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Biomedical subjects

K Köhler

Publications and source records attributed to K Köhler.

At least 19 recordsLinked to original sources
PubMed2006

[Value of different measurements of the preoperative visual acuity and perception of Purkinje's vessel shadows for prediction of the postoperative visual acuity after vitrectomy in diabetic vitreous hemorrhage].

BACKGROUND: In cases of strong vitreous hemorrhage due to diabetic vitreo-retinopathy there is an uncertainty for the prediction of postoperative visual acuity after vitrectomy. This study compares the value of different preoperative measurements for the prognosis of postoperative visual acuity. METHOD AND PATIENTS: We evaluated retrospectively the reports of all patients who have been operated by vitrectomy due to diabetic vitreous hemorrhage at our hospital in 2004 (first vitreoretinal surgery). The following measurements were evaluated: preoperative distance and reading VA, last known VA before hemorrhage, laser interference VA, Purkinje's vessel shadow and postoperative distance VA. RESULTS: 42 patients had entire documentation of all evaluated parameters. The preoperative distance VA was 20/1000 (light perception to 20/60), only 3 patients had a reading VA. Laser interference VA was better than red light perception in 13 patients (7 without red light perception). Purkinje's vessel shadows were positive in 22 patients, negative in 17 patients, but 3 patients did not understand the procedure. Prehemorrhage VA was known in 19 patients. Laser interference VA and last known VA prior to hemorrhage (in mean 20 months old) had the best correlation to postoperative VA (p > 0.05). Purkinje's vessel shadow predicts -- if positive -- a postoperative VA of 20/300 or better. CONCLUSIONS: Postoperative VA after vitrectomy due to diabetic vitreous hemorrhage is best predicted by prehemorrhage VA or laser interference VA, especially if no prehemorrhage VA is known. Positive Purkinje's vessel shadow predicts a postoperative VA of 20/300 or better.

Comorbidity↗
PubMed2006

[Management of pancreatic metastases from renal cell carcinoma report of five cases].

Pancreatic metastases from renal cell carcinoma are rare. In most cases metastases occur many years after nephrectomy. Solitary pancreatic metastases of renal cell cancer can be the only manifestation of tumor dissemination. Between 1995 and 2005 five patients after nephrectomy due to renal cell cancer were suspected of having malignant pancreatic tumor and underwent an operation. The histology revealed metastases of renal cancer. The intervals from primary renal tumor resection to recognition of metastases in the pancreas varied from 6-17 years. The prognosis of metastatic invasion to the pancreas is better than that of primary pancreatic carcinoma. Radical resection of the tumor is the treatment of choice for isolated solitary late metastases of renal cell cancer in the pancreas.

Aged↗
PubMed2006

Case-control association tests correcting for population stratification.

In case-control association studies unobserved population stratification may act as a confounder, leading to an increased number of false positive results. Methods accounting for population structure by using additional genetic markers broadly follow one of two concepts: Genomic Control (GC) and Structured Association (SA). While extending existing methods of Structured Association we show that it is necessary to incorporate phenotypic information when inferring population structure, otherwise a systematic bias is introduced. Moreover, for moderate population stratification a Wald test statistic should be preferred as a Structured Association test statistic in comparison to a likelihood ratio test. The introduced extensions are compared to existing methods of Structured Association, as well as to Genomic Control, in a simulation study which is based on realistic situations of large case-control studies with moderate population stratification. A disadvantage of Genomic Control turns out to be the large variation in estimating the variance inflation factor, as well as the power loss if population structure increases. We come to the overall conclusion that Structured Association, if applied correctly, is superior to Genomic Control, at least in the case of simple population structure as simulated here.

Case-Control Studies↗
PubMed2002

Functional studies on a split type II Na/P(i)-cotransporter.

Analysis of rat and mouse proximal tubular brush-border membrane expression of the type IIa Na/P(i)-cotransporter provides evidence for its cleavage in the large extracellular loop (ECL-2). To study functional properties and membrane distribution of this split NaP(i)-IIa transporter we followed two strategies. In one strategy we expressed the transporter as two complementary parts (p40 and p45) in Xenopus laevis oocytes and as another strategy we cleaved the WT protein with trypsin. Both strategies resulted in a split NaP(i)-IIa protein located in the plasma membrane. The two domains were tied together by a disulfide bridge, most likely involving the cysteines 306 and 334. Surface expression of the NaP(i)-IIa fragments was dependent on the presence of both domains. If both domains were coexpressed, the transporter was functional and transport characteristics were identical to those of the WT-NaP(i)-IIa protein. Corresponding to this, the transporter cleaved by trypsin also retains its transport capacity. These data indicate that cleavage of the type IIa Na/P(i)-cotransporter at ECL-2 is compatible with its cotransport function.

