) were easily achieved, as well as step displacements of the head with accelerations on the order of 1000 degrees/s2. Limitation of the maximum torque and lack of any rigid attachment of the head to a fixed structure made the technique safe and comfortable. Eye and head rotations were recorded, independently of head translations, with eye and head search coils in a homogeneous a.c. magnetic field. In normal subjects, gain was near unity at 2 Hz: above 8 Hz, gain increased progressively toward 1.1-1.3 at 20 Hz. Phase lag increased from a few degrees at 2 Hz to about 45 degrees at 20 Hz. Above 2 Hz, these results were unaffected by visual conditions; lower gains and increased phase lags were found in subjects with bilateral or unilateral vestibular loss. For step displacements, gain (measured in the first 100 ms) was near unity for normals, near zero after bilateral vestibular loss and strongly asymmetrical after unilateral vestibular loss. Thus, the technique seems highly effective in testing vestibular function with minimal contamination by other systems.

Acceleration↗
PubMed1994

Human vestibulo-ocular responses to rapid, helmet-driven head movements.

High-frequency head rotations in the 2-20 Hz range and passive, unpredictable head acceleration impulses were produced by a new technique, utilizing a helmet with a torque motor oscillating a mass. Unrestrained head and eye movements were recorded using magnetic sensor coils in a homogeneous magnetic field. In order to analyze the influence of the visual system on the vestibulo-ocular reflex (VOR), we took measurements under three experimental conditions: (1) with a stationary visual target; (2) in total darkness with the subject imagining the stationary target; and (3) with a head-fixed target. The results in 15 healthy subjects were highly consistent. At 2 Hz, VOR gain was near unity; above 2 Hz, VOR gain started to decrease, but this trend reversed beyond 8 Hz, where the gain increased continuously up to 1.1-1.3 at 20 Hz. Phase lag increased with frequency, from a few deg at 2 Hz to about 45 degrees at 20 Hz. Above 2 Hz, VOR gain was not significantly different for the three experimental conditions. Head acceleration impulses produced a VOR with near-unity gain in both directions. We also tested three subjects with clinically total bilateral loss of labyrinthine functions. These labyrinthine-defective subjects showed, in comparison to the normal subjects, strikingly lower gains and much longer delays in the VOR during sinusoidal and step-like head movements. These results suggest that our new torque-driven helmet technique is effective, safe and convenient, enabling the assessment of the VOR at relatively high frequencies where both visual and mental influences are minimized.

Eye Movements↗