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Biomedical subjects

H J Merker

Publications and source records attributed to H J Merker.

At least 19 recordsLinked to original sources
PubMed1999

Signal transduction by beta1 integrin receptors in human chondrocytes in vitro: collaboration with the insulin-like growth factor-I receptor.

We have examined the mechanism by which collagen-binding integrins co-operate with insulin-like growth factor-I (IGF-I) receptors (IGF-IR) to regulate chondrocyte phenotype and differentiation. Adhesion of chondrocytes to anti-beta1 integrin antibodies or collagen type II leads to phosphorylation of cytoskeletal and signalling proteins localized at focal adhesions, including alpha-actinin, vinculin, paxillin and focal adhesion kinase (FAK). These stimulate docking proteins such as Shc (Src-homology collagen). Moreover, exposure of collagen type II-cultured chondrocytes to IGF-I leads to co-immunoprecipitation of Shc protein with the IGF-IR and with beta1, alpha1 and alpha5 integrins, but not with alpha3 integrin. Shc then associates with growth factor receptor-bound protein 2 (Grb2), an adaptor protein and extracellular signal-regulated kinase. The expression of the docking protein Shc occurs only when chondrocytes are bound to collagen type II or integrin antibodies and increases when IGF-I is added, suggesting a collaboration between integrins and growth factors in a common/shared biochemical signalling pathway. Furthermore, these results indicate that focal adhesion assembly may facilitate signalling via Shc, a potential common target for signal integration between integrin and growth-factor signalling regulatory pathways. Thus, the collagen-binding integrins and IGF-IR co-operate to regulate focal adhesion components and these signalling pathways have common targets (Shc-Grb2 complex) in subcellular compartments, thereby linking to the Ras-mitogen-activated protein kinase signalling pathway. These events may play a role during chondrocyte differentiation.

Adaptor Proteins, Signal Transducing↗
PubMed1999

Beta1-integrins in the cartilage matrix.

Integrins are cell-surface receptors that mediate cell attachment to extracellular matrix components. The pericellular matrix in cartilage not only is a mechanical framework, but is also important for chondrocyte differentiation and stabilization of the phenotype. The interaction between chondrocytes and pericellular matrix is mediated, in part, by integrin receptors. We have previously demonstrated the presence of beta1-integrins in the cartilage matrix of organoid culture of limb buds from 12-day-old mouse embryos by immunohistological methods. In order to corroborate these findings, we have further investigated the distribution of integrins in the cartilage matrix by immunoelectron microscopy and by immunoprecipitation methods. Cartilage tissue of limb buds of 17-day-old mouse embryos was treated with collagenase and the cell-free and cellular protein-free supernatant was removed and used for immunoprecipitation experiments. Immunoprecipitation with antibodies against beta1-, alpha1-, alpha3-, and alpha5beta1-integrins and collagen type II, followed by immunoblotting with the same antibodies, demonstrated the presence of these integrins and collagen type II in the supernatant. The integrins found in the cartilage matrix could have been either secreted or shed by the cells. The question as to whether they have a function in the cartilage matrix, such as interlinking, in the matrix organization or in the stabilization of matrix components remains to be elucidated.

Animals↗
PubMed1998

Reproductive toxicity and tissue concentrations of low doses of 2,3,7,8-tetrachlorodibenzo-p-dioxin in male offspring rats exposed throughout pregnancy and lactation.

