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Biomedical subjects

H Holzer

Publications and source records attributed to H Holzer.

At least 55 records · Page 3Linked to original sources
PubMed1996

Differentiation of delayed kidney graft function with gadolinium-DTPA-enhanced magnetic resonance imaging and Doppler ultrasound.

RATIONALE AND OBJECTIVES: The authors differentiate acute tubular necrosis from transplant rejection in patients with delayed kidney graft function using gadolinium (Gd)-DTPA enhanced magnetic resonance (MR) imaging. METHODS: Twenty-four patients after renal transplantation (10 with normal graft function, 14 with delayed graft function) underwent conventional and Doppler sonography and MR imaging examination after bolus application of Gd-DTPA. Within a time period of 512 seconds, 39 single-slice MR images were obtained. Measurements of signal intensity in three regions of interests (cortex, medulla, renal pelvis) resulted in a graphic description of the dynamics of the contrast enhancement. The time between the start of the scan and the peaks of the curves was measured. RESULTS: In patients with normal graft function the curves reached the peaks between 39 and 55 seconds (cortex), 44 and 61 seconds (medulla), and between 161 and 318 seconds (renal pelvis). Six patients with acute tubular necrosis showed normal values for the curves 1 and 2 but markedly prolonged time for curve 3 (between 420 and 512 seconds). In all patients with histologically proven transplant rejection, the peaks of all curves were not reached before the ends of the scans. CONCLUSION: The authors' preliminary results suggest that MR imaging seems to be a sensitive, noninvasive diagnostic tool to differentiate acute tubular necrosis from transplant rejection in the critical early postoperative period.

Adult↗
PubMed1995

Isolation and characterization of a novel yeast gene, ATH1, that is required for vacuolar acid trehalase activity.

We have isolated a plasmid containing a gene, ATH1, that results in eight- to ten-fold higher acid trehalase activity in yeast cells when present in high copy. The screening procedure was based on overproduction-induced mislocalization of acid trehalase activity; overproduction of vacuolar enzymes that transit through the secretory pathway leads to secretion to the cell surface. A DNA fragment that confers cell surface expression of acid trehalase activity was cloned and sequenced. The deduced amino acid sequence displayed no homology to known proteins, indicating that we have identified a novel gene. A deletion in the genomic copy of the ATH1 gene eliminates vacuolar acid trehalase activity. These results suggest that ATH1 may be the structural gene encoding vacuolar acid trehalase or that the gene product may be essential regulatory component involved in control of trehalase activity.

Amino Acid Sequence↗
PubMed1995

Expression and function of the trehalase genes NTH1 and YBR0106 in Saccharomyces cerevisiae.

The biological function of the trehalose-degrading yeast enzyme neutral trehalase consists of the control of the concentration of trehalose, which is assumed to play a role in thermotolerance, in germination of spores, and in other life functions of yeast. Resequencing of the neutral trehalase gene NTH1 on chromosome IV resulted in the observation of two possible start codons (Kopp, M., Nwaka, S., and Holzer, H. (1994) Gene (Amst.) 150, 403-404). We show here that only the most upstream start codon which initiates translation of the longest possible ORF is used for expression of NTH1 in vivo. A gene with 77% identity with NTH1, YBR0106, which was discovered during sequencing of chromosome II (Wolfe, K. H., and Lohan, A. J. E. (1994) Yeast 10, S41-S46), is shown here to be expressed into mRNA. Experiments with a mutant disrupted in the YBR0106 ORF showed, in contrast to a NTH1 deletion mutant, no changes in trehalase activity and in trehalose concentration. However, similar to the NTH1 gene a requirement of the intact YBR0106 gene for thermotolerance is demonstrated in experiments with the respective mutants. This indicates that the products of the likely duplicated YBR0106 gene and the NTH1 gene serve a heat shock protein function. In case of the YBR0106 gene, this is the only phenotypic feature found at present.

Adaptation, Physiological↗
PubMed1995

Phenotypic features of trehalase mutants in Saccharomyces cerevisiae.

In the yeast Saccharomyces cerevisiae, some studies have shown that trehalose and its hydrolysis may play an important physiological role during the life cycle of the cell. Recently, other studies demonstrated a close correlation between trehalose levels and tolerance to heat stress, suggesting that trehalose may be a protectant which contributes to thermotolerance. We had reported lack of correlation between trehalose accumulation and increase in thermotolerance under certain conditions, suggesting that trehalose may not mediate thermotolerance [Nwaka, S., et al. (1994) FEBS Lett. 344, 225-228]. Using mutants of the trehalase genes, NTH1 and YBR0106, we have demonstrated the necessity of these genes in recovery of yeast cells after heat shock, suggesting a role of these genes in thermotolerance (Nwaka, S., Kopp, M., and Holzer, H., submitted for publication). In the present paper, we have analysed the expression of the trehalase genes under heat stress conditions and present genetic evidence for the 'poor-heat-shock-recovery' phenotype associated with NTH1 and YBR0106 mutants. Furthermore, we show a growth defect of neutral and acid trehalase-deficient mutants during transition from glucose to glycerol, which is probably related to the 'poor-heat-shock-recovery' phenomenon.

Gene Expression Regulation, Fungal↗
PubMed1995

Development and critical evaluation of an improved comprehensive multicompartment model for the exchange processes during hemodialysis.

An improved comprehensive multicompartment model for the simulation of the most important metabolic state variables in the patient during dialysis is presented. With this approach time courses of urea, creatinine, K+, Na+, Cl-, HCO3-, H+ and CO2 can be predicted. Additionally, osmotic water shifts as well as resting membrane potentials are calculated. The model contains the following extensions compared to classical approaches: For the calculation of osmotic water shifts, not only sodium, but also urea, potassium, chloride and unspecified indiffusable ions are taken into account. Furthermore, hemodynamic aspects are considered by assuming two tissue groups with different perfusion. Thus it is possible to estimate the influence of hemodynamic parameters (e.g. cardiac output or blood flow distribution) on the exchange processes. The model can be adjusted individually by several system parameters. This adjustment is performed by minimizing the sum of the quadratic differences between simulated and measured plasma concentrations of the considered substances. A first validation has been performed successfully with measured data from 18 dialysis patients. After the effective whole-body exchange area of the resting cell membranes for potassium, sodium and chloride had been estimated, rebound effects for those electrolytes could be simulated successfully.

Acid-Base Equilibrium↗
PubMed1995

System identification of the low-dose kinetics of p-aminohippuric acid.

The renal clearance of p-aminohippuric acid, due to tubular secretion in addition to glomerular filtration, can only be determined by kinetic experiments. Maximal information can be gained from observed temporal marker concentration profiles by fitting dynamic mathematical models of the processes involved, such as absorption, distribution, and elimination, to the kinetic data. Thereby the values of the system constants, such as fractional elimination or fractional distribution rates, and their accuracy measures are determined by methods which are based firstly on measured time-dependent data elicited in an individual test object by perturbing inputs and secondly, on mathematical formulations of prior knowledge of the underlying physiological system. Such methods of model adaptation are called system identification. In this context a computer-based method of system identification and error estimation for the system constants of two-compartment models matched a dynamic concentration profiles of p-aminohippuric acid is presented. The method is used of single-injection experiments to demonstrate that such a technique is able to correctly estimate the clearance of p-aminohippuric acid if sufficiently long experimental protocols are chosen, and to ascertain the sufficient length of a protocol for an individual subject. The renal clearance of p-aminohippuric acid is known to exhibit concentration-dependence generally, but to achieve its maximal value when low doses are applied. The present study deals with the low-dose kinetics of p-aminohippuric acid.

Adult↗
PubMed1995

Determination of the glomerular filtration rate by identification of sinistrin kinetics.

A computer-based method of system identification and estimation of parameter variance for two-compartment models matched to dynamic sinistrin concentration profiles for the determination of glomerular filtration rate is described. Thereby a procedure for the judgment of the optimal sampling time horizon is presented. Since single-injection techniques are suspected of yielding systematic overestimation of the glomerular filtration rate, a method is demonstrated confirming that such a technique employing sinistrin kinetics can be used to correctly determine the glomerular filtration rate. The validation of the system parameters gained by the single-injection method is made through prediction of the concentration contour under a constant infusion regimen in the same subject on a different occasion. This was performed in healthy controls and in patients with various degrees of renal insufficiency. Upon consideration of the dependence of the clearance estimates and their variances on the protocol duration in test subjects examined from four to ten hours, an adaptive design of the protocol length is developed.

Adult↗
PubMed1995

Intradialytic parenteral nutrition in malnourished patients on chronic haemodialysis therapy.

BACKGROUND: Malnutrition is frequently encountered in patients on regular haemodialysis therapy and presents an important determinant of morbidity and mortality. Usual therapeutic approaches to alleviate malnutrition have been unsuccessful. The objective of this study was to assess the impact of intradialytic parenteral nutrition (IDPN) with amino acids (in combination with a glucose-containing dialysate) on nutritional parameters and immunocompetence in patients on regular haemodialysis treatment. METHODS: Effects of IDPN were evaluated in 16 malnourished patients. After a run-in period of 4 weeks (to define stable baseline conditions) 0.8 g amino acids/kg bodyweight using a novel amino-acid solution (adapted to metabolic alteration of uraemia and including the dipeptide glycyl-tyrosine as tyrosine source) was infused thrice weekly during each haemodialysis session for 16 weeks. RESULTS: Intradialytic amino-acid infusion was well tolerated and the dipeptide was rapidly utilized with only traces being detectable in plasma after dialysis. Visceral protein synthesis was improved, serum albumin, prealbumin, and cholinesterase increased during IDPN (P < 0.05). As indicators of augmented immunocompetence skin test reactivity against multiple antigens was improved (P < 0.02) and total lymphocyte count was raised (P < 0.05). Plasma amino acid pattern did not deteriorate but failed to normalize during IDPN and phenylalanine/tyrosine ratio remained stable. Anthropometric measurements and eating behaviour as assessed by dietary records were not altered during IDPN. CONCLUSIONS: Even using a simple and limited intradialytic nutritional support with amino acids can improve visceral protein status and stimulate immunocompetence in malnourished patients on regular haemodialysis therapy.

Amino Acids↗
PubMed1994

Is thermotolerance of yeast dependent on trehalose accumulation?

During heat stress, trehalose concentration increases in yeast cells in parallel to thermotolerance. This parallelism suggested that trehalose mediated thermotolerance. We show in this work that, under certain conditions, trehalose accumulation and increase in thermotolerance do not go in parallel. A mutant deficient in the trehalose-degrading neutral trehalase shows, after shift from 40 degrees C to 30 degrees C, low thermotolerance in spite of a high trehalose concentration. When glucose is added to stationary yeast cells with high trehalose concentration and high thermotolerance, trehalose concentration decreases while thermotolerance remains high. A mutant deficient in ubiquitin-conjugating genes, ubc4ubc5, shows during exponential growth a low trehalose concentration, but a high thermotolerance, in contrast to wild-type cells. Because the ubc4ubc5 mutant synthesizes heat-shock proteins constitutively, it is proposed that, under these conditions, accumulation of heat-shock proteins, and not trehalose [corrected], mediates thermotolerance.

Gene Deletion↗
PubMed1994

Serum levels of the soluble receptor for tumor necrosis factor in patients with renal disease.

Tumor necrosis factor-alpha (TNF-alpha) has been found to be elevated in patients during hemodialysis and is thought to mediate some of the immune and metabolic dysfunctions in these patients. It has been speculated that infusions of soluble TNF receptor (sTNF-R) may prevent some of the cytotoxic effects of TNF. However, little is still known about preexisting serum TNF-R levels in patients with chronic renal failure, with or without hemodialysis. Therefore we analyzed serum samples of sTNF-R in 26 patients with chronic renal failure (group I), 61 hemodialysis patients (group II), 9 renal transplant recipients with acute renal failure requiring posttransplant dialysis (group III), 13 renal transplant patients with rejection and moderate kidney dysfunction (group IV), and 21 renal transplant recipients with borderline kidney dysfunction and diverse infectious complications (group V). Control groups consisted of 34 blood donors and diseased controls (11 renal transplant recipients with normal kidney function without complications). All patient groups showed significantly higher sTNF-R levels compared to the control groups. In groups I, IV, and V comparable levels were observed. In group I there was a clear correlation between sTNF-R levels and serum creatinine. The highest sTNF-R serum levels were seen in groups II and III, but there was no correlation with creatinine. In the posttransplant cases (group III and diseased controls) there was a decrease in sTNF-R with improvement of kidney function. These data strongly suggest that sTNF-R serum levels are dependent on kidney function.

Adult↗
PubMed1994

Identification and characterization of a novel yeast gene: the YGP1 gene product is a highly glycosylated secreted protein that is synthesized in response to nutrient limitation.

Nutrient starvation in the yeast Saccharomyces cerevisiae leads to a number of physiological changes that accompany entry into stationary phase. The expression of genes whose products play a role in stress adaptation is regulated in a manner that allows the cell to sense and respond to changing environmental conditions. We have identified a novel yeast gene, YGP1, that displays homology to the sporulation-specific SPS100 gene. The expression of YGP1 is regulated by nutrient availability. The gene is expressed at a basal level during "respiro-fermentative" (logarithmic) growth. When the glucose concentration in the medium falls below 1%, the YGP1 gene is derepressed and the gene product, gp37, is synthesized at levels up to 50-fold above the basal level. The glucose-sensing mechanism is independent of the SNF1 pathway and does not operate when cells are directly shifted to a low glucose concentration. The expression of YGP1 also responds to the depletion of nitrogen and phosphate, indicating a general response to nutrient deprivation. These results suggest that the YGP1 gene product may be involved in cellular adaptations prior to stationary phase and may be a useful marker protein for monitoring early events associated with the stress response.

Alkaline Phosphatase↗
PubMed1993

Secretin inhibits gastric emptying in rats via a capsaicin-sensitive vagal afferent pathway.

In awake rats, fitted with chronic gastric fistulas, secretin (30 and 300 pmol intraperitoneal, i.p.) inhibited gastric emptying of a non-nutrient liquid by 16% (NS) and 38% (P < 0.01) respectively. Functional ablation of vagal, but not spinal, capsaicin-sensitive afferents reversed the action of secretin by 61%. Inhibition of gastric emptying induced by cholecystokinin (CCK) (30 pmol i.p.) was reversed by around 50% by ablation of either the vagal or spinal capsaicin-sensitive afferent pathway. These results suggest that hormones released after a meal can inhibit gastric emptying via activation of visceral afferent pathways.

Afferent Pathways↗
PubMed1993

Molecular analysis of the neutral trehalase gene from Saccharomyces cerevisiae.

Neutral trehalase (EC 3.2.1.28) is a trehalose hydrolyzing enzyme of the yeast Saccharomyces cerevisiae (App, H., and Holzer, H. (1989) J. Biol. Chem. 264, 17583-17588). The gene of neutral trehalase was cloned by complementation of a neutral trehalase-deficient yeast mutant which was obtained by ethylmethanesulfonate mutagenesis. Three mutants without detectable neutral trehalase activity were obtained and characterized by tetrad analysis and found to belong to the same complementation group. The mutants were transformed with a S. cerevisiae genomic library in YEp24. Two overlapping plasmids were isolated, containing the neutral trehalase gene NTH1 with an open reading frame of 2079 base pairs (bp), encoding a protein of 693 amino acids, corresponding to a molecular mass of 79,569 Da. Several putative TATA boxes were found in the 5'-nontranslated region of the NTH1 gene. In positions -652 to -641 a possible binding sequence for the MIG1 protein, a multicopy inhibitor of the GAL1 promotor, which also binds to the promotor sequences of the SUC2 and the FBP1 gene, was found. The start codon of the neutral trehalase is located about 2500 bp upstream of the centromere 4 consensus sequence elements I, II, and III (Mann, C., and Davis, R. W. (1986) Mol. Cell. Biol. 6, 241-245). Vicinity to a centromere is known to have a depressing influence on the number of plasmid copies per cell. This probably explains why transformation with pNTH does not lead to overexpression of neutral trehalase. The four consensus sequences AATAAA contained in the centromeric elements and reconfirmed by our sequencing data might be polyadenylation signals for NTH1-mRNA transcription termination. Northern blot analysis yielded a single mRNA species of approximately 2.3 kilobase(s). The neutral trehalase protein has a putative cAMP-dependent phosphorylation consensus sequence RRGS from amino acid positions 22-25. Therefore, the previously described activation of neutral trehalase by cAMP-dependent phosphorylation is probably due to phosphorylation of serine 25. Three potential N-glycosylation sites (Asn-X-Ser/Thr) occur in the open reading frame of the neutral trehalase gene. However, no evidence for glycosylation could be detected by Western blotting.(ABSTRACT TRUNCATED AT 400 WORDS)

Amino Acid Sequence↗