Amino Acid Sequence↗
PubMed2002

Modulation of renal type IIa Na+/Pi cotransporter kinetics by the arginine modifier phenylglyoxal.

The effects of the arginine-modifying reagent phenylglyoxal on the kinetics of the type IIa Na + /Pi cotransporter expressed in Xenopus, oocytes were studied by means of 32Pi uptake and electrophysiology. Phenylglyoxal incubation induced up to 60% loss of cotransport function but only marginally altered the Na+-leak. Substrate activation and pH dependency remained essentially unaltered, whereas the voltage dependency of Pi-induced change in electrogenic response was significantly reduced. Presteady-state charge movements were suppressed and the equilibrium charge distribution was shifted slightly towards hyperpolarizing potentials. Charge movements in the absence of external Na+ were also suppressed, which indicated that the empty-carrier kinetics were modified. These effects were incorporated into an ordered alternating access model for NaPi-IIa, whereby the arginine modification by phenylglyoxal was modeled as altered apparent electrical distances moved by mobile charges, together with a slower rate of translocation of the electroneutral, fully loaded carrier.

Animals↗
PubMed2002

Comparison of functional outcome after anterior cruciate ligament reconstruction resulting in low, normal and increased laxity.

The aim of the study was to analyse and compare the results after arthroscopic anterior cruciate ligament (ACL) reconstruction using patellar tendon autografts in three groups of patients. The groups were determined by knee laxity as measured with the KT-1000 arthrometer at the follow-up two to five years after the reconstruction. Group A (n=15) had an anterior side-to-side laxity difference of <-3 mm (i.e. the reconstructed knee was less lax than the contralateral non-injured knee), Group B (n=376) had a difference of > or = -1, but < or = +2 mm and Group C (n=38) had a difference of > or g=6 mm. All the patients had a normal contralateral knee. In Group A, 7/15 (47%) patients and, in Group B, 82/375 (22%) patients had an extension deficit of > or =5 degrees (P=0.052). The corresponding values in terms of flexion deficit were 8/15 (53%) and 99/375 (26%) respectively (P=0.04) (one missing value in Group B). In Group C, 14/38 (37%) had an extension deficit (P=0.04; Group B vs Group C). Group C displayed worse results than Group B in terms of the Lysholm score and the one-leg-hop test (P=0.001 and P=0.011 respectively). The corresponding comparison between Group A and Group B revealed no significant differences. We conclude that a considerable number of patients showed persisting deficits in range of motion (ROM) after an ACL reconstruction. No major differences were found if they were analysed in subgroups with decreased, near normal or with increased knee laxity. The worst residual functional impairment, as measured with the Lysholm score and one-leg-hop test, was found in the group with increased knee laxity and most ROM deficits in the knees with decreased laxity.

Adolescent↗
PubMed2001

Elucidation of structure and location of V(IV) ions in heteropolyacid catalysts H4PVMo11O40 as studied by hyperfine sublevel correlation spectroscopy and pulsed electron nuclear double resonance at W- and X-band frequencies.

Electron spin resonance, pulsed electron nuclear double resonance (ENDOR) spectroscopy at W- and X-band frequencies, and hyperfine sublevel correlation (HYSCORE) spectroscopy have been employed to determine the location of the V(IV) ions in H4PVMo11O40 heteropolyacid catalysts. In these materials the heteropolyanions have the well-known structure of the Keggin molecule. Interactions of the unpaired electrons of the paramagnetic vanadyl ions (VO(2+)) with all relevant nuclei 1H, 31P, and 51V) could be resolved. The complete analysis of the hyperfine coupling tensor for the phosphorus nucleus in the fourth coordination sphere of the V(IV) ion allowed for the first time a detailed structural analysis of the paramagnetic ions in heteropolyacids in hydrated and dehydrated catalysts. The 31P and 1H ENDOR results show that V(IV) ions are incorporated as vanadyl pentaaqua complexes [VO(H2O)5](2+) in the void space between the heteropolyanions in the hydrated heteropolyacid. For the dehydrated H4PVMo11O40 materials the distance between the V(IV) ion and the central phosphorus atom of the Keggin molecule could be determined with high accuracy on the basis of orientation-selective 31P ENDOR experiments and HYSCORE spectroscopy. The results give a first direct experimental evidence that the paramagnetic vanadium species are not incorporated at molybdenum sites into the Keggin structure of H4PVMo11O40 and also do not act as bridges between two Keggin units after calcination of the catalyst. The vanadyl species are found to be directly attached to the Keggin molecules. The VO(2+) ions are coordinated to four or three outer oxygen atoms from one PVMo11 heteropolyanion in a trigonal-pyramidal or slightly distorted square-pyramidal coordination geometry, respectively.

Journal Article↗
PubMed2001

Investigating the surface expression of the renal type IIa Na+/Pi-cotransporter in Xenopus laevis oocytes.

We have combined a functional assay, surface labeling and immunocytochemical methods to compare total and surface-exposed renal type IIa Na+/Pi cotransporter protein. The wild-type type cotransporter (NaPi-IIa) and its functionally comparable cysteine mutant S460C were expressed in Xenopus oocytes. S460C contains a novel cysteine residue that, when modified by preincubation with methanethiosulfonate reagents, leads to complete suppression of cotransport function. This allowed surface labeling of the S460C using MTSEA-Biotin and confirmation by electrophysiology on the same cell. Protein was analyzed by Western blotting before and after streptavidin precipitation and by immunocytochemistry and immunogold electronmicroscopy. MTSEA-Biotin treatment resulted in a complete inhibition of S460C-mediated Na+/Pi-cotransport activity, which indicated that all transporters at the surface were biotinylated. After biotinylation, only a small fraction of total S460C protein was precipitated by streptavidin compared with the total amount of S460C protein detected in the lysate. Light- and electron-microscopy analysis of oocytes showed a large amount of WT and S460C transporter protein beneath the oocyte membrane. These data indicate that the apparent weak labeling efficiencies of surface-biotinylation-based assays of membrane proteins heterologously expressed in oocytes can be related to diminished incorporation of the protein in the oolemma.

Animals↗
PubMed2001

Field-induced delocalization and Zener breakdown in semiconductor superlattices.

We investigate the energy spectrum and the electron dynamics of a band in a semiconductor superlattice as a function of the electric field. Linear optical spectroscopy shows that, for high fields, the well-known localization of the Bloch states is followed by a field-induced delocalization, associated with Zener breakdown. Using time-resolved measurements, we observe Bloch oscillations in a regime where they are damped by Zener breakdown.

Journal Article↗
PubMed2001

Preconditioning patellar tendon autografts in arthroscopic anterior cruciate ligament reconstruction: a prospective randomized study.

This prospective randomized evaluated the effect of preconditioning patellar tendon autografts before implantation and fixation during anterior cruciate ligament (ACL) reconstruction. Fifty-three patients with a unilateral ACL rupture were included in the study. One group of patients had their patellar tendon autograft preconditioned by passive stretching at a constant load of 39 N for 10 min immediately prior to implantation (group P). The other group underwent no preconditioning before the implantation of the graft (group NP). The follow-up examination was performed by independent observers after 26 months (23-29) in group P and after 25 months (23-30) in group NP (n.s.). At follow-up the KT-1000 laxity test revealed a total side-to-side difference of 2.5 mm (-1.5 to +8.5) in group P and 3.0 mm (-7 to +6.5) in group NP (n.s.). The Lysholm score was 86 points (47-100) in group P and 94 points (44-100) in group NP (n.s.). The Tegner activity level was 6 (2-9) in group P and 7 (3-9) in group NP (n.s.). There was no significant difference between the study groups regarding IKDC classification. Patients who underwent ACL reconstruction using a preconditioned patellar tendon autograft had no advantages in terms of restoration of laxity or clinical outcome at 2-year follow-up.

Adolescent↗
PubMed2001

Evaluation of the reproducibility of the KT-1000 arthrometer.

The aim of the study was to examine whether the KT-1000 arthrometer was reliable when it came to distinguishing between a group of patients with a chronic anterior cruciate ligament (ACL) rupture and a group of patients without an ACL rupture, and to examine the reproducibility of the examination between two experienced examiners. The aim was also to examine whether the KT-1000 measurements were dependent on whether the patients were awake or under anaesthesia. The study comprised 40 patients: Group A consisted of 20 patients who had a chronic unilateral ACL rupture and Group B consisted of 20 patients who were scheduled for arthroscopy due to knee problems other than an ACL rupture. The KT-1000 examination was performed before surgery by two experienced physiotherapists (PT I and PT II). PT II subsequently performed a retest of the patients under anaesthesia. The mean anterior side-to-side laxity difference between PT I and PT II was 0.2 mm in Group A and 1.8 mm in Group B (n.s., P=0.03). The anterior side-to-side measurements of knee laxity revealed significant differences between Group A and Group B, independent of who the measurements were made by when the patients were awake (PT I P=0.011, PT II P=0.001). However, no significant difference (P=0.063) was found when the patients were under anaesthesia. The interclass correlation coefficient (ICC) between PT I and PT II in Group A was 0.55 (P=0.005) for the anterior side-to-side laxity, while it was 0.60 (P=0.002) in Group B. There were no significant differences within Group A or Group B between the measurements made when people were awake compared with those under anaesthesia. The conclusions of the study were that the KT-1000 arthrometer was able to distinguish a group of patients with an ACL rupture from a group without one. The reproducibility of the KT-1000 measurements of anterior knee laxity between two experienced examiners was considered as fair. Furthermore, the measurements were not dependent on whether the patients were awake or under anaesthesia.

Adolescent↗
PubMed2001

Cysteine mutagenesis reveals novel structure-function features within the predicted third extracellular loop of the type IIa Na(+)/P(i) cotransporter.

The transport function of the rat type IIa Na(+)/P(i) cotransporter is inhibited after binding the cysteine modifying reagent 2-aminoethyl methanethiosulfonate hydrobromide (MTSEA) to a cysteine residue substituted for a serine at position 460 (S460C) in the predicted third extracellular loop. This suggests that Ser-460 lies in a functionally important region of the protein. To establish a "structure-function" profile for the regions that flank Ser-460, the substituted cysteine accessibility method was employed. 18 mutants were constructed in which selected amino acids from Arg-437 through Leu-465 were substituted one by one for a cysteine. Mutants were expressed in Xenopus oocytes and transport function (cotransport and slippage) and kinetics were assayed by electrophysiology with or without prior treatment with cysteine modifying (methanethiosulfonate, MTS) reagents. Except for mutant I447C, mutants with cysteines at sites from Arg-437 through Thr-449, as well as Pro-461, were inactive. Cotransport function of mutants with Cys substitutions at sites Arg-462 through Leu-465 showed low sensitivity to MTS reagents. The preceding mutants (Cys substitution at Thr-451 to Ser-460) showed a periodic accessibility pattern that would be expected for an alpha-helix motif. Apart from loss of transport function, exposure of mutants A453C and A455C to MTSEA or 2-(triethylammonium)ethyl MTS bromide (MTSET) increased the uncoupled slippage current, which implicated the mutated sites in the leak pathway. Mutants from Ala-453 through Ala-459 showed less pH dependency, but generally stronger voltage dependency compared with the wild type, whereas those flanking this group were more sensitive to pH and showed weaker voltage dependence of cotransport mode kinetics. Our data indicate that parts of the third extracellular loop are involved in the translocation of the fully loaded carrier and show a membrane-associated alpha-helical structure.

Carrier Proteins↗
PubMed2001

Imaging of the human vomeronasal duct.

The human vomeronasal duct (VND) is described as a tubular or pouch-like mucosal invagination of the anterior nasal septum. This study investigated shape, size and orientation of the VND using magnetic resonance imaging (MRI). Fifteen subjects participated (eight women, seven men; mean age 39 years, age range 18-66 years); they had been pre-selected with regard to the presence of a VND opening of 1 mm. MRI was performed before and after application of diluted gadolinium-diethylene-triamino-penta-acetic actetate (Gd-DTPA) into the left or right VND. A tubular structure was found in 12 subjects with a median length of 7 mm (range 3-22 mm; one VND with a length 47 mm). In three subjects a nearly circular, pouch-like structure was observed. Seven of the tubular VNDs were slightly bent upwards, the other five VNDs ran parallel to the floor of the nasal cavity. There was no significant gender-related difference in the length of VNDs. These data indicate considerable variability of shape, size and orientation of the human VND.

Adolescent↗
PubMed2000

The functional unit of the renal type IIa Na+/Pi cotransporter is a monomer.

The composition of the functional unit of the rat renal type IIa Na(+)/P(i) cotransporter (NaPi-IIa) was investigated by using two approaches based on the differential sensitivities of the wild type (WT) and mutant S460C proteins to 2-aminoethylmethanethiosulfonate hydrobromide (MTSEA), a charged cysteine modifier. Transport activity of S460C is completely blocked after incubation in MTSEA, whereas that of the WT remains unaffected. First, Xenopus laevis oocytes were coinjected with cRNAs coding for the WT and S460C in different proportions, and the transport inhibition after MTSEA incubation was assayed by electrophysiology. The relationship between MTSEA inhibition and proportion of cRNA was consistent with that for a functional monomer. Second, concatameric proteins were constructed that either comprised two WT proteins (WT-WT), two S460C mutants (S460C-S460C), or one of each (WT-S460C). Western blots of oocytes injected with fusion protein cRNA showed bands at approximately 200 kDa, whereas a main band at approximately 90 kDa was obtained for the WT cRNA alone. The kinetic properties of concatamers were the same as for the single proteins. Transport activity of the WT-WT concatamer was unaffected by MTSEA incubation, fully inhibited for S460C-S460C, but 50% inhibited for WT-S460C. This behavior was also consistent with NaPi-IIa being a functional monomer.

Animals↗
PubMed2000

A clinical and radiographic comparison of absorbable and non-absorbable suture anchors in open shoulder stabilisation.

The aim of this study was to compare the clinical and radiographic results using either absorbable or non-absorbable suture anchors in patients with recurrent unidirectional, post-traumatic shoulder dislocations. All patients had a Bankart lesion. One surgeon operated on 33 consecutive patients, 27 males and six females. Group A comprised 15 shoulders and group B 18 shoulders, all of which underwent a standardised open Bankart reconstruction using 3.7-mm TAG suture anchors. In group A, absorbable anchors were used, while in group B, non-absorbable ones were used. There was one re-dislocation in each group. In group A, the Rowe and Constant scores were 89 (69-98) and 89 (76-99) points, respectively. The corresponding values in group B were 87 (44-98) (not significant; NS) and 90 (71-100) points (NS). The strength measurements revealed 8.1 (3.8-12.3) kg in 90 degrees abduction in group A and 10.0 (6.7-12.0) kg in group B. Healthy control shoulders revealed 10.2 (4.5-13.2) kg (NS A and B versus controls). The external rotation in abduction was 70 degrees (40-90) in group A and 80 degrees (40-100) in group B. The value for the controls was 90 degrees (80-120) [P < 0.001 (A versus controls), P < 0.05 (A versus B) and P < 0.001 (B versus controls)]. The radiographs revealed that 9/15 (60%) in group A and 10/15 (66%) in group B had visible drill holes or cystic formations in conjunction with the drill holes (NS). Furthermore, 11/15 (73%) in group A and 10/15 (66%) in group B had signs of minor degeneration (NS). We conclude that, in terms of stability and clinical results, no differences were found between the study groups. Both groups demonstrated a restriction in external rotation as compared with the healthy shoulders in the same cohort. On the radiographs, visible drill holes or cystic formations in conjunction with the drill holes were seen with equal frequency, regardless of whether absorbable or non-absorbable suture anchors were used.

Absorbable Implants↗
PubMed1999

Highly selective palladium-catalyzed Heck reactions of aryl bromides with cycloalkenes.

[reaction: see text] The influence of palladium catalysts and reaction conditions on the selectivity of Heck reactions of aryl bromides with cyclohexene and cyclopentene has been investigated. It is shown that the addition of DMSO as a cosolvent leads to improved selectivities of nonconjugated aryl olefins. On the other hand, high selectivities for conjugated arylcyclopentenes have been obtained with the catalytic system DMA/Na2CO3/Pd2(dba)3 x dba/PCy3.

Journal Article↗
PubMed1999

Serial magnetic resonance imaging of the donor site after harvesting the central third of the patellar tendon. A prospective study of 37 patients after arthroscopic anterior cruciate ligament reconstruction.

The aim of this prospective study was to follow the development of repair tissue in the donor-site area using serial magnetic resonance imaging (MRI) evaluation and to assess whether the MRI findings were correlated with donor-site morbidity. Thirty-seven consecutive patients with unilateral anterior cruciate ligament injuries undergoing elective reconstruction of the ligament were included in the study. They were aged 27 (range 14-50) years. The graft was harvested through two 25-mm vertical incisions with the aim of protecting the infrapatellar nerve and sparing the paratenon. The tendon defect was left open. The patients underwent MRI evaluation at 6 weeks, 6 months and 27 months postoperatively. A final clinical follow-up was made 25 (range 23-29) months postoperatively. MRI demonstrated that the donor-site gap, i.e. the area corresponding to a pathological non-tendinous-like tissue signal, was 9 (range 4-18) mm at 6 weeks, 5 (range 2-14) mm at 6 months and 2 (range 0-5) mm at 27 months. The size of the donor-site gap had significantly decreased at 6 months compared with 6 weeks (P = 0.0001), as well as at 27 months compared with 6 months (P = 0.0001). We conclude that the patellar tendon at the donor site healed gradually, as expressed by a decrease in the area of non-tendinous-like tissue signal on the serial MRI evaluations.

Adolescent↗