The effects of low doses of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) on the reproductive system of male offspring rats were examined. The dams were treated subcutaneously 2 weeks prior to mating and throughout mating, pregnancy, and lactation. They received an initial loading dose of 25, 60, or 300 ng TCDD/kg body wt, followed by a weekly maintenance dose of 5, 12, or 60 ng TCCD/kg body wt (TCDD 25/5, TCDD 60/12, and TCDD 300/60). Three dams per group were killed on Gestation Day 21 and the fetuses were removed. The concentration of TCDD in the maternal liver and fat was measured. After birth, developmental landmarks in male rats were monitored. At weaning, the concentration of TCDD in the offspring liver and testis was determined. Effects on male reproduction were studied on Postnatal Days (PND) 70 and 170. At weaning, the concentration of TCDD in the offspring liver was 0.24, 0.39, and 1.78 ng/g in the TCDD 25/5, TCDD 60/12, and TCDD 300/60 groups, respectively. In the testes, the concentration of TCDD was 0.25 ng/g in the TCDD 25/5 and TCDD 60/12 groups and 0.28 ng/g in the TCDD 300/60 group. The number of sperm per cauda epididymis was reduced in TCDD groups at puberty and at adulthood. Daily sperm production was permanently decreased as was the sperm transit rate in the TCDD-exposed male rats, thus increasing the time required by the sperm to pass through the cauda epididymis. Moreover, the male rats of the TCDD groups showed an increased number of abnormal sperm when investigated at adulthood. Similarly, mounting and intromission latencies were significantly increased in the TCDD 25/5 and TCDD 300/60 groups. In the highest dose group, serum testosterone concentration was decreased at adulthood. Likewise, in this dose group permanent changes including pyknotic nuclei and the occurrence of cell debris in the lumen were revealed. The lowest adverse effect level and the no observed effect level can be estimated to be substantially lower than the estimated daily dose of the lowest dose which is 0.8 ng/kg body wt/day. Sperm parameters were more susceptible than the other end points investigated. However, the question as to whether such doses exposed throughout gestation and lactation induce subtle changes in humans remains to be determined.

Adipose Tissue↗
PubMed1998

[Electron microscopy studies of the human vomeronasal organ].

The vomeronasal organ, or Jacobson's organ, is essential for pheromone detection and reproductive behavior in most mammals. In humans, it has been described as a blind diverticulum in the anterior nasal septum, but without a documented function. The purpose of this study is to describe the fine structure of the human adult vomeronasal organ in 14 specimens. Our studies showed a duct-like invagination of the epithelium that was surrounded by numerous exocrine glands with short ducts. The fine structure of these glands suggested a serous secretion. In the depth of the invagination, pseudostratified columnar epithelial cells were seen that had plump processes, kinocilia and microvilli at the apical cell membrane. Several cell types were seen that differed regarding their organelles and electron density, with light sensory cells exhibiting neurofilaments. Underneath the typical basement membrane, numerous myelinated and unmyelinated axons were present in the very vascular lamina proprion. These morphological findings are unique in the human body and suggest that a chemosensory epithelium corresponding to a vomeronasal organ may exist. Its central connections and the possible functional significance of this tubed organ for pheromone detection are unknown and need further study.

Adolescent↗
PubMed1998

The electron microscopic morphology of the common carotid artery in rats.

The common carotid arteries of normal adult rats were investigated electron-microscopically after tannic acid fixation. This fixation technique yields a better demonstrability of the structures of the connective tissue, the basal laminae and the surface coat of the cell membrane. The common carotid artery represents a vessel of the elastic type. The intima consists of an endothelium and a narrow gap of connective tissue (0.1-1 micron) which contains single collagenous fibrils and small elastic structures. This space is only occasionally as wide as 3 microns, especially beneath gaps of the internal elastic membrane. In these areas, single cells and structures of densely packed filaments are additionally observed which can neither be attributed to collagenous fibrils nor to elastic fibres. The intima is demarcated from the outside by an internal elastic membrane (1 micron) which shows a number of gaps. The media exhibits 3 to 4 elastic membranes without gaps. Smooth muscle cells of the contractile type stretch in an oblique direction between these membranes, i.e. they are not arranged in a circular or spiral manner. Most of their process-rich ends are inserted directly into the elastic material and not via a basal lamina. Processes from these smooth muscle cells, collagenous fibrils and elastic fibres are seen in the intercellular spaces. The muscle cells are occasionally interlinked by gap junctions. The basal lamina does not surround the muscle cells continuously. The adventitia contains bundles of collagenous fibrils, fibrocytes, a few small vessels and nerves with a perineuronal envelope. Nerves could not be demonstrated in the media. The oblique course of the smooth muscle cells and the insertion into the elastic membranes indicate that these cells do not predominantly contribute to changes in the width of the lumen but also serve the stabilisation and resetting of the elastic membranes. Contraction is probably induced by an opening of stretch-dependent Ca2+ channels. Due to the interlinkage with gap junctions, the muscle cells of one layer respond as a functional unit. Our findings provide a morphological basis for elucidating commonly encountered changes, such as smooth muscle migration through a normally interrupted inner elastic lamina.

Animals↗
PubMed1998

Red cell membrane skeletal changes in marathon runners.

Hemolysis in endurance exercise may be related to structural changes in red blood cell (RBC) membrane skeletal proteins. To test this hypothesis, we studied 13 male subjects before and after a marathon race. RBC membrane skeletons were observed with scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Plasma haptoglobin was measured. RBCs were affixed on poly-l-lysine coated glass supports for SEM and copper grids with formvar were prepared for TEM. Cytoplasmatic materials and lipid membranes were extracted with Triton-X-100 solution. TEM specimens were negatively stained and air dried. For SEM, the remaining RBC membrane skeletons were fixed, postfixed and sputtered with platinum. RBC membrane skeletal areas on SEM micrographs were measured by digitizer table planimetry. No RBC changes were observed with TEM. On the other hand, SEM showed disrupted RBC membrane skeletons. Furthermore, there appeared to be a loss of membrane material in RBC after the race, compared to RBC before the race. RBC membrane skeletal areas were increased by 30% (p<0.01). Hemolysis was indicated by a 57% decrease in plasma haptoglobin values (p<0.001). Thus, structural changes in RBC membrane skeletons occur after a marathon race. These changes can be identified with SEM but not with TEM. They may be related to increased susceptibility to chemical and physical stress and may contribute to hemolysis in endurance exercise.

Adult↗
PubMed1998

[Glands of the human nasal mucosa--electron microscopy and immunohistochemical studies].

BACKGROUND: Ultrastructural characteristics of the nasal glands are presented and possible changes concerning different diseases of the nasal mucosa are investigated. METHODS AND PATIENTS: Specimens from 23 patients suffering from primary ciliary dyskinesia, allergic rhinopathy, and chronic inflammatory hyperplasia were the subject of electron microscopic and immunohistochemical studies. RESULTS: All preparations exclusively showed glands of the serous type. The end segments of the glands were surrounded by contractile myoepithelial cells in a basket-like fashion. Distinct differences in the fine structure of the glands were not observed between the individual groups. The epithelial cells of the efferent ducts consisted of numerous rows forming one layer with pronounced interlockings. These cells in particular showed a high content of mitochondria. This segment of the duct probably has the function of changing the content of water and ions in the nasal secretion. CONCLUSIONS: Our immunofluorescence and electronmicroscopic investigations present the ultrastructure of the nasal glands in detail. We assume an influence of the efferent ducts on the composition of the nasal secretion.

Biopsy↗
PubMed1998

Chondrotoxicity and toxicokinetics of sparfloxacin in juvenile rats.

Sparfloxacin is a fluoroquinolone with improved antibacterial activity against gram-positive pathogens. Like other quinolones, use of this drug is contraindicated in children and adolescents because of its potential chondrotoxicity in juveniles. We performed histological and immunohistochemical studies on the knee joint cartilage in 5-week-old rats after treatment with 600 or 1,800 mg of sparfloxacin/kg of body weight. Treatment with single or multiple oral doses of 600 mg of sparfloxacin/kg was not sufficient to induce joint cartilage lesions. However, five of eight rats treated with a single oral dose of 1,800 mg of sparfloxacin/kg of body weight showed typical cartilage lesions in the femoral part of the knee joint. The concentrations of the drug in plasma measured 0.25, 0.75, 1.5, 3, 6, 12, and 24 h after the administration of an oral dose of 600 mg of sparfloxacin/kg were 6.3 +/- 1.8, 9.2 +/- 1.7, 9.6 +/- 2.7, 13.0 +/- 1.8, 12.3 +/- 1.6, 3.4 +/- 0.4, and 0.30 +/- 0.20 mg/liter, respectively (mean +/- standard deviation [SD]; n = 5 to 6 per group). The concentrations in plasma measured 0.75, 1.5, 3, 6, 24, and 48 h after the administration of an oral dose of 1,800 mg of sparfloxacin/kg were 10.9 +/- 1.5, 15.9 +/- 1.6, 19.1 +/- 1.7, 14.9 +/- 3.1, 4.1 +/- 0.6, and 0.46 +/- 0.37 mg/liter, respectively (mean +/- SD; n = 3 to 4 per group). The concentrations of sparfloxacin in joint cartilage were significantly higher at all time points studied (114.8 +/- 80, 99.4 +/- 31.5, 84.9 +/- 16.8, 44.4 +/- 13.9, and 14.2 +/- 4.8 mg of sparfloxacin/kg at 1.5, 3, 6, 24, and 48 h after the administration of 1,800 mg/kg, respectively). The range of concentrations in bone were similar to the range of concentrations in cartilage (peak, 115 +/- 12 mg/kg after 3 h). Our data indicate that chondrotoxic doses of sparfloxacin in juvenile rats are approximately 300 times higher than the doses of sparfloxacin used therapeutically (1,800 versus approximately 6 mg/kg of body weight), but due to species differences in kinetics, concentrations in plasma differ by a factor of only approximately 15. More data on quinolone concentrations in cartilage from animals and humans could provide a better basis for a reasonable risk assessment.

Animals↗
PubMed1998

Effects on developmental landmarks and reproductive capability of 3,3',4,4'-tetrachlorobiphenyl and 3,3',4,4',5-pentachlorobiphenyl in offspring of rats exposed during pregnancy.

1. Pregnant Wistar rats were treated orally with a single dose of 100 microg 3,3',4,4'-tetrachlorobiphenyl (PCB 77)/kg b.w. or 10 microg 3,3',4,4',5 pentachlorobiphenyl (PCB 126)/kg b.w. on day 15 of pregnancy. The control rats received peanut oil at the same day. Developmental landmarks were assessed in all offspring rats and reproductive effects of PCB 77 and PCB 126 on male offspring were studied on postnatal day 65 (at puberty) and on postnatal day 140 (at adulthood). 2. The ano-genital distance as well as the ratio ano-genital distance to body length was reduced in male pups of the PCB 126 group and the age at vaginal opening was significantly delayed in the female pups. 3. Testis, brain weights and daily sperm production were permanently increased and seminal vesicle weights were decreased in male offspring of the PCB 77 group. In male rats of PCB 126 group, the brain weights were permanently increased and ventral prostate weights permanently reduced. In both PCB groups, however, serum testosterone concentration was reduced only at adulthood. Additionally, the male rats of the PCB 126 group showed alterations in sexual behavior. In these rats the number of mounts with intromissions was significantly increased. 4. The results of this study show that PCB 126 elicits some TCDD-like reproductive effects after in utero exposure, while the reproductive effects of in utero exposure to PCB 77 on male offspring may be attributed to the neonatal hypothyroidism induced by the substance during early fetal development. Further studies using multiple doses and providing thyroid hormone data will be necessary to support this hypothesis.

Administration, Oral↗
PubMed1997

Integrin expression and collagen type II implicated in maintenance of chondrocyte shape in monolayer culture: an immunomorphological study.

Chondrocytes grown in monolayer culture at low density, with serum added, either dedifferentiate after several days whereby their cell shape or they are overgrown by fibroblast-like cells. The aim of this study was to optimize the cultivation of chondrocytes in monolayer culture and to slow down their transformation or their overgrowth by fibroblast-like cells. For this purpose freshly isolated chondrocytes of cartilage anlagen from 17-day-old mouse embryos were grown on plastic or collagen type II-coated substrates. With this model: (a) chondrocytes grown on plastic substrates had almost completely changed to fibroblast-like cells after 5 days in culture. (b) When grown on collagen type II, the chondrocytes maintained their round phenotype for more than 2 weeks in culture. (c) Immunomorphological investigations showed that chondrocytes produce collagen type II and fibronectin and express specific surface receptors (integrins of the beta 1-group) on the membrane from day 1 until the end of the culture period when grown on collagen type II. (d) Treatment with beta 1-integrin antibodies clearly reduces chondrocyte adhesion on collagen type II by about 70%. Hence, these data indicate that the most probable influence of collagen type II on cellular behaviour depends on the integrins participating in a chondrocyte-collagen type II interaction, and this model represents a pure chondrocyte culture which allows cell growth for an extended period.

Alkaline Phosphatase↗
PubMed1997

Electron microscopic and immunomorphological investigations on the mucosa of the human paranasal sinuses.

The morphology of the mucosa from the human paranasal sinuses was investigated by electron microscopy. A total of 27 specimens was taken from 11 patients following midfacial fractures. All tissue samples were biopsied during surgery after informed consent had been given. In accordance with light microscopic investigations, the mucosa represented a highly prismatic epithelium consisting of kinocilia-carrying and mucus-producing (goblet) cells. Other cell types, such as those occurring in the respiratory epithelium of other areas, could not be demonstrated. Electron microscopic and immunomorphological investigations revealed collagen type VII beneath the lamina densa of the basal lamina. According to findings obtained to date, this collagen type accompanies only a multilayered epithelium. Another peculiarity was the small number of basophils and eosinophils. Pronounced acute reactions of the mucosa in this area cannot be expected, which is in contrast to that of the nasal mucosa.

Adult↗
PubMed1997

[Comparative stability evaluation of dynamic hip screw and gamma-nail osteosyntheses in unstable pertrochanteric femoral osteotomies].

In 24 human cadaver femora standardized instable pertrochanteric osteotomies were created. The right and left femur of each pair were alternately selected for osteosyntheses with the gamma nail and the dynamic hip screw. Afterwards an examination of stability was performed. Cyclical loads were increased in 500 N increments to the maximum loading capacity, while the deformation rate was continuously measured. Radiographs were taken to prove the results of loading. The mean deformation was much greater in the DHS group than for the gamma nail, the maximum load to failure was significantly lower. Femoral shaft fractures caused by the loading occurred five times as often in the gamma nail osteosyntheses than in the DHS.

Aged↗
PubMed1997

Quinolone-induced arthropathy: exposure of magnesium-deficient aged rats or immature rats, mineral concentrations in target tissues and pharmacokinetics.

Quinolone treatment or magnesium deficiency induce identical cartilage lesions in juvenile rats and show additive arthropathogenic effects. It has been shown previously that neither condition is arthropathogenic in 8-week-old rats. Joint cartilage from aged individuals is rather prone to pathological alterations but information on prolonged quinolone treatment and/or dietarily induced magnesium deficiency in aged animals is not available. We treated magnesium-deficient (n = 9) aged Wistar rats (age 15 months) and age-matched controls with daily doses of 600 mg ofloxacin/kg body wt. by gastric intubation for 28 days. Further groups of magnesium-deficient and control rats (n = 9 and n = 10, respectively) received the vehicle only. Peak plasma concentrations of ofloxacin in adult rats were 20.5 +/- 5.6 mg/l (mean +/- SD) following treatment with a single dose of 600 mg/kg body wt. At the end of the experiment the degree of magnesium deficiency was most pronounced in plasma (Mg2+-def., 0.33 +/- 0.12 mmol/l; control, 0.97 +/- 0.08 mmol/l) and less pronounced in sternal cartilage (Mg2+-def., 10.8 +/- 3.6 mmol/kg dry wt; control, 13.3 +/- 2.8 mmol/kg dry wt), whereas the magnesium concentration in femoral bone remained unchanged (Mg2+-def., 201 +/- 13 mmol/kg dry wt; control, 204 +/- 11 mmol/kg dry wt). Histological investigation of the knee joints revealed no cartilage lesions following ofloxacin treatment, magnesium deficiency or a combination of both conditions. By contrast, cartilage lesions such as scars and erosions of the joint surface, chondrocyte clusters within acellular areas of the cartilage matrix and persisting clefts were detectable in knee joints from 7 of 10 adult rats (age 9 months) which had been treated with 4 x 600 mg fleroxacin/kg body wt. at 5 weeks of age. Mean plasma concentration of fleroxacin in juvenile rats was approx. 50 mg/l between 1.5 and 6 h after dosing and the drug was still detectable in plasma 48 h after dosing (0.4 +/- 0.1 mg/l). Our data indicate that joint cartilage in aged rats is not altered by a 4-week quinolone treatment, even during magnesium deficiency. Cartilage lesions in adult rats were only detectable if the animals had been treated during the sensitive phase at 5 weeks postnatally.

Age Factors↗
PubMed1997

Morphology of capillary-like structures in a three-dimensional aorta/collagen gel culture.

The morphology of capillary-like tubes was investigated by electron microscopy (TEM and SEM) using an in vitro model of capillarogenesis (aorta/collagen type I gel). This model allowed morphological comparisons with in vivo capillaries and an evaluation of the functional maturity of the endothelium to be made. The lumina developing in vitro were demarcated by endothelial cells of varying thickness (0.1-2 microns). Pericytes were resting on the outside. The endothelial cells were characterized by contacts of varying length with tight and gap junctions and occasional indentations. The inner surface exhibited areas both with pronounced and without any endocytotic activity. In addition to a large Golgi apparatus, a varying number of cell organelles occurred depending on the thickness of the endothelium. Bundles consisting of microfilaments were often located underneath the outer cell membrane and in the vicinity of contact areas. A lamina densa was in the process of formation. The capillaries grown in vitro closely resembled those in vivo and showed a high degree of differentiation. Hence, this in vitro model allows the study of a number of functions of endothelial cells.

Animals↗
PubMed1997

Formation of new capillary-like tubes in a three-dimensional in vitro model (aorta/collagen gel).

Direct sprouting (angiogenesis) does not occur during the formation of capillary-like tubes in an aorta/ collagen gel in the in vitro model. However, emigration of cells which stretch, arrange themselves side by side, form contacts (unspecific, tight and gap junctions), develop a lumen and show differentiation of endothelial cells (including the formation of a lamina densa and the appearance of pericytes) have been observed, i.e. vasculogenesis occurs. The origin of long, stretched cells is not known with certainty. They possibly represent smooth muscle cells. In addition, other cell types have been found, such as fibrocyte-like and fibroblast-like cells, elastoblasts, fat cells, monocytes and macrophages. All these cells are able to produce factors that promote the formation of new capillaries. Hence, a knowledge of these cells appears to be important for the analysis of in vitro systems. Moreover, the occurrence of these cell types must be considered when assessing possible effects.

Animals↗
PubMed1997

Testis damage induced by zinc deficiency in rats.

Male Wistar rats were fed a Zn-deficient diet (1.2 mg/kg of Zn) for 28 days. Testes were then studied by light and electron microscopy. Zn deficiency induced necroses of precursors of germ cells leading to tubular atrophy and affected differentiation of spermatids. This was expressed by the occurrence of 2-4 axoneme-dense fibre-mitochondria complexes in one spermatid. Moreover, outer dense fibres, which normally contain 90% of sperm Zn, were "uncoiled" and flattened. The multiplication of the axoneme-dense fibre-mitochondria complexes induced by Zn deficiency might have been produced by an increase of Fe in spermatids and an increased formation of oxygen free radicals.

Animals↗
PubMed1997

Reproductive toxicity and toxicokinetics of lindane in the male offspring of rats exposed during lactation.

1. Reproductive toxicity and toxicokinetics of lindane during lactation were studied. For the reproductive toxicity study the dams were treated with a single dose of 6 mg/kg on day 9 or 14 of lactation, or with 1 mg/kg on days 9 to 14 of lactation. The male offspring were investigated at puberty and adulthood. For the toxicokinetic study, two groups of dams were treated with 6 mg/kg on day 9 or 14 of lactation. The concentration of lindane was measured in maternal plasma and milk, as well as in male offspring organs. 2. At adulthood, testicular weight and the number of sperm and spermatids were significantly reduced in all treated groups. 3. The testosterone level of the groups treated with 6 mg/ kg was significantly reduced to approximately 50% at puberty as well as in adulthood. In the group treated with 1 mg/kg, the testosterone level was in both age periods reduced, however, only at puberty was the reduction statistically significant. 4. The concentration of lindane in the testis was similar to that found in brain and was half the concentration found in the liver. 5. Histologically some areas of the testis exhibited distinct alterations ranging from small changes to a pronounced effect. 6. Exposure to lindane during lactation induces reproductive hazards to male offspring rats which are detectable at adulthood.

Animals↗