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T Hofmann

Publications and source records attributed to T Hofmann.

At least 37 records · Page 2Linked to original sources
PubMed2001

[Pneumatization of the zygomatic arch on pantomography].

BACKGROUND: The pneumatized spaces of the zygomatic arch (zygomatic air cell defect) are a clinically asymptomatic variation of the temporal bone. The empty spaces of the articular eminence and temporal bone of the zygomatic arch are depicted on radiographs as a sharply demarcated osteolytic lesion of round or oval shape. The aim of this study was to determine the prevalence and characteristics of the ZACD in our outpatients. MATERIALS AND METHODS: We investigated the panoramic radiographs of 1,084 patients who were treated during 1 February and 31 July 2000. The mean age of the 1,084 patients was 41.9 years (SD: 17.2 years; range: 2-96): 628 patients were male (58%) and 456 female (42%). A ZACD was found in 20 of 1,084 patients (prevalence: 1.85%). The mean age of the patients with a ZACD was 43.2 years (SD: 18.4 years; range: 7-87): 11 were female (55%) and 9 male (45%). RESULTS: A bilateral ZACD was found in 20% (four patients). Interestingly, one of these ZACD patients was a 7-year-old boy. Up to now, it had generally been accepted that pneumatization of the zygomatic arch takes place after puberty with the youngest persons with ZACD being 15 years of age. Our findings should prompt consecutive studies on the prevalence of ZACD in children. This finding can be relevant in patients treated for spreading otitis media or mastoiditis.

Adolescent↗
PubMed2001

Structure determination of a novel 3(6H)-pyranone chromophore and clarification of its formation from carbohydrates and primary amino acids.

An intensely orange compound, which has recently been evaluated as one of the main colored compounds formed in Maillard reactions of hexoses, could be unequivocally identified as (Z)-2-[(2-furyl)methylidene]-5,6-di(2-furyl)-6H-pyran-3-one (1) by application of several NMR and LC-MS experiments. To clarify its formation, the effectiveness of certain carbohydrate degradation products as precursors of 1 was studied in a quantitative experiment demonstrating hydroxy-2-propanone, furan-2-aldehyde, and 3-deoxy-2-hexosulose as precursors of the colorant. Site-specific labeling experiments with D-1-[(13)C]glucose and D-6-[(13)C]glucose, respectively, were performed to elucidate the formation pathway of 1 involving a cleavage of the hexose skeleton between carbon atoms C(5) and C(6). In addition, pentoses could be shown to generate 1 via a similar formation pathway involving the 3-deoxy-2-pentosulose.

Amino Acids↗
PubMed2001

Characterization of an intense bitter-tasting 1H,4H-quinolizinium-7-olate by application of the taste dilution analysis, a novel bioassay for the screening and identification of taste-active compounds in foods.

Thermal treatment of aqueous solutions of xylose and primary amino acids led to rapid development of a bitter taste of the reaction mixture. To characterize the key compound causing this bitter taste, a novel bioassay, which is based on the determination of the taste threshold of reaction products in serial dilutions of HPLC fractions, was developed to select the most intense taste compounds in the complex mixture of Maillard reaction products. By application of this so-called taste dilution analysis (TDA) 21 fractions were obtained, among which 1 fraction was evaluated with by far the highest taste impact. Carefully planned LC-MS as well as 1D and 2D NMR experiments were, therefore, focused on the compound contributing the most to the intense bitter taste of the Maillard mixture and led to its unequivocal identification as the previously unknown 3-(2-furyl)-8-[(2-furyl)methyl]-4-hydroxymethyl-1-oxo-1H,4H-quinolizinium-7-olate. This novel compound, which we name quinizolate, exhibited an intense bitter taste at an extraordinarily low detection threshold of 0.00025 mmol/kg of water. As this novel taste compound was found to have 2000- and 28-fold lower threshold concentrations than the standard bitter compounds caffeine and quinine hydrochloride, respectively, quinizolate might be one of the most intense bitter compounds reported so far.

Caffeine↗
PubMed2001

Model studies on the influence of coffee melanoidins on flavor volatiles of coffee beverages.

Addition of the total melanoidin fraction isolated by water extraction from medium-roasted coffee powder to a model solution containing a set of 25 aroma compounds mimicking the aroma of a coffee brew reduced, in particular, the intensity of the roasty, sulfury aroma quality. Model studies performed by static headspace analysis revealed that especially three well-known coffee odorants, that is, 2-furfurylthiol (FFT), 3-methyl-2-butene-1-thiol, and 3-mercapto-3-methylbutyl formate, were significantly reduced in the headspace above an aqueous model solution when melanoidins were added. In particular, the low molecular weight melanoidins (1500-3000 Da) led to the most significant decrease in FFT. In contrast, for example, aldehydes remained unaffected by melanoidin addition.

Chromatography, Gas↗
PubMed2001

Characterization of natural "cooling" compounds formed from glucose and l-proline in dark malt by application of taste dilution analysis.

Gel permeation chromatography of the solvent extractables isolated from a thermally treated glucose/L-proline mixture and sensory analysis of the fractions collected led to the discovery of the presence of "cooling" compounds in Maillard reactions. To characterize the key compounds imparting this cooling sensation to the oral cavity, a taste dilution analysis was performed by determining the taste threshold of reaction products in serial dilutions of HPLC fractions to select the most intense "cooling" compounds in the complex GPC fraction of the Maillard reaction mixture. Systematic (13)C-labeling experiments and GC-MS, LC-MS, and 1D- and 2D-NMR measurements, followed by synthesis, led to the unequivocal identification of 3-methyl-2-(1-pyrrolidinyl)-2-cyclopenten-1-one (3-MPC), 5-methyl-2-(1-pyrrolidinyl)-2-cyclopenten-1-one (5-MPC), and 2,5-dimethyl-4-(1-pyrrolidinyl)-3(2H)-furanone (DMPF) as the key compounds contributing the most to the cooling sensation. Although these structures were described earlier with regard to Maillard reactions, this is the first time that Maillard reaction products are reported to cause intense cooling sensations by degustation. Finally, the detection of 5-MPC (101.3 microg/kg), 3-MPC (9.4 microg/kg), and DMPF (11.5 microg/kg) in dark malt verified their natural occurrence in thermally processed foods.

Chromatography, Gas↗
PubMed2001

Systematic studies on structure and physiological activity of cyclic alpha-keto enamines, a novel class of "cooling" compounds.

3-Methyl- and 5-methyl-2-(1-pyrrolidinyl)-2-cyclopenten-1-one were recently identified as intense cooling compounds in roasted dark malt. To gain more insights into the molecular requirements of these compounds for imparting a cooling sensation, 26 cyclic alpha-keto enamine derivatives were synthesized, and their physiological cooling activities were evaluated. Any modification of the amino moiety, the carbocyclic ring size, or incorporation of additional methyl groups led to a significant increase of the cooling threshold. Insertion of an oxygen atom into the 2-cyclopenten-1-one ring, however, increased the cooling activity, e.g., the cooling threshold of the 5-methyl-4-(1-pyrrolidinyl)-3(2H)-furanone was found to be 16-fold below the threshold concentration determined for the 3-methyl-2-(1-pyrrolidinyl)-2-cyclopenten-1-one. Shifting the oxygen atom from the 4- into the 5-position of the cyclopentenone ring resulted in a even more drastic increase in cooling activity, e.g., the 4-methyl-3-(1-pyrrolidinyl)-2(5H)-furanone exhibited the strongest cooling effect at the low oral threshold concentration of 0.02-0.06 mmol/L, which is 35-fold below the value determined for (-)-menthol. In contrast to the minty smelling (-)-menthol, most of the alpha-keto enamines were found to be virtually odorless but impart a sensation of "cooling" to the oral cavity as well as to the skin, thus illustrating that there is no physiological link between cooling activity and mint-like odors.

Amines↗
PubMed2000

Cloning, expression and subcellular localization of two novel splice variants of mouse transient receptor potential channel 2.

Transient receptor potential channels (TRPCs) are known as candidate molecular correlates of receptor-activated or store-operated calcium entry. While functional roles for most TRPCs have been suggested, the physiological relevance of TRPC2 remains obscure. Whereas human and bovine TRPC2 are candidate pseudogenes, full-length rodent TRPC2 transcripts have been reported. There is, however, considerable controversy concerning mRNA splicing, tissue distribution and the function of these proteins. We report the molecular cloning of two novel murine TRPC2 splice variants, mTRPC2alpha and mTRPC2beta. mTRPC2alpha RNA is expressed at low levels in many tissues and cell systems, while mTRPC2beta is exclusively and abundantly expressed in the vomeronasal organ (VNO). When expressed in human embryonic kidney (HEK)-293 cells, mTRPC2 did not enhance receptor- or store-activated calcium entry. In order to investigate the basis of such a functional defect, mTRPC2-green fluorescent protein fusion proteins were examined by confocal microscopy. Fusion proteins were retained in endomembranes when expressed in HEK-293 or other cells of epithelial or neuronal origin. Co-expression of TRPC2 with other TRPCs did not restore plasma-membrane trafficking. We conclude that TRPC2 may form functional channels in the cellular context of the VNO, but is unlikely to have a physiological function in other tissues.

Alternative Splicing↗
PubMed2000

Receptor-mediated regulation of the nonselective cation channels TRPC4 and TRPC5.

Mammalian transient receptor potential channels (TRPCs) form a family of Ca(2+)-permeable cation channels currently consisting of seven members, TRPC1-TRPC7. These channels have been proposed to be molecular correlates for capacitative Ca(2+) entry channels. There are only a few studies on the regulation and properties of the subfamily consisting of TRPC4 and TRPC5, and there are contradictory reports concerning the possible role of intracellular Ca(2+) store depletion in channel activation. We therefore investigated the regulatory and biophysical properties of murine TRPC4 and TRPC5 (mTRPC4/5) heterologously expressed in human embryonic kidney cells. Activation of G(q/11)-coupled receptors or receptor tyrosine kinases induced Mn(2+) entry in fura-2-loaded mTRPC4/5-expressing cells. Accordingly, in whole-cell recordings, stimulation of G(q/11)-coupled receptors evoked large, nonselective cation currents, an effect mimicked by infusion of guanosine 5'-3-O-(thio)triphosphate (GTPgammaS). However, depletion of intracellular Ca(2+) stores failed to activate mTRPC4/5. In inside-out patches, single channels with conductances of 42 and 66 picosiemens at -60 mV for mTRPC4 and mTRPC5, respectively, were stimulated by GTPgammaS in a membrane-confined manner. Thus, mTRPC4 and mTRPC5 form nonselective cation channels that integrate signaling pathways from G-protein-coupled receptors and receptor tyrosine kinases independently of store depletion. Furthermore, the biophysical properties of mTRPC4/5 are inconsistent with those of I(CRAC), the most extensively characterized store-operated current.

Animals↗
PubMed2000

Transient receptor potential channels as molecular substrates of receptor-mediated cation entry.

Calcium is a versatile multitarget intracellular second messenger in eukaryotic cells. In addition to calcium release from intracellular stores and influx via voltage- or ligand-operated channels, agonist-induced calcium entry constitutes one of the main pathways by which cytosolic calcium is elevated. Receptor-stimulated currents are initiated in response to agonist binding to G-protein-coupled receptors and to receptor tyrosine kinases. Within the past few years our knowledge about the molecular identity of receptor-stimulated channels has expanded substantially. Drosophila melanogaster visual transduction channels associated with the transient receptor potential (trp) and the trp-like (trpl) mutant visual phenotypes were the first members of this category of channels to be identified at the molecular level. Since then an entire mammalian gene family of TRP homologues has been discovered by homology cloning. Only now are we beginning to fully understand the functional roles of TRP channels in mammalian cells. We review recent findings in TRP channel research and discuss the role of these proteins for receptor-activated cation entry.

Animals↗
PubMed2000

Impact of intravascular ultrasound guidance on directional coronary atherectomy.

In contrast to the luminogram of coronary angiography, intravascular ultrasound (IVUS) has proven to accurately assess both coronary lumen and vessel morphology due to its 360 degrees imaging capacity. Directional coronary atherectomy (DCA) improves the coronary lumen by removing plaque mass rather than stretching the vessel and compressing the plaque as with conventional percutaneous transluminal coronary angioplasty. In an attempt to optimize the procedural result of DCA we prospectively investigated the impact of IVUS guidance in a head to head comparison to on-line quantitative coronary angiography (QCA) on the result of DCA. In 16 consecutive patients IVUS demonstrated significant residual plaque mass after DCA irrespective of a satisfactory angiographic result. After a mean of 9 +/- 2 cuts luminal improvement was obtained with an area stenosis by angiography of 39 +/- 17% and by IVUS of 50 +/- 10% (p < 0.05), a diameter stenosis by angiography of 23 +/- 10% and IVUS of 35 +/- 14% (p < 0.05) and finally a minimal lumen diameter (MLD) by angiography of 2.9 +/- 0.5 mm and by IVUS of 2.3 +/- 0.5 mm (p < 0.005). After both on-line QCA and IVUS measurements a second series of 7 +/- 2 cuts were initiated to debulk more atheroma and improve stenosis dimensions. After additional cuts IVUS revealed further luminal improvement with an area stenosis by angiography of 25 +/- 16% and IVUS of 21 +/- 18% (n.s.), a diameter stenosis by angiography of 16 +/- 11% and by IVUS of 13 +/- 19% (n.s.) and finally a MLD by angiography of 3.1 +/- 0.5 mm and by IVUS of 2.8 +/- 0.3 mm (p < 0.05). Intraprocedural use of IVUS is superior to on-line QCA to assess the immediate result of DCA. IVUS-guided DCA results in more effective atheroma debulking than luminographic evaluation. Results of larger follow-up studies are needed to substantiate the intraprocedural advantage of IVUS with DCA.

Adult↗
PubMed2000

HLA patterns in patients with nasal polyposis.

The etiology of nasal polyposis is still unknown, although risk factors include Aspirin intolerance, asthma, cystic fibrosis and primary ciliary dyskinesia. We studied frequencies of HLA A, B, DR and DQ in patients with nasal polyposis in order to determine a possible genetic component in the multifactorial pathogenesis of nasal polyps. Previous work has suggested an association of HLA-A1B8 with nasal polyposis and Aspirin intolerance. We investigated 89 patients with nasal polyposis, 11 of whom had Aspirin-intolerance, 19 asthma and 22 allergies to inhalation allergens. HLA patterns of these patients were compared to the ones of 1,070 healthy controls. No significant association of HLA-A1B8 was found with nasal polyps in the Aspirin-sensitive subgroup of our patients, but a significant association was seen with HLA-A74 and nasal polyposis.

Aspirin↗
PubMed2000

Formation of aroma-active strecker-aldehydes by a direct oxidative degradation of Amadori compounds.

alpha-Dicarbonyls, generated by sugar degradation, catalyze the formation of the so-called Strecker aldehydes from alpha-amino acids. To check the effectiveness of Amadori compounds (suggested as important intermediates in alpha-dicarbonyl formation from carbohydrates) in Strecker aldehyde formation, the amounts of phenylacetaldehyde (PA) formed from either an aqueous solution of L-phenylalanine/glucose or the corresponding Amadori compound N-(1-deoxy-D-fructosyl-1-yl)-L-phenylalanine (ARP-Phe) were compared. The results revealed the ARP-Phe as a much more effective precursor in PA generation. On the contrary, a binary mixture of glucose/phenylalanine yielded preferentially phenylacetic acid, in particular, when reacted in the presence of oxygen and copper ions. Further model experiments gave evidence that a transition-metal-catalyzed oxidation of the ARP-Phe by air oxygen into the 2-hexosulose-(phenylalanine) imine is the key step responsible for the favored formation of phenylacetaldehyde from the Amadori compound. This mechanism might explain differences in the ratios of Strecker aldehydes and the corresponding acids depending on the structures of carbohydrate degradation products involved.

Aldehydes↗
PubMed2000

Characterization of key chromophores formed by nonenzymatic browning of hexoses and L-alanine by using the color activity concept.

Thermal treatment of an aqueous solution of D-glucose and L-alanine in the presence of the carbohydrate degradation product furan-2-aldehyde resulted in the formation of a variety of colored compounds, among which (Z)-2-[(2-furyl)methylidene]-5, 6-di(2-furyl)-6H-pyran-3-one (I), [E]- and [Z]-1, 2-bis(2-furyl)-1-pentene-3,4-dione (IIa/IIb), 4, 5-bis(2-furyl)-2-methyl-3H-furan-2-one (III), and (S,S)- and (S, R)-2-[4, 5-bis(2-furyl)-2-hydroxy-2-methyl-3(2H)-pyrrol-1-yl]propionic acid (IVa/IVb) as well as 2-[(2-furyl)methylidene]-4-hydroxy-5-[(E)-(2-furyl)methylidene]methyl -2H-furan-3-one (V) were successfully identified as the most intense by application of the color dilution analysis. To measure the contribution of these colorants to the overall color of the browned Maillard mixture, color activity values were calculated as the ratio of the concentration to the visual detection threshold of each colorant. By application of this color activity concept, 16.0% of the overall color of the Maillard mixture accounted for these five types of colorants, thus confirming them as key chromophores. On the basis of synthetic model experiments, the formation pathways leading to the chromophores IIa/IIb, III, and IVa/IVb were proposed.

Alanine↗
PubMed2000

Studies on the key odorants formed by roasting of wild mango seeds (Irvingia gabonensis).

Application of the aroma extract dilution analysis on a concentrate of volatiles obtained by solvent extraction and high vacuum distillation from roasted seeds (180 degrees C; 15 min) of wild mango (Irvingia gabonensis) revealed 32 odor-active compounds with flavor dilution (FD) factors ranging from 8 (low odor activity) to 2048 (high odor activity). The identification experiments based on the use of reference odorants revealed methional (cooked potato-like) followed by 2-acetyl-1-pyrroline (roasty, popcorn-like), butan-2,3-dione, pentan-2,3-dione, 2-ethyl-3,5-dimethylpyrazine, and 2,3-diethyl-5-methylpyrazine as the key aroma compounds among the 27 odorants identified. All odorants are reported for the first time as components of roasted wild mango seeds.

Flavoring Agents↗
PubMed2000

Quantitative model studies on the formation of aroma-active aldehydes and acids by strecker-type reactions.

Application of aroma extract dilution analysis on the volatiles formed by reacting glucose and L-phenylalanine (30 min, 100 degrees C) revealed the Strecker aldehyde, phenylacetaldehyde (PA), and, in addition, phenylacetic acid (PAA) as the two key odorants among the volatiles formed. Quantitative measurements on alpha-dicarbonyl formation revealed that the 3-deoxyosone and glyoxal were formed as the first prominent sugar degradation products, whereas 2-oxopropanal became predominant after approximately 4 h at 100 degrees C. Among the four alpha-dicarbonyls analyzed, 2-oxopropanal proved to be the most effective in generating PA as well as PAA from phenylalanine, but the reaction parameters significantly influenced the ratio of both odorants; for example, at pH 3.0 the ratio of PA to PAA was 3:1, whereas at pH 9.0 the ratio was 1:5. Furthermore, in the presence of oxygen and copper ions the formation of the acid was further increased. 3-Deoxyosone and glucosone were found to be effective precursors of phenylacetaldehyde, but neither was very effective in acid generation. On the basis of the results, a new oxygen-dependent formation pathway of the Strecker reaction is proposed.

Acetaldehyde↗
PubMed2000

Penicillopepsin-JT2, a recombinant enzyme from Penicillium janthinellum and the contribution of a hydrogen bond in subsite S3 to k(cat).

The nucleotide sequence of the gene (pepA) of a zymogen of an aspartic proteinase from Penicillium janthinellum with a 71% identity in the deduced amino acid sequence to penicillopepsin (which we propose to call penicillopepsin-JT1) has been determined. The gene consists of 60 codons for a putative leader sequence of 20 amino acid residues, a sequence of about 150 nucleotides that probably codes for an activation peptide and a sequence with two introns that codes for the active aspartic proteinase. This gene, inserted into the expression vector pGPT-pyrG1, was expressed in an aspartic proteinase-free strain of Aspergillus niger var. awamori in high yield as a glycosylated form of the active enzyme that we call penicillopepsin-JT2. After removal of the carbohydrate component with endoglycosidase H, its relative molecular mass is between 33,700 and 34,000. Its kinetic properties, especially the rate-enhancing effects of the presence of alanine residues in positions P3 and P2' of substrates, are similar to those of penicillopepsin-JT1, endothiapepsin, rhizopuspepsin, and pig pepsin. Earlier findings suggested that this rate-enhancing effect was due to a hydrogen bond between the -NH- of P3 and the hydrogen bond accepting oxygen of the side chain of the fourth amino acid residue C-terminal to Asp215. Thr219 of penicillopepsin-JT2 was mutated to Ser, Val, Gly, and Ala. Thr219Ser showed an increase in k(cat) when a P3 residue was present in the substrate, which was similar to that of the wild-type, whereas the mutants Thr219Val, Thr219Gly, and Thr219Ala showed no significant increase when a P3 residue was added. The results show that the putative hydrogen bond alone is responsible for the increase. We propose that by locking the -NH- of P3 to the enzyme, the scissile peptide bond between P1 and P1' becomes distorted toward a tetrahedral conformation and becomes more susceptible to nucleophilic attack by the catalytic apparatus without the need of a conformational change in the enzyme.

Amino Acid Sequence↗
PubMed2000

Endolacrimal laser assisted lacrimal surgery.

AIMS: To utilise the improved optical qualities of newly developed lacrimal endoscopes and newly miniaturised laser fibres for diagnostic visualisation and laser surgery of the lacrimal system. METHODS: A KTP laser (wavelength 532 nm, 10 W energy) was used for laser assisted dacryocystorhinostomy (DCR) with endolacrimal visualisation in 26 patients. Bicanalicular silicone intubation was placed in all patients for at least 3 months. RESULTS: After 3-9 months of follow up, the silicone tube in all 21 patients who underwent KTP laser DCR are still patent, three patients have eye watering in extremely cold weather and two required a conventional DCR. CONCLUSIONS: The KTP laser generates enough power to open the bony window in DCR surgery. Precise endolacrimal visualisation via a specially designed miniendoscope is essential for surgical success.

Dacryocystorhinostomy